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Sample records for laser-based angle-resolved photoemission

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

    NASA Astrophysics Data System (ADS)

    Jiang, Rui; Mou, Daixiang; Wu, Yun; Huang, Lunan; McMillen, Colin D.; Kolis, Joseph; Giesber, Henry G.; Egan, John J.; Kaminski, Adam

    2014-03-01

    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 1014 photon/s. We demonstrate that this energy range is sufficient to measure the kz dispersion in an iron arsenic high temperature superconductor, which was previously only possible at synchrotron facilities.

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

    SciTech Connect

    Jiang, Rui; Mou, Daixiang; Wu, Yun; Huang, Lunan; Kaminski, Adam; McMillen, Colin D.; Kolis, Joseph; Giesber, Henry G.; Egan, John J.

    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.

  3. Development of a vacuum ultraviolet laser-based angle-resolved photoemission system with a superhigh energy resolution better than 1 meV.

    PubMed

    Liu, Guodong; Wang, Guiling; Zhu, Yong; Zhang, Hongbo; Zhang, Guochun; Wang, Xiaoyang; Zhou, Yong; Zhang, Wentao; Liu, Haiyun; Zhao, Lin; Meng, Jianqiao; Dong, Xiaoli; Chen, Chuangtian; Xu, Zuyan; Zhou, X J

    2008-02-01

    The design and performance of the first vacuum ultraviolet (VUV) laser-based angle-resolved photoemission (ARPES) system are described. The VUV laser with a photon energy of 6.994 eV and bandwidth of 0.26 meV is achieved from the second harmonic generation using a novel nonlinear optical crystal KBe2BO3F2. The new VUV laser-based ARPES system exhibits superior performance, including superhigh energy resolution better than 1 meV, high momentum resolution, superhigh photon flux, and much enhanced bulk sensitivity, which are demonstrated from measurements on a typical Bi2Sr2CaCu2O8 high temperature superconductor. Issues and further development related to the VUV laser-based photoemission technique are discussed.

  4. Angle-resolved photoemission extended fine structure

    SciTech Connect

    Barton, J.J.

    1985-03-01

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

  5. Angle resolved photoemission spectroscopy and surface states

    NASA Astrophysics Data System (ADS)

    Kar, Nikhiles

    2016-10-01

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

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

    SciTech Connect

    Dakovski, Georgi L; Li, Yinwan; Durakiewicz, Tomasz; Rodriguez, George

    2009-01-01

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

  7. Coexistence of two sharp-mode couplings and their unusual momentum dependence in the superconducting state of Bi2Sr2CaCu2O(8+δ) revealed by laser-based angle-resolved photoemission.

    PubMed

    He, Junfeng; Zhang, Wentao; Bok, Jin Mo; Mou, Daixiang; Zhao, Lin; Peng, Yingying; He, Shaolong; Liu, Guodong; Dong, Xiaoli; Zhang, Jun; Wen, J S; Xu, Z J; Gu, G D; Wang, Xiaoyang; Peng, Qinjun; Wang, Zhimin; Zhang, Shenjin; Yang, Feng; Chen, Chuangtian; Xu, Zuyan; Choi, H-Y; Varma, C M; Zhou, X J

    2013-09-06

    High-resolution laser-based angle-resolved photoemission measurements have been carried out on Bi2Sr2CaCu2O(8+δ) (Bi2212) superconductors to investigate momentum dependence of electron coupling with collective excitations (modes). Two coexisting energy scales are clearly revealed over a large momentum space for the first time in the superconducting state of the overdoped Bi2212 superconductor. These two energy scales exhibit distinct momentum dependence: one keeps its energy near 78 meV over a large momentum space while the other changes its energy from ∼40  meV near the antinodal region to ∼70  meV near the nodal region. These observations provide a new picture on momentum evolution of electron-boson coupling in Bi2212 that electrons are coupled with two sharp modes simultaneously over a large momentum space in the superconducting states. Their unusual momentum dependence poses a challenge to our current understanding of electron-mode-coupling and its role for high-temperature superconductivity in cuprate superconductors.

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

    SciTech Connect

    Palczewski, Ari Deibert

    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 consistent

  9. Time- and angle-resolved photoemission spectroscopy of hydrated electrons near a liquid water surface.

    PubMed

    Yamamoto, Yo-ichi; Suzuki, Yoshi-Ichi; Tomasello, Gaia; Horio, Takuya; Karashima, Shutaro; Mitríc, Roland; Suzuki, Toshinori

    2014-05-09

    We present time- and angle-resolved photoemission spectroscopy of trapped electrons near liquid surfaces. Photoemission from the ground state of a hydrated electron at 260 nm is found to be isotropic, while anisotropic photoemission is observed for the excited states of 1,4-diazabicyclo[2,2,2]octane and I- in aqueous solutions. Our results indicate that surface and subsurface species create hydrated electrons in the bulk side. No signature of a surface-bound electron has been observed.

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

    SciTech Connect

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

    2016-01-15

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

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

    PubMed

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-01-01

    We developed a table-top vacuum ultraviolet (VUV) laser with 113.778 nm wavelength (10.897 eV) and demonstrated its viability as a photon source for high resolution angle-resolved photoemission spectroscopy (ARPES). This sub-nanosecond pulsed VUV laser operates at a repetition rate of 10 MHz, provides a flux of 2 × 1012 photons/s, and enables photoemission with energy and momentum resolutions better than 2 meV and 0.012 Å-1, respectively. Space-charge induced energy shifts and spectral broadenings can be reduced below 2 meV. The setup reaches electron momenta up to 1.2 Å-1, granting full access to the first Brillouin zone of most materials. Control over the linear polarization, repetition rate, and photon flux of the VUV source facilitates ARPES investigations of a broad range of quantum materials, bridging the application gap between contemporary low energy laser-based ARPES and synchrotron-based ARPES. We describe the principles and operational characteristics of this source and showcase its performance for rare earth metal tritellurides, high temperature cuprate superconductors, and iron-based superconductors.

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

    SciTech Connect

    Huff, W.R.A.; Kellar, S.A.; Moler, E.J. |; Chen, Y.; Wu, H.; Shirley, D.A.; Hussain, Z.

    1995-08-01

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

  14. Interlayer Interaction and Electronic Screening in Multilayer Graphene Investigated with Angle-Resolved Photoemission Spectroscopy

    NASA Astrophysics Data System (ADS)

    Ohta, Taisuke; Bostwick, Aaron; McChesney, J. L.; Seyller, Thomas; Horn, Karsten; Rotenberg, Eli

    2007-05-01

    The unusual transport properties of graphene are the direct consequence of a peculiar band structure near the Dirac point. We determine the shape of the π bands and their characteristic splitting, and find the transition from two-dimensional to bulk character for 1 to 4 layers of graphene by angle-resolved photoemission. By detailed measurements of the π bands we derive the stacking order, layer-dependent electron potential, screening length, and strength of interlayer interaction by comparison with tight binding calculations, yielding a comprehensive description of multilayer graphene’s electronic structure.

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

    SciTech Connect

    Zheng, Y. |; Shirley, D.A.

    1995-02-01

    The authors show by Fourier analyses of experimental data, with no further treatment, that the positions of all the strong peaks in Fourier transforms of angle-resolved photoemission extended fine structure (ARPEFS) from adsorbed surfaces can be explicitly predicted from a trial structure with an accuracy of about {+-} 0.3 {angstrom} based on a single-scattering cluster model together with the concept of a strong backscattering cone, and without any additional analysis. This characteristic of ARPEFS Fourier transforms can be developed as a simple method for determining the structures of adsorbed surfaces to an accuracy of about {+-} 0.1 {angstrom}.

  16. Electron self-energy of high temperature superconductors as revealed by angle-resolved photoemission.

    SciTech Connect

    Ding, H.; Norman, M. R.; Randeria, M.

    1997-12-05

    In this paper, we review some of the work our group has done in the past few years to obtain the electron self-energy of high temperature superconductors by analysis of angle-resolved photoemission data. We focus on three examples which have revealed: (1) a d-wave superconducting gap, (2) a collective mode in the superconducting state, and (3) pairing correlations in the pseudogap phase. In each case, although a novel result is obtained which captures the essence of the data, the conventional physics used leads to an incomplete picture. This indicates that new physics needs to be developed to obtain a proper understanding of these materials.

  17. Angle-resolved photoemission spectroscopy of liquid water at 29.5 eV

    PubMed Central

    Nishitani, Junichi; West, Christopher W.; Suzuki, Toshinori

    2017-01-01

    Angle-resolved photoemission spectroscopy of liquid water was performed using extreme ultraviolet radiation at 29.5 eV and a time-of-flight photoelectron spectrometer. SiC/Mg coated mirrors were employed to select the single-order 19th harmonic from laser high harmonics, which provided a constant photon flux for different laser polarizations. The instrument was tested by measuring photoemission anisotropy for rare gases and water molecules and applied to a microjet of an aqueous NaI solution. The solute concentration was adjusted to eliminate an electric field gradient around the microjet. The observed photoelectron spectra were analyzed considering contributions from liquid water, water vapor, and an isotropic background. The anisotropy parameters of the valence bands (1b1, 3a1, and 1b2) of liquid water are considerably smaller than those of gaseous water, which is primarily attributed to electron scattering in liquid water.

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

    NASA Astrophysics Data System (ADS)

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

    2017-02-01

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

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

    PubMed Central

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

    2017-01-01

    Material line defects are one-dimensional structures but the search and proof of electron behaviour consistent with the reduced dimension of such defects has been so far unsuccessful. Here we show using angle resolved photoemission spectroscopy that twin-grain boundaries in the layered semiconductor MoSe2 exhibit parabolic metallic bands. The one-dimensional nature is evident from a charge density wave transition, whose periodicity is given by kF/π, consistent with scanning tunnelling microscopy and angle resolved photoemission measurements. Most importantly, we provide evidence for spin- and charge-separation, the hallmark of one-dimensional quantum liquids. Our studies show that the spectral line splits into distinctive spinon and holon excitations whose dispersions exactly follow the energy-momentum dependence calculated by a Hubbard model with suitable finite-range interactions. Our results also imply that quantum wires and junctions can be isolated in line defects of other transition metal dichalcogenides, which may enable quantum transport measurements and devices. PMID:28165445

  20. First-principles approach to excitons in time-resolved and angle-resolved photoemission spectra

    NASA Astrophysics Data System (ADS)

    Perfetto, E.; Sangalli, D.; Marini, A.; Stefanucci, G.

    2016-12-01

    In this work we put forward a first-principles approach and propose an accurate diagrammatic approximation to calculate the time-resolved (TR) and angle-resolved photoemission spectrum of systems with excitons. We also derive an alternative formula to the TR photocurrent which involves a single time-integral of the lesser Green's function. The diagrammatic approximation applies to the relaxed regime characterized by the presence of quasistationary excitons and vanishing polarization. The nonequilibrium self-energy diagrams are evaluated using excited Green's functions; since this is not standard, the analytic derivation is presented in detail. The final result is an expression for the lesser Green's function in terms of quantities that can all be calculated in a first-principles manner. The validity of the proposed theory is illustrated in a one-dimensional model system with a direct gap. We discuss possible scenarios and highlight some universal features of the exciton peaks. Our results indicate that the exciton dispersion can be observed in TR and angle-resolved photoemission.

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

    SciTech Connect

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

    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.

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

    PubMed

    Heinzmann, Ulrich; Dil, J Hugo

    2012-05-02

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

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

    PubMed

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

    2015-08-21

    Recently studied hyperbolic materials host unique phonon-polariton (PP) modes. The ultrashort wavelengths of these modes, as well as their low damping, hold promise for extreme subdiffraction nanophotonics schemes. Polar hyperbolic materials such as hexagonal boron nitride can be used to realize long-range coupling between PP modes and extraneous charge degrees of freedom. The latter, in turn, can be used to control and probe PP modes. Here we analyze coupling between PP modes and plasmons in an adjacent graphene sheet, which opens the door to accessing PP modes by angle-resolved photoemission spectroscopy (ARPES). A rich structure in the graphene ARPES spectrum due to PP modes is predicted, providing a new probe of PP modes and their coupling to graphene plasmons.

  4. Angle resolved photo-emission spectroscopy signature of the resonant excitonic state

    NASA Astrophysics Data System (ADS)

    Montiel, X.; Kloss, T.; Pépin, C.

    2016-09-01

    We calculate the angle resolved photo-emission spectroscopy (ARPES) signature of the resonant excitonic state (RES) that was proposed as the pseudo-gap state of cuprate superconductors (Kloss T. et al., arXiv:1510.03038 (2015)). This new state can be described as a set of excitonic (particle-hole) patches with an internal checkerboard modulation. Here, we modelize the RES as a charge order with 2\\textbf{p}F wave vectors, where 2\\textbf{p}F is the ordering vector connecting two opposite sides of the Fermi surface. We calculate the spectral weight and the density of states in the RES and we find that our model correctly reproduces the opening of the PG in Bi-2201.

  5. Resonant interaction between two Cu quantum wells investigated by angle-resolved photoemission spectroscopy

    NASA Astrophysics Data System (ADS)

    Wu, Y. Z.; Won, C.; Rotenberg, E.; Zhao, H. W.; Xue, Qi-Kun; Kim, W.; Owens, T. L.; Smith, N. V.; Qiu, Z. Q.

    2006-03-01

    Double quantum wells (QWs) of Cu thin films were investigated using angle-resolved photoemission spectroscopy. The thickness ratio of the two Cu QW films was chosen to be 1:1 and 2:1 to purposely group the QW states of the two Cu films into degenerate and nondegenerate states. The energy spectra of the valence band show that only the degenerate QW states interact resonantly to split each degenerate state into two separate states. Furthermore, by investigating the interaction of two Cu films across a Ni/Cu [14 monolayer (ML)]/Ni QW, we show clearly that resonant splitting occurs at the quantized energy levels of the middle 14 ML Cu QW film.

  6. Substrate interactions with suspended and supported monolayer MoS2: Angle-resolved photoemission spectroscopy

    DOE PAGES

    Jin, Wencan; Yeh, Po -Chun; Zaki, Nader; ...

    2015-03-17

    We report the directly measured electronic structure of exfoliated monolayer molybdenum disulfide (MoS₂) using micrometer-scale angle-resolved photoemission spectroscopy. Measurements of both suspended and supported monolayer MoS₂ elucidate the effects of interaction with a substrate. Thus, a suggested relaxation of the in-plane lattice constant is found for both suspended and supported monolayer MoS₂ crystals. For suspended MoS₂, a careful investigation of the measured uppermost valence band gives an effective mass at Γ¯ and Κ¯ of 2.00m₀ and 0.43m₀, respectively. We also measure an increase in the band linewidth from the midpoint of Γ¯Κ¯ to the vicinity of Κ¯ and briefly discussmore » its possible origin.« less

  7. Valence band dispersion measurements of perovskite single crystals using angle-resolved photoemission spectroscopy.

    PubMed

    Wang, Congcong; Ecker, Benjamin R; Wei, Haotong; Huang, Jinsong; Meng, Jian-Qiao; Gao, Yongli

    2017-02-15

    The electronic structure of a cleaved perovskite (CH3NH3PbBr3) single crystal was studied in an ultra-high vacuum (UHV) system using angle-resolved photoemission spectroscopy (ARPES) and inverse photoelectron spectroscopy (IPES). Highly reproducible dispersive features of the valence bands were observed with symmetry about the Brillouin zone center and boundaries. The largest dispersion width was found to be ∼0.73 eV and ∼0.98 eV along the ΓX and ΓM directions, respectively. The effective mass of the holes was estimated to be ∼0.59m0. The quality of the surface was verified using atomic force microscopy (AFM) and scanning electron microscopy (SEM). The elemental composition was investigated using high resolution X-ray photoelectron spectroscopy (XPS). The experimental electronic structure shows a good agreement with the theoretical calculation.

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

    PubMed

    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.

  9. Stacking-Dependent Electronic Structure of Trilayer Graphene Resolved by Nanospot Angle-Resolved Photoemission Spectroscopy.

    PubMed

    Bao, Changhua; Yao, Wei; Wang, Eryin; Chen, Chaoyu; Avila, José; Asensio, Maria C; Zhou, Shuyun

    2017-03-08

    The crystallographic stacking order in multilayer graphene plays an important role in determining its electronic structure. In trilayer graphene, rhombohedral stacking (ABC) is particularly intriguing, exhibiting a flat band with an electric-field tunable band gap. Such electronic structure is distinct from simple hexagonal stacking (AAA) or typical Bernal stacking (ABA) and is promising for nanoscale electronics and optoelectronics applications. So far clean experimental electronic spectra on the first two stackings are missing because the samples are usually too small in size (μm or nm scale) to be resolved by conventional angle-resolved photoemission spectroscopy (ARPES). Here, by using ARPES with a nanospot beam size (NanoARPES), we provide direct experimental evidence for the coexistence of three different stackings of trilayer graphene and reveal their distinctive electronic structures directly. By fitting the experimental data, we provide important experimental band parameters for describing the electronic structure of trilayer graphene with different stackings.

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

    PubMed Central

    Park, Sang Han; Kwon, Soonnam

    2016-01-01

    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. PMID:27164313

  11. Preparation of layered thin film samples for angle-resolved photoemission spectroscopy

    SciTech Connect

    Harrison, S. E.; Zhou, B.; Huo, Y.; Harris, J. S.; Pushp, A.; Kellock, A. J.; Parkin, S. S. P.; Chen, Y.; Hesjedal, T.

    2014-09-22

    Materials with layered van der Waals crystal structures are exciting research topics in condensed matter physics and materials science due to outstanding physical properties associated with their strong two dimensional nature. Prominent examples include bismuth tritelluride and triselenide topological insulators (TIs), which are characterized by a bulk bandgap and pairwise counter-propagating spin-polarized electronic surface states. Angle-resolved photoemission spectroscopy (ARPES) of ex-situ grown thin film samples has been limited by the lack of suitable surface preparation techniques. We demonstrate the shortcomings of previously successful conventional surface preparation techniques when applied to ternary TI systems which are susceptible to severe oxidation. We show that in-situ cleaving is a simple and effective technique for preparation of clean surfaces on ex-situ grown thin films for high quality ARPES measurements. The method presented here is universally applicable to other layered van der Waals systems as well.

  12. Angle-resolved photoemission and first-principles studies of topological thin films

    NASA Astrophysics Data System (ADS)

    Bian, Guang

    Dirac cones centered at the time-reversal-invariant M¯ points at the zone boundary. The critical behavior of the TI film near the quantum critical point is also studied theoretically. When the strength of the spin-orbit coupling (SOC) is tuned across the critical point, the topological surface states, while protected by symmetry in the bulk limit, can be missing completely in topological films even at large film thicknesses. We have observed, using angle-resolved photoemission, a structural phase transformation of Bi films deposited on Si(111)-(7x7). Films with thicknesses 20 to ~100 A, upon annealing, first order into a metastable pseudocubic (PC) phase and then transform into a stable rhombohedral (RH) phase with very different topologies for the quantum well subband structures. The PC phase shows a surface band with a maximum near the Fermi level at G , whereas the RH phase shows a Dirac-like subband around M¯ along K¯ -- M¯ -- K¯ . The formation of the metastable phase over a wide thickness range can be attributed to a surface nucleation mechanism. Finally, we have studied the electronic structure of the Bi/Ag surface alloy, a system possessing a huge Rashba splitting in its surface bands. The Bi/Ag surface alloy is prepared by depositing Bi onto ultrathin Ag films followed by annealing. The electronic structure of the system is measured using circular angle resolved photoemission spectroscopy (CARPES). The results reveal two interesting phenomena: the hybridization of spin polarized surface states with Ag bulk quantum well states and the umklapp scattering by the perturbed surface potential. In addition, our CARPES spectra show clearly a unique dichroism pattern which is closely related to the spin texture of this 2D strongly spin-orbit coupled electron system.

  13. Electronic structure of dense Pb overlayers on Si(111) investigated using angle-resolved photoemission

    NASA Astrophysics Data System (ADS)

    Choi, W. H.; Koh, H.; Rotenberg, E.; Yeom, H. W.

    2007-02-01

    Dense Pb overlayers on Si(111) are important as the wetting layer for anomalous Pb island growth as well as for their own complex “devil’s-staircase” phases. The electronic structures of dense Pb overlayers on Si(111) were investigated in detail by angle-resolved photoemission. Among the series of ordered phases found recently above one monolayer, the low-coverage 7×3 and the high-coverage 14×3 phases are studied; they are well ordered and form reproducibly in large areas. The band dispersions and Fermi surfaces of the two-dimensional (2D) electronic states of these overlayers are mapped out. A number of metallic surface-state bands are identified for both phases with complex Fermi contours. The basic features of the observed Fermi contours can be explained by overlapping 2D free-electron-like Fermi circles. This analysis reveals that the 2D electrons near the Fermi level of the 7×3 and 14×3 phases are mainly governed by strong 1×1 and 3×3 potentials, respectively. The origins of the 2D electronic states and their apparent Fermi surface shapes are discussed based on recent structure models.

  14. Extracting the temperature of hot carriers in time- and angle-resolved photoemission.

    PubMed

    Ulstrup, Søren; Johannsen, Jens Christian; Grioni, Marco; Hofmann, Philip

    2014-01-01

    The interaction of light with a material's electronic system creates an out-of-equilibrium (non-thermal) distribution of optically excited electrons. Non-equilibrium dynamics relaxes this distribution on an ultrafast timescale to a hot Fermi-Dirac distribution with a well-defined temperature. The advent of time- and angle-resolved photoemission spectroscopy (TR-ARPES) experiments has made it possible to track the decay of the temperature of the excited hot electrons in selected states in the Brillouin zone, and to reveal their cooling in unprecedented detail in a variety of emerging materials. It is, however, not a straightforward task to determine the temperature with high accuracy. This is mainly attributable to an a priori unknown position of the Fermi level and the fact that the shape of the Fermi edge can be severely perturbed when the state in question is crossing the Fermi energy. Here, we introduce a method that circumvents these difficulties and accurately extracts both the temperature and the position of the Fermi level for a hot carrier distribution by tracking the occupation statistics of the carriers measured in a TR-ARPES experiment.

  15. Ultrafast electron dynamics in epitaxial graphene investigated with time- and angle-resolved photoemission spectroscopy

    NASA Astrophysics Data System (ADS)

    Ulstrup, Søren; Johannsen, Jens Christian; Crepaldi, Alberto; Cilento, Federico; Zacchigna, Michele; Cacho, Cephise; Chapman, Richard T.; Springate, Emma; Fromm, Felix; Raidel, Christian; Seyller, Thomas; Parmigiani, Fulvio; Grioni, Marco; Hofmann, Philip

    2015-04-01

    In order to exploit the intriguing optical properties of graphene it is essential to gain a better understanding of the light-matter interaction in the material on ultrashort timescales. Exciting the Dirac fermions with intense ultrafast laser pulses triggers a series of processes involving interactions between electrons, phonons and impurities. Here we study these interactions in epitaxial graphene supported on silicon carbide (semiconducting) and iridium (metallic) substrates using ultrafast time- and angle-resolved photoemission spectroscopy (TR-ARPES) based on high harmonic generation. For the semiconducting substrate we reveal a complex hot carrier dynamics that manifests itself in an elevated electronic temperature and an increase in linewidth of the π band. By analyzing these effects we are able to disentangle electron relaxation channels in graphene. On the metal substrate this hot carrier dynamics is found to be severely perturbed by the presence of the metal, and we find that the electronic system is much harder to heat up than on the semiconductor due to screening of the laser field by the metal.

  16. Extracting the temperature of hot carriers in time- and angle-resolved photoemission

    SciTech Connect

    Ulstrup, Søren; Hofmann, Philip; Johannsen, Jens Christian; Grioni, Marco

    2014-01-15

    The interaction of light with a material's electronic system creates an out-of-equilibrium (non-thermal) distribution of optically excited electrons. Non-equilibrium dynamics relaxes this distribution on an ultrafast timescale to a hot Fermi-Dirac distribution with a well-defined temperature. The advent of time- and angle-resolved photoemission spectroscopy (TR-ARPES) experiments has made it possible to track the decay of the temperature of the excited hot electrons in selected states in the Brillouin zone, and to reveal their cooling in unprecedented detail in a variety of emerging materials. It is, however, not a straightforward task to determine the temperature with high accuracy. This is mainly attributable to an a priori unknown position of the Fermi level and the fact that the shape of the Fermi edge can be severely perturbed when the state in question is crossing the Fermi energy. Here, we introduce a method that circumvents these difficulties and accurately extracts both the temperature and the position of the Fermi level for a hot carrier distribution by tracking the occupation statistics of the carriers measured in a TR-ARPES experiment.

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

    NASA Astrophysics Data System (ADS)

    Ronning, F.

    2002-03-01

    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 Ca2-xNaxCuO2Cl2. 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 La2-xSrxCuO4 where the chemical potential remains fixed and states are created inside the gap. Furthermore, the low energy excitations (ie the Fermi surface) in metallic Ca1.9Na0.1CuO2Cl2 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 new avenue for understanding the evolution of the Mott insulator to

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

    SciTech Connect

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

    2011-06-03

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

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

    NASA Astrophysics Data System (ADS)

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

    2008-02-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-10-01

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

  1. An experimental setup for high resolution 10.5 eV laser-based angle-resolved photoelectron spectroscopy using a time-of-flight electron analyzer.

    PubMed

    Berntsen, M H; Götberg, O; Tjernberg, O

    2011-09-01

    We present an experimental setup for laser-based angle-resolved time-of-flight photoemission. Using a picosecond pulsed laser, photons of energy 10.5 eV are generated through higher harmonic generation in xenon. The high repetition rate of the light source, variable between 0.2 and 8 MHz, enables high photoelectron count rates and short acquisition times. By using a time-of-flight analyzer with angle-resolving capabilities, electrons emitted from the sample within a circular cone of up to ±15° can be collected. Hence, simultaneous acquisition of photoemission data for a complete area of the Brillouin zone is possible. The current photon energy enables bulk sensitive measurements, high angular resolution, and the resulting covered momentum space is large enough to enclose the entire Brillouin zone in cuprate high-T(c) superconductors. Fermi edge measurements on polycrystalline Au shows an energy resolution better than 5 meV. Data from a test measurement of the Au(111) surface state are presented along with measurements of the Fermi surface of the high-T(c) superconductor Bi(2)Sr(2)CaCu(2)O(8 + δ) (Bi2212).

  2. Design of a High Resolution and High Flux Beam line for VUV Angle-Resolved Photoemission at UVSOR-II

    SciTech Connect

    Kimura, Shin-ichi; Ito, Takahiro; Nakamura, Eiken; Hosaka, Masahito; Katoh, Masahiro

    2007-01-19

    A high-energy-resolution angle-resolved photoemission beamline in the vacuum-ultraviolet (VUV) region has been designed for a 750 MeV synchrotron light source UVSOR-II. The beamline equips an APPLE-II-type undulator with the horizontally/vertically linear and right/left circular polarizations, a modified Wadsworth-type monochromator and a high-resolution photoelectron analyzer. The monochromator covers the photon energy range of 6 - 40 eV. The energy resolution (hv/{delta}hv) and the photon flux on samples are expected to be 2 x 104 and 1012 photons/sec at 10 eV, 4 x 104 and 5 x 1011 photons/sec at 20 eV, and 6 x 104 and 1011 photons/sec at 40 eV, respectively. The beamline provides the high-resolution angle-resolved photoemission spectroscopy less than 1 meV in the whole VUV energy range.

  3. Angle-resolved photoemission spectroscopy of the insulating NaxWO3: Anderson localization, polaron formation, and remnant Fermi surface.

    PubMed

    Raj, S; Hashimoto, D; Matsui, H; Souma, S; Sato, T; Takahashi, T; Sarma, D D; Mahadevan, Priya; Oishi, S

    2006-04-14

    The electronic structure of the insulating sodium tungsten bronze, Na(0.025)WO(3), is investigated by high-resolution angle-resolved photoemission spectroscopy. We find that near-E(F) states are localized due to the strong disorder arising from random distribution of Na+ ions in the WO(3) lattice, which makes the system insulating. The temperature dependence of photoemission spectra provides direct evidence for polaron formation. The remnant Fermi surface of the insulator is found to be the replica of the real Fermi surface in the metallic system.

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

    SciTech Connect

    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.

  5. Electron-electron correlation in graphite: a combined angle-resolved photoemission and first-principles study.

    PubMed

    Grüneis, A; Attaccalite, C; Pichler, T; Zabolotnyy, V; Shiozawa, H; Molodtsov, S L; Inosov, D; Koitzsch, A; Knupfer, M; Schiessling, J; Follath, R; Weber, R; Rudolf, P; Wirtz, L; Rubio, A

    2008-01-25

    The full three-dimensional dispersion of the pi bands, Fermi velocities, and effective masses are measured with angle-resolved photoemission spectroscopy and compared to first-principles calculations. The band structure by density-functional theory underestimates the slope of the bands and the trigonal warping effect. Including electron-electron correlation on the level of the GW approximation, however, yields remarkable improvement in the vicinity of the Fermi level. This demonstrates the breakdown of the independent electron picture in semimetallic graphite and points toward a pronounced role of electron correlation for the interpretation of transport experiments and double-resonant Raman scattering for a wide range of carbon based materials.

  6. Band splitting and Weyl nodes in trigonal tellurium studied by angle-resolved photoemission spectroscopy and density functional theory

    NASA Astrophysics Data System (ADS)

    Nakayama, K.; Kuno, M.; Yamauchi, K.; Souma, S.; Sugawara, K.; Oguchi, T.; Sato, T.; Takahashi, T.

    2017-03-01

    We have performed high-resolution angle-resolved photoemission spectroscopy (ARPES) on trigonal tellurium consisting of helical chains in the crystal. Through the band-structure mapping in the three-dimensional Brillouin zone, we found a definitive evidence for the band splitting originating from the chiral nature of crystal. A direct comparison of the band dispersion between the ARPES results and the first-principles band-structure calculations suggests the presence of Weyl nodes and tiny spin-polarized hole pockets around the H point. The present result opens a pathway toward studying the interplay among crystal symmetry, band structure, and exotic physical properties in chiral crystals.

  7. Initial Development of a sub-micron Angle Resolved Photoemission Microscope

    NASA Astrophysics Data System (ADS)

    Bostwick, Aaron; McChesney, Jessica; Rotenberg, Eli

    2007-03-01

    -abstract- We have begun initial development of a sub-micron angle resolved photoemmision microscope. The current test system consists of an SES-200 detector and a zone plate based focusing system operating at 180eV photon energy. We have measured angle resolved spectra using the SES-200 angle-dispersive collection mode at resolution of ˜500nm. We have used this to show orientational contrast on highly oriented pyrolytic graphite (HOPG). The domains on HOPG are on the order of 1-20 microns and are well orientated along the c-axis but show random azimuthal order. We are able to clearly image these domains even though they show no chemical contrast, and can measure the single crystal band structure on disordered polycrystalline sample. We believe this demonstrates the promise of such a system for the measurement of materials which cannot be found in bulk single crystals.

  8. SAMRAI: A novel variably polarized angle-resolved photoemission beamline in the VUV region at UVSOR-II

    SciTech Connect

    Kimura, Shin-Ichi; Ito, Takahiro; Hosaka, Masahito; Katoh, Masahiro; Sakai, Masahiro; Nakamura, Eiken; Kondo, Naonori; Horigome, Toshio; Hayashi, Kenji; Goto, Tomohiro; Ejima, Takeo; Soda, Kazuo

    2010-05-15

    A novel variably polarized angle-resolved photoemission spectroscopy beamline in the vacuum-ultraviolet (VUV) region has been installed at the UVSOR-II 750 MeV synchrotron light source. The beamline is equipped with a 3 m long APPLE-II type undulator with horizontally/vertically linear and right/left circular polarizations, a 10 m Wadsworth type monochromator covering a photon energy range of 6-43 eV, and a 200 mm radius hemispherical photoelectron analyzer with an electron lens of a {+-}18 deg. acceptance angle. Due to the low emittance of the UVSOR-II storage ring, the light source is regarded as an entrance slit, and the undulator light is directly led to a grating by two plane mirrors in the monochromator while maintaining a balance between high-energy resolution and high photon flux. The energy resolving power (h{nu}/{Delta}h{nu}) and photon flux of the monochromator are typically 1x10{sup 4} and 10{sup 12} photons/s, respectively, with a 100 {mu}m exit slit. The beamline is used for angle-resolved photoemission spectroscopy with an energy resolution of a few meV covering the UV-to-VUV energy range.

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

    SciTech Connect

    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

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

    PubMed

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

    2015-04-16

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

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

    SciTech Connect

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

    1989-08-01

    Recent photoemission studies of Y 123 and Bi 2212 performed with high energy and angular resolution have provided detailed information on the nature of the states near the Fermi level. Measurements of the superconducting gap, band dispersion, and the density of states near the Fermi level in the normal state all support a Fermi liquid description of these materials. 5 refs., 4 figs.

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

    SciTech Connect

    Leem, C.S.

    2010-06-02

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

  13. Angle-Resolved Photoemission Spectroscopy of Tetragonal CuO: Evidence for Intralayer Coupling Between Cupratelike Sublattices

    NASA Astrophysics Data System (ADS)

    Moser, S.; Moreschini, L.; Yang, H.-Y.; Innocenti, D.; Fuchs, F.; Hansen, N. H.; Chang, Y. J.; Kim, K. S.; Walter, A. L.; Bostwick, A.; Rotenberg, E.; Mila, F.; Grioni, M.

    2014-10-01

    We investigate by angle-resolved photoemission the electronic structure of in situ grown tetragonal CuO, a synthetic quasi-two-dimensional edge-sharing cuprate. We show that, in spite of the very different nature of the copper oxide layers, with twice as many Cu in the CuO layers of tetragonal CuO as compared to the CuO2 layers of the high-Tc cuprates, the low-energy electronic excitations are surprisingly similar, with a Zhang-Rice singlet dispersing on weakly coupled cupratelike sublattices. This system should thus be considered as a member of the high-Tc cuprate family, with, however, interesting differences due to the intralayer coupling between the cupratelike sublattices.

  14. Substrate interactions with suspended and supported monolayer MoS2: Angle-resolved photoemission spectroscopy

    SciTech Connect

    Jin, Wencan; Yeh, Po -Chun; Zaki, Nader; Zhang, Datong; Liou, Jonathan T.; Dadap, Jerry I.; Barinov, Alexey; Yablonskikh, Mikhail; Sadowski, Jerzy T.; Sutter, Peter; Herman, Irving P.; Osgood, Jr., Richard M.

    2015-03-17

    We report the directly measured electronic structure of exfoliated monolayer molybdenum disulfide (MoS₂) using micrometer-scale angle-resolved photoemission spectroscopy. Measurements of both suspended and supported monolayer MoS₂ elucidate the effects of interaction with a substrate. Thus, a suggested relaxation of the in-plane lattice constant is found for both suspended and supported monolayer MoS₂ crystals. For suspended MoS₂, a careful investigation of the measured uppermost valence band gives an effective mass at Γ¯ and Κ¯ of 2.00m₀ and 0.43m₀, respectively. We also measure an increase in the band linewidth from the midpoint of Γ¯Κ¯ to the vicinity of Κ¯ and briefly discuss its possible origin.

  15. Bulk and surface electronic structure of hexagonal structured PtBi2 studied by angle-resolved photoemission spectroscopy

    NASA Astrophysics Data System (ADS)

    Yao, Q.; Du, Y. P.; Yang, X. J.; Zheng, Y.; Xu, D. F.; Niu, X. H.; Shen, X. P.; Yang, H. F.; Dudin, P.; Kim, T. K.; Hoesch, M.; Vobornik, I.; Xu, Z.-A.; Wan, X. G.; Feng, D. L.; Shen, D. W.

    2016-12-01

    PtBi2 with a layered hexagonal crystal structure was recently reported to exhibit an unconventional large linear magnetoresistance, while the mechanism involved is still elusive. Using high-resolution angle-resolved photoemission spectroscopy, we present a systematic study on its bulk and surface electronic structure. Through careful comparison with first-principle calculations, our experiment distinguishes the low-lying bulk bands from entangled surface states, allowing the estimation of the real composition of samples. We find significant electron doping in PtBi2, implying a substantial Bi-deficiency-induced disorder therein. Intriguingly, we discover a Dirac-cone-like surface state on the boundary of the Brillouin zone, which is identified as an accidental Dirac band without topological protection. Our findings exclude linear band dispersion in the quantum limit as the cause of the unconventional large linear magnetoresistance but give support to the classical disorder model from the perspective of the electronic structure.

  16. Evolution of electronic structure of few-layer phosphorene from angle-resolved photoemission spectroscopy of black phosphorous

    NASA Astrophysics Data System (ADS)

    Ehlen, N.; Senkovskiy, B. V.; Fedorov, A. V.; Perucchi, A.; Di Pietro, P.; Sanna, A.; Profeta, G.; Petaccia, L.; Grüneis, A.

    2016-12-01

    A complete set of tight-binding parameters for the description of the quasiparticle dispersion relations of black phosphorous (BP) and N -layer phosphorene with N =1 ...∞ is presented. The parameters, which describe valence and conduction bands, are fit to angle-resolved photoemission spectroscopy (ARPES) data of pristine and lithium doped BP. We show that zone-folding of the experimental three-dimensional electronic band structure of BP is a simple and intuitive method to obtain the layer-dependent two-dimensional electronic structure of few-layer phosphorene. Zone folding yields the band gap of N -layer phosphorene in excellent quantitative agreement to experiments and ab initio calculations. A combined analysis of optical absorption and ARPES spectra of pristine and doped BP is used to estimate a value for the exciton binding energy of BP.

  17. Electronic structure of the iron chalcogenide KFeAgTe2 revealed by angle-resolved photoemission spectroscopy

    NASA Astrophysics Data System (ADS)

    Ang, R.; Nakayama, K.; Yin, W.-G.; Sato, T.; Lei, Hechang; Petrovic, C.; Takahashi, T.

    2013-10-01

    We have performed angle-resolved photoemission spectroscopy (ARPES) of KFeAgTe2, and revealed the absence of band crossing at the Fermi level (EF) indicative of the unconventional insulating nature of this material. Comparison of the ARPES-derived band dispersions with the first-principles calculations based on local density approximation and the inclusion of electron correlation U demonstrated that the ground state of KFeAgTe2 is not a simple band insulator. And also, our fitting result on the ARPES experimental density of states near EF plausibly excludes the possibility of Anderson insulator. We suggest that KFeAgTe2 is most likely a Mott insulator or a Hund insulator, providing a deep insight into the insulating ground state.

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

    NASA Astrophysics Data System (ADS)

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

    2011-03-01

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

  19. Interlayer-state-driven superconductivity in CaC6 studied by angle-resolved photoemission spectroscopy

    NASA Astrophysics Data System (ADS)

    Kyung, Wonshik; Kim, Yeongkwan; Han, Garam; Leem, Choonshik; Kim, Chul; Koh, Yoonyoung; Kim, Beomyoung; Kim, Youngwook; Kim, Jun Sung; Kim, Keun Su; Rotenberg, Eli; Denlinger, Jonathan D.; Kim, Changyoung

    2015-12-01

    We performed angle-resolved photoemission experiments on CaC6 and measured kz-dependent electronic structures to investigate the interlayer states. The results reveal a spherical interlayer Fermi surface centered at the Γ point. We also find that the graphene-driven band possesses a weak kz dispersion. The overall electronic structure shows a peculiar single-graphene-layer periodicity in the kz direction although the CaC6 unit cell is supposed to contain three graphene layers. This suggests that the c -axis ordering of Ca has little effect on the electronic structure of CaC6. In addition to CaC6, we also studied the a low-temperature superconductor BaC6. For BaC6, the graphene-band Dirac-point energy is smaller than that of CaC6. Based on data from CaC6 and BaC6, we rule out the Cx y phonon mode as the origin of the superconductivity in CaC6, which strongly suggests interlayer-state-driven superconductivity.

  20. Non-equilibrium Dirac carrier dynamics in graphene investigated with time- and angle-resolved photoemission spectroscopy.

    PubMed

    Gierz, Isabella; Link, Stefan; Starke, Ulrich; Cavalleri, Andrea

    2014-01-01

    We have used time- and angle-resolved photoemission spectroscopy (tr-ARPES) to assess the influence of many-body interactions on the Dirac carrier dynamics in graphene. From the energy-dependence of the measured scattering rates we directly determine the imaginary part of the self-energy, visualizing the existence of a relaxation bottleneck associated with electron-phonon coupling. A comparison with static line widths obtained by high-resolution ARPES indicates that the dynamics of photo-excited carriers in graphene are solely determined by the equilibrium self-energy. Furthermore, the subtle interplay of different many-body interactions in graphene may allow for carrier multiplication, where the absorption of a single photon generates more than one electron-hole pair via impact ionization. We find that, after photo-excitation, the number of carriers in the conduction band along the ΓK-direction keeps increasing for about 40 fs after the pump pulse is gone. A definite proof of carrier multiplication in graphene, however, requires a more systematic study, carefully taking into account the contribution of momentum relaxation on the measured rise time.

  1. Predicted electronic markers for polytypes of LaOBi S2 examined via angle-resolved photoemission spectroscopy

    NASA Astrophysics Data System (ADS)

    Zhou, Xiaoqing; Liu, Qihang; Waugh, J. A.; Li, Haoxiang; Nummy, T.; Zhang, Xiuwen; Zhu, Xiangde; Cao, Gang; Zunger, Alex; Dessau, D. S.

    2017-02-01

    The natural periodic stacking of symmetry-inequivalent planes in layered compounds can lead to the formation of natural superlattices; albeit close in total energy, (thus in their thermodynamic stability), such polytype superlattices can exhibit different structural symmetries, thus have markedly different electronic properties which can in turn be used as "structural markers". We illustrate this general principle on the layered LaOBi S2 compound where density-functional theory (DFT) calculations on the (Bi S2 )/(LaO)/(Bi S2 ) polytype superlattices reveal both qualitatively and quantitatively distinct electronic structure markers associated with the Rashba physics, yet the total energies are only ˜ 0.1 meV apart. This opens the exciting possibility of identifying subtle structural features via electronic markers. We show that the pattern of removal of band degeneracies in different polytypes by the different forms of symmetry breaking leads to Rashba "minigaps" with characteristic Rashba parameters that can be determined from spectroscopy, thereby narrowing down the physically possible polytypes. By identifying these distinct DFT-predicted fingerprints via angle-resolved photoemission spectroscopy (ARPES) measurements on LaBiO S2 we found the dominant polytype with small amounts of mixtures of other polytypes. This conclusion, consistent with neutron scattering results, establishes ARPES detection of theoretically established electronic markers as a powerful tool to delineate energetically quasidegenerate polytypes.

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

    NASA Astrophysics Data System (ADS)

    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

    2014-03-01

    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. This work was supported by the National Research Foundation (NRF) of Korea Grant funded by the Korean Government (MEST) (Nos. 2010-0010771 and 2012M2B2A4029607). K.K. and B.I.M. acknowledge the support of NRF (Nos. 2009-0079947 and 2011-0025237) and KISTI.

  3. Measuring the electronic structure of atomically uniform silver films grown on silicon using angle-resolved photoemission spectroscopy

    NASA Astrophysics Data System (ADS)

    Speer, Nathan James

    Electronic structures derived from Valence electrons in thin films and at surfaces are often much different from those of their bulk counter parts. When the film thickness is less than the electron-coherence length, the boundary conditions at the surface and interface can give rise to standing-wave-like quantum-well states. Electrons in these states are often described as particles in a box. Confinement in the perpendicular direction gives rise to a quantized band structure along the same direction, where the energy spacing is determined by the film thickness. Changing the film by a single atomic layer can cause properties derived from the band structure to vary like ˜ 1/N , where N is the number of monolayers. Recent advances in thin film techniques have made it possible to fabricate films with atomically uniform thickness. Because the electronic structure is a function of film thickness, such techniques are crucial to efforts for a comprehensive understanding of thin films. In this thesis, the electronic properties of atomically uniform Ag films grown on Si(111) substrates are studied using angle-resolved photoemission spectroscopy (ARPES). Using molecular beam epitaxy (MBE) deposition at low temperatures, we are able to fabricate atomically uniform, ultra-thin Ag films on Si substrates for the first time, and the electronic structures are measured using ARPES. The electrons in these uniform film systems have very long coherence lengths and occupy standing-wave-like quantum-well states that propagate through the film and, surprisingly, can reach deep into the substrate despite a lattice mismatched, incommensurate interface. This interaction with the substrate is so strong that it can produce an electronic interference pattern in the photoemission spectra. As the film thickness increases, the electronic structure evolves to form the bulk band continuum plus separates surfaces states. A careful analysis of this evolution allows us to separate surface from bulk

  4. Ultrafast scattering processes of hot electrons in InSb studied by time- and angle-resolved photoemission spectroscopy

    NASA Astrophysics Data System (ADS)

    Tanimura, H.; Kanasaki, J.; Tanimura, K.

    2015-01-01

    Ultrafast scattering processes of hot electrons photoinjected into the conduction band of InSb have been studied using time- and angle-resolved photoemission spectroscopy. The nascent distributions of hot-electron packets are captured directly in energy and momentum spaces, and their ultrafast scattering processes are traced at femtosecond temporal resolution on a state-resolved basis. Hot electrons injected in the Γ valley with excess energies above the minimum of the L valley show ultrafast intervalley scattering, with transition times of the order of 40 fs. The relaxation processes in the L valley are resolved in energy and momentum spaces, including their backscattering into the Γ valley during relaxation. In contrast, relaxation of hot electrons with excess energy below the minimum of the L valley is governed by the direct impact ionization (IMP). We reveal state-selective features of the IMP process, and we have determined the direct IMP rate to be 7 ×1012s-1 for hot electrons with excess energy in the range of 0.35 to 0.6 eV. The direct IMP process results in a rapid increase, within 300 fs after excitation, of the electron density at the conduction band minimum (CBM), and phonon-assisted IMP by hot electrons scattered in the L valley and those backscattered into the Γ valley persistently enhances the electron density up to 8 ps after excitation. By analyzing correlations between the IMP rates of hot electrons and the electron densities near the CBM, an important role of a transient Auger recombination is proposed to quantify the yield of low-energy electrons generated in the IMP process.

  5. Angle-resolved photoemission spectroscopy studies of the Mott insulator to superconductor evolution in calcium-sodium-copper-chloride

    NASA Astrophysics Data System (ADS)

    Shen, Kyle Michael

    The parent compounds of the high-temperature cuprate superconductors are antiferromagnetic Mott insulators. To explain the microscopic mechanism behind high-temperature superconductivity, it is first necessary to understand how the electronic states evolve from the parent Mott insulator into the superconducting compounds. This dissertation presents angle-resolved photoemission spectroscopy (ARPES) studies of one particular family of the cuprate superconductors, Ca 2-xNaxCuO 2Cl2, to investigate how the single-electron excitations develop throughout momentum space as the system is hole doped from the Mott insulator into a superconductor with a transition temperature of 22 K. These measurements indicate that, due to very strong electron-boson interactions, the quasiparticle residue, Z, approaches zero in the parent Mott insulator due to the formation of small lattice polarons. As a result, many fundamental quantities such as the chemical potential, quasiparticle excitations, and the Fermi surface evolve in manners wholly unexpected from conventional weakly-interacting theories. In addition, highly anisotropic interactions have been observed in momentum space where quasiparticle-like excitations persist to low doping levels along the nodal direction of the d-wave super-conducting gap, in contrast to the unusual excitations near the d-wave antinode. This anisotropy may reflect the propensity of the lightly doped cuprates towards forming a competing, charge-ordered state. These results provide a novel and logically consistent explanation of the hole doping evolution of the lineshape, spectral weight, chemical potential, quasiparticle dispersion, and Fermi surface as Ca2- xNaxCuO2Cl2 evolves from the parent Mott insulator into a high-temperature superconductor.

  6. VUV photodynamics of free tholins nanoparticles investigated by imaging Angle-Resolved Photoemission with the Synchrotron Radiation

    NASA Astrophysics Data System (ADS)

    Tigrine, Sarah; Nahon, Laurent; Carrasco, Nathalie; Garcia-Macias, Gustavo

    2016-06-01

    Thanks to the Cassini Huygens mission, it is now established that the aerosols appear from an altitude of 1,000 km in Titan's atmosphere. Once they are formed and through their descent towards the surface, those grains will still interact with persistent UV/VUV radiations, at different energies, that can reach lower atmospheric layers. This interaction has some impact, for example on the radiative transfer or on the ionization yield of the atmospheric compounds. Models are a good way to study those processes, but the lack of data on the refractive index or the absolute absorption/ionization cross subsections of the aerosols can be an obstacle. In order to shed some light and quantify those processes, we ionize analogs of aerosols produced with the PAMPRE experiment (LATMOS) on the SAPHIRS platform from the DESIRS VUV beamline at the synchrotron SOLEIL, equipped with an aerodynamic lens. The aerosols are injected directly under vacuum as isolated free nanoparticles and do not need to take the form of a film deposited on a substrate. The generated photoelectrons are then collected with a Velocity Map Imaging detector and their energetic and angular signatures are analyzed using the ARPES method (Angle-Resolved PhotoElectron Spectroscopy). Both the nanoparticles size distribution and the incident wavelength determine the parameters governing the photoemission process (intra-particles electron mean free path, photon penetration depth) as revealed by the angular distribution of the photoelectron showing in same cases a marked forward/backward asymmetry with respect to the photon axis. Those parameters may provide us with information on the optical behavior of the aerosols. In addition we can extract the ionization potential in direct connection with the absorption cross subsections of the aerosol, from which altitude dependent photodynamics can be unraveled. We will present here the experiments performed, at different VUV energies, on Titan's aerosol analogs with the

  7. Angle-resolved photoemission spectra, electronic structure and spin dependent scattering in Ni_1-xFex permalloys

    NASA Astrophysics Data System (ADS)

    Sahrakorpi, S.; Mijnarends, P. E.; Lindroos, M.; Bansil, A.

    2002-03-01

    We present the all electron charge and spin self-consistent electronic structure of Ni_1-xFex permalloys for a range of Fe concentrations, using the first principles Korringa-Kohn-Rostoker coherent potential approximation (KKR-CPA) scheme to treat disorder and the local spin density (LSD) approximation to incorporate exchange-correlation effects. Recent high resolution angle-resolved photoemission spectroscopy (ARPES) experiments on Ni_0.90Fe_0.10 and Ni_0.80Fe_0.20 permalloys are analyzed in terms of the spectral density function, A_B( k_allel, k_⊥= 0,E_F), computed from the KKR-CPA Green function for k_allel values varying along the Γ-K direction in the Brillouin zone (BZ). The widths of the majority as well as the minority spin peaks in the theoretical spectra are in excellent accord with the corresponding ARPES results in all cases, suggesting that spin-dependent disorder scattering constitutes the main scattering mechanism for the carriers in the permalloys. Majority spin states of Ni are virtually undamped by the Fe impurities, while the minority spins at the Fermi energy (E_F) are heavily damped. The nature of the Ni and Fe potentials in the permalloys is explored in detail. The effective disorder parameter in the alloy is found to be strongly dependent on the energy, momentum, spin and symmetry of the specific states involved. The evolution of the electronic states on the Ni and Fe sites as a function of Fe concentration is discussed. The magnetic moments on Ni as well as on Fe are found to remain essentially unchanged with increasing Fe content.

  8. Surface structure determination of Au(1 ML)/Fe(15 ML)/Au(100) using angle-resolved photoemission extended fine structure

    NASA Astrophysics Data System (ADS)

    Kellar, S. A.; Chen, Y.; Huff, W. R. A.; Moler, E. J.; Hussain, Z.; Shirley, D. A.

    1998-01-01

    We have determined the atomic surface structure of a thin film of Fe (15 ML) grown on the Au(100) surface, Au(1 ML)/Fe(15 ML)/Au(100), with angle-resolved photoemission extended fine structure (ARPEFS) using the Au 4f7/2 core level. We have confirmed that a bcc crystalline Fe film grows epitaxially on the Au(100) substrate with 1 ML of Au atoms remaining on the surface using angle-resolved photoemission spectroscopy. We analyzed the ARPEFS oscillations using an electron-scattering code based on the Rehr-Albers scattering matrix formalism. Our analysis finds that the surface Au atoms are positioned in the fourfold hollow sites 1.67+/-0.02 Å above the Fe surface. We also find that the grown Fe layers are very like bulk bcc Fe, with an interlayer spacing of 1.43+/-0.03 Å.

  9. Angle-resolved photoemission with circularly polarized light in the nodal mirror plane of underdoped Bi2Sr2CaCu2O8+δ superconductor

    DOE PAGES

    He, Junfeng; Mion, Thomas R.; Gao, Shang; ...

    2016-10-31

    Unraveling the nature of pseudogap phase in high-temperature superconductors holds the key to understanding their superconducting mechanisms and potentially broadening their applications via enhancement of their superconducting transition temperatures. Angle-resolved photoemission spectroscopy (ARPES) experiments using circularly polarized light have been proposed to detect possible symmetry breaking state in the pseudogap phase of cuprates. Here, the presence (absence) of an electronic order which breaks mirror symmetry of the crystal would in principle induce a finite (zero) circular dichroism in photoemission. Different orders breaking reflection symmetries about different mirror planes can also be distinguished by the momentum dependence of the measured circularmore » dichroism.« less

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

    NASA Astrophysics Data System (ADS)

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

    2016-06-01

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

  11. Angle-resolved photoemission spectroscopy of strontium lanthanum copper oxide thin films grown by molecular-beam epitaxy

    NASA Astrophysics Data System (ADS)

    Harter, John Wallace

    Among the multitude of known cuprate material families and associated structures, the archetype is "infinite-layer" ACuO2, where perfectly square and flat CuO2 planes are separated by layers of alkaline earth atoms. The infinite-layer structure is free of magnetic rare earth ions, oxygen chains, orthorhombic distortions, incommensurate superstructures, ordered vacancies, and other complications that abound among the other material families. Furthermore, it is the only cuprate that can be made superconducting by both electron and hole doping, making it a potential platform for decoding the complex many-body interactions responsible for high-temperature superconductivity. Research on the infinite-layer compound has been severely hindered by the inability to synthesize bulk single crystals, but recent progress has led to high-quality superconducting thin film samples. Here we report in situ angle-resolved photoemission spectroscopy measurements of epitaxially-stabilized Sr1-chiLa chiCuO2 thin films grown by molecular-beam epitaxy. At low doping, the material exhibits a dispersive lower Hubbard band typical of other cuprate parent compounds. As carriers are added to the system, a continuous evolution from Mott insulator to superconducting metal is observed as a coherent low-energy band develops on top of a concomitant remnant lower Hubbard band, gradually filling in the Mott gap. For chi = 0.10, our results reveal a strong coupling between electrons and (pi,pi) anti-ferromagnetism, inducing a Fermi surface reconstruction that pushes the nodal states below the Fermi level and realizing nodeless superconductivity. Electron diffraction measurements indicate the presence of a surface reconstruction that is consistent with the polar nature of Sr1-chiLachiCuO2. Most knowledge about the electron-doped side of the cuprate phase diagram has been deduced by generalizing from a single material family, Re2-chi CechiCuO4, where robust antiferromagnetism has been observed past chi

  12. Calculation of angle-resolved photoemission and tunneling for a CuO[sub 2] layer in the normal and superconducting states

    SciTech Connect

    Dickinson, P.H.; Doniach, S. )

    1993-05-01

    We represent the normal-state electronic structure of a CuO[sub 2] layer in terms of a three-band model having an infinite Cu intrasite Coulomb repulsion. We express the Lagrangian for this model using a slave-boson formalism and approximate it in a large-[ital N] expansion to order 1/[ital N] in the zero-temperature limit. The angle-resolved spectral weight determined from the resulting Green's functions suggests that within this picture higher-order corrections in 1/[ital N] are necessary for good agreement with the corresponding angle-resolved photoemission data. We phenomenologically add spin-dependent Heisenberg interactions between neighboring Cu sites and neighboring Cu and O sites. These interactions form the basis of a nonretarded calculation of the superconducting state. For the case of an interaction between neighboring Cu spins only, the lowest-energy solution possesses [ital d]([ital x][sup 2][minus][ital y][sup 2]) symmetry. The use of a three-band model leads to the possibility of the addition of the interaction between Cu and O spins. The resulting [ital d]+[ital idp] superconducting state involves pairing of carriers in Cu orbitals both with themselves and with holes on the O orbitals. This additional pairing will remove the node in the [ital d]-wave state at [ital T]=0 by an amount that depends on the Cu-O coupling parameter; however, the mixed-symmetry state occurs only for a narrow range of coupling parameters. The angle-resolved photoemission and tunneling results are calculated and compared to experimental findings.

  13. Electronic and geometric structure of thin CoO(100) films studied by angle-resolved photoemission spectroscopy and Auger electron diffraction

    NASA Astrophysics Data System (ADS)

    Heiler, M.; Chassé, A.; Schindler, K.-M.; Hollering, M.; Neddermeyer, H.

    2000-05-01

    We have prepared ordered thin films of CoO by evaporating cobalt in an O 2 atmosphere on to a heated (500 K) Ag(100) substrate. The geometric and electronic structure of the films was characterized by means of Auger electron diffraction (AED) and angle-resolved photoemission spectroscopy (ARUPS), respectively. The experimental AED results were compared with simulated data, which showed that the film grows in (100) orientation on the Ag(100) substrate. Synchrotron-radiation-induced photoemission investigations were performed in the photon energy range from 25 eV to 67 eV. The dispersion of the transitions was found to be similar to that of previous results on a single-crystal CoO(100) surface. The resonance behaviour of the photoemission lines in the valence-band region was investigated by constant-initial-state (CIS) spectroscopy. The implications of this behaviour for assignment of the photoemission lines to specific electronic transitions is discussed and compared with published theoretical models of the electronic structure.

  14. Evidence for phonon-like charge and spin fluctuations from an analysis of angle-resolved photoemission spectra of La2-xSrxCuO4 superconductors

    NASA Astrophysics Data System (ADS)

    Mazza, G.; Grilli, M.; Di Castro, C.; Caprara, S.

    2013-01-01

    In high temperature superconductors we provide evidence of spin and mixed phonon-charge collective modes as mediators of the effective electron-electron interaction and suggestive of a charge and spin density wave instability competing with superconductivity. Indeed, we show that the so-called kinks and waterfalls observed in angle-resolved photoemission spectra of La2-xSrxCuO4, a prototypical high-Tc superconducting cuprate, are due to the coupling of quasiparticles with two distinct nearly critical collective modes with finite characteristic wave vectors, typical of charge and spin fluctuations. The simultaneous presence of these two modes reconciles the long standing dichotomy whether kinks are due to phonons or spin waves.

  15. Fermi Surface and Quasiparticle Dynamics of Na0.7CoO2 Investigated by Angle-Resolved Photoemission Spectroscopy

    NASA Astrophysics Data System (ADS)

    Hasan, M. Z.; Chuang, Y.-D.; Qian, D.; Li, Y. W.; Kong, Y.; Kuprin, A.; Fedorov, A. V.; Kimmerling, R.; Rotenberg, E.; Rossnagel, K.; Hussain, Z.; Koh, H.; Rogado, N. S.; Foo, M. L.; Cava, R. J.

    2004-06-01

    We present the first angle-resolved photoemission study of Na0.7CoO2, the host material of the superconducting NaxCoO2·nH2O series. Our results show a hole-type Fermi surface, a strongly renormalized quasiparticle band, a small Fermi velocity, and a large Hubbard U. The quasiparticle band crosses the Fermi level from M toward Γ suggesting a negative sign of effective single-particle hopping teff (about 10meV) which is on the order of magnetic exchange coupling J in this system. Quasiparticles are well defined only in the T-linear resistivity (non-Fermi-liquid) regime. Unusually small single-particle hopping and unconventional quasiparticle dynamics may have implications for understanding the phase of matter realized in this new class of a strongly interacting quantum system.

  16. Temperature-Induced Electronic Structure Evolution of ZrTe5 Revealed by High resolution & Laser Angle-Resolved Photoemission Spectroscopy (ARPES)

    NASA Astrophysics Data System (ADS)

    Zhang, Yan; Wang, Chenlu; Liu, Guodong; Chen, Genfu; Yu, Li; He, Shaolong; Zhao, Lin; Chen, Chuangtian; Xu, Zuyan; Zhou, Xingjiang

    The transition metal pentatellurides ZrTe5 have attracted consideration attention since the 70s, due to the unusual transport properties like resistivity peak at ~140K and the sign change of the Hall coefficient and thermopower. The origin of the most peculiar resistivity peak remains controversial. In this talk we will present high resolution angle-resolved photoemission (ARPES) study on the Fermi surface and band structure of ZrTe5, by using our high resolution ARPES system equipped with the VUV laser and the time-of-flight (TOF) electron energy analyzer. Upon cooling down, we found a gradual transition from hole-like band into electron-like band around the Brillouin zone center. Such an electron state transition forms the underlying physics for the abnormal transport properties. We will also comment on the possibility of a Dirac semimetal in ZrTe5.

  17. Intermolecular energy-band dispersion in oriented thin films of bis(1,2,5-thiadiazolo)-p-quinobis(1,3-dithiole) by angle-resolved photoemission

    NASA Astrophysics Data System (ADS)

    Hasegawa, Shinji; Mori, Takehiko; Imaeda, Kenichi; Tanaka, Shoji; Yamashita, Yoshiro; Inokuchi, Hiroo; Fujimoto, Hitoshi; Seki, Kazuhiko; Ueno, Nobuo

    1994-05-01

    Angle-resolved ultraviolet photoemission spectra using synchrotron radiation were measured for oriented thin films of bis(1,2,5-thiadiazolo)-p-quinobis(1,3-dithiole) (BTQBT) on graphite. From the photon energy dependence of normal emission spectra, the energy-band dispersion of π-bands were observed for the highest (HOMO) and next highest (NHOMO) bands. This is the first observation of intermolecular dispersion in a single-component organic molecular crystal. The results demonstrate that the BTQBT molecules have a strong intermolecular interaction, which can be derived from the introduction of a covalent interaction between sulfur atoms in addition to the usual intermolecular interaction by van der Waals forces.

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

    SciTech Connect

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

    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. Bulk Electronic Structure of Superconducting LaRu2P2 Single Crystals Measured by Soft-X-Ray Angle-Resolved Photoemission Spectroscopy

    NASA Astrophysics Data System (ADS)

    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.

    2012-06-01

    We present a soft x-ray angle-resolved photoemission spectroscopy (SX-ARPES) study of the stoichiometric pnictide superconductor LaRu2P2. 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 LaRu2P2 even though the mass enhancement is similar in both systems. Our results suggest that the superconductivity in LaRu2P2 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.

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

    NASA Astrophysics Data System (ADS)

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

    2009-09-01

    We use microprobe angle-resolved photoemission spectroscopy to study the Fermi surface and band dispersion of the CuO2 planes in the high-temperature superconductor, YBa2Cu4O8 . We find a strong in-plane asymmetry of the electronic structure between directions along a and b axes. The saddle point of the antibonding band lies at a significantly higher energy in the a direction (π,0) than the b direction (0,π) , whereas the bonding band displays the opposite behavior. We demonstrate that the abnormal band shape is due to a strong asymmetry of the bilayer band splitting, likely caused by a nontrivial hybridization between the planes and chains. This asymmetry has an important implication for interpreting key properties of the Y-Ba-Cu-O family, especially the superconducting gap, transport, and results of inelastic neutron scattering.

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

    SciTech Connect

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2013-10-01

    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 which the SW profile is scanned through the depth of the sample. We have studied the buried interface in a prototypical magnetic tunnel junction La0.7Sr0.3MnO3/SrTiO3. Depth-and momentum-resolved maps of Mn 3d eg and t2g states from the central, bulk-like and interface-like regions of La0.7Sr0.3MnO3 exhibit distinctly different behavior consistent with a change in the Mn bonding at the interface. We compare the experimental results to state-of-the-art density-functional and one-step photoemission theory, with encouraging agreement that suggests wide future applications of this technique.

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

    PubMed

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

    2016-09-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-09-01

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

  5. Strong anisotropy of Dirac cones in SrMnBi2 and CaMnBi2 revealed by angle-resolved photoemission spectroscopy.

    PubMed

    Feng, Ya; Wang, Zhijun; Chen, Chaoyu; Shi, Youguo; Xie, Zhuojin; Yi, Hemian; Liang, Aiji; He, Shaolong; He, Junfeng; Peng, Yingying; Liu, Xu; Liu, Yan; Zhao, Lin; Liu, Guodong; Dong, Xiaoli; Zhang, Jun; Chen, Chuangtian; Xu, Zuyan; Dai, Xi; Fang, Zhong; Zhou, X J

    2014-06-20

    The Dirac materials, such as graphene and three-dimensional topological insulators, have attracted much attention because they exhibit novel quantum phenomena with their low energy electrons governed by the relativistic Dirac equations. One particular interest is to generate Dirac cone anisotropy so that the electrons can propagate differently from one direction to the other, creating an additional tunability for new properties and applications. While various theoretical approaches have been proposed to make the isotropic Dirac cones of graphene into anisotropic ones, it has not yet been met with success. There are also some theoretical predictions and/or experimental indications of anisotropic Dirac cone in novel topological insulators and AMnBi2 (A = Sr and Ca) but more experimental investigations are needed. Here we report systematic high resolution angle-resolved photoemission measurements that have provided direct evidence on the existence of strongly anisotropic Dirac cones in SrMnBi2 and CaMnBi2. Distinct behaviors of the Dirac cones between SrMnBi2 and CaMnBi2 are also observed. These results have provided important information on the strong anisotropy of the Dirac cones in AMnBi2 system that can be governed by the spin-orbital coupling and the local environment surrounding the Bi square net.

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

    SciTech Connect

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

    2013-09-15

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

  7. Universal High Energy Anomaly in the Angle-Resolved Photoemission Spectra of High Temperature Superconductors: Possible Evidence of Spinon and Holon Branches

    NASA Astrophysics Data System (ADS)

    Graf, J.; Gweon, G.-H.; McElroy, K.; Zhou, S. Y.; Jozwiak, C.; Rotenberg, E.; Bill, A.; Sasagawa, T.; Eisaki, H.; Uchida, S.; Takagi, H.; Lee, D.-H.; Lanzara, A.

    2007-02-01

    A universal high energy anomaly in the single particle spectral function is reported in three different families of high temperature superconductors by using angle-resolved photoemission spectroscopy. As we follow the dispersing peak of the spectral function from the Fermi energy to the valence band complex, we find dispersion anomalies marked by two distinctive high energy scales, E1≈0.38eV and E2≈0.8eV. E1 marks the energy above which the dispersion splits into two branches. One is a continuation of the near parabolic dispersion, albeit with reduced spectral weight, and reaches the bottom of the band at the Γ point at ≈0.5eV. The other is given by a peak in the momentum space, nearly independent of energy between E1 and E2. Above E2, a bandlike dispersion reemerges. We conjecture that these two energies mark the disintegration of the low-energy quasiparticles into a spinon and holon branch in the high Tc cuprates.

  8. Origin of robust nanoscale ferromagnetism in Fe-doped Ge revealed by angle-resolved photoemission spectroscopy and first-principles calculation

    NASA Astrophysics Data System (ADS)

    Sakamoto, S.; Wakabayashi, Y. K.; Takeda, Y.; Fujimori, S.-i.; Suzuki, H.; Ban, Y.; Yamagami, H.; Tanaka, M.; Ohya, S.; Fujimori, A.

    2017-02-01

    Ge1 -xFex (Ge:Fe) shows ferromagnetic behavior up to a relatively high temperature of 210 K and hence is a promising material for spintronic applications compatible with Si technology. Unlike the prototypical system (Ga,Mn)As where itinerant holes induce long-range ferromagnetic order of the Mn spins, however, its ferromagnetism evolves from robust nanoscale ferromagnetic domains formed in Fe-rich regions. We have studied its underlying electronic structure by soft x-ray angle-resolved photoemission spectroscopy measurements and first-principles supercell calculation. We observed finite Fe 3 d components in the states at the Fermi level (EF) in a wide region of momentum space, and the EF was located ˜0.35 eV above the valence-band maximum of the host Ge. Our calculation indicates that the EF is also within the deep acceptor-level impurity band induced by the strong p -d (t2) hybridization. We conclude that the additional minority-spin d (e ) electron characteristic of the Fe2 + state is responsible for the short-range ferromagnetic coupling between Fe atoms, making the magnetism markedly different from that of (Ga,Mn)As.

  9. High-Energy Anomaly in the Angle-Resolved Photoemission Spectra of Nd2-xCexCuO4: Evidence for a Matrix Element Effect

    NASA Astrophysics Data System (ADS)

    Rienks, E. D. L.; ńrrälä, M.; Lindroos, M.; Roth, F.; Tabis, W.; Yu, G.; Greven, M.; Fink, J.

    2014-09-01

    We use polarization-dependent angle-resolved photoemission spectroscopy (ARPES) to study the high-energy anomaly (HEA) in the dispersion of Nd2-xCexCuO4, x =0.123. We find that at particular photon energies the anomalous, waterfall-like dispersion gives way to a broad, continuous band. This suggests that the HEA is a matrix element effect: it arises due to a suppression of the intensity of the broadened quasiparticle band in a narrow momentum range. We confirm this interpretation experimentally, by showing that the HEA appears when the matrix element is suppressed deliberately by changing the light polarization. Calculations of the matrix element using atomic wave functions and simulation of the ARPES intensity with one-step model calculations provide further evidence for this scenario. The possibility to detect the full quasiparticle dispersion further allows us to extract the high-energy self-energy function near the center and at the edge of the Brillouin zone.

  10. High-energy anomaly in Nd2-xCexCuO4 investigated by angle-resolved photoemission spectroscopy and quantum Monte Carlo simulations

    NASA Astrophysics Data System (ADS)

    Schmitt, F.; Moritz, B.; Johnston, S.; Mo, S.-K.; Hashimoto, M.; Moore, R. G.; Lu, D.-H.; Motoyama, E.; Greven, M.; Devereaux, T. P.; Shen, Z.-X.

    2011-05-01

    Recent high-binding-energy angle-resolved photoemission spectroscopy (ARPES) experiments reveal a change in band dispersion in the high-temperature superconducting cuprates (HTSCs) known as the high-energy anomaly (HEA). Despite considerable experimental and theoretical attention, the origin of the HEA remains a topic of some controversy. In this paper we present systematic and comprehensive experimental evidence on the origin of the HEA from ARPES measurements on the electron-doped HTSC material Nd2-xCexCuO4 at a number of dopings across the phase diagram and over the entire Brillouin zone (BZ). Comparing these new experimental findings to quantum Monte Carlo simulations of the single-band Hubbard model across the BZ and for various dopings demonstrates that this simple model qualitatively reproduces the key experimental features of the HEA and points to significant self-energy and band renormalization effects accompanying strong electron correlations as its origin rather than coupling to any one emergent bosonic mode, e.g., antiferromagnetic spin fluctuations. We conclude from comparison to this simple model that the HEA in these systems should be regarded as a crossover from a coherent quasiparticle band at low binding energies, emergent from the upper Hubbard band in electron-doped HTSCs due to doping and modified by subsequent strong band renormalization effects, to oxygen valence bands at higher binding energy that would be revealed in simulations explicitly incorporating these important orbital degrees of freedom.

  11. Strong Anisotropy of Dirac Cones in SrMnBi2 and CaMnBi2 Revealed by Angle-Resolved Photoemission Spectroscopy

    PubMed Central

    Feng, Ya; Wang, Zhijun; Chen, Chaoyu; Shi, Youguo; Xie, Zhuojin; Yi, Hemian; Liang, Aiji; He, Shaolong; He, Junfeng; Peng, Yingying; Liu, Xu; Liu, Yan; Zhao, Lin; Liu, Guodong; Dong, Xiaoli; Zhang, Jun; Chen, Chuangtian; Xu, Zuyan; Dai, Xi; Fang, Zhong; Zhou, X. J.

    2014-01-01

    The Dirac materials, such as graphene and three-dimensional topological insulators, have attracted much attention because they exhibit novel quantum phenomena with their low energy electrons governed by the relativistic Dirac equations. One particular interest is to generate Dirac cone anisotropy so that the electrons can propagate differently from one direction to the other, creating an additional tunability for new properties and applications. While various theoretical approaches have been proposed to make the isotropic Dirac cones of graphene into anisotropic ones, it has not yet been met with success. There are also some theoretical predictions and/or experimental indications of anisotropic Dirac cone in novel topological insulators and AMnBi2 (A = Sr and Ca) but more experimental investigations are needed. Here we report systematic high resolution angle-resolved photoemission measurements that have provided direct evidence on the existence of strongly anisotropic Dirac cones in SrMnBi2 and CaMnBi2. Distinct behaviors of the Dirac cones between SrMnBi2 and CaMnBi2 are also observed. These results have provided important information on the strong anisotropy of the Dirac cones in AMnBi2 system that can be governed by the spin-orbital coupling and the local environment surrounding the Bi square net. PMID:24947490

  12. Electronic structure of layered 1T-TaSe2 in commensurate charge-density-wave phase studied by angle-resolved photoemission spectroscopy

    NASA Astrophysics Data System (ADS)

    Aiura, Y.; Bando, H.; Kitagawa, R.; Maruyama, S.; Nishihara, Y.; Horiba, K.; Oshima, M.; Shiino, O.; Nakatake, M.

    2003-08-01

    We present a detailed angle-resolved photoemission study of the electronic structure of layered 1T-TaSe2 in the commensurate charge-density-wave (CDW) phase. A considerable reduction in the spectral weight of a quasiparticle band centered at the binding energy of about 0.25 eV below the Fermi level is observed in the momentum space ranging from the end of the first surface Brillouin zone to the second surface Brillouin zone. Moreover, no crossings of the Fermi level are visible in the whole Brillouin zone, meaning that the Fermi level lies in a pseudogap created by the tails of two overlapping Hubbard subbands. Our results indicate that not only the electron-phonon coupling, which is responsible for the formation of the CDW, but also the subsequent electron correlation effects in the Ta 5d band play an important role for the establishment of electronic structure of 1T-TaSe2 in the commensurate CDW phase.

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

    SciTech Connect

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

    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.

  14. Determination of the band parameters of bulk 2H-MX2 (M = Mo, W; X = S, Se) by angle-resolved photoemission spectroscopy

    PubMed Central

    Kim, Beom Seo; Rhim, Jun-Won; Kim, Beomyoung; Kim, Changyoung; Park, Seung Ryong

    2016-01-01

    Monolayer MX2 (M = Mo, W; X = S, Se) has recently been drawn much attention due to their application possibility as well as the novel valley physics. On the other hand, it is also important to understand the electronic structures of bulk MX2 for material applications since it is very challenging to grow large size uniform and sustainable monolayer MX2. We performed angle-resolved photoemission spectroscopy and tight binding calculations to investigate the electronic structures of bulk 2H-MX2. We could extract all the important electronic band parameters for bulk 2H-MX2, including the band gap, direct band gap size at K (-K) point and spin splitting size. Upon comparing the parameters for bulk 2H-MX2 (our work) with mono- and multi-layer MX2 (published), we found that stacked layers, substrates for thin films, and carrier concentration significantly affect the parameters, especially the band gap size. The origin of such effect is discussed in terms of the screening effect. PMID:27805019

  15. Electronic structure of Ce2RhIn8: A two-dimensional heavy-fermion system studied by angle-resolved photoemission spectroscopy

    DOE PAGES

    Jiang, Rui; Mou, Daixing; Liu, Chang; ...

    2015-04-01

    We use angle-resolved photoemission spectroscopy (ARPES) to study the 2D heavy fermion superconductor, Ce₂RhIn₈. The Fermi surface is rather complicated and consists of several hole and electron pockets with one of the sheets displaying strong nesting properties with a q-vector of (0.32, 0.32) π/a. We do not observe kz dispersion of the Fermi sheets, which is consistent with the expected 2D character of the electronic structure. Comparison of the ARPES data to band structure calculations suggests that a localized picture of the f-electrons works best. While there is some agreement in the overall band dispersion and location of the Fermimore » sheets, the model does not reproduce all observed bands and is not completely accurate for those it does. As a result, our data paves the way for improving the band structure calculations and the general understanding of the transport and thermodynamical properties of this material.« less

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

    SciTech Connect

    Liu, Rong.

    1990-09-21

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

  17. Adsorption site and structure determination of c(2 × 2) N2/Ni(100) using angle-resolved photoemission extended fine structure

    NASA Astrophysics Data System (ADS)

    Moler, Edward J.; Kellar, Scot A.; Huff, W. R. A.; Hussain, Zahid; Zheng, Yu; Hudson, Eric A.; Chen, Yufeng; Shirley, David A.

    1997-01-01

    We have determined the atomic spatial structure of c(2 × 2) N2/Ni(100) with angle-resolved photoemission extended fine structure using the nitrogen 1s core level. The chemically shifted N 1s peak intensities were summed to obtain ARPEFS curves for both nitrogen atoms in the molecule. We used a new, highly optimized program based on the Rehr-Albers scattering matrix formalism to find the adsorption site and to determine the bond lengths quantitatively. The nitrogen molecule stands upright at an atop site, with a NNi bond length of 2.25(1) Å, a NN bond length of 1.10(7) Å, and a first layer NiNi spacing of 1.76(4) Å. 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.

  18. Controlling the Carrier Concentration of the High-Temperature Superconductor Bi2Sr2CaCu2O8+δ in Angle-resolved Photoemission Spectroscopy Experiments

    SciTech Connect

    Palczewski, A.D.; Wen, J.; Kondo, T.; Xu, G.Z.J., Gu, G; Kaminski, A.

    2010-03-19

    We study the variation of the electronic properties at the surface of a high-temperature superconductor as a function of vacuum conditions in angle-resolved photoemission spectroscopy experiments. Normally, under inadequate ultrahigh vacuum (UHV) conditions the carrier concentration of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} (Bi2212) increases with time due to the absorption of oxygen from CO{sub 2}/CO molecules that are prime contaminants present in UHV systems. We find that in an optimal vacuum environment at low temperatures, the surface of Bi2212 is quite stable (the carrier concentration remains constant); however at elevated temperatures the carrier concentration decreases due to the loss of oxygen atoms from the Bi-O layer. These two effects can be used to control the carrier concentration in situ. Our finding opens the possibility of studying the electronic properties of the cuprates as a function of doping across the phase diagram on the same surface of sample (i.e., with the same impurities and nondopant defects). We envision that this method could be utilized in other surface sensitive techniques such as scanning tunneling microscopy/spectroscopy.

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

    SciTech Connect

    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{sup 2} V{sup −1} s{sup −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.

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

    PubMed Central

    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

  1. Development of soft x-ray time-resolved photoemission spectroscopy system with a two-dimensional angle-resolved time-of-flight analyzer at SPring-8 BL07LSU

    NASA Astrophysics Data System (ADS)

    Ogawa, Manami; Yamamoto, Susumu; Kousa, Yuka; Nakamura, Fumitaka; Yukawa, Ryu; Fukushima, Akiko; Harasawa, Ayumi; Kondoh, Hiroshi; Tanaka, Yoshihito; Kakizaki, Akito; Matsuda, Iwao

    2012-02-01

    We have developed a soft x-ray time-resolved photoemission spectroscopy system using synchrotron radiation (SR) at SPring-8 BL07LSU and an ultrashort pulse laser system. Two-dimensional angle-resolved measurements were performed with a time-of-flight-type analyzer. The photoemission spectroscopy system is synchronized to light pulses of SR and laser using a time control unit. The performance of the instrument is demonstrated by mapping the band structure of a Si(111) crystal over the surface Brillouin zones and observing relaxation of the surface photo-voltage effect using the pump (laser) and probe (SR) method.

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

    NASA Astrophysics Data System (ADS)

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

    2016-07-01

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

  3. Angle-resolved environmental X-ray photoelectron spectroscopy: A new laboratory setup for photoemission studies at pressures up to 0.4 Torr

    NASA Astrophysics Data System (ADS)

    Mangolini, F.; Åhlund, J.; Wabiszewski, G. E.; Adiga, V. P.; Egberts, P.; Streller, F.; Backlund, K.; Karlsson, P. G.; Wannberg, B.; Carpick, R. W.

    2012-09-01

    The paper presents the development and demonstrates the capabilities of a new laboratory-based environmental X-ray photoelectron spectroscopy system incorporating an electrostatic lens and able to acquire spectra up to 0.4 Torr. The incorporation of a two-dimensional detector provides imaging capabilities and allows the acquisition of angle-resolved data in parallel mode over an angular range of 14° without tilting the sample. The sensitivity and energy resolution of the spectrometer have been investigated by analyzing a standard Ag foil both under high vacuum (10-8 Torr) conditions and at elevated pressures of N2 (0.4 Torr). The possibility of acquiring angle-resolved data at different pressures has been demonstrated by analyzing a silicon/silicon dioxide (Si/SiO2) sample. The collected angle-resolved spectra could be effectively used for the determination of the thickness of the native silicon oxide layer.

  4. Angle-resolved photoemission studies on bi-layer colossal magnetoresistive oxides lanthanum(2-2x)strontium(1+2x)manganese(2)oxide(7)

    NASA Astrophysics Data System (ADS)

    Sun, Zhe

    In recent years the studies of manganites have flourished initially because of their Colossal Magnetoresistance (CMR) effect. However the scientific community quickly realized that the fundamental physics is abundant, exotic and challenging. Strong correlations of charge, lattice, spin and orbital degrees of freedom have been found to be responsible for many interesting physical phenomena. Of manganites, La2-2xSr 1+2xMn2O 7 has naturally layered crystal structure. The reduced two-dimensional character amplifies fluctuations of electronic, magnetic, and orbital degrees of freedom and interactions of them, which provides good opportunities for an understanding of the rich physics in manganites. In crystals, electrons have intrinsic charge, spin and orbital degrees of freedom, and the electron-phonon interaction has been an active topic for many decades, thus studies of electrons will definitely shed light on important physics in manganites. Angle-resolved photoemission spectroscopy (ARPES) is an ideal probe of electrons, and so by performing ARPES measurements on La2-2 xSr1+2xMn2 O7 we have obtained abundant knowledge of the physics of strong correlations of various degrees of freedom. We have made many new discoveries by exploring the physics in this com-pound. For the first time we resolved bi-layer split band structure of the prototype of bi-layer manganites, which was predicted by theoretical calculations long time ago. We observed minority-spin states in La2-2 xSr1+2xMn 2O7 (x = 0.36--0.39), which gives direct evidence that this system is not a half-metal in this doping iv range. We gave the first direct measurement of electron-phonon coupling strength in manganites and identified the phonon branches to which electrons couple. In addition to band insulator and Mott insulator there is another type of insulator, in which metallic domains and insulating domains coexist and phase separation and percolation effect play important roles in the metal

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

    SciTech Connect

    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

  6. Laser angle-resolved photoemission as a probe of initial state kz dispersion, final-state band gaps, and spin texture of Dirac states in the Bi2Te3 topological insulator

    NASA Astrophysics Data System (ADS)

    Ä; rrälä, Minna; Hafiz, Hasnain; Mou, Daixiang; Wu, Yun; Jiang, Rui; Riedemann, Trevor; Lograsso, Thomas A.; Barbiellini, Bernardo; Kaminski, Adam; Bansil, Arun; Lindroos, Matti

    2016-10-01

    We have obtained angle-resolved photoemission spectroscopy (ARPES) spectra from single crystals of the topological insulator material Bi2Te3 using a tunable laser spectrometer. The spectra were collected for 11 different photon energies ranging from 5.57 to 6.70 eV for incident light polarized linearly along two different in-plane directions. Parallel first-principles, fully relativistic computations of photointensities were carried out using the experimental geometry within the framework of the one-step model of photoemission. A reasonable overall accord between theory and experiment is used to gain insight into how properties of the initial- and final-state band structures as well as those of the topological surface states and their spin textures are reflected in the laser-ARPES spectra. Our analysis reveals that laser-ARPES is sensitive to both the initial-state kz dispersion and the presence of delicate gaps in the final-state electronic spectrum.

  7. 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

    SciTech Connect

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

    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.

  8. Electron scattering, charge order, and pseudogap physics in La1.6–xNd0.4SrxCuO4: An angle-resolved photoemission spectroscopy study

    DOE PAGES

    Matt, C. E.; Fatuzzo, C. G.; Sassa, Y.; ...

    2015-10-27

    We report an angle-resolved photoemission study of the charge stripe ordered La1.6–xNd0.4SrxCuO4 (Nd-LSCO) system. A comparative and quantitative line-shape analysis is presented as the system evolves from the overdoped regime into the charge ordered phase. On the overdoped side (x = 0.20), a normal-state antinodal spectral gap opens upon cooling below 80 K. In this process, spectral weight is preserved but redistributed to larger energies. A correlation between this spectral gap and electron scattering is found. A different line shape is observed in the antinodal region of charge ordered Nd-LSCO x = 1/8. Significant low-energy spectral weight appears to bemore » lost. As a result, these observations are discussed in terms of spectral-weight redistribution and gapping originating from charge stripe ordering.« less

  9. Universal versus Material-Dependent Two-Gap Behaviors in the High-Tc Cuprates: Angle-Resolved Photoemission Study of La_2-xSr_xCuO_4

    SciTech Connect

    Yoshida, T.

    2010-06-04

    We have investigated the doping and temperature dependences of the pseudogap/superconducting gap in the single-layer cuprate La{sub 2-x}Sr{sub x}CuO{sub 4} by angle-resolved photoemission spectroscopy. The results clearly exhibit two distinct energy and temperature scales, namely, the gap around ({pi}, 0) of magnitude {Delta}{asterisk} and the gap around the node characterized by the d-wave order parameter {delta}{sub 0}, like the double-layer cuprate Bi2212. In comparison with Bi2212 having higher T{sub c}'s, {delta}{sub 0} is smaller, while {delta}{asterisk} and T{ampersand} are similar. This result suggests that {delta}{asterisk} and T{asterisk} are approximately material-independent properties of a single Cu0{sub 2} plane, in contrast the material-dependent {delta}{sub 0}, representing the pairing strength.

  10. Angle-resolved photoemission observation of Mn-pnictide hybridization and negligible band structure renormalization in BaMn2As2 and BaMn2Sb2

    DOE PAGES

    Zhang, W. -L.; Richard, P.; van Roekeghem, A.; ...

    2016-10-31

    We performed an angle-resolved photoemission spectroscopy study of BaMn2As2 and BaMn2Sb2, which are isostructural to the parent compound BaFe2As2 of the 122 family of ferropnictide superconductors. We show the existence of a strongly kz-dependent band gap with a minimum at the Brillouin zone center, in agreement with their semiconducting properties. Despite the half filling of the electronic 3d shell, we show that the band structure in these materials is almost not renormalized from the Kohn-Sham bands of density functional theory. Finally, our photon-energy-dependent study provides evidence for Mn-pnictide hybridization, which may play a role in tuning the electronic correlations inmore » these compounds.« less

  11. Angle-resolved photoemission observation of Mn-pnictide hybridization and negligible band structure renormalization in BaMn2As2 and BaMn2Sb2

    NASA Astrophysics Data System (ADS)

    Zhang, W.-L.; Richard, P.; van Roekeghem, A.; Nie, S.-M.; Xu, N.; Zhang, P.; Miao, H.; Wu, S.-F.; Yin, J.-X.; Fu, B. B.; Kong, L.-Y.; Qian, T.; Wang, Z.-J.; Fang, Z.; Sefat, A. S.; Biermann, S.; Ding, H.

    2016-10-01

    We performed an angle-resolved photoemission spectroscopy study of BaMn2As2 and BaMn2Sb2 , which are isostructural to the parent compound BaFe2As2 of the 122 family of ferropnictide superconductors. We show the existence of a strongly kz-dependent band gap with a minimum at the Brillouin zone center, in agreement with their semiconducting properties. Despite the half filling of the electronic 3 d shell, we show that the band structure in these materials is almost not renormalized from the Kohn-Sham bands of density functional theory. Our photon-energy-dependent study provides evidence for Mn-pnictide hybridization, which may play a role in tuning the electronic correlations in these compounds.

  12. CuPc/Au(1 1 0): Determination of the azimuthal alignment by a combination of angle-resolved photoemission and density functional theory

    PubMed Central

    Lüftner, Daniel; Milko, Matus; Huppmann, Sophia; Scholz, Markus; Ngyuen, Nam; Wießner, Michael; Schöll, Achim; Reinert, Friedrich; Puschnig, Peter

    2014-01-01

    Here we report on a combined experimental and theoretical study on the structural and electronic properties of a monolayer of Copper-Phthalocyanine (CuPc) on the Au(1 1 0) surface. Low-energy electron diffraction reveals a commensurate overlayer unit cell containing one adsorbate species. The azimuthal alignment of the CuPc molecule is revealed by comparing experimental constant binding energy (kxky)-maps using angle-resolved photoelectron spectroscopy with theoretical momentum maps of the free molecule's highest occupied molecular orbital (HOMO). This structural information is confirmed by total energy calculations within the framework of van-der-Waals corrected density functional theory. The electronic structure is further analyzed by computing the molecule-projected density of states, using both a semi-local and a hybrid exchange-correlation functional. In agreement with experiment, the HOMO is located about 1.2 eV below the Fermi-level, while there is no significant charge transfer into the molecule and the CuPc LUMO remains unoccupied on the Au(1 1 0) surface. PMID:25284953

  13. Laser angle-resolved photoemission as a probe of initial state kz dispersion, final-state band gaps, and spin texture of Dirac states in the Bi2Te3 topological insulator

    DOE PAGES

    Ärrälä, Minna; Hafiz, Hasnain; Mou, Daixiang; ...

    2016-10-27

    Here, we have obtained angle-resolved photoemission (ARPES) spectra from single crystals of the topological insulator material Bi2Te3 using tunable laser spectrometer. The spectra were collected for eleven different photon energies ranging from 5.57 to 6.70 eV for incident light polarized linearly along two different in-plane directions. Parallel first-principles, fully relativistic computations of photo-intensities were carried out using the experimental geometry within the framework of the one-step model of photoemission. Good overall accord between theory and experiment is used to gain insight into how properties of the initial and final state band structures as well as those of the topological surfacemore » states and their spin-textures are reflected in the laser-ARPES spectra. In conclusion, our analysis reveals that laser-ARPES is sensitive to both the initial state kz dispersion and the presence of delicate gaps in the final state electronic spectrum.« less

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

    PubMed

    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.

  15. Novel Electron-Phonon Relaxation Pathway in Graphite Revealed by Time-Resolved Raman Scattering and Angle-Resolved Photoemission Spectroscopy

    PubMed Central

    Yang, Jhih-An; Parham, Stephen; Dessau, Daniel; Reznik, Dmitry

    2017-01-01

    Time dynamics of photoexcited electron-hole pairs is important for a number of technologies, in particular solar cells. We combined ultrafast pump-probe Raman scattering and photoemission to directly follow electron-hole excitations as well as the G-phonon in graphite after an excitation by an intense laser pulse. This phonon is known to couple relatively strongly to electrons. Cross-correlating effective electronic and phonon temperatures places new constraints on model-based fits. The accepted two-temperature model predicts that G-phonon population should start to increase as soon as excited electron-hole pairs are created and that the rate of increase should not depend strongly on the pump fluence. Instead we found that the increase of the G-phonon population occurs with a delay of ~65 fs. This time-delay is also evidenced by the absence of the so-called self-pumping for G phonons. It decreases with increased pump fluence. We show that these observations imply a new relaxation pathway: Instead of hot carriers transferring energy to G-phonons directly, the energy is first transferred to optical phonons near the zone boundary K-points, which then decay into G-phonons via phonon-phonon scattering. Our work demonstrates that phonon-phonon interactions must be included in any calculations of hot carrier relaxation in optical absorbers even when only short timescales are considered. PMID:28102368

  16. Novel Electron-Phonon Relaxation Pathway in Graphite Revealed by Time-Resolved Raman Scattering and Angle-Resolved Photoemission Spectroscopy

    NASA Astrophysics Data System (ADS)

    Yang, Jhih-An; Parham, Stephen; Dessau, Daniel; Reznik, Dmitry

    2017-01-01

    Time dynamics of photoexcited electron-hole pairs is important for a number of technologies, in particular solar cells. We combined ultrafast pump-probe Raman scattering and photoemission to directly follow electron-hole excitations as well as the G-phonon in graphite after an excitation by an intense laser pulse. This phonon is known to couple relatively strongly to electrons. Cross-correlating effective electronic and phonon temperatures places new constraints on model-based fits. The accepted two-temperature model predicts that G-phonon population should start to increase as soon as excited electron-hole pairs are created and that the rate of increase should not depend strongly on the pump fluence. Instead we found that the increase of the G-phonon population occurs with a delay of ~65 fs. This time-delay is also evidenced by the absence of the so-called self-pumping for G phonons. It decreases with increased pump fluence. We show that these observations imply a new relaxation pathway: Instead of hot carriers transferring energy to G-phonons directly, the energy is first transferred to optical phonons near the zone boundary K-points, which then decay into G-phonons via phonon-phonon scattering. Our work demonstrates that phonon-phonon interactions must be included in any calculations of hot carrier relaxation in optical absorbers even when only short timescales are considered.

  17. Novel Electron-Phonon Relaxation Pathway in Graphite Revealed by Time-Resolved Raman Scattering and Angle-Resolved Photoemission Spectroscopy.

    PubMed

    Yang, Jhih-An; Parham, Stephen; Dessau, Daniel; Reznik, Dmitry

    2017-01-19

    Time dynamics of photoexcited electron-hole pairs is important for a number of technologies, in particular solar cells. We combined ultrafast pump-probe Raman scattering and photoemission to directly follow electron-hole excitations as well as the G-phonon in graphite after an excitation by an intense laser pulse. This phonon is known to couple relatively strongly to electrons. Cross-correlating effective electronic and phonon temperatures places new constraints on model-based fits. The accepted two-temperature model predicts that G-phonon population should start to increase as soon as excited electron-hole pairs are created and that the rate of increase should not depend strongly on the pump fluence. Instead we found that the increase of the G-phonon population occurs with a delay of ~65 fs. This time-delay is also evidenced by the absence of the so-called self-pumping for G phonons. It decreases with increased pump fluence. We show that these observations imply a new relaxation pathway: Instead of hot carriers transferring energy to G-phonons directly, the energy is first transferred to optical phonons near the zone boundary K-points, which then decay into G-phonons via phonon-phonon scattering. Our work demonstrates that phonon-phonon interactions must be included in any calculations of hot carrier relaxation in optical absorbers even when only short timescales are considered.

  18. Hard and soft x-ray standing-wave photoelectron spectroscopy and angle-resolved photoemission spectroscopy study of LaNiO3/SrTiO 3 superlattice and its interfaces

    NASA Astrophysics Data System (ADS)

    Eiteneer, Daria N.

    Abstract Many classes of materials that exhibit interesting characteristics in the modulation of the electronic and magnetic properties when they are made of more than one compound, often arranged in multilayers and superlattices. In such cases, the electronic, electric, and magnetic properties of the multilayer, as well as their densities-of-states, are vastly different from the properties of the constituent materials, with the most important features often located at the interfaces. Specifically, perovskite nickelates are examples of materials that lie at the heart of correlated electron physics. Prior studies have been done on superlattices that contain multilayers of two perovskites. Specifically, it has been shown that LaNiO3 (LNO) undergoes a Mott metal-insulator transition when sandwiched between the layers of SrTiO3 (STO). However, even with prior theoretical simulations and experimental studies, no conclusion has been reached so far as to the exact reason for such a transition. To further the investigation of these ideas, we are undertaking a detailed study of the electronic structure of a LaNiO3/SrTiO3 superlattice with 10 repeats of [4 unit-cell LNO/3 unit-cell STO] bilayer grown on an (LaAlO3)0.3(Sr2AlTaO6)0.7 substrate. To provide a complete characterization of this superlattice, it is crucial to characterize the core levels of the atoms at the interface, as well as to measure the depth-dependent density of states and the element-specific magnetization through the interface. The standing-wave photoemission technique provides a unique capability for characterizing the LNO/STO interfaces by depth-resolving the electronic structure of the superlattice, particularly in its momentum-resolving form of standing-wave angle-resolved photoemission using soft x-rays in the ca. 1 keV regime. The main advantages of SW-XPS are its non-destructiveness, large effective attenuation length, and the enhanced depth resolution for buried interfaces via standing

  19. Signature of the CuO{sub 2} plane related bands in YBa{sub 2}Cu{sub 3}O{sub 6.9} as seen by angle-resolved photoemission

    SciTech Connect

    Lindroos, M.; Bansil, A.; Gofron, K.; Campuzano, J.C.; Ding, H. |; Liu, R. |; Veal, B.W.

    1992-09-01

    The authors present first-principles computations together with corresponding angle-resolved photoemission measurements in order to delineate the shape and polarization dependence of the spectral feature associated with the CuO{sub 2} plane-related bands from the (001) surface of YBa{sub 2}Cu{sub 3}O{sub 6.9}. Theoretical predictions are found to be in remarkable agreement with the observed character of the spectral feature between 0 and 0.3 eV binding energy (for k{sub {parallel}} values along the {Gamma}-S line), and indicate that the local-density-approximation based wave-functions implicit in the theory provide a reasonable description of the CuO{sub 2} plane band states near the Fermi energy. The computations also show that of the six possible surface terminations, the ARPES spectra from Y123(001) surface are reasonably described by the BaO/CuO{sub 2} ideal surface termination, i.e. by assuming a BaO layer followed by a CuO{sub 2} plane layer below.

  20. Surface metallization on Si(001) at elevated temperatures studied by angle-resolved photoemission spectroscopy and near-edge x-ray absorption fine structure: Effect of thermal adatoms

    NASA Astrophysics Data System (ADS)

    Jeon, C.; Hwang, C. C.; Kang, T.-H.; Kim, K.-J.; Kim, B.; Kim, Y.; Noh, D. Y.; Park, C.-Y.

    2009-10-01

    We report the metallization of the Si(001)2×1 surface at elevated temperatures using angle-resolved photoemission spectroscopy (ARPES) and near-edge x-ray absorption fine structure (NEXAFS). A metallic state (Sm) over the EF , which corresponds to the empty (π∗) state of the 2×1 asymmetric dimer model, increases in the ARPES spectra, while the π∗ state decreases in the NEXAFS spectra with increasing temperature. Since Sm is observed even at 400 K, the structural phase transition at ˜900K [Phys. Rev. Lett. 91, 126103 (2003); Phys. Rev. Lett. 77, 3869 (1996)] is not related to the metallization. Thermal excitation seems to be too small to detect in ARPES in initial stage of the metallization and cannot account for the different behavior of Sm and the filled surface state of the up-dimer upon oxidation. We suggest, based on the existence of Sm even at 400 K and the oxidation behavior, that the metallization is attributed to thermal adatoms.

  1. 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

    SciTech Connect

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

    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.

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

    SciTech Connect

    Nemšák, S.; Conti, G.; Palsson, G. K.; Conlon, C.; Fadley, C. S.; Cho, S.; Rault, J. E.; Avila, J.; Asensio, M.-C.; Jackson, C. A.; Moetakef, P.; Janotti, A.; Bjaalie, L.; Himmetoglu, B.; Van de Walle, C. G.; Stemmer, S.; Balents, L.; Schneider, C. M.

    2015-12-07

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

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

    DOE PAGES

    Dakovski, Georgi L.; Durakiewicz, Tomasz; Zhu, Jian-Xin; ...

    2015-10-12

    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 20.15eV, 12 fs pulses we show for the first time the evolution of quasiparticles in the antinodal region of Bi2Sr2CaCu2O8+δ and demonstrate thatmore » nonmonotonic 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 severe contrast to the monotonic relaxation in the nodal and off-nodal regions.« less

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

    SciTech Connect

    Huff, Welcome Rex Anthony

    1996-02-01

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

  5. Angle-resolved photoemission with circularly polarized light in the nodal mirror plane of underdoped Bi2Sr2CaCu2O8+δ superconductor

    SciTech Connect

    He, Junfeng; Mion, Thomas R.; Gao, Shang; Myers, Gavin T.; Arita, Masashi; Shimada, Kenya; Gu, G. D.; He, Rui -Hua

    2016-10-31

    Unraveling the nature of pseudogap phase in high-temperature superconductors holds the key to understanding their superconducting mechanisms and potentially broadening their applications via enhancement of their superconducting transition temperatures. Angle-resolved photoemission spectroscopy (ARPES) experiments using circularly polarized light have been proposed to detect possible symmetry breaking state in the pseudogap phase of cuprates. Here, the presence (absence) of an electronic order which breaks mirror symmetry of the crystal would in principle induce a finite (zero) circular dichroism in photoemission. Different orders breaking reflection symmetries about different mirror planes can also be distinguished by the momentum dependence of the measured circular dichroism.

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

    NASA Astrophysics Data System (ADS)

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

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

  7. High-power, narrow-band, high-repetition-rate, 5.9 eV coherent light source using passive optical cavity for laser-based angle-resolved photoelectron spectroscopy.

    PubMed

    Omachi, J; Yoshioka, K; Kuwata-Gonokami, M

    2012-10-08

    We demonstrate a scheme for efficient generation of a 5.9 eV coherent light source with an average power of 23 mW, 0.34 meV linewidth, and 73 MHz repetition rate from a Ti: sapphire picosecond mode-locked laser with an output power of 1 W. Second-harmonic light is generated in a passive optical cavity by a BiB(3)O(6) crystal with a conversion efficiency as high as 67%. By focusing the second-harmonic light transmitted from the cavity into a β-BaB(2)O(4) crystal, we obtain fourth-harmonic light at 5.9 eV. This light source offers stable operation for at least a week. We discuss the suitability of the laser light source for high-resolution angle-resolved photoelectron spectroscopy by comparing it with other sources (synchrotron radiation facilities and gas discharge lamp).

  8. Electron scattering, charge order, and pseudogap physics in La1.6–xNd0.4SrxCuO4: An angle-resolved photoemission spectroscopy study

    SciTech Connect

    Matt, C. E.; Fatuzzo, C. G.; Sassa, Y.; Mansson, M.; Fatale, S.; Bitetta, V.; Shi, X.; Pailhes, S.; Berntsen, M. H.; Kurosawa, T.; Oda, M.; Momono, N.; Lipscombe, O. J.; Hayden, S. M.; Yan, J. -Q.; Zhou, J. -S.; Goodenough, J. B.; Pyon, S.; Takayama, T.; Takagi, H.; Patthey, L.; Bendounan, A.; Razzoli, E.; Shi, M.; Plumb, N. C.; Radovic, M.; Grioni, M.; Mesot, J.; Tjernberg, O.; Chang, J.

    2015-10-27

    We report an angle-resolved photoemission study of the charge stripe ordered La1.6–xNd0.4SrxCuO4 (Nd-LSCO) system. A comparative and quantitative line-shape analysis is presented as the system evolves from the overdoped regime into the charge ordered phase. On the overdoped side (x = 0.20), a normal-state antinodal spectral gap opens upon cooling below 80 K. In this process, spectral weight is preserved but redistributed to larger energies. A correlation between this spectral gap and electron scattering is found. A different line shape is observed in the antinodal region of charge ordered Nd-LSCO x = 1/8. Significant low-energy spectral weight appears to be lost. As a result, these observations are discussed in terms of spectral-weight redistribution and gapping originating from charge stripe ordering.

  9. Laser angle-resolved photoemission as a probe of initial state kz dispersion, final-state band gaps, and spin texture of Dirac states in the Bi2Te3 topological insulator

    SciTech Connect

    Ärrälä, Minna; Hafiz, Hasnain; Mou, Daixiang; Wu, Yun; Jiang, Rui; Riedemann, Trevor; Lograsso, Thomas A.; Barbiellini, Bernardo; Kaminski, Adam; Bansil, Arun; Lindroos, Matti

    2016-10-27

    Here, we have obtained angle-resolved photoemission (ARPES) spectra from single crystals of the topological insulator material Bi2Te3 using tunable laser spectrometer. The spectra were collected for eleven different photon energies ranging from 5.57 to 6.70 eV for incident light polarized linearly along two different in-plane directions. Parallel first-principles, fully relativistic computations of photo-intensities were carried out using the experimental geometry within the framework of the one-step model of photoemission. Good overall accord between theory and experiment is used to gain insight into how properties of the initial and final state band structures as well as those of the topological surface states and their spin-textures are reflected in the laser-ARPES spectra. In conclusion, our analysis reveals that laser-ARPES is sensitive to both the initial state kz dispersion and the presence of delicate gaps in the final state electronic spectrum.

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

    SciTech Connect

    Taniuchi, Toshiyuki Kotani, Yoshinori; Shin, Shik

    2015-02-15

    We report the first experiments carried out on a new chemical and magnetic imaging system, which combines the high spatial resolution of a photoemission electron microscope (PEEM) with a continuous-wave deep-ultraviolet laser. Threshold photoemission is sensitive to the chemical and magnetic structures of the surface of materials. The spatial resolution of PEEM is limited by space charging when using pulsed photon sources as well as aberrations in the electron optics. We show that the use of a continuous-wave laser enabled us to overcome such a limit by suppressing the space-charge effect, allowing us to obtain a resolution of approximately 2.6 nm. With this system, we demonstrated the imaging of surface reconstruction domains on Si(001) by linear dichroism with normal incidence of the laser beam. We also succeeded in magnetic imaging of thin films with the use of magnetic circular dichroism near the Fermi level. The unique features of the ultraviolet laser will give us fast switching of the incident angles and polarizations of the photon source, which will be useful for the characterization of antiferromagnetic materials as well as ferromagnetic materials.

  11. Electronic structure of Ce2RhIn8: A two-dimensional heavy-fermion system studied by angle-resolved photoemission spectroscopy

    SciTech Connect

    Jiang, Rui; Mou, Daixing; Liu, Chang; Zhao, Xin; Yao, Yongxin; Ryu, Hyejin; Petrovic, C.; Ho, Kai -Ming; Kaminski, Adam

    2015-04-01

    We use angle-resolved photoemission spectroscopy (ARPES) to study the 2D heavy fermion superconductor, Ce₂RhIn₈. The Fermi surface is rather complicated and consists of several hole and electron pockets with one of the sheets displaying strong nesting properties with a q-vector of (0.32, 0.32) π/a. We do not observe kz dispersion of the Fermi sheets, which is consistent with the expected 2D character of the electronic structure. Comparison of the ARPES data to band structure calculations suggests that a localized picture of the f-electrons works best. While there is some agreement in the overall band dispersion and location of the Fermi sheets, the model does not reproduce all observed bands and is not completely accurate for those it does. As a result, our data paves the way for improving the band structure calculations and the general understanding of the transport and thermodynamical properties of this material.

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

    SciTech Connect

    Dakovski, Georgi L.; Durakiewicz, Tomasz; Zhu, Jian-Xin; Riseborough, Peter S.; Gu, Genda; Gilbertson, Steve M.; Taylor, Antoinette; Rodriguez, George

    2015-10-12

    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 20.15eV, 12 fs pulses we show for the first time the evolution of quasiparticles in the antinodal region of Bi2Sr2CaCu2O8+δ and demonstrate that nonmonotonic 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 severe contrast to the monotonic relaxation in the nodal and off-nodal regions.

  13. Angle-resolved photoemission observation of Mn-pnictide hybridization and negligible band structure renormalization in BaMn2As2 and BaMn2Sb2

    SciTech Connect

    Zhang, W. -L.; Richard, P.; van Roekeghem, A.; Nie, S. -M.; Xu, N.; Zhang, P.; Miao, H.; Wu, S. -F.; Yin, J. -X.; Fu, B. B.; Kong, L. -Y.; Qian, T.; Wang, Z. -J.; Fang, Z.; Sefat, Athena Safa; Biermann, S.; Ding, H.

    2016-10-31

    We performed an angle-resolved photoemission spectroscopy study of BaMn2As2 and BaMn2Sb2, which are isostructural to the parent compound BaFe2As2 of the 122 family of ferropnictide superconductors. We show the existence of a strongly kz-dependent band gap with a minimum at the Brillouin zone center, in agreement with their semiconducting properties. Despite the half filling of the electronic 3d shell, we show that the band structure in these materials is almost not renormalized from the Kohn-Sham bands of density functional theory. Finally, our photon-energy-dependent study provides evidence for Mn-pnictide hybridization, which may play a role in tuning the electronic correlations in these compounds.

  14. Angle-resolved optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Desjardins, Adrien Emmanuel

    Optical coherence tomography (OCT) has emerged as a powerful tool for probing the microstructure of biological tissue non-invasively at high-speed. OCT measures depth-resolved reflectance of infrared light, generating cross-sectional images non-invasively with micron-scale resolution. As with other imaging modalities that employ coherent detection, OCT images are confounded by speckle noise. Speckle imposes a grainy texture on images that reduces the signal-to-noise ratio to near unity values. As a result, it conceals subtle differences in scattering properties known to be crucial for differentiating normal from diseased tissue states. In this thesis, we developed a novel OCT modality called "Angle-Resolved OCT" in which depth scans (A-lines) are obtained simultaneously from a broad range of backscattering angles. We demonstrated that high levels of speckle reduction can be achieved by averaging the magnitudes of A-lines corresponding to the same transverse locations. With both experimental and analytic approaches, we demonstrated that this averaging method does not lead to a substantial loss in spatial resolution. We developed two different imaging systems for performing Angle-Resolved OCT. With the first system, angular data was acquired simultaneously; with the second, it was acquired sequentially. The first system had superior speckle-reduction capabilities but image quality degraded significantly with small sample movements. The second system allowed for in vivo imaging, as demonstrated with Resolved OCT systems, the speckle-reduced images showed hitherto unprecedented delineation of tissue microstructure.

  15. Tachometer Derived From Brushless Shaft-Angle Resolver

    NASA Technical Reports Server (NTRS)

    Howard, David E.; Smith, Dennis A.

    1995-01-01

    Tachometer circuit operates in conjunction with brushless shaft-angle resolver. By performing sequence of straightforward mathematical operations on resolver signals and utilizing simple trigonometric identity, generates voltage proportional to rate of rotation of shaft. One advantage is use of brushless shaft-angle resolver as main source of rate signal: no brushes to wear out, no brush noise, and brushless resolvers have proven robustness. No switching of signals to generate noise. Another advantage, shaft-angle resolver used as shaft-angle sensor, tachometer input obtained without adding another sensor. Present circuit reduces overall size, weight, and cost of tachometer.

  16. Spectral angle resolved scattering of thin film coatings.

    PubMed

    Schröder, Sven; Unglaub, David; Trost, Marcus; Cheng, Xinbin; Zhang, Jinlong; Duparré, Angela

    2014-02-01

    The light scattering of interference coatings is strongly dependent on the wavelength. In addition to the general strong increase of scattering as the wavelengths get shorter, dramatic scatter effects in and around the resonance regions can occur. This is discussed in detail for highly reflective and chirped mirrors. A new instrument is presented which enables spectral angle resolved scatter measurements of high-quality optical components to be performed between 250 and 1500 nm.

  17. Angle-resolved diffraction grating biosensor based on porous silicon

    NASA Astrophysics Data System (ADS)

    Lv, Changwu; Jia, Zhenhong; Liu, Yajun; Mo, Jiaqing; Li, Peng; Lv, Xiaoyi

    2016-03-01

    In this study, an optical biosensor based on a porous silicon composite structure was fabricated using a simple method. This structure consists of a thin, porous silicon surface diffraction grating and a one-dimensional porous silicon photonic crystal. An angle-resolved diffraction efficiency spectrum was obtained by measuring the diffraction efficiency at a range of incident angles. The angle-resolved diffraction efficiency of the 2nd and 3rd orders was studied experimentally and theoretically. The device was sensitive to the change of refractive index in the presence of a biomolecule indicated by the shift of the diffraction efficiency spectrum. The sensitivity of this sensor was investigated through use of an 8 base pair antifreeze protein DNA hybridization. The shifts of the angle-resolved diffraction efficiency spectrum showed a relationship with the change of the refractive index, and the detection limit of the biosensor reached 41.7 nM. This optical device is highly sensitive, inexpensive, and simple to fabricate. Using shifts in diffraction efficiency spectrum to detect biological molecules has not yet been explored, so this study establishes a foundation for future work.

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

    NASA Astrophysics Data System (ADS)

    Huang, Lunan

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

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

    SciTech Connect

    Liu, Chang

    2011-01-01

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

  20. Angle-Resolved photoemission spectroscopy on Tl2Ba2CuO6+δ

    NASA Astrophysics Data System (ADS)

    Levy, G.; Raichle, M.; Fournier, D.; Mottershead, J.; Veenstra, C.; Rosen, J.; Bostwick, A.; Rotenberg, E.; Liang, R.; Hardy, W.; Bonn, D.; Damascelli, A.

    2010-03-01

    Tl2201 is characterized by a simple and undistorted crystal structure, as well as less disorder than other high-Tc cuprate-based materials. On the very overdoped side of the phase diagram, a remarkable agreement has already been achieved between transport (i.e., AMRO and dHvA) and ARPES studies [1-3]. We here will present ARPES data on high-quality Tl2201 single crystals and compare them with transport results from the same material across the phase diagram, with emphasis on the evolution of Fermi surface volume, Fermi velocity, and many-body renormalization. We will also discuss the possibility of driving the doping on this material into the underdoped regime by in-situ potassium evaporation.[4pt] [1] N. E. Hussey et al., Nature 425, 814 (2003).[0pt] [2] M. Plat'e et al., Phys. Rev. Lett. 95, 077001 (2005).[0pt] [3] B. Vignolle et al., Nature 455, 952 (2008).

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

    SciTech Connect

    Heinemann, Thomas Klapp, Sabine H. L.; Palczynski, Karol Dzubiella, Joachim

    2014-12-07

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

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

    PubMed

    Heinemann, Thomas; Palczynski, Karol; Dzubiella, Joachim; Klapp, Sabine H L

    2014-12-07

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

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

    NASA Astrophysics Data System (ADS)

    Heinemann, Thomas; Palczynski, Karol; Dzubiella, Joachim; Klapp, Sabine H. L.

    2014-12-01

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

  4. Materials characterisation by angle-resolved scanning transmission electron microscopy

    NASA Astrophysics Data System (ADS)

    Müller-Caspary, Knut; Oppermann, Oliver; Grieb, Tim; Krause, Florian F.; Rosenauer, Andreas; Schowalter, Marco; Mehrtens, Thorsten; Beyer, Andreas; Volz, Kerstin; Potapov, Pavel

    2016-11-01

    Solid-state properties such as strain or chemical composition often leave characteristic fingerprints in the angular dependence of electron scattering. Scanning transmission electron microscopy (STEM) is dedicated to probe scattered intensity with atomic resolution, but it drastically lacks angular resolution. Here we report both a setup to exploit the explicit angular dependence of scattered intensity and applications of angle-resolved STEM to semiconductor nanostructures. Our method is applied to measure nitrogen content and specimen thickness in a GaNxAs1‑x layer independently at atomic resolution by evaluating two dedicated angular intervals. We demonstrate contrast formation due to strain and composition in a Si- based metal-oxide semiconductor field effect transistor (MOSFET) with GexSi1‑x stressors as a function of the angles used for imaging. To shed light on the validity of current theoretical approaches this data is compared with theory, namely the Rutherford approach and contemporary multislice simulations. Inconsistency is found for the Rutherford model in the whole angular range of 16–255 mrad. Contrary, the multislice simulations are applicable for angles larger than 35 mrad whereas a significant mismatch is observed at lower angles. This limitation of established simulations is discussed particularly on the basis of inelastic scattering.

  5. Angle resolved scatter measurement of bulk scattering in transparent ceramics

    NASA Astrophysics Data System (ADS)

    Sharma, Saurabh; Miller, J. Keith; Shori, Ramesh K.; Goorsky, Mark S.

    2015-02-01

    Bulk scattering in polycrystalline laser materials (PLM), due to non-uniform refractive index across the bulk, is regarded as the primary loss mechanism leading to degradation of laser performance with higher threshold and lower output power. The need for characterization techniques towards identifying bulk scatter and assessing the quality. Assessment of optical quality and the identification of bulk scatter have been by simple visual inspection of thin samples of PLMs, thus making the measurements highly subjective and inaccurate. Angle Resolved Scatter (ARS) measurement allows for the spatial mapping of scattered light at all possible angles about a sample, mapping the intensity for both forward scatter and back-scatter regions. The cumulative scattered light intensity, in the forward scatter direction, away from the specular beam is used for the comparison of bulk scattering between samples. This technique employ the detection of scattered light at all angles away from the specular beam directions and represented as a 2-D polar map. The high sensitivity of the ARS technique allows us to compare bulk scattering in different PLM samples which otherwise had similar transmitted beam wavefront distortions.

  6. Materials characterisation by angle-resolved scanning transmission electron microscopy

    PubMed Central

    Müller-Caspary, Knut; Oppermann, Oliver; Grieb, Tim; Krause, Florian F.; Rosenauer, Andreas; Schowalter, Marco; Mehrtens, Thorsten; Beyer, Andreas; Volz, Kerstin; Potapov, Pavel

    2016-01-01

    Solid-state properties such as strain or chemical composition often leave characteristic fingerprints in the angular dependence of electron scattering. Scanning transmission electron microscopy (STEM) is dedicated to probe scattered intensity with atomic resolution, but it drastically lacks angular resolution. Here we report both a setup to exploit the explicit angular dependence of scattered intensity and applications of angle-resolved STEM to semiconductor nanostructures. Our method is applied to measure nitrogen content and specimen thickness in a GaNxAs1−x layer independently at atomic resolution by evaluating two dedicated angular intervals. We demonstrate contrast formation due to strain and composition in a Si- based metal-oxide semiconductor field effect transistor (MOSFET) with GexSi1−x stressors as a function of the angles used for imaging. To shed light on the validity of current theoretical approaches this data is compared with theory, namely the Rutherford approach and contemporary multislice simulations. Inconsistency is found for the Rutherford model in the whole angular range of 16–255 mrad. Contrary, the multislice simulations are applicable for angles larger than 35 mrad whereas a significant mismatch is observed at lower angles. This limitation of established simulations is discussed particularly on the basis of inelastic scattering. PMID:27849001

  7. Materials characterisation by angle-resolved scanning transmission electron microscopy.

    PubMed

    Müller-Caspary, Knut; Oppermann, Oliver; Grieb, Tim; Krause, Florian F; Rosenauer, Andreas; Schowalter, Marco; Mehrtens, Thorsten; Beyer, Andreas; Volz, Kerstin; Potapov, Pavel

    2016-11-16

    Solid-state properties such as strain or chemical composition often leave characteristic fingerprints in the angular dependence of electron scattering. Scanning transmission electron microscopy (STEM) is dedicated to probe scattered intensity with atomic resolution, but it drastically lacks angular resolution. Here we report both a setup to exploit the explicit angular dependence of scattered intensity and applications of angle-resolved STEM to semiconductor nanostructures. Our method is applied to measure nitrogen content and specimen thickness in a GaNxAs1-x layer independently at atomic resolution by evaluating two dedicated angular intervals. We demonstrate contrast formation due to strain and composition in a Si- based metal-oxide semiconductor field effect transistor (MOSFET) with GexSi1-x stressors as a function of the angles used for imaging. To shed light on the validity of current theoretical approaches this data is compared with theory, namely the Rutherford approach and contemporary multislice simulations. Inconsistency is found for the Rutherford model in the whole angular range of 16-255 mrad. Contrary, the multislice simulations are applicable for angles larger than 35 mrad whereas a significant mismatch is observed at lower angles. This limitation of established simulations is discussed particularly on the basis of inelastic scattering.

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

    SciTech Connect

    Berrah, N.; Langer, B.; Gorczyca, T.W.

    1997-04-01

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

  9. A New Spin on Photoemission Spectroscopy

    SciTech Connect

    Jozwiak, Chris

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

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

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

  11. Spin-dependent quantum interference in photoemission process from spin-orbit coupled states

    PubMed Central

    Yaji, Koichiro; Kuroda, Kenta; Toyohisa, Sogen; Harasawa, Ayumi; Ishida, Yukiaki; Watanabe, Shuntaro; Chen, Chuangtian; Kobayashi, Katsuyoshi; Komori, Fumio; Shin, Shik

    2017-01-01

    Spin–orbit interaction entangles the orbitals with the different spins. The spin–orbital-entangled states were discovered in surface states of topological insulators. However, the spin–orbital-entanglement is not specialized in the topological surface states. Here, we show the spin–orbital texture in a surface state of Bi(111) by laser-based spin- and angle-resolved photoelectron spectroscopy (laser-SARPES) and describe three-dimensional spin-rotation effect in photoemission resulting from spin-dependent quantum interference. Our model reveals that, in the spin–orbit-coupled systems, the spins pointing to the mutually opposite directions are independently locked to the orbital symmetries. Furthermore, direct detection of coherent spin phenomena by laser-SARPES enables us to clarify the phase of the dipole transition matrix element responsible for the spin direction in photoexcited states. These results permit the tuning of the spin polarization of optically excited electrons in solids with strong spin–orbit interaction. PMID:28232721

  12. Spin-dependent quantum interference in photoemission process from spin-orbit coupled states.

    PubMed

    Yaji, Koichiro; Kuroda, Kenta; Toyohisa, Sogen; Harasawa, Ayumi; Ishida, Yukiaki; Watanabe, Shuntaro; Chen, Chuangtian; Kobayashi, Katsuyoshi; Komori, Fumio; Shin, Shik

    2017-02-24

    Spin-orbit interaction entangles the orbitals with the different spins. The spin-orbital-entangled states were discovered in surface states of topological insulators. However, the spin-orbital-entanglement is not specialized in the topological surface states. Here, we show the spin-orbital texture in a surface state of Bi(111) by laser-based spin- and angle-resolved photoelectron spectroscopy (laser-SARPES) and describe three-dimensional spin-rotation effect in photoemission resulting from spin-dependent quantum interference. Our model reveals that, in the spin-orbit-coupled systems, the spins pointing to the mutually opposite directions are independently locked to the orbital symmetries. Furthermore, direct detection of coherent spin phenomena by laser-SARPES enables us to clarify the phase of the dipole transition matrix element responsible for the spin direction in photoexcited states. These results permit the tuning of the spin polarization of optically excited electrons in solids with strong spin-orbit interaction.

  13. Angle-resolved PED and AED calculations for different structures of the diamond C(111) surface

    NASA Astrophysics Data System (ADS)

    Niebergall, L.; Rennert, P.; Chassé, A.; Kucherenko, Yu

    1998-05-01

    Angle-resolved (AR) photoelectron diffraction (PED) spectra for electrons excited from the C 1s core state and angle-resolved KVV Auger electron diffraction (AED) spectra are calculated for the Pandey and the Tsai stucture models of diamond C(111) which extend previous investigations of the ideal structure. It is shown how to decide on the structure model by comparing PE spectra for different directions and by comparing PED and AED spectra. Calculations have been performed by evaluating the scattering path operator for a finite cluster in a curved-wave approximation. The different matrix elements for the photoelectron excitation and for the Auger process, respectively, are included. It is shown that the PED intensities are very sensitive to the surface reconstruction for polar angles in the range of 80°. In the AED intensities, polar scans in the plane perpendicular to the chain direction can be considered.

  14. Optical coherence tomography-based angle-resolved backscattering studies on bovine tendon and cartilage

    NASA Astrophysics Data System (ADS)

    Kasaragod, Deepa K.; Lu, Zenghai; Matcher, Stephen J.

    2012-01-01

    The difference in the genetic make up of the constituent molecules in collagen fibers in tendon and articular cartilage is what makes them mechanically and functionally different. A comparative study carried out on the differences in the angle-resolved back-scattering properties obtained from optical coherence tomography based studies on the two different types of scatterers: collagen I and collagen II fibers in bovine tendon and bovine articular cartilage sample, respectively, is reported here. Tendon sample shows greater anisotropy in the angle-resolved scattering profile compared to that obtained from articular cartilage sample. Rayleigh-Gans scattering approximation is used to provide the qualitative support needed to substantiate differences in the light scattering profiles obtained from the two tissues based on the size and type of the scatterers involved.

  15. Angle-resolved scattering spectroscopy of explosives using an external cavity quantum cascade laser

    SciTech Connect

    Suter, Jonathan D.; Bernacki, Bruce E.; Phillips, Mark C.

    2012-04-01

    Investigation of angle-resolved scattering from solid explosives residues on a car door for non-contact sensing geometries. Illumination with a mid-infrared external cavity quantum cascade laser tuning between 7 and 8 microns was detected both with a sensitive single point detector and a hyperspectral imaging camera. Spectral scattering phenomena were discussed and possibilities for hyperspectral imaging at large scattering angles were outlined.

  16. Quantitative analysis of angle-resolved scattering properties of ovarian tissue using optical coherence tomography

    PubMed Central

    Yang, Yi; Wang, Tianheng; Brewer, Molly

    2012-01-01

    Abstract. Angle-resolved optical scattering properties of ovarian tissue, on different optical coherence tomography (OCT) imaging planes, were quantitatively measured by fitting the compounded OCT A-lines into a single scattering model. Higher cross correlation value of angle-resolved scattering coefficients between different OCT imaging planes was found in normal ovaries than was present in malignant ovaries. The mean cross correlation coefficient (MCC) was introduced in this pilot study to characterize and differentiate normal, n=6, and malignant, n=4, ovaries. A specificity of 100 percent and a sensitivity of 100 percent were achieved by setting MCC threshold at 0.6. Collagen properties, within the OCT imaging penetration depth, were also qualitatively studied in terms of their content, structure and directivity. The homogeneous three-dimensional collagen fiber network, observed in the normal ovary, effectively explains the stronger cross correlation of angle-resolved scattering properties on different imaging planes while the heterogeneity, observed in the malignant ovary, suggests a weaker correlation. PMID:23085900

  17. A photoemission study of the diamond and the single crystal C60

    SciTech Connect

    Wu, Jin

    1994-03-01

    This report studied the elctronic structure of diamond (100) and diamond/metal interface and C60, using angle-resolved and core level photoemission. The C(100)-(2X1) surface electronic structure was studied using both core level and angle resolved valence band photoemission spectroscopy. The surface component of the C 1s core level spectrum agrees with theoretical existence of only symmetrical dimers. In the case of metal/diamond interfaces, core level and valence photoelectron spectroscopy and LEED studies WERE MADE OF B and Sb on diamond (100) and (111) surfaces. In the case of single-crystal C60, photoemission spectra show sharp molecular features, indicating that the molecular orbitals are relatively undisturbed in solid C60.

  18. Angle-resolved magnetotransport studies in anisotropic MgB2 single crystals

    NASA Astrophysics Data System (ADS)

    Pradhan, A. K.; Tokunaga, M.; Shi, Z. X.; Takano, Y.; Togano, K.; Kito, H.; Ihara, H.; Tamegai, T.

    2002-04-01

    We report the angle-resolved magnetotransport measurements on MgB2 single crystals that exhibit moderate anisotropy (γ) in upper critical fields with γ=2.6+/-0.1. Unusual ``kink'' features in resistivity are observed, which appear most clearly for field parallel to the c axis. We discuss the origin of the ``kink'' features in relation with the vortex-lattice melting and the recently proposed model of two-gap superconductivity. The influences of anisotropy on superconducting properties including the kink features are also demonstrated.

  19. Angle-Resolved Second-Harmonic Light Scattering from Colloidal Particles

    SciTech Connect

    Yang, N.; Angerer, W. E.; Yodh, A. G.

    2001-09-03

    We report angle-resolved second-harmonic generation (SHG) measurements from suspensions of centrosymmetric micron-size polystyrene spheres with surface-adsorbed dye (malachite green). The second-harmonic scattering profiles differ qualitatively from linear light scattering profiles of the same particles. We investigated these radiation patterns using several polarization configurations and particle diameters. We introduce a simple Rayleigh-Gans-Debye model to account for the SHG scattering anisotropy. The model compares favorably with our experimental data. Our measurements suggest scattering anisotropy may be used to isolate particle nonlinear optics from other bulk nonlinear optical effects in suspension.

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

    SciTech Connect

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

    2014-12-15

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

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

    PubMed

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

    2014-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    1997-03-01

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

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

    SciTech Connect

    Gubbiotti, G.; Tacchi, S.; Madami, M.; Carlotti, G.; Ding, J.; Adeyeye, A. O.

    2015-06-29

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

  4. Angle-resolved Auger electron spectra induced by neon ion impact on aluminum

    NASA Technical Reports Server (NTRS)

    Pepper, S. V.; Aron, P. R.

    1986-01-01

    Auger electron emission from aluminum bombarded with 1 to 5 keV neon ions was studied by angle-resolved electron spectroscopy. The position and shape of the spectral features depended on the incident ion energy, angle of ion incidence, and electron take-off angle with respect to the aluminum surface. These spectral dependencies were interpreted in terms of the Doppler shift given to the Auger electron velocity by the excited atom ejected into the vacuum. For oblique ion incidence it is concluded that a flux of high energy atoms are ejected in a direction close to the projection of the ion beam on the target surface. In addition, a new spectral feature was found and identified as due to Auger emission from excited neon in the aluminum matrix.

  5. A high-order harmonic generation apparatus for time- and angle-resolved photoelectron spectroscopy

    SciTech Connect

    Frietsch, B.; Gahl, C.; Teichmann, M.; Weinelt, M.; Carley, R.; Döbrich, K.; Schwarzkopf, O.; Wernet, Ph.

    2013-07-15

    We present a table top setup for time- and angle-resolved photoelectron spectroscopy to investigate band structure dynamics of correlated materials driven far from equilibrium by femtosecond laser pulse excitation. With the electron-phonon equilibration time being in the order of 1–2 ps it is necessary to achieve sub-picosecond time resolution. Few techniques provide both the necessary time and energy resolution to map non-equilibrium states of the band structure. Laser-driven high-order harmonic generation is such a technique. In our experiment, a grating monochromator delivers tunable photon energies up to 40 eV. A photon energy bandwidth of 150 meV and a pulse duration of 100 fs FWHM allow us to cover the k-space necessary to map valence bands at different k{sub z} and detect outer core states.

  6. Comparison of models and measurements of angle-resolved scatter from irregular aerosols

    NASA Astrophysics Data System (ADS)

    Milstein, Adam B.; Richardson, Jonathan M.

    2015-01-01

    We have developed and validated a method for modeling the elastic scattering properties of biological and inert aerosols of irregular shape at near- and mid-wave infrared wavelengths. The method, based on Gaussian random particles, calculates the ensemble-average optical cross section and Mueller scattering matrix, using the measured aerodynamic size distribution and previously-reported refractive index as inputs. The utility of the Gaussian particle model is that it is controlled by only two parameters (σ and Γ) which we have optimized such that the model best reproduces the full angle-resolved Mueller scattering matrices measured at λ=1.55 μm in the Standoff Aerosol Active Signature Testbed (SAAST). The method has been applied to wet-generated singlet biological spore samples, dry-generated biological spore clusters, and kaolin. The scattering computation is performed using the Discrete Dipole Approximation (DDA), which requires significant computational resources, and is thus implemented on LLGrid, a large parallel grid computer. For the cases presented, the best fit Gaussian particle model is in good qualitative correspondence with microscopy images of the corresponding class of particles. The measured and computed cross sections agree well within a factor of two overall, with certain cases bearing closer correspondence. In particular, the DDA reproduces the shape of the measured scatter function more accurately than Mie predictions. The DDA-computed depolarization factors are also in good agreement with measurement.

  7. Diversification of nanostructure morphology by modifying angle-resolved heterogeneous shadow mask.

    PubMed

    Wang, Chaoguang; Wu, Xuezhong; Dong, Peitao; Wang, Junfeng; Di, Di; Chen, Jian; Wang, Haoxu

    2013-12-01

    This article presents a facile and generally applicable methodology for the morphology diversification of two-dimensional (2D) nanostructure arrays by modifying angle-resolved heterogeneous shadow mask (AR-HSM). Colloid spheres are used to prepare scalable well-organized monolayer film by self-assembly method and then etched in oxygen plasma to reduce size. Subsequently, the heterogeneous layer is generated by tilted metal deposition technique, then utilized as shadow mask in the substrate etching process, and finally removed by wet etching technique. As a result, the controllable fabrication of a series of complex morphologies, ranging from the crescent structure to the hoof-like structure and the stripes with apexes, is realized. The morphology of the nanostructure array is depend on the profile of the heterogeneous shadow mask (HSM) which is correlated to the incidence angle of the metal vapor. Therefore, a theoretical model is built for the prediction and design of the nanostructure morphology. This AR-HSM aided approach provides a novel and accessible route for the diversification of nanostructure morphology; and can be readily extended to other functional substrates which may be applied in photovoltaic devices or bio-chemical sensors.

  8. High resolution spin- and angle-resolved photoelectron spectroscopy for 3D spin vectorial analysis

    NASA Astrophysics Data System (ADS)

    Okuda, Taichi; Miyamoto, Koji; Kimura, Akio; Namatame, Hirofumi; Taniguchi, Masaki

    2013-03-01

    Spin- and angle-resolved photoelectron spectroscopy (SARPES) is the excellent tool which can directly observe the band structure of crystals with separating spin-up and -down states. Recent findings of new class of materials possessing strong spin orbit interaction such as Rashba spin splitting systems or topological insulators stimulate to develop new SARPES apparatuses and many sophisticated techniques have been reported recently. Here we report our newly developed a SARPES apparatus for spin vectorial analysis with high precision at Hiroshima Synchrotron Radiation Center. Highly efficient spin polarimeter utilizing very low energy electron diffraction (VLEED) makes high resolution (ΔE < 10 meV, Δθ ~ +/- 0.2 °) compatible with the SARPES measurement. By placing two VLEED spin detectors orthogonally we have realized the polarization measurement of all spin components (x, y and z) with the high resolution. Some examples of the three-dimensional spin observation will be presented. This work is supported by KAKENHI (23244066), Grant-in-Aid for Scientific Research (A) of Japan Society for the Promotion of Science.

  9. Identifying ferroelectric phase and domain structure using angle-resolved piezoresponse force microscopy

    SciTech Connect

    Kim, K. L.; Huber, J. E.

    2014-03-24

    We used angle-resolved piezoresponse force microscopy (AR-PFM), vertical PFM (VPFM), and electron backscatter diffraction (EBSD) to provide a systematic interpretation of domain patterns in polycrystalline, near-morphotropic lead zirconate titanate. This material was used to illustrate the power of AR-PFM methods in resolving complex domain patterns where multiple phases may be present. AR-PFM was carried out with a 30° rotation interval, and the resulting data were analysed to identify the orientation of the underlying axis of piezoelectricity. The additional information provided by AR-PFM was studied, comparing its capabilities to those of 3-dimensional PFM, consisting of one VPFM image and two orthogonal lateral PFM (LPFM) images. We show that, in certain conditions, using AR-PFM can identify the phases present at the sub-grain scale. This was confirmed using VPFM and EBSD data. Furthermore, the method can discriminate laminated domain patterns that appear similar in VPFM and can reliably expose domain patterns that may not be seen in LPFM data from a single orientation, or even in 3D PFM data.

  10. Mapping of ferroelectric domain structure using angle-resolved piezoresponse force microscopy

    SciTech Connect

    Kim, K. L.; Huber, J. E.

    2015-01-15

    Angle-resolved piezoresponse force microscopy (AR-PFM) was used in conjunction with electron backscatter diffraction (EBSD) to study ferroelectric domain structure in polycrystalline near-morphotropic lead zirconate titanate (PZT). We introduce the details of AR-PFM including experimental method, the process to generate AR-PFM maps, and the interpretation of AR-PFM map, using domain patterns observed in bulk PZT. The spatial distortion caused by scanner creep and non-linearity in scanning probe microscopy was corrected through image registration, taking advantage of the features present in topography images. Domain structures were mapped using AR-PFM data, and the maps consistently show alternating piezoresponse axes in a lamellar pattern of non-180° domain structure. Comparison of AR-PFM and EBSD data showed a discrepancy between the direction of lateral surface displacement and the in-plane polarization direction. Additionally, using suitable domain patterns, AR-PFM enabled discrimination between the tetragonal and rhombohedral phases at the sub-grain scale.

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

    SciTech Connect

    Menchero, Jose Gabriel

    1997-05-01

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

  12. Development of a portable frequency-domain angle-resolved low coherence interferometry system

    NASA Astrophysics Data System (ADS)

    Pyhtila, John W.; Wax, Adam

    2007-02-01

    Improved methods for detecting dysplasia, or pre-cancerous growth, are a current clinical need. Random biopsy and subsequent diagnosis through histological analysis is the current gold standard in endoscopic surveillance for dysplasia. However, this approach only allows limited examination of the at-risk tissue and has the drawback of a long delay in time-to-diagnosis. In contrast, optical scattering spectroscopy methods offer the potential to assess cellular structure and organization in vivo, thus allowing for instantaneous diagnosis and increased coverage of the at-risk tissue. Angle-resolved low coherence interferometry (a/LCI), a novel scattering spectroscopy technique, combines the ability of low-coherence interferometry to isolate scattered light from sub-surface tissue layers with the ability of light scattering spectroscopy to obtain structural information on sub-wavelength scales, specifically by analyzing the angular distribution of the backscattered light. In application to examining tissue, a/LCI enables depthresolved quantitative measurements of changes in the size and texture of cell nuclei, which are characteristic biomarkers of dysplasia. The capabilities of a/LCI were demonstrated initially by detecting pre-cancerous changes in epithelial cells within intact, unprocessed, animal tissues. Recently, we have developed a new frequency-domain a/LCI system, with sub-second acquisition time and a novel fiber optic probe. Preliminary results using the fa/LCI system to examine human esophageal tissue in Barrett's esophagus patients demonstrate the clinical viability of the approach. In this paper, we present a new portable system which improves upon the design of the fa/LCI system to allow for higher quality data to be collected in the clinic. Accurate sizing of polystyrene microspheres and cell nuclei from ex vivo human esophageal tissue is presented. These results demonstrate the promise of a/LCI as a clinically viable diagnostic tool.

  13. Multiphoton electron emission from Cu and W: An angle-resolved study

    SciTech Connect

    Damascelli, A.; Gabetta, G.; Lumachi, A.; Fini, L.; Parmigiani, F.

    1996-09-01

    The experimental results of multiphoton electron emission from Cu and W induced by 2-eV 100-fs laser pulses with {ital s} and {ital p} polarizations at incidence angles between 0{degree} and 85{degree} and different intensities are reported. The data show a third-order nonlinear photoemission process for Cu and a fourth-order behavior for W. For both metals the electron emission is higher for the polarization in the incidence plane, with a maximum value at the pseudo-Brewster angle, while the electron yield as a function of the incidence angle exhibits an unambiguous dependence on the bulk absorption coefficient and it can be accounted for on the basis of the Fresnel equations. {copyright} {ital 1996 The American Physical Society.}

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

    NASA Astrophysics Data System (ADS)

    Fujimori, Shin-ichi

    2016-04-01

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

  15. Developing a clinically viable angle-resolved low coherence interferometry optical biopsy system

    NASA Astrophysics Data System (ADS)

    Pyhtila, John W.

    2007-12-01

    Non-invasive optical biopsy techniques, which interrogate tissue in situ, offer a potential method to improve the detection of dysplasia, a pre-cancerous tissue state. Specifically, monitoring of Barrett's esophagus (BE) patients for dysplasia, currently done through systematic biopsy, can be improved by increasing the proportion of at-risk tissue examined. Angle-resolved low coherence interferometry (a/LCI) is an optical spectroscopic technique which measures the depth resolved nuclear morphology of tissue, a key biomarker for identifying dysplasia. Using an animal carcinogenesis model, it was shown that a/LCI can detect dysplasia with great sensitivity and specificity. However, for the clinical application of a/LCI, numerous hurdles must be overcome. This dissertation presents the development of three new a/LCI systems which incrementally address the three main obstacles preventing the clinical application of a/LCI. First, data acquisition time is reduced by implementing a frequency-domain detection scheme using an imaging spectrograph that collects the complete depth resolved angular scattering distribution in parallel. This advance reduces data collection time to a clinically acceptable 40 ms. Second, a fiber probe is developed to enable the endoscopic application of a/LCI. The probe incorporates a single fiber for delivering light and a coherent fiber bundle for collecting the angular distribution of scattered light. Third, a portable device is created through miniaturization of the optical design, and a flexible fiber probe is created using polarization maintaining fiber to deliver the light. These advances allow for the clinical application of the system to ex vivo human tissue samples. The performance of each described system is evaluated through a number of validation studies, including the sizing of polystyrene microspheres, a typical model used in light scattering studies, and the measurement of in vitro cell nuclear diameters, accomplished with sub

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

    PubMed

    Fujimori, Shin-ichi

    2016-04-20

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

  17. Clinical detection of dysplasia using angle-resolved low coherence interferometry

    NASA Astrophysics Data System (ADS)

    Terry, Neil Gordon

    2011-12-01

    Cancer is now the leading cause of death in developed countries. Despite advances in strategies aimed at the prevention and treatment of the disease, early detection of precancerous growths remains the most effective method of reducing associated morbidity and mortality. Pathological examination of physical tissues that are collected via systematic biopsy is the current "gold standard" in this pursuit. Despite widespread acceptance of this methodology and high confidence in its performance, it is not without limitations. Recently, much attention has been given to the development of optical biopsy techniques that can be used clinically and are able to overcome these limitations. This dissertation describes one such optical biopsy technique, angle-resolved low coherence interferometry (a/LCI), its adaptation to a clinical technology, and its evaluation in clinical studies. The dissertation presents the theory that underlies the operation of the a/LCI technique, the design and validation of the clinical instrument, and its evaluation by means of two clinical trials. First, an account of the manner in which the depth-resolved angular scattering profiles that are collected by a/LCI can be used to determine nuclear characteristics of the investigated tissues is given. The design of the clinical system that is able to collect these scattering profiles through an optical fiber probe that can be passed through the accessory channel of an endoscope for in vivo use is presented. To demonstrate the ability of this system to accurately determine the size of cell nuclei, a set of validation experiments are described. In order to evaluate the clinical utility of this a/LCI system, two clinical trials intended to assess the ability of a/LCI to detect the presence of early, pre-cancerous dysplasias in human tissues are presented. The first of these, an in vivo study of Barrett's esophagus (BE) patients undergoing routine surveillance for the early signs of esophageal adenocarcinoma

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

    NASA Astrophysics Data System (ADS)

    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. .

  19. Theory of probing attosecond electron wave packets via two-path interference of angle-resolved photoelectrons

    SciTech Connect

    Choi, N. N.; Jiang, T. F.; Morishita, T.; Lee, M.-H.; Lin, C. D.

    2010-07-15

    We study theoretically the electron wave packet generated by an attosecond pulse train (APT) which is probed with a time-delayed infrared (IR) laser pulse. The APT creates an excited state and a continuum electron wave packet. By ionizing the excited state with an IR, a delayed new continuum electron wave packet is created. The interference of the wave packets from the two paths, as reflected in angle-resolved photoelectron spectra, is analyzed analytically. Using the analytical expressions, we examine the possibility of retrieving information on the electron wave packet generated by the APT.

  20. Near E{sub F} Electronic Structure of Graphite from Photoemission and Inverse Photoemission Studies

    SciTech Connect

    Sekhar, B. R.; Kundu, R.; Mishra, P.; Maniraj, M.; Barman, S. R.

    2011-10-20

    A comparative study of the electronic band structure of single crystal and highly oriented pyrolitic graphite is presented. We have used angle resolved photoelectron spectroscopy and angle resolved inverse photoelectron spectroscopy to map the occupied and unoccupied electronic states respectively.

  1. Widespread spin polarization effects in photoemission from topological insulators

    SciTech Connect

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

    2011-06-22

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

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

    PubMed

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

    2016-03-01

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

  3. Quantifying electronic band interactions in van der Waals materials using angle-resolved reflected-electron spectroscopy

    PubMed Central

    Jobst, Johannes; van der Torren, Alexander J. H.; Krasovskii, Eugene E.; Balgley, Jesse; Dean, Cory R.; Tromp, Rudolf M.; van der Molen, Sense Jan

    2016-01-01

    High electron mobility is one of graphene's key properties, exploited for applications and fundamental research alike. Highest mobility values are found in heterostructures of graphene and hexagonal boron nitride, which consequently are widely used. However, surprisingly little is known about the interaction between the electronic states of these layered systems. Rather pragmatically, it is assumed that these do not couple significantly. Here we study the unoccupied band structure of graphite, boron nitride and their heterostructures using angle-resolved reflected-electron spectroscopy. We demonstrate that graphene and boron nitride bands do not interact over a wide energy range, despite their very similar dispersions. The method we use can be generally applied to study interactions in van der Waals systems, that is, artificial stacks of layered materials. With this we can quantitatively understand the ‘chemistry of layers' by which novel materials are created via electronic coupling between the layers they are composed of. PMID:27897180

  4. Quantifying electronic band interactions in van der Waals materials using angle-resolved reflected-electron spectroscopy

    NASA Astrophysics Data System (ADS)

    Jobst, Johannes; van der Torren, Alexander J. H.; Krasovskii, Eugene E.; Balgley, Jesse; Dean, Cory R.; Tromp, Rudolf M.; van der Molen, Sense Jan

    2016-11-01

    High electron mobility is one of graphene's key properties, exploited for applications and fundamental research alike. Highest mobility values are found in heterostructures of graphene and hexagonal boron nitride, which consequently are widely used. However, surprisingly little is known about the interaction between the electronic states of these layered systems. Rather pragmatically, it is assumed that these do not couple significantly. Here we study the unoccupied band structure of graphite, boron nitride and their heterostructures using angle-resolved reflected-electron spectroscopy. We demonstrate that graphene and boron nitride bands do not interact over a wide energy range, despite their very similar dispersions. The method we use can be generally applied to study interactions in van der Waals systems, that is, artificial stacks of layered materials. With this we can quantitatively understand the `chemistry of layers' by which novel materials are created via electronic coupling between the layers they are composed of.

  5. Si(111)(\\sqrt{3}× \\sqrt{3})-Al Surface Studied by Angle-Resolved Electron-Energy-Loss Spectroscopy

    NASA Astrophysics Data System (ADS)

    Li, Sung-Te; Hasegawa, Shigehiko; Nakamura, Shogo; Nakashima, Hisao

    1991-09-01

    The surface electronic structures of Si(111)(\\sqrt{3}× \\sqrt{3})-Al are investigated with the use of angle-resolved electron-energy-loss spectroscopy. Three new surface one-electron transitions (in specular reflection) are found at 1.8, 7.2, and 13.1 eV. Compared with the surface state band structures calculated by Northrup and STM results by Hamers and Demuth, the loss peak at 1.8 eV is ascribed to the one-electron transition between the occupied and unoccupied surface state bands which originate from the Al adatoms. The other two peaks are considered to be due to the Si-Si strained back bonds.

  6. Elasticity of Tantalum to 105 Gpa using a stress and angle-resolved x-ray diffraction

    SciTech Connect

    Cynn, H; Yoo, C S

    1999-08-11

    Determining the mechanical properties such as elastic constants of metals at Mbar pressures has been a difficult task in experiment. Following the development of anisotropic elastic theory by Singh et al. [l], Mao et a1.[2] have recently developed a novel experimental technique to determine the elastic constants of Fe by using the stress and energy-dispersive x-ray diffraction (SEX). In this paper, we present an improved complementary technique, stress and angle-resolved x-ray diffraction (SAX), which we have applied to determine the elastic constants of tantalum to 105 GPa. The extrapolation of the tantalum elastic data shows an excellent agreement with the low-pressure ultrasonic data [3]. We also discuss the improvement of this SAX method over the previous SEX. [elastic constant, anisotropic elastic theory, angle-dispersive synchrotron x-ray diffraction, mechanical properties

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

    PubMed

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

    2014-05-28

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

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

    PubMed Central

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

    2014-01-01

    Two-dimensional angle-resolved light scattering maps of individual rod-shaped bacteria are measured at the single-cell level. Using quantitative phase imaging and Fourier transform light scattering techniques, the light scattering patterns of individual bacteria in four rod-shaped species (Bacillus subtilis, Lactobacillus casei, Synechococcus elongatus, and Escherichia coli) are measured with unprecedented sensitivity in a broad angular range from −70° to 70°. The measured light scattering patterns are analyzed along the two principal axes of rod-shaped bacteria in order to systematically investigate the species-specific characteristics of anisotropic light scattering. In addition, the cellular dry mass of individual bacteria is calculated and used to demonstrate that the cell-to-cell variations in light scattering within bacterial species is related to the cellular dry mass and growth. PMID:24867385

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

  10. High-energy angle resolved reflection spectroscopy on three-dimensional photonic crystals of self-organized polymeric nanospheres.

    PubMed

    Schutzmann, S; Venditti, I; Prosposito, P; Casalboni, M; Russo, M V

    2008-01-21

    We report on the optical characterization of three-dimensional opal-like photonic crystals made by self-organized nanospheres of poly[styrene-(co-2-hydroxyethyl methacrylate)] having a face centred cubic (fcc) structure oriented along the [111] direction. A detailed optical characterization of the samples is presented using angle resolved reflection spectroscopy in specular geometry. The investigated energies are between a/lambda=0.5 and a/lambda=1.5 (where a is the lattice parameter and lambda is the light wavelength), a region in which both first and second-order Bragg diffraction are expected. Some interesting features as branching of the Bragg peak dispersion and high energy reflection peaks are revealed. We compare the experimental data with theoretical calculations using both Bragg diffraction and band structure approach. A comparison with recent results reported in the literature is also presented.

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

    PubMed Central

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

    2015-01-01

    The spectral specular reflectance of conventional and novel reflective materials for solar concentrators is measured with an acceptance angle of 17.5 mrad over the wavelength range 300−2500 nm at incidence angles 15–60° using a spectroscopic goniometry system. The same experimental setup is used to determine the spectral narrow-angle transmittance of semi-transparent materials for solar collector covers at incidence angles 0–60°. In addition, the angle-resolved surface scattering of reflective materials is recorded by an area-scan CCD detector over the spectral range 350–1050 nm. A comprehensive summary, discussion, and interpretation of the results are included in the associated research article “Spectral reflectance, transmittance, and angular scattering of materials for solar concentrators” in Solar Energy Materials and Solar Cells. PMID:26862556

  12. Spin-Resolved Photoemission of Surface States of W(110)-(1×1)H

    NASA Astrophysics Data System (ADS)

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

    2002-11-01

    The surface electronic states of W(110)-(1×1)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% 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¯ symmetry point. In contrast, no measurable polarization of nearby bulk states is observed.

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

    SciTech Connect

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

    2007-11-29

    Morphology- and layer-dependent electronic structure and dynamics at the PTCDA/Ag(111) interface have been studied with angle-resolved two-photon photoemission. In Stranski-Krastanov growth modes, the exposed wetting layer inhibited the evolution of the vacuum level and valence band to bulk values. For layer-by-layer growth, we observed the transition of electron structure from monolayer to bulk values within eight monolayers. Effective masses and lifetimes of the conduction band and the n=1 image potential state were measured to be larger for disordered layers. The effective mass was interpreted in the context of charge mobility measurements.

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

    SciTech Connect

    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.

  15. Probing quasiparticle states in strongly interacting atomic gases by momentum-resolved Raman photoemission spectroscopy

    NASA Astrophysics Data System (ADS)

    Dao, Tung-Lam; Carusotto, Iacopo; Georges, Antoine

    2009-08-01

    We investigate a momentum-resolved Raman spectroscopy technique which is able to probe the one-body spectral function and the quasiparticle states of a gas of strongly interacting ultracold atoms. This technique is inspired by angle-resolved photoemission spectroscopy, a powerful experimental probe of electronic states in solid-state systems. Quantitative examples of experimentally accessible spectra are given for the most significant regimes along the BEC-BCS crossover. When the theory is specialized to rf spectroscopy, agreement is found with recent experimental data. The main advantages of this Raman spectroscopy over existing techniques are pointed out.

  16. Signature of polaron formation in Na0.025WO3: Photoemission and X-ray diffraction investigations

    NASA Astrophysics Data System (ADS)

    Paul, Sanhita; Ghosh, Anirudha; Raj, Satyabrata

    2013-06-01

    We have carried out temperature dependent high-resolution angle-resolved photoemission spectroscopy and x-ray diffraction studies on non-stoichiometric sodium tungsten bronzes (NaxWO3 for x=0.025). Our photoemission investigation shows evidence for polaron formation at the valence band edge and the photoemission spectra collected in different modes of the electron analyzer suggest that the density of states at valence band edge gradually moves to other k-points in the Brillouin zone with increasing temperature and explain the dynamics of polaron formation in Na0.025WO3. Infact our x-ray diffraction measurements reveal a structural modification of Na0.025WO3 around 230K. The corner sharing WO6 octadedra gets sufficiently distorted at low temperature due to displacement of tugsten and oxygen atoms from their mean position. This structural modification induces polaron formation in Na0.025WO3 below 230K.

  17. Orbital-differentiated coherence-incoherence crossover identified by photoemission spectroscopy in LiFeAs

    NASA Astrophysics Data System (ADS)

    Miao, H.; Yin, Z. P.; Wu, S. F.; Li, J. M.; Ma, J.; Lv, B.-Q.; Wang, X. P.; Qian, T.; Richard, P.; Xing, L.-Y.; Wang, X.-C.; Jin, C. Q.; Haule, K.; Kotliar, G.; Ding, H.

    2016-11-01

    In iron-based superconductors (FeSCs), orbital differentiation is an important phenomenon, whereby correlations stronger on the dx y orbital than on the dx z/dy z orbital yield quasiparticles with a dx y orbital character having larger mass renormalization and an abnormal temperature evolution. However, the physical origin of this orbital differentiation is debated between the Hund's coupling-induced unbinding of spin and orbital degrees of freedom and the Hubbard interaction instigated orbital-selective Mott transition. Here we use angle-resolved photoemission spectroscopy to identify an orbital-dependent correlation-induced quasiparticle (QP) anomaly in LiFeAs. The excellent agreement between our photoemission measurements and first-principles many-body theory calculations shows that the orbital-differentiated QP lifetime anomalies in LiFeAs are controlled by the Hund's coupling.

  18. Orbital-differentiated coherence-incoherence crossover identified by photoemission spectroscopy in LiFeAs

    DOE PAGES

    Miao, H.; Yin, Z. P.; Wu, S. F.; ...

    2016-11-14

    In the iron-based superconductors (FeSCs), orbital differentiation is an important phenomenon, whereby correlations stronger on the dxy orbital than on the dxz/dyz orbital yield quasi-particles with dxy orbital character having larger mass renormalization and abnormal temperature evolution. However, the physical origin of this orbital di erentiation is debated between the Hund's coupling induced unbinding of spin and orbital degrees of freedom and the Hubbard interaction instigated orbital selective Mott transition. Here we use angle-resolved photoemission spectroscopy to identify an orbital-dependent correlation-induced quasi-particle (QP) anomaly in LiFeAs. Lastly, the excellent agreement between our photoemission measurements and first-principles many-body theory calculations showsmore » that the orbital-differentiated QP lifetime anomalies in LiFeAs are controlled by the Hund's coupling.« less

  19. Orbital-differentiated coherence-incoherence crossover identified by photoemission spectroscopy in LiFeAs

    SciTech Connect

    Miao, H.; Yin, Z. P.; Wu, S. F.; Li, J. M.; Ma, J.; Lv, B. -Q.; Wang, X. P.; Qian, T.; Richard, P.; Xing, L. -Y.; Wang, X. -C.; Jin, C. Q.; Haule, K.; Kotliar, G.; Ding, H.

    2016-11-14

    In the iron-based superconductors (FeSCs), orbital differentiation is an important phenomenon, whereby correlations stronger on the dxy orbital than on the dxz/dyz orbital yield quasi-particles with dxy orbital character having larger mass renormalization and abnormal temperature evolution. However, the physical origin of this orbital di erentiation is debated between the Hund's coupling induced unbinding of spin and orbital degrees of freedom and the Hubbard interaction instigated orbital selective Mott transition. Here we use angle-resolved photoemission spectroscopy to identify an orbital-dependent correlation-induced quasi-particle (QP) anomaly in LiFeAs. Lastly, the excellent agreement between our photoemission measurements and first-principles many-body theory calculations shows that the orbital-differentiated QP lifetime anomalies in LiFeAs are controlled by the Hund's coupling.

  20. Electronic and spin structures of solids investigated by means of synchrotron radiation photoemission

    NASA Astrophysics Data System (ADS)

    Taniguchi, M.; Iwasawa, H.; Miyamoto, K.; Okuda, T.

    2013-12-01

    Recent progress in research on electronic and spin structures of solids and instrumentation on spin-resolved photoemission at Hiroshima Synchrotron Radiation Center are reported. The fine details of electron dynamics of a typical multiband superconductor Sr2RuO4 were uncovered by high-resolution angle-resolved photoemission spectroscopy (ARPES) with tunable polarizations, and the surface of W(1 1 0) was found to have a Dirac-corn-like state of d character with nearly massless energy dispersion by high-resolution ARPES and spin-resolved ARPES (SARPES). The SARPES system with very low energy electron diffraction spin detector and modified VG-SCIENTA R4000 electron analyzer brought a breakthrough in spin detection efficiency as well as energy and angular resolution, and enables precise SARPES measurements for materials that require high energy and angular resolution.

  1. Anisotropic Superconducting Gap Revealed by Angle Resolved Specific Heat, Point Contact Tunneling and Scanning Tunneling Microscope in Iron Pnictide Superconductors

    NASA Astrophysics Data System (ADS)

    Wen, Hai-Hu

    2011-03-01

    Angle resolved specific heat was measured in FeSe 0.55 Te 0.45 single crystals. A four-fold oscillation of C/T, with the minimum locating at the Fe-Fe bond direction, was observed when the sample was rotated at 9 T, which can be understood as due to the gap modulation on the electron pocket within the scheme of S +/- pairing. Accordingly, by measuring the point contact Andreev reflection spectrum on the BaFe 2-x Ni x As 2 single crystals in wide doping regimes, we found a crossover from nodeless to nodal feature of the superconducting gap. In K-doped BaFe 2 As 2 single crystals, we performed the low temperature STM measurements and observed a well ordered vortex lattice in local region. In addition, the statistics on over 3000 dI/dV spectra illustrate clear evidence of two gaps with magnitude of 7.6 meV and 3.3 meV, respectively. Detailed fitting to the tunneling spectrum shows an isotropic superconducting gap. Work collaborated with B. Zeng, C. Ren, L. Shan, Y. L. Wang, B. Shen, G. Mu, H. Q. Luo, T. Xiang, H. Yang, I. I. Mazin and P. C. Dai. This work was supported by the Natural Science Foundation of China, the Ministry of Science and Technology of China (2011CB605900, No. 2006CB921802), and Chinese Academy of Sciences. IIM was supported by the Office of the Naval Research.

  2. Atomic Auger decay in core-excited HBr by angle-resolved two-dimensional photoelectron spectroscopy

    SciTech Connect

    Feng, Ximao; Wills, Antony A.; Wiedenhoeft, Marco; Berrah, Nora; Sokell, Emma

    2006-01-15

    Angle-resolved two-dimensional photoelectron spectroscopy has been used to study HBr in the vicinity of the Br 3d ionization thresholds. The energy positions of the two 3d{sub 5/2,3/2}{yields}{sigma}{sup *} resonances have been measured directly and found to be at 70.89(6) eV and 71.92(6) eV, respectively, giving a spin-orbit splitting of 1.03(3) eV for the two Br 3d components. Br Auger lines (26 eV

  3. A universal high energy anomaly in angle resolved photoemissionspectra of high temperature superconductors -- possible evidence ofspinon and holon branches

    SciTech Connect

    Graf, J.; Gweon, G.-H.; McElroy, K.; Zhou, S.Y.; Jozwiak, C.; Rotenberg, E.; Bill, A.; Sasagawa, T.; Eisaki, H.; Uchida, S.; Takagi,H.; Lee, D.-H.; Lanzara A.

    2006-12-19

    A universal high energy anomaly in the single particlespectral function is reported in three different families of hightemperature superconductors by using angle-resolved photoemissionspectroscopy. As we follow the dispersing peak of the spectral functionfrom the Fermi energy to the valence band complex, we find dispersionanomalies marked by two distinctive high energy scales, E_1 approx 0.38eV and E_2 approx 0.8 eV. E_1 marks the energy above which the dispersionsplits into two branches. One is a continuation of the near parabolicdispersion, albeit with reduced spectral weight, and reaches the bottomof the band at the Gamma point at approx 0.5 eV. The other is given by apeak in the momentum space, nearly independent of energy between E_1 andE_2. Above E_2, a band-like dispersion re-emerges. We conjecture thatthese two energies mark the disintegration of the low energyquasiparticles into a spinon and holon branch in the high T_c cuprates.

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

    PubMed

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

    2014-10-28

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

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

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

    PubMed

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

    2016-05-01

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

  7. Label-free, high-throughput measurements of dynamic changes in cell nuclei using angle-resolved low coherence interferometry.

    PubMed

    Chalut, Kevin J; Chen, Sulin; Finan, John D; Giacomelli, Michael G; Guilak, Farshid; Leong, Kam W; Wax, Adam

    2008-06-01

    Accurate measurements of nuclear deformation, i.e., structural changes of the nucleus in response to environmental stimuli, are important for signal transduction studies. Traditionally, these measurements require labeling and imaging, and then nuclear measurement using image analysis. This approach is time-consuming, invasive, and unavoidably perturbs cellular systems. Light scattering, an emerging biophotonics technique for probing physical characteristics of living systems, offers a promising alternative. Angle-resolved low-coherence interferometry (a/LCI), a novel light scattering technique, was developed to quantify nuclear morphology for early cancer detection. In this study, a/LCI is used for the first time to noninvasively measure small changes in nuclear morphology in response to environmental stimuli. With this new application, we broaden the potential uses of a/LCI by demonstrating high-throughput measurements and by probing aspherical nuclei. To demonstrate the versatility of this approach, two distinct models relevant to current investigations in cell and tissue engineering research are used. Structural changes in cell nuclei due to subtle environmental stimuli, including substrate topography and osmotic pressure, are profiled rapidly without disrupting the cells or introducing artifacts associated with traditional measurements. Accuracy > or = 3% is obtained for the range of nuclear geometries examined here, with the greatest deviations occurring for the more complex geometries. Given the high-throughput nature of the measurements, this deviation may be acceptable for many biological applications that seek to establish connections between morphology and function.

  8. Inverse-Photoemission Spectroscopy of Iron Oxides, Silver

    NASA Astrophysics Data System (ADS)

    Kim, Bongsoo

    1990-01-01

    I measured the inverse-photoemission spectra (IPES) of iron oxides grown on an Fe substrate, and calculated the band structure of paramagnetic FeO to analyze the IPES. The band calculation showed some overlap between Fe _3_{rm d} states and O_2_{rm p} states in the region of occupied states, and s,p-like states of Fe in the unoccupied region. Isochromatic IPES showed structures at ~2.5 eV and ~7.5 eV above the Fermi energy. I estimate the full band gap of FeO as 2.5 eV from the IPES data. Angle-resolved inverse-photoemission spectra (ARIPES) have been measured on single-crystal Ag. The results are compared with the predictions of bulk band-structure theory and a free-electron model. The latter gives good agreement for the structure with a final state near the Fermi energy. Band theory is needed for the structure 17 eV above the Fermi energy. This structure is very nondispersive, indicating the existence of a very flat band throughout the IXUL plane.

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

    NASA Astrophysics Data System (ADS)

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

    2016-01-01

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

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

    SciTech Connect

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

    2016-01-22

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

  11. Spin Polarization and Attosecond Time Delay in Photoemission from Spin Degenerate States of Solids.

    PubMed

    Fanciulli, Mauro; Volfová, Henrieta; Muff, Stefan; Braun, Jürgen; Ebert, Hubert; Minár, Jan; Heinzmann, Ulrich; Dil, J Hugo

    2017-02-10

    After photon absorption, electrons from a dispersive band of a solid require a finite time in the photoemission process before being photoemitted as free particles, in line with recent attosecond-resolved photoemission experiments. According to the Eisenbud-Wigner-Smith model, the time delay is due to a phase shift of different transitions that occur in the process. Such a phase shift is also at the origin of the angular dependent spin polarization of the photoelectron beam, observable in spin degenerate systems without angular momentum transfer by the incident photon. We propose a semiquantitative model which permits us to relate spin and time scales in photoemission from condensed matter targets and to better understand spin- and angle-resolved photoemission spectroscopy (SARPES) experiments on spin degenerate systems. We also present the first experimental determination by SARPES of this time delay in a dispersive band, which is found to be greater than 26 as for electrons emitted from the sp-bulk band of the model system Cu(111).

  12. Spin Polarization and Attosecond Time Delay in Photoemission from Spin Degenerate States of Solids

    NASA Astrophysics Data System (ADS)

    Fanciulli, Mauro; Volfová, Henrieta; Muff, Stefan; Braun, Jürgen; Ebert, Hubert; Minár, Jan; Heinzmann, Ulrich; Dil, J. Hugo

    2017-02-01

    After photon absorption, electrons from a dispersive band of a solid require a finite time in the photoemission process before being photoemitted as free particles, in line with recent attosecond-resolved photoemission experiments. According to the Eisenbud-Wigner-Smith model, the time delay is due to a phase shift of different transitions that occur in the process. Such a phase shift is also at the origin of the angular dependent spin polarization of the photoelectron beam, observable in spin degenerate systems without angular momentum transfer by the incident photon. We propose a semiquantitative model which permits us to relate spin and time scales in photoemission from condensed matter targets and to better understand spin- and angle-resolved photoemission spectroscopy (SARPES) experiments on spin degenerate systems. We also present the first experimental determination by SARPES of this time delay in a dispersive band, which is found to be greater than 26 as for electrons emitted from the sp-bulk band of the model system Cu(111).

  13. A display-type analyzer with an image-processing system for angle-resolved photoelectron spectroscopy

    NASA Astrophysics Data System (ADS)

    Rieger, D.; Schnell, R. D.; Steinmann, W.; Saile, V.

    1983-04-01

    A two-dimensional, multi-angle energy analyzer for photoemission spectroscopy has been developed which consists of an ellipsoidal mirror low pass filter, a retarding field high pass filter, CEMA plates as an area detector and a rapid image processing system for data acquisition. With this analyzer, angular distribution pictures within a cone of 88° at a fixed energy ( ΔE=0.28 eV resolution) can be taken with an angular resolution of δθ=±1.5° and a signal-to-noise ratio of 50-100 in a time of 9s. First results of Ag(111) and GeS(100) are reported.

  14. Angle Resolved Photoelectron and Auger Electron Diffraction as a Structural Probe for Surfaces, Interfaces, and Epitaxial Films.

    NASA Astrophysics Data System (ADS)

    Li, Hong

    The recently developed techniques of angle-resolved photoelectron and Auger electron diffraction (ARXPD/AED) have shown promise in identifying the structures of epitaxial films. This is due to the realization that electrons scattered by other atoms are enhanced along the forward direction. In this dissertation research, we have further investigated the capabilities of the ARXPD/AED technique. First, the complete polar angle distribution of the Auger electron intensity from Cu(001) was measured from the (100) to the (110) azimuth. The presentation of the ARAED in the form of a contour map clearly shows the relationship of the constructive and destructive interference of electron scattering to the crystallographic index of the crystal. Secondly, the angular distributions of electron emissions with initial states of 3p, 3d, 4d, and the Auger emission with electron kinetic energies ranging from 348 eV to 1477 eV were measured for single crystal Ag(001). The results show that all of these electron emissions have similar electron forward scattering enhancements along the directions of nearest and next nearest neighbour atoms in the crystal. The forward scattering enhancements do not shift as the electron kinectic energy changes. The ARXPD/AED combined with low energy electron diffraction (LEED) has been demonstrated to be a very powerful technique in probing both the long range order and the short range order of the epitaxial films. The epitaxial films studied include Co on Cu(001), Fe on Ag(001), Co on Ag(001), and Co on an ultra-thin film of Fe(001), which was epitaxially grown on Ag(001). We find that up to 20 ML thickness of high quality metastable fcc Co can be stabilized on Cu(001) at room temperature. We have directly verified that the Fe on Ag(001) is bcc. The Co on Ag(001) is neither bcc nor fcc for coverages of less than 3 ML. Thick films of Co on Ag(001) are disordered, of which a very small portion has a local structure of bcc. The bcc Co phases has been

  15. Does the influence of substituents impact upon the surface composition of pyrrolidinium-based ionic liquids? An angle resolved XPS study.

    PubMed

    Men, Shuang; Hurisso, Bitu Birru; Lovelock, Kevin R J; Licence, Peter

    2012-04-21

    The surface chemistry of a series of four pyrrolidinium based ionic liquids, [C(n)C(1)Pyrr][Tf(2)N] where n = 4-10, is investigated by angle resolved X-ray photoelectron spectroscopy (ARXPS). The importance of sample purity is demonstrated and the stability of the ionic liquids under X-ray irradiation investigated. It is apparent that the surface chemistry and orientation is broadly analogous to that of similar imidazolium-based systems.

  16. Two-Photon Photoemission Study of the Coverage-Dependent Electronic Structure of Chemisorbed Alkali Atoms on a Ag(111) Surface

    SciTech Connect

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

    2011-09-01

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

  17. Plasmon Enhanced Photoemission

    NASA Astrophysics Data System (ADS)

    Polyakov, Aleksandr N.

    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 1.5mu J 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

  18. Plasmon Enhanced Photoemission

    SciTech Connect

    Polyakov, Aleksandr

    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

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

    PubMed

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

    2016-04-01

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

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

    PubMed Central

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

    2016-01-01

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

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

    SciTech Connect

    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. (author)

  2. Interband quasiparticle scattering in superconducting LiFeAs reconciles photoemission and tunneling measurements.

    PubMed

    Hess, Christian; Sykora, Steffen; Hänke, Torben; Schlegel, Ronny; Baumann, Danny; Zabolotnyy, Volodymyr B; Harnagea, Luminita; Wurmehl, Sabine; van den Brink, Jeroen; Büchner, Bernd

    2013-01-04

    Several angle-resolved photoemission spectroscopy (ARPES) studies reveal a poorly nested Fermi surface of LiFeAs, far away from a spin density wave instability, and clear-cut superconducting gap anisotropies. On the other hand a very different, more nested Fermi surface and dissimilar gap anisotropies have been obtained from quasiparticle interference (QPI) data, which were interpreted as arising from intraband scattering within holelike bands. Here we show that this ARPES-QPI paradox is completely resolved by interband scattering between the holelike bands. The resolution follows from an excellent agreement between experimental quasiparticle scattering data and T-matrix QPI calculations (based on experimental band structure data), which allows disentangling interband and intraband scattering processes.

  3. Interband Quasiparticle Scattering in Superconducting LiFeAs Reconciles Photoemission and Tunneling Measurements

    NASA Astrophysics Data System (ADS)

    Hess, Christian; Sykora, Steffen; Hänke, Torben; Schlegel, Ronny; Baumann, Danny; Zabolotnyy, Volodymyr B.; Harnagea, Luminita; Wurmehl, Sabine; van den Brink, Jeroen; Büchner, Bernd

    2013-01-01

    Several angle-resolved photoemission spectroscopy (ARPES) studies reveal a poorly nested Fermi surface of LiFeAs, far away from a spin density wave instability, and clear-cut superconducting gap anisotropies. On the other hand a very different, more nested Fermi surface and dissimilar gap anisotropies have been obtained from quasiparticle interference (QPI) data, which were interpreted as arising from intraband scattering within holelike bands. Here we show that this ARPES-QPI paradox is completely resolved by interband scattering between the holelike bands. The resolution follows from an excellent agreement between experimental quasiparticle scattering data and T-matrix QPI calculations (based on experimental band structure data), which allows disentangling interband and intraband scattering processes.

  4. Observation of Dirac cone band dispersions in FeSe thin films by photoemission spectroscopy

    NASA Astrophysics Data System (ADS)

    Tan, Shiyong; Fang, Yun; Xie, Donghua; Feng, Wei; Wen, Chenhaoping; Song, Qi; Chen, Qiuyun; Zhang, Wen; Zhang, Yun; Luo, Liuzhu; Xie, Binping; Lai, Xinchun; Feng, Donglai; Feng Group Team; Lai Group Team

    The search for novel materials with Dirac cone band dispersion is one of the most challenging and important works for both fundamental physics and technological applications. Here, we studied the electronic structure of FeSe thin films grown on SrTiO3 substrates by angle-resolved photoemission spectroscopy (ARPES). We reveal the existence of Dirac cone band dispersions in FeSe thin films thicker than 1 Unit Cell below the nematic transition temperature, whose apexes are located -10 meV below Fermi energy. The evolution of electronic structures for FeSe thin films as function of temperature, thickness and cobalt doping are systematically studied. The Dirac cones are found to be coexisted with the nematicity in FeSe, disappear when nematicity is suppressed. Our results provide useful guidelines for understanding the novel electronic structure, nematicity and superconductivity in FeSe system..

  5. Observation of Dirac cone band dispersions in FeSe thin films by photoemission spectroscopy

    NASA Astrophysics Data System (ADS)

    Tan, S. Y.; Fang, Y.; Xie, D. H.; Feng, W.; Wen, C. H. P.; Song, Q.; Chen, Q. Y.; Zhang, W.; Zhang, Y.; Luo, L. Z.; Xie, B. P.; Lai, X. C.; Feng, D. L.

    2016-03-01

    The search for novel materials with Dirac cone band dispersion is one of the most challenging and important works for both fundamental physics and technological applications. Here, we studied the electronic structure of FeSe thin films grown on SrTi O3 substrates by angle-resolved photoemission spectroscopy (ARPES). We revealed the existence of Dirac cone band dispersions in FeSe thin films thicker than 1 unit cell below the nematic transition temperature, whose apexes are located -10 meV below Fermi energy. The evolution of electronic structures for FeSe thin films as a function of temperature, thickness, and cobalt doping were systematically studied. The Dirac cones coexist with the nematicity in FeSe and disappear when nematicity is suppressed. Our results provide useful guidelines for understanding the novel electronic structure, nematicity, and superconductivity in the FeSe system.

  6. Nesting-driven multipolar order in CeB6 from photoemission tomography

    PubMed Central

    Koitzsch, A.; Heming, N.; Knupfer, M.; Büchner, B.; Portnichenko, P. Y.; Dukhnenko, A. V; Shitsevalova, N. Y.; Filipov, V. B.; Lev, L. L.; Strocov, V. N.; Ollivier, J.; Inosov, D. S.

    2016-01-01

    Some heavy fermion materials show so-called hidden-order phases which are invisible to many characterization techniques and whose microscopic origin remained controversial for decades. Among such hidden-order compounds, CeB6 is of model character due to its simple electronic configuration and crystal structure. Apart from more conventional antiferromagnetism, it shows an elusive phase at low temperatures, which is commonly associated with multipolar order. Here we show that this phase roots in a Fermi surface instability. This conclusion is based on a full 3D tomographic sampling of the electronic structure by angle-resolved photoemission and comparison with inelastic neutron scattering data. The hidden order is mediated by itinerant electrons. Our measurements will serve as a paradigm for the investigation of hidden-order phases in f-electron systems, but also generally for situations where the itinerant electrons drive orbital or spin order. PMID:26976632

  7. Nonequilibrium Band Mapping of Unoccupied Bulk States below the Vacuum Level by Two-Photon Photoemission

    SciTech Connect

    Johnson, P.D.; Hao, Z.; Dadap, J.I.; Knox, K.R.; Yilmaz, M.B.; Zaki, N.; Osgood, R.M.

    2010-07-01

    We demonstrate angle-resolved, tunable, two-photon photoemission (2PPE) to map a bulk unoccupied band, viz. the Cu sp band 0 to 1 eV below the vacuum level, in the vicinity of the L point. This short-lived bulk band is seen due to the strong optical pump rate, and the observed transition energies and their dispersion with photon energy {h_bar}{omega}, are in excellent agreement with tight-binding band-structure calculations. The variation of the final-state energy with {h_bar}{omega} has a measured slope of -1.64 in contrast to values of 1 or 2 observed for 2PPE from two-dimensional states. This unique variation illustrates the significant role of the perpendicular momentum {h_bar}k{perpendicular} in 2PPE.

  8. Nonequilibrium Band Mapping of Unoccupied Bulk States below the Vacuum Level by Two-Photon Photoemission

    SciTech Connect

    Hao Zhaofeng; Dadap, J. I.; Knox, K. R.; Zaki, N.; Osgood, R. M.; Yilmaz, M. B.; Johnson, P. D.

    2010-07-02

    We demonstrate angle-resolved, tunable, two-photon photoemission (2PPE) to map a bulk unoccupied band, viz. the Cu sp band 0 to 1 eV below the vacuum level, in the vicinity of the L point. This short-lived bulk band is seen due to the strong optical pump rate, and the observed transition energies and their dispersion with photon energy ({h_bar}/2{pi}){omega}, are in excellent agreement with tight-binding band-structure calculations. The variation of the final-state energy with ({h_bar}/2{pi}){omega} has a measured slope of {approx}1.64 in contrast to values of 1 or 2 observed for 2PPE from two-dimensional states. This unique variation illustrates the significant role of the perpendicular momentum ({h_bar}/2{pi})k{sub perpendicular} in 2PPE.

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

    NASA Astrophysics Data System (ADS)

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

    2016-09-01

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

  10. [Laser-based radiometric calibration].

    PubMed

    Li, Zhi-gang; Zheng, Yu-quan

    2014-12-01

    Increasingly higher demands are put forward to spectral radiometric calibration accuracy and the development of new tunable laser based spectral radiometric calibration technology is promoted, along with the development of studies of terrestrial remote sensing, aeronautical and astronautical remote sensing, plasma physics, quantitative spectroscopy, etc. Internationally a number of national metrology scientific research institutes have built tunable laser based spectral radiometric calibration facilities in succession, which are traceable to cryogenic radiometers and have low uncertainties for spectral responsivity calibration and characterization of detectors and remote sensing instruments in the UK, the USA, Germany, etc. Among them, the facility for spectral irradiance and radiance responsivity calibrations using uniform sources (SIRCCUS) at the National Institute of Standards and Technology (NIST) in the USA and the Tunable Lasers in Photometry (TULIP) facility at the Physikalisch-Technische Bundesanstalt (PTB) in Germany have more representatives. Compared with lamp-monochromator systems, laser based spectral radiometric calibrations have many advantages, such as narrow spectral bandwidth, high wavelength accuracy, low calibration uncertainty and so on for radiometric calibration applications. In this paper, the development of laser-based spectral radiometric calibration and structures and performances of laser-based radiometric calibration facilities represented by the National Physical Laboratory (NPL) in the UK, NIST and PTB are presented, technical advantages of laser-based spectral radiometric calibration are analyzed, and applications of this technology are further discussed. Laser-based spectral radiometric calibration facilities can be widely used in important system-level radiometric calibration measurements with high accuracy, including radiance temperature, radiance and irradiance calibrations for space remote sensing instruments, and promote the

  11. Collapse of long-range charge order tracked by time-resolved photoemission at high momenta.

    PubMed

    Rohwer, Timm; Hellmann, Stefan; Wiesenmayer, Martin; Sohrt, Christian; Stange, Ankatrin; Slomski, Bartosz; Carr, Adra; Liu, Yanwei; Avila, Luis Miaja; Kalläne, Matthias; Mathias, Stefan; Kipp, Lutz; Rossnagel, Kai; Bauer, Michael

    2011-03-24

    Intense femtosecond (10(-15) s) light pulses can be used to transform electronic, magnetic and structural order in condensed-matter systems on timescales of electronic and atomic motion. This technique is particularly useful in the study and in the control of materials whose physical properties are governed by the interactions between multiple degrees of freedom. Time- and angle-resolved photoemission spectroscopy is in this context a direct and comprehensive, energy- and momentum-selective probe of the ultrafast processes that couple to the electronic degrees of freedom. Previously, the capability of such studies to access electron momentum space away from zero momentum was, however, restricted owing to limitations of the available probing photon energy. Here, using femtosecond extreme-ultraviolet pulses delivered by a high-harmonic-generation source, we use time- and angle-resolved photoemission spectroscopy to measure the photoinduced vaporization of a charge-ordered state in the potential excitonic insulator 1T-TiSe(2 )(refs 12, 13). By way of stroboscopic imaging of electronic band dispersions at large momentum, in the vicinity of the edge of the first Brillouin zone, we reveal that the collapse of atomic-scale periodic long-range order happens on a timescale as short as 20 femtoseconds. The surprisingly fast response of the system is assigned to screening by the transient generation of free charge carriers. Similar screening scenarios are likely to be relevant in other photoinduced solid-state transitions and may generally determine the response times. Moreover, as electron states with large momenta govern fundamental electronic properties in condensed matter systems, we anticipate that the experimental advance represented by the present study will be useful to study the ultrafast dynamics and microscopic mechanisms of electronic phenomena in a wide range of materials.

  12. Photoemission studies of novel charge density wave systems

    NASA Astrophysics Data System (ADS)

    Kidd, Timothy Edward

    Photoelectron spectroscopy is a powerful tool for probing the properties of surfaces and interfaces. Linked with a tunable light source such as the Synchrotron Radiation Center in Stoughton, WI, one is able to obtain information concerning the sample's crystal structure, the interfacial properties of thin films, valence band structure, and chemical environment. This thesis is mainly focused on the use of angle-resolved photoemission to study the electronic structure of charge density wave (CDW) systems. CDW systems undergo a temperature dependent structural phase transition accompanied by a modulation of the conduction electron density. These materials share many properties with complex systems. These systems display many novel properties including high-Tc superconductivity and the colossal magnetoresistance effect. One of the shared properties of these systems is a high sensitivity to doping and defects. This sensitivity will be explored in the context of two CDW systems in this thesis. The first system to be studied was the 1/3 ML Sn/Ge(111) surface. It is a simple 2D binary semiconductor system which appears to undergo a CDW phase transition at low temperatures. Photoemission spectroscopy was used to determine the mechanism for the phase transition, and the influence of defects upon the system. It appears the defects play a strong role in defining both the normal and ground state for the system, and are perhaps essential for the phase transition. The second system studied is the layered compound TiSe2. Unlike other group IV transition metal dichalcogenides, TiSe2 undergoes a CDW phase transition at low temperatures. Although the system has been studied for decades, there is still no consensus on the mechanism driving the phase transition. There is also some doubt as to whether the normal state is semi-metallic or semiconducting. Again, defects have a strong effect upon the system. Photoemission studies were used to measure the system's electronic structure near

  13. Crystal momentum dependence of the correlation satellite intensity in the 3p → 3d resonant photoemission spectra of Bi2Sr2CaCu2O8 + δ

    NASA Astrophysics Data System (ADS)

    Goldoni, A.; Corradini, V.; del Pennino, U.; Sangalli, P.; Parmigiani, F.; Avila, J.; Teodorescu, C.

    2000-05-01

    Angle-resolved resonant photoemission measurements at the Cu3p → Cu3d threshold have been performed on the superconducting cuprate Bi2Sr2CaCu2O8 + δ. We have investigated in particular the correlation satellite appearing in the valence band photoemission spectrum to investigate the effect of solid state on the interference effect occurring at resonance. We found that the intensity of the correlation satellite changes with the electron take-off angle in a way that depends on the particular crystallographic direction and on the sample hole doping. These results indicate that the intensity enhancement at the absorption edge is a real resonance albeit the intermediate state in the autoionization process is partly delocalised. This fact does not prevent the occurrence of interference between indirect and direct photoemission.

  14. Auger-electron angular distributions calculated without the two-step approximation: Calculation of angle-resolved resonant Auger spectra of C2 H2

    NASA Astrophysics Data System (ADS)

    Colle, Renato; Embriaco, Davide; Massini, Michol; Simonucci, Stefano; Taioli, Simone

    2004-10-01

    Analytic expressions for the direct, resonant, and interference contributions to the differential cross section of a resonant Auger process, produced by the inner-shell photoionization of a linear molecule either “fixed in space” or belonging to a gas of randomly oriented molecules, have been derived following Dill’s procedures [ Dill , Phys. Rev. Lett. 45, 1393 (1980) ], but going beyond the two-step approximation. Angle-resolved Auger spectra of the C2H2 molecule measured on top of the C1s→π* resonance [ Kivimäki , J. Phys. B 30, 4279 (1997) ] have been calculated together with asymmetry parameters, analyzing also the different contributions to the electron angular distributions.

  15. Molecular orientation in thin films of bis(1,2,5-thiadiazolo)-p-quinobis(1,3-dithiole) on graphite studied by angle-resolved photoelectron spectroscopy

    NASA Astrophysics Data System (ADS)

    Hasegawa, Shinji; Tanaka, Shoji; Yamashita, Yoshiro; Inokuchi, Hiroo; Fujimoto, Hitoshi; Kamiya, Koji; Seki, Kazuhiko; Ueno, Nobuo

    1993-07-01

    Angle-resolved ultraviolet photoelectron spectra using synchrotron radiation were measured for oriented thin films of bis(1,2,5-thiadiazolo)-p-quinobis(1,3-dithiole) on a cleaved highly oriented pyrolytic graphite (HOPG) surface. The observed takeoff angle dependence of the photoelectron intensity was analyzed by using the independent-atomic-center approximation and modified neglect of diatomic overlap molecular-orbital calculations. The calculated results agree well with the experimental ones. From the comparison between these results, the molecules in the thin film are estimated to lie flat with the inclination angle β<=10° to the HOPG surface. This analysis method is useful as a first step to a quantitative analysis for angular distribution of photoelectrons from thin films of large and complex organic molecules.

  16. The surface study of ReFeO3 (Re =Lu, Yb) thin films by X-ray Photoemission Spectroscopy and Density Function Calculation

    NASA Astrophysics Data System (ADS)

    Cao, Shi; Paudel, Tula; Sinha, Kishan; Jiang, Xuanyuan; Wang, Wenbin; Tsymbal, Evgeny; Xu, Xiaoshan; Dowben, Peter

    2015-03-01

    The rare-earth ferrites, ReFeO3, may have a large magneto-electric response, with high surface/interface polarization, thus the surfaces are of considerable interest. We have characterized the surfaces of hexagonal ReFeO3 (Re = Lu, Yb) and orthorhombic LuFeO3 thin films by angle resolved X-ray photoemission spectroscopy (ARXPS) and compared with density function theory (DFT). The surfaces will terminate in either Fe-O or Re-O depending on whether in the hexagonal or orthorhombic phase of the rare earth ferrite, but consistent with the expectations of DFT. The orthorhombic or hexagonal phases of these rare earth ferrites have the Fe in different crystal fields, which in turn affects the of Fe-O ligands. These changes in electronegativity are experimentally evident as differences in the Fe 2p core level photoemission satellite features. Surface preparation also effects surface termination and will be discussed.

  17. Rotatable spin-polarized electron source for inverse-photoemission experiments

    SciTech Connect

    Stolwijk, S. D. Wortelen, H.; Schmidt, A. B.; Donath, M.

    2014-01-15

    We present a ROtatable Spin-polarized Electron source (ROSE) for the use in spin- and angle-resolved inverse-photoemission (SR-IPE) experiments. A key feature of the ROSE is a variable direction of the transversal electron beam polarization. As a result, the inverse-photoemission experiment becomes sensitive to two orthogonal in-plane polarization directions, and, for nonnormal electron incidence, to the out-of-plane polarization component. We characterize the ROSE and test its performance on the basis of SR-IPE experiments. Measurements on magnetized Ni films on W(110) serve as a reference to demonstrate the variable spin sensitivity. Moreover, investigations of the unoccupied spin-dependent surface electronic structure of Tl/Si(111) highlight the capability to analyze complex phenomena like spin rotations in momentum space. Essentially, the ROSE opens the way to further studies on complex spin-dependent effects in the field of surface magnetism and spin-orbit interaction at surfaces.

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

    PubMed Central

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

    2016-01-01

    We show the three-dimensional electronic structure of the Kondo lattice CeIn3 using soft x-ray angle resolved photoemission spectroscopy in the paramagnetic state. For the first time, we have directly observed the three-dimensional topology of the Fermi surface of CeIn3 by photoemission. The Fermi surface has a complicated hole pocket centred at the Γ-Z line and an elliptical electron pocket centred at the R point of the Brillouin zone. Polarization and photon-energy dependent photoemission results both indicate the nearly localized nature of the 4f electrons in CeIn3, consistent with the theoretical prediction by means of the combination of density functional theory and single-site dynamical mean-field theory. Those results illustrate that the f electrons of CeIn3, which is the parent material of CeMIn5 compounds, are closer to the localized description than the layered CeMIn5 compounds. PMID:27641364

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

    NASA Astrophysics Data System (ADS)

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

    2016-09-01

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

  20. Momentum resolution in inverse photoemission

    SciTech Connect

    Zumbülte, A.; Schmidt, A. B.; Donath, M.

    2015-01-15

    We present a method to determine the electron beam divergence, and thus the momentum resolution, of an inverse-photoemission setup directly from a series of spectra measured on Cu(111). Simulating these spectra with different beam divergences shows a distinct influence of the divergence on the appearance of the Shockley surface state. Upon crossing the Fermi level, its rise in intensity can be directly linked with the beam divergence. A comparison of measurement and simulation enables us to quantify the momentum resolution independent of surface quality, energy resolution, and experimental geometry. With spin resolution, a single spectrum taken around the Fermi momentum of a spin-split surface state, e.g., on Au(111), is sufficient to derive the momentum resolution of an inverse-photoemission setup.

  1. Photoemission-based microelectronic devices

    PubMed Central

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

    2016-01-01

    The vast majority of modern microelectronic devices rely on carriers within semiconductors due to their integrability. Therefore, the performance of these devices is limited due to natural semiconductor properties such as band gap and electron velocity. Replacing the semiconductor channel in conventional microelectronic devices with a gas or vacuum channel may scale their speed, wavelength and power beyond what is available today. However, liberating electrons into gas/vacuum in a practical microelectronic device is quite challenging. It often requires heating, applying high voltages, or using lasers with short wavelengths or high powers. Here, we show that the interaction between an engineered resonant surface and a low-power infrared laser can cause enough photoemission via electron tunnelling to implement feasible microelectronic devices such as transistors, switches and modulators. The proposed photoemission-based devices benefit from the advantages of gas-plasma/vacuum electronic devices while preserving the integrability of semiconductor-based devices. PMID:27811946

  2. Photoemission-based microelectronic devices

    NASA Astrophysics Data System (ADS)

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

    2016-11-01

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

  3. Study of Photoemissive Dusty Plasma

    SciTech Connect

    Gavrikov, A. V.; Fortov, V. E.; Petrov, O. F.; Babichev, V. N.; Filippov, A. V.; Pal', A. F.; Starostin, A. N.

    2008-09-07

    The present work deals with the experimental and theoretical investigation of photoemissive charging of polydisperse dust particles. The characteristic size of dust particles under consideration was 0.1-25 mkm. The experimental part of this work was devoted to the study of positive charging of macroparticles under UV-radiation that acted on dusty formations. Investigations were carried out in argon at normal pressure with particles of different materials. Dust structure was subjected to radiation. The power and frequency spectrum of this radiation was close to corresponding parameters of sun radiation near the top layers of Earth atmosphere. Owing to electron photoemission the macroparticles became positively charged. On the basis of experimental data the estimation of this charge was performed. It was about 500 elementary charges for micron particles. The theoretical part of present work included the numerical simulation of photoemissive dusty plasma decay in a drift-diffusion approximation. The model included equilibrium equation for positively charged macroparticles (in experiment, the percent of these particles was about 90), negatively charged dust particles (about 10%), positive ions (those were born by electron strike of buffered gas atoms) and electrons. Also the model included the Poisson equation for determination of potential distribution in the discharge region. The results of numerical calculations were in a satisfactory correspondence with experimental data both for time dependences of positively and negatively charged macroparticles concentrations and for their velocities.

  4. Study of Photoemissive Dusty Plasma

    NASA Astrophysics Data System (ADS)

    Gavrikov, A. V.; Fortov, V. E.; Petrov, O. F.; Babichev, V. N.; Filippov, A. V.; Pal', A. F.; Starostin, A. N.

    2008-09-01

    The present work deals with the experimental and theoretical investigation of photoemissive charging of polydisperse dust particles. The characteristic size of dust particles under consideration was 0.1-25 mkm. The experimental part of this work was devoted to the study of positive charging of macroparticles under UV-radiation that acted on dusty formations. Investigations were carried out in argon at normal pressure with particles of different materials. Dust structure was subjected to radiation. The power and frequency spectrum of this radiation was close to corresponding parameters of sun radiation near the top layers of Earth atmosphere. Owing to electron photoemission the macroparticles became positively charged. On the basis of experimental data the estimation of this charge was performed. It was about 500 elementary charges for micron particles. The theoretical part of present work included the numerical simulation of photoemissive dusty plasma decay in a drift-diffusion approximation. The model included equilibrium equation for positively charged macroparticles (in experiment, the percent of these particles was about 90), negatively charged dust particles (about 10%), positive ions (those were born by electron strike of buffered gas atoms) and electrons. Also the model included the Poisson equation for determination of potential distribution in the discharge region. The results of numerical calculations were in a satisfactory correspondence with experimental data both for time dependences of positively and negatively charged macroparticles concentrations and for their velocities.

  5. Photocathode device that replenishes photoemissive coating

    SciTech Connect

    Moody, Nathan A.; Lizon, David C.

    2016-06-14

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

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

    NASA Astrophysics Data System (ADS)

    Högström, Jonas; Fredriksson, Wendy; Edstrom, Kristina; Björefors, Fredrik; Nyholm, Leif; Olsson, Claes-Olof A.

    2013-11-01

    An approach for determining depth gradients of metal-ion concentrations in passive films on stainless steel using angle-resolved X-ray photoelectron spectroscopy (ARXPS) is described. The iterative method, which is based on analyses of the oxidised metal peaks, provides increased precision and hence allows faster ARXPS measurements to be carried out. The method was used to determine the concentration depth profiles for molybdenum, iron and chromium in passive films on 316L/EN 1.4432 stainless steel samples oxidised in 0.5 M H2SO4 and acetic acid diluted with 0.02 M Na2B4O7 · 10H2O and 1 M H2O, respectively. The molybdenum concentration in the film is pin-pointed to the oxide/metal interface and the films also contained an iron-ion-enriched surface layer and a chromium-ion-dominated middle layer. Although films of similar composition and thickness (i.e., about 2 nm) were formed in the two electrolytes, the corrosion currents were found to be three orders of magnitude larger in the acetic acid solution. The differences in the layer composition, found for the two electrolytes as well as different oxidation conditions, can be explained based on the oxidation potentials of the metals and the dissolution rates of the different metal ions.

  7. Band alignment of HfO2/In0.18Al0.82N determined by angle-resolved x-ray photoelectron spectroscopy

    NASA Astrophysics Data System (ADS)

    Owen, Man Hon Samuel; Bhuiyan, Maruf Amin; Zhang, Zheng; Pan, Ji Sheng; Tok, Eng Soon; Yeo, Yee-Chia

    2014-07-01

    The band-alignment of atomic layer deposited (ALD)-HfO2/In0.18Al0.82N was studied by high resolution angle-resolved X-ray photoelectron spectroscopy measurements. The band bending near the HfO2/In0.18Al0.82N interface was investigated, and the potential variation across the interface was taken into account in the band alignment calculation. It is observed that the binding energies for N 1s and Al 2p in In0.18Al0.82N decreases and the corresponding extracted valence band offsets increases with increasing θ (i.e., closer to the HfO2/In0.18Al0.82N interface), as a result of an upward energy band bending towards the HfO2/In0.18Al0.82N interface. The resultant valence band offset and the conduction band offset for the ALD-HfO2/In0.18Al0.82N interface calculated was found to be 0.69 eV and 1.01 eV, respectively.

  8. Angle-resolved X-ray photoelectron spectroscopy study of poly(vinylidene fluoride)/poly(N-dodecylacrylamide) Langmuir-Blodgett nanofilms

    NASA Astrophysics Data System (ADS)

    Zhu, Huie; Gao, Yu; Yamamoto, Shunsuke; Miyashita, Tokuji; Mitsuishi, Masaya

    2016-03-01

    Our earlier research prepared ferroelectric poly(vinylidene fluoride) (PVDF) homopolymer monolayers at the air-water interface using amphiphilic poly(N-dodecylacrylamide) (pDDA) nanosheets with Langmuir-Blodgett (LB) technique. However, the miscibility of solvent for PVDF with the water sub-phase in the Langmuir trough makes the film composition unclear in spite of the feeding ratio of \\text{PVDF}:\\text{pDDA} (50:1). In this study, angle-resolved X-ray photoelectron spectroscopy (AR-XPS) was used to investigate the surface chemical composition and the depth profile of the PVDF/pDDA LB nanofilms. The X-ray photoelectron spectroscopy (XPS) spectra confirmed by the detection of fluorine atoms that PVDF molecules were deposited successfully onto the substrate. The constant chemical composition with increasing takeoff angle from 15 to 75° reflects a well-regular layer structure of the PVDF LB nanofilm. The mixing ratio of \\text{PVDF}:\\text{pDDA} is 33:1, which contributes 89.8 wt % PVDF and 10.2 wt % in the PVDF/pDDA LB nanofilms.

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

    PubMed

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

    2011-11-01

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

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

    PubMed

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

    2016-07-15

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

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

    PubMed

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

    2011-01-01

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

  12. Evolution of cobalt nanocluster and electronic structure deposited on stepped Cu(7 5 5) studied by angle-resolved ultraviolet photoelectron spectroscopy

    NASA Astrophysics Data System (ADS)

    Ogawa, Koji; Nakanishi, Koji; Namba, Hidetoshi

    2004-09-01

    Using Cu(7 5 5) stepped surface as a template, we prepared nanoclusters of Co and investigated their electronic structure by angle-resolved ultraviolet photoelectron spectroscopy using synchrotron radiation. From 0.28 to 1.6-ML Co coverage one broad peak is observed at 0.7 eV below the Fermi level. On the other hand, from 0.02 to 0.14-ML coverages non-dispersing two peaks are clearly resolved at 0.3 and 1.1 eV, respectively. The existence of the other peaks and the natures of these peaks are discussed based on the angular, step-orientation, and polarization dependences. The detailed assignments of each peak are done by the comparison with the literature. The spectral change dependent on the coverage was due to the shifts of these peaks. The peak shifts are explained by the enhanced exchange splitting at the low coverages due to both energetic and spatial localization which is consistent with the nanocluster model.

  13. Influence of surface hydroxylation on 3-aminopropyltriethoxysilane growth mode during chemical functionalization of GaN Surfaces: an angle-resolved X-ray photoelectron spectroscopy Study.

    PubMed

    Arranz, A; Palacio, C; García-Fresnadillo, D; Orellana, G; Navarro, A; Muñoz, E

    2008-08-19

    A comparative study of the chemical functionalization of undoped, n- and p-type GaN layers grown on sapphire substrates by metal-organic chemical vapor deposition was carried out. Both types of samples were chemically functionalized with 3-aminopropyltriethoxysilane (APTES) using a well-established silane-based approach for functionalizing hydroxylated surfaces. The untreated surfaces as well as those modified by hydroxylation and APTES deposition were analyzed using angle-resolved X-ray photoelectron spectroscopy. Strong differences were found between the APTES growth modes on n- and p-GaN surfaces that can be associated with the number of available hydroxyl groups on the GaN surface of each sample. Depending on the density of surface hydroxyl groups, different mechanisms of APTES attachment to the GaN surface take place in such a way that the APTES growth mode changes from a monolayer to a multilayer growth mode when the number of surface hydroxyl groups is decreased. Specifically, a monolayer growth mode with a surface coverage of approximately 78% was found on p-GaN, whereas the formation of a dense film, approximately 3 monolayers thick, was observed on n-GaN.

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

    NASA Astrophysics Data System (ADS)

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

    2011-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

  16. A Dust Grain Photoemission Experiment

    NASA Technical Reports Server (NTRS)

    Venturini, C. C.; Spann, J. F., Jr.; Abbas, M. M.; Comfort, R. H.

    2000-01-01

    A laboratory experiment has been developed at Marshall Space Flight Center to study the interaction of micron-sized particles with plasmas and FUV radiation. The intent is to investigate the conditions under which particles of various compositions and sizes become charged, or discharged, while exposed to an electron beam and/or UV radiation. This experiment uses a unique laboratory where a single charged micron size particle is suspended in a quadrupole trap and then subjected to a controlled environment. Tests are performed using different materials and sizes, ranging from 10 microns to 1 micron, to determine the particle's charge while being subjected to an electron beam and /or UV radiation. The focus of this presentation will be on preliminary results from UV photoemission tests, but past results from electron beam, secondary electron emission tests will also be highlighted. A monochromator is used to spectrally resolve UV in the 120 nm to 300 nm range. This enables photoemission measurements as a function of wavelength. Electron beam tests are conducted using I to 3 micron sized aluminum oxide particles subjected to energies between 100 eV to 3 KeV. It was found that for both positive and negative particles the potential tended toward neutrality over time with possible equilibrium potentials between -0.8 Volts and 0.8 Volts.

  17. Photoemission studies of a new topological insulator class: Experimental discovery of the bismuth-X3 topological insulator class

    NASA Astrophysics Data System (ADS)

    Xia, Yuqi

    Topological insulators are materials with a bulk band gap, which carry conducting surface states that are protected against disorder. In three dimensions, the insulators carry 2D Dirac fermions on their surfaces. The opening of a magnetic surface gap can exhibit a topological magnetoelectric effect, and support Majorana fermions which can be manipulated for quantum computation. Previous spin and angle-resolved photoemission studies have shown that Bi 1-xSbx alloy belongs to this class of materials, with a characteristic number nu 0 = 1. Some materials challenges with Bi1-x Sbx alloy however are the significant degree of bulk disorder and a small band gap. Both problems make gating difficult for the manipulation and control of the charge carriers. While ordinary materials such as superconductors and liquid crystals can be described by an order parameter, topological insulators are not associated with a local order parameter resulting from a spontaneous broken symmetry. Rather, they manifest a topological order which requires a direct probe of how their energy bands are connected. Measurement techniques designed to detect a particular order parameter are therefore insufficient to identify the topological character of a material. Alternatively, one can look for properties analogous to the quantum Hall effect as a signature of a topologically ordered system. However, using transport probes to isolate the surface states of the topological insulator requires a pristine bulk with minimal charge carrier density. While advances have been made recently in this direction, a good candidate for such measurements has been elusive. In this thesis, we describe a systematic study of a new topological insulator class with a large band gap and a single surface state Fermi surface. Using synchrochon-based angle-resolved photoemission spectroscopy (ARPES), we measured the topological character of these materials by observing the dispersion of their metallic electronic states confined

  18. A versatile apparatus for time-resolved photoemission spectroscopy via femtosecond pump-probe experiments.

    PubMed

    Carpene, E; Mancini, E; Dallera, C; Ghiringhelli, G; Manzoni, C; Cerullo, G; De Silvestri, S

    2009-05-01

    A laser-based system for time-resolved photoemission spectroscopy using up to 6.2 eV photons is presented. The versatility of the laser source permits several combinations of pump and probe photon energies with pulse durations of 50-100 fs. The ultrahigh vacuum system, equipped with evaporators, a low energy electron diffraction system and an Auger spectrometer, grants the possibility to grow and characterize thin films in situ. The electron energy analyzer is a time-of-flight spectrometer with a multianode detector allowing high count rates. The performance of the whole experimental setup is investigated on Cu(100), Cu(111), and Ag(111) single crystals.

  19. Coherent and incoherent processes in resonant photoemission

    SciTech Connect

    Magnuson, M.; Karis, O.; Weinelt, M.

    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.

  20. Laser-assisted photoemission from surfaces

    SciTech Connect

    Saathoff, G.; Miaja-Avila, L.; Murnane, M. M.; Kapteyn, H. C.; Aeschlimann, M.

    2008-02-15

    We investigate the laser-assisted photoelectric effect from a solid surface. By illuminating a Pt(111) sample simultaneously with ultrashort 1.6 and 42 eV pulses, we observe sidebands in the extreme ultraviolet photoemission spectrum, and accurately extract their amplitudes over a wide range of laser intensities. Our results agree with a simple model, in which soft x-ray photoemission is accompanied by the interaction of the photoemitted electron with the laser field. This strong effect can definitively be distinguished from other laser surface interaction phenomena, such as hot electron excitation, above-threshold photoemission, and space-charge acceleration. Thus, laser-assisted photoemission from surfaces promises to extend pulse duration measurements to higher photon energies, as well as opening up measurements of femtosecond-to-attosecond electron dynamics in solid and surface-adsorbate systems.

  1. High resolution photoemission experiments on copper oxide superconductors

    NASA Astrophysics Data System (ADS)

    Rameau, Jonathan David

    The mechanism for achieving high transition temperatures (T c) in copper oxide superconductors and the nature of the mysterious "pseudogap" phase from which this phenomenon arises are two of the most pressing issues in solid state physics. High resolution angle resolved photoemission spectroscopy (ARPES), which can directly probe the momentum and energy dependence of the electronic structure of a crystal, is considered one of the foremost tools for unraveling these mysteries. In this thesis we present work on both the further development of the ARPES technique itself and the results of two experiments on the high temperature superconductor Bi2Sr2CaCu2O8+delta (BSCCO)---the drosophila of copper oxide superconductors---based upon these analytical and experimental advances. On the analytical side we have shown that the precision of any ARPES experiment can be radically enhanced by using the Lucy-Richardson method (LRM) of iterative deconvolution to remove the worst effects of experimental resolution broadening present in all ARPES spectra. On the experimental side we have constructed a deep ultraviolet laser system capable of increasing our data acquisition rate by more than an order of magnitude compared to what is possible using traditional synchrotron radiation sources at the same momentum and energy resolutions. Using the LRM, in conjunction with synchrotron radiation, spectroscopic evidence was found for the existence of incoherent Cooper pairs in underdoped BSCCO in the normal pseudogap state (above Tc). At the same time an asymmetry between the particle and hole states of BSCCO was found, implying that doped Mott insulators, of which BSCCO is a primordial example, are characterized by the presence of a Fermi-Luttinger surface, rather than a Fermi surface, as would be the case for a simple metal. This study provided the first spectroscopic evidence for either phenomenon. In our second experiment we were able to use the LRM on data acquired with the laser ARPES

  2. Recent Photoemission Results for the Electron-Doped Superconductors

    NASA Astrophysics Data System (ADS)

    Matsui, Hiroaki

    2006-03-01

    Recent improvement in the energy and angular resolution of angle-resolved photoemission spectroscopy (ARPES) enabled us to investigate the detailed electronic structure in electron-doped high-temperature superconductors (HTSC), which have a relatively smaller energy-scale of superconductivity compared to hole-doped systems. In this talk, we report our recent ARPES results1,2 focusing on the many-body interaction and the superconducting-gap symmetry in electron-doped HTSC. We have performed high-resolution ARPES measurements on Nd2-xCexCuO4 and observed that the quasiparticle (QP) effective mass around oπ sg&_slash;p is strongly enhanced due to opening of an antiferromagnetic (AF) pseudogap. Both the QP effective mass and the AF pseudogap are strongly anisotropic with the largest magnitude near the hot spot, which is defined as an intersection point of the Fermi surface and the AF zone boundary. Temperature-dependent measurements have revealed that the AF pseudogap survives at temperatures much higher than TN (N'{e}el temperature), possibly due to the short-range AF correlation remaining even above TN. The AF pseudogap gradually decreases with doping and is abruptly filled up near the boundary between the AF and superconducting phases. To study the anisotropy of superconducting gap in electron-doped HTSC, we have performed high-resolution ARPES on Pr0.89LaCe0.11CuO4. We observed that the momentum dependence of superconducting gap is basically consistent with the dx2-y2-wave symmetry, but it obviously deviates from the simple dx2-y2 gap function. The maximum superconducting gap is not observed at the zone boundary as expected from the simple dx2-y2 gap symmetry, but it is located around the hot spot where electrons are thought to be strongly coupled to the AF spin fluctuation. All these ARPES results suggest that the electronic stricture and the superconducting behavior are strongly dominated by the AF interaction in electron-doped HTSC. 1) H. Matsui, K. Terashima

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

    DOE PAGES

    Tan, S. Y.; Jiang, J.; Ye, Z. R.; ...

    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 atmore » 7 K, indicating that Na₂Ti₂Sb₂O is likely a weakly correlated CDW material in the strong electron-phonon interaction regime. (author)« less

  4. Bi2-Bi2Se3 Superlattice Materials Studied by Photoemission Spectroscopy

    NASA Astrophysics Data System (ADS)

    Weber, Andrew; Pletikosic, Ivo; Gibson, Quinn; Ji, Huiwen; Schoop, Leslie; Sadowski, Jurek; Caruso, Anthony; Vescovo, Elio; Fedorov, Alexei; Cava, Robert; Valla, Tonica

    2014-03-01

    Although searches are carried out independently for new 2D quantum spin Hall or 3D topological materials for their robust, spin-polarized edge or surface conduction states, little has been done to experimentally show that both phases can coexist in a single material or explore how they may interact. The superlattice series Bi2m(Bi2Se3)n , featuring stacked layers of Bi2 and Bi2Se3, may contain systems where a combination of 2D and 3D topological phenomena should be at play, the latter of which can be identified by combined computational and spin-and angle-resolved photoemission spectroscopy studies. We find that several members of the series, (m =0, n =1), (m =1, n =1) and (m =2, n =1) have spin-chiral surface states at the center of the surface Brillouin zone, a trait of strong topological insulators. The characterization of the topological surface states will be discussed for these series members.

  5. Time-resolved photoemission apparatus achieving sub-20-meV energy resolution and high stability

    SciTech Connect

    Ishida, Y.; Togashi, T.; Yamamoto, K.; Tanaka, M.; Kiss, T.; Otsu, T.; Kobayashi, Y.; Shin, S.

    2014-12-15

    The paper describes a time- and angle-resolved photoemission apparatus consisting of a hemispherical analyzer and a pulsed laser source. We demonstrate 1.48-eV pump and 5.92-eV probe measurements at the ⩾10.5-meV and ⩾240-fs resolutions by use of fairly monochromatic 170-fs pulses delivered from a regeneratively amplified Ti:sapphire laser system operating typically at 250 kHz. The apparatus is capable to resolve the optically filled superconducting peak in the unoccupied states of a cuprate superconductor, Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+δ}. A dataset recorded on Bi(111) surface is also presented. Technical descriptions include the followings: A simple procedure to fine-tune the spatio-temporal overlap of the pump-and-probe beams and their diameters; achieving a long-term stability of the system that enables a normalization-free dataset acquisition; changing the repetition rate by utilizing acoustic optical modulator and frequency-division circuit.

  6. X-Ray Photoemission Analysis of Chemically Treated CdZnTe Semiconductor Surfaces

    NASA Astrophysics Data System (ADS)

    Nelson, Art; Vazquez, Daniel; Bliss, Ann; Evans, Cheryl; Ferreira, Jim; Nikoloc, Rebecca; Payne, Steve

    2007-03-01

    Device-grade Cd(1-x)ZnxTe was subjected to various chemical treatments commonly used in device fabrication to determine the resulting microscopic surface composition/morphology and the effect on contact formation. Br-MeOH (2% Br), N2H4, NH4F/H2O2, and (NH4)2S solutions were used to modify the surface chemistry of the Cd(1-x)ZnxTe crystals. Scanning electron microscopy was used to evaluate the resultant surface morphology. Angle-resolved high-resolution photoemission measurements on the valence band electronic structure and Zn 2p, Cd 3d, Te 3d, O 1s core lines were used to evaluate the chemistry of the chemically treated surfaces. Metal overlayers were then deposited on these chemically treated surfaces and the I-V characteristics were measured. The measurements were correlated to understand the effect of interface chemistry on the electronic structure at these interfaces with the goal of optimizing the metal/Cd(1-x)ZnxTe Schottky barrier for radiation detector devices. This work was performed under the auspices of the U.S. Dept. of Energy by the University of California Lawrence Livermore National Laboratory under Contract No. W-7405-Eng-48.

  7. Electronic structure of the Sr/Si(001) Zintl template from density functional theory and photoemission

    NASA Astrophysics Data System (ADS)

    Seo, Hosung; Choi, Miri; Hatch, Richard; Posadas, Agham; Demkov, Alexander

    2013-03-01

    Since the first demonstration of epitaxial growth of crystalline SrTiO3 on Si(001) by Mckee and co-workers, sub-monolayer Sr on Si(001) has been extensively investigated. Charge transfer induced by half-monolayer of Sr has been shown to be a key element enabling wetting of Si by SrTiO3. However, a detailed understanding of the electronic structure reconstruction is not complete. Such knowledge could be extended and applied to the other epitaxial crystalline oxides on semiconductors. Recently, using in-situ x-ray core-level spectroscopy, we have studied the change in electronic structure of Si(001) induced by sub-monolayer Sr deposition in terms of surface core level shift. One of the interesting features is shift of the Si 2p level toward the higher binding energy by 0.49eV after Sr deposition. In this talk, we present a detailed theoretical investigation of the surface core level shifts in sub-monolayer Sr/Si(001). Using the final state theory, we calculate the bulk 2p binding energy to be increased by 0.42eV when half-monolayer of Sr is deposited in excellent agreement with experiment. We are able to compare the calculated evolution of the surface band structure in sub-monolayer Sr/Si(001) to angle-resolved photoemission spectroscopy (ARPES) data.

  8. Calculations of Photoemission from Rutile

    NASA Astrophysics Data System (ADS)

    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.

  9. Photoemission studies of semiconductor nanocrystals

    SciTech Connect

    Hamad, K. S.; Roth, R.; Alivisatos, A. P.

    1997-04-01

    Semiconductor nanocrystals have been the focus of much attention in the last ten years due predominantly to their size dependent optical properties. Namely, the band gap of nanocrystals exhibits a shift to higher energy with decreasing size due to quantum confinement effects. Research in this field has employed primarily optical techniques to study nanocrystals, and in this respect this system has been investigated extensively. In addition, one is able to synthesize monodisperse, crystalline particles of CdS, CdSe, Si, InP, InAs, as well as CdS/HgS/CdS and CdSe/CdS composites. However, optical spectroscopies have proven ambiguous in determining the degree to which electronic excitations are interior or surface admixtures or giving a complete picture of the density of states. Photoemission is a useful technique for understanding the electronic structure of nanocrystals and the effects of quantum confinement, chemical environments of the nanocrystals, and surface coverages. Of particular interest to the authors is the surface composition and structure of these particles, for they have found that much of the behavior of nanocrystals is governed by their surface. Previously, the authors had performed x-ray photoelectron spectroscopy (XPS) on CdSe nanocrystals. XPS has proven to be a powerful tool in that it allows one to determine the composition of the nanocrystal surface.

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

    SciTech Connect

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

    1989-01-01

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

  11. Fermi Surface Evolution and Luttinger Theorem in NaxCoO2: A Systematic Photoemission Study

    SciTech Connect

    Yang, H. B.; Pan, Z. H.; Sekharan, A. K. P.; Sato, T.; Souma, S.; Takahashi, T.; Jin, Rongying; Sales, Brian C; Mandrus, David; Fedorov, A. V.; Wang, Z.; Ding, H.

    2005-01-01

    We report a systematic angle-resolved photoemission study on Na{sub x}CoO{sub 2} for a wide range of Na concentrations (0.3 {le} x {le} 0.72). In all the metallic samples at different x, we observed (i) only a single holelike Fermi surface centered around {Gamma} and (ii) its area changes with x according to the Luttinger theorem. We also observed a surface state that exhibits a larger Fermi surface area. The e{prime}{sub g} band and the associated small Fermi surface pockets near the K points predicted by band calculations are found to sink below the Fermi energy in a manner almost independent of the doping and temperature.

  12. Angle-Resolved Photoelectron Spectrometry Studies of the Autoionization of the 2s{sup 2}2p {sup 2}P Triply Excited State of Atomic Lithium: Experimental Results and R -Matrix Calculations

    SciTech Connect

    Diehl, S.; Cubaynes, D.; Zhou, H. L.; VoKy, L.; Wuilleumier, F. J.; Kennedy, E. T.; Bizau, J. M.; Manson, S. T.; Morgan, T. J.; Blancard, C.

    2000-02-21

    We have measured the angle-resolved energy dependence of the electrons emitted over the energy range of the triply excited 2s{sup 2}2p P{sup 2} lithium resonance using synchrotron radiation. We have also calculated the behavior of the angular distribution parameter {beta} using the R -matrix approximation. Experimental and theoretical results are in good agreement and show deep minima in the 1s2p P{sup 1,} {sup 3} ionic channels. The energy at which the minima occur does not coincide with the resonance energy, but is shifted towards higher energy. (c) 2000 The American Physical Society.

  13. Bulk photoemission from metal films and nanoparticles

    SciTech Connect

    Ikhsanov, R Sh; Babicheva, V E; Protsenko, I E; Uskov, A V; Guzhva, M E

    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)

  14. Domain imaging on multiferroic BiFeO{sub 3}(001) by linear and circular dichroism in threshold photoemission

    SciTech Connect

    Sander, Anke; Christl, Maik; Chiang, Cheng-Tien; Alexe, Marin; Widdra, Wolf

    2015-12-14

    We demonstrate ferroelectric domain imaging at BiFeO{sub 3}(001) single crystal surfaces with laser-based threshold photoemission electron microscopy (PEEM). Work function differences and linear dichroism allow for the identification of the eight independent ferroelectric domain configurations in the PEEM images. There, the determined domain structure is consistent with piezoresponse force microscopy of the sample surface and can also be related to the circular dichroic PEEM images. Our results provide a method for efficient mapping of complex ferroelectric domains with laser-excited PEEM and may allow lab-based time-resolved studies of the domain dynamics in the future.

  15. Laser Based Information Systems (Selected Pages),

    DTIC Science & Technology

    1986-05-22

    CO lasers . Microwaves, 1967, M* 7. 85. W e I s s P. F., T o h n s o n R. E. Laser tracking wiht automatic reacquisi- tion capability. Appl. Optics, 1968, Vol. 7, M* 6. I it 313 lab- Now - ...DIVISIONCD LASER BASED INFORMATION SYSTEMS (Selected Pages) bDTIC L.Z. Kriksunov EL’, %N16 86 4. I’, Approved for public release; Distribution...HUMAN TRANSLATION FTD-ID(RS)T-0563-85 22 May 1986 MICROFICHE NR: FTD-86-C-O01863 LASER BASED INFORMATION SYSTEMS (Selected Pages) By: L.Z.

  16. Photoemission study of diamond (100) surface

    SciTech Connect

    Wu, J.; Cao, R.; Yang, X.; Pianetta, P.; Lindau, I.

    1993-03-01

    The electronic structure of the diamond C(100)-(2 {times} 1)/(2 {times} 2) has been investigated by means of angle-resolved photoelectron spectroscopy for the first time. A surface-related shift has been observed in the C 1s core level spectrum. The surface-state band dispersion was measured along the symmetry axis {Gamma}-J{prime} in the surface Brillouin zone. For k{sub {parallel}} = 0, there is a very pronounced surface state 1.5 eV below Fermi level E{sub F}, and it disperses downwards with increasing k{sub {parallel}}. Near the boundary of the surface Brillouin zone J{prime}, we find two states with binding energies of 1.9 and 2.4 eV with respect to E{sub F}.

  17. The initial oxidation of Al-Mg alloys: Depth-resolved quantitative analysis by angle-resolved x-ray photoelectron spectroscopy and real-time in situ ellipsometry

    NASA Astrophysics Data System (ADS)

    Panda, E.; Jeurgens, L. P. H.; Mittemeijer, E. J.

    2009-12-01

    Real-time in situ spectroscopic ellipsometry and in situ, angle-resolved x-ray photoelectron spectroscopy (AR-XPS) have been applied to establish the relationships between the growth kinetics and the developing microstructure of ultrathin (<3 nm) oxide films grown on clean Al-1.12 at. % Mg alloy surfaces by thermal oxidation in the temperature range T =300-485 K. To this end, procedures for the depth-resolved quantitative AR-XPS analysis of ultrathin, multiple-element, and/or multiphase oxide overgrowths on binary alloy surfaces were developed. As a result, the relationships between the relative depth distributions of Al and Mg in the developing oxide films, the oxide-film growth kinetics, and the oxidation-induced compositional changes in the AlMg alloy substrate could be established as a function of the oxidation conditions.

  18. Auger-electron angular distributions calculated without the two-step approximation: Calculation of angle-resolved resonant Auger spectra of C{sub 2}H{sub 2}

    SciTech Connect

    Colle, Renato; Embriaco, Davide; Massini, Michol; Simonucci, Stefano; Taioli, Simone

    2004-10-01

    Analytic expressions for the direct, resonant, and interference contributions to the differential cross section of a resonant Auger process, produced by the inner-shell photoionization of a linear molecule either 'fixed in space' or belonging to a gas of randomly oriented molecules, have been derived following Dill's procedures [Dill et al., Phys. Rev. Lett. 45, 1393 (1980)], but going beyond the two-step approximation. Angle-resolved Auger spectra of the C{sub 2}H{sub 2} molecule measured on top of the C 1s{yields}{pi}* resonance [Kivimaeki et al., J. Phys. B 30, 4279 (1997)] have been calculated together with asymmetry parameters, analyzing also the different contributions to the electron angular distributions.

  19. Two photon photoemission of deposited silver clusters

    NASA Astrophysics Data System (ADS)

    Busolt, U.; Cottancin, E.; Röhr, H.; Socaciu, L.; Leisner, T.; Wöste, L.

    We use time resolved two photon photoemission to study the stability of size selected silver clusters deposited onto highly oriented pyrolytic graphite (HOPG) substrates. Size-selected Agn+ clusters (n=2-9) are deposited at low coverage onto HOPG surfaces at liquid nitrogen temperatures. After deposition, the samples are irradiated by a series of ultrashort laser pulse pairs. Photoelectrons created by two photon photoemission are collected in a magnetic bottle type time-of-flight photoelectron spectrometer. Their kinetic energy distribution is recorded as a function of the delay time between subsequent light pulses. With the exception of Ag3 the size dependence of the photoelectron spectra reveals a pronounced odd/even effect, which is well known for gas phase silver clusters. This indicates that the deposited clusters retain their size and identity on the sample. The lifetime of the photoexcitation rises with cluster size. This is attributed to an increasing electronic density of states for larger clusters.

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

    PubMed Central

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

    2013-01-01

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

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

    PubMed

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

    2013-10-29

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

  2. 5f Resonant photoemission from plutonium

    NASA Astrophysics Data System (ADS)

    Terry, J.; Schulze, R. K.; Farr, J. D.; Zocco, T.; Heinzelman, K.; Rotenberg, E.; Shuh, D. K.; Van der Laan, G.; Arena, D. A.; Tobin, J. G.

    2002-02-01

    Experimental resonant photoemission (ResPes) results for α-Pu and δ-Pu bulk samples are presented and compared to the results of an atomic model calculation. Both Pu samples exhibit limited agreement with the atomic model calculations. As expected, α-Pu appears to have more 5f valence band delocalization than δ-Pu. Evidence of an enhanced sensitivity to surface corruption, by using synchrotron radiation as the excitation, is presented.

  3. Laser Based 3D Volumetric Display System

    DTIC Science & Technology

    1993-03-01

    Literature, Costa Mesa, CA July 1983. 3. "A Real Time Autostereoscopic Multiplanar 3D Display System", Rodney Don Williams, Felix Garcia, Jr., Texas...8217 .- NUMBERS LASER BASED 3D VOLUMETRIC DISPLAY SYSTEM PR: CD13 0. AUTHOR(S) PE: N/AWIU: DN303151 P. Soltan, J. Trias, W. Robinson, W. Dahlke 7...laser generated 3D volumetric images on a rotating double helix, (where the 3D displays are computer controlled for group viewing with the naked eye

  4. Aerodynamic measurement techniques. [laser based diagnostic techniques

    NASA Technical Reports Server (NTRS)

    Hunter, W. W., Jr.

    1976-01-01

    Laser characteristics of intensity, monochromatic, spatial coherence, and temporal coherence were developed to advance laser based diagnostic techniques for aerodynamic related research. Two broad categories of visualization and optical measurements were considered, and three techniques received significant attention. These are holography, laser velocimetry, and Raman scattering. Examples of the quantitative laser velocimeter and Raman scattering measurements of velocity, temperature, and density indicated the potential of these nonintrusive techniques.

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

    SciTech Connect

    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.

  6. Anomalous correlation effects and unique phase diagram of electron-doped FeSe revealed by photoemission spectroscopy

    PubMed Central

    Wen, C. H. P.; Xu, H. C.; Chen, C.; Huang, Z. C.; Lou, X.; Pu, Y. J.; Song, Q.; Xie, B. P.; Abdel-Hafiez, Mahmoud; Chareev, D. A.; Vasiliev, A. N.; Peng, R.; Feng, D. L.

    2016-01-01

    FeSe layer-based superconductors exhibit exotic and distinctive properties. The undoped FeSe shows nematicity and superconductivity, while the heavily electron-doped KxFe2−ySe2 and single-layer FeSe/SrTiO3 possess high superconducting transition temperatures that pose theoretical challenges. However, a comprehensive study on the doping dependence of an FeSe layer-based superconductor is still lacking due to the lack of a clean means of doping control. Through angle-resolved photoemission spectroscopy studies on K-dosed thick FeSe films and FeSe0.93S0.07 bulk crystals, here we reveal the internal connections between these two types of FeSe-based superconductors, and obtain superconductivity below ∼46 K in an FeSe layer under electron doping without interfacial effects. Moreover, we discover an exotic phase diagram of FeSe with electron doping, including a nematic phase, a superconducting dome, a correlation-driven insulating phase and a metallic phase. Such an anomalous phase diagram unveils the remarkable complexity, and highlights the importance of correlations in FeSe layer-based superconductors. PMID:26952215

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

    NASA Astrophysics Data System (ADS)

    Paggel, J. J.; Miller, T.; Chiang, T.-C.

    2000-01-01

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

  8. High resolution synchrotron radiation based photoemission study of the in situ deposition of molecular sulphur on the atomically clean InGaAs surface

    NASA Astrophysics Data System (ADS)

    Chauhan, Lalit; Hughes, Greg

    2012-06-01

    High resolution synchrotron radiation core level photoemission studies were performed on atomically clean 0.5 μm thick In0.53Ga0.47As (100) epilayers lattice matched to InP substrates following the removal of a 100 nm protective arsenic cap at 410 °C. Both n-type (Si doped 5 × 1017 cm-3) and p-type (Be doped 5 × 1017 cm-3) InGaAs samples were subsequently exposed in situ to molecular sulphur at room temperature, and the resulting changes in the surface chemical composition were recorded. The photoemission spectra indicate evidence of As-S, Ga-S, and In-S bond formation and the substitution of As in the near surface region by sulphur. Annealing to 400 °C results in the complete removal of the As-S bonding component with both Ga-S and In-S bonding configurations remaining. After the anneal, the Fermi level position for both n-type and p-type samples resides at the top of the bandgap indicating a near flat band condition for n-type and significant band bending on the p-type sample. The results of angle resolved photoemission measurements suggest that the sulphur has substituted arsenic in the near surface region resulting in both samples displaying n-type surface behaviour. Annealing to higher temperatures results in the loss of In from the surface without any significant change in the Ga, As, or S signals. Work function measurements on both doping types after sulphur deposition and anneal show similar behaviour displaying a value close to 6 eV which is indicative of the formation of a surface dipole layer related to the presence of sulphur on the surface.

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

    SciTech Connect

    Park, Jongik

    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.

  10. Photoemission Studies of Low Dimensional Metals

    NASA Astrophysics Data System (ADS)

    Grioni, Marco

    1998-03-01

    High-resolution angle resolved photoelectron spectroscopy (ARPES) is a powerful probe of the electronic structure and instabilities of low-dimensional metals. Quasi-2 dimensional materials, like the layered transition metal dichalcogenides, exhibit dispersing quasiparticle bands, normal Fermi liquid lineshapes, and the expected partial or total Fermi surface collapse induced by charge density wave transitions. By contrast, ARPES reveals unexpected and peculiar spectral properties in quasi 1D compounds. Quite generally, a strong suppression of spectral weight near the chemical potential (a pseudogap) is observed in the metallic state, indicative of strong correlations. This non-standard behavior is confirmed by ARPES results on typical 1D organic conductors like TTF-TCNQ and the Bechgaard salts (TMTSF)_2X (X=PF_6,ClO_4)(F. Zwick et al., Phys. Rev. Lett. 79), 3982 (1997). The absence of traces of the Fermi surface, and the spectral lineshapes, are incompatible with a Fermi liquid scenario, and hint to the charge-spin separation predicted by models for correlated fermions in 1D.

  11. Commercialization plan laser-based decoating systems

    SciTech Connect

    Freiwald, J.; Freiwald, D.A.

    1998-01-01

    F2 Associates Inc. (F2) is a small, high-technology firm focused on developing and commercializing environmentally friendly laser ablation systems for industrial-rate removal of surface coatings from metals, concrete, and delicate substrates such as composites. F2 has a contract with the US Department of Energy Federal Energy Technology Center (FETC) to develop and test a laser-based technology for removing contaminated paint and other contaminants from concrete and metal surfaces. Task 4.1 in Phase 2 of the Statement of Work for this DOE contract requires that F2 ``document its plans for commercializing and marketing the stationary laser ablation system. This document shall include a discussion of prospects for commercial customers and partners and may require periodic update to reflect changing strategy. This document shall be submitted to the DOE for review.`` This report is being prepared and submitted in fulfillment of that requirement. This report describes the laser-based technology for cleaning and coatings removal, the types of laser-based systems that have been developed by F2 based on this technology, and the various markets that are emerging for this technology. F2`s commercialization and marketing plans are described, including how F2`s organization is structured to meet the needs of technology commercialization, F2`s strategy and marketing approach, and the necessary steps to receive certification for removing paint from aircraft and DOE certification for D and D applications. The future use of the equipment built for the DOE contract is also discussed.

  12. Near-field focused photoemission from polystyrene microspheres studied with photoemission electron microscopy

    SciTech Connect

    Peppernick, Samuel J.; Joly, Alan G.; Beck, Kenneth M.; Hess, Wayne P.

    2012-07-07

    We use photoemission electron microscopy(PEEM) to image 3 μm diameter polystyrene spheres supported on a metalthin film illuminated by 400 nm (~3.1 eV) and 800 nm (~1.5 eV) femtosecond (fs) laser pulses. Intense photoemission is generated by microspheres even though polystyrene is an insulator and its ionization threshold is well above the photon energies employed. We observe intense photoemission from the far side (the side opposite the incident light) of the illuminated microsphere that is attributed to light focusing within the microsphere. For the case of p-polarized, 800 nm fs laser pulses, we observe photoemission exclusively from the far side of the microsphere and additionally resolve sub-50 nm hot spots in the supporting Pt/Pd thin film that are located only within the focal region of the microsphere. We compare the PEEM images with finite difference time domain(FDTD) electrodynamic simulations to model our experimental results. Finally, the FDTD simulations predict light focusing in the microsphere and subsequent interaction with the supporting metal surface that is consistent with the experimental observations.

  13. Monochromatic electron photoemission from diamondoid monolayers

    SciTech Connect

    Yang, Wanli; Yang, Wanli L.; Fabbri, J.D.; Willey, T.M.; Lee, J.R.I.; Dahl, J.E.; Carlson, R.M.K.; Schreiner, P.R.; Fokin, A.A.; Tkachenko, B.A.; Fokina, N.A.; Meevasana, W.; Mannella, N.; Tanaka, K.; Zhou, X.J.; van Buuren, T.; Kelly, M.A.; Hussain, Z.; Melosh, N.A.; Shen, Z.-X.

    2007-02-27

    We found monochromatic electron photoemission from large-area self-assembled monolayers of a functionalized diamondoid, [121]tetramantane-6-thiol. Photoelectron spectra of the diamondoid monolayers exhibited a peak at the low-kinetic energy threshold; up to 68percent of all emitted electrons were emitted within this single energy peak. The intensity of the emission peak is indicative of diamondoids being negative electron affinity materials. With an energy distribution width of less than 0.5 electron volts, this source of monochromatic electrons may find application in technologies such as electron microscopy, electron beam lithography, and field-emission flatpanel displays.

  14. Monochromatic Electron Photoemission from DiamondoidMonolayers

    SciTech Connect

    Yang, W.L.

    2010-04-15

    We found monochromatic electron photoemission from large-area self-assembled monolayers of a functionalized diamondoid, [121]tetramantane-6-thiol. Photoelectron spectra of the diamondoid monolayers exhibited a peak at the low-kinetic energy threshold; up to 68% of all emitted electrons were emitted within this single energy peak. The intensity of the emission peak is indicative of diamondoids being negative electron affinity materials. With an energy distribution width of less than 0.5 electron volts, this source of monochromatic electrons may find application in technologies such as electron microscopy, electron beam lithography, and field-emission flat-panel displays.

  15. Resonant photoemission in f-electron systems: Pu and Gd

    NASA Astrophysics Data System (ADS)

    Tobin, J. G.; Chung, B. W.; Schulze, R. K.; Terry, J.; Farr, J. D.; Shuh, D. K.; Heinzelman, K.; Rotenberg, E.; Waddill, G. D.; van der Laan, G.

    2003-10-01

    Resonant photoemission in the Pu 5f and Pu 6p states is compared to that in the Gd 4f and Gd 5p states. Spectral simulations, based upon an atomic model with angular momentum coupling, are compared to the Gd and Pu results. Additional spectroscopic measurements of Pu, including core level photoemission and x-ray absorption, are also presented.

  16. Resonant Photoemission in f Electron Systems: Pu& Gd

    SciTech Connect

    Tobin, J G; Chung, B W; Schulze, R K; Terry, J; Farr, J D; Shuh, D K; Heinzelman, K; Rotenberg, E; Waddill, G D; van der Laan, G

    2003-03-07

    Resonant photoemission in the Pu5f and Pu6p states is compared to that in the Gd4f and Gd5p states. Spectral simulations, based upon and atomic model with angular momentum coupling, are compared to the Gd and Pu results. Additional spectroscopic measurements of Pu, including core level photoemission and x-ray absorption are also presented.

  17. Resonant photoemission in f electron systems: Pu and Gd

    SciTech Connect

    Tobin, J.G.; Chung, B.W.; Waddill, G.D.; Schulze, R.K.; Terry,J.; Farr, J.D.; Zocco, T.; Shuh, D.K.; Heinzelman, K.; Rotenberg, E.; Vander Laan, G.

    2003-10-14

    Resonant photoemission in the Pu 5f and Pu 6p states is compared to that in the Gd 4f and Gd 5p states. Spectral simulations, based upon an atomic model with angular momentum coupling, are compared to the Gd and Pu results. Additional spectroscopic measurements of Pu, including core level photoemission and x-ray absorption, are also presented.

  18. Laser-based detection of chemical contraband

    NASA Astrophysics Data System (ADS)

    Clemmer, Robert G.; Kelly, James F.; Martin, Steven W.; Mong, Gary M.; Sharpe, Steven W.

    1997-02-01

    The goal of our work is tow fold; 1) develop a portable and rapid laser based air sampler for detection of specific chemical contraband and 2) compile a spectral data base in both the near- and mid-IR of sufficiently high quality to be useful for gas phase spectroscopic identification of chemical contraband. During the synthesis or 'cooking' of many illicit chemical substances, relatively high concentrations of volatile solvents, chemical precursors and byproducts are unavoidably released to the atmosphere. In some instances, the final product may have sufficient vapor pressure to be detectable in the surrounding air. The detection of a single high-value effluent or the simultaneous detection of two or more low-value effluents can be used as reliable indicators of a nearby clandestine cooking operation. The designation of high- versus low-value effluent reflects both the commercial availability and legitimate usage of a specific chemical. This paper will describe PNNL's progress and efforts towards the development of a portable laser based air sampling system for the detection of clandestine manufacturing of methamphetamine. Although our current efforts ar focused on methamphetamine, we see no fundamental limitations on detection of other forms of chemical contraband manufacturing. This also includes the synthesis of certain classes of chemical weapons that have recently been deployed by terrorist groups.

  19. Investigation on the interfacial chemical state and band alignment for the sputtering-deposited CaF2/p-GaN heterojunction by angle-resolved X-ray photoelectron spectroscopy

    NASA Astrophysics Data System (ADS)

    Zhang, Kexiong; Liao, Meiyong; Sumiya, Masatomo; Koide, Yasuo; Sang, Liwen

    2016-11-01

    The interfacial chemical state and the band alignment of the sputtering-deposited CaF2/p-GaN hetero-structure were investigated by angle-resolved X-ray photoelectron spectroscopy. The dependence of Ga 3p core-level positions on the collection angles proves that the downward band bending of p-GaN is reduced from 1.51 to 0.85 eV after the deposition of CaF2, which may be due to the reduction of Mg-Ga-O-related interface states by the oxygen-free deposition of CaF2. The band gap of sputtering-deposited CaF2 is estimated to be about 7.97 eV with a potential gradient of 0.48 eV obtained by the variation of the Ca 2p3/2 position on different collection angles. By taking into account the p-GaN surface band bending and potential gradient in the CaF2 layer, large valence and conduction band offsets of 2.66 ± 0.20 and 1.92 ± 0.20 eV between CaF2 and p-GaN are obtained. These results indicate that CaF2 is a promising gate dielectric layer on the p-GaN for the application of metal-insulator-semiconductor devices.

  20. Angle-resolved ultraviolet photoelectron spectroscopy of thin films of bis(1,2,5-thiadiazolo)-p-quinobis (1,3-dithiole) on the MoS2 surface

    NASA Astrophysics Data System (ADS)

    Ueno, Nobuo; Kitamura, Akinori; Okudaira, Koji K.; Miyamae, Takayuki; Harada, Yoshiya; Hasegawa, Sinji; Ishii, Hisao; Inokuchi, Hiroo; Fujikawa, Takashi; Miyazaki, Takafumi; Seki, Kazuhiko

    1997-08-01

    In this paper we report on the angle-resolved ultraviolet photoelectron spectroscopy on ultrathin films of bis(1,2,5-thiadiazolo)-p-quinobis (1,3-dithiole) (BTQBT) deposited on a MoS2 surface with synchrotron radiation, and describe the quantitative analysis of the angular distribution of photoelectron from the highest occupied state. The observed angular distributions were better explained by those calculated with the single-scattering approximation combined with molecular orbital calculation considering intramolecularly scattered waves than the previously used independent-atomic-center approximation combined with molecular orbital calculation. Further, the low-energy-electron diffraction measurements were performed on the film. From the low-energy-electron diffraction, the two-dimensional lattice of the ultrathin films on the MoS2 was found to be MoS2(0001)-(√13 ×√13, R=±13.9°)-BTQBT, and from the analysis of the photoelectron angular distributions, it was found that at the lattice points the molecules lie flat with azimuthal orientations of 19° and 47° with respect to each surface crystal axis of MoS2. On the basis of these results, the full structure of the thin film, the two-dimensional lattice, and full molecular orientations at the lattice points, is proposed.

  1. Ambient pressure photoemission spectroscopy of metal surfaces

    NASA Astrophysics Data System (ADS)

    Baikie, Iain D.; Grain, Angela C.; Sutherland, James; Law, Jamie

    2014-12-01

    We describe a novel photoemission technique utilizing a traditional Kelvin probe as a detector of electrons/atmospheric ions ejected from metallic surfaces (Au, Ag, Cu, Fe, Ni, Ti, Zn, Al) illuminated by a deep ultra-violet (DUV) source under ambient pressure. To surmount the limitation of electron scattering in air the incident photon energy is rastered rather than applying a variable retarding electric field as is used with UPS. This arrangement can be applied in several operational modes: using the DUV source to determine the photoemission threshold (Φ) with 30-50 meV resolution and also the Kelvin probe, under dark conditions, to measure contact potential difference (CPD) between the Kelvin probe tip and the metallic sample with an accuracy of 1-3 meV. We have studied the relationship between the photoelectric threshold and CPD of metal surfaces cleaned in ambient conditions. Inclusion of a second spectroscopic visible source was used to confirm a semiconducting oxide, possibly Cu2O, via surface photovoltage measurements with the KP. This dual detection system can be easily extended to controlled gas conditions, relative humidity control and sample heating/cooling.

  2. Photoemission study of cerium silicate model systems

    NASA Astrophysics Data System (ADS)

    Skála, Tomáš; Matolín, Vladimír

    2013-01-01

    Interaction of silicon with cerium oxide was studied by photoelectron spectroscopy using two model systems CeOx/Si(1 1 1) and Si/CeO2(1 1 1)/Cu(1 1 1) which can be used for fundamental studies in the field of microelectronics and heterogeneous catalysis. The interaction was found to be strong and lead to a formation of cerium silicate films of the proposed stoichiometry Ce4.67Si3O13. Their maximum thickness was limited by diffusion of silicon. Beside silicate other compounds were growing on the surface - SiO2, Si2O, Si, and CeO2. The assignment of the formed species is based on the interpretation of photoemission spectra involving the measurements of various reference O/Si and Sisbnd O/Cu systems.

  3. Time-resolved photoemission using attosecond streaking

    NASA Astrophysics Data System (ADS)

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

    2014-04-01

    We theoretically study time-resolved photoemission in atoms as probed by attosecond streaking. We review recent advances in the study of the photoelectric efect in the time domain and show that the experimentally accessible time shifts can be decomposed into distinct contributions that stem from the feld-free photoionization process itself and from probe-field induced corrections. We perform accurate quantum-mechanical as well as classical simulations of attosecond streaking for efective one-electron systems and determine all relevant contributions to the time delay with attosecond precision. In particular, we investigate the properties and limitations of attosecond streaking for the transition from short-ranged potentials (photodetachment) to long-ranged Coulomb potentials (photoionization). As an example for a more complex system, we study time-resolved photoionization for endohedral fullerenes A@C60 and discuss how streaking time shifts are modifed due to the interaction of the C60 cage with the probing infrared streaking field.

  4. Timing analysis of two-electron photoemission

    NASA Astrophysics Data System (ADS)

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

    2011-05-01

    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 Schrödinger 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.

  5. A comparative photoemission study of polar and nonpolar SiC surfaces oxidized in N 2O

    NASA Astrophysics Data System (ADS)

    Johansson, L. I.; Virojanadara, C.; Eickhoff, Th; Drube, W.

    2004-03-01

    Photoemission studies of oxidized SiC samples grown ex situ in N 2O, at a temperature of 900 °C, on the (0 0 0 1), (0 0 0 1¯), (1 1 2¯ 0) and (1 0 1¯ 0) surfaces are reported. Angle resolved data from the Si 1s and Si 2p core levels and the Si KL 2,3L 2,3 Auger transitions are analyzed and compared to data from a sample grown in O 2 on the (0 0 0 1) surface. The results show oxide growth and no oxy-nitride formation. The growth rate is found to be smallest for the Si-terminated (0 0 0 1) surface and highest for the nonpolar (1 0 1¯ 0) surface. The presence of two oxidation states, Si +4 and a suboxide, are required to explain and model recorded Si 1s, Si 2p and Si KLL spectra. The SiO 2 shift is found to be smaller on the (0 0 0 1) surface than on the other three surfaces, which is attributed to an oxide thickness dependence of the shift. A layer attenuation model describes satisfactorily the intensity variations observed in the core level components versus electron emission angle when assuming the suboxide at the interface. Estimates made of the thickness of the oxide layers show that the oxidation rate for the (0 0 0 1) surfaces is about half of that for the (1 0 1¯ 0) surface and that the oxidation rate for the (1 1 2¯ 0) and (0 0 0 1¯) surfaces are similar but somewhat smaller than for the (1 0 1¯ 0) surface. The amount of suboxide is found to be smaller on the nonpolar than on the polar surfaces.

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

    PubMed

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

    2016-05-01

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

  7. Correlation of polycrystalline Cu(In,Ga)Se{sub 2} device efficiency with homojunction depth and interfacial structure: X-ray photoemission and positron annihilation spectroscopic characterization

    SciTech Connect

    Nelson, A.J.; Sobol, P.E.; Gabor, A.M.; Contreras, M.A.; Asoka-Kumar, P.; Lynn, K.G.

    1994-06-01

    Angled-resolved high resolution photoemission measurements on valence band electronic structure and Cu 2p, In 3d, Ga 2p, and Se 3d core lines were used to evaluate surface and near-surface chemistry of CuInSe{sub 2} and Cu(In,Ga)Se{sub 2} device grade thin films. XPS compositional depth profiles were also acquired from the near-surface region, and bonding of the Cu, In, Ga, and Se was determined as a function of depth. A Cu-poor region was found, indicating CuIn{sub 5}Se{sub 8} or a CuIn{sub 3}Se{sub 5}-In{sub 2}Se{sub 3} mixture. Correlation between the depth of the Cu-poor region/bulk interface and device efficiency showed that the depth was 115 {angstrom} for a 16.4% CIGS device, 240 {angstrom} for a 15.0% CIGS, and 300 {angstrom} for 14.0% CIGS, with similar trends for CIS films. The surface region is n-type, the bulk is p-type, with a 0.5 eV valence band offset. Depth of homojunction may be the determining factor in device performance. Positron annihilation spectroscopy gave similarly illuminating results.

  8. Theory of hot electron photoemission from graphene

    NASA Astrophysics Data System (ADS)

    Ang, Lay Kee; Liang, Shijun

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

  9. Spin-orbit delays in photoemission

    NASA Astrophysics Data System (ADS)

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

    2017-01-01

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

  10. Ultrahigh-resolution Photoemission of Correlated Systems

    NASA Astrophysics Data System (ADS)

    Grioni, Marco

    2001-03-01

    Photoelectron spectroscopy (ARPES) offers a unique k-selective view of the electronic excitations in solids. This capability can be fully exploited by a new generation of very high energy and momentum resolution experiments which directly probe the properties of the elementary quasiparticle excitations. I will discuss recent ARPES results addressing fundamental aspects of the electronic properties of strongly correlated materials. In model normal metal systems like TiTe2 ARPES can test the range of validity of standard Fermi liquid predictions. From a temperature-dependent lineshape analysis it is possible to identify and separately evaluate the strength of the various quasiparticle scattering processes. Photoemission can also clarify the mechanisms leading to electronic phase transitions, e.g. the role of the Fermi surface topology in charge-density-wave (CDW) instabilities in one- and two-dimensions. In these Peierls systems ARPES can probe the momentum and temperature dependence of the energy gap, but also the unconventional nature of the quasiparticles, and their response to the conflicting lattice and CDW periodicities [1]. [1] J. Voit, L. Perfetti, F. Zwick, H. Berger, G. Margaritondo, G. Gruner, H. Hoechst, and M. Grioni, Science 290, 501 (2000).

  11. Laser based combustion laboratory at NTH/SINTEF applied thermodynamics

    NASA Astrophysics Data System (ADS)

    Tichy, F.; Bjoerge, T.

    1993-12-01

    During the SPUNG-program, a laser based laboratory has been built up at NTH/SINTEF Applied Thermodynamics by the funding from that program. The laser based laboratory consists of a Nd:YAG laser and an image intensifier electronic camera system. There are numerous different laser based techniques that can be used, using the laser based laboratory, but we have concentrated on laser induced fluorescence (LIF). By shaping the laser beam into a flat plane, 2D imaging of combustion radicals (OH, CH) and emission species (NO) are possible. This can give valuable information about flame structure, flame stabilization, turbulence scales and so on, but at the time being not quantitative concentrations.

  12. Laser-Based Measurement Of Torsional Vibration

    NASA Astrophysics Data System (ADS)

    Eastwood, P. G.; Halliwell, N. A.

    1986-07-01

    Investigations of the torsional vibration characteristics of shaft systems which transmit pulsating torques are an important part of a machinery designer's responsibility. Satisfactory operation of such systems depends to a large extent on successful treatment of this vibration problem, since incorrectly or insufficiently controlled torsional oscillations can lead to fatigue failure, rapid bearing wear, gear hammer etc. The problem is particularly severe in engine crankshaft design where numerous failures have been traced to abnormal vibration at "critical" speeds. Traditionally, the monitoring of torsional oscillation has been performed using strain gauges, slip rings and a variety of mechanical and electrical "torsiographs". More recently systems employing slotted discs or toothed wheels together with proximity transducers have been preferred, but a disadvantage arises from all these methods in that they require contact with the rotating component which necessitates "downtime" for transducer attachment. Moreover, physical access to the rotating surface is often restricted thus making the use of such methods impractical. The "cross-beam" laser velocimeter provides a means of measuring torsional vibration by a non-contact method, thus effectively overcoming the disadvantages of previous measurement systems. This well established laser-based instrument provides a time-resolved voltage analogue of shaft tangential surface velocity and laboratory and field tests have shown it to be both accurate and reliable. The versatility of this instrument, however, is restricted by the need for accurate positioning, since the velocimeter must be arranged so that the rotating surface always traverses the beam intersection region, which is typically only a fraction of a millimetre in length. As a consequence use is restricted to components of circular cross section. This paper compares and contrasts the "cross-beam" system with a new laser instrument, the laser torsional vibrometer

  13. Performance of laser based optical imaging system

    NASA Astrophysics Data System (ADS)

    Shah, Dhrupesh S.; Banerjee, Arup; Vora, Anup; Biswas, Amiya; Patel, Naimesh; Kurulkar, Amit; Dutt, Ashutosh

    2016-05-01

    night imaging and higher frame rate (more than 100fps). Taking advantage of these, laser based camera system configuration was worked out and presented in this paper using scientific grade CMOS sensor and NIR Laser. Camera can image target range from 4km to 5km with resolution of 5cm. Camera can have instantaneous coverage of 100mx100m (at 5km). Scientific grade CMOS sensor could also be used for clear sky day time imaging conditions with Laser off condition. To reduce the laser energy requirement, FPA required to be operated in multi-integration mode where multiple low energy pulses could be thrown within given integration time and detector and its associated electronics will collect and accumulate only those photons which are reflected back from the target of interest using appropriate gating control mechanism. Paper will bring out system engineering aspects for finalization of imaging spectrum, optical parameters in terms of aperture & focal length, required laser energy, highlighting advantage of pulse mode operation of laser compared to continuous mode operation in terms of laser energy & back-scattered light, silicon based optical detector performance results and post processing aspects for target detection. Paper will also discuss achieved performance of proto-model camera.

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

    SciTech Connect

    Not Available

    1992-02-01

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

  15. Photoemission Electron Microscopy of a Plasmonic Silver Nanoparticle Trimer

    SciTech Connect

    Peppernick, Samuel J.; Joly, Alan G.; Beck, Kenneth M.; Hess, Wayne P.; Wang, Jinyong; Wang, Yi-Chung; Wei, Wei

    2013-07-01

    We present a combined experimental and theoretical study to investigate the spatial distribution of photoelectrons emitted from core-shell silver (Ag) nanoparticles. We use two-photon photoemission microscopy (2P-PEEM) to spatially resolve electron emission from a trimeric core-shell aggregate of triangular symmetry. Finite difference time domain (FDTD) simulations are performed to model the intensity distributions of the electromagnetic near-fields resulting from femtosecond (fs) laser excitation of localized surface plasmon oscillations in the triangular core-shell structure. We demonstrate that the predicted FDTD near-field intensity distribution reproduces the 2P-PEEM photoemission pattern.

  16. Real-time observation of collective excitations in photoemission

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

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

  17. Einstein's Photoemission from Quantum Confined Superlattices.

    PubMed

    Debbarma, S; Ghatak, K P

    2016-01-01

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

  18. One-step theory of two-photon photoemission

    NASA Astrophysics Data System (ADS)

    Braun, J.; Rausch, R.; Potthoff, M.; Ebert, H.

    2016-09-01

    A theoretical frame for two-photon photoemission is derived from the general theory of pump-probe photoemission, assuming that not only the probe but also the pump pulse is sufficiently weak. This allows us to use a perturbative approach to compute the lesser Green function within the Keldysh formalism. Two-photon photoemission spectroscopy is a widely used analytical tool to study nonequilibrium phenomena in solid materials. Our theoretical approach aims at a material-specific, realistic, and quantitative description of the time-dependent spectrum based on a picture of effectively independent electrons as described by the local-density approximation in band-structure theory. To this end we follow Pendry's one-step theory of the photoemission process as close as possible and heavily make use of concepts of relativistic multiple-scattering theory, such as the representation of the final state by a time-reversed low-energy electron diffraction state. The formalism allows for a quantitative calculation of the time-dependent photocurrent for moderately correlated systems like simple metals or more complex compounds like topological insulators. An application to the Ag(100) surface is discussed in detail.

  19. Photoemission of Single Dust Grains for Heliospheric Conditions

    NASA Technical Reports Server (NTRS)

    Spann, James F., Jr.; Venturini, Catherine C.; Abbas, Mian M.; Comfort, Richard H.

    2000-01-01

    Initial results of an experiment to measure the photoemission of single dust grains as a function of far ultraviolet wavelengths are presented. Coulombic forces dominate the interaction of the dust grains in the heliosphere. Knowledge of the charge state of dust grains, whether in a dusty plasma (Debye length < intergrain distance) or in the diffuse interplanetary region, is key to understanding their interaction with the solar wind and other solar system constituents. The charge state of heliospheric grains is primarily determined by primary electron and ion collisions, secondary electron emission and photoemission due to ultraviolet sunlight. We have established a unique experimental technique to measure the photoemission of individual micron-sized dust grains in vacuum. This technique resolves difficulties associated with statistical measurements of dust grain ensembles and non-static dust beams. The photoemission yield of Aluminum Oxide 3-micron grains For wavelengths from 120-300 nm with a spectral resolution of 1 nm FWHM is reported. Results are compared to interplanetary conditions.

  20. Photoemission of Mn6Cr single-molecule magnets

    NASA Astrophysics Data System (ADS)

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

    2009-11-01

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

  1. A Monte Carlo photocurrent/photoemission computer program

    NASA Technical Reports Server (NTRS)

    Chadsey, W. L.; Ragona, C.

    1972-01-01

    A Monte Carlo computer program was developed for the computation of photocurrents and photoemission in gamma (X-ray)-irradiated materials. The program was used for computation of radiation-induced surface currents on space vehicles and the computation of radiation-induced space charge environments within space vehicles.

  2. Relativistic calculations of angle-dependent photoemission time delay

    NASA Astrophysics Data System (ADS)

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

    2016-07-01

    Angular dependence of photoemission time delay for the valence n p3 /2 and n p1 /2 subshells of Ar, Kr, and Xe is studied in the dipole relativistic random phase approximation. Strong angular anisotropy of the time delay is reproduced near respective Cooper minima while the spin-orbit splitting affects the time delay near threshold.

  3. Electronic Properties of Pseudomorphic Metallic Films: Photoemission and Inverse Photoemission Measurements

    NASA Astrophysics Data System (ADS)

    Mankey, Gary Jay

    Recent developments in experimental physics have made possible the production and characterization of ultrathin metallic films of atomic dimension. The methods used to grow pseudomorphic fcc films of Ni, Co, and Fe on Cu(001) are described. High-quality epitaxial films are produced by vapor deposition in an ultra-high vacuum environment on suitably prepared substrates. The morphology of these films is characterized using a variety of experimental techniques: Auger electron spectroscopy, low-energy electron diffraction, reflection high-energy electron diffraction, and thermal desorption spectroscopy of adsorbed hydrogen. The magnetic properties of the films are measured with a surface magneto-optic Kerr effect magnetometer. The occupied and unoccupied electronic band dispersions and critical point energies are determined with photoemission and inverse photoemission measurements. These measurements are used as eigenvalues for an empirical combined interpolation scheme bandstructure calculation of the energy bands along the fcc(001) surface normal. Results are presented for Cu(001), Ni(001), Co(001), and paramagnetic Fe(001). Changes in the unoccupied electronic states in the ultrathin film limit are determined for Co and Fe films on Cu(111). The Co films exhibit a bulk-like electronic structure similar to hcp Co(0001) down to films one atomic layer thick. The low-spin ferromagnetic phase of fcc Fe is produced on Cu(111) for films below 5 atomic layers thick. Above this thickness, the Fe films revert to a bulk-like bcc(110) phase. The development of the electronic structure is measured for ultrathin Cu films grown on a specially prepared fcc Co(001) substrate. The Cu 3d band is significantly narrowed for films 1 atomic layer thick and bulk-like for films 3 atomic layers thick (one fcc unit cell). The s, p band exhibits quantum-well states due to the discretization of reciprocal space in the direction perpendicular to the film surface. These quantum-well states are

  4. Laser-based direct-write techniques for cell printing.

    PubMed

    Schiele, Nathan R; Corr, David T; Huang, Yong; Raof, Nurazhani Abdul; Xie, Yubing; Chrisey, Douglas B

    2010-09-01

    Fabrication of cellular constructs with spatial control of cell location (+/-5 microm) is essential to the advancement of a wide range of applications including tissue engineering, stem cell and cancer research. Precise cell placement, especially of multiple cell types in co- or multi-cultures and in three dimensions, can enable research possibilities otherwise impossible, such as the cell-by-cell assembly of complex cellular constructs. Laser-based direct writing, a printing technique first utilized in electronics applications, has been adapted to transfer living cells and other biological materials (e.g., enzymes, proteins and bioceramics). Many different cell types have been printed using laser-based direct writing, and this technique offers significant improvements when compared to conventional cell patterning techniques. The predominance of work to date has not been in application of the technique, but rather focused on demonstrating the ability of direct writing to pattern living cells, in a spatially precise manner, while maintaining cellular viability. This paper reviews laser-based additive direct-write techniques for cell printing, and the various cell types successfully laser direct-written that have applications in tissue engineering, stem cell and cancer research are highlighted. A particular focus is paid to process dynamics modeling and process-induced cell injury during laser-based cell direct writing.

  5. Laser-based direct-write techniques for cell printing

    PubMed Central

    Schiele, Nathan R; Corr, David T; Huang, Yong; Raof, Nurazhani Abdul; Xie, Yubing; Chrisey, Douglas B

    2016-01-01

    Fabrication of cellular constructs with spatial control of cell location (±5 μm) is essential to the advancement of a wide range of applications including tissue engineering, stem cell and cancer research. Precise cell placement, especially of multiple cell types in co- or multi-cultures and in three dimensions, can enable research possibilities otherwise impossible, such as the cell-by-cell assembly of complex cellular constructs. Laser-based direct writing, a printing technique first utilized in electronics applications, has been adapted to transfer living cells and other biological materials (e.g., enzymes, proteins and bioceramics). Many different cell types have been printed using laser-based direct writing, and this technique offers significant improvements when compared to conventional cell patterning techniques. The predominance of work to date has not been in application of the technique, but rather focused on demonstrating the ability of direct writing to pattern living cells, in a spatially precise manner, while maintaining cellular viability. This paper reviews laser-based additive direct-write techniques for cell printing, and the various cell types successfully laser direct-written that have applications in tissue engineering, stem cell and cancer research are highlighted. A particular focus is paid to process dynamics modeling and process-induced cell injury during laser-based cell direct writing. PMID:20814088

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

    SciTech Connect

    Johns, James E.

    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

  7. Attosecond Time-Resolved Photoelectron Dispersion and Photoemission Time Delays

    NASA Astrophysics Data System (ADS)

    Liao, Q.; Thumm, U.

    2014-01-01

    We compute spectrograms and relative time delays for laser-assisted photoemission by single attosecond extreme ultraviolet pulses from valence band (VB) and 2p core levels (CLs) of a Mg(0001) surface within a quantum-mechanical model. Comparing the time-dependent dispersion of photoelectron (PE) wave packets for VB and CL emission, we find striking differences in their dependence on the (i) electron mean free path (MFP) in the solid, (ii) screening of the streaking laser field, and (iii) chirp of the attosecond pulse. The relative photoemission delay between VB and 2p PEs is shown to be sensitive to the electron MFP and screening of the streaking laser field inside the solid. Our model is able to reproduce a recent attosecond-streaking experiment [S. Neppl et al., Phys. Rev. Lett. 109, 087401 (2012)], which reveals no relative streaking time delay between VB and 2p PEs.

  8. Soft X-ray photoemission studies of Hf oxidation

    SciTech Connect

    Suzer, S.; Sayan, S.; Banaszak Holl, M.M.; Garfunkel, E.; Hussain, Z.; Hamdan, N.M.

    2002-02-01

    Soft X-Ray Photoemission Spectroscopy using surface sensitive Synchrotron Radiation has been applied to accurately determine the binding energy shifts and the valence band offset of the HfO2 grown on Hf metal. Charging of oxide films under x-rays (or other irradiation) is circumvented by controlled and sequential in-situ oxidation. Photoemission results show the presence of metallic Hf (from the substrate) with the 4f7/2 binding energy of 14.22 eV, fully oxidized Hf (from HfO2) with the 4f7/2 binding energy of 18.16 eV, and at least one clear suboxide peak. The position of the valence band of HfO2 with respect to the Hf(m) Fermi level is determined as 4.05 eV.

  9. Angle- and spin-resolved photoemission from ferromagnets

    NASA Astrophysics Data System (ADS)

    Cherepkov, N. A.; Kuznetsov, V. V.

    1996-07-01

    Equations for angle- and spin-resolved photoemission from core levels of ferromagnets are derived using the atomic model. They are applied to the n p subshells and to the particular geometries of experiment with the photoemission normal to the surface, which have been used already in several experiments. It is shown that for these geometries the spin-resolved spectra obtained with linearly polarized light are especially simple and contain the contribution of only one or two magnetic sublevels of the 0953-8984/8/27/008/img5 state, and of only one sublevel of the 0953-8984/8/27/008/img6 state, which allow one to resolve the magnetic splitting of core levels. The use of circularly polarized or unpolarized light gives a less transparent picture.

  10. The origin of Monochromatic Photoemission Peak in Diamondod Monolayer

    SciTech Connect

    Clay, W. A.

    2010-02-24

    Recent photoemission experiments have discovered a highly monochromatized secondary electron peak emitted from diamondoid self-assembled monolayers on metal substrates. New experimental data and simulation results are presented to show that a combination of negative electron affinity and strong electron-phonon scattering is responsible for this behavior. The simulation results are generated using a simple Monte Carlo transport algorithm. The simulated spectra recreate the main spectral features of the measured ones.

  11. Bulk sensitive hard x-ray photoemission electron microscopy

    SciTech Connect

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

    2014-11-15

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

  12. Photoemission Experiments for Charge Characteristics of Individual Dust Grains

    NASA Technical Reports Server (NTRS)

    Abbas, M. M.; Craven, P. D.; Spann, J. F.; West, E.; Pratico, J.; Tankosic, D.; Venturini, C. C.; Six, N. Frank (Technical Monitor)

    2001-01-01

    Photoemission experiments with UV radiation have been performed to investigate the microphysics and charge characteristics of individual isolated dust grains of various compositions and sizes by using the electrodynamic balance facility at NASA Marshall Space Flight Center. Dust particles of 2-10 gm diameter are levitated in a vacuum chamber at pressures approximately 10(exp-5) torr and exposed to a collimated beam of UV radiation in the 120-200 nm spectral range from a deuterium lamp source with a MgF2 window. A monochromator is used to select the UV wavelength with a spectral resolution of 8 nm. The electrodynamic facility permits measurements of the charge and diameters of particles of known composition, and monitoring of photoemission rates with the incident UV radiation. Experiments have been conducted on test particles of silica and polystyrene to determine the photoelectric yields and surface equilibrium potentials when exposed to UV radiation. A brief description of an experimental procedure for photoemission studies is given and some preliminary laboratory measurements of the photoelectric yields of individual dust particles are presented.

  13. Photoemission Experiments for Charge Characteristics of Individual Dust Grains

    NASA Technical Reports Server (NTRS)

    Abbas, M. M.; Spann, James F., Jr.; Craven, Paul D.; West, E.; Pratico, Jared; Scheianu, D.; Tankosic, D.; Venturini, C. C.; Whitaker, Ann F. (Technical Monitor)

    2001-01-01

    Photoemission experiments with UV radiation have been performed to investigate the microphysics and charge characteristics of individual isolated dust grains of various compositions and sizes by using the electrodynamic balance facility at NASA Marshall Space Flight Center. Dust particles of 1 - 100 micrometer diameter are levitated in a vacuum chamber at pressures approx. 10(exp -5) torr and exposed to a collimated beam of UV radiation in the 120-300 nanometers spectral range from a deuterium lamp source with a MgF2 window. A monochromator is used to select the UV radiation wavelength with a spectral resolution of 8 nanometers. The electrodynamic facility permits measurements of the charge and diameters of particles of known composition, and monitoring of photoemission rates with the incident UV radiation. Experiments have been conducted on Al2O3 and silicate particles, and in particular on JSC-1 Mars regolith simulants, to determine the photoelectron yields and surface equilibrium potentials of dust particles when exposed to UV radiation in the 120-250 micrometers spectral range. A brief discussion of the experimental procedure, the results of photoemission experiments, and comparisons with theoretical models will be presented.

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

    NASA Astrophysics Data System (ADS)

    Zeng, Lingkun

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

  15. Mode-locked fiber lasers based on doped fiber arrays.

    PubMed

    Zhang, Xiao; Song, Yanrong

    2014-05-10

    We designed a new kind of mode-locked fiber laser based on fiber arrays, where the central core is doped. A theoretical model is given for an all-fiber self-starting mode-locked laser based on this kind of doped fiber array. Two different kinds of fiber lasers with negative dispersion and positive dispersion are simulated and discussed. The stable mode-locked pulses are generated from initial noise conditions by the realistic parameters. The process of self-starting mode-locking multipulse transition and the relationship between the energy of the central core and the propagation distance of the pulses are discussed. Finally, we analyze the difference between the averaged mode-locked laser and the discrete mode-locked laser.

  16. Infrared laser-based sensing in medical applications

    NASA Astrophysics Data System (ADS)

    Sigrist, Markus W.; Bartlome, Richard; Gianella, Michele

    2010-01-01

    Laser-spectroscopic applications in medicine increase in importance. We present two medical applications of laser-based analyses of trace gases. The analysis of exhaled breath concerns the determination of the D/H isotope ratio after intake of a small amount of heavy water. The D/H isotope ratio can be used to deduce the total body water weight and lays the foundation for many other laser-based clinical applications. An elevated D/H ratio could be monitored in breath samples up to 30 days after ingestion of only 5 ml of D2O. A second example concerns the analysis of surgical smoke produced in minimally invasive laparoscopic surgery with electroknives. The quantitative determination of harmless and hazardous compounds down to the ppm level is demonstrated. A specific example is the presence of sevoflurane at concentrations of 80 to 300 ppm, an anesthetic, which to our knowledge is measured for the first time in an abdominal cavity.

  17. Laser-based ultraviolet absorption detection in capillary electrophoresis

    SciTech Connect

    Xue, Y.; Yeung, E.S. )

    1994-04-01

    Laser-based UV absorption in capillary electrophoresis is demonstrated. The use of vacuum photodiodes and an all-electronic noise canceller provides adequate baseline stability despite the large inherent intensity noise in UV lasers. A 4-fold improvement in the detection limit is achieved in comparison to that of commercial instruments. The main advantage here is the better optical coupling with small capillary tubes, maximizing the available optical pathlength for absorption.

  18. Te concentration dependent photoemission and inverse-photoemission study of FeSe1−xTex

    PubMed Central

    Yokoya, Takayoshi; Yoshida, Rikiya; Utsumi, Yuki; Tsubota, Koji; Okazaki, Hiroyuki; Wakita, Takanori; Mizuguchi, Yoshikazu; Takano, Yoshihiko; Muro, Takayuki; Kato, Yukako; Kumigashira, Hiroshi; Oshima, Masaharu; Harima, Hisatomo; Aiura, Yoshihiro; Sato, Hitoshi; Ino, Akihiro; Namatame, Hirofumi; Taniguchi, Masaki; Hirai, Masaaki; Muraoka, Yuji

    2012-01-01

    We have characterized the electronic structure of FeSe1−xTex for various x values using soft x-ray photoemission spectroscopy (SXPES), high-resolution photoemission spectroscopy (HRPES) and inverse photoemission spectroscopy (IPES). The SXPES valence band spectral shape shows that the 2 eV feature in FeSe, which was ascribed to the lower Hubbard band in previous theoretical studies, becomes less prominent with increasing x. HRPES exhibits systematic x dependence of the structure near the Fermi level (EF): its splitting near EF and filling of the pseudogap in FeSe. IPES shows two features, near EF and approximately 6 eV above EF; the former may be related to the Fe 3d states hybridized with chalcogenide p states, while the latter may consist of plane-wave-like and Se d components. In the incident electron energy dependence of IPES, the density of states near EF for FeSe and FeTe has the Fano lineshape characteristic of resonant behavior. These compounds exhibit different resonance profiles, which may reflect the differences in their electronic structures. By combining the PES and IPES data the on-site Coulomb energy was estimated at 3.5 eV for FeSe. PMID:27877521

  19. Plasmon-enhanced internal photoemission for photovoltaics: Theoretical efficiency limits

    NASA Astrophysics Data System (ADS)

    White, Thomas P.; Catchpole, Kylie R.

    2012-08-01

    Plasmon-enhanced internal photoemission in metal-semiconductor Schottky junctions has recently been proposed as an alternative photocurrent mechanism for solar cells. Here, we identify and discuss the requirements for efficient operation of such cells and analyze their performance limits under standard solar illumination. We show that the maximum efficiency limit is <8% even if perfect optical absorption can be achieved using plasmonic nanostructures. This limit results from the fundamental electronic properties of metallic absorbers. Modifying the electron density of states of the absorber could increase the efficiency to >20%.

  20. Photon Detector For Inverse Photoemission Spectroscopy With Improved Energy Resolution

    SciTech Connect

    Maniraj, M.; D'Souza, S. W.; Barman, S. R.

    2011-07-15

    We present the results from newly designed and fabricated double window photon detector to improve the overall energy resolution for inverse photoemission spectroscopy (IPES). This simple design allows us to introduce an absorption gas (Krypton) to decrease the band-width of the energy selective photon detector and thus improve the resolution. Resonance absorption line of Kr of wavelength of 123.6 nm was used. By fitting the Fermi edge of the IPES spectrum of silver, we find an overall energy resolution improved by 73 meV. The design is modular and ensures ease and safety of handling.

  1. Temperature dependent core photoemission in Ce 24Co 11

    NASA Astrophysics Data System (ADS)

    Abbati, I.; Braicovich, L.; Michelis, B.; Fasana, A.; Olcese, G. L.; Canepa, F.; Costa, G. A.

    1985-09-01

    We present Ce 3 d photoemission results (XPS with Al Kα) in the temperature range 100-660°K. The mixed valence behaviour of Ce is very clear with an increase of the valence at lower temperature. A model analysis (of the Gunnarsson and Schönhammer type) gives the weight of the ⨍ 0 configuration equal to 0.19 at 300°K and equal to 0.23 at 100°K. This soft temperature dependence is discussed in connection with the temperature dependence of magnetic properties and with the chemistry of Ce intermetallics.

  2. Spin polarized photoemission studies of interfacial and thin film magnetism

    SciTech Connect

    Johnson, P.D.; Brookes, N.B.; Chang, Y.; Garrison, K.

    1993-01-01

    Spin polarized photoemission is used to study the electronic structure of noble metals deposited on ferromagnetic substrates. Studies of Ag deposited on an Fe(001) substrate reveal a series of minority spin interface or quantum well states with binding energies dependent on the thickness of the silver. Similar behavior is observed for Cu films deposited on a fct Co(001) substrate. Tight-binding modeling reproduces many of the observations and shows that hybridization of the sp-bands with the noble metal d-bands cannot be ignored.

  3. Spin polarized photoemission studies of interfacial and thin film magnetism

    SciTech Connect

    Johnson, P.D.; Brookes, N.B.; Chang, Y.; Garrison, K.

    1993-06-01

    Spin polarized photoemission is used to study the electronic structure of noble metals deposited on ferromagnetic substrates. Studies of Ag deposited on an Fe(001) substrate reveal a series of minority spin interface or quantum well states with binding energies dependent on the thickness of the silver. Similar behavior is observed for Cu films deposited on a fct Co(001) substrate. Tight-binding modeling reproduces many of the observations and shows that hybridization of the sp-bands with the noble metal d-bands cannot be ignored.

  4. Surface plasmon enhanced photodetectors based on internal photoemission

    NASA Astrophysics Data System (ADS)

    Alavirad, Mohammad; Roy, Langis; Berini, Pierre

    2016-10-01

    Surface plasmon photodetectors are of broad interest. They are promising for several applications including telecommunications, photovoltaic solar cells, photocatalysis, color-sensitive detection, and sensing, as they can provide highly enhanced fields and strong confinement (to subwavelength scales). Such photodetectors typically combine a nanometallic structure that supports surface plasmons with a photodetection structure based on internal photoemission or electron-hole pair creation. Photodetector architectures are highly varied, including waveguides, gratings, nanoparticles, nanoislands, or nanoantennas. We review the operating principles behind surface plasmon photodetectors based on the internal photoelectric effect, and we survey and compare the most recent and leading edge concepts reported in the literature.

  5. Laser-Based Diagnostic Measurements of Low Emissions Combustor Concepts

    NASA Technical Reports Server (NTRS)

    Hicks, Yolanda R.

    2011-01-01

    This presentation provides a summary of primarily laser-based measurement techniques we use at NASA Glenn Research Center to characterize fuel injection, fuel/air mixing, and combustion. The report highlights using Planar Laser-Induced Fluorescence, Particle Image Velocimetry, and Phase Doppler Interferometry to obtain fuel injector patternation, fuel and air velocities, and fuel drop sizes and turbulence intensities during combustion. We also present a brief comparison between combustors burning standard JP-8 Jet fuel and an alternative fuels. For this comparison, we used flame chemiluminescence and high speed imaging.

  6. Comparison of laser-based rapid prototyping techniques

    NASA Astrophysics Data System (ADS)

    Humphreys, Hugh; Wimpenny, David

    2002-04-01

    A diverse range of Rapid Prototyping, or layer manufacturing techniques have evolved since the introduction of the first process in the late 1980s. Many, although not all, rapid prototyping processes rely on lasers to provide a localised and controllable source of light for curing a liquid photopolymer or heat to fuse thermoplastic powders to form objects. This paper will provide an overview of laser based rapid prototyping methods and discuss the future direction of this technology in light of the threats posed by low cost 3D printing techniques and the opportunity for the direct manufacture of metal components.

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

    NASA Astrophysics Data System (ADS)

    Pasmans, P. L. E. M.; van Vugt, D. C.; van Lieshout, J. P.; Brussaard, G. J. H.; Luiten, O. J.

    2016-10-01

    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.

  8. Simple laser-based pipeline corrosion assessment system

    SciTech Connect

    Bruce, W.A.; Yapp, D.; Barborak, D.M.; Fingerhut, M.P.; Kania, R.

    1997-03-01

    The article focuses on development and use of a simpler laser-based system for accurately and efficiently measuring and assessing corrosion damage on the external surface of an exposed pipeline. The system uses a laser-based range sensor, which relies on optical spray, sensor movement, and the principal of triangulation to construct a three-dimensional measurement. Baseline subtraction, where a polynomial curve-fit is used to approximate the ideal pipe profile above the corroded area, is used. Future profiles are subtracted from the ideal profile, and when differences are significant, corrosion depth measurements are made by constructing normal vectors at points along the ideal profile. The use of such a system for accurately mapping corrosion damage allows more accurate assessments, thereby reducing the number of unnecessary repairs and cut outs, and reduces the risk of non-conservative assessments. The use of this system also results in reduced labor costs associated with mapping corrosion damage and allows the assessment process to be carried out over a much shorter period of time. The system can also be used to develop an accurate correlation between inline inspection (ILI) results and corrosion geometry during the first few excavations following ILI, resulting in the need to excavate fewer areas.

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

    SciTech Connect

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

    2014-07-17

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

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

    PubMed

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

    2016-12-21

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-12-01

    Recently, α-RuCl3 has attracted much attention as a possible material to realize the honeycomb Kitaev model of a quantum-spin-liquid state. Although the magnetic properties of α-RuCl3 have been extensively studied, its electronic structure, which is strongly related to its Kitaev physics, is poorly understood. Here, the electronic structure of α-RuCl3 was investigated by photoemission (PE) and inverse-photoemission (IPE) spectroscopies. The band gap was directly measured from the PE and IPE spectra and was found to be 1.9 eV, much larger than previously estimated values. Local density approximation (LDA) calculations showed that the on-site Coulomb interaction U could open the band gap without spin-orbit coupling (SOC). However, the SOC should also be incorporated to reproduce the proper gap size, indicating that the interplay between U and SOC plays an essential role. Several features of the PE and IPE spectra could not be explained by the results of LDA calculations. To explain such discrepancies, we performed configuration-interaction calculations for a RuCl63‑ cluster. The experimental data and calculations demonstrated that the 4d compound α-RuCl3 is a Jeff = 1/2 Mott insulator rather than a quasimolecular-orbital insulator. Our study also provides important physical parameters required for verifying the proposed Kitaev physics in α-RuCl3.

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

    PubMed Central

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

    2016-01-01

    Recently, α-RuCl3 has attracted much attention as a possible material to realize the honeycomb Kitaev model of a quantum-spin-liquid state. Although the magnetic properties of α-RuCl3 have been extensively studied, its electronic structure, which is strongly related to its Kitaev physics, is poorly understood. Here, the electronic structure of α-RuCl3 was investigated by photoemission (PE) and inverse-photoemission (IPE) spectroscopies. The band gap was directly measured from the PE and IPE spectra and was found to be 1.9 eV, much larger than previously estimated values. Local density approximation (LDA) calculations showed that the on-site Coulomb interaction U could open the band gap without spin-orbit coupling (SOC). However, the SOC should also be incorporated to reproduce the proper gap size, indicating that the interplay between U and SOC plays an essential role. Several features of the PE and IPE spectra could not be explained by the results of LDA calculations. To explain such discrepancies, we performed configuration-interaction calculations for a RuCl63− cluster. The experimental data and calculations demonstrated that the 4d compound α-RuCl3 is a Jeff = 1/2 Mott insulator rather than a quasimolecular-orbital insulator. Our study also provides important physical parameters required for verifying the proposed Kitaev physics in α-RuCl3. PMID:28000731

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

    PubMed

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

    2014-07-17

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

  14. Simultaneous measurements of photoemission and morphology of various Al alloys during mechanical deformation

    SciTech Connect

    Cai, M.; Li, W.; Dickinson, J. T.

    2006-11-15

    We report simultaneous measurements of strain and photoelectron emission from high purity Al (1350), Al-Mg (5052), Al-Mn (3003), Al-Cu (2024), and Al-Mg-Si (6061) alloys under uniaxial tension due to pulsed excimer laser radiation (248 nm). The emission of low-energy photoelectrons is sensitive to deformation-induced changes in surface morphology, including the formation of slip lines and slip bands. Alloy composition and surface treatment significantly influence the photoemission during deformation. Surface oxide enhances the signal-to-noise level during photoemission measurement. In the early stage of deformation (strain {<=}0.04), photoemission intensity increases gradually in a nonlinear fashion. While subsequent photoemission increases almost linearly with strain until failure in samples with thin oxide layer ({approx}31 A ring ), there are two linear segments of photoemission for the samples with oxide of 45 A ring . The onset of strain localization corresponds to the intersection point of two linear segments, usually at a strain of 0.08-0.20. A constitutive model incorporating microstructure evolution and work hardening during tensile deformation is proposed to qualitatively interpret the growth of the photoemission as a function of strain. Photoemissions from various alloys are interpreted in the light of surface treatment, work function, composition, and microstructural development during deformation.

  15. Axion search by laser-based experiment OSQAR

    NASA Astrophysics Data System (ADS)

    Sulc, M.; Pugnat, P.; Ballou, R.; Deferne, G.; Duvillaret, L.; Flekova, L.; Finger, M.; Finger, M.; Hosek, J.; Husek, T.; Jost, R.; Kral, M.; Kunc, S.; Macuchova, K.; Meissner, K. A.; Morville, J.; Romanini, D.; Schott, M.; Siemko, A.; Slunecka, M.; Vitrant, G.; Zicha, J.

    2013-08-01

    Laser-based experiment OSQAR in CERN is aimed to the search of the axions by two methods. The photon regeneration experiment is using two LHC dipole magnets of the length 14.3 m and magnetic field 9.5 T equipped with an optical barrier at the end of the first magnet. It looks as light shining through the wall. No excess of events above the background was detected at this arrangement. Nevertheless, this result extends the exclusion region for the axion mass. The second method wants to measure the ultra-fine vacuum magnetic birefringence for the first time. An optical scheme with electro-optical modulator has been proposed, validated and subsequently improved. Cotton-Mouton constant for air was determined in this experiment setup.

  16. Pulsed diode laser-based monitor for singlet molecular oxygen

    PubMed Central

    Lee, Seonkyung; Zhu, Leyun; Minhaj, Ahmed M.; Hinds, Michael F.; Vu, Danthu H.; Rosen, David I.; Davis, Steven J.; Hasan, Tayyaba

    2010-01-01

    Photodynamic therapy (PDT) is a promising cancer treatment. PDT uses the affinity of photosensitizers to be selectively retained in malignant tumors. When tumors, pretreated with the photosensitizer, are irradiated with visible light, a photochemical reaction occurs and tumor cells are destroyed. Oxygen molecules in the metastable singlet delta state O2(1Δ) are believed to be the species that destroys cancerous cells during PDT. Monitoring singlet oxygen produced by PDT may lead to more precise and effective PDT treatments. Our approach uses a pulsed diode laser-based monitor with optical fibers and a fast data acquisition system to monitor singlet oxygen during PDT. We present results of in vitro singlet oxygen detection in solutions and in a rat prostate cancer cell line as well as PDT mechanism modeling. PMID:18601555

  17. Laser-based instrumentation for the detection of chemical agents

    SciTech Connect

    Hartford, A. Jr.; Sander, R.K.; Quigley, G.P.; Radziemski, L.J.; Cremers, D.A.

    1982-01-01

    Several laser-based techniques are being evaluated for the remote, point, and surface detection of chemical agents. Among the methods under investigation are optoacoustic spectroscopy, laser-induced breakdown spectroscopy (LIBS), and synchronous detection of laser-induced fluorescence (SDLIF). Optoacoustic detection has already been shown to be capable of extremely sensitive point detection. Its application to remote sensing of chemical agents is currently being evaluated. Atomic emission from the region of a laser-generated plasma has been used to identify the characteristic elements contained in nerve (P and F) and blister (S and Cl) agents. Employing this LIBS approach, detection of chemical agent simulants dispersed in air and adsorbed on a variety of surfaces has been achieved. Synchronous detection of laser-induced fluorescence provides an attractive alternative to conventional LIF, in that an artificial narrowing of the fluorescence emission is obtained. The application of this technique to chemical agent simulants has been successfully demonstrated. 19 figures.

  18. Diode laser based water vapor DIAL using modulated pulse technique

    NASA Astrophysics Data System (ADS)

    Pham, Phong Le Hoai; Abo, Makoto

    2014-11-01

    In this paper, we propose a diode laser based differential absorption lidar (DIAL) for measuring lower-tropospheric water vapor profile using the modulated pulse technique. The transmitter is based on single-mode diode laser and tapered semiconductor optical amplifier with a peak power of 10W around 800nm absorption band, and the receiver telescope diameter is 35cm. The selected wavelengths are compared to referenced wavelengths in terms of random error and systematic errors. The key component of modulated pulse technique, a macropulse, is generated with a repetition rate of 10 kHz, and the modulation within the macropulse is coded according to a pseudorandom sequence with 100ns chip width. As a result, we evaluate both single pulse modulation and pseudorandom coded pulse modulation technique. The water vapor profiles conducted from these modulation techniques are compared to the real observation data in summer in Japan.

  19. A laser-based vision system for weld quality inspection.

    PubMed

    Huang, Wei; Kovacevic, Radovan

    2011-01-01

    Welding is a very complex process in which the final weld quality can be affected by many process parameters. In order to inspect the weld quality and detect the presence of various weld defects, different methods and systems are studied and developed. In this paper, a laser-based vision system is developed for non-destructive weld quality inspection. The vision sensor is designed based on the principle of laser triangulation. By processing the images acquired from the vision sensor, the geometrical features of the weld can be obtained. Through the visual analysis of the acquired 3D profiles of the weld, the presences as well as the positions and sizes of the weld defects can be accurately identified and therefore, the non-destructive weld quality inspection can be achieved.

  20. Electric field stimulation setup for photoemission electron microscopes.

    PubMed

    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.

  1. Electric field stimulation setup for photoemission electron microscopes

    SciTech Connect

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

    2015-08-15

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

  2. heterojunction interface investigated by X-ray photoemission spectroscopy

    NASA Astrophysics Data System (ADS)

    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.

  3. Electric field stimulation setup for photoemission electron microscopes

    NASA Astrophysics Data System (ADS)

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

    2015-08-01

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

  4. Photoemission microscopy from magnetically coupled thin-film systems

    NASA Astrophysics Data System (ADS)

    Schneider, C. M.; de Haas, O.; Muschiol, U.; Cramer, N.; Oelsner, A.; Klais, M.; Schmidt, O.; Fecher, G. H.; Jark, W.; Schönhense, G.

    2001-07-01

    The magnetic microstructure and magnetic coupling phenomena in thin-film systems, relevant for applications in magneto-electronics, are investigated by means of photoemission electron microscopy. Element-selective magnetic information is obtained by exploiting magnetic circular dichroism in the soft X-ray regime. The domain shape and sizes found at the surface of antiferromagnetically coupled metallic multilayers indicate the presence of a ferromagnetic coupling contribution, presumably caused by a build-up of roughness during the growth process. The magnetic domain patterns in FeNi microstructures on sputtered NiO films reflect the presence of a local exchange anisotropy, causing the phenomenon of exchange biasing or pinning of the ferromagnetic layer.

  5. Calculation of 3s photoemission spectra of vanadium on graphite

    SciTech Connect

    Krueger, P.; Taguchi, M.; Parlebas, J.C.; Kotani, A.

    1997-06-01

    A few years ago, a satellite structure in the vanadium 3s x-ray photoemission spectroscopy (XPS) spectrum of V clusters upon graphite was observed and attributed to the presence of magnetic moments on the V surface. Here, we present calculations of these spectra using a cluster model that takes into account intra-atomic d-d and d{endash}core electron correlation and hybridization between V d and graphite {pi} states. When the V-graphite distance is increased from 1.5 to 2.0 {Angstrom} the system undergoes a low-to-high spin transition, which is clearly evidenced in the evolution of the XPS line shape. Although direct comparison with experiment is difficult, our study suggests that the observed satellite is due to core hole screening rather than a magnetic moment on the V atom. {copyright} {ital 1997} {ital The American Physical Society}

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

    NASA Astrophysics Data System (ADS)

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

    2017-01-01

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

  7. Photoemission characteristics of thin GaAs-based heterojunction photocathodes

    SciTech Connect

    Feng, Cheng; Zhang, Yijun Qian, Yunsheng; Shi, Feng; Zou, Jijun; Zeng, Yugang

    2015-01-14

    To better understand the different photoemission mechanism of thin heterojunction photocathodes, the quantum efficiency models of reflection-mode and transmission-mode GaAs-based heterojunction photocathodes are revised based on one-dimensional continuity equations, wherein photoelectrons generated from both the emission layer and buffer layer are taken into account. By comparison of simulated results between the revised and conventional models, it is found that the electron contribution from the buffer layer to shortwave quantum efficiency is closely related to some factors, such as the thicknesses of emission layer and buffer layer and the interface recombination velocity. Besides, the experimental quantum efficiency data of reflection-mode and transmission-mode AlGaAs/GaAs photocathodes are well fitted to the revised models, which confirm the applicability of the revised quantum efficiency models.

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

    NASA Astrophysics Data System (ADS)

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

    2017-03-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1977-01-01

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

  10. Inverse photoemission of adsorbed xenon multilayers on Ru(001): Refutation of final-state screening effects

    NASA Astrophysics Data System (ADS)

    Wandelt, K.; Jacob, W.; Memmel, N.; Dose, V.

    1986-09-01

    In this Letter we describe photoemission and inverse photoemission spectra of adsorbed xenon multilayers on Ru(001). Electron energy-loss spectra of xenon adsorbed on gold by Demuth, Avouris, and Schmeisser are included in the discussion. The observed layer-dependent shifts of the inverse photoemission spectra closer to the Fermi level clearly invalidate image screening effects as being the dominant cause of these shifts but support a ``floating'' of the adsorbed Xe potential well as a whole with the surface potential in the initial state.

  11. Angle-resolved heat capacity of heavy fermion superconductors

    NASA Astrophysics Data System (ADS)

    Sakakibara, Toshiro; Kittaka, Shunichiro; Machida, Kazushige

    2016-09-01

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

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

    PubMed

    Sakakibara, Toshiro; Kittaka, Shunichiro; Machida, Kazushige

    2016-09-01

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

  13. Angle-resolved reflectance of obliquely aligned silver nanorods.

    PubMed

    Wang, X J; Abell, J L; Zhao, Y-P; Zhang, Z M

    2012-04-01

    Arrays of silver nanorods (AgNRs) formed by oblique-angle deposition (OAD) are strongly anisotropic, with either metallic or dielectric characteristics depending on the polarization of incident light, and may be used to enhance Raman scattering and surface plasmon polaritons. This work investigates the polarization-dependent reflectance of inclined AgNR arrays at the wavelengths of 635 and 977 nm. The specular reflectance at various incidence angles and the bidirectional reflectance distribution function were measured with a laser scatterometer, while the directional-hemispherical reflectance was measured with an integrating sphere. The AgNR layer is modeled as an effectively homogenous, optically uniaxial material using the effective medium theory to elucidate the dielectric or metallic response for differently polarized incidence. The thin-film optics formulation is modified considering optical anisotropy and surface scattering. This study helps gain a better understanding of optical properties of nanostructured materials.

  14. Angle-Resolved Polarimetry of Antenna-Mediated Fluorescence

    NASA Astrophysics Data System (ADS)

    Mohtashami, Abbas; Osorio, Clara I.; Koenderink, A. Femius

    2015-11-01

    Optical phase-array antennas can be used to control not only the angular distribution but also the polarization of fluorescence from quantum emitters. The emission pattern of the resulting system is determined by the properties of the antenna, the properties of the emitters, and the strength of the antenna-emitter coupling. Here we show that Fourier polarimetry can be used to characterize these three contributions. To this end, we measure the angle- and Stokes-parameter-resolved emission of bullseye plasmon antennas as well as spiral antennas excited by an ensemble of emitters. We estimate the average antenna-emitter coupling on the basis of the degree of polarization and determine the effect of anisotropy in the intrinsic emitter orientation on polarization of the resulting emission pattern. Our results provide not only new insights into the behavior of bullseye and spiral antennas but also demonstrate the potential of Fourier polarimetry when characterizing antenna-mediated fluorescence.

  15. Photoemission studies of classic and novel thermoelectric materials

    NASA Astrophysics Data System (ADS)

    Greanya, Viktoria Augusta

    Thermoelectric materials have been studied vigorously since the 1950s. Recent advances in materials synthesis and theory have rejuvinated the field in the last decade. The thermoelectric properties of materials are related to their electronic structure. In addition, many of these materials behave quasi-low-dimensionally, making them ideal candidates for study using angle resolved and angle integrated photoelectron spectroscopy (ARPES and AIPES). We report the first detailed study of the valence band electronic structure of Bi2Te3, Bi2Se3 and CsBi 4Te6 using ARPES and AIPES. Experimental results are compared with local density approximation (LDA) band structure calculations and (when available) with de Haas-van Alphen and Shubnikov-de Haas experiments. Bi2Te3 is currently the best room temperature thermoelectric material known. Dispersions of the valence bands were determined using ARPES. A six-fold k-space degeneracy in the valence band maximum is found. The quasi-two-dimensional nature of the electronic structure was demonstrated by the weakly dispersive bands along the Gamma-Z direction. The density of states (DOS) for this material was also studied using AIPES. Spectra were taken at multiple photon energies. Six valence band peaks were found. Good correspondence with the calculated DOS was found. Bi2Se3 is isostructural to Bi2Te 3 but its thermoelectric performance is significantly worse. The valence band dispersions for this material have been determined, as well as the DOS. We find the valence band maximum to be located at Gamma. Ten easily identifiable bands are seen within 4 eV of the Fermi level. The energy bands in the Gamma-Z direction are found to be flatter than those predicted by theory. The APES measurements revealed a total of nine bands, which correspond well to the calculated DOS. CsBi4Te6 is a novel thermoelectric material, recently discovered in the chemistry department of Michigan State University. This material exhibits quasi

  16. Surface studies of solids using integral X-ray-induced photoemission yield

    PubMed Central

    Stoupin, Stanislav; Zhernenkov, Mikhail; Shi, Bing

    2016-01-01

    X-ray induced photoemission yield contains structural information complementary to that provided by X-ray Fresnel reflectivity, which presents an advantage to a wide variety of surface studies if this information is made easily accessible. Photoemission in materials research is commonly acknowledged as a method with a probing depth limited by the escape depth of the photoelectrons. Here we show that the integral hard-X-ray-induced photoemission yield is modulated by the Fresnel reflectivity of a multilayer structure and carries structural information that extends well beyond the photoelectron escape depth. A simple electric self-detection of the integral photoemission yield and Fourier data analysis permit extraction of thicknesses of individual layers. The approach does not require detection of the reflected radiation and can be considered as a framework for non-invasive evaluation of buried layers with hard X-rays under grazing incidence. PMID:27874041

  17. Quantitative Analysis of Valence Photoemission Spectra and Quasiparticle Excitations at Chromophore-Semiconductor Interfaces

    NASA Astrophysics Data System (ADS)

    Patrick, Christopher E.; Giustino, Feliciano

    2012-09-01

    Investigating quasiparticle excitations of molecules on surfaces through photoemission spectroscopy forms a major part of nanotechnology research. Resolving spectral features at these interfaces requires a comprehensive theory of electron removal and addition processes in molecules and solids which captures the complex interplay of image charges, thermal effects, and configurational disorder. Here, we develop such a theory and calculate the quasiparticle energy-level alignment and the valence photoemission spectrum for the prototype biomimetic solar cell interface between anatase TiO2 and the N3 chromophore. By directly matching our calculated photoemission spectrum to experimental data, we clarify the atomistic origin of the chromophore peak at low binding energy. This case study sets a new standard in the interpretation of photoemission spectroscopy at complex chromophore-semiconductor interfaces.

  18. Surface studies of solids using integral x-ray-induced photoemission yield

    DOE PAGES

    Stoupin, Stanislav; Zhernenkov, Mikhail; Shi, Bing

    2016-11-22

    X-ray induced photoemission yield contains structural information complementary to that provided by X-ray Fresnel reflectivity, which presents an advantage to a wide variety of surface studies if this information is made easily accessible. Photoemission in materials research is commonly acknowledged as a method with a probing depth limited by the escape depth of the photoelectrons. Here we show that the integral hard-X-ray-induced photoemission yield is modulated by the Fresnel reflectivity of a multilayer structure and carries structural information that extends well beyond the photoelectron escape depth. A simple electric self-detection of the integral photoemission yield and Fourier data analysis permitmore » extraction of thicknesses of individual layers. The approach does not require detection of the reflected radiation and can be considered as a framework for non-invasive evaluation of buried layers with hard X-rays under grazing incidence.« less

  19. Surface studies of solids using integral x-ray-induced photoemission yield

    SciTech Connect

    Stoupin, Stanislav; Zhernenkov, Mikhail; Shi, Bing

    2016-11-22

    X-ray induced photoemission yield contains structural information complementary to that provided by X-ray Fresnel reflectivity, which presents an advantage to a wide variety of surface studies if this information is made easily accessible. Photoemission in materials research is commonly acknowledged as a method with a probing depth limited by the escape depth of the photoelectrons. Here we show that the integral hard-X-ray-induced photoemission yield is modulated by the Fresnel reflectivity of a multilayer structure and carries structural information that extends well beyond the photoelectron escape depth. A simple electric self-detection of the integral photoemission yield and Fourier data analysis permit extraction of thicknesses of individual layers. The approach does not require detection of the reflected radiation and can be considered as a framework for non-invasive evaluation of buried layers with hard X-rays under grazing incidence.

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

    NASA Astrophysics Data System (ADS)

    Zhang, Jiandi

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

  1. Subjective speckle suppression in laser-based stereo photogrammetry

    NASA Astrophysics Data System (ADS)

    Stark, Andreas Walter; Wong, Eugene; Weigel, Daniel; Babovsky, Holger; Schott, Thomas; Kowarschik, Richard

    2016-12-01

    The use of objective speckles as patterns is of high interest for the ongoing development of stereo photogrammetry. The depth of focus of the projected speckle patterns, which can be found to be several meters, can hardly be matched by other projection principles. On the downside, the use of coherent light leads to subjective speckles generated by the rough surface of the object under test. This effect decreases the accuracy under which objects can be reconstructed. We show how laser-based stereo photogrammetry can be adjusted to increase the measurement accuracy of three-dimensional (3-D)-surface measurements while preserving the advantages of speckles projection. Therefore, we present a method to decrease the contrast of subjective speckles in the images by pixel-wise shifting the cameras orthogonally to their viewing direction and back shifting the taken images numerically, accordingly. This leads to an increase in 3-D-reconstruction quality, as seen in a decrease in standard deviation, peak-to-valley value and in an increase in the number of reconstructed points for measured test objects.

  2. Damage detection technique by measuring laser-based mechanical impedance

    SciTech Connect

    Lee, Hyeonseok; Sohn, Hoon

    2014-02-18

    This study proposes a method for measurement of mechanical impedance using noncontact laser ultrasound. The measurement of mechanical impedance has been of great interest in nondestructive testing (NDT) or structural health monitoring (SHM) since mechanical impedance is sensitive even to small-sized structural defects. Conventional impedance measurements, however, have been based on electromechanical impedance (EMI) using contact-type piezoelectric transducers, which show deteriorated performances induced by the effects of a) Curie temperature limitations, b) electromagnetic interference (EMI), c) bonding layers and etc. This study aims to tackle the limitations of conventional EMI measurement by utilizing laser-based mechanical impedance (LMI) measurement. The LMI response, which is equivalent to a steady-state ultrasound response, is generated by shooting the pulse laser beam to the target structure, and is acquired by measuring the out-of-plane velocity using a laser vibrometer. The formation of the LMI response is observed through the thermo-mechanical finite element analysis. The feasibility of applying the LMI technique for damage detection is experimentally verified using a pipe specimen under high temperature environment.

  3. Stochastic resonance-enhanced laser-based particle detector.

    PubMed

    Dutta, A; Werner, C

    2009-01-01

    This paper presents a Laser-based particle detector whose response was enhanced by modulating the Laser diode with a white-noise generator. A Laser sheet was generated to cast a shadow of the object on a 200 dots per inch, 512 x 1 pixels linear sensor array. The Laser diode was modulated with a white-noise generator to achieve stochastic resonance. The white-noise generator essentially amplified the wide-bandwidth (several hundred MHz) noise produced by a reverse-biased zener diode operating in junction-breakdown mode. The gain in the amplifier in the white-noise generator was set such that the Receiver Operating Characteristics plot provided the best discriminability. A monofiber 40 AWG (approximately 80 microm) wire was detected with approximately 88% True Positive rate and approximately 19% False Positive rate in presence of white-noise modulation and with approximately 71% True Positive rate and approximately 15% False Positive rate in absence of white-noise modulation.

  4. Detecting Molecular Properties by Various Laser-Based Techniques

    SciTech Connect

    Hsin, Tse-Ming

    2007-01-01

    Four different laser-based techniques were applied to study physical and chemical characteristics of biomolecules and dye molecules. These techniques are liole burning spectroscopy, single molecule spectroscopy, time-resolved coherent anti-Stokes Raman spectroscopy and laser-induced fluorescence microscopy. Results from hole burning and single molecule spectroscopy suggested that two antenna states (C708 & C714) of photosystem I from cyanobacterium Synechocystis PCC 6803 are connected by effective energy transfer and the corresponding energy transfer time is ~6 ps. In addition, results from hole burning spectroscopy indicated that the chlorophyll dimer of the C714 state has a large distribution of the dimer geometry. Direct observation of vibrational peaks and evolution of coumarin 153 in the electronic excited state was demonstrated by using the fs/ps CARS, a variation of time-resolved coherent anti-Stokes Raman spectroscopy. In three different solvents, methanol, acetonitrile, and butanol, a vibration peak related to the stretch of the carbonyl group exhibits different relaxation dynamics. Laser-induced fluorescence microscopy, along with the biomimetic containers-liposomes, allows the measurement of the enzymatic activity of individual alkaline phosphatase from bovine intestinal mucosa without potential interferences from glass surfaces. The result showed a wide distribution of the enzyme reactivity. Protein structural variation is one of the major reasons that are responsible for this highly heterogeneous behavior.

  5. Diode-Laser-Based Spectrometer for Sensing Gases

    NASA Technical Reports Server (NTRS)

    Silver, Joel A.

    2005-01-01

    A diode-laser-based spectrometer has been developed for measuring concentrations of gases and is intended particularly for use in analyzing and monitoring combustion processes under microgravitational conditions in a drop tower or a spacecraft. This instrument is also well suited for use on Earth in combustion experiments and for such related purposes as fire-safety monitoring and monitoring toxic and flammable gases in industrial settings. Of the gas-sensing spectrometers available prior to the development of this instrument, those that were sensitive enough for measuring the combustion gases of interest were too large, required critical optical alignments, used far too much electrical power, and were insufficiently rugged for use under the severe conditions of spacecraft launch and space flight. In contrast, the present instrument is compact, consumes relatively little power, and is rugged enough to withstand launch vibrations and space flight. In addition, this instrument is characterized by long-term stability, accuracy, and reliability. The diode laser in this spectrometer is operated in a wavelength-modulation mode. Different gases to be measured can be selected by changing modular laser units. The operation of the laser is controlled by customized, low-power electronic circuitry built around a digital signal-processor board. This customized circuitry also performs acquisition and analysis of data, controls communications, and manages errors.

  6. Dental hard tissue characterization using laser-based ultrasonics

    NASA Astrophysics Data System (ADS)

    Blodgett, David W.; Massey, Ward L.

    2003-07-01

    Dental health care and research workers require a means of imaging the structures within teeth in vivo. One critical need is the detection of tooth decay in its early stages. If decay can be detected early enough, the process can be monitored and interventional procedures, such as fluoride washes and controlled diet, can be initiated to help re-mineralize the tooth. Currently employed x-ray imaging is limited in its ability to visualize interfaces and incapable of detecting decay at a stage early enough to avoid invasive cavity preparation followed by a restoration. To this end, non-destructive and non-contact in vitro measurements on extracted human molars using laser-based ultrasonics are presented. Broadband ultrasonic waves are excited in the extracted sections by using a pulsed carbon-dioxide (CO2) laser operating in a region of high optical absorption in the dental hard tissues. Optical interferometric detection of the ultrasonic wave surface displacements in accomplished with a path-stabilized Michelson-type interferometer. Results for bulk and surface in-vitro characterization of caries are presented on extracted molars with pre-existing caries.

  7. Beam shaping for laser-based adaptive optics in astronomy.

    PubMed

    Béchet, Clémentine; Guesalaga, Andrés; Neichel, Benoit; Fesquet, Vincent; González-Núñez, Héctor; Zúñiga, Sebastián; Escarate, Pedro; Guzman, Dani

    2014-06-02

    The availability and performance of laser-based adaptive optics (AO) systems are strongly dependent on the power and quality of the laser beam before being projected to the sky. Frequent and time-consuming alignment procedures are usually required in the laser systems with free-space optics to optimize the beam. Despite these procedures, significant distortions of the laser beam have been observed during the first two years of operation of the Gemini South multi-conjugate adaptive optics system (GeMS). A beam shaping concept with two deformable mirrors is investigated in order to provide automated optimization of the laser quality for astronomical AO. This study aims at demonstrating the correction of quasi-static aberrations of the laser, in both amplitude and phase, testing a prototype of this two-deformable mirror concept on GeMS. The paper presents the results of the preparatory study before the experimental phase. An algorithm to control amplitude and phase correction, based on phase retrieval techniques, is presented with a novel unwrapping method. Its performance is assessed via numerical simulations, using aberrations measured at GeMS as reference. The results predict effective amplitude and phase correction of the laser distortions with about 120 actuators per mirror and a separation of 1.4 m between the mirrors. The spot size is estimated to be reduced by up to 15% thanks to the correction. In terms of AO noise level, this has the same benefit as increasing the photon flux by 40%.

  8. Ceramic Coating Inspection Using Laser-Based Ultrasonics and Nanoindentation

    SciTech Connect

    Steen, T. L.; Murray, T. W.; Basu, S. N.; Sarin, V. K.

    2007-03-21

    A combination of laser-based ultrasonic (LBU) inspection and nanoindentation testing is used to evaluate the thickness uniformity and through-thickness mechanical property distributions in 5-20 {mu}m thick CVD environmental barrier coatings. Mullite (3Al2O3{center_dot}2SiO2) coatings grown on silicon carbide substrates are studied in order to provide feedback on the growth process under a range of operating conditions. Nanoindentation tests are performed on polished coating cross sections, and the depth dependence of the elastic modulus of each coating is found. In the LBU experiments, a modulated continuous wave (CW) source is used for surface wave generation. The source is held at a fixed temporal frequency as it is scanned over the surface of the coating. At each temporal frequency of interest, the spatial frequencies of the acoustic modes are found, allowing for phase velocities to be determined. The mean values of elastic moduli found using the LBU approach compare well with the nanoindentation results.

  9. Advances in laser-based isotope ratio measurements: selected applications

    NASA Astrophysics Data System (ADS)

    Kerstel, E.; Gianfrani, L.

    2008-09-01

    Small molecules exhibit characteristic ro-vibrational transitions in the near- and mid-infrared spectral regions, which are strongly influenced by isotopic substitution. This gift of nature has made it possible to use laser spectroscopy for the accurate analysis of the isotopic composition of gaseous samples. Nowadays, laser spectroscopy is clearly recognized as a valid alternative to isotope ratio mass spectrometry. Laser-based instruments are leaving the research laboratory stage and are being used by a growing number of isotope researchers for significant advances in their own field of research. In this review article, we discuss the current status and new frontiers of research on high-sensitivity and high-precision laser spectroscopy for isotope ratio analyses. Although many of our comments will be generally applicable to laser isotope ratio analyses in molecules of environmental importance, this paper concerns itself primarily with water and carbon dioxide, two molecules that were studied extensively in our respective laboratories. A complete coverage of the field is practically not feasible in the space constraints of this issue, and in any case doomed to fail, considering the large body of work that has appeared ever since the review by Kerstel in 2004 ( Handbook of Stable Isotope Analytical Techniques, Chapt. 34, pp. 759-787).

  10. Versatile optofluidic ring resonator lasers based on microdroplets.

    PubMed

    Lee, Wonsuk; Luo, Yunhan; Zhu, Qiran; Fan, Xudong

    2011-09-26

    We develop a novel nL-sized microdroplet laser based on the capillary optofluidic ring resonator (OFRR). The microdroplet is generated in a microfluidic channel using two immiscible fluids and is subsequently delivered to the capillary OFRR downstream. Despite the presence of the high refractive index (RI) carrier fluid, the lasing emission can still be achieved for the droplet formed by low RI solution. The lasing threshold of 1.54 µJ/mm(2) is achieved, >6 times lower than the state-of-the-art, thanks to the high Q-factor of the OFRR. Furthermore, the lasing emission can be conveniently coupled into an optical fiber. Finally, tuning of the lasing wavelength is achieved via highly efficient fluorescence resonance energy transfer processes by merging two different dye droplets in the microfluidic channel. Versatility combined with improved lasing characteristics makes our OFRR droplet laser an attractive platform for high performance optofluidic lasers and bio/chemical sensing with small sample volumes.

  11. Residual Stress Determination from a Laser-Based Curvature Measurement

    SciTech Connect

    Swank, William David; Gavalya, Rick Allen; Wright, Julie Knibloe; Wright, Richard Neil

    2000-05-01

    Thermally sprayed coating characteristics and mechanical properties are in part a result of the residual stress developed during the fabrication process. The total stress state in a coating/substrate is comprised of the quench stress and the coefficient of thermal expansion (CTE) mismatch stress. The quench stress is developed when molten particles impact the substrate and rapidly cool and solidify. The CTE mismatch stress results from a large difference in the thermal expansion coefficients of the coating and substrate material. It comes into effect when the substrate/coating combination cools from the equilibrated deposit temperature to room temperature. This paper describes a laser-based technique for measuring the curvature of a coated substrate and the analysis required to determine residual stress from curvature measurements. Quench stresses were determined by heating the specimen back to the deposit temperature thus removing the CTE mismatch stress. By subtracting the quench stress from the total residual stress at room temperature, the CTE mismatch stress was estimated. Residual stress measurements for thick (>1mm) spinel coatings with a Ni-Al bond coat on 304 stainless steel substrates were made. It was determined that a significant portion of the residual stress results from the quenching stress of the bond coat and that the spinel coating produces a larger CTE mismatch stress than quench stress.

  12. Residual stress determination from a laser-based curvature measurement

    SciTech Connect

    W. D. Swank; R. A. Gavalya; J. K. Wright; R. N. Wright

    2000-05-08

    Thermally sprayed coating characteristics and mechanical properties are in part a result of the residual stress developed during the fabrication process. The total stress state in a coating/substrate is comprised of the quench stress and the coefficient of thermal expansion (CTE) mismatch stress. The quench stress is developed when molten particles impact the substrate and rapidly cool and solidify. The CTE mismatch stress results from a large difference in the thermal expansion coefficients of the coating and substrate material. It comes into effect when the substrate/coating combination cools from the equilibrated deposit temperature to room temperature. This paper describes a laser-based technique for measuring the curvature of a coated substrate and the analysis required to determine residual stress from curvature measurements. Quench stresses were determined by heating the specimen back to the deposit temperature thus removing the CTE mismatch stress. By subtracting the quench stress from the total residual stress at room temperature, the CTE mismatch stress was estimated. Residual stress measurements for thick (>1mm) spinel coatings with a Ni-Al bond coat on 304 stainless steel substrates were made. It was determined that a significant portion of the residual stress results from the quenching stress of the bond coat and that the spinel coating produces a larger CTE mismatch stress than quench stress.

  13. High-energy photoemission studies of oxide interfaces

    NASA Astrophysics Data System (ADS)

    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

  14. Implementation and Optimization of an Inverse Photoemission Spectroscopy Setup

    NASA Astrophysics Data System (ADS)

    Gina, Ervin

    Inverse photoemission spectroscopy (IPES) is utilized for determining the unoccupied electron states of materials. It is a complementary technique to the widely used photoemission spectroscopy (PES) as it analyzes what PES cannot, the states above the Fermi energy. This method is essential to investigating the structure of a solid and its states. IPES has a broad range of uses and is only recently being utilized. This thesis describes the setup, calibration and operation of an IPES experiment. The IPES setup consists of an electron gun which emits electrons towards a sample, where photons are released, which are measured in isochromat mode via a photon detector of a set energy bandwidth. By varying the electron energy at the source, a spectrum of the unoccupied density of states can be obtained. Since IPES is not commonly commercially available the design consists of many custom made components. The photon detector operates as a bandpass filter with a mixture of acetone/argon and a CaF2 window setting the cutoff energies. The counter electronics consist of a pre-amplifier, amplifier and analyzer to detect the count rate at each energy level above the Fermi energy. Along with designing the hardware components, a Labview program was written to capture and log the data for further analysis. The software features several operating modes including automated scanning which allows the user to enter the desired scan parameters and the program will scan the sample accordingly. Also implemented in the program is the control of various external components such as the electron gun and high voltage power supply. The new setup was tested for different gas mixtures and an optimum ratio was determined. Subsequently, IPES scans of several sample materials were performed for testing and optimization. A scan of Au was utilized for the determination of the Fermi edge energy and for comparison to literature spectra. The Fermi edge energy was then used in a measurement of indium tin

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

    PubMed

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

    2015-01-28

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

  16. Photoemission study of Au on a-Si:H

    NASA Astrophysics Data System (ADS)

    Pi, Tun-Wen; Yang, A.-B.; Olson, C. G.; Lynch, D. W.

    1990-11-01

    We report a high-resolution photoemission study of Au evaporated on rf-sputtered a-Si:H at room temperature. Three regions of coverage can be classified according to the behavior of the valence-band and core-level spectra: an unreacted region with an equivalent thickness of 2 Å, followed by an intermixed Au/a-Si overlayer (~9 Å), and a dual-phase region at higher coverage. Au adatoms are dispersed in the unreacted region. They subsequently cluster in the intermixed region, where they attach to Si atoms that are not hydrogen bonded, suggesting that the intermixed Si is mainly from those that have dangling bonds. In the dual-phase region, two sets of Au 4f core levels evolve with higher binding energy, one from Au intermixed with Si, and the lower one exhibiting pure gold character. The interface eventually ends up with the sequence: a-Si:H(sub.)+(pure Au mixed with intermixed Au/Si)+(vac). This is unlike the case of Au on c-Si, which has a pure gold layer sandwiched by intermixed Au/Si complexes along the surface normal. Traces of silicon atoms on top of composite surfaces appear even at the highest coverage, 205 Å, of the gold deposit. The applicability of the four models previously used for the Au/c-Si interface is also briefly discussed.

  17. Photoemission studies using femtosecond pulses for high brightness electron beams

    NASA Astrophysics Data System (ADS)

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

    1990-06-01

    We present the results of a series of experiments where various metal photocathodes are irradiated with ultrashort laser pulses, whose characteristics are: (lambda) = 625 nm, (tau) = 100 fs, PRR = 89.5 MHz, H(nu) = 2 eV and average power 25 mW in each of the two beams. The quantum efficiency of the metals range from approximately 10(exp -12) to 10(exp -8) at a power density of 100 MW/sq cm at normal incidence. Since all the electrons are emitted due to multiphoton processes, these efficiencies are expected to increase substantially at large intensities. The efficiency at 100 MW/sq cm was increased by using p-polarized light at oblique incidence by approximately 20 x and by mediating the electron emission through surface plasmon excitation by approximately 10(exp 3) x. For the low intensities used in these experiments, the electron pulse duration is almost the same as the laser pulse duration for both the bulk and the surface plasmon mediated photoemission.

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

    SciTech Connect

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

    1997-04-01

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

  19. Photoemission experiments of a large area scandate dispenser cathode

    NASA Astrophysics Data System (ADS)

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

    2010-09-01

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

  20. Laser-based gluing of diamond-tipped saw blades

    NASA Astrophysics Data System (ADS)

    Hennigs, Christian; Lahdo, Rabi; Springer, André; Kaierle, Stefan; Hustedt, Michael; Brand, Helmut; Wloka, Richard; Zobel, Frank; Dültgen, Peter

    2016-03-01

    To process natural stone such as marble or granite, saw blades equipped with wear-resistant diamond grinding segments are used, typically joined to the blade by brazing. In case of damage or wear, they must be exchanged. Due to the large energy input during thermal loosening and subsequent brazing, the repair causes extended heat-affected zones with serious microstructure changes, resulting in shape distortions and disadvantageous stress distributions. Consequently, axial run-out deviations and cutting losses increase. In this work, a new near-infrared laser-based process chain is presented to overcome the deficits of conventional brazing-based repair of diamond-tipped steel saw blades. Thus, additional tensioning and straightening steps can be avoided. The process chain starts with thermal debonding of the worn grinding segments, using a continuous-wave laser to heat the segments gently and to exceed the adhesive's decomposition temperature. Afterwards, short-pulsed laser radiation removes remaining adhesive from the blade in order to achieve clean joining surfaces. The third step is roughening and activation of the joining surfaces, again using short-pulsed laser radiation. Finally, the grinding segments are glued onto the blade with a defined adhesive layer, using continuous-wave laser radiation. Here, the adhesive is heated to its curing temperature by irradiating the respective grinding segment, ensuring minimal thermal influence on the blade. For demonstration, a prototype unit was constructed to perform the different steps of the process chain on-site at the saw-blade user's facilities. This unit was used to re-equip a saw blade with a complete set of grinding segments. This saw blade was used successfully to cut different materials, amongst others granite.

  1. Laser-based techniques for living cell pattern formation

    NASA Astrophysics Data System (ADS)

    Hopp, Béla; Smausz, Tomi; Papdi, Bence; Bor, Zsolt; Szabó, András; Kolozsvári, Lajos; Fotakis, Costas; Nógrádi, Antal

    2008-10-01

    In the production of biosensors or artificial tissues a basic step is the immobilization of living cells along the required pattern. In this paper the ability of some promising laser-based methods to influence the interaction between cells and various surfaces is presented. In the first set of experiments laser-induced patterned photochemical modification of polymer foils was used to achieve guided adherence and growth of cells to the modified areas: (a) Polytetrafluoroethylene was irradiated with ArF excimer laser ( λ=193 nm, FWHM=20 ns, F=9 mJ/cm2) in presence of triethylene tetramine liquid photoreagent; (b) a thin carbon layer was produced by KrF excimer laser ( λ=248 nm, FWHM=30 ns, F=35 mJ/cm2) irradiation on polyimide surface to influence the cell adherence. It was found that the incorporation of amine groups in the PTFE polymer chain instead of the fluorine atoms can both promote and prevent the adherence of living cells (depending on the applied cell types) on the treated surfaces, while the laser generated carbon layer on polyimide surface did not effectively improve adherence. Our attempts to influence the cell adherence by morphological modifications created by ArF laser irradiation onto polyethylene terephtalate surface showed a surface roughness dependence. This method was effective only when the Ra roughness parameter of the developed structure did not exceed the 0.1 micrometer value. Pulsed laser deposition with femtosecond KrF excimer lasers ( F=2.2 J/cm2) was effectively used to deposit structured thin films from biomaterials (endothelial cell growth supplement and collagen embedded in starch matrix) to promote the adherence and growth of cells. These results present evidence that some surface can be successfully altered to induce guided cell growth.

  2. Novel remote phosphor design for laser-based white lighting application

    NASA Astrophysics Data System (ADS)

    Lee, Tsung-Xian; Chou, Ching-Chia; Chang, Shuo-Chieh

    2016-09-01

    Recently, there is an interest in the laser-based white light source for illumination and display applications. The laser-based white lights inherently have much higher luminance than the corresponding LEDs. Moreover, laser diodes are often more efficient when operating at higher current densities and are with smaller form factors, which may outperform LEDs in the future. Based on this, in this paper, we combine the design of the light guide and reflective type remote phosphor structures in order to improve the overall performance of the laser-based white light source. In addition, these well-designed white light sources will provide the more flexible architecture for designing the subsequent lighting system. With the introduction of the innovative design for the laser-based illumination system, multiple applications incorporating laser and remote phosphor elements for improving lighting efficiency and quality were obtained.

  3. Photoemission and magnetic circular dichroism studies of magnetic semiconductors

    NASA Astrophysics Data System (ADS)

    Fujimori, Atsushi

    2005-03-01

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

  4. Xe and Ar nanobubbles in Al studied by photoemission spectroscopy

    SciTech Connect

    Dhaka, R. S.; Biswas, C.; Shukla, A. K.; Barman, S. R.; Chakrabarti, Aparna

    2008-03-01

    We have studied xenon and argon bubbles formed in the subsurface region of Al(111) by x-ray photoelectron spectroscopy. As a consequence of the nanometer size of the bubbles, the photohole formed by Xe 3d or Ar 2p photoemission is screened by the Al conduction electrons, which substantially lowers the binding energy (BE) as compared to the gas phase. As the bubble size increases, the Al conduction electron screening decreases and the BE increases. On the basis of density functional theory, we show that the change in the bubble pressure with size is not responsible for the BE shift of inner shell core levels, such as Xe 3d or Ar 2p. On the other hand, an increase in BE with bubble size for outer shell core levels, such as Ar 3p, could be due to a decrease in both pressure and Al conduction electron screening. The core level line shape also changes with bubble size. For example, the spectra are broadened due to the distribution of the bubble radius around its mean value, and an asymmetry for small bubbles is observed that decreases for larger bubbles. An annealing of Xe and Ar bubbles after an implantation up to 640 K shows that the BE increases with annealing temperature. Since it is well known that bubble size increases with annealing temperature, this further supports our contention of BE shift with bubble size. A defect induced partial disorder of the Al(111) surface by Xe and Ar bombardment is observed by low energy electron diffraction, but this does not affect the Al 2p BE and line shape.

  5. Development and testing of a laser-based decontamination system

    NASA Astrophysics Data System (ADS)

    Anthofer, A.; Lippmann, W.; Hurtado, A.

    2013-06-01

    Decontamination of radioactive concrete surfaces may be necessary during operation or decommissioning of nuclear power plants. Usually only the upper layers of the concrete structure are contaminated and are removed using labor-intensive mechanical milling processes. Production of a large amount of dust, which can lead to secondary contamination, is inherent to these processes. Improvements in high-energy laser technology have now made it possible for laser radiation to be used in decontamination technologies for the removal of concrete layers. A decontamination unit comprising a diode laser with a beam power of 10 kW in continuous wave (CW) mode in combination with an autonomous manipulator was developed for use in nuclear plants. The laser beam melts the concrete surface to a depth of approximately 5 mm. Compressed air jets then detach the molten layer from the concrete surface and convey it to a suction system, with which it is transported to a collection container. Most of the radionuclides are trapped in the solidifying melt particles, which form an extremely stable effluent well suited to long-term storage. A relatively small amount of dust is generated in the process. Because there is no backlash during energy transfer, the laser device carrier can be designed to be lightweight and flexible. A specially developed manipulator that can move freely along walls and ceilings by means of suction plates is used for the carrier unit. This results in short setup times for preparing for use of the device and minimal personnel exposure to the radiation. Experiments were conducted on a concrete wall to demonstrate the functionality of the overall system in realistic conditions. An optimal ablation rate of 2.16 m²/h at an ablation depth of 1-5 mm was achieved. Today's commercially available diode lasers with powers higher than 50 kW enable ablation rates of >10 m²/h to be achieved and hence make these laser-based systems competitive alternatives to mechanical systems.

  6. Electrically tunable laser based on heliconical cholesteric (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Xiang, Jie; Varanytsia, Andrii; Minkowski, Fred; Paterson, Daniel A.; Imrie, Corrie T.; Lavrentovich, Oleg D.; Palffy-Muhoray, Peter

    2016-09-01

    STUDENT CONTRIBUTION: Cholesteric liquid crystals (CLC) self-assemble into a periodic supramolecular helical structure with properties of a one-dimensional photonic crystal. The CLCs doped with a fluorescent dye and optical pump enable a distributed feedback cavity and lasing [1]. Although lasing was observed in range of wavelength from near UV to near IR, a practical method of tuning of emission wavelength from a dye-doped CLC without structural destruction of a helix is not demonstrated yet. In this work, we demonstrate an electrically tunable dye-doped CLC laser based on the so-called oblique helicoidal, or heliconical, CLC state [2,3]. In this state, the molecules twist around the helicoidal axis, making an angle smaller than 90 degrees with the axis. Molecular tilt makes the heliconical structure different from the regular CLC (in which the molecules are perpendicular to the axis) and enable electric tunability [2,3]. An electric field applied parallel to the heliconical axis changes the pitch but does not realign the axis. When the field increases, the pitch decreases. As a result, the selective reflection band and a lasing wavelength move towards shorter wavelength. Using heliconical CLC and two laser dyes DCM and LD688, we demonstrate effective tuning of the laser emission wavelength from 574 nm to 722 nm. With appropriate laser dyes, the spectrum can be extended from near UV to near IR. Efficient electric tuning in the broad spectral range and small size of the heliconical cholesteric lasers makes them potentially useful for optical and biomedical applications. [1] P. Palffy-Muhoay, W.Y. Cao, M. Moreira, B. Taheri, A. Munoz, Photonics and lasing in liquid crystal [2] J. Xiang, S.V. Shiyanovskii, C.T. Imrie, O.D. Lavrentovich, Electrooptic Response of Chiral Nematic Liquid Crystals with Oblique Helicoidal Director, Phys Rev Lett, 112 (2014) 217801. [3] J. Xiang, Y.N. Li, Q. Li, D.A. Paterson, J.M.D. Storey, C.T. Imrie, O.D. Lavrentovich, Electrically

  7. Isotope effect on electron-phonon interaction in the multiband superconductor MgB2

    DOE PAGES

    Mou, Daixiang; Manni, Soham; Taufour, Valentin; ...

    2016-04-07

    We investigate the effect of isotope substitution on the electron-phonon interaction in the multiband superconductor MgB2 using tunable laser-based angle-resolved photoemission spectroscopy. The kink structure around 70 meV in the σ band, which is caused by electron coupling to the E2g phonon mode, is shifted to higher binding energy by ~3.5 meV in Mg10B2 and the shift is not affected by superconducting transition. Furthermore, these results serve as the benchmark for investigations of isotope effects in known, unconventional superconductors and newly discovered superconductors where the origin of pairing is unknown.

  8. Fermi Arcs and Their Topological Character in the Candidate Type-II Weyl Semimetal MoTe2

    NASA Astrophysics Data System (ADS)

    Tamai, A.; Wu, Q. S.; Cucchi, I.; Bruno, F. Y.; Riccò, S.; Kim, T. K.; Hoesch, M.; Barreteau, C.; Giannini, E.; Besnard, C.; Soluyanov, A. A.; Baumberger, F.

    2016-07-01

    We report a combined experimental and theoretical study of the candidate type-II Weyl semimetal MoTe2 . Using laser-based angle-resolved photoemission, we resolve multiple distinct Fermi arcs on the inequivalent top and bottom (001) surfaces. All surface states observed experimentally are reproduced by an electronic structure calculation for the experimental crystal structure that predicts a topological Weyl semimetal state with eight type-II Weyl points. We further use systematic electronic structure calculations simulating different Weyl point arrangements to discuss the robustness of the identified Weyl semimetal state and the topological character of Fermi arcs in MoTe2 .

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

    PubMed

    Thomas, Sebastian; Holzwarth, Ronald; Hommelhoff, Peter

    2012-06-18

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

  10. Resonant-photoemission identification of the valence states of NiPS 3

    NASA Astrophysics Data System (ADS)

    Kelly, M. K.; Daniels, R. R.; Margaritondo, G.; Lévy, F.

    1984-04-01

    We monitored the resonant behavior of the Ni d satellite peaks in the valence band photoemission spectra of NiPS 3 at photon energies immediately below and immediately above the Ni3p threshold. The observed resonance gives an unequivocal identification of the satellite peaks and of the corresponding main Ni d features. The study of the electronic structure of this material and of the related compounds FePS 3 and HgPS 3 was extended to unoccupied states by means of partial-yield synchrotron-radiation photoemission spectroscopy.

  11. Polarity effects in the x-ray photoemission of ZnO and other wurtzite semiconductors

    NASA Astrophysics Data System (ADS)

    Allen, M. W.; Zemlyanov, D. Y.; Waterhouse, G. I. N.; Metson, J. B.; Veal, T. D.; McConville, C. F.; Durbin, S. M.

    2011-03-01

    Significant polarity-related effects were observed in the near-surface atomic composition and valence band electronic structure of ZnO single crystals, investigated by x-ray photoemission spectroscopy using both Al Kα (1486.6 eV) and synchrotron radiation (150 to 1486 eV). In particular, photoemission from the lowest binding energy valence band states was found to be significantly more intense on the Zn-polar face compared to the O-polar face. This is a consistent effect that can be used as a simple, nondestructive indicator of crystallographic polarity in ZnO and other wurtzite semiconductors.

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

    NASA Astrophysics Data System (ADS)

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

    2016-11-01

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

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

    PubMed

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

    2016-11-18

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

  14. Quantum-electrodynamic treatment of photoemission by a single-electron wave packet

    SciTech Connect

    Corson, John P.; Peatross, Justin

    2011-11-15

    A quantum-field-theory description of photoemission by a laser-driven single-electron wave packet is presented. We show that, when the incident light is represented with multimode coherent states then, to all orders of perturbation theory, the relative phases of the electron's constituent momenta have no influence on the amount of scattered light. These results are extended using the Furry picture, where the (unidirectional) arbitrary incident light pulse is treated nonperturbatively with Volkov functions. This analysis increases the scope of our prior results in [Phys. Rev. A 84, 053831 (2011)], which demonstrate that the spatial size of the electron wave packet does not influence photoemission.

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

    PubMed

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

    2016-01-01

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

  16. The Organic LED Surface:. a Synchrotron Radiation Photoemission Study

    NASA Astrophysics Data System (ADS)

    Pi, Tun-Wen; Yu, T. C.

    Tris(8-hydroxyquinolato) aluminum (Alq3), a prototypical molecule for organic light-emitting devices, has been studied via synchrotron radiation photoemission to investigate (1) the surface electronic structure of the molecules at room temperature and at elevated temperatures, (2) adsorption onto the inorganic Si(001)-2×1 surface, and (3) doping with the alkaline metal Mg. For case (1), three chemical environments of carbon are resolved. Moreover, the shake-up satellite structures are detected in all the N 1s, C 1s, O 1s, and Al 2p core-level spectra, but with different magnitudes. Annealing allows for a charge redistribution within Alq3 itself. As to case (2), the organic molecules not only passivate the dangling bonds, but also rupture the dimer bonds. The wave function of the surface dangling bonds and of the pyridyl side of an 8-quinolinol ligand overlaps greatly so that charge is polarized towards, the organic adlayer. However, the polarization diminishes at greater coverage. With regard to case (3), the N 1s core-level spectra appear as an Mg-induced charge-transfer component with a binding energy lower than the original component. This new component grows gradually in intensity with increasing concentration of the dopant. Moreover, Mg also affects the O 1s core, as manifested by a component lying at a +1.09 eV higher binding energy than the original component. The Mg 2p core-level spectra, although rather broad, exhibit a shift toward a lower binding energy with increasing Mg vapor. Upon examining all these experimental results, we propose that Mg in the surface Alq3 molecules forms clusters. Each cluster attaches to a pyridyl ring, affecting not only the nitrogen atom at that ring, but also the oxygen atom in the adjacent phenoxide ring. The depleted charge in the affected oxygen then flows about its adherent ligand and resides on the pyridyl ring at that ligand, resulting in a high Alq3 anion state.

  17. Long-Wavelength Stacked Si(sub 1-x)/Si Heterojunction Internal Photoemission Infrared Detectors

    NASA Technical Reports Server (NTRS)

    Park, J. S.; Lin, T. L.; Jones, E. W.; Castillo, H. M. Del; George, T.; Gunapala, S. D.

    1993-01-01

    Utilizing the low temperature silicon molecular beam epitaxy (MBE) growth of degenerately doped SiGe layers on Si, long wavelength stacked SiGe/Si heterojunction internal photoemission (HIP) infrared detectors with multiple SiGe/Se layers have been fabricated and demonstrated.

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

    SciTech Connect

    Cousland, G. P.; Cui, X. Y.; Smith, A. E.; Stampfl, C. M.; Wong, L.; Tayebjee, M.; Yu, D.; Triani, G.; Evans, P. J.; Ruppender, H.-J.; Jang, L.-Y.; Stampfl, A. P. J.

    2014-04-14

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

  19. Comparative time-resolved photoemission from the Cu(100) and Cu(111) surfaces

    NASA Astrophysics Data System (ADS)

    Ambrosio, Marcelo J.; Thumm, Uwe

    2016-12-01

    Motivated by the striking dependence of the valence electronic structure of transition metal surfaces on their crystallographic orientation, and by emerging experiments on laser-assisted extended ultraviolet (XUV) photoemission from solid surfaces, we calculate photoemission spectra from Cu(100) and Cu(111) surfaces as a function of the photoelectron final kinetic energy and the delay between the ionizing attosecond XUV pulse train and assisting infrared (IR) laser pulse. Our numerical simulations predict distinct differences in delay-dependent photoelectron energy distributions and photoemission time delays for Cu(100) and Cu(111) surfaces. These differences can be scrutinized experimentally with existing technology in a suggested in situ comparative RABBITT (reconstruction of attosecond beating by interference of two-photon transitions) configuration by placing the two surfaces on a sliding platform while keeping all optical components and pathlengths fixed. Our calculations also show that the inclusion of the Fresnel-reflected incident IR pulse at the metal-vacuum interface modifies photoelectron spectra and photoemission time delays in a characteristic way that reveals the degree of spatial location of the initial electronic states.

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

    NASA Technical Reports Server (NTRS)

    Vasquez, R.

    1993-01-01

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

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

    SciTech Connect

    JOHNSON, P.D.; VALLA, T.

    2006-08-01

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

  2. Streaking and Wigner time delays in photoemission from atoms and surfaces

    SciTech Connect

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

    2011-09-15

    Streaked photoemission metrology allows the observation of an apparent relative time delay between the detection of photoelectrons from different initial electronic states. This relative delay is obtained by recording the photoelectron yield as a function of the delay between an ionizing ultrashort extended ultraviolet pulse and a streaking infrared (IR) pulse. Theoretically, photoemission delays can be defined based on (i) the phase shift the photoelectron wave function accumulates during the release and propagation of the photoelectron (''Wigner delay'') and, alternatively, (ii) the streaking trace in the calculated photoemission spectrum (''streaking delay''). We investigate the relation between Wigner and streaking delays in the photoemission from atomic and solid-surface targets. For solid targets and assuming a vanishing IR skin depth, both Wigner and streaking delays can be interpreted as an average propagation time needed by photoelectrons to reach the surface, while the two delays differ for nonvanishing skin depths. For atomic targets, the difference between Wigner and streaking delays depends on the range of the ionic potential.

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

    NASA Astrophysics Data System (ADS)

    Ahn, B.; Schötz, J.; Kang, M.; Okell, W. A.; Mitra, S.; Förg, B.; Zherebtsov, S.; Süßmann, F.; Burger, C.; Kübel, M.; Liu, C.; Wirth, A.; Di Fabrizio, E.; Yanagisawa, H.; Kim, D.; Kim, B.; Kling, M. F.

    2017-03-01

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

  4. Exchange Bias Realignment Using a Laser-based Direct-write Technique

    NASA Astrophysics Data System (ADS)

    Berthold, I.; Löschner, U.; Schille, J.; Ebert, R.; Exner, H.

    We report on selective realignment of the exchange biased magnetization direction in spintronic layer stacks using rapidly deflected focused laser radiation in a direct-write technique. Laser-based magnetic field cooling by applying either pulsed or continuous wave laser radiation was investigated. The magnetic properties of laser-based field cooled layer stacks were investigated by using magneto optical Kerr effect (MOKE) measurements. The dependencies of the processing parameters peak intensity and external magnetic field strength on the resulting exchange bias field strength were evaluated. In addition, temperature field simulations gain deeper insights into the mechanisms of laser-based field cooling. Our results show significant influence of the laser processing regime. Field cooling induced by continuous laser radiation caused higher exchange bias field strengths, compared to pulsed laser radiation. Moreover, the external magnetic field strength affected the resulting exchange bias field strength only by irradiating low-intensity laser beams.

  5. Advances in Diode-Laser-Based Water Vapor Differential Absorption Lidar

    NASA Astrophysics Data System (ADS)

    Spuler, Scott; Repasky, Kevin; Morley, Bruce; Moen, Drew; Weckwerth, Tammy; Hayman, Matt; Nehrir, Amin

    2016-06-01

    An advanced diode-laser-based water vapor differential absorption lidar (WV-DIAL) has been developed. The next generation design was built on the success of previous diode-laser-based prototypes and enables accurate measurement of water vapor closer to the ground surface, in rapidly changing atmospheric conditions, and in daytime cloudy conditions up to cloud base. The lidar provides up to 1 min resolution, 150 m range resolved measurements of water vapor in a broad range of atmospheric conditions. A description of the instrument and results from its initial field test in 2014 are discussed.

  6. Laser-based instrumentation for detection of chemical-warfare agents

    SciTech Connect

    Quigley, G.P.; Radziemski, L.J.; Sander, R.K.; Hartford, A. Jr.

    1981-01-01

    Several laser-based techniques are being developed for remote, point, and surface contamination detection of chemical warfare agents. These techniques include optoacoustic spectroscopy, laser-induced breakdown spectroscopy, and synchronous detection of laser-induced fluorescence. Detection limits in the part-per-million to part-per-billion regime have been demonstrated.

  7. 76 FR 81518 - Notice of Issuance of Final Determination Concerning Laser-Based Multi-Function Office Machines

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-12-28

    ... SECURITY U.S. Customs and Border Protection Notice of Issuance of Final Determination Concerning Laser... laser-based multi-function office machines. Based upon the facts presented, CBP has concluded in the... of the laser-based multi-function office machine, and it is at their assembly and programming...

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

    NASA Astrophysics Data System (ADS)

    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.

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

    NASA Astrophysics Data System (ADS)

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2017-02-01

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

  11. Interference of spin states in resonant photoemission induced by circularly polarized light from magnetized Gd

    SciTech Connect

    Mueller, N.; Khalil, T.; Pohl, M.; Uphues, T.; Heinzmann, U.; Polcik, M.; Rader, O.; Heigl, F.; Starke, K.; Fritzsche, S.; Kabachnik, N. M.

    2006-10-15

    We have observed the spin-state interference by measuring the photoelectron spin polarization in the resonant preedge 4d{yields}4f photoemission from magnetized Gd. The photoemission is induced by circularly polarized light which determines one preferential direction of electron spin orientation due to polarization transfer and spin-orbit interaction. Another direction perpendicular to the first one is determined by the target electron spin orientation connected with the target magnetization. We have measured the component of spin polarization perpendicular to those two directions which can only appear due to spin-state interference which implies coherence of the spin states produced by the two mechanisms of the photoelectron spin polarization.

  12. One-step model of photoemission from single-crystal surfaces

    NASA Astrophysics Data System (ADS)

    Karkare, Siddharth; Wan, Weishi; Feng, Jun; Chiang, Tai C.; Padmore, Howard A.

    2017-02-01

    In this paper, we present a three-dimensional one-step photoemission model that can be used to calculate the quantum efficiency and momentum distributions of electrons photoemitted from ordered single-crystal surfaces close to the photoemission threshold. Using Ag(111) as an example, we show that the model can not only calculate the quantum efficiency from the surface state accurately without using any ad hoc parameters, but also provides a theoretical quantitative explanation of the vectorial photoelectric effect. This model in conjunction with other band structure and wave function calculation techniques can be effectively used to screen single-crystal photoemitters for use as electron sources for particle accelerator and ultrafast electron diffraction applications.

  13. Cluster-surface interaction studied by time-resolved two-photon photoemission

    NASA Astrophysics Data System (ADS)

    Busolt, U.; Cottancin, E.; Röhr, H.; Socaciu, L.; Leisner, T.; Wöste, L.

    We use time-resolved two-photon photoemission to study the stability of size selected Agn+ clusters (n=2-9)deposited onto highly oriented pyrolytic graphite (HOPG) substrates at liquid nitrogen temperatures. The deposition was carried out with variable kinetic energies of the clusters. Clusters deposited with high kinetic energy (up to 60 eV/cluster) become fragmented upon impact. For low deposition energies (1-4 eV/cluster) the size dependence of the photoelectron spectra reveals a pronounced odd/even effect, which is well known for gas phase silver clusters. This indicates that the soft deposited clusters retain their size and identity on the sample. The phase of the odd/even effect suggests that transient negatively charged cluster ions serve as an intermediate step in the two-photon photoemission process. The lifetime of the anions rises with cluster size. This is attributed to an increasing electronic density of states for larger clusters.

  14. Quantum-electrodynamic treatment of photoemission by a single-electron wave packet

    NASA Astrophysics Data System (ADS)

    Corson, John P.; Peatross, Justin

    2011-11-01

    A quantum-field-theory description of photoemission by a laser-driven single-electron wave packet is presented. We show that, when the incident light is represented with multimode coherent states then, to all orders of perturbation theory, the relative phases of the electron's constituent momenta have no influence on the amount of scattered light. These results are extended using the Furry picture, where the (unidirectional) arbitrary incident light pulse is treated nonperturbatively with Volkov functions. This analysis increases the scope of our prior results in [Phys. Rev. APLRAAN1050-294710.1103/PhysRevA.84.053831 84, 053831 (2011)], which demonstrate that the spatial size of the electron wave packet does not influence photoemission.

  15. A sample holder with integrated laser optics for an ELMITEC photoemission electron microscope

    SciTech Connect

    Gierster, L.; Pape, L.; Ünal, A. A.; Kronast, F.

    2015-02-15

    We present a new sample holder compatible with ELMITEC Photoemission Electron Microscopes (PEEMs) containing an optical lens and a mirror. With the integrated optical elements, a laser beam is focused from the back side of the sample at normal incidence, yielding a minimum spot size of about 1 μm. This opens up new possibilities for local laser excitations in PEEM experiments such as imaging all-optical magnetization switching at a small length scale.

  16. Time-resolved photoemission electron microscopy imaging of mode coupling between three interacting magnetic vortices

    SciTech Connect

    Wang, Xiao; Cheng, X. M.; Keavney, D. J.; Asmat-Uceda, M.; Buchanan, K. S.; Melikyan, A.

    2014-09-08

    The interactions between three magnetic vortices in a planar equilateral triangular arrangement were studied by time-resolved photoemission electron microscopy. The gyrotropic resonance frequencies of the three individual vortices in the tri-disk system are different from one another and also shifted from that of an isolated vortex by as much as 12%. A comparison with analytical calculations and numerical simulations shows that the observed frequency shifts result from the dipolar interaction between the vortices.

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

    SciTech Connect

    Drummond, J.L.; Steinberg, A.D.; Krauss, A.R.

    1997-08-01

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

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

    SciTech Connect

    Mårsell, Erik; Larsen, Esben W.; Arnold, Cord L.; Xu, Hongxing; Mauritsson, Johan; Mikkelsen, Anders

    2015-02-28

    We image the field enhancement at Ag nanostructures using femtosecond laser pulses with a center wavelength of 1.55 μm. Imaging is based on non-linear photoemission observed in a photoemission electron microscope (PEEM). The images are directly compared to ultra violet PEEM and scanning electron microscopy (SEM) imaging of the same structures. Further, we have carried out atomic scale scanning tunneling microscopy on the same type of Ag nanostructures and on the Au substrate. Measuring the photoelectron spectrum from individual Ag particles shows a larger contribution from higher order photoemission processes above the work function threshold than would be predicted by a fully perturbative model, consistent with recent results using shorter wavelengths. Investigating a wide selection of both Ag nanoparticles and nanowires, field enhancement is observed from 30% of the Ag nanoparticles and from none of the nanowires. No laser-induced damage is observed of the nanostructures neither during the PEEM experiments nor in subsequent SEM analysis. By direct comparison of SEM and PEEM images of the same nanostructures, we can conclude that the field enhancement is independent of the average nanostructure size and shape. Instead, we propose that the variations in observed field enhancement could originate from the wedge interface between the substrate and particles electrically connected to the substrate.

  19. Plasmonic Field Enhancement of Individual Nanoparticles by Correlated Scanning and Photoemission Electron Microscopy

    SciTech Connect

    Peppernick, Samuel J.; Joly, Alan G.; Beck, Kenneth M.; Hess, Wayne P.

    2011-01-21

    We present results of a combined two-photon photoemission and scanning electron microscopy investigation to determine the electromagnetic enhancement factors of silver-coated spherical nanoparticles deposited on an atomically flat mica substrate. Femtosecond laser excitation, of the nanoparticles, produces intense photoemission, attributed to near-resonant excitation of localized surface plasmons. Enhancement factors are determined by comparing the respective two-photon photoemission yield measured for equal areas between single nanoparticles to that of the surrounding flat surface. For s-polarized, 400 nm (~ 3.1 eV) femtosecond radiation a distribution of enhancement factors are found with a large percentage (77%) of the nanoparticles falling within a median range. A correlated scanning electron microscopy analysis demonstrated that the nanoparticles typifying the median of the distribution were characterized by ideal spherical shapes and defect-free morphologies. The single largest enhancement factors were in contrast produced by a very small percentage (8%) of the total, for which evidence of silver defect anomalies were found that contributed to the overall structure of the nanoparticle. Comparisons are made between the experimentally measured enhancement factors and previously reported theoretical predictions of the localized surface plasmon near-field intensities for isolated nanometer-sized silver spheres.

  20. Bypassing the energy-time uncertainty in time-resolved photoemission

    NASA Astrophysics Data System (ADS)

    Randi, Francesco; Fausti, Daniele; Eckstein, Martin

    2017-03-01

    The energy-time uncertainty is an intrinsic limit for time-resolved experiments imposing a tradeoff between the duration of the light pulses used in experiments and their frequency content. In standard time-resolved photoemission, this limitation maps directly onto a tradeoff between the time resolution of the experiment and the energy resolution that can be achieved on the electronic spectral function. Here we propose a protocol to disentangle the energy and time resolutions in photoemission. We demonstrate that dynamical information on all time scales can be retrieved from time-resolved photoemission experiments using suitably shaped light pulses of quantum or classical nature. As a paradigmatic example, we study the dynamical buildup of the Kondo peak, a narrow feature in the electronic response function arising from the screening of a magnetic impurity by the conduction electrons. After a quench, the electronic screening builds up on timescales shorter than the inverse width of the Kondo peak and we demonstrate that the proposed experimental scheme could be used to measure the intrinsic time scales of such electronic screening. The proposed approach provides an experimental framework to access the nonequilibrium response of collective electronic properties beyond the spectral uncertainty limit and will enable the direct measurement of phenomena such as excited Higgs modes and, possibly, the retarded interactions in superconducting systems.

  1. Femtosecond laser based enucleation of porcine oocytes for somatic cell nuclear transfer

    NASA Astrophysics Data System (ADS)

    Kütemeyer, K.; Lucas-Hahn, A.; Petersen, B.; Hassel, P.; Lemme, E.; Niemann, H.; Heisterkamp, A.

    2009-07-01

    Cloning of several mammalian species has been achieved by somatic cell nuclear transfer (SCNT) in recent years. However, this method still results in very low efficiencies around 1% which originate from suboptimal culture conditions and highly invasive techniques for oocyte enucleation and injection of the donor cell using micromanipulators. In this paper, we present a new minimal invasive method for oocyte imaging and enucleation based on the application of femtosecond (fs) laser pulses. After imaging of the oocyte with multiphoton microscopy, ultrashort pulses are focused onto the metaphase plate of MII-oocytes in order to ablate the DNA molecules. We show that fs laser based enucleation of porcine oocytes completely inhibits the first mitotic cleavage after parthenogenetic activation while maintaining intact oocyte morphology in most cases. In contrast, control groups without previous irradiation of the metaphase plate are able to develop to the blastocyst stage. Further experiments have to clarify the suitability of fs laser based enucleated oocytes for SCNT.

  2. Comparison of laser-based and monochromator-based thermodynamic temperature measurements

    SciTech Connect

    Eppeldauer, G. P.; Yoon, H. W.; Gibson, C. E.; Smith, A. W.; Neira, J.; Khromchenko, V. B.

    2013-09-11

    In this work, we describe comparisons between a laser-based and a monochromator-based radiance responsivity calibration of a radiation thermometer. The spectral selection of the radiation thermometer is performed using a spectrally broad photopic-response filter which was selected to minimize effects of convolution differences due to the spectral width of the laser-and the monochromator-based sources. The photopic-response filter is physically thick, which should also reduce possible interference fringes which can be problematic in the laser-based calibrations. We compare the radiance responsivities obtained using the two approaches and also compare the blackbody temperatures determined using the detector/monochromator based and the gold-point based calibration methods.

  3. Power scaling of a picosecond vortex laser based on a stressed Yb-doped fiber amplifier.

    PubMed

    Koyama, Mio; Hirose, Tetsuya; Okida, Masahito; Miyamoto, Katsuhiko; Omatsu, Takashige

    2011-01-17

    Power scaling of a picosecond vortex laser based on a stressed Yb-doped fiber amplifier is analyzed. An output power of 25 W was obtained for 53 W of pumping, with a peak power of 37 kW. Frequency doubling of the vortex output was demonstrated using a nonlinear PPSLT crystal. A second-harmonic output power of up to 1.5 W was measured at a fundamental power of 11.2 W.

  4. Diode Laser-Based Detection of Combustor Instabilities with Application to a Scramjet Engine

    DTIC Science & Technology

    2010-02-01

    combustion instability has focused primarily on subsonic turbulent combustors [7]. NOx emission regulations on gas turbines have driven the use of...Optical Access Laser Beam Location ermocouple eholder) Static Pressure Taps (Open circles)holders Combustor w, direct-connect scramjet flowpath. 4.8 s...AFRL-RZ-WP-TP-2010-2055 DIODE LASER-BASED DETECTION OF COMBUSTOR INSTABILITIES WITH APPLICATION TO A SCRAMJET ENGINE (POSTPRINT) Campbell

  5. Investigation of Plant-Pathogen Interaction by Laser-Based Photoacoustic Spectroscopy

    NASA Astrophysics Data System (ADS)

    Puiu, A.; Giubileo, G.; Lai, A.

    2014-12-01

    The laser-based photoacoustic spectroscopy apparatus, constructed at ENEA Frascati (Italy), was applied to monitor trace amounts of ethylene emitted by plants in a stress condition. More specifically, in the present work, the biotic stress response of tomato mutant plants after inoculation with Phthorimaea operculella larvae ( Lepidoptera: Gelechiidae) was investigated. The principle of the method, the photoacoustic setup, the experimental work, and the results are being reported.

  6. A comparison of NH{sub 3} point monitoring and diode laser based path integrated measurements

    SciTech Connect

    Goldstein, N.; Richtsmeier, S.C.; Lee, J.; Bien, F.; Fetzer, G.J.; Groff, K.W.

    1994-12-31

    Measurements made using two different types of ammonia monitors during a two-month field study in the summer of 1994 are discussed. The first was a diode-laser based open path monitor designed for automated operation in an industrial environment. The second is a monitoring analyzer based on thermal decomposition of ammonia to NO and subsequent analysis by O{sub 3}-NO chemiluminescence. The two monitors provided consistent measurements of ammonia concentration during weeks of continuous unattended operation.

  7. Tomographic Imaging of Glass/Epoxy Composite with a Laser Based Ultrasonics Setup

    SciTech Connect

    Khanna, N.; Raghuram, V.; Munshi, P.; Kishore, N. N.; Arnold, W.

    2008-09-26

    The present work is an attempt to augment the classical laser-based-ultrasonics setup for tomographic imaging purposes. A Glass/epoxy composite with steel insert is the test specimen and time-of-flight data has been used for tomographic reconstruction. Multiplicative algebraic reconstruction technique is used for this limited-view experiment. The resulting image is able to bring out the strong metal features.

  8. Status of Real-Time Laser Based Ion Engine Diagnostics at NASA Glenn Research Center

    NASA Technical Reports Server (NTRS)

    Domonkos, Matthew T.; Williams, George J., Jr.

    2001-01-01

    The development status of laser based erosion diagnostics for ion engines at the NASA Glenn Research Center is discussed. The diagnostics are being developed to enhance component life-prediction capabilities. A direct measurement of the erosion product density using laser induced fluorescence (LIF) is described. Erosion diagnostics based upon evaluation of the ion dynamics are also under development, and the basic approach is presented. The planned implementation of the diagnostics is discussed.

  9. Advanced Laser-Based Techniques for Gas-Phase Diagnostics in Combustion and Aerospace Engineering.

    PubMed

    Ehn, Andreas; Zhu, Jiajian; Li, Xuesong; Kiefer, Johannes

    2017-03-01

    Gaining information of species, temperature, and velocity distributions in turbulent combustion and high-speed reactive flows is challenging, particularly for conducting measurements without influencing the experimental object itself. The use of optical and spectroscopic techniques, and in particular laser-based diagnostics, has shown outstanding abilities for performing non-intrusive in situ diagnostics. The development of instrumentation, such as robust lasers with high pulse energy, ultra-short pulse duration, and high repetition rate along with digitized cameras exhibiting high sensitivity, large dynamic range, and frame rates on the order of MHz, has opened up for temporally and spatially resolved volumetric measurements of extreme dynamics and complexities. The aim of this article is to present selected important laser-based techniques for gas-phase diagnostics focusing on their applications in combustion and aerospace engineering. Applicable laser-based techniques for investigations of turbulent flows and combustion such as planar laser-induced fluorescence, Raman and Rayleigh scattering, coherent anti-Stokes Raman scattering, laser-induced grating scattering, particle image velocimetry, laser Doppler anemometry, and tomographic imaging are reviewed and described with some background physics. In addition, demands on instrumentation are further discussed to give insight in the possibilities that are offered by laser flow diagnostics.

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

    SciTech Connect

    Bormann, Reiner; Strauch, Stefanie; Schäfer, Sascha Ropers, Claus

    2015-11-07

    We experimentally and numerically investigate the performance of an advanced ultrafast electron source, based on two-photon photoemission from a tungsten needle cathode incorporated in an electron microscope gun geometry. Emission properties are characterized as a function of the electrostatic gun settings, and operating conditions leading to laser-triggered electron beams of very low emittance (below 20 nm mrad) are identified. The results highlight the excellent suitability of optically driven nano-cathodes for the further development of ultrafast transmission electron microscopy.

  11. Inverse-photoemission spectroscopy of GaSe and InSe

    NASA Astrophysics Data System (ADS)

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

    1994-04-01

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

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

    SciTech Connect

    Gray, Alexander; Kronast, Florian; Papp, Christian; Yang, See-Hun; Cramm, Stefan; Krug, Ingo P.; Salmassi, Farhad; Gullikson, Eric M.; Hilken, Dawn L.; Anderson, Erik H.; Fischer, Peter; Durr, Hermann A.; Schneider, Claus M.; Fadley, Charles S.

    2010-10-29

    We demonstrate the addition of depth resolution to the usual two-dimensional images in photoelectron emission microscopy (PEEM), with application to a square array of circular magnetic Co microdots. The method is based on excitation with soft x-ray standing-waves generated by Bragg reflection from a multilayer mirror substrate. Standing wave is moved vertically through sample simply by varying the photon energy around the Bragg condition. Depth-resolved PEEM images were obtained for all of the observed elements. Photoemission intensities as functions of photon energy were compared to x-ray optical calculations in order to quantitatively derive the depth-resolved film structure of the sample.

  13. Measurement of Electron Beam Polarization from Unstrained Bulk GaAs via Two Photon Photoemission

    SciTech Connect

    J L McCarter, T J Gay, J Hansknecht, M Poelker, M L Stutzman

    2011-06-01

    This paper describes measurements of the beam polarization and quantum efficiency for photoemission using two-photon excitation from unstrained bulk GaAs illuminated with pulsed, high intensity 1560nm laser light. Quantum efficiency is linearly proportional to 1560nm peak laser intensity, which was varied in three independent ways, indicating that the emitted electrons are promoted from the valence to the conduction band via two-photon absorption. Beam polarization was measured using a microMott polarimeter, with a value of 16.8(4)% polarization at 1560nm, which is roughly half the measured value of 33.4(8)% using 778 nm light.

  14. Theory of photoemission from cesium antimonide using an alpha-semiconductor model

    NASA Astrophysics Data System (ADS)

    Jensen, Kevin L.; Jensen, Barbara L.; Montgomery, Eric J.; Feldman, Donald W.; O'Shea, Patrick G.; Moody, Nathan

    2008-08-01

    A model of photoemission from cesium antimonide (Cs3Sb) that does not rely on adjustable parameters is proposed and compared to the experimental data of Spicer [Phys. Rev. 112, 114 (1958)] and Taft and Philipp [Phys. Rev. 115, 1583 (1959)]. It relies on the following components for the evaluation of all relevant parameters: (i) a multidimensional evaluation of the escape probability from a step-function surface barrier, (ii) scattering rates determined using a recently developed alpha-semiconductor model, and (iii) evaluation of the complex refractive index using a harmonic oscillator model for the evaluation of reflectivity and extinction coefficient.

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

    NASA Astrophysics Data System (ADS)

    Igarashi, J.

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

  16. Optical communication with two-photon coherent states. III - Quantum measurements realizable with photoemissive detectors

    NASA Technical Reports Server (NTRS)

    Yuen, H. P.; Shapiro, J. H.

    1980-01-01

    Homodyne detection is shown to achieve the same signal-to-noise ratio as the quantum field quadrature measurement, thus providing a receiver which realizes linear modulation TCS performance gain. The full equivalence of homodyne detection and single-quadrature field measurement is established. A heterodyne configuration which uses a TCS image-band oscillator in addition to the usual coherent state local oscillator is studied. Results are obtained by means of a representation theorem which shows that photoemissive detection realizes the photon flux density measurement.

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

    SciTech Connect

    Kushida, Soh; Yamamoto, Yohei; Braam, Daniel; Lorke, Axel

    2015-12-31

    Poly[2-methoxy-5-(3,7-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMOPPV) self-assembles to form well-defined spheres with several micrometers in diameter upon addition of a methanol vapor into a chloroform solution of MDMOPPV. The single sphere of MDMOPPV with 5.7 µm diameter exhibits whispering gallery mode (WGM) photoemission upon excitation with focused laser beam. The periodic emission lines are characterized by transverse electric and magnetic WGMs, and Q-factor reaches ∼345 at the highest.

  18. Two-color photoemission produced by femtosecond laser pulses on copper

    NASA Astrophysics Data System (ADS)

    Muggli, P.; Brogle, R.; Joshi, C.

    1995-04-01

    Single-color illumination of a copper surface by a red or an ultraviolet femtosecond laser pulse yields a three-photon (red) or a two-photon (UV) photoemission process. A multicolor, multiphoton process is generated when the red and the UV pulses overlap both in space and in time on the photocathode. It is shown that this emission process results from the absorption by an electron of one red and one UV photon. It provides a means to correlate ultrashort laser pulses of different wavelengths. femtosecond phenomena, beams, electron, correlation

  19. Observation of the Quantum Well Interference in Magnetic Nanostructures by Photoemission

    SciTech Connect

    Kawakami, R.K.; Escorcia-Aparicio, E.J.; Choi, H.J.; Qiu, Z.Q.; Rotenberg, E.; Smith, N.V.; Cummins, T.R.; Tobin, J.G.

    1998-02-01

    The Cu/Co/Ni/Co(100) system was investigated by photoemission to study the interference between the Cu quantum well and the Ni layer. By varying their separation, we found that the density of states of the Cu quantum well states were biperiodically modulated. This result provides clear evidence for the quantum interference between two quantum wells in magnetic nanostructures. The biperiodicity was identified to correspond to the two Fermi vectors of the Co minority energy bands. {copyright} {ital 1998} {ital The American Physical Society}

  20. Induced photoemission from driven nonadiabatic dynamics in an avoided crossing system

    SciTech Connect

    Arasaki, Yasuki; Mizuno, Yuta; Takatsuka, Kazuo; Scheit, Simona

    2014-12-21

    When vibrational dynamics on an ionic state (large dipole moment) is coupled to that on a neutral state (small dipole moment) such as at an avoided crossing in the alkali halide system, the population transfer between the states cause oscillation of the molecular dipole, leading to dipole emission. Such dynamics may be driven by an external field. We study how the coupled wavepacket dynamics is affected by the parameters (intensity, frequency) of the driving field with the aim of making use of the photoemission as an alternative detection scheme of femtosecond and subfemtosecond vibrational and electronic dynamics or as a characteristic optical source.

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

    SciTech Connect

    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.

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

    NASA Astrophysics Data System (ADS)

    de la Figuera, Juan; Tusche, Christian

    2017-01-01

    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. Real-time quantum cascade laser-based infrared microspectroscopy in-vivo

    NASA Astrophysics Data System (ADS)

    Kröger-Lui, N.; Haase, K.; Pucci, A.; Schönhals, A.; Petrich, W.

    2016-03-01

    Infrared microscopy can be performed to observe dynamic processes on a microscopic scale. Fourier-transform infrared spectroscopy-based microscopes are bound to limitations regarding time resolution, which hampers their potential for imaging fast moving systems. In this manuscript we present a quantum cascade laser-based infrared microscope which overcomes these limitations and readily achieves standard video frame rates. The capabilities of our setup are demonstrated by observing dynamical processes at their specific time scales: fermentation, slow moving Amoeba Proteus and fast moving Caenorhabditis elegans. Mid-infrared sampling rates between 30 min and 20 ms are demonstrated.

  4. Collinearity alignment of probe beams in a laser-based Faraday effect diagnostica)

    NASA Astrophysics Data System (ADS)

    Lin, L.; Ding, W. X.; Brower, D. L.

    2012-10-01

    Two counter-rotating circularly polarized beams are used in a laser-based polarimetry diagnostic providing a phase measurement of the Faraday effect. Collinearity of these beams is a key issue that affects measurement accuracy. Spatial offset from even small misalignment induces systematic error due to density gradient and path length difference. Here, we report an alignment technique using a rotating dielectric wedge, which is capable of reducing spatial offset of two probe beams below 0.1 mm for beams with 40 mm diameter. With optimized alignment, 0.05° Faraday effect fluctuations associated with global tearing modes are resolved with an uncertainty below 0.01°.

  5. Quantum cascade laser-based substance detection: approaching the quantum noise limit

    NASA Astrophysics Data System (ADS)

    Kuffner, Peter C.; Conroy, Kathryn J.; Boyson, Toby K.; Milford, Greg; Mabrok, Mohamed A.; Kallapur, Abhijit G.; Petersen, Ian R.; Calzada, Maria E.; Spence, Thomas G.; Kirkbride, Kennith P.; Harb, Charles C.

    2011-06-01

    A consortium of researchers at University of New South Wales (UNSW@ADFA), and Loyola University New Orleans (LU NO), together with Australian government security agencies (e.g., Australian Federal Police), are working to develop highly sensitive laser-based forensic sensing strategies applicable to characteristic substances that pose chemical, biological and explosives (CBE) threats. We aim to optimise the potential of these strategies as high-throughput screening tools to detect prohibited and potentially hazardous substances such as those associated with explosives, narcotics and bio-agents.

  6. Single-mode fiber laser based on core-cladding mode conversion.

    PubMed

    Suzuki, Shigeru; Schülzgen, Axel; Peyghambarian, N

    2008-02-15

    A single-mode fiber laser based on an intracavity core-cladding mode conversion is demonstrated. The fiber laser consists of an Er-doped active fiber and two fiber Bragg gratings. One Bragg grating is a core-cladding mode converter, and the other Bragg grating is a narrowband high reflector that selects the lasing wavelength. Coupling a single core mode and a single cladding mode by the grating mode converter, the laser operates as a hybrid single-mode laser. This approach for designing a laser cavity provides a much larger mode area than conventional large-mode-area step-index fibers.

  7. A New Femtosecond Laser-Based Three-Dimensional Tomography Technique

    NASA Astrophysics Data System (ADS)

    Echlin, McLean P.

    2011-12-01

    Tomographic imaging has dramatically changed science, most notably in the fields of medicine and biology, by producing 3D views of structures which are too complex to understand in any other way. Current tomographic techniques require extensive time both for post-processing and data collection. Femtosecond laser based tomographic techniques have been developed in both standard atmosphere (femtosecond laser-based serial sectioning technique - FSLSS) and in vacuum (Tri-Beam System) for the fast collection (10 5mum3/s) of mm3 sized 3D datasets. Both techniques use femtosecond laser pulses to selectively remove layer-by-layer areas of material with low collateral damage and a negligible heat affected zone. To the authors knowledge, femtosecond lasers have never been used to serial section and these techniques have been entirely and uniquely developed by the author and his collaborators at the University of Michigan and University of California Santa Barbara. The FSLSS was applied to measure the 3D distribution of TiN particles in a 4330 steel. Single pulse ablation morphologies and rates were measured and collected from literature. Simultaneous two-phase ablation of TiN and steel matrix was shown to occur at fluences of 0.9-2 J/cm2. Laser scanning protocols were developed minimizing surface roughness to 0.1-0.4 mum for laser-based sectioning. The FSLSS technique was used to section and 3D reconstruct titanium nitride (TiN) containing 4330 steel. Statistical analysis of 3D TiN particle sizes, distribution parameters, and particle density were measured. A methodology was developed to use the 3D datasets to produce statistical volume elements (SVEs) for toughness modeling. Six FSLSS TiN datasets were sub-sampled into 48 SVEs for statistical analysis and toughness modeling using the Rice-Tracey and Garrison-Moody models. A two-parameter Weibull analysis was performed and variability in the toughness data agreed well with Ruggieri et al. bulk toughness measurements. The Tri

  8. Two-frequency picosecond laser based on composite vanadate crystals with {sigma}-polarised radiation

    SciTech Connect

    Sirotkin, A A; Sadovskiy, S P; Garnov, Sergei V

    2013-07-31

    A two-frequency picosecond laser based on {alpha}-cut Nd:YVO{sub 4}-YVO{sub 4} composite vanadate crystals is experimentally studied for the s-polarised radiation at the {sup 4}F{sub 3/2} - {sup 4}I{sub 11/2} transition with frequency tuning using Fabry-Perot etalons of different thickness. The difference between the radiation wavelengths was tuned within the range of 1.2-4.4 nm. In the mode-locking regime, the two-frequency radiation power was 280 mW at an absorbed pump power of 12 W. (lasers)

  9. Laser-Based Methods for Detection of Nitric Oxide in Plants.

    PubMed

    Mandon, Julien; Mur, Luis A J; Harren, Frans J M; Cristescu, Simona M

    2016-01-01

    Nitric oxide (NO) plays an important role in plant signaling and in response to various stress conditions. Therefore, real-time measurements of NO production provide better insights into understanding plant processes and can help developing strategies to improve food production and postharvest quality. Using laser-based spectroscopic methods, sensitive, online, in planta measurements of plant-pathogen interactions are possible. This chapter introduces the basic principle of the optical detectors using different laser sources for accurate monitoring of fast dynamic changes of NO production. Several applications are also presented to demonstrate the suitability of these detectors for detection of NO in plants.

  10. Algal Biomass Analysis by Laser-Based Analytical Techniques—A Review

    PubMed Central

    Pořízka, Pavel; Prochazková, Petra; Prochazka, David; Sládková, Lucia; Novotný, Jan; Petrilak, Michal; Brada, Michal; Samek, Ota; Pilát, Zdeněk; Zemánek, Pavel; Adam, Vojtěch; Kizek, René; Novotný, Karel; Kaiser, Jozef

    2014-01-01

    Algal biomass that is represented mainly by commercially grown algal strains has recently found many potential applications in various fields of interest. Its utilization has been found advantageous in the fields of bioremediation, biofuel production and the food industry. This paper reviews recent developments in the analysis of algal biomass with the main focus on the Laser-Induced Breakdown Spectroscopy, Raman spectroscopy, and partly Laser-Ablation Inductively Coupled Plasma techniques. The advantages of the selected laser-based analytical techniques are revealed and their fields of use are discussed in detail. PMID:25251409

  11. Ultra-short DBR fiber laser based sensor for arterial pulse monitoring

    NASA Astrophysics Data System (ADS)

    Sun, Qizhen; Wo, Jianghai; Wang, He; Liu, Deming

    2014-05-01

    An ultra-short DBR fiber laser based device for arterial pulse wave monitoring is proposed and demonstrated. As the sensing element, the 10mm length laser cavity is mounted onto a soft plastic plate and then embedded into textile. Deformation of the textile, involving the transverse force subjected by the laser cavity, is proportional to the vibration caused by the arterial pulse. The sensing principle is based on the linear relationship between the beat frequency of the laser and the transverse force. Laboratory studies demonstrate that the sensor could achieve real-time and accurate measurement of the weak and dynamical arterial pulse signal.

  12. Multi-wavelength erbium-doped fiber laser based on random distributed feedback

    NASA Astrophysics Data System (ADS)

    Liu, Yuanyang; Dong, Xinyong; Jiang, Meng; Yu, Xia; Shum, Ping

    2016-09-01

    We experimentally demonstrated a multi-wavelength erbium-doped fiber laser based on random distributed feedback via a 20-km-long single-mode fiber together with a Sagnac loop mirror. The number of channels can be modulated from 2 to 8 at room temperature when the pump power is changed from 30 to 180 mW, indicating that wavelength competition caused by homogenous gain broadening of erbium-doped fiber is significantly suppressed. Other advantages of the laser include low cost, low-threshold pump power and simple fabrication.

  13. Mutual injection phase locking coherent combination of solid-state lasers based on corner cube.

    PubMed

    Cheng, Yong; Liu, Xu; Wan, Qiang; Zhu, Mengzhen; Mi, Chaowei; Tan, Chaoyong; Wei, Shangfang; Chen, Xia

    2013-12-01

    Coherent beam combination is an effective way to develop high-power lasers with high beam quality and high brightness. Coherent combination of six solid-state lasers based on the technique of mutual injection phase locking by using the natural coherent combination property of corner cube is first investigated. The coherent combination with 15.3 J of output energy, 1.7 mrad of divergent angle is obtained, and the combining efficiency is as high as 95.6% at 10 Hz and 85 A. The far-field profile is flattened protuberance.

  14. A laser-based sensor system for tire tread deformation measurement

    NASA Astrophysics Data System (ADS)

    Xiong, Yi; Tuononen, Ari

    2014-11-01

    Optical tire sensors are powerful engineering tools that can reveal the mechanisms behind tire-road interactions. This paper presents a laser-based sensor system to measure tire-tread block deformation. The methodology and corresponding procedure for the system are introduced. Practical issues, such as tire sensor localization, are discussed. Validation experiments were conducted on a chassis dynamometer, and an asymmetric tire tread deformation along the contact patch was observed. It is proposed that asymmetric tread deformation is due to rolling resistance. The measurements under different operational conditions, including the rolling direction, wheel load, rolling velocity, and inflation pressure, were analyzed in the context of rolling resistance.

  15. Cleaning of optical components for high-power laser-based firing systems

    SciTech Connect

    Sparrow, B.D.; Hendrix, J.L.

    1993-08-01

    This report discusses the progress of AlliedSignal Inc., Kansas City Division (KCD), in addressing the issues of cleaning of hardware and optical components for laser-based firing sets. These issues are acceptability of cleaning processes and techniques of other government programs to the quality, reliability, performance, stockpile life, materials compatibility issues, and, perhaps most important, environmentally conscious manufacturing requirements of the Department of Energy (DOE). A review of ``previous cleaning art`` is presented using Military Standards (MIL STDs) and Military Interim Specifications (MISs) as well as empirical data compiled by the authors. Observations on processes and techniques used in building prototype hardware and plans for future work are presented.

  16. Time-domain study on reproducibility of laser-based soft-error simulation

    NASA Astrophysics Data System (ADS)

    Itsuji, Hiroaki; Kobayashi, Daisuke; Lourenco, Nelson E.; Hirose, Kazuyuki

    2017-04-01

    Studied is the soft error issue, which is a circuit malfunction caused by ion-radiation-induced noise currents. We have developed a laser-based soft-error simulation system to emulate the noise and evaluate its reproducibility in the time domain. It is found that this system, which utilizes a two-photon absorption process, can reproduce the shape of ion-induced transient currents, which are assumed to be induced from neutrons at the ground level. A technique used to extract the initial carrier structure inside the device is also presented.

  17. Development of Field-deployable Diode-laser-based Water Vapor Dial

    NASA Astrophysics Data System (ADS)

    Pham Le Hoai, Phong; Abo, Makoto; Sakai, Tetsu

    2016-06-01

    In this paper, a field-deployable diode-laser-based differential absorption lidar (DIAL) has been developed for lower-tropospheric water vapor observation in Tokyo, Japan. A photoacoustic cell is used for spectroscopy experiment around absorption peaks of 829.022 nm and 829.054 nm. The water vapor density extracted from the observational data agrees with the referenced radiosonde data. Furthermore, we applied modulated pulse technique for DIAL transmitter. It enables DIAL to measure water vapor profile for both low and high altitude regions.

  18. Investigation of droplet ignition under microgravity conditions using laser-based techniques—an overview

    NASA Astrophysics Data System (ADS)

    Burkert, A.; Paa, W.; Schmidl, G.; Triebel, W.; Eigenbrod, Ch

    2004-08-01

    Laser-based diagnostics like Laser Induced Fluorescence (LIF) and Particle Imaging Velocimetry are well established methods for combustion research under microgravity conditions. Especially the investigation of the ignition behaviour of single droplets and droplet arrays is important for future developments of internal combustion engines and power plants. Novel developments of experimental components like an solid state laser source (Advanced disk laser, ADL) and a high pressure insert (European High Pressure Insert, EHPI) for use in NASA's Combustion Integrated Rack are described. Innovative measuring methods to observe in a quantitative way the ignition process of droplets using LIF of formaldehyde and infrared absorption in carbon monoxide induced by quantum cascade lasers are presented.

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

    SciTech Connect

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

    2007-10-02

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

  20. Iron resonant photoemission spectroscopy on anodized hematite points to electron hole doping during anodization.

    PubMed

    Braun, Artur; Chen, Qianli; Flak, Dorota; Fortunato, Giuseppino; Gajda-Schrantz, Krisztina; Grätzel, Michael; Graule, Thomas; Guo, Jinghua; Huang, Tzu-Wen; Liu, Zhi; Popelo, Anastasiya V; Sivula, Kevin; Wadati, Hiroki; Wyss, Pradeep P; Zhang, Liang; Zhu, Junfa

    2012-08-27

    Anodization of α-Fe(2)O(3) (hematite) electrodes in alkaline electrolyte under constant potential conditions the electrode surface in a way that an additional current wave occurs in the cyclic voltammogram. The energy position of this current wave is closely below the potential of the anodization treatment. Continued cycling or exchanging of the electrolyte causes depletion of this new feature. The O 1s and Fe 2p core-level X-ray photoelectron spectra (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectra of such conditioned hematite exhibit a chemical shift towards higher binding energies, in line with the general perception that anodization generates oxide species with dielectric properties. The valence band XPS and particularly the iron resonant valence band photoemission spectra, however, are shifted towards the opposite direction, that is, towards the Fermi energy, suggesting that hole doping on hematite has taken place during anodization. Quantitative analysis of the Fe 2p resonant valence band photoemission spectra shows that the spectra obtained at the Fe 2p absorption threshold are shifted by virtually the same energy as the anodization potential towards the Fermi energy. The tentative interpretation of this observation is that anodization forms a surface film on the hematite that is specific to the anodization potential.

  1. Modeling Photoemission of Spin-Polarized Electrons from NEA GaAs Photocathodes

    NASA Astrophysics Data System (ADS)

    Chubenko, Oksana; Afanasev, Andrei

    2015-04-01

    At present, photoemission from strained GaAs activated to negative electron affinity (NEA) is a main source of polarized electrons for modern nuclear-physics and particle-physics facilities. Future experiments at advanced electron colliders will require high-current polarized electron beams, which could provide high polarization and luminosity. This sets new requirements for photocathodes in terms of high quantum efficiency (QE) (>>1%) and spin polarization (~85%). Detailed simulation and modeling of physics processes in photocathodes is important for optimization of their design in order to achieve high QE and reduce depolarization mechanisms. The purpose of the present work was to develop a semi-phenomenological model, which could predict photoemission and electron spin polarization from NEA GaAs photocathodes. Effect of the presence of nanostructures was also studied. Simulation results were compared to the experimental results obtained by the polarized electron source group at Thomas Jefferson National Accelerator Facility. Work supported by Thomas Jefferson Accelerator Facility and George Washington University.

  2. Probing the electronic and spintronic properties of buried interfaces by extremely low energy photoemission spectroscopy

    NASA Astrophysics Data System (ADS)

    Fetzer, Roman; Stadtmüller, Benjamin; Ohdaira, Yusuke; Naganuma, Hiroshi; Oogane, Mikihiko; Ando, Yasuo; Taira, Tomoyuki; Uemura, Tetsuya; Yamamoto, Masafumi; Aeschlimann, Martin; Cinchetti, Mirko

    2015-02-01

    Ultraviolet photoemission spectroscopy (UPS) is a powerful tool to study the electronic spin and symmetry features at both surfaces and interfaces to ultrathin top layers. However, the very low mean free path of the photoelectrons usually prevents a direct access to the properties of buried interfaces. The latter are of particular interest since they crucially influence the performance of spintronic devices like magnetic tunnel junctions (MTJs). Here, we introduce spin-resolved extremely low energy photoemission spectroscopy (ELEPS) to provide a powerful way for overcoming this limitation. We apply ELEPS to the interface formed between the half-metallic Heusler compound Co2MnSi and the insulator MgO, prepared as in state-of-the-art Co2MnSi/MgO-based MTJs. The high accordance between the spintronic fingerprint of the free Co2MnSi surface and the Co2MnSi/MgO interface buried below up to 4 nm MgO provides clear evidence for the high interface sensitivity of ELEPS to buried interfaces. Although the absolute values of the interface spin polarization are well below 100%, the now accessible spin- and symmetry-resolved wave functions are in line with the predicted existence of non-collinear spin moments at the Co2MnSi/MgO interface, one of the mechanisms evoked to explain the controversially discussed performance loss of Heusler-based MTJs at room temperature.

  3. Probing the electronic and spintronic properties of buried interfaces by extremely low energy photoemission spectroscopy.

    PubMed

    Fetzer, Roman; Stadtmüller, Benjamin; Ohdaira, Yusuke; Naganuma, Hiroshi; Oogane, Mikihiko; Ando, Yasuo; Taira, Tomoyuki; Uemura, Tetsuya; Yamamoto, Masafumi; Aeschlimann, Martin; Cinchetti, Mirko

    2015-02-23

    Ultraviolet photoemission spectroscopy (UPS) is a powerful tool to study the electronic spin and symmetry features at both surfaces and interfaces to ultrathin top layers. However, the very low mean free path of the photoelectrons usually prevents a direct access to the properties of buried interfaces. The latter are of particular interest since they crucially influence the performance of spintronic devices like magnetic tunnel junctions (MTJs). Here, we introduce spin-resolved extremely low energy photoemission spectroscopy (ELEPS) to provide a powerful way for overcoming this limitation. We apply ELEPS to the interface formed between the half-metallic Heusler compound Co2MnSi and the insulator MgO, prepared as in state-of-the-art Co2MnSi/MgO-based MTJs. The high accordance between the spintronic fingerprint of the free Co2MnSi surface and the Co2MnSi/MgO interface buried below up to 4 nm MgO provides clear evidence for the high interface sensitivity of ELEPS to buried interfaces. Although the absolute values of the interface spin polarization are well below 100%, the now accessible spin- and symmetry-resolved wave functions are in line with the predicted existence of non-collinear spin moments at the Co2MnSi/MgO interface, one of the mechanisms evoked to explain the controversially discussed performance loss of Heusler-based MTJs at room temperature.

  4. Probing the electronic and spintronic properties of buried interfaces by extremely low energy photoemission spectroscopy

    PubMed Central

    Fetzer, Roman; Stadtmüller, Benjamin; Ohdaira, Yusuke; Naganuma, Hiroshi; Oogane, Mikihiko; Ando, Yasuo; Taira, Tomoyuki; Uemura, Tetsuya; Yamamoto, Masafumi; Aeschlimann, Martin; Cinchetti, Mirko

    2015-01-01

    Ultraviolet photoemission spectroscopy (UPS) is a powerful tool to study the electronic spin and symmetry features at both surfaces and interfaces to ultrathin top layers. However, the very low mean free path of the photoelectrons usually prevents a direct access to the properties of buried interfaces. The latter are of particular interest since they crucially influence the performance of spintronic devices like magnetic tunnel junctions (MTJs). Here, we introduce spin-resolved extremely low energy photoemission spectroscopy (ELEPS) to provide a powerful way for overcoming this limitation. We apply ELEPS to the interface formed between the half-metallic Heusler compound Co2MnSi and the insulator MgO, prepared as in state-of-the-art Co2MnSi/MgO-based MTJs. The high accordance between the spintronic fingerprint of the free Co2MnSi surface and the Co2MnSi/MgO interface buried below up to 4 nm MgO provides clear evidence for the high interface sensitivity of ELEPS to buried interfaces. Although the absolute values of the interface spin polarization are well below 100%, the now accessible spin- and symmetry-resolved wave functions are in line with the predicted existence of non-collinear spin moments at the Co2MnSi/MgO interface, one of the mechanisms evoked to explain the controversially discussed performance loss of Heusler-based MTJs at room temperature. PMID:25702631

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

    SciTech Connect

    Leenheer, Andrew J.; Narang, Prineha; Atwater, Harry A.; Lewis, Nathan S.

    2014-04-07

    Collection of hot electrons generated by the efficient absorption of light in metallic nanostructures, in contact with semiconductor substrates can provide a basis for the construction of solar energy-conversion devices. Herein, we evaluate theoretically the energy-conversion efficiency of systems that rely on internal photoemission processes at metal-semiconductor Schottky-barrier diodes. In this theory, the current-voltage characteristics are given by the internal photoemission yield as well as by the thermionic dark current over a varied-energy barrier height. The Fowler model, in all cases, predicts solar energy-conversion efficiencies of <1% for such systems. However, relaxation of the assumptions regarding constraints on the escape cone and momentum conservation at the interface yields solar energy-conversion efficiencies as high as 1%–10%, under some assumed (albeit optimistic) operating conditions. Under these conditions, the energy-conversion efficiency is mainly limited by the thermionic dark current, the distribution of hot electron energies, and hot-electron momentum considerations.

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

    NASA Astrophysics Data System (ADS)

    Dowek, D.; Picard, Y. J.; Billaud, P.; Elkharrat, C.; Houver, J. C.

    2009-04-01

    Molecular frame photoemission is a very sensitive probe of the photoionization (PI) dynamics of molecules. This paper reports a comparative study of non-resonant and resonant photoionization of D2 induced by VUV circularly polarized synchrotron radiation at SOLEIL at the level of the molecular frame photoelectron angular distributions (MFPADs). We use the vector correlation method which combines imaging and time-of-flight resolved electron-ion coincidence techniques, and a generalized formalism for the expression of the I(χ, θe, varphie) MFPADs, where χ is the orientation of the molecular axis with respect to the light quantization axis and (θe, varphie) the electron emission direction in the molecular frame. Selected MFPADs for a molecule aligned parallel or perpendicular to linearly polarized light, or perpendicular to the propagation axis of circularly polarized light, are presented for dissociative photoionization (DPI) of D2 at two photon excitation energies, hν = 19 eV, where direct PI is the only channel opened, and hν = 32.5 eV, i.e. in the region involving resonant excitation of Q1 and Q2 doubly excited state series. We discuss in particular the properties of the circular dichroism characterizing photoemission in the molecular frame for direct and resonant PI. In the latter case, a remarkable behavior is observed which may be attributed to the interference occurring between undistinguishable autoionization decay channels.

  7. Two-photon photoemission from image-potential states of epitaxial graphene

    NASA Astrophysics Data System (ADS)

    Gugel, Dieter; Niesner, Daniel; Eickhoff, Christian; Wagner, Stefanie; Weinelt, Martin; Fauster, Thomas

    2015-12-01

    Using angle- and time-resolved two-photon photoelectron spectroscopy we observe a single series of image-potential states of graphene on monolayer (MLG) and bilayer graphene (BLG) on SiC(0001). The first image-potential state on MLG (BLG) has a binding energy of 0.93 eV (0.84 eV). Lifetimes of the first three image-potential states of MLG are 9, 44 and 110 fs. On hydrogen-intercalated, quasi-freestanding graphene no unoccupied states are observed. We attribute this to the absence of occupied initial states for direct transitions into image-potential states at photon energies below the work function used in two-photon photoemission. The work function varies between 4.14 and 4.79 eV, but the vacuum level stays ∼4.5 eV above the Dirac point for all surfaces studied. This finding suggests that direct excitation of image-potential states cannot be achieved by doping and the electron dynamics for free-standing graphene is not accessible by two-photon photoemission using photon energies below the work function.

  8. Core-level photoemission from nanocluster-matrix composites: Au clusters in amorphous carbon

    NASA Astrophysics Data System (ADS)

    Calliari, L.; Minati, L.; Speranza, G.; Paris, A.; Baranov, A.; Fanchenko, S.

    2014-09-01

    We investigate a system consisting of Au nano-clusters and amorphous carbon (a-C) via core-level photoemission. While the ability of photoemission to characterize nano-sized metal clusters is well-known, still some issues deserve investigation. For example, the well-established dominance of final-state relaxation effects in core-level spectra from nano-clusters necessarily involves a crucial role of the cluster dielectric-environment. To the best of our knowledge however, a thorough discussion on this point is lacking. We thus intend to investigate dielectric-environment effects by considering several configurations for Au clusters, i.e. supported and embedded, with the latter obtained either by depositing a-C on top of supported clusters or by co-depositing a-C and Au. We analyze the Au4 f spectrum from clusters accounting for both cluster size and cluster location with respect to the a-C matrix. We show that spectral changes caused by a-C deposition are entirely explained in terms of changes in the cluster dielectric environment. Moreover, we prove that supported clusters are in a well-characterized dielectric environment, while embedded clusters are not. This is because embedded clusters, whatever the method of production, are spatially distributed over the matrix surface-region which is characterized by rapid fluctuations in the dielectric constant.

  9. Final Report: Laser-Based Optical Trap for Remote Sampling of Interplanetary and Atmospheric Particulate Matter

    NASA Technical Reports Server (NTRS)

    Stysley, Paul

    2016-01-01

    Applicability to Early Stage Innovation NIAC Cutting edge and innovative technologies are needed to achieve the demanding requirements for NASA origin missions that require sample collection as laid out in the NRC Decadal Survey. This proposal focused on fully understanding the state of remote laser optical trapping techniques for capturing particles and returning them to a target site. In future missions, a laser-based optical trapping system could be deployed on a lander that would then target particles in the lower atmosphere and deliver them to the main instrument for analysis, providing remote access to otherwise inaccessible samples. Alternatively, for a planetary mission the laser could combine ablation and trapping capabilities on targets typically too far away or too hard for traditional drilling sampling systems. For an interstellar mission, a remote laser system could gather particles continuously at a safe distance; this would avoid the necessity of having a spacecraft fly through a target cloud such as a comet tail. If properly designed and implemented, a laser-based optical trapping system could fundamentally change the way scientists designand implement NASA missions that require mass spectroscopy and particle collection.

  10. Innovative laser based approaches to laryngeal cancer: what an engineer and physicist need to know

    NASA Astrophysics Data System (ADS)

    Burns, James A.

    2008-02-01

    Innovative laser-based approaches to laryngeal cancer include the clinical applications of two new technologies, photoangiolysis using a 532nm wavelength pulsed-KTP laser and fiber-based cutting using a 2μm wavelength thulium laser. Photoangiolysis is well-suited for treatment of minimally invasive glottic cancer and allows maximum preservation of phonatory surfaces needed for optimal voicing. The thulium laser offers an alternative to the carbon dioxide laser as an endolaryngeal cutting tool due to its enhanced hemostatic properties and fiber-based delivery. Clinical examples of pulsed-KTP laser involution of early glottic cancer will be presented in order to highlight the concept of targeting tumor angiogenesis in treating laryngeal cancer. The surgical experience using the thulium laser for complex endoscopic endolaryngeal excisions of large laryngeal cancers is presented to demonstrate the expanded clinical applications of endolaryngeal cutting offered by this laser. The laryngeal tissue effects of various laser power and pulse width (PW) settings, mode of delivery, active cooling to reduce thermal trauma, and wavelength selection have been extensively studied for the KTP and thulium lasers in both ex-vivo and live-perfusing models. The results from these studies, included herein, determine the clinical efficacy and safety of these innovative laser-based approaches to laryngeal cancer.

  11. Modern technology in artwork conservation: a laser-based approach for process control and evaluation

    NASA Astrophysics Data System (ADS)

    Tornari, V.; Zafiropulos, V.; Bonarou, A.; Vainos, N. A.; Fotakis, C.

    2000-10-01

    The present work includes a laser-based methodology for the cleaning of artworks, with emphasis on the preservation of their structural integrity and identity. Modern laser-based techniques and instrumentation offer new tools in the field of artwork and antiquities conservation, aiming to alleviate the traditionally applied methods from existing weaknesses. Although in several cases the use of lasers may give rise to superior results, there are still problems to be resolved in relation to the optimization of procedures for safeguarding from potential damage. Furthermore, several operational parameters have to be simultaneously controlled and the long-term effects induced by laser irradiation must be assessed in detail before a full exploitation of the new methods is established. The control of material removal during laser cleaning is achieved by using laser-induced breakdown spectroscopy (LIBS). This control relies on the collection of spectroscopic data by LIBS, which correspond to the in-depth compositional profile of the artifact. This technique may be combined with structural analysis by holographic interferometry. The latter is important for assessing structural changes, which may be induced during laser ablation. Selected examples of this type of applications in a carefully considered methodology are presented.

  12. High-spatial-resolution sub-surface imaging using a laser-based acoustic microscopy technique.

    PubMed

    Balogun, Oluwaseyi; Cole, Garrett D; Huber, Robert; Chinn, Diane; Murray, Todd W; Spicer, James B

    2011-01-01

    Scanning acoustic microscopy techniques operating at frequencies in the gigahertz range are suitable for the elastic characterization and interior imaging of solid media with micrometer-scale spatial resolution. Acoustic wave propagation at these frequencies is strongly limited by energy losses, particularly from attenuation in the coupling media used to transmit ultrasound to a specimen, leading to a decrease in the depth in a specimen that can be interrogated. In this work, a laser-based acoustic microscopy technique is presented that uses a pulsed laser source for the generation of broadband acoustic waves and an optical interferometer for detection. The use of a 900-ps microchip pulsed laser facilitates the generation of acoustic waves with frequencies extending up to 1 GHz which allows for the resolution of micrometer-scale features in a specimen. Furthermore, the combination of optical generation and detection approaches eliminates the use of an ultrasonic coupling medium, and allows for elastic characterization and interior imaging at penetration depths on the order of several hundred micrometers. Experimental results illustrating the use of the laser-based acoustic microscopy technique for imaging micrometer-scale subsurface geometrical features in a 70-μm-thick single-crystal silicon wafer with a (100) orientation are presented.

  13. Laser-based ultrasonic inspection with a fiber-coupled scanning Cassegrain system.

    PubMed

    McKie, Andrew D W; Addison, Robert C

    2002-12-01

    State-of-the-art integrally stiffened composite materials, manufactured for use in the next generation of commercial and military aircraft, are increasingly being used for structural components such as wings and fuselages. However, the complexity of the manufacturing processes can produce small variations in the shape of integrally stiffened composite structures. Thus, a priori knowledge of the nominal part shape often does not provide sufficient accuracy to allow an automated conventional ultrasonic inspection. In contrast, automated inspections of integrally stiffened structures can be performed using laser-based ultrasound techniques since a priori knowledge of the nominal part shape is adequate to scan the laser beams over the structure. This paper addresses the issues associated with the extension of laser-based ultrasonics to inspections in remote and limited access areas, and describes the implementation of a fiber-based remote and limited access LBU inspection system based upon a Cassegrain scanning and optical collection system. The ability to quickly and directly manipulate flexible low mass optical fibers equipped with specialized endoscopic scanning optics make fiber systems an attractive method for the development of limited and remote access inspection systems. The Cassegrain optical system is described in detail and both numerical and experimental validation of the system operational characteristics are presented.

  14. Development and use of a laser-based pipeline corrosion assessment system

    SciTech Connect

    Bruce, W.A.; Yapp, D.; Barborak, D.M.; Fingerhut, M.P.; Kania, R.

    1997-05-01

    The development and use of a simple laser-based system for accurately and efficiently measuring and assessing corrosion damage on the external surface of an exposed pipeline is described. The system uses a laser-based range sensor, which relies on optical spray, sensor movement, and the principal of triangulation to construct a three-dimensional measurement. Baseline subtraction, where a polynomial curve-fit is used to approximate the ideal pipe profile above the corroded area, is used. Future profiles are subtracted; from the ideal profile, and when differences are significant, corrosion depth measurements are made by constructing normal vectors at points along the ideal profile. A software program titled CorrosionPro 2.1 was developed to provide a means to playback and display data files generated by the system. The program uses the RSTRENG algorithm to assess the significance of the damage. Examples of the application of this system on large-diameter gas and oil pipelines are also described.

  15. Development of a laser-based process chain for manufacturing free form optics

    NASA Astrophysics Data System (ADS)

    Heidrich, S.; Richmann, A.; Willenborg, E.

    2012-06-01

    This paper presents the development of a laser based process chain for manufacturing fused silica optics. Due to disadvantages of conventional methods concerning costs and time when manufacturing optics with nonspherical shape, this process chain focuses on aspherical and free form surface geometries, but it is also capable of producing spherical optics. It consists of three laser based processing steps, which in combination produce the optics. In a first step, fused silica is ablated with laser radiation to produce the geometry of the optics. A subsequent laser polishing step reduces the surface roughness and a third step uses laser micro ablation to remove the last remaining redundant material. Most of the conducted experiments are carried out using CO2 laser radiation, but it is also possible to ablate material with ultra short pulse laser radiation. Besides describing the experimental setup and the mechanisms of the ablation and polishing step, the paper presents and discusses results achieved to date. Although the process chain is still under development, the single process steps already reach promising results for themselves and moreover, first elements are manufactured using the first two process steps together.

  16. Photoemission from cesium-oxide-activated InGaAsP.

    NASA Technical Reports Server (NTRS)

    James, L. W.; Antypas, G. A.; Moon, R. L.; Edgecumbe, J.; Bell, R. L.

    1973-01-01

    Zinc-doped InGaAsP quaternary III-V material of the proper composition range shows superior photoemission properties to either InGaAs or InAsP ternary material. The minority-carrier diffusion length in the quaternary material is at least as long as that in InAsP and much longer than observed in InGaAs. The barrier height at the InGaAsP-Cs2O interface is lowered by cooling, giving increased electron escape probability and new highs in quantum efficiency over a wide wavelength range. For example, a 1.06-micron quantum efficiency of 7.5%/incident photon was observed at -90 C.

  17. Novel Si(1-x)Ge(x)/Si heterojunction internal photoemission long-wavelength infrared detectors

    NASA Technical Reports Server (NTRS)

    Lin, T. L.; Maserjian, J.

    1990-01-01

    The feasibility of a novel p(+)-Si(1-x)Ge(x)-p-Si heterojunction internal photoemission (HIP) IR detector is demonstrated. A degenerately doped p(x)-Si(1-x)Ge(x) layer is required for strong IR absorption to generate photoexcited holes. The Si(1-x)Ge(x) layers are grown by molecular beam epitaxy, with boron concentrations up to 10 to the 20th/cu cm achieved by using an HBO2 source. Photoresponse at wavelengths ranging from 2 to 10 microns has been obtained with quantum efficiencies above 1 percent. The tailorable cutoff wavelength of the HIP detector has been demonstrated by varying the Ge composition ratio in the Si(1-x)Ge(x) layers.

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

    SciTech Connect

    Mishra, S.; Gammon, W.J.; Pappas, D.P.

    1997-04-01

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

  19. Time-resolved magnetic imaging in an aberration-corrected, energy-filtered photoemission electron microscope.

    PubMed

    Nickel, F; Gottlob, D M; Krug, I P; Doganay, H; Cramm, S; Kaiser, A M; Lin, G; Makarov, D; Schmidt, O G; Schneider, C M

    2013-07-01

    We report on the implementation and usage of a synchrotron-based time-resolving operation mode in an aberration-corrected, energy-filtered photoemission electron microscope. The setup consists of a new type of sample holder, which enables fast magnetization reversal of the sample by sub-ns pulses of up to 10 mT. Within the sample holder current pulses are generated by a fast avalanche photo diode and transformed into magnetic fields by means of a microstrip line. For more efficient use of the synchrotron time structure, we developed an electrostatic deflection gating mechanism capable of beam blanking within a few nanoseconds. This allows us to operate the setup in the hybrid bunch mode of the storage ring facility, selecting one or several bright singular light pulses which are temporally well-separated from the normal high-intensity multibunch pulse pattern.

  20. Study of non-linear photoemission effects in III-V semiconductors

    SciTech Connect

    Tang, H.; Alley, R.K.; Aoyagi, H.

    1993-10-01

    Our experience at SLAC with photoemission-based polarized electron sources has shown that charge limit is an important phenomenon that may significantly limit the performance of a photocathode for applications requiring high intensity electron beams. In the process of developing high performance photocathodes for the ongoing and future SLC high energy physics programs, we have studied the various aspects of the charge limit phenomenon. We find that the charge limit effect arises as a result of non-linear response of a photocathode to high intensity light illumination. The size of the charge limit not only depends on the quantum efficiency of the cathode but also depends critically on the extraction electric field. In addition, we report the observation of charge oversaturation when the intensity of the incident light becomes too large.