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Sample records for spin-resolved photoemission experiments

  1. 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, ...

  2. 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.

  3. 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.

  4. 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

  5. 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.

  6. First spin-resolved electron distributions in crystals from combined polarized neutron and X-ray diffraction experiments

    Directory of Open Access Journals (Sweden)

    Maxime Deutsch

    2014-05-01

    Full Text Available Since the 1980s it has been possible to probe crystallized matter, thanks to X-ray or neutron scattering techniques, to obtain an accurate charge density or spin distribution at the atomic scale. Despite the description of the same physical quantity (electron density and tremendous development of sources, detectors, data treatment software etc., these different techniques evolved separately with one model per experiment. However, a breakthrough was recently made by the development of a common model in order to combine information coming from all these different experiments. Here we report the first experimental determination of spin-resolved electron density obtained by a combined treatment of X-ray, neutron and polarized neutron diffraction data. These experimental spin up and spin down densities compare very well with density functional theory (DFT calculations and also confirm a theoretical prediction made in 1985 which claims that majority spin electrons should have a more contracted distribution around the nucleus than minority spin electrons. Topological analysis of the resulting experimental spin-resolved electron density is also briefly discussed.

  7. 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 ...

  8. 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.

  9. 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.

  10. 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...

  11. 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...

  12. Spin-resolved magnetic studies of focused ion beam etched nano-sized magnetic structures

    International Nuclear Information System (INIS)

    Li Jian; Rau, Carl

    2005-01-01

    Scanning ion microscopy with polarization analysis (SIMPA) is used to study the spin-resolved surface magnetic structure of nano-sized magnetic systems. SIMPA is utilized for in situ topographic and spin-resolved magnetic domain imaging as well as for focused ion beam (FIB) etching of desired structures in magnetic or non-magnetic systems. Ultra-thin Co films are deposited on surfaces of Si(1 0 0) substrates, and ultra-thin, tri-layered, bct Fe(1 0 0)/Mn/bct Fe(1 0 0) wedged magnetic structures are deposited on fcc Pd(1 0 0) substrates. SIMPA experiments clearly show that ion-induced electrons emitted from magnetic surfaces exhibit non-zero electron spin polarization (ESP), whereas electrons emitted from non-magnetic surfaces such as Si and Pd exhibit zero ESP, which can be used to calibrate sputtering rates in situ. We report on new, spin-resolved magnetic microstructures, such as magnetic 'C' states and magnetic vortices, found at surfaces of FIB patterned magnetic elements. It is found that FIB milling has a negligible effect on surface magnetic domain and domain wall structures. It is demonstrated that SIMPA can evolve into an important and efficient tool to study magnetic domain, domain wall and other structures as well as to perform magnetic depth profiling of magnetic nano-systems to be used in ultra-high density magnetic recording and in magnetic sensors

  13. Spin-resolved quantum transport in graphene-based nanojunctions

    Science.gov (United States)

    Li, Jian-Wei; Wang, Bin; Yu, Yun-Jin; Wei, Ya-Dong; Yu, Zhi-Zhou; Wang, Yin

    2017-08-01

    First-principles calculations were performed to explore the spin-resolved electronic and thermoelectric transport properties of a series of graphene-nanoribbon-based nanojunctions. By flipping the magnetic moments in graphene leads from parallel to antiparallel, very large tunneling magnetoresistance can be obtained under different gate voltages for all the structures. Spin-resolved alternating-current conductance increases versus frequency for the short nanojunctions but decreases for the long nanojunctions. With increasing junction length, the behavior of the junctions changes from capacitive-like to inductive-like. Because of the opposite signs of spin-up thermopower and spin-down thermopower near the Fermi level, pure spin currents can be obtained and large figures of merit can be achieved by adjusting the gate voltage and chemical potential for all the nanojunctions.

  14. Very efficient spin polarization analysis (VESPA): new exchange scattering-based setup for spin-resolved ARPES at APE-NFFA beamline at Elettra.

    Science.gov (United States)

    Bigi, Chiara; Das, Pranab K; Benedetti, Davide; Salvador, Federico; Krizmancic, Damjan; Sergo, Rudi; Martin, Andrea; Panaccione, Giancarlo; Rossi, Giorgio; Fujii, Jun; Vobornik, Ivana

    2017-07-01

    Complete photoemission experiments, enabling measurement of the full quantum set of the photoelectron final state, are in high demand for studying materials and nanostructures whose properties are determined by strong electron and spin correlations. Here the implementation of the new spin polarimeter VESPA (Very Efficient Spin Polarization Analysis) at the APE-NFFA beamline at Elettra is reported, which is based on the exchange coupling between the photoelectron spin and a ferromagnetic surface in a reflectometry setup. The system was designed to be integrated with a dedicated Scienta-Omicron DA30 electron energy analyzer allowing for two simultaneous reflectometry measurements, along perpendicular axes, that, after magnetization switching of the two targets, allow the three-dimensional vectorial reconstruction of the spin polarization to be performed while operating the DA30 in high-resolution mode. VESPA represents the very first installation for spin-resolved ARPES (SPARPES) at the Elettra synchrotron in Trieste, and is being heavily exploited by SPARPES users since autumn 2015.

  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. 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.

  17. 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...

  18. 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.

  19. 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.

  20. Equal-Spin Andreev Reflection on Junctions of Spin-Resolved Quantum Hall Bulk State and Spin-Singlet Superconductor.

    Science.gov (United States)

    Matsuo, Sadashige; Ueda, Kento; Baba, Shoji; Kamata, Hiroshi; Tateno, Mizuki; Shabani, Javad; Palmstrøm, Christopher J; Tarucha, Seigo

    2018-02-22

    The recent development of superconducting spintronics has revealed the spin-triplet superconducting proximity effect from a spin-singlet superconductor into a spin-polarized normal metal. In addition recently superconducting junctions using semiconductors are in demand for highly controlled experiments to engineer topological superconductivity. Here we report experimental observation of Andreev reflection in junctions of spin-resolved quantum Hall (QH) states in an InAs quantum well and the spin-singlet superconductor NbTi. The measured conductance indicates a sub-gap feature and two peaks on the outer side of the sub-gap feature in the QH plateau-transition regime increases. The observed structures can be explained by considering transport with Andreev reflection from two channels, one originating from equal-spin Andreev reflection intermediated by spin-flip processes and second arising from normal Andreev reflection. This result indicates the possibility to induce the superconducting proximity gap in the the QH bulk state, and the possibility for the development of superconducting spintronics in semiconductor devices.

  1. 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.)

  2. 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.)

  3. Spin-resolved tunneling studies of the exchange field in EuS/Al bilayers.

    Science.gov (United States)

    Xiong, Y M; Stadler, S; Adams, P W; Catelani, G

    2011-06-17

    We use spin-resolved electron tunneling to study the exchange field in the Al component of EuS/Al bilayers, in both the superconducting and normal-state phases of the Al. Contrary to expectation, we show that the exchange field H(ex) is a nonlinear function of applied field, even in applied fields that are well beyond the EuS coercive field. Furthermore, the magnitude H(ex) is unaffected by the superconducting phase. In addition, H(ex) decreases significantly with increasing temperature in the temperature range of 0.1-1 K. We discuss these results in the context of recent theories of generalized spin-dependent boundary conditions at a superconductor-ferromagnet interface.

  4. Spin-resolved correlations in the warm-dense homogeneous electron gas

    Science.gov (United States)

    Arora, Priya; Kumar, Krishan; Moudgil, R. K.

    2017-04-01

    We have studied spin-resolved correlations in the warm-dense homogeneous electron gas by determining the linear density and spin-density response functions, within the dynamical self-consistent mean-field theory of Singwi et al. The calculated spin-resolved pair-correlation function gσσ'(r) is compared with the recent restricted path-integral Monte Carlo (RPIMC) simulations due to Brown et al. [Phys. Rev. Lett. 110, 146405 (2013)], while interaction energy Eint and exchange-correlation free energy Fxc with the RPIMC and very recent ab initio quantum Monte Carlo (QMC) simulations by Dornheim et al. [Phys. Rev. Lett. 117, 156403 (2016)]. g↑↓(r) is found to be in good agreement with the RPIMC data, while a mismatch is seen in g↑↑(r) at small r where it becomes somewhat negative. As an interesting result, it is deduced that a non-monotonic T-dependence of g(0) is driven primarily by g↑↓(0). Our results of Eint and Fxc exhibit an excellent agreement with the QMC study due to Dornheim et al., which deals with the finite-size correction quite accurately. We observe, however, a visible deviation of Eint from the RPIMC data for high densities ( 8% at rs = 1). Further, we have extended our study to the fully spin-polarized phase. Again, with the exception of high density region, we find a good agreement of Eint with the RPIMC data. This points to the need of settling the problem of finite-size correction in the spin-polarized phase also. Interestingly, we also find that the thermal effects tend to oppose spatial localization as well as spin polarization of electrons. Supplementary material in the form of one zip file available from the Journal web page at http://https://doi.org/10.1140/epjb/e2017-70532-y

  5. 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.

  6. Spin-resolved electron waiting times in a quantum-dot spin valve

    Science.gov (United States)

    Tang, Gaomin; Xu, Fuming; Mi, Shuo; Wang, Jian

    2018-04-01

    We study the electronic waiting-time distributions (WTDs) in a noninteracting quantum-dot spin valve by varying spin polarization and the noncollinear angle between the magnetizations of the leads using the scattering matrix approach. Since the quantum-dot spin valve involves two channels (spin up and down) in both the incoming and outgoing channels, we study three different kinds of WTDs, which are two-channel WTD, spin-resolved single-channel WTD, and cross-channel WTD. We analyze the behaviors of WTDs in short times, correlated with the current behaviors for different spin polarizations and noncollinear angles. Cross-channel WTD reflects the correlation between two spin channels and can be used to characterize the spin-transfer torque process. We study the influence of the earlier detection on the subsequent detection from the perspective of cross-channel WTD, and define the influence degree quantity as the cumulative absolute difference between cross-channel WTDs and first-passage time distributions to quantitatively characterize the spin-flip process. We observe that influence degree versus spin-transfer torque for different noncollinear angles as well as different polarizations collapse into a single curve showing universal behaviors. This demonstrates that cross-channel WTDs can be a pathway to characterize spin correlation in spintronics system.

  7. Spin resolved electronic transport through N@C20 fullerene molecule between Au electrodes: A first principles study

    Science.gov (United States)

    Caliskan, Serkan

    2018-05-01

    Using first principles study, through Density Functional Theory combined with Non Equilibrium Green's Function Formalism, electronic properties of endohedral N@C20 fullerene molecule joining Au electrodes (Au-N@C20) was addressed in the presence of spin property. The electronic transport behavior across the Au-N@C20 molecular junction was investigated by spin resolved transmission, density of states, molecular orbitals, differential conductance and current-voltage (I-V) characteristics. Spin asymmetric variation was clearly observed in the results due to single N atom encapsulated in the C20 fullerene cage, where the N atom played an essential role in the electronic behavior of Au-N@C20. This N@C20 based molecular bridge, exhibiting a spin dependent I-V variation, revealed a metallic behavior within the bias range from -1 V to 1 V. The induced magnetic moment, spin polarization and other relevant quantities associated with the spin resolved transport were elucidated.

  8. 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

  9. 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

  10. 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

  11. Double-finger-gate controlled spin-resolved resonant quantum transport in the presence of a Rashba-Zeeman gap.

    Science.gov (United States)

    Tang, Chi-Shung; Tseng, Shu-Ting; Gudmundsson, Vidar; Cheng, Shun-Jen

    2015-03-04

    We investigate double finger gate (DFG) controlled spin-resolved resonant transport properties in an n-type quantum channel with a Rashba-Zeeman (RZ) subband energy gap. By appropriately tuning the DFG in the strong Rashba coupling regime, resonant state structures in conductance can be found that are sensitive to the length of the DFG system. Furthermore, a hole-like bound state feature below the RZ gap and an electron-like quasi-bound state feature at the threshold of the upper spin branch can be found that is insensitive to the length of the DFG system.

  12. 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.

  13. 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

  14. Plasmon Enhanced Photoemission

    Energy Technology Data Exchange (ETDEWEB)

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

    2012-05-08

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

  15. 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

  16. 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...

  17. 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...

  18. When combined X-ray and polarized neutron diffraction data challenge high-level calculations: spin-resolved electron density of an organic radical.

    Science.gov (United States)

    Voufack, Ariste Bolivard; Claiser, Nicolas; Lecomte, Claude; Pillet, Sébastien; Pontillon, Yves; Gillon, Béatrice; Yan, Zeyin; Gillet, Jean Michel; Marazzi, Marco; Genoni, Alessandro; Souhassou, Mohamed

    2017-08-01

    Joint refinement of X-ray and polarized neutron diffraction data has been carried out in order to determine charge and spin density distributions simultaneously in the nitronyl nitroxide (NN) free radical Nit(SMe)Ph. For comparison purposes, density functional theory (DFT) and complete active-space self-consistent field (CASSCF) theoretical calculations were also performed. Experimentally derived charge and spin densities show significant differences between the two NO groups of the NN function that are not observed from DFT theoretical calculations. On the contrary, CASSCF calculations exhibit the same fine details as observed in spin-resolved joint refinement and a clear asymmetry between the two NO groups.

  19. 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.

  20. 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

  1. 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.

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

    DEFF Research Database (Denmark)

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

    2015-01-01

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

  3. 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.

  4. 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.

  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. 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.

  7. 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)

  8. 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.

  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. 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.

  11. 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.

  12. 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.

  13. 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

  14. 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

  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. 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

  17. 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

  18. 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...

  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. 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.

  1. 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.

  2. 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. 

  3. 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.

  4. 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.

  5. 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.

  6. 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)

  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. 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.

  9. 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.

  10. 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.)

  11. 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.

  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. 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.

  14. 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.

  15. 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...

  16. 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

  17. 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).

  18. 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

  19. 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

  20. 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.

  1. 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

  2. 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

  3. 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)

  4. 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.

  5. 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.

  6. 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

  7. 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

  8. 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

  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. 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...

  11. 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

  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. Volume and surface photoemission from tungsten. II. Experiment

    DEFF Research Database (Denmark)

    Feuerbacher, B.; Egede Christensen, N.

    1974-01-01

    Energy-distribution spectra of photoelectrons emitted normal to three single-crystal faces of tungsten have been measured for photon energies between 7.7 and 21.2 eV. The results are interpreted in terms of one-dimensional electronic properties along the symmetry lines in k space that correspond ...

  14. 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.

  15. 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.

  16. 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.

  17. 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

  18. 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.

  19. 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

  20. 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.

  1. 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

  2. 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

  3. 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

  4. 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.

  5. 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.

  6. 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

  7. 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

  8. 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)

  9. 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.

  10. 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.

  11. 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

  12. 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

  13. 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

  14. 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

  15. 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....

  16. 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

  17. 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.)

  18. 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.

  19. 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)

  20. 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).

  1. 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.

  2. 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.

  3. 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.

  4. 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

  5. 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

  6. 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.

  7. 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

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

    International Nuclear Information System (INIS)

    Zhang Yi-Jun; Zou Ji-Jun; Wang Xiao-Hui; Chang Ben-Kang; Qian Yun-Sheng; Zhang Jun-Ju; Gao Pin

    2011-01-01

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

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

    CERN Document Server

    Weinelt, M

    2002-01-01

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

  10. 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)

  11. 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...

  12. 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

  13. 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

  14. 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.

  15. 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.)

  16. 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.

  17. X-ray photoemission spectroscopy and ion backscattering analysis of leached simulated waste glass containing UO3

    International Nuclear Information System (INIS)

    Karim, D.P.; Lam, D.J.

    1980-01-01

    UO 3 has been dissolved into several complex borosilicate glasses including Battelle simulated waste glasses 76-68, 3008, and 76-101. The glass surfaces were examined before and after leaching using x-ray photoemission spectroscopy and backscattered ion beam profiling. Samples leached in distilled water showed enhanced surface layer concentrations of several elements including uranium, titanium, zinc, iron and rare earths. For the case of uranium in 76-101, a simple experiment involving leaching two glasses in the same container showed that this surface enhancement is probably not due to redeposition from solution. Similar samples behaved quite differently when leached in a pH = 3.5 nitric acid solution, showing a surface layer high in SiO 2

  18. 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....

  19. 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.

  20. 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.

  1. 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.

  2. 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

  3. 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.

  4. 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,

  5. 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...

  6. 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...

  7. 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.

  8. 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

  9. 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

  10. 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

  11. 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.

  12. 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.

  13. 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.

  14. 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...

  15. 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.

  16. 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)

  17. 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.

  18. 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

  19. 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)

  20. 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

  1. 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....

  2. 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

  3. 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.

  4. 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.

  5. 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.

  6. X-ray photoemission spectroscopy (XPS) and extended x-ray absorption fine structure (EXAFS) studies of silicate based glasses

    International Nuclear Information System (INIS)

    Karim, D.; Lam, D.J.

    1979-01-01

    The application of the x-ray photoemission spectroscopy (XPS) technique to study the electronic structure and bonding of heavy metal oxides in alkali- and alkali-earth-silicate glasses had been demonstrated. The bonding characteristics of the iron oxide and uranium oxide in sodium silicate glasses were deduced from the changes in the oxygen 1s levels and the heavy metal core levels. It is reasonable to expect that the effect of leaching on the heavy metal ions can be monitored using the appropriate core levels of these ions. To study the effect of leaching on the glass forming network, the valence band structure of the bridging and nonbridging oxygens in sodium silicate glasses were investigated. The measurement of extended x-ray absorption fine-structure (EXAFS) is a relatively new analytical technique for obtaining short range (<5 A) structural information around atoms of a selected species in both solid and fluid systems. Experiments have recently begun to establish the feasibility of using EXAFS to study the bonding of actinides in silicate glasses. Because of the ability of EXAFS to yield specific structural data even in complex multicomponent systems, it could prove to be an invaluable tool in understanding glass structure

  7. A soft x-ray photoemission study of the chemisorption and reaction of diethylsilane on Si(100)

    International Nuclear Information System (INIS)

    Lapiano-Smith, D.A.; Himpsel, F.J.

    1993-06-01

    Soft x-ray synchrotron radiation was utilized as the excitation source in a high-resolution photoemission experiment on chemisorption and subsequent reaction of diethylsilane on the Si(100) surface. We have found that diethylsilane chemisorbs dissociatively to form Si-CH 2 CH 3 surface species on Si(100) following a room temperature exposure. These species are identified by two very sharp peaks observed in the valence band spectra positioned at 17.9 and 14.3 eV binding energy. In addition, C 1s core level spectra, measured following exposures of Si(100) substrates as a function of surface temperature, show that carbon, in some form, exists on the Si surface following exposures at every temperature from room temperature to about 600C. While only -CH 2 CH 3 , ethyl groups are observed on the surface at room temperature, these species appear to partially dehydrogenate at 300C, producing a mixture of -CH 2 CH 3 groups and other intermediate carbonaceous species. At a growth temperature of about 400C the intermixing of elemental carbon with Si begins. At higher temperatures, we observe the continued degradation of diethylsilane to produce a Si + C alloy on the surface at 600C. Results indicate that diethylsilane has potential as a molecular precursor for SiC formation by chemical vapor deposition techniques

  8. 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.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-01-01

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

  10. 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.

  11. 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.

  12. 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)

  13. 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

  14. 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.

  15. 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

  16. 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)

  17. 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.

  18. 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.

  19. 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...

  20. 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

  1. 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.

  2. 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

  3. 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.

  4. 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

  5. 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.

  6. 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.

  7. 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

  8. 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

  9. 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

  10. 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.

  11. 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.

  12. 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.

  13. 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

  14. 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

  15. 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).

  16. 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.

  17. 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

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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

  7. 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)

  8. 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.

  9. 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.

  10. 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.

  11. 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

  12. 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'

  13. 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...

  14. 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

  15. 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

  16. 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.

  17. 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.

  18. 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.

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

    CERN Document Server

    Sekiyama, A

    2003-01-01

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

  20. 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

  1. 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.

  2. 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

  3. 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

  4. 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

  5. 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 ($

  6. 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

  7. 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

  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. 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.)

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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

  16. 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.

  17. 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.}

  18. 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.

  19. 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.

  20. 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

  1. 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).

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

    Energy Technology Data Exchange (ETDEWEB)

    Kay, Alexander William [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)

    2000-09-01

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

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

    International Nuclear Information System (INIS)

    Kay, Alexander William

    2000-01-01

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

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

    International Nuclear Information System (INIS)

    El Manouni, A.

    1990-12-01

    The development of research in the domain of photocathode (electron sources) illuminated by laser light to produce intense multiple bunches of electrons in short time is needed by many applications as linear collider e + e - , free electron laser, lasertron, etc... In this way, after a study of field emission, of photoemission and of photofield emission, we prepared microscopical emitters in silicium heavy and weakly doped a boron using a technique of microlithography. Then, we realized a system of ultra-high vacuum of studying property of emission from photocathodes realized. The experiment results obtained in field emission and photofield emission have shown that a behaviour unexpected for P-silicium tips array compared to P + -silicon tips array. With P-type silicon, a quantum yield of 21 percent has been measured for laser power of 140 mW and for applied field of 1.125 x 10 7 V/m and an instantaneous response to laser light beam has been observed. It has been noted that presence of oxyde at the surface of photocathode limits extensively the emission current. The fluctuations of emission current are due to quality of vacuum [fr

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

    CERN Document Server

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

    1997-01-01

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

  6. 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.

  7. 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

  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. 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.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2008-05-01

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

  11. 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

  12. 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.

  13. 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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2013-12-02

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

  17. 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)

  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. 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.

  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. 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.

  5. 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)

  6. 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.

  7. 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

  8. 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.

  9. 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}

  10. 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

  11. 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

  12. 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.

  13. Probing the energy levels of perovskite solar cells via Kelvin probe and UV ambient pressure photoemission spectroscopy.

    Science.gov (United States)

    Harwell, J R; Baikie, T K; Baikie, I D; Payne, J L; Ni, C; Irvine, J T S; Turnbull, G A; Samuel, I D W

    2016-07-20

    The field of organo-lead halide perovskite solar cells has been rapidly growing since their discovery in 2009. State of the art devices are now achieving efficiencies comparable to much older technologies like silicon, while utilising simple manufacturing processes and starting materials. A key parameter to consider when optimising solar cell devices or when designing new materials is the position and effects of the energy levels in the materials. We present here a comprehensive study of the energy levels present in a common structure of perovskite solar cell using an advanced macroscopic Kelvin probe and UV air photoemission setup. By constructing a detailed map of the energy levels in the system we are able to predict the importance of each layer to the open circuit voltage of the solar cell, which we then back up through measurements of the surface photovoltage of the cell under white illumination. Our results demonstrate the effectiveness of air photoemission and Kelvin probe contact potential difference measurements as a method of identifying the factors contributing to the open circuit voltage in a solar cell, as well as being an excellent way of probing the physics of new materials.

  14. 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

  15. 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.

  16. Photoemission and photo-field-emission from photocathodes with arrays of silicon tips under continuous and pulsed lasers action; Photoemission et photoemission de champ a partir de photocathodes a reseaux de pointes de silicium sous l`action de lasers continus et pulses

    Energy Technology Data Exchange (ETDEWEB)

    Laguna, M.

    1995-11-01

    The electron machines`s development and improvement go through the discovery of new electron sources of high brightness. After reminding the interests in studying silicon cathodes with array of tips as electron sources, I describe, in the three steps model, the main phenomenological features related to photoemission and photoemission and photo-field-emission from a semi-conductor. the experimental set-ups used for the measurements reported in chapter four, five and six are described in chapter three. In chapter three. In chapter four several aspects of photo-field-emission in continuous and nanosecond regimes, studied on the Clermont-Ferrand`s test bench are tackled. We have measured quantum efficacies of 0.4 percent in the red (1.96 eV). Temporal responses in the nanoseconds range (10 ns) were observed with the Nd: YLF laser. With the laser impinging at an oblique angle we obtained ratios of photocurrent to dark current of the order of twenty. The issue of the high energy extracted photocurrent saturation is addressed and I give a preliminary explanation. In collaboration with the L.A.L. (Laboratoire de l`Accelerateur Lineaire) some tests with shortened pulsed laser beam (Nd: YAG laser 35 ps) were performed. Satisfactory response times have been obtained within the limitation of the scope (400 ps). (authors). 101 refs. 93 figs., 27 tabs., 3 photos., 1 append.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    1997-04-01

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

  18. The band 12 issue in the electron momentum spectra of norbornane: a comparison with additional Green's Function calculations and ultraviolet photoemission measurements.

    Science.gov (United States)

    Knippenberg, S; Deleuze, M S; Cleij, T J; François, J-P; Cederbaum, L S; Eland, J H D

    2005-05-19

    In continuation of a recent study of the electronic structure of norbornane [J. Chem. Phys., 2004, 121, 10525] by means of electron momentum spectroscopy (EMS), we present Green's Function calculations of the ionization spectrum of this compound at the ADC(3) level using basis sets of varying quality, along with accurate evaluations at the CCSD(T) level of the vertical (26.5 eV) and adiabatic (22.1 eV) double ionization thresholds under C(2v) symmetry. The obtained results are compared with newly recorded ultraviolet photoemission spectra (UPS), up to binding energies of 40 eV. The theoretical predictions are entirely consistent with experiment and indicate that, in a vertical depiction of ionization, shake-up states at binding energies larger than approximately 26.5 eV tend to decay via emission of a second electron in the continuum. A band of s-type symmetry that has been previously seen at approximately 25 eV in the electron impact ionization spectra of norbornane is entirely missing in the UPS measurements and theoretical ADC(3) spectra. With regard to these results and to the time scales characterizing electron-electron interactions in EMS (10(-17) s) as compared with that (10(-13) s) of photon-electron interactions in UPS, and considering the p-type symmetry of the electron momentum distributions for the nearest 1b(1) and 1b(2) orbitals, this additional band can certainly not be due to adiabatic double ionization processes starting from the ground electronic state of norbornane, or to exceptionally strong vibronic coupling interactions between cationic states derived from ionization of the latter orbitals. It is therefore tentatively ascribed to autoionization processes via electronically excited and possibly dissociating states.

  19. Advanced Photoemission Spectroscopy Investigations Correlated with DFT Calculations on the Self-Assembly of 2D Metal Organic Frameworks Nano Thin Films.

    Science.gov (United States)

    Elzein, Radwan; Chang, Chun-Min; Ponomareva, Inna; Gao, Wen-Yang; Ma, Shengqian; Schlaf, Rudy

    2016-11-16

    Metal-organic frameworks (MOFs) deposited from solution have the potential to form 2-dimensional supramolecular thin films suitable for molecular electronic applications. However, the main challenges lie in achieving selective attachment to the substrate surface, and the integration of organic conductive ligands into the MOF structure to achieve conductivity. The presented results demonstrate that photoemission spectroscopy combined with preparation in a system-attached glovebox can be used to characterize the electronic structure of such systems. The presented results demonstrate that porphyrin-based 2D MOF structures can be produced and that they exhibit similar electronic structure to that of corresponding conventional porphyrin thin films. Porphyrin MOF multilayer thin films were grown on Au substrates prefunctionalized with 4-mercaptopyridine (MP) via incubation in a glovebox, which was connected to an ultrahigh vacuum system outfitted with photoelectron spectroscopy. The thin film growth process was carried out in several sequential steps. In between individual steps the surface was characterized by photoemission spectroscopy to determine the valence bands and evaluate the growth mode of the film. A comprehensive evaluation of X-ray photoemission spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), and inverse photoemission spectroscopy (IPES) data was performed and correlated with density functional theory (DFT) calculations of the density of states (DOS) of the films involved to yield the molecular-level insights into the growth and the electronic properties of MOF-based 2D thin films.

  20. X-ray photoemission study of the infinite-layer cuprate superconductor Sr(0.9) La (0.1) CuO(2)

    Science.gov (United States)

    Vasquez, R. P.; Jung, C. U.; Kim, J. Y.; Kim, M. S.; Lee, S. Y.; Lee, S. I.

    2001-01-01

    The electron-doped infinite-layer superconductor Sr(0.9)La(0.1) CuO(2) is studied with x-ray photoemission spectroscopy (XPS). A nonaqueous chemical etchant is shown to effectively remove contaminants and to yield surfaces from which signals intrinsic to the superconductor dominate.

  1. 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

  2. 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

  3. 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

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

    NARCIS (Netherlands)

    Slooten, E.; Zhong, Zhicheng; Molegraaf, Hajo; Eerkes, P.D.; de Jong, S.; Massee, F.; van Heumen, E.; Kruize, Michelle; Wenderich, Sander; Kleibeuker, J.E.; Gorgoi, M.; Hilgenkamp, Johannes W.M.; Brinkman, Alexander; Huijben, Mark; Rijnders, Augustinus J.H.M.; Blank, David H.A.; Koster, Gertjan; Kelly, Paul J.; Golden, M.S.

    2013-01-01

    A combined experimental and theoretical investigation of the electronic structure of the archetypal oxide heterointerface system LaAlO3 on SrTiO3 is presented. High-resolution, hard x-ray photoemission is used to uncover the occupation of Ti 3d states and the relative energetic alignment—and hence

  5. 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

  6. 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

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

    Directory of Open Access Journals (Sweden)

    Ivan V. Bazarov

    2008-10-01

    Full Text Available We present a comparison between space charge calculations and direct measurements of the transverse phase space of space charge dominated electron bunches from a high voltage dc photoemission gun followed by an emittance compensation solenoid magnet. The measurements were performed using a double-slit emittance measurement system over a range of bunch charge and solenoid current values. The data are compared with detailed simulations using the 3D space charge codes GPT and Parmela3D. The initial particle distributions were generated from measured transverse and temporal laser beam profiles at the photocathode. The beam brightness as a function of beam fraction is calculated for the measured phase space maps and found to approach within a factor of 2 the theoretical maximum set by the thermal energy and the accelerating field at the photocathode.

  8. 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.

  9. 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}.

  10. 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)

  11. Real-time observation of initial stages of thermal oxidation on Si(001) surface by using synchrotron radiation photoemission spectroscopy

    CERN Document Server

    Yoshigoe, A; Moritani, K

    2003-01-01

    Real-time observation of initial stages of thermal oxidation processes on the Si(001) surface using O sub 2 gas (1x10 sup - sup 4 Pa) was performed by means of the O-1s and Si-2p photoemission spectroscopy with synchrotron radiation. From the analysis of the time evolution of oxygen uptake curves on the basis of the reaction kinetics model, the oxide-layer growth depending on the surface temperature was categorized by the Langmuir adsorption and the auto-catalytic reaction models, respectively. It was found that the oxidation rates increased with increasing the surface temperature. The time evolution of Si oxidation states depending on the surface temperature was well monitored. We found that the surface temperature enhanced the diffusion and/or migration of adsorbed oxygen and the bulk Si atom. (author)

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

    International Nuclear Information System (INIS)

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

    2015-01-01

    The electronic properties of co-evaporated mixtures (blends) of manganese phthalocyanine and the fullerene C 60 (MnPc:C 60 ) have been studied as a function of the concentration of the two constituents using two supplementary electron spectroscopic methods, photoemission spectroscopy (PES) and electron energy-loss spectroscopy (EELS) in transmission. Our PES measurements provide a detailed picture of the electronic structure measured with different excitation energies as well as different mixing ratios between MnPc and C 60 . Besides a relative energy shift, the occupied electronic states of the two materials remain essentially unchanged. The observed energy level alignment is different compared to that of the related CuPc:C 60 bulk heterojunction. Moreover, the results from our EELS investigations show that, despite the rather small interface interaction, the MnPc related electronic excitation spectrum changes significantly by admixing C 60 to MnPc thin films

  13. An energy-dependent photoemission study on line-shape analysis in determining the absolute coverage of metallic thin films

    International Nuclear Information System (INIS)

    Cheng, C-M; Tsuei, K-D; Luh, D-A

    2008-01-01

    Energy-dependent photoemission was measured to investigate the validity of the analysis of line shape in determining the absolute coverage of atomically flat, metallic thin films. The surface states of two Ag/Au(1 1 1) thin films with carefully controlled coverage of Ag were measured and analysed. Our results confirm that line-shape analysis is a valid procedure; the absolute error associated with this technique is within 0.1 ML, which makes the technique advantageous over other techniques to determine the film coverage. The experimental procedure in our work provides a routine to determine an appropriate photon energy for use in line-shape analysis. Our results indicate that the widely accessible He Iα line is a suitable excitation source to utilize line-shape analysis for confined states in a Ag film

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

    CERN Document Server

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

    2003-01-01

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

  15. Adsorption of 3,4-ethylenedioxythiophene (EDOT) on noble metal surfaces: A photoemission and X-ray absorption study

    International Nuclear Information System (INIS)

    Pasquali, L.; Terzi, F.; Montecchi, M.; Doyle, B.P.; Lukkari, J.; Zanfrognini, B.; Seeber, R.; Nannarone, S.

    2009-01-01

    The adsorption of 3,4-ethylenedioxythiophene (EDOT) on Au and Pt surfaces is studied by core level and valence band photoemission using synchrotron radiation and by near edge X-ray absorption spectroscopy. To closer simulate real applications, the films are grown from aqueous solution at room temperature and are compared to an 'ideal' film prepared by dosing the molecules from the vapour phase on a clean Au(1 1 1) single crystal. The S 2p, C 1s and O 1s levels show multiple components which are associated to molecular fragmentation. NEXAFS confirms that fragmentation takes place at the surface. Thiophene species as well as alkyl chains and S n species are identified as the most probable fragmentation products.

  16. 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.

  17. 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

  18. Nondestructive imaging of buried interfaces in SiC and GaN Schottky contacts using scanning internal photoemission microscopy

    Science.gov (United States)

    Shiojima, Kenji; Yamamoto, Shingo; Kihara, Yuhei; Mishima, Tomoyoshi

    2015-04-01

    We demonstrate a nondestructive characterization of buried interfaces in metal/wide-bandgap semiconductor contacts by using scanning internal photoemission microscopy. For Ni/n-SiC contacts annealed at temperatures above 400 °C, a reduction of the Schottky barrier height owing to partial interfacial reaction was visualized. In Au/Ni/n-GaN contacts, upon annealing at 400 °C, thermal degradation from a scratch on the dot was observed. Forward current-voltage curves were reproduced by lowering the Schottky barrier height and the area of the reacted regions by using this method. The present imaging method exploits its nondestructive highly sensitive extinction for characterizing the contacts formed on wide-gap materials.

  19. Optimizing the performance of bandpass photon detectors for inverse photoemission: Transmission of alkaline earth fluoride window crystals

    International Nuclear Information System (INIS)

    Thiede, Christian; Schmidt, Anke B.; Donath, Markus

    2015-01-01

    Bandpass photon detectors are widely used in inverse photoemission in the isochromat mode at energies in the vacuum-ultraviolet spectral range. The energy bandpass of gas-filled counters is usually formed by the ionization threshold of the counting gas as high-pass filter and the transmission cutoff of an alkaline earth fluoride window as low-pass filter. The transmission characteristics of the window have, therefore, a crucial impact on the detector performance. We present transmission measurements in the vacuum-ultraviolet spectral range for alkaline earth fluoride window crystals in the vicinity of the transmission cutoff as a function of crystal purity, surface finish, surface contamination, temperature, and thickness. Our findings reveal that the transmission characteristics of the window crystal and, thus, the detector performance depend critically on these window parameters

  20. 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 .

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

    International Nuclear Information System (INIS)

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

    2003-01-01

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

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

    Science.gov (United States)

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

    2008-10-01

    We present a comparison between space charge calculations and direct measurements of the transverse phase space of space charge dominated electron bunches from a high voltage dc photoemission gun followed by an emittance compensation solenoid magnet. The measurements were performed using a double-slit emittance measurement system over a range of bunch charge and solenoid current values. The data are compared with detailed simulations using the 3D space charge codes GPT and Parmela3D. The initial particle distributions were generated from measured transverse and temporal laser beam profiles at the photocathode. The beam brightness as a function of beam fraction is calculated for the measured phase space maps and found to approach within a factor of 2 the theoretical maximum set by the thermal energy and the accelerating field at the photocathode.

  3. Poly[2-methoxy-5-(2'-ethyl-hexyloxy)-p-phenylene vinylene] (MEH-PPV)/poly(3-hexylthiophene-2,5-diyl) (P3HT) heterolayer film on gold: two-photon photoemission spectroscopy

    International Nuclear Information System (INIS)

    Sohn, Youngku; Stuckless, J Todd

    2008-01-01

    The interfacial electronic structure and photoexcitation kinetics of MEH-PPV/P3HT heterolayer film on gold were studied using two-photon photoemission spectroscopy. We observed that the photoelectron kinetic energy distribution and the photoexcitation kinetics exhibit the characteristics of the MEH-PPV layer, and the absolute two-photon photoemission yield is determined by the P3HT layer. On the basis of the photoexcitation kinetics and the photoelectron kinetic energy distribution, we conclude that a charge transfer occurs efficiently from P3HT to MEH-PPV before photoemission

  4. Revisiting the origin of satellites in core-level photoemission of transparent conducting oxides: The case of n -doped SnO2

    Science.gov (United States)

    Borgatti, Francesco; Berger, J. A.; Céolin, Denis; Zhou, Jianqiang Sky; Kas, Joshua J.; Guzzo, Matteo; McConville, C. F.; Offi, Francesco; Panaccione, Giancarlo; Regoutz, Anna; Payne, David J.; Rueff, Jean-Pascal; Bierwagen, Oliver; White, Mark E.; Speck, James S.; Gatti, Matteo; Egdell, Russell G.

    2018-04-01

    The longstanding problem of interpretation of satellite structures in core-level photoemission spectra of metallic systems with a low density of conduction electrons is addressed using the specific example of Sb-doped SnO2. Comparison of ab initio many-body calculations with experimental hard x-ray photoemission spectra of the Sn 4 d states shows that strong satellites are produced by coupling of the Sn core hole to the plasma oscillations of the free electrons introduced by doping. Within the same theoretical framework, spectral changes of the valence band spectra are also related to dynamical screening effects. These results demonstrate that, for the interpretation of electron correlation features in the core-level photoelectron spectra of such narrow-band materials, going beyond the homogeneous electron gas electron-plasmon coupling model is essential.

  5. 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.

  6. 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.

  7. Circularly polarized near-field optical mapping of spin-resolved quantum Hall chiral edge states.

    Science.gov (United States)

    Mamyouda, Syuhei; Ito, Hironori; Shibata, Yusuke; Kashiwaya, Satoshi; Yamaguchi, Masumi; Akazaki, Tatsushi; Tamura, Hiroyuki; Ootuka, Youiti; Nomura, Shintaro

    2015-04-08

    We have successfully developed a circularly polarized near-field scanning optical microscope (NSOM) that enables us to irradiate circularly polarized light with spatial resolution below the diffraction limit. As a demonstration, we perform real-space mapping of the quantum Hall chiral edge states near the edge of a Hall-bar structure by injecting spin polarized electrons optically at low temperature. The obtained real-space mappings show that spin-polarized electrons are injected optically to the two-dimensional electron layer. Our general method to locally inject spins using a circularly polarized NSOM should be broadly applicable to characterize a variety of nanomaterials and nanostructures.

  8. Spin-resolved Andreev levels and parity crossings in hybrid superconductor-semiconductor nanostructures.

    Science.gov (United States)

    Lee, Eduardo J H; Jiang, Xiaocheng; Houzet, Manuel; Aguado, Ramón; Lieber, Charles M; De Franceschi, Silvano

    2014-01-01

    The physics and operating principles of hybrid superconductor-semiconductor devices rest ultimately on the magnetic properties of their elementary subgap excitations, usually called Andreev levels. Here we report a direct measurement of the Zeeman effect on the Andreev levels of a semiconductor quantum dot with large electron g-factor, strongly coupled to a conventional superconductor with a large critical magnetic field. This material combination allows spin degeneracy to be lifted without destroying superconductivity. We show that a spin-split Andreev level crossing the Fermi energy results in a quantum phase transition to a spin-polarized state, which implies a change in the fermionic parity of the system. This crossing manifests itself as a zero-bias conductance anomaly at finite magnetic field with properties that resemble those expected for Majorana modes in a topological superconductor. Although this resemblance is understood without evoking topological superconductivity, the observed parity transitions could be regarded as precursors of Majorana modes in the long-wire limit.

  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. 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.

  11. 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.

  12. In situ photoemission spectroscopy using synchrotron radiation for O2 translational kinetic energy induced oxidation processes of partially-oxidized Si(001) surfaces

    International Nuclear Information System (INIS)

    Teraoka, Yuden; Yoshigoe, Akitaka

    2001-01-01

    The influence of translational kinetic energy of incident O 2 molecules for the passive oxidation process of partially-oxidized Si(001) surfaces has been studied by photoemission spectroscopy. The translational kinetic energy of O 2 molecules was controlled up to 3 eV by a supersonic seed beam technique using a high temperature nozzle. Two translational kinetic energy thresholds (1.0 eV and 2.6 eV) were found out in accordance with the first-principles calculation for the oxidation of clean surfaces. Si-2p photoemission spectra measured in representative translational kinetic energies revealed that the translational kinetic energy dependent oxidation of dimers and the second layer (subsurface) backbonds were caused by the direct dissociative chemisorption of O 2 molecules. Moreover, the difference in chemical bonds for oxygen atoms was found out to be as low and high binding energy components in O-1s photoemission spectra. Especially, the low binding energy component increased with increasing the translational kinetic energy that indicates the translational kinetic energy induced oxidation in backbonds. (author)

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-12-01

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

  14. Structure and Electronic Properties of Cerium Orthophosphate: Theory and Experiment

    Energy Technology Data Exchange (ETDEWEB)

    Adelstein, Nicole; Mun, B. Simon; Ray, Hannah; Ross Jr, Phillip; Neaton, Jeffrey; De Jonghe, Lutgard

    2010-07-27

    Structural and electronic properties of cerium orthophosphate (CePO{sub 4}) are calculated using density functional theory (DFT) with the local spin-density approximation (LSDA+U), with and without gradient corrections (GGA-(PBE)+U), and compared to X-ray diffraction and photoemission spectroscopy measurements. The density of states is found to change significantly as the Hubbard parameter U, which is applied to the Ce 4f states, is varied from 0 to 5 eV. The calculated structural properties are in good agreement with experiment and do not change significantly with U. Choosing U = 3 eV for LDSA provides the best agreement between the calculated density of states and the experimental photoemission spectra.

  15. A photoemission moments model using density functional and transfer matrix methods applied to coating layers on surfaces: Theory

    Science.gov (United States)

    Jensen, Kevin L.; Finkenstadt, Daniel; Shabaev, Andrew; Lambrakos, Samuel G.; Moody, Nathan A.; Petillo, John J.; Yamaguchi, Hisato; Liu, Fangze

    2018-01-01

    Recent experimental measurements of a bulk material covered with a small number of graphene layers reported by Yamaguchi et al. [NPJ 2D Mater. Appl. 1, 12 (2017)] (on bialkali) and Liu et al. [Appl. Phys. Lett. 110, 041607 (2017)] (on copper) and the needs of emission models in beam optics codes have lead to substantial changes in a Moments model of photoemission. The changes account for (i) a barrier profile and density of states factor based on density functional theory (DFT) evaluations, (ii) a Drude-Lorentz model of the optical constants and laser penetration depth, and (iii) a transmission probability evaluated by an Airy Transfer Matrix Approach. Importantly, the DFT results lead to a surface barrier profile of a shape similar to both resonant barriers and reflectionless wells: the associated quantum mechanical transmission probabilities are shown to be comparable to those recently required to enable the Moments (and Three Step) model to match experimental data but for reasons very different than the assumption by conventional wisdom that a barrier is responsible. The substantial modifications of the Moments model components, motivated by computational materials methods, are developed. The results prepare the Moments model for use in treating heterostructures and discrete energy level systems (e.g., quantum dots) proposed for decoupling the opposing metrics of performance that undermine the performance of advanced light sources like the x-ray Free Electron Laser. The consequences of the modified components on quantum yield, emittance, and emission models needed by beam optics codes are discussed.

  16. X-ray photoemission spectroscopy analysis of N-containing carbon-based cathode catalysts for polymer electrolyte fuel cells

    Science.gov (United States)

    Niwa, Hideharu; Kobayashi, Masaki; Horiba, Koji; Harada, Yoshihisa; Oshima, Masaharu; Terakura, Kiyoyuki; Ikeda, Takashi; Koshigoe, Yuka; Ozaki, Jun-ichi; Miyata, Seizo; Ueda, Shigenori; Yamashita, Yoshiyuki; Yoshikawa, Hideki; Kobayashi, Keisuke

    We report on the electronic structure of three different types of N-containing carbon-based cathode catalysts for polymer electrolyte fuel cells observed by hard X-ray photoemission spectroscopy. Prepared samples are derived from: (1) melamine and poly(furfuryl alcohol), (2) nitrogen-doped carbon black and (3) cobalt phthalocyanine and phenolic resin. C 1 s spectra show the importance of sp 2 carbon network formation for the oxygen reduction reaction (ORR) activity. N 1 s spectra of the carbon-based cathode catalysts are decomposed into four components identified as pyridine-like, pyrrole- or cyanide-like, graphite-like, and oxide nitrogen. Samples having high oxygen reduction reaction activity in terms of oxygen reduction potential contain high concentration of graphite-like nitrogen. O 1 s spectra are similar among carbon-based cathode catalysts of different oxygen reduction reaction activity. There is no correlation between the ORR activity and oxygen content. Based on a quantitative analysis of our results, the oxygen reduction reaction activity of the carbon-based cathode catalysts will be improved by increasing concentration of graphite-like nitrogen in a developed sp 2 carbon network.

  17. Observation of Image Potential State in Oxygen Intercalated Graphene on Iridium by Two-Photon-Photoemission Spectroscopy

    Science.gov (United States)

    Lin, Yi; Li, Yunzhe; Sadowski, Jerzy; Dadap, Jerry; Jin, Wencan; Osgood, Richard

    In this talk, we report our experimental results on the first direct observation of image potential state (IPS) in oxygen-intercalated graphene on iridium by two-photo-photoemission spectroscopy. We demonstrate how oxygen intercalation influences the IPS in Gr/Ir and decouples the interlayer interaction. We present measurements of the electronic dispersion and work function in pristine Gr/Ir, oxygen-intercalated Gr/O/Ir, and deintercalated Gr/Ir. LEED patterns are measured during the pristine, oxygen-intercalated, and deintercalated phases of the Gr/Ir sample. Based on these measurements, relative to the pristine case, the work function and the energy location of n =1 IPS relative to the Fermi level increases by 0.39 eV and 0.3 eV, respectively, due to oxygen intercalation, whereas the effective mass of n =1 IPS is hardly influenced by the intercalation process. Moreover, we achieve the quenching and restoration of the resonance from Ir Rashba states to n =1 IPS in Gr/Ir by oxygen intercalation and deintercalation. This work was supported by the DOE, Office of Basic Energy Sciences, Division of MSE under Contract No. DE-FG 02-04-ER-46157. This research used resources of the CFN, which is the U.S. DOE Office of Science User Facility, under Contract No. DE-SC0012704.

  18. Sulfur amino acids and alanine on pyrite (100) by X-ray photoemission spectroscopy: Surface or molecular role?

    Energy Technology Data Exchange (ETDEWEB)

    Sanchez-Arenillas, M.; Galvez-Martinez, S.; Mateo-Marti, E., E-mail: mateome@cab.inta-csic.es

    2017-08-31

    Highlights: • Surface annealing pretreatment on pyrite surfaces can select molecular adsorption. • Enriched monosulfide species on pyrite (100) surface favors NH{sub 2} adsorption form. • Enriching disulfide species on pyrite (100) surface promotes NH{sub 3}{sup +} adsorption form. • Unique structure of each aminoacid provides a particular fingerprint in the process. • Spectroscopy evidence, pretreatment surface processes drives molecular adsorption. - Abstract: This paper describes the first successful adsorption of the cysteine, cystine, methionine and alanine amino acids on the pyrite (100) surface under ultra-high vacuum conditions with crucial chemical adsorption parameters driving the process. We have demonstrated by X-ray photoemission spectroscopy (XPS) that the surface pretreatment annealing process on pyrite surfaces is a critical parameter driving surface reactivity. The presence of enriched monosulfide species on the pyrite (100) surface favours the amino acid NH{sub 2} chemical form, whereas a longer annealing surface pretreatment of over 3 h repairs the sulfur vacancies in the pyrite, enriching disulfide species on the pyrite surface, which promotes NH{sub 3}{sup +} adsorption due to the sulfur vacancies in the pyrite being replaced by sulfur atom dimers (S{sub 2}{sup 2−}) on the surface. Furthermore, even if the surface chemistry (monosulfide or disulfide species enrichment) is the main factor promoting a partial conversion from NH{sub 2} to NH{sub 3}{sup +} species, the unique chemical structure of each amino acid provides a particular fingerprint in the process.

  19. Sulfur amino acids and alanine on pyrite (100) by X-ray photoemission spectroscopy: Surface or molecular role?

    Science.gov (United States)

    Sanchez-Arenillas, M.; Galvez-Martinez, S.; Mateo-Marti, E.

    2017-08-01

    This paper describes the first successful adsorption of the cysteine, cystine, methionine and alanine amino acids on the pyrite (100) surface under ultra-high vacuum conditions with crucial chemical adsorption parameters driving the process. We have demonstrated by X-ray photoemission spectroscopy (XPS) that the surface pretreatment annealing process on pyrite surfaces is a critical parameter driving surface reactivity. The presence of enriched monosulfide species on the pyrite (100) surface favours the amino acid NH2 chemical form, whereas a longer annealing surface pretreatment of over 3 h repairs the sulfur vacancies in the pyrite, enriching disulfide species on the pyrite surface, which promotes NH3+ adsorption due to the sulfur vacancies in the pyrite being replaced by sulfur atom dimers (S22-) on the surface. Furthermore, even if the surface chemistry (monosulfide or disulfide species enrichment) is the main factor promoting a partial conversion from NH2 to NH3+ species, the unique chemical structure of each amino acid provides a particular fingerprint in the process.

  20. 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)

  1. Thermal stability and chemical bonding states of AlOxNy/Si gate stacks revealed by synchrotron radiation photoemission spectroscopy

    International Nuclear Information System (INIS)

    He, G.; Toyoda, S.; Shimogaki, Y.; Oshima, M.

    2010-01-01

    Annealing-temperature dependence of the thermal stability and chemical bonding states of AlO x N y /SiO 2 /Si gate stacks grown by metalorganic chemical vapor deposition (MOCVD) using new chemistry was investigated by synchrotron radiation photoemission spectroscopy (SRPES). Results have confirmed the formation of the AlN and AlNO compounds in the as-deposited samples. Annealing the AlO x N y samples in N 2 ambient in 600-800 deg. C promotes the formation of SiO 2 component. Meanwhile, there is no formation of Al-O-Si and Al-Si binding states, suggesting no interdiffusion of Al with the Si substrate. A thermally induced reaction between Si and AlO x N y to form volatile SiO and Al 2 O is suggested to be responsible for the full disappearance of the Al component that accompanies annealing at annealing temperature of 1000 deg. C. The released N due to the breakage of the Al-N bonding will react with the SiO 2 interfacial layer and lead to the formation of the Si 3 -N-O/Si 2 -N-O components at the top of Si substrate. These results indicate high temperature processing induced evolution of the interfacial chemistry and application range of AlO x N y /Si gate stacks in future CMOS devices.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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

    We explore the effects of disordered charged defects on the electronic excitations observed in the photoemission spectra of doped transition metal oxides in the Mott insulating regime by the example of the R1 -xCaxVO3 perovskites, where R = La, ⋯, Lu. A fundamental characteristic of these vanadium d2 compounds with partly filled t2 g valence orbitals is the persistence of spin and orbital order up to high doping, in contrast to the loss of magnetic order in high-Tc cuprates at low defect concentration. We study the disordered electronic structure of such doped Mott-Hubbard insulators within the unrestricted Hartree-Fock approximation and, as a result, manage to explain the spectral features that occur in photoemission and inverse photoemission. In particular, (i) the atomic multiplet excitations in the inverse photoemission spectra and the various defect-related states and satellites are qualitatively well reproduced, (ii) a robust Mott gap survives up to large doping, and (iii) we show that the defect states inside the Mott gap develop a soft gap at the Fermi energy. The soft defect-states gap, which separates the highest occupied from the lowest unoccupied states, can be characterized by a shape and a scale parameter extracted from a Weibull statistical sampling of the density of states near the chemical potential. These parameters provide a criterion and a comprehensive schematization for the insulator-metal transition in disordered systems. Our results provide clear indications that doped holes are bound to charged defects and form small spin-orbital polarons whose internal kinetic energy is responsible for the opening of the soft defect-states gap. We show that this kinetic gap survives disorder fluctuations of defects and is amplified by the long-range electron-electron interactions, whereas we observe a Coulomb singularity in the atomic limit. The small size of spin-orbital polarons is inferred by an analysis of the inverse participation ratio and by

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

    DEFF Research Database (Denmark)

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

    2014-01-01

    We theoretically study the characteristics of photoelectron emission in plasmonic nanoparticle arrays. Nanoparticles are partially embedded in a semiconductor, forming Schottky barriers at metal/semiconductor interfaces through which photoelectrons can tunnel from the nanoparticle into the semico......-based photodetectors and photovoltaic devices. The results may provide clues to designing an experiment where the contributions of surface and volume photoelectric effects to the overall photocurrent would be defined....

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

    Energy Technology Data Exchange (ETDEWEB)

    Molodtsova, Olga

    2006-07-01

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

  9. Band Edge Energetics of Heterostructured Nanorods: Photoemission Spectroscopy and Waveguide Spectroelectrochemistry of Au-Tipped CdSe Nanorod Monolayers.

    Science.gov (United States)

    Ehamparam, Ramanan; Pavlopoulos, Nicholas G; Liao, Michael W; Hill, Lawrence J; Armstrong, Neal R; Pyun, Jeffrey; Saavedra, S Scott

    2015-09-22

    Conduction and valence band energies (ECB, EVB) for CdSe nanorods (NRs) functionalized with Au nanoparticle (NP) tips are reported here, referenced to the vacuum scale. We use (a) UV photoemission spectroscopy (UPS) to measure EVB for NR films, utilizing advanced approaches to secondary electron background correction, satellite removal to enhance spectral contrast, and correction for shifts in local vacuum levels; and (b) waveguide-based spectroelectrochemistry to measure ECB from onset potentials for electron injection into NR films tethered to ITO. For untipped CdSe NRs, both approaches show EVB = 5.9-6.1 eV and ECB = 4.1-4.3 eV. Addition of Au tips alters the NR band edge energies and introduces midgap states, in ways that are predicted to influence the efficiency of these nanomaterials as photoelectrocatalysts. UPS results show that Au tipping shifts EVB closer to vacuum by up to 0.4 eV, shifts the apparent Fermi energy toward the middle of the band gap, and introduces additional states above EVB. Spectroelectrochemical results confirm these trends: Au tipping shifts ECB closer to vacuum, by 0.4-0.6 eV, and introduces midgap states below ECB, which are assigned as metal-semiconductor interface (MSI) states. Characterization of these band edge energies and understanding the origins of MSI states is needed to design energy conversion systems with proper band alignment between the light absorbing NR, the NP catalyst, and solution electron donors and acceptors. The complementary characterization protocols presented here should be applicable to a wide variety of thin films of heterogeneous photoactive nanomaterials, aiding in the identification of the most promising material combinations for photoelectrochemical energy conversion.

  10. Photoemission study of the Poly(3-hexylthiophene)/TiO2 interface and the role of 4-Mercaptopyridine

    Energy Technology Data Exchange (ETDEWEB)

    Calloni, A., E-mail: alberto1.calloni@mail.polimi.it [CNISM and Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo Da Vinci 32, 20133 Milano (Italy); Berti, G.; Ferrari, A.; Brambilla, A.; Bussetti, G. [CNISM and Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo Da Vinci 32, 20133 Milano (Italy); Canesi, E.V.; Petrozza, A. [Center for Nano Science and Technology @ Polimi, Istituto Italiano di Tecnologia, via Pascoli 70/3, 20133 Milano (Italy); Duò, L. [CNISM and Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo Da Vinci 32, 20133 Milano (Italy)

    2014-06-02

    We report on a combined X-ray and UV photoemission spectroscopy study (XPS, UPS) of the interface between Poly(3-hexylthiophene) (P3HT) and mesoporous titanium dioxide (TiO{sub 2}), a key element in the development of hybrid solar cells. We employed the elemental specificity of XPS to directly probe, on the complete P3HT/TiO{sub 2} heterostructure, the changes in the electronic levels alignment at the interface upon the addition of 4-Mercaptopyridine (4-MPy) molecules. We estimate an upper limit of 50 meV to the contribution of 4-MPy to the P3HT/TiO{sub 2} interfacial dipole. In addition, UPS was used to provide a quantitative estimate of the relevant parameters controlling the transfer of charge through the hybrid interface, such as the binding energy of the TiO{sub 2} valence and conduction bands and of the P3HT highest occupied/lowest unoccupied molecular orbitals. In both cases, we confirm that the alignment of P3HT energy levels to those of the substrate is not influenced by the position of the Fermi level inside the TiO{sub 2} band gap. - Highlights: • We studied the electronic structure of the Poly(3-hexylthiophene)/TiO{sub 2} interface. • 4-mercaptopyridine (4-MPy) molecules were used as interface modifiers. • The contribution of 4-MPy to the interfacial dipole is limited to 50 meV. • No pinning of Poly(3-hexylthiophene) energy levels to the Fermi level is observed.

  11. Characterization of free-standing InAs quantum membranes by standing wave hard x-ray photoemission spectroscopy

    Science.gov (United States)

    Conti, G.; Nemšák, S.; Kuo, C.-T.; Gehlmann, M.; Conlon, C.; Keqi, A.; Rattanachata, A.; Karslıoǧlu, O.; Mueller, J.; Sethian, J.; Bluhm, H.; Rault, J. E.; Rueff, J. P.; Fang, H.; Javey, A.; Fadley, C. S.

    2018-05-01

    Free-standing nanoribbons of InAs quantum membranes (QMs) transferred onto a (Si/Mo) multilayer mirror substrate are characterized by hard x-ray photoemission spectroscopy (HXPS) and by standing-wave HXPS (SW-HXPS). Information on the chemical composition and on the chemical states of the elements within the nanoribbons was obtained by HXPS and on the quantitative depth profiles by SW-HXPS. By comparing the experimental SW-HXPS rocking curves to x-ray optical calculations, the chemical depth profile of the InAs(QM) and its interfaces were quantitatively derived with ångström precision. We determined that (i) the exposure to air induced the formation of an InAsO4 layer on top of the stoichiometric InAs(QM); (ii) the top interface between the air-side InAsO4 and the InAs(QM) is not sharp, indicating that interdiffusion occurs between these two layers; (iii) the bottom interface between the InAs(QM) and the native oxide SiO2 on top of the (Si/Mo) substrate is abrupt. In addition, the valence band offset (VBO) between the InAs(QM) and the SiO2/(Si/Mo) substrate was determined by HXPS. The value of VBO = 0.2 ± 0.04 eV is in good agreement with literature results obtained by electrical characterization, giving a clear indication of the formation of a well-defined and abrupt InAs/SiO2 heterojunction. We have demonstrated that HXPS and SW-HXPS are non-destructive, powerful methods for characterizing interfaces and for providing chemical depth profiles of nanostructures, quantum membranes, and 2D layered materials.

  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. 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.

  14. Doping the Copper-Oxygen Planes with Electrons: The View with Photoemission

    Energy Technology Data Exchange (ETDEWEB)

    Armitage, Norman P.

    2002-03-07

    The undoped parent compounds of high-temperature cuprate superconductors are known to be antiferromagnetic Mott insulators. As the CuO{sub 2} planes are doped with charge carriers, the antiferromagnetic phase subsides and superconductivity emerges. The symmetry, or the lack thereof, between doping with electrons (n-type) or holes (p-type) has important theoretical implications as most models implicitly assume symmetry. However, most of what we know about these superconductors comes from experiments performed on p-type materials. The much fewer number of measurements from n-type compounds suggest that there may be both commonalities and differences between the two sides of the phase diagram. This issue of electron/hole symmetry has not been seriously discussed, perhaps, because the experimental database of n-type results is very limited.

  15. Adaptive electron beam shaping using a photoemission gun and spatial light modulator

    Science.gov (United States)

    Maxson, Jared; Lee, Hyeri; Bartnik, Adam C.; Kiefer, Jacob; Bazarov, Ivan

    2015-02-01

    The need for precisely defined beam shapes in photoelectron sources has been well established. In this paper, we use a spatial light modulator and simple shaping algorithm to create arbitrary, detailed transverse laser shapes with high fidelity. We transmit this shaped laser to the photocathode of a high voltage dc gun. Using beam currents where space charge is negligible, and using an imaging solenoid and fluorescent viewscreen, we show that the resultant beam shape preserves these detailed features with similar fidelity. Next, instead of transmitting a shaped laser profile, we use an active feedback on the unshaped electron beam image to create equally accurate and detailed shapes. We demonstrate that this electron beam feedback has the added advantage of correcting for electron optical aberrations, yielding shapes without skew. The method may serve to provide precisely defined electron beams for low current target experiments, space-charge dominated beam commissioning, as well as for online adaptive correction of photocathode quantum efficiency degradation.

  16. Adaptive electron beam shaping using a photoemission gun and spatial light modulator

    Directory of Open Access Journals (Sweden)

    Jared Maxson

    2015-02-01

    Full Text Available The need for precisely defined beam shapes in photoelectron sources has been well established. In this paper, we use a spatial light modulator and simple shaping algorithm to create arbitrary, detailed transverse laser shapes with high fidelity. We transmit this shaped laser to the photocathode of a high voltage dc gun. Using beam currents where space charge is negligible, and using an imaging solenoid and fluorescent viewscreen, we show that the resultant beam shape preserves these detailed features with similar fidelity. Next, instead of transmitting a shaped laser profile, we use an active feedback on the unshaped electron beam image to create equally accurate and detailed shapes. We demonstrate that this electron beam feedback has the added advantage of correcting for electron optical aberrations, yielding shapes without skew. The method may serve to provide precisely defined electron beams for low current target experiments, space-charge dominated beam commissioning, as well as for online adaptive correction of photocathode quantum efficiency degradation.

  17. Reversed interfacial fractionation of carbonate and bicarbonate evidenced by X-ray photoemission spectroscopy

    Science.gov (United States)

    Lam, Royce K.; Smith, Jacob W.; Rizzuto, Anthony M.; Karslıoǧlu, Osman; Bluhm, Hendrik; Saykally, Richard J.

    2017-03-01

    The fractionation of ions at liquid interfaces and its effects on the interfacial structure are of vital importance in many scientific fields. Of particular interest is the aqueous carbonate system, which governs both the terrestrial carbon cycle and physiological respiration systems. We have investigated the relative fractionation of carbonate, bicarbonate, and carbonic acid at the liquid/vapor interface finding that both carbonate (CO32-) and carbonic acid (H2CO3) are present in higher concentrations than bicarbonate (HCO3-) in the interfacial region. While the interfacial enhancement of a neutral acid relative to a charged ion is expected, the enhancement of doubly charged, strongly hydrated carbonate anion over the singly charged, less strongly hydrated bicarbonate ion is surprising. As vibrational sum frequency generation experiments have concluded that both carbonate and bicarbonate anions are largely excluded from the air/water interface, the present results suggest that there exists a significant accumulation of carbonate below the depletion region outside of the area probed by sum frequency generation.

  18. 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.

  19. Studies on effect of europium concentration on the photoemission of laser ablated Y2O3:Eu based nano-phosphors

    International Nuclear Information System (INIS)

    Nissamudeen, K.M.; Krishnan, Renju R.; Rajan, Geo; Gopchandran, K.G.

    2007-01-01

    Full text: Phosphors are essential materials in display applications. Oxide-based phosphors are likely to emerge as the potential choice for the FED red phosphor. Among those oxide-based phosphors, there has been significant research interest in the development of Y 2 O 3 :Eu thin films as one of the most promising oxide based red phosphor systems. Yttrium oxide mixed with europium exhibit strong UV and cathode-ray-excited luminescence that are useful in lamp and display applications. Dielectric Y 2 O 3 film has recently attracted much attention for its potential application as an electric insulation layer in electroluminescent devices and high-density dynamic random access memory gate dielectrics because of its high band gap (5.8 eV) and large dielectric constant (14 to 18). Another important application of Y 2 O 3 has been in luminescent displays as a host material for rare-earth ions, specifically europium, in order to get emission of red light. In the present study thin films were deposited under a vacuum of 10 -6 mbar on fused amorphous quartz substrates using a Q-switched Nd: YAG laser, 532 nm, pulse width 9 n sec, and repetition frequency of 10 Hz, with sintered Y 2 O 3 pellets having different europium concentration as target material. Attempts were made to understand the effect of europium concentration and annealing process on the photoemission properties of the films. A europium concentration of 8 wt% and an annealing temperature of 1173 K were found to be optimum conditions for maximum photoemission. The dependence of structure and morphology of the films on the photoemission intensity are described with XRD patterns and images obtained from AFM and SEM studies

  20. 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.

  1. 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.

  2. Anomalous metallic state with strong charge fluctuations in BaxTi8O16 +δ revealed by hard x-ray photoemission spectroscopy

    Science.gov (United States)

    Dash, S.; Kajita, T.; Okawa, M.; Saitoh, T.; Ikenaga, E.; Saini, N. L.; Katsufuji, T.; Mizokawa, T.

    2018-04-01

    We have studied a charge-orbital driven metal-insulator transition (MIT) in hollandite-type BaxTi8O16 +δ by means of hard x-ray photoemission spectroscopy (HAXPES). The Ti 2 p HAXPES indicates strong Ti3 +/Ti4 + charge fluctuation in the metallic phase above the MIT temperature. The metallic phase is characterized by a power-law spectral function near the Fermi level which would be a signature of bad metal with non-Drude polaronic behavior. The power-law spectral shape is associated with the large Seebeck coefficient of the metallic phase in BaxTi8O16 +δ .

  3. 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

  4. 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.

  5. Temperature-dependent photoemission and x-ray absorption studies of the metal-insulator transition in Bi1-xLaxNiO3

    Science.gov (United States)

    Wadati, Hiroki; Tanaka, Kiyohisa; Fujimori, Atsushi; Mizokawa, Takashi; Kumigashira, Hiroshi; Oshima, Masaharu; Ishiwata, Shintaro; Azuma, Masaki; Takano, Mikio

    2007-11-01

    Perovskite-type BiNiO3 is an insulating antiferromagnet in which a charge disproportionation occurs at the Bi site. La substitution for Bi suppresses the charge disproportionation and makes the system metallic, and for 0.05≤x≤0.1 a broad metal-insulator transition (MIT) occurs as a function of temperature. We have measured the temperature dependence of the photoemission and x-ray absorption (XAS) spectra of Bi1-xLaxNiO3 to investigate how the electronic structure changes across the MIT. From the Ni2p XAS spectra of x=0.05 , we found almost no change in the valence of Ni across the MIT. In the valence-band photoemission spectra, the Fermi cutoff disappeared for x=0.05 at a low temperature, whereas for x=0.1 and 0.2, it remained at all temperatures but the intensity at the Fermi level decreased gradually with decreasing temperature. Our experimental results suggest that the MIT is caused by the localization of holes in the O2p band and that the “insulating” phase below the MIT is indeed a mixture of insulating and metallic regions.

  6. 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

  7. One-step photoemission calculations for ideal GaAs(001) and AlAs(001) surfaces and (GaAs).sub.m./sub. (AlAs).sub.n./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.

    2001-01-01

    Roč. 63, - (2001), s. 195321-1-195321-10 ISSN 0163-1829 Institutional research plan: CEZ:AV0Z1010914 Keywords : superlattices * III/V semiconductors * photoemission * one-step model Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.070, year: 2001

  8. 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

  9. Stoner vs. spin-mixing behavior in the bulk magnetism of Gd: A spin ...

    Indian Academy of Sciences (India)

    The temperature dependence of the rare-earth 2-bulk band has been regarded as an exemplary case which realizes the simple Stoner behavior. We examined the evolution of Gd2 bulk bands with temperature in the range 0.5 ≤ /C ≤ 1 with spin-resolved, photoemission spectroscopy. The direct observation of the ...

  10. Pramana – Journal of Physics | Indian Academy of Sciences

    Indian Academy of Sciences (India)

    ... bands with temperature in the range 0.5 ≤ /C ≤ 1 with spin-resolved, photoemission spectroscopy. The direct observation of the spin-dependent spectral line shapes reveals a complex temperature dependence and manifests a clear inadequacy of the Stoner model to the description of the magnetism in rare earths.

  11. 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.

  12. Band alignment at the Cu2SnS3/In2S3 interface measured by X-ray photoemission spectroscopy

    Science.gov (United States)

    Jia, Hongjie; Cheng, Shuying; Zhang, Hong; Yu, Jinling; Lai, Yunfeng

    2015-10-01

    This paper focused on investigating the band alignment at the Cu2SnS3 (CTS)/In2S3 heterojunction interface by X-ray photoemission spectroscopy. An In2S3 over-layer was grown on a CTS thin film, which was grown by sulfurization of vacuum thermal evaporated Sn-Cu metallic precursors in a H2S:N2 atmosphere. The valence band offset (VBO) at the CTS/In2S3 interface was measured to be 1.27 ± 0.10 eV. The conduction band offset (CBO) was calculated from the measured VBO, giving (0.58 ± 0.10) eV. These values show that the CBO has a spike-like behavior and the interface is a 'type I'.

  13. Recent progress in energy-filtered high energy X-ray photoemission electron microscopy using a Wien filter type energy analyzer

    Science.gov (United States)

    Niimi, H.; Tsutsumi, T.; Matsudaira, H.; Kawasaki, T.; Suzuki, S.; Chun, W.-J.; Kato, M.; Kitajima, Y.; Iwasawa, Y.; Asakura, K.

    2004-10-01

    Energy-filtered X-ray photoemission electron microscopy (EXPEEM) is a microscopy technique which has the potential to provide surface chemical mapping during surface chemical processes on the nanometer scale. We studied the possibilities of EXPEEM using a Wien filter type energy analyzer in the high energy X-ray region above 1000 eV. We have successfully observed the EXPEEM images of Au islands on a Ta sheet using Au 3d 5/2 and Ta 3d 5/2 photoelectron peaks which were excited by 2380 eV X-rays emitted from an undulator (BL2A) at Photon Factory. Our recent efforts to improve the sensitivity of the Wien filter energy analyzer will also be discussed.

  14. Observation of Element-Specific Energy-Filtered X-Ray Photoemission Electron Microscopy Images of Au on Ta Using a Wien Filter Type Energy Analyzer

    Science.gov (United States)

    Yasufuku, Hideyuki; Ohminami, Yusuke; Tsutsumi, Tetsuya; Niimi, Hironobu; Matsudaira, Nobuaki; Asakura, Kiyotaka; Kato, Makoto; Sakai, Yuji; Kitajima, Yoshinori; Iwasawa, Yasuhiro

    2004-11-01

    We have shown the possibility of a Wien filter as an energy analyzer for the energy-filtered X-ray photoemission electron microscopy (EXPEEM) by obtaining images of Au islands on a Ta substrate using an inner shell photoelectron excited by an X-ray with a photon energy of 2300 eV. When the photoelectron with kinetic energy of nearly 0 eV was selected, brighter Au islands were observed. When the kinetic energies of photoelectrons passing the Wien filter are set at those of Au 3d5/2 and Ta 3p3/2 photoelectrons, the Au and Ta regions appeared brighter, respectively, indicating that the chemical imaging was successful using a high energy X-ray and a Wien filter energy analyzer.

  15. Recent progress in energy-filtered high energy X-ray photoemission electron microscopy using a Wien filter type energy analyzer

    Energy Technology Data Exchange (ETDEWEB)

    Niimi, H. [Catalysis Research Center, Hokkaido University, Sapporo 001-0021 (Japan); Tsutsumi, T. [Catalysis Research Center, Hokkaido University, Sapporo 001-0021 (Japan); Matsudaira, H. [Catalysis Research Center, Hokkaido University, Sapporo 001-0021 (Japan); Kawasaki, T. [Catalysis Research Center, Hokkaido University, Sapporo 001-0021 (Japan); Suzuki, S. [Catalysis Research Center, Hokkaido University, Sapporo 001-0021 (Japan); Chun, W.-J. [Catalysis Research Center, Hokkaido University, Sapporo 001-0021 (Japan); Core Research for Evolutional Science and Technology, Japan Science and Technology Corporation, Tokyo (Japan); Kato, M. [JEOL Ltd, 3-1-2 Musashino, Akishima, Tokyo 196-8558 (Japan); Kitajima, Y. [Photon Factory, Institute of Materials Structure Science, Tsukuba 305-0801 (Japan); Iwasawa, Y. [Department of Chemistry, Graduate School of Science, The University of Tokyo, Tokyo 113-0033 (Japan); Asakura, K. [Catalysis Research Center, Hokkaido University, Sapporo 001-0021 (Japan)]. E-mail: askr@cat.hokudai.ac.jp

    2004-10-15

    Energy-filtered X-ray photoemission electron microscopy (EXPEEM) is a microscopy technique which has the potential to provide surface chemical mapping during surface chemical processes on the nanometer scale. We studied the possibilities of EXPEEM using a Wien filter type energy analyzer in the high energy X-ray region above 1000 eV. We have successfully observed the EXPEEM images of Au islands on a Ta sheet using Au 3d{sub 5/2} and Ta 3d{sub 5/2} photoelectron peaks which were excited by 2380 eV X-rays emitted from an undulator (BL2A) at Photon Factory. Our recent efforts to improve the sensitivity of the Wien filter energy analyzer will also be discussed.

  16. Valence band electronic structure of Ho-doped La0.67Ca0.33MnO3 using ultra-violet photoemission spectroscopy

    Science.gov (United States)

    Rout, S. K.; Mukharjee, R. N.; Mishra, D. K.; Roul, B. K.; Sekhar, B. R.; Dalai, M. K.

    2017-05-01

    In this manuscript we report the valence band electronic structure of Ho doped La0.67Ca0.33MnO3 using ultraviolet photoemission spectroscopy. We compared the density of states of La0.67Ca0.33MnO3, La0.67Ca0.3Ho0.03MnO3 and La0.64Ho0.03Ca0.33MnO3 near the Fermi level at various temperatures. Significant amount of changes have been observed at higher temperatures (220 K and 300 K) where the near Fermi level density of states increases with Ho doping into La0.67Ca0.33MnO3 indicating the enhancement of magnitude of change in metallicity (conductivity).

  17. X-ray photoemission spectroscopy investigation of the early stages of the oxygen aided Cr growth on Fe(0 0 1)

    Energy Technology Data Exchange (ETDEWEB)

    Brambilla, A., E-mail: alberto.brambilla@polimi.it [CNISM and Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo Da Vinci 32, 20133 Milano (Italy); Calloni, A.; Picone, A.; Finazzi, M.; Duò, L.; Ciccacci, F. [CNISM and Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo Da Vinci 32, 20133 Milano (Italy)

    2013-02-15

    We report on an X-ray photoemission spectroscopy investigation of the early stages of growth of ultra-thin Cr films on the oxygen-passivated Fe(0 0 1)–p(1 × 1)O surface. The Cr coverages ranged from sub-monolayer up to a few atomic layers. Cr has been grown either at 380 K or at 570 K. Our investigation reveals that during the Cr film growth oxygen floats toward the free surface. The presence of a metallic Cr signal from the very beginning of film growth is discussed in relation to Cr–Fe intermixing and alloy formation at the interface. Our findings are independent from the growth temperature, indicating that it has a very little influence on the chemical interactions at the interface, at variance with the oxygen-free Cr/Fe interface.

  18. 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.

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

    Energy Technology Data Exchange (ETDEWEB)

    Hwang, Harold

    2011-08-19

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

  20. Carbon 1s photoemission line analysis of C-based adsorbate on (111)In2O3 surface: The influence of reducing and oxidizing conditions

    Science.gov (United States)

    Brinzari, V.; Cho, B. K.; Korotcenkov, G.

    2016-12-01

    Synchrotron radiation photoemission study of C 1s line of (111) In2O3 surface was carried out under HV (high vacuum) doses of oxygen, carbon monoxide and water. Gas interaction with the surface was activated by heating of In2O3 monocrystalline film at temperatures of 160 or 250 °C. The study of complex structure of C 1 s line and evolution of its fine components allowed to establish their nature and to propose possible surface adsorbed species and reactions, including a direct chemisorption and dissociation of CO molecules. Reduction or oxidation of the surface determines whether the first (chemisorption) or the second (dissociation) process takes place. The latter is responsible for additional formation of ionosorbed oxygen. Both processes have not been previously reported for In2O3 and for conductive metal oxides.

  1. 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.

  2. 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

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

    Science.gov (United States)

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

    2016-07-13

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

  4. Soft x-ray photoemission spectroscopy of the Ba atomic layer deposition on the ceramic multiferroic BiFeO{sub 3}

    Energy Technology Data Exchange (ETDEWEB)

    Benemanskaya, G.V., E-mail: galina.benemanskaya@mail.ioffe.ru [Ioffe Institute, Politekhnicheskaya str. 26, St. Petersburg, 194021 (Russian Federation); Dementev, P.A.; Lapushkin, M.N. [Ioffe Institute, Politekhnicheskaya str. 26, St. Petersburg, 194021 (Russian Federation); Timoshnev, S.N. [St Petersburg Academic University, Khlopina str.8/3, St. Petersburg, 194021 (Russian Federation); Senkovskiy, B. [Helmholts-Zentrum Berlin, Elektronenspeicherring BESSY II, Albert-Einstein-Strasse 15, D-12489 Berlin (Germany)

    2017-04-01

    Highlights: • Ba/BiFeO{sub 3} interface was studied by X-ray synchrotron- photoemission spectroscopy. • Ba adsorption is found to modify the Bi 4f, O 1s and Fe 2p core level spectra. • Ba induced charge transfer causes increasing in Bi-valency and O-ionicity. • Ba adsorption results in increasing the amount of Fe{sup 2+} ions in the surface region. - Abstract: Electronic structure of the ceramic multiferroic BiFeO{sub 3} and the Ba/BiFeO{sub 3} nanointerface is investigated in situ in an ultrahigh vacuum by synchrotron-based photoemission spectroscopy with the excited photon energy from 120 eV to 900 eV. The Bi 4f, O 1s, Fe 2p, and Ba 5p core-levels spectra are studied. The Ba atomic layer deposition is found to induce a significant change in spectra that is originated from the charge transfer between Ba adatoms and Bi, O surface atoms with increasing the Bi-valency and O-ionicity. The Fe 2p{sub 3/2} core level spectrum for the clean BiFeO{sub 3} is shown to contain both the Fe{sup 2+} and Fe{sup 3+} ion components with the atomic ratio of Fe{sup 2+}/Fe{sup 3+} ∼1. The Ba adsorption is found to increase the ratio up to ∼1.5. This new effect is clearly caused by recharge between Fe{sup 3+} ↔ Fe{sup 2+} ions with increasing the amount of Fe{sup 2+} ions.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-09-15

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

  6. Characterization of heterojunctions via x-ray and uv photoemission spectroscopy: energy level implications for single and mixed monolayer SAMs, cadmium selenide nanoparticle films, and organic semiconductor depositions

    Science.gov (United States)

    Graham, Amy L.

    This work has centered on the interface dipoles arising at heterojunctions between metals, semiconductor nanoparticles, self-assembled monolayers, and organic semiconductor materials. Alkanethiol self-assembled monolayers, CdSe nanocrystals, and the organic semiconductors zinc phthalocyanine (ZnPc) and Buckminster fullerene (C60) were the basis of these investigations. UV photoemission spectroscopy has proven to be an invaluable tool to observe the vacuum level shifts for these analyses while using XPS to corroborate surface structure. With a full evaluation of these surfaces, the shifts in the vacuum level, valence ionizations, and core ionizations, the impact of these interfaces, as well as their influence on the subsequent deposition of organic semiconductor layers is established. Alkanethiols possessing varying dipole moments were examined on gold and silver substrates. The viability of these alkanethiols was demonstrated to predictively adjust the work function of these metals as a function of their intrinsic dipole moments projected to surface normal, and established differences between Ag---S and Au---S bonds. The capability of the SAMs to modify the work function of gold provided an opportunity for mixed monolayers of the alkanethiols to produce a precise range of work functions by minimal adjustments of solution concentration, which were examined with a simple point dipole model. Photoemission spectroscopy offers a thorough analysis of CdSe nanoparticle films. Despite a plethora of research on these nanocrystals, there still is controversy on the magnitude of the shift in the valence band with diameter. In our research we found the majority of the valence band shift could be attributed to the interface dipole, ignored previously. Meanwhile, the valence band tethered films was obscured by the sulfur of the thiol tether. Finally, organic semiconductor layers deposited on SAMs on gold exhibited various interface dipole effects at these heterojunctions. Charge

  7. Electric- and magnetic-field tuning of spin-resolved one-dimensional subbands in an InSb nanowire

    DEFF Research Database (Denmark)

    Estrada Saldana, Juan Carlos; Cleuziou, J.P.; Lee, E.H.

    2017-01-01

    We report an experimental study of one-dimensional (1D) electronic transport in an InSb semiconducting nanowire. Three bottom gates are used to locally deplete the nanowire creating a ballistic quantum point contact with only a few conducting channels. In a magnetic field, the Zeeman splitting of...

  8. 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}.

  9. Ultraviolet photoelectron spectroscopy and inverse photoemission spectroscopy of [6,6]-phenyl-C61-butyric acid methyl ester in gas and solid phases

    International Nuclear Information System (INIS)

    Akaike, Kouki; Nishi, Toshio; Ouchi, Yukio; Seki, Kazuhiko; Kanai, Kaname; Yoshida, Hiroyuki; Tsutsumi, Jun'ya; Sato, Naoki

    2008-01-01

    The electronic structure of [6,6]-phenyl-C 61 -butyric acid methyl ester (PCBM) was studied using ultraviolet photoelectron spectroscopy of vapor and thin film and inverse photoemission spectroscopy of thin film. The threshold ionization energy of PCBM was found to be 7.17±0.04 eV in gas phase and 5.96±0.02 eV in solid phase. The threshold electron affinity was 3.9±0.1 eV in solid phase. These values are 0.4-0.6 eV smaller than C 60 . The density functional theory calculations gave consistent results with these trends and suggested that the electron donation from the side chain to C 60 backbone raised the C 60 -backbone-derived π orbitals of PCBM. The polarization energy of PCBM is 1.21 eV, which is almost the same as C 60 but is about 0.5 eV smaller than the value of typical aromatic hydrocarbons

  10. 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.

  11. X-ray photoemission spectroscopy investigation of CaTiO3:Eu for luminescence property: effect of Eu3+ ion

    International Nuclear Information System (INIS)

    Wang, Kaichen; Zhao, Baijun; Gao, Lu

    2016-01-01

    Graphical abstract: The influence on the photoluminescent performance due to the electronic structure change in Eu-doped CaTiO 3 of the specific core-level and valence band spectrum via X-ray photoemission spectroscopy were characterized. - Highlights: • Single phase CaTiO 3 and CaTiO 3 : Eu crystals were prepared under mild hydrothermal method. • Crystal structure, doping level and the relations to their luminescent property were discussed. • Charge compensation mechanism was discussed via valance band spectrum by XPS. - Abstract: Charge compensation of on-site Eu 4f–5d transition that determines the luminescent performance was confirmed with valance band spectrum. Influence of photoelectrons from CaTiO 3 : Eu to the corresponding luminescent performance was discussed based on the crystal structure, doping level and the relations to their luminescent property. This paper is important to further optimize the luminescent performance for improving the efficiency and reducing the cost in light emitting diode industry.

  12. Observation of band bending of metal/high-k Si capacitor with high energy x-ray photoemission spectroscopy and its application to interface dipole measurement

    Science.gov (United States)

    Kakushima, K.; Okamoto, K.; Tachi, K.; Song, J.; Sato, S.; Kawanago, T.; Tsutsui, K.; Sugii, N.; Ahmet, P.; Hattori, T.; Iwai, H.

    2008-11-01

    Band bendings of Si substrates have been observed using hard x-ray photoemission spectroscopy. With a capability of collecting photoelectrons generated as deep as 40 nm, the binding energy shift in a core level caused by the potential profile at the surface of the substrate results in a spectrum broadening. The broadening is found to be significant when heavily doped substrates are used owing to its steep potential profile. The surface potential of the substrate can be obtained by deconvolution of the spectrum. This method has been applied to observe the band bending profile of metal-oxide-semiconductor capacitors with high-k gate dielectrics. By comparing the band bending profiles of heavily-doped n+- and p+-Si substrates, the interface dipoles presented at interfaces can be estimated. In the case of W gated La2O3/La-silicate capacitor, an interface dipole to shift the potential of -0.45 V has been estimated at La-silicate/Si interface, which effectively reduces the apparent work function of W. On the other hand, an interface dipole of 0.03-0.07 V has been found to exist at Hf-silicate/SiO2 interface for W gated HfO2/Hf-silicate/SiO2 capacitor.

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

    Directory of Open Access Journals (Sweden)

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

    2013-01-01

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

  14. Experimental investigation of an optimum configuration for a high-voltage photoemission gun for operation at ≥500  kV

    Directory of Open Access Journals (Sweden)

    Nobuyuki Nishimori

    2014-05-01

    Full Text Available We demonstrated the generation of a 500-keV electron beam from a high dc voltage photoemission gun for an energy recovery linac light source [N. Nishimori et al., Appl. Phys. Lett. 102, 234103 (2013]. This demonstration was achieved by addressing two discharge problems that lead to vacuum breakdown in the dc gun. One is field emission generated from a central stem electrode. We employed a segmented insulator to protect the ceramic insulator surface from the field emission. The other is microdischarge at an anode electrode or a vacuum chamber, which is triggered by microparticle transfer or field emission from a cathode electrode. An experimental investigation revealed that a larger acceleration gap, optimized mainly to reduce the surface electric field of the anode electrode, suppresses the microdischarge events that accompany gas desorption. It was also found that nonevaporable getter pumps placed around the acceleration gap greatly help to suppress those microdischarge events. The applied voltage as a function of the total gas desorption is shown to be a good measure for finding the optimum dc gun configuration.

  15. 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 ...

  16. 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

  17. 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.

  18. Evolution of the nanostructure of Pt and Pt-Co polymer electrolyte membrane fuel cell electrocatalysts at successive degradation stages probed by X-ray photoemission

    Science.gov (United States)

    Ali, Mushtaq; Witkowska, Agnieszka; Abbas, Mamatimin; Gunnella, Roberto; Di Cicco, Andrea

    2014-12-01

    We present a set of XPS (X-ray photoemission spectroscopy) measurements and detailed data-analysis of electrodes for polymer electrolyte membrane fuel cell (PEMFC) based on carbon supported catalysts (Pt and Pt-Co) subjected to a step-like potential cycling (accelerated degradation test). The results of the measurements complete and corroborate parallel TEM (transmission electron microscopy), XRD (X-ray diffraction) and XAS (X-ray absorption spectroscopy) results pointing at a modification of the nanostructure of the catalyst grains. The surface sensitivity of the XPS measurements is used to study the modification of the reactive surface structure of the nanoparticles and the interplay of reactivity and dissolution/precipitation/agglomeration of metal clusters during the catalyst work. The combination of XPS results with XRD, XAS and TEM ones allowed us to obtain a model for the structural changes in Pt-Co nanoparticles occurring during operation. The main structural modifications, in which predominantly Co atoms are involved, occur during the first hours of catalyst operation changing the stoichiometry and degree of disorder in external particles shell. In the last stages of the degradation process, core-shell particles structure, with ordered Pt4Co core and Pt-rich shell (and finally Pt-skin), is formed possibly explaining higher Pt-Co catalyst stability (structural and electrochemical) than pure Pt catalyst.

  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. Electronic structure, photoemission spectra, and vacuum-ultraviolet optical spectra of CsPbCl3 and CsPbBr3

    Science.gov (United States)

    Heidrich, K.; Schäfer, W.; Schreiber, M.; Söchtig, J.; Trendel, G.; Treusch, J.; Grandke, T.; Stolz, H. J.

    1981-11-01

    Optical spectra of CsPbCl3 and CsPbBr3 have been measured in the range from 2 to 10 eV and have been combined with ultraviolet-photoemission-spectroscopy (UPS)-measurements at 21.1 and 40.8 eV. A quantitative band calculation is presented, which takes into account anion-anion interaction as well as electronic states of the Cs+ ion. The prominent features of earlier band models and measurements are reestablished through our measurements and calculations, namely that the valence band consists of anionic p functions and Pb 6s functions, the lowest conduction band being Pb 6p type, and the lowest gap occuring at the R point of the Brillouin zone. Inclusion of a further (Cs 6s-type) conduction band, however, is necessary to bring the calculated joint density of states into agreement with vacuum-ultraviolet optical spectra. The calculated densities of states of the valence bands are in quantitative agreement with those deduced from our UPS measurements.

  5. Ground Testing and Flight Demonstration of Charge Management of Insulated Test Masses Using UV LED Electron Photoemission

    OpenAIRE

    Saraf, Shailendhar; Buchman, Sasha; Balakrishnan, Karthik; Lui, Chin Yang; Soulage, Michael; Faied, Dohy; Hanson, John; Ling, Kuok; Jaroux, Belgacem; AlRashed, Abdullah; Nassban, Badr Al; Suwaidan, Badr Al; Harbi, Mohammed Al; Salamah, Badr Bin; Othman, Mohammed Bin

    2016-01-01

    The UV LED mission demonstrates the precise control of the potential of electrically isolated test masses that is essential for the operation of space accelerometers and drag free sensors. Accelerometers and drag free sensors were and remain at the core of geodesy, aeronomy, and precision navigation missions as well as gravitational science experiments and gravitational wave observatories. Charge management using photoelectrons generated by the 254 nm UV line of Hg was first demonstrated on G...

  6. X-ray photo-emission studies of Cu1-xTlxBa2Ca3Cu4O12-y superconductor thin films

    International Nuclear Information System (INIS)

    Khan, Nawazish A.; Mumtaz, M.; Ahadian, M.M.; Iraji-zad, Azam

    2006-01-01

    X-ray photo-emission spectroscopy (XPS) studies of Cu 1-x Tl x Ba 2 Ca 3 Cu 4 O 12-y superconductor thin films have been carried out for understanding the mechanism of superconductivity and to find out the reasons for the increase of zero resistivity critical temperature T c (R = 0) with post-annealing in a nitrogen atmosphere. It is observed from these studies that reduction of charge state of thallium is a source of doping of carriers to the CuO 2 planes. The reduced charge state of thallium (i.e. Tl 1+ ) promotes lower oxygen concentration in the charge reservoir layer, which possibly results in movement of electrons to the conducting CuO 2 planes. The higher density of electrons in the CuO 2 planes optimizes the hole concentration 'n p ' in these planes. The reduced charge state of thallium in the Cu 1-x Tl x Ba 2 O 4-δ charge reservoir layer is also supported by a shift of the Ba 3d 5/2 and Ba 3d 3/2 XPS lines to lower binding energies with post-annealing in nitrogen atmosphere. Moreover, the movement of the valance band spectrum to lower binding energies suggested that the electronic density of states changes in the valance band with the post-annealing in nitrogen, which possibly becomes a source of doping of carriers to the CuO 2 planes. The increased doping of electrons to the CuO 2 planes optimizes the Fermi-vector K F and Fermi-velocity V F of the carriers and increases the T c (R = 0) of final compound

  7. Photoemission and low energy electron microscopy study on the formation and nitridation of indium droplets on Si (111)7 × 7 surfaces

    International Nuclear Information System (INIS)

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

    2013-01-01

    The formation and nitridation of indium (In) droplets on Si (111)7 × 7, with regard to In droplet epitaxy growth of InN nanostructures, were studied using a spectroscopic photoemission and low energy electron microscopy, for the In coverages from 0.07 to 2.3 monolayer (ML). The results reveal that the In adatoms formed well-ordered clusters while keeping the Si (111)7 × 7 surface periodicity at 0.07 ML and a single √(3)×√(3) phase at 0.3 ML around 440–470 °C. At 0.82 ML, owing to the presence of structurally defect areas beside the 7 × 7 domains, 3-D In droplets evolved concomitantly with the formation of 4 × 1-In cluster chains, accompanied by a transition in surface electric property from semiconducting to metallic. Further increasing the In to 2.3 ML led to a moderate increase in number density and an appreciable lateral growth of the droplets, as well as the multi-domain In phases. Upon nitridation with NH 3 at ∼ 480 °C, besides the nitridation of the In droplets, the N radicals also dissociated the In-Si bonds to form Si-N. This caused a partial disintegration of the ordered In phase and removal of the In adatoms between the In droplets. - Highlights: ► Formation and nitridation of indium (In) droplets on Si (111) were studied. ► In droplets evolved with the 4 × 1-In cluster chains at 0.82 monolayer (ML). ► In droplets grow in density and lateral size with In coverage increased to 2.3 ML. ► The multi-domain In phases were formed at 2.3 ML. ► Nitridation of In droplets is accompanied by a disintegration of layering In phase

  8. 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

  9. High-resolution X-ray photoemission spectroscopy study of AlN nano-columns grown by nitridation of Al nano-squares on Si(111) substrates with ammonia

    International Nuclear Information System (INIS)

    Qi, B.; Agnarsson, B.; Goethelid, M.; Olafsson, S.; Gislason, H.P.

    2010-01-01

    The growth of AlN nano-columns by ammonium nitridation of Al nano-squares embedded in SiO 2 on Si(111) substrates was studied by high-resolution X-ray photoemission spectroscopy from a synchrotron radiation source and scanning electron microscopy (SEM). Selective nitridation of the Al nano-squares on the SiO 2 mask was obtained in the temperature window of 600 o C-700 o C. The well-shaped AlN nano-column arrays with diameters confined by the lateral size of the Al nano-squares (∼ 100 nm) were observed in SEM.

  10. 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.

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

    Science.gov (United States)

    Greco, Andrés; Bejas, Matías

    2014-12-03

    One of the puzzling characteristics of the pseudogap phase of high-Tc cuprates is the nodal-antinodal dichotomy. While the nodal quasiparticles have a Fermi liquid behaviour, the antinodal ones show non-Fermi liquid features and an associated pseudogap. Angle-resolved photoemission spectroscopy and electronic Raman scattering are two valuable tools which have shown universal features which are rather material-independent, and presumably intrinsic to the pseudogap phase. The doping and temperature dependence of the Fermi arcs and the pseudogap observed by photoemission near the antinode correlates with the non-Fermi liquid behaviour observed by Raman for the B(1g) mode. In contrast, and similar to the nodal quasiparticles detected by photoemission, the Raman B(2g) mode shows Fermi liquid features. We show that these two experiments can be analysed, in the context of the t-J model, by self-energy effects in the proximity to a D-wave flux-phase order instability. This approach supports a crossover origin for the pseudogap, and a scenario of two competing phases. The B(2g) mode shows, in an underdoped case, a depletion at intermediate energy which has attracted renewed interest. We study this depletion and discuss its origin and relation with the pseudogap.

  12. Resonant inelastic x-ray scattering and photoemission measurement of O2: Direct evidence for dependence of Rydberg-valence mixing on vibrational states in O 1s → Rydberg states

    Science.gov (United States)

    Gejo, T.; Oura, M.; Tokushima, T.; Horikawa, Y.; Arai, H.; Shin, S.; Kimberg, V.; Kosugi, N.

    2017-07-01

    High-resolution resonant inelastic x-ray scattering (RIXS) and low-energy photoemission spectra of oxygen molecules have been measured for investigating the electronic structure of Rydberg states in the O 1s → σ* energy region. The electronic characteristics of each Rydberg state have been successfully observed, and new assignments are made for several states. The RIXS spectra clearly show that vibrational excitation is very sensitive to the electronic characteristics because of Rydberg-valence mixing and vibronic coupling in O2. This observation constitutes direct experimental evidence that the Rydberg-valence mixing characteristic depends on the vibrational excitation near the avoided crossing of potential surfaces. We also measured the photoemission spectra of metastable oxygen atoms (O*) from O2 excited to 1s → Rydberg states. The broadening of the 4p Rydberg states of O* has been found with isotropic behavior, implying that excited oxygen molecules undergo dissociation with a lifetime of the order of 10 fs in 1s → Rydberg states.

  13. Nanoscale Phase Separation and Lattice Complexity in VO2: The Metal–Insulator Transition Investigated by XANES via Auger Electron Yield at the Vanadium L23-Edge and Resonant Photoemission

    Directory of Open Access Journals (Sweden)

    Augusto Marcelli

    2017-12-01

    Full Text Available Among transition metal oxides, VO2 is a particularly interesting and challenging correlated electron material where an insulator to metal transition (MIT occurs near room temperature. Here we investigate a 16 nm thick strained vanadium dioxide film, trying to clarify the dynamic behavior of the insulator/metal transition. We measured (resonant photoemission below and above the MIT transition temperature, focusing on heating and cooling effects at the vanadium L23-edge using X-ray Absorption Near-Edge Structure (XANES. The vanadium L23-edges probe the transitions from the 2p core level to final unoccupied states with 3d orbital symmetry above the Fermi level. The dynamics of the 3d unoccupied states both at the L3- and at the L2-edge are in agreement with the hysteretic behavior of this thin film. In the first stage of the cooling, the 3d unoccupied states do not change while the transition in the insulating phase appears below 60 °C. Finally, Resonant Photoemission Spectra (ResPES point out a shift of the Fermi level of ~0.75 eV, which can be correlated to the dynamics of the 3d// orbitals, the electron–electron correlation, and the stability of the metallic state.

  14. High-resolution, hard x-ray photoemission investigation of BaFe2As2: Moderate influence of the surface and evidence for a low degree of Fe 3d-As 4p hybridization of electronic states near the Fermi energy

    NARCIS (Netherlands)

    de Jong, S.; Huang, Y.; Huisman, R.; Massee, F.; Thirupathaiah, R.; Gorgoi, M.; Schaefers, F.; Follath, F.; Goedkoop, J.B.; Golden, M.S.

    2009-01-01

    Photoemission data taken with hard x-ray radiation on cleaved single crystals of the barium parent compound of the MFe2As2 pnictide high-temperature superconductor family are presented. Making use of the increased bulk sensitivity upon hard x-ray excitation, and comparing the results to data taken

  15. 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

  16. Stoner vs. spin-mixing behavior in the bulk magnetism of Gd: A spin ...

    Indian Academy of Sciences (India)

    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, D-52428 Jülich, Germany. 3Consiglio ...

  17. A New Collinear-Type Energy-Filtered X-ray Photoemission Electron Microscope Equipped with a Multi-Pole Aberration-Corrected Air-Core Coil Wien Filter

    Science.gov (United States)

    Miyamoto, Takeshi; Wada, Takahiro; Niimi, Hironobu; Suzuki, Shushi; Kato, Makoto; Kudo, Masato; Asakura, Kiyotaka

    2012-04-01

    We present the prototype of a new, collinear-type energy-filtered X-ray photoemission electron microscope (EXPEEM) using a multi-pole, aberration-corrected air-core coil Wien filter (WF) analyzer. We have designed the new WF with 12-pole electrodes and magnetic poles to reduce spherical aberrations and fringe effects. We assess the performance of the WF using an electron energy analyzer for PEEM. The sensitivity is enhanced 10-100 fold compared with a simple, two electrodes plus two magnetic poles type WF. Cu 2p3/2 and Au 4f7/2 photoelectron energy selected images are obtained in a laboratory-scale source within several minutes. The energy and spatial resolutions of our prototype EXPEEM are estimated to be 3 eV and 7 µm, respectively.

  18. 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.

  19. 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.

  20. Carbon 1s photoemission line analysis of C-based adsorbate on (111)In{sub 2}O{sub 3} surface: The influence of reducing and oxidizing conditions

    Energy Technology Data Exchange (ETDEWEB)

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

    2016-12-30

    Highlights: • C 1s PE line of (111)In{sub 2}O{sub 3} layer after cleaning and gas probing in HV was studied. • C 1s line fine structure is formed by various residual C-based adsorbates. • Some C 1s line features were interpreted as CO adsorption and dissociation. • Redox properties of surface determine either adsorption or dissociation of CO. • Dissociation of CO on oxidized surface is responsible for acceptor-like effect. - Abstract: Synchrotron radiation photoemission study of C 1s line of (111) In{sub 2}O{sub 3} surface was carried out under HV (high vacuum) doses of oxygen, carbon monoxide and water. Gas interaction with the surface was activated by heating of In{sub 2}O{sub 3} monocrystalline film at temperatures of 160 or 250 °C. The study of complex structure of C 1 s line and evolution of its fine components allowed to establish their nature and to propose possible surface adsorbed species and reactions, including a direct chemisorption and dissociation of CO molecules. Reduction or oxidation of the surface determines whether the first (chemisorption) or the second (dissociation) process takes place. The latter is responsible for additional formation of ionosorbed oxygen. Both processes have not been previously reported for In{sub 2}O{sub 3} and for conductive metal oxides.

  1. X-ray photoemission studies of Zn doped Cu1-xTl xBa2Ca2Cu 3-yZn yO10-δ (y = 0, 2.65) superconductors

    International Nuclear Information System (INIS)

    Khan, Nawazish A.; Mumtaz, M.; Ahadian, M.M.; Iraji-zad, Azam

    2007-01-01

    The X-ray photoemission (XPS) measurements of Cu 1-x Tl x Ba 2 Ca 2 Cu 3-y Zn y O 10-δ (y = 0, 2.65) superconductors have been performed and compared. These studies revealed that the charge state of thallium in the Cu 0.5 Tl 0.5 Ba 2 O 4-δ charge reservoir layer in Zn doped samples is Tl 1+ , while it is a mix of Tl 1+ and Tl 2+ in Zn free samples. The binding energy of Ba atoms in the Zn doped samples is shifted to higher energy, which when considered along with the presence of Tl 1+ suggested that it more efficiently directed the carriers to ZnO 2 and CuO 2 planes. The evidence of improved inter-plane coupling witnessed in X-ray diffraction is also confirmed by XPS measurements of Ca atoms in the Zn doped samples. The shift of the valance band spectrum in these Zn doped samples to higher energies suggested that the electrons at the top edge of the valance band were tied to a higher binding energy (relative to samples without Zn doping), which most likely resulted in a much lower energy state of the system in the superconducting state. The stronger superconducting state arising out of these effects is witnessed in the form of increased T c (R 0), J c and the extent of diamagnetism in the final compound

  2. Room temperature redox reaction by oxide ion migration at carbon/Gd-doped CeO2 heterointerface probed by an in situ hard x-ray photoemission and soft x-ray absorption spectroscopies

    Directory of Open Access Journals (Sweden)

    Takashi Tsuchiya, Shogo Miyoshi, Yoshiyuki Yamashita, Hideki Yoshikawa, Kazuya Terabe, Keisuke Kobayashi and Shu Yamaguchi

    2013-01-01

    Full Text Available In situ hard x-ray photoemission spectroscopy (HX-PES and soft x-ray absorption spectroscopy (SX-XAS have been employed to investigate a local redox reaction at the carbon/Gd-doped CeO2 (GDC thin film heterointerface under applied dc bias. In HX-PES, Ce3d and O1s core levels show a parallel chemical shift as large as 3.2 eV, corresponding to the redox window where ionic conductivity is predominant. The window width is equal to the energy gap between donor and acceptor levels of the GDC electrolyte. The Ce M-edge SX-XAS spectra also show a considerable increase of Ce3+ satellite peak intensity, corresponding to electrochemical reduction by oxide ion migration. In addition to the reversible redox reaction, two distinct phenomena by the electrochemical transport of oxide ions are observed as an irreversible reduction of the entire oxide film by O2 evolution from the GDC film to the gas phase, as well as a vigorous precipitation of oxygen gas at the bottom electrode to lift off the GDC film. These in situ spectroscopic observations describe well the electrochemical polarization behavior of a metal/GDC/metal capacitor-like two-electrode cell at room temperature.

  3. Effect of elastic strain on the band gaps, band alignment, and electronic structure of epitaxial ASnO3 (A = Ca, Sr, and Ba) films and heterostructures revealed through in situ photoemission, spectroscopic ellipsometry, and density functional theory

    Science.gov (United States)

    Baniecki, John; Yamazaki, Takashi; Aso, Hiroyuki; Imanaka, Yoshihiko; Ricinschi, Dan

    The alkaline earth stannates ASnO3 (A = Ba, Sr, and Ca) are emerging as important materials. Band gaps in stannates are remarkably dependent on volumetric strain with a decrease in volumetric strain of 3 percent in SrSnO3 resulting in an increase in the band gap of 0.35 eV. However, little understanding of volumetric strain dependence on the valence band (VB) electronic structure and band alignments between stannates and other oxides exits. In this talk we will examine the effect of elastic strain on the band gaps, band alignment, and electronic structure of stannate films and heterostructures through in situ photoemission, spectroscopic ellipsometry, scanning transmission electron microscopy with geometric phase analysis, and density functional theory. CaSnO3 (CSO), SrSnO3 (SSO) and La-doped BaSnO3 (BLSO) thin films were grown by pulsed laser epitaxy with strain control via epitaxial buffer layers. While the VB electronic structure is strain dependent VB offsets do not vary significantly with strain, which resulted in ascribing most of the difference in band alignment to the conduction band (CB) edge. Significantly, strain-induced tuning of CB offset differences are as large as 0.6 eV for SSO and may provide a pathway to enhance stannate-based devices.

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

    CERN Document Server

    Teraoka, Y; Moritani, K

    2003-01-01

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

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

    Science.gov (United States)

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

    2016-06-01

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

  6. 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.

  7. 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.

  8. A comparison of experiment, CEPXS/ONETRAN, TIGERP, and TIGER net electron emission coefficients for various bremsstrahlung spectra

    International Nuclear Information System (INIS)

    Ballard, W.P.; Lorence, L.J. Jr.; Snowden, D.P.; Van Lint, V.A.J.; Beale, E.S.

    1987-01-01

    This work compares a carefully designed experiment to measure photoemission with the predictions of three different codes (CEPXS/ONETRAN, TIGERP, and TIGER) for the complex bremsstrahlung spectra typical of very intense pulsed power x-ray generators. The Monte Carlo codes TIGER and TIGERP can calculate the net photon-induced electron emission but accurate results may require that statistical error be minimized. CEPXS/ONETRAN is a new deterministic coupled electron/photon transport code that is faster than Monte Carlo and is not subject to statistical error. The comparison of net yields is a sensitive test of the relative accuracy and efficiency of these various codes. The authors find that all of the codes substantially agree with the experiments for the forward net yields. However, for reverse net yields from high-Z materials, the codes overpredict relative to measurements

  9. Multipactor experiment on a dielectric surface

    Science.gov (United States)

    Anderson, Rex Beach, III

    2001-12-01

    with a bead pull perturbation method are used to calculate the threshold rf fields at the dielectric surface when multipactor occurs. This experiment is the first to measure electron current from the dielectric using an electron probe. The electron probe provides temporal measurements of the multipactor electron current with respect to the microwave pulses. Another unique electron diagnostic utilized in this multipactor experiment is phosphor. Phosphor on the dielectric surface is used to detect multipactor electrons by photoemission. Phosphors with different excitation energies are used as a crude electron energy analyzer. Experimental results from these diagnostics match well with theoretical calculations.

  10. 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.

  11. A novel approach for the characterization of a bilayer of phenyl-c71-butyric-acid-methyl ester and pentacene using ultraviolet photoemission spectroscopy and argon gas cluster ion beam sputtering process

    International Nuclear Information System (INIS)

    Yun, Dong-Jin; Chung, JaeGwan; Jung, Changhoon; Chung, Yeonji; Kim, SeongHeon; Lee, Seunghyup; Kim, Ki-Hong; Han, Hyouksoo; Park, Gyeong-Su; Park, SungHoon

    2013-01-01

    The material arrangement and energy level alignment of an organic bilayer comprising of phenyl-c71-butyric-acid-methyl ester (PCBM-71) and pentacene were studied using ultraviolet photoelectron spectroscopy (UPS) and the argon gas cluster ion beam (GCIB) sputtering process. Although there is a small difference in the full width at half maximum of the carbon C 1s core level peaks and differences in the oxygen O 1s core levels of an X-ray photoemission spectroscopy spectra, these differences are insufficient to clearly distinguish between PCBM-71 and pentacene layers and to classify the interface and bulk regions. On the other hand, the valence band structures in the UPS spectra contain completely distinct configurations for the PCBM-71 and pentacene layers, even when they have similar atomic compositions. According to the valence band structures of the PCBM-71/pentacene/electrodes, the highest unoccupied molecular orbital (HOMO) region of pentacene is at least 0.8 eV closer to the Fermi level than that of PCBM-71 and it does not overlap with any of the chemical states in the valence band structure of PCBM-71. Therefore, by just following the variations in the area of the HOMO region of pentacene, the interface/bulk regions of the PCBM/pentacene layers were distinctly categorized. Besides, the variation of valence band structures as a function of the Ar GCIB sputtering time fully corroborated with the surface morphologies observed in the atomic force microscope images. In summary, we believe that the novel approach, which involves UPS analysis in conjunction with Ar GCIB sputtering, can be one of the best methods to characterize the material distribution and energy level alignments of stacks of organic layers

  12. From epitaxial growth of ferrite thin films to spin-polarized tunnelling

    International Nuclear Information System (INIS)

    Moussy, Jean-Baptiste

    2013-01-01

    This paper presents a review of the research which is focused on ferrite thin films for spintronics. First, I will describe the potential of ferrite layers for the generation of spin-polarized currents. In the second step, the structural and chemical properties of epitaxial thin films and ferrite-based tunnel junctions will be presented. Particular attention will be given to ferrite systems grown by oxygen-assisted molecular beam epitaxy. The analysis of the structure and chemistry close to the interfaces, a key-point for understanding the spin-polarized tunnelling measurements, will be detailed. In the third part, the magnetic and magneto-transport properties of magnetite (Fe 3 O 4 ) thin films as a function of structural defects such as the antiphase boundaries will be explained. The spin-polarization measurements (spin-resolved photoemission, tunnel magnetoresistance) on this oxide predicted to be half-metallic will be discussed. Fourth, the potential of magnetic tunnel barriers, such as CoFe 2 O 4 , NiFe 2 O 4 or MnFe 2 O 4 , whose insulating behaviour and the high Curie temperatures make it exciting candidates for spin filtering at room temperature will be described. Spin-polarized tunnelling experiments, involving either Meservey–Tedrow or tunnel magnetoresistance measurements, will reveal significant spin-polarizations of the tunnelling current at low temperatures but also at room temperatures. Finally, I will mention a few perspectives with ferrite-based heterostructures. (topical review)

  13. Magneto-Spin-Orbit Graphene: Interplay between Exchange and Spin-Orbit Couplings.

    Science.gov (United States)

    Rybkin, Artem G; Rybkina, Anna A; Otrokov, Mikhail M; Vilkov, Oleg Yu; Klimovskikh, Ilya I; Petukhov, Anatoly E; Filianina, Maria V; Voroshnin, Vladimir Yu; Rusinov, Igor P; Ernst, Arthur; Arnau, Andrés; Chulkov, Evgueni V; Shikin, Alexander M

    2018-03-14

    A rich class of spintronics-relevant phenomena require implementation of robust magnetism and/or strong spin-orbit coupling (SOC) to graphene, but both properties are completely alien to it. Here, we for the first time experimentally demonstrate that a quasi-freestanding character, strong exchange splitting and giant SOC are perfectly achievable in graphene at once. Using angle- and spin-resolved photoemission spectroscopy, we show that the Dirac state in the Au-intercalated graphene on Co(0001) experiences giant splitting (up to 0.2 eV) while being by no means distorted due to interaction with the substrate. Our calculations, based on the density functional theory, reveal the splitting to stem from the combined action of the Co thin film in-plane exchange field and Au-induced Rashba SOC. Scanning tunneling microscopy data suggest that the peculiar reconstruction of the Au/Co(0001) interface is responsible for the exchange field transfer to graphene. The realization of this "magneto-spin-orbit" version of graphene opens new frontiers for both applied and fundamental studies using its unusual electronic bandstructure.

  14. Topological Electride Y2C.

    Science.gov (United States)

    Huang, Huaqing; Jin, Kyung-Hwan; Zhang, Shunhong; Liu, Feng

    2018-02-22

    Two-dimensional (2D) electrides are layered ionic crystals in which anionic electrons are confined in the interlayer space. Here, we report a discovery of nontrivial [Formula: see text] topology in the electronic structures of 2D electride Y 2 C. Based on first-principles calculations, we found a topological [Formula: see text] invariant of (1; 111) for the bulk band and topologically protected surface states in the surfaces of Y 2 C, signifying its nontrivial electronic topology. We suggest a spin-resolved angle-resolved photoemission spectroscopy (ARPES) measurement to detect the unique helical spin texture of the spin-polarized topological surface state, which will provide characteristic evidence for the nontrivial electronic topology of Y 2 C. Furthermore, the coexistence of 2D surface electride states and topological surface state enables us to explain the outstanding discrepancy between the recent ARPES experiments and theoretical calculations. Our findings establish a preliminary link between the electride in chemistry and the band topology in condensed-matter physics, which are expected to inspire further interdisciplinary research between these fields.

  15. Customer experience

    OpenAIRE

    Koperdáková, Zuzana

    2016-01-01

    Bachelor thesis deals with the theme of customer experience and terms related to this topic. The thesis consists of three parts. The first part explains the terms generally, as the experience or customer loyalty. The second part is dedicated to medotology used for Customer Experience Management. In the third part is described application of Customer Experience Management in practice, particularly in the context Touch Point Analyses in GE Money Bank.

  16. OPERA experiment

    International Nuclear Information System (INIS)

    Komatsu, M.

    2003-01-01

    OPERA is an accelerator experiment designed to explore Super-Kamiokande suggested ν μ ↔ν τ oscillation region in CNGS beam from CERN to LNGS. The key technique in OPERA is modern emulsion read out which applied to CHORUS and DONUT experiments. ECC technique which used in DONUT and OPERA has good modularity to enlarge apparatus for future Neutrino Factory experiments

  17. 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. .

  18. OPERA experiment

    CERN Document Server

    Komatsu, M

    2003-01-01

    OPERA is an accelerator experiment designed to explore Super- Kamiokande suggested nu//mu arrow left right nu//tau oscillation region in CNGS beam from CERN to LNGS. The key technique in OPERA is modern emulsion read out which applied to CHORUS and DONUT experiments. ECC technique which used in DONUT and OPERA has good modularity to enlarge apparatus for future Neutrino Factory experiments.

  19. TRIO experiment

    Energy Technology Data Exchange (ETDEWEB)

    Clemmer, R.G.; Finn, P.A.; Malecha, R.F.; Misra, B.; Billone, M.C.; Bowers, D.L.; Fischer, A.K.; Greenwood, L.R.; Mattas, R.F.; Tam, S.W.

    1984-09-01

    The TRIO experiment is a test of in-situ tritium recovery and heat transfer performance of a miniaturized solid breeder blanket assembly. The assembly (capsule) was monitored for temperature and neutron flux profiles during irradiation and a sweep gas flowed through the capsule to an anaytical train wherein the amounts of tritium in its various chemical forms were determined. The capsule was designed to operate at different temperatures and sweep gas conditions. At the end of the experiment the amount of tritium retained in the solid was at a concentration of less than 0.1 wppM. More than 99.9% of tritium generated during the experiment was successfully recovered. The results of the experiment showed that the tritium inventories at the beginning and at the end of the experiment follow a relationship which appears to be characteristic of intragranular diffusion.

  20. Pixel Experiments

    DEFF Research Database (Denmark)

    Petersen, Kjell Yngve; Søndergaard, Karin; Augustesen, Christina

    2015-01-01

    Pixel Experiments The term pixel is traditionally defined as any of the minute elements that together constitute a larger context or image. A pixel has its own form and is the smallest unit seen within a larger structure. In working with the potentials of LED technology in architectural lighting...... for using LED lighting in lighting design practice. The speculative experiments that have been set-up have aimed to clarify the variables that can be used as parameters in the design of lighting applications; including, for example, the structuring and software control of light. The experiments also...... elucidate and exemplify already well-known problems in relation to the experience of vertical and horizontal lighting. Pixel Experiments exist as a synergy between speculative test setups and lighting design in practice. This book is one of four books that is published in connection with the research...

  1. Collaborative experience

    DEFF Research Database (Denmark)

    Mortensen, Thomas Bøtker

    Literature review: Collaborative experience has been shown to have a positive effect on the collaborative outcome in general (Anand & Khanna, 2000; Kale, Dyer & Singh, 2002). Furthermore, it has been linked to the ability to exploit the network of the firm for learning (Powell, Koput and Smith...... experience was largest the higher the hypothesized ambiguity. Theoretically contribution: This research project aims at contributing to existing literature by arguing, that collaborative experience is a moderating variable which moderates the effects on collaborative outcome from the level of complexity......, that the largest effects from collaborative experience is from recent collaborative experience, since knowledge depreciates when it is not used. Methodologically contribution: The research project studies the dyad and aims at introducing, to this field of research, an established way of collecting data, a new...

  2. On-Ball Doping of Fullerenes : The Electronic Structure of C59N Dimers from Experiment and Theory

    NARCIS (Netherlands)

    Pichler, Thomas; Knupfer, Martin; Golden, Mark S.; Haffner, Stefan; Friedlein, Rainer; Fink, Jörg; Andreoni, Wanda; Curioni, Alessandro; Keshavarz-K, Majid; Bellavia-Lund, Cheryl; Sastre, Angela; Hummelen, Jan-Cornelis; Wudl, Fred

    1997-01-01

    We present the first studies of the electronic structure of the heterofullerene (C59N)2 using electron energy-loss spectroscopy in transmission, photoemission spectroscopy, and density functional theory calculations. Both the C 1s excitation spectra and valence band photoemission show negligible

  3. Mixture Experiments

    Energy Technology Data Exchange (ETDEWEB)

    Piepel, Gregory F.

    2007-12-01

    A mixture experiment involves combining two or more components in various proportions or amounts and then measuring one or more responses for the resulting end products. Other factors that affect the response(s), such as process variables and/or the total amount of the mixture, may also be studied in the experiment. A mixture experiment design specifies the combinations of mixture components and other experimental factors (if any) to be studied and the response variable(s) to be measured. Mixture experiment data analyses are then used to achieve the desired goals, which may include (i) understanding the effects of components and other factors on the response(s), (ii) identifying components and other factors with significant and nonsignificant effects on the response(s), (iii) developing models for predicting the response(s) as functions of the mixture components and any other factors, and (iv) developing end-products with desired values and uncertainties of the response(s). Given a mixture experiment problem, a practitioner must consider the possible approaches for designing the experiment and analyzing the data, and then select the approach best suited to the problem. Eight possible approaches include 1) component proportions, 2) mathematically independent variables, 3) slack variable, 4) mixture amount, 5) component amounts, 6) mixture process variable, 7) mixture of mixtures, and 8) multi-factor mixture. The article provides an overview of the mixture experiment designs, models, and data analyses for these approaches.

  4. Simulated experiments

    International Nuclear Information System (INIS)

    Bjerknes, R.

    1977-01-01

    A cybernetic model has been developed to elucidate some of the main principles of the growth regulation system in the epidermis of the hairless mouse. A number of actual and theoretical biological experiments have been simulated on the model. These included simulating the cell kinetics as measured by pulse labelling with tritiated thymidine and by continuous labelling with tritiated thymidine. Other simulated experiments included steady state, wear and tear, painting with a carcinogen, heredity and heredity and tumour. Numerous diagrams illustrate the results of these simulated experiments. (JIW)

  5. Researching experiences

    DEFF Research Database (Denmark)

    Gjedde, Lisa; Ingemann, Bruno

    , dialogue, moods, values and narratives have been investigated qualitatively with more than sixty informants in a range of projects. The processual methodological insights are put into a theoretical perspective and also presented as pragmatic dilemmas. Researching Experiences is relevant not only...... for students and researchers in media and communication studies but also for practitioners within the fields of media, communication and experience design....... for researching experiences in a variety of settings ranging from the museum, to news photography, and interactive media. The research led to the development of a set of methodological tools and approaches we term the reflexivity lab. The interaction in the experimental situation between the media and body...

  6. Researching experiences

    DEFF Research Database (Denmark)

    Gjedde, Lisa; Ingemann, Bruno

    In the beginning was - not the word - but the experience. This phenomenological approach provides the basis for this book, which focuses on how a person-in-situation experiences and constructs meaning from a variety of cultural visual events. This book presents video-based processual methods...... for researching experiences in a variety of settings ranging from the museum, to news photography, and interactive media. The research led to the development of a set of methodological tools and approaches we term the reflexivity lab. The interaction in the experimental situation between the media and body......, dialogue, moods, values and narratives have been investigated qualitatively with more than sixty informants in a range of projects. The processual methodological insights are put into a theoretical perspective and also presented as pragmatic dilemmas. Researching Experiences is relevant not only...

  7. Interpretive Experiments

    Science.gov (United States)

    DeHaan, Frank, Ed.

    1977-01-01

    Describes an interpretative experiment involving the application of symmetry and temperature-dependent proton and fluorine nmr spectroscopy to the solution of structural and kinetic problems in coordination chemistry. (MLH)

  8. Antimatter Experiments

    CERN Multimedia

    2004-01-01

    Antimatter should behave in identical fashion to matter if a form of spacetime symmetry called CPT invariance holds. Two experiments at CERN near Geneva are testing this hypothesis using antihydrogen atoms

  9. Media experiences

    DEFF Research Database (Denmark)

    Buhl, Mie

    2010-01-01

    on their particular iconic systems of meaning perceived through form, lines, contrasts, colours, structures textures, rhythm and composite qualities with embedded interdependent codes and culturally conditioned potential for construction of knowledge and meaning. Mediated experience adds new perspectives...

  10. Experiment Databases

    Science.gov (United States)

    Vanschoren, Joaquin; Blockeel, Hendrik

    Next to running machine learning algorithms based on inductive queries, much can be learned by immediately querying the combined results of many prior studies. Indeed, all around the globe, thousands of machine learning experiments are being executed on a daily basis, generating a constant stream of empirical information on machine learning techniques. While the information contained in these experiments might have many uses beyond their original intent, results are typically described very concisely in papers and discarded afterwards. If we properly store and organize these results in central databases, they can be immediately reused for further analysis, thus boosting future research. In this chapter, we propose the use of experiment databases: databases designed to collect all the necessary details of these experiments, and to intelligently organize them in online repositories to enable fast and thorough analysis of a myriad of collected results. They constitute an additional, queriable source of empirical meta-data based on principled descriptions of algorithm executions, without reimplementing the algorithms in an inductive database. As such, they engender a very dynamic, collaborative approach to experimentation, in which experiments can be freely shared, linked together, and immediately reused by researchers all over the world. They can be set up for personal use, to share results within a lab or to create open, community-wide repositories. Here, we provide a high-level overview of their design, and use an existing experiment database to answer various interesting research questions about machine learning algorithms and to verify a number of recent studies.

  11. Researching Experiences

    DEFF Research Database (Denmark)

    Gjedde, Lisa; Ingemann, Bruno

    In the beginning was - not the word - but the experience. This phenomenological approach provides the basis for this book, which focuses on how a person-in-situation experiences and constructs meaning from a variety of cultural visual events. This book presents video-based processual methods for ...... for students and researchers in media and communication studies but also for practitioners within the fields of media, communication and experience design.......In the beginning was - not the word - but the experience. This phenomenological approach provides the basis for this book, which focuses on how a person-in-situation experiences and constructs meaning from a variety of cultural visual events. This book presents video-based processual methods...... for researching experiences in a variety of settings ranging from the museum, to news photography, and interactive media. The research led to the development of a set of methodological tools and approaches we term the ReflexivityLab. The interaction in the experimental situation between the media and body...

  12. Photoemission from tin and lead cluster anions

    International Nuclear Information System (INIS)

    Gantefoer, G.; Gausa, M.; Meiwes-Broer, K.H.; Lutz, H.O.

    1989-01-01

    Photoelectrons from mass-identified jet-cooled tin and lead cluster anions (Sn n - , Pb n - ) are detached by ultraviolet laser light (hν=3.68 eV). The photoelectron energy spectra give the detachment energies of ground state cluster anions (electron affinities) as well as excitation energies of neutral clusters in the geometry of the anions. The energy spectra for Sn n - are dominated by flat thresholds with an n-dependence similar to that of other group IV clusters. In contrast, for Pb n - we find pronounced narrow lines close to threshold, generally followed by a 0.3-1.4 eV gap which indicates closed-shell behaviour of Pb n - for nearly all n. (orig.)

  13. 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).

  14. Molecular photoemission studies using synchrotron radiation

    International Nuclear Information System (INIS)

    Truesdale, C.M.

    1983-04-01

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

  15. Field assisted photoemission by silicon photocathodes

    International Nuclear Information System (INIS)

    Aboubacar, A.; Dupont, M.; El Manouni, A.; Querrou, M.; Says, L.P.

    1991-01-01

    Silicon photocathodes with arrays of tips have been prepared using microlithographic techniques. Current emission due to field effect has been measured in the case of heavy and weakly doped boron Silicon. An Argon continuous laser has been used to produce photocurrent. An instantaneous current (600 μA) with a moderate laser power (83 mW), has been produced on weakly doped photocathodes. This current corresponds to an average quantum yield (purely photoelectric) of about 1.7%, and a local current density in the range of a few 10 6 A m -2

  16. Ultrafast Multiphoton Thermionic Photoemission from Graphite

    Directory of Open Access Journals (Sweden)

    Shijing Tan

    2017-01-01

    Full Text Available Electronic heating of cold crystal lattices in nonlinear multiphoton excitation can transiently alter their physical and chemical properties. In metals where free electron densities are high and the relative fraction of photoexcited hot electrons is low, the effects are small, but in semimetals, where the free electron densities are low and the photoexcited densities can overwhelm them, the intense femtosecond laser excitation can induce profound changes. In semimetal graphite and its derivatives, strong optical absorption, weak screening of the Coulomb potential, and high cohesive energy enable extreme hot electron generation and thermalization to be realized under femtosecond laser excitation. We investigate the nonlinear interactions within a hot electron gas in graphite through multiphoton-induced thermionic emission. Unlike the conventional photoelectric effect, within about 25 fs, the memory of the excitation process, where resonant dipole transitions absorb up to eight quanta of light, is erased to produce statistical Boltzmann electron distributions with temperatures exceeding 5000 K; this ultrafast electronic heating causes thermionic emission to occur from the interlayer band of graphite. The nearly instantaneous thermalization of the photoexcited carriers through Coulomb scattering to extreme electronic temperatures characterized by separate electron and hole chemical potentials can enhance hot electron surface femtochemistry, photovoltaic energy conversion, and incandescence, and drive graphite-to-diamond electronic phase transition.

  17. 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.

  18. The experience of an experience

    DEFF Research Database (Denmark)

    Rasmussen, Alexandra Marie

    2016-01-01

    This paper examines a popular phenomenon that allows us to see ourselves from various perspectives, and allows us to perpetuate moments enabling us to relive experiences in a different state of mind or at a different time. To examine the phenomenon of experiencing an experience hermeneutic...... is a tool to create a particular mindset, in the developer, to generate a new way of thinking. This model is dynamic by nature and although it is not completed in every branch, it is complete in relation to experiencing your own experience. A company can apply the PoC to gain insight into primary...

  19. The Experiment

    Science.gov (United States)

    Mariana Nicoara, Floare

    2016-04-01

    My name is Nicoara Floarea and I am teacher at Secondary School Calatele and I teach students from preparatory class and the second grade . They are six-eight years old. In my activity, for introducing scientific concepts to my students, I use various and active methods or traditional methods including experiments. The experiment stimulates students' curiosity, their creativity, the understanding and knowledge taught accessibility. I propose you two such experiments: The life cycle of the plants (long-term experiment, with rigorous observation time):We use beans, wheat or other; They are grown in pots and on the cotton soaked with water,keeping under students' observation protecting them ( just soak them regularly) and we waiting the plants rise. For discussions and comments of plant embryo development we use the plants which rose on the cotton soaked with water plants at the end of the first week. Last school year we had in the pot climbing beans which in May made pods. They were not too great but our experiment was a success. The students could deduce that there will develop those big beans which after drying will be planted again. The influence of light on plants (average duration experiment with the necessary observation time): We use two pots in which plants are of the same type (two geraniums), one of them is situated so as to get direct sunlight and other plant we put in a closed box. Although we wet both plants after a week we see that the plant that benefited from sunlight has turned strain in direct sunlight, developing normally in return the plant out of the box I have yellowed leaves, photosynthesis does not She has occurred . Students will understand the vital role of the Sun in plants' life, both in the classroom and in nature. The experiment is a method of teaching students extremely pleasant, with a remarkable percentage of acquiring more knowledge.

  20. Pixel Experiments

    DEFF Research Database (Denmark)

    Søndergaard, Karin; Petersen, Kjell Yngve; Augustesen, Christina

    2015-01-01

    Pixel Experiments The term pixel is traditionally defined as any of the minute elements that together constitute a larger context or image. A pixel has its own form and is the smallest unit seen within a larger structure. In working with the potentials of LED technology in architectural lighting...... design it became relevant to investigate the use of LEDs as the physical equivalent of a pixel as a design approach. In this book our interest has been in identifying how the qualities of LEDs can be used in lighting applications. With experiences in the planning and implementation of architectural...... lighting design in practice, one quickly experiences and realises that there are untapped potentials in the attributes of LED technology. In this research, speculative studies have been made working with the attributes of LEDs in architectural contexts, with the ambition to ascertain new strategies...

  1. Researching Experiences

    DEFF Research Database (Denmark)

    Gjedde, Lisa; Ingemann, Bruno

    , dialogue, moods, values and narratives have been investigated qualitatively with more than sixty informants in a range of projects. The processual methodological insights are put into a theoretical perspective and also presented as pragmatic dilemmas.      Researching Experiences is relevant not only...... for students and researchers in media and communication studies but also for practitioners within the fields of media, communication and experience design....... for researching experiences in a variety of settings ranging from the museum, to news photography, and interactive media. The research led to the development of a set of methodological tools and approaches we term the ReflexivityLab. The interaction in the experimental situation between the media and body...

  2. EXPERIENCE WITH

    African Journals Online (AJOL)

    SURGERY DEPT

    Abstract. Background:Island flap techniques currently used in urethroplasty utilize the prepuce and the dorsal penile skin. Our experience with a one-stage island flap urethroplasty for urethral strictures utilizing the ventral penile skin is described. Patients and Method: This is a longitudinal study of seventy six consecutive ...

  3. Superconducting pairing symmetry and energy gaps of the two-orbital t-t'-J-J' model: comparisons with the ARPES experiments in iron pnictides.

    Science.gov (United States)

    Lu, Feng; Zou, Liang-Jian

    2009-06-24

    Motivated by the discovery of the iron-based superconductors, we present the theoretical results on the superconducting phase diagram, the temperature-dependent Fermi surface structures in normal state and the angle-resolved photoemission spectroscopy (ARPES) character of quasiparticles of the two-orbital t-t'-J-J' model. In the reasonable physical parameter region of LaFeAsO(1-x)F(x), we find the superconducting phase is stable, and the pairing symmetry is weakly anisotropic and nodeless d(x(2)-ηy(2))+S(x(2)y(2))-wave, qualitatively in agreement with the ARPES experiments in iron pnictide superconductors. Nevertheless, the two ratios of the energy gaps to T(c) deviate from the ARPES data, suggesting that a more elaborate theoretical model is needed.

  4. Extending Experiences

    DEFF Research Database (Denmark)

    A computer game's player is experiencing not only the game as a designer-made artefact, but also a multitude of social and cultural practices and contexts of both computer game play and everyday life. As a truly multidisciplinary anthology, Extending Experiences sheds new light on the mesh...... of possibilities and influences the player engages with. Part one, Experiential Structures of Play, considers some of the key concepts commonly used to address the experience of a computer game player. The second part, Bordering Play, discusses conceptual and practical overlaps of games and everyday life...... and the impacts of setting up, crossing and breaking the boundaries of game and non-game. Part three, Interfaces of Play, looks at games as technological and historical artefacts and commodities. The fourth part, Beyond Design, introduces new models for the practical and theoretical dimensions of game design....

  5. Dirac experiment

    Energy Technology Data Exchange (ETDEWEB)

    Gomez, F.; Adeva, B.; Afanasev, L.; Benayoun, M.; Brekhovskikh, V.; Caragheorgheopol, G.; Cechak, T.; Chiba, M.; Constantinescu, S.; Doudarev, A.; Dreossi, D.; Drijard, D.; Ferro-Luzzi, M.; Gallas, M.V.; Gerndt, J.; Giacomich, R.; Gianotti, P.; Goldin, D.; Gorin, A.; Gortchakov, O.; Guaraldo, C.; Hansroul, M.; Hosek, R.; Iliescu, M.; Jabitski, M.; Kalinina, N.; Karpoukhine, V.; Kluson, J.; Kobayashi, M.; Kokkas, P.; Komarov, V.; Koulikov, A.; Kouptsov, A.; Krouglov, V.; Krouglova, L.; Kuroda, K.-I.; Lanaro, A.; Lapshine, V.; Lednicky, R.; Leruste, P.; Levisandri, P.; Lopez Aguera, A.; Lucherini, V.; Maki, T.; Manuilov, I.; Montanet, L.; Narjoux, J.-L.; Nemenov, L.; Nikitin, M.; Nunez Pardo, T.; Okada, K.; Olchevskii, V.; Pazos, A.; Pentia, M.; Penzo, A.; Perreau, J.-M.; Petrascu, C.; Plo, M.; Ponta, T.; Pop, D.; Riazantsev, A.; Rodriguez, J.M.; Rodriguez Fernandez, A.; Rykaline, V.; Santamarina, C.; Saborido, J.; Schacher, J.; Sidorov, A.; Smolik, J.; Takeutchi, F.; Tarasov, A.; Tauscher, L.; Tobar, M.J.; Trusov, S.; Vazquez, P.; Vlachos, S.; Yazkov, V.; Yoshimura, Y.; Zrelov, P

    2001-04-01

    The main objective of DIRAC experiment is the measurement of the lifetime {tau} of the exotic hadronic atom consisting of {pi}{sup +} and {pi}{sup -} mesons. The lifetime of this atom is determined by the decay mode {pi}{sup +} {pi}{sup -} {yields} {pi}{sup 0} {pi}{sup 0} due to the strong interaction. Through the precise relationship between the lifetime and the S-wave pion-pion scattering length difference |a{sub 0} - a{sub 2}| for isospin 0 and 2 (respectively), a measurement of {tau} with an accuracy of 10% will allow a determination of |a{sub 0} - a{sub 2}| at a 5% precision level. Pion-pion scattering lengths have been calculated in the framework of chiral perturbation theory with an accuracy below 5%. In this way DIRAC experiment will provide a crucial test of the chiral symmetry breaking scheme in QCD effective theories at low energies.

  6. Dirac experiment

    CERN Document Server

    Gómez, F; Afanasev, L; Benayoun, M; Brekhovskikh, V; Caragheorgheopol, G; Cechák, T; Chiba, M; Constantinescu, S; Doudarev, A; Dreossi, D; Drijard, Daniel; Ferro-Luzzi, M; Gallas, M V; Gerndt, J; Giacomich, R; Gianotti, P; Goldin, D; Gorin, A; Gortchakov, O; Guaraldo, C; Hansroul, M; Hosek, R; Iliescu, M; Jabitski, M; Kalinina, N; Karpoukhine, V; Kluson, J; Kobayshi, M; Kokkas, P; Komarov, V; Koulikov, A; Kouptsov, A; Krouglov, V; Krouglova, L; Kuroda, K I; Lanaro, A; Lapshine, B; Lednicky, R; Leruste, P; Levisandri, P; López-Aguera, A; Lucherini, V; Mäki, T; Manuilov, I; Montanet, L; Narjoux, J L; Nemenov, L; Nikitin, M; Nunez Pardo, T; Okada, K; Olchevskii, V; Pazos, A; Pentia, M; Penzo, Aldo L; Perreau, J M; Petrascu, C; Pló, M; Ponta, T; Pop, D; Riazantsev, A; Rodríguez, J M; Rodriguez Fernandez, A; Rykaline, V; Santamarina, C; Saborido, J; Schacher, J; Sidorov, A; Smolik, J; Takeutchi, F; Tarasov, A; Tauscher, L; Tobar, M J; Trusov, S; Vasquez, P; Vlachos, S; Yazkov, V; Yoshimura, Y; Zrelov, P

    2001-01-01

    The main objective of DIRAC experiment is the measurement of the lifetime tau of the exotic hadronic atom consisting of pi /sup +/ and pi /sup -/ mesons. The lifetime of this atom is determined by the decay mode pi /sup +/ pi /sup -/ to pi /sup 0/ pi /sup 0/ due to the strong interaction. Through the precise relationship between the lifetime and the S-wave pion-pion scattering length difference a/sub 0/-a/sub 2/ for isospin 0 and 2 (respectively), a measurement of tau with an accuracy of 10% will allow a determination of a/sub 0/-a/sub 2/at a 5% precision level. Pion-pion scattering lengths have been calculated in the framework of chiral perturbation theory with an accuracy below 5%. In this way DIRAC experiment will provide a crucial test of the chiral symmetry breaking scheme in QCD effective theories at low energies. (19 refs).

  7. Experiment 7

    CERN Multimedia

    CERN PhotoLab

    1968-01-01

    Over-all view of the arrangement of counters around the polarized target in the kaon-polarized proton experiment. The beam enters through the quadrupole magnet on the left, and strikes the target placed in a 18.5 kG field (one pole of the magnet is just visible above the ring of counters). The scatterred kaon and recoil proton are detected by the counters on the ring and recorded onto magnetic tape.

  8. QUBIC Experiment

    OpenAIRE

    Stolpovskiy, Mikhail

    2016-01-01

    QUBIC is a ground-based experiment, currently under construction, that uses the novel bolometric interferometry technology. It is dedicated to measure the primordial B-modes of CMB. As a bolometric interferometer, QUBIC has high sensitivity and good systematics control. Dust contamination is controlled by operating with two bands -- 150 and 220 GHz. There are two possible sites for QUBIC: either Concordia station in Antarctic or in the Argentinian Puna desert. It is planned to see the first l...

  9. Experiments expectations

    OpenAIRE

    Gorini, B; Meschi, E

    2014-01-01

    This paper presents the expectations and the constraints of the experiments relatively to the commissioning procedure and the running conditions for the 2015 data taking period. The views about the various beam parameters for the p-p period, like beam energy, maximum pileup, bunch spacing and luminosity limitation in IP2 and IP8, are discussed. The goals and the constraints of the 2015 physics program are also presented, including the heavy ions period as well as the special...

  10. Experimenting with a design experiment

    Directory of Open Access Journals (Sweden)

    Bakker, Judith

    2012-12-01

    Full Text Available The design experiment is an experimental research method that aims to help design and further develop new (policy instruments. For the development of a set of guidelines for the facilitation of citizens’ initiatives by local governments, we are experimenting with this method. It offers good opportunities for modeling interventions by testing their instrumental validity –the usefulness for the intended practical purposes. At the same time design experiments are also useful for evaluating the empirical validity of theoretical arguments and the further development of these arguments in the light of empirical evidence (by using e.g. the technique of pattern matching. We describe how we have applied this methodology in two cases and discuss our research approach. We encountered some unexpected difficulties, especially in the cooperation with professionals and citizens. These difficulties complicate the valid attribution of causal effects to the use of the new instrument. However, our preliminary conclusion is that design experiments are useful in our field of study

    El experimento de diseño es un método de investigación experimental que tiene como objetivo diseñar y desarrollar posteriormente nuevas herramientas (políticas. En este artículo experimentamos con este método para desarrollar un conjunto de directrices que permitan a los gobiernos locales facilitar las iniciativas ciudadanas. El método ofrece la oportunidad de modelar las intervenciones poniendo a prueba su validez instrumental (su utilidad para el fin práctico que se proponen. Al mismo tiempo, los experimentos de diseño son útiles también para evaluar la validez empírica de las discusiones teóricas y el posterior desarrollo de esas discusiones a la luz de la evidencia empírica (usando, por ejemplo, técnicas de concordancia de patrones. En este trabajo describimos cómo hemos aplicado este método a dos casos y discutimos nuestro enfoque de

  11. Operating experience

    International Nuclear Information System (INIS)

    McRae, L.P.; Six, D.E.

    1991-01-01

    In 1987, Westinghouse Hanford Company began operating a first-generation integrated safeguards system in the Plutonium Finishing Plant storage vaults. This Vault Safety and Inventory System is designed to integrate data into a computer-based nuclear material inventory monitoring system. The system gathers, in real time, measured physical parameters that generate nuclear material inventory status data for thousands of stored items and sends tailored report to the appropriate users. These data include canister temperature an bulge data reported to Plant Operations and Material Control and Accountability personnel, item presence and identification data reported to Material Control and Accountability personnel, and unauthorized item movement data reported to Security response forces and Material Control and Accountability personnel. The Westinghouse Hanford Company's experience and operational benefits in using this system for reduce radiation exposure, increase protection against insider threat, and real-time inventory control are discussed in this paper

  12. Management Experiences

    Directory of Open Access Journals (Sweden)

    Gheorghe Popovici

    2016-12-01

    Full Text Available The paper presents the results of the survey about the changes in modern management, identified from the experience of Romanian managers. By this online study one presents both the obstacles encountered and the recommendations for such a type of management that the present and future mangers must take into account. What motivated the respondent Romanian managers most to open their own business is the independence it offered them. They work in the field they have liked since they were young. The second reason was the perspective to have an additional income from the business development. The third argument in favour of opening a business is the possibility to assure the balance between personal life and career.

  13. Correlation effects in magnetic materials: An ab initio investigation on electronic structure and spectroscopy

    International Nuclear Information System (INIS)

    Minár, J.; Braun, J.; Ebert, H.

    2013-01-01

    Highlights: ► We compare spin-resolved ARPES data of ferromagnetic 3d transition metals to many-body LSDA + DMFT based spectroscopic calculations. ► We document LSDA + DMFT provides a detailed and reliable interpretation of the data. ► We demonstrate that local correlations are dominant in Ni, whereas non-local correlations are important in Fe and Co. ► We reproduce the 6 eV satellite structure in ferromagnetic Ni LDSDA + DMFT in combination with the one-step model of photoemission provides a more or less complete description of the electronic structure of Fe, Co and Ni. -- Abstract: Various technical developments enlarged the potential of angle-resolved photoemission spectroscopy (ARPES) tremendously during the last two decades. In particular improved momentum and energy resolution in combination with spin-resolution as well as the use of photon energies from few eV up to several keV makes ARPES a rather unique tool to investigate the electronic properties of solids and surfaces. Obviously, this rises the need for a corresponding theoretical formalism that allows to accompany experimental ARPES studies in an adequate way. As will be demonstrated by several examples this goal could be achieved by various recent developments on the basis of density functional theory (DFT) in combination with dynamical mean field theory (DMFT) and with the one-step model of photoemission (1SM). A concrete realization of electronic structure calculations in the framework of multiple scattering theory further more provides direct access to the spectral function of the initial states via the one-electron Green function. Based on this bare spectral function matrix-element and final-state effects as well as surface related features may be calculated in addition using the one-step formalism that offers the possibility to analyse corresponding angle-resolved photoemission experiments in a quantitative sense. The impact of chemical disorder can be handled by means of the coherent

  14. Particle physics experiments 1983

    International Nuclear Information System (INIS)

    Stuart, G.W.

    1983-01-01

    The report describes work carried out in 1983 on experiments approved by the Particle Physics Experiments Selection Panel. The contents consist of unedited contributions from each experiment. (author)

  15. Sleep Monitoring Experiment - Skylab Experiment M133

    Science.gov (United States)

    1970-01-01

    This 1970 photograph shows equipment for the Skylab's Sleep Monitoring Experiment (M133), a medical evaluation designed to objectively determine the amount and quality of crewmembers' inflight sleep. The experiment monitored and recorded electroencephalographic (EEG) and electrooculographic (EOG) activity during astronauts' sleep periods. One of the astronauts was selected for this experiment and wore a fitted cap during his sleep periods. The Marshall Space Flight Center had program management responsibility for the development of Skylab hardware and experiments.

  16. Design of modern experiments

    International Nuclear Information System (INIS)

    Park, Sung Hweon

    1984-03-01

    This book is for researchers and engineers, which is written to focus on practical design of experiments. It gives descriptions of conception of design of experiments, basic statistics theory, one way design of experiment, two-way layout without repetition, two-way layout with repetition, partition, a correlation analysis and regression analysis, latin squares, factorial design, design of experiment by table of orthogonal arrays, design of experiment of response surface, design of experiment on compound, Evop, and design of experiment of taguchi.

  17. Data acquisition. GRAAL experiment. Hybrid reactor experiment. AMS experiment

    International Nuclear Information System (INIS)

    Barancourt, D.; Barbier, G.; Bosson, G.; Bouvier, J.; Gallin-Martel, L.; Meillon, B.; Stassi, P.; Tournier, M.

    1997-01-01

    The main activity of the data acquisition team has consisted in hardware and software developments for the GRAAL experiment with the trigger board, for the 'Reacteurs Hybrides' group with an acquisition board ADCVME8V and for the AMS experiment with the monitoring of the aerogel detector. (authors)

  18. The two-component spin-fermion model for high-Tc cuprates: its applications in neutron scattering and ARPES experiments

    International Nuclear Information System (INIS)

    Bang, Yunkyu

    2012-01-01

    Motivated by neutron scattering experiments in high-T c cuprates, we propose the two-component spin-fermion model as a minimal phenomenological model, which has both local spins and itinerant fermions as independent degrees of freedom (d.o.f.). Our calculations of the dynamic spin correlation function provide a successful description of the puzzling neutron experiment data and show that: (i) the upward dispersion branch of magnetic excitations is mostly due to local spin excitations; (ii) the downward dispersion branch is from collective particle-hole excitations of fermions; and (iii) the resonance mode is a mixture of both d.o.f. Using the same model with the same set of parameters, we calculated the renormalized quasiparticle (q.p.) dispersion and successfully reproduced one of the key features of the angle-resolved photoemission spectroscopy (ARPES) experiments, namely the high-energy kink structure in the fermion q.p. dispersion, thus supporting the two-component spin-fermion phenomenology. (paper)

  19. Particle physics experiments 1989

    International Nuclear Information System (INIS)

    Bairstow, R.

    1990-01-01

    This report describes work carried out in 1989 on experiments approved by the Particle Physics Experiments Selection Panel of Rutherford Appleton Laboratory. The contents consist of unedited contributions from each experiment. (author)

  20. Particle physics experiments

    International Nuclear Information System (INIS)

    Stuart, G.W.

    1986-01-01

    The report of the Rutherford Appleton Laboratory describes the work carried out in 1985 on experiments approved by the Particle Physics Experiments Selection Panel. The contents consist of unedited contributions from each experiment. (author)

  1. Particle physics experiments 1987

    International Nuclear Information System (INIS)

    Stuart, G.W.

    1988-01-01

    This report describes work carried out in 1987 on experiments approved by the Particle Physics Experiments Selection Panel (United Kingdom). The contents consist of unedited contributions from each experiment. (author)

  2. Particle physics experiments 1986

    International Nuclear Information System (INIS)

    Stuart, G.W.

    1987-01-01

    The paper presents research work carried out in 1986 on 52 elementary particle experiments approved by the Particle Physics Experiments Selection Panel. Most of the experiments were collaborative and involved research groups from different countries. About half of the experiments were conducted at CERN, the remaining experiments employed the accelerators: LAMPT, LEP, PETRA, SLAC, and HERA. The contents consist of unedited contributions from each experiment. (U.K.)

  3. Data acquisition. GRAAL experiment. Hybrid reactor experiment. AMS experiment; Acquisition de donnees. Experience GRAAL. Experience reacteurs hybrides. Experience AMS

    Energy Technology Data Exchange (ETDEWEB)

    Barancourt, D.; Barbier, G.; Bosson, G.; Bouvier, J.; Gallin-Martel, L.; Meillon, B.; Stassi, P.; Tournier, M. [Inst. des Sciences Nucleaires, Grenoble-1 Univ., 38 (France)

    1997-12-31

    The main activity of the data acquisition team has consisted in hardware and software developments for the GRAAL experiment with the trigger board, for the `Reacteurs Hybrides` group with an acquisition board ADCVME8V and for the AMS experiment with the monitoring of the aerogel detector. (authors) 2 figs.

  4. An angular-selective electron source for the KATRIN experiment

    Czech Academy of Sciences Publication Activity Database

    Beck, M.; Bokeloh, K.; Hein, H.; Bauer, S.; Baumeister, H.; Bonn, J.; Ortjohann, H.W.; Ostrick, B.; Rosendahl, S.; Streubel, S.; Valerius, K.; Zbořil, Miroslav; Weinheimer, C.

    2014-01-01

    Roč. 9, č. 11 (2014), č. článku 11020. ISSN 1748-0221 R&D Projects: GA ČR(CZ) GAP203/12/1896 Institutional support: RVO:61389005 Keywords : spectrometers * photoemission * detector alignment and calibration methods Subject RIV: BF - Elementary Particles and High Energy Physics OBOR OECD: Particles and field physics Impact factor: 1.399, year: 2014

  5. Particle physics experiments 1982

    International Nuclear Information System (INIS)

    Rousseau, M.D.; Stuart, G.

    1983-01-01

    Work carried out in 1982 on 52 experiments approved by the Particle Physics Experiments Selection Panel is described. Each experiment is listed under title, collaboration, technique, accelerator, year of running, status and spokesman. Unedited contributions are given from each experiment. (U.K.)

  6. The User Experience

    Science.gov (United States)

    Schmidt, Aaron

    2010-01-01

    User experience (UX) is about arranging the elements of a product or service to optimize how people will interact with it. In this article, the author talks about the importance of user experience and discusses the design of user experiences in libraries. He first looks at what UX is. Then he describes three kinds of user experience design: (1)…

  7. Indian summer monsoon experiments

    OpenAIRE

    Bhat, GS; Narasimha, R

    2007-01-01

    Eight major field experiments have been carried out so far addressing the Indian summer monsoon. While these experiments were international and the impetus was external till 1980, India’s own monsoon programmes evolved since then. In this article, objectives and outcomes from some of these experiments are described. It is shown that monsoon experiments have contributed in several ways. Each experiment enhanced the infrastructure facilities in the country, brought together scientists from diff...

  8. Adaptive structures flight experiments

    Science.gov (United States)

    Martin, Maurice

    The topics are presented in viewgraph form and include the following: adaptive structures flight experiments; enhanced resolution using active vibration suppression; Advanced Controls Technology Experiment (ACTEX); ACTEX program status; ACTEX-2; ACTEX-2 program status; modular control patch; STRV-1b Cryocooler Vibration Suppression Experiment; STRV-1b program status; Precision Optical Bench Experiment (PROBE); Clementine Spacecraft Configuration; TECHSAT all-composite spacecraft; Inexpensive Structures and Materials Flight Experiment (INFLEX); and INFLEX program status.

  9. The ERASMUS experiment archive

    Science.gov (United States)

    Isakeit, Dieter; Sabbatini, Massimo; Carey, William

    2005-08-01

    The Erasmus Experiment Archive is an electronic database, accessible through the Internet, that collects in a single reference repository scientific, technical and operational information regarding the experiments performed in the experiment facilities which fall under the responsibility of the ESA Directorate of Human Spaceflight, Microgravity and Exploration. The archive is operated, filled with content and kept up-to-date by the Erasmus User Centre. which forms part of the Directorate. The archive shares its records and is interoperable with similar experiment archives of the partner agencies NASA USA) and JAXA (Japan) through a mutually agreed standard for experiment records called the International Distributed Experiment Archive (IDEA).

  10. Experiment WA1 (CDHS Neutrino Experiment)

    CERN Multimedia

    CERN PhotoLab

    1977-01-01

    Experiment WA1, also known under CDHS (CERN, Dortmund, Heidelberg, Saclay; spokesman Jack Steinberger), was the first neutrino experiment on the SPS, in its West Area. Magnetized iron (with a toroidal field) forms the core of the detector. On its outside we see drift chambers and photomultipliers (detecting the light from the plastic scintillators further in). Peter Schilly is wearing a white coat. See also CERN Annual Report 1976, p.57.

  11. Particle physics experiments 1984

    International Nuclear Information System (INIS)

    Stuart, G.

    1985-01-01

    The Rutherford Appleton laboratory report describes work carried out in 1984 on experiments approved by the Particle Physics selection panel. The contents consist of unedited contributions from each experiment. (author)

  12. GARP Atlantic Tropical Experiment

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The GARP Atlantic Tropical Experiment (GATE) was the first major international experiment of the Global Atmospheric Research Program (GARP). It was conducted over...

  13. Social experience infrastructure

    DEFF Research Database (Denmark)

    Kvistgaard, Peter

    2006-01-01

    and explorative fashion to share with others thoughts and ideas concerning the development of new ways to construct/reconstruct recreational spaces with a better coherence with regard to designing experiences. This article claims that it is possible to design recreational spaces with good social experience...... infrastructure in order to create experience spaces for personal experiences (in line with Schultze’s social constructivist view of experiences) without completely adhering to the economic rationalist thoughts and guidelines of Pine & Gilmore that claim that experiences can be designed and controlled...... by experience designers. The notion of social experience infrastructure may be placed in the cross field between the social constructivist and the economic rationalist approach....

  14. Organic chemistry experiment

    International Nuclear Information System (INIS)

    Mun, Seok Sik

    2005-02-01

    This book deals with organic chemistry experiments, it is divided five chapters, which have introduction, the way to write the experiment report and safety in the laboratory, basic experiment technic like recrystallization and extraction, a lot of organic chemistry experiments such as fischer esterification, ester hydrolysis, electrophilic aromatic substitution, aldol reaction, benzoin condensation, wittig reaction grignard reaction, epoxidation reaction and selective reduction. The last chapter introduces chemistry site on the internet and way to find out reference on chemistry.

  15. The Experiment Factory: standardizing behavioral experiments

    Directory of Open Access Journals (Sweden)

    Vanessa V Sochat

    2016-04-01

    Full Text Available The administration of behavioral and experimental paradigms for psychology research is hindered by lack of a coordinated effort to develop and deploy standardized paradigms. While several frameworks (de Leeuw (2015; McDonnell et al. (2012; Mason and Suri (2011; Lange et al. (2015 have provided infrastructure and methods for individual research groups to develop paradigms, missing is a coordinated effort to develop paradigms linked with a system to easily deploy them. This disorganization leads to redundancy in development, divergent implementations of conceptually identical tasks, disorganized and error-prone code lacking documentation, and difficulty in replication. The ongoing reproducibility crisis in psychology and neuroscience research (Baker (2015; Open Science Collaboration (2015 highlights the urgency of this challenge: reproducible research in behavioral psychology is conditional on deployment of equivalent experiments. A large, accessible repository of experiments for researchers to develop collaboratively is most efficiently accomplished through an open source framework. Here we present the Experiment Factory, an open source framework for the development and deployment of web-based experiments. The modular infrastructure includes experiments, virtual machines for local or cloud deployment, and an application to drive these components and provide developers with functions and tools for further extension. We release this infrastructure with a deployment (http://www.expfactory.org that researchers are currently using to run a set of over 80 standardized web-based experiments on Amazon Mechanical Turk. By providing open source tools for both deployment and development, this novel infrastructure holds promise to bring reproducibility to the administration of experiments, and accelerate scientific progress by providing a shared community resource of psychological paradigms.

  16. Designing Urban Experiences

    DEFF Research Database (Denmark)

    Jantzen, Christian; Vetner, Mikael

    2008-01-01

    , and deals with how urban experiences can be designed through careful consideration of how experiences are constituted. Taking the psychological structure of experiences into account when designing urbanity is not only interesting, but also highly relevant as Zuidas is competing with other international...

  17. Virtual neutron scattering experiments

    DEFF Research Database (Denmark)

    Overgaard, Julie Hougaard; Bruun, Jesper; May, Michael

    2016-01-01

    We describe how virtual experiments can be utilized in a learning design that prepares students for hands-on experiments at large-scale facilities. We illustrate the design by showing how virtual experiments are used at the Niels Bohr Institute in a master level course on neutron scattering....... In the last week of the course, students travel to a large-scale neutron scattering facility to perform real neutron scattering experiments. Through student interviews and survey answers, we argue, that the virtual training prepares the students to engage more fruitfully with experiments by letting them focus...

  18. Virtual neutron scattering experiments

    DEFF Research Database (Denmark)

    Overgaard, Julie Hougaard; Bruun, Jesper; May, Michael

    2017-01-01

    We describe how virtual experiments can be utilized in a learning design that prepares students for hands-on experiments at large-scale facilities. We illustrate the design by showing how virtual experiments are used at the Niels Bohr Institute in a master level course on neutron scattering....... In the last week of the course, students travel to a large-scale neutron scattering facility to perform real neutron scattering experiments. Through student interviews and survey answers, we argue, that the virtual training prepares the students to engage more fruitfully with experiments by letting them focus...

  19. Experiments in physical chemistry

    CERN Document Server

    Wilson, J M; Denaro, A R

    1968-01-01

    Experiments in Physical Chemistry, Second Edition provides a compilation of experiments concerning physical chemistry. This book illustrates the link between the theory and practice of physical chemistry. Organized into three parts, this edition begins with an overview of those experiments that generally have a simple theoretical background. Part II contains experiments that are associated with more advanced theory or more developed techniques, or which require a greater degree of experimental skill. Part III consists of experiments that are in the nature of investigations wherein these invest

  20. The Belle II Experiment

    CERN Document Server

    Kahn, J

    2017-01-01

    Set to begin data taking at the end of 2018, the Belle II experiment is the next-generation B-factory experiment hosted at KEK in Tsukuba, Japan. The experiment represents the cumulative effort from the collaboration of experimental and detector physics, computing, and software development. Taking everything learned from the previous Belle experiment, which ran from 1998 to 2010, Belle II aims to probe deeper than ever before into the field of heavy quark physics. By achieving an integrated luminosity of 50 ab−1 and accumulating 50 times more data than the previous experiment across its lifetime, along with a rewritten analysis framework, the Belle II experiment will push the high precision frontier of high energy physics. This paper will give an overview of the key components and development activities that make the Belle II experiment possible.

  1. Diagnostics for pellet experiments

    International Nuclear Information System (INIS)

    Johnson, R.R.

    1978-01-01

    The target diagnostics which are being used and planned in current laser driven ICF Experiments are described. Most of these diagnostics can be easily applied to future ion-beam fusion experiments. The status of laser fusion diagnostics has been much improved in the last 5 years and further improvements can be expected and should be available when the first ICF experiments using ion beams are performed. As an example, x-ray temporal and spatial resolutions are now approximately 5 psec and 3 μm, which is approximately a factor of 4 better than the resolution reported in the first implosion experiments. As one plans ahead for ion-beam fusion experiments it should be emphasized that high yield experiments are easier to diagnose provided adequate shielding is employed. However, in the event that the first high yield experiments fail it will be necessary to have diagnostics available to determine where the problems lie. In laser fusion it is interesting to note that higher laser powers are required now for breakeven experiments than first anticipated, mainly because some aspects of the laser-interaction physics were not recognized until the experiments were carefully diagnosed. Thus as has been pointed out, it may be necessary to increase the energy of the ion-beam driver to enable us to do breakeven experiments with high confidence

  2. Learning and Experience

    DEFF Research Database (Denmark)

    Olesen, Henning Salling

    2017-01-01

    Abstract: This chapter introduces a psycho-societal approach to theorizing learning, combining a materialist theory of socialization with a hermeneutic interpretation methodology. The term "approach" indicates the intrinsic connection between theory, empirical research process and epistemic subject....... Learning is theorized as dynamic subjective experience of (socially situated) realities, counting on individual subjectivity as well as subjective aspects of social interaction. This psycho-societal theory of subjective experiences conceptualizes individual psychic development as interactional experience...... of societal relations, producing an inner psycho-dynamic as a conscious and unconscious individual resource in future life. The symbolization of immediate sensual experiences form an individual life experience of social integration, language use being the medium of collective, social experience (knowledge...

  3. Experiment, right or wrong

    CERN Document Server

    Franklin, Allan

    2008-01-01

    In Experiment, Right or Wrong, Allan Franklin continues his investigation of the history and philosophy of experiment presented in his previous book, The Neglect of Experiment. In this new study, Franklin considers the fallibility and corrigibility of experimental results and presents detailed histories of two such episodes: 1) the experiment and the development of the theory of weak interactions from Fermi's theory in 1934 to the V-A theory of 1957 and 2) atomic parity violation experiments and the Weinberg-Salam unified theory of electroweak interactions of the 1970s and 1980s. In these episodes Franklin demonstrates not only that experimental results can be wrong, but also that theoretical calculations and the comparison between experiment and theory can also be incorrect. In the second episode, Franklin contrasts his view of an "evidence model" of science in which questions of theory choice, confirmation, and refutation are decided on the basis of reliable experimental evidence, with that proposed by the ...

  4. Stimulated Brillouin scattering experiments

    International Nuclear Information System (INIS)

    Slater, D.C.; Berger, R.L.; Busch, G.; Kinzer, C.M.; Mayer, F.J.; Powers, L.V.; Tanner, D.J.

    1981-01-01

    This report describes two experiments in which SBS would be expected to play an important role. In the first experiment, we find a clear signature of the Brillouin backscatter of a short (100 psec) pulse from a long (approx. 50 μm) gradient length gas target plasma. The second experiment used much longer (approx. 1 nsec) pulses on spherical glass shell targets. These experiments were done with both narrow ( 30A) bandwidth laser light. Using one-dimensional, spherically symmetric fluid simulations, we have attempted to model many of the laser-plasma interaction processes which combine to determine the amount of absorbed energy in the long-pulse experiments. These simulations indicate that modest laser bandwidths are successful in reducing the level of SBS at the irradiances ( 15 W/cm 2 ) used in these experiments

  5. Experience composite worth: A combination of experience quality ...

    African Journals Online (AJOL)

    This research suggests that experience quality and experience value be combined into a single multi-dimensional construct, termed experience composite worth. It briefly describes customer experience, experience quality and experience value and the overlap in the dimensions used in outlining experience quality and ...

  6. Linking consumer experiences

    DEFF Research Database (Denmark)

    Smed, Karina Madsen

    become part of the individual self, worldview, and behaviour. This paper seeks to explore links between consumer experiences through the exploration of narrative sequences in travel blogs. Findings indicate that non-consumption is a central element to the bloggers and also indicative of a community......Consumers consume products in various ways serving a number of purposes. Much attention has been paid to experiences attached to consumption, sometimes very explicitly, e.g. in tourism, the essence of which is experiences of various sorts, but often also implicitly as internalised experiences...

  7. Real Life Experiences with Experience Design

    DEFF Research Database (Denmark)

    Dalsgård, Peter; Halskov, Kim

    2006-01-01

    technologies for knowledge dissemination and marketing, in cooperation with public institutions and businesses. We argue that collaborative formulation of core design intentions and values is a valuable instrument in guiding experience design processes, and present three cases from this project, two of which...... resulted in interactive installations. The case installations range from walk-up-and-use consoles, to immersive, responsive, environments based on bodily interaction. We compare the installations, and discuss the interrelations between the resulting interfaces and the intentions for creating...

  8. Experience with MODSIM II

    International Nuclear Information System (INIS)

    Streets, J.; Berg, D.; Oleynik, G.; Pordes, R.; Slimmer, D.

    1992-02-01

    We present results of computer simulations for Data Acquisition systems for large fixed target experiments in an object oriented simulation language, MODSIM. This paper summarizes our experiences and presents preliminary results from the simulation already completed. We also indicate the resources required for this project

  9. Experiments as politics

    NARCIS (Netherlands)

    Spears, R; Smith, HJ

    The purpose of this paper is to illustrate the political nature of laboratory experiments. Such experiments can be construed as paradigms of power, open to construction and debate, where different agents and interests are involved in a process of struggle over both (re)presentation and substance.

  10. Long baseline neutrino experiments

    Indian Academy of Sciences (India)

    High statistics experiment with NNO = 3000/year. Can measure P(νµ → νe). So good sensitivity to θ13 and CP violation but not to matter effects. BNL to Homestake: L = 2540 km, being planned. Ultimate accelerator beam experiment with very high statistics with NNO = 3000/year. Can achieve all the goals listed above with a ...

  11. ATLAS Experiment Brochure - Italian

    CERN Multimedia

    2018-01-01

    ATLAS is one of the four major experiments at the Large Hadron Collider at CERN. It is a general-purpose particle physics experiment run by an international collaboration, and is designed to exploit the full discovery potential and the huge range of physics opportunities that the LHC provides.

  12. ATLAS Experiment Brochure - Serbian

    CERN Multimedia

    2018-01-01

    ATLAS is one of the four major experiments at the Large Hadron Collider at CERN. It is a general-purpose particle physics experiment run by an international collaboration, and is designed to exploit the full discovery potential and the huge range of physics opportunities that the LHC provides.

  13. ATLAS Experiment Brochure

    CERN Multimedia

    AUTHOR|(INSPIRE)INSPIRE-00085461

    2016-01-01

    ATLAS is one of the four major experiments at the Large Hadron Collider at CERN. It is a general-purpose particle physics experiment run by an international collaboration, and is designed to exploit the full discovery potential and the huge range of physics opportunities that the LHC provides.

  14. Realisation, experience, and purification

    DEFF Research Database (Denmark)

    Sobisch, Jan-Ulrich

    2013-01-01

    Often Buddhist mantra practises are portrayed as making and maintaining meditation experiences. Jigten Sumgön explains in his dGongs gcig (5.19) that such a 'making and maintaining' is only a mental fabrication and needs to be purified. Realisation does not arise from experience, but from...

  15. Neutrino oscillation experiments

    International Nuclear Information System (INIS)

    Camilleri, L.

    1996-01-01

    Neutrino oscillation experiments (ν μ →ν e and ν μ →ν τ ) currently being performed at accelerators are reviewed. Future plans for short and long base-line experiments are summarized. (author) 10 figs., 2 tabs., 29 refs

  16. On the Poggendorff Experiment

    Science.gov (United States)

    Coelho, Ricardo Lopes; Silva, P. A. S.; Borges, Paulo de Faria

    2015-01-01

    Poggendorff showed experimentally, in the middle of the 19th century, that the weight of an Atwood machine is reduced when it is brought to motion. His experiment has been revisited from time to time, making use of instrumentation that reflects the technological development of the moment. In this paper, the evolution of the experiment is briefly…

  17. Particle physics experiments 1992

    International Nuclear Information System (INIS)

    Roberts, B.A.

    1993-03-01

    The research programs described here were carried out in 1992 at Rutherford Appleton Laboratory and funded by the United Kingdom Science and Engineering Research Council. The area covered in these experiments is particle physics. Unedited contributions from over forty experimental programs are included. Experiments are listed according to their current status, the accelerator used and its years of operation. (UK)

  18. Ball Collision Experiments

    Science.gov (United States)

    Cross, R.

    2015-01-01

    Experiments are described on collisions between two billiard balls and between a bat and a ball. The experiments are designed to extend a student's understanding of collision events and could be used either as a classroom demonstration or for a student project.

  19. Neutrino oscillation experiments

    Energy Technology Data Exchange (ETDEWEB)

    Camilleri, L. [European Organization for Nuclear Research, Geneva (Switzerland)

    1996-11-01

    Neutrino oscillation experiments ({nu}{sub {mu}}{yields}{nu}{sub e} and {nu}{sub {mu}}{yields}{nu}{sub {tau}}) currently being performed at accelerators are reviewed. Future plans for short and long base-line experiments are summarized. (author) 10 figs., 2 tabs., 29 refs.

  20. Future of neutrino experiments

    Indian Academy of Sciences (India)

    January 2009 physics pp. 109–117. Future of neutrino experiments. TAKAAKI KAJITA. ICRR and IPMU, University of Tokyo, Kashiwa-no-ha 5-1-5, Kashiwa, Chiba 277-8582,. Japan. E-mail: kajita@icrr.u-tokyo.ac.jp. Abstract. Atmospheric, solar, reactor and accelerator neutrino oscillation experiments have measured Δm2.