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Sample records for angle resolved photoemission

  1. Direct angle resolved photoemission spectroscopy and ...

    Indian Academy of Sciences (India)

    Keywords. Condensed matter physics; high-c superconductivity; electronic properties; photoemission spectroscopy; angle resolved photoemission spectroscopy; cuprates; films; strain; pulsed laser deposition.

  2. Direct angle resolved photoemission spectroscopy and ...

    Indian Academy of Sciences (India)

    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.

  3. Photoemission Electron Spectroscopy IV: Angle-resolved photoemission spectroscopy

    OpenAIRE

    Lee, J. D.; Nagatomi, T. (Translator); Mizutani, G. (Translator); Endo, K. (Translation Supervisor)

    2010-01-01

    The angle-resolved photoemission spectroscopy (ARPES) is a powerful experimental tool to probe themomentum-resolved electronic structure, i.e., the electronic band dispersion ε(k), of solids and their surfaces. ARPES is also an ideal tool to address the question concerning the electron correlation effect on quasiparticle excitations in the low-dimensional (one- or two-dimensional) correlated electron systems. In this issue, we briefly introduce representative studies of ARPES and their fruitf...

  4. Angle-resolved photoemission extended fine structure

    International Nuclear Information System (INIS)

    Barton, J.J.

    1985-03-01

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

  5. 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

  6. 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

  7. Angle-resolved photoemission spectroscopy with quantum gas microscopes

    Science.gov (United States)

    Bohrdt, A.; Greif, D.; Demler, E.; Knap, M.; Grusdt, F.

    2018-03-01

    Quantum gas microscopes are a promising tool to study interacting quantum many-body systems and bridge the gap between theoretical models and real materials. So far, they were limited to measurements of instantaneous correlation functions of the form 〈O ̂(t ) 〉 , even though extensions to frequency-resolved response functions 〈O ̂(t ) O ̂(0 ) 〉 would provide important information about the elementary excitations in a many-body system. For example, single-particle spectral functions, which are usually measured using photoemission experiments in electron systems, contain direct information about fractionalization and the quasiparticle excitation spectrum. Here, we propose a measurement scheme to experimentally access the momentum and energy-resolved spectral function in a quantum gas microscope with currently available techniques. As an example for possible applications, we numerically calculate the spectrum of a single hole excitation in one-dimensional t -J models with isotropic and anisotropic antiferromagnetic couplings. A sharp asymmetry in the distribution of spectral weight appears when a hole is created in an isotropic Heisenberg spin chain. This effect slowly vanishes for anisotropic spin interactions and disappears completely in the case of pure Ising interactions. The asymmetry strongly depends on the total magnetization of the spin chain, which can be tuned in experiments with quantum gas microscopes. An intuitive picture for the observed behavior is provided by a slave-fermion mean-field theory. The key properties of the spectra are visible at currently accessible temperatures.

  8. Constant Matrix Element Approximation to Time-Resolved Angle-Resolved Photoemission Spectroscopy

    Directory of Open Access Journals (Sweden)

    James K. Freericks

    2016-11-01

    Full Text Available We discuss several issues associated with employing a constant matrix element approximation for the coupling of light to multiband electrons in the context of time-resolved angle-resolved photoemission spectroscopy (TR-ARPES. In particular, we demonstrate that the “constant matrix element approximation” —even when reasonable—only holds for specific choices of the one-electron basis, and changing to other bases, requires including nonconstant corrections to the matrix element. We also discuss some simplifying approximations, where a constant matrix element is employed in multiple bases, and the consequences of this further approximation (especially with respect to the calculated TR-ARPES signal becoming negative. We also discuss issues related to gauge invariance of the final spectra.

  9. Theory of angle-resolved photoemission from the cuprate superconductors

    International Nuclear Information System (INIS)

    Hedegard, P.; Pedersen, M.B.

    1990-01-01

    We show that the photoemission spectrum for an RVB state with bosonic spins and fermionic charges consists of a peak on top of a broad background. The 'Fermi surface' corresponds to hole pockets around certain k-vectors. The theoretical predictions are compared with the available experimental data, and with the results obtained by other approaches. (orig.)

  10. Electronic structure studies of BaFe2As2 by angle-resolved photoemission spectroscopy

    NARCIS (Netherlands)

    Fink, J.; Thirupathaiah, R.; Ovsyannikov, R.; Dürr, H.A.; Follath, R.; Huang, Y.; de Jong, S.; Golden, M.S.; Zhang, Y.Z.; Jeschke, H.O.; Valentí, R.; Felser, C.; Dastjani Farahani, S.; Rotter, M.; Johrendt, D.

    2009-01-01

    We report high resolution angle-resolved photoemission spectroscopy (ARPES) studies of the electronic structure of BaFe2As2, which is one of the parent compounds of the Fe-pnictide superconductors. ARPES measurements have been performed at 20 and 300 K, corresponding to the orthorhombic

  11. Dynamics of Molecular Orientation Observed Using Angle Resolved Photoemission Spectroscopy during Deposition of Pentacene on Graphite.

    Science.gov (United States)

    Park, Sang Han; Kwon, Soonnam

    2016-04-19

    A real-time method to observe both the structural and the electronic configuration of an organic molecule during deposition is reported for the model system of pentacene on graphite. Structural phase transition of the thin films as a function of coverage is monitored by using in situ angle resolved photoemission spectroscopy (ARPES) results to observe the change of the electronic configuration at the same time. A photoemission theory that uses independent atomic center approximations is introduced to identify the molecular orientation from the ARPES technique. This study provides a practical insight into interpreting ARPES data regarding dynamic changes of molecular orientation during initial growth of molecules on a well-defined surface.

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

    International Nuclear Information System (INIS)

    Moler, E.J.; Kellar, S.A.; Huff, W.R.A.

    1997-01-01

    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 (√3x√3)R30 CO/Cu(111) and p2mg(2xl)CO/Ni(110), nitrogen 1s from c(2x2) N 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

  13. 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.

  14. A tunable low-energy photon source for high-resolution angle-resolved photoemission spectroscopy

    International Nuclear Information System (INIS)

    Harter, John W.; Monkman, Eric J.; Shai, Daniel E.; Nie Yuefeng; Uchida, Masaki; Burganov, Bulat; Chatterjee, Shouvik; King, Philip D. C.; Shen, Kyle M.

    2012-01-01

    We describe a tunable low-energy photon source consisting of a laser-driven xenon plasma lamp coupled to a Czerny-Turner monochromator. The combined tunability, brightness, and narrow spectral bandwidth make this light source useful in laboratory-based high-resolution photoemission spectroscopy experiments. The source supplies photons with energies up to ∼7 eV, delivering under typical conditions >10 12 ph/s within a 10 meV spectral bandwidth, which is comparable to helium plasma lamps and many synchrotron beamlines. We first describe the lamp and monochromator system and then characterize its output, with attention to those parameters which are of interest for photoemission experiments. Finally, we present angle-resolved photoemission spectroscopy data using the light source and compare its performance to a conventional helium plasma lamp.

  15. 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.

  16. Electronic structure of Sr2RuO4 studied by angle-resolved photoemission spectroscopy

    International Nuclear Information System (INIS)

    Iwasawa, H.; Aiura, Y.; Saitoh, T.; Yoshida, Y.; Hase, I.; Ikeda, S.I.; Bando, H.; Kubota, M.; Ono, K.

    2007-01-01

    Electronic structure of the monolayer strontium ruthenate Sr 2 RuO 4 was investigated by high-resolution angle-resolved photoemission spectroscopy. We present photon-energy (hν) dependence of the electronic structure near the Fermi level along the ΓM line. The hν dependence has shown a strong spectral weight modulation of the Ru 4d xy and 4d zx bands

  17. Study of High Temperature Superconductors with Angle-Resolved Photoemission Spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Dunn, Lisa

    2003-05-13

    The Angle Resolved Photoemission Spectroscopy (ARPES) recently emerged as a powerful tool for the study of highly correlated materials. This thesis describes the new generation of ARPES experiment, based on the third generation synchrotron radiation source and utilizing very high resolution electron energy and momentum analyzer. This new setup is used to study the physics of high temperature superconductors. New results on the Fermi surfaces, dispersions, scattering rate and superconducting gap in high temperature superconductors are presented.

  18. 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.

  19. Bogoliubov Angle, Particle-Hole Mixture and Angular Resolved Photoemission Spectroscopy in Superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Balatsky, A.

    2010-05-04

    Superconducting excitations - Bogoliubov quasiparticles - are the quantum mechanical mixture of negatively charged electron (-e) and positively charged hole (+e). We propose a new observable for Angular Resolved Photoemission Spectroscopy (ARPES) studies that is the manifestation of the particle-hole entanglement of the superconducting quasiparticles. We call this observable a Bogoliubov angle. This angle measures the relative weight of particle and hole amplitude in the superconducting (Bogoliubov) quasiparticle. We show how this quantity can be measured by comparing the ratio of spectral intensities at positive and negative energies.

  20. Electronic structure of superconducting Bi2212 crystal by angle resolved ultra violet photoemission

    International Nuclear Information System (INIS)

    Saini, N.L.; Shrivastava, P.; Garg, K.B.

    1993-01-01

    The electronic structure of a high quality superconducting Bi 2 Sr 2 CaCu 2 Osub(8+δ) (Bi2212) single crystal is studied by angle resolved ultra violet photoemission (ARUPS) using He I (21.2 eV). Our results appear to show two bands crossing the Fermi level in ΓX direction of the Brillouin zone as reported by Takahashi et al. The bands at higher binding energy do not show any appreciable dispersion. The nature of the states near the Fermi level is discussed and the observed band structure is compared with the band structure calculations. (author)

  1. Determination of electronic states in crystalline semiconductors and metals by angle-resolved photoemission

    International Nuclear Information System (INIS)

    Mills, K.A.

    1979-08-01

    An important part of the theoretical description of the solid state is band structure, which relies on the existence of dispersion relations connecting the electronic energy and wavevector in materials with translational symmetry. These relations determine the electronic behavior of such materials. The elaboration of accurate band structures, therefore, is of considerable fundamental and practical importance. Angle-resolved photoemission (ARP) spectroscopy provides the only presently available method for the detailed experimental investigation of band structures. This work is concerned with its application to both semiconducting and metallic single crystals

  2. An experimentalist's guide to the matrix element in angle resolved photoemission

    International Nuclear Information System (INIS)

    Moser, Simon

    2017-01-01

    Highlights: • An introduction to the art of angle resolved photoemission is presented. • Matrix element effects are described by a nearly free electron final state model. • ARPES spectral weight of a Bloch band can be calculated from the Fourier transform of its Wannier orbital. • Experimental handedness and improper polarization introduce dichroism. • Instructive showcases from modern ARPES are discussed in detail. - Abstract: Angle resolved photoemission spectroscopy (ARPES) is commonly known as a powerful probe of the one-electron removal spectral function in ordered solid state. With increasing efficiency of light sources and spectrometers, experiments over a wide range of emission angles become more and more common. Consequently, the angular variation of ARPES spectral weight – often times termed “matrix element effect” – enters as an additional source of information. In this tutorial, we develop a simple but instructive free electron final state approach based on the three-step model to describe the intensity distribution in ARPES. We find a compact expression showing that the ARPES spectral weight of a given Bloch band is essentially determined by the momentum distribution (the Fourier transform) of its associated Wannier orbital – times a polarization dependent pre-factor. While the former is giving direct information on the symmetry and shape of the electronic wave function, the latter can give rise to surprising geometric effects. We discuss a variety of modern and instructive experimental showcases for which this simplistic formalism works astonishingly well and discuss the limits of this approach.

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

    Science.gov (United States)

    Park, Sang Han; Kwon, Soonnam

    2016-05-10

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

  4. Dimensional Crossover in a Charge Density Wave Material Probed by Angle-Resolved Photoemission Spectroscopy

    Science.gov (United States)

    Nicholson, C. W.; Berthod, C.; Puppin, M.; Berger, H.; Wolf, M.; Hoesch, M.; Monney, C.

    2017-05-01

    High-resolution angle-resolved photoemission spectroscopy data reveal evidence of a crossover from one-dimensional (1D) to three-dimensional (3D) behavior in the prototypical charge density wave (CDW) material NbSe3 . In the low-temperature 3D regime, gaps in the electronic structure are observed due to two incommensurate CDWs, in agreement with x-ray diffraction and electronic-structure calculations. At higher temperatures we observe a spectral weight depletion that approaches the power-law behavior expected in one dimension. From the warping of the quasi-1D Fermi surface at low temperatures, we extract the energy scale of the dimensional crossover. This is corroborated by a detailed analysis of the density of states, which reveals a change in dimensional behavior dependent on binding energy. Our results offer an important insight into the dimensionality of excitations in quasi-1D materials.

  5. 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.

  6. Angle-resolved photoemission spectra of graphene from first-principles calculations.

    Science.gov (United States)

    Park, Cheol-Hwan; Giustino, Feliciano; Spataru, Catalin D; Cohen, Marvin L; Louie, Steven G

    2009-12-01

    Angle-resolved photoemission spectroscopy (ARPES) is a powerful experimental technique for directly probing electron dynamics in solids. The energy versus momentum dispersion relations and the associated spectral broadenings measured by ARPES provide a wealth of information on quantum many-body interaction effects. In particular, ARPES allows studies of the Coulomb interaction among electrons (electron-electron interactions) and the interaction between electrons and lattice vibrations (electron-phonon interactions). Here, we report ab initio simulations of the ARPES spectra of graphene including both electron-electron and electron-phonon interactions on the same footing. Our calculations reproduce some of the key experimental observations related to many-body effects, including the indication of a mismatch between the upper and lower halves of the Dirac cone.

  7. A brief update of angle-resolved photoemission spectroscopy on a correlated electron system.

    Science.gov (United States)

    Lee, W S; Vishik, I M; Lu, D H; Shen, Z-X

    2009-04-22

    In this paper, we briefly summarize the capabilities of state-of-the-art angle-resolved photoemission spectroscopy (ARPES) in the field of experimental condensed matter physics. Due to the advancement of the detector technology and the high flux light sources, ARPES has become a powerful tool to study the low energy excitations of solids, especially those novel quantum materials in which many-body physics are at play. To benchmark today's state-of-the-art ARPES technique, we demonstrate that the precision of today's ARPES has advanced to a regime comparable to the bulk-sensitive de Haas-van Alphen (dHvA) measurements. Finally, as an example of new discoveries driven by the advancement of the ARPES technique, we summarize some of our recent ARPES measurements on underdoped high-T(c) superconducting cuprates, which have provided further insight into the complex pseudogap problem.

  8. Angle-resolved photoemission spectroscopy for the study of two-dimensional materials

    Science.gov (United States)

    Mo, Sung-Kwan

    2017-03-01

    Quantum systems in confined geometries allow novel physical properties that cannot easily be attained in their bulk form. These properties are governed by the changes in the band structure and the lattice symmetry, and most pronounced in their single layer limit. Angle-resolved photoemission spectroscopy (ARPES) is a direct tool to investigate the underlying changes of band structure to provide essential information for understanding and controlling such properties. In this review, recent progresses in ARPES as a tool to study two-dimensional atomic crystals have been presented. ARPES results from few-layer and bulk crystals of material class often referred as "beyond graphene" are discussed along with the relevant developments in the instrumentation.

  9. Direct observation of superconducting gaps in MgB 2 by angle-resolved photoemission spectroscopy

    Science.gov (United States)

    Souma, S.; Machida, Y.; Sato, T.; Takahashi, T.; Matsui, H.; Wang, S.-C.; Ding, H.; Kaminski, A.; Campuzano, J. C.; Sasaki, S.; Kadowaki, K.

    2004-08-01

    High-resolution angle-resolved photoemission spectroscopy has been carried out to clarify the anomalous superconductivity of MgB 2. We observed three bands crossing the Fermi level, which are ascribed to B2p-σ, π and surface bands. We have succeeded for the first time in directly observing the superconducting gaps of these bands separately. We have found that the superconducting-gap sizes of σ and surface bands are 6.5 ± 0.5 and 6.0 ± 0.5 meV, respectively, while that of the π band is much smaller (1.5 ± 0.5 meV). The present experimental result unambiguously demonstrates the validity of the two-band superconductivity in MgB 2.

  10. Direct observation of superconducting gaps in MgB2 by angle-resolved photoemission spectroscopy

    International Nuclear Information System (INIS)

    Souma, S.; Machida, Y.; Sato, T.; Takahashi, T.; Matsui, H.; Wang, S.-C.; Ding, H.; Kaminski, A.; Campuzano, J.C.; Sasaki, S.; Kadowaki, K.

    2004-01-01

    High-resolution angle-resolved photoemission spectroscopy has been carried out to clarify the anomalous superconductivity of MgB 2 . We observed three bands crossing the Fermi level, which are ascribed to B2p-σ, π and surface bands. We have succeeded for the first time in directly observing the superconducting gaps of these bands separately. We have found that the superconducting-gap sizes of σ and surface bands are 6.5 ± 0.5 and 6.0 ± 0.5 meV, respectively, while that of the π band is much smaller (1.5 ± 0.5 meV). The present experimental result unambiguously demonstrates the validity of the two-band superconductivity in MgB 2

  11. Tunable vacuum ultraviolet laser based spectrometer for angle resolved photoemission spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Jiang, Rui; Mou, Daixiang; Wu, Yun; Huang, Lunan; Kaminski, Adam [Division of Materials Science and Engineering, Ames Laboratory, Ames, Iowa 50011 (United States); Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011 (United States); McMillen, Colin D.; Kolis, Joseph [Department of Chemistry, Clemson University, Clemson, South Carolina 29634 (United States); Giesber, Henry G.; Egan, John J. [Advanced Photonic Crystals LLC, Fort Mill, South Carolina 29708 (United States)

    2014-03-15

    We have developed an angle-resolved photoemission spectrometer with tunable vacuum ultraviolet laser as a photon source. The photon source is based on the fourth harmonic generation of a near IR beam from a Ti:sapphire laser pumped by a CW green laser and tunable between 5.3 eV and 7 eV. The most important part of the set-up is a compact, vacuum enclosed fourth harmonic generator based on potassium beryllium fluoroborate crystals, grown hydrothermally in the US. This source can deliver a photon flux of over 10{sup 14} photon/s. We demonstrate that this energy range is sufficient to measure the k{sub z} dispersion in an iron arsenic high temperature superconductor, which was previously only possible at synchrotron facilities.

  12. Angle-resolved and resonant photoemission spectroscopy of rare-earth and actinide intermetallics

    Science.gov (United States)

    Reihl, Bruno

    1985-07-01

    In this paper, some aspects of our angle-resolved and resonant photoemission work on rare-earth and actinide intermetallics will be summarized. The systems specifically mentioned are Gd(0001), UIr 3(100), UN(100), UO 2, α-γ- Ce 0.9Th 0.1, U xTh 1- xSb, USb xTe 1- x, UPd 3, UCu xNi 5- x, CeCu 2Si 2, UBe 13, U 2Zn 17 , SmAl 2, EuPd 13, YbBe 13, TmS, Yb xY 1- xAl 2, EuPd 2Si 2, TmSe, and UAs xSe 1- x.

  13. Soft X-ray angle-resolved photoemission with micro-positioning techniques for metallic V2O3

    Science.gov (United States)

    Fujiwara, Hidenori; Kiss, Takayuki; Wakabayashi, Yuki K.; Nishitani, Yoshito; Mori, Takeo; Nakata, Yuki; Kitayama, Satoshi; Fukushima, Kazuaki; Ikeda, Shinji; Fuchimoto, Hiroto; Minowa, Yosuke; Mo, Sung-Kwan; Denlinger, Jonathan D.; Allen, James W.; Metcalf, Patricia; Imai, Masaki; Yoshimura, Kazuyoshi; Suga, Shigemasa; Muro, Takayuki; Sekiyama, Akira

    2015-01-01

    Soft X-ray angle-resolved photoemission has been performed for metallic V2O3. By combining a microfocus beam (40 µm × 65 µm) and micro-positioning techniques with a long-working-distance microscope, it has been possible to observe band dispersions from tiny cleavage surfaces with a typical size of several tens of µm. The photoemission spectra show a clear position dependence, reflecting the morphology of the cleaved sample surface. By selecting high-quality flat regions on the sample surface, it has been possible to perform band mapping using both photon-energy and polar-angle dependences, opening the door to three-dimensional angle-resolved photoemission spectroscopy for typical three-dimensional correlated materials where large cleavage planes are rarely obtained. PMID:25931096

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

    Science.gov (United States)

    He, Yu; Vishik, Inna M; Yi, Ming; Yang, Shuolong; Liu, Zhongkai; Lee, James J; Chen, Sudi; Rebec, Slavko N; Leuenberger, Dominik; Zong, Alfred; Jefferson, C Michael; Moore, Robert G; Kirchmann, Patrick S; Merriam, Andrew J; Shen, Zhi-Xun

    2016-01-01

    We developed a table-top vacuum ultraviolet (VUV) laser with 113.778 nm wavelength (10.897 eV) and demonstrated its viability as a photon source for high resolution angle-resolved photoemission spectroscopy (ARPES). This sub-nanosecond pulsed VUV laser operates at a repetition rate of 10 MHz, provides a flux of 2 × 10(12) photons/s, and enables photoemission with energy and momentum resolutions better than 2 meV and 0.012 Å(-1), respectively. Space-charge induced energy shifts and spectral broadenings can be reduced below 2 meV. The setup reaches electron momenta up to 1.2 Å(-1), granting full access to the first Brillouin zone of most materials. Control over the linear polarization, repetition rate, and photon flux of the VUV source facilitates ARPES investigations of a broad range of quantum materials, bridging the application gap between contemporary low energy laser-based ARPES and synchrotron-based ARPES. We describe the principles and operational characteristics of this source and showcase its performance for rare earth metal tritellurides, high temperature cuprate superconductors, and iron-based superconductors.

  15. Valence-band structure of cubic CdS as determined by angle-resolved photoemission

    Science.gov (United States)

    Stampfl, A. P. J.; Hofmann, Ph.; Schaff, O.; Bradshaw, A. M.

    1997-04-01

    The valence-band structure of cubic CdS along the Γ-Σ-X direction and at all high-symmetry points has been experimentally determined using angle-resolved photoemission and compared to two local density approximation (LDA) calculations as well as to a recent quasiparticle calculation. The Cd 4d level was found to be semibandlike with an energy dispersion of up to 1 eV. The energy difference between the experimental and our calculated linear-muffin-tin orbital (LMTO) LDA energies falls, as expected, along a line of positive gradient. The quasiparticle calculation by Pollmann and co-workers fits the experimental values somewhat better than the LMTO calculation, although a difference of ~1.0 eV was still found to occur for the Cd 4d band. The self-interaction and relaxation-corrected pseudopotential LDA results by the same group give the best fit to within ~+/-0.5 eV for nearly all critical energies measured. Comparison with previously reported photoemission results on the wurtzite structure shows that energies at equivalent symmetry points agree within experimental error.

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

    International Nuclear Information System (INIS)

    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(2x1)CO/Ni(110) and the p(2x2)K/Ni(111) adsorption. For the dense p2mg(2x1)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±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±0.02 Angstrom. The first- to second-layer spacing of Ni is 1.27±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 ∼ 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(2x2)K/Ni(111) overlayer, ARPEFS χ(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

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

    International Nuclear Information System (INIS)

    Paul, Sanhita; Kumari, Spriha; Raj, Satyabrata

    2016-01-01

    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 0.25 WO 3 ) and phosphate (P 4 W 12 O 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.

  18. Angle-resolved photoemission spectroscopy of rare earth LaSb{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Michiardi, Matteo; Arnold, Fabian; Faerch Fisher, Karl Frederik; Svane, Axel; Bianchi, Marco; Brummerstedt Iversen, Bo; Hofmann, Philip [Aarhus University (Denmark); Shwetha, G.; Kanchana, V. [IIT-Hyderabad (India); Ganapathy, Vaitheeswaran [University of Hyderabad (India)

    2016-07-01

    Several rare earth diantimonides have been found to exhibit intriguing electronic properties such as anisotropic linear and non-saturating magnetoresistance. Among these materials, LaSb{sub 2} is not only considered for application in magnetoresistive devices but it is also found to be superconducting at low temperatures and it is investigated as candidate material to host charge density wave phases. Despite the several studies on its transport properties, the electronic structure of LaSb{sub 2} is still largely unknown. Here we present an angle-resolved photoemission spectroscopy and ab-initio calculation study of LaSb{sub 2}(001). The observed band structure is found to be in good agreement with theoretical predictions. Our results reveal that LaSb{sub 2} is a semimetal with a strongly nested two-dimensional Fermi surface. The low energy spectrum is characterized by four massive hole pockets and by four shallow, strongly directional, electron pockets that exhibit Dirac-like dispersion. We speculate on the possibility that this peculiar electronic structure drives the magnetoresistance to its quantum limit, explaining its unconventional behavior.

  19. Angle-resolved photoemission spectroscopy studies of metallic surface and interface states of oxide insulators

    Science.gov (United States)

    Plumb, Nicholas C.; Radović, Milan

    2017-11-01

    Over the last decade, conducting states embedded in insulating transition metal oxides (TMOs) have served as gateways to discovering and probing surprising phenomena that can emerge in complex oxides, while also opening opportunities for engineering advanced devices. These states are commonly realized at thin film interfaces, such as the well-known case of LaAlO3 (LAO) grown on SrTiO3 (STO). In recent years, the use of angle-resolved photoemission spectroscopy (ARPES) to investigate the k-space electronic structure of such materials led to the discovery that metallic states can also be formed on the bare surfaces of certain TMOs. In this topical review, we report on recent studies of low-dimensional metallic states confined at insulating oxide surfaces and interfaces as seen from the perspective of ARPES, which provides a direct view of the occupied band structure. While offering a fairly broad survey of progress in the field, we draw particular attention to STO, whose surface is so far the best-studied, and whose electronic structure is probably of the most immediate interest, given the ubiquitous use of STO substrates as the basis for conducting oxide interfaces. The ARPES studies provide crucial insights into the electronic band structure, orbital character, dimensionality/confinement, spin structure, and collective excitations in STO surfaces and related oxide surface/interface systems. The obtained knowledge increases our understanding of these complex materials and gives new perspectives on how to manipulate their properties.

  20. Electronic properties of novel topological quantum materials studied by angle-resolved photoemission spectroscopy (ARPES)

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Yun [Iowa State Univ., Ames, IA (United States)

    2016-12-17

    The discovery of quantum Hall e ect has motivated the use of topology instead of broken symmetry to classify the states of matter. Quantum spin Hall e ect has been proposed to have a separation of spin currents as an analogue of the charge currents separation in quantum Hall e ect, leading us to the era of topological insulators. Three-dimensional analogue of the Dirac state in graphene has brought us the three-dimensional Dirac states. Materials with three-dimensional Dirac states could potentially be the parent compounds for Weyl semimetals and topological insulators when time-reversal or space inversion symmetry is broken. In addition to the single Dirac point linking the two dispersion cones in the Dirac/Weyl semimetals, Dirac points can form a line in the momentum space, resulting in a topological node line semimetal. These fascinating novel topological quantum materials could provide us platforms for studying the relativistic physics in condensed matter systems and potentially lead to design of new electronic devices that run faster and consume less power than traditional, silicon based transistors. In this thesis, we present the electronic properties of novel topological quantum materials studied by angle-resolved photoemission spectroscopy (ARPES).

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

    NARCIS (Netherlands)

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

    2013-01-01

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

  2. Beamline for angle-resolved photoemission spectroscopy at low-temperature constructed at NTT Atsugi R and D Center

    International Nuclear Information System (INIS)

    Suzuki, Satoru; Yamamoto, Hideki; Maeda, Fumihiko; Watanabe, Yoshio; Yamada, Koji; Kiyokura, Takanori

    2005-01-01

    A vacuum ultra-violet beamline for in situ angle-resolved photoemission spectroscopy of MBE-grown high-T c superconductors at low temperature has been constructed at beamline ABL-6B of the normal-conducting ring in the synchrotron radiation facility of the NTT Atsugi R and D Center. The constant-deviation-angle varied-line-spacing plane grating monochromator covers the energy range of 20-200 eV by using two gratings. A photon flux of the order of 10 11 s -1 with a resolving power of 2000 or more was achieved in the whole energy range. The endstation is equipped with an angle-resolved photoelectron spectrometer, an rf-stimulated He discharge lamp, a custom-designed sample manipulator for low-temperature measurements and a loadlock system for in situ measurements. Total energy resolution of about 13 meV has been obtained for the photoemission spectrum of the Au Fermi edge, in spite of the bending-magnet light source of a second-generation synchrotron radiation ring

  3. 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.

  4. 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.

  5. Nano-Angle Resolved Photoemission Spectroscopy on Topological insulator Sb2Te3 nanowires responsible of quantum transport

    Science.gov (United States)

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

    2017-06-01

    Using high-resolution Nano-Angle Resolved Photoemission Spectroscopy (Nano-ARPES), we have determined the electronic structure of the surface and bulk states of topological insulator Sb2Te3 nanowires, which have been also characterized by magnetoresistance measurements. The observed Aharonov-Bohm-type oscillations could be unambiguously related to the transport by topological protected surface states directly recorded by photoemission. We have measured Nano-ARPES on individual nanowires of a few nanometers wide to provide direct evidence of the existence of the nontrivial topological surface states, as well as their doping. Our findings are consistent with theoretical predictions and confirm that the surface states of intrinsically doped unidimensional topological insulator nanowires are responsible for the quantum transport.

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

    Energy Technology Data Exchange (ETDEWEB)

    Zhou, X.J.

    2010-04-30

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

  7. Direct observation of superconducting gaps in MgB{sub 2} by angle-resolved photoemission spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Souma, S.; Machida, Y.; Sato, T.; Takahashi, T.; Matsui, H.; Wang, S.-C.; Ding, H.; Kaminski, A.; Campuzano, J.C.; Sasaki, S.; Kadowaki, K

    2004-08-01

    High-resolution angle-resolved photoemission spectroscopy has been carried out to clarify the anomalous superconductivity of MgB{sub 2}. We observed three bands crossing the Fermi level, which are ascribed to B2p-{sigma}, {pi} and surface bands. We have succeeded for the first time in directly observing the superconducting gaps of these bands separately. We have found that the superconducting-gap sizes of {sigma} and surface bands are 6.5 {+-} 0.5 and 6.0 {+-} 0.5 meV, respectively, while that of the {pi} band is much smaller (1.5 {+-} 0.5 meV). The present experimental result unambiguously demonstrates the validity of the two-band superconductivity in MgB{sub 2}.

  8. Electronic anisotropies revealed by detwinned angle-resolved photo-emission spectroscopy measurements of FeSe

    Science.gov (United States)

    Watson, Matthew D.; Haghighirad, Amir A.; Rhodes, Luke C.; Hoesch, Moritz; Kim, Timur K.

    2017-10-01

    We report high resolution angle-resolved photo-emission spectroscopy (ARPES) measurements of detwinned FeSe single crystals. The application of a mechanical strain is used to promote the volume fraction of one of the orthorhombic domains in the sample, which we estimate to be 80 % detwinned. While the full structure of the electron pockets consisting of two crossed ellipses may be observed in the tetragonal phase at temperatures above 90 K, we find that remarkably, only one peanut-shaped electron pocket oriented along the longer a axis contributes to the ARPES measurement at low temperatures in the nematic phase, with the expected pocket along b being not observed. Thus the low temperature Fermi surface of FeSe as experimentally determined by ARPES consists of one elliptical hole pocket and one orthogonally-oriented peanut-shaped electron pocket. Our measurements clarify the long-standing controversies over the interpretation of ARPES measurements of FeSe.

  9. Direct Observation of Localized Spin Antiferromagnetic Transition in PdCrO2 by Angle-Resolved Photoemission Spectroscopy

    Science.gov (United States)

    Noh, Han-Jin; Jeong, Jinwon; Chang, Bin; Jeong, Dahee; Moon, Hyun Sook; Cho, En-Jin; Ok, Jong Mok; Kim, Jun Sung; Kim, Kyoo; Min, B. I.; Lee, Han-Koo; Kim, Jae-Young; Park, Byeong-Gyu; Kim, Hyeong-Do; Lee, Seongsu

    2014-01-01

    We report the first case of the successful measurements of a localized spin antiferromagnetic transition in delafossite-type PdCrO2 by angle-resolved photoemission spectroscopy (ARPES). This demonstrates how to circumvent the shortcomings of ARPES for investigation of magnetism involved with localized spins in limited size of two-dimensional crystals or multi-layer thin films that neutron scattering can hardly study due to lack of bulk compared to surface. Also, our observations give direct evidence for the spin ordering pattern of Cr3+ ions in PdCrO2 suggested by neutron diffraction and quantum oscillation measurements, and provide a strong constraint that has to be satisfied by a microscopic mechanism for the unconventional anomalous Hall effect recently reported in this system. PMID:24419488

  10. Electronic structure of K0.5CoO2 studied by angle-resolved photoemission spectroscopy

    International Nuclear Information System (INIS)

    Usui, H.; Iwasawa, H.; Hirose, M.; Maeda, Y.; Saitoh, T.; Osada, H.; Kyomen, T.; Hanaya, M.; Aiura, Y.; Kotani, Y.; Kubota, M.; Ono, K.

    2010-01-01

    We have investigated the electronic structure of K 0.5 CoO 2 in the metallic phase by high-resolution angle-resolved photoemission spectroscopy at a low temperature. An observed Fermi surface of K 0.5 CoO 2 was a large hexagonal one around the Γ point only, with no hole pockets on the Γ-K lines which was typically predicted by band-structure calculations with local-density approximation (LDA). We also found that a modulation of the Fermi velocity, which was the largest at K point and the smallest at M point, was again opposite to the prediction by LDA band-theory. In spite of this conflicting with LDA band-theory, our results are both in agreement with what was observed in Na x CoO 2 .

  11. High Resolution Angle Resolved Photoemission Studies on Quasi-Particle Dynamics in Graphite

    Energy Technology Data Exchange (ETDEWEB)

    Leem, C.S.

    2010-06-02

    We obtained the spectral function of the graphite H point using high resolution angle resolved photoelectron spectroscopy (ARPES). The extracted width of the spectral function (inverse of the photo-hole lifetime) near the H point is approximately proportional to the energy as expected from the linearly increasing density of states (DOS) near the Fermi energy. This is well accounted by our electron-phonon coupling theory considering the peculiar electronic DOS near the Fermi level. And we also investigated the temperature dependence of the peak widths both experimentally and theoretically. The upper bound for the electron-phonon coupling parameter is 0.23, nearly the same value as previously reported at the K point. Our analysis of temperature dependent ARPES data at K shows that the energy of phonon mode of graphite has much higher energy scale than 125K which is dominant in electron-phonon coupling.

  12. Dissimilarities between the electronic structure of chemically doped and chemically pressurized iron pnictides from an angle-resolved photoemission spectroscopy study

    NARCIS (Netherlands)

    Thirupathaiah, S.; Rienks, E.D.L.; Jeevan, H.S.; Ovsyannikov, R.; Slooten, E.; Kaas, J.; van Heumen, E.; de Jong, S.; Duerr, H.A.; Siemensmeyer, K.; Follath, R.; Gegenwart, P.; Golden, M.S.; Fink, J.

    2011-01-01

    We have studied the electronic structure of EuFe2As2-xPx using high-resolution angle-resolved photoemission spectroscopy. Upon substituting As with the isovalent P, which leads to chemical pressure and to superconductivity, we observe a nonrigid-band-like change of the electronic structure along the

  13. Dissimilarities between the electronic structure of chemically doped and chemically pressurized iron pnictides from an angle-resolved photoemission spectroscopy study

    NARCIS (Netherlands)

    Thirupathaiah, S.; Rienks, E.D.L.; Jeevan, H.S.; Ovsyannikov, R.; Slooten, E.; Kaas, J.; van Heumen, E.; de Jong, S.; Dürr, H.A.; Siemensmeyer, K.; Follath, R.; Gegenwart, P.; Golden, M.S.; Fink, J.

    2010-01-01

    We have studied the electronic structure of EuFe2As2-xPx using high resolution angle-resolved photoemission spectroscopy. Upon substituting As with the isovalent P, which leads to a chemical pressure and to superconductivity, we observe a non-rigid-band like change of the electronic structure along

  14. Theory of angle-resolved photoemission experiments on a two-band model

    OpenAIRE

    De Cao, Tian

    2008-01-01

    Considering the electron states inside and outside the solid, we derive a formula of photoemission intensity. A general theoretical way to determine electronic structures of solids from ARPES experiments is outlined. It is shown that the spectral function inside the solids cannot be measured directly by ARPES, the effects of free electron states on the electronic structure observed by ARPES measurements must be considered, and the results from ARPES experiments cannot be understood until thes...

  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. Electronic band structure of epitaxial PbTe (111) thin films observed by angle-resolved photoemission spectroscopy

    Science.gov (United States)

    Ye, Zhenyu; Cui, Shengtao; Shu, Tianyu; Ma, Songsong; Liu, Yang; Sun, Zhe; Luo, Jun-Wei; Wu, Huizhen

    2017-04-01

    Using angle-resolved photoemission spectroscopy (ARPES), we studied bulk and surface electronic band structures of narrow-gap semiconductor lead telluride (PbTe) thin films grown by molecular beam epitaxy both perpendicular and parallel to the Γ -L direction. The comparison of ARPES data with the first-principles calculation reveals the details of band structures, orbital characters, spin-orbit splitting energies, and surface states. The photon-energy-dependent spectra show the bulk character. Both the L and Σ valence bands are observed and their energy difference is determined. The spin-orbit splitting energies at L and Γ points are 0.62 eV and 0.88 eV, respectively. The surface states below and close to the valence band maximum are identified. The valence bands are composed of a mixture of Pb 6 s and Te 5 pz orbitals with dominant in-plane even parity, which is attributed to the layered distortion in the vicinity of the PbTe (111) surface. These findings provide insights into PbTe fundamental properties and shall benefit relevant thermoelectric and optoelectronic applications.

  17. Evidence for Itinerant Carriers in an Anisotropic Narrow-Gap Semiconductor by Angle-Resolved Photoemission Spectroscopy.

    Science.gov (United States)

    Ju, Sailong; Bai, Wei; Wu, Liming; Lin, Hua; Xiao, Chong; Cui, Shengtao; Li, Zhou; Kong, Shuai; Liu, Yi; Liu, Dayong; Zhang, Guobin; Sun, Zhe; Xie, Yi

    2018-01-01

    The ability to accurately determine the electronic structure of solids has become a key prerequisite for modern functional materials. For example, the precise determination of the electronic structure helps to balance the three thermoelectric parameters, which is the biggest challenge to design high-performance thermoelectric materials. Herein, by high-resolution, angle-resolved photoemission spectroscopy (ARPES), the itinerant carriers in CsBi 4 Te 6 (CBT) are revealed for the first time. CBT is a typical anisotropic, narrow-gap semiconductor used as a practical candidate for low-temperature thermoelectric applications, and p-doped CBT series show superconductivity at relatively low carrier concentrations. The ARPES results show a significantly larger bandwidth near the Fermi surface than calculations, which means the carriers transport anisotropically and itinerantly in CBT. It is reasonable to believe that these newly discovered features of carriers in narrow-gap semiconductors are promising for designing optimal thermoelectric materials and superconductors. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  18. 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.

  19. Evidence for Anionic Excess Electrons in a Quasi-Two-Dimensional Ca2N Electride by Angle-Resolved Photoemission Spectroscopy.

    Science.gov (United States)

    Oh, Ji Seop; Kang, Chang-Jong; Kim, Ye Ji; Sinn, Soobin; Han, Moonsup; Chang, Young Jun; Park, Byeong-Gyu; Kim, Sung Wng; Min, Byung Il; Kim, Hyeong-Do; Noh, Tae Won

    2016-03-02

    Angle-resolved photoemission spectroscopy (ARPES) study of a layered electride Ca2N was carried out to reveal its quasi-two-dimensional electronic structure. The band dispersions and the Fermi-surface map are consistent with the density functional theory results except for a chemical potential shift that may originate from the high reactivity of surface excess electrons. Thus, the existence of anionic excess electrons in the interlayer region of Ca2N is strongly supported by ARPES.

  20. Review of the theoretical description of time-resolved angle-resolved photoemission spectroscopy in electron-phonon mediated superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Kemper, A.F. [Department of Physics, North Carolina State University, Raleigh, NC (United States); Sentef, M.A. [Max Planck Institute for the Structure and Dynamics of Matter, Center for Free Electron Laser Science, Hamburg (Germany); Moritz, B. [Stanford Institute for Materials and Energy Sciences (SIMES), SLAC National Accelerator Laboratory, Menlo Park, CA (United States); Devereaux, T.P. [Stanford Institute for Materials and Energy Sciences (SIMES), SLAC National Accelerator Laboratory, Menlo Park, CA (United States); Geballe Laboratory for Advanced Materials, Stanford University, Stanford, CA (United States); Freericks, J.K. [Department of Physics, Georgetown University, Washington, DC (United States)

    2017-09-15

    We review recent work on the theory for pump/probe photoemission spectroscopy of electron-phonon mediated superconductors in both the normal and the superconducting states. We describe the formal developments that allow one to solve the Migdal-Eliashberg theory in nonequilibrium for an ultrashort laser pumping field, and explore the solutions which illustrate the relaxation as energy is transferred from electrons to phonons. We focus on exact results emanating from sum rules and approximate numerical results which describe rules of thumb for relaxation processes. In addition, in the superconducting state, we describe how Anderson-Higgs oscillations can be excited due to the nonlinear coupling with the electric field and describe mechanisms where pumping the system enhances superconductivity. (copyright 2017 by WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  1. Electronic structure of R Sb (R =Y , Ce, Gd, Dy, Ho, Tm, Lu) studied by angle-resolved photoemission spectroscopy

    Science.gov (United States)

    Wu, Yun; Lee, Yongbin; Kong, Tai; Mou, Daixiang; Jiang, Rui; Huang, Lunan; Bud'ko, S. L.; Canfield, P. C.; Kaminski, Adam

    2017-07-01

    We use high-resolution angle-resolved photoemission spectroscopy (ARPES) and electronic structure calculations to study the electronic properties of rare-earth monoantimonides RSb (R = Y, Ce, Gd, Dy, Ho, Tm, Lu). The experimentally measured Fermi surface (FS) of RSb consists of at least two concentric hole pockets at the Γ point and two intersecting electron pockets at the X point. These data agree relatively well with the electronic structure calculations. Detailed photon energy dependence measurements using both synchrotron and laser ARPES systems indicate that there is at least one Fermi surface sheet with strong three-dimensionality centered at the Γ point. Due to the "lanthanide contraction", the unit cell of different rare-earth monoantimonides shrinks when changing the rare-earth ion from CeSb to LuSb. This results in the differences in the chemical potentials in these compounds, which are demonstrated by both ARPES measurements and electronic structure calculations. Interestingly, in CeSb, the intersecting electron pockets at the X point seem to be touching the valence bands, forming a fourfold-degenerate Dirac-like feature. On the other hand, the remaining rare-earth monoantimonides show significant gaps between the upper and lower bands at the X point. Furthermore, similar to the previously reported results of LaBi, a Dirac-like structure was observed at the Γ point in YSb, CeSb, and GdSb, compounds showing relatively high magnetoresistance. This Dirac-like structure may contribute to the unusually large magnetoresistance in these compounds.

  2. Unusually large chemical potential shift in a degenerate semiconductor: Angle-resolved photoemission study of SnSe and Na-doped SnSe

    Science.gov (United States)

    Maeda, M.; Yamamoto, K.; Mizokawa, T.; Saini, N. L.; Arita, M.; Namatame, H.; Taniguchi, M.; Tan, G.; Zhao, L. D.; Kanatzidis, M. G.

    2018-03-01

    We have studied the electronic structure of SnSe and Na-doped SnSe by means of angle-resolved photoemission spectroscopy. The valence-band top reaches the Fermi level by the Na doping, indicating that Na-doped SnSe can be viewed as a degenerate semiconductor. However, in the Na-doped system, the chemical potential shift with temperature is unexpectedly large and is apparently inconsistent with the degenerate semiconductor picture. The large chemical potential shift and anomalous spectral shape are key ingredients for an understanding of the novel metallic state with the large thermoelectric performance in Na-doped SnSe.

  3. 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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-08-31

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

  5. Tuning across the BCS-BEC crossover in the multiband superconductor Fe1+ySe x Te1-x: An angle-resolved photoemission study.

    Science.gov (United States)

    Rinott, Shahar; Chashka, K B; Ribak, Amit; Rienks, Emile D L; Taleb-Ibrahimi, Amina; Le Fevre, Patrick; Bertran, François; Randeria, Mohit; Kanigel, Amit

    2017-04-01

    The crossover from Bardeen-Cooper-Schrieffer (BCS) superconductivity to Bose-Einstein condensation (BEC) is difficult to realize in quantum materials because, unlike in ultracold atoms, one cannot tune the pairing interaction. We realize the BCS-BEC crossover in a nearly compensated semimetal, Fe 1+ y Se x Te 1- x , by tuning the Fermi energy ε F via chemical doping, which permits us to systematically change Δ/ε F from 0.16 to 0.50, where Δ is the superconducting (SC) gap. We use angle-resolved photoemission spectroscopy to measure the Fermi energy, the SC gap, and characteristic changes in the SC state electronic dispersion as the system evolves from a BCS to a BEC regime. Our results raise important questions about the crossover in multiband superconductors, which go beyond those addressed in the context of cold atoms.

  6. Bulk electronic structure of superconducting LaRu2P2 single crystals measured by soft-X-ray angle-resolved photoemission spectroscopy.

    Science.gov (United States)

    Razzoli, E; Kobayashi, M; Strocov, V N; Delley, B; Bukowski, Z; Karpinski, J; Plumb, N C; Radovic, M; Chang, J; Schmitt, T; Patthey, L; Mesot, J; Shi, M

    2012-06-22

    We present a soft x-ray angle-resolved photoemission spectroscopy (SX-ARPES) study of the stoichiometric pnictide superconductor LaRu(2)P(2). The observed electronic structure is in good agreement with density functional theory (DFT) calculations. However, it is significantly different from its counterpart in high-temperature superconducting Fe pnictides. In particular, the bandwidth renormalization present in the Fe pnictides (~2-3) is negligible in LaRu(2)P(2) even though the mass enhancement is similar in both systems. Our results suggest that the superconductivity in LaRu(2) P(2) has a different origin with respect to the iron pnictides. Finally, we demonstrate that the increased probing depth of SX-ARPES, compared to the widely used ultraviolet ARPES, is essential in determining the bulk electronic structure in the experiment.

  7. Multiple Nodeless Superconducting Gaps in (Ba0.6K0.4)Fe2As2 Superconductor from Angle-Resolved Photoemission Spectroscopy

    International Nuclear Information System (INIS)

    Lin, Zhao; Hai-Yun, Liu; Wen-Tao, Zhang; Jian-Qiao, Meng; Xiao-Wen, Jia; Guo-Dong, Liu; Xiao-Li, Dong; Wei, Lu; Xing-Jiang, Zhou; Gen-Fu, Chen; Jian-Lin, Luo; Nan-Lin, Wang; Gui-Ling, Wang; Yong, Zhou; Zu-Yan, Xu; Yong, Zhu; Xiao-Yang, Wang; Chuang-Tian, Chen

    2008-01-01

    High resolution angle-resolved photoemission measurements have been carried out to study the superconducting gap in the (Ba 0.6 K 0.4 )Fe 2 As 2 superconductor with T e = 35 K. Two hole-like Fermi surface sheets around the I' point exhibit different superconducting gaps. The inner Fermi surface sheet shows larger (10 ∼ 12 meV) and slightly momentum-dependent gap while the outer one has smaller (7 ∼ 8meV) and nearly isotropic gap. The lack of gap node in both Fermi surface sheets favours s-wave superconducting gap symmetry. Superconducting gap opening is also observed at the M(π, π) point. The two Fermi surface spots near the M point are gapped below T e but the gap persists above T e. The rich and detailed superconducting gap information will provide key insights and constraints in understanding pairing mechanism in the iron-based superconductors

  8. Time- and angle-resolved photoemission spectroscopy with optimized high-harmonic pulses using frequency-doubled Ti:Sapphire lasers

    International Nuclear Information System (INIS)

    Eich, S.; Stange, A.; Carr, A.V.; Urbancic, J.; Popmintchev, T.; Wiesenmayer, M.; Jansen, K.; Ruffing, A.; Jakobs, S.; Rohwer, T.; Hellmann, S.; Chen, C.; Matyba, P.; Kipp, L.; Rossnagel, K.; Bauer, M.; Murnane, M.M.; Kapteyn, H.C.; Mathias, S.; Aeschlimann, M.

    2014-01-01

    Highlights: • We present a scheme to generate high intensity XUV pulses from HHG with variable time-bandwidth product. • Shorter-wavelength driven high-harmonic XUV trARPES provides higher photon flux and increased energy resolution. • High-quality high-harmonic XUV trARPES data with sub 150 meV energy and sub 30 fs time resolution is presented. - Abstract: Time- and angle-resolved photoemission spectroscopy (trARPES) using femtosecond extreme ultraviolet high harmonics has recently emerged as a powerful tool for investigating ultrafast quasiparticle dynamics in correlated-electron materials. However, the full potential of this approach has not yet been achieved because, to date, high harmonics generated by 800 nm wavelength Ti:Sapphire lasers required a trade-off between photon flux, energy and time resolution. Photoemission spectroscopy requires a quasi-monochromatic output, but dispersive optical elements that select a single harmonic can significantly reduce the photon flux and time resolution. Here we show that 400 nm driven high harmonic extreme-ultraviolet trARPES is superior to using 800 nm laser drivers since it eliminates the need for any spectral selection, thereby increasing photon flux and energy resolution to <150 meV while preserving excellent time resolution of about 30 fs

  9. Identification of Ni2C electronic states in graphene-Ni(111) growth through resonant and dichroic angle-resolved photoemission at the C K -edge

    Science.gov (United States)

    Drera, G.; Cepek, C.; Patera, L. L.; Bondino, F.; Magnano, E.; Nappini, S.; Africh, C.; Lodi-Rizzini, A.; Joshi, N.; Ghosh, P.; Barla, A.; Mahatha, S. K.; Pagliara, S.; Giampietri, A.; Pintossi, C.; Sangaletti, L.

    2017-10-01

    The graphene-Ni(111) (GrNi) growth via chemical vapor deposition has been explored by resonant, angle-resolved, and dichroic photoemission spectroscopy (soft x-ray Res-ARPES) in order to identify the possible contributions to the electronic structure deriving from different phases that can coexist in this complex system. We provide evidences of electronic states so far unexplored at the Γ ¯ point of GrNi, appearing at the C K -edge resonance. These states show both circular dichroism (CD) and k dependence, suggesting a long-range orbital ordering, as well as a coherent matching with the underlying lattice. Through a comparison of core-level photoemission, valence band resonances, and constant initial-state spectroscopy, we demonstrate that these states are actually induced by a low residual component of nickel carbide (Ni2C ). These results also show that caution must be exercised while interpreting x-ray magnetic circular dichroism collected on C K -edge with Auger partial yield method, due to the presence of CD in photoelectron spectra unrelated to magnetic effects.

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

    Science.gov (United States)

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

    2013-09-01

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

  11. 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

  12. Characterization of the α-SN/CDTE(110) interface by angle-resolved X-ray photoemission

    International Nuclear Information System (INIS)

    Lin, T.S.; Partin, W.J.; Chung, Y.W.

    1987-01-01

    Stoichiometric and atomically clean CdTe(110) surfaces have been prepared by suitable chemical etching, followed by argon sputtering, and sample annealing in ultra-high vacuum. Cubic (α) -tin was grown on CdTe(110) by tin evaporation from a tungsten filament at a substrate temperature of 30 0 C. Angle-resolved X-ray photoelectron spectroscopy (ARXPS) was used to determine the α-Sn growth mechanism and the composition profile of this semiconductor heterostructure nondestructively. From their analyses, the authors conclude that α-Sn grows on CdTe(110) at 30 0 C by a layer by layer mechanism and forms an abrupt junction with CdTe(110)

  13. 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.

  14. Multiple π-bands and Bernal stacking of multilayer graphene on C-face SiC, revealed by nano-Angle Resolved Photoemission.

    Science.gov (United States)

    Johansson, Leif I; Armiento, Rickard; Avila, Jose; Xia, Chao; Lorcy, Stephan; Abrikosov, Igor A; Asensio, Maria C; Virojanadara, Chariya

    2014-02-24

    Only a single linearly dispersing π-band cone, characteristic of monolayer graphene, has so far been observed in Angle Resolved Photoemission (ARPES) experiments on multilayer graphene grown on C-face SiC. A rotational disorder that effectively decouples adjacent layers has been suggested to explain this. However, the coexistence of μm-sized grains of single and multilayer graphene with different azimuthal orientations and no rotational disorder within the grains was recently revealed for C-face graphene, but conventional ARPES still resolved only a single π-band. Here we report detailed nano-ARPES band mappings of individual graphene grains that unambiguously show that multilayer C-face graphene exhibits multiple π-bands. The band dispersions obtained close to the K-point moreover clearly indicate, when compared to theoretical band dispersion calculated in the framework of the density functional method, Bernal (AB) stacking within the grains. Thus, contrary to earlier claims, our findings imply a similar interaction between graphene layers on C-face and Si-face SiC.

  15. Angle-resolved photoemission spectroscopy for VO{sub 2} thin films grown on TiO{sub 2} (0 0 1) substrates

    Energy Technology Data Exchange (ETDEWEB)

    Muraoka, Y., E-mail: ymuraoka@cc.okayama-u.ac.j [Graduate School of Natural Science and Technology, Okayama University, 3-1-1 Tsushima-naka, Kita-ku, Okayama 700-8530 (Japan); Faculty of Science, Research Laboratory for Surface Science, Okayama University, 3-1-1 Tsushima-naka, Kita-ku, Okayama 700-8530 (Japan); Saeki, K.; Yao, Y. [Graduate School of Natural Science and Technology, Okayama University, 3-1-1 Tsushima-naka, Kita-ku, Okayama 700-8530 (Japan); Wakita, T. [Faculty of Science, Research Laboratory for Surface Science, Okayama University, 3-1-1 Tsushima-naka, Kita-ku, Okayama 700-8530 (Japan); Hirai, M.; Yokoya, T. [Graduate School of Natural Science and Technology, Okayama University, 3-1-1 Tsushima-naka, Kita-ku, Okayama 700-8530 (Japan); Faculty of Science, Research Laboratory for Surface Science, Okayama University, 3-1-1 Tsushima-naka, Kita-ku, Okayama 700-8530 (Japan); Eguchi, R.; Shin, S. [RIKEN/SPring-8, 1-1-1 Kouto, Sayo, Hyogo 679-5148 (Japan)

    2010-08-15

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

  16. 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 ...

  17. High-resolution angle-resolved photoemission studies of high Tc superconductor Bi2Sr2CaCu2O8

    International Nuclear Information System (INIS)

    Liu, Rong.

    1990-01-01

    An angle-resolved photoemission study of the normal and superconducting states in Bi 2 Sr 2 CaCu 2 O 8 was performed. Measurements in the normal state show bands dispersing through the Fermi level from at least 350 meV below E 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

  18. Electronic Structure of Epitaxial Thin Films of the Transparent Conducting Oxide La:BaSnO3 Measured By In-Situ Angle-Resolved Photoemission Spectroscopy

    Science.gov (United States)

    Lochocki, Edward; Paik, Hanjong; Uchida, Masaki; Schlom, Darrell; Shen, Kyle

    Lanthanum-doped barium stannate (La:BaSnO3) is a transparent conducting oxide where single crystals have exhibited unusually high mobility and oxygen stability. Here we present in-situ angle-resolved photoemission (ARPES) measurements of La:BaSnO3 epitaxial films that were co-deposited onto lattice-matched rare-earth scandate substrates by molecular-beam epitaxy (MBE). Density functional theory (DFT) calculations agree well with the observed valence bands and predict a parabolic conduction band. However, the features observed near the Fermi energy (EF) are non-dispersive yet localized in momentum space. This unusual appearance may be the result of quasi-localized charge carriers or out-of-plane momentum broadening. Over long measurement periods, we also observe changes to the valence band and near-EF feature that bear a strong resemblance to the beam-induced two-dimensional electron gases previously reported in SrTiO3 and KTaO3. The origin of these unexpected phenomena and their relationship to the structural and transport properties of these films will be discussed.

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

    Directory of Open Access Journals (Sweden)

    Teppei eYoshida

    2014-04-01

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

  20. 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.

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

    Science.gov (United States)

    Yamane, Hiroyuki; Kosugi, Nobuhiro

    2014-12-14

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

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

    Science.gov (United States)

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

    2016-01-01

    We report on low-temperature transport and electronic band structure of p-type Sb2Te3 nanowires, grown by chemical vapor deposition. Magnetoresistance measurements unravel quantum interference phenomena, which depend on the cross-sectional dimensions of the nanowires. The observation of periodic Aharonov-Bohm-type oscillations is attributed to transport in topologically protected surface states in the Sb2Te3 nanowires. The study of universal conductance fluctuations demonstrates coherent transport along the Aharonov-Bohm paths encircling the rectangular cross-section of the nanowires. We use nanoscale angle-resolved photoemission spectroscopy on single nanowires (nano-ARPES) to provide direct experimental evidence on the nontrivial topological character of those surface states. The compiled study of the bandstructure and the magnetotransport response unambiguosly points out the presence of topologically protected surface states in the nanowires and their substantial contribution to the quantum transport effects, as well as the hole doping and Fermi velocity among other key issues. The results are consistent with the theoretical description of quantum transport in intrinsically doped quasi-one-dimensional topological insulator nanowires. PMID:27581169

  3. 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.

  4. A spin-resolved photoemission study

    Indian Academy of Sciences (India)

    Stoner vs. spin-mixing behavior in the bulk magnetism of Gd: A spin-resolved photoemission study. K MAITI1,2,∗. , M C MALAGOLI2, A DALLMEYER2 and C CARBONE2,3. 1Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400 005, India. 2Institut für Festkörperforschung, Forschungszentrum Jülich, ...

  5. Insights from angle-resolved photoemission spectroscopy on the metallic states of YbB6(001): E(k) dispersion, temporal changes, and spatial variation

    NARCIS (Netherlands)

    Frantzeskakis, E.; de Jong, N.; Zhang, J.X.; Zhang, X.; Li, Z.; Liang, C.L.; Wang, Y.; Varykhalov, A.; Huang, Y.K.; Golden, M.S.

    2014-01-01

    We report high-resolution angle-resolved photoelectron spectroscopy (ARPES) results on the (001) cleavage surface of YbB6, a rare-earth compound that has been recently predicted to host surface electronic states with topological character. We observe two types of well-resolved metallic states, whose

  6. Strong electron correlations in the normal state of the iron-based FeSe0.42Te0.58 superconductor observed by angle-resolved photoemission spectroscopy.

    Science.gov (United States)

    Tamai, A; Ganin, A Y; Rozbicki, E; Bacsa, J; Meevasana, W; King, P D C; Caffio, M; Schaub, R; Margadonna, S; Prassides, K; Rosseinsky, M J; Baumberger, F

    2010-03-05

    We investigate the normal state of the "11" iron-based superconductor FeSe0.42Te0.58 by angle-resolved photoemission. Our data reveal a highly renormalized quasiparticle dispersion characteristic of a strongly correlated metal. We find sheet dependent effective carrier masses between approximately 3 and 16m{e} corresponding to a mass enhancement over band structure values of m{*}/m{band} approximately 6-20. This is nearly an order of magnitude higher than the renormalization reported previously for iron-arsenide superconductors of the "1111" and "122" families but fully consistent with the bulk specific heat.

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

    Science.gov (United States)

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

    2016-07-13

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

  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. 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

  10. Angle-resolved photoemission spectroscopy of (Ca, Na) sub 2 CuO sub 2 Cl sub 2 crystals: Fingerprints of a magnetic insulator in a heavily underdoped superconductor

    CERN Document Server

    Kohsaka, Y; Ronning, F

    2003-01-01

    Electric evolution from an antiferromagnet to a high-T sub c superconductor is revealed by angle-resolved photoemission experiments on tetragonal Ca sub 1 sub . sub 9 Na sub 0 sub . sub 1 CuO sub 2 Cl sub 2 single crystals, which were successfully grown for the first time under high pressures. In this underdoped superconductor, we found clear fingerprints of the parent insulator: a shadow band and a large pseudogap. These observations are most likely described by a 'chemical potential shift', which contrasts clearly with the prevailing wisdom of the pinned chemical potential' learned from the prototype La sub 2 sub - sub x Sr sub x CuO sub 4 , demonstrating that the route to a high-T sub c superconductor is not unique. (author)

  11. Absence of a holelike fermi surface for the iron-based K0.8F1.7Se2 superconductor revealed by angle-resolved photoemission spectroscopy.

    Science.gov (United States)

    Qian, T; Wang, X-P; Jin, W-C; Zhang, P; Richard, P; Xu, G; Dai, X; Fang, Z; Guo, J-G; Chen, X-L; Ding, H

    2011-05-06

    We have performed an angle-resolved photoemission spectroscopy study of the new iron-based superconductor K(0.8)Fe(1.7)Se(2) (T(c)∼30 K). Clear band dispersion is observed with the overall bandwidth renormalized by a factor of 2.5 compared to our local density approximation calculations, indicating relatively strong correlation effects. Only an electronlike band crosses the Fermi energy, forming a nearly circular Fermi surface (FS) at M (π, 0). The holelike band at Γ sinks ∼90 meV below the Fermi energy, with an indirect band gap of 30 meV, to the bottom of the electronlike band. The observed FS topology in this superconductor favors (π, π) inter-FS scattering between the electronlike FSs at the M points, in sharp contrast to other iron-based superconductors which favor (π, 0) inter-FS scattering between holelike and electronlike FSs.

  12. Reaffirming the d(x2-y2) superconducting gap using the autocorrelation angle-resolved photoemission spectroscopy of Bi1.5Pb0.55Sr1.6La0.4CuO(6+δ).

    Science.gov (United States)

    Hashimoto, M; He, R-H; Testaud, J P; Meevasana, W; Moore, R G; Lu, D H; Yoshida, Y; Eisaki, H; Devereaux, T P; Hussain, Z; Shen, Z-X

    2011-04-22

    Knowledge of the gap function is important to understand the pairing mechanism for high-temperature (T(c)) superconductivity. However, Fourier transform scanning tunneling spectroscopy (FT STS) and angle-resolved photoemission spectroscopy (ARPES) in the cuprates have reported contradictory gap functions, with FT-STS results deviating strongly from a canonical d(x2-y2) form. By applying an "octet model" analysis to autocorrelation ARPES, we reveal that a contradiction occurs because the octet model does not consider the effects of matrix elements and the pseudogap. This reaffirms the canonical d(x2-y2) superconducting gap around the node, which can be directly determined from ARPES. Further, our study suggests that the FT-STS reported fluctuating superconductivity around the node at far above T(c) is not necessary to explain the existence of the quasiparticle interference at low energy.

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

    Directory of Open Access Journals (Sweden)

    Georgi L. Dakovski

    2015-09-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    1997-04-01

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

  15. Angle-Resolved Photoemission Study of the Evolution of Band Structure And Charge Density Wave Properties in Rte (3) (R=Y, La, Ce, Sm, Gd, Tb, And Dy)

    Energy Technology Data Exchange (ETDEWEB)

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

    2009-05-12

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2010-02-15

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

  17. Direct angle resolved photoemission spectroscopy and ...

    Indian Academy of Sciences (India)

    [3] Karl Alex Mueller, personal communications (2006). In contrast, see P W Anderson, Nature Phys. 2, 626 (2006) or the whole issue Nature. Phys. - 20 years of HTSC (March 2006). [4] G Baskaran, personal communication, Kanpur (2006), also CM9910161v1. [5] T Timusk and B Statt, Rep. Prog. Phys. 62(1), 61 (1999).

  18. Direct angle resolved photoemission spectroscopy and ...

    Indian Academy of Sciences (India)

    We gratefully acknowledge financial support by the EPFL and the Swiss National. Fund for Scientific Research. This work is based upon research conducted at the. Synchrotron Radiation Center, University of Wisconsin-Madison, which is sup- ported by the NSF under Award No. DMR-0084402. DP gratefully acknowledges.

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

    International Nuclear Information System (INIS)

    Marczynski-Buehlow, Martin

    2012-01-01

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

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

    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

  1. Spin-resolved photoemission of surface states of W(110)-(1x1)H

    International Nuclear Information System (INIS)

    Hochstrasser, M.; Tobin, J.G.; Rotenberg, Eli; Kevan, S.D.

    2002-01-01

    The surface electronic states of W(110)-(1x1)H have been measured using spin- and angle-resolved photoemission. We directly demonstrate that the surface bands are both split and spin-polarized by the spin-orbit interaction in association with the loss of inversion symmetry near a surface. We observe 100 percent spin polarization of the surface states, with the spins aligned in the plane of the surface and oriented in a circular fashion relative to the S-bar symmetry point. In contrast, no measurable polarization of nearby bulk states is observed

  2. 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.

  3. 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...

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2010-04-13

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

  5. The Verwey transition observed by spin-resolved photoemission electron microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Figuera, Juan de la, E-mail: juan.delafiguera@iqfr.csic.es [Instituto de Química Física “Rocasolano”, CSIC, Madrid E-28006 (Spain); Tusche, Christian [Max Planck Institute of Microstructure Physics, Halle D-06120 (Germany); Forschungszentrum Jülich GmbH, Peter Grünberg Institut (PGI-6), D-52425 Jülich (Germany)

    2017-01-01

    Highlights: • First observations of magnetic domains on magnetite (001) by spin-resolved PEEM. • Spin-polarization through the Verwey transitions does not change appreciably. • Shape and distribution of domains has been observed through the Verwey transition. - Abstract: We have imaged the magnetic domains on magnetite (001) through the Verwey transition by means of spin-resolved photoemission electron microscopy. A He laboratory source is used for illumination. The magnetic domains walls above the Verwey transition are aligned with 〈110〉 in-plane directions. Below the Verwey transition, the domain structure is interpreted as arising from a distribution of areas with different monoclinic c-axis, with linear 180° domain walls within each area and ragged edges when the magnetic domain boundaries coincide with structural domain walls. The domains evolve above the Verwey transition, while they are static below.

  6. Photoemission and ferromagnetism

    International Nuclear Information System (INIS)

    Johnson, P.D.

    1994-01-01

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

  7. Linear and circular dichroism in angle resolved Fe 3p photomission. Revision 1

    International Nuclear Information System (INIS)

    Tamura, E.; Waddill, G.D.; Tobin, J.G.; Sterne, P.A.

    1994-01-01

    Using a recently developed spin-polarized, fully relativistic, multiple scattering approach based on the layer KKR Green function method, we have reproduced the Fe 3p angle-resolved soft x-ray photoemission spectra and analyzed the associated large magnetic dichroism effects for excitation with both linearly and circularly polarized light. Comparison between theory and experiment yields a spin-orbit splitting of 1.0--1.2 eV and an exchange splitting of 0.9-- 1.0 eV for Fe 3p. These values are 50--100% larger than those hitherto obtained experimentally

  8. Thermal Stability of Au/NbOx/Nb and Au/Nb2O5/W Model Catalysts Studied by Angle-resolved X-ray Photoelectron Spectroscopy

    Czech Academy of Sciences Publication Activity Database

    Lykhach, Yaroslava; Plšek, Jan; Spirovová, Ilona; Bastl, Zdeněk

    2003-01-01

    Roč. 68, č. 10 (2003), s. 1791-1804 ISSN 0010-0765 R&D Projects: GA ČR GA104/02/0664 Institutional research plan: CEZ:AV0Z4040901 Keywords : model metal catalysts * angle resolved photoemission * depth profiles Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 1.041, year: 2003

  9. 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

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

  10. Indoor Measurement of Angle Resolved Light Absorption by Black Silicon

    DEFF Research Database (Denmark)

    Amdemeskel, Mekbib Wubishet; Iandolo, Beniamino; Davidsen, Rasmus Schmidt

    2017-01-01

    Angle resolved optical spectroscopy of photovoltaic (PV) samples gives crucial information on PV panels under realistic working conditions. Here, we introduce measurements of angle resolved light absorption by PV cells, performed indoors using a collimated high radiance broadband light source. Our...... indoor method offers a significant simplification as compared to measurements by solar trackers. As a proof-of-concept demonstration, we show characterization of black silicon solar cells. The experimental results showed stable and reliable optical responses that makes our setup suitable for indoor......, angle resolved characterization of solar cells....

  11. Deflection gating for time-resolved x-ray magnetic circular dichroism-photoemission electron microscopy using synchrotron radiation

    Science.gov (United States)

    Wiemann, C.; Kaiser, A. M.; Cramm, S.; Schneider, C. M.

    2012-06-01

    In this paper, we present a newly developed gating technique for a time-resolving photoemission microscope. The technique makes use of an electrostatic deflector within the microscope's electron optical system for fast switching between two electron-optical paths, one of which is used for imaging, while the other is blocked by an aperture stop. The system can be operated with a switching time of 20 ns and shows superior dark current rejection. We report on the application of this new gating technique to exploit the time structure in the injection bunch pattern of the synchrotron radiation source BESSY II at Helmholtz-Zentrum Berlin for time-resolved measurements in the picosecond regime.

  12. 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.

  13. Photoemission electronic states of epitaxially grown magnetite films

    International Nuclear Information System (INIS)

    Zalecki, R.; Kolodziejczyk, A.; Korecki, J.; Spiridis, N.; Zajac, M.; Kozlowski, A.; Kakol, Z.; Antolak, D.

    2007-01-01

    The valence band photoemission spectra of epitaxially grown 300 A single crystalline magnetite films were measured by the angle-resolved ultraviolet photoemission spectroscopy (ARUPS) at 300 K. The samples were grown either on MgO(0 0 1) (B termination) or on (0 0 1) Fe (iron-rich A termination), thus intentionally presenting different surface stoichiometry, i.e. also different surface electronic states. Four main features of the electron photoemission at about -1.0, -3.0, -5.5 and -10.0 eV below a chemical potential show systematic differences for two terminations; this difference depends on the electron outgoing angle. Our studies confirm sensitivity of angle resolved PES technique on subtleties of surface states

  14. Angle-resolved photoluminescence spectrum of a uniform phosphor layer

    Science.gov (United States)

    Fujieda, Ichiro; Ohta, Masamichi

    2017-10-01

    A photoluminescence spectrum depends on an emission angle due to self-absorption in a phosphor material. Assuming isotropic initial emission and Lambert-Beer's law, we have derived simple expressions for the angle-resolved spectra emerging from the top and bottom surfaces of a uniform phosphor layer. The transmittance of an excitation light through the phosphor layer can be regarded as a design parameter. For a strongly-absorbing phosphor layer, the forward flux is less intense and more red-shifted than the backward flux. The red-shift is enhanced as the emission direction deviates away from the plane normal. When we increase the transmittance, the backward flux decreases monotonically. The forward flux peaks at a certain transmittance value. The two fluxes become similar to each other for a weakly-absorbing phosphor layer. We have observed these behaviors in experiment. In a practical application, self-absorption decreases the efficiency of conversion and results in angle-dependent variations in chromaticity coordinates. A patterned phosphor layer with a secondary optical element such as a remote reflector alleviates these problems.

  15. Angle-resolved photoluminescence spectrum of a uniform phosphor layer

    Directory of Open Access Journals (Sweden)

    Ichiro Fujieda

    2017-10-01

    Full Text Available A photoluminescence spectrum depends on an emission angle due to self-absorption in a phosphor material. Assuming isotropic initial emission and Lambert-Beer’s law, we have derived simple expressions for the angle-resolved spectra emerging from the top and bottom surfaces of a uniform phosphor layer. The transmittance of an excitation light through the phosphor layer can be regarded as a design parameter. For a strongly-absorbing phosphor layer, the forward flux is less intense and more red-shifted than the backward flux. The red-shift is enhanced as the emission direction deviates away from the plane normal. When we increase the transmittance, the backward flux decreases monotonically. The forward flux peaks at a certain transmittance value. The two fluxes become similar to each other for a weakly-absorbing phosphor layer. We have observed these behaviors in experiment. In a practical application, self-absorption decreases the efficiency of conversion and results in angle-dependent variations in chromaticity coordinates. A patterned phosphor layer with a secondary optical element such as a remote reflector alleviates these problems.

  16. 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.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2011-01-01

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

  18. Probing long-range structural order in SnPc/Ag(111) by umklapp process assisted low-energy angle-resolved photoelectron spectroscopy

    Science.gov (United States)

    Jauernik, Stephan; Hein, Petra; Gurgel, Max; Falke, Julian; Bauer, Michael

    2018-03-01

    Laser-based angle-resolved photoelectron spectroscopy is performed on tin-phthalocyanine (SnPc) adsorbed on silver Ag(111). Upon adsorption of SnPc, strongly dispersing bands are observed which are identified as secondary Mahan cones formed by surface umklapp processes acting on photoelectrons from the silver substrate as they transit through the ordered adsorbate layer. We show that the photoemission data carry quantitative structural information on the adsorbate layer similar to what can be obtained from a conventional low-energy electron diffraction (LEED) study. More specifically, we compare photoemission data and LEED data probing an incommensurate-to-commensurate structural phase transition of the adsorbate layer. Based on our results we propose that Mahan-cone spectroscopy operated in a pump-probe configuration can be used in the future to probe structural dynamics at surfaces with a temporal resolution in the sub-100-fs regime.

  19. Angle-resolved photoelectron cross section of CF4

    International Nuclear Information System (INIS)

    Carlson, T.A.; Fahlman, A.; Svensson, W.A.; Krause, M.O.; Whitley, T.A.; Grimm, F.A.; Piancastelli, M.N.; Taylor, J.W.

    1984-01-01

    Partial photoelectron cross sections sigma and angular distribution parameters β were obtained for the first five valence orbitals in CF 4 : 1t 1 , 4t 2 , 1e, 3t 2 , and 4a 1 , as a function of photon energy from 17 to 70 eV. These data were taken with the aid of angle-resolved photoelectron spectroscopy and synchrotron radiation. The results were compared with earlier data on CCl 4 . Substantial differences were found. These are explained partly in terms of the absence of a Cooper minimum with a fluorine compound as opposed to the presence of a Cooper minimum with chlorine compounds and partly in terms of the position of shape resonances. Data on CF 4 were also compared with recent calculations of Stephens et al., who used the multiple-scattering Xα method. Structure in the photoelectron spectrum of CF 4 lying on the low energy side of the third band was identified as due to autoionization and evidence is given as to its specific nature

  20. 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.

  1. Time-resolved two-photon photoemission at the Si(001)-surface. Hot electron dynamics and two-dimensional Fano resonance; Zeitaufgeloeste Zweiphotonen-Photoemission an der Si(001)-Oberflaeche. Dynamik heisser Elektronen und zweidimensionaler Fano-Effekt

    Energy Technology Data Exchange (ETDEWEB)

    Eickhoff, Christian

    2010-10-27

    By combining ultrafast laser excitation with energy-, angle- and time-resolved twophoton photoemission (2PPE), the electronic properties of bulk silicon and the Si(001) surface are investigated in this thesis. A custom-built laser- and UHV-systemequipped with a display type 2D-CCD-detector gives new insight into the relaxation dynamics of excited carriers on a femtosecond timescale. The bandgap between occupied valence bands and unoccupied conduction bands characteristically influences the dynamics of excited electrons in the bulk, as well as in surface states and resonances. For the electron-phonon interaction this leads to the formation of a bottleneck during the relaxation of hot electrons in the conduction band, which maintains the elevated electronic temperature for several picoseconds. During relaxation, excited electrons also scatter from the conduction band into the unoccupied dangling-bond surface state D{sub down}. Depending on the excitation density this surface recombination is dominated by electron-electron- or electron-phonon scattering. The relaxation of the carriers in the D{sub down}-band is again slowed down by the formation of a bottleneck in electron-phonon coupling. Furthermore, the new laser system has allowed detection of the Rydberg-like series of image-potential resonances on the Si(001)-surface. It is shown that the lifetime of these image-potential resonances in front of the semiconducting surface exhibits the same behavior as those in front of metallic surfaces. Moreover the electron-phonon coupling in the first image-potential resonance was investigated and compared to the D{sub down}-surface state. For the first time, Fano-type lineprofiles are demonstrated and analyzed in a 2PPEprocess on a surface. Tuning the photon energy of the pump-laser across the resonance between the occupied dangling-bond state D{sub up}, and the unoccupied image-potential resonance n=1, reveals a clear intensity variation that can be successfully described

  2. Time resolved photoemission spectroscopy of electronic cooling and localization in CH$_3$NH$_3$PbI$_3$ crystals

    OpenAIRE

    Chen, Zhesheng; Lee, Min-i; Zhang, Zailan; Diab, Hiba; Garrot, Damien; Lédée, Ferdinand; Fertey, Pierre; Papalazarou, Evangelos; Marsi, Marino; Ponseca, Carlito; Deleporte, Emmanuelle; Tejeda, Antonio; Perfetti, Luca

    2017-01-01

    We measure the surface of CH$_3$NH$_3$PbI$_3$ single crystals by making use of two photon photoemission spectroscopy. Our method monitors the electronic distribution of photoexcited electrons, explicitly discriminating the initial thermalization from slower dynamical processes. The reported results disclose the fast dissipation channels of hot carriers (0.25 ps), set a upper bound to the surface induced recombination velocity ($

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

    Energy Technology Data Exchange (ETDEWEB)

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

    1997-04-01

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

  4. Future directions in standing-wave photoemission

    International Nuclear Information System (INIS)

    Gray, Alexander X.

    2014-01-01

    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

  5. New Light Source Setup for Angle Resolved Light Absorption measurement of PV samples

    DEFF Research Database (Denmark)

    Amdemeskel, Mekbib Wubishet; Poulsen, Peter Behrensdorff; Thorsteinsson, Sune

    Here, we introduce measurements of angle resolved light absorption by PV cells, using broadband laser driven white light source with a bright, stable, broad spectral range and well collimated light.......Here, we introduce measurements of angle resolved light absorption by PV cells, using broadband laser driven white light source with a bright, stable, broad spectral range and well collimated light....

  6. New Light Source Setup for Angle Resolved Light Absorption measurement of PV sample

    DEFF Research Database (Denmark)

    Amdemeskel, Mekbib Wubishet; Poulsen, Peter Behrensdorff; Thorsteinsson, Sune

    Here, we introduce measurements of angle resolved light absorption by PV cells, using broadband laser driven white light source with a bright, stable, broad spectral range and well collimated light.......Here, we introduce measurements of angle resolved light absorption by PV cells, using broadband laser driven white light source with a bright, stable, broad spectral range and well collimated light....

  7. Time-resolved photoemission spectroscopy of electronic cooling and localization in CH3NH3PbI3 crystals

    Science.gov (United States)

    Chen, Zhesheng; Lee, Min-i.; Zhang, Zailan; Diab, Hiba; Garrot, Damien; Lédée, Ferdinand; Fertey, Pierre; Papalazarou, Evangelos; Marsi, Marino; Ponseca, Carlito; Deleporte, Emmanuelle; Tejeda, Antonio; Perfetti, Luca

    2017-09-01

    We measure the surface of CH3NH3PbI3 single crystals by making use of two-photon photoemission spectroscopy. Our method monitors the electronic distribution of photoexcited electrons, explicitly discriminating the initial thermalization from slower dynamical processes. The reported results disclose the fast-dissipation channels of hot carriers (0.25 ps), set an upper bound to the surface-induced recombination velocity (PbI3 samples is consistent with the progressive reduction of photoconversion efficiency in operating devices. Minimizing the density of shallow traps and solving the aging problem may boost the macroscopic efficiency of solar cells to the theoretical limit.

  8. General survey of recent development of photoemission spectroscopy

    International Nuclear Information System (INIS)

    Edamoto, Kazuyuki

    1994-01-01

    On the present state of the recent development of photoemission spectroscopy, by limiting the topics to the development of the spectroscopy proper and the development contributing to the progress of surface science, general explanation is made. As to the development that enabled to heighten spectrum resolution, surface core-level shift and the precise measurement of the Fermi surface of surface level are described, showing the example. Also a number of the developments which enabled the utilization of the light source, of which the wavelength is variable, and which was brought about by synchrotron radiation beam, were mentioned. Besides, spin polarized photoelectron spectroscopy, the development of photoelectron microscope and others are outlined. Photoemission spectroscopy is very useful for analyzing the electron condition of solid surfaces. There are two factors in heightening core level spectrum resolution, namely, heightening the resolution of an electron energy analyzer proper and the utilization of synchrotron radiation as a light source. High resolution core-level spectra, angle-resolved photoemission spectroscopy, and as the light source of which the wavelength is variable, resonance photoemission spectroscopy, constant initial state spectroscopy and soft X-ray photoemission spectroscopy, and as the recently developed spectroscopy, spin polarized photoemission spectroscopy, Auger photoelectron coincidence spectroscopy and photoelectron microscope are explained. (K.I.)

  9. Time-Resolved Small-Angle X-Ray Scattering

    NARCIS (Netherlands)

    ten Elshof, Johan E.; Besselink, R.; Stawski, Tomasz; Castricum, H.L.; Levy, D.; Zayat, M.

    2015-01-01

    This chapter focuses on time-resolved studies of nanostructure development in sol-gel liquids, that is, diluted sols, wet gels, and drying thin fffilms. The most commonly investigated classes of sol-gel materials are silica, organically modified silica, template-directed mesostructured silica,

  10. Angle Resolved Performance Measurements on PV Glass and Modules

    DEFF Research Database (Denmark)

    Juutilainen, Line Tollund; Thorsteinsson, Sune; Poulsen, Peter Behrensdorff

    2016-01-01

    The angular response of PV-modules has significant impact on the energy production. This is especially pronounced in BIPV where installation angles often are far from optimal. Nevertheless, a gain in energy yield may be obtained by choosing a proper glass as superstrate. In this work we present t...

  11. Time- and energy resolved photoemission electron microscopy-imaging of photoelectron time-of-flight analysis by means of pulsed excitations

    International Nuclear Information System (INIS)

    Oelsner, Andreas; Rohmer, Martin; Schneider, Christian; Bayer, Daniela; Schoenhense, Gerd; Aeschlimann, Martin

    2010-01-01

    The present work enlightens the developments in time- and energy resolved photoemission electron microscopy over the past few years. We describe basic principles of the technique and demonstrate different applications. An energy- and time-filtering photoemission electron microscopy (PEEM) for real-time spectroscopic imaging can be realized either by a retarding field or hemispherical energy analyzer or by using time-of-flight optics with a delay line detector. The latter method has the advantage of no data loss at all as all randomly incoming particles are measured not only by position but also by time. This is of particular interest for pump-probe experiments in the femtosecond and attosecond time scale where space charge processes drastically limit the maximum number of photoemitted electrons per laser pulse. This work focuses particularly on time-of-flight analysis using a novel delay line detector. Time and energy resolved PEEM instruments with delay line detectors enable 4D imaging (x, y, Δt, E Kin ) on a true counting basis. This allows a broad range of applications from real-time observation of dynamic phenomena at surfaces to fs time-of-flight spectro-microscopy and even aberration correction. By now, these time-of-flight analysis instruments achieve intrinsic time resolutions of 108 ps absolute and 13.5 ps relative. Very high permanent measurement speeds of more than 4 million events per second in random detection regimes have been realized using a standard USB2.0 interface. By means of this performance, the time-resolved PEEM technique enables to display evolutions of spatially resolved (<25 nm) and temporal sliced images life on any modern computer. The method allows dynamics investigations of variable electrical, magnetic, and optical near fields at surfaces and great prospects in dynamical adaptive photoelectron optics. For dynamical processes in the ps time scale such as magnetic domain wall movements, the time resolution of the delay line detectors

  12. Multichannel spin polarimeter for energy- and angle-dispersive photoemission measurements; Vielkanal-Spinpolarimeter fuer energie- und winkeldispersive Photoemissionsmessungen

    Energy Technology Data Exchange (ETDEWEB)

    Kolbe, Michaela

    2011-09-09

    Spin polarization measurements of free electrons remain challenging since their first realization by Mott. The relevant quantity of a spin polarimeter is its figure of merit, FoM=S{sup 2}I/I{sub 0}, with the asymmetry function S and the ratio between scattered and primary intensity I/I{sub 0}. State-of-the-art devices are based on single-channel scattering (spin-orbit or exchange interaction) which is characterized by FoM {approx_equal}10{sup -4}. On the other hand, modern hemispherical analyzers feature an efficient multichannel detection of spin-integral intensity with more than 10{sup 4} data points simultaneously. In comparison between spin-resolved and spin-integral electron spectroscopy we are thus faced with a difference in counting efficiency by 8 orders of magnitude. The present work concentrates on the development and investigation of a novel technique for increasing the efficiency in spin-resolved electron spectroscopy by multichannel detection. The spin detector was integrated in a {mu}-metal shielded UHV-chamber and mounted behind a conventional hemispherical analyzer. The electrostatic lens system's geometry was determined by electron-optical simulations. The basic concept is the k {sub parallel} -conserving elastic scattering of the (0,0)-beam on a W(100) scattering crystal under 45 impact angle. It could be demonstrated that app. 960 data points (15 energy and 64 angular points) could be displayed simultaneously on a delayline detector in an energy interval of {approx_equal}3 eV. This leads to a two-dimensional figure of merit of FoM{sub 2D}=1.7. Compared to conventional spin detectors, the new type is thus characterized by a gain in efficiency of 4 orders of magnitude. The operational reliability of the new spin polarimeter could be proven by measurements with a Fe/MgO(100) and O p(1 x 1)/Fe(100)-sample, where results from the literature were reproduced with strongly decreased measuring time. Due to the high intensity it becomes possible, to

  13. Angle-resolved photoelectron spectrometry: new electron optics and detection system

    International Nuclear Information System (INIS)

    Hoof, H.A. van.

    1980-01-01

    A new spectrometer system is described, designed to measure angle-resolved energy distributions of photoemitted electrons efficiently. Some results are presented of measurements on a Si(001) surface. (Auth.)

  14. Simulation and Measurement of Angle Resolved Reflectance from Black Si Surfaces

    DEFF Research Database (Denmark)

    Davidsen, Rasmus Schmidt; Wu, Kaiyu; Schmidt, Michael Stenbæk

    2015-01-01

    In this work angle-resolved reflectance from nanostructured Si surfaces realized by maskless RIE texturing has been simulated and measured. The simulation and experimental measurement data show the same trend. Experimentally a total reflectance below 1% for incident angles below 30o and specular...

  15. A high performance angle-resolving electron spectrometer

    CERN Document Server

    Rossnagel, K; Skibowski, M; Harm, S

    2001-01-01

    We report on our new versatile photoelectron spectrometer Angular Spectrometer for Photoelectrons with High Energy REsolution (ASPHERE) which is part of beamline W3.2 (photon energies from 5 to 40 eV) but also compatible with beamline BW3 (40-1500 eV) at the Hamburger Synchrotronstrahlungslabor (HASYLAB). ASPHERE is a 180 deg. spherical analyzer (r sub 0 =100 mm) with a four-element input lens and is mounted on a two-axes goniometer with computer-controlled stepper motors which enables sequential angle-scanned measurements. The input lens is equipped with an iris aperture so that the angular resolution can be continuously adjusted from 0.2 deg. to 5 deg. sign . The fringe field of the condenser has been corrected for by tilting the angle of the input lens against the base plane of the hemispheres resulting in an overall energy resolution of 10 meV. To improve the speed of data acquisition three standard channeltron detectors are installed in the image plane of the analyzer which will be replaced by a multidet...

  16. Photoemission and the origin of high temperature superconductivity

    Energy Technology Data Exchange (ETDEWEB)

    Norman, M. R.; Randeria, M.; Janko, B.; Campuzano, J. C.

    2000-03-01

    The condensation energy can be shown to be a moment of the change in the occupied part of the spectral function when going from the normal to the superconducting state. As a consequence, there is a one to one correspondence between the energy gain associated with forming the superconducting ground state, and the dramatic changes seen in angle resolved photoemission spectra. Some implications this observation has are offered.

  17. Photoemission and the origin of high temperature superconductivity

    International Nuclear Information System (INIS)

    Norman, M. R.; Randeria, M.; Janko, B.; Campuzano, J. C.

    2000-01-01

    The condensation energy can be shown to be a moment of the change in the occupied part of the spectral function when going from the normal to the superconducting state. As a consequence, there is a one to one correspondence between the energy gain associated with forming the superconducting ground state, and the dramatic changes seen in angle resolved photoemission spectra. Some implications this observation has are offered

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

    International Nuclear Information System (INIS)

    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 ω less than or equal 175 is discussed

  19. 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

    Fusion research aims at the exploitation of the deuterium-tritium reaction for energy production. Next step on the roadmap is the construction of the experimental reactor ITER. The three elements beryllium, carbon and tungsten are to be used as armour materials for the vacuum vessel. After erosion due to plasma processes, these materials are transported and redeposited together with plasma impurities like oxygen from surface oxides. This leads to the formation of compounds by chemical reactions and diffusive processes, induced both by elevated temperatures and implantation of energetic particles. Due to the complexity of the induced surface processes, a method is required which is capable of both qualitative and quantitative analysis of the involved chemical species. X-ray photoelectron spectroscopy (XPS) provides the chemical analysis. Since diffusive processes play an important role in solid-state reactions, a depth-resolved method is required. In this work, energy-resolved XPS using synchrotron radiation with variable photon energies is extended towards a quantitative depth-resolved analysis. For the quantitative analysis a new model is derived which calculates the depth-resolved composition and the respective composition-dependent electron inelastic mean free path in a self-consistent way. Input is the XPS data which is normalized with all parameters influencing the photoelectron intensities. This fully quantitative model is applied to describe the interaction of energetic oxygen ions with the beryllium-tungsten alloy Be{sub 2}W. Oxygen ions from the plasma are able to interact with plasma facing materials. Formation of Be{sub 2}W is to be expected at the first wall and in the divertor region of ITER. Irradiation of this alloy leads to its decompositions. After decomposition, formation of beryllium oxide BeO is preferred compared to formation of tungsten oxides. Heating to 600K leads to chemical reduction of tungsten oxides. Metallic Be acts as reduction agent

  20. Angle-resolved imaging of single-crystal materials with MeV helium ions

    International Nuclear Information System (INIS)

    Strathman, M.D.; Baumann, S.

    1992-01-01

    The simplest form of angle-resolved mapping for single-crystal materials is the creation of a channeling angular scan. Several laboratories have expanded this simple procedure to include mapping as a function of two independent tilts. These angle-resolved images are particularly suited to the assessment of crystal parameters including disorder, lattice location of impurities, and lattice stress. This paper will describe the use of the Charles Evans and Associates RBS-400 scattering chamber for acquisition, display, and analysis of angle-resolved images obtained from backscattered helium ions. Typical data acquisition times are 20 min for a ±2deg X-Y tilt scan with 2500 pixels (8/100deg resolution), and 10 nC per pixel. In addition, we will present a method for automatically aligning crystals for channeling measurements based on this imaging technology. (orig.)

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

    International Nuclear Information System (INIS)

    Hellings, G.J.A.

    1986-01-01

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

  2. Time-resolved small-angle neutron scattering study on soap-free emulsion polymerization

    International Nuclear Information System (INIS)

    Motokawa, Ryuhei; Koizumi, Satoshi; Hashimoto, Takeji; Nakahira, Takayuki; Annaka, Masahiko

    2006-01-01

    We investigated an aqueous soap-free emulsion polymerization process of Poly(N-isopropylacrylamide)-block-poly(ethylene glycol) by ultra-small-angle and time-resolved small-angle neutron scattering methods. The results indicate that the compartmentalization of chain end radicals into solid-like micelle cores crucially leads to the quasi-living behavior of the radical polymerization by prohibiting recombination process

  3. Angle resolved characterization of nanostructured and conventionally textured silicon solar cells

    DEFF Research Database (Denmark)

    Davidsen, Rasmus Schmidt; Ormstrup, Jeppe; Ommen, Martin Lind

    2015-01-01

    current, open circuit voltage, fill factor (FF) and power conversion efficiency are each measured as function of the relative incident angle between the solar cell and the light source. The relative incident angle is varied from 0° to 90° in steps of 10° in orthogonal axes, such that each solar cell......We report angle resolved characterization of nanostructured and conventionally textured silicon solar cells. The nanostructured solar cells are realized through a single step, mask-less, scalable reactive ion etching (RIE) texturing of the surface. Photovoltaic properties including short circuit...

  4. Review of RDC Soft Computing Techniques for Accurate Measurement of Resolver Rotor Angle

    Directory of Open Access Journals (Sweden)

    Chandra Mohan Reddy Sivappagari

    2013-03-01

    Full Text Available A resolver is a position sensor or transducer that measures the instantaneous angular position of the rotating shaft to which it is attached. Resolver produces two amplitude modulated signals; SIN and COS as output signals. These two signals need to be demodulated and converted to digital signals before they can be used for control. There are several techniques available in the literature to measure the rotor shaft angle. This paper focuses on the design of both hardware and software based resolver to digital converter (RDC techniques available in the literature. This literature review helps the researchers to know about all these methods and plan future work on RDCs to improve the angle tracking performance.

  5. Angle - resolved photoemission study of two phases of the GaAs(100)-c(4x4) surface

    Czech Academy of Sciences Publication Activity Database

    Cukr, Miroslav; Jiříček, Petr; Bartoš, Igor; Sadowski, J.

    2008-01-01

    Roč. 100, - (2008), 072017/1-072017/4 ISSN 1742-6588 R&D Projects: GA AV ČR IAA100100628; GA ČR GA202/07/0601 Institutional research plan: CEZ:AV0Z10100521 Keywords : gallium arsenide * molecular beam epitaxy * photoelectron spectroscopy * surface reconstruction * surface phases * electron states Subject RIV: BM - Solid Matter Physics ; Magnetism

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

    DEFF Research Database (Denmark)

    Bianchi, Marco; Hatch, Richard; Guan, Dandan

    2012-01-01

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

  7. Pitch angle resolved measurements of escaping charged fusion products in TFTR

    Energy Technology Data Exchange (ETDEWEB)

    Zweben, S.J.

    1989-01-01

    Measurements of the flux of charged fusion products escaping from the TFTR plasma have been made with a new type of detector which can resolve the particle flux vs. pitch angle, energy, and time. The design of this detector is described, and results from the 1987 TFTR run are presented. These results are roughly consistent with predictions from a simple first-orbit particle loss model with respect to the pitch angle, energy, time, and plasma current dependence of the signals. 11 refs., 9 figs.

  8. Valence band photoemission studies of clean metals

    Energy Technology Data Exchange (ETDEWEB)

    Wehner, P.S.

    1978-04-01

    The application of Angle-Resolved Photoelectron Spectroscopy (ARPES) to crystalline solids and the utilization of such studies to illuminate several questions concerning the detailed electronic structure of such materials, are discussed. Specifically, by construction of a Direct Transition (DT) model and the utilization of energy-dependent angle-resolved normal photoemission in the photon energy range 32 eV < or = h..nu.. < or = 200 eV, the bulk band structure of copper is experimentally mapped out along three different directions in the Brillouin Zone; GAMMA to K, GAMMA to L, and GAMMA to X. In addition, various effects which influence the obtainable resolution in vector k-space, namely, thermal disorder, momentum broadening, and band mixing, are discussed and are shown to place severe limitations on the applicability of the DT model. Finally, a model for Angle-Resolved X-ray Photoelectron Spectroscopy (ARXPS) based on the symmetry of the initial-state wavefunctions is presented and compared to experimental results obtained from copper single crystals.

  9. The ALOISA end station at Elettra: a novel multicoincidence spectrometer for angle resolved APECS

    CERN Document Server

    Gotter, R; Morgante, A; Cvetko, D; Floreano, L; Tommasini, F; Stefani, G

    2001-01-01

    Coincidence measurements have been extensively performed in atomic and molecular physics since early 1970s. To apply this methodology to solids and surfaces has been a major target since early days, but the long average time needed to complete a coincidence experiment has hampered its attainment. In particular the coincidence technique has not been yet applied in an angle resolved way such for studying the momentum correlation in the ejection of electron pairs from solid surfaces. The experimental chamber at the ALOISA beamline at Elettra, by means of a set of seven homemade electron analyzers, is the first apparatus able to perform Angle Resolved - Auger Photoelectron Coincidence Spectroscopy (AR-APECS) from solid surfaces. In the typical setup ten different pairs of coincident electrons can be measured simultaneously, so reducing the acquisition time by one order of magnitude.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    1996-07-01

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

  11. Mapping unoccupied electronic states of freestanding graphene by angle-resolved low-energy electron transmission

    OpenAIRE

    Wicki Flavio; Longchamp Jean-Nicolas; Latychevskaia Tatiana; Escher Conrad; Fink Hans-Werner

    2016-01-01

    We report angle-resolved electron transmission measurements through freestanding graphene sheets in the energy range of 18 to 30 eV above the Fermi level. The measurements are carried out in a low-energy electron point source microscope, which allows simultaneously probing the transmission for a large angular range. The characteristics of low-energy electron transmission through graphene depend on its electronic structure above the vacuum level. The experimental technique described here allow...

  12. Angle-resolved reflection spectroscopy of high-quality PMMA opal crystal

    Science.gov (United States)

    Nemtsev, Ivan V.; Tambasov, Igor A.; Ivanenko, Alexander A.; Zyryanov, Victor Ya.

    2018-02-01

    PMMA opal crystal was prepared by a simple hybrid method, which includes sedimentation, meniscus formation and evaporation. We investigated three surfaces of this crystal by angle-resolved reflective light spectroscopy and SEM study. The angle-resolved reflective measurements were carried out in the 400-1100 nm range. We have determined the high-quality ordered surface of the crystal region. Narrow particle size distribution of the surface has been revealed. The average particle diameter obtained with SEM was nearly 361 nm. The most interesting result was that reflectivity of the surface turned out up to 98% at normal light incidence. Using a fit of dependences of the maximum reflectivity wavelength from an angle based on the Bragg-Snell law, the wavelength of maximum 0° reflectivity, the particle diameter and the fill factor have been determined. For the best surface maximum reflectivity wavelength of a 0° angle was estimated to be 869 nm. The particle diameter and fill factor were calculated as 372 nm and 0.8715, respectively. The diameter obtained by fitting is in excellent agreement with the particle diameter obtained with SEM. The reflectivity maximum is assumed to increase significantly when increasing the fill factor. We believe that using our simple approach to manufacture PMMA opal crystals will significantly increase the fabrication of high-quality photonic crystal templates and thin films.

  13. Electronic structure of single crystal UPd{sub 3}, UGe{sub 2}, and USb{sub 2} from hard X-ray and angle-resolved photoelectron spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Beaux, M.F., E-mail: mbeaux@lanl.gov [MPA Division, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Durakiewicz, T. [MPA Division, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Moreschini, L.; Grioni, M. [IPN, Ecole Polytechnique Federale (EPFL), CH-1015 Lausanne (Switzerland); Offi, F. [CNISM and Dipartimento de Fisica, Universita Roma Tre, Via della Vasca Navale 84, 1-00146 Rome (Italy); Monaco, G. [European Synchrotron Radiation Facility, B.P. 220, F-38042 Grenoble (France); Panaccione, G. [Istituto Officina dei Materiali CNR, Laboratorio TASC, Area Science Park, Basovizza S.S. 14 Km 163.5, I-34012 Trieste, 9 (Italy); Joyce, J.J.; Bauer, E.D.; Sarrao, J.L. [MPA Division, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Butterfield, M.T. [KLA-Tencor, 1 Technology Drive, Milpitas, CA (United States); Guziewicz, E. [Institute of Physics, Polish Academy of Sciences, Warsaw (Poland)

    2011-11-15

    Highlights: {yields} Electronic structure of single crystal UPd{sub 3}, UGe{sub 2}, and USb{sub 2} was measured by hard X-ray and angle-resolved photoemission spectroscopy. {yields} Angle resolved photoemission results demonstrate hybridization between U 5f and Pd 4d electrons within UPd{sub 3}. {yields} HAXPES probing of bulk features within of UPd{sub 3}, UGe{sub 2}, and USb{sub 2} samples with native oxide contamination demonstrated. {yields} Two distinct spectral features identified for Sb I and Sb II sites within USb{sub 2} HAXPES spectrum. {yields} Line shape analysis reveals correlations between Doniach-Sunjic asymmetry coefficients and 5f localization. - Abstract: Electronic structure of single crystal UPd{sub 3}, UGe{sub 2}, and USb{sub 2} has been measured from hard X-ray photoelectron spectroscopy (HAXPES) with 7.6 keV photons at the European Synchrotron Radiation Facility (ESRF). Lower photon energy angle-resolved photoelectron spectroscopy (ARPES) was also performed at the Synchrotron Radiation Center (SRC). Herein the following results are presented: (i) ARPES results demonstrate hybridization between the U 5f and Pd 4d electrons within UPd{sub 3}. (ii) The greatly reduced surface sensitivity of HAXPES enabled observation of the bulk core levels in spite of surface oxidation. Photoelectron mean-free-path versus oxide layer thickness considerations were used to model the effectiveness of HAXPES for probing bulk features of in-air cleaved samples. (iii) Two distinct features separated by 800 meV were observed for the Sb 3d core level. These two features are attributed to manifestations of two distinct Sb sites within the USb{sub 2} single crystal as supported by consideration of interatomic distances and enthalpy-of-formation. (iv) Doniach-Sunjic line shape analysis of core level spectral features revealed correlations between asymmetry coefficients and 5f localization.

  14. Robust depth selectivity in mesoscopic scattering regimes using angle-resolved measurements.

    Science.gov (United States)

    González-Rodríguez, P; Kim, A D; Moscoso, M

    2013-03-01

    We study optical imaging of tissues in the mesoscopic scattering regime in which light multiply scatters in tissues but is not fully diffusive. We use the radiative transport equation to model light propagation and an ℓ1-optimization method to solve the inverse source problem. We show that recovering the location and strength of several point-like sources that are close to each other is not possible when using angle-averaged measurements. The image reliability is limited by a spatial scale that is on the order of the transport mean-free path, even under the most ideal conditions. However, by using just a few angle-resolved measurements, the proposed method is able to overcome this limitation.

  15. Setup for angle-resolved electron spectrometry using monochromatised synchrotron radiation

    International Nuclear Information System (INIS)

    Derenbach, H.; Franke, C.; Malutzki, R.; Wachter, A.; Schmidt, V.

    1987-01-01

    An apparatus is described which is well suited for angle-resolved electron spectrometry of free atoms and molecules using monochromatised synchrotron radiation. Two variations are presented, one for room temperature gaseous species, the other for metallic vapours. The analyser is of the cylindrical mirror type, designed, however, so as to accept with one sector the entire source volume independently of the photon beam diameter. It can be equipped with a positon-sensitive detector instead of a channeltron, which extends its potentiality. The system consists of up to three cylindrical mirror sector analysers (CMAs) where a double-sector CMA can be rotated around the photon beam direction, allowing angular distribution measurements, and another sector CMA is mounted in a fixed position providing a signal for reference purposes. A detailed description and experimental tests are given for the performance of the CMA, i.e. its imaging properties, resolution and transmissions, as well as for possible instrumental asymmetries affecting angle-resolved experiments. (orig.)

  16. Design of angle-resolved illumination optics using nonimaging bi-telecentricity for 193 nm scatterfield microscopy.

    Science.gov (United States)

    Sohn, Martin Y; Barnes, Bryan M; Silver, Richard M

    2018-03-01

    Accurate optics-based dimensional measurements of features sized well-below the diffraction limit require a thorough understanding of the illumination within the optical column and of the three-dimensional scattered fields that contain the information required for quantitative metrology. Scatterfield microscopy can pair simulations with angle-resolved tool characterization to improve agreement between the experiment and calculated libraries, yielding sub-nanometer parametric uncertainties. Optimized angle-resolved illumination requires bi-telecentric optics in which a telecentric sample plane defined by a Köhler illumination configuration and a telecentric conjugate back focal plane (CBFP) of the objective lens; scanning an aperture or an aperture source at the CBFP allows control of the illumination beam angle at the sample plane with minimal distortion. A bi-telecentric illumination optics have been designed enabling angle-resolved illumination for both aperture and source scanning modes while yielding low distortion and chief ray parallelism. The optimized design features a maximum chief ray angle at the CBFP of 0.002° and maximum wavefront deviations of less than 0.06 λ for angle-resolved illumination beams at the sample plane, holding promise for high quality angle-resolved illumination for improved measurements of deep-subwavelength structures using deep-ultraviolet light.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-06-29

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

  18. Observation of cross-shaped anisotropy in spin-resolved small-angle neutron scattering

    Science.gov (United States)

    Michels, Andreas; Honecker, Dirk; Döbrich, Frank; Dewhurst, Charles D.; Suzuki, Kiyonori; Heinemann, André

    2012-05-01

    We report the results of spin-resolved small-angle neutron scattering (SANS) experiments on the two-phase nanocrystalline alloy NANOPERM. At a saturating applied magnetic field of 1.27T we observe a cross-shaped angular anisotropy in the non-spin-flip SANS cross section Σ++. This feature—for this class of materials only visible at saturation in Σ++—is attributed to the specific ratio of nuclear to magnetic scattering being smaller than unity. Analysis of the non-spin-flip and spin-flip cross sections provides the nuclear and magnetic SANS and allows us to estimate the magnitude of the respective scattering-length density contrast at the interphase between the nanoparticles and the amorphous magnetic matrix.

  19. Time-resolved small-angle neutron scattering of a micelle-to-vesicle transition

    Energy Technology Data Exchange (ETDEWEB)

    Egelhaaf, S.U. [Institut Max von Laue - Paul Langevin (ILL), 38 -Grenoble (France); Schurtenberger, P. [Eidgenoessische Technische Hochschule, Zurich (Switzerland)

    1997-04-01

    Amphiphilic molecules spontaneously self-assemble in solution to form a variety of aggregates. Only limited information is available on the kinetics of the structural transitions as well as on the existence of non-equilibrium or metastable states. Aqueous mixtures of lecithin and bile salt are very interesting biological model-systems which exhibit a spontaneous transition from polymer-like mixed micelles to vesicles upon dilution. The small-angle neutron scattering (SANS) instrument D22, with its very high neutron flux and the broad range of scattering vectors covered in a single instrumental setting, allowed us for the first time to perform time-resolved scattering experiments in order to study the micelle-to-vesicle transition. The temporal evolution of the aggregate structures were followed and detailed information was obtained even on molecular length-scales. (author). 5 refs.

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

    Science.gov (United States)

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

    2010-02-01

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

  1. Detection of intestinal dysplasia using angle-resolved low coherence interferometry

    Science.gov (United States)

    Terry, Neil; Zhu, Yizheng; Thacker, Julie K. M.; Migaly, John; Guy, Cynthia; Mantyh, Christopher R.; Wax, Adam

    2011-10-01

    Angle-resolved low coherence interferometry (a/LCI) is an optical biopsy technique that allows for depth-resolved, label-free measurement of the average size and optical density of cell nuclei in epithelial tissue to assess the tissue health. a/LCI has previously been used clinically to identify the presence of dysplasia in Barrett's Esophagus patients undergoing routine surveillance. We present the results of a pilot, ex vivo study of tissues from 27 patients undergoing partial colonic resection surgery, conducted to evaluate the ability of a/LCI to identify dysplasia. Performance was determined by comparing the nuclear morphology measurements with pathological assessment of co-located physical biopsies. A statistically significant correlation between increased average nuclear size, reduced nuclear density, and the presence of dysplasia was noted at the basal layer of the epithelium, at a depth of 200 to 300 μm beneath the tissue surface. Using a decision line determined from a receiver operating characteristic, a/LCI was able to separate dysplastic from healthy tissues with a sensitivity of 92.9% (13/14), a specificity of 83.6% (56/67), and an overall accuracy of 85.2% (69/81). The study illustrates the extension of the a/LCI technique to the detection of intestinal dysplasia, and demonstrates the need for future in vivo studies.

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

    International Nuclear Information System (INIS)

    Lindle, D.W.

    1983-12-01

    Photoelectron spectroscopy, in conjunction with synchrotron radiation, has been used to study inner-shell photoemission from atoms and molecules. The time structure of the synchrotron radiation permits the measurements of time-of-flight (TOF) spectra of Auger and photoelectrons, thereby increasing the electron collection efficiency. The double-angle TOF method yielded angle-resolved photoelectron intensities, which were used to determine photoionization cross sections and photoelectron angular distributions in several cases. Comparison to theoretical calculations has been made where possible to help explain observed phenomena in terms of the electronic structure and photoionization dynamics of the systems studied. 154 references, 23 figures, 7 tables

  3. Widespread spin polarization effects in photoemission from topological insulators

    Energy Technology Data Exchange (ETDEWEB)

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

    2011-06-22

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

  4. Electronic structure and photoemission spectra of thin (GaAs).sub.n./sub. (AlAs).sub.n./sub. superlattices

    Czech Academy of Sciences Publication Activity Database

    Bartoš, Igor; Strasser, T.; Schattke, W.

    507-510, - (2002), s. 160-164 ISSN 0039-6028 R&D Projects: GA AV ČR IAA1010108 Institutional research plan: CEZ:AV0Z1010914 Keywords : electron density * excitation spectra calculations * Green's function methods * angle resolved photoemission * photoelectron emission * Gallium arsenide * low index single crystal surfaces * superlattices Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 2.140, year: 2002

  5. Photoemission from alfa and beta phases of the GaAs(001)-c(4x4) surface

    Czech Academy of Sciences Publication Activity Database

    Jiříček, Petr; Cukr, Miroslav; Bartoš, Igor; Sadowski, J.

    2009-01-01

    Roč. 603, č. 20 (2009), s. 3088-3093 ISSN 0039-6028 R&D Projects: GA ČR GA202/07/0601; GA AV ČR IAA100100628 Institutional research plan: CEZ:AV0Z10100521 Keywords : gallium arsenide * angle resolved photoemission * synchrotron radiation photoelectron spectroscopy * molecular beam epitaxy * surface core level shift Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.798, year: 2009

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

    Energy Technology Data Exchange (ETDEWEB)

    Spanier, M., E-mail: mspanier@physik.tu-berlin.de; Herzog, C.; Grötzsch, D.; Kramer, F.; Mantouvalou, I.; Malzer, W.; Kanngießer, B. [Institute for Optics and Atomic Physics, Technische Universität Berlin, Hardenbergstraße 36, 10623 Berlin (Germany); Lubeck, J.; Weser, J.; Streeck, C.; Beckhoff, B. [Physikalisch-Technische Bundesanstalt, Abbestraße 2-12, 10587 Berlin (Germany)

    2016-03-15

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

  7. Growth of mesoporous silica nanoparticles monitored by time-resolved small-angle neutron scattering.

    Science.gov (United States)

    Hollamby, Martin J; Borisova, Dimitriya; Brown, Paul; Eastoe, Julian; Grillo, Isabelle; Shchukin, Dmitry

    2012-03-06

    Since the first development of surfactant-templated mesoporous silicas, the underlying mechanisms behind the formation of their structures have been under debate. Here, for the first time, time-resolved small-angle neutron scattering (tr-SANS) is applied to study the complete formation of mesoporous silica nanoparticles. A distinct advantage of this technique is the ability to detect contributions from the whole system, enabling the visualization not only of particle genesis and growth but also the concurrent changes to the coexistent micelle population. In addition, using contrast-matching tr-SANS, it is possible to highlight the individual contributions from the silica and surfactant. An analysis of the data agrees well with the previously proposed "current bun" model describing particle growth: Condensing silica oligomers adsorb to micelles, reducing intermicellar repulsion and resulting in aggregation to form initial particle nuclei. From this point, the growth occurs in a cooperative manner, with condensing silica filling the gaps between further aggregating micelles. The mechanistic results are discussed with respect to different reaction conditions by changing either the concentration of the silica precursor or the temperature. In doing so the importance of in situ techniques is highlighted, in particular, tr-SANS, for mechanism elucidation in the broad field of materials science.

  8. Formation of complexes between functionalized chitosan membranes and copper: A study by angle resolved XPS

    Energy Technology Data Exchange (ETDEWEB)

    Jurado-López, Belén [Departamento de Química Inorgánica, Facultad de Ciencias, Universidad de Málaga, 29071 Málaga (Spain); Vieira, Rodrigo Silveira [Chemical Engineering Department, Universidade Federal do Ceará, UFC, 60455-760 Fortaleza, CE (Brazil); Rabelo, Rodrigo Balloni; Beppu, Marisa Masumi [School of Chemical Engineering, University of Campinas, UNICAMP, P.O. Box 6066, 13081-970 Campinas, SP (Brazil); Casado, Juan [Departamento de Química-Física, Facultad de Ciencias, Universidad de Málaga, 29071 Málaga (Spain); Rodríguez-Castellón, Enrique, E-mail: castellon@uma.es [Departamento de Química Inorgánica, Facultad de Ciencias, Universidad de Málaga, 29071 Málaga (Spain)

    2017-01-01

    Chitosan is a biopolymer with potential applications in various fields. Recently, it has been used for heavy metals removal like copper, due to the presence of amino and hydroxyl groups in its structure. Chitosan membranes were crosslinked with epichlorohydrin and bisoxirano and functionalized with chelating agents, such as iminodiacetic acid, aspartic acid and tris-(2-amino-ethyl) polyamine. These membranes were used for copper adsorption and the formed complexes were characterized. Thermal and crystalline properties of chitosan membranes were studied by TG-DCS and X-ray diffraction. Raman, XPS and FT-IR data confirmed that copper is linked to the modified chitosan membranes by the amino groups. The oxidation state of copper-chitosan membranes were also studied by angle resolved XPS, and by UV–Vis diffuse reflectance spectroscopy. - Highlights: • Chitosan membranes were crosslinked with epichlorohydrin and bisoxirano and functionalized with chelating agents. • The chelating agent were iminodiacetic acid, aspartic acid and tris-(2-amino-ethyl) polyamine. • The functionalized membranes were used for copper adsorption and studied by ARXPS, Raman, TG-DCS, FT-IR and XRD. • Spectroscopic data confirmed that copper is linked to the modified chitosan membranes by the amino groups.

  9. Field-angle-resolved anisotropy in superconducting CeCoIn5 using realistic Fermi surfaces

    Science.gov (United States)

    Das, Tanmoy; Vorontsov, A. B.; Vekhter, I.; Graf, Matthias J.

    2013-05-01

    We compute the field-angle-resolved specific heat and thermal conductivity using realistic model band structures for the heavy-fermion superconductor CeCoIn5 to identify the gap structure and location of nodes. We use a two-band tight-binding parametrization of the band dispersion as input for the self-consistent calculations in the quasiclassical formulation of the superconductivity. Systematic analysis shows that modest in-plane anisotropy in the density of states and Fermi velocity in tetragonal crystals significantly affects the fourfold oscillations in thermal quantities, when the magnetic field is rotated in the basal plane. The Fermi-surface anisotropy substantially shifts the location of the lines in the H-T plane, where the oscillations change sign compared to quasicylindrical model calculations. In particular, at high fields, the anisotropy and sign reversal are found even for isotropic gaps. Our findings imply that a simultaneous analysis of the specific heat and thermal conductivity, with an emphasis on the low-energy sector, is needed to restrict potential pairing scenarios in multiband superconductors. We discuss the impact of our results on recent measurements of the Ce-115 family, namely, CeTIn5 with T= Co, Rh, Ir.

  10. Angle Resolved Core-Level Spectroscopy of Zr1Nb Alloy Oxidation by Oxygen, Water and Hydrogen Peroxide

    Czech Academy of Sciences Publication Activity Database

    Bastl, Zdeněk; Senkevich, A. I.; Spirovová, Ilona; Vrtílková, V.

    2002-01-01

    Roč. 34, - (2002), s. 477-480 ISSN 0142-2421 Institutional research plan: CEZ:AV0Z4040901 Keywords : Zr-Nb alloy * oxide films * angle-resolved x-ray photoelectron spectroscopy Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 1.071, year: 2002

  11. Measurements of polarization-dependent angle-resolved light scattering from individual microscopic samples using Fourier transform light scattering

    Science.gov (United States)

    Jung, JaeHwang; Kim, Jinhyung; Seo, Min-Kyo; Park, YongKeun

    2018-03-01

    We present a method to measure the vector-field light scattering of individual microscopic objects. The polarization-dependent optical field images are measured with quantitative phase imaging at the sample plane, and then numerically propagated to the far-field plane. This approach allows the two-dimensional polarization-dependent angle-resolved light scattered patterns from individual object to be obtained with high precision and sensitivity. Using this method, we present the measurements of the polarization-dependent light scattering of a liquid crystal droplet and individual silver nanowires over scattering angles of 50{\\deg}. In addition, the spectroscopic extension of the polarization-dependent angle-resolved light scattering is demonstrated using wavelength-scanning illumination.

  12. Plasmon Enhanced Photoemission

    Energy Technology Data Exchange (ETDEWEB)

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

    2012-05-08

    this work, the structure consisted of rectangular nano-grooves (NGs) arranged in a subwavelength grating on a metal surface is presented that provides a dramatic increase in the metal’s absorption, field localization, and field enhancement. When light is polarized perpendicular to the orientation of the grooves a standing SPP wave is excited along the vertical walls in the NGs, that act as Fabry-Perot resonators. By adjusting the geometry of the NGs and the period of the subwavelength grating the resonance can be fine tuned to a desired position, for example, the laser fundamental wavelength, anywhere from the UV to the near infrared (NIR). Two types of gratings are presented: (a) a gold grating with period of 600 nm, and (b) an aluminum-gold grating with a period of 100 nm; both with resonance at 720 nm. In each case, strong on-resonance absorption was observed, with over 98% for grating (b). Unlike the grating-coupled SPP waves, where the angle is well defined by the momentum matching condition, the resonant NGs allow coupling to the standing modes at a range of angles of incidence, referred to as the angular bandwidth. A new model for the on-resonance absorption based on the ensamble action of the NGs is presented that serves as the basis for a design of an NG grating with an ultrawide spectral as well as angular bandwidth. For sample (b), the angular bandwidth is 80 degrees, corresponding to an opening angle of 160 degrees. The photoemission enhancement for such a grating was measured to be seven orders of magnitude for a four-photon photoemission. This is an incredible result demonstrating the power of the plasmonic grating presented, which is an efficient light trapper and field enhancer for a non-linear processes. These results demonstrate that the metal photocathode prepared with a NG grating on the metal surface will provide sufficient pulse charge driven by a 1 μJ 15fs pulsed laser at 800 nm for the optimum FEL operation.

  13. Branch Point Withdrawal in Elongational Startup Flow by Time-Resolved Small Angle Neutron Scattering

    KAUST Repository

    Ruocco, N.

    2016-05-27

    We present a small angle neutron scattering (SANS) investigation of a blend composed of a dendritic polymer and a linear matrix with comparable viscosity in start-up of an elongational flow at Tg + 50. The two-generation dendritic polymer is diluted to 10% by weight in a matrix of a long well-entangled linear chains. Both components consist of mainly 1,4-cis-polyisoprene but differ in isotopic composition. The resulting scattering contrast is sufficiently high to permit time-resolved measurements of the system structure factor during the start-up phase and to follow the retraction processes involving the inner sections of the branched polymer in the nonlinear deformation response. The outer branches and the linear matrix, on the contrary, are in the linear deformation regime. The linear matrix dominates the rheological signature of the blend and the influence of the branched component can barely be detected. However, the neutron scattering intensity is predominantly that of the (branched) minority component so that its dynamics is clearly evident. In the present paper, we use the neutron scattering data to validate the branch point withdrawal process, which could not be unambiguously discerned from rheological measurements in this blend. The maximal tube stretch that the inner branches experience, before the relaxed outer arm material is incorporated into the tube is determined. The in situ scattering experiments demonstrate for the first time the leveling-off of the strain as the result of branch point withdrawal and chain retraction directly on the molecular level. We conclude that branch point motion in the mixture of architecturally complex polymers occurs earlier than would be expected in a purely branched system, presumably due to the different topological environment that the linear matrix presents to the hierarchically deep-buried tube sections. © 2016 American Chemical Society.

  14. Developments in inverse photoemission spectroscopy

    International Nuclear Information System (INIS)

    Sheils, W.; Leckey, R.C.G.; Riley, J.D.

    1996-01-01

    In the 1950's and 1960's, Photoemission Spectroscopy (PES) established itself as the major technique for the study of the occupied electronic energy levels of solids. During this period the field divided into two branches: X-ray Photoemission Spectroscopy (XPS) for photon energies greater than ∼l000eV, and Ultra-violet Photoemission Spectroscopy (UPS) for photon energies below ∼100eV. By the 1970's XPS and UPS had become mature techniques. Like XPS, BIS (at x-ray energies) does not have the momentum-resolving ability of UPS that has contributed much to the understanding of the occupied band structures of solids. BIS moved into a new energy regime in 1977 when Dose employed a Geiger-Mueller tube to obtain density of unoccupied states data from a tantalum sample at a photon energy of ∼9.7eV. At similar energies, the technique has since become known as Inverse Photoemission Spectroscopy (IPS), in acknowledgment of its complementary relationship to UPS and to distinguish it from the higher energy BIS. Drawing on decades of UPS expertise, IPS has quickly moved into areas of interest where UPS has been applied; metals, semiconductors, layer compounds, adsorbates, ferromagnets, and superconductors. At La Trobe University an IPS facility has been constructed. This presentation reports on developments in the experimental and analytical techniques of IPS that have been made there. The results of a study of the unoccupied bulk and surface bands of GaAs are presented

  15. Intra- and intercycle interference of angle-resolved electron emission in laser-assisted XUV atomic ionization

    Science.gov (United States)

    Gramajo, A. A.; Della Picca, R.; López, S. D.; Arbó, D. G.

    2018-03-01

    A theoretical study of ionization of the hydrogen atom due to an XUV pulse in the presence of an infrared (IR) laser is presented. Well-established theories are usually used to describe the laser-assisted photoelectron effect: the well-known soft-photon approximation firstly posed by Maquet et al (2007 J. Mod. Opt. 54 1847) and Kazansky’s theory in (2010 Phys. Rev. A 82, 033420). However, these theories completely fail to predict the electron emission perpendicularly to the polarization direction. Making use of a semiclassical model (SCM), we study the angle-resolved energy distribution of PEs for the case that both fields are linearly polarized in the same direction. We thoroughly analyze and characterize two different emission regions in the angle-energy domain: (i) the parallel-like region with contribution of two classical trajectories per optical cycle and (ii) the perpendicular-like region with contribution of four classical trajectories per optical cycle. We show that our SCM is able to assess the interference patterns of the angle-resolved PE spectrum in the two different mentioned regions. Electron trajectories stemming from different optical laser cycles give rise to angle-independent intercycle interferences known as sidebands. These sidebands are modulated by an angle-dependent coarse-grained structure coming from the intracycle interference of the electron trajectories born during the same optical cycle. We show the accuracy of our SCM as a function of the time delay between the IR and the XUV pulses and also as a function of the laser intensity by comparing the semiclassical predictions of the angle-resolved PE spectrum with the continuum-distorted wave strong field approximation and the ab initio solution of the time-dependent Schrödinger equation.

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

    Science.gov (United States)

    Fujimori, Shin-ichi

    2016-04-20

    Recent remarkable progress in angle-resolved photoelectron spectroscopy (ARPES) has enabled the direct observation of the band structures of 4f and 5f materials. In particular, ARPES with various light sources such as lasers (hν ~ 7 eV) or high-energy synchrotron radiations (hν >/~ 400 eV) has shed light on the bulk band structures of strongly correlated materials with energy scales of a few millielectronvolts to several electronvolts. The purpose of this paper is to summarize the behaviors of 4f and 5f band structures of various rare-earth and actinide materials observed by modern ARPES techniques, and understand how they can be described using various theoretical frameworks. For 4f-electron materials, ARPES studies of CeMIn5(M = Rh, Ir, and Co) and YbRh2Si2 with various incident photon energies are summarized. We demonstrate that their 4f electronic structures are essentially described within the framework of the periodic Anderson model, and that the band-structure calculation based on the local density approximation cannot explain their low-energy electronic structures. Meanwhile, electronic structures of 5f materials exhibit wide varieties ranging from itinerant to localized states. For itinerant U5f compounds such as UFeGa5, their electronic structures can be well-described by the band-structure calculation assuming that all U5f electrons are itinerant. In contrast, the band structures of localized U5f compounds such as UPd3 and UO2 are essentially explained by the localized model that treats U5f electrons as localized core states. In regards to heavy fermion U-based compounds such as the hidden-order compound URu2Si2, their electronic structures exhibit complex behaviors. Their overall band structures are generally well-explained by the band-structure calculation, whereas the states in the vicinity of EF show some deviations due to electron correlation effects. Furthermore, the electronic structures of URu2Si2 in the paramagnetic and hidden-order phases are

  17. Angle-resolved conical emission spectra from filamentation in a solid with an Airy pattern and a Gaussian laser beam.

    Science.gov (United States)

    Gong, Cheng; Li, ZiXi; Hua, LinQiang; Quan, Wei; Liu, XiaoJun

    2016-09-15

    Filamentation dynamics in fused silica are investigated using an Airy pattern and a Gaussian laser beam. The angle-resolved conical emission spectra are measured and compared with the predictions of several models. Our experimental observations are consistent with the X-waves model in both cases. This indicates that both laser beams spontaneously evolve into nonlinear X-waves and suggests a universal evolution of filaments in fused silica, regardless of the initial laser beam profile.

  18. The use of angle resolved electron and photon stimulated desorption for the determination of molecular structure at surfaces

    International Nuclear Information System (INIS)

    Madey, T.E.; Stockbauer, R.

    1983-01-01

    A brief review of recent data related to the use of angle-resolved electron stimulated desorption and photon stimulated desorption in determining the structures of molecules at surfaces is made. Examples include a variety of structural assignments based on ESIAD (electron stimulated desorption ion angular distributions), the observation of short-range local ordering effects induced in adsorbed molecules by surface impurities, and the application of photon stimulated desorption to both ionic and covalent adsorbate systems. (Author) [pt

  19. Assessment of waveguiding properties of gallium oxide nanostructures by angle resolved cathodoluminescence in a scanning electron microscope

    International Nuclear Information System (INIS)

    Nogales, Emilio; Mendez, Bianchi; Piqueras, Javier

    2011-01-01

    Cathodoluminescence (CL) of Ga 2 O 3 nanowires and planar microstructures has been studied in a scanning electron microscope, as a function of the orientation angle of the structures relative to the position of the light detection system in the microscope chamber. CL contrast shows a marked dependence on the detection angle due to the waveguiding behaviour of the structures. The angle resolved cathodoluminescence (ARCL) measurements enable to evaluate the optical losses of guided blue-ultraviolet light in nanowires with diameters in the sub-wavelength range, deposited on graphite tape or silicon. In planar, branched feather-like microstructures, ARCL images demonstrate the directional-dependant light guiding behaviour of the nano-branches. -- Highlights: → Waveguiding behaviour of gallium oxide nanowires is studied using angle resolved CL. → Quantitative analysis of optical losses in sub-wavelength nanowires is carried out. → There is a strong dependence of the optical losses on the substrate. → Directional-dependant light guiding is observed in branched planar microstructures.

  20. Photoemission perspective on pseudogap, superconducting fluctuations, and charge order: a review of recent progress.

    Science.gov (United States)

    Vishik, Inna

    2018-03-29

    In the course of seeking the microscopic mechanism of superconductivity in cuprate high temperature superconductors, the pseudogap phase\\textemdash the very abnormal 'normal' state on the hole-doped side\\textemdash has proven to be as big of a quandary as superconductivity itself. Angle-resolved photoemission spectroscopy (ARPES) is a powerful tool for assessing the momentum-dependent phenomenology of the pseudogap, and recent technological developments have permitted a more detailed understanding. This report reviews recent progress in understanding the relationship between superconductivity and the pseudogap, the Fermi arc phenomena, and the relationship between charge order and pseudogap from the perspective of ARPES measurements. © 2018 IOP Publishing Ltd.

  1. Phase-resolved detection of the spin Hall angle by optical ferromagnetic resonance in perpendicularly magnetized thin films

    Science.gov (United States)

    Capua, Amir; Wang, Tianyu; Yang, See-Hun; Rettner, Charles; Phung, Timothy; Parkin, Stuart S. P.

    2017-02-01

    The conversion of charge current to spin current by the spin Hall effect is of considerable current interest from both fundamental and technological perspectives. Measurement of the spin Hall angle, especially for atomically thin systems with large magnetic anisotropies, is not straightforward. Here we demonstrate a hybrid phase-resolved optical-electrical ferromagnetic resonance method that we show can robustly determine the spin Hall angle in heavy-metal/ferromagnet bilayer systems with large perpendicular magnetic anisotropy. We present an analytical model of the ferromagnetic resonance spectrum in the presence of the spin Hall effect, in which the spin Hall angle can be directly determined from the changes in the amplitude response as a function of the spin current that is generated from a dc charge current passing through the heavy-metal layer. Increased sensitivity to the spin current is achieved by operation under conditions for which the magnetic potential is shallowest at the "Smit point." Study of the phase response reveals that the spin Hall angle can be reliably extracted from a simplified measurement that does not require scanning over time or magnetic field but rather only on the dc current. The method is applied to the Pt-Co/Ni/Co system whose spin Hall angle was to date characterized only indirectly and that is especially relevant for spin-orbit torque devices.

  2. Multi-angle lensless digital holography for depth resolved imaging on a chip

    Science.gov (United States)

    Su, Ting-Wei; Isikman, Serhan O.; Bishara, Waheb; Tseng, Derek; Erlinger, Anthony; Ozcan, Aydogan

    2010-01-01

    A multi-angle lensfree holographic imaging platform that can accurately characterize both the axial and lateral positions of cells located within multi-layered micro-channels is introduced. In this platform, lensfree digital holograms of the micro-objects on the chip are recorded at different illumination angles using partially coherent illumination. These digital holograms start to shift laterally on the sensor plane as the illumination angle of the source is tilted. Since the exact amount of this lateral shift of each object hologram can be calculated with an accuracy that beats the diffraction limit of light, the height of each cell from the substrate can be determined over a large field of view without the use of any lenses. We demonstrate the proof of concept of this multi-angle lensless imaging platform by using light emitting diodes to characterize various sized microparticles located on a chip with sub-micron axial and lateral localization over ~60 mm2 field of view. Furthermore, we successfully apply this lensless imaging approach to simultaneously characterize blood samples located at multi-layered micro-channels in terms of the counts, individual thicknesses and the volumes of the cells at each layer. Because this platform does not require any lenses, lasers or other bulky optical/mechanical components, it provides a compact and high-throughput alternative to conventional approaches for cytometry and diagnostics applications involving lab on a chip systems. PMID:20588819

  3. Electronic states localized at surface defects on Cu(755) studied by angle-resolved ultraviolet photoelectron spectroscopy using synchrotron radiation

    CERN Document Server

    Ogawa, K; Namba, H

    2003-01-01

    'Regularly stepped' and 'defective' surfaces of Cu(755) were prepared by low- and high-temperature annealing, respectively, of a clean specimen. Electronic states on both surfaces were studied by angle-resolved ultraviolet photoelectron spectroscopy using synchrotron radiation. On the defective Cu(755), we found a new photoelectron peak due to surface defects just below the Fermi level. The dispersion profile of the defect state is derived to be almost flat, which demonstrates the localized nature of the defects. High activity to oxygen adsorption of the defect state was revealed. (author)

  4. Tuning the electronic structure of bulk FeSe with chemical pressure using quantum oscillations and angle resolved photoemission spectroscopy (ARPES)

    Science.gov (United States)

    Coldea, Amalia

    FeSe is a unique and intriguing superconductor which can be tuned into a high temperature superconducting state using applied pressure, chemical intercalation and surface doping. In the absence of magnetism, the structural transition in FeSe is believed to be electronically driven, with the orbital degrees of freedom playing an important part. This scenario supports the stabilization of a nematic state in FeSe, which manifests as a Fermi surface deformation in the presence of strong interactions, as detected by ARPES. Another manifestation of the nematicity is the enhanced nematic susceptibility determined from elastoresistance measurements under applied strain. Isovalent Sulphur substitution onto the Selenium site constitutes a chemical pressure, which subtly modifies the electronic structure of FeSe, suppressing the structural transition without inducing high temperature superconductivity. I will present the evolution of the electronic structure with chemical pressure in FeSe, as determined from quantum oscillations and ARPES studies and I will discuss the suppression of the nematic electronic state and the role of electronic correlations. Experiments were performed at high magnetic field facilities in Tallahassee, Nijmegen and Toulouse and Diamond Light Source, UK. This work is mainly supported by EPSRC, UK (EP/I004475/1, EP/I017836/1) and I acknowledge my collaborators from Refs. .

  5. Critical-angle x-ray transmission grating spectrometer with extended bandpass and resolving power > 10,000

    Science.gov (United States)

    Heilmann, Ralf K.; Bruccoleri, Alexander R.; Kolodziejczak, Jeffery; Gaskin, Jessica A.; O'Dell, Stephen L.; Bhatia, Ritwik; Schattenburg, Mark L.

    2016-07-01

    A number of high priority subjects in astrophysics can be addressed by a state-of-the-art soft x-ray grating spectrometer, such as the role of Active Galactic Nuclei in galaxy and star formation, characterization of the Warm-Hot Intergalactic Medium and the missing baryon problem, characterization of halos around the Milky Way and nearby galaxies, as well as stellar coronae and surrounding winds and disks. An Explorer-scale, largearea (> 1,000 cm2), high resolving power (R =λ/Δλ > 3,000) soft x-ray grating spectrometer is highly feasible based on Critical-Angle Transmission (CAT) grating technology, even for telescopes with angular resolution of 5-10 arcsec. Still, significantly higher performance can be provided by a CAT grating spectrometer on an X-ray- Surveyor-type mission. CAT gratings combine the advantages of blazed reflection gratings (high efficiency, use of higher diffraction orders) with those of conventional transmission gratings (lowmass, relaxed alignment tolerances and temperature requirements, transparent at higher energies) with minimalmission resource requirements. They are high-efficiency blazed transmission gratings that consist of freestanding, ultra-high aspect-ratio grating bars fabricated from silicon-on-insulator (SOI) wafers using advanced anisotropic dry and wet etch techniques. Blazing is achieved through grazing-incidence reflection off the smooth grating bar sidewalls. The reflection properties of silicon are well matched to the soft x-ray band, and existing silicon CAT gratings can exceed 30% absolute diffraction efficiency, with clear paths for further improvement. Nevertheless, CAT gratings with sidewalls made of higher atomic number elements allow extension of the CAT grating principle to higher energies and larger dispersion angles, thus enabling higher resolving power at shorter wavelengths. We show x-ray data from CAT gratings coated with a thin layer of platinum using atomic layer deposition, and demonstrate efficient

  6. Neutron Imaging of Laser Melted SS316 Test Objects with Spatially Resolved Small Angle Neutron Scattering

    Directory of Open Access Journals (Sweden)

    Adam J. Brooks

    2017-12-01

    Full Text Available A novel neutron far field interferometer is explored for sub-micron porosity detection in laser sintered stainless steel alloy 316 (SS316 test objects. The results shown are images and volumes of the first quantitative neutron dark-field tomography at various autocorrelation lengths, ξ . In this preliminary work, the beam defining slits were adjusted to an uncalibrated opening of 0.5 mm horizontal and 5 cm vertical; the images are blurred along the vertical direction. In spite of the blurred attenuation images, the dark-field images reveal structural information at the micron-scale. The topics explored include: the accessible size range of defects, potentially 338 nm to 4.5 μ m, that can be imaged with the small angle scattering images; the spatial resolution of the attenuation image; the maximum sample dimensions compatible with interferometry optics and neutron attenuation; the procedure for reduction of the raw interferogram images into attenuation, differential phase contrast, and small angle scattering (dark-field images; and the role of neutron far field interferometry in additive manufacturing to assess sub-micron porosity.

  7. Fourier Transform Photoemission Spectroscopy

    NARCIS (Netherlands)

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

    1996-01-01

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

  8. Fourier transform photoemission spectroscopy

    NARCIS (Netherlands)

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

    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

  9. Carbon Condensation during High Explosive Detonation with Time Resolved Small Angle X-ray Scattering

    Science.gov (United States)

    Hammons, Joshua; Bagge-Hansen, Michael; Nielsen, Michael; Lauderbach, Lisa; Hodgin, Ralph; Bastea, Sorin; Fried, Larry; May, Chadd; Sinclair, Nicholas; Jensen, Brian; Gustavsen, Rick; Dattelbaum, Dana; Watkins, Erik; Firestone, Millicent; Ilavsky, Jan; van Buuren, Tony; Willey, Trevor; Lawrence Livermore National Lab Collaboration; Los Alamos National Laboratory Collaboration; Washington State University/Advanced Photon Source Team

    Carbon condensation during high-energy detonations occurs under extreme conditions and on very short time scales. Understanding and manipulating soot formation, particularly detonation nanodiamond, has attracted the attention of military, academic and industrial research. An in-situ characterization of these nanoscale phases, during detonation, is highly sought after and presents a formidable challenge even with today's instruments. Using the high flux available with synchrotron X-rays, pink beam small angle X-ray scattering is able to observe the carbon phases during detonation. This experimental approach, though powerful, requires careful consideration and support from other techniques, such as post-mortem TEM, EELS and USAXS. We present a comparative survey of carbon condensation from different CHNO high explosives. This work was performed under the auspices of the US DOE by LLNL under Contract DE-AC52-07NA27344.

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

    Science.gov (United States)

    Jo, YoungJu; Jung, JaeHwang; Lee, Jee Woong; Shin, Della; Park, HyunJoo; Nam, Ki Tae; Park, Ji-Ho; Park, YongKeun

    2014-05-28

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

  11. From Non-equilibrium to Equilibrium: Micellar Kinetics seen by Time-resolved Small-angle Scattering

    Science.gov (United States)

    Lund, Reidar

    The kinetic pathways of self-assembled nanostructures are not fully understood. Time-resolved small-angle X-ray/neutron scattering (TR-SAXS/SANS) is powerful technique1 that allows kinetics processes such as nucleation processes2,3 and morphological transitions4,5 to be followed with structural resolution over time scales starting from milliseconds. Neutrons offer the additional advantage of facile contrast variation through H/D substitution schemes, which also allow equilibrium processes such as molecular exchange and diffusion to be studied1 , 6 , 7. Here we will highlight the current capabilities of TR-SAS and show results on the kinetics of polymeric micelles. We will address how the understanding of kinetic pathways can be used control the nanostructure.

  12. Crank-angle resolved imaging of biacetyl laser-induced fluorescence in an optical internal combustion engine

    Science.gov (United States)

    Smith, J. D.; Sick, V.

    2005-09-01

    The use of a frequency-tripled, diode-pumped Nd:YAG laser in combination with a CMOS camera lens-coupled to a three-stage image intensifier allowed the visualization of the fuel distribution with crank angle resolution for hundreds of consecutive engine cycles. Biacetyl, doped into iso-octane, was excited at rates of 12 kHz with 100 ns pulses. Pulse energies are high enough to allow single-pulse imaging of the vapor-phase fuel distribution for motored and fired operation in an optical engine. The repetition rate of the setup is adequate to resolve critical steps in the development of the fuel cloud around the spark plug of a direct-injection gasoline engine.

  13. Time-resolved small angle neutron scattering measurements of asphaltene nanoparticle aggregation kinetics in incompatible crude oil mixtures

    International Nuclear Information System (INIS)

    Mason, Thomas G.; Lin, Min Y.

    2003-01-01

    We use time-resolved-small angle neutron scattering to study the kinetics of asphaltene nanoparticle aggregation in incompatible crude oil mixtures. We induce asphaltene aggregation by mixing asphaltene-rich Syrian crude oil (SACO) with a paraffinic British crude oil and observe the scattered neutron intensity, I, as a function of wave number, q, over times, t, ranging from twenty minutes to about a week. We observe a growth in I at low q as the nanoscale asphaltenes agglomerate into microscale aggregates and interpret this growth as an increase in surface scattering from the aggregates. We fit I(q,t) to an empirical model and measure the growth in the power-law exponent, α, associated with the low-q logarithmic slope of I(q). We define a time, τ α , associated with the first appearance of the aggregates when α>3; τ α increases as a function of the volume fraction, φ m , of SACO in the mixture. The surface scattering intensity initially increases and then saturates at long times when the aggregate structures no longer evolve at the length scales we probe. Based on this saturation, we define a time scale, τ I , which is larger than τ α but has essentially the same dependence on φ m . We interpret τ α (φ m ) and τ I (φ m ) in terms of a simple aggregation model based on diffusion-limited kinetics and a repulsive potential barrier that models the effective solvent quality

  14. Combined angle-resolved X-ray photoelectron spectroscopy, density functional theory and kinetic study of nitridation of gallium arsenide

    Science.gov (United States)

    Mehdi, H.; Monier, G.; Hoggan, P. E.; Bideux, L.; Robert-Goumet, C.; Dubrovskii, V. G.

    2018-01-01

    The high density of interface and surface states that cause the strong Fermi pinning observed on GaAs surfaces can be reduced by depositing GaN ultra-thin films on GaAs. To further improve this passivation, it is necessary to investigate the nitridation phenomena by identifying the distinct steps occurring during the process and to understand and quantify the growth kinetics of GaAs nitridation under different conditions. Nitridation of the cleaned GaAs substrate was performed using N2 plasma source. Two approaches have been combined. Firstly, an AR-XPS (Angle Resolved X-ray Photoelectron Spectroscopy) study is carried out to determine the chemical environments of the Ga, As and N atoms and the composition depth profile of the GaN thin film which allow us to summarize the nitridation process in three steps. Moreover, the temperature and time treatment have been investigated and show a significant impact on the formation of the GaN layer. The second approach is a refined growth kinetic model which better describes the GaN growth as a function of the nitridation time. This model clarifies the exchange mechanism of arsenic with nitrogen atoms at the GaN/GaAs interface and the phenomenon of quasi-saturation of the process observed experimentally.

  15. Particle evolution of Composition B-3 studied by time-resolved small angle x-ray scattering

    Science.gov (United States)

    Huber, R.; Podlesak, D.; Dattelbaum, D.; Firestone, M.; Gustavsen, R.; Jensen, B.; Ringstrand, B.; Watkins, E.; Bagge-Hansen, M.; Hodgin, R.; Lauderbach, L.; Willey, T.; van Buuren, T.; Graber, T.; Rigg, P.; Sinclair, N.; Seifert, S.

    Accessing various pressures and temperatures of the carbon phase diagram through high explosive (HE) detonations, as a means of synthesis, provides an exciting opportunity to study new carbon allotropes. Carbon allotropes in HE detonations are thought to form through collision of free carbon within the detonation cloud; however direct confirmation of real-time product formation is limited due to experimental restraints. Time-resolved small angle x-ray scattering (TRSAXS) of in-line detonations provides information about particle formation behind the detonation front on the 100's of nanoseconds timescale. The only set-up of its kind in the United States is at Argonne National Laboratory at the Advanced Photon Source in the Dynamic Compression Sector (DCS). Through empirical and analytical analysis of the TRSAXS data, parameters such as particle size and morphology can be deduced with respect to time. In the case of Composition B-3 (40% TNT/60% RDX) particle formation morphs from spherical core-shell structure to an elongated structure at long times ( 2 us) under vacuum. To complete the timeline of carbon formation, the post detonation soot is also analyzed to confirm this elongated structure as the majority carbon product. LA-UR-16-28691

  16. Time-Resolved Small-Angle X-ray Scattering Reveals Millisecond Transitions of a DNA Origami Switch.

    Science.gov (United States)

    Bruetzel, Linda K; Walker, Philipp U; Gerling, Thomas; Dietz, Hendrik; Lipfert, Jan

    2018-04-11

    Self-assembled DNA structures enable creation of specific shapes at the nanometer-micrometer scale with molecular resolution. The construction of functional DNA assemblies will likely require dynamic structures that can undergo controllable conformational changes. DNA devices based on shape complementary stacking interactions have been demonstrated to undergo reversible conformational changes triggered by changes in ionic environment or temperature. An experimentally unexplored aspect is how quickly conformational transitions of large synthetic DNA origami structures can actually occur. Here, we use time-resolved small-angle X-ray scattering to monitor large-scale conformational transitions of a two-state DNA origami switch in free solution. We show that the DNA device switches from its open to its closed conformation upon addition of MgCl 2 in milliseconds, which is close to the theoretical diffusive speed limit. In contrast, measurements of the dimerization of DNA origami bricks reveal much slower and concentration-dependent assembly kinetics. DNA brick dimerization occurs on a time scale of minutes to hours suggesting that the kinetics depend on local concentration and molecular alignment.

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

    Science.gov (United States)

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

    2016-01-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2016-01-22

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

  19. 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...

  20. Theory of temperature dependent photoemission spectrum of heavy fermion semiconductors

    International Nuclear Information System (INIS)

    Riseborough, P.S.

    1998-01-01

    The heavy fermion semiconductors are a class of strongly correlated materials, that at high temperatures show properties similar to those of heavy fermion materials, but at low temperatures show a cross-over into a semi-conducting state. The low temperature insulating state is characterized by an anomalously small energy gap, varying between 10 and 100 K. The smallness of the gap is attributed to the result of a many-body renormalization, and is temperature dependent. The temperature dependence of the electronic spectral density of states is calculated, using the Anderson lattice model at half filling. The spectrum is calculated to second order in 1/N, where N is the degeneracy of the 'f' orbitals, using a slave boson technique. The system is an indirect gap semi-conductor, with an extremely temperature dependent electronic spectral density A(k, ω). The indirect gap is subject to a temperature dependent many-body renormalization, and leads to a sharp temperature dependent structure in the angle resolved photo-emission spectrum at the indirect threshold. The theoretical predictions are compared with experimental observations on FeSi. (Copyright (1998) World Scientific Publishing Co. Pte. Ltd)

  1. Angle-resolved spectral Fabry-Pérot interferometer for single-shot measurement of refractive index dispersion over a broadband spectrum

    Science.gov (United States)

    Dong, J. T.; Ji, F.; Xia, H. J.; Liu, Z. J.; Zhang, T. D.; Yang, L.

    2018-01-01

    An angle-resolved spectral Fabry-Pérot interferometer is reported for fast and accurate measurement of the refractive index dispersion of optical materials with parallel plate shape. The light sheet from the wavelength tunable laser is incident on the parallel plate with converging angles. The transmitted interference light for each angle is dispersed and captured by a 2D sensor, in which the rows and the columns are used to simultaneously record the intensities as a function of wavelength and incident angle, respectively. The interferogram, named angle-resolved spectral intensity distribution, is analyzed by fitting the phase information instead of finding the fringe peak locations that present periodic ambiguity. The refractive index dispersion and the physical thickness can be then retrieved from a single-shot interferogram within 18 s. Experimental results of an optical substrate standard indicate that the accuracy of the refractive index dispersion is less than 2.5  ×  10-5 and the relative uncertainty of the thickness is 6  ×  10-5 mm (3σ) due to the high stability and the single-shot measurement of the proposed system.

  2. Inverse photoemission of uranium oxides

    International Nuclear Information System (INIS)

    Roussel, P.; Morrall, P.; Tull, S.J.

    2009-01-01

    Understanding the itinerant-localised bonding role of the 5f electrons in the light actinides will afford an insight into their unusual physical and chemical properties. In recent years, the combination of core and valance band electron spectroscopies with theoretic modelling have already made significant progress in this area. However, information of the unoccupied density of states is still scarce. When compared to the forward photoemission techniques, measurements of the unoccupied states suffer from significantly less sensitivity and lower resolution. In this paper, we report on our experimental apparatus, which is designed to measure the inverse photoemission spectra of the light actinides. Inverse photoemission spectra of UO 2 and UO 2.2 along with the corresponding core and valance electron spectra are presented in this paper. UO 2 has been reported previously, although through its inclusion here it allows us to compare and contrast results from our experimental apparatus to the previous Bremsstrahlung Isochromat Spectroscopy and Inverse Photoemission Spectroscopy investigations

  3. Photoemission study of S adsorption on GaAs (0 0 1)

    International Nuclear Information System (INIS)

    Strasser, T; Kipp, L; Skibowski, M; Schattke, W

    2005-01-01

    Angle-resolved photoemission spectra have been calculated with the one-step model for S/GaAs(0 0 1) and compared with experimental distributions. The data are analysed in terms of the ideal 1 x 1 and, furthermore, of the reconstructed 2 x 6 surface which is assumed to be closest to the experimentally realized structure. Emissions are characterized by electronic structure terms such as energy bands and orbital composition, though partly also by geometric properties. In particular, the determination of the second layer as consisting of Ga atoms has been achieved because of the distinct differences in the theoretical spectra with S-Ga and those with S-As bonds

  4. Stable five axes cryogenic photoemission manipulator without a differentially pumped rotary feedthrough

    International Nuclear Information System (INIS)

    Kim, Bum Joon; Kim, Hyeong-Do; Cho, Deok-Yong; Kim, Myongjin; Oh, S.-J.; Kim, Changyoung

    2005-01-01

    We report on the design and construction of an ultrahigh vacuum compatible cryogenic manipulator for angle resolved photoemission spectroscopy. Unlike designs that have been used so far, our design allows five motions (three translational and two angular) without a differentially pumped rotary feedthrough. The design greatly reduces the sample motion upon rotation, which is crucial in automatic data acquisition over a large area in the momentum space. The constructed manipulator shows smooth motions in vacuum and the lowest temperature it could reach is about 8 K at the sample position. Angular reproducibilities are found to be about 0.02 deg. for both of the angular motions. The wobbling motion from the rotation around the vertical rotation axis is found to be virtually nonexistent (less than 0.1 mm)

  5. Time-resolved ARPES with sub-15 fs temporal and near Fourier-limited spectral resolution.

    Science.gov (United States)

    Rohde, G; Hendel, A; Stange, A; Hanff, K; Oloff, L-P; Yang, L X; Rossnagel, K; Bauer, M

    2016-10-01

    An experimental setup for time- and angle-resolved photoelectron spectroscopy with sub-15 fs temporal resolution is presented. A hollow-fiber compressor is used for the generation of 6.5 fs white light pump pulses, and a high-harmonic-generation source delivers 11 fs probe pulses at a photon energy of 22.1 eV. A value of 13 fs full width at half-maximum of the pump-probe cross correlation signal is determined by analyzing a photoemission intensity transient probing a near-infrared interband transition in 1T-TiSe 2 . Notably, the energy resolution of the setup conforms to typical values reported in conventional time-resolved photoemission studies using high harmonics, and an ultimate resolution of 170 meV is feasible.

  6. Applicability of magic angle for angle-resolved X-ray photoelectron spectroscopy of corrugated SiO.sub.2./sub./Si surfaces: Monte Carlo calculations

    Czech Academy of Sciences Publication Activity Database

    Olejník, Kamil; Zemek, Josef

    2008-01-01

    Roč. 602, - (2008), s. 2581-2586 ISSN 0039-6028 R&D Projects: GA ČR GA202/06/0459 Institutional research plan: CEZ:AV0Z10100521 Keywords : photoelectron spectroscopy * surface roughness * Monte Carlo calculations * magic angle * overlayer thickness Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.731, year: 2008

  7. Angular momentum-induced delays in solid-state photoemission enhanced by intra-atomic interactions.

    Science.gov (United States)

    Siek, Fabian; Neb, Sergej; Bartz, Peter; Hensen, Matthias; Strüber, Christian; Fiechter, Sebastian; Torrent-Sucarrat, Miquel; Silkin, Vyacheslav M; Krasovskii, Eugene E; Kabachnik, Nikolay M; Fritzsche, Stephan; Muiño, Ricardo Díez; Echenique, Pedro M; Kazansky, Andrey K; Müller, Norbert; Pfeiffer, Walter; Heinzmann, Ulrich

    2017-09-22

    Attosecond time-resolved photoemission spectroscopy reveals that photoemission from solids is not yet fully understood. The relative emission delays between four photoemission channels measured for the van der Waals crystal tungsten diselenide (WSe 2 ) can only be explained by accounting for both propagation and intra-atomic delays. The intra-atomic delay depends on the angular momentum of the initial localized state and is determined by intra-atomic interactions. For the studied case of WSe 2 , the photoemission events are time ordered with rising initial-state angular momentum. Including intra-atomic electron-electron interaction and angular momentum of the initial localized state yields excellent agreement between theory and experiment. This has required a revision of existing models for solid-state photoemission, and thus, attosecond time-resolved photoemission from solids provides important benchmarks for improved future photoemission models. Copyright © 2017 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.

  8. Large-angle magnetization dynamics investigated by vector-resolved magnetization-induced optical second-harmonic generation

    NARCIS (Netherlands)

    Gerrits, T.; Silva, T.J.; Nibarger, J.P.; Rasing, T.H.M.

    2004-01-01

    We examine the relationship between nonlinear magnetic responses and the change in the Gilbert damping parameter alpha for patterned and unpatterned thin Permalloy films when subjected to pulsed magnetic fields. An improved magnetization-vector-resolved technique utilizing magnetization-induced

  9. Size effects in van der Waals clusters studied by spin and angle-resolved electron spectroscopy and multi-coincidence ion imaging

    International Nuclear Information System (INIS)

    Rolles, D; Pesic, Z D; Zhang, H; Bilodeau, R C; Bozek, J D; Berrah, N

    2007-01-01

    We have studied the valence and inner-shell photoionization of free rare-gas clusters by means of angle and spin resolved photoelectron spectroscopy and momentum resolving electron-multi-ion coincidence spectroscopy. The electron measurements probe the evolution of the photoelectron angular distribution and spin polarization parameters as a function of photon energy and cluster size, and reveal a strong cluster size dependence of the photoelectron angular distributions in certain photon energy regions. In contrast, the spin polarization parameter of the cluster photoelectrons is found to be very close to the atomic value for all covered photon energies and cluster sizes. The ion imaging measurements, which probe the fragmentation dynamics of multiply charged van der Waals clusters, also exhibit a pronounced cluster size dependence

  10. Low-temperature dynamics of magnetic colloids studied by time-resolved small-angle neutron scattering

    NARCIS (Netherlands)

    Wiedenmann, A.; Keiderling, U.; Meissner, M.; Wallacher, D.; Gähler, R.; May, R.P.; Prévost, S.; Klokkenburg, M.; Erne, B.H.; Kohlbrecher, J.

    2008-01-01

    The dynamics of ordering and relaxation processes in magnetic colloids has been studied by means of stroboscopic small angle neutron scattering techniques in an oscillating magnetic field. Surfactant stabilized ferrofluids (FFs) of Fe3O4 and Co nanoparticles have been investigated as a function of

  11. Angle-resolved electron and ion spectroscopy apparatus on the soft X-ray photochemistry beamline BL27SU at SPring-8

    CERN Document Server

    Ueda, K; Senba, Y; Okada, K; Shimizu, Y; Chiba, H; Ohashi, H; Tamenori, Y; Okumura, H; Saitô, N; Nagaoka, S; Hiraya, A; Ishiguro, E; Ibuki, T; Suzuki, I H; Koyano, I

    2001-01-01

    We have designed and constructed the apparatus for the angular distribution measurements of photoejected electrons and ions from free molecules, as a part of the endstation of the c-branch of the beamline BL27SU, a soft X-ray photochemistry beamline at SPring-8. The experimental procedures are described in combination with the use of a capability to switch the horizontal and vertical directions of the linear polarization of the light produced by the figure-8 undulator. As a typical example of the experimental results, we present angle-resolved energetic ion yield spectra in the O 1s excitation region of CO sub 2.

  12. Photoemission spectroscopy using synchrotron radiation

    International Nuclear Information System (INIS)

    Kobayashi, K.L.I.

    1980-01-01

    It is an epoch making event for photoemission spectroscopy that the light sources of continuous wavelength from vacuum ultra-violet to X-ray region have become available by the advent of synchrotron radiation. Specifically the progress after stable intense light has become obtainable from storage rings is very significant. One of the features of these synchrotron radiation is its extreme polarization of radiating pattern. Though the elementary processes of photoemission out of solids are the basic themes, phenomenalistic 3-stage model is usually applied to the analysis of experiments. In this model, the process of photoemission is considered by dividing into three stages, namely the generation of photoelectrons due to optical transition between electron status -- the transportation of photoelectrons to solid surfaces -- breaking away from the surfaces. The spectrometers, the energy analyzers of photoelectrons, and sample-preparing room used for photoemission spectroscopy are described. Next, energy distribution curves are explained. At the end, photoelectron yield spectroscopy, CFS (constant final energy spectroscopy) and CIS (constant initial energy spectroscopy), Auger yield and interatomic Auger yield, the determination of surface structure by normal emission CIS, and surface EXAFS (extended X-ray absorption fine structure) are described. As seen above, the application specifically to surface physics is promising in the future. (Wakatsuki, Y.)

  13. Vacuum scanning capillary photoemission microscopy

    DEFF Research Database (Denmark)

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

    2017-01-01

    We demonstrate the use of a conical capillary in a scanning probe microscopy for surface analysis. The probe can measure photoemission from a substrate by transmitting photoelectrons along the capillary as a function of probe position. The technique is demonstrated on a model substrate consisting...

  14. Time- and angle-resolved x-ray diffraction to probe structural and chemical evolution during Al-Ni intermetallic reactions.

    Science.gov (United States)

    Yoo, Choong-Shik; Wei, Haoyan; Chen, Jing-Yin; Shen, Guoyin; Chow, Paul; Xiao, Yuming

    2011-11-01

    We present novel time- and angle-resolved x-ray diffraction (TARXD) capable of probing structural and chemical evolutions during rapidly propagating exothermic intermetallic reactions between Ni-Al multilayers. The system utilizes monochromatic synchrotron x-rays and a two-dimensional (2D) pixel array x-ray detector in combination of a fast-rotating diffraction beam chopper, providing a time (in azimuth) and angle (in distance) resolved x-ray diffraction image continuously recorded at a time resolution of ~30 μs over a time period of 3 ms. Multiple frames of the TARXD images can also be obtained with time resolutions between 30 and 300 μs over three to several hundreds of milliseconds. The present method is coupled with a high-speed camera and a six-channel optical pyrometer to determine the reaction characteristics including the propagation speed of 7.6 m/s, adiabatic heating rate of 4.0 × 10(6) K/s, and conductive cooling rate of 4.5 × 10(4) K/s. These time-dependent structural and temperature data provide evidences for the rapid formation of intermetallic NiAl alloy within 45 μs, thermal expansion coefficient of 1.1 × 10(-6) K for NiAl, and crystallization of V and Ag(3)In in later time. © 2011 American Institute of Physics

  15. SAXSANA: an interactive program for the analysis and monitoring of static and time-resolved small-angle X-ray solution scattering measurements.

    Science.gov (United States)

    Hiragi, Yuzuru; Sano, Yoh; Matsumoto, Tomoharu

    2003-03-01

    An interactive analytical program, SAXSANA, for small-angle X-ray scattering measurements of solutions is described. The program processes scattered data without disciplined knowledge of small-angle scattering. SAXSANA also assists in finding the best experimental conditions, thus avoiding blind runs of experiments. SAXSANA consists of the following procedures: (i) determination of the centre of scattered X-rays and moment transfer Q (Q = 4pisintheta/lambda, where 2theta is the scattering angle and lambda is the wavelength) for each measured channel; (ii) conversion of the data format to the format of Q versus scattered intensities J(Q); (iii) truncation of unnecessary data and smoothing of scattering curves by cubic-spline function; (iv) correction of the absorption effect and subtraction of the scattered intensity of the buffer (solvent) solution from that of the sample solution; (v) creation of a data file for a three-dimensional representation of time-resolved scattering curves; (vi) determination of radii of gyration by Guinier plots; (vii) determination of persistent lengths by Kratky plots; (viii) extrapolation of the small-angle part by Guinier plots; (ix) extrapolation of the wide-angle part by Porod's & Luzzati's laws for the Hankel transformation in order to obtain the distance distribution function p(r); (x) calculation of p(r) and computation of the invariant, the chord length, the Volume, the spherical radius, the maximum dimension D(max) and the radius of gyration (Rg). SAXSANA also serves as an on-site monitor for the validity of an experimental result during the measurements.

  16. Time-Resolving Study of Stress-Induced Transformations of Isotactic Polypropylene through Wide Angle X-ray Scattering Measurements

    Directory of Open Access Journals (Sweden)

    Finizia Auriemma

    2018-02-01

    Full Text Available The development of a highly oriented fiber morphology by effect of tensile deformation of stereodefective isotactic polypropylene (iPP samples, starting from the unoriented γ form, is studied by following the transformation in real time during stretching through wide angle X-ray scattering (WAXS measurements. In the stretching process, after yielding, the initial γ form transforms into the mesomorphic form of iPP through mechanical melting and re-crystallization. The analysis of the scattering invariant measured in the WAXS region highlights that the size of the mesomorphic domains included in the well oriented fiber morphology obtained at high deformations increases through a process which involves the coalescence of the small fragments formed by effect of tensile stress during lamellar destruction with the domain of higher dimensions.

  17. Photoemission beyond the sudden approximation

    Science.gov (United States)

    Almbladh, Carl-Olof

    2006-04-01

    The many-body theory of photoemission in solids is reviewed with emphasis on methods based on response theory. The classification of diagrams into loss and no-loss diagrams is discussed and related to Keldysh path-ordering book-keeping. Some new results on energy losses in valence-electron photoemission from free-electron-like metal surfaces are presented. A way to group diagrams is presented in which spectral intensities acquire a Golden-Rule-like form which guarantees positiveness. This way of regrouping should be useful also in other problems involving spectral intensities, such as the problem of improving the one-electron spectral function away from the quasiparticle peak.

  18. Critical-angle transmission grating technology development for high resolving power soft x-ray spectrometers on Arcus and Lynx

    Science.gov (United States)

    Heilmann, Ralf K.; Bruccoleri, Alexander R.; Song, Jungki; Kolodziejczak, Jeffery; Gaskin, Jessica A.; O'Dell, Stephen L.; Cheimetz, Peter; Hertz, Edward; Smith, Randall K.; Burwitz, Vadim; Hartner, Gisela; La Caria, Marlis-Madeleine; Schattenburg, Mark L.

    2017-08-01

    Soft x-ray spectroscopy with high resolving power (R = λ/Δλ) and large effective area (A) addresses numerous unanswered science questions about the physical laws that lead to the structure of our universe. In the soft x-ray band R > 1000 can currently only be achieved with diffraction grating-based spectroscopy. Criticalangle transmission (CAT) gratings combine the advantages of blazed reflection gratings (high efficiency, use of higher diffraction orders) with those of conventional transmission gratings (relaxed alignment tolerances and temperature requirements, transparent at higher energies, low mass), resulting in minimal mission resource requirements, while greatly improving figures of merit. Diffraction efficiency > 33% and R > 10, 000 have been demonstrated for CAT gratings. Last year the technology has been certified at Technology Readiness Level 4 based on a probe class mission concept. The Explorer-scale (A > 450 cm2 , R > 2500) grating spectroscopy Arcus mission can be built with today's CAT grating technology and has been selected in the current Explorer round for a Phase A concept study. Its figure of merit for the detection of weak absorption lines will be an order of magnitude larger than current instruments on Chandra and XMM-Newton. Further CAT grating technology development and improvements in the angular resolution of x-ray optics can provide another order of magnitude improvement in performance, as is envisioned for the X-ray Surveyor/Lynx mission concept currently under development for input into the 2020 Decadal Survey. For Arcus we have tested CAT gratings in a spectrometer setup in combination with silicon pore optics (SPO) and obtained resolving power results that exceed Arcus requirements before and after environmental testing of the gratings. We have recently fabricated the largest (32 mm x 32 mm) CAT gratings to date, and plan to increase grating size further. We mounted two of these large gratings to frames and aligned them in the

  19. Relaxation of strongly coupled electron and phonon fields after photoemission and high-energy part of ARPES spectra of cuprates

    Science.gov (United States)

    Myasnikova, A. E.; Zhileeva, E. A.; Moseykin, D. V.

    2018-03-01

    An approach to considering systems with a high concentration of correlated carriers and strong long-range electron–phonon interaction and to calculating the high-energy part of the angle-resolved photoemission spectroscopy (ARPES) spectra of such systems is suggested. Joint relaxation of strongly coupled fields—a field of correlated electrons and phonon field—after photoemission is studied to clarify the nature of characteristic features observed in the high-energy part of the ARPES spectra of cuprate superconductors. Such relaxation occurs in systems with strong predominantly long-range electron–phonon interaction at sufficiently high carrier concentration due to the coexistence of autolocalized and delocalized carriers. A simple method to calculate analytically a high-energy part of the ARPES spectrum arising is proposed. It takes advantage of using the coherent states basis for the phonon field in the polaron and bipolaron states. The approach suggested yields all the high-energy spectral features like broad Gaussian band and regions of ‘vertical dispersion’ being in good quantitative agreement with the experiments on cuprates at any doping with both types of carriers. Demonstrated coexistence of autolocalized and delocalized carriers in superconducting cuprates changes the idea about their ground state above the superconducting transition temperature that is important for understanding transport and magnetic properties. High density of large-radius autolocalized carriers revealed may be a key to the explanation of charge ordering in doped cuprates.

  20. Fermi surface and effective masses in photoemission response of the (Ba1-xKx)Fe2As2superconductor.

    Science.gov (United States)

    Derondeau, Gerald; Bisti, Federico; Kobayashi, Masaki; Braun, Jürgen; Ebert, Hubert; Rogalev, Victor A; Shi, Ming; Schmitt, Thorsten; Ma, Junzhang; Ding, Hong; Strocov, Vladimir N; Minár, Ján

    2017-08-18

    The angle-resolved photoemission spectra of the superconductor (Ba 1-x K x )Fe 2 As 2 have been investigated accounting coherently for spin-orbit coupling, disorder and electron correlation effects in the valence bands combined with final state, matrix element and surface effects. Our results explain the previously obscured origins of all salient features of the ARPES response of this paradigm pnictide compound and reveal the origin of the Lifshitz transition. Comparison of calculated ARPES spectra with the underlying DMFT band structure shows an important impact of final state effects, which result for three-dimensional states in a deviation of the ARPES spectra from the true spectral function. In particular, the apparent effective mass enhancement seen in the ARPES response is not an entirely intrinsic property of the quasiparticle valence bands but may have a significant extrinsic contribution from the photoemission process and thus differ from its true value. Because this effect is more pronounced for low photoexcitation energies, soft-X-ray ARPES delivers more accurate values of the mass enhancement due to a sharp definition of the 3D electron momentum. To demonstrate this effect in addition to the theoretical study, we show here new state of the art soft-X-ray and polarisation dependent ARPES measurments.

  1. Weak antilocalization effect in exfoliated black phosphorus revealed by temperature- and angle-dependent magnetoconductivity

    KAUST Repository

    Hou, Zhipeng

    2018-01-10

    Recently, there have been increasingly debates on whether there exists a surface resonance state (SRS) in black phosphorus (BP), as suggested by recent angle-resolved photoemission spectroscopy (ARPES) results. To resolve this issue, we have performed temperature- and angle-dependent magnetoconductivity measurements on exfoliated, high-quality BP single crystals. A pronounced weak-antilocalization (WAL) effect was observed within a narrow temperature range of 8 - 16 K, with the electrical current flowing parallel to the cleaved ac-plane (along the a- or c-axis) and the magnetic field along the b-axis. The angle-dependent magnetoconductivity and the Hikami-Larkin-Nagaoka (HLN) model-fitted results have revealed that the observed WAL effect shows surface-bulk coherent features, which supports the existence of SRS in black phosphorus.

  2. Preirradiation Graft Polymerization of Styrene in a Poly(tetrafluoroethylene Film Investigated by Time-Resolved Small-Angle Neutron Scattering

    Directory of Open Access Journals (Sweden)

    Hiroki Iwase

    2011-01-01

    Full Text Available Preirradiation graft polymerization of styrene in a poly(tetrafluoroethylene (PTFE film was examined by time-resolved small-angle neutron scattering (SANS. A crosslinked PTFE film, thickness of which is about 50 μm, was irradiated by γ-ray and immersed in a mixed solvent of styrene monomer and toluene. SANS elucidated that graft polymerization proceeds by two reaction processes (I and (II. In process (I at 0<<200 min, graft polymerization occurs at an interface between crystalline and amorphous PTFE domains and the grafted polystyrene segregates from PTFE, forming a thin layer with a sharp interface. In process (II at 200<<600 min, grafted PS layer starts to bridge between crystalline domains. At the end of process (II, 40% of total crystalline PTFE domain is covered by the grafted PS chains.

  3. Dynamics of field-induced ordering in magnetic colloids studied by new time-resolved small-angle neutron-scattering techniques.

    Science.gov (United States)

    Wiedenmann, A; Keiderling, U; Habicht, K; Russina, M; Gähler, R

    2006-08-04

    The reversal of magnetic moments of nanoparticles in concentrated Co ferrofluids was monitored in an oscillating magnetic field by new time-resolved stroboscopic small-angle neutron-scattering techniques. Time resolution in the micros range was achieved by using a pulsed beam technique, TISANE, while in continuous mode resolution was limited by the wavelength spread to about 1 ms. The frequency dependence of anisotropic scattering patterns has been modeled using Langevin dynamics. The dynamics follows a two step mechanism: field-induced ordering is governed by fast Brownian rotation of nanoparticles with a characteristic time of about 160 micros. Magnetic relaxation of locally ordered domains of about 100 nm in size takes place within a few seconds by Brownian rotation or by Néel type rotation of magnetic moments.

  4. Enhanced ultrafast relaxation rate in the Weyl semimetal phase of MoTe2 measured by time- and angle-resolved photoelectron spectroscopy

    Science.gov (United States)

    Crepaldi, A.; Autès, G.; Gatti, G.; Roth, S.; Sterzi, A.; Manzoni, G.; Zacchigna, M.; Cacho, C.; Chapman, R. T.; Springate, E.; Seddon, E. A.; Bugnon, Ph.; Magrez, A.; Berger, H.; Vobornik, I.; Kalläne, M.; Quer, A.; Rossnagel, K.; Parmigiani, F.; Yazyev, O. V.; Grioni, M.

    2017-12-01

    MoTe2 has recently been shown to realize in its low-temperature phase the type-II Weyl semimetal (WSM). We investigated by time- and angle- resolved photoelectron spectroscopy (tr-ARPES) the possible influence of the Weyl points on the electron dynamics above the Fermi level EF, by comparing the ultrafast response of MoTe2 in the trivial and topological phases. In the low-temperature WSM phase, we report an enhanced relaxation rate of electrons optically excited to the conduction band, which we interpret as a fingerprint of the local gap closure when Weyl points form. By contrast, we find that the electron dynamics of the related compound WTe2 is slower and temperature independent, consistent with a topologically trivial nature of this material. Our results shows that tr-ARPES is sensitive to the small modifications of the unoccupied band structure accompanying the structural and topological phase transition of MoTe2.

  5. Nodal gap structure of superconducting BaFe2(As1-xPx)2 from angle-resolved thermal conductivity in a magnetic field

    Science.gov (United States)

    Yamashita, M.; Senshu, Y.; Shibauchi, T.; Kasahara, S.; Hashimoto, K.; Watanabe, D.; Ikeda, H.; Terashima, T.; Vekhter, I.; Vorontsov, A. B.; Matsuda, Y.

    2011-08-01

    The structure of the superconducting order parameter in the iron-pnictide superconductor BaFe2(As0.67P0.33)2 (Tc=31 K) with line nodes is studied by the angle-resolved thermal conductivity measurements in a magnetic field rotated within the basal plane. We find that the thermal conductivity displays distinct fourfold oscillations with minima when the field is directed at ±45∘ with respect to the tetragonal a axis. We discuss possible gap structures that can account for the data, and conclude that the observed results are most consistent with the closed nodal loops located at the flat parts of the electron Fermi surface with high Fermi velocity.

  6. The complementary nature of x-ray photoelectron spectroscopy and angle-resolved x-ray diffraction part II: Analysis of oxides on dental alloys

    Science.gov (United States)

    Kerber, S. J.; Barr, T. L.; Mann, G. P.; Brantley, W. A.; Papazoglou, E.; Mitchell, J. C.

    1998-06-01

    X-ray photoelectron spectroscopy (XPS) and angle-resolved x-ray diffraction (ARXRD) were used to analyze the oxide layer on three palladium-gallium-based dental casting alloys. The oxide layers were approximately 10 Μm thick. The use of the techniques helped to determine which mechanism was responsible for oxide formation—either (a) oxide layer growth via diffusion of oxygen through the scale to the metal, causing the scale to grow at the metal-oxide interface, or (b) an oxide layer formed by metal ions diffusing through the scale to the surface and reacting with oxygen, causing the scale to grow at the oxide-air interface. The oxide growth mechanisms were correlated to previous layer adhesion results determined with biaxial flexure testing.

  7. Determining the thickness of aliphatic alcohol monolayers covalently attached to silicon oxide surfaces using angle-resolved X-ray photoelectron spectroscopy

    Science.gov (United States)

    Lee, Austin W. H.; Kim, Dongho; Gates, Byron D.

    2018-04-01

    The thickness of alcohol based monolayers on silicon oxide surfaces were investigated using angle-resolved X-ray photoelectron spectroscopy (ARXPS). Advantages of using alcohols as building blocks for the formation of monolayers include their widespread availability, ease of handling, and stability against side reactions. Recent progress in microwave assisted reactions demonstrated the ease of forming uniform monolayers with alcohol based reagents. The studies shown herein provide a detailed investigation of the thickness of monolayers prepared from a series of aliphatic alcohols of different chain lengths. Monolayers of 1-butanol, 1-hexanol, 1-octanol, 1-decanol, and 1-dodecanol were each successfully formed through microwave assisted reactions and characterized by ARXPS techniques. The thickness of these monolayers consistently increased by ∼1.0 Å for every additional methylene (CH2) within the hydrocarbon chain of the reagents. Tilt angles of the molecules covalently attached to silicon oxide surfaces were estimated to be ∼35° for each type of reagent. These results were consistent with the observations reported for thiol based or silane based monolayers on either gold or silicon oxide surfaces, respectively. The results of this study also suggest that the alcohol based monolayers are uniform at a molecular level.

  8. Determination of strain localization in aluminum alloys using photoemission measurements

    Science.gov (United States)

    Cai, Mingdong; Langford, Stephen; Levine, Lyle; Dickinson, Thomas

    2004-03-01

    We report photoemission measurements during uniaxial tensile deformation of aluminum (1200), Al-Mn (3003), Al-Mg (5052), and Al-Mg-Si (6061) alloys during exposure to pulsed excimer laser radiation (248-nm). Photostimulated electron emission increases with strain as slip exposes fresh metal to the vacuum; strain localization alters the production rate of slip bands and hence can be monitored by this technique. All samples were annealed at 300 °C for three hours immediately after polishing to produce a relatively thick (typically 40-nm) surface oxide. This oxide reduces photoemission from undeformed material. Time-resolved electron emission measurements after each laser pulse show two or more photoemission peaks. The intensity of the late (slow) peaks changes little during deformation and apparently reflects electron emission from oxidized, undeformed portions of the sample and other nearby surfaces. The intensity of the first (fast) electron peak reflects emission from fresh metal along slip lines/bands generated by deformation. As strain proceeds, the intensity of the fast peak shows three stages of growth: a gradually increasing, incipient growth during the onset of deformation, followed by two linear increasing stages. We provide evidence that the transition between the two linear stages corresponds to the onset of strain localization.

  9. Introducing a standard method for experimental determination of the solvent response in laser pump, x-ray probe time-resolved wide-angle x-ray scattering experiments on systems in solution

    DEFF Research Database (Denmark)

    Kjær, Kasper Skov; Brandt van Driel, Tim; Kehres, Jan

    2013-01-01

    In time-resolved laser pump, X-ray probe wide-angle X-ray scattering experiments on systems in solution the structural response of the system is accompanied by a solvent response. The solvent response is caused by reorganization of the bulk solvent following the laser pump event, and in order...... response-the solvent term-experimentally when applying laser pump, X-ray probe time-resolved wide-angle X-ray scattering. The solvent term describes difference scattering arising from the structural response of the solvent to changes in the hydrodynamic parameters: pressure, temperature and density. We...... is demonstrated to exhibit first order behaviour with respect to the amount of energy deposited in the solution. We introduce a standardized method for recording solvent responses in laser pump, X-ray probe time-resolved X-ray wide-angle scattering experiments by using dye mediated solvent heating. Furthermore...

  10. Photoelectron spectra of N2 +: Rotational line profiles studied with He;I endash excited angle-resolved spectroscopy and with synchrotron radiation

    International Nuclear Information System (INIS)

    Oehrwall, G.; Baltzer, P.; Bozek, J.

    1999-01-01

    We have recorded angle-resolved He I photoelectron spectra of the three outermost valence states in N 2 + , with high enough resolution to observe rotational line profiles. For the two Σ states, the X 2 Σ g + and the B 2 Σ u + , we found that the rotational branches corresponding to different changes in rotational quantum number can differ dramatically in β value. The well-known difference in β value for the ν=0 and ν=1 vibrations of the X 2 Σ g + state was found to be due to different rotational branching ratios and also different β values of the rotational branches. For the ν=0 endash 2 vibrations of the A 2 Π u state, the β value difference between rotational branches is much less pronounced than in the X and B states. We have also recorded synchrotron-radiation-excited photoelectron spectra of the ν=0 vibrational peaks of the X 2 Σ g + and B 2 Σ u + states where rotational line profiles are resolved. The intensities of the rotational branches were studied as function of photon energy, the X state between 23 and 65 eV, and the B state between 23 and 45 eV. The results for the X state have recently been presented in a Letter [G. Oehrwall, P. Baltzer, and J. Bozek, Phys. Rev. Lett. 81, 546, 1998]. The rotational branching ratios of the two states have very different behaviors as functions of photon energy. The relative intensities of the rotational branches in the X state change significantly over the studied energy range. The 3σ g →kσ u shape resonance apparently gives rise to a non-Franck-Condon-like behavior for the rotational branching ratio of the X state. In the B state, the rotational branching ratios remain essentially constant over the studied energy range. copyright 1999 The American Physical Society

  11. Electronic structure of transferred graphene/h-BN van der Waals heterostructures with nonzero stacking angles by nano-ARPES.

    Science.gov (United States)

    Wang, Eryin; Chen, Guorui; Wan, Guoliang; Lu, Xiaobo; Chen, Chaoyu; Avila, Jose; Fedorov, Alexei V; Zhang, Guangyu; Asensio, Maria C; Zhang, Yuanbo; Zhou, Shuyun

    2016-11-09

    In van der Waals heterostructures, the periodic potential from the Moiré superlattice can be used as a control knob to modulate the electronic structure of the constituent materials. Here we present a nanoscale angle-resolved photoemission spectroscopy (nano-ARPES) study of transferred graphene/h-BN heterostructures with two different stacking angles of 2.4° and 4.3° respectively. Our measurements reveal six replicas of graphene Dirac cones at the superlattice Brillouin zone (SBZ) centers. The size of the SBZ and its relative rotation angle to the graphene BZ are in good agreement with Moiré superlattice period extracted from atomic force microscopy (AFM) measurements. Comparison to the epitaxial graphene/h-BN with 0° stacking angles suggests that the interaction between graphene and h-BN decreases with increasing stacking angle.

  12. Photoemission studies using laboratory and synchrotron sources

    International Nuclear Information System (INIS)

    Phase, D.M.

    2012-01-01

    Synchrotron radiation sources, providing intense, polarized and stable beams of ultra violet soft and hard X-ray photons, are having great impact on physics, chemistry, biology materials science and other areas research. In particular synchrotron radiation has revolutionized photoelectron spectroscopy by enhancing its capabilities for investigating the electronic properties of solids. The first Indian synchrotron storage ring, Indus- 1 is in operation at RRCAT, Indore. The UGC-DAE CSR with the help of university scientist had designed and developed an angle integrated photoelectron spectroscopy (PES) beamline on this 450 MeV storage ring. A storage ring of this kind is most suitable for investigation in the energy range from few electron volts to around five hundred electron volts. In this lecture we will describe the details of PES beamline and its experimental station. Till date the different university users carried out photoemission measurements on variety of samples. Some of the spectra recorded by users will be presented in order to show the capability of this beamline. In the later part we will report a review of our recent research work carried out on dilute magnetic thin films using this beamline. (author)

  13. Experimental set-up for time resolved small angle X-ray scattering studies of nanoparticles formation using a free-jet micromixer

    Energy Technology Data Exchange (ETDEWEB)

    Marmiroli, Benedetta [Institute for Biophysics and Nanosystem Research, Austrian Academy of Science, Schmiedlstrasse 6, Graz (Austria); Grenci, Gianluca [TASC INFM/CNR, SS 14 km 163.5, Basovizza, TS (Italy); Cacho-Nerin, Fernando; Sartori, Barbara; Laggner, Peter [Institute for Biophysics and Nanosystem Research, Austrian Academy of Science, Schmiedlstrasse 6, Graz (Austria); Businaro, Luca [TASC INFM/CNR, SS 14 km 163.5, Basovizza, TS (Italy); Amenitsch, Heinz, E-mail: heinz.amenitsch@elettra.trieste.i [Institute for Biophysics and Nanosystem Research, Austrian Academy of Science, Schmiedlstrasse 6, Graz (Austria)

    2010-02-15

    Recently, we have designed, fabricated and tested a free-jet micromixer for time resolved small angle X-ray scattering (SAXS) studies of nanoparticles formation in the <100 mus time range. The microjet has a diameter of 25 mum and a time of first accessible measurement of 75 mus has been obtained. This result can still be improved. In this communication, we present a method to estimate whether a given chemical or biological reaction can be investigated with the micromixer, and to optimize the beam size for the measurement at the chosen SAXS beamline. Moreover, we describe a system based on stereoscopic imaging which allows the alignment of the jet with the X-ray beam with a precision of 20 mum. The proposed experimental procedures have been successfully employed to observe the formation of calcium carbonate (CaCO{sub 3}) nanoparticles from the reaction of sodium carbonate (Na{sub 2}CO{sub 3}) and calcium chloride (CaCl{sub 2}). The induction time has been estimated in the order of 200 mus and the determined radius of the particles is about 14 nm.

  14. Cation profiling of passive films on stainless steel formed in sulphuric and acetic acid by deconvolution of angle-resolved X-ray photoelectron spectra

    Energy Technology Data Exchange (ETDEWEB)

    Högström, Jonas, E-mail: jhogstrom@gmail.com; Fredriksson, Wendy, E-mail: wendy.fredriksson@kemi.uu.se; Edstrom, Kristina, E-mail: kristina.edstrom@kemi.uu.se; Björefors, Fredrik, E-mail: fredrik.bjorefors@kemi.uu.se; Nyholm, Leif, E-mail: leif.nyholm@kemi.uu.se; Olsson, Claes-Olof A., E-mail: drclabbe@kth.se

    2013-11-01

    An approach for determining depth gradients of metal-ion concentrations in passive films on stainless steel using angle-resolved X-ray photoelectron spectroscopy (ARXPS) is described. The iterative method, which is based on analyses of the oxidised metal peaks, provides increased precision and hence allows faster ARXPS measurements to be carried out. The method was used to determine the concentration depth profiles for molybdenum, iron and chromium in passive films on 316L/EN 1.4432 stainless steel samples oxidised in 0.5 M H{sub 2}SO{sub 4} and acetic acid diluted with 0.02 M Na{sub 2}B{sub 4}O{sub 7} · 10H{sub 2}O and 1 M H{sub 2}O, respectively. The molybdenum concentration in the film is pin-pointed to the oxide/metal interface and the films also contained an iron-ion-enriched surface layer and a chromium-ion-dominated middle layer. Although films of similar composition and thickness (i.e., about 2 nm) were formed in the two electrolytes, the corrosion currents were found to be three orders of magnitude larger in the acetic acid solution. The differences in the layer composition, found for the two electrolytes as well as different oxidation conditions, can be explained based on the oxidation potentials of the metals and the dissolution rates of the different metal ions.

  15. 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......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...... photoemission rate and transition absorption for nanoparticles surrounded by various media with a broad range of permittivities and show that photoemission rate and transition absorption follow the same dependence on the permittivity. Thus, we conclude that transition absorption is responsible...

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

    Energy Technology Data Exchange (ETDEWEB)

    Inosov, Dmytro S.

    2008-06-18

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

  17. Electronic Structures of Magnetic Iron and Cobalt Thin Films on TUNGSTEN(001): a Spin-Polarized Inverse Photoemission Study

    Science.gov (United States)

    Cai, Qing

    Electronic structure is a central question in metallic magnetism as well as in magnetic materials research. The electronic properties in a two-dimensional system such as thin films of a few atomic layers is an important issue in surface science. The epitaxial thin film preparation and morphology are of special technological interests. In this thesis, these questions are addressed. Spin-polarized inverse photoemission spectroscopy is used to study the unoccupied electron band states in magnetic thin film magnets of Fe and Co epitaxially grown on W(001) surface. The clean W(001) surface was studied by angle -resolved inverse photoemission spectroscopy and the bulk band dispersion was determined. Ultrathin Fe overlayers on W(001) show a square lateral crystal structure similar to the bcc-Fe(001) surface. The electronic structure develops into a structure that is close to that of bulk Fe at about four atomic layers. In the normal-incidence spin polarized inverse photoemission spectra, direct transitions to the majority and minority final states near the H^'_ {25} point are identified in good agreement with the theoretical calculations. One Fe monolayer, or multilayers less than four, showed behavior corresponding to a gradually reduced Curie temperature. When the film thickness is reduced, the spin-resolved spectral behavior show that the majority spin signal peak moves from near the Fermi energy to about 1.3 eV while the minority peak stays at about the same position near 1.3 eV. The results are used to examine the spatial correlation of the spin fluctuations in the system in comparison with a theoretical spectral calculation, and favors the disordered-local-moment picture in the contemporary theory of itinerant magnetism. The Co overlayer shows an overlayer structure that consists of equivalent, mutually rotated domains of distorted hexagonal lateral structure. For one atomic layer of Co in that structure, which has a nominal lateral atomic density twice that of the

  18. 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.

  19. Intact Dirac Cones at Broken Sublattice Symmetry: Photoemission Study of Graphene on Ni and Co

    Directory of Open Access Journals (Sweden)

    A. Varykhalov

    2012-12-01

    Full Text Available The appearance of massless Dirac fermions in graphene requires two equivalent carbon sublattices of trigonal shape. While the generation of an effective mass and a band gap at the Dirac point remains an unresolved problem for freestanding extended graphene, it is well established by breaking translational symmetry by confinement and by breaking sublattice symmetry by interaction with a substrate. One of the strongest sublattice-symmetry-breaking interactions with predicted and measured band gaps ranging from 400 meV to more than 3 eV has been attributed to the interfaces of graphene with Ni and Co, which are also promising spin-filter interfaces. Here, we apply angle-resolved photoemission to epitaxial graphene on Ni(111 and Co(0001 to show the presence of intact Dirac cones 2.8 eV below the Fermi level. Our results challenge the common belief that the breaking of sublattice symmetry by a substrate and the opening of the band gap at the Dirac energy are in a straightforward relation. A simple effective model of a biased bilayer structure composed of graphene and a sublattice-symmetry-broken layer, corroborated by density-functional-theory calculations, demonstrates the general validity of our conclusions.

  20. 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.

  1. Characterization of weakly absorbing thin films by multiple linear regression analysis of absolute unwrapped phase in angle-resolved spectral reflectometry.

    Science.gov (United States)

    Dong, Jingtao; Lu, Rongsheng

    2018-04-30

    The simultaneous determination of t, n(λ), and κ(λ) of thin films can be a tough task for the high correlation of fit parameters. The strong assumptions about the type of dispersion relation are commonly used as a consequence to alleviate correlation concerns by reducing the free parameters before the nonlinear regression analysis. Here we present an angle-resolved spectral reflectometry for the simultaneous determination of weakly absorbing thin film parameters, where a reflectance interferogram is recorded in both angular and spectral domains in a single-shot measurement for the point of the sample being illuminated. The variations of the phase recovered from the interferogram as functions of t, n, and κ reveals that the unwrapped phase is monotonically related to t, n, and κ, thereby allowing the problem of correlation to be alleviated by multiple linear regression. After removing the 2π ambiguity of the unwrapped phase, the merit function based on the absolute unwrapped phase performs a 3D data cube with variables of t, n and κ at each wavelength. The unique solution of t, n, and κ can then be directly determined from the extremum of the 3D data cube at each wavelength with no need of dispersion relation. A sample of GaN thin film grown on a polished sapphire substrate is tested. The experimental data of t and [n(λ), κ(λ)] are confirmed by the scanning electron microscopy and the comparison with the results of other related works, respectively. The consistency of the results shows the proposed method provides a useful tool for the determination of the thickness and optical constants of weakly absorbing thin films.

  2. Growth kinetics of lipid-based nanodiscs to unilamellar vesicles-a time-resolved small angle neutron scattering (SANS) study.

    Science.gov (United States)

    Mahabir, Suanne; Small, Darcy; Li, Ming; Wan, Wankei; Kučerka, Norbert; Littrell, Kenneth; Katsaras, John; Nieh, Mu-Ping

    2013-03-01

    Mixtures of dimyristoyl-phosphatidylcholine (DMPC), dimyristoyl-phosphatidylglycerol (DMPG) and dihexanoyl-phosphatidylcholine (DHPC) in aqueous solutions spontaneously form monodisperse, bilayered nanodiscs (also known as "bicelles") at or below the melting transition temperature of DMPC (T(M) ~23°C). In dilute systems above the main transition temperature T(M) of DMPC, bicelles coalesce (increasing their diameter) and eventually self-fold into unilamellar vesicles (ULVs). Time-resolved small angle neutron scattering was used to study the growth kinetics of nanodiscs below and equal to T(M) over a period of hours as a function of temperature at two lipid concentrations in presence or absence of NaCl salt. Bicelles seem to undergo a sudden initial growth phase with increased temperature, which is then followed by a slower reaction-limited growth phase that depends on ionic strength, lipid concentration and temperature. The bicelle interaction energy was derived from the colloidal theory of Derjaguin and Landau, and Verwey and Overbeek (DLVO). While the calculated total energy between discs is attractive and proportional to their growth rate, a more detailed mechanism is proposed to describe the mechanism of disc coalescence. After annealing at low temperature (low-T), samples were heated to 50°C in order to promote the formation of ULVs. Although the low-T annealing of samples has only a marginal effect on the mean size of end-state ULVs, it does affect their polydispersity, which increases with increased T, presumably driven by the entropy of the system. Published by Elsevier B.V.

  3. Time-resolved small-angle x-ray scattering study of the early stage of amyloid formation of an apomyoglobin mutant

    Science.gov (United States)

    Ortore, Maria Grazia; Spinozzi, Francesco; Vilasi, Silvia; Sirangelo, Ivana; Irace, Gaetano; Shukla, Anuj; Narayanan, Theyencheri; Sinibaldi, Raffaele; Mariani, Paolo

    2011-12-01

    The description of the fibrillogenesis pathway and the identification of “on-pathway” or “off-pathway” intermediates are key issues in amyloid research as they are concerned with the mechanism for onset of certain diseases and with therapeutic treatments. Recent results on the fibril formation process revealed an unexpected complexity both in the number and in the types of species involved, but the early aggregation events are still largely unknown, mainly because of their experimental inaccessibility. To provide information on the early stage events of self-assembly of an amyloidogenic protein, during the so-called lag phase, stopped-flow time-resolved small angle x-ray scattering (SAXS) experiments were performed. Using a global fitting analysis, the structural and aggregation properties of the apomyoglobin W7FW14F mutant, which is monomeric and partly folded at acidic pH but forms amyloid fibrils after neutralization, were derived from the first few milliseconds onward. SAXS data indicated that the first aggregates appear in less than 20 ms after the pH jump to neutrality and further revealed the simultaneous presence of diverse species. In particular, worm-like unstructured monomers, very large assemblies, and elongated particles were detected, and their structural features and relative concentrations were derived as a function of time on the basis of our model. The final results show that, during the lag phase, early assembling occurs due to the presence of transient monomeric species very prone to association and through successive competing aggregation and rearrangement processes leading to coexisting on-pathway and off-pathway transient species.

  4. 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.

  5. Calculations of Photoemission from Rutile

    Science.gov (United States)

    Hjalmarson, Harold; Schultz, Peter; Moore, Chris

    2015-03-01

    Photoemission is a well-known mechanism for release of electrons from a surface during electrical breakdown of a gas such as air. During air breakdown, UV photons, which are emitted from the highly excited gas molecules, are absorbed in the surfaces such as the cathode and the anode. These absorbed photons create energetic electrons, and a small portion of these electrons reach the surface. Those that overcome the potential energy barrier at the surface tend to be emitted. In this talk, the Boltzmann equation that describes these phenomena is formulated. A Monte Carlo probabilistic method is used to obtain the rate of electron emission as a function of photon energy. The role of bandstructure effects will be discussed. This bandstructure information is obtained by using a density-functional theory (DFT) method. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

  6. Time-resolved ARPES at LACUS: Band Structure and Ultrafast Electron Dynamics of Solids.

    Science.gov (United States)

    Crepaldi, Alberto; Roth, Silvan; Gatti, Gianmarco; Arrell, Christopher A; Ojeda, José; van Mourik, Frank; Bugnon, Philippe; Magrez, Arnaud; Berger, Helmuth; Chergui, Majed; Grioni, Marco

    2017-05-31

    The manipulation of the electronic properties of solids by light is an exciting goal, which requires knowledge of the electronic structure with energy, momentum and temporal resolution. Time- and angle-resolved photoemission spectroscopy (tr-ARPES) is the most direct probe of the effects of an optical excitation on the band structure of a material. In particular, tr-ARPES in the extreme ultraviolet (VUV) range gives access to the ultrafast dynamics over the entire Brillouin zone. VUV tr-ARPES experiments can now be performed at the ASTRA (ARPES Spectrometer for Time-Resolved Applications) end station of Harmonium, at LACUS. Its capabilities are illustrated by measurements of the ultrafast electronic response of ZrSiTe, a novel topological semimetal characterized by linearly dispersing states located at the Brillouin zone boundary.

  7. Direct observation of spin-resolved full and empty electron states in ferromagnetic surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Berti, G., E-mail: giulia.berti@polimi.it; Calloni, A.; Brambilla, A.; Bussetti, G.; Duò, L.; Ciccacci, F. [Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo da Vinci 32, I-20133, Milano (Italy)

    2014-07-15

    We present a versatile apparatus for the study of ferromagnetic surfaces, which combines spin-polarized photoemission and inverse photoemission spectroscopies. Samples can be grown by molecular beam epitaxy and analyzed in situ. Spin-resolved photoemission spectroscopy analysis is done with a hemispherical electron analyzer coupled to a 25 kV-Mott detector. Inverse photoemission spectroscopy experiments are performed with GaAs crystals as spin-polarized electron sources and a UV bandpass photon detector. As an example, measurements on the oxygen passivated Fe(100)-p(1×1)O surface are presented.

  8. Bulk photoemission from metal films and nanoparticles

    Energy Technology Data Exchange (ETDEWEB)

    Ikhsanov, R Sh [Research Institute of Scientific Instruments, ' Rosatom' ' State Atomic Energy Corporation (Russian Federation); Babicheva, V E [Technical University of Denmark (Denmark); Protsenko, I E; Uskov, A V [P N Lebedev Physics Institute, Russian Academy of Sciences, Moscow (Russian Federation); Guzhva, M E [St. Petersburg State Politechnical University, St. Petersburg (Russian Federation)

    2015-01-31

    Internal emission of photoelectrons from metal films and nanoparticles (nanowires and nanospheres) into a semiconductor matrix is studied theoretically by taking into account the jump of the effective electron mass at the metal – semiconductor interface and the cooling effect of hot electrons due to electron – electron collisions in the metal. The internal quantum efficiency of photoemission for the film and nanoparticles of two types (nanospheres and nanowires) is calculated. It is shown that the reduction of the effective mass of the electron during its transition from metal to semiconductor may lead to a significant (orders of magnitude and higher) decrease in the internal quantum efficiency of bulk photoemission. (nanostructures)

  9. 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..

  10. Depth distribution of secondary phases in kesterite Cu2ZnSnS4 by angle-resolved X-ray absorption spectroscopy

    Science.gov (United States)

    Just, J.; Lützenkirchen-Hecht, D.; Müller, O.; Frahm, R.; Unold, T.

    2017-12-01

    The depth distribution of secondary phases in the solar cell absorber material Cu2ZnSnS4 (CZTS) is quantitatively investigated using X-ray Absorption Near Edge Structure (XANES) analysis at the K-edge of sulfur at varying incidence angles. Varying information depths from several nanometers up to the full thickness is achieved. A quantitative profile of the phase distribution is obtained by a self-consistent fit of a multilayer model to the XANES spectra for different angles. Single step co-evaporated CZTS thin-films are found to exhibit zinc and copper sulfide secondary phases preferentially at the front or back interfaces of the film.

  11. 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.

  12. Photoemission study of the electronic structure and charge density waves of Na2Ti2Sb2O.

    Science.gov (United States)

    Tan, S Y; Jiang, J; Ye, Z R; Niu, X H; Song, Y; Zhang, C L; Dai, P C; Xie, B P; Lai, X C; Feng, D L

    2015-04-30

    The electronic structure of Na2Ti2Sb2O single crystal is studied by photon energy and polarization dependent angle-resolved photoemission spectroscopy (ARPES). The obtained band structure and Fermi surface agree well with the band structure calculation of Na2Ti2Sb2O in the non-magnetic state, which indicates that there is no magnetic order in Na2Ti2Sb2O and the electronic correlation is weak. Polarization dependent ARPES results suggest the multi-band and multi-orbital nature of Na2Ti2Sb2O. Photon energy dependent ARPES results suggest that the electronic structure of Na2Ti2Sb2O is rather two-dimensional. Moreover, we find a density wave energy gap forms below the transition temperature and reaches 65 meV at 7 K, indicating that Na2Ti2Sb2O is likely a weakly correlated CDW material in the strong electron-phonon interaction regime.

  13. Femtosecond spectroscopic imaging by time-of-flight photoemission electron microscopy

    Science.gov (United States)

    Min, Chang-Ki; Kim, Jeong Won; Park, Yongsup

    2007-10-01

    Advances in electron optics and fast-pulsed light sources have enabled the imaging of nanoscale structures with simultaneous energy and time resolutions. We present the results obtained from a time-resolved time-of-flight photoemission electron microscopy (TR-TOF-PEEM) system. This system combined the spatial resolution of conventional PEEM with the time resolution of a femtosecond-pulsed laser and the energy resolution of a TOF energy analyzer. The TOF-PEEM system consists of three electrostatic lenses in front, a drift tube for the measurement of TOF, and a delay line detector (DLD) at the end of the optics. The excitation source is femtosecond pulses from a cavity-dumped Ti:sapphire oscillator that is frequency-doubled to 400 nm using a β-barium borate (BBO) crystal. Using a pump-probe two-photon photoemission technique, we demonstrate an example of sub-100 nm space-resolved ultrafast time evolution of the electron energy spectra for the plasmon resonance of an Ag-coated Si nanostructure, which exhibited unexpectedly intense high energy photoemission signals that show different time evolution between bright and dark regions in a PEEM image.

  14. Depth distribution of secondary phases in kesterite Cu2ZnSnS4 by angle-resolved X-ray absorption spectroscopy

    Directory of Open Access Journals (Sweden)

    J. Just

    2017-12-01

    Full Text Available The depth distribution of secondary phases in the solar cell absorber material Cu2ZnSnS4 (CZTS is quantitatively investigated using X-ray Absorption Near Edge Structure (XANES analysis at the K-edge of sulfur at varying incidence angles. Varying information depths from several nanometers up to the full thickness is achieved. A quantitative profile of the phase distribution is obtained by a self-consistent fit of a multilayer model to the XANES spectra for different angles. Single step co-evaporated CZTS thin-films are found to exhibit zinc and copper sulfide secondary phases preferentially at the front or back interfaces of the film.

  15. Hard X-ray photoemission spectroscopy

    International Nuclear Information System (INIS)

    Kobayashi, Keisuke

    2009-01-01

    Except in the very early stage of the development of X-ray photoemission spectroscopy (XPS) by Kai Siegbahn and his coworkers, the excitation sources for XPS studies have predominantly been the Al Kα and Mg Kα emission lines. The advent of synchrotron radiation sources opened up the possibility of tuning the excitation photon energy with much higher throughputs for photoemission spectroscopy, however the excitation energy range was limited to the vacuum ultra violet and soft X-ray regions. Over the past 5-6 years, bulk-sensitive hard X-ray photoemission spectroscopy using high-brilliance high-flux X-rays from third generation synchrotron radiation facilities has been developed. This article reviews the history of HXPES covering the period from Kai Siegbahn and his coworkers' pioneering works to the present, and describes the fundamental aspects, instrumentation, applications to solid state physics, applied physics, materials science, and industrial applications of HXPES. Finally, several challenging new developments which have been conducted at SPring-8 by collaborations among several groups are introduced.

  16. Recurrent dislocations of the atlantooccipital and atlantoaxial joints in a halo vest fixator are resolved by backrest elevation in an elevation angle-dependent manner.

    Science.gov (United States)

    Kato, Go; Kawaguchi, Kenichi; Tsukamoto, Nobuaki; Komiyama, Keisuke; Mizuta, Kazutaka; Onohara, Takayuki; Okano, Hirofumi; Hotokezaka, Shunsuke; Mae, Takao

    2015-10-01

    Halo fixation is now universally performed in the initial reduction and fixation of unstable upper cervical spine injuries; however, persistent high instability and recurrent dislocations of the atlantooccipital and atlantoaxial joints after fixation are not well recognized. The aim was to describe persistent instability of traumatic dislocations of the atlantooccipital and atlantoaxial joints after halo fixation and a useful method for preventing instability. This was a case report of a patient who survived traumatic dislocations of the atlantooccipital and atlantoaxial joints. A 73-year-old woman diagnosed with dislocations of the atlantooccipital and atlantoaxial joints along with multiple other injuries sustained in a traffic accident was included. After initial closed reduction and halo fixation, congruity of the atlantooccipital and atlantoaxial joints was evaluated using, condylar gap, atlantodental interval, and flexion angulation of C1-C2 after the initial examination and before surgery. Changes in parameters 12 hours after halo fixation revealed re-dislocations and instability of the joints. Backrest elevation with halo fixation tended to reduce re-dislocations. Therefore, we carefully increased the backrest angle and measured the parameters at several angles of elevation within a range that did not affect vital signs to observe the effectiveness of elevation against re-dislocations. Elevation changed the parameters in an elevation angle-dependent manner, and these changes suggested that elevation was effective for reducing re-dislocation of both the atlantooccipital and atlantoaxial joints during halo fixation. With no major complications, this method enabled us to maintain good congruity of the joints for approximately 2 weeks until posterior spinal fusion with internal fixation. Backrest elevation with halo fixation appears safe to be performed without any other devices and is beneficial for blocking re-dislocation of both the atlantooccipital and

  17. Time-Resolved 2PPE and Time-Resolved PEEM as a Probe of LSP's in Silver Nanoparticles

    Directory of Open Access Journals (Sweden)

    D. Bayer

    2008-01-01

    Full Text Available The time-resolved two-photon photoemission technique (TR-2PPE has been applied to study static and dynamic properties of localized surface plasmons (LSP in silver nanoparticles. Laterally, integrated measurements show the difference between LSP excitation and nonresonant single electron-hole pair creation. Studies below the optical diffraction limit were performed with the detection method of time-resolved photoemission electron microscopy (TR-PEEM. This microscopy technique with a resolution down to 40 nm enables a systematic study of retardation effects across single nanoparticles. In addition, as will be shown in this paper, it is a highly sensitive sensor for coupling effects between nanoparticles.

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

    International Nuclear Information System (INIS)

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

    1996-01-01

    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. copyright 1996 American Institute of Physics

  19. 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...

  20. Circularly polarized light interaction in topological insulators investigated by time-resolved ARPES

    Science.gov (United States)

    Bugini, D.; Hedayat, H.; Boschini, F.; Yi, H.; Chen, C.; Zhou, X.; Manzoni, C.; Dallera, C.; Cerullo, G.; Carpene, E.

    2017-10-01

    Topological Insulators (TI) represent a hot-topic for both basic physics and promising applications because of the in-plane spin-polarized surface states (TSS) arising within the bulk insulating energy gap. The backscattering protection and the control of the spin polarization using ultrashort light pulses open new scenarios in the use of this class of materials for future opto-spintronic devices. Using time- and angle-resolved photoemission spectroscopy on Sb x Bi(2‑x )Se y Te(3‑y ) class we studied the response of spin-polarized electrons to ultrashort circularly-polarized pulses. Here, we report for the first time the experimental evidence of a direct coupling between light and empty topological surface states (ESS) and the establishment of a flow of spin-polarized electrons in k-space i.e. a photon-induced spin-current.

  1. UNCONTROLLED PHOTOMULTIPLIER CURRENT IN PHOTOEMISSION ANALYSIS

    Directory of Open Access Journals (Sweden)

    K. A. Viazava

    2016-01-01

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

  2. Scanning photoemission microscopy with synchrotron radiation

    Science.gov (United States)

    Ade, Harald W.

    1992-08-01

    Progress in photoemission spectro-microscopy at various synchrotron radiation facilities is reviewed. Microprobe devices such as MAXIMUM at the SRC in Wisconsin, the X1-SPEM at the NSLS at BNL, as well as the ellipsoidal ring mirror microscope at DESY in Hamburg, recorded first images during the last few years. The present status of these devices which achieve their lateral resolution by focusing X-rays to a small spot is the primary focus of this paper, but work representing other approaches to spectro-microscopy is also discussed.

  3. Differences between GaAs/GaInP and GaAs/AlInP interfaces grown by movpe revealed by depth profiling and angle-resolved X-ray photoelectron spectroscopies

    Energy Technology Data Exchange (ETDEWEB)

    López-Escalante, M.C., E-mail: mclopez@uma.es [Nanotech Unit, Laboratorio de Materiales y Superficies, Departamento de Ingeniería Química, Facultad de Ciencias, Universidad de Málaga, 29071 Málaga (Spain); Gabás, M. [The Nanotech Unit, Depto. de Física Aplicada I, Andalucía Tech, Universidad de Málaga, Campus de Teatinos s/n, 29071 Málaga Spain (Spain); García, I.; Barrigón, E.; Rey-Stolle, I.; Algora, C. [Instituto de Energía Solar, Universidad Politécnica de Madrid, Avda. Complutense 30, 28040 Madrid Spain (Spain); Palanco, S.; Ramos-Barrado, J.R. [The Nanotech Unit, Depto. de Física Aplicada I, Andalucía Tech, Universidad de Málaga, Campus de Teatinos s/n, 29071 Málaga Spain (Spain)

    2016-01-01

    Graphical abstract: - Highlights: • GaAs, AlInP and GaInP epi-layers grown in a MOVPE facility. • GaAs/GaInP and GaAs/AlInP interfaces studied through the combination of angle resolved and depth profile X-ray photoelectros spectroscopies. • GaAs/GaInP interface shows no features appart from GaAs, GaInP and mixed GaInAs or GaInAsP phases. • GaAs/AlInP interface shows traces of an anomalous P environment, probably due to P-P clusters. - Abstract: GaAs/GaInP and GaAs/AlInP interfaces have been studied using photoelectron spectroscopy tools. The combination of depth profile through Ar{sup +} sputtering and angle resolved X-ray photoelectron spectroscopy provides reliable information on the evolution of the interface chemistry. Measurement artifacts related to each particular technique can be ruled out on the basis of the results obtained with the other technique. GaAs/GaInP interface spreads out over a shorter length than GaAs/AlInP interface. The former could include the presence of the quaternary GaInAsP in addition to the nominal GaAs and GaInP layers. On the contrary, the GaAs/AlInP interface exhibits a higher degree of compound mixture. Namely, traces of P atoms in a chemical environment different to the usual AlInP coordination were found at the top of the GaAs/AlInP interface, as well as mixed phases like AlInP, GaInAsP or AlGaInAsP, located at the interface.

  4. 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

  5. Timing analysis of two-electron photoemission

    International Nuclear Information System (INIS)

    Kheifets, A S; Ivanov, I A; Bray, Igor

    2011-01-01

    We predict a significant delay of two-electron photoemission from the helium atom after absorption of an attosecond XUV pulse. We establish this delay by solving the time-dependent Schroedinger equation and by subsequently tracing the field-free evolution of the two-electron wave packet. This delay can also be related to the energy derivative of the phase of the complex double-photoionization (DPI) amplitude which we evaluate by using the convergent close-coupling method. Our observations indicate that future attosecond time delay measurements on DPI of He can provide information on the absolute quantum phase and elucidate various mechanisms of this strongly correlated ionization process. (fast track communication)

  6. Final state selection in the 4p photoemission of Rb by combining laser spectroscopy with soft-x-ray photoionization

    International Nuclear Information System (INIS)

    Schulz, J.; Tchaplyguine, M.; Rander, T.; Bergersen, H.; Lindblad, A.; Oehrwall, G.; Svensson, S.; Heinaesmaeki, S.; Sankari, R.; Osmekhin, S.; Aksela, S.; Aksela, H.

    2005-01-01

    Fine structure resolved 4p photoemission studies have been performed on free rubidium atoms in the ground state and after excitation into the [Kr]5p 2 P 1/2 and 2 P 3/2 states. The 4p 5 5p final states have been excited in the 4p 6 5s→4p 5 5p conjugate shakeup process from ground state atoms as well as by direct photoemission from laser excited atoms. The relative intensities differ considerably in these three excitation schemes. The differences in the laser excited spectra could be described well using calculations based on the pure jK-coupling scheme. Thereby it was possible to specify the character of the various final states. Furthermore it has been possible to resolve two of the final states whose energy separation is smaller than the experimental resolution by selectively exciting them in a two step scheme, where the laser selects the spin-orbit coupling in the intermediate state and determines the final state coupling after x-ray photoemission

  7. Angle-resolved catholdoluminescence imaging polarimetry

    NARCIS (Netherlands)

    Osorio, C.I.; Coenen, T.; Brenny, B.J.M.; Polman, A.; Koenderink, A.F.

    2015-01-01

    Cathodoluminescence spectroscopy (CL) allows characterizing light emission in bulk and nanostructured materials and is a key tool in fields ranging from materials science to nanophotonics. Previously, CL measurements focused on the spectral content and angular distribution of emission, while the

  8. Electronic structure of ThRu2Si2 studied by angle-resolved photoelectron spectroscopy: Elucidating the contribution of U 5 f states in URu2Si2

    Science.gov (United States)

    Fujimori, Shin-ichi; Kobata, Masaaki; Takeda, Yukiharu; Okane, Tetsuo; Saitoh, Yuji; Fujimori, Atsushi; Yamagami, Hiroshi; Matsumoto, Yuji; Yamamoto, Etsuji; Tateiwa, Naoyuki; Haga, Yoshinori

    2017-09-01

    The electronic structure of ThRu2Si2 was studied using angle-resolved photoelectron spectroscopy (ARPES) with incident photon energies of h ν =655 -745 eV. Detailed band structure and the three-dimensional shapes of Fermi surfaces were derived experimentally, and their characteristic features were mostly explained by means of band-structure calculations based on density-functional theory. Comparison of the experimental ARPES spectra of ThRu2Si2 with those of URu2Si2 shows that they have considerably different spectral profiles, particularly in the energy range of 1 eV from the Fermi level, suggesting that U 5 f states are substantially hybridized in these bands. The relationship between the ARPES spectra of URu2Si2 and ThRu2Si2 is very different from the one between the ARPES spectra of CeRu2Si2 and LaRu2Si2 , where the intrinsic difference in their spectra is limited only in the very vicinity of the Fermi energy. The present result suggests that the U 5 f electrons in URu2Si2 have strong hybridization with ligand states and have an essentially itinerant character.

  9. Study of adsorption states for lubricant molecule using hard X-ray photoemission spectroscopy

    International Nuclear Information System (INIS)

    Ikenaga, E.; Kobata, M.; Kim, J.J.; Wakabayashi, A.; Nishino, Y.; Tamasaku, K.; Sakane, Y.; Ishikawa, T.; Komiya, S.; Kobayashi, K.

    2007-01-01

    The adsorption states for lubricant molecules have been investigated using hard X-ray (hν = 7.95 keV) photoemission spectroscopy (HX-PES). This method has the advantage for the organic molecules to be able to measure damage few. Being aware of the fact that P atoms exist only in cyclotriphosphazene base, we measured the take-off angle dependence of the P1s spectra. Each spectrum consists from two peaks, that is, substrate NiP peak and cyclotriphosphazene P peak. The cyclotriphosphazene P peak rapidly disappears with increasing take-off angle. We have also measured C1s spectra. Combining these experimental results, we have found that the adsorption state of cyclotriphosphazene end group is undergoing

  10. Comparison between laser-induced photoemissions and phototransmission of hard tissues using fibre-coupled Nd:YAG and Er(3+)-doped fibre lasers.

    Science.gov (United States)

    El-Sherif, Ashraf Fathy

    2012-07-01

    During pulsed laser irradiation of dental enamel, laser-induced photoemissions result from the laser-tissue interaction through mechanisms including fluorescence and plasma formation. Fluorescence induced by non-ablative laser light interaction has been used in tissue diagnosis, but the photoemission signal accompanying higher power ablative processes may also be used to provide real-time monitoring of the laser-tissue interaction. The spectral characteristics of the photoemission signals from normal and carious tooth enamel induced by two different pulsed lasers were examined. The radiation sources compared were a high-power extra-long Q-switched Nd:YAG laser operating at a wavelength of 1,066 nm giving pulses (with pulse durations in the range 200-250 μs) in the near infrared and a free-running Er(3+)-doped ZBLAN fibre laser operating at a wavelength near 3 μm with similar pulse durations in the mid-infrared region. The photoemission spectra produced during pulsed laser irradiation of enamel samples were recorded using a high-resolution spectrometer with a CCD array detector that enabled an optical resolution as high as 0.02 nm (FWHM). The spectral and time-dependence of the laser-induced photoemission due to thermal emission and plasma formation were detected during pulsed laser irradiation of hard tissues and were used to distinguish between normal and carious teeth. The use of these effects to distinguish between hard and soft biological tissues during photothermal ablation with a pulsed Nd:YAG laser or an Er fibre laser appears feasible. The real-time spectrally resolved phototransmission spectrum produced during pulsed Nd:YAG laser irradiation of human tooth enamel samples was recorded, with a (normalized) relative transmission coefficient of 1 (100%) for normal teeth and 0.6 (60%) for the carious teeth. The photoemission signal accompanying ablative events may also be used to provide real-time monitoring of the laser-tissue interaction.

  11. DC photoemission electron guns as ERL sources

    International Nuclear Information System (INIS)

    Sinclair, Charles K.

    2006-01-01

    Very-high-voltage DC electron guns, delivering moderate duration bunches from photoemission cathodes, and followed by conventional drift bunching and acceleration, offer a practical solution for an ERL injector. In a variant of this scheme, a DC gun is placed in close proximity to a superconducting RF accelerator cavity, with few or no active elements between the gun and cavity. The principal technical challenge with such electron guns arises from field emission from the cathode electrode and its support structure. Field emission may result in voltage breakdown across the cathode-anode gap, or a punch-through failure of the insulator holding off the cathode potential, as well as lesser though still serious problems. Various means to mitigate these problems are described. The operational lifetime of high quantum efficiency photocathodes in these guns is determined by the vacuum conditions, through phenomena such as chemical poisoning and ion back-bombardment. Minimization of the field strength on electrode structures pushes high-voltage DC guns toward large dimensions and, correspondingly, large outgassing loads, but it is also true that these guns offer many opportunities for achieving excellent vacuum conditions. Good solutions to vacuum problems that had previously limited cathode lifetime have been demonstrated in recent years. Designs for DC guns presently in use and planned for the near future will be described. The parameters necessary for a 100 mA average current, very-high-voltage DC gun with a photocathode operational lifetime greater than 100 h appear to be within reach, but have yet to be demonstrated. A 1 A average current source with good cathode operational lifetime will require developments beyond the present state-of-the-art

  12. Study of photoemission mechanism for varied doping GaN photocathode

    Science.gov (United States)

    Qiao, Jianliang; Xu, Yuan; Niu, Jun; Gao, Youtang; Chang, Benkang

    2015-10-01

    Negative electron affinity (NEA) GaN photocathode has many virtues, such as high quantum efficiency, low dark current, concentrated electrons energy distribution and angle distribution, adjustive threshold and so on. The quantum efficiency is an important parameter for the preparation and evaluation of NEA GaN photocathode. The varied doping GaN photocathode has the directional inside electric field within the material, so the higher quantum efficiency can be obtained. The varied doping NEA GaN photocathode has better photoemission performance. According to the photoemission theory of NEA GaN photocathode, the quantum efficiency formulas for uniform doping and varied doping NEA GaN photocathodes were given. In the certain condition, the quantum efficiency formula for varied doping GaN photocathode consists with the uniform doping. The activation experiment was finished for varied doping GaN photocathode. The cleaning method and technics for varied doping GaN photocathode were given in detail. To get an atom clean surface, the heat cleaning must be done after the chemical cleaning. Using the activation and evaluation system for NEA photocathode, the varied doping GaN photocathode was activated with Cs and O, and the photocurrent curve for varied doping GaN photocathode was gotten.

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

    International Nuclear Information System (INIS)

    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

  14. 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.

  15. Simulation and characterization of the crystal growth by photoemission

    International Nuclear Information System (INIS)

    Fazouan, N.

    1994-01-01

    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 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

  16. High-Resolution Resonance Photoemission Study of CeNi

    International Nuclear Information System (INIS)

    Sekiyama, A.; Kadono, K.; Iwasaki, T.; Imada, S.; Kasai, S.; Suga, S.; Araki, S.; Onuki, Y.

    2003-01-01

    We have performed the high-resolution Ce 3d - 4f resonance photoemission study of a considerably hybridized CeNi with the Kondo temperature of ∼ 150 K. The tail of the Kondo-resonance peak is predominantly observed in the bulk Ce 4f photoemission spectra, where its spin-orbit partner is suppressed compared with the so far reported surface-sensitive Ce 4d-4f resonance spectrum. Our results show that the bulk 4f electronic states are essentially understood by the single impurity Anderson model. (author)

  17. Development of in-lab energy-filtered X-ray photoemission electron microscope using air-core-coil-type multipole Wien filter

    Science.gov (United States)

    Niimi, H.; Kato, M.; Kawasaki, T.; Miyamoto, T.; Suzuki, S.; Chun, W.-J.; Kudo, M.; Kawahara, N.; Doi, M.; Tsukamoto, K.; Asakura, K.

    2007-10-01

    We have developed an in-lab energy-filtered X-ray photoemission electron microscopy (EXPEEM) combining a high-brilliance X-ray source and a new Wien filter-type energy analyzer, which can accept photoelectrons in a wide angle. To obtain high energy resolution, we enlarged the inner diameter of the filter and reduced aberrations of an analyzer using multipole electrodes and air-core coils. We obtained an energy-filtered image of photoelectrons.

  18. 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.

  19. Electronic structure of elemental curium studied by photoemission

    Czech Academy of Sciences Publication Activity Database

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

    2011-01-01

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

  20. 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...

  1. CALCULATION OF CU 2P RESONANT PHOTOEMISSION SPECTRA IN CUO

    NARCIS (Netherlands)

    SEINO, Y; OGASAWARA, H; KOTANI, A; THOLE, BT; VANDERLAAN, G

    We investigated theoretically the Cu 2p resonance of 3d, 3p and 3s X-ray photoemission spectra (XPS) in CuO using a cluster model including multiplet coupling, crystal field and anisotropic hybridization. The spectra were calculated by taking into account the radiative transitions up to the first

  2. Time-resolved photoelectron nano-spectroscopy of individual silver particles: Perspectives and limitations

    DEFF Research Database (Denmark)

    Rohmer, Martin; Bauer, Michael; Leissner, Till

    2010-01-01

    Simultaneous time- and energy-resolved two-photon photoemission with nanometer resolution is demonstrated for the first time. We monitor the energy dependence of the decay dynamics of electron excitations in individual silver particles, which were deposited from a gas aggregation cluster source...

  3. 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

  4. Scoliosis angle

    International Nuclear Information System (INIS)

    Marklund, T.

    1978-01-01

    The most commonly used methods of assessing the scoliotic deviation measure angles that are not clearly defined in relation to the anatomy of the patient. In order to give an anatomic basis for such measurements it is proposed to define the scoliotic deviation as the deviation the vertebral column makes with the sagittal plane. Both the Cobb and the Ferguson angles may be based on this definition. The present methods of measurement are then attempts to measure these angles. If the plane of these angles is parallel to the film, the measurement will be correct. Errors in the measurements may be incurred by the projection. A hypothetical projection, called a 'rectified orthogonal projection', is presented, which correctly represents all scoliotic angles in accordance with these principles. It can be constructed in practice with the aid of a computer and by performing measurements on two projections of the vertebral column; a scoliotic curve can be represented independent of the kyphosis and lordosis. (Auth.)

  5. 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...

  6. Core-level photoemission revealing the Mott transition

    International Nuclear Information System (INIS)

    Kim, Hyeong-Do; Noh, Han-Jin; Kim, K.H.; Oh, S.-J.

    2005-01-01

    Ru 3d core-level X-ray photoemission spectra of various ruthenates are examined. They show in general two-peak structures, which can be assigned as the screened and unscreened peaks. The screened peak is absent in a Mott insulator, but develops into a main peak as the correlation strength becomes weak. This spectral behavior is well explained by the dynamical mean-field theory calculation for the single-band Hubbard model with the on-site core-hole potential using the exact diagonalization method. The new mechanism of the core-level photoemission satellite can be utilized to reveal the Mott transition phenomenon in various strongly correlated electron systems

  7. Nanoscale spatial analysis of clay minerals containing cesium by synchrotron radiation photoemission electron microscopy

    Science.gov (United States)

    Yoshigoe, Akitaka; Shiwaku, Hideaki; Kobayashi, Toru; Shimoyama, Iwao; Matsumura, Daiju; Tsuji, Takuya; Nishihata, Yasuo; Kogure, Toshihiro; Ohkochi, Takuo; Yasui, Akira; Yaita, Tsuyoshi

    2018-01-01

    A synchrotron radiation photoemission electron microscope (SR-PEEM) was applied to demonstrate the pinpoint analysis of micrometer-sized weathered biotite clay particles with artificially adsorbed cesium (Cs) atoms. Despite the insulating properties of the clay, we observed the spatial distributions of constituent elements (Si, Al, Cs, Mg, and Fe) without charging issues and clarified reciprocal site-correlations among these elements with nanometer resolution. We found that Cs atoms were likely to be adsorbed evenly over the entire particle; however, we identified an occupational conflict between Cs and Mg atoms, implying that Cs sorption involves ion exchange processes. Spatially resolved X-ray absorption spectra (XAS) of the Cs4,5 M-edge region showed Cs to be present in a monocation state (Cs+) as typically observed for Cs compounds. Further pinpoint XAS measurements were also performed at the Fe L2,3-edge to determine the chemical valence of the Fe atoms. The shapes of the spectra were similar to those for Fe2O3, indicating that Fe in the clay was in a 3+ oxidation state. From these observations, we infer that charge compensation facilitates Cs adsorption in the vicinity of a substitution site where Si4+ ions are replaced by Fe3+ ions in SiO4 tetrahedral sheets. Our results demonstrate the utility of SR-PEEM as a tool for spatially resolved chemical analyses of various environmental substances, which is not limited by the poor conductivity of samples.

  8. Bulk sensitive hard x-ray photoemission electron microscopy.

    Science.gov (United States)

    Patt, M; Wiemann, C; Weber, N; Escher, M; Gloskovskii, A; Drube, W; Merkel, M; Schneider, C M

    2014-11-01

    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 SrTiO3 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.

  9. Photoelectron diffraction of C6H8/Si(001) : A model case for photoemission study of organic molecules adsorbed on silicon surfaces

    Science.gov (United States)

    Gunnella, R.; Shimomura, M.; D'Amico, F.; Abukawa, T.; Kono, S.

    2006-06-01

    The core-level photoemission of 1,4-cyclohexadiene molecules on the quasi-single-domain 2×1-Si(001) surface below the saturation condition was studied. Taking advantage of core-level-shift photoelectron diffraction of the C 1s core level, the details of the surface structure were found. The model was essentially constituted by an unbuckled (planar) molecule chemisorbed on the surface, inclined at an angle of about 18° with respect to the surface normal, keeping one double bond unsaturated. An accurate analysis of the line shape parameters of the strongly asymmetric C 1s core level was mandatory for the structural study. Conversely, the success of the structural determination represented a confirmation of the correct deconvolution procedure. Such a feedback loop was decisive in reducing the indeterminacy affecting the analysis of core-level photoemission in the case of complex molecules adsorbed on surfaces.

  10. First studies on pulsed photoemission with a power laser

    International Nuclear Information System (INIS)

    Bergeret, H.; Boussoukaya, M.; Chehab, R.; Leblond, B.

    1985-07-01

    In lasertron studies, the photocathode emission investigation represents an essential part. For that, in order to determine the photo-emissivity of different materials we studied the lanthanum hexaboride as a first step. Obtained results with a Nd.YAG laser with different wavelengthes from 1064 to 355 nm, concern emission densities from some mA/cm 2 to 7kA/cm 2 with quantum efficiencies from 2.10 -7 to 10 -3 . Some of that results are in good agreement with those obtained by J. Lafferty in 1950 [fr

  11. Reflection and photoemission studies of neutron-irradiated graphite

    International Nuclear Information System (INIS)

    Fukutani, Hirohito; Yamada, Akio; Yagi, Kazutoshi; Ooe, Satoshi; Higashiyama, Kazuyuki; Kato, Hiroo; Iwata, Tadao.

    1990-01-01

    Neutron-irradiated graphites were studied by reflectivity and photoemission (UPS, ARUPS, XPS) measurements. The π-band reflectivity peak of graphite, located at 5 eV, changed significantly and a small absorption band ascribed to vacancies produced by neutron bombardment was found to grow around 3 eV. Modification of the valence band by neutron irradiation was studied by ARUPS. The π-valence band shifts to lower binding energy towards the Fermi level and its band width becomes smaller. These results were also confirmed by the optical joint density of states obtained from K-K analysis of the reflectivity. (author)

  12. Extreme regimes of femtosecond photoemission from a copper cathode in a dc electron gun

    Directory of Open Access Journals (Sweden)

    P. L. E. M. Pasmans

    2016-10-01

    Full Text Available The femtosecond photoemission yield from a copper cathode and the emittance of the created electron beams has been studied in a 12  MeV/m, 100 keV dc electron gun over a wide range of laser fluence, from the linear photoemission regime until the onset of image charge limitations and cathode damaging. The measured photoemission curves can be described well with available theory which includes the Schottky effect, second-order photoemission, and image charge limitation. The second-order photoemission can be explained by thermally assisted one-photon photoemission (1PPE and by above-threshold two-photon photoemission (2PPE. Measurements with a fresh cathode suggest that the 2PPE process is dominant. The beam emittance has been measured for the entire range of initial surface charge densities as well. The emittance measurements of space-charge dominated beams can be described well by an envelope equation with generalized perveance. The dc gun produces 0.1 pC bunches with 25 nm rms normalized emittance, corresponding to a normalized brightness usually associated with rf photoguns. In this experimental study the limits of femtosecond photoemission from a copper cathode have been explored and analyzed in great detail, resulting in improved understanding of the underlying mechanisms.

  13. Giant Cu 2p Resonances in CuO Valence-Band Photoemission

    NARCIS (Netherlands)

    Tjeng, L.H.; Chen, C.T.; Ghijsen, J.; Rudolf, P.; Sette, F.

    1991-01-01

    We report the observation of a giant resonance in the Cu 2p resonant-photoemission spectra of CuO. The study allows the unambiguous identification of the local Cu 3d8 configuration in the valence-band photoemission spectrum, providing conclusive evidence for the charge-transfer nature of the

  14. Iron 1s X-ray photoemission of Fe2O3

    NARCIS (Netherlands)

    Miedema, P. S.; Borgatti, F.; Offi, F.; Panaccione, G.; de Groot, F. M. F.

    We present the Is X-ray photoemission spectrum of alpha-Fe2O3 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

  15. 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.

  16. 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.

  17. Iron 1s X-ray photoemission of Fe2O3

    International Nuclear Information System (INIS)

    Miedema, P.S.; Borgatti, F.; Offi, F.; Panaccione, G.; Groot, F.M.F. de

    2015-01-01

    Highlights: • Three peaks of 1s XPS of Fe 2 O 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 2 O 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

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

    International Nuclear Information System (INIS)

    Wadati, H.; Fujimori, A.

    2013-01-01

    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

  19. First results from the high energy resolution photoemission beam line at ELETTRA

    International Nuclear Information System (INIS)

    Quaresima, C.; Astaldi, C.; Zacchigna, M.; Romanzin, L.; Savoia, A.

    1995-01-01

    We report the first results obtained from the high energy resolution beam line at the storage ring ELETTRA of Trieste. The beam line has been designed to perform photoemission experiments in the vacuum ultraviolet (VUV) and soft X-ray (SXR) energy range. The radiation source is an undulator which consists of three sections, with 36 periods and a period length of 12.5 cm. It allows scanning of an energy range 17-900 eV using the 1st, 3rd and 5th harmonics. The monochromator is a spherical grating type and the resolving power at 400 eV, estimated from the K-shell photoabsorption of the N 2 molecule is well above 10 000. The spectra are better than any other spectra taken while operating with high flux, i.e. first order diffraction and grating not masked. Measurements taken at the oxygen and neon K-edges, the argon L 2,3 edges and of the helium double ionization spectra, indicate that the resolution is excellent from 65 to 870 eV. (orig.)

  20. 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....

  1. Development of high energy resolution inverse photoemission technique

    International Nuclear Information System (INIS)

    Asakura, D.; Fujii, Y.; Mizokawa, T.

    2004-01-01

    Full text: It is highly important to study occupied and unoccupied electronic states in order to understand electronic properties of strongly correlated electron systems. Photoemission spectroscopy (PES) and inverse photoemission spectroscopy (IPES) are complementary to each other and very powerful experimental methods to study the electronic structure. While PES directly investigates the occupied states below the Fermi level, IPES observes the unoccupied states above it. Although the energy resolution of 2 meV has been achieved for PES, the energy resolution of IPES is still around 200 meV. The poor energy resolution of IPES considerably limits information of unoccupied states. In order to investigate unoccupied states of strongly correlated electron systems, we have designed and constructed a new IPES instrument based on two ideas: off-plane Eagle mounting of the optical system [1, 2] and dispersion matching between incoming electron and outgoing ultraviolet light. In the IPES system, a parallel plate electron analyzer is employed to give the energy dispersion to the incoming electron beam. The outgoing ultraviolet light is monochromatized by a concave grating. The sample, the grating, and the position sensitive detector are arranged in the off-plane Eagle mounting to achieve a good focusing of light. Ray-trace simulations have shown that the energy resolution of 20 meV is expected for the perfect dispersion matching. We will present the principle, mechanism, and current status of our IPES instrument

  2. Direct momentum-resolved observation of one-dimensional confinement of externally doped electrons within a single subnanometer-scale wire.

    Science.gov (United States)

    Song, Inkyung; Oh, Dong-Hwa; Shin, Ha-Chul; Ahn, Sung-Joon; Moon, Youngkwon; Woo, Sun-Hee; Choi, Hyoung Joon; Park, Chong-Yun; Ahn, Joung Real

    2015-01-14

    Cutting-edge research in the band engineering of nanowires at the ultimate fine scale is related to the minimum scale of nanowire-based devices. The fundamental issue at the subnanometer scale is whether angle-resolved photoemission spectroscopy (ARPES) can be used to directly measure the momentum-resolved electronic structure of a single wire because of the difficulty associated with assembling single wire into an ordered array for such measurements. Here, we demonstrated that the one-dimensional (1D) confinement of electrons, which are transferred from external dopants, within a single subnanometer-scale wire (subnanowire) could be directly measured using ARPES. Convincing evidence of 1D electron confinement was obtained using two different gold subnanowires with characteristic single metallic bands that were alternately and spontaneously ordered on a stepped silicon template, Si(553). Noble metal atoms were adsorbed at room temperature onto the gold subnanowires while the overall structure of the wires was maintained. Only one type of gold subnanowire could be controlled using external noble metal dopants without transforming the metallic band of the other type of gold subnanowires. This result was confirmed by scanning tunnelling microscopy experiments and first-principles calculations. The selective control clearly showed that externally doped electrons could be confined within a single gold subnanowire. This experimental evidence was used to further investigate the effects of the disorder induced by external dopants on a single subnanowire using ARPES.

  3. 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.

  4. Photoemission of graded-doping GaN photocathode

    International Nuclear Information System (INIS)

    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 3.19×10 17 cm −3 . The graded-doping GaN photocathode with higher performance can be realized by further optimizing the doping profile. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

  5. Photoemission of graded-doping GaN photocathode

    Science.gov (United States)

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

    2011-03-01

    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. Project supported by the National Natural Science Foundation of China (Grant No. 60871012) and the Research Fund of Nanjing University of Science and Technology (Grant No. 2010ZYTS032).

  6. 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.

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

    Energy Technology Data Exchange (ETDEWEB)

    Halavanau, A. [Northern Illinois Univ., DeKalb, IL (United States); Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Ha, G. [Argonne National Lab. (ANL), Argonne, IL (United States); Pohang Univ. of Science and Technology (POSTECH) (Korea, Republic of); Qiang, G. [Argonne National Lab. (ANL), Argonne, IL (United States); Tsinghua Univ., Beijing (China); Gai, W. [Argonne National Lab. (ANL), Argonne, IL (United States); Power, J. [Argonne National Lab. (ANL), Argonne, IL (United States); Piot, P. [Northern Illinois Univ., DeKalb, IL (United States); Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Wisniewski, E. [Argonne National Lab. (ANL), Argonne, IL (United States); Edstrom, D. [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Ruan, J. [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Santucci, J. [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)

    2016-09-06

    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.

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

    Directory of Open Access Journals (Sweden)

    Kevin L. Jensen

    2003-08-01

    Full Text Available 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.

  9. 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 ...

  10. Energy band dispersion in photoemission spectra of argon clusters

    International Nuclear Information System (INIS)

    Foerstel, Marko; Mucke, Melanie; Arion, Tiberiu; Lischke, Toralf; Barth, Silko; Ulrich, Volker; Ohrwall, Gunnar; Bjoerneholm, Olle; Hergenhahn, Uwe; Bradshaw, Alex M.

    2011-01-01

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

  11. Synchrotron radiation photoemission studies of core level excitation effects

    International Nuclear Information System (INIS)

    Williams, G.P.; Lapeyre, G.J.; Anderson, J.; Cerrina, F.; Dietz, R.E.; Yafet, Y.

    1979-01-01

    The recent availability of intense polarized radiation tunable over the range 20-150 eV enables several core levels to be excited. Several remarkable effects have recently been reported when core excitation thresholds have been reached. For example, an increase in yield of 50% was observed in GaSe at the Se 3d threshold (h omega approx. = 57 eV). A considerable increase in photoemission intensity at 6 eV binding energy has been reported by Guillot et al. for Ni at the 3p threshold. A very careful study was made using the CIS, CFS, and EDC modes of photoemission spectroscopy of core threshold effects in Ni, Pt, and GaSe. A modulation of the Ni Fermi edge emission as a function of photon energy is found which is attributed to a configuration interaction between 3p 5 3d 10 4s and 3p 6 3d 8 4s epsilon f. Similar effects occur in Pt at the 4f threshold involving the configurations 4f 13 5d 10 6s and 4f 14 5d 8 6s. Further, the lineshapes of the Pt and Ni upper valence band CIS's resemble those obtained by electron energy loss (ELS) and photoabsorption, all of which can be fitted theoretically to a Fano model. Emission from levels lying well below the Fermi level often has superimposed contributions due to incoherent effects which complicate the interpretation. In cases in which core levels are excited well above threshold, the CIS technique may be used to examinefinal states. Of particular interest is the possible consequent determination of adsorbate site geometry. Data are presented for 2p emission from a c(2x2) Na overlayer on Ni

  12. Multidimensional photoemission spectroscopy—the space-charge limit

    Science.gov (United States)

    Schönhense, B.; Medjanik, K.; Fedchenko, O.; Chernov, S.; Ellguth, M.; Vasilyev, D.; Oelsner, A.; Viefhaus, J.; Kutnyakhov, D.; Wurth, W.; Elmers, H. J.; Schönhense, G.

    2018-03-01

    Photoelectron spectroscopy, especially at pulsed sources, is ultimately limited by the Coulomb interaction in the electron cloud, changing energy and angular distribution of the photoelectrons. A detailed understanding of this phenomenon is crucial for future pump-probe photoemission studies at (x-ray) free electron lasers and high-harmonic photon sources. Measurements have been performed for Ir(111) at hν = 1000 eV with photon flux densities between ˜102 and 104 photons per pulse and μm2 (beamline P04/PETRA III, DESY Hamburg), revealing space-charge induced energy shifts of up to 10 eV. In order to correct the essential part of the energy shift and restore the electron distributions close to the Fermi energy, we developed a semi-analytical theory for the space-charge effect in cathode-lens instruments (momentum microscopes, photoemission electron microscopes). The theory predicts a Lorentzian profile of energy isosurfaces and allows us to quantify the charge cloud from measured energy profiles. The correction is essential for the determination of the Fermi surface, as we demonstrate by means of ‘k-space movies’ for the prototypical high-Z material tungsten. In an energy interval of about 1 eV below the Fermi edge, the bandstructure can be restored up to substantial shifts of ˜7 eV. Scattered photoelectrons strongly enhance the inelastic background in the region several eV below E F, proving that the majority of scattering events involves a slow electron. The correction yields a gain of two orders of magnitude in usable intensity compared with the uncorrected case (assuming a tolerable shift of 250 meV). The results are particularly important for future experiments at SASE-type free electron lasers, since the correction also works for strongly fluctuating (but known) pulse intensities.

  13. Fingerprints of spin-orbital polarons and of their disorder in the photoemission spectra of doped Mott insulators with orbital degeneracy

    Science.gov (United States)

    Avella, Adolfo; Oleś, Andrzej M.; Horsch, Peter

    2018-04-01

    means of a complementary many-body polaron theory, which yields a similar robust spin and orbital order as the Hartree-Fock approximation. Using realistic parameters for the vanadium perovskite La1 -xCaxVO3 , we show that its soft gap is reproduced as well as the marginal doping dependence of the position of the chemical potential relative to the center of the lower Hubbard band. The present theory uncovers also the reasons why the d1→d0 satellite excitations, which directly probe the effect of the random defect fields on the polaron state, are not well resolved in the available experimental photoemission spectra for La1 -xCaxVO3 .

  14. Development of high current electron source using photoemission from metals with ultrashort laser pulses

    International Nuclear Information System (INIS)

    Tsang, T.; Srinivasan-Rao, T.; Fischer, J.

    1990-10-01

    We summarize the studies of photoemission from metal photocathodes using picosecond pulses in the UV (4.66 eV) wavelength and femtosecond laser pulses in the visible (2 eV) wavelengths. To achieve high current density yield from metal photocathodes, multiphoton photoemission using femtosecond laser pulses are suggested. Electron yield improvement incorporating surface photoemission and surface plasmon resonance in metals and metal films are demonstrated. We examine the possibility of the nonlinear photoemission process overtaking the linear process, and identity some possible complexity. To extract the large amount of electrons free of space charge, a pulsed high voltage is designed; the results of the preliminary test are presented. Finally, for the first time, the width of the electron temporal profiles are measured, utilizing the nonlinear photoelectric effect, to below 100 fsec time regime. The results indicated that the electron pulse duration follows the laser pulses and are not limited by the material. 8 refs., 15 figs

  15. Experiments recently carried out on the photoemission station at Beijing Synchrotron Radiation Facility

    International Nuclear Information System (INIS)

    Kurash Ibrahim; Wu Ziyu; Qian Haijie; Zhang Jing; Abbas, M.I.; Chen Zhigang; Su Run; Liu Fengqin

    2003-01-01

    With a sustained and steady operation of the photoemission station at Beijing Synchrotron Radiation Facility, users from different research fields have carried out their investigation on the electronic structure of metal surface-interface, metal doped fullerene as well as colossal magneto-resistance materials utilizing different experimental modes provided by the photoemission station. In this paper authors would present some representative experimental results obtained on the station

  16. Small angle neutron scattering from glassy SiO2

    International Nuclear Information System (INIS)

    Spooner, S.; Hastings, J.B.

    1976-01-01

    The present investigation of neutron scattering from glassy silica was undertaken to resolve whether the small angle scattering observed by Renninger and Uhlmann could also be seen in the bulk samples typically used in neutron-scattering experiments. Within the rather large error bars of this experiment no small angle scattering increase at small angles could be seen. (Auth.)

  17. A photoemission study of Mn grown on GaAs(100)

    International Nuclear Information System (INIS)

    James, D.; Riley, J.; Leckey, R.; Usher, B.; Sieber, N.; Seyller, Th.; Ley, L.

    2002-01-01

    Full text: Metal contacts on semiconductors have been an important area for device manufacture. The possibility of lattice matched growth of magnetic metals on semiconductors was once thought to be a unobtainable goal. More recently it has been found that transition metals can react with the semiconductor substrates, forming another lattice with a more comparable lattice constant, from which epitaxial growth can then proceed. Al grows epitaxially on GaN even with a lattice mismatch greater than 10%. In this instance, Al displaces Ga being driven by a larger heat of formation to produce an AlN buffer layer, on which Al can then grow. This paper investigates the room temperature deposition of Mn onto GaAs(100) at room temperature. The Photoemission study was carried out at the UEL56/2 PGM2 beam line at BESSY II in Berlin, Germany. Synchrotron radiation was used to observe the surface as thin layers of Mn were deposited. The interaction of manganese with the substrate tends to donate electron density to neighbouring atoms, decreasing binding energy. No further segregation of substitutional or interstitial Mn and Ga can be seen from angle dependence data at this temperature, with metallic manganese eventually attenuating the bulk Ga signal to the point where it is indistinguishable from the background. It is concluded that there the metal reacts with the semiconductor surface with some indiffusion as confirmed using SIMS. Previously, the reaction was only thought to have taken place above room temperature. The resulting structure consists of a Ga-As-Mn buffer layer as with the higher temperature depositions

  18. 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.

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

    International Nuclear Information System (INIS)

    Tobin, J.G.; Goodman, K.W.; Schumann, F.O.

    1997-01-01

    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

  20. 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...

  1. Study of Si-N amorphous compounds combining XPS (X photoemission) and EELS (electron energy loss spectra) optical measurements. Internal levels photoemission. Pt. 2

    International Nuclear Information System (INIS)

    Guraya, M.M.; Acolani, H.; Zampieri, G.E.; Silva, J.H. Dias da; Cisneros, J.I.; Cantao, M.; Marques, F.C.

    1990-01-01

    A Si-N non-stoichiometric hydrogenated amorphous compounds study with different N- contents is presented. The shape and shifts of the photoemission peaks corresponding to the N - 1s and Si - 2p internal levels are analyzed. Based on the latter, the homogeneity of the samples and the Si - N bonds charge transfer is discussed. (Author) [es

  2. Angle-resolved polarimetry of antenna-mediated fluorescence

    NARCIS (Netherlands)

    Mohtashami, A.; Osorio, C.I.; Koenderink, A.F.

    2015-01-01

    Optical phase-array antennas can be used to control not only the angular distribution but also the polarization of fluorescence from quantum emitters. The emission pattern of the resulting system is determined by the properties of the antenna, the properties of the emitters, and the strength of the

  3. 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.

  4. 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...... 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....

  5. 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

    2017-09-08

    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.

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

    Directory of Open Access Journals (Sweden)

    D. V. Minko

    2012-01-01

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

  7. Probing the switching state of a surface-mounted azobenzene derivative using femtosecond XUV photoemission

    Science.gov (United States)

    Grunau, Jan; Heinemann, Nils; Rohwer, Timm; Zargarani, Dordaneh; Kuhn, Sonja; Jung, Ullrich; Kipp, Lutz; Magnussen, Olaf; Herges, Rainer; Bauer, Michael

    2012-03-01

    Photoemission spectroscopy using femtosecond XUV light pulses is applied to probe the isomerization state of the molecular switch 3-(4-(4-hexyl-phenylazo)-phenoxy)-propane-1-thiol deposited by liquid phase self-assembly on Au(111). Spectral shifts of valence-electronic signatures that we associate with the carbon C2s orbital enable us to distinguish the trans and the cis isomerization state of the adsorbed molecules. These preliminary results envision the potential to probe reversible switching processes of surface-mounted molecules in real time by tracking the temporal evolution of the electronic and nuclear degrees of freedom in a femtosecond XUV photoemission experiment.

  8. Real-time monitoring of initial thermal oxidation on Si(001) surfaces by synchrotron radiation photoemission spectroscopy

    CERN Document Server

    Yoshigoe, A; Teraoka, Y

    2003-01-01

    The thermal oxidation of Si(001) surfaces at 860 K, 895 K, 945 K and 1000 K under the O sub 2 pressure of 1 x 10 sup - sup 4 Pa has been investigated by time-resolved photoemission measurements with synchrotron radiation. Based on time evolution analyses by reaction kinetics models, it was found that the oxidation at 860 K, 895 K and 945 K has progressed with the Langmuir adsorption type, whereas the oxidation at 1000 K has showed the character of the two-dimensional island growth involving SiO desorption. The oxidation rates increases with increasing surface temperature in the passive oxidation condition. The time evolution of each Si oxidation state (Si sup n sup + : n = 1, 2, 3, 4) derived from the Si-2p core-level shifts has also been analyzed. The results revealed that the thermal energy contribution to the migration process of the adsorbed oxygen and the emission of the bulk silicon atoms. Thus, the fraction of the Si sup 4 sup + bonding state, i.e. SiO sub 2 structure, was increased. (author)

  9. Photoemission of Bi_{2}Se_{3} with Circularly Polarized Light: Probe of Spin Polarization or Means for Spin Manipulation?

    Directory of Open Access Journals (Sweden)

    J. Sánchez-Barriga

    2014-03-01

    Full Text Available Topological insulators are characterized by Dirac-cone surface states with electron spins locked perpendicular to their linear momenta. Recent theoretical and experimental work implied that this specific spin texture should enable control of photoelectron spins by circularly polarized light. However, these reports questioned the so far accepted interpretation of spin-resolved photoelectron spectroscopy. We solve this puzzle and show that vacuum ultraviolet photons (50–70 eV with linear or circular polarization indeed probe the initial-state spin texture of Bi_{2}Se_{3} while circularly polarized 6-eV low-energy photons flip the electron spins out of plane and reverse their spin polarization, with its sign determined by the light helicity. Our photoemission calculations, taking into account the interplay between the varying probing depth, dipole-selection rules, and spin-dependent scattering effects involving initial and final states, explain these findings and reveal proper conditions for light-induced spin manipulation. Our results pave the way for future applications of topological insulators in optospintronic devices.

  10. Observation and resonant x-ray optical interpretation of multi-atom resonant photoemission effects in O 1s emission from NiO

    International Nuclear Information System (INIS)

    Mannella, N.; Yang, S.-H.; Mun, B.S.; Garcia de Abajo, F.J.; Kay, A.W.; Sell, B.C.; Watanabe, M.; Ohldag, H.; Arenholz, E.; Young, A.T.; Hussain, Z.; Van Hove, M.A.; Fadley, C.S.

    2006-01-01

    We present experimental and theoretical results for the variation of the O 1s intensity from a NiO(001) surface as the excitation energy is varied through the Ni 2p1/2,3/2 absorption resonances, and as the incidence angle of the radiation is varied from grazing to larger values. For grazing incidence, a strong multi-atom resonant photoemission(MARPE) effect is seen on the O 1s intensity as the Ni 2p resonances are crossed, but its magnitude decreases rapidly as the incidence angle is increased. Resonant x-ray optical (RXRO) calculations are found to predict these effects very well, although the experimental effects are found to decrease at higher incidence angles faster than those in theory. The potential influence of photoelectron diffraction effects on such measurements are also considered, including experimental data with azimuthal-angle variation and corresponding multiple-scattering-diffraction calculations, but we conclude that they do not vary beyond what is expected on the basis of the change in photoelectron kinetic energy. Varying from linear polarization to circular polarization is found to enhance these effects in NiO considerably, although the reasons are not clear. We also discuss the relationship of these measurements to other related interatomic resonance experiments and theoretical developments, and make some suggestions for future studies in this area

  11. 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

  12. Internal photoemission for photovoltaic using p-type Schottky barrier: Band structure dependence and theoretical efficiency limits

    Science.gov (United States)

    Shih, Ko-Han; Chang, Yin-Jung

    2018-01-01

    Solar energy conversion via internal photoemission (IPE) across a planar p-type Schottky junction is quantified for aluminum (Al) and copper (Cu) in the framework of direct transitions with non-constant matrix elements. Transition probabilities and k-resolved group velocities are obtained based on pseudo-wavefunction expansions and realistic band structures using the pseudopotential method. The k-resolved number of direct transitions, hole photocurrent density, quantum yield (QY), and the power conversion efficiency (PCE) under AM1.5G solar irradiance are subsequently calculated and analyzed. For Al, the parabolic and "parallel-band" effect along the U-W-K path significantly enhances the transition rate with final energies of holes mainly within 1.41 eV below the Fermi energy. For Cu, d-state hot holes mostly generated near the upper edge of 3d bands dominate the hole photocurrent and are weekly (strongly) dependent on the barrier height (metal film thickness). Hot holes produced in the 4s band behave just oppositely to their d-state counterparts. Non-constant matrix elements are shown to be necessary for calculations of transitions due to time-harmonic perturbation in Cu. Compared with Cu, Al-based IPE in p-type Schottky shows the highest PCE (QY) up to about 0.2673% (5.2410%) at ΦB = 0.95 eV (0.5 eV) and a film thickness of 11 nm (20 nm). It is predicted that metals with relatively dispersionless d bands (such as Cu) in most cases do not outperform metals with photon-accessible parallel bands (such as Al) in photon energy conversion using a planar p-type Schottky junction.

  13. Spectrally resolved measurements of the terahertz beam profile generated from a two-color air plasma

    DEFF Research Database (Denmark)

    Pedersen, Pernille Klarskov; Zalkovskij, Maksim; Strikwerda, Andrew

    2014-01-01

    Using a THz camera and THz bandpass filters, we measure the frequency - resolved beam profile emitted from a two - color air plasma. We observe a frequency - independent emission angle from the plasma .......Using a THz camera and THz bandpass filters, we measure the frequency - resolved beam profile emitted from a two - color air plasma. We observe a frequency - independent emission angle from the plasma ....

  14. Aberration-corrected multipole Wien filter for energy-filtered x-ray photoemission electron microscopy

    OpenAIRE

    Niimi, Hironobu; Chun, Wang-Jae; Suzuki, Shushi; Asakura, Kiyotaka; Kato, Makoto

    2007-01-01

    The aberration of a multipole Wien filter for energy-filtered x-ray photoemission electron microscopy was analyzed and the optimized Fourier components of the electric and magnetic fields for the third-order aperture aberration corrections were obtained. It was found that the third-order aperture aberration correction requires 12 electrodes and magnetic poles. ©2007 American Institute of Physics

  15. Aberration-corrected multipole Wien filter for energy-filtered x-ray photoemission electron microscopy

    Science.gov (United States)

    Niimi, Hironobu; Chun, Wang-Jae; Suzuki, Shushi; Asakura, Kiyotaka; Kato, Makoto

    2007-06-01

    The aberration of a multipole Wien filter for energy-filtered x-ray photoemission electron microscopy was analyzed and the optimized Fourier components of the electric and magnetic fields for the third-order aperture aberration corrections were obtained. It was found that the third-order aperture aberration correction requires 12 electrodes and magnetic poles.

  16. 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,

  17. 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. A d...

  18. 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...

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

    Directory of Open Access Journals (Sweden)

    B. Ahn

    2017-03-01

    Full Text Available 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. Effect of wave-function localization on the time delay in photoemission from surfaces

    International Nuclear Information System (INIS)

    Zhang, C.-H.; Thumm, U.

    2011-01-01

    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 latt of attractive Gaussian-shaped core potentials of width σ. The parameter σ/a latt thus controls the overlap between adjacent core potentials and localization of the electronic eigenfunctions on the lattice points. Small values of σ/a latt 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 σ/a latt =0.3 from relatively large values below σ/a latt ∼0.2 to much smaller delays above σ/a latt ∼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.

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

    Czech Academy of Sciences Publication Activity Database

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

    2016-01-01

    Roč. 28, č. 31 (2016), s. 1-15, č. článku 315301. ISSN 0953-8984 R&D Projects: GA ČR(CZ) GBP108/12/G108 Institutional support: RVO:68378271 Keywords : photoemission * laser excitation * surface plasmon * plasmonics Subject RIV: BH - Optics, Masers, Lasers Impact factor: 2.649, year: 2016

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

    International Nuclear Information System (INIS)

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

    1983-09-01

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

  3. 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.

  4. Glancing angle x-ray studies of oxide films

    International Nuclear Information System (INIS)

    Davenport, A.J.; Isaacs, H.S.

    1989-01-01

    High brightness synchrotron radiation incident at glancing angles has been used to study inhibiting species present in low concentrations in oxide films on aluminum. Glancing incident angle fluorescence measurements give surface-sensitive information on the valence state of elements from the shape of the x-ray absorption edge. Angle-resolved measurements show the depth distribution of the species present. 15 refs., 4 figs

  5. Contact Angle Goniometer

    Data.gov (United States)

    Federal Laboratory Consortium — Description:The FTA32 goniometer provides video-based contact angle and surface tension measurement. Contact angles are measured by fitting a mathematical expression...

  6. Observation of two-photon photoemission from cesium telluride photocathodes excited by a near-infrared laser

    Science.gov (United States)

    Panuganti, H.; Piot, P.

    2017-02-01

    We explore the nonlinear photoemission in cesium telluride (Cs2Te) photocathodes where an ultrashort (˜100 fs full width at half max) 800-nm infrared laser is used as the drive-laser in lieu of the typical ˜266-nm ultraviolet laser. An important figure of merit for photocathodes, the quantum efficiency, we define here for nonlinear photoemission processes in order to compare with linear photoemission. The charge against drive-laser (infrared) energy is studied for different laser energy and intensity values and cross-compared with previously performed similar studies on copper [P. Musumeci et al., Phys. Rev. Lett. 104, 084801 (2010)], a metallic photocathode. We particularly observe two-photon photoemission in Cs2Te using the infrared laser in contrast to the anticipated three-photon process as observed for metallic photocathodes.

  7. Resonant photoemission of La and Yb at the 3d absorption edge

    CERN Document Server

    Lagarde, P; Ogasawara, H; Kotani, A

    2003-01-01

    Resonant photoemission and resonant Auger experiments at the 3d threshold are presented for La and Yb over a binding energy domain which extends up to the 4p levels. These experimental results are well explained by calculations in the framework of full-multiplet Hartree-Fock theory with an atomic model. Strong participator and spectator Auger transitions are observed without ordinary Auger transition, indicating that the 4f wavefunction is well localized in the intermediate state even in the case of La. The 4d sub 3 sub / sub 2 and 4d sub 5 sub / sub 2 branching ratio of the 4d resonant photoemission of La at the M sub 4 and M sub 5 edges is observed experimentally and analyzed theoretically. The difference in the resonant processes behavior for La and Yb is discussed based upon the different 4f occupation number.

  8. Recent Developments at the High-Charge PHIN Photoinjector and the CERN Photoemission Laboratory

    CERN Document Server

    Hessler, C; Doebert, S; Fedosseev, V; Martini, I; Martyanov, M; Perillo Marcone, A; Sroka, S

    2014-01-01

    The high-charge PHIN photoinjector has originally been developed to study the feasibility of a photoinjector option for the drive beam of the CLIC Test Facility 3 (CTF3) at CERN and is now being used to inevestigate the feasibility of a drive beam photoinjector for CLIC. In this paper recent R&D efforts to improve the parameters of the existing system towards CLIC requirements will be discussed. This includes studies of a feedback loop for intensity stabilization, the upgrade of the PHIN vacuum system and the planned upgrade of the driving laser system. For photocathode production and R&D a dedicated photoemission laboratory is available at CERN. To increase the production rate of photocathodes and the availability of the photoemission lab for other studies, an upgrade of the photocathode preparation system with a load-lock system is under study and will also be presented.

  9. DC High Voltage Conditioning of Photoemission Guns at Jefferson Lab FEL

    International Nuclear Information System (INIS)

    DC high voltage photoemission electron guns with GaAs photocathodes have been used to produce polarized electron beams for nuclear physics experiments for about 3 decades with great success. In the late 1990s, Jefferson Lab adopted this gun technology for a free electron laser (FEL), but to assist with high bunch charge operation, considerably higher bias voltage is required compared to the photoguns used at the Jefferson Lab Continuous Electron Beam Accelerator Facility. The FEL gun has been conditioned above 400 kV several times, albeit encountering non-trivial challenges with ceramic insulators and field emission from electrodes. Recently, high voltage processing with krypton gas was employed to process very stubborn field emitters. This work presents a summary of the high voltage techniques used to high voltage condition the Jefferson Lab FEL photoemission gun.

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

    DEFF Research Database (Denmark)

    Christensen, N. Egede; Feuerbacher, B.

    1974-01-01

    of photoemission spectra from W single crystals. The nondirect as well as the direct models for bulk photoemission processes are investigated. The emission from the three low-index surfaces (100), (110), and (111) exhibits strong dependence on direction and acceptance cone. According to the present band model...... there should essentially be no emission normal to the (110) face for photon energies between 9.4 and 10.6 eV. Experimental observation of emission in this gap, however, implies effects not included in the simple bulk models. In particular, effects arising from surface emission have been considered, i.......e., emission of those electrons which are excited in a single-step process from initial states near the surface to final states outside the crystal. The electrons that are emitted from the surface in directions perpendicular to the crystal planes carry information on the one-dimensional surface density...

  11. Coherent Peaks and Minimal Probing Depth in Photoemission Spectroscopy of Mott-Hubbard Systems

    Science.gov (United States)

    Panaccione, G.; Altarelli, M.; Fondacaro, A.; Georges, A.; Huotari, S.; Lacovig, P.; Lichtenstein, A.; Metcalf, P.; Monaco, G.; Offi, F.; Paolasini, L.; Poteryaev, A.; Tjernberg, O.; Sacchi, M.

    2006-09-01

    We have measured hard x-ray photoemission spectra of pure vanadium sesquioxide (V2O3) across its metal-insulator transition. We show that, in the metallic phase, a clear correlation exists between the shakedown satellites observed in the vanadium 2p and 3p core-level spectra and the coherent peak measured at the Fermi level. Comparing experimental results and dynamical mean-field theory calculations, we estimate the Hubbard energy U in V2O3 (4.20±0.05eV). From our bulk-sensitive photoemission spectra we infer the existence of a critical probing depth for investigating electronic properties in strongly correlated solids.

  12. 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...

  13. Introduction of spectroscopic photoemission and low energy electron microscope in SPring-8

    International Nuclear Information System (INIS)

    Guo, FangZhun; Kobayashi, Keisuke; Kinoshita, Toyohiko

    2005-01-01

    An upright configuration SPELEEM (Spectroscopic PhotoEmission and Low Energy Electron Microscope) has been introduced in SPring-8 in the framework of the nanotechnology support project of Ministry of Education, Culture, Sport, Science and Technology (MEXT), Japan. SPELEEM combines microscopy, spectroscopy and diffraction in one system, which allows a comprehensive characterization of the specimen. The combination of SPELEEM and polarized (circularly or linearly) soft X-rays in SPring-8 is expected to realize the highest performance. The characteristics of SPELEEM and typical results, for example nano-XANES (X-ray absorption near edge structure) of Fe oxide on Fe(100) surface, nano-XPS (X-ray photoemission spectroscopy) of indium (In) on Si(111) and antiferro-magnetic domain structure images of NiO(001) single crystal, are reported. (author)

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

    International Nuclear Information System (INIS)

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

    2012-01-01

    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. - Highlights: ► Photoemission electron attachment ion mobility spectrometry (PE-EA-IMS) was developed to study electron attachment reaction. ► The rate constants of electron attachment to CCl 4 and CHCl 3 were determined. ► The present experimental results are in good agreement with the previously reported data.

  15. 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.

  16. Core and valence level photoemission and photoabsorption study of icosahedral Al-Pd-Mn quasicrystals

    International Nuclear Information System (INIS)

    Horn, K; Theis, W; Paggel, J J; Barman, S R; Rotenberg, E; Ebert, Ph; Urban, K

    2006-01-01

    The electronic structure of quasicrystalline Al-Pd-Mn is investigated by means of valence and core level photoelectron spectroscopy. Variations of the photoionization cross section in the constituents' valence electronic levels as a function of photon energy are used to identify contributions from the different atomic species, in particular near the Pd 4d Cooper minimum. Resonant photoemission at the Mn 2p absorption edge shows the contribution of the Mn 3d states to the density of states in a region near the Fermi level. The asymmetry of Pd 3d and Mn 2p core level photoemission lines, and its difference for emission from metallic and quasicrystalline phases, are utilized to infer the contributions of the different constituents to the density of states at the Fermi level

  17. Photoemission in the Anderson model for rare earth compounds with floating valences

    International Nuclear Information System (INIS)

    Frota, H.O. da.

    1985-01-01

    X-ray photoemission spectra (XPS) are calculated for the spin-degenerate Anderson model of valence fluctuation compounds. Based on the renormalization group technique originally introduced by Wilson to calculate the magnetic susceptibility for the Kondo model, the numerical calculation has uniform accuracy over the entire parameter space of the Anderson model; at any given photoelectron energy, a maximum error of 4% is estimated for the calculated photoemission current. The calculated spectra display two peaks associated with the two possible x-ray induced transitions between the n f = 0,1 or 2 occupations of the f-orbital: a first ionization peak corresponding to the n f = 2 → n f = 1 transition and a second ionization peak due to the n f 1 → n f = 0 transition. (author)

  18. Dilution effect on the U 5f states in Au matrix: a photoemission spectroscopy study

    Czech Academy of Sciences Publication Activity Database

    Eloirdi, R.; Gouder, T.; Wastin, F.; Huber, F.; Shick, Alexander; Kolorenč, Jindřich

    2011-01-01

    Roč. 84, č. 23 (2011), 235143/1-235143/7 ISSN 1098-0121 R&D Projects: GA ČR(CZ) GAP204/10/0330; GA AV ČR IAA100100912 Institutional research plan: CEZ:AV0Z10100520 Keywords : x-ray photoemission * electronic-structure * photoelectron-spectroscopy * fermion systems Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.691, year: 2011

  19. 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 it is un...... it is unaffected by detrimental hot electron collisions. Transient ab sorption results from dielectric permittivity discontinuity at the nanoparticle boundary and leads to a substantial (by ~5 times) increase of the photoelectron emission rate....

  20. Photoemission study of 5f localization in UPd3 - x(Pt,Rh)x

    Science.gov (United States)

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

    1988-04-01

    Photoemission measurements in the two systems UPd3-x(Pt,Rh)x show that the 5f spectra are consistent with localized 5f electrons (peak in spectral weight is below EF for all x within the double hexagonal DO24 phase) while at both phase transitions the 5f peaks lock in at EF consistent with intinerancy. A satellite 5f peak which we attribute to d screening is observed in both localized and itinerant systems.

  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. The HBN Angle

    Directory of Open Access Journals (Sweden)

    Harsh Bhagvatiprasad Dave

    2015-01-01

    Full Text Available Aim: The purpose of this study was to establish a new cephalometric measurement, named the Harsh Bhagvatiprasad Nita angle (HBN, to assess the sagittal jaw relationship with accuracy and reproducibility. Materials and Methods: Three hundred pretreatment lateral cephalograms (100 each of Class I, II, and III were taken from the Department of Orthodontics and Dentofacial Orthopedics of Rajasthan Dental College and Hospital, Jaipur (Rajasthan and were subdivided into skeletal Class I, II, and III based on ANB, Wits appraisal, and Beta angle. This angle uses 3 skeletal landmarks the "C" (apparent axis of the condyle, "M" (midpoint of the premaxilla, and "G" (center of the largest circle that is tangent to the internal inferior, anterior, and posterior surfaces of the mandibular symphysis. Results: The result of the mean and standard deviation for the HBN angle were calculated in all three skeletal groups. After using one-way analysis of variance and post-hoc multiple comparisons by using Tukey′s honestly significant difference, homogeneous subsets, receiver operating characteristics (ROC curve - to differentiate Class II with Class I, ROC curve - to differentiate Class III with Class I, Reliability analysis with interclass correlation of HBN angle with other angles, we obtained results that showed that a patient with a HBN angle 40° and 46° can be considered to have a Class I skeletal pattern. Conclusions: A new angle, the HBN angle, was developed as a diagnostic aid to evaluate the sagittal jaw relationship more consistently. HBN angle 40° and 46° can be considered to have a Class I skeletal pattern, a more acute HBN angle indicates a Class II skeletal pattern, and a more obtuse HBN angle indicates a Class III skeletal pattern.

  3. Reading Angles in Maps

    Science.gov (United States)

    Izard, Véronique; O'Donnell, Evan; Spelke, Elizabeth S.

    2014-01-01

    Preschool children can navigate by simple geometric maps of the environment, but the nature of the geometric relations they use in map reading remains unclear. Here, children were tested specifically on their sensitivity to angle. Forty-eight children (age 47:15-53:30 months) were presented with fragments of geometric maps, in which angle sections…

  4. Optimal reconstruction angles

    International Nuclear Information System (INIS)

    Cook, G.O. Jr.; Knight, L.

    1979-07-01

    The question of optimal projection angles has recently become of interest in the field of reconstruction from projections. Here, studies are concentrated on the n x n pixel space, where literative algorithms such as ART and direct matrix techniques due to Katz are considered. The best angles are determined in a Gauss--Markov statistical sense as well as with respect to a function-theoretical error bound. The possibility of making photon intensity a function of angle is also examined. Finally, the best angles to use in an ART-like algorithm are studied. A certain set of unequally spaced angles was found to be preferred in several contexts. 15 figures, 6 tables

  5. Radiofrequency encoded angular-resolved light scattering

    DEFF Research Database (Denmark)

    Buckley, Brandon W.; Akbari, Najva; Diebold, Eric D.

    2015-01-01

    The sensitive, specific, and label-free classification of microscopic cells and organisms is one of the outstanding problems in biology. Today, instruments such as the flow cytometer use a combination of light scatter measurements at two distinct angles to infer the size and internal complexity...... of cells at rates of more than 10,000 per second. However, by examining the entire angular light scattering spectrum it is possible to classify cells with higher resolution and specificity. Current approaches to performing these angular spectrum measurements all have significant throughput limitations...... Encoded Angular-resolved Light Scattering (REALS), this technique multiplexes angular light scattering in the radiofrequency domain, such that a single photodetector captures the entire scattering spectrum from a particle over approximately 100 discrete incident angles on a single shot basis. As a proof...

  6. Photoelectric angle converter

    Science.gov (United States)

    Podzharenko, Volodymyr A.; Kulakov, Pavlo I.

    2001-06-01

    The photo-electric angle transmitter of rotation is offered, at which the output voltage is linear function of entering magnitude. In a transmitter the linear phototransducer is used on the basis of pair photo diode -- operating amplifier, which output voltage is linear function of the area of an illuminated photosensitive stratum, and modulator of a light stream of the special shape, which ensures a linear dependence of this area from an angle of rotation. The transmitter has good frequent properties and can be used for dynamic measurements of an angular velocity and angle of rotation, in systems of exact drives and systems of autocontrol.

  7. Non-contact measurement of rotation angle with solo camera

    Science.gov (United States)

    Gan, Xiaochuan; Sun, Anbin; Ye, Xin; Ma, Liqun

    2015-02-01

    For the purpose to measure a rotation angle around the axis of an object, a non-contact rotation angle measurement method based on solo camera was promoted. The intrinsic parameters of camera were calibrated using chessboard on principle of plane calibration theory. The translation matrix and rotation matrix between the object coordinate and the camera coordinate were calculated according to the relationship between the corners' position on object and their coordinates on image. Then the rotation angle between the measured object and the camera could be resolved from the rotation matrix. A precise angle dividing table (PADT) was chosen as the reference to verify the angle measurement error of this method. Test results indicated that the rotation angle measurement error of this method did not exceed +/- 0.01 degree.

  8. Angles in hyperbolic lattices

    DEFF Research Database (Denmark)

    Risager, Morten S.; Södergren, Carl Anders

    2017-01-01

    It is well known that the angles in a lattice acting on hyperbolic n -space become equidistributed. In this paper we determine a formula for the pair correlation density for angles in such hyperbolic lattices. Using this formula we determine, among other things, the asymptotic behavior of the den......It is well known that the angles in a lattice acting on hyperbolic n -space become equidistributed. In this paper we determine a formula for the pair correlation density for angles in such hyperbolic lattices. Using this formula we determine, among other things, the asymptotic behavior...... of the density function in both the small and large variable limits. This extends earlier results by Boca, Pasol, Popa and Zaharescu and Kelmer and Kontorovich in dimension 2 to general dimension n . Our proofs use the decay of matrix coefficients together with a number of careful estimates, and lead...

  9. 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.

  10. Physical origin of satellites in photoemission of doped graphene: an ab initio GW plus cumulant study.

    Science.gov (United States)

    Lischner, Johannes; Vigil-Fowler, Derek; Louie, Steven G

    2013-04-05

    We calculate the photoemission spectra of suspended and epitaxial doped graphene using an ab initio cumulant expansion of the Green's function based on the GW self-energy. Our results are compared to experiment and to standard GW calculations. For doped graphene on a silicon carbide substrate, we find, in contrast to earlier calculations, that the spectral function from GW only does not reproduce experimental satellite properties. However, ab initio GW plus cumulant theory combined with an accurate description of the substrate screening results in good agreement with experiment, but gives no plasmaron (i.e., no extra well-defined excitation satisfying Dyson's equation).

  11. 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.

  12. Molecular frame photoelectron angular distribution for oxygen 1s photoemission from CO2 molecules

    International Nuclear Information System (INIS)

    Saito, N; Ueda, K; De Fanis, A

    2005-01-01

    We have measured photoelectron angular distributions in the molecular frame (MF-PADs) for O 1s photoemission from CO 2 , using photoelectron-O + -CO + coincidence momentum imaging. Results for the molecular axis at 0, 45 and 90 0 to the electric vector of the light are reported. The major features of the MF-PADs are fairly well reproduced by calculations employing a relaxed-core Hartree-Fock approach. Weak asymmetric features are seen through a plane perpendicular to the molecular axis and attributed to symmetry lowering by anti-symmetric stretching motion. (letter to the editor)

  13. 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.

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

    DEFF Research Database (Denmark)

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

    2014-01-01

    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...... 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...

  15. Athermal electron distribution probed by femtosecond multiphoton photoemission from image potential states

    International Nuclear Information System (INIS)

    Ferrini, Gabriele; Giannetti, Claudio; Pagliara, Stefania; Banfi, Francesco; Galimberti, Gianluca; Parmigiani, Fulvio

    2005-01-01

    Image potential states are populated through indirect, scattering-mediated multiphoton absorption induced by femtosecond laser pulses and revealed by single-photon photoemission. The measured effective mass is significantly different from that obtained with direct, resonant population. These features reveal a strong coupling of the electrons residing in the image potential state, outside the solid, with the underlying hot electron population created by the laser pulse. The coupling is mediated by a many-body scattering interaction between the image potential state electrons and bulk electrons in highly excited states

  16. CONTUR: A program for X-ray photoemission spectroscopic personal computer-based data analysis

    Science.gov (United States)

    Contini, G.; Turchini, S.

    1996-03-01

    CONTUR, a computer program for photoemission data analysis written in QuickBasic that operates using an IBM personal computer (PC) or compatible, is described. It includes the following functions: plotting of up to four files, files saving, spectra comparison (including addition, subtraction and division) smoothing and median filtering, data marking, differentiating, resizing of X and Y scales, transforming binding into kinetic energy and vice versa, X axis cutting, showing X and Y values of the files, spikes removing, linear and Shirley background subtraction, calculating the area of the peaks, determination of maxima of the file, DOS shell. A brief description of the program and its capabilities is given.

  17. Observation of injection and pinning of domain walls in magneticnanowires using photoemission electron microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Thomas, Luc; Rettner, Charles; Hayashi, Masamitsu; Samant, MaheshG.; Parkin Stuart S.P.; Doran, Andrew; Scholl, Andreas

    2005-12-19

    Photoemission electron microscopy is used to explore the injection and pinning of magnetic domain walls in 250-nm-wide, 20-nm-thick Permalloy nanowires. Domain walls are injected from a micron-sized elliptical nucleation pad at one end of the nanowire. A vortex-like structure is readily nucleated in this pad at low magnetic fields 15 Oe, whereas injection of a domain wall into the nanowire requires significantly larger fields 60 Oe. Domain walls are pinned in the nanowire at notches patterned along the wires edges. The domain walls are observed to have vortex-like structures with chiralities that vary in successive experiments.

  18. Observation of injection and pinning of domain walls in magnetic nanowires using photoemission electron microscopy

    Science.gov (United States)

    Thomas, Luc; Rettner, Charles; Hayashi, Masamitsu; Samant, Mahesh G.; Parkin, Stuart S. P.; Doran, Andrew; Scholl, Andreas

    2005-12-01

    Photoemission electron microscopy is used to explore the injection and pinning of magnetic domain walls in 250-nm-wide, 20-nm-thick Permalloy nanowires. Domain walls are injected from a micron-sized elliptical nucleation pad at one end of the nanowire. A vortex-like structure is readily nucleated in this pad at low magnetic fields (<15Oe), whereas injection of a domain wall into the nanowire requires significantly larger fields (˜60Oe). Domain walls are pinned in the nanowire at notches patterned along the wire's edges. The domain walls are observed to have vortex-like structures with chiralities that vary in successive experiments.

  19. High resolution hard X-ray photoemission using synchrotron radiation as an essential tool for characterization of thin solid films

    International Nuclear Information System (INIS)

    Kim, J.J.; Ikenaga, E.; Kobata, M.; Takeuchi, A.; Awaji, M.; Makino, H.; Chen, P.P.; Yamamoto, A.; Matsuoka, T.; Miwa, D.; Nishino, Y.; Yamamoto, T.; Yao, T.; Kobayashi, K.

    2006-01-01

    Recently, we have shown that hard X-ray photoemission spectroscopy using undulator X-rays at SPring-8 is quite feasible with both high resolution and high throughput. Here we report an application of hard X-ray photoemission spectroscopy to the characterization of electronic and chemical states of thin solid films, for which conventional PES is not applicable. As a typical example, we focus on the problem of the scatter in the reported band-gap values for InN. We show that oxygen incorporation into the InN film strongly modifies the valence and plays a crucial role in the band gap problem. The present results demonstrate the powerful applicability of high resolution photoemission spectroscopy with hard X-rays from a synchrotron source

  20. High resolving power spectrometer for beam analysis

    Science.gov (United States)

    Moshammer, H. W.; Spencer, J. E.

    1992-03-01

    We describe a system designed to analyze the high energy, closely spaced bunches from individual RF pulses. Neither a large solid angle nor momentum range is required so this allows characteristics that appear useful for other applications such as ion beam lithography. The spectrometer is a compact, double-focusing QBQ design whose symmetry allows the Quads to range between F or D with a correspondingly large range of magnifications, dispersion, and resolving power. This flexibility insures the possibility of spatially separating all of the bunches along the focal plane with minimal transverse kicks and bending angle for differing input conditions. The symmetry of the system allows a simple geometric interpretation of the resolving power in terms of thin lenses and ray optics. We discuss the optics and the hardware that is proposed to measure emittance, energy, energy spread, and bunch length for each bunch in an RF pulse train for small bunch separations. We also discuss how to use such measurements for feedback and feedforward control of these bunch characteristics as well as maintain their stability.

  1. ZnO nanocrystals on SiO2/Si surfaces thermally cleaned in ultrahigh vacuum and characterized using spectroscopic photoemission and low energy electron microscopy

    International Nuclear Information System (INIS)

    Ericsson, Leif K. E.; Magnusson, Kjell O.; Zakharov, Alexei A.

    2010-01-01

    Thermal cleaning in ultrahigh vacuum of ZnO nanocrystals distributed on SiO 2 /Si surfaces has been studied using spectroscopic photoemission and low energy electron microscopy (SPELEEM). This study thus concern weakly bound ZnO nanocrystals covering only 5%-10% of the substrate. Chemical properties, crystallinity, and distribution of nanocrystals are used to correlate images acquired with the different techniques showing excellent correspondence. The nanocrystals are shown to be clean enough after thermal cleaning at 650 deg. C to be imaged by LEEM and x-ray PEEM as well as chemically analyzed by site selective x-ray photoelectron spectroscopy (μ-XPS). μ-XPS shows a sharp Zn 3d peak and resolve differences in O 1s states in oxides. The strong LEEM reflections together with the obtained chemical information indicates that the ZnO nanocrystals were thermally cleaned, but do not indicate any decomposition of the nanocrystals. μ-XPS was also used to determine the thickness of SiO 2 on Si. This article is the first to our knowledge where the versatile technique SPELEEM has been used to characterize ZnO nanocrystals.

  2. Study on photoemission surface of varied doping GaN photocathode

    Science.gov (United States)

    Qiao, Jianliang; Du, Ruijuan; Ding, Huan; Gao, Youtang; Chang, Benkang

    2014-09-01

    For varied doping GaN photocathode, from bulk to surface the doping concentrations are distributed from high to low. The varied doping GaN photocathode may produce directional inside electric field within the material, so the higher quantum efficiency can be obtained. The photoemission surface of varied doping GaN photocathode is very important to the high quantum efficiency, but the forming process of the surface state after Cs activation or Cs/O activation has been not known completely. Encircling the photoemission mechanism of varied GaN photocathode, considering the experiment phenomena during the activation and the successful activation results, the varied GaN photocathode surface model [GaN(Mg):Cs]:O-Cs after activation with cesium and oxygen was given. According to GaN photocathode activation process and the change of electronic affinity, the comparatively ideal NEA property can be achieved by Cs or Cs/O activation, and higher quantum efficiency can be obtained. The results show: The effective NEA characteristic of GaN can be gotten only by Cs. [GaN(Mg):Cs] dipoles form the first dipole layer, the positive end is toward the vacuum side. In the activation processing with Cs/O, the second dipole layer is formed by O-Cs dipoles, A O-Cs dipole includes one oxygen atom and two Cs atoms, and the positive end is also toward the vacuum side thus the escape of electrons can be promoted.

  3. Highly resolving computerized tomography

    International Nuclear Information System (INIS)

    Kurtz, B.; Petersen, D.; Walter, E.

    1984-01-01

    With the development of highly-resolving devices for computerized tomography, CT diagnosis of the lumbar vertebral column has gained increasing importance. As an ambulatory, non-invasive method it has proved in comparative studies to be at least equivalent to myelography in the detection of dislocations of inter-vertebral disks (4,6,7,15). Because with modern devices not alone the bones, but especially the spinal soft part structures are clearly and precisely presented with a resolution of distinctly below 1 mm, a further improvement of the results is expected as experience will increase. The authors report on the diagnosis of the lumbar vertebral column with the aid of a modern device for computerized tomography and wish to draw particular attention to the possibility of doing this investigation as a routine, and to the diagnostic value of secondary reconstructions. (BWU) [de

  4. Inverse photoemission

    International Nuclear Information System (INIS)

    Namatame, Hirofumi; Taniguchi, Masaki

    1994-01-01

    Photoelectron spectroscopy is regarded as the most powerful means since it can measure almost perfectly the occupied electron state. On the other hand, inverse photoelectron spectroscopy is the technique for measuring unoccupied electron state by using the inverse process of photoelectron spectroscopy, and in principle, the similar experiment to photoelectron spectroscopy becomes feasible. The development of the experimental technology for inverse photoelectron spectroscopy has been carried out energetically by many research groups so far. At present, the heightening of resolution of inverse photoelectron spectroscopy, the development of inverse photoelectron spectroscope in which light energy is variable and so on are carried out. But the inverse photoelectron spectroscope for vacuum ultraviolet region is not on the market. In this report, the principle of inverse photoelectron spectroscopy and the present state of the spectroscope are described, and the direction of the development hereafter is groped. As the experimental equipment, electron guns, light detectors and so on are explained. As the examples of the experiment, the inverse photoelectron spectroscopy of semimagnetic semiconductors and resonance inverse photoelectron spectroscopy are reported. (K.I.)

  5. open angle glaucoma (poag)?

    African Journals Online (AJOL)

    there is a build up of pressure due to poor outflow of aqueous humor. The outflow obstruction could occur at the trabecular meshwork of the anterior chamber angle or subsequently in the episcleral vein due to raised venous pressure. Such build up of pressure results in glaucoma . Elevated intraocular pressure remains the ...

  6. The quadriceps angle

    DEFF Research Database (Denmark)

    Miles, James Edward; Frederiksen, Jane V.; Jensen, Bente Rona

    2012-01-01

    : Pelvic limbs from red foxes (Vulpes vulpes). METHODS: Q angles were measured on hip dysplasia (HD) and whole limb (WL) view radiographs of each limb between the acetabular rim, mid-point (Q1: patellar center, Q2: femoral trochlea), and tibial tuberosity. Errors of 0.5-2.0 mm at measurement landmarks...

  7. At Right Angles

    Indian Academy of Sciences (India)

    Home; Journals; Resonance – Journal of Science Education; Volume 17; Issue 9. At Right Angles. Shailesh A Shirali. Information and Announcements Volume 17 Issue 9 September 2012 pp 920-920. Fulltext. Click here to view fulltext PDF. Permanent link: https://www.ias.ac.in/article/fulltext/reso/017/09/0920-0920 ...

  8. The lateral angle revisited

    DEFF Research Database (Denmark)

    Morgan, Jeannie; Lynnerup, Niels; Hoppa, R.D.

    2013-01-01

    This article presents the results of a validation study of a previously published method of sex determination from the temporal bone. The purpose of this study was to evaluate the lateral angle method for the internal acoustic canal for accurately determining the sex of human skeletal remains usi...... method appears to be of minimal practical use in forensic anthropology and archeology....

  9. Small angle neutron scattering

    International Nuclear Information System (INIS)

    Gupta, Sanjay

    1982-01-01

    The technique of small angle neutron scattering was first used in Germany less than two decades ago. Since then it has developed very rapidly, and today it is regarded as one of the most powerful techniques in materials, chemical and biological research. During the last decade the combination of high flux reactors and sophisticated instrumentation has revolutionized the technique. This paper endeavours to present a brief but comprehensive review of small angle scattering of neutrons and its applications in solid state research. The domain in which small angle neutron scattering is particularly useful is delineated and some of the methods used in the analysis of data are discussed with special emphasis on recent developments. Typical small angle neutron scattering cameras are described. Finally some experimental results on heterogeneities in metallic systems (both static and dynamic studies), radiation damage in materials, superconductivity, magnetic materials and the technologically very important area of non-destructive testing are reviewed in order to illustrate the wide range of applicability of this technique to problems in solid state research. (author)

  10. Neutron small angle scattering

    International Nuclear Information System (INIS)

    Ibel, K.

    1975-01-01

    The neutron small-angle scattering system at the High-Flux Reactor in Grenoble consists of three major parts: the supply of cold neutrons via bent neutron guides; the small angle camera D11; and the data handling facilities. The camera D11 has an overall length of 80 m. The effective length of the camera is variable. The length of the collimator before the fixed sample position can be reduced by movable neutron guides; the secondary flight path of 40 m full length contains detector sites in various positions. Thus, a large domain of momentum transfers can be exploited. Scattering angles between 5.10 -4 and 0.5 rad and neutron wavelengths from 0.2 to 2.0 nm are available with the same instrument and the same relative resolution. A large-area position-sensitive detector is used which allows simultaneous recording of intensities scattered into different angles; it is a multiwire proportional chamber. 3808 elements of 1 cm 2 are arranged in a two-dimensional matrix. Future development comprises an increase of the limit in the count rate due to the electronic interface between the detector and on-line computer, actually at 5.10 4 per sec. by one order of magnitude

  11. At Right Angles

    Indian Academy of Sciences (India)

    Home; Journals; Resonance – Journal of Science Education; Volume 17; Issue 9. At Right Angles. Shailesh A Shirali. Information and Announcements Volume 17 Issue 9 September 2012 pp 920-920. Fulltext. Click here to view fulltext PDF. Permanent link: http://www.ias.ac.in/article/fulltext/reso/017/09/0920-0920 ...

  12. Dynamical Processes in Open Quantum Systems from a TDDFT Perspective: Resonances and Electron Photoemission.

    Science.gov (United States)

    Larsen, Ask Hjorth; De Giovannini, Umberto; Rubio, Angel

    2016-01-01

    We present a review of different computational methods to describe time-dependent phenomena in open quantum systems and their extension to a density-functional framework. We focus the discussion on electron emission processes in atoms and molecules addressing excited-state lifetimes and dissipative processes. Initially we analyze the concept of an electronic resonance, a central concept in spectroscopy associated with a metastable state from which an electron eventually escapes (electronic lifetime). Resonances play a fundamental role in many time-dependent molecular phenomena but can be rationalized from a time-independent context in terms of scattering states. We introduce the method of complex scaling, which is used to capture resonant states as localized states in the spirit of usual bound-state methods, and work on its extension to static and time-dependent density-functional theory. In a time-dependent setting, complex scaling can be used to describe excitations in the continuum as well as wave packet dynamics leading to electron emission. This process can also be treated by using open boundary conditions which allow time-dependent simulations of emission processes without artificial reflections at the boundaries (i.e., borders of the simulation box). We compare in detail different schemes to implement open boundaries, namely transparent boundaries using Green functions, and absorbing boundaries in the form of complex absorbing potentials and mask functions. The last two are regularly used together with time-dependent density-functional theory to describe the electron emission dynamics of atoms and molecules. Finally, we discuss approaches to the calculation of energy and angle-resolved time-dependent pump-probe photoelectron spectroscopy of molecular systems.

  13. A theoretical investigation of photoemission spectra from (GaAs).sub.2./sub. (AlAs).sub.2./sub. superlattices

    Czech Academy of Sciences Publication Activity Database

    Strasser, T.; Solterbeck, C.; Schattke, W.; Bartoš, Igor; Cukr, Miroslav; Jiříček, Petr; Fadley, C. S.; Van Hove, M. A.

    114-116, - (2001), s. 1127-1132 ISSN 0368-2048 Institutional research plan: CEZ:A02/98:Z1-010-914 Keywords : superlattices * III/V semiconductors * photoemission * one-step model Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.259, year: 2001

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

    NARCIS (Netherlands)

    Alkemade, C.T.J.

    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

  15. 3d spin-orbit photoemission spectrum of nonferromagnetic materials : The test cases of CoO and Cu

    NARCIS (Netherlands)

    Ghiringhelli, G; Tjeng, LH; Tanaka, A; Tjernberg, O; Mizokawa, T; de Boer, JL; Brookes, NB

    2002-01-01

    The x-ray photoemission spectrum of the valence states of 3d transition-metal systems is spin polarized when using circularly polarized photons. The integral of the spin-orbit spectrum is proportional to the expectation value of the angular part of the 3d spin-orbit operator in the initial state. We

  16. Resolving inventory differences

    International Nuclear Information System (INIS)

    Weber, J.H.; Clark, J.P.

    1991-01-01

    Determining the cause of an inventory difference (ID) that exceeds warning or alarm limits should not only involve investigation into measurement methods and reexamination of the model assumptions used in the calculation of the limits, but also result in corrective actions that improve the quality of the accountability measurements. An example illustrating methods used by Savannah River Site (SRS) personnel to resolve an ID is presented that may be useful to other facilities faced with a similar problem. After first determining that no theft or diversion of material occurred and correcting any accountability calculation errors, investigation into the IDs focused on volume and analytical measurements, limit of error of inventory difference (LEID) modeling assumptions, and changes in the measurement procedures and methods prior to the alarm. There had been a gradual gain trend in IDs prior to the alarm which was reversed by the alarm inventory. The majority of the NM in the facility was stored in four large tanks which helped identify causes for the alarm. The investigation, while indicating no diversion or theft, resulted in changes in the analytical method and in improvements in the measurement and accountability that produced a 67% improvement in the LEID

  17. Time-resolved studies

    International Nuclear Information System (INIS)

    Mills, D.M.

    1992-01-01

    When new or more powerful probes become available that offer both shorter data-collection times and the opportunity to apply innovative approaches to established techniques, it is natural that investigators consider the feasibility of exploring the kinetics of time-evolving systems. This stimulating area of research not only can lead to insights into the metastable or excited states that a system may populate on its way to a ground state, but can also lead to a better understanding of that final state. Synchrotron radiation, with its unique properties, offers just such a tool to extend X-ray measurements from the static to the time-resolved regime. The most straight-forward application of synchrotron radiation to the study of transient phenomena is directly through the possibility of decreased data-collection times via the enormous increase in flux over that of a laboratory X-ray system. Even further increases in intensity can be obtained through the use of novel X-ray optical devices. Widebandpass monochromators, e.g., that utilize the continuous spectral distribution of synchrotron radiation, can increase flux on the sample several orders of magnitude over conventional X-ray optical systems thereby allowing a further shortening of the data-collection time. Another approach that uses the continuous spectral nature of synchrotron radiation to decrease data-collection times is the open-quote parallel data collectionclose quotes method. Using this technique, intensities as a function of X-ray energy are recorded simultaneously for all energies rather than sequentially recording data at each energy, allowing for a dramatic decrease in the data-collection time

  18. Aberration correction in photoemission microscopy and applications in photonics and plasmonics

    Energy Technology Data Exchange (ETDEWEB)

    Koenenkamp, Rolf [Portland State Univ., Portland, OR (United States)

    2017-09-28

    We report on the design, assembly, operation and application of an aberration-corrected photoemission electron microscope. The instrument used novel hyperbolic mirror-correctors with two and three electrodes that allowed simultaneous correction of spherical and chromatic aberrations. A spatial resolution of 5.4nm was obtained with this instrument in 2009, and 4.7nm in subsequent years. New imaging methodology was introduced involving interferometric imaging of light diffraction. This methodology was applied in nano-photonics and in the characterization of surface-plasmon polaritons. Photonic crystals and waveguides, optical antennas and new plasmonic devices such as routers, localizers and filters were designed and demonstrated using the new capabilities offered by the microscope.

  19. Influence of Al fraction on photoemission performance of AlGaN photocathode.

    Science.gov (United States)

    Hao, Guanghui; Chang, Benkang; Shi, Feng; Zhang, Junju; Zhang, Yijun; Chen, Xinlong; Jin, Muchun

    2014-06-10

    To research the photoemission performance of a transmission-mode Al(1-x)Ga(x)N photocathode, Al0.24Ga0.76N and GaN photocathodes with the same structure were activated, their spectral responses were measured using a multi-information measurement system at room temperature, and the photocathode parameters were obtained by fitting quantum efficiency curves. The results showed that both the reflective-mode and transmission-mode spectral responses of the AlGaN photocathode were lower than those of the GaN photocathode. Compared with the GaN photocathode, the short-wavelength spectral response of the Al0.24Ga0.76N photocathode was less seriously affected by lattice defects between the buffer and emission layers. The Al atom at the AlGaN photocathode surface could affect the optimal Cs adsorption position, which mainly affects the surface electron escape probability of the photocathode.

  20. A new aberration correction method for photoemission electron microscopy by means of moving focus

    International Nuclear Information System (INIS)

    Koshikawa, T; Shimizu, H; Amakawa, R; Ikuta, T; Yasue, T; Bauer, E

    2005-01-01

    A new aberration correction method has been developed for photoemission electron microscopy (PEEM). In order to correct the spherical and chromatic aberrations, a moving focus method was adopted. Several experimental limitations to achieving optimal resolution have also been overcome. A high brightness Hg lamp system has been developed to overcome the insufficient brightness of the conventional Hg lamp. An improvement of brightness by over 100 times as compared with the conventional lamp was achieved. Image blur was also found due to a weak environmental AC magnetic field caused by essential microscope components, i.e., the power transformer and CCD camera. After implementing the high brightness lamp and eliminating stray magnetic field by proper shielding, preliminary experiments demonstrate that aberration correction by moving focus can improve the PEEM image resolution

  1. Common Features in Electronic Structure of the Oxypnictide Superconductors from Photoemission Spectroscopy

    International Nuclear Information System (INIS)

    Xiao-Wen, Jia; Hai-Yun, Liu; Wen-Tao, Zhang; Lin, Zhao; Jian-Qiao, Meng; Guo-Dong, Liu; Xiao-Li, Dong; Zhi-An, Ren; Wei, Yi; Guang-Can, Che; Zhong-Xian, Zhao; Gang, Wu; Rong-Hua, Liu; Xian-Hui, Chen; Gen-Fu, Chen; Nan-Lin, Wang; Yong, Zhu; Xiao-Yang, Wang; Gui-Ling, Wang; Yong, Zhou

    2008-01-01

    High resolution photoemission measurements are carried out on non-superconducting LaFeAsO parent compound and various superconducting RFeAs(O 1-x F x ) (R=La, Ce and Pr) compounds. It is found that the parent LaFeAsO compound shows a metallic character. By extensive measurements, several common features are identified in the electronic structure of these Fe-based compounds: (1) 0.2 eV feature in the valence band, (2) a universal 13-16 meV feature, (3) near Ef spectral weight suppression with decreasing temperature. These universal features can provide important information about band structure, superconducting gap and pseudogap in these Fe-based materials

  2. Hard X-ray PhotoEmission Spectroscopy of strongly correlated systems

    Science.gov (United States)

    Panaccione, Giancarlo; Offi, Francesco; Sacchi, Maurizio; Torelli, Piero

    2008-06-01

    Hard X-ray PhotoEmission Spectroscopy (HAXPES) is a new tool for the study of bulk electronic properties of solids using synchrotron radiation. We review recent achievements of HAXPES, with particular reference to the VOLPE project, showing that high energy resolution and bulk sensitivity can be obtained at kinetic energies of 6-8 keV. We present also the results of recent studies on strongly correlated materials, such as vanadium sesquioxide and bilayered manganites, revealing the presence of different screening properties in the bulk with respect to the surface. We discuss the relevant experimental features of the metal-insulator transition in these materials. To cite this article: G. Panaccione et al., C. R. Physique 9 (2008).

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

    Directory of Open Access Journals (Sweden)

    G. Biasotto

    2010-01-01

    Full Text Available CaBi4Ti4O15 (CBTi144 thin films were grown on Pt/Ti/SiO2/Si substrates using a soft chemical solution and spin-coating method. Structure and morphology of the films were characterized by the X-ray Diffraction (XRD, Fourier-transform infrared spectroscopy (FT-IR, Raman analysis, X-ray photoemission spectroscopy (XPS, and transmission electron microscopy (TEM. The films present a single phase of layered-structured perovskite with polar axis orient. The a/b-axis orientation of the ferroelectric film is considered to be associated with the preferred orientation of the Pt bottom electrode. XPS measurements were employed to understand the nature of defects on the retention behavior of CBTi144 films. We have observed that the main source of retention-free characteristic of the capacitors is the oxygen environment in the CBTi144 lattice.

  4. Absence of U 5f band states in resonant photoemission spectra of UPd2Al3

    Science.gov (United States)

    Fujimori, Shin-Ichi; Saito, Yasuharu; Seki, Masaharu; Tamura, Koji; Mizuta, Munenori; Yamaki, Ken-Ichiro; Sato, Ken; Tanaka, Akinori; Sato, Noriaki; Suzuki, Shoji; Sato, Shigeru; Okane, Tetsuo; Komatsubara, Takemi; Tezuka, Yasuhisa; Shin, Shik; Ishii, Takehiko

    1999-04-01

    The U 5f spectral weight of UxLa1-xPd2Al3 (x=0.1, 0.25, 0.6, and 1.0) is obtained by the resonant photoemission spectroscopy (RPES), and is compared with the results of the band-structure calculations. We have found that the spectrum of UPd2Al3 (x=1) could not be reproduced by the calculated U 5f density of states in shape and position, even if the contribution from U 6d states is considered. Moreover, the essential spectral shape did not change until x=0.1, where most of the uranium atoms are substituted with lanthanum atoms. All these results indicate that the U 5f band states are not observed in the RPES spectrum of UPd2Al3, and the single site effects govern it.

  5. The interaction of oxygen with TiC(001): Photoemission and first-principles studies

    International Nuclear Information System (INIS)

    Rodriguez, J.A.; Liu, P.; Dvorak, J.; Jirsak, T.; Gomes, J.; Takahashi, Y.; Nakamura, K.

    2004-01-01

    High-resolution photoemission and first-principles density-functional slab calculations were used to study the interaction of oxygen with a TiC(001) surface. Atomic oxygen is present on the TiC(001) substrate after small doses of O 2 at room temperature. A big positive shift (1.5-1.8 eV) was detected for the C 1s core level. These photoemission studies suggest the existence of strong O↔C interactions. A phenomenon corroborated by the results of first-principles calculations, which show a CTiTi hollow as the most stable site for the adsorption of O. Ti and C atoms are involved in the adsorption and dissociation of the O 2 molecule. In general, the bond between O and the TiC(001) surface contains a large degree of ionic character. The carbide→O charge transfer is substantial even at high coverages (>0.5 ML) of oxygen. At 500 K and large doses of O 2 , oxidation of the carbide surface occurs with the removal of C and formation of titanium oxides. There is an activation barrier for the exchange of Ti-C and Ti-O bonds which is overcome only by the formation of C-C or C-O bonds on the surface. The mechanism for the removal of a C atom as CO gas involves a minimum of two O adatoms, and three O adatoms are required for the formation of CO 2 gas. Due to the high stability of TiC, an O adatom alone cannot induce the generation of a C vacancy in a flat TiC(001) surface

  6. Progresses in low energy electron microscopy and photoemission electron microscopy studies (LEEM and PEEM)

    International Nuclear Information System (INIS)

    Koshikawa, Takanori; Yasue, Tsuneo; Kobayashi, Keisuke; Kinoshita, Toyohiko; Ono, Kanta

    2008-02-01

    Photon factory workshop on low energy electron microscopy (LEEM) and photoemission electron microscopy (PEEM) studies was held on October 12-13, 2005. The workshop had 18 presentations and 8 contributions to the poster session with 62 attendees. The workshop started with an invitation presentation about nano-imaging and nano-spectroscopy by photoemission electron microscope using synchrotron radiation x-rays. Next two reports were about antiferromagnetic domain structure observations of a NiO(100) surface using a combined method of PEEM and soft x-ray linear dichroism. Recent development of spin SEM (scanning electron microscope) and the observation of magnetic domains of La 1.36 Sr 1.64 Mn 2 O 7 were reported. A new method for observing magnetic domain structures with SEM was developed in which the image is the result of spin polarization of secondary electrons. This method is called spin SEM. A lecture about observation of ultra-high speed phenomena by PEEM and the invitation presentation about spin dynamics in nano-scale magnetic materials attracted much attention. Structural studies of surfaces by LEEM and PEEM were actively discussed. Summaries about the measurements of Au-Si alloy island at atomic steps on Si(111), fabrication of Ga nano-dots in SiO 2 , growth of pentacene films on thin bismuth film and graphite, the surface phase transition on metal surfaces of In/Cu(001) and Sn/Cu(001), and Cu thin film growth on W(110) were also compiled in this report. Many contributions in this report were resulted from the experiments by LEEM and PEEM using SPring-8 synchrotron radiations. (Y.K.)

  7. Magnetic dichroism in photoemission: a new element-specific magnetometer with atomic-layer resolution

    International Nuclear Information System (INIS)

    Starke, K.; Arenholz, E.; Kaindl, G.

    1998-01-01

    Full text: Magnetic coupling in layered metallic structures has become a key issue in thin-film magnetism since the observation of oscillatory exchange coupling across non-ferromagnetic spacer layers. Although this phenomenon was discovered in rare earths (RE) superlattices, mostly transition-metal systems have been studied and are now applied in data-storage industry. An understanding of the coupling mechanisms has been reached after a fabrication of high-quality interfaces became possible. It allowed, in particular, the experimental finding of induced ferromagnetic order in 'nonmagnetic' atomic layers near an interface, using element-specific probes such as magnetic circular dichroism in x-ray absorption. - In layered RE systems, by contrast, the well known intermiscibility has prevented a preparation of atomically sharp interfaces, and all RE superlattices studied so far showed interdiffusion zones of several atomic layers. In the present overview, we report the first fabrication of atomically flat heteromagnetic RE interfaces, their structural characterization and their magnetic analysis using magnetic dichroism in photoemission (MDPE). This new tool gives access to the magnetization of individual atomic layers near interfaces in favourite cases. Merits of MDPE as a magnetometer are demonstrated at the example of Eu/Gd(0001), where chemical shifts of core-level photoemission lines allow to spectroscopically separate up to four different atomic layers. The high surface sensitivity of MDPE, together with the well known dependence of the core-level binding energies on the coordination number of the photo emitting atom, opens the door to future site-specific studies of magnetism in sub-monolayer systems such as 'nanowires'

  8. Characterizing the effects of regolith surface roughness on photoemission from surfaces in space

    Science.gov (United States)

    Dove, A.; Horanyi, M.; Wang, X.

    2017-12-01

    Surfaces of airless bodies and spacecraft in space are exposed to a variety of charging environments. A balance of currents due to plasma bombardment, photoemission, electron and ion emission and collection, and secondary electron emission determines the surface's charge. Photoelectron emission is the dominant charging process on sunlit surfaces in the inner solar system due to the intense solar UV radiation. This can result in a net positive surface potential, with a cloud of photoelectrons immediately above the surface, called the photoelectron sheath. Conversely, the unlit side of the body will charge negatively due the collection of the fast-moving solar wind electrons. The interaction of charged dust grains with these positively and negatively charged surfaces, and within the photoelectron and plasma sheaths may explain the occurrence of dust lofting, levitation and transport above the lunar surface. The surface potential of exposed objects is also dependent on the material properties of their surfaces. Composition and particle size primarily affect the quantum efficiency of photoelectron generation; however, surface roughness can also control the charging process. In order to characterize these effects, we have conducted laboratory experiments to examine the role of surface roughness in generating photoelectrons in dedicated laboratory experiments using solid and dusty surfaces of the same composition (CeO2), and initial comparisons with JSC-1 lunar simulant. Using Langmuir probe measurements, we explore the measured potentials above insulating surfaces exposed to UV and an electric field, and we show that the photoemission current from a dusty surface is largely reduced due to its higher surface roughness, which causes a significant fraction of the emitted photoelectrons to be re-absorbed within the surface. We will discuss these results in context of similar situations on planetary surfaces.

  9. Metasurface Enabled Wide-Angle Fourier Lens.

    Science.gov (United States)

    Liu, Wenwei; Li, Zhancheng; Cheng, Hua; Tang, Chengchun; Li, Junjie; Zhang, Shuang; Chen, Shuqi; Tian, Jianguo

    2018-04-19

    Fourier optics, the principle of using Fourier transformation to understand the functionalities of optical elements, lies at the heart of modern optics, and it has been widely applied to optical information processing, imaging, holography, etc. While a simple thin lens is capable of resolving Fourier components of an arbitrary optical wavefront, its operation is limited to near normal light incidence, i.e., the paraxial approximation, which puts a severe constraint on the resolvable Fourier domain. As a result, high-order Fourier components are lost, resulting in extinction of high-resolution information of an image. Other high numerical aperture Fourier lenses usually suffer from the bulky size and costly designs. Here, a dielectric metasurface consisting of high-aspect-ratio silicon waveguide array is demonstrated experimentally, which is capable of performing 1D Fourier transform for a large incident angle range and a broad operating bandwidth. Thus, the device significantly expands the operational Fourier space, benefitting from the large numerical aperture and negligible angular dispersion at large incident angles. The Fourier metasurface will not only facilitate efficient manipulation of spatial spectrum of free-space optical wavefront, but also be readily integrated into micro-optical platforms due to its compact size. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  10. Empirical relationship between x-ray photoemission spectra and electrical conductivity in a colossal magnetoresistive manganite La_{1-x}Sr_{x}MnO_{3}

    OpenAIRE

    Hishida, T.; Ohbayashi, K.; Kobata, M.; Ikenaga, E.; Sugiyama, T.; Kobayashi, K.; Okawa, M.; Saitoh, T.

    2013-01-01

    By using laboratory x-ray photoemission spectroscopy (XPS) and hard x-ray photoemission spectroscopy (HX-PES) at a synchrotron facility, we report an empirical semi-quantitative relationship between the valence/core-level x-ray photoemission spectral weight and electrical conductivity in La_{1-x}Sr_{x}MnO_{3} as a function of x. In the Mn 2p_{3/2} HX-PES spectra, we observed the shoulder structure due to the Mn^{3+} well-screened state. However, the intensity at x=0.8 was too small to explain...

  11. Spatially resolved investigation of all optical magnetization switching in TbFe alloys.

    Science.gov (United States)

    Arora, Ashima; Mawass, Mohamad-Assaad; Sandig, Oliver; Luo, Chen; Ünal, Ahmet A; Radu, Florin; Valencia, Sergio; Kronast, Florian

    2017-08-25

    Optical control of magnetization using femtosecond laser without applying any external magnetic field offers the advantage of switching magnetic states at ultrashort time scales. Recently, all-optical helicity-dependent switching (AO-HDS) has drawn a significant attention for potential information and data storage device applications. In this work, we employ element and magnetization sensitive photoemission electron microscopy (PEEM) to investigate the role of heating in AO-HDS for thin films of the rare-earth transition-metal alloy TbFe. Spatially resolved measurements in a 3-5 μm sized stationary laser spot demonstrate that AO-HDS is a local phenomenon in the vicinity of thermal demagnetization in a 'ring' shaped region. The efficiency of AO-HDS further depends on a local temperature profile around the demagnetized region and thermally activated domain wall motion. We also demonstrate that the thickness of the film determines the preferential switching direction for a particular helicity.

  12. Recent trends in spin-resolved photoelectron spectroscopy

    Science.gov (United States)

    Okuda, Taichi

    2017-12-01

    Since the discovery of the Rashba effect on crystal surfaces and also the discovery of topological insulators, spin- and angle-resolved photoelectron spectroscopy (SARPES) has become more and more important, as the technique can measure directly the electronic band structure of materials with spin resolution. In the same way that the discovery of high-Tc superconductors promoted the development of high-resolution angle-resolved photoelectron spectroscopy, the discovery of this new class of materials has stimulated the development of new SARPES apparatus with new functions and higher resolution, such as spin vector analysis, ten times higher energy and angular resolution than conventional SARPES, multichannel spin detection, and so on. In addition, the utilization of vacuum ultra violet lasers also opens a pathway to the realization of novel SARPES measurements. In this review, such recent trends in SARPES techniques and measurements will be overviewed.

  13. Test technology on divergence angle of laser range finder based on CCD imaging fusion

    Science.gov (United States)

    Shi, Sheng-bing; Chen, Zhen-xing; Lv, Yao

    2016-09-01

    Laser range finder has been equipped with all kinds of weapons, such as tank, ship, plane and so on, is important component of fire control system. Divergence angle is important performance and incarnation of horizontal resolving power for laser range finder, is necessary appraised test item in appraisal test. In this paper, based on high accuracy test on divergence angle of laser range finder, divergence angle test system is designed based on CCD imaging, divergence angle of laser range finder is acquired through fusion technology for different attenuation imaging, problem that CCD characteristic influences divergence angle test is solved.

  14. Relationship between the angle of repose and angle of internal ...

    African Journals Online (AJOL)

    Abstract. Click on the link to view the abstract. Keywords: Angle of repose, angle of internal friction, granular materials, triaxial compression machine, moisture content. Tanzania J. Agric. Sc. (1998) Vol.1 No.2, 187-194 ...

  15. Critical angle laser refractometer

    International Nuclear Information System (INIS)

    Castrejon-Pita, J.R.; Morales, A.; Castrejon-Garcia, R.

    2006-01-01

    A simple laser refractometer based on the detection of the critical angle for liquids is presented. The calibrated refractometer presents up to 0.000 11 of uncertainty when the refractive index is in the range between 1.300 00 and 1.340 00. The experimental setup is easy to construct and the material needed is available at most optics laboratories. The calibration method is simple and can be used in other devices. The refractive index measurements in aqueous solutions of sodium chloride were carried out to test the device and a linear dependence between the refractive index and the salt concentration was found

  16. Studies in small angle scattering techniques

    International Nuclear Information System (INIS)

    Moellenbach, K.

    1980-03-01

    Small angle scattering of neutrons, X-rays and γ-rays are found among the spectroscopic methods developed in the recent years. Although these techniques differ from each other in many respects, e.g. radiation sources and technical equipment needed, their power to resolve physical phenomena and areas of application can be discussed in a general scheme. Selected examples are given illustrating the use of specific technical methods. Jahn-Teller driven structural phase transitions in Rare Earth zircons were studied with neutron scattering as well as small angle γ-ray diffraction. The study of neutron scattering from formations of magnetic domains in the Ising ferromagnet LiTbF 4 is a second example. Both these examples represent more than experimental test cases since the theoretical interpretations of the data obtained are discussed as well. As a last example the use of small angle scattering methods for the study of molecular biological samples is discussed. In particular the experimental procedures used in connection with scattering from aqueous solutions of proteins and protein complexes are given. (Auth.)

  17. THE ALGOL TRIPLE SYSTEM SPATIALLY RESOLVED AT OPTICAL WAVELENGTHS

    International Nuclear Information System (INIS)

    Zavala, R. T.; Hutter, D. J.; Hummel, C. A.; Boboltz, D. A.; Ojha, R.; Shaffer, D. B.; Tycner, C.; Richards, M. T.

    2010-01-01

    Interacting binaries typically have separations in the milliarcsecond regime, and hence it has been challenging to resolve them at any wavelength. However, recent advances in optical interferometry have improved our ability to discern the components in these systems and have now enabled the direct determination of physical parameters. We used the Navy Prototype Optical Interferometer to produce for the first time images resolving all three components in the well-known Algol triple system. Specifically, we have separated the tertiary component from the binary and simultaneously resolved the eclipsing binary pair, which represents the nearest and brightest eclipsing binary in the sky. We present revised orbital elements for the triple system, and we have rectified the 180 0 ambiguity in the position angle of Algol C. Our directly determined magnitude differences and masses for this triple star system are consistent with earlier light curve modeling results.

  18. Scaling of misorientation angle distributions

    DEFF Research Database (Denmark)

    Hughes, D.A.; Chrzan, D.C.; Liu, Q.

    1998-01-01

    The measurement of misorientation angle distributions following different amounts of deformation in cold-rolled aluminum and nickel and compressed stainless steel is reported. The sealing of the dislocation cell boundary misorientation angle distributions is studied. Surprisingly, the distributio...

  19. Angle performance on optima MDxt

    Energy Technology Data Exchange (ETDEWEB)

    David, Jonathan; Kamenitsa, Dennis [Axcelis Technologies, Inc., 108 Cherry Hill Dr, Beverly, MA 01915 (United States)

    2012-11-06

    Angle control on medium current implanters is important due to the high angle-sensitivity of typical medium current implants, such as halo implants. On the Optima MDxt, beam-to-wafer angles are controlled in both the horizontal and vertical directions. In the horizontal direction, the beam angle is measured through six narrow slits, and any angle adjustment is made by electrostatically steering the beam, while cross-wafer beam parallelism is adjusted by changing the focus of the electrostatic parallelizing lens (P-lens). In the vertical direction, the beam angle is measured through a high aspect ratio mask, and any angle adjustment is made by slightly tilting the wafer platen prior to implant. A variety of tests were run to measure the accuracy and repeatability of Optima MDxt's angle control. SIMS profiles of a high energy, channeling sensitive condition show both the cross-wafer angle uniformity, along with the small-angle resolution of the system. Angle repeatability was quantified by running a channeling sensitive implant as a regular monitor over a seven month period and measuring the sheet resistance-to-angle sensitivity. Even though crystal cut error was not controlled for in this case, when attributing all Rs variation to angle changes, the overall angle repeatability was measured as 0.16 Degree-Sign (1{sigma}). A separate angle repeatability test involved running a series of V-curves tests over a four month period using low crystal cut wafers selected from the same boule. The results of this test showed the angle repeatability to be <0.1 Degree-Sign (1{sigma}).

  20. Variable angle correlation spectroscopy

    International Nuclear Information System (INIS)

    Lee, Y.K.; Lawrence Berkeley Lab., CA

    1994-05-01

    In this dissertation, a novel nuclear magnetic resonance (NMR) technique, variable angle correlation spectroscopy (VACSY) is described and demonstrated with 13 C nuclei in rapidly rotating samples. These experiments focus on one of the basic problems in solid state NMR: how to extract the wealth of information contained in the anisotropic component of the NMR signal while still maintaining spectral resolution. Analysis of the anisotropic spectral patterns from poly-crystalline systems reveal information concerning molecular structure and dynamics, yet in all but the simplest of systems, the overlap of spectral patterns from chemically distinct sites renders the spectral analysis difficult if not impossible. One solution to this problem is to perform multi-dimensional experiments where the high-resolution, isotropic spectrum in one dimension is correlated with the anisotropic spectral patterns in the other dimensions. The VACSY technique incorporates the angle between the spinner axis and the static magnetic field as an experimental parameter that may be incremented during the course of the experiment to help correlate the isotropic and anisotropic components of the spectrum. The two-dimensional version of the VACSY experiments is used to extract the chemical shift anisotropy tensor values from multi-site organic molecules, study molecular dynamics in the intermediate time regime, and to examine the ordering properties of partially oriented samples. The VACSY technique is then extended to three-dimensional experiments to study slow molecular reorientations in a multi-site polymer system

  1. Variable angle correlation spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Young Kyo [Univ. of California, Berkeley, CA (United States)

    1994-05-01

    In this dissertation, a novel nuclear magnetic resonance (NMR) technique, variable angle correlation spectroscopy (VACSY) is described and demonstrated with 13C nuclei in rapidly rotating samples. These experiments focus on one of the basic problems in solid state NMR: how to extract the wealth of information contained in the anisotropic component of the NMR signal while still maintaining spectral resolution. Analysis of the anisotropic spectral patterns from poly-crystalline systems reveal information concerning molecular structure and dynamics, yet in all but the simplest of systems, the overlap of spectral patterns from chemically distinct sites renders the spectral analysis difficult if not impossible. One solution to this problem is to perform multi-dimensional experiments where the high-resolution, isotropic spectrum in one dimension is correlated with the anisotropic spectral patterns in the other dimensions. The VACSY technique incorporates the angle between the spinner axis and the static magnetic field as an experimental parameter that may be incremented during the course of the experiment to help correlate the isotropic and anisotropic components of the spectrum. The two-dimensional version of the VACSY experiments is used to extract the chemical shift anisotropy tensor values from multi-site organic molecules, study molecular dynamics in the intermediate time regime, and to examine the ordering properties of partially oriented samples. The VACSY technique is then extended to three-dimensional experiments to study slow molecular reorientations in a multi-site polymer system.

  2. Resolved Hapke parameter maps of the Moon

    Science.gov (United States)

    Sato, H.; Robinson, M. S.; Hapke, B.; Denevi, B. W.; Boyd, A. K.

    2014-08-01

    We derived spatially resolved near-global Hapke photometric parameter maps of the Moon from 21 months of Lunar Reconnaissance Orbiter Camera (LROC) Wide Angle Camera (WAC) multispectral observations using a novel "tile-by-tile method" (1° latitude by 1° longitude bins). The derived six parameters (w,b,c,BS0,hS, andθ¯p) for each tile were used to normalize the observed reflectance (standard angles i = g = 60°, e = 0° instead of the traditional angles i = g = 30°, e = 0°) within each tile, resulting in accurate normalization optimized for the local photometric response. Each pixel in the seven-color near-global mosaic (70°S to 70°N and 0°E to 360°E) was computed by the median of normalized reflectance from large numbers of repeated observations (UV: ˜50 and visible: ˜126 on average). The derived mosaic exhibits no significant artifacts with latitude or along the tile boundaries, demonstrating the quality of the normalization procedure. The derived Hapke parameter maps reveal regional photometric response variations across the lunar surface. The b, c (Henyey-Greenstein double-lobed phase function parameters) maps demonstrate decreased backscattering in the maria relative to the highlands (except 321 nm band), probably due to the higher content of both SMFe (submicron iron) and ilmenite in the interiors of back scattering agglutinates in the maria. The hS (angular width of shadow hiding opposition effect) map exhibits relatively lower values in the maria than the highlands and slightly higher values for immature highland crater ejecta, possibly related to the variation in a grain size distribution of regolith.

  3. Photoemission spectroscopy of the charge-ordering transition in Pr0.5Sr0.5MnO3

    International Nuclear Information System (INIS)

    Chainani, A.; Kumigashira, H.; Takahashi, T.; Tomioka, Y.; Kuwahara, H.; Tokura, Y.

    1996-01-01

    In this paper, the electronic structure of the magnetite Pr 0.5 Sr 0.5 MnO 3 across the charge ordering transition is studied using temperature-dependent photoemission spectroscopy. Ultra-violet photoemission spectroscopy have been performed as a function of temperature (25-300K) to investigate the changes in the single-particle density of states across the metal-nonmetal and the para-ferro transitions

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

    CERN Document Server

    Sekiyama, A

    2003-01-01

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

  5. Calculation of fluctuations and photoemission properties in a tetrahedral-cluster model for an intermediate-valence system

    International Nuclear Information System (INIS)

    Reich, A.; Falicov, L.M.

    1986-01-01

    An exact solution of a four-site tetrahedral-crystal model, the smallest face-centered-cubic crystal, is presented in the case of an intermediate-valence system. The model consists of the following: (a) one extended orbital and one localized orbital per atom, (b) an interatomic transfer term between extended orbitals, (c) an interatomic hybridization between the localized and extended orbitals, (d) strong intra-atomic Coulomb repulsion between opposite-spin localized states, and (e) intermediate-strength intra-atomic Coulomb repulsion between the localized and extended states. These competing effects are examined as they manifest themselves in the intermediate-valence, photoemission, inverse-photoemission, and thermodynamic properties

  6. Small angle neutron scattering

    International Nuclear Information System (INIS)

    Dasannacharya, B.A.; Goyal, P.S.

    1997-01-01

    Small angle neutron scattering (SANS) is one of the most popular neutron scattering technique both for the basic research and as a tool in the hands of applied scientist. SANS is used for studying the structure of a material on a length scale of 10 - 1000 A. SANS is a diffraction experiment that involves scattering of a monocromatic beam of neutrons in order to obtain structural information about macromolecules and heterogeneities. This paper will discuss the design of SANS spectrometers with a special emphasis on the instruments which are better suited for medium flux reactors. The design of several different types of SANS spectrometers will be given. The optimization procedures and appropriate modifications to suit the budget and the space will be discussed. As an example, the design of a SANS spectrometer at CIRUS reactor Trombay will be given. (author)

  7. Femto-second dynamics probed by resonant photoemission and coincidence techniques

    International Nuclear Information System (INIS)

    Miron, C.; Ceolin, D.; Morin, P.

    2004-01-01

    Full text: It is well known nowadays that inner-shell excitation induces very rich dynamics where nuclear motion and electronic decay compete on a very short time scale, like in the case of ultra-fast molecular dissociation. Since the st experimental evidence was given by P. Morin and I. Nenner in 1986 for HBr and until now, it was shown that it acted as a general phenomenon taking place in a large variety of molecular systems. A nice consequence of such a process was shown by Prof. Svensson's group in Sweden by resonant photoemission measurements of the decay of the O 1s → σ * core-excited state in O 2 : the Auger-Doppler effect. More recently, a Japanese group demonstrated that the Auger-Doppler effect may be employed as a probe of the Auger emission anisotropy. The present talk will mainly deal with the mechanisms of intra-molecular ultra-fast chemical reaction pathways induced by inner-shell excitation and probed by energy selected resonant Auger electron-ion coincidences (ES-RAEPICO) and resonant photoemission measurements. Such a reactive pathway could be revealed through the appearance of rearrangement products. The dynamics of such ultra-fast chemical reactions, if they occur, will be entirely governed by the competition between the nuclear motion in the core-excited state and electronic decay (Auger decay). Since the chemical reaction is able to occur only during the lifetime of the core-excited state, the Auger decay may be seen in this context as a chemical reaction inhibitor, which leads the excited system towards a different relaxation pathway. The measurement in coincidence of the kinetic energy of the ejected Auger electrons and of fragment ions is able to reveal in such a case the energetics and kinematics of the possible decay mechanisms. Moreover, the photon energy detuning with respect to the nominal core-excitation energy allows changing the energy of the reactants and influence the chemical dynamics on a femtosecond time scale

  8. Direct comparison of photoemission spectroscopy and in situ Kelvin probe work function measurements on indium tin oxide films

    International Nuclear Information System (INIS)

    Beerbom, M.M.; Laegel, B.; Cascio, A.J.; Doran, B.V.; Schlaf, R.

    2006-01-01

    The work function of commercially available indium tin oxide (ITO) films on glass substrates was measured using photoemission spectroscopy (PES) and ultra-high vacuum (UHV) Kelvin probe in direct comparison. Absolute Kelvin probe work function values were determined via calibration of the measured contact potential difference (CPD) using an in situ sputtered Au reference sample. The Kelvin probe data confirmed that ultraviolet photoemission spectroscopy (UPS) measurements change the work function of ITO surfaces previously exposed to ambient environment, when measured without in situ surface cleaning procedures. The results also demonstrate that both Kelvin probe and PES yield virtually identical work function values, as long as the Kelvin probe data are calibrated against a known standard. As a consequence, previously reported higher work function values determined with Kelvin probe as compared to values obtained with UPS on similar samples are likely related to a photochemically generated surface dipole during UPS measurements. Comparison between Kelvin probe and low intensity X-ray photoemission spectroscopy (LIXPS) work function measurements demonstrated that accurate work function measurements on ITO previously exposed to the ambient are possible with PES

  9. Time resolved techniques: An overview

    International Nuclear Information System (INIS)

    Larson, B.C.; Tischler, J.Z.

    1990-06-01

    Synchrotron sources provide exceptional opportunities for carrying out time-resolved x-ray diffraction investigations. The high intensity, high angular resolution, and continuously tunable energy spectrum of synchrotron x-ray beams lend themselves directly to carrying out sophisticated time-resolved x-ray scattering measurements on a wide range of materials and phenomena. When these attributes are coupled with the pulsed time-structure of synchrotron sources, entirely new time-resolved scattering possibilities are opened. Synchrotron beams typically consist of sub-nanosecond pulses of x-rays separated in time by a few tens of nanoseconds to a few hundred nanoseconds so that these beams appear as continuous x-ray sources for investigations of phenomena on time scales ranging from hours down to microseconds. Studies requiring time-resolution ranging from microseconds to fractions of a nanosecond can be carried out in a triggering mode by stimulating the phenomena under investigation in coincidence with the x-ray pulses. Time resolution on the picosecond scale can, in principle, be achieved through the use of streak camera techniques in which the time structure of the individual x-ray pulses are viewed as quasi-continuous sources with ∼100--200 picoseconds duration. Techniques for carrying out time-resolved scattering measurements on time scales varying from picoseconds to kiloseconds at present and proposed synchrotron sources are discussed and examples of time-resolved studies are cited. 17 refs., 8 figs

  10. A study of Al/Si interface by photoemission, Auger electron yield and Auger electron spectroscopies

    International Nuclear Information System (INIS)

    Kobayashi, K.L.I.; Barth, J.; Gerken, F.; Kunz, C.; Deutsches Elektronen-Synchrotron

    1980-06-01

    Photoemission, Auger electron yield and Auger electron spectra were observed for Al/Si(111) interfaces with various Al coverage prepared by successive deposition using a molecular beam source. The Al 3p derived states are introduced at around the top of the valence band by the Al coverage of less than one monolayer. The Al surface layer behaves as a 'metal' and the Fermi level is stabilized in the Al 3p derived states at about 0.3 eV above the top of the valence band of Si. The Schottky barrier height in this stage is about 0.8 eV and further increase in Al coverage does not change the barrier height. A covalent bonding model of the Al/Si interface based on the experimental results is proposed. The present result favors the on-top geometry of Al atoms on Si(111) surface among the geometries used in the pseudopotential calculation by Zhang and Schlueter. (orig.)

  11. Surface photovoltage investigation of gold chains on Si(111) by two-photon photoemission

    Energy Technology Data Exchange (ETDEWEB)

    Otto, Sebastian; Biedermann, Kerstin; Fauster, Thomas [Lehrstuhl fuer Festkoerperphysik, Universitaet Erlangen-Nuernberg, Staudtstr. 7, D-91058 Erlangen (Germany)

    2011-07-01

    We present surface photovoltage measurements on Si(111)-(7 x 7) with monoatomic gold chains. The gold coverage was varied between zero and 0.6 ML, where the Si(111)-(5 x 2)-Au reconstruction covers the surface completely. During the two-photon photoemission experiments the p- or n-doped samples were illuminated by infrared (IR, E{sub IR}=1.55 eV) and ultraviolet (UV, E{sub UV}=4.65 eV) laser pulses. For all coverages the photovoltage was determined for sample temperatures of 90 K and 300 K by variation of the IR and UV laser power. P-doped as well as n-doped Si(111) wafers show a linear dependence of the photovoltage on gold coverage. This stands in contrast to scanning tunneling spectroscopy measurements, which show a coverage-independent photovoltage over a wide coverage range for n-doped wafers. While for p-doped wafers our experimentally determined photovoltage is in agreement with previous reports, for n-doped wafers the observed values are lower than expected.

  12. Metal-organic semiconductor interfacial barrier height determination from internal photoemission signal in spectral response measurements

    Science.gov (United States)

    Kumar, Sandeep; Iyer, S. Sundar Kumar

    2017-04-01

    Accurate and convenient evaluation methods of the interfacial barrier ϕb for charge carriers in metal semiconductor (MS) junctions are important for designing and building better opto-electronic devices. This becomes more critical for organic semiconductor devices where a plethora of molecules are in use and standardised models applicable to myriads of material combinations for the different devices may have limited applicability. In this paper, internal photoemission (IPE) from spectral response (SR) in the ultra-violet to near infra-red range of different MS junctions of metal-organic semiconductor-metal (MSM) test structures is used to determine more realistic MS ϕb values. The representative organic semiconductor considered is [6, 6]-phenyl C61 butyric acid methyl ester, and the metals considered are Al and Au. The IPE signals in the SR measurement of the MSM device are identified and separated before it is analysed to estimate ϕb for the MS junction. The analysis of IPE signals under different bias conditions allows the evaluation of ϕb for both the front and back junctions, as well as for symmetric MSM devices.

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

    International Nuclear Information System (INIS)

    Anders, Simone; Stammler, Thomas; Padmore, Howard A.; Terminello, Louis J.; Jankowski, Alan F.; Stoehr, Joachim; Diaz, Javier; Cossy-Favre, Aline; Singh, Sangeet

    1998-01-01

    Photoemission Electron Microscopy using X-rays (X-PEEM) 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 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

  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. 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.}

  16. Oxide effects on photoemission from high current GaAs photocathodes

    International Nuclear Information System (INIS)

    Garwin, E.L.; Kirby, R.E.; Sinclair, C.K.; Roder, A.

    1981-03-01

    During four years of on line operation of the SLAC polarized electron gun (PEGGY) and polarized LEED (PLEED) system, we have observed and characterized the failure modes of the GaAs (100) photocathodes (PC's) used in these systems. Several modes are observed. Gradual decreases in electron polarization and intensity are attributed to the physisorption of CO 2 on the PC's during running at LN 2 temperatures. Such PC's can be rejuvenated by warming to 90K, i.e., above the CO 2 desorption temperature. These PC's recover 90% of their original intensity. A second well-characterized failure mode results from overheating the PC during in-situ heat cleaning prior to activation. In this mode, As is preferentially evaporated from the GaAs, leaving a Ga 2 O 3 layer on the surface. This effect has been studied by AES sputter profiling which indicates that the substantial thickness of the oxide layer blocks photoemission. These PC's may only be recovered by chemically removing the oxide layer. A third mode which is not as well characterized appears for thin Ga oxide layers. Properties of these PC's include reduced emission and the presence of a cutoff bias level. Such PC's are also not recoverable in-situ

  17. Generalization of the Euler Angles

    Science.gov (United States)

    Bauer, Frank H. (Technical Monitor); Shuster, Malcolm D.; Markley, F. Landis

    2002-01-01

    It is shown that the Euler angles can be generalized to axes other than members of an orthonormal triad. As first shown by Davenport, the three generalized Euler axes, hereafter: Davenport axes, must still satisfy the constraint that the first two and the last two axes be mutually perpendicular if these axes are to define a universal set of attitude parameters. Expressions are given which relate the generalized Euler angles, hereafter: Davenport angles, to the 3-1-3 Euler angles of an associated direction-cosine matrix. The computation of the Davenport angles from the attitude matrix and their kinematic equation are presented. The present work offers a more direct development of the Davenport angles than Davenport's original publication and offers additional results.

  18. Enforcement actions: Significant actions resolved

    International Nuclear Information System (INIS)

    1989-06-01

    This compilation summarizes significant enforcement actions that have been resolved during one quarterly period (January--March 1989) and includes copies of letters, Notices, and Orders sent by the Nuclear Regulatory Commission to licensees with respect to these enforcement actions. Also included are a number of enforcement actions that had been previously resolved but not published in this NUREG. It is anticipated that the information in this publication will be widely disseminated to managers and employees engaged in activities licensed by the NRC, so that actions can be taken to improve safety by avoiding future violations similar to those described in this publication

  19. Enforcement actions: Significant actions resolved

    International Nuclear Information System (INIS)

    1990-05-01

    This compilation summarizes significant enforcement actions that have been resolved during one quarterly period (January--March 1990) and includes copies of letters, Notices, and Orders sent by the Nuclear Regulatory Commission to licensees with respect to these enforcement actions. Also included are a number of enforcement actions that had been previously resolved but not published in this NUREG. It is anticipated that the information in this publication will be widely disseminated to managers and employees engaged in activities licensed by the NRC, so that actions can be taken to improve safety by avoiding future violations similar to those described in this publication

  20. Angle Performance on Optima XE

    International Nuclear Information System (INIS)

    David, Jonathan; Satoh, Shu

    2011-01-01

    Angle control on high energy implanters is important due to shrinking device dimensions, and sensitivity to channeling at high beam energies. On Optima XE, beam-to-wafer angles are controlled in both the horizontal and vertical directions. In the horizontal direction, the beam angle is measured through a series of narrow slits, and any angle adjustment is made by steering the beam with the corrector magnet. In the vertical direction, the beam angle is measured through a high aspect ratio mask, and any angle adjustment is made by slightly tilting the wafer platen during implant.Using a sensitive channeling condition, we were able to quantify the angle repeatability of Optima XE. By quantifying the sheet resistance sensitivity to both horizontal and vertical angle variation, the total angle variation was calculated as 0.04 deg. (1σ). Implants were run over a five week period, with all of the wafers selected from a single boule, in order to control for any crystal cut variation.

  1. Relationship between the Angle of Repose and Angle of Internal ...

    African Journals Online (AJOL)

    ghum and rice. The angles have a big influence on the design offlow and storage structures of ... the angles of internal friction for the same grains and same moisture contents. The data ob- tained were fed into SAS statistical software for step-wise regression analysis. A model of the ..... tion, Application and Validation of En-.

  2. Resolving the inner disk of UX Orionis

    Science.gov (United States)

    Kreplin, A.; Madlener, D.; Chen, L.; Weigelt, G.; Kraus, S.; Grinin, V.; Tambovtseva, L.; Kishimoto, M.

    2016-05-01

    Aims: The cause of the UX Ori variability in some Herbig Ae/Be stars is still a matter of debate. Detailed studies of the circumstellar environment of UX Ori objects (UXORs) are required to test the hypothesis that the observed drop in photometry might be related to obscuration events. Methods: Using near- and mid-infrared interferometric AMBER and MIDI observations, we resolved the inner circumstellar disk region around UX Ori. Results: We fitted the K-, H-, and N-band visibilities and the spectral energy distribution (SED) of UX Ori with geometric and parametric disk models. The best-fit K-band geometric model consists of an inclined ring and a halo component. We obtained a ring-fit radius of 0.45 ± 0.07 AU (at a distance of 460 pc), an inclination of 55.6 ± 2.4°, a position angle of the system axis of 127.5 ± 24.5°, and a flux contribution of the over-resolved halo component to the total near-infrared excess of 16.8 ± 4.1%. The best-fit N-band model consists of an elongated Gaussian with a HWHM ~ 5 AU of the semi-major axis and an axis ration of a/b ~ 3.4 (corresponding to an inclination of ~72°). With a parametric disk model, we fitted all near- and mid-infrared visibilities and the SED simultaneously. The model disk starts at an inner radius of 0.46 ± 0.06 AU with an inner rim temperature of 1498 ± 70 K. The disk is seen under an nearly edge-on inclination of 70 ± 5°. This supports any theories that require high-inclination angles to explain obscuration events in the line of sight to the observer, for example, in UX Ori objects where orbiting dust clouds in the disk or disk atmosphere can obscure the central star. Based on observations made with ESO telescopes at Paranal Observatory under program IDs: 090.C-0769, 074.C-0552.

  3. Small angle neutron scattering

    Directory of Open Access Journals (Sweden)

    Cousin Fabrice

    2015-01-01

    Full Text Available Small Angle Neutron Scattering (SANS is a technique that enables to probe the 3-D structure of materials on a typical size range lying from ∼ 1 nm up to ∼ a few 100 nm, the obtained information being statistically averaged on a sample whose volume is ∼ 1 cm3. This very rich technique enables to make a full structural characterization of a given object of nanometric dimensions (radius of gyration, shape, volume or mass, fractal dimension, specific area… through the determination of the form factor as well as the determination of the way objects are organized within in a continuous media, and therefore to describe interactions between them, through the determination of the structure factor. The specific properties of neutrons (possibility of tuning the scattering intensity by using the isotopic substitution, sensitivity to magnetism, negligible absorption, low energy of the incident neutrons make it particularly interesting in the fields of soft matter, biophysics, magnetic materials and metallurgy. In particular, the contrast variation methods allow to extract some informations that cannot be obtained by any other experimental techniques. This course is divided in two parts. The first one is devoted to the description of the principle of SANS: basics (formalism, coherent scattering/incoherent scattering, notion of elementary scatterer, form factor analysis (I(q→0, Guinier regime, intermediate regime, Porod regime, polydisperse system, structure factor analysis (2nd Virial coefficient, integral equations, characterization of aggregates, and contrast variation methods (how to create contrast in an homogeneous system, matching in ternary systems, extrapolation to zero concentration, Zero Averaged Contrast. It is illustrated by some representative examples. The second one describes the experimental aspects of SANS to guide user in its future experiments: description of SANS spectrometer, resolution of the spectrometer, optimization of

  4. Resolving Ethical Issues at School

    Science.gov (United States)

    Benninga, Jacques S.

    2013-01-01

    Although ethical dilemmas are a constant in teachers' lives, the profession has offered little in the way of training to help teachers address such issues. This paper presents a framework, based on developmental theory, for resolving professional ethical dilemmas. The Four-Component Model of Moral Maturity, when used in conjunction with a…

  5. Time-resolved quantitative phosphoproteomics

    DEFF Research Database (Denmark)

    Verano-Braga, Thiago; Schwämmle, Veit; Sylvester, Marc

    2012-01-01

    proteins involved in the Ang-(1-7) signaling, we performed a mass spectrometry-based time-resolved quantitative phosphoproteome study of human aortic endothelial cells (HAEC) treated with Ang-(1-7). We identified 1288 unique phosphosites on 699 different proteins with 99% certainty of correct peptide...

  6. Time-resolved vibrational spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Tokmakoff, Andrei [Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States); Champion, Paul [Northeastern Univ., Boston, MA (United States); Heilweil, Edwin J. [National Inst. of Standards and Technology (NIST), Boulder, CO (United States); Nelson, Keith A. [Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States); Ziegler, Larry [Boston Univ., MA (United States)

    2009-05-14

    This document contains the Proceedings from the 14th International Conference on Time-Resolved Vibrational Spectroscopy, which was held in Meredith, NH from May 9-14, 2009. The study of molecular dynamics in chemical reaction and biological processes using time-resolved spectroscopy plays an important role in our understanding of energy conversion, storage, and utilization problems. Fundamental studies of chemical reactivity, molecular rearrangements, and charge transport are broadly supported by the DOE's Office of Science because of their role in the development of alternative energy sources, the understanding of biological energy conversion processes, the efficient utilization of existing energy resources, and the mitigation of reactive intermediates in radiation chemistry. In addition, time-resolved spectroscopy is central to all fiveof DOE's grand challenges for fundamental energy science. The Time-Resolved Vibrational Spectroscopy conference is organized biennially to bring the leaders in this field from around the globe together with young scientists to discuss the most recent scientific and technological advances. The latest technology in ultrafast infrared, Raman, and terahertz spectroscopy and the scientific advances that these methods enable were covered. Particular emphasis was placed on new experimental methods used to probe molecular dynamics in liquids, solids, interfaces, nanostructured materials, and biomolecules.

  7. Small Angle Scattering in Neutron Imaging—A Review

    Directory of Open Access Journals (Sweden)

    Markus Strobl

    2017-12-01

    Full Text Available Conventional neutron imaging utilizes the beam attenuation caused by scattering and absorption through the materials constituting an object in order to investigate its macroscopic inner structure. Small angle scattering has basically no impact on such images under the geometrical conditions applied. Nevertheless, in recent years different experimental methods have been developed in neutron imaging, which enable to not only generate contrast based on neutrons scattered to very small angles, but to map and quantify small angle scattering with the spatial resolution of neutron imaging. This enables neutron imaging to access length scales which are not directly resolved in real space and to investigate bulk structures and processes spanning multiple length scales from centimeters to tens of nanometers.

  8. Transition from the adiabatic to the sudden limit in core-electron photoemission

    Science.gov (United States)

    Hedin, Lars; Michiels, John; Inglesfield, John

    1998-12-01

    Experimental results for core-electron photoemission Jk(ω) are often compared with the one-electron spectral function Ac(ɛk-ω), where ω is the photon energy, ɛk is the photoelectron energy, and the optical transition matrix elements are taken as constant. Since Jk(ω) is nonzero only for ɛk>0, we must actually compare it with Ac(ɛk-ω)θ(ɛk). For metals Ac(ω) is known to have a quasiparticle (QP) peak with an asymmetric power-law [theories of Mahan, Nozières, de Dominicis, Langreth, and others (MND)] singularity due to low-energy particle-hole excitations. The QP peak starts at the core-electron energy ɛc, and is followed by an extended satellite (shakeup) structure at smaller ω. For photon energies ω just above threshold, ωth=-ɛc, Ac(ɛk-ω)θ(ɛk) as a function of ɛk (ω constant) is cut just behind the quasiparticle peak, and neither the tail of the MND line nor the plasmon satellites are present. The sudden (high-energy) limit is given by a convolution of Ac(ω) and a loss function, i.e., by the Berglund-Spicer two-step expression. Thus Ac(ω) alone does not give the correct photoelectron spectrum, neither at low nor at high energies. We present an extension of the quantum-mechanical (QM) models developed earlier by Inglesfield, and by Bardyszewski and Hedin to calculate Jk(ω). It includes recoil and damping, as well as shakeup effects and extrinsic losses, is exact in the high-energy limit, and allows calculations of Jk(ω) including the MND line and multiple plasmon losses. The model, which involves electrons coupled to quasibosons, is motivated by detailed arguments. As an illustration we have made quantitative calculations for a semi-infinite jellium with the density of aluminum metal and an embedded atom. The coupling functions (fluctuation potentials) between the electron and the quasibosons are related to the random-phase-approximation dielectric function, and different levels of approximations are evaluated numerically. The differences

  9. Measurement of the angle gamma

    International Nuclear Information System (INIS)

    Aleksan, R.; Sphicas, P.; Massachusetts Inst. of Tech., Cambridge, MA

    1993-12-01

    The angle γ as defined in the Wolfenstein approximation is not completely out of reach of current or proposed dedicated B experiments. This work represents but a first step in the direction of extracting the third angle of the unitarity triangle by study the feasibility of using new decay modes in a hadronic machine. (A.B.). 11 refs., 1 fig., 7 tabs

  10. Nucleation of small angle boundaries

    CSIR Research Space (South Africa)

    Nabarro, FRN

    1996-12-01

    Full Text Available The internal stresses induced by the strain gradients in an array of lattice cells delineated by low-angle dislocation boundaries are partially relieved by the creation of new low-angle boundaries. This is shown to be a first-order transition...

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2013-08-15

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

  12. Chemical bonding in Tl cuprates studied by x-ray photoemission

    International Nuclear Information System (INIS)

    Vasquez, R.P.; Siegal, M.P.; Overmyer, D.L.; Ren, Z.F.; Lao, J.Y.; Wang, J.H.

    1999-01-01

    Epitaxial thin films of the Tl cuprate superconductors Tl 2 Ba 2 CaCu 2 O 8 , Tl 2 Ba 2 Ca 2 Cu 3 O 10 , and Tl 0.78 Bi 0.22 Ba 0.4 Sr 1.6 Ca 2 Cu 3 O 9-δ are studied with x-ray photoemission spectroscopy. These data, together with previous measurements in this lab of Tl 2 Ba 2 CuO 6+δ and TlBa 2 CaCu 2 O 7-δ , comprise a comprehensive data set for a comparative study of Tl cuprates with a range of chemical and electronic properties. In the Cu 2p spectra, a larger energy separation between the satellite and main peaks (E s -E m ) and a lower intensity ratio (I s /I m ) are found to correlate with higher values of T c . Analysis of these spectra within a simple configuration interaction model suggests that higher values of T c are related to low values of the O 2p→Cu 3d charge transfer energy. In the O 1s region, a smaller bond length between Ba and Cu-O planar oxygen is found to correlate with a lower binding energy for the signal associated with Cu-O bonding, most likely resulting from the increased polarization screening by Ba 2+ ions. For samples near optimum doping, maximum T c is observed to occur when the Tl 4f 7/2 binding energy is near 117.9 eV, which is near the middle of the range of values observed for Tl cuprates. Higher Tl 4f 7/2 binding energies, corresponding to formal oxidation states nearer Tl 1+ , are also found to correlate with longer bond lengths between Ba and Tl-O planar oxygen, and with higher binding energies of the O 1s signal associated with Tl-O bonding. copyright 1999 The American Physical Society

  13. Efficiency Limits of Solar Energy Harvesting via Internal Photoemission in Carbon Materials

    Directory of Open Access Journals (Sweden)

    Svetlana V. Boriskina

    2018-02-01

    Full Text Available We describe strategies to estimate the upper limits of the efficiency of photon energy harvesting via hot electron extraction from gapless absorbers. Gapless materials such as noble metals can be used for harvesting the whole solar spectrum, including visible and near-infrared light. The energy of photo-generated non-equilibrium or ‘hot’ charge carriers can be harvested before they thermalize with the crystal lattice via the process of their internal photo-emission (IPE through the rectifying Schottky junction with a semiconductor. However, the low efficiency and the high cost of noble metals necessitates the search for cheaper abundant alternative materials, and we show here that carbon can serve as a promising IPE material candidate. We compare the upper limits of performance of IPE photon energy-harvesting platforms, which incorporate either gold or carbon as the photoactive material where hot electrons are generated. Through a combination of density functional theory, joint electron density of states calculations, and Schottky diode efficiency modeling, we show that the material electron band structure imposes a strict upper limit on the achievable efficiency of the IPE devices. Our calculations reveal that graphite is a good material candidate for the IPE absorber for harvesting visible and near-infrared photons. Graphite electron density of states yields a sizeable population of hot electrons with energies high enough to be collected across the potential barrier. We also discuss the mechanisms that prevent the IPE device efficiency from reaching the upper limits imposed by their material electron band structures. The proposed approach is general and allows for efficient pre-screening of materials for their potential use in IPE energy converters and photodetectors within application-specific spectral windows.

  14. Photoemission intensity oscillations in the valence bands of C70 film

    International Nuclear Information System (INIS)

    Li Yanjun; Wang Peng; Ni Jingfu; Meng Liang; Wang Xiaobo; Sheng Chunqi; Li Hongnian; Zhang Wenhua; Xu Yang; Xu Faqiang; Zhu Junfa

    2011-01-01

    Highlights: → The article develops a procedure for obtaining the accurate spectral intensities in the studies of the photoionization cross-section oscillation of C 70 . → The article fulfills the observation of all oscillating periods of the cross-section oscillation of C 70 . → The article reports the oscillating data for more molecular orbitals (feature C in the article) as compared with the published works. → The article reveals that some simple theoretical models based on the spherical symmetric approximation survive for the ellipsoidally shaped C 70 . - Abstract: We have measured and analyzed the photoemission spectra (PES) of a C 70 film in the photon energy region from 13.4 eV to 98.4 eV. The photoelectron intensities of two C 2p π-derived features (denoted by A and B) oscillate regularly in the whole energy region with some fine structures below ∼30 eV. To obtain the detailed information of the oscillations, we have developed a sophisticated but practical procedure for intensity calculation. The procedure consists of two core concepts. The first is ascribing the PES features to their corresponding molecular orbitals with the help of density functional calculations. The second is a background subtraction algorithm. With this procedure, we obtained the oscillating behavior for individual features (A and B), which is by and large consistent with the predictions based on the spherical symmetric approximation although C 70 has the ellipsoidal shape. Owing to the solid state effect, the oscillating amplitudes of the A/B intensity ratios are smaller than those of gas phase C 70 , but an orbital shift reported recently was not observed on our sample. The oscillating curve of a deeper feature, which consists of both σ and π states, are also reported.

  15. 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

    2014-05-07

    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.

  16. Attosecond-Resolved Electron Dynamics in Many-Electron Atoms: Quantitative Theory and Comparison with Measurements

    Directory of Open Access Journals (Sweden)

    Cleanthes Anthony Nicolaides

    2018-03-01

    Full Text Available A variety of processes originating from the interaction of atomic or molecular N-electron states with strong and/or hypershort radiation pulses can be understood quantitatively only by first determining with good accuracy the solutions of the many-electron time-dependent Schrödinger equation (METDSE that describe the corresponding physics. The METDSE is solvable nonperturbatively via the state-specific expansion approach (SSEA. SSEA solutions have been used, or can be used, for quantitative explanation and numerically reliable predictions of quantities that have been measured or are measurable in modern laser-driven experiments that can track, with hypershort (attosecond time resolution, the effects of electron rearrangements in atoms and molecules. The calculations take into account in a transparent way the interplay between the phenomena and the electronic structures of the physically significant states in discrete and multichannel continuous spectra, including multiply- and inner-hole–excited resonance states. The discussion focuses on novel topics of time-resolved many-electron physics and includes a comparison of our predictions to recent quantitative measurements of attosecond-resolved generation of the profile of the doubly excited resonance state of helium during photoionization and of the relative time delay in photoemission of the (2s,2p electrons of neon.

  17. Resolving runaway electron distributions in space, time, and energy

    Science.gov (United States)

    Paz-Soldan, C.; Cooper, C. M.; Aleynikov, P.; Eidietis, N. W.; Lvovskiy, A.; Pace, D. C.; Brennan, D. P.; Hollmann, E. M.; Liu, C.; Moyer, R. A.; Shiraki, D.

    2018-05-01

    Areas of agreement and disagreement with present-day models of runaway electron (RE) evolution are revealed by measuring MeV-level bremsstrahlung radiation from runaway electrons (REs) with a pinhole camera. Spatially resolved measurements localize the RE beam, reveal energy-dependent RE transport, and can be used to perform full two-dimensional (energy and pitch-angle) inversions of the RE phase-space distribution. Energy-resolved measurements find qualitative agreement with modeling on the role of collisional and synchrotron damping in modifying the RE distribution shape. Measurements are consistent with predictions of phase-space attractors that accumulate REs, with non-monotonic features observed in the distribution. Temporally resolved measurements find qualitative agreement with modeling on the impact of collisional and synchrotron damping in varying the RE growth and decay rate. Anomalous RE loss is observed and found to be largest at low energy. Possible roles for kinetic instability or spatial transport to resolve these anomalies are discussed.

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

    International Nuclear Information System (INIS)

    Dell'Angela, M.; Anniyev, T.; Coffee, R.; Föhlisch, A.; Nilsson, A.; Nordlund, D.; Wolf, M.; Wurth, W.

    2015-01-01

    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

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

    International Nuclear Information System (INIS)

    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 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

  20. Photoelectron yield spectroscopy and inverse photoemission spectroscopy evaluations of p-type amorphous silicon carbide films prepared using liquid materials

    Energy Technology Data Exchange (ETDEWEB)

    Murakami, Tatsuya, E-mail: mtatsuya@jaist.ac.jp, E-mail: mtakashi@jaist.ac.jp [Center for Nano Materials and Technology, Japan Advanced Institute of Science and Technology (JAIST), 1-1 Asahidai, Nomi, Ishikawa 923-1292 (Japan); Masuda, Takashi, E-mail: mtatsuya@jaist.ac.jp, E-mail: mtakashi@jaist.ac.jp; Inoue, Satoshi; Shimoda, Tatsuya [Green Device Research Center, Japan Advanced Institute of Science and Technology, Nomi, Ishikawa 923-1211 (Japan); Yano, Hiroshi; Iwamuro, Noriyuki [Graduate School of Pure and Applied Sciences, University of Tsukuba, Tennoudai, Tsukuba, Ibaraki 305-8573 (Japan)

    2016-05-15

    Phosphorus-doped amorphous silicon carbide films were prepared using a polymeric precursor solution. Unlike conventional polymeric precursors, this polymer requires neither catalysts nor oxidation for its synthesis and cross-linkage, providing semiconducting properties in the films. The valence and conduction states of resultant films were determined directly through the combination of inverse photoemission spectroscopy and photoelectron yield spectroscopy. The incorporated carbon widened energy gap and optical gap comparably in the films with lower carbon concentrations. In contrast, a large deviation between the energy gap and the optical gap was observed at higher carbon contents because of exponential widening of the band tail.

  1. Heavy Fermion Behavior of Pr 4f Electrons in Filled Skutterudites Studied by Bulk-Sensitive Photoemission

    International Nuclear Information System (INIS)

    Yamasaki, A.Y.; Imada, S.; Masuda, T.; Sekiyama, H.; Suga, S.; Nanba, T.; Sugawara, H.; Matsuda, T.D.; Sato, H.; Sekine, C.; Shirotani, I.; Harima, H.

    2003-01-01

    Pr 4 f electronic structures in Pr-based filled skutterudites PrT 4 X 12 (T = Fe and Ru; X = P and Sb) have been studied by the high-resolution bulk-sensitive Pr 3d → 4f resonance photoemission spectroscopy. A very strong Pr 4f spectral intensity is observed just below the Fermi level in the heavy-Fermion PrFe 4 P 12 . This is the first observation of the Kondo resonance due to the quadrupolar Kondo effect, the origin of which is attributed to the strong hybridization between the Pr 4f and the conduction electrons. (author)

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2014-10-07

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

  3. Pseudogap and Superconducting Gap in Sm FeAs(O1-xFx) Superconductor from Photoemission Spectroscopy

    International Nuclear Information System (INIS)

    Hai-Yun, Liu; Xiao-Wen, Jia; Wen-Tao, Zhang; Lin, Zhao; Jian-Qiao, Meng; Guo-Dong, Liu; Xiao-Li, Dong; Zhi-An, Ren; Wei, Yi; Guang-Can, Che; Zhong-Xian, Zhao; Gang, Wu; Rong-Hua, Liu; Xian-Hui, Chen; Gen-Fu, Chen; Nan-Lin, Wang; Gui-Ling, Wang; Yong, Zhou; Yong, Zhu; Xiao-Yang, Wang

    2008-01-01

    High resolution photoemission measurements are carried out on non-superconducting SmOFeAs parent compound and superconducting SmFeAs(O 1-x F x ) (x = 0.12, and 0.15) compounds. The momentum-integrated spectra exhibit a clear Fermi cutoff that shows little leading-edge shift in the superconducting state. A robust feature at 13meV is identified in all these samples. Spectral weight suppression near Ef with decreasing temperature is observed in both undoped and doped samples that points to a possible existence of a pseudogap in these Fe-based compounds

  4. Minimum resolvable power contrast model

    Science.gov (United States)

    Qian, Shuai; Wang, Xia; Zhou, Jingjing

    2018-01-01

    Signal-to-noise ratio and MTF are important indexs to evaluate the performance of optical systems. However,whether they are used alone or joint assessment cannot intuitively describe the overall performance of the system. Therefore, an index is proposed to reflect the comprehensive system performance-Minimum Resolvable Radiation Performance Contrast (MRP) model. MRP is an evaluation model without human eyes. It starts from the radiance of the target and the background, transforms the target and background into the equivalent strips,and considers attenuation of the atmosphere, the optical imaging system, and the detector. Combining with the signal-to-noise ratio and the MTF, the Minimum Resolvable Radiation Performance Contrast is obtained. Finally the detection probability model of MRP is given.

  5. Enforcement actions: Significant actions resolved

    International Nuclear Information System (INIS)

    1994-03-01

    This compilation summarizes significant enforcement actions that have been resolved during one quarterly period (October - December 1993) and includes copies of letters, Notices, and Orders sent by the Nuclear Regulatory Commission to licensees with respect to these enforcement actions. It is anticipated that the information in this publication will be widely disseminated to managers and employees engaged in activities licensed by the NRC, so that actions can be taken to improve safety by avoiding future violations similar to those described in this publication

  6. Enforcement actions: Significant actions resolved

    International Nuclear Information System (INIS)

    1992-11-01

    This compilation summarizes significant enforcement actions that have been resolved during one quarterly period (July - September 1992) and includes copies of letters, Notices, and Orders sent by the Nuclear Regulatory Commission to licensees with respect to these enforcement actions. It is anticipated that the information in this publication will be widely disseminated to managers and employees engaged in activities licensed by the NRC, so that actions can be taken to improve safety by avoiding future violations similar to those described in this publication

  7. Rare-Earth Fourth-Order Multipole Moment in Cubic ErCo2 Probed by Linear Dichroism in Core-Level Photoemission

    Science.gov (United States)

    Abozeed, Amina A.; Kadono, Toshiharu; Sekiyama, Akira; Fujiwara, Hidenori; Higashiya, Atsushi; Yamasaki, Atsushi; Kanai, Yuina; Yamagami, Kohei; Tamasaku, Kenji; Yabashi, Makina; Ishikawa, Tetsuya; Andreev, Alexander V.; Wada, Hirofumi; Imada, Shin

    2018-03-01

    We developed a method to experimentally quantify the fourth-order multipole moment of the rare-earth 4f orbital. Linear dichroism (LD) in the Er 3d5/2 core-level photoemission spectra of cubic ErCo2 was measured using bulk-sensitive hard X-ray photoemission spectroscopy. Theoretical calculation reproduced the observed LD, and the result showed that the observed result does not contradict the suggested Γ 83 ground state. Theoretical calculation further showed a linear relationship between the LD size and the size of the fourth-order multipole moment of the Er3+ ion, which is proportional to the expectation value , where Onm are the Stevens operators. These analyses indicate that the LD in 3d photoemission spectra can be used to quantify the average fourth-order multipole moment of rare-earth atoms in a cubic crystal electric field.

  8. Real-time observation of initial stage on Si(001) oxidation studied by O-1s photoemission spectroscopy using synchrotron radiation

    CERN Document Server

    Yoshigoe, A; Teraoka, Y

    2003-01-01

    The real-time photoemission measurements of the initial thermal oxidation on the Si(001) surface with O sub 2 gas (1 x 10 sup - sup 4 Pa) at the surface temperatures of 860, 895, 945 and 1000 K have been performed by using synchrotron radiation. In order to study the oxide-layer growth mode depending on the surface temperature, the time evolution of integrated peak area intensity of O-1s photoemission spectra was analyzed on the basis of the Langmuir-type and the auto-catalytic reaction kinetics models. It was found that the oxidation at 860, 895 and 945 K has progressed with the Langmuir-type adsorption. On the other hand, the oxidation at 1000 K has shown the characteristic of the auto-catalytic growth. We have succeeded in analyzing the reaction kinetics of thermal Si(001) oxidation by using the real-time in-situ O-1s photoemission measurements. (author)

  9. The Dark Energy Survey: Prospects for resolved stellar populations

    Energy Technology Data Exchange (ETDEWEB)

    Rossetto, Bruno M. [Observatorio Nacional, Rio de Janeiro (Brazil); Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); Santiago, Basílio X. [Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); Instituto de Fisica, Porto Alegre (Brazil); Girardi, Léo [Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); Osservatorio Astronomica di Padova-INAF, Padova (Italy); Camargo, Julio I. B. [Observatorio Nacional, Rio de Janeiro (Brazil); Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); Balbinot, Eduardo [Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); Instituto de Fisica, Porto Alegre (Brazil); da Costa, Luiz N. [Observatorio Nacional, Rio de Janeiro (Brazil); Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); Yanny, Brian [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Maia, Marcio A. G. [Observatorio Nacional, Rio de Janeiro (Brazil); Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); Makler, Martin [Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); Centro Brasileiro de Pesquisas Fisicas, Rio de Janeiro (Brazil); Ogando, Ricardo L. C. [Observatorio Nacional, Rio de Janeiro (Brazil); Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); Pellegrini, Paulo S. [Observatorio Nacional, Rio de Janeiro (Brazil); Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); Ramos, Beatriz [Observatorio Nacional, Rio de Janeiro (Brazil); Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); de Simoni, Fernando [Observatorio Nacional, Rio de Janeiro (Brazil); Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); Armstrong, R. [Univ. of Illinois, Urbana, IL (United States); Bertin, E. [Univ. Pierre et Marie Curie, Paris (France); Desai, S. [Univ. of Illinois, Urbana, IL (United States); Kuropatkin, N. [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Lin, H. [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Mohr, J. J. [Max-Planck-Institut fur extraterrestrische Physik, Garching (Germany); Tucker, D. L. [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)

    2011-05-06

    Wide angle and deep surveys, regardless of their primary purpose, always sample a large number of stars in the Galaxy and in its satellite system. We here make a forecast of the expected stellar sample resulting from the Dark Energy Survey and the perspectives that it will open for studies of Galactic structure and resolved stellar populations in general. An estimated 1.2 x 108 stars will be sampled in DES grizY filters in the southern equatorial hemisphere. This roughly corresponds to 20% of all DES sources. Most of these stars belong to the stellar thick disk and halo of the Galaxy.

  10. Multiconfiguration Dirac-Fock calculations of angle- and spin-resolved Auger spectra

    Energy Technology Data Exchange (ETDEWEB)

    Kleiman, U., E-mail: kleiman@mpipks-dresden.mpg.d [Max-Planck-Institut fuer Physik komplexer Systeme, Abteilung Endliche Systeme, Noethnitzer Str. 38, D-01187 Dresden (Germany); Lohmann, B. [Westfaelische Wilhelms-Universitaet Muenster, Institut fuer Theoretische Physik, Wilhelm-Klemm-Str. 9, D-48149 Muenster (Germany)

    2010-11-15

    The energies, line intensities as well as angular anisotropy and spin polarization parameters have been calculated for the L{sub 2,3}M{sub 1}M{sub 4,5} Auger spectra of Zn, Kr, Sr, Pd, Cd, Xe, Ba, Yb, Hg, Rn, Ra and No, the M{sub 2,3}N{sub 1}N{sub 4,5} Auger spectra of Pd, Cd, Xe, Ba, Yb, Hg, Rn, Ra and No, the N{sub 2,3}O{sub 1}O{sub 4,5} Auger spectra of Hg, Rn, Ra and No, the M{sub 4,5}N{sub 1}N{sub 2,3} Auger spectra of Kr, Sr, Pd, Cd, Xe, Ba, Yb, Hg, Rn, Ra and No, and the N{sub 4,5}O{sub 1}O{sub 2,3} Auger spectra of Xe, Ba, Yb, Hg, Rn, Ra and No. The calculations have been performed describing the Auger emission process in the context of scattering theory (relativistic distorted wave approximation) where the Auger transition amplitudes and scattering phases have been evaluated applying a relaxed orbital method within a multiconfiguration Dirac-Fock approach. Comparisons with other theoretical and experimental data are made wherever possible.

  11. Angle-resolved energy distributions of laser ablated silver ions in vacuum

    DEFF Research Database (Denmark)

    Hansen, T.N.; Schou, Jørgen; Lunney, J.G.

    1998-01-01

    The energy distributions of ions ablated from silver in vacuum have been measured in situ for pulsed laser irradiation at 355 nm. We have determined the energy spectra for directions ranging from 5 degrees to 75 degrees with respect to the normal in the intensity range from 100 to 400 MW/cm(2...

  12. Angle-Resolved Electron Spectra of {{\\rm{F}}}^{-} Ions by Few-Cycle Laser Pulses

    Science.gov (United States)

    Chen, Jian-Hong; Zhao, Song-Feng; Wang, Guo-Li; Zheng, Xiao-Ping; Zhang, Zheng-Rong

    2017-06-01

    Not Available Supported by the National Natural Science Foundation of China under Grant Nos 11647150, 11464026, 11664035 and 11364038, the Young Talents Program of Gansu Province in 2016, the Scientific Research Program of the Higher Education Institutions of Gansu Province under Grant No 2016A-068, and the Doctoral Scientific Research Foundation of Lanzhou City University under Grant No LZCU-BS2015-04.

  13. On angle resolved RF magnetron sputtering of Ge-Sb-Te thin films

    Czech Academy of Sciences Publication Activity Database

    Gutwirth, J.; Wágner, T.; Bezdička, Petr; Hrdlička, M.; Vlček, Milan; Frumar, M.

    2009-01-01

    Roč. 355, 37-42 (2009), s. 1935-1938 ISSN 0022-3093 R&D Projects: GA MŠk LC523; GA ČR GA203/06/1368 Institutional research plan: CEZ:AV0Z40320502; CEZ:AV0Z40500505 Keywords : amorphous semiconductors * films and coatings * sputtering Subject RIV: CA - Inorganic Chemistry Impact factor: 1.252, year: 2009

  14. Indoor measurement of angle resolved light absorption by antireflective glass in solar panels

    DEFF Research Database (Denmark)

    Amdemeskel, Mekbib Wubishet; Benatto, Gisele Alves dos Reis; Riedel, Nicholas

    2017-01-01

    measurements with trackers. The experimental results showed optical responses that are stable and suitable for indoor characterization of solar cells. We find the characteristic optical response of six different antireflective glasses, and based on such measurements, we perform PVsyst simulations and present...

  15. Angle-resolved investigation of ion dynamics in high power impulse magnetron sputtering deposition system

    Czech Academy of Sciences Publication Activity Database

    Čada, Martin; Adámek, Petr; Straňák, V.; Kment, Štěpán; Olejníček, Jiří; Hubička, Zdeněk; Hippler, R.

    2013-01-01

    Roč. 549, DEC (2013), s. 177-183 ISSN 0040-6090 R&D Projects: GA MŠk LD12002 Institutional support: RVO:68378271 Keywords : HiPIMS * titania * Katsumata probe * ion sensitive probe * IVDF * angular resolution Subject RIV: BL - Plasma and Gas Discharge Physics Impact factor: 1.867, year: 2013 http://www.sciencedirect.com/science/article/pii/S0040609013011127

  16. Electrostatic mass spectrometer for concurrent mass-, energy- and angle-resolved measurements

    International Nuclear Information System (INIS)

    Golikov, Yu.K.; Krasnova, N.K.

    1999-01-01

    A new electron-optical scheme is considered. An energy- and mass-analyser with angular resolution are combined in one device, in which a time-of-flight principle of mass separation is used. The tool is created on the basis of electrostatic field of quasi-conical systems possessing the high-energy dispersion and high-angular resolution. A regime of simultaneous angular and energy resolution is found. If there is an ion-pulsed source then the ion groups of equal mass will be registered at the same time at a position-sensitive detector located at the edge of the field. Real parameters of the suggested scheme are calculated

  17. Observations at large zenith angles

    CERN Document Server

    Schroeder, F

    2000-01-01

    Cherenkov telescope observations at zenith angles >70 deg. are capable of providing large collection areas for high energy gamma-induced air showers. In order to provide a full Monte Carlo simulation of the large zenith angle observations the air shower simulation code CORSIKA was modified to treat particles in a curved geometry. First results of studies with the stand alone telescope HEGRA CT1 are presented.

  18. Photoemission of heavy fermion superconductor PrOs4Sb12 and other Pr compounds

    International Nuclear Information System (INIS)

    Imada, S.; Yamasaki, A.; Sekiyama, A.; Settai, R.; Onuki, Y.; Suga, S.; Sugawara, H.; Sato, H.; Ochiai, A.

    2004-01-01

    Full text: Strongly correlated electronic states due to Pr 4f electrons found in several Pr compounds have recently been attracting much attention. The Pr 4f electrons are much more localized than in Ce due to the lanthanoid contraction. Therefore, the number of the Pr systems that show strong electron correlation is much smaller than Ce systems. We will present a comparative study of Pr 4f electronic states in such systems as the heavy fermion superconductor PrOs 4 Sb 12 , the Kondo system PrSn 3 and the localized 4f systems Pr 4 X 3 (X = Sb and Bi). The Pr 4f electronic state was probed by means of the Pr 3d → 4f resonant photoemission (RPES). Because the kinetic energy (E K ) of the photoelectrons is as high as ∼ 900 eV, this method is much more bulk sensitive than the 4d → 4f RPES with E K ∼ 100 eV. The energy resolution could be set to about 100 meV by utilizing the soft X-rays from BL25SU in SPring-8 and the SCIENTA SES-200 analyzer. The Pr 4f excitation spectrum of PrSn 3 was found to show a very strong intensity at the Fermi level (E F ). This can be interpreted as the Kondo resonance which has been observed in the Kondo Ce and Yb compounds. In the Pr 4f spectrum of the heavy fermion superconductor PrOs 4 Sb 12 , the intensity at E F was smaller than in PrSn 3 . This clearly shows that the Kondo temperature (T K ) is much lower in PrOs 4 Sb 12 than in PrSn 3 . We have further found a strong excitation energy dependence in the RPES line shape. In the case of Pr 4 X 3 (X = Sb and Bi), the intensity at E B was much smaller than PrSn 3 and PrOs 4 Sb 12 , which is consistent with the localized character of Pr 4f electrons in Pr 4 X 3 . The Pr 4f spectra of these localized systems are qualitatively well reproduced by a cluster model calculation that takes into account the hybridization between the Pr 4f orbital and the conduction and valence bands made up by the X p and Pr 5d states

  19. Chemical Bonding in Tl Cuprates Studied by X-Ray Photoemission

    Energy Technology Data Exchange (ETDEWEB)

    Lao, J.Y.; Overmyer, D.L.; Ren, Z.F.; Siegal, M.P.; Vasquez, R.P.; Wang, J.H.

    1999-04-05

    Epitaxial thin films of the Tl cuprate superconductors Tl{sub 2}Ba{sub 2}CaCu{sub 2}O{sub 8}, Tl{sub 2}Ba{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10}, and TL{sub 0.78}Bi{sub 0.22}Ba{sub 0.4}Sr{sub 1.6}Ca{sub 2}Cu{sub 3}O{sub 9{minus}{delta}} are studied with x-ray photoemission spectroscopy. These data, together with previous measurements in this lab of Tl{sub 2}Ba{sub 2}CuO{sub 6+{delta}} and TlBa{sub 2}CaCu{sub 2}O{sub 7{minus}{delta}}, comprise a comprehensive data set for a comparative study of Tl cuprates with a range of chemical and electronic properties. In the Cu 2p spectra, a larger energy separation between the satellite and main peaks (E{sub s}-E{sub m}) and a lower intensity ratio (I{sub s}/I{sub m}) are found to correlate with higher values of T{sub c}. Analysis of these spectra within a simple configuration interaction model suggests that higher values of T{sub c} are related to low values of the O 2p {r_arrow} Cu 3d charge transfer energy. In the O 1s region, a smaller bond length between Ba and Cu-O planar oxygen is found to correlate with a lower binding energy for the signal associated with Cu-O bonding, most likely resulting from the increased polarization screening by Ba{sup 2+} ions. For samples near optimum doping, maximum T{sub c} is observed to occur when the Tl 4f{sub 7/2} binding energy is near 117.9 eV, which is near the middle of the range of values observed for Tl cuprates. Higher Tl 4f{sub 7/2} binding energies, corresponding to formal oxidation states nearer Tl{sup 1+}, are also found to correlate with longer bond lengths between Ba and Tl-O planar oxygen, and with higher binding energies of the O 1s signal associated with Tl-O bonding.

  20. Chemical bonding in Tl cuprates studied by x-ray photoemission

    Energy Technology Data Exchange (ETDEWEB)

    Vasquez, R.P. [Center for Space Microelectronics Technology, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109-8099 (United States); Siegal, M.P.; Overmyer, D.L. [Sandia National Laboratories, Albuquerque, New Mexico 87185-1421 (United States); Ren, Z.F.; Lao, J.Y.; Wang, J.H. [Materials Synthesis Laboratory, Department of Chemistry, State University of New York, Buffalo, New York 14260-3000 (United States)

    1999-08-01

    Epitaxial thin films of the Tl cuprate superconductors Tl{sub 2}Ba{sub 2}CaCu{sub 2}O{sub 8}, Tl{sub 2}Ba{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10}, and Tl{sub 0.78}Bi{sub 0.22}Ba{sub 0.4}Sr{sub 1.6}Ca{sub 2}Cu{sub 3}O{sub 9{minus}{delta}} are studied with x-ray photoemission spectroscopy. These data, together with previous measurements in this lab of Tl{sub 2}Ba{sub 2}CuO{sub 6+{delta}} and TlBa{sub 2}CaCu{sub 2}O{sub 7{minus}{delta}}, comprise a comprehensive data set for a comparative study of Tl cuprates with a range of chemical and electronic properties. In the Cu 2p spectra, a larger energy separation between the satellite and main peaks (E{sub s}{minus}E{sub m}) and a lower intensity ratio (I{sub s}/I{sub m}) are found to correlate with higher values of T{sub c}. Analysis of these spectra within a simple configuration interaction model suggests that higher values of T{sub c} are related to low values of the O&hthinsp;2p{r_arrow}Cu&hthinsp;3d charge transfer energy. In the O&hthinsp;1s region, a smaller bond length between Ba and Cu-O planar oxygen is found to correlate with a lower binding energy for the signal associated with Cu-O bonding, most likely resulting from the increased polarization screening by Ba{sup 2+} ions. For samples near optimum doping, maximum T{sub c} is observed to occur when the Tl 4f{sub 7/2} binding energy is near 117.9 eV, which is near the middle of the range of values observed for Tl cuprates. Higher Tl&hthinsp;4f{sub 7/2} binding energies, corresponding to formal oxidation states nearer Tl{sup 1+}, are also found to correlate with longer bond lengths between Ba and Tl-O planar oxygen, and with higher binding energies of the O&hthinsp;1s signal associated with Tl-O bonding. {copyright} {ital 1999} {ital The American Physical Society}

  1. A Photoemission Electron Microscope Investigation of Chemical Vapor Deposition Diamond Films and Diamond Nucleation

    Science.gov (United States)

    Wang, Congjun

    1993-01-01

    CVD diamond nucleation is investigated using the hot filament technique. The stability of CVD diamond at elevated temperatures in vacuum, O_2, and atomic hydrogen environments are studied using photoemission electron microscopy (PEEM) combined with in-vacuo x-ray photoelectron spectroscopy (XPS). Dissolution, oxidation, and atomic hydrogen etching processes of CVD diamond are observed in real-time. Low field cold electron emission from CVD diamond films has been observed for the first time by PEEM. Nucleation density Mo substrates could be increased from 10^4 to rm 10 ^8/cm^2 by polishing. Heating the substrate to 870^circC in vacuum prior to deposition, or above 1000^ circC at the beginning of deposition, reduced nucleation by more than 100-fold. Reduction in nucleation sites is attributed to annealing. Nucleation on Mo _2C substrates was found to be very poor rm (10^4/cm^2), which shows carbide alone does not promote nucleation. Carbide formation may remove nucleation sites. CVD diamond was found to dissolve into the Mo substrate in vacuum at about 1200^circ C. XPS showed formation of Mo_2 C when the diamond dissolved. Diamond oxidation to gas phase products occurred directly at about 600 ^circC, with no observable participation by the substrate. No detectable etching by atomic hydrogen at a pressure of 1times10^{-4 } torr was observed. Boron doped and "pure" CVD diamond films were found to emit electrons at room temperature under the action of the accelerating electric field of the PEEM (about 30 kV/cm) without photon excitation. The mechanism underlying this phenomenon was investigated with PEEM and by studying the emission current-vs-voltage characteristics of the CVD diamond films. Morphology and crystalline orientation were found to play only a minor role. Impurities in the CVD diamond structure lowers the potential barrier substantially; tunneling of electrons into the vacuum is facile. The effective work function of the emitting CVD diamond films is

  2. Angle-selective all-dielectric Huygens’ metasurfaces

    Science.gov (United States)

    Arslan, D.; Chong, K. E.; Miroshnichenko, A. E.; Choi, D.-Y.; Neshev, D. N.; Pertsch, T.; Kivshar, Y. S.; Staude, I.

    2017-11-01

    We experimentally and numerically study the angularly resolved transmission properties of dielectric metasurfaces consisting of silicon nanodisks which support electric and magnetic dipolar Mie-type resonances in the near-infrared spectral range. First, we concentrate on Huygens’ metasurfaces which are characterised by a spectral overlap of the fundamental electric and magnetic dipole resonances of the silicon nanodisks at normal incidence. Huygens’ metasurfaces exhibit a high transmitted intensity over the spectral width of the resonances due to impedance matching, while the transmitted phase shows a variation of 2π as the wavelength is swept across the width of the resonances. We observe that the transmittance of the Huygens’ metasurfaces depends on the incidence angle and is sensitive to polarisation for non-normal incidence. As the incidence angle is increased starting from normal incidence, the two dipole resonances are shifted out of the spectral overlap and the resonant features appear as pronounced transmittance minima. Next, we consider a metasurface with an increased nanodisk radius as compared to the Huygens’ metasurface, which supports spectrally separate electric and magnetic dipole resonances at normal incidence. We show that for TM polarisation, we can shift the resonances of this metasurface into spectral overlap and regain the high resonant transmittance characteristic of Huygens’ metasurfaces at a particular incidence angle. Furthermore, both metasurfaces are demonstrated to reject all TM polarised light incident under angles other than the design overlap angle at their respective operation frequency. Our experimental observations are in good qualitative agreement with numerical calculations.

  3. Design and optimization of high-performance slot-microring Si-photodetector based on internal photoemission effect

    Science.gov (United States)

    Hosseinifar, Mitra; Ahmadi, Vahid; Ebnali-Heidari, Majid

    2017-08-01

    This paper presents the design and optimization of a microring resonator enhanced-internal photoemission effect-photodetectors (MRRE-IPE-PDs) suitable for optical communication. Two PD configurations are considered: the first consists of an MRR that is partially surrounded by a nanolayer of silicide with a single Schottky barrier on p-Si MRR; and the second consists of a silicide film buried in the width midpoints of a Si-based MRR where photoemission occurs over the two Schottky barriers. Several silicides are considered for the stripe (PtSi, Pd2Si, TaSi2 and CoSi2). The important features of the device, such as quantum efficiency (QE), responsivity, CW sensitivity and dark current are discussed and the trade-off between 3 dB bandwidth and QE are analyzed for nanoscaled absorption layer. In this regard, some design curves are presented for the optimized MRRE-IPE-PDs. Additionally, this paper reveals substantial improvement via comparisons with QE and responsivity measurements reported in the literature. Bandwidth-efficiency product of 61-71 GHz, responsivities of 0.8-0.9 and QE of 64-71% and the minimum receiver sensitivity of -65 to -66 dBm are also predicted for single and double Schottky barriers, respectively.

  4. 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.

  5. Enforcement actions: Significant actions resolved

    International Nuclear Information System (INIS)

    1993-03-01

    This compilation summarizes significant enforcement actions that have been resolved during one quarterly period (October--December 1992) and includes copies of letters, Notices, and Orders sent by the Nuclear Regulatory Commission to licensees with respect to these enforcement actions. It is anticipated that the information in this publication will be widely disseminated to managers and employees engaged in activities licensed by the NRC, so that actions can be taken to improve safety by avoiding future violations similar to those described in this publication

  6. Enforcement actions: Significant actions resolved

    International Nuclear Information System (INIS)

    1991-02-01

    This compilation summarizes significant enforcement actions that have been resolved during one quarterly period (October--December 1990) and includes copies of letters, Notices, and Orders sent by the Nuclear Regulatory Commission to licensees with respect to these enforcement actions. It is anticipated that the information in this publication will be widely disseminated to managers and employees engaged in activities licensed by the NRC, so that actions can be taken to improve safety by avoiding future violations similar to those described in this publication

  7. Enforcement actions: Significant actions resolved

    International Nuclear Information System (INIS)

    1992-08-01

    This compilation summarizes significant enforcement actions that have been resolved during one quarterly period (April--June 1992) and includes copies of letters, Notices, and Orders sent by the Nuclear Regulatory Commission to licensees with respect to these enforcement actions. It is anticipated that the information in this publication will be widely disseminated to managers and employees engaged in activities licensed by the NRC, so that actions can be taken to improve safety by avoiding future violations similar to those described in this publication

  8. Enforcement actions: Significant actions resolved

    International Nuclear Information System (INIS)

    1992-03-01

    This compilation summarizes significant enforcement actions that have been resolved during one quarterly period (October--December 1991) and includes copies of letters, Notices, and Orders sent by the Nuclear Regulatory Commission to licensees with respect to these enforcement actions. It is anticipated that the information in this publication will be widely disseminated to managers and employees engaged in activities licensed by the NRC, so that actions can be taken to improve safety by avoiding future violations similar to those described in this publication

  9. Enforcement actions: Significant actions resolved

    International Nuclear Information System (INIS)

    1991-07-01

    This compilation summarizes significant enforcement actions that have been resolved during one quarterly period (April-June 1991) and includes copies of letters, Notices, and Orders sent by the Nuclear Regulatory Commission to licensees with respect to these enforcement actions. It is anticipated that the information in this publication will be widely disseminated to managers and employees engaged in activities licensed by the NRC, so that actions can be taken to improve safety by avoiding future violations similar to those described in this publication

  10. Enforcement actions: Significant actions resolved

    International Nuclear Information System (INIS)

    1993-12-01

    This compilation summarizes significant enforcement actions that have been resolved during one quarterly period (July--September 1993) and includes copies of letters, Notices, and Orders sent by the Nuclear Regulatory Commission to licensees with respect to these enforcement actions. It is anticipated that the information in this publication will be widely disseminated to managers and employees engaged in activities licensed by the NRC, so that actions can be taken to improve safety by avoiding future violations similar to those described in this publication

  11. Enforcement actions: Significant actions resolved

    International Nuclear Information System (INIS)

    1993-06-01

    This compilation summarizes significant enforcement actions that have been resolved during one quarterly period (January--March 1993) and includes copies of letters, Notices, and Orders sent by the Nuclear Regulatory Commission to licensees with respect to these enforcement actions. It is anticipated that the information in this publication will be widely disseminated to managers and employees engaged in activities licensed by the NRC, so that actions can be taken to improve safety by avoiding future violations similar to those described in this publication

  12. Enforcement actions: Significant actions resolved

    International Nuclear Information System (INIS)

    1992-05-01

    This compilation summarizes significant enforcement actions that have been resolved during one quarterly period (January--March 1992) and includes copies of letters, Notices, and Orders sent by the Nuclear Regulatory Commission to licensees with respect to these enforcement actions. It is anticipated that the information in this publication will be widely disseminated to managers and employees engaged in activities licensed by the NRC, so that actions can be taken to improve safety by avoiding future violations similar to those described in this publication

  13. Enforcement actions: Significant actions resolved

    International Nuclear Information System (INIS)

    1990-11-01

    This compilation summarizes significant enforcement actions that have been resolved during one quarterly period (July--September 1990) and includes copies of letters, notices, and orders sent by the Nuclear Regulatory Commission to licensees with respect to these enforcement actions. It is anticipated that the information in this publication will be widely disseminated to managers and employees engaged in activities licensed by the NRC, so that actions can be taken to improve safety by avoiding future violations similar to those described in this publication

  14. Enforcement actions: Significant actions resolved

    International Nuclear Information System (INIS)

    1991-11-01

    This compilation summarizes significant enforcement actions that have been resolved during one quarterly period (July--September 1991) and includes copies of letters, Notices, and Orders sent by the Nuclear Regulatory Commission to licensees with respect to these enforcement actions. It is anticipated that the information in this publication will be widely disseminated to managers and employees engaged in activities licensed by the NRC, so that actions can be taken to improve safety by avoiding future violations similar to those described in this publication

  15. Enforcement actions: Significant actions resolved

    International Nuclear Information System (INIS)

    1990-03-01

    This compilation summarizes significant enforcement actions that have been resolved during one quarterly period (October--December 1989) and includes copies of letters, Notices, and Orders sent by the Nuclear Regulatory Commission to licensees with respect to these enforcement actions. It is anticipated that the information in this publication will be widely disseminated to managers and employees engaged in activities licensed by the NRC, so that actions can be taken to improve safety by avoiding future violations similar to those described in this publication

  16. Enforcement actions: Significant actions resolved

    International Nuclear Information System (INIS)

    1989-12-01

    This compilation summarizes significant enforcement actions that have been resolved during one quarterly period (July--September 1989) and includes copies of letters, Notices, and Orders sent by the Nuclear Regulatory Commission to licensees with respect to these enforcement actions. It is anticipated that the information in this publication will be widely disseminated to managers and employees engaged in activities licensed by the NRC, so that actions can be taken to improve safety by avoiding future violations similar to those described in this publication

  17. Enforcement actions: Significant actions resolved

    International Nuclear Information System (INIS)

    1991-05-01

    This compilation summarizes significant enforcement actions that have been resolved during one quarterly period (January--March 1991) and includes copies of letters, Notices, and Orders sent by the Nuclear Regulatory Commission to licensees with respect to these enforcement actions. It is anticipated that the information in this publication will be widely disseminated to managers and employees engaged in activities licensed by the NRC, so that actions can be taken to improve safety by avoiding future violations similar to those described in this publication

  18. Enforcement actions: Significant actions resolved

    International Nuclear Information System (INIS)

    1993-09-01

    This compilation summarizes significant enforcement actions that have been resolved during one quarterly period (April--June 1993) and includes copies of letters, Notices, and Orders sent by the Nuclear Regulatory Commission to licensees with respect to these enforcement actions. It is anticipated that the information in this publication will be widely disseminated to managers and employees engaged in activities licensed by the NRC, so that actions can be taken to improve safety by avoiding future violations similar to those described in this publication

  19. Effects of slant angle and illumination angle on MTF estimations

    CSIR Research Space (South Africa)

    Vhengani, LM

    2012-07-01

    Full Text Available angle d(?) was not constant. It was also noted that the iris of the imaging system was in most cases adjusted during initial setups of each measurements. After each measurement, the knife-edge target was replaced with the ISO 12233 MTF target (shown....085 0.09 0.095 K:\\Working Folder\\Project_On_orbit MTF\\edgetargets\\MTF_Lab_Measurements _20120302_Edge Slant Angle (degrees) Ny qu ist MT F (c yc le/p ixe l) Data Regression -18 -16 -14 -12 -10 -8 -6 -4 -2 0.05 0.055 0.06 0...

  20. Full-Circle Resolver-to-Linear-Analog Converter

    Science.gov (United States)

    Alhorn, Dean C.; Smith, Dennis A.; Howard, David E.

    2005-01-01

    A circuit generates sinusoidal excitation signals for a shaft-angle resolver and, like the arctangent circuit described in the preceding article, generates an analog voltage proportional to the shaft angle. The disadvantages of the circuit described in the preceding article arise from the fact that it must be made from precise analog subcircuits, including a functional block capable of implementing some trigonometric identities; this circuitry tends to be expensive, sensitive to noise, and susceptible to errors caused by temperature-induced drifts and imprecise matching of gains and phases. These disadvantages are overcome by the design of the present circuit. The present circuit (see figure) includes an excitation circuit, which generates signals Ksin(Omega(t)) and Kcos(Omega(t)) [where K is an amplitude, Omega denotes 2(pi)x a carrier frequency (the design value of which is 10 kHz), and t denotes time]. These signals are applied to the excitation terminals of a shaft-angle resolver, causing the resolver to put out signals C sin(Omega(t)-Theta) and C cos(Omega(t)-Theta). The cosine excitation signal and the cosine resolver output signal are processed through inverting comparator circuits, which are configured to function as inverting squarers, to obtain logic-level or square-wave signals .-LL[cos(Omega(t)] and -LL[cos(Omega(t)-Theta)], respectively. These signals are fed as inputs to a block containing digital logic circuits that effectively measure the phase difference (which equals Theta between the two logic-level signals). The output of this block is a pulse-width-modulated signal, PWM(Theta), the time-averaged value of which ranges from 0 to 5 VDC as Theta ranges from .180 to +180deg. PWM(Theta) is fed to a block of amplifying and level-shifting circuitry, which converts the input PWM waveform to an output waveform that switches between precise reference voltage levels of +10 and -10 V. This waveform is processed by a two-pole, low-pass filter, which removes