Kazuhiko Mase

High Energy Accelerator Research Organization, Tsukuba, Ibaraki, Japan

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Publications (105)145.45 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Interaction of O atoms with the (111) surface of a Cu-Zn alloy with a face-centered cubic structure (α-brass) is investigated by photoelectron spectroscopy utilizing synchrotron radiation. The O adatoms interact mainly with the Zn atoms to form the ZnO islands, whereas the Cu–O bond formation is negligible in the initial oxidation stages at room temperature. O adsorption induces a binding-energy shift of the Shockley-type surface states towards the Fermi level. Also induced is a lowering of the work function of the α-brass (111) surface. These O-induced changes resemble those on the alkali-metal-covered Cu (111) surface. Similarity between Zn on the brass surface and alkali metals adsorbed on Cu (111) in initial oxidation is discussed.
    Surface Science. 01/2014;
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    ABSTRACT: We investigated the interactions of CO and O2 with Ru(101¯0) single crystal surfaces, and studied the in-situ catalytic oxidation reaction of CO on the surface under near realistic pressure conditions by using a combination of near-ambient-pressure x-ray photoelectron spectroscopy and differential pumping mass spectroscopy. At lower temperatures (T < 190 °C), most of the surface keeps metallic and is covered by both chemisorbed atomic oxygen and CO, and the CO2 formation rate is relatively slow. At higher temperatures, the reaction rate significantly increases and reaches the saturation, where the Ru surface is dominated by a bulk oxide (i.e. RuO2).
    Surface Science. 01/2014; 621:128–132.
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    ABSTRACT: Angle-resolved photoelectron spectroscopy has been applied to investigate the Shockley-type surface state on the (111) surface of α -brass, a Cu-Zn alloy with a face-centered cubic structure. An energy position and an effective mass of the Shockley-state band are determined, respectively, to be 0.51 eV and 0.52 me with me being the rest mass of an electron. A decay length of the Shockley-state wave function into the bulk is also estimated to be 0.43 nm. These parameters are compared with those of the Shockley state on Cu(111), and it is concluded that the Cu sp orbitals in α -brass have a more isolated nature than those in Cu.Also examined in this study is the response of the Shockley state to oxygen adsorption. The behavior of the Shockley state upon oxygen adsorption strongly depends on the substrate temperature. At room temperature, the Shockley state is quenched along with the binding-energy shift towards the Fermi level. Contrastingly, oxygen adsorption at low temperatures (≤ 180 K) hardly affects the energy position of the Shockley state. The conversion of the surface oxidation process at a certain temperature between 180 K and room temperature is proposed.
    Surface Science. 01/2014;
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    ABSTRACT: CO oxidation reaction on a Pd(110) single crystal surface at various temperatures under near-ambient-pressure conditions has been investigated using in situ X-ray photoemission spectroscopy and mass spectroscopy. At lower temperature conditions, the CO2 formation rate is low, where the surface is covered by CO molecules (i.e., CO poisoning). Above a critical temperature 165 °C the Pd(110) surface converts to a catalytically active surface and is dominated by chemisorbed oxygen species. Further at the higher temperatures up to 320 °C, the CO2 formation rate is gradually decreased to about 80% of the maximum rate. At this moment, the amount of chemisorbed O was also decreased, which suggests that the CO oxidation reaction proceeds via the conventional Langmuir–Hinshelwood mechanism even under near-ambient pressure conditions.
    The Journal of Physical Chemistry C. 09/2013; 117(40):20617–20624.
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    ABSTRACT: We report molecular CO and NO adsorption structures on Pd(100) single crystal surfaces under sub-Torr pressure conditions at room temperature. A combination of ambient pressure X-ray photoelectron spectroscopy and density functional theory based calculations indicates that CO molecules adsorb at 2-fold bridge sites with (2√2 × √2)R45°, (3√2 × √2)R45° and (4√2 × √2)R45° structures under the CO gas pressures at room temperature. Furthermore a higher-density adsorption structure is reversibly formed at 0.5 Torr CO, where all the CO molecules keep sitting on the bridge sites. In case of NO adsorption, at 10‑ 7 Torr, a (2√2 × √2)R45° structure with occupying bridge sites is formed, which is the same as the case of CO. However, subsequent gas introduction up to 0.5 Torr causes additional site occupation of on-top sites. Furthermore NO molecules partially dissociate into atomic N and O species but they disappear from the surface due to further reaction with NO under ambient conditions.
    Surface Science 09/2013; · 1.84 Impact Factor
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    ABSTRACT: We report on the present status of a vacuum ultraviolet and soft X-ray undulator beamline, BL-13A, located at the Photon Factory. BL-13A is mainly dedicated to the study of organic thin films adsorbed on well-defined surfaces, using angle-resolved photoelectron spectroscopy (ARPES), X-ray photoelectron spectroscopy (XPS), and X-ray absorption spectroscopy (XAS). The photon-energy resolution (E/ΔE) is estimated to be about 10000 at a photon energy of 64 eV with an exit-slit width of 30 μm. The photon intensity is estimated to be 2.9 × 1012 to 5.6 × 108 photons/s for photon energies of 30-1600 eV with an exit-slit width of 100 μm at the ring current of 450 mA. An ultrahigh vacuum (UHV) chamber equipped with an electron-energy analyzer (Gamma Data/Scienta, SES 200) is used as the main end station for ARPES, XPS, and XAS measurements. A sample can be transferred from a UHV chamber for sample preparation or from a UHV chamber for the evaporation of organic materials. The sample-holder acceptors are equipped with a heating and cooling system. The overall electron-energy resolution is estimated to be about 12 meV at a photon energy of 30 eV.
    Journal of Physics Conference Series 03/2013; 425(15):152019.
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    ABSTRACT: High resolution photoelectron spectroscopy is utilized to investigate degradation of rubber-to-brass adhesion by thermal aging. Special attention is given to the role of water in the environment surrounding brass-embedded rubber so that three aging processes are employed; hydrothermal aging, moist-heat aging and dry-heat aging. All aging processes lead to the decrease in the amount of S at the rubber/brass interface. This desulfurization accompanies the decrease in the ratio of CuxS (x ≃ 2) to CuS, i.e., CuxS/CuS, and the increase in the amount of ZnO, Zn(OH)2 and ZnS, all of which are key factors for degradation of adhesion. The changes in the chemical composition are enhanced by water in the surrounding environment during the aging treatments, indicating that the water molecules accelerate degradation of rubber-to-brass adhesion.
    Applied Surface Science 03/2013; 268:117–123. · 2.54 Impact Factor
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    ABSTRACT: Ion desorption from condensed F3SiCD2CH2Si(CH3)3 induced by Si-2p core-level ionizations of the F3Si and the Si(CH3)3 sites (Si[F] and Si[Me]) was investigated using photoelectron photoion coincidence (PEPICO) spectroscopy, Auger photoelectron coincidence spectroscopy (APECS) and Auger electron photoion coincidence (AEPICO) spectroscopy. A Si-2p-F+ PEPICO peak appeared selectively in the Si[F]-2p region. Si-2p-H+ PEPICO peaks were, on the other hand, observed in both the Si[Me]- and Si[F]-2p regions. The structure of the Si-L23VV-Si[F]-2p Auger photoelectron coincidence spectrum (APECS) was quite different from that of the Si-L23VV-Si[Me]-2p APECS. Ab initio molecular orbital calculations qualitatively reproduced the measured APECSs. The peak positions in the Si-L23VV-F+ AEPICO spectrum were in good agreement with those in the Si-L23VV-Si[F]-2p APECS. The Si-L23VV-H+ AEPICO spectrum, on the other hand, showed no characteristic peaks. Based on these results we have concluded that the site-specific F+ desorption is stimulated by Si[F]-L23VV Auger processes, and that both the Si[Me]- and Si[F]-L23VV Auger decays are responsible for the non-site-specific H+ desorption.
    Surface Science 01/2013; 607:174–180. · 1.84 Impact Factor
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    ABSTRACT: High resolution photoelectron spectroscopy is utilized to investigate the chemical composition at the rubber/brass interface to elucidate the origin of strong adhesion as well as the degradation between rubber and brass. Special attention has been given to copper sulfides formed at the interface during the vulcanization reaction at 170 °C. At least five sulfur-containing species are identified in the adhesive interlayer including crystalline CuS and amorphous CuxS (x ≃ 2). These copper sulfide species are not uniformly distributed within the layer, but there exits the concentration gradation; the concentration of CuxS is high in the region on the rubber side and is diminished in the deeper region, while vice versa for that of CuS. Degradation of the interface adhesive strength by prolonged vulcanization arises from the decrease in the CuxS/CuS ratio accompanying desulfurization of the adhesive layer.
    Applied Surface Science 01/2013; 264:297–304. · 2.54 Impact Factor
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    ABSTRACT: Catalytic CO oxidation reaction on a Pd(100) single-crystal surface under several hundred mTorr pressure conditions has been studied by ambient pressure X-ray photoelectron spectroscopy and mass spectroscopy. In-situ observation of the reaction reveals that two reaction pathways switch over alternatively depending on the surface temperature. At lower temperatures, the Pd(100) surface is covered by CO molecules and the CO2 formation rate is low, indicating CO poisoning. At higher temperatures above 190 °C, an O–Pd–O trilayer surface oxide phase is formed on the surface and the CO2 formation rate drastically increases. It is likely that the enhanced rate of CO2 formation is associated with an active oxygen species that is located at the surface of the trilayer oxide.
    Journal of Physical Chemistry Letters 10/2012; 3(21):3182–3187. · 6.59 Impact Factor
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    ABSTRACT: Carbon contamination of optics is a serious issue in all soft X-ray beamlines because it decreases the quality of experimental data, such as near-edge X-ray absorption fine structure, resonant photoemission and resonant soft X-ray emission spectra in the carbon K-edge region. Here an in situ method involving the use of oxygen activated by zeroth-order synchrotron radiation was used to clean the optics in a vacuum ultraviolet and soft X-ray undulator beamline, BL-13A at the Photon Factory in Tsukuba, Japan. The carbon contamination of the optics was removed by exposing them to oxygen at a pressure of 10(-1)-10(-4) Pa for 17-20 h and simultaneously irradiating them with zeroth-order synchrotron radiation. After the cleaning, the decrease in the photon intensity in the carbon K-edge region reduced to 2-5%. The base pressure of the beamline recovered to 10(-7)-10(-8) Pa in one day without baking. The beamline can be used without additional commissioning.
    Journal of Synchrotron Radiation 09/2012; 19(Pt 5):722-7. · 2.19 Impact Factor
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    ABSTRACT: The CO oxidation reaction on the Pd(111) model catalyst at various temperatures (200–400 °C) under hundreds mTorr pressure conditions has been monitored by in situ ambient pressure X-ray photoelectron spectroscopy and mass spectroscopy. In situ observation of the reaction revealed that the Pd(111) surface is covered by CO molecules at a lower temperature (200 °C), while at higher temperatures (300–400 °C) several oxide phases are formed on the surface. We found that the reactivity is enhanced in the presence of a surface oxide and significantly suppressed by formation of a cluster oxide and the PdO bulk oxide. CO titration experiments suggest that less coordinated oxygen atoms are more reactive for CO oxidation.
    The Journal of Physical Chemistry C. 08/2012; 116(35):18691–18697.
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    ABSTRACT: To clarify the factors governing the local valence electronic states of SiO2 ultrathin films, we have measured the Si-L23VV--Sin+-2p Auger-electron photoelectron coincidence spectra (n = 0, 1, 2, 3, 4, where n represents the number of oxygen atoms bonded to Si) of SiO2 thermally grown on a Si(111)-7×7 surface [SiO2/Si(111)]. The results indicate that the valence electronic states in the vicinity of the Sin+ sites shift to deeper binding energies as n increases. Furthermore, Si4+-L23VV Auger electron spectra, measured as a function of SiO2 thickness, taken in coincidence with Si4+-2p photoelectron emission show that the valence-band maximum (VBM) of the SiO2 layer shifts by 2.7 ± 1.0 eV toward the Fermi level when SiO2 thickness is decreased to ≈1 monolayer (ML). This upward shift is much larger than that for a SiO2 layer with a thickness of ≈1 ML thermally grown on Si(100)-2×1 (about 1.6 eV). We attribute the large shift in the VBM of SiO2/Si(111) with a 1-ML-thick SiO2 layer to the formation of SiO2 islands on the 7×7 structure and to the presence of Si1+ atoms adjacent to the SiO2 sites.
    Journal of the Physical Society of Japan 07/2012; 81(7):4706-. · 2.09 Impact Factor
  • Journal of the Vacuum Society of Japan 01/2012; 55(8):403-404.
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    ABSTRACT: Adsorption states of tetrathiafulvalene (TTF) on single-crystal zinc oxide (ZnO) surfaces are examined by photoelectron spectroscopy and X-ray absorption spectroscopy utilizing synchrotron radiation light. Comparison of TTF coverages, its adsorption states, and TTF-induced band bending is made among three ZnO surfaces with orientations of (0001), (101̅0), and (0001̅). TTF adsorbs both molecularly and dissociatively on all three ZnO surfaces at room temperature. The total amount of TTF at the saturation coverage is proportional to the surface Zn density. Contrastingly, there is a negative correlation between the amount of dissociated TTF and the surface Zn density. These indicate that TTF is bonded mainly to the surface Zn atoms, while the surface O atoms are necessary for TTF decomposition. The formation of the TTF overlayer induces downward band bending on ZnO(101̅0) and (0001̅), whereas the band is bent upward in energy on ZnO(0001). The origin of the surface dependence of band bending is discussed in terms of charge donor/acceptor behavior of the overlayer on the ZnO surfaces.
    The Journal of Physical Chemistry C. 10/2011; 115(44).
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    ABSTRACT: The local valence electronic states of the surface, interface, and substrate for SiO2 ultrathin films thermally grown on a Si(100)-2×1 have been investigated using Si-L23VV Auger-electron Sin+-2p photoelectron coincidence spectroscopy (n represents the number of oxygen atoms bonded to the Si). A series of Si-L23VV Auger electron spectra (AES) measured in coincidence with Sin+-2p photoelectron indicate that the valence electronic states in the vicinity of the Sin+ sites shift to the deeper binding-energy side as n increases. Furthermore, the Si4+-L23VV AES measured as a function of the thickness of the SiO2, show that the valence-band maximum of SiO2 shifts ˜1.6 eV toward the Fermi level when the thickness of the SiO2 film is decreased to 1.7--1.5 Å. This shift is attributed to a decrease in the number of Si4+ and an increase in the number of Si3+, Si2+, Si1+, and Si0 in the vicinity of the topmost SiO2 layer.
    Journal of the Physical Society of Japan 08/2011; 80(8):4703-. · 2.09 Impact Factor
  • Kenichi Ozawa, Kazuhiko Mase
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    ABSTRACT: Synchrotron-radiation angle-resolved photoelectron spectroscopy has been utilized to study the interaction of atomic H with the nonpolar ZnO(101̅ 0) surface and polar ZnO(0001̅ ) and (0001) surfaces. H adsorption leads to the semiconductor-to-metal transition on the ZnO(101̅ 0) and (0001̅ ) surfaces. Metallization is a consequence of the formation of a single metallic band within the potential well between the surface/vacuum interface barrier and the edge of the conduction band, which is bent downwardly at the surface. The electrons confined in the potential well exhibit a free-electron-like behavior along the surface parallel, realizing a two-dimensional electron gas system. For the H/ZnO(0001) system, on the other hand, no feature associated with the metallic band is observed. Higher reactivity of the ZnO(0001) surface toward H than the other two ZnO surfaces is responsible for the different behavior for the modification of the surface electronic structure by H adsorption.
    Physical review. B, Condensed matter 01/2011; 83(12). · 3.77 Impact Factor
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    ABSTRACT: Present Status of a New Vacuum Ultraviolet and Soft X-Ray Undulator Beamline BL-13A for the Study of Organic Thin Films Adsorbed on Surfaces
    Journal of the Vacuum Society of Japan 01/2011; 54(11):580-584.
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    ABSTRACT: Valence electronic states of a clean Si(111)-7x7 surface are investigated in a surface-site-selective way using high-resolution coincidence measurements of Si pVV Auger electrons and Si 2p photoelectrons. The Si LVV Auger electron spectra measured in coincidence with energy-selected Si 2p photoelectrons show that the valence band at the highest density of states in the vicinity of the rest atoms is shifted by 0.95 eV toward the Fermi level (E{sub F}) relative to that in the vicinity of the pedestal atoms (atoms directly bonded to the adatoms). The valence-band maximum in the vicinity of the rest atoms, on the other hand, is shown to be shifted by 0.53 eV toward E{sub F} relative to that in the vicinity of the pedestal atoms. The Si 2p photoelectron spectra of Si(111)-7x7 measured in coincidence with energy-selected Si LVV Auger electrons identify the topmost surface components, and suggest that the dimers and the rest atoms are negatively charged while the pedestal atoms are positively charged. Furthermore, the Si 2p-Si LVV photoelectron Auger coincidence spectroscopy directly verifies that the adatom Si 2p component (usually denoted by C) is correlated with the surface state just below E{sub F} (usually denoted by S), as has been observed in previous angle-resolved photoelectron spectroscopy studies.
    Physical review. B, Condensed matter 01/2011; 83(3):035320-035320. · 3.77 Impact Factor
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    ABSTRACT: The Si-L23VV Auger electron Si-2p photoelectron coincidence spectra (Si-L23VV-Si-2p APECS) of a hydrogenated Si(111)-1×1 surface are measured with an analyzer that is used for electron-electron and electron-ion coincidence measurements of surfaces. The Si-L23VV-Si-2p APECS show a sharp peak, a small shoulder, and a broad large peak at electron kinetic energies of about 85, about 80.5, and about 70 eV, respectively. The clarity of the last two peaks is lower in the Si-L23VV-Si-2p APECS of a clean Si(111)-7×7 surface. We attribute the three peaks to the Si-L23V3pV3p, Si-L23V3pV3s, and Si-L23V3sV3s Auger lines, respectively. The three-peak structure indicates that the local density of states of the 3s + 3p band is reduced in the case of the hydrogenated Si(111)-1×1 surface. This finding is consistent with that of a previous study on valence electronic states of hydrogenated Si(111) using ultraviolet photoemission spectroscopy.
    Journal of Physics Conference Series 01/2011; 288(1).

Publication Stats

274 Citations
145.45 Total Impact Points

Institutions

  • 2002–2014
    • High Energy Accelerator Research Organization
      • • Institute of Materials Structure Science
      • • Photon Factory
      Tsukuba, Ibaraki, Japan
  • 2010
    • Ehime University
      • Department of Chemistry
      Matuyama, Ehime, Japan
  • 2007–2008
    • The Graduate University for Advanced Studies
      • School of High Energy Accelerator Science
      Miura, Kanagawa-ken, Japan
  • 2001–2007
    • Chiba University
      • Faculty of Engineering
      Chiba-shi, Chiba-ken, Japan
  • 2005
    • Max Planck Institute of Microstructure Physics
      Halle-on-the-Saale, Saxony-Anhalt, Germany
    • Indian Institute of Technology Madras
      • Department of Chemistry
      Chennai, State of Tamil Nadu, India
  • 2004
    • Princeton University
      • Department of Electrical Engineering
      Princeton, NJ, United States
  • 1997
    • Hiroshima University
      • Department of Biomaterials Science
      Hiroshima-shi, Hiroshima-ken, Japan
  • 1991–1993
    • The University of Tokyo
      • Institute for Solid State Physics
      Tokyo, Tokyo-to, Japan