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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. 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.

  4. 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.

  5. Anomalous doping variation of the nodal low-energy feature of superconducting (Bi,Pb)2(Sr,La)2CuO(6+δ) crystals revealed by laser-based angle-resolved photoemission spectroscopy.

    PubMed

    Kondo, Takeshi; Nakashima, Y; Malaeb, W; Ishida, Y; Hamaya, Y; Takeuchi, Tsunehiro; Shin, S

    2013-05-24

    The nodal band dispersion in (Bi,Pb)(2)(Sr,La)(2)CuO(6+δ) (Bi2201) is investigated over a wide range of doping by using 7-eV laser-based angle-resolved photoemission spectroscopy. We find that the low-energy band renormalization ("kink"), recently discovered in Bi(2)Sr(2)CaCu(2)O(8+δ) (Bi2212), also occurs in Bi2201, but at a binding energy around half that in Bi2212. Surprisingly, the coupling energy dramatically increases with a decrease of carrier concentration, showing a sharp enhancement across the optimal doping. These properties (material and doping dependence of the coupling energy) demonstrate the significant correlation among the mode coupling, the energy gap close to the node, and the strong electron correlation. Our results suggest forward scattering arising from the interplay between the electrons and in-plane polarized acoustic phonon branch as the origin of the low-energy renormalization.

  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. Angle-resolved photoemission spectroscopy at ultra-low temperatures.

    PubMed

    Borisenko, Sergey V; Zabolotnyy, Volodymyr B; Kordyuk, Alexander A; Evtushinsky, Danil V; Kim, Timur K; Carleschi, Emanuela; Doyle, Bryan P; Fittipaldi, Rosalba; Cuoco, Mario; Vecchione, Antonio; Berger, Helmut

    2012-10-09

    The physical properties of a material are defined by its electronic structure. Electrons in solids are characterized by energy (ω) and momentum (k) and the probability to find them in a particular state with given ω and k is described by the spectral function A(k, ω). This function can be directly measured in an experiment based on the well-known photoelectric effect, for the explanation of which Albert Einstein received the Nobel Prize back in 1921. In the photoelectric effect the light shone on a surface ejects electrons from the material. According to Einstein, energy conservation allows one to determine the energy of an electron inside the sample, provided the energy of the light photon and kinetic energy of the outgoing photoelectron are known. Momentum conservation makes it also possible to estimate k relating it to the momentum of the photoelectron by measuring the angle at which the photoelectron left the surface. The modern version of this technique is called Angle-Resolved Photoemission Spectroscopy (ARPES) and exploits both conservation laws in order to determine the electronic structure, i.e. energy and momentum of electrons inside the solid. In order to resolve the details crucial for understanding the topical problems of condensed matter physics, three quantities need to be minimized: uncertainty* in photon energy, uncertainty in kinetic energy of photoelectrons and temperature of the sample. In our approach we combine three recent achievements in the field of synchrotron radiation, surface science and cryogenics. We use synchrotron radiation with tunable photon energy contributing an uncertainty of the order of 1 meV, an electron energy analyzer which detects the kinetic energies with a precision of the order of 1 meV and a He(3) cryostat which allows us to keep the temperature of the sample below 1 K. We discuss the exemplary results obtained on single crystals of Sr2RuO4 and some other materials. The electronic structure of this material can be

  10. 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 (Bi1.35Pb0.85)(Sr1.47La0.38)CuO6+δ (Bi2201) Tc,max 35 K. The aim of the study was to provide some insight into the reasons why single layer cuprate's maximum transition temperatures are so different. The study found two major di erences in the band structure. First, the Fermi surface segments close to ( π,0) are more parallel in Tl2201 than in Bi2201. Second, the shadow band usually related to crystal structure is only present in Bi2201, but absent in higher Tc Tl2201. The second study looks at the different ways of doping Bi2Sr2CaCu2O8+δ (Bi2212) in-situ by only changing the post bake-out vacuum conditions and temperature. The aim of the study is to systematically look into the generally overlooked experimental conditions that change the doping of a cleaved sample in ultra high vacuum (UHV) experiments. The study found two major experimental facts. First, in inadequate UHV conditions the carrier concentration of Bi2212 increases with time, due to the absorption of oxygen from CO2/CO molecules, prime contaminants present in UHV systems. Second, in a very clean UHV system at elevated temperatures (above about 200 K), the carrier concentration decreases due to the loss of oxygen atoms from the Bi-O layer. The final study probed the particle-hole symmetry of the pseudogap phase in high temperature superconducting cuprates by looking at the thermally excited bands above the Fermi level. The data showed a particle-hole symmetric pseudogap which symmetrically closes away from the nested FS before the node. The data is consistent with a

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. Development of the Experimental System for Time- and Angle-resolved Photoemission Spectroscopy

    SciTech Connect

    Takahashi, Kazutoshi; Azuma, Junpei; Tokudomi, Shinji; Kamada, Masao

    2007-01-19

    Experimental system for the time- and angle-resolved photoemission spectroscopy have been constructed at BL13 in SAGA Light Source, in order to study the electronic non-equilibrium in the surface layer of laser-excited materials The experimental system is very useful for photoemission spectroscopy in the wide temporal and angular ranges. The time- and angle-resolved photoemission spectra can be obtained with using the gate electronics for the MCP detector of the photoemission spectrometer. The gated MCP detector is synchronized with the laser pulse from Ti:sapphire regenerative amplifier with the repetition frequency of 10 to 300 kHz. The time-window of the gated MCP detector can be changed between 10 nano- and 160 micro-second. The time-resolved measurement in pico-second region can be performed with using the pump-probe technique which uses fundamental, second and third harmonics from the Ti:sapphire laser as the excitation source. Using these systems, we can perform the time- and angle-resolved photoemission study for various photo-excited phenomena and surface dynamics.

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

    SciTech Connect

    Dunn, Lisa

    2003-05-13

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

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

    NASA Astrophysics Data System (ADS)

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

    1997-01-01

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

  18. 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.

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

    PubMed

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

    2013-09-01

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

  20. 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}.

  1. 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.

  2. 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.

  3. 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. PMID:28405592

  4. 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.

  5. 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

  6. 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.

  7. 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.

  8. a Study on SODIUM(110) and Other Nearly Free Electron Metals Using Angle Resolved Photoemission Spectroscopy.

    NASA Astrophysics Data System (ADS)

    Lyo, In-Whan

    Electronic properties of the epitaxially grown Na(110) film have been studied using angle resolved ultraviolet photoemission spectroscopy with synchrotron radiation as the light source. Na provides an ideal ground to study the fundamental aspects of the electron-electron interactions in metals, because of its simple Fermi surface and small pseudopotential. The absolute band structure of Na(110) using angle resolved photoemission spectroscopy has been mapped out using the extrema searching method. The advantage of this approach is that the usual assumption of the unoccupied state dispersion is not required. We have found that the dispersion of Na(1l0) is very close to the parabolic band with the effective mass 1.21 M_{rm e} at 90 K. Self-consistent calculations of the self-energy for the homogeneous electron gas have been performed using the Green's function technique within the framework of the GW approximation, in the hope of understanding the narrowing mechanism of the bandwidth observed for all the nearly-free-electron (NFE) metals. Good agreements between the experimental data and our calculated self-energy were obtained not only for our data on k-dependency from Na(l10), but also for the total bandwidth corrections for other NFE metals, only if dielectric functions beyond the random phase approximation were used. Our findings emphasize the importance of the screening by long wavelength plasmons. Off-normal spectra of angle resolved photoemission from Na(110) show strong asymmetry of the bulk peak intensity for the wide range of photon energies. Using a simple analysis, we show this asymmetry has an origin in the interference of the surface Umklapp electrons with the normal electrons. We have also performed the detailed experimental studies of the anomalous Fermi level structure observed in the forbidden gap region of Na. This was claimed by A. W. Overhauser as the evidence of the charge density wave in the alkali metal. The possibility of this hypothesis is

  9. 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.

  10. 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.

  11. 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

  12. Tracking Cooper pairs in a cuprate superconductor by ultrafast angle-resolved photoemission.

    PubMed

    Smallwood, Christopher L; Hinton, James P; Jozwiak, Christopher; Zhang, Wentao; Koralek, Jake D; Eisaki, Hiroshi; Lee, Dung-Hai; Orenstein, Joseph; Lanzara, Alessandra

    2012-06-01

    In high-temperature superconductivity, the process that leads to the formation of Cooper pairs, the fundamental charge carriers in any superconductor, remains mysterious. We used a femtosecond laser pump pulse to perturb superconducting Bi(2)Sr(2)CaCu(2)O(8+δ) and studied subsequent dynamics using time- and angle-resolved photoemission and infrared reflectivity probes. Gap and quasiparticle population dynamics revealed marked dependencies on both excitation density and crystal momentum. Close to the d-wave nodes, the superconducting gap was sensitive to the pump intensity, and Cooper pairs recombined slowly. Far from the nodes, pumping affected the gap only weakly, and recombination processes were faster. These results demonstrate a new window into the dynamical processes that govern quasiparticle recombination and gap formation in cuprates.

  13. An ultrafast angle-resolved photoemission apparatus for measuring complex materials.

    PubMed

    Smallwood, Christopher L; Jozwiak, Christopher; Zhang, Wentao; Lanzara, Alessandra

    2012-12-01

    We present technical specifications for a high resolution time- and angle-resolved photoemission spectroscopy setup based on a hemispherical electron analyzer and cavity-dumped solid state Ti:sapphire laser used to generate pump and probe beams, respectively, at 1.48 and 5.93 eV. The pulse repetition rate can be tuned from 209 Hz to 54.3 MHz. Under typical operating settings the system has an overall energy resolution of 23 meV, an overall momentum resolution of 0.003 Å(-1), and an overall time resolution of 310 fs. We illustrate the system capabilities with representative data on the cuprate superconductor Bi(2)Sr(2)CaCu(2)O(8+δ). The descriptions and analyses presented here will inform new developments in ultrafast electron spectroscopy.

  14. 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.

  15. Unexpected Large Hole Effective Masses in SnSe Revealed by Angle-Resolved Photoemission Spectroscopy

    NASA Astrophysics Data System (ADS)

    Lu, Qiangsheng; Wu, Minghui; Wu, Di; Chang, Cheng; Guo, Yan-Ping; Zhou, Chun-Sheng; Li, Wei; Ma, Xiao-Ming; Wang, Gan; Zhao, Li-Dong; Huang, Li; Liu, Chang; He, Jiaqing

    2017-09-01

    SnSe has emerged as an efficient thermoelectric material since a high value of the thermoelectric figure of merit (Z T ) has been reported recently. Here we show with systematic angle resolved photoemission spectroscopy data that the low-lying electronic structures of undoped and hole-doped SnSe crystals exhibit noticeable temperature variation from 80 to 600 K. In particular, the hole effective masses for the two lowest lying valence band maxima are found to be very large and increase with decreasing temperature. Thermoelectric parameters derived from such hole-mass enhancement agree well with the transport values, indicating comprehensively a reduced impact of multivalley transport to the system's thermoelectric performance.

  16. 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.

  17. Photon energy dependent circular dichroism in angle-resolved photoemission from Au(111) surface states

    NASA Astrophysics Data System (ADS)

    Ryu, Hanyoung; Song, Inkyung; Kim, Beomyoung; Cho, Soohyun; Soltani, Shoresh; Kim, Timur; Hoesch, Moritz; Kim, Choong H.; Kim, Changyoung

    2017-03-01

    We performed angle-resolved photoemission experiments on Au(111) surface with circularly polarized light. Data were taken with photon energies in the range between 20 and 100 eV in order to investigate the photon energy dependent behavior in the circular dichroism (CD). While the magnitude of the normalized CD value varies with a maximum value of about 70%, the sign of CD does not change for the photon energy within the range, inconsistent with the prediction based on the density-functional theory (DFT) calculation. Our calculation of the CD using DFT initial state and free electron final state shows a better consistency with experimental results than an earlier study using the inverse low-energy electron diffraction state as the final state. We briefly discuss the dominating factor that determines the CD from Au(111) states.

  18. 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.

  19. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2017-05-01

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

  1. 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

  2. Angle resolved photoemission studies of the Rashba states in ferroelectric GeTe

    NASA Astrophysics Data System (ADS)

    Kim, Beomyoung; Kyung, Wonshik; Han, Garam; Kim, Yeongkwan; Denlinger, Jonathan; Chung, In; Kim, Changyoung

    2015-03-01

    There has been significant increase in the research of spin orbit coupling (SOC) induced exotic phenomena. The Rashba effect, theoretically predicted to exist, is one of the SOC related phenomena. The phenomenon was later experimentally observed in the surface states of metals and topological insulators as well as interfaces of hetero structures that have inversion symmetry breaking (ISB). Even bulk states with intrinsic ISB such as BiTe is found to have Rashba split bands. It was very recently proposed that ferroelectric GeTe has Rashba effect in the bulk. This is a unique situation where ISB is provided not by the structure ISB but by an electrical polarization. We have performed angle-resolved photoemission spectroscopy (ARPES) on GeTe single crystals to investigate the unique bulk Rashba state. Our results indeed show the existence of a Rashba-type band splitting as theoretically predicted. We discuss various aspect of the Rashba state in GeTe.

  3. 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.

  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. 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.

  6. 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.

  7. Angle-resolved photoemission study of the Kitaev candidate α -RuCl3

    NASA Astrophysics Data System (ADS)

    Zhou, Xiaoqing; Li, Haoxiang; Waugh, J. A.; Parham, S.; Kim, Heung-Sik; Sears, J. A.; Gomes, A.; Kee, Hae-Young; Kim, Young-June; Dessau, D. S.

    2016-10-01

    α -RuCl3 has been hinted to be a spin-orbital-assisted Mott insulator in proximity to a Kitaev spin liquid state. Here we present angle-resolved photoemission measurements on single-crystal α -RuCl3 in both the pristine and electron-doped states, and combine them with Local Density Approximation (LDA)+Spin Orbital Coupling (SOC)+U calculations performed for several low-energy competing magnetically ordered states as well as the paramagnetic state. A large Mott gap is found in the measured band structure of the pristine compound that persists to more than 30 times beyond the magnetic ordering temperature, though the paramagnetic calculation shows almost no gap. Upon electron doping, spectral weight is transferred into the gap but the new states still maintain a sizable gap from the Fermi edge. These findings are most consistent with a Mott insulator with a somewhat exotic evolution out of the Mott state with both temperature and doping, likely related to unusually strong spin fluctuations.

  8. 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.

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

    PubMed

    Plumb, Nicholas C; Radović, Milan

    2017-09-29

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

  10. 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.

  11. 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.

  12. 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

  13. 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

  14. Electronic structure of Ge(111)c(2×8) : STM, angle-resolved photoemission, and theory

    NASA Astrophysics Data System (ADS)

    Razado-Colambo, I.; He, Jiangping; Zhang, H. M.; Hansson, G. V.; Uhrberg, R. I. G.

    2009-05-01

    The surface electronic structure of Ge(111)c(2×8) was studied by experimental techniques [low-energy electron diffraction, scanning tunneling microscopy (STM), and angle-resolved photoelectron spectroscopy (ARPES)] and theoretical band-structure calculations. Bias-dependent STM images exhibit two different types of adatoms (AT,AR) and rest atoms (RT,RR) confirming the presence of asymmetries within the c(2×8) cell. The ARPES study resulted in a more detailed picture of the surface electronic structure of the Ge(111)c(2×8) surface compared to earlier studies. The energy dispersion curves showed the presence of seven surface bands labeled A1, A2, A2' , A3, A4, A4' , and A5. The experimental surface bands were compared to the calculated band structure of the full c(2×8) unit cell. The most important results are (i) we have identified a split surface-state band in the photoemission data that matches a split between RT and RR derived rest atom bands in the calculated surface band structure. This allows us to identify the upper A2 band with the RR and the lower A2' band with the RT rest atoms. (ii) The uppermost highly dispersive band (A1) originates from states below the adatom and rest atom layers and should not be confused with rest atom bands A2 and A2' . (iii) The bias-dependent changes in the adatom/rest atom contrast in the experimental STM images were closely reproduced by simulated STM images generated from the calculated electronic structure. (iv) A split was observed in the back-bond derived surface band at higher emission angles (A4 and A4' ).

  15. 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.

  16. 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}.

  17. 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.

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

    SciTech Connect

    Huang, Zhengqing

    1992-10-01

    Angle-resolved photoemission extended fine structure (ARPEFS) was used to study molecular and metallic overlayers on metal surfaces through analysis of p2mg(2x1)CO/Ni(110) and the p(2x2)K/Ni(111) adsorption. For the dense p2mg(2x1)CO/Ni(110) surface layer, photoemission intensities from C 1s level were measured in three directions at photoelectron kinetic energies 60-400 eV. Using multiple-scattering spherical-wave (MSSW) modeling, it was found that CO molecules are adsorbed on short-bridge sites, with adjacent CO along the [110] direction displaced alternatively in opposite directions towards the [001] azimuths to form a zigzag chain geometry. The tilt angle is 16±2° from the surface normal for the direction linking the C atom and the center of the Ni bridge. The carbon C-Ni interatomic distance was determined to be 1.94±0.02Å. The first- to second-layer spacing of Ni is 1.27±0.04Å, up from 1.10Å for the clean Ni(110) surface, but close to the 1.25Å Ni interlayer spacing in the bulk. The C-O bond length and tilt angle were varied within small ranges (1.10--1.20Å and 15--23°) in our MSSW simulations. Best agreement between experiment and simulations was achieved at 1.16Å and 19°. This yields an O-O distance of 2.95Å for the two nearest CO molecules, (van der Waals` radius ~ 1.5 Å for oxygen). Two different partial-wave phase-shifts were used in MSSW, and structural results from both are in very good agreement. For the p(2x2)K/Ni(111) overlayer, ARPEFS {chi}(k) curves from K 1s level measured along [111] and [771] at 130K showed that the K atoms are preferentially adsorbed on the atop sites, in agreement with a LEED study of the same system.

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

    SciTech Connect

    Huang, Z.

    1992-10-01

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

  20. 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).

  1. 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.

  2. 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.

  3. 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.

  4. Anisotropy in ordered sexithiophene thin films studied by angle-resolved photoemission using combined laser and synchrotron radiation

    NASA Astrophysics Data System (ADS)

    Heiner, C. E.; Dreyer, J.; Hertel, I. V.; Koch, N.; Ritze, H.-H.; Widdra, W.; Winter, B.

    2005-08-01

    We present angle-resolved photoemission (PE) spectra of ordered multilayer sexithiophene (6T) films, 200nm thick, grown on a Au(110) single crystal. However, the measurement of sharp and nonshifted PE spectral features from the low-conducting organic material is only possible if the positive surface charge, generated in the PE process, is fully compensated. We have accomplished this by simultaneous laser irradiation. On the basis of the resulting data we found that for these thick films the 6T molecules are preferentially oriented with their long axes nearly normal to the surface.

  5. Electronic structure of electron doped BaAs2Fe2 superconductors revealed by Angle Resolved Photoemission

    NASA Astrophysics Data System (ADS)

    Vilmercati, P.; Vobornik, I.; Unnikrishnan, M.; Fedorov, A.; Goldoni, A.; Panaccione, G.; Safa-Sefat, A.; Jin, R.; McGuire, M. A.; Sales, B. C.; Singh, D. J.; Mandrus, D.; Mannella, N.

    2009-03-01

    The electronic structure in the normal state of Co-doped BaAs2Fe2 superconductors has been measured by Angle Resolved photoemission (ARPES). Co doping on the Fe site results in electron doping [A. S. Sefat et al., Phys. Rev. Lett. 101, 117004 (2008)]. The data qualitatively reveal that Co-doping results in raising the chemical potential, as expected with electron doping. The Fermi surface topology and the possible relevance to the mechanism of spin fluctuation will also be discussed.

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

    PubMed

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

    2010-05-01

    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 degrees 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 (hnu/Deltahnu) and photon flux of the monochromator are typically 1 x 10(4) and 10(12) photons/s, respectively, with a 100 microm 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.

  10. 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

  11. 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.

  12. 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.

  13. 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.

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

    PubMed Central

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

    2014-01-01

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

  15. 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.

  16. Charge-density wave transition of 1T-VSe2 studied by angle-resolved photoemission spectroscopy

    NASA Astrophysics Data System (ADS)

    Terashima, K.; Sato, T.; Komatsu, H.; Takahashi, T.; Maeda, N.; Hayashi, K.

    2003-10-01

    High-resolution angle-resolved photoemission spectroscopy (ARPES) has been performed on a layered transition-metal dichalcogenide (TMDC) 1T-VSe2 to study the (4×4) charge-density wave (CDW) mechanism. We observed a partial Fermi-surface (FS) nesting on the electronlike FS centered at the M (L) point. The spectral weight near EF is considerably suppressed below the transition temperature (Tc=110 K) around the nested portion, while a negligible spectral change is observed even across Tc in other portions of FS. This suggests that the CDW transition in 1T-VSe2 is caused by the three-dimensional FS nesting. Implications are discussed in relation to the physical properties of 1T-VSe2 as well as the ARPES results of other TMDC’s.

  17. 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.

  18. 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.

  19. 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.

  20. Numerical study of the isotope effect in underdoped high-temperature superconductors: Calculation of the angle-resolved photoemission spectra

    NASA Astrophysics Data System (ADS)

    Mishchenko, A. S.; Nagaosa, N.

    2006-03-01

    We present a numerical study of the isotope effect on the angle resolved photoemission spectra (ARPES) in the undoped cuprates. By the systematic-error-free diagrammatic Monte Carlo method, the Lehman spectral function of a single hole in the tt't″-J model in the regime of intermediate and strong couplings to optical phonons is calculated for normal and isotope substituted systems. We found that the isotope effect is strongly energy-momentum dependent, and is anomalously enhanced in the intermediate coupling regime while it approaches that of the localized hole model in the strong coupling regime. We predict the strengths of effect as well as the fine details of the ARPES line shape change. Implications to the doped case are also discussed.

  1. 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.

  2. 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).

  3. 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.

  4. Surface geometry of (1×1)PHx/Ge(111) determined with angle-resolved photoemission extended fine structure

    NASA Astrophysics Data System (ADS)

    Terminello, L. J.; Leung, K. T.; Hussain, Z.; Hayashi, T.; Zhang, X. S.; Shirley, D. A.

    1990-06-01

    Angle-resolved photoemission extended fine structure (ARPEFS) obtained from the phosphorus 1s core level was studied to determine the chemisorption geometry of (1×1)PHx/Ge(111), prepared by partial dissociation of PH3 adsorbed on Ge(111). We determined that the phosphorus adsorbs 2.26 Å above a first-layer germanium atom, and preferentially tilts toward the second-layer germanium atom with a 0.63-Å lateral displacement from a true atop position. Other geometrical parameters determined from the multiple-scattering, spherical-wave analysis of the ARPEFS include the first- to second-layer germanium Ge(1)-Ge(2) spacing (0.68 Å) and the second- to third-layer germanium Ge(2)-Ge(3) spacing (2.68 Å). This represents a 17% contraction for Ge(1)-Ge(2) and a 9% expansion for Ge(2)-Ge(3). The importance of adsorbate scattering and how it affects data interpretation are also discussed. Comparison of this chemisorption system with other systems is made.

  5. 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.

  6. 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.

  7. Intermolecular band dispersion of quasi-single crystalline organic semiconductor monolayer measured by angle-resolved photoemission spectroscopy

    NASA Astrophysics Data System (ADS)

    Ohtomo, Manabu; Shimada, Toshihiro; Hasegawa, Tetsuya

    2010-03-01

    Band structure of organic semiconductors is important knowledge to improve the molecular design. Angle-Resolved Photoemission Spectroscopy (ARPES) studies using highly conductive single domain samples grown in-situ is the most direct technique. In this study, we developed a novel method to grow quasi-single crystalline monolayer on conductive substrate and electronic structure was investigated. As a template for orientation control, we used a step-bunched Si(111) substrate with dangling bond termination. In case of pentacene, it was confirmed that the crystal is quasi-single crystal with 2.2^o rotated twins. The band dispersion was identical to that of thin-film phase. The effective mass and transfer integrals are evaluated using two-dimensional tight binding fit and compared with band calculations [1]. We also report the growth of 2,7-Dipheny[1]benzothieno[3,2-b]benzothiophene (DPh-BTBT) [2] on Bi-Si substrate and compare discuss its band structure. [4pt] [1] M.Ohtomo et al., APL 95, 123308 (2009).[0pt] [2] K.Takimiya, JACS 128, 3044 (2006).

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

    NASA Astrophysics Data System (ADS)

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

    2017-09-01

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

  9. 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.

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

    SciTech Connect

    Ronning, Filip

    2002-03-19

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

  11. 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

  12. Electronic band structure of ReS2 by high-resolution angle-resolved photoemission spectroscopy

    NASA Astrophysics Data System (ADS)

    Webb, James L.; Hart, Lewis S.; Wolverson, Daniel; Chen, Chaoyu; Avila, Jose; Asensio, Maria C.

    2017-09-01

    The rhenium-based transition metal dichalcogenides (TMDs) are atypical of the TMD family due to their highly anisotropic crystalline structure and are recognized as promising materials for two-dimensional heterostructure devices. The nature of the band gap (direct or indirect) for bulk, few-, and single-layer forms of ReS2 is of particular interest, due to its comparatively weak interplanar interaction. However, the degree of interlayer interaction and the question of whether a transition from indirect to direct gap is observed on reducing thickness (as in other TMDs) are controversial. We present a direct determination of the valence band structure of bulk ReS2 using high-resolution angle-resolved photoemission spectroscopy. We find a clear in-plane anisotropy due to the presence of chains of Re atoms, with a strongly directional effective mass which is larger in the direction orthogonal to the Re chains (2.2 me ) than along them (1.6 me ). An appreciable interplane interaction results in an experimentally measured difference of ≈100 -200 meV between the valence band maxima at the Z point (0,0,1/2 ) and the Γ point (0,0,0) of the three-dimensional Brillouin zone. This leads to a direct gap at Z and a close-lying but larger gap at Γ , implying that bulk ReS2 is marginally indirect. This may account for recent conflicting transport and photoluminescence measurements and the resulting uncertainty about the nature of the band gap in this material.

  13. 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.

  14. 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

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

    DOE PAGES

    Wu, Yun; Lee, Yongbin; Kong, Tai; ...

    2017-07-15

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

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

    NASA Astrophysics Data System (ADS)

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

    2017-07-01

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

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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

  2. 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

  3. Dependence of Band Renormalization Effect on the Number of Copper-oxide Layers in Tl-based Copper-oxide Superconductor using Angle-resolved Photoemission Spectroscopy

    SciTech Connect

    Lee, Wei-Sheng

    2010-06-02

    Here we report the first angle-resolved photoemission measurement on nearly optimally doped multilayer Tl-based superconducting cuprates (Tl-2212 and Tl-1223) and a comparison study to single-layer (Tl-2201) compound. A kink in the band dispersion is found in all three compounds but exhibits different momentum dependence for the single-layer and multilayer compounds, reminiscent to that of Bi-based cuprates. This layer number dependent renormalization effect strongly implies that the spin-resonance mode is unlikely to be responsible for the dramatic renormalization effect near the antinodal region.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. Electronic structure of the topological insulator Bi2Se3 using angle-resolved photoemission spectroscopy: evidence for a nearly full surface spin polarization.

    PubMed

    Pan, Z-H; Vescovo, E; Fedorov, A V; Gardner, D; Lee, Y S; Chu, S; Gu, G D; Valla, T

    2011-06-24

    We performed high-resolution spin- and angle-resolved photoemission spectroscopy studies of the electronic structure and the spin texture on the surface of Bi2Se3, a model TI. By tuning the photon energy, we found that the topological surface state is well separated from the bulk states in the vicinity of kz = Z plane of the bulk Brillouin zone. The spin-resolved measurements in that region indicate a very high degree of spin polarization of the surface state, ~0.75, much higher than previously reported. Our results demonstrate that the topological surface state on Bi2Se3 is highly spin polarized and that the dominant factors limiting the polarization are mainly extrinsic.

  10. Electronic Structure of the Topological Insulator Bi2Se3 Using Angle-Resolved Photoemission Spectroscopy: Evidence for a Nearly Full Surface Spin Polarization

    SciTech Connect

    Pan, Z.H.; Vescovo, E.; Fedorov, A.V.; Gardner, D.; Lee, Y.S.; Chu, S.; Gu, G.D.; Valla, T.

    2011-06-22

    We performed high-resolution spin- and angle-resolved photoemission spectroscopy studies of the electronic structure and the spin texture on the surface of Bi{sub 2}Se{sub 3}, a model TI. By tuning the photon energy, we found that the topological surface state is well separated from the bulk states in the vicinity of k{sub z} = Z plane of the bulk Brillouin zone. The spin-resolved measurements in that region indicate a very high degree of spin polarization of the surface state, {approx}0.75, much higher than previously reported. Our results demonstrate that the topological surface state on Bi{sub 2}Se{sub 3} is highly spin polarized and that the dominant factors limiting the polarization are mainly extrinsic.

  11. Electronic Structure of the Topological Insulator Bi2Se3 Using Angle-Resolved Photoemission Spectroscopy: Evidence for a Nearly Full Surface Spin Polarization

    SciTech Connect

    Z Pan; E Vescovo; A Fedorov; D Gardner; Y Lee; S Chu; G Gu; T Valla

    2011-12-31

    We performed high-resolution spin- and angle-resolved photoemission spectroscopy studies of the electronic structure and the spin texture on the surface of Bi{sub 2}Se{sub 3}, a model TI. By tuning the photon energy, we found that the topological surface state is well separated from the bulk states in the vicinity of k{sub z} = Z plane of the bulk Brillouin zone. The spin-resolved measurements in that region indicate a very high degree of spin polarization of the surface state, {approx}0.75, much higher than previously reported. Our results demonstrate that the topological surface state on Bi{sub 2}Se{sub 3} is highly spin polarized and that the dominant factors limiting the polarization are mainly extrinsic.

  12. 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.

  13. 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.

  14. Effects of strain on the electronic structure, superconductivity, and nematicity in FeSe studied by angle-resolved photoemission spectroscopy

    NASA Astrophysics Data System (ADS)

    Phan, G. N.; Nakayama, K.; Sugawara, K.; Sato, T.; Urata, T.; Tanabe, Y.; Tanigaki, K.; Nabeshima, F.; Imai, Y.; Maeda, A.; Takahashi, T.

    2017-06-01

    One of central issues in iron-based superconductors is the role of structural change to the superconducting transition temperature (Tc). It was found in FeSe that the lattice strain leads to a drastic increase in Tc, accompanied by suppression of nematic order. By angle-resolved photoemission spectroscopy on tensile- or compressive-strained and strain-free FeSe, we experimentally show that the in-plane strain causes a marked change in the energy overlap (Δ Eh -e ) between the hole and electron pockets in the normal state. The change in Δ Eh -e modifies the Fermi-surface volume, leading to a change in Tc. Furthermore, the strength of nematicity is also found to be characterized by Δ Eh -e . These results suggest that the key to understanding the phase diagram is the fermiology and interactions linked to the semimetallic band overlap.

  15. 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.

  16. 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.

  17. 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.

  18. Circular dichroism in the angle-resolved photoemission spectrum of the high-temperature Bi_{2}Sr_{2}CaCu_{2}O_{8+delta} superconductor: can these measurements be interpreted as evidence for time-reversal symmetry breaking?

    PubMed

    Arpiainen, V; Bansil, A; Lindroos, M

    2009-08-07

    We report first-principles computations of the angle-resolved photoemission response with circularly polarized light in Bi_{2}Sr_{2}CaCu_{2}O_{8+delta} for the purpose of delineating contributions to the circular dichroism resulting from distortions and modulations of the crystal lattice. Comparison with available experimental results shows that the measured circular dichroism from antinodal mirror planes is reproduced in quantitative detail in calculations employing the average orthorhombic crystal structure. We thus conclude that the existing angle-resolved photoemission measurements can be understood essentially within the framework of the conventional picture, without the need to invoke unconventional mechanisms.

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

    NASA Astrophysics Data System (ADS)

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

    2016-10-01

    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. 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. Here, we report ARPES experiment on an underdoped Bi2Sr2CaCu2O8+δ (Bi2212) superconductor in the Γ (0,0)-Y (π,π) nodal mirror plane using circularly polarized light. No circular dichroism is observed on the level of ˜2% at low temperature, which places a clear constraint on the forms of possible symmetry breaking orders in this sample. Meanwhile, we find that the geometric dichroism remains substantial very close to its perfect extinction such that a very small sample angular offset is sufficient to induce a sizeable dichroic signal. It highlights the importance to establish a perfect extinction of geometric dichroism as a prerequisite for the identification of any intrinsic circular dichroism in this material.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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

  8. 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.

  9. 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.

  10. 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.

  11. 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

  12. 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.

  13. Evolution of the band structure of superconducting NaFeAs from optimally doped to heavily overdoped Co substitution using angle-resolved photoemission spectroscopy

    NASA Astrophysics Data System (ADS)

    Cui, S. T.; Zhu, S. Y.; Wang, A. F.; Kong, S.; Ju, S. L.; Luo, X. G.; Chen, X. H.; Zhang, G. B.; Sun, Z.

    2012-10-01

    Using angle-resolved photoemission spectroscopy, we studied the evolution of electronic structure of NaFe1-xCoxAs from an optimally doped superconducting compound (x=0.028) to a heavily overdoped nonsuperconducting one (x=0.109). As in “122”-type iron pnictides, our data suggest that the Co dopant in NaFe1-xCoxAs supplies extra charge carriers and shifts the Fermi level accordingly. The overall band renormalization remains basically the same throughout the doping range we studied, suggesting that the local magnetic and electronic correlations are not affected by carrier doping. In the x=0.109 compound, the holelike bands around the zone center Γ move to deeper binding energies and an electron pocket appears instead, resulting in a Fermi surface topology similar to that of AxFe2-ySe2 (A=K, Cs, Rb, Tl). Our data suggest that a balance between itinerant properties of mobile carriers and local interactions plays an important role for the superconductivity in these materials.

  14. A review of electron-phonon coupling seen in the high-Tc superconductors by angle-resolved photoemission studies (ARPES)

    NASA Astrophysics Data System (ADS)

    Cuk, T.; Lu, D. H.; Zhou, X. J.; Shen, Z.-X.; Devereaux, T. P.; Nagaosa, N.

    2005-01-01

    This issue of pss (b) - basic solid state physics contains a collection of Review Articles on the rather controversially discussed topic of Electron-Phonon Interaction in High-Temperature Superconductors, guest-edited by Miodrag Kuli, Johann Wolfgang Goethe-Universität Frankfurt/Main, Germany, with a Preface written by V. L. Ginzburg and E. G. Maksimov [1].The cover picture, taken from the review [2] by T. Cuk et al., shows plots of the electron-phonon coupling vertex, g2(k, k), where k, k are the initial and final electron momentum for electrons scattered by the bond-buckling phonon B1g (the out-of-phase vibration of the in-plane oxygen) in a tight-binding model of the copper-oxygen plane. The momentum dependence of this vertex, along with the d-wave superconducting gap and the van Hove singularity at the anti-node, accounts for the momentum dependence of the collective mode coupling seen in angle-resolved photoemission data on Bi2212.The present issue also sees the start of our rapid research letters, the fastest peer-reviewed publication medium in solid state physics. For more information see www.pss-rapid.com and the Editorial by the Editor-in-Chief Martin Stutzmann on page 7 [3].

  15. 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.

  16. 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

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

    NASA Astrophysics Data System (ADS)

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

    2017-09-01

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

  18. 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.

  19. Electronic structure of the Na-adsorbed Si(100)2×1 surface studied by inverse and direct angle-resolved photoemission

    NASA Astrophysics Data System (ADS)

    Johansson, L. S. O.; Reihl, B.

    1993-01-01

    The surface electronic band structure of the Na-saturated Si(100)2×1 surface has been studied with angle-resolved inverse and direct photoemission. Single-domain 2×1-reconstructed surfaces were obtained by using vicinal samples. At a sodium coverage of roughly half the saturation coverage, an overlayer-derived empty surface state appears at the Γ¯ point 1.5 eV above the Fermi level. With increasing Na coverage, it moves downward in energy to 0.7 eV at saturation, where it displays a weak upward dispersion along both the Γ¯-J¯ and the Γ¯-J¯' direction. The filled dangling-bond surface band of the clean surface is split by the Na adsorption into two peaks, which also move downward in energy with increasing coverage. As a result, the surface band structure stays semiconducting at saturation with a band gap of about 2.1 eV. This electronic structure is similar to that of the Si(100)2×1-K surface. However, significant differences exist regarding energy positions and dispersions, indicating a weaker interaction within the overlayer and a stronger alkali-substrate interaction in the case of Na, which is also consistent with recent theoretical studies.

  20. 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.

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

    SciTech Connect

    Meevasana, W.

    2010-04-30

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

  2. 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

  3. 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.

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

    SciTech Connect

    Shen, Z. X.

    2011-08-15

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

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

  6. Bond stretching phonon softening and angle-resolved photoemission kinks in optimally doped Bi2Sr1:6La0:4Cu2O6+sigma superconductors

    SciTech Connect

    Graf, Jeff; d'Astuto, M.; Jozwiak, C.; Garcia, D.R.; Saini, N.L.; Krisch, M.; Ikeuchi, K.; Baron, A.Q.R.; Eisaki, H.; Lanzara, Alessandra

    2008-05-08

    We report the first measurement of the Cu-O bond stretching phonon dispersion in optimally doped Bi2Sr1.6La0.4Cu2O6+delta using inelastic x-ray scattering. We found a softening of this phonon at q=(0.25,0,0) from 76 to 60 meV, similar to the one reported in other cuprates. A comparison with angle-resolved photoemission data on the same sample revealed an excellent agreement in terms of energy and momentum between the angle-resolved photoemission nodal kink and the soft part of the bond stretching phonon. Indeed, we find that the momentum space where a 63+-5 meV kink is observed can be connected with a vector q=(xi,0,0) with xi>= 0.22, corresponding exactly to the soft part of the bond stretching phonon.

  7. 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.

  8. 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

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

    SciTech Connect

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

    2012-09-15

    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 Degree-Sign 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{sup -8} Torr) conditions and at elevated pressures of N{sub 2} (0.4 Torr). The possibility of acquiring angle-resolved data at different pressures has been demonstrated by analyzing a silicon/silicon dioxide (Si/SiO{sub 2}) sample. The collected angle-resolved spectra could be effectively used for the determination of the thickness of the native silicon oxide layer.

  10. 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.

  11. 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

  12. 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

  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

    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.

  14. 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.

  15. 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

  16. Angle-resolved photoemission spectroscopy of the Fe-Based Ba0.6K0.4Fe2As2 high temperature superconductor: evidence for an orbital selective electron-mode coupling.

    PubMed

    Richard, P; Sato, T; Nakayama, K; Souma, S; Takahashi, T; Xu, Y-M; Chen, G F; Luo, J L; Wang, N L; Ding, H

    2009-01-30

    We have performed an angle-resolved photoemission spectroscopy study of the new superconductor Ba0.6K0.4Fe2As2 in the low energy range. We report the observation of an anomaly around 25 meV in the dispersion of superconducting Ba0.6K0.4Fe2As2 samples that nearly vanishes above T_{c}. The energy scale of the related mode (13+/-2 meV) and its strong dependence on orbital and temperature indicates that it is unlikely related to phonons. Moreover, the momentum locations of the kink can be connected by the antiferromagnetic wave vector. Our results point towards an unconventional electronic origin of the mode and the superconducting pairing in the Fe-based superconductors, and strongly support the antiphase s-wave pairing symmetry.

  17. 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.

  18. 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

  19. 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.

  20. 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

  1. 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

  2. Joys and pitfalls of fermi surface mapping in Bi(2)Sr(2)CaCu(2)O(8+delta) using angle resolved photoemission

    PubMed

    Borisenko; Golden; Legner; Pichler; Durr; Knupfer; Fink; Yang; Abell; Berger

    2000-05-08

    On the basis of angle-scanned photoemission data recorded using unpolarized radiation, with high (E,k) resolution, and an extremely dense sampling of k space, we resolve the current controversy regarding the normal state Fermi surface (FS) in Bi(2)Sr(2)CaCu(2)O(8+delta). The true picture is simple, self-consistent, and robust: the FS is holelike, with the form of rounded tubes centered on the corners of the Brillouin zone. Two further types of features are also clearly observed: shadow FSs, which are most likely to be due to short range antiferromagnetic spin correlations, and diffraction replicas of the main FS caused by passage of the photoelectrons through the modulated Bi-O planes.

  3. 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.

  4. 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.

  5. 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

  6. 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.

  7. Angle-resolved UV photoemission studies of the two-dimensional band structures of sulfur, selenium, and tellurium monolayers adsorbed on aluminium (111)

    NASA Astrophysics Data System (ADS)

    Jacobi, K.; Muschwitz, C. V.; Kambe, K.

    1980-03-01

    On A1(111) surfaces adsorbate layers of S, Se, and Te were prepared by reaction with H 2S and evaporation of selenium and tellurium. Two condensation processes of different rate were found by measuring the photoemission intensity of the adsorbate p-levels as a function of dosis or evaporation time. The first process was identified as the build-up of a monolayer. By LEED and angular resolved UPS it was found that the atoms of the monolayers are hexagonally close packed and aligned to, but not in registry with the substrate. The nearest neighbour distances are 0.35 nm for S, 0.37 nm for Se, and 0.40 nm for Te. These distances are only somewhat smaller than the Van der Waals diameters. By measuring the kinetic energy and emission angle of photoelectrons from the adsorbate p-levels using polarized and unpolarized Hel (21.2eV) radiation the two-dimensional band structures could be constructed. They were found to be similar for all three adsorbate systems and only shifted as a whole to lower binding energies with increasing Z. The two-dimensional band structures were also calculated using a simple tight-binding model. The main features of the experimentally obtained bands could be reproduced by a calculation using only two parameters. The main differences between the calculated and experimentally evaluated bands could be attributed to the interaction of the monolayer with the substrate. For Te no important influence of the spin-orbit coupling was found.

  8. 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

  9. 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.

  10. 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.

  11. 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.

  12. Coupled commensurate charge density wave and lattice distortion in Na2Ti2P n2O (P n =As ,Sb ) determined by x-ray diffraction and angle-resolved photoemission spectroscopy

    NASA Astrophysics Data System (ADS)

    Davies, N. R.; Johnson, R. D.; Princep, A. J.; Gannon, L. A.; Ma, J.-Z.; Qian, T.; Richard, P.; Li, H.; Shi, M.; Nowell, H.; Baker, P. J.; Shi, Y. G.; Ding, H.; Luo, J.; Guo, Y. F.; Boothroyd, A. T.

    2016-09-01

    We report single-crystal x-ray-diffraction measurements on Na2Ti2P n2O (P n =As ,Sb ) which reveal a charge superstructure that appears below the density wave transitions previously observed in bulk data. From symmetry-constrained structure refinements we establish that the associated distortion mode can be described by two propagation vectors q1=(1 /2 ,0 ,l ) and q2=(0 ,1 /2 ,l ) with l =0 (Sb) or l =1 /2 (As) and primarily involves in-plane displacements of the Ti atoms perpendicular to the Ti-O bonds. We also present angle-resolved photoemission spectroscopy measurements, which show band folding and backbending consistent with a density wave with the same wave-vectors q1 and q2 associated with Fermi-surface nesting, and muon-spin relaxation data, which show no indication of spin density wave order. The results provide direct evidence for phonon-assisted charge density wave order in Na2Ti2P n2O and fully characterize a proximate ordered phase that could compete with superconductivity in doped BaTi2Sb2O .

  13. 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.

  14. Ultrafast melting of spin density wave order in BaFe2As2 observed by time- and angle-resolved photoemission spectroscopy with extreme-ultraviolet higher harmonic generation

    NASA Astrophysics Data System (ADS)

    Suzuki, H.; Okazaki, K.; Yamamoto, T.; Someya, T.; Okada, M.; Koshiishi, K.; Fujisawa, M.; Kanai, T.; Ishii, N.; Nakajima, M.; Eisaki, H.; Ono, K.; Kumigashira, H.; Itatani, J.; Fujimori, A.; Shin, S.

    2017-04-01

    The transient single-particle spectral function of BaFe2As2 , a parent compound of iron-based superconductors, has been studied by time- and angle-resolved photoemission spectroscopy with an extreme-ultraviolet laser generated by higher harmonics from Ar gas, which enables us to investigate the dynamics in the entire Brillouin zone. We observed electronic modifications from the spin density wave (SDW) ordered state within ˜1 ps after the arrival of a 1.5 eV pump pulse. We observed optically excited electrons at the zone center above EF at 0.12 ps, and their rapid decay. After the fast decay of the optically excited electrons, a thermalized state appears and survives for a relatively long time. From a comparison with the density-functional theory band structure for the paramagnetic and SDW states, we interpret the experimental observations as the melting of the SDW. Exponential decay constants for the thermalized state to recover back to the SDW ground state are ˜0.60 ps both around the zone center and the zone corner.

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

    PubMed

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

    2013-05-15

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

  16. 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

  17. 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.

  18. 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.

  19. 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.

  20. 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).

  1. 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.

  2. Linking dynamic and thermodynamic properties of cuprates: An angle-resolved photoemission study of (CaxLa1-x)(Ba1.75-xLa0.25+x)Cu3Oy (x =0.1 and 0.4)

    NASA Astrophysics Data System (ADS)

    Drachuck, Gil; Razzoli, Elia; Ofer, Rinat; Bazalitsky, Galina; Dhaka, R. S.; Kanigel, Amit; Shi, Ming; Keren, Amit

    2014-03-01

    We report angle-resolved photoemission spectroscopy on two families of high-temperature superconductors (CaxLa1-x)(Ba1.75-x La 0.25+x)Cu3Oy with x =0.1 (Tcmax=56 K) and x=0.4 (Tcmax=82 K). The Fermi surface (FS) is found to be independent of x or y, and its size indicates extreme sample-surface overdoping. This universal FS allows the comparison of dynamical properties between superconductors of similar structure and identical doping, but different Tcmax. We find that the high-energy (|E|>50 meV) nodal velocity in the x =0.4 family is higher than in the x =0.1 family. The implied correlation between Tcmax and the hopping rate t supports the notion of kinetic energy driven superconductivity in the cuprates. We also find that the antinodal gap is higher for the x =0.4 family.

  3. 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.

  4. 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.

  5. 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

    In this study, we use angle-resolved photoemission spectroscopy (ARPES) to study the two-dimensional (2D) heavy-fermion superconductor, Ce2 RhIn8. 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. Our data paves the way for improving the band-structure calculations and the general understanding of the transport and thermodynamical properties of this material.

  6. 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.

  7. Development of laser-based scanning µ-ARPES system with ultimate energy and momentum resolutions.

    PubMed

    Iwasawa, Hideaki; Schwier, Eike F; Arita, Masashi; Ino, Akihiro; Namatame, Hirofumi; Taniguchi, Masaki; Aiura, Yoshihiro; Shimada, Kenya

    2017-11-01

    We have developed a laser-based scanning angle-resolved photoemission spectroscopy system (µ-ARPES) equipped with a high precision 6-axis control system, realizing not only high-resolution photoemission spectroscopy in energy and momentum, but also spatial resolution of a µm scale. This enables our µ-ARPES system to probe fine details of intrinsic electronic states near the Fermi level such as the superconducting gaps and lifetime broadening. Copyright © 2017 The Authors. Published by Elsevier B.V. All rights reserved.

  8. 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.

  9. Angle-resolved RABBITT: theory and numerics

    NASA Astrophysics Data System (ADS)

    Hockett, Paul

    2017-08-01

    Angle-resolved (AR) RABBITT measurements offer a high information content measurement scheme, due to the presence of multiple, interfering, ionization channels combined with a phase-sensitive observable in the form of angle and time-resolved photoelectron interferograms. In order to explore the characteristics and potentials of AR-RABBITT, a perturbative 2-photon model is developed; based on this model, example AR-RABBITT results are computed for model and real systems, for a range of RABBITT schemes. These results indicate some of the phenomena to be expected in AR-RABBITT measurements, and suggest various applications of the technique in photoionization metrology.

  10. 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.

  11. 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.

  12. 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.

  13. A spin- and angle-resolving photoelectron spectrometer

    SciTech Connect

    Berntsen, M. H.; Tjernberg, O.; Palmgren, P.; Leandersson, M.; Hahlin, A.; Aahlund, J.; Wannberg, B.; Maansson, M.

    2010-03-15

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

  14. 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.

  15. 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.

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

    SciTech Connect

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

    2016-03-07

    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.

  17. In Situ Electronic Structure Study of Epitaxial Niobium Thin Films by Angle-Resolved Photoemission Spectroscopy

    NASA Astrophysics Data System (ADS)

    Xiang, Pai; Liu, Ji-Shan; Li, Ming-Ying; Yang, Hai-Feng; Liu, Zheng-Tai; Fan, Cong-Cong; Shen, Da-Wei; Wang, Zhen; Liu, Zhi

    2017-07-01

    Not Available Supported by the National Key Research and Development Program of China under Grant No 2016YFA0300204, the National Natural Science Foundation of China under Grant Nos 11274332, 11574337, 11404360 and 11227902, the Natural Science Foundation of Shanghai under Grant No 14ZR1447600, the Strategic Priority Research Program (B) of the Chinese Academy of Sciences under Grant No XDB04040300, and the Youth Innovation Promotion Association CAS.

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

    SciTech Connect

    Huang, Lunan

    2016-01-01

    This dissertation consists of three parts. First, we study magnetic domains in Nd2Fe14B single crystals using high resolution magnetic force microscopy (MFM). In addition to the elongated, wavy nano-domains reported by a previous MFM study, we found that the micrometer size, star-shaped fractal pattern is constructed of an elongated network of nano-domains about 20 nm in width, with resolution-limited domain walls thinner than 2 nm. Second, we studied extra Dirac cones of multilayer graphene on SiC surface by ARPES and SPA-LEED. We discovered extra Dirac cones on Fermi surface due to SiC 6 x 6 and graphene 6√ 3 6√ 3 coincidence lattice on both single-layer and three-layer graphene sheets. We interpreted the position and intensity of the Dirac cone replicas, based on the scattering vectors from LEED patterns. We found the positions of replica Dirac cones are determined mostly by the 6 6 SiC superlattice even graphene layers grown thicker. Finally, we studied the electronic structure of MoTe2 by ARPES and experimentally con rmed the prediction of type II Weyl state in this material. By combining the result of Density Functional Theory calculations and Berry curvature calculations with out experimental data, we identi ed Fermi arcs, track states and Weyl points, all features predicted to exist in a type II Weyl semimetal. This material is an excellent playground for studies of exotic Fermions.

  19. 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.

  20. 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.

  1. 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).

  2. 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.

  3. 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.

  4. 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.

  5. Angle-resolved spectroscopy: a tissue-mimicking phantom study

    NASA Astrophysics Data System (ADS)

    Zhang, Yan; Vasefi, Fartash; Chamson-Reig, Astrid; Najiminainia, Mohamadreza; Kaminska, Bozena; Carson, Jeffrey J. L.

    2012-03-01

    The Radial Angular Filter Array (RAFA) is a novel optical filter consisting of a radially-distributed series of micromachined channels with a focal length of a few millimeters. The RAFA filters photons passing through the focal point according to the propagation direction and has proven to be capable of collecting the angular distribution and the spectral information of photons simultaneously and non-invasively, which allows angle-resolved spectroscopic measurement of a turbid medium. To explore the feasibility of using this device to characterize the optical abnormalities in human tissues, we tested the performance of an angle-resolved RAFA-based spectroscopy system to detect absorption targets embedded within a tissue-mimicking phantom. The body of the phantom was made of 0.1% IntralipidTM/agarose gel (7 mm in thickness) and the targets were spherical (1.5 mm in radius) and contained 10 μM Indocyanine Green (ICG). The illumination source was a broadband near infrared (NIR) collimated beam. Photons were angularly filtered by the RAFA and spectrally resolved by a pushbroom spectrometer. The experimental results confirmed that the RAFA preferentially filtered photons that carried absorption and scattering information of the embedded targets.

  6. 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.

  7. 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

  8. 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.

  9. 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.

  10. 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.

  11. 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.

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

    PubMed

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

    2016-05-13

    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 CH_{4} 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.

  13. Using high energy angle resolved photoelectron spectroscopy to reveal the charge density in solids.

    PubMed

    Månsson, M; Claesson, T; Finazzi, M; Dallera, C; Brookes, N B; Tjernberg, O

    2008-11-28

    The charge density in solids is a fundamental parameter. Here we demonstrate that the charge density can be determined by the use of angle resolved photoelectron spectroscopy. The method, which involves a Fourier-like transform from momentum space to real space, is demonstrated by utilizing soft x-ray angle resolved photoelectron spectroscopy to sample the complete three-dimensional Brillouin zone of copper. It is also shown that this can be done in an energy resolved way as to extract the charge density contribution from states of a particular energy.

  14. 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.

  15. Angle-Resolved Photoemission Study of AuGa2 and AuIn2 Intermetallic Compounds.

    DTIC Science & Technology

    1984-12-01

    separation ad should be evident as a narrowing is the &-band structure of these mestals. Euxsmiaiag the emeg boads of the"e materials at the r Point of the...as a fuoctioa of primsrfil7 isteratesic distas. As is an extremely wll-atudied material # bet most previous iinestigtis of the oloctrosio structure...compared with other materials . The binding eneorgies for the Go 3d or Is 4d levels in each series of materials agree with one another to within 0.1 sV. which

  16. Phenomenological Model for the Normal-State Angle-Resolved Photoemission Spectroscopy Line Shapes of High-Temperature Superconductors

    NASA Astrophysics Data System (ADS)

    Matsuyama, Kazue; Gweon, G.-H.

    2013-12-01

    Providing a full theoretical description of the single-particle spectral function observed for high-temperature superconductors in the normal state is an important goal, yet unrealized. Here, we present a phenomenological model approaching towards this goal. The model results from implementing key phenomenological improvement in the so-called extremely correlated Fermi-liquid model. The model successfully describes the dichotomy of the spectral function as functions of momentum and energy and fits data for different materials (Bi2Sr2CaCu2O8+δ and La2-xSrxCuO4), with an identical set of intrinsic parameters. The current analysis goes well beyond the prevalent analysis of the spectral function as a function of momentum alone.

  17. Photoemission studies of high-tc superconductors: the superconducting gap.

    PubMed

    Shen, Z X; Spicer, W E; King, D M; Dessau, D S; Wells, B O

    1995-01-20

    Over the last several years there have been great improvements in the energy resolution and detection efficiency of angle-resolved photoemission spectroscopy. These improvements have made it possible to discover a number of fascinating features in the electronic structure of the high transition temperature (T(c)) superconductors: apparently bandlike Fermi surfaces, flat-band saddle points, and nested Fermi surface sections. Recent work suggests that these features, previously thought explainable only by one-electron band theory, may be better understood with a many-body approach. Furthermore, other properties of the high-T(c) superconductors, which are difficult to understand with band theory, are well described using a many-body picture. Angle-resolved photoemission spectroscopy has also been used to investigate the nature of the superconducting pairing state, revealing an anisotropic gap consistent with a d-wave order parameter and fueling the current debate over s-wave versus d-wave superconductivity.

  18. Spin-polarized photoemission spectroscopy of magnetic surfaces using undulator radiation

    NASA Astrophysics Data System (ADS)

    Johnson, P. D.; Brookes, N. B.; Hulbert, S. L.; Klaffky, R.; Clarke, A.; Sinković, B.; Smith, N. V.; Celotta, R.; Kelly, M. H.; Pierce, D. T.; Scheinfein, M. R.; Waclawski, B. J.; Howells, M. R.

    1992-03-01

    A beamline has been established at the National Synchrotron Light Source to perform angle-resolved photoemission experiments on magnetic surfaces with spin sensitivity. The system has two novel features: it uses a miniature electron-spin polarization analyzer and it also uses synchrotron radiation from an undulator rather than a bending magnet.

  19. 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.

  20. 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

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

    NASA Astrophysics Data System (ADS)

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

    2017-02-01

    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.

  2. 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.

  3. 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.

  4. 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.

  5. 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

  6. Photoemission from solids: the transition from solid-state to atomic physics

    SciTech Connect

    Shirley, D.A.

    1980-08-01

    As the photon energy is increased, photoemission from solids undergoes a slow transition from solid-state to atomic behavior. However, throughout the energy range h..nu.. = 10 to 1000 eV or higher both types of phenomena are present. Thus angle-resolved photoemission can only be understood quantitatively if each experimenter recognizes the presence of band-structure, photoelectron diffraction, and photoelectron asymmetry effects. The quest for this understanding will build some interesting bridges between solid-state and atomic physics and should also yield important new insights about the phenomena associated with photoemission.

  7. 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.

  8. Effect of surface steps on the diffusion of adsorbates investigated with angle-resolved photoelectron spectroscopy

    NASA Astrophysics Data System (ADS)

    Luh, Dah-An; Chen, Chi-Lu; Liang, Xihui; Cheng, Cheng-Maw; Tsuei, Ku-Ding

    2012-07-01

    To investigate the surface diffusion of chemisorbed H on Ag/Au(111) thin films with surface steps, we characterized the distribution of H atoms on the surface by measuring the Shockley states of these surfaces with angle-resolved photoelectron spectroscopy. Our results show that H atoms tend to diffuse and to remain on the terrace at the lower side of the surface steps during annealing. This diffusive behavior is explained qualitatively through the existence of an Ehrlich-Schwoebel potential barrier associated with the surface steps.

  9. Bulk sensitive angle-resolved photoelectron spectroscopy on Nd(O,F)BiS2

    NASA Astrophysics Data System (ADS)

    Terashima, K.; Sonoyama, J.; Sunagawa, M.; Fujiwara, H.; Nagayama, T.; Muro, T.; Nagao, M.; Watauchi, S.; Tanaka, I.; Okazaki, H.; Takano, Y.; Mizuguchi, Y.; Usui, H.; Suzuki, K.; Kuroki, K.; Wakita, T.; Muraoka, Y.; Yokoya, T.

    2016-02-01

    Bulk electronic structure of novel layered superconductor Nd(O,F)BiS2 was studied by using soft x-ray angle-resolved photoelectron spectroscopy (ARPES). Electron-like Fermi surface centered at the X(R) point was observed, consistent with earlier ARPES reports on surface-sensitive VUV light source. Based on the comparison of the electronic structure between Nd(O,F)BiS2 and La(O,F)BiS2, we discuss possible important factors for the superconductivity in this series of material.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. Identifying the crystalline orientation of black phosphorus using angle-resolved polarized Raman spectroscopy.

    PubMed

    Wu, Juanxia; Mao, Nannan; Xie, Liming; Xu, Hua; Zhang, Jin

    2015-02-16

    An optical anisotropic nature of black phosphorus (BP) is revealed by angle-resolved polarized Raman spectroscopy (ARPRS), and for the first time, an all-optical method was realized to identify the crystal orientation of BP sheets, that is, the zigzag and armchair directions. We found that Raman intensities of Ag(1), B2g, and Ag(2) modes of BP not only depend on the polarization angle α, but also relate to the sample rotation angle θ. Furthermore, their intensities reach the local maximum or minimum values when the crystalline orientation is along with the polarization direction of scattered light (es). Combining with the angle-resolved conductance, it is confirmed that Ag(2) mode intensity achieves a relative larger (or smaller) local maximum under parallel polarization configuration when armchair (or zigzag) direction is parallel to es. Therefore, ARPRS can be used as a rapid, precise, and nondestructive method to identify the crystalline orientation of BP layers. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  16. Angle-resolved molecular beam scattering of NO at the gas-liquid interface

    NASA Astrophysics Data System (ADS)

    Zutz, Amelia; Nesbitt, David J.

    2017-08-01

    This study presents first results on angle-resolved, inelastic collision dynamics of thermal and hyperthermal molecular beams of NO at gas-liquid interfaces. Specifically, a collimated incident beam of supersonically cooled NO (2 Π 1/2, J = 0.5) is directed toward a series of low vapor pressure liquid surfaces ([bmim][Tf2N], squalane, and PFPE) at θinc = 45(1)°, with the scattered molecules detected with quantum state resolution over a series of final angles (θs = -60°, -30°, 0°, 30°, 45°, and 60°) via spatially filtered laser induced fluorescence. At low collision energies [Einc = 2.7(9) kcal/mol], the angle-resolved quantum state distributions reveal (i) cos(θs) probabilities for the scattered NO and (ii) electronic/rotational temperatures independent of final angle (θs), in support of a simple physical picture of angle independent sticking coefficients and all incident NO thermally accommodating on the surface. However, the observed electronic/rotational temperatures for NO scattering reveal cooling below the surface temperature (Telec < Trot < TS) for all three liquids, indicating a significant dependence of the sticking coefficient on NO internal quantum state. Angle-resolved scattering at high collision energies [Einc = 20(2) kcal/mol] has also been explored, for which the NO scattering populations reveal angle-dependent dynamical branching between thermal desorption and impulsive scattering (IS) pathways that depend strongly on θs. Characterization of the data in terms of the final angle, rotational state, spin-orbit electronic state, collision energy, and liquid permit new correlations to be revealed and investigated in detail. For example, the IS rotational distributions reveal an enhanced propensity for higher J/spin-orbit excited states scattered into near specular angles and thus hotter rotational/electronic distributions measured in the forward scattering direction. Even more surprisingly, the average NO scattering angle (

  17. 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.

  18. Cellular organization and substructure measured using angle-resolved low-coherence interferometry.

    PubMed Central

    Wax, Adam; Yang, Changhuei; Backman, Vadim; Badizadegan, Kamran; Boone, Charles W; Dasari, Ramachandra R; Feld, Michael S

    2002-01-01

    We measure the organization and substructure of HT29 epithelial cells in a monolayer using angle-resolved low-coherence interferometry. This new technique probes cellular structure by measuring scattered light, as in flow cytometry, but offers an advantage in that the structure can be examined in situ, avoiding the need to disrupt the cell monolayer. We determine the size distribution of the cell nuclei by fitting measured light-scattering spectra to the predictions of Mie theory. In addition, we obtain information about the cellular organization and substructure by examining the spatial correlations within the monolayer. A remarkable finding is that the spatial correlations over small length scales take the form of an inverse power law, indicating the fractal nature of the packing of the subcellular structures. We also identify spatial correlations on a scale large compared with the size of a cell, indicating an overlying order within the monolayer. PMID:11916880

  19. 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.

  20. 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.

  1. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-08-01

    We report angle-resolved electron transmission measurements through freestanding graphene sheets in the energy range of 18 to 30 eV above the Fermi level. The measurements are carried out in a low-energy electron point source microscope, which allows simultaneously probing the transmission for a large angular range. The characteristics of low-energy electron transmission through graphene depend on its electronic structure above the vacuum level. The experimental technique described here allows mapping of the unoccupied band structure of freestanding two-dimensional materials as a function of the energy and probing angle, respectively, in-plane momentum. Our experimental findings are consistent with theoretical predictions of a resonance in the band structure of graphene above the vacuum level [V. U. Nazarov, E. E. Krasovskii, and V. M. Silkin, Phys. Rev. B 87, 041405 (2013), 10.1103/PhysRevB.87.041405].

  3. Two-photon photoemission and the dynamics of electrons at interfaces

    SciTech Connect

    Padowitz, D.F.; Harris, C.B.; Jordan, R.E.; Lingle, R.L. Jr.; McNeill, J.D.; Merry, W.R.

    1994-01-01

    A new instrument for angle-resolved two-photon photoemission with exceptional sensitivity and energy resolution has allowed a detailed examination of the interaction of image-state electrons with adsorbates. In addition to measuring the electrostatic properties of molecular-thickness films, the technique serves as a probe of adsorbate growth modes, and provides new opportunities to explore the dynamics of electrons in well-controlled two-dimensional systems.

  4. 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.

  5. 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.

  6. Angle-resolved X-ray photoelectron spectroscopy of the surface of imidazolium ionic liquids.

    PubMed

    Lockett, Vera; Sedev, Rossen; Bassell, Chris; Ralston, John

    2008-03-07

    The surfaces of three imidazolium based ionic liquids with a common anion were studied with angle-resolved X-ray photoelectron spectroscopy (XPS). The room temperature ionic liquids (RTILs): 1-butyl-3-methylimidazolium (bmim), 1-hexyl-3-methylimidazolium (hmim), and 1-octyl-3-methylimidazolium (omim) tetrafluoroborates, were meticulously purified and dried under vacuum. Survey and high-resolution spectra were obtained at different take-off angles (0-84 degrees ), thus increasing the surface sensitivity of the measurement. No impurities were detected and the survey spectra at normal emission (0 degrees ) confirmed the stoichiometric composition of the liquids. However, the spectra at take-off angles of 60, 70, 80 and 84 degrees indicated a higher amount of carbon. High resolution spectra of C1s, at these angles, showed an increased amount of aliphatic carbon when compared to the spectra at normal emission. The longer the side chain (R) of the imidazolium cation (Rmim), the larger was the amount of aliphatic carbon detected. Previous studies with other surface sensitive techniques have yielded contradictory conclusions about the surface orientation of the Rmim. We conclude unequivocally that the alkyl chain of the imidazolium ring of the investigated RTILs is oriented away from the liquid. Our study demonstrates the ability of XPS to probe the structure, along with the composition, of the free liquid surface by comparing signals from different penetration depths.

  7. Angle-resolved Landau spectrum of electrons and holes in bismuth

    NASA Astrophysics Data System (ADS)

    Zhu, Zengwei; Fauqué, Benoît; Fuseya, Yuki; Behnia, Kamran

    2011-09-01

    In elemental bismuth, emptying the low-index Landau levels is accompanied by giant Nernst quantum oscillations. The Nernst response sharply peaks each time a Landau level intersects the chemical potential. By studying the evolution of these peaks when the field rotates in three perpendicular planes defined by three high-symmetry axes, we have mapped the angle-resolved Landau spectrum of the system up to 12 T. A theoretical model treating electrons at the L point with an extended Dirac Hamiltonian is confronted with the experimentally resolved spectrum. We obtain a set of theoretical parameters yielding a good but imperfect agreement between theory and experiment for all orientations of the magnetic field in space. The results confirm the relevance of the Dirac spectrum to the electron pockets and settle the long-standing uncertainty about the magnitude of the g factor for holes. According to our analysis, a magnetic field exceeding 2.5 T applied along the bisectrix axis puts all carriers of the three electron pockets in their lowest (j=0) spin-polarized Landau level. On top of this complex angle-dependent spectrum, experiment detects additional and unexpected Nernst peaks of unidentified origin.

  8. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2011-10-01

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

  10. Angle resolved XPS for selective characterization of internal and external surface of porous silicon

    NASA Astrophysics Data System (ADS)

    Lion, Anna; Laidani, Nadhira; Bettotti, Paolo; Piotto, Chiara; Pepponi, Giancarlo; Barozzi, Mario; Scarpa, Marina

    2017-06-01

    Selective functionalization of the external/internal pore surface of porous silicon is of interest for the numerous potential applications of this material, in particular in pharmacology. With the aim of obtaining porous silicon platforms compatible with the aqueous environment and providing hydrophobic pores to load poorly water soluble molecules, we set-up a three step functionalization procedure consisting in two hydrosilylation reactions separated by the selective etching of the external surface. This procedure was applied both, to porous layers and porous microparticles. The characterization of the functionalized material by conventional techniques such as contact angle and FTIR showed a change of the properties of porous structures in line with the expected surface modifications. However, these techniques do not permit to clearly distinguish between internally and externally grafted functional groups. For this reason, an innovative procedure based on angle-resolved XPS was set-up and applied to differently functionalized pSi layers. By this technique, we obtained indications of prevalent grafting of hydrophilic moieties on the external surface and hydrophobic ones inside the pores.

  11. 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.

  12. 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.

  13. Scattering angle resolved optical coherence tomography for in vivo murine retinal imaging

    NASA Astrophysics Data System (ADS)

    Gardner, Michael R.; Katta, Nitesh; McElroy, Austin; Baruah, Vikram; Rylander, H. G.; Milner, Thomas E.

    2017-02-01

    Optical coherence tomography (OCT) retinal imaging contributes to understanding central nervous system (CNS) diseases because the eye is an anatomical "window to the brain" with direct optical access to nonmylenated retinal ganglion cells. However, many CNS diseases are associated with neuronal changes beyond the resolution of standard OCT retinal imaging systems. Though studies have shown the utility of scattering angle resolved (SAR) OCT for particle sizing and detecting disease states ex vivo, a compact SAR-OCT system for in vivo rodent retinal imaging has not previously been reported. We report a fiber-based SAR-OCT system (swept source at 1310 nm +/- 65 nm, 100 kHz scan rate) for mouse retinal imaging with a partial glass window (center aperture) for angular discrimination of backscattered light. This design incorporates a dual-axis MEMS mirror conjugate to the ocular pupil plane and a high collection efficiency objective. A muring retina is imaged during euthanasia, and the proposed SAR-index is examined versus time. Results show a positive correlation between the SAR-index and the sub-cellular hypoxic response of neurons to isoflurane overdose during euthanasia. The proposed SAR-OCT design and image process technique offer a contrast mechanism able to detect sub-resolution neuronal changes for murine retinal imaging.

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

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

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

  15. Application of the Lucy–Richardson Deconvolution Procedure to High Resolution Photoemission Spectra

    SciTech Connect

    Rameau, J.; Yang, H.-B.; Johnson, P.D.

    2010-07-01

    Angle-resolved photoemission has developed into one of the leading probes of the electronic structure and associated dynamics of condensed matter systems. As with any experimental technique the ability to resolve features in the spectra is ultimately limited by the resolution of the instrumentation used in the measurement. Previously developed for sharpening astronomical images, the Lucy-Richardson deconvolution technique proves to be a useful tool for improving the photoemission spectra obtained in modern hemispherical electron spectrometers where the photoelectron spectrum is displayed as a 2D image in energy and momentum space.

  16. 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.

  17. 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.

  18. 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.}

  19. 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

  20. 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

  1. 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

  2. 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

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

    SciTech Connect

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

    2010-02-15

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

  4. Insights from angle-resolved photoemission spectroscopy of an undoped four-layered two-gap high-T(c) superconductor.

    PubMed

    Xie, Wenhui; Jepsen, O; Andersen, O K; Chen, Yulin; Shen, Z-X

    2007-01-26

    An undoped cuprate with apical fluorine and inner (i) and outer (o) CuO(2) layers is a 60 K superconductor whose Fermi surface has large n- and p-doped sheets with the superconducting gap on the n sheet twice that on the p sheet. The Fermi surface is not reproduced by the local density approximation, but the screening must be substantially reduced due to electronic correlations, and oxygen in the o layers must be allowed to dimple outwards. This charges the i layers by 0.01|e|, causes a 0.4 eV Madelung-potential difference between the i and o layers, quenches the i-o hopping, and localizes the n sheets onto the i layers, thus protecting their d-wave pairs from being broken by scattering on impurities in the BaF layers. The correlation-reduced screening strengthens the coupling to z-axis phonons.

  5. 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. .

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. Theoretical and experimental study of the Suzuki-phase photonic crystal lattice by angle-resolved photoluminescence spectroscopy.

    PubMed

    Alija, Alfonso R; Martínez, Luis J; Postigo, Pablo A; Sánchez-Dehesa, Jose; Galli, Matteo; Politi, Alberto; Patrini, Maddalena; Andreani, Lucio C; Seassal, Christian; Viktorovitch, Pierre

    2007-01-22

    A complete theoretical and experimental analysis of the photonic band structure for the Suzuki-phase lattice is presented. The band diagrams were calculated by two-dimensional plane wave expansion and three-dimensional guided-mode expansion methods. Angle resolved photoluminescence spectroscopy has been used to measure the emission of the photonic crystal structure realized in active InAsP/InP slabs. Photonic bands with a very low group velocity along an entire direction of the reciprocal lattice have been measured, which may have important applications on future photonic devices. The experimentally determined dispersion is in very good agreement with the calculated photonic bands. The presence of defect modes produced by microcavities in the Suzuki-phase lattice has also been established.

  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. 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.

  13. Angle-resolved x-ray spectroscopic scheme to determine overlapping hyperfine splittings in highly charged heliumlike ions

    NASA Astrophysics Data System (ADS)

    Wu, Z. W.; Volotka, A. V.; Surzhykov, A.; Fritzsche, S.

    2017-07-01

    An angle-resolved x-ray spectroscopic scheme is presented for determining the hyperfine splitting of highly charged ions. For heliumlike ions, in particular, we propose to measure either the angular distribution or polarization of the 1 s 2 p P31,F →1 s2 S10,Ff emission following the stimulated decay of the initial 1 s 2 s S10,Fi level. It is found that both the angular and polarization characteristics of the emitted x-ray photons strongly depend on the (relative) splitting of the partially overlapping hyperfine 1 s 2 p P31,F resonances and may thus help resolve their hyperfine structure. The proposed scheme is feasible with present-day photon detectors and allows a measurement of the hyperfine splitting of heliumlike ions with a relative accuracy of about 10-4.

  14. 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.

  15. 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

  16. 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.

  17. Phenomenological study of the normal state angle resolved photoelectron spectroscopy line shapes of high temperature superconducting cuprates

    NASA Astrophysics Data System (ADS)

    Matsuyama, Kazue; Dilip, Rohit; Gweon, G.-H.

    2015-03-01

    Understanding the normal state properties of high temperature (high-Tc) superconducting cuprates remains a central mystery in the high-Tc problem. Standing out among those mysterious properties are the anomalous angle resolved photoelectron spectroscopy (ARPES) line shapes. The extremely correlated Fermi liquid (ECFL) theory recently introduced by Shastry has renewed interest in quantitatively understanding ARPES line shapes. In this talk, we combine certain phenomenological considerations with the ECFL framework in order to describe the ARPES data. Our phenomenological models have the property of preserving the universal property of the original ECFL theory, while introducing phenomenological changes in a non-universal property. Our models describe, with unprecedented fidelity, the key aspects of the dichotomy between momentum distribution curves (MDCs) and energy distribution curves (EDCs) of high-Tc ARPES data. Therefore, our study goes well beyond the prevailing studies that discuss only MDCs and EDCs.

  18. 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

  19. 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

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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

  11. 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.

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

    SciTech Connect

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

    2016-04-15

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

  13. 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.

  14. 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.

  15. 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.

  16. Investigation of the structure of water at hydrophobic and hydrophilic interfaces by angle-resolved TIR Raman spectroscopy.

    PubMed

    Ota, Chikashi

    2015-10-21

    To analyse the surface- or interface-specific molecular structure of a condensed molecular system, it is important to measure the spectra of molecules near the surface. Total internal reflection (TIR) Raman spectroscopy is a sensitive technique for surface or interfacial analysis because it retrieves spectra in the region within ca. 100 nm of a surface. However, since the width of the interface itself is often on a molecular scale (one to a few nm), conventional TIR Raman spectroscopy intrinsically lacks surface sensitivity. To overcome this problem, the combination of multiple-angle TIR Raman spectroscopy and principal component analysis (PCA) is expected to enable effective differentiation between the spectra of minute chemical species at the interface and those of dominant species. In the present study, angle-resolved TIR Raman spectroscopy with PCA was applied to SiO2/water and SAM/water interfaces to detect minute species located within a few nm of each interface. This method will likely lead to progress in various surface and interfacial analyses, not only those related to the structure of water, but also those used to determine the interactions among absorbed species.

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

    SciTech Connect

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

    2016-05-15

    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{sup ∘} 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.

  18. Angle-resolved Auger study of 10-keV Ar+-ion-induced Si LMM atomic lines

    NASA Astrophysics Data System (ADS)

    Bonanno, A.; Xu, F.; Camarca, M.; Siciliano, R.; Oliva, A.

    1990-06-01

    We present a detailed, angle-resolved Si L-shell Auger study by bombarding a single-crystalline Si sample with 10-keV Ar+ ions. We have observed a new atomic line at kinetic energy of ~99 eV which is tentatively assigned to an Auger transition involving two 2p holes in Si+. The existence of two atomic peaks at 61.36 and 91.1 eV has also been clearly confirmed. Our Auger spectra show well-split Doppler peaks for the principal Si0 and Si+ atomic lines and a strong dependence of the shift amplitude on both incidence and detection angles. Successful computer fitting of the angular dependence of Doppler shift has been achieved by using a simple binary-collision model with the Molière approximation to the Thomas-Fermi screening potential. These results suggest that the first violent Ar-Si asymmetric collisions contribute remarkably to the Si 2p-vacancy creation process and are responsible for the ejection of energetic Si(*) particles which is highly directional. The critical minimum Ar-Si approach distance for Si 2p-hole excitation is 0.355 Å, in very good agreement with the value predicted by molecular-orbital theory.

  19. 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

  20. 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.

  1. 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.

  2. PHOTOEMISSION PROPERTIES OF LEAD.

    SciTech Connect

    SMEDLEY,J.; RAO,T.; WARREN,J.; SEKUTOWICZ,J.; LEFFERTS,R.; LIPSKI,A.

    2004-07-05

    In this paper we present a study of the photoemission properties of lead at several UV wavelengths, including a study of the damage threshold of electroplated lead under laser cleaning. A quantum efficiency in excess of 0.1% has been achieved for a laser cleaned, electroplated lead sample with a laser wavelength of 193 nm. Niobium cathodes have been measured for comparison, and lead is found to be a superior photoemitter for all measured wavelengths.

  3. 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.

  4. 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.

  5. 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).

  6. 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).

  7. 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.

  8. 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

  9. 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.

  10. 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

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

    SciTech Connect

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

    2016-06-14

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

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

  13. Low-energy electron diffraction and photoemission study of epitaxial films of Cu on Ag l brace 001 r brace

    SciTech Connect

    Li, H.; Tian, D.; Quinn, J.; Li, Y.S.; Jona, F. ); Marcus, P.M. )

    1991-03-15

    The epitaxy of Cu on Ag{l brace}001{r brace} is studied by qualitative and quantitative low-energy electron diffraction (LEED) and by angle-resolved photoemission. LEED indicates that ultrathin (two- to three-atomic-layer) films have a limited amount of long-range order, and the ordered component has interlayer spacings of 1.45{plus minus}0.06 A, which compares well with the theoretically determined cubic lattice constant 2.87{plus minus}0.06 A of a metastable body-centered-cubic (bcc) modification of Cu. Thicker (10- to 12-layer) films have almost no long-range order, and photoemission indicates that regions of bcc and fcc Cu coexist amid large amounts of defects.

  14. 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

  15. 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

  16. 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.

  17. 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

  18. Two-Source Double-Slit Interference in Angle-Resolved High-Energy Above-Threshold Ionization Spectra of Diatoms

    SciTech Connect

    Okunishi, M.; Itaya, R.; Shimada, K.; Pruemper, G.; Ueda, K.; Busuladzic, M.; Gazibegovic-Busuladzic, A.; Milosevic, D. B.; Becker, W.

    2009-07-24

    When an electron from a diatomic molecule undergoes tunneling-rescattering ionization, a novel form of destructive interference can be realized that involves all four geometric orbits that are available to the electron when it is freed, because both ionization and rescattering may take place at the same or at different centers. We find experimentally and confirm theoretically that in orientation-averaged angle-resolved high-order above-threshold ionization spectra the corresponding destructive interference is visible for O{sub 2} but not for N{sub 2}. This effect is different from the suppression of ionization that is well known to occur for O{sub 2}.

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

    NASA Astrophysics Data System (ADS)

    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.

    2016-03-01

    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.

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

    PubMed

    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

    2016-03-15

    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.

  1. 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

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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..

  7. 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.

  8. 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.

  9. 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)

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

    SciTech Connect

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

    2007-08-12

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

  11. [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

  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. Photoemission study of some novel materials: Rare earth/transition metal interface, Ba*(0.6)*K*(0.4)*BiO3* and AlPdMn

    NASA Astrophysics Data System (ADS)

    Wu, Xilin

    1995-02-01

    Synchrotron radiation photoemission spectroscopy and low energy electron diffraction (LEED) are applied to explore several novel materials: (1) Ce epitaxial growth on W (110) surfaces; (2) Eu epitaxial growth on Ta (110) surfaces; (3) Sm epitaxial growth on Ta (110) surfaces; (4) quasicrystalline AlPdMn; and (5) superconducting Ba(1-x)K(x)BiO3. In the case of rare earth overlayers on transition metal surface, resonance photoemission spectroscopy is used to enhance the 4f features. The metal surface phase transition is investigated on an atomic-scale. In the case of quasicrystalline AlPdMn and superconducting Ba(1-x)K(x)BiO3 the electronic structures are investigated by angle-resolved photoemission.

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

    NASA Astrophysics Data System (ADS)

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

    1998-06-01

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

  17. Anisotropic structure of the order parameter in FeSe0.45Te0.55 revealed by angle-resolved specific heat

    PubMed Central

    Zeng, B.; Mu, G.; Luo, H.Q.; Xiang, T.; Mazin, I.I.; Yang, H.; Shan, L.; Ren, C.; Dai, P.C.; Wen, H.-H.

    2010-01-01

    The central issues for understanding iron (Fe)-based superconductors are the symmetry and structure of the superconducting gap. So far the experimental data and theoretical models have been highly controversial. Some experiments favor two or more constant or nearly constant gaps, others indicate strong anisotropy and yet others suggest gap zeros ('nodes'). A unique method for addressing this issue, and one of very few methods that are bulk and angle resolved, is measuring the electronic-specific heat in a rotating magnetic field. In this study, we present the first such measurement for an Fe-based high-Tc superconductor. We observed a fourfold oscillation of the specific heat as a function of the in-plane magnetic field direction. Our results are consistent with the expectations for an extended s-wave model, with a significant gap anisotropy on the electron pockets and the gap minima along the ΓM (Fe–Fe bond) direction. PMID:21081910

  18. Angle-resolved electron spectroscopy of laser-assisted Auger decay induced by a few-femtosecond x-ray pulse.

    PubMed

    Meyer, M; Radcliffe, P; Tschentscher, T; Costello, J T; Cavalieri, A L; Grguras, I; Maier, A R; Kienberger, R; Bozek, J; Bostedt, C; Schorb, S; Coffee, R; Messerschmidt, M; Roedig, C; Sistrunk, E; Di Mauro, L F; Doumy, G; Ueda, K; Wada, S; Düsterer, S; Kazansky, A K; Kabachnik, N M

    2012-02-10

    Two-color (x-ray+infrared) electron spectroscopy is used for investigating laser-assisted KLL Auger decay following 1s photoionization of atomic Ne with few-femtosecond x-ray pulses from the Linac Coherent Light Source. In an angle-resolved experiment, the overall width of the laser-modified Auger-electron spectrum and its structure change significantly as a function of the emission angle. The spectra are characterized by a strong intensity variation of the sidebands revealing a gross structure. This variation is caused, as predicted by theory, by the interference of electrons emitted at different times within the duration of one optical cycle of the infrared dressing laser, which almost coincides with the lifetime of the Ne 1s vacancy.

  19. 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.

  20. Determination of the absolute carrier-envelope phase by angle-resolved photoelectron spectra of Ar by intense circularly polarized few-cycle pulses

    NASA Astrophysics Data System (ADS)

    Fukahori, Shinichi; Ando, Toshiaki; Miura, Shun; Kanya, Reika; Yamanouchi, Kaoru; Rathje, Tim; Paulus, Gerhard G.

    2017-05-01

    The angle-resolved photoelectron spectra of Ar are recorded using intense circularly polarized near-infrared few-cycle laser pulses, and the effect of the depletion of Ar atoms by the ionization and the effect of the Coulombic potential are examined by the classical trajectory Monte Carlo simulations. On the basis of the comparison between the experimental and theoretical photoelectron spectra, a procedure for estimating the absolute carrier-envelope phase (CEP) of the few-cycle laser pulses interacting with atoms and molecules is proposed. It is confirmed that the absolute CEP can securely be estimated without any numerical calculations once the angular distribution of the yield of photoelectrons having the kinetic energy larger than 30 eV is measured with the peak laser intensity in the range between 1 ×1014 and 5 ×1014W /c m2 .

  1. 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.

  2. 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.

  3. a Photoemission Study of the Electronic Structure and Oxidation Properties of Mercury-Cadmium Telluride.

    NASA Astrophysics Data System (ADS)

    Silberman, Joel Abraham

    The study of electronic structure and oxidation properties of the random substitutional alloy Mercury Cadmium Telluride is of general interest in relating the electronic structure and surface properties of a semiconductor alloy with a strongly aperiodic potential to these aspects of the binary compounds that represent the composition extremes. It is also of practical value, as study of the electronic structure and oxidation properties provides an underpinning of fundamental knowledge for further technological development. Angle-integrated and polarization dependent angle -resolved photoemission spectroscopy (along the normal) from the (110) cleavage face of the alloy and the binaries Cadmium Telluride and Mercury Telluride were performed to examine the composition dependence of the electronic structure and bonding. Emission from the valence states documents the breakdown of the virtual crystal approximation and the success of the coherent potential approximation in treating the alloy potential. The consequences of this finding for the bonding and materials properties are described. Detailed dispersion relations as a function of composition have been deduced from the angle-resolved data for a portion of the band structure along (110) and are compared to theory. To augment the discussion of the photoemission final states and the polarization dependence of the data, a nonlocal pseudopotential calculation extending to 30 eV above the valence band maximum was executed. In the oxidation studies, core level photoemission spectroscopy was used to characterize the clean surface and monitor the growth of native oxide films a few monolayers thick formed on the semi- conductor at room temperature by exposure to oxygen in the gas phase activated by contact with a hot filament. The cleaved (110) surface of p-type solid state recrystallized alloy samples was found to be stoichiometric, stable against Hg loss over time in vacuum at room temperature, but converted to n

  4. 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.

  5. 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

  6. 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

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. INVESTIGATION OF PHOTOEMISSION SOLAR ENERGY CONVERTERS

    DTIC Science & Technology

    The feasibility of making a photoemissive solar energy converter was investigated theoretically and in practical devices. Theoretical...practical device was only one-tenth of one percent. In support of the work done directly in fabrication of photoemissive solar energy converters, numerous...measurements were made of the properties of photoemitters under the high light and high current conditions typical of photoemissives solar energy converter

  13. 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.

  14. Initial and steady-state Ru growth by atomic layer deposition studied by in situ Angle Resolved X-ray Photoelectron Spectroscopy

    NASA Astrophysics Data System (ADS)

    Egorov, Konstantin V.; Lebedinskii, Yury Yu.; Soloviev, Anatoly A.; Chouprik, Anastasia A.; Azarov, Alexander Yu.; Markeev, Andrey M.

    2017-10-01

    The clear substrate-dependent growth and delayed film continuity are essential challenges of Ru atomic layer deposition (ALD) demanding adequate and versatile approaches for their study. Here, we report on the application of in situ Angle Resolved X-ray Phototelectron Spectroscopy (ARXPS) for investigation of initial and steady-state ALD growth of Ru using Ru(EtCp)2 and O2 as precursors. Using ARXPS surface analysis technique we determine such parameters of Ru ALD initial growth as incubation period, fractional coverage and the thickness of islands/film depending on the substrate chemical state, governed by the presence/absence of NH3/Ar plasma pretreatment. It was demonstrated that NH3/Ar plasma pretreatment allows to obtain the lowest incubation period (∼7 ALD cycles) resulting in a continuous ultrathin (∼20 Å) and smooth Ru films after 70 ALD cycles. In situ XPS at UHV was used at steady state Ru growth for analysis of half-cycle reactions that revealed formation of RuOx (x ≈ 2) layer with thickness of ∼8 Å after O2 pulse (first half-cycle). It was also shown that oxygen of RuOx layer combusts Ru(EtCp)2 ligands in the second half-cycle reaction and the observed Ru growth of ∼0.34 Å per cycle is in a good agreement with the amount of oxygen in the RuOx layer.

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

    SciTech Connect

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

    2011-12-09

    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 {approx}30 {micro}s over a time period of 3 ms. Multiple frames of the TARXD images can also be obtained with time resolutions between 30 and 300 {micro}s 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 x 10{sup 6} K/s, and conductive cooling rate of 4.5 x 10{sup 4} K/s. These time-dependent structural and temperature data provide evidences for the rapid formation of intermetallic NiAl alloy within 45 {micro}s, thermal expansion coefficient of 1.1 x 10{sup -6} K for NiAl, and crystallization of V and Ag{sub 3}In in later time.

  16. 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.

  17. 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.

  18. 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.

  19. Investigation on Surface Polarization of Al2O3-capped GaN/AlGaN/GaN Heterostructure by Angle-Resolved X-ray Photoelectron Spectroscopy.

    PubMed

    Duan, Tian Li; Pan, Ji Sheng; Wang, Ning; Cheng, Kai; Yu, Hong Yu

    2017-08-17

    The surface polarization of Ga-face gallium nitride (GaN) (2 nm)/AlGaN (22 nm)/GaN channel (150 nm)/buffer/Si with Al2O3 capping layer is investigated by angle-resolved X-ray photoelectron spectroscopy (ARXPS). It is found that the energy band varies from upward bending to downward bending in the interface region, which is believed to be corresponding to the polarization variation. An interfacial layer is formed between top GaN and Al2O3 due to the occurrence of Ga-N bond break and Ga-O bond forming during Al2O3 deposition via the atomic layer deposition (ALD). This interfacial layer is believed to eliminate the GaN polarization, thus reducing the polarization-induced negative charges. Furthermore, this interfacial layer plays a key role for the introduction of the positive charges which lead the energy band downward. Finally, a N2 annealing at 400 °C is observed to enhance the interfacial layer growth thus increasing the density of positive charges.

  20. N2 emission in steady-state N2O + CO and NO + CO reactions on Ir(110) by means of angle-resolved desorption

    NASA Astrophysics Data System (ADS)

    Matsushima, Tatsuo; Kokalj, Anton

    2017-08-01

    This paper confirms the intermediate N2O(a) pathway to N2 in the NO reduction on iridium surfaces. The spatial distributions of desorbing product N2 have been compared with each other in steady-state N2O + CO and NO + CO reactions on Ir(110) by means of angle-resolved desorption. In the former reaction, the N2 emission is fairly concentrated on the normally directed plane in the [001] direction and split into two-directional ways, being collimated at 46-58° off normal. In the latter reaction, the N2 desorption consists of a normally directed component and two-directional components. The former component shows remarkable anisotropy; i.e., the distribution is sharp on the normally directed plane in the [001] direction and broad on the plane perpendicular to it. This component originates from the association of adsorbed nitrogen atoms. The other components are collimated at around 54° off normal towards the [001] and [ 00 1 bar ] directions and they come from the decomposition of intermediate N2O(a). The off-normal components significantly share the total N2 emission below approximately 550 K. At higher temperatures, these become minor and mostly invisible above 650 K. The desorption of counter-product CO2 is normally directed and shows anisotropy in both reactions.

  1. 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.

  2. 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.

  3. 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.

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

    PubMed Central

    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. PMID:21280890

  5. 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.

  6. Investigation on Surface Polarization of Al2O3-capped GaN/AlGaN/GaN Heterostructure by Angle-Resolved X-ray Photoelectron Spectroscopy

    NASA Astrophysics Data System (ADS)

    Duan, Tian Li; Pan, Ji Sheng; Wang, Ning; Cheng, Kai; Yu, Hong Yu

    2017-08-01

    The surface polarization of Ga-face gallium nitride (GaN) (2 nm)/AlGaN (22 nm)/GaN channel (150 nm)/buffer/Si with Al2O3 capping layer is investigated by angle-resolved X-ray photoelectron spectroscopy (ARXPS). It is found that the energy band varies from upward bending to downward bending in the interface region, which is believed to be corresponding to the polarization variation. An interfacial layer is formed between top GaN and Al2O3 due to the occurrence of Ga-N bond break and Ga-O bond forming during Al2O3 deposition via the atomic layer deposition (ALD). This interfacial layer is believed to eliminate the GaN polarization, thus reducing the polarization-induced negative charges. Furthermore, this interfacial layer plays a key role for the introduction of the positive charges which lead the energy band downward. Finally, a N2 annealing at 400 °C is observed to enhance the interfacial layer growth thus increasing the density of positive charges.

  7. 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.

  8. Fiber laser based hydrophone systems

    NASA Astrophysics Data System (ADS)

    Azmi, Asrul Izam; Leung, Ian; Chen, Xiaobao; Zhou, Shaoling; Zhu, Qing; Gao, Kan; Childs, Paul; Peng, Gangding

    2011-09-01

    We report our recent work on distributed feedback fiber laser based hydrophones. Some issues related to sensitivity, such as fiber laser phase condition, demodulation, and packaging, are also discussed. With the development of appropriate digital signal processing (DSP) techniques and packaging designs, an interferometric-type distributed feedback (DFB) fiber laser hydrophone system with acoustic sensitivity of 58.0 dB·re·μPa·Hz-0.5 at 1 kHz or a minimum detectable acoustic pressure below 800 μPa during field test is attained. We have also investigated an intensity-type DFB fiber laser hydrophone system and its performance.

  9. 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

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

    PubMed Central

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

    2010-01-01

    The concepts and technical realisation of the high-resolution soft X-ray beamline ADRESS operating in the energy range from 300 to 1600 eV and intended for resonant inelastic X-ray scattering (RIXS) and angle-resolved photoelectron spectroscopy (ARPES) are described. The photon source is an undulator of novel fixed-gap design where longitudinal movement of permanent magnetic arrays controls not only the light polarization (including circular and 0–180° rotatable linear polarizations) but also the energy without changing the gap. The beamline optics is based on the well established scheme of plane-grating monochromator operating in collimated light. The ultimate resolving power E/ΔE is above 33000 at 1 keV photon energy. The choice of blazed versus lamellar gratings and optimization of their profile parameters is described. Owing to glancing angles on the mirrors as well as optimized groove densities and profiles of the gratings, the beamline is capable of delivering high photon flux up to 1 × 1013 photons s−1 (0.01% BW)−1 at 1 keV. Ellipsoidal refocusing optics used for the RIXS endstation demagnifies the vertical spot size down to 4 µm, which allows slitless operation and thus maximal transmission of the high-resolution RIXS spectrometer delivering E/ΔE > 11000 at 1 keV photon energy. Apart from the beamline optics, an overview of the control system is given, the diagnostics and software tools are described, and strategies used for the optical alignment are discussed. An introduction to the concepts and instrumental realisation of the ARPES and RIXS endstations is given. PMID:20724785

  11. Feasibility of clinical detection of cervical dysplasia using angle-resolved low coherence interferometry measurements of depth-resolved nuclear morphology.

    PubMed

    Ho, Derek; Drake, Tyler K; Smith-McCune, Karen K; Darragh, Teresa M; Hwang, Loris Y; Wax, Adam

    2017-03-15

    This study sought to establish the feasibility of using in situ depth-resolved nuclear morphology measurements for detection of cervical dysplasia. Forty enrolled patients received routine cervical colposcopy with angle-resolved low coherence interferometry (a/LCI) measurements of nuclear morphology. a/LCI scans from 63 tissue sites were compared to histopathological analysis of co-registered biopsy specimens which were classified as benign, low-grade squamous intraepithelial lesion (LSIL), or high-grade squamous intraepithelial lesion (HSIL). Results were dichotomized as dysplastic (LSIL/HSIL) versus non-dysplastic and HSIL versus LSIL/benign to determine both accuracy and potential clinical utility of a/LCI nuclear morphology measurements. Analysis of a/LCI data was conducted using both traditional Mie theory based processing and a new hybrid algorithm that provides improved processing speed to ascertain the feasibility of real-time measurements. Analysis of depth-resolved nuclear morphology data revealed a/LCI was able to detect a significant increase in the nuclear diameter at the depth bin containing the basal layer of the epithelium for dysplastic versus non-dysplastic and HSIL versus LSIL/Benign biopsy sites (both p < 0.001). Both processing techniques resulted in high sensitivity and specificity (>0.80) in identifying dysplastic biopsies and HSIL. The hybrid algorithm demonstrated a threefold decrease in processing time at a slight cost in classification accuracy. The results demonstrate the feasibility of using a/LCI as an adjunctive clinical tool for detecting cervical dysplasia and guiding the identification of optimal biopsy sites. The faster speed from the hybrid algorithm offers a promising approach for real-time clinical analysis. © 2016 UICC.

  12. 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.

  13. 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.

  14. 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

  15. 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.

  16. Photoemission using femtosecond laser pulses

    SciTech Connect

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

    1991-10-01

    Successful operation of short wavelength FEL requires an electron bunch of current >100 A and normalized emittance < 1 mm-mrad. Recent experiments show that RF guns with photocathodes as the electron source may be the ideal candidate for achieving these parameters. To reduce the emittance growth due to space charge and RF dynamics effects, the gun may have to operate at high field gradient (hence at high RF frequency) and a spot size small compared to the aperture. This may necessitate the laser pulse duration to be in the subpicosecond regime to reduce the energy spread. We will present the behavior of metal photocathodes upon irradiation with femtosecond laser beams, comparison of linear and nonlinear photoemission, and scalability to high currents. Theoretical estimate of the intrinsic emittance at the photocathode in the presence of the anomalous heating of the electrons, and the tolerance on the surface roughness of the cathode material will be discussed.

  17. Angle-dependent time delay in two-color XUV+IR photoemission of He and Ne

    NASA Astrophysics Data System (ADS)

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

    2017-07-01

    We solve the time-dependent Schrödinger equation for a noble gas atom (He and Ne) driven by an ionizing XUV and dressing IR fields. From this solution we deduce an angular dependence of the photoemission time delay as measured by the RABBITT (reconstruction of attosecond beating by interference of two-photon transitions) technique. We use a recent angle-resolved RABBITT measurement on helium [S. Heuser et al., Phys. Rev. A 94, 063409 (2016), 10.1103/PhysRevA.94.063409] to test and calibrate our theoretical model. Based on this calibration, we find no significant difference between the time delay in He measured in the angle-integrated RABBITT experiments [C. Palatchi et al., J. Phys. B 47, 245003 (2014), 10.1088/0953-4075/47/24/245003 and D. Guénot et al., J. Phys. B 47, 245602 (2014), 10.1088/0953-4075/47/24/245602] and measured or calculated in the polarization axis direction. The angular dependence of the photoemission time delay of Ne is shown to be qualitatively different from He because of the different orbital character of the valence 2 p orbital. The angular momentum projection dependence of the time delay in Ne is also investigated.

  18. 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.

  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. Photoemission delay: The White Rabbit's clock

    NASA Astrophysics Data System (ADS)

    Calegari, Francesca

    2017-03-01

    Without a very precise timer one can never catch up with the electron released in photoemission. Attosecond streaking spectroscopy allows such a chronometer clock to be set to zero and reveals the role of electron correlations.

  1. Laser-based communication link

    NASA Astrophysics Data System (ADS)

    Stenersen, Knut; Landroe, Stig; Christensen, Oeyvind

    1993-04-01

    A prototype of a laser based communication link for point to point transmission of data through the atmosphere is described. The link has a laser transmitter and a receiver at each end, which allows full duplex communication. The link has a EUROCOM B interface and can be used for transmission of 512 kbit/s data between two switches in the Norwegian military tactical communication system TADKOM. The data are transmitted through the air as FSK (Frequency Shift Keying) modulated laser light. The laser transmitter is an eyesafe 10 mW diode laser with 1.55 micrometer wavelength. The transmitter and receiver lobes have an angular divergence of about 1.5 mrad, and the system requires an alignment accuracy of better than 0.5 mrad for good performance. The maximum range of the link is slightly larger than the optical visibility for optical visibilities below 2 km. For 10 km visibility the maximum range is about 5 km. Based on available visibility statistics, it was calculated that a 1 km link should be in operation 97 to 99% of the time (average over one year) for typical locations in Norway. The link was tested with TADKOM equipment in laboratory.

  2. Absence of superconductivity in the hole-doped Fe pnictide Ba(Fe1-xMnx)2As2: Photoemission and x-ray absorption spectroscopy studies

    NASA Astrophysics Data System (ADS)

    Suzuki, H.; Yoshida, T.; Ideta, S.; Shibata, G.; Ishigami, K.; Kadono, T.; Fujimori, A.; Hashimoto, M.; Lu, D. H.; Shen, Z.-X.; Ono, K.; Sakai, E.; Kumigashira, H.; Matsuo, M.; Sasagawa, T.

    2013-09-01

    We have studied the electronic structure of Ba(Fe1-xMnx)2As2 (x=0.08), which fails to become a superconductor in spite of the formal hole doping like Ba1-xKxFe2As2, with photoemission spectroscopy and x-ray absorption spectroscopy (XAS). With decreasing temperature, a transition from the paramagnetic phase to the antiferromagnetic phase was clearly observed by angle-resolved photoemission spectroscopy. XAS results indicated that the substituted Mn atoms form a strongly hybridized ground state. Resonance-photoemission spectra at the Mn L3 edge revealed that the Mn 3d partial density of states is distributed over a wide energy range of 2-13 eV below the Fermi level (EF), with little contribution around EF. This indicates that the dopant Mn 3d states are localized in spite of the strong Mn 3d-As 4p hybridization and split into the occupied and unoccupied parts due to the on-site Coulomb and exchange interaction. The absence of superconductivity in Ba(Fe1-xMnx)2As2 can thus be ascribed both to the absence of carrier doping in the FeAs plane and to the stabilization of the competing G-type antiferromagnetic order by the Mn impurities.

  3. 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

  4. 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

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

    SciTech Connect

    Grass, Michael E.; Karlsson, Patrik G.; Lundqvist, Maans; Aksoy, Funda; Wannberg, Bjoern; Mun, Bongjin S.; Hussain, Zahid; Liu, Zhi

    2010-05-15

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

  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. 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.

  8. PASSIVATION OF SEMICONDUCTOR SURFACES FOR IMPROVED RADIATION DETECTORS: X-RAY PHOTOEMISSION ANALYSIS

    SciTech Connect

    Nelson, A; Conway, A; Reinhardt, C; Ferreira, J; Nikolic, R; Payne, S

    2007-12-10

    Surface passivation of device-grade radiation detector materials was investigated using x-ray photoelectron spectroscopy in combination with transport property measurements before and after various chemical treatments. Specifically Br-MeOH (2% Br), KOH with NH{sub 4}F/H{sub 2}O{sub 2} and NH{sub 4}OH solutions were used to etch, reduce and oxidize the surface of Cd{sub (1-x)}Zn{sub x}Te semiconductor crystals. Scanning electron microscopy was used to evaluate the resultant microscopic surface morphology. Angle-resolved high-resolution photoemission measurements on the valence band electronic structure and core lines were used to evaluate the surface chemistry of the chemically treated surfaces. Metal overlayers were then deposited on these chemically treated surfaces and the I-V characteristics 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 Schottky barrier height for improved radiation detector devices.

  9. 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.

  10. 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

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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)

  18. 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.

  19. Laser-based displays: a review.

    PubMed

    Chellappan, Kishore V; Erden, Erdem; Urey, Hakan

    2010-09-01

    After the invention of lasers, in the past 50 years progress made in laser-based display technology has been very promising, with commercial products awaiting release to the mass market. Compact laser systems, such as edge-emitting diodes, vertical-cavity surface-emitting lasers, and optically pumped semiconductor lasers, are suitable candidates for laser-based displays. Laser speckle is an important concern, as it degrades image quality. Typically, one or multiple speckle reduction techniques are employed in laser displays to reduce speckle contrast. Likewise, laser safety issues need to be carefully evaluated in designing laser displays under different usage scenarios. Laser beam shaping using refractive and diffractive components is an integral part of laser displays, and the requirements depend on the source specifications, modulation technique, and the scanning method being employed in the display. A variety of laser-based displays have been reported, and many products such as pico projectors and laser televisions are commercially available already.

  20. 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}.

  1. Structural and electronic properties of V{sub 2}O{sub 3} ultrathin film on Ag(001): LEED and photoemission study

    SciTech Connect

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

    2016-05-06

    V{sub 2}O{sub 3} ultrathin films were grown on Ag(001) substrate by reactive evaporation of vanadium (V) metal in presence of oxygen and their structural and electronic properties were studied by Low Energy Electron Diffraction (LEED), X-ray Photo Electron Spectroscopy (XPS) and Angle Resolved Photoemission Spectroscopic (ARPES) techniques, respectively. On top of square symmetry substrate Ag(001), hexagonal surface of V{sub 2}O{sub 3} (0001) is stabilized in the form of two domain structure, rotated by 30°(or 90°)to each other, has been observed by LEED. Rather than epitaxial flat monolayer, formation of well-ordered V{sub 2}O{sub 3} (0001) island has been confirmed from the LEED and the Photoemission Spectroscopic (PES) study. Stoichiometry of the grown film was confirmed by the XPS study. Evolution of valance band electronic structure of V{sub 2}O{sub 3} (0001) surface has been studied as a function of film thickness by ARPES.

  2. 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.

  3. 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.

  4. Raising Photoemission Efficiency with Surface Acoustic Waves

    SciTech Connect

    A. Afanasev, F. Hassani, C.E. Korman, V.G. Dudnikov, R.P. Johnson, M. Poelker, K.E.L. Surles-Law

    2012-07-01

    We are developing a novel technique that may help increase the efficiency and reduce costs of photoelectron sources used at electron accelerators. The technique is based on the use of Surface Acoustic Waves (SAW) in piezoelectric materials, such as GaAs, that are commonly used as photocathodes. Piezoelectric fields produced by the traveling SAW spatially separate electrons and holes, reducing their probability of recombination, thereby enhancing the photoemission quantum efficiency of the photocathode. Additional advantages could be increased polarization provided by the enhanced mobility of charge carriers that can be controlled by the SAW and the ionization of optically-generated excitons resulting in the creation of additional electron-hole pairs. It is expected that these novel features will reduce the cost of accelerator operation. A theoretical model for photoemission in the presence of SAW has been developed, and experimental tests of the technique are underway.

  5. 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.

  6. 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.

  7. 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

  8. 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.

  9. 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

  10. 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.

  11. 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.

  12. 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.

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

    PubMed

    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

    2016-03-08

    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.

  14. 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

  15. Band alignment in organic devices: Photoemission studies of model oligomers on In{sub 2}O{sub 3}

    SciTech Connect

    Blyth, R. I. R.; Duschek, R.; Koller, G.; Netzer, F. P.; Ramsey, M. G.

    2001-07-01

    The interfaces of In{sub 2}O{sub 3}, a model for indium{endash}tin{endash}oxide (ITO), with benzene, thiophene, and benzaldehyde, models for technologically important organic molecules, are studied using angle resolved ultraviolet photoemission and work function measurements. Band alignment diagrams for hypothetical Al/organic/ITO devices have been drawn, using values determined from this work and previously published studies of these molecules on Al(111). The similarity between the bonding of benzene and thiophene on Al(111) and In{sub 2}O{sub 3}, i.e., largely electrostatic, leads to near identical alignment at both metal and oxide interfaces. This indicates that clean Al and ITO will make a very poor electron/hole injecting pair. We suggest that the apparent efficiency of Al as an electron injecting contact in real devices is due to the presence of oxygen at the Al/organic interface. For benzaldehyde the interaction with In{sub 2}O{sub 3} is largely electrostatic, in contrast to the covalent bonds formed on Al(111). This leads to very different alignment at the Al and oxide interfaces, showing the importance of the particular organic{endash}inorganic interaction in determining band alignment. {copyright} 2001 American Institute of Physics.

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

    NASA Astrophysics Data System (ADS)

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

    1996-02-01

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

  17. 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.

  18. 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.

  19. Monte Carlo simulations of electron photoemission from cesium antimonide

    NASA Astrophysics Data System (ADS)

    Gupta, Pranav; Cultrera, Luca; Bazarov, Ivan

    2017-06-01

    We report on the results from semi-classical Monte Carlo simulations of electron photoemission (photoelectric emission) from cesium antimonide (Cs3Sb) and compare them with experimental results at 90 K and room temperature, with an emphasis on near-threshold photoemission properties. Interfacial effects, impurities, and electron-phonon coupling are central features of our Monte Carlo model. We use these simulations to predict photoemission properties at the ultracold cryogenic temperature of 20 K and to identify critical material parameters that need to be properly measured experimentally for reproducing the electron photoemission properties of Cs3Sb and other materials more accurately.

  20. Measurement of an enhanced superconducting phase and a pronounced anisotropy of the energy gap of a strained FeSe single layer in FeSe/Nb:SrTiO3/KTaO3 heterostructures using photoemission spectroscopy.

    PubMed

    Peng, R; Shen, X P; Xie, X; Xu, H C; Tan, S Y; Xia, M; Zhang, T; Cao, H Y; Gong, X G; Hu, J P; Xie, B P; Feng, D L

    2014-03-14

    Single-layer FeSe films with an extremely expanded in-plane lattice constant of 3.99±0.02  Å are fabricated by epitaxially growing FeSe/Nb:SrTiO3/KTaO3 heterostructures and studied by in situ angle-resolved photoemission spectroscopy. Two elliptical electron pockets at the Brillouin zone corner are resolved with negligible hybridization between them, indicating that the symmetry of the low-energy electronic structure remains intact as a freestanding single-layer FeSe, although it is on a substrate. The superconducting gap closes at a record high temperature of 70 K for the iron-based superconductors. Intriguingly, the superconducting gap distribution is anisotropic but nodeless around the electron pockets, with minima at the crossings of the two pockets. Our results place strong constraints on current theories.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. Laser based accelerator for ultracold atoms.

    PubMed

    Rakonjac, A; Deb, A B; Hoinka, S; Hudson, D; Sawyer, B J; Kjærgaard, N

    2012-03-15

    We present our first results on our implementation of a laser based accelerator for ultracold atoms. Atoms cooled to a temperature of 420 nK are confined and accelerated by means of laser tweezer beams, and the atomic scattering is directly observed in laser absorption imaging. The optical collider has been characterized using 87Rb atoms in the |F=2, m(F)=2] state, but the scheme is not restricted to atoms in any particular magnetic substates and can readily be extended to other atomic species as well.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2017-09-01

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

  14. 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.

  15. 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.

  16. 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.

  17. Multiatom Resonant Photoemission: Theory and Systematics

    SciTech Connect

    Garcia de Abajo, F.J.; Fadley, C.S.; Van Hove, M.A.; Garcia de Abajo, F.J.

    1999-05-01

    A first-principles calculation of the recently discovered interatomic multiatom resonant photoemission (MARPE) effect is presented. In this phenomenon, core photoelectron intensities are enhanced when the photon energy is tuned to a core-level absorption edge of nonidentical neighboring atoms, thus enabling direct determination of near-neighbor atomic identities. Both the multiatom character of MARPE and retardation effects in the photon and electron interactions in the resonant channel are shown to be crucial. Measured peak-intensity enhancements of 40{percent} in MnO and spectral shapes similar to the corresponding x-ray absorption profiles are well reproduced by this theory. {copyright} {ital 1999} {ital The American Physical Society}

  18. Antiferromagnetically Induced Photoemission Band in the Cuprates

    NASA Astrophysics Data System (ADS)

    Haas, Stephan; Moreo, Adriana; Dagotto, Elbio

    1995-05-01

    Strong antiferromagnetic correlations in models of high critical temperature (high- Tc) cuprates produce quasiparticlelike features in photoemission (PES) calculations above the Fermi momentum pF corresponding to weakly interacting electrons. This effect, discussed before by Kampf and Schrieffer [Phys. Rev. B 41, 6399 (1990)], is analyzed here using computational techniques in strong coupling. It is concluded that weight above pF should be observable in PES data for underdoped compounds, while in the overdoped regime it will be hidden in the experimental background. At optimal doping the signal is weak. The order of magnitude of our results is compatible with experimental data by Aebi et al. [Phys. Rev. Lett. 72, 2757 (1994)] for Bi2Sr2CaCu2O8.

  19. 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.

  20. Photoemission Investigations of the Bonding and Interactions of Simple Molecules on Metal Surfaces.

    NASA Astrophysics Data System (ADS)

    Heskett, David Robert

    Various experimental techniques, particularly angle-resolved photoemission, have been used to probe the bonding of CO and N(,2) to metal surfaces, the intermolecular interactions within an adsorbate overlayer, and the effects of coadsorbing CO or N(,2) with an alkali metal. The two-dimensional band-like dispersion of the CO and N(,2) 4(sigma) and 5(sigma) valence levels of the systems CO/Co(0001), CO/Ru(001), CO/Cu(111), and N(,2)/Ru(001) have been measured. In almost all cases of CO adsorbed on a transition metal surface, the bandwidth of the 4(sigma) level is directly related to the CO spacing and geometry in the overlayer. This dispersion results from the direct overlap of the 4(sigma) orbitals of neighboring molecules, with the substrate not playing a significant role. The 5(sigma) bandwidths, on the other hand, are not consistently related to the CO spacing. We attribute this to the greater 5(sigma)-substrate interaction vs. the 4(sigma) level. In cases of weak chemisorption, one or both of the (sigma) bandwidths is anomalously small compared with the strongly chemisorbed cases above. We show that this is a many-body effect related to the presence of intense multielectron excitations, or shake-up peaks, in the valence regions of these latter systems. Many chemisorption properties of CO adsorbed to copper vs. transition metal surfaces are compared. A number of qualitative and quantitative differences are found. This suggests that there is a fundamentally different bonding mechanism on these two types of surfaces, which we propose is related to the degree of CO 2(pi) occupancy in these systems. We have performed detailed UPS investigations of the systems CO + K/Cu(100) and CO + K/Ru(001). Our results are quite similar in these two systems and to previous investigations. In both cases, we have observed a strong hybridization and splitting of the CO 5(sigma) and 1(pi) levels in the presence of K and significant changes in the line shape of the K 3p core level when

  1. 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.

  2. Pushing the limits of first-principles electron-phonon calculations: from photoemission kinks to band gaps

    NASA Astrophysics Data System (ADS)

    Giustino, Feliciano

    2012-02-01

    The electron-phonon interaction is key to some of the most intriguing and technologically important phenomena in condensed matter physics, ranging from superconductivity to charge density waves, electrical resistivity, and thermoelectricity. Starting from the late nineties first-principles calculations of electron-phonon interactions in metals have become increasingly popular, mainly in connection with the study of conventional superconductors and with the interpretation of angle-resolved photoemission experiments. In contrast, progress on first-principles calculations of electron-phonon interactions in insulators has been comparatively slower. This delay is arguably due to the conventional wisdom that the signatures of electron-phonon interactions in semiconductor band structures are so small that they fall within the error bar of the most accurate electronic structure calculations. In order to fill this gap we developed, within the context of state-of-the-art density-functional techniques, a theory proposed by Allen and Heine for calculating the temperature dependence of band gaps in semiconductors [P. B. Allen, V. Heine, J. Phys. C: Solid State Phys. 69, 2305 (1976)]. This methodology allows us to calculate both the temperature dependence of the quasiparticle energies and the renormalization due to zero-point quantum fluctuations. In order to demonstrate this technique an application to the intriguing case of diamond will be discussed [F. Giustino, S. G. Louie, M. L. Cohen, Phys. Rev. Lett. 105, 265501 (2010)]. In this case the calculated temperature dependence of the direct band gap agrees well with spectroscopic ellipsometry data, and the renormalization due to the electron-phonon interaction is found to be spectacularly large (>0.6 eV). This unexpected finding might be only the tip of the iceberg in a research area which remains largely unexplored and which, from a first glimpse, appears rich of surprises.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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).

  8. 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.

  9. 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

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. Photoemission from Ag, Cu, and CsI

    SciTech Connect

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

    1992-06-01

    Photoemission characteristics of three different cathodes, CsI, Ag film and Cu were investigated. CsI, upon irradiation by 213 nm, 10ps laser pulse yields a quantum efficiency of 4% at O.2[mu]J input energy. The saturation mechanism observed at higher input energies require further investigation. Ag film, upon irradiation by 630 nm, 300 fs laser emit prompt photoelectrons after absorbing 2 photons. There was no evidence of optical damage of the film up to 10[sup 11] W/cm[sup 2]. At low intensities, photoemission from Cu is a simple [nu]-e[sup [minus

  15. Photoemission studies from metal by UV lasers

    NASA Astrophysics Data System (ADS)

    Caretto, G.; Doria, D.; Nassisi, V.; Siciliano, M. V.

    2007-04-01

    Studies of electron emission by photoelectric process from pure Zn cathodes by UV laser beams were performed. As UV sources, two different wavelength excimer lasers were utilized in order to investigate the photoemission as pure photoelectric process and multiphoton process. The Schottky effect was also considered. The utilized laser sources were a KrF operating at 248nm wavelength (5eV), 23ns full width at half maximum (FWHM), and a XeCl operating at 308nm wavelength (4.02eV), 10ns FWHM. The cathode work function was 4.33eV, a value lower and higher than the photon energies of KrF and XeCl lasers, respectively. The photocathodes were tested in a vacuum photodiode cell at 10-7mbar. The cathodes were irradiated at normal incidence and the anode-cathode distance was set to 3.7mm. Due to the electrical breakdown into the photodiode gap, the maximum applied accelerating voltage was 20kV. Under the above experimental conditions a maximum of 5.4MV/m electric field resulted. Under the space charge effect, the electron emission was higher than the one expected by the Child-Langmuir law. In saturation regime the electron emission increased with the accelerating voltage owing to the Schottky effect and plasma formation. The highest output current was achieved with the KrF laser at 14mJ laser energy. Its value was about 12A, corresponding to a global quantum efficiency of approximately 1×10-4, while the temporal quantum efficiency presented a maximum value of 1.1×10-4 located at the tail of the laser pulse. The estimated efficiencies with the XeCl laser were lower than the KrF ones as well as the output current and the plasma formation, although higher energy values than the KrF ones were utilized. By the results obtained, we conclude that the plasma generation is strongly due to the extracted current but weakly to the used laser intensity.

  16. 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

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. Femtosecond Fiber Lasers Based on Dissipative Processes for Nonlinear Microscopy.

    PubMed

    Wise, Frank W

    2012-01-01

    Recent progress in the development of femtosecond-pulse fiber lasers with parameters appropriate for nonlinear microscopy is reviewed. Pulse-shaping in lasers with only normal-dispersion components is briefly described, and the performance of the resulting lasers is summarized. Fiber lasers based on the formation of dissipative solitons now offer performance competitive with that of solid-state lasers, but with the benefits of the fiber medium. Lasers based on self-similar pulse evolution in the gain section of a laser also offer a combination of short pulse duration and high pulse energy that will be attractive for applications in nonlinear bioimaging.

  4. Femtosecond Fiber Lasers Based on Dissipative Processes for Nonlinear Microscopy

    PubMed Central

    Wise, Frank W.

    2012-01-01

    Recent progress in the development of femtosecond-pulse fiber lasers with parameters appropriate for nonlinear microscopy is reviewed. Pulse-shaping in lasers with only normal-dispersion components is briefly described, and the performance of the resulting lasers is summarized. Fiber lasers based on the formation of dissipative solitons now offer performance competitive with that of solid-state lasers, but with the benefits of the fiber medium. Lasers based on self-similar pulse evolution in the gain section of a laser also offer a combination of short pulse duration and high pulse energy that will be attractive for applications in nonlinear bioimaging. PMID:23869163

  5. 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

  6. 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

  7. 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.

  8. 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

  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. 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.

  11. Photoemission from Ag, Cu, and CsI

    SciTech Connect

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

    1992-06-01

    Photoemission characteristics of three different cathodes, CsI, Ag film and Cu were investigated. CsI, upon irradiation by 213 nm, 10ps laser pulse yields a quantum efficiency of 4% at O.2{mu}J input energy. The saturation mechanism observed at higher input energies require further investigation. Ag film, upon irradiation by 630 nm, 300 fs laser emit prompt photoelectrons after absorbing 2 photons. There was no evidence of optical damage of the film up to 10{sup 11} W/cm{sup 2}. At low intensities, photoemission from Cu is a simple {nu}-e{sup {minus}} interaction, the nonlinearity of the process depending strongly on trace impurities. At higher intensities, there appears to be a change in the emission mechanism.

  12. Anharmonic surface vibrations in photoemission from alkali metals

    SciTech Connect

    Wertheim, G.K.; Riffe, D.M.; Citrin, P.H. )

    1994-01-15

    The phonon widths of outermost core-electron photoemission spectra from (110)-oriented overlayers of Na, K, and Rb metals show the expected Debye behavior for the bulk atoms, but significant deviations for the surface atoms. The data indicate a softening of the surface vibrational mode above 200 K. This effect, which is weak in Na but strong in K and Rb, demonstrates that the vibrational mode normal to the surface is anharmonic.

  13. 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.

  14. Progress In Developing Laser Based Post Irradiation Examination Infrastructure

    SciTech Connect

    Smith, James A.; Scott, Clark L.; Benefiel, Brad C.

    2016-09-01

    To be able to understand the performance of reactor fuels and materials, irradiated materials must be characterized effectively and efficiently in a high rad environment. The characterization work must be performed remotely and in an environment hostile to instrumentation. Laser based characterization techniques provide the ability to be remote and robust in a hot-cell environment. Laser based instrumentation also can provide high spatial resolution suitable for scanning and imaging large areas. The INL is currently developing three laser based Post Irradiation Examination (PIE) stations for the Hot Fuel Examination Facility at the INL. These laser based systems will characterize irradiated materials and fuels. The characterization systems are the following: Laser Shock Laser based ultrasonic C-scan system Gas Assay, Sample, and Recharge system (GASR, up-grade to an existing system). The laser shock technique will characterize material properties and failure loads/mechanisms in various materials such as LWR fuel, plate fuel, and next generation fuel forms, for PIE in high radiation areas. The laser shock-technique induces large amplitude shock waves to mechanically characterize interfaces such as the fuel-clad bond. The shock wave travels as a compression wave through the material to the free (unconfined) back surface and reflects back through the material under test as a rarefaction (tensile) wave. This rarefaction wave is the physical mechanism that produces internal de-lamination failure. As part of the laser shock system, a laser-based ultrasonic C-scan system will be used to detect and characterize debonding caused by the laser shock technique. The laser ultrasonic system will be fully capable of performing classical non-destructive evaluation testing and imaging functions such as microstructure characterization, flaw detection and dimensional metrology in complex components. The purpose of the GASR is to measure the pressure/volume of the plenum of an

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

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

    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.

  1. 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.

  2. Laser-Based Lighting: Experimental Analysis and Perspectives.

    PubMed

    Trivellin, Nicola; Yushchenko, Maksym; Buffolo, Matteo; De Santi, Carlo; Meneghini, Matteo; Meneghesso, Gaudenzio; Zanoni, Enrico

    2017-10-11

    This paper presents an extensive analysis of the operating principles, theoretical background, advantages and limitations of laser-based lighting systems. In the first part of the paper we discuss the main advantages and issues of laser-based lighting, and present a comparison with conventional LED-lighting technology. In the second part of the paper, we present original experimental data on the stability and reliability of phosphor layers for laser lighting, based on high light-intensity and high-temperature degradation tests. In the third part of the paper (for the first time) we present a detailed comparison between three different solutions for laser lighting, based on (i) transmissive phosphor layers; (ii) a reflective/angled phosphor layer; and (iii) a parabolic reflector, by discussing the advantages and drawbacks of each approach. The results presented within this paper can be used as a guideline for the development of advanced lighting systems based on laser diodes.

  3. 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.

  4. An investigation of resonant photoemission in Gd with x-ray linear dichroism

    SciTech Connect

    Tobin, J G

    1998-07-01

    The constructive summing of direct and indirect channels above the absorption threshold of a core level can cause a massive increase in the emission cross section, leading to a phenomenon called "resonant photoemission". Using novel magnetic linear dichroism in angular distribution photoelectron spectroscopy experiments and theoretical simulations, we have probed the nature of the resonant photoemission process in Gd metal. It now appears that temporal matching as well as energy matching is a requirement for true resonant photoemission.

  5. 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

  6. Resource Letter: LBOT-1: Laser-based optical tweezers.

    PubMed

    Lang, Matthew J; Block, Steven M

    2003-03-01

    This Resource Letter provides a guide to the literature on optical tweezers, also known as laser-based, gradient-force optical traps. Journal articles and books are cited for the following main topics: general papers on optical tweezers, trapping instrument design, optical detection methods, optical trapping theory, mechanical measurements, single molecule studies, and sections on biological motors, cellular measurements and additional applications of optical tweezers.

  7. Laser-Based Alkene Sensors for Shock Tube Kinetics

    DTIC Science & Technology

    2016-06-28

    during pyrolysis and oxidation should be feasible. These state-of-the-art sensors will also be used in the training and education of the next generation...other existing laser-based species sensors, a substantially complete picture of the intermediate decomposition products that form during pyrolysis and...spectra of these species overlap, producing blended spectra during pyrolysis of real fuels. Our approach to dealing with this problem has been to

  8. Resource Letter: LBOT-1: Laser-based optical tweezers

    PubMed Central

    Lang, Matthew J.; Block, Steven M.

    2006-01-01

    This Resource Letter provides a guide to the literature on optical tweezers, also known as laser-based, gradient-force optical traps. Journal articles and books are cited for the following main topics: general papers on optical tweezers, trapping instrument design, optical detection methods, optical trapping theory, mechanical measurements, single molecule studies, and sections on biological motors, cellular measurements and additional applications of optical tweezers. PMID:16971965

  9. 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.

  10. 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.

  11. The photoemissive cell of a vacuum ultraviolet radiation detector array

    NASA Astrophysics Data System (ADS)

    Il'ichev, E. A.; Kuleshov, A. E.; Nabiev, R. M.; Petrukhin, G. N.; Rychkov, G. S.; Teverovskaya, E. G.

    2017-04-01

    A photoemissive "solar-blind" cell of a vacuum ultraviolet detector array for the 50-225 nm wavelength range is described. The cell is a cavity in the shape of frustum of a pyramid in a silicon wafer, the walls of which are coated by polycrystalline diamond film acting the part of a photosensitive cathode. The design of the cell allows one to manage the work of the detector in the "pass through" mode; i.e., photons fall to one side of the wafer, and photoelectrons release from its opposite side. Estimation of photosensitivity of the cell gives a value of about ten photons.

  12. 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.

  13. 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.

  14. Comparative photoemission study of amorphous and crystalline As

    NASA Astrophysics Data System (ADS)

    Takahashi, T.; Harada, Y.; Hamanaka, H.

    1981-09-01

    Careful photoemission (ultraviolet, UPS and x-ray, XPS) studies were performed for amorphous and crystalline As in order to terminate the long-standing controversy upon the feature of the 4p-derived portion of the density of valence states of rhombohedral As. The 4p band of rhombohedral As exhibits a twin-peak structure as in the case of amorphous As. The present results are in line with Shevchik's data rather than those of Ley et al., in which only one broad band is observed in the 4p-derived portion in the spectrum of rhombohedral As.

  15. 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%.

  16. 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.

  17. 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.

  18. 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.

  19. A laser based reusable microjet injector for transdermal drug delivery

    NASA Astrophysics Data System (ADS)

    Han, Tae-hee; Yoh, Jack J.

    2010-05-01

    A laser based needle-free liquid drug injection device has been developed. A laser beam is focused inside the liquid contained in the rubber chamber of microscale. The focused laser beam causes explosive bubble growth, and the sudden volume increase in a sealed chamber drives a microjet of liquid drug through the micronozzle. The exit diameter of a nozzle is 125 μm and the injected microjet reaches an average velocity of 264 m/s. This device adds the time-varying feature of microjet to the current state of liquid injection for drug delivery.

  20. 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.