顔写真

ヤマモト ススム
山本 達
Susumu Yamamoto
所属
国際放射光イノベーション・スマート研究センター 横幹研究部門 次世代検出法スマートラボ
職名
准教授
学位
  • 博士(理学)(東京大学)

  • 修士(理学)(東京大学)

e-Rad 研究者番号
50554705
Researcher ID

経歴 6

  • 2020年10月 ~ 継続中
    東北大学 国際放射光イノベーション・スマート研究センター 准教授

  • 2019年11月 ~ 継続中
    東北大学 多元物質科学研究所 准教授

  • 2009年10月 ~ 2019年10月
    東京大学物性研究所 極限コヒーレント光科学研究センター 軌道放射物性研究施設 助教

  • 2008年6月 ~ 2009年10月
    オランダ原子分子国立研究所、 Mischa Bonn 研究室 日本学術振興会海外特別研究員

  • 2008年4月 ~ 2008年5月
    オランダ原子分子国立研究所 Mischa Bonn 研究室 客員研究員

  • 2005年4月 ~ 2008年3月
    スタンフォード大学・放射光研究施設 Anders Nilsson 研究室 博士研究員

︎全件表示 ︎最初の5件までを表示

学歴 2

  • 東京大学 理学系研究科 化学専攻

    2000年4月 ~ 2005年3月

  • 国際基督教大学 教養学部 理学科・化学専攻

    1996年4月 ~ 2000年3月

委員歴 6

  • 日本表面真空学会 東北・北海道支部 幹事

    2021年4月 ~ 継続中

  • VUV・SX高輝度光源利用者懇談会 幹事

    2020年4月 ~ 継続中

  • 日本表面真空学会 関西支部役員

    2018年4月 ~ 2020年3月

  • 日本放射光学会 第31回日本放射光学会年会・放射光科学合同シンポジウム プログラム委員

    2017年6月 ~ 2018年1月

  • 日本放射光学会 第30回日本放射光学会年会・放射光科学合同シンポジウム プログラム委員

    2016年6月 ~ 2017年1月

  • 日本放射光学会 行事委員

    2013年10月 ~ 2015年9月

︎全件表示 ︎最初の5件までを表示

所属学協会 7

  • 日本表面真空学会

  • 日本物理学会

  • American Vacuum Society

  • American Physical Society

  • American Chemical Society

  • 日本放射光学会

  • 日本化学会

︎全件表示 ︎最初の5件までを表示

研究キーワード 17

  • オペランド

  • 触媒

  • プラズモニック化学反応

  • CO2

  • 光電子分光

  • 軟X線

  • 放射光

  • 表面物性

  • 電子励起反応

  • レーザー分光法

  • X線分光法

  • 振動分光法

  • 酸化物表面

  • 金属表面

  • 表面化学

研究分野 5

  • エネルギー / 量子ビーム科学 / 放射光

  • ナノテク・材料 / 基礎物理化学 /

  • 自然科学一般 / 半導体、光物性、原子物理 /

  • ナノテク・材料 / ナノ構造物理 /

  • ナノテク・材料 / ナノ構造化学 /

受賞 5

  1. 会誌賞

    2021年 日本表面真空学会 "Surface Chemistry of Carbon Dioxide on Copper Model Catalysts Studied by Ambient-Pressure X-ray Photoelectron Spectroscopy"

  2. 会誌賞

    2020年 日本表面真空学会 "A Surface Science Approach to Unveiling the TiO2 Photocatalytic Mechanism: Correlation between Photocatalytic Activity and Carrier Lifetime"

  3. 日本学術振興会海外特別研究員

    2008年

  4. 第5回表面エレクトロニクス研究会 Student prize

    2004年

  5. 東京大学大学院学生学術研究奨励金

    2004年

論文 96

  1. Hydrogen‐induced Sulfur Vacancies on the MoS2 Basal Plane Studied by Ambient Pressure XPS and DFT Calculations 査読有り

    Fumihiko Ozaki, Shunsuke Tanaka, YoungHyun Choi, Wataru Osada, Kozo Mukai, Mitsuaki Kawamura, Masahiro Fukuda, Masafumi Horio, Takanori Koitaya, Susumu Yamamoto, Iwao Matsuda, Taisuke Ozaki, Jun Yoshinobu

    ChemPhysChem e202300477 2023年9月25日

    DOI: 10.1002/cphc.202300477  

  2. In Situ Electrical Detection of Methane Oxidation on Atomically Thin IrO2 Nanosheet Films Down to Room Temperature 査読有り

    Yoshiaki Ishihara, Takanori Koitaya, Yuto Hamahiga, Wataru Sugimoto, Susumu Yamamoto, Iwao Matsuda, Jun Yoshinobu, Ryo Nouchi

    Advanced Materials Interfaces 2023年6月

    DOI: 10.1002/admi.202300258  

  3. Surface Exchange Reaction of Mixed Conductive La<sub>0.65</sub>Ca<sub>0.35</sub>FeO<sub>3−δ</sub> during Oxygen Evolution and Incorporation as Traced by Operando X-ray Photoelectron Spectroscopy 査読有り

    Isao Kagomiya, Tomohiro Hirano, Yutaro Yagi, Ken-ichi Kakimoto, Susumu Yamamoto, Iwao Matsuda

    ACS Applied Materials &amp; Interfaces 14 (42) 48194-48199 2022年10月26日

    出版者・発行元:American Chemical Society (ACS)

    DOI: 10.1021/acsami.2c10700  

    ISSN:1944-8244

    eISSN:1944-8252

  4. Resolving decay-time dependent photoluminescence induced by phonon-dressed excitons in ZnO 査読有り

    Ryu Yukawa, Susumu Yamamoto, Ren Arita, Yuki Minami, Kohei Yamanoi, Kenichi Ozawa, Kazuyuki Sakamoto, Toshihiko Shimizu, Nobuhiko Sarukura, Iwao Matsuda

    Physical Review Materials 6 (10) 2022年10月21日

    出版者・発行元:American Physical Society (APS)

    DOI: 10.1103/physrevmaterials.6.104607  

    eISSN:2475-9953

  5. Functionalization of the MoS2 basal plane for activation of molecular hydrogen by Pd deposition 査読有り

    Fumihiko Ozaki, Shunsuke Tanaka, Wataru Osada, Kozo Mukai, Masafumi Horio, Takanori Koitaya, Susumu Yamamoto, Iwao Matsuda, Jun Yoshinobu

    Applied Surface Science 593 153313-153313 2022年8月

    出版者・発行元:Elsevier BV

    DOI: 10.1016/j.apsusc.2022.153313  

    ISSN:0169-4332

  6. Hydrogen absorption and diffusion behaviors in cube-shaped palladium nanoparticles revealed by ambient-pressure X-ray photoelectron spectroscopy 査読有り

    Jiayi Tang, Okkyun Seo, David S. Rivera Rocabado, Takanori Koitaya, Susumu Yamamoto, Yusuke Nanba, Chulho Song, Jaemyung Kim, Akitaka Yoshigoe, Michihisa Koyama, Shun Dekura, Hirokazu Kobayashi, Hiroshi Kitagawa, Osami Sakata, Iwao Matsuda, Jun Yoshinobu

    Applied Surface Science 587 152797-152797 2022年6月

    出版者・発行元:Elsevier BV

    DOI: 10.1016/j.apsusc.2022.152797  

    ISSN:0169-4332

  7. Hole Dynamics in Photoexcited Hematite Studied with Femtosecond Oxygen K-edge X-ray Absorption Spectroscopy 査読有り

    Yohei Uemura, Ahmed S. M. Ismail, Sang Han Park, Soonnam Kwon, Minseok Kim, Hebatalla Elnaggar, Federica Frati, Hiroki Wadati, Yasuyuki Hirata, Yujun Zhang, Kohei Yamagami, Susumu Yamamoto, Iwao Matsuda, Ufuk Halisdemir, Gertjan Koster, Christopher Milne, Markus Ammann, Bert M. Weckhuysen, Frank M. F. de Groot

    The Journal of Physical Chemistry Letters 13 (19) 4207-4214 2022年5月19日

    出版者・発行元:American Chemical Society (ACS)

    DOI: 10.1021/acs.jpclett.2c00295  

    ISSN:1948-7185

    eISSN:1948-7185

  8. Fast and versatile polarization control of X-ray by segmented cross undulator at SPring-8 招待有り 査読有り

    Jun Miyawaki, Susumu Yamamoto, Yasuyuki Hirata, Masafumi Horio, Yoshihisa Harada, Iwao Matsuda

    AAPPS Bulletin 31 (1) 2021年12月

    出版者・発行元:Springer Science and Business Media LLC

    DOI: 10.1007/s43673-021-00026-z  

    eISSN:2309-4710

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    <title>Abstract</title>An X-ray is the well-known probe to examine structure of materials, including our own bodies. The X-ray beam, especially at the wavelength of nanometers, has also become significant to directly investigate electronic states of a sample. Such an X-ray is called a soft X-ray and polarization dependence of the light-matter interaction further unveils the microscopic properties, such as orbitals or spins of electrons. Generation of high brilliant beams of the polarized X-ray has linked to development of our experimental science, and it has been made by radiation from relativistic electrons at the synchrotron radiation facilities over the world. Recently, we constructed a new polarization-controlled X-ray source, the segmented cross undulator, at SPring-8, the largest synchrotron radiation facility in the world. The operation is based on interference of X-ray beams, which is sharply contrast to the conventional method of regulating electron trajectory by the mechanical control of magnets. The paradigm shift opened the measurement innovations and allowed us to design new experimental approaches to capture signals that have been hidden in materials. The present review describes the novel X-ray source with the principle of operation and the technical details of optimization. Examples of the frontier spectroscopies that use unique optical properties of the source are introduced, followed by the future prospects for next generation synchrotron radiation facilities.

  9. Comparative Study of H2O and O2 Adsorption on the GaN Surface 査読有り

    Masahiro Sato, Yuki Imazeki, Takahito Takeda, Masaki Kobayashi, Susumu Yamamoto, Iwao Matsuda, Jun Yoshinobu, Yoshiaki Nakano, Masakazu Sugiyama

    The Journal of Physical Chemistry C 125 (46) 25807-25815 2021年11月25日

    出版者・発行元:American Chemical Society (ACS)

    DOI: 10.1021/acs.jpcc.1c07110  

    ISSN:1932-7447

    eISSN:1932-7455

  10. Influence of Stacking Order of Phthalocyanine and Fullerene Layers on the Photoexcited Carrier Dynamics in Model Organic Solar Cell 査読有り

    Kenichi Ozawa, Susumu Yamamoto, Tetsuya Miyazawa, Keita Yano, Koji Okudaira, Kazuhiko Mase, Iwao Matsuda

    The Journal of Physical Chemistry C 125 (25) 13963-13970 2021年7月1日

    出版者・発行元:American Chemical Society (ACS)

    DOI: 10.1021/acs.jpcc.1c03584  

    ISSN:1932-7447

    eISSN:1932-7455

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    Metal phthalocyanine and fullerene are typical p-type and n-type organic semiconductors and are often used as constituents of model systems of organic photovoltaics (OPVs). The light-electricity conversion efficiency of the OPVs is influenced by many factors, and a composite structure is one of them. In the present study, time-resolved X-ray photoelectron spectroscopy has been utilized to examine the influence of the stacking order of copper phthalocyanine (CuPc) and fullerene (C-60) on photoexcited carrier dynamics in layered CuPc-C-60 thin-film OPVs fabricated on a rutile TiO2(110) substrate. TiO2 is a strong n-type semiconductor and is found to serve as an electron acceptor, which collects the excited electrons in both CuPc and C-60 layers irrespective of their stacking order. However, a clear difference is found in the electron transfer from C-60 to TiO2 in short delay times below 1 ns; an electron transfer is facilitated in CuPc/C-60/TiO2 stacking, whereas the fast electron transfer is suppressed in C-60/CuPc/TiO2 stacking. The insertion of the CuPc layer between C-60 and TiO2 is effective to block the C-60. TiO2 electron transfer even though the CuPc layer has a monolayer thickness.

  11. Band Bending of n-GaN under Ambient H2O Vapor Studied by X-ray Photoelectron Spectroscopy 査読有り

    Yuki Imazeki, Masahiro Sato, Takahito Takeda, Masaki Kobayashi, Susumu Yamamoto, Iwao Matsuda, Jun Yoshinobu, Masakazu Sugiyama, Yoshiaki Nakano

    The Journal of Physical Chemistry C 125 (17) 9011-9019 2021年5月6日

    出版者・発行元:American Chemical Society (ACS)

    DOI: 10.1021/acs.jpcc.0c11174  

    ISSN:1932-7447

    eISSN:1932-7455

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    To improve the performance of semiconductor photoelectrodes for water splitting, the amount of band bending in the depletion layer of a semiconductor should be accurately ascertained, since it determines the splitting efficiency of photo-generated carriers. Band bending has been determined by X-ray photoelectron spectroscopy (XPS) from the valence band maximum (VBM), which has been calculated from the Ga 3d peak using the energy difference between VBM and Ga 3d (Delta EVBM-3d). This work validates several values for Delta EVBM-3d which have been reported previously, by analyzing the spectrum around the VBM and its distance from Ga 3d for the n-GaN(0001) surface under both ultrahigh vacuum (UHV) and ambient H2O center dot Delta EVBM-3d is estimated to be between 17.36 and 17.55 eV. By adopting 17.5 eV as Delta EVBM-3d, the amounts of band-bending were 0.5 eV under UHV and 0.1 eV under a relative humidity of 46%, respectively. For the latter condition, a surface photovoltage of 20 meV was observed upon Xe lamp irradiation, confirming the existence of band bending even with H2O adsorption on the surface. The origin of such band bending seems to be Fermi level pinning to the subsurface states which cannot be compensated by H2O.

  12. Femtosecond Charge Density Modulations in Photoexcited CuWO4 査読有り

    Yohei Uemura, Ahmed S. M. Ismail, Sang Han Park, Soonnam Kwon, Minseok Kim, Yasuhiro Niwa, Hiroki Wadati, Hebatalla Elnaggar, Federica Frati, Ties Haarman, Niko Höppel, Nils Huse, Yasuyuki Hirata, Yujun Zhang, Kohei Yamagami, Susumu Yamamoto, Iwao Matsuda, Tetsuo Katayama, Tadashi Togashi, Shigeki Owada, Makina Yabashi, Uufuk Halisdemir, Gertjan Koster, Toshihiko Yokoyama, Bert M. Weckhuysen, Frank M. F. de Groot

    The Journal of Physical Chemistry C 125 (13) 7329-7336 2021年3月26日

    出版者・発行元:American Chemical Society (ACS)

    DOI: 10.1021/acs.jpcc.0c10525  

    ISSN:1932-7447

    eISSN:1932-7455

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    Copper tungstate (CuWO4) is an important semiconductor with a sophisticated and debatable electronic structure that has a direct impact on its chemistry. Using the PAL-XFEL source, we study the electronic dynamics of photoexcited CuWO4. The Cu L-3 X-ray absorption spectrum shifts to lower energy upon photoexcitation, which implies that the photoexcitation process from the oxygen valence band to the tungsten conduction band effectively increases the charge density on the Cu atoms. The decay time of this spectral change is 400 fs indicating that the increased charge density exists only for a very short time and relaxes electronically. The initial increased charge density gives rise to a structural change on a time scale longer than 200 ps.

  13. Valence Fluctuations in Yb(Al,Fe)B<sub>4</sub> Studied by Nanosecond-time-resolved Photoemission Spectroscopy Using Synchrotron Radiation 査読有り

    M. Okawa, K. Akikubo, S. Yamamoto, I. Matsuda, T. Saitoh

    e-Journal of Surface Science and Nanotechnology 19 (0) 20-23 2021年3月18日

    出版者・発行元:Surface Science Society Japan

    DOI: 10.1380/ejssnt.2021.20  

    eISSN:1348-0391

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    Temporal variations of valence states of the α-YbAl1−xFexB4 crystals (x = 0, 0.013, and 0.098) are experimentally examined in a nanosecond time-scale by time-resolved photoemission experiments using synchrotron radiation. The Yb 4f spectral features show no apparent change with time during relaxations after the optical pumping. The present experimental result indicates that dynamics of valence fluctuations in the material are likely dominated by a picosecond or much faster time-scale. The time-resolved measurement at the time-resolution limit at synchrotron radiation captured the trace of valence fluctuations.

  14. Time-resolved X-ray photoelectron diffraction using an angle-resolved time-of-flight electron analyzer 査読有り

    Artoni Kevin R. Ang, Yuichiro Fukatsu, Koji Kimura, Yuta Yamamoto, Takahiro Yonezawa, Hirokazu Nitta, Antoine Fleurence, Susumu Yamamoto, Iwao Matsuda, Yukiko Yamada-Takamura, Kouichi Hayashi

    Japanese Journal of Applied Physics 59 (10) 100902-100902 2020年10月1日

    出版者・発行元:IOP Publishing

    DOI: 10.35848/1347-4065/abb57e  

    ISSN:0021-4922

    eISSN:1347-4065

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    X-ray photoelectron diffraction (XPD) provides atomic resolution, element sensitive local structure information about the surfaces and interfaces of materials. In the work reported in this paper, a two-dimensional angle resolved time-of-flight (2DARTOF) system is used to perform time-resolved XPD experiments on epitaxial silicene. The two Si 2p peak components from the different atomic sites in the silicene layer allow extraction of the individual XPD patterns. Time-resolved measurements captured small angle shifts in the forward focusing peak, indicating laser-induced changes in the silicene structure. At 10 ns, the XPD patterns appear to relax back to the equilibrium state. This work demonstrates that 2DARTOF systems are well suitable for time-resolved XPD measurements.

  15. Atomistic-Level Description of GaN/Water Interface by a Combined Spectroscopic and First-Principles Computational Approach 査読有り

    Masahiro Sato, Yuki Imazeki, Takahito Takeda, Masaki Kobayashi, Susumu Yamamoto, Iwao Matsuda, Jun Yoshinobu, Yoshiaki Nakano, Masakazu Sugiyama

    The Journal of Physical Chemistry C 124 (23) 12466-12475 2020年6月11日

    出版者・発行元:American Chemical Society (ACS)

    DOI: 10.1021/acs.jpcc.0c02192  

    ISSN:1932-7447

    eISSN:1932-7455

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    Photocatalytic water splitting takes place at the semiconductor/electrolyte interface. Although the reactions are strongly affected by the subtle changes in the interface structure, little is known about the interface from an atomistic point of view. In this study, we investigate the GaN(0001)/water interface structure by combining first-principles calculation and ambient pressure X-ray photoelectron spectroscopy (AP-XPS). In particular, the relationship between the geometric and electronic structure of the interface is revealed. First, the evolution of the GaN/water interface structure upon water adsorption is predicted from firstprinciples calculations. Computational results indicate that (1) at low coverage (below 3/4 monolayer), the Fermi level is pinned to the surface states originating from surface Ga atom dangling bonds, and water adsorbs dissociatively, forming oxygen atoms as well as hydroxyl groups, and (2) at higher coverage (above 3/4 monolayer), the Fermi level becomes free from the pinning, and adsorption of intact water becomes dominant. AP-XPS measurements were carried out for the water coverage ranging from submonolayer (low coverage) to several monolayers (high coverage). The core-level binding energies calculated from first-principles were used successfully to assign the adsorbate species to experimental O is peaks. Both the electronic and geometric structures predicted by the first-principles calculation explain well the experimental spectra obtained by the AP-XPS measurements. The results demonstrate that the combined spectroscopic and first-principles computational approach offers a detailed atomic level understanding of the solid/liquid interface structures.

  16. Element-selectively tracking ultrafast demagnetization process in Co/Pt multilayer thin films by the resonant magneto-optical Kerr effect 査読有り

    Kohei Yamamoto, Souliman El Moussaoui, Yasuyuki Hirata, Susumu Yamamoto, Yuya Kubota, Shigeki Owada, Makina Yabashi, Takeshi Seki, Koki Takanashi, Iwao Matsuda, Hiroki Wadati

    Applied Physics Letters 116 (17) 172406-172406 2020年4月27日

    出版者・発行元:AIP Publishing

    DOI: 10.1063/5.0005393  

    ISSN:0003-6951

    eISSN:1077-3118

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    We examined the photo-induced dynamics of ferromagnetic Co/Pt thin films exhibiting perpendicular magnetic anisotropy by means of the resonant polar magneto-optical Kerr effect with element specificity. The investigation was conducted at Pt N-6,N-7 and Co M-2,M-3 edges using an x-ray free electron laser. The obtained results showed a clear element dependence of photo-induced demagnetization time scales:taudemag .Co = 80 +/- 60fs andtaudemag .Pt = 640 +/- 140fs. This dependence is explained by the induced moment of the Pt atom by current flow from the Co layer through the interfaces. The observed magnetization dynamics can be attributed to the characteristics of photo-induced Co/Pt thin film phenomena including all-optical switching.

  17. Erratum: A surface science approach to understand-ing TiO<inf>2</inf>photocatalyst: Correlation between carrier lifetime and photocatalytic activity (e-Journal of Surface Science and Nanotechnology (2019) 17 (130-147) DOI: 10.1380/ejssnt.2019.130)

    Kenichi Ozawa, Susumu Yamamoto, Kazuhiko Mase, Iwao Matsuda

    e-Journal of Surface Science and Nanotechnology 18 100 2020年3月19日

    DOI: 10.1380/EJSSNT.2020.100  

    eISSN:1348-0391

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    Surface indices of rutile TiO2were wrongly displayed in Table 3 in the original article [1]. The correct table is shown below. This revision does not affect the conclusion. (Table Presented).

  18. A computational examination of the electric-field-induced proton transfer along the interface hydrogen bond between proton donating and accepting self-assembled monolayers 査読有り

    Yusuke Kanematsu, Hiroyuki S. Kato, Shinya Yoshimoto, Akira Ueda, Susumu Yamamoto, Hatsumi Mori, Jun Yoshinobu, Iwao Matsuda, Masanori Tachikawa

    Chemical Physics Letters 741 137091-137091 2020年2月

    出版者・発行元:Elsevier BV

    DOI: 10.1016/j.cplett.2020.137091  

    ISSN:0009-2614

  19. Direct observation of the electronic states of photoexcited hematite with ultrafast 2p3d X-ray absorption spectroscopy and resonant inelastic X-ray scattering 査読有り

    Ahmed S. M. Ismail, Yohei Uemura, Sang Han Park, Soonnam Kwon, Minseok Kim, Hebatalla Elnaggar, Federica Frati, Yasuhiro Niwa, Hiroki Wadati, Yasuyuki Hirata, Yujun Zhang, Kohei Yamagami, Susumu Yamamoto, Iwao Matsuda, Ufuk Halisdemir, Gertjan Koster, Bert M. Weckhuysen, Frank M. F. de Groot

    Physical Chemistry Chemical Physics 22 (5) 2685-2692 2020年

    出版者・発行元:Royal Society of Chemistry (RSC)

    DOI: 10.1039/c9cp03374b  

    ISSN:1463-9076

    eISSN:1463-9084

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    <p>Ultrafast Fe L<sub>3</sub> XAS and 2p3d RIXS elucidate the photoexcitation process of hematite.</p>

  20. Surface Chemistry of Carbon Dioxide on Copper Model Catalysts Studied by Ambient-Pressure X-ray Photoelectron Spectroscopy 査読有り

    Takanori Koitaya, Susumu Yamamoto, Iwao Matsuda, Jun Yoshinobu

    e-Journal of Surface Science and Nanotechnology 17 (0) 169-178 2019年11月2日

    出版者・発行元:Surface Science Society Japan

    DOI: 10.1380/ejssnt.2019.169  

    ISSN:1348-0391

    eISSN:1348-0391

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    In-situ analysis of heterogeneous catalysts under reaction condition is indispensable to understand reaction mechanisms and nature of active sites. Ambient-pressure X-ray photoelectron spectroscopy (AP-XPS) is one of the powerful methods to investigate chemical states of catalysts and reaction intermediates adsorbed on the surface. In this review, reaction of carbon dioxide on Cu(997) and Zn-deposited Cu(997) surfaces are discussed as an example of surface chemistry of weakly adsorbed molecules, together with a brief overview of recent progress in AP-XPS methods.

  21. Reversible low-temperature redox activity and selective oxidation catalysis derived from the concerted activation of multiple metal species on Cr and Rh-incorporated ceria catalysts 査読有り

    Ikemoto Satoru, Huang Xiubing, Muratsugu Satoshi, Nagase Shoko, Koitaya Takanori, Matsui Hirosuke, Yokota Gen-ichi, Sudoh Takatoshi, Hashimoto Ayako, Tan Yuanyuan, Yamamoto Susumu, Tang Jiayi, Matsuda Iwao, Yoshinobu Jun, Yokoyama Toshihiko, Kusaka Shinpei, Matsuda Ryotaro, Tada Mizuki

    PHYSICAL CHEMISTRY CHEMICAL PHYSICS 21 (37) 20868-20877 2019年10月7日

    出版者・発行元:None

    DOI: 10.1039/c9cp04625a  

    ISSN:1463-9076

    eISSN:1463-9084

  22. Photoinduced valence dynamics in EuNi2(Si0.21Ge0.79)2 studied via time-resolved x-ray absorption spectroscopy 査読有り

    Y. Yokoyama, K. Kawakami, Y. Hirata, K. Takubo, K. Yamamoto, K. Abe, A. Mitsuda, H. Wada, T. Uozumi, S. Yamamoto, I. Matsuda, S. Kimura, K. Mimura, H. Wadati

    Physical Review B 100 (11) 2019年9月12日

    出版者・発行元:American Physical Society (APS)

    DOI: 10.1103/physrevb.100.115123  

    ISSN:2469-9950

    eISSN:2469-9969

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    The photoinduced valence dynamics of EuNi2(Si0.21Ge0.79)2 were investigated using time-resolved x-ray absorption spectroscopy for Eu M5 edge. Through the pump-probe technique with synchrotron x-ray and Ti:sapphire laser pulses, a photoinduced valence transition was observed from Eu3+ to Eu2+. Because the lifetime of a photoinduced state can be up to 3 ns, a metastable state is considered to be realized. By comparing the experimental results with the theoretical calculations, the photoinduced valence transition between Eu 4f and conduction electrons was quantitatively evaluated.

  23. A Surface Science Approach to Unveiling the TiO<sub>2</sub> Photocatalytic Mechanism: Correlation between Photocatalytic Activity and Carrier Lifetime 査読有り

    Kenichi Ozawa, Susumu Yamamoto, Kazuhiko Mase, Iwao Matsuda

    e-Journal of Surface Science and Nanotechnology 17 (0) 130-147 2019年9月7日

    出版者・発行元:Surface Science Society Japan

    DOI: 10.1380/ejssnt.2019.130  

    ISSN:1348-0391

    eISSN:1348-0391

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    Establishing an accurate view of the photocatalytic mechanism of titanium dioxide (TiO2) has been a challenging task since the discovery of the Honda-Fujishima effect. Despite the great success of catalytic studies in elucidating the chemical and physical aspects of photocatalysis, many questions remain. A surface science approach, which is characterized by the use of atomically well-defined surfaces in precisely controlled environments, is a powerful tool to shed light on the fundamental mechanism, especially the dynamics of photoexcited carriers. In the present contribution, recent progress in photocatalytic research that correlates photocatalytic activity and carrier dynamics on rutile and anatase TiO2 is reviewed. A special focus, is placed on the lifetime of photoexcited carriers. We present a method to determine the carrier lifetime; pump-probe time-resolved soft X-ray photoelectron spectroscopy, utilizing an ultraviolet laser as a pump light and a synchrotron radiation as a probe light. The carrier lifetime is found to be linearly correlated with the photocatalync decomposition/desorption rate of acetic acid adsorbed on single-crystal TiO2 surfaces. The important role of a potential barrier on the TiO2 surface, which influences the carrier lifetime and the photo catalytic activity, is discussed.

  24. Mass transport in the PdCu phase structures during hydrogen adsorption and absorption studied by XPS under hydrogen atmosphere 査読有り

    Jiayi Tang, Susumu Yamamoto, Takanori Koitaya, Akitaka Yoshigoe, Takuma Tokunaga, Kozo Mukai, Iwao Matsuda, Jun Yoshinobu

    Applied Surface Science 480 419-426 2019年6月

    出版者・発行元:Elsevier {BV}

    DOI: 10.1016/j.apsusc.2019.02.180  

  25. CO2 Activation and Reaction on Zn-Deposited Cu Surfaces Studied by Ambient-Pressure X-ray Photoelectron Spectroscopy 査読有り

    Takanori Koitaya, Susumu Yamamoto, Yuichiro Shiozawa, Yuki Yoshikura, Masahiro Hasegawa, Jiayi Tang, Kaori Takeuchi, Kozo Mukai, Shinya Yoshimoto, Iwao Matsuda, Jun Yoshinobu

    ACS Catalysis 9 4539-4550 2019年5月3日

    出版者・発行元:American Chemical Society ({ACS})

    DOI: 10.1021/acscatal.9b00041  

  26. Direct Evidence of Interfacial Hydrogen Bonding in Proton-Electron Concerted 2D Organic Bilayer on Au Substrate 査読有り

    Susumu Yamamoto, Hiroyuki S. Kato, Akira Ueda, Shinya Yoshimoto, Yasuyuki Hirata, Jun Miyawaki, Kohei Yamamoto, Yoshihisa Harada, Hiroki Wadati, Hatsumi Mori, Jun Yoshinobu, Iwao Matsuda

    e-Journal of Surface Science and Nanotechnology 17 (0) 49-55 2019年4月27日

    出版者・発行元:Surface Science Society Japan

    DOI: 10.1380/ejssnt.2019.49  

    ISSN:1348-0391

    eISSN:1348-0391

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    Recent advances in the molecular design of organic materials have uncovered various novel functional properties. One of them is the coupling of proton dynamics and electrical conductivity, which can only be achieved in 3D organic crystals. However, reduction of dimensionality to two dimensions is essential in organic electronics application. In this study, we prepared and characterized a 2D organic bilayer with "proton-electron" concerted functionality on a solid surface. It consisted of catechol-fused bis (methylthio) tetrathiafulvalene (H(2)Cat-BMT-TTF) deposited onto an imidazole-terminated alkanethiolate self-assembled monolayer (Im-SAM) on a Au surface. Direct evidence of interfacial hydrogen bonding(H-bonding) was obtained by scanning tunneling microscopy(STM), infrared reflection absorption spectroscopy (IRAS), and near edge X-ray absorption fine structure(NEXAFS) spectroscopy. STM images showed the deposited H(2)Cat-BMT-TTF molecules as grains with the thickness of a single molecular layer. The OH stretching vibrational modes of H(2)Cat-BMT-TTF in the IRAS spectra showed a large red shift and substantial broadening upon adsorption on Im-SAM, indicating that the OH groups of H(2)Cat-BMT-TTF act as the H+ donor sites. The counterpart H+ acceptor sites were pinpointed by N K-edge NEXAFS. The pi* peak of the imino N atoms of the imidazole rings in Im-SAM shifted to higher energy upon the adsorption of H(2)Cat-BMT-TTF. Therefore, H-bonds form between the imino N atoms (H+ acceptor sites) of Im-SAM and the OH groups (H+ donor sites) of H(2)Cat-BMT-TTF. The present work is a steady step toward the realization of 2D organic functional materials, and the experimental methods adopted herein will serve as powerful tools for the detection of their functions.

  27. Segmented Undulator for Extensive Polarization Controls in ≤1 nm-rad Emittance Rings 査読有り

    I. Matsuda, S. Yamamoto, J. Miyawaki, T. Abukawa, T. Tanaka

    e-Journal of Surface Science and Nanotechnology 17 41-48 2019年4月27日

    DOI: 10.1380/ejssnt.2019.41  

    ISSN:1348-0391

  28. Semimetallicity of free-standing hydrogenated monolayer boron from MgB2 査読有り

    I. Tateishi, N. T. Cuong, C. A. S. Moura, M. Cameau, R. Ishibiki, A. Fujino, S. Okada, A. Yamamoto, M. Araki, S. Ito, S. Yamamoto, M. Niibe, T. Tokushima, D. E. Weibel, T. Kondo, M. Ogata, I. Matsuda

    Physical Review Materials 3 (2) 2019年2月22日

    出版者・発行元:American Physical Society (APS)

    DOI: 10.1103/physrevmaterials.3.024004  

    ISSN:2475-9953

    eISSN:2475-9953

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    Electronic states of a free-standing hydrogenated monolayer boron (HB) sheet were studied via soft X-ray spectroscopies at the B K-shell absorption edge and first-principles calculations. The HB sheet is semimetallic with electron and hole pockets at the Y and Γ points, respectively. The electron band results from the B-H-B bonds formed during synthesis from a MgB2 crystal, while the hole band is kept through the process and originates from a honeycomb lattice boron layer or borophene in MgB2. Our results suggest that the HB sheet is a promising two-dimensional material for realizing new boron-based or superconducting nanodevices.

  29. Enhanced Photoresponsivity of Fullerene in the Presence of Phthalocyanine: A Time-Resolved X-ray Photoelectron Spectroscopy Study of Phthalocyanine/C60/TiO2(110) 査読有り

    Kenichi Ozawa, Susumu Yamamoto, Marie D’angelo, Yuto Natsui, Naoya Terashima, Kazuhiko Mase, Iwao Matsuda

    The Journal of Physical Chemistry C 123 4388-4395 2019年2月21日

    出版者・発行元:American Chemical Society ({ACS})

    DOI: 10.1021/acs.jpcc.9b00186  

  30. Reversible low-temperature redox activity and selective oxidation catalysis derived from the concerted activation of multiple metal species on Cr and Rh-incorporated ceria catalysts 査読有り

    Susumu Yamamoto

    Physical Chemistry Chemical Physics 2019年

    DOI: 10.1039/c9cp04625a  

    ISSN:1463-9084

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    <p>The low-temperature redox activity of Cr and Rh-incorporated ceria catalyst was derived from the concerted activation of all three metal species.</p>

  31. Hydrogen adsorption and absorption on a Pd-Ag alloy surface studied using in-situ X-ray photoelectron spectroscopy under ultrahigh vacuum and ambient pressure 査読有り

    Tang, Jiayi, Yamamoto, Susumu, Koitaya, Takanori, Yoshikura, Yuki, Mukai, Kozo, Yoshimoto, Shinya, Matsuda, Iwao, Yoshinobu, Jun

    Applied Surface Science 463 1161-1167 2019年

    DOI: 10.1016/j.apsusc.2018.07.078  

  32. Resonant magneto-optical Kerr effect measurement system with polarization analysis using a high harmonic generation laser 査読有り

    Yamamoto, Sh., Oumbarek, D., Fujisawa, M., Someya, T., Takahashi, Y., Yamamoto, T., Ishii, N., Yaji, K., Yamamoto, S., Kanai, T., Okazaki, K., Kotsugi, M., Itatani, J., Shin, S., Matsuda, I.

    Journal of Electron Spectroscopy and Related Phenomena 222 68-73 2018年

    DOI: 10.1016/j.elspec.2017.09.001  

  33. Element Selectivity in Second-Harmonic Generation of GaFeO3 by a Soft-X-Ray Free-Electron Laser 査読有り

    Yamamoto, Sh., Omi, T., Akai, H., Kubota, Y., Takahashi, Y., Suzuki, Y., Hirata, Y., Yamamoto, K., Yukawa, R., Horiba, K., Yumoto, H., Koyama, T., Ohashi, H., Owada, S., Tono, K., Yabashi, M., Shigemasa, E., Yamamoto, S., Kotsugi, M., Wadati, H., Kumigashira, H., Arima, T., Shin, S., Matsuda, I.

    Physical Review Letters 120 (22) 2018年

    DOI: 10.1103/PhysRevLett.120.223902  

  34. Controlling the surface photovoltage on WSe2 by surface chemical modification 査読有り

    Liu, Ro-Ya, Ozawa, Kenichi, Terashima, Naoya, Natsui, Yuto, Feng, Baojie, Ito, Suguru, Chen, Wei-Chuan, Cheng, Cheng-Maw, Yamamoto, Susumu, Kato, Hiroo, Chiang, Tai-Chang, Matsuda, Iwao

    Applied Physics Letters 112 (21) 2018年

    DOI: 10.1063/1.5026351  

  35. Strong Hydrogen Bonds at the Interface between Proton-Donating and -Accepting Self-Assembled Monolayers on Au(111) 査読有り

    Kato, Hiroyuki S., Yoshimoto, Shinya, Ueda, Akira, Yamamoto, Susumu, Kanematsu, Yusuke, Tachikawa, Masanori, Mori, Hatsumi, Yoshinobu, Jun, Matsuda, Iwao

    Langmuir 34 (5) 2189-2197 2018年

    出版者・発行元:American Chemical Society ({ACS})

    DOI: 10.1021/acs.langmuir.7b03451  

  36. Correlation between Photocatalytic Activity and Carrier Lifetime: Acetic Acid on Single-Crystal Surfaces of Anatase and Rutile TiO2 査読有り

    Ozawa, Kenichi, Yamamoto, Susumu, Yukawa, Ryu, Liu, Ro-Ya, Terashima, Naoya, Natsui, Yuto, Kato, Hiroo, Mase, Kazuhiko, Matsuda, Iwao

    Journal of Physical Chemistry C 122 (17) 9562-9569 2018年

    出版者・発行元:American Chemical Society ({ACS})

    DOI: 10.1021/acs.jpcc.8b02259  

  37. Interfacial carrier dynamics of graphene on SiC, traced by the full-range time-resolved core-level photoemission spectroscopy 査読有り

    Someya, T., Fukidome, H., Endo, N., Takahashi, K., Yamamoto, S., Matsuda, I

    Applied Physics Letters 113 (5) 2018年

    DOI: 10.1063/1.5043223  

  38. Femtosecond resonant magneto-optical Kerr effect measurement on an ultrathin magnetic film in a soft X-ray free electron laser 査読有り

    Yamamoto, Shingo, Kubota, Yuya, Yamamoto, Kohei, Takahashi, Yoshinobu, Maruyama, Kohei, Suzuki, Yuta, Hobara, Rei, Fujisawa, Masami, Oshima, Daiki, Owada, Shigeki, Togashi, Tadashi, Tono, Kensuke, Yabashi, Makina, Hirata, Yasuyuki, Yamamoto, Susumu, Kotsugi, Masato, Wadati, Hiroki, Kato, Takeshi, Iwata, Satoshi, Shin, Shik, Matsuda, Iwao

    Japanese Journal of Applied Physics 57 (9) 2018年

    DOI: 10.7567/JJAP.57.09TD02  

  39. Enhancement of CO2 adsorption on oxygen-functionalized epitaxial graphene surface under near-ambient conditions 査読有り

    Yamamoto, Susumu, Takeuchi, Kaori, Hamamoto, Yuji, Liu, Ro-Ya, Shiozawa, Yuichiro, Koitaya, Takanori, Someya, Takashi, Tashima, Keiichiro, Fukidome, Hirokazu, Mukai, Kozo, Yoshimoto, Shinya, Suemitsu, Maki, Morikawa, Yoshitada, Yoshinobu, Jun, Matsuda, Iwao

    Physical Chemistry Chemical Physics 20 (29) 19532-19538 2018年

    出版者・発行元:Royal Society of Chemistry ({RSC})

    DOI: 10.1039/c8cp03251c  

  40. Interface electronic structure at the topological insulator-ferrimagnetic insulator junction 査読有り

    Kubota, Y., Murata, K., Miyawaki, J., Ozawa, K., Onbasli, M. C., Shirasawa, T., Feng, B., Yamamoto, Sh, Liu, R-Y, Yamamoto, S., Mahatha, S. K., Sheverdyaeva, P., Moras, P., Ross, C. A., Suga, S., Harada, Y., Wang, K. L., Matsuda, I.

    Journal of Physics-Condensed Matter 29 (5) 2017年

    出版者・発行元:IOP PUBLISHING LTD

    DOI: 10.1088/1361-648X/29/5/055002  

    ISSN:0953-8984

    eISSN:1361-648X

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    An interface electron state at the junction between a three-dimensional topological insulator film, Bi2Se3, and a ferrimagnetic insulator film, Y3Fe5O12 (YIG), was investigated by measurements of angle-resolved photoelectron spectroscopy and x-ray absorption magnetic circular dichroism. The surface state of the Bi2Se3 film was directly observed and localized 3d spin states of the Fe3+ in the YIG film were confirmed. The proximity effect is likely described in terms of the exchange interaction between the localized Fe 3d electrons in the YIG film and delocalized electrons of the surface and bulk states in the Bi2Se3 film.

  41. Determination of the element-specific complex permittivity using a soft x-ray phase modulator 査読有り

    Kubota, Y., Hirata, Y., Miyawaki, J., Yamamoto, S., Akai, H., Hobara, R., Yamamoto, Sh., Yamamoto, K., Someya, T., Takubo, K., Yokoyama, Y., Araki, M., Taguchi, M., Harada, Y., Wadati, H., Tsunoda, M., Kinjo, R., Kagamihata, A., Seike, T., Takeuchi, M., Tanaka, T., Shin, S., Matsuda, I.

    Physical Review B 96 (21) 2017年

    出版者・発行元:AMER PHYSICAL SOC

    DOI: 10.1103/PhysRevB.96.214417  

    ISSN:2469-9950

    eISSN:2469-9969

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    We report on directly determining the complex permittivity tensor using a method combining a developed light source from a segmented cross undulator of synchrotron radiation and the magneto-optical Kerr effect. The empirical permittivity, which carries the electronic and magnetic information of a material, has element specificity and has perfect confirmation using the quantum-mechanical calculation for itinerant electrons systems. These results help in understanding the interaction of light and matter, and they provide an interesting approach to seek the best materials as optical elements, for example, in extended-ultraviolet lithographic technologies or in state-of-the-art laser technologies.

  42. Capturing ultrafast magnetic dynamics by time-resolved soft x-ray magnetic circular dichroism 査読有り

    Takubo, Kou, Yamamoto, Kohei, Hirata, Yasuyuki, Yokoyama, Yuichi, Kubota, Yuya, Yamamoto, Shingo, Yamamoto, Susumu, Matsuda, Iwao, Shin, Shik, Seki, Takeshi, Takanashi, Koki, Wadati, Hiroki

    Applied Physics Letters 110 (16) 2017年

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.4981769  

    ISSN:0003-6951

    eISSN:1077-3118

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    Experiments of time-resolved x-ray magnetic circular dichroism (Tr-XMCD) and resonant x-ray scattering at a beamline BL07LSU in SPring-8 with a time-resolution of under 50 ps are presented. A micro-channel plate is utilized for the Tr-XMCD measurements at nearly normal incidence in both the partial electron and total fluorescence yield (PEY and TFY) modes at the L-2,L-3 absorption edges of the 3d transition-metals in the soft x-ray region. The ultrafast photo-induced demagnetization within 50 ps is observed on the dynamics of a magnetic material of FePt thin films, having a distinct threshold of the photon density. The spectrum in the PEY mode is less-distorted at both the L-2,L-3 edges compared with that in the TFY mode and has the potential to apply the sum rule analysis for XMCD spectra in pump-probed experiments. Published by AIP Publishing.

  43. Adsorption of CO2 on Graphene: A Combined TPD, XPS, and vdW-DF Study 査読有り

    Takeuchi, Kaori, Yamamoto, Susumu, Hamamoto, Yuji, Shiozawa, Yuichiro, Tashima, Keiichiro, Fukidome, Hirokazu, Koitaya, Takanori, Mukai, Kozo, Yoshimoto, Shinya, Suemitsu, Maki, Morikawa, Yoshitada, Yoshinobu, Jun, Matsuda, Iwao

    Journal of Physical Chemistry C 121 (5) 2807-2814 2017年

    出版者・発行元:AMER CHEMICAL SOC

    DOI: 10.1021/acs.jpcc.6b11373  

    ISSN:1932-7447

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    The adsorption of CO2 molecules on monolayer epitaxial graphene on a SiC(0001) surface at 30 K was investigated by temperature-programmed desorption and X-ray photoelectron spectroscopy. The desorption energy of CO, on graphene was :determined to be (30.1+25.1) +/- 1.5 kJ/mol at low coverages and approached the sublimation energy of dry ice (27-25 kJ/mol) with increasing the coverage. The adsorption of CO2 on graphene was thus categorized into physisorption, which was further supported by the binding energies of CO2 in core-level spectra. 'The adsoriptiOn states of CO2 on graphene Were theoretically examined by means of the van der WadIS density functional (vdW-DF) method that includes nonlocal correlation. The experimental desorption energy was successfully reproduced with high accuracy using vdW-DF calculations; the optB86b-vdW functional was found to be most appropriate to reproduCe the desorption energy in the present system.

  44. Suppression of supercollision carrier cooling in high mobility graphene on SiC(000(1)over-bar) 査読有り

    Someya, Takashi, Fukidome, Hirokazu, Watanabe, Hiroshi, Yamamoto, Takashi, Okada, Masaru, Suzuki, Hakuto, Ogawa, Yu, Iimori, Takushi, Ishii, Nobuhisa, Kanai, Teruto, Tashima, Keiichiro, Feng, Baojie, Yamamoto, Susumu, Itatani, Jiro, Komori, Fumio, Okazaki, Kozo, Shin, Shik, Matsuda, Iwao

    Physical Review B 95 (16) 2017年

    出版者・発行元:AMER PHYSICAL SOC

    DOI: 10.1103/PhysRevB.95.165303  

    ISSN:2469-9950

    eISSN:2469-9969

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    Graphene, a two-dimensional carbon crystal with a gas of massless Dirac fermions, has promise as a material that is useful in photonic and optoelectronic devices. A comprehensive understanding of carrier cooling in photoexcited graphene is necessary for their applications, however, as competing cooling processes, electronphonon scattering, and supercollisions, complicate the problem. Specifically, in energy harvesting, supercollision promotes further carrier cooling and, therefore, leads to lower efficiency, placing doubt on the feasibility of device applications. Herewe present evidence of suppressed supercollisions in trilayer graphene on a SiC(000 (1) over bar) substrate by directly observing photoexcited carriers and numerically analyzing a phenomenological two-temperature model. Knowing that supercollisions restrict the capabilities of graphene-based devices, our results provide a breakthrough for improving their performance.

  45. Polarization dependence of resonant magneto-optical Kerr effect measured by two types of figure-8 undulators 査読有り

    Kubota, Y., Yamamoto, Sh., Someya, T., Hirata, Y., Takubo, K., Araki, M., Fujisawa, M., Yamamoto, K., Yokoyama, Y., Taguchi, M., Yamamoto, S., Tsunoda, M., Wadati, H., Shin, S., Matsuda, I.

    Journal of Electron Spectroscopy and Related Phenomena 220 17-20 2017年

    出版者・発行元:ELSEVIER SCIENCE BV

    DOI: 10.1016/j.elspec.2016.11.008  

    ISSN:0368-2048

    eISSN:1873-2526

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    The resonant magneto-optical Kerr effect of an Fe nanofilm at the L-edge was investigated by theoretically and experimentally using the polarization controlled undulator. Large values of the Kerr rotation angle (Be) were measured at the L-2 and L-3 absorption edges for both of s- and p-polarized incident lights. Furthermore, the sign changes of OK depending on the photon energy and the polarization of incident light were also observed. (C) 2016 Elsevier B.V. All rights reserved.

  46. L-edge resonant magneto-optical Kerr effect of a buried Fe nanofilm 査読有り

    Kubota, Y., Taguchi, M., Akai, H., Yamamoto, Sh., Someya, T., Hirata, Y., Takubo, K., Araki, M., Fujisawa, M., Yamamoto, K., Yokoyama, Y., Yamamoto, S., Tsunoda, M., Wadati, H., Shin, S., Matsuda, I.

    Physical Review B 96 (13) 2017年

    出版者・発行元:AMER PHYSICAL SOC

    DOI: 10.1103/PhysRevB.96.134432  

    ISSN:2469-9950

    eISSN:2469-9969

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    The Fe L-edge resonant magneto-optical Kerr effect of a buried Fe nanofilm was investigated by rotating-analyzer ellipsometry and the results were compared with those from three theoretical simulations. The reversal of the Kerr rotation angle theta(K) between the L-3 and L-2 edges, observed in the experiment, was consistent with classical electromagnetic simulation using empirical optical constants. The wspectral theta(K) feature was reproduced by the first-principles calculation of the KKR-Green's function method on the itinerant electronic system. The demonstration indicates that spectra of the L-edge resonant MOKE can be understood in terms of both the macroscopic and microscopic pictures.

  47. Time-resolved soft X-ray core-level photoemission spectroscopy at 880 degrees C using the pulsed laser and synchrotron radiation and the pulse heating current 査読有り

    Abukawa, T., Yamamoto, S., Yukawa, R., Kanzaki, S., Mukojima, K., Matsuda, I.

    Surface Science 656 43-47 2017年

    出版者・発行元:ELSEVIER SCIENCE BV

    DOI: 10.1016/j.susc.2016.09.006  

    ISSN:0039-6028

    eISSN:1879-2758

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    We developed a time-resolved photoemission spectroscopy system for tracking the temporal variation in an electronic state of a heated sample. Our pump-probe method used laser and synchrotron radiation pulses on a silicon surface that was heated by a synchronized pulse current that did not interfere with the measurements. The transient surface photovoltage effect on the Si 2p core spectra was measured from room temperature to 880 degrees C and was found to be consistent with the thermal carrier distributions in silicon crystals at the corresponding temperatures. This versatile technique may have applications studying molecular dynamics on high temperature surfaces such as in catalytic reactions.

  48. Investigation of Photo-carrier Generation Processes of Organic Solar Cells Using Time Resolved X-ray Photoelectron Spectroscopy 査読有り

    SAKURAI, TAKEAKI, Ozawa, Kenichi, Yukawa, Ryu, K.Akikubo, K.Takeuchi, S.Yamamoto, Matsuda, Iwao

    Extended Abstracts of the 2016 International Conference on Solid State Devices and Materials (SSDM) 277-278 2016年9月

  49. Tailoring Photovoltage Response at SrRuO3/SrTiO3 Heterostructures 査読有り

    Yukawa, Ryu, Yamamoto, Susumu, Akikubo, Kazuma, Takeuchi, Kaori, Ozawa, Kenichi, Kumigashira, Hiroshi, Matsuda, Iwao

    Advanced Materials Interfaces 3 (22) 1600527-n/a 2016年

    出版者・発行元:WILEY

    DOI: 10.1002/admi.201600527  

    ISSN:2196-7350

  50. Phonon-dressed two-dimensional carriers on the ZnO surface 査読有り

    Yukawa, R., Ozawa, K., Yamamoto, S., Iwasawa, H., Shimada, K., Schwier, E. F., Yoshimatsu, K., Kumigashira, H., Namatame, H., Taniguchi, M., Matsuda, I.

    Physical Review B 94 (16) 2016年

    出版者・発行元:AMER PHYSICAL SOC

    DOI: 10.1103/PhysRevB.94.165313  

    ISSN:2469-9950

    eISSN:2469-9969

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    Two-dimensional (2D) metallic states formed on the ZnO(10 (1) over bar0) surface by hydrogen adsorption have been investigated using angle-resolved photoelectron spectroscopy (ARPES). The observed metallic state is characterized by a peak-dip-hump structure at just below the Fermi level and a long tail structure extending up to 600 meV in binding energy. The peak and hump positions are separated by about 70 meV, a value close to the excitation energy of longitudinal optical (LO) phonons. Spectral functions formulated on the basis of the 2D electron-phonon coupling well reproduce the ARPES intensity distribution of the metallic states. This spectral analysis suggests that the 2D electrons accumulated on the ZnO surface couple to the LO phonons and that this coupling is the origin of the anomalous long tail. Our results indicate that the 2D electrons at the ZnO surface are described as the electron liquid model.

  51. What Determines the Lifetime of Photoexcited Carriers on TiO2 Surfaces? 査読有り

    Ozawa, Kenichi, Yamamoto, Susumu, Yukawa, Ryu, Liu, Roya, Emori, Masato, Inoue, Koki, Higuchi, Taku, Sakama, Hiroshi, Mase, Kazuhiko, Matsuda, Iwao

    Journal of Physical Chemistry C 120 (51) 29283-29289 2016年

    出版者・発行元:American Chemical Society ({ACS})

    DOI: 10.1021/acs.jpcc.6b10136  

    ISSN:1932-7447

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    Pump-probe time-resolved X-ray photoelectron spectroscopy measurements have been carried out to comparatively assess the relaxation process of the photoexcited states on pristine and Ar+-sputtered TiO2(110) surfaces and a TiO2(011)-2 x 1 surface, on which the accumulation-type space charge layers are developed. Ultraviolet laser irradiation induces a surface photovoltage (SPV) of around 0.1 eV. The SPV relaxation time on pristine TiO2(110) is determined to be approximately 100 ns and is doubled on the sputtered surface. In contrast, a much shorter time of 1 ns is observed on TiO2(011)-2 x 1. The difference in the relaxation time on the two TiO2(110) surfaces is explained by differences in the O vacancy density on the surface as well as the barrier height of the surface potential for the photoexcited holes. A large hole capture cross section of a state characteristic of TiO2(011)-2 x 1 is, on the other hand, responsible for the fast SPV relaxation on this surface.

  52. Real-Time Observation of Reaction Processes of CO2 on Cu(997) by Ambient-Pressure X-ray Photoelectron Spectroscopy 査読有り

    Koitaya, Takanori, Yamamoto, Susumu, Shiozawa, Yuichiro, Takeuchi, Kaori, Liu, Ro-Ya, Mukai, Kozo, Yoshimoto, Shinya, Akikubo, Kazuma, Matsuda, Iwao, Yoshinobu, Jun

    Topics in Catalysis 59 (5-7) 526-531 2016年

    出版者・発行元:SPRINGER/PLENUM PUBLISHERS

    DOI: 10.1007/s11244-015-0535-1  

    ISSN:1022-5528

    eISSN:1572-9028

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    The reaction of CO2 on the vicinal Cu(997) surface at 340 K under CO2 gas pressure of 0.8 mbar was investigated by ambient pressure X-ray photoelectron spectroscopy. A main reaction product on the surface was identified as carbonate (CO3), based on estimation of the composition ratio of oxygen to carbon. CO3 was produced on the surface through the reaction of CO2 with oxygen formed from CO2 dissociation. The amount of adsorbed CO3 was increased and saturated as time elapsed. After saturation of adsorbed CO3, atomic oxygen appeared on the surface, indicating that CO2 dissociation into CO and O continued to take place. The present study shows the importance of CO3 intermediate in the CO2 chemistry on stepped Cu surfaces.

  53. Capturing transiently charged states at the C-60/TiO2(110) interface by time-resolved soft X-ray photoelectron spectroscopy 査読有り

    Ozawa, Kenichi, Yamamoto, Susumu, Yukawa, Ryu, Akikubo, Kazuma, Emori, Masato, Sakama, Hiroshi, Matsuda, Iwao

    Organic Electronics 31 98-103 2016年

    出版者・発行元:ELSEVIER SCIENCE BV

    DOI: 10.1016/j.orgel.2016.01.020  

    ISSN:1566-1199

    eISSN:1878-5530

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    Time-resolved soft X-ray photoelectron spectroscopy is utilized to determine an energy level alignment and the photoexcited carrier dynamics at a C-60/TiO2(110) interface. The interface electronic structure is characterized by a type II junction, which favors an injection of photoexcited electrons from C-60 to TiO2. Ultraviolet (UV) laser pulse irradiation induces transient shifts of both C 1s and Ti 2p core levels towards the higher binding energies. These energy shifts are caused by a laser-induced charge transfer between the C-60 layer and the TiO2(110) surface. Upon UV absorption, valence electrons of C-60 are promoted to unoccupied levels, followed by a resonant transfer to TiO2, leaving C-60 in a cationized state. On the TiO2(110) side, the electrons are injected into the conduction band to raise the carrier density so that downward bending of the TiO2 band is induced. The UV-excited states of C-60 and TiO2 have sufficiently longer lifetime than the lifetime of the electron-hole pairs in solid C-60. The C-60/TiO2(110) interface is, thus, proved to be efficient for separating the electronehole pairs generated within the C-60 layer. (c) 2016 Elsevier B.V. All rights reserved.

  54. Anisotropic effective mass approximation model to calculate multiple subband structures at wide-gap semiconductor surfaces: Application to accumulation layers of SrTiO3 and ZnO 査読有り

    R. Yukawa, K. Ozawa, S. Yamamoto, R. -Y. Liu, I. Matsuda

    SURFACE SCIENCE 641 224-230 2015年11月

    出版者・発行元:ELSEVIER SCIENCE BV

    DOI: 10.1016/j.susc.2015.07.007  

    ISSN:0039-6028

    eISSN:1879-2758

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    We propose a simplified theoretical model that well reproduces the dispersion curves of the multiple subbands in a two-dimensional electron gas in the accumulation layer at the surfaces of wide-gap semiconductors. The electronic band structures containing multiple subbands with different orbital characteristics are derived by self-consistently solving the Poisson-Schrodinger equations with anisotropic effective mass approximations. Calculations were carried out on the two-dimensional electron gas states formed at the surfaces of SrTiO3 and ZnO for comparison. The calculated subband structures at the SrTiO3 surface were in excellent agreement with available angle-resolved photoelectron spectroscopy data, confirming the validity of the present model. The calculations further indicate the existence of a high electron density, exceeding 2 x 10(21) cm(-3) and a high electric field of 20 MVcm(-1) at the surface. Moreover, photoelectron-escape depths are discussed quantitatively and photoelectrons from the first subband are found to dominate the total photoelectron intensity in the spectra. (C) 2015 Elsevier B.V. All rights reserved.

  55. Ultrafast spin-switching of a ferrimagnetic alloy at room temperature traced by resonant magneto-optical Kerr effect using a seeded free electron laser 査読有り

    Sh. Yamamoto, M. Taguchi, T. Someya, Y. Kubota, S. Ito, H. Wadati, M. Fujisawa, F. Capotondi, E. Pedersoli, M. Manfredda, L. Raimondi, M. Kiskinova, J. Fujii, P. Moras, T. Tsuyama, T. Nakamura, T. Kato, T. Higashide, S. Iwata, S. Yamamoto, S. Shin, I. Matsuda

    REVIEW OF SCIENTIFIC INSTRUMENTS 86 (8) 2015年8月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.4927828  

    ISSN:0034-6748

    eISSN:1089-7623

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    Ultrafast magnetization reversal of a ferrimagnetic metallic alloy GdFeCo was investigated by time-resolved resonant magneto-optical Kerr effect measurements using a seeded free electron laser. The GdFeCo alloy was pumped by a linearly polarized optical laser pulse, and the following temporal evolution of the magnetization of Fe in GdFeCo was element-selectively traced by a probe free electron laser pulse with a photon energy tuned to the Fe M-edge. The results have been measured using rotating analyzer ellipsometry method and confirmed magnetization switching caused by ultrafast heating. (C) 2015 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.

  56. Development of an electromagnetic phase shifter using a pair of cut-core coils for a cross undulator 査読有り

    I. Matsuda, A. Kuroda, J. Miyawaki, Y. Kosegawa, S. Yamamoto, T. Seike, T. Bizen, Y. Harada, T. Tanaka, H. Kitamura

    NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT 767 296-299 2014年12月

    出版者・発行元:ELSEVIER SCIENCE BV

    DOI: 10.1016/j.nima.2014.08.037  

    ISSN:0168-9002

    eISSN:1872-9576

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    This paper describes the development of a phase shifter that can be used in cross undulators for fast polarization switching. The phase shifter is composed of a pair of cut-core coils and a thin-walled stainless steel duct. Evaluation of the magnetic fields of the phase shifter indicates that the switching frequency of this simple and low-cost device can exceed 30 Hz. (C) 2014 Elsevier B.V. All rights reserved.

  57. Electron-hole recombination on ZnO(0001) single-crystal surface studied by time-resolved soft X-ray photoelectron spectroscopy 査読有り

    R. Yukawa, S. Yamamoto, K. Ozawa, M. Emori, M. Ogawa, Sh Yamamoto, K. Fujikawa, R. Hobara, S. Kitagawa, H. Daimon, H. Sakama, I. Matsuda

    APPLIED PHYSICS LETTERS 105 (15) 2014年10月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.4897934  

    ISSN:0003-6951

    eISSN:1077-3118

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    Time-resolved soft X-ray photoelectron spectroscopy (PES) experiments were performed with time scales from picoseconds to nanoseconds to trace relaxation of surface photovoltage on the ZnO(0001) single crystal surface in real time. The band diagram of the surface has been obtained numerically using PES data, showing a depletion layer which extends to 1 mu m. Temporal evolution of the photovoltage effect is well explained by a recombination process of a thermionic model, giving the photoexcited carrier lifetime of about 1 ps at the surface under the flat band condition. This lifetime agrees with a temporal range reported by the previous time-resolved optical experiments. (C) 2014 AIP Publishing LLC.

  58. Non-linear kinetic model for oscillatory relaxation of the photovoltage effect on a Si(111)7 x 7 surface 査読有り

    M. Ogawa, R. -Y. Liu, C. -H. Lin, S. Yamamoto, R. Yukawa, R. Hobara, S. -J. Tang, I. Matsuda

    SURFACE SCIENCE 624 70-75 2014年6月

    出版者・発行元:ELSEVIER SCIENCE BV

    DOI: 10.1016/j.susc.2014.01.014  

    ISSN:0039-6028

    eISSN:1879-2758

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    Oscillatory relaxation of surface photovoltage has been observed by time-resolved photoemission spectroscopy on a Si(111)7 x 7 surface with a temporal period of several tens of nanoseconds. The oscillation was reproduced by solving non-linear Master equations that describe surface recombination of electron-hole pairs associated with the formation of exciton-like states at the surface. Appearance of non-linear phenomena is naturally expected by the model when high density photo-excited carriers are generated by the high power laser pulse. (c) 2014 Elsevier B.V. All rights reserved.

  59. Electron-Hole Recombination Time at TiO2 Single-Crystal Surfaces: Influence of Surface Band Bending 査読有り

    Kenichi Ozawa, Masato Emori, Susumu Yamamoto, Ryu Yukawa, Shingo Yamamoto, Rei Hobara, Kazushi Fujikawa, Hiroshi Sakama, Iwao Matsuda

    JOURNAL OF PHYSICAL CHEMISTRY LETTERS 5 (11) 1953-1957 2014年6月

    出版者・発行元:AMER CHEMICAL SOC

    DOI: 10.1021/jz500770c  

    ISSN:1948-7185

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    Photocatalytic activity is determined by the transport property of photoexcited carriers from the interior to the surface of photocatalysts. Because the carrier dynamics is influenced by a space charge layer (SCL) in the subsurface region, an understanding of the effect of the potential barrier of the SCL on the carrier behavior is essential. Here we have investigated the relaxation time of the photoexcited carriers on single-crystal anatase and rutile TiO2 surfaces by time-resolved photoelectron spectroscopy and found that carrier recombination, taking a nanosecond time scale at room temperature, is strongly influenced by the barrier height of the SCL. Under the flat-band condition, which is realized in nanometer-sized photocatalysts, the carriers have a longer lifetime on the anatase surface than the rutile one, naturally explaining the higher photocatalytic activity for anatase than rutile.

  60. Observing hot carrier distribution in an n-type epitaxial graphene on a SiC substrate 査読有り

    T. Someya, H. Fukidome, Y. Ishida, R. Yoshida, T. Iimori, R. Yukawa, K. Akikubo, Sh Yamamoto, S. Yamamoto, T. Yamamoto, T. Kanai, K. Funakubo, M. Suemitsu, J. Itatani, F. Komori, S. Shin, I. Matsuda

    APPLIED PHYSICS LETTERS 104 (16) 2014年4月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.4871381  

    ISSN:0003-6951

    eISSN:1077-3118

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    Hot carrier dynamics in the Dirac band of n-type epitaxial graphene on a SiC substrate were traced in real time using femtosecond-time-resolved photoemission spectroscopy. The spectral evolution directly reflects the energetically linear density of states superimposed with a Fermi-Dirac distribution. The relaxation time is governed by the internal energy dissipation of electron-electron scattering, and the observed electronic temperature indicates cascade carrier multiplication. (C) 2014 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.

  61. Erratum: Relaxations of the surface photovoltage effect on the atomically controlled semiconductor surfaces studied by time-resolved photoemission spectroscopy (Physical Review B - Condensed Matter and Materials Physics (2013) 88 (165313))

    M. Ogawa, S. Yamamoto, K. Fujikawa, R. Hobara, R. Yukawa, Sh Yamamoto, S. Kitagawa, D. Pierucci, M. G. Silly, C. H. Lin, R. Y. Liu, H. Daimon, F. Sirotti, S. J. Tang, I. Matsuda

    Physical Review B - Condensed Matter and Materials Physics 89 (11) 2014年3月24日

    DOI: 10.1103/PhysRevB.89.119904  

    ISSN:1098-0121

    eISSN:1550-235X

  62. Erratum: Oscillatory relaxation of surface photovoltage on a silicon surface (Physical Review B - Condensed Matter and Materials Physics (2013) 87 (235308))

    M. Ogawa, S. Yamamoto, R. Yukawa, R. Hobara, C. H. Lin, R. Y. Liu, S. J. Tang, I. Matsuda

    Physical Review B - Condensed Matter and Materials Physics 89 (11) 2014年3月24日

    DOI: 10.1103/PhysRevB.89.119903  

    ISSN:1098-0121

    eISSN:1550-235X

  63. New soft X-ray beamline BL07LSU at SPring-8 査読有り

    Susumu Yamamoto, Yasunori Senba, Takashi Tanaka, Haruhiko Ohashi, Toko Hirono, Hiroaki Kimura, Masami Fujisawa, Jun Miyawaki, Ayumi Harasawa, Takamitsu Seike, Sunao Takahashi, Nobuteru Nariyama, Tomohiro Matsushita, Masao Takeuchi, Toru Ohata, Yukito Furukawa, Kunikazu Takeshita, Shunji Goto, Yoshihisa Harada, Shik Shin, Hideo Kitamura, Akito Kakizaki, Masaharu Oshima, Iwao Matsuda

    JOURNAL OF SYNCHROTRON RADIATION 21 352-365 2014年3月

    出版者・発行元:WILEY-BLACKWELL

    DOI: 10.1107/S1600577513034796  

    ISSN:0909-0495

    eISSN:1600-5775

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    A new soft X-ray beamline, BL07LSU, has been constructed at SPring-8 to perform advanced soft X-ray spectroscopy for materials science. The beamline is designed to achieve high energy resolution (E/Delta E&gt; 10000) and high photon flux [&gt;10(12) photons s(-1) (0.01% bandwidth)(-1)] in the photon energy range 250-2000 eV with controllable polarization. To realise this state-of-the-art performance, a novel segmented cross undulator was developed and adopted as a light source. The details of the undulator light source and beamline monochromator design are described. The achieved performance of the beamline, such as the photon flux, energy resolution and the state of polarization, is reported.

  64. Observation of a giant Kerr rotation in a ferromagnetic transition metal by M-edge resonant magneto-optic Kerr effect 査読有り

    Sh. Yamamoto, M. Taguchi, M. Fujisawa, R. Hobara, S. Yamamoto, K. Yaji, T. Nakamura, K. Fujikawa, R. Yukawa, T. Togashi, M. Yabashi, M. Tsunoda, S. Shin, I. Matsuda

    PHYSICAL REVIEW B 89 (6) 2014年2月

    出版者・発行元:AMER PHYSICAL SOC

    DOI: 10.1103/PhysRevB.89.064423  

    ISSN:1098-0121

    eISSN:1550-235X

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    The M-edge resonant magneto-optical Kerr effect of a transition metal film was measured using rotating analyzer ellipsometry and compared with theoretical calculations based on resonant scattering theory. A large Kerr rotation angle of over 10 degrees was observed at room temperature.

  65. Relaxations of the surface photovoltage effect on the atomically controlled semiconductor surfaces studied by time-resolved photoemission spectroscopy 査読有り

    M. Ogawa, S. Yamamoto, K. Fujikawa, R. Hobara, R. Yukawa, Sh. Yamamoto, S. Kitagawa, D. Pierucci, M. G. Silly, C-H Lin, R-Y Liu, H. Daimon, F. Sirotti, S-J Tang, I. Matsuda

    PHYSICAL REVIEW B 88 (16) 2013年10月

    出版者・発行元:AMER PHYSICAL SOC

    DOI: 10.1103/PhysRevB.88.165313  

    ISSN:1098-0121

    eISSN:1550-235X

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    We have systematically investigated relaxation of the surface photovoltage effect on the atomically controlled In/Si(111) surfaces with distinctive surface states and different amounts of the surface band bending. The temporal variations were traced in real time by time-resolved photoemission spectroscopy using soft x-ray synchrotron radiation. The relaxation is found to be temporally limited by two steps of the carrier transfer from the bulk to the surface: the tunneling process at a delay time &lt;= 100 ns and the thermionic process on the following time scale (&gt;= 100 ns). Crossover of the two mechanisms can be understood by breakdown of the quantum tunneling regime by the increase in width of the space-charge layer during the relaxation.

  66. Oscillatory relaxation of surface photovoltage on a silicon surface 査読有り

    M. Ogawa, S. Yamamoto, R. Yukawa, R. Hobara, C. H. Lin, R. Y. Liu, S. J. Tang, I. Matsuda

    Physical Review B - Condensed Matter and Materials Physics 87 (23) 2013年6月17日

    DOI: 10.1103/PhysRevB.87.235308  

    ISSN:1098-0121 1550-235X

    eISSN:1550-235X

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    Time-resolved measurement of photoemission spectroscopy was made to trace a change of surface potential after the surface photovoltage effect on a Si(111) 7×7 surface. Two relaxation processes were found with decay times of nanoseconds and hundreds of nanoseconds, which are explained in terms of the tunneling and the thermionic relaxation schemes, respectively. At the high laser power density, the relaxation has become oscillatory with a temporal period of several tens of nanoseconds. © 2013 American Physical Society.

  67. Electronic structure of the hydrogen-adsorbed SrTiO3(001) surface studied by polarization-dependent photoemission spectroscopy 査読有り

    R. Yukawa, S. Yamamoto, K. Ozawa, M. D'Angelo, M. Ogawa, M. G. Silly, F. Sirotti, I. Matsuda

    PHYSICAL REVIEW B 87 (11) 2013年3月

    出版者・発行元:AMER PHYSICAL SOC

    DOI: 10.1103/PhysRevB.87.115314  

    ISSN:1098-0121

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    The metallic band structure of the hydrogen-adsorbed SrTiO3(001) surface is studied by polarization-dependent photoemission spectroscopy measurements. With the dipole-transition selection arguments, we attributed the metallic peaks into the Ti 3d(xz), 3d(yz), and 3d(xy) bands. These t(2g) bands are partially filled with electrons upon H-induced downward band bending at the surface. Energy splitting of the Ti 3d t(2g) bands is considered to be induced by a quantum confinement along the surface normal (z) direction. The metallic peaks are accompanied by the incoherent states induced by many-body interactions, which likely indicates that the electronic system forms a two-dimensional liquid phase. Also emerged by H exposure are an in-gap state and a sigma(O - H) state. The possible origin and the feature of these states are discussed from the polarization dependence of the photoemission intensity. DOI:10.1103/PhysRevB.87.115314

  68. Time-Resolved Photoelectron Spectroscopies Using Synchrotron Radiation: Past, Present, and Future 査読有り

    Susumu Yamamoto, Iwao Matsuda

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 82 (2) 2013年2月

    出版者・発行元:PHYSICAL SOC JAPAN

    DOI: 10.7566/JPSJ.82.021003  

    ISSN:0031-9015

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    We present a review on a variety of time-resolved photoelectron spectroscopies (PES) using synchrotron radiation, which can reveal dynamical processes in a wide range of time scale from second to sub-femtosecond by taking advantage of time resolution of detectors or light sources or electronic transitions in matter. As a representative example of light source-based time-resolved PES, the newly developed time-resolved PES system at SPring-8 BL07LSU is introduced along with studies of carrier dynamics on a semiconductor surface. In addition, future direction of time-resolved PES furthered by the recent advances of light sources such as x-ray free electron laser will be discussed.

  69. Highly Compressed Two-Dimensional Form of Water at Ambient Conditions 査読有り

    Sarp Kaya, Daniel Schlesinger, Susumu Yamamoto, John T. Newberg, Hendrik Bluhm, Hirohito Ogasawara, Tom Kendelewicz, Gordon E. Brown, Lars G. M. Pettersson, Anders Nilsson

    SCIENTIFIC REPORTS 3 2013年1月

    出版者・発行元:NATURE PUBLISHING GROUP

    DOI: 10.1038/srep01074  

    ISSN:2045-2322

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    The structure of thin-film water on a BaF2(111) surface under ambient conditions was studied using x-ray absorption spectroscopy from ambient to supercooled temperatures at relative humidity up to 95%. No hexagonal ice-like structure was observed in spite of the expected templating effect of the lattice-matched (111) surface. The oxygen K-edge x-ray absorption spectrum of liquid thin-film water on BaF2 exhibits, at all temperatures, a strong resemblance to that of high-density phases for which the observed spectroscopic features correlate linearly with the density. Surprisingly, the highly compressed, high-density thin-film liquid water is found to be stable from ambient (300 K) to supercooled (259 K) temperatures, although a lower-density liquid would be expected at supercooled conditions. Molecular dynamics simulations indicate that the first layer water on BaF2(111) is indeed in a unique local structure that resembles high-density water, with a strongly collapsed second coordination shell.

  70. Elucidation of Rh-Induced In-Gap States of Rh:SrTiO3 Visible-Light-Driven Photocatalyst by Soft X-ray Spectroscopy and First-Principles Calculations 査読有り

    Seiji Kawasaki, Kazuto Akagi, Kan Nakatsuji, Susumu Yamamoto, Iwao Matsuda, Yoshihisa Harada, Jun Yoshinobu, Fumio Komori, Ryota Takahashi, Mikk Lippmaa, Chikako Sakai, Hideharu Niwa, Masaharu Oshima, Katsuya Iwashina, Akihiko Kudo

    JOURNAL OF PHYSICAL CHEMISTRY C 116 (46) 24445-24448 2012年11月

    出版者・発行元:AMER CHEMICAL SOC

    DOI: 10.1021/jp3082529  

    ISSN:1932-7447

    eISSN:1932-7455

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    The occupied and unoccupied in-gap electronic states of a Rh-doped SrTiO3 photocatalyst were investigated by X-ray emission spectroscopy and X-ray absorption spectroscopy for different Rh impurity valence states and doping levels. An unoccupied midgap Rh4+ acceptor state was found 1.5 eV below the SrTiO3 conduction band minimum. Both Rh4+ and Rh3+ dopants were found to have an occupied donor level close to the valence band maximum of SrTiO3. The density of states obtained from first-principles calculations show that all observed spectral features can be assigned to electronic states Of substitutional Rh at the Ti site and that Rh:SrTiO3 is an unusual titanate compound with a characteristic p-type, electronic structure. The Rh doping results in a large decrease of the bandgap energy, making Rh:SrTiO3 an attractive material for use as a visible-light-driven H-2-evolving photocatalyst in a solar water splitting reaction.

  71. Hydrogen-Induced Surface Metallization of SrTiO3(001) 査読有り

    M. D'Angelo, R. Yukawa, K. Ozawa, S. Yamamoto, T. Hirahara, S. Hasegawa, M. G. Silly, F. Sirotti, I. Matsuda

    PHYSICAL REVIEW LETTERS 108 (11) 2012年3月

    出版者・発行元:AMER PHYSICAL SOC

    DOI: 10.1103/PhysRevLett.108.116802  

    ISSN:0031-9007

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    Surface metallization of SrTiO3(001) by hydrogen adsorption is experimentally confirmed for the first time by photoemission spectroscopy and surface conductivity measurements. The metallic state is assigned to a quantized state in the space-charge layer induced by electron doping from hydrogen atoms. The measured two-dimensional (2D) conductivity is well above the 2D Ioffe-Regel limit indicating that the system is in a metallic conduction regime. The mean free path of the surface electron is estimated to be several nanometers at room temperature.

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

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

    REVIEW OF SCIENTIFIC INSTRUMENTS 83 (2) 2012年2月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.3687428  

    ISSN:0034-6748

    eISSN:1089-7623

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    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. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3687428]

  73. New soft X-ray beamline BL07LSU for long undulator of SPring-8: Design and status 査読有り

    Y. Senba, S. Yamamoto, H. Ohashi, I. Matsuda, M. Fujisawa, A. Harasawa, T. Okuda, S. Takahashi, N. Nariyama, T. Matsushita, T. Ohata, Y. Furukawa, T. Tanaka, K. Takeshita, S. Goto, H. Kitamura, A. Kakizaki, M. Oshima

    NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT 649 (1) 58-60 2011年9月

    出版者・発行元:ELSEVIER SCIENCE BV

    DOI: 10.1016/j.nima.2010.12.242  

    ISSN:0168-9002

    eISSN:1872-9576

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    We report the design and current status of a soft X-ray beamline BL07LSU with a 27-m-long undulator at SPring-8. The long undulator consists of eight figure-8 undulator segments, and generates circularly and linearly polarized soft X-rays. This beamline covers a wide energy range (250-2000 eV) with both high energy resolution and high photon flux. Commissioning of this beamline was started with only four undulator segments since October 2009. The resolving power was evaluated to be 10,000 at 401 eV by total-ion yield X-ray absorption spectra of N-2. (C) 2011 Elsevier B.V. All rights reserved.

  74. Autocatalytic Surface Hydroxylation of MgO(100) Terrace Sites Observed under Ambient Conditions 査読有り

    John T. Newberg, David E. Starr, Susumu Yamamoto, Sarp Kaya, Tom Kendelewicz, Erin R. Mysak, Soeren Porsgaard, Miquel B. Salmeron, Gordon E. Brown, Anders Nisson, Hendrik Bluhm

    JOURNAL OF PHYSICAL CHEMISTRY C 115 (26) 12864-12872 2011年7月

    出版者・発行元:AMER CHEMICAL SOC

    DOI: 10.1021/jp200235v  

    ISSN:1932-7447

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    We have investigated the reaction of water vapor with the MgO(100) surface using ambient pressure X-ray photoelectron spectroscopy (AP-XPS), which permits the study of the chemical composition of the MgO/water vapor interface at p(H2O) in the Torr range. Water dissociation on thin MgO(100) films of 4-5.5 monolayers (ML) grown on Ag(100) was studied under isobaric conditions at p(H2O) ranging from 0.005 to 0.5 Torr and temperatures from 380 to -10 degrees C, up to a maximum relative humidity (RH) of 20%. At RH &lt; 0.01% dissociative adsorption occurs only at defect sites (similar to 0.08 ML) while terrace sites remain unreactive toward water dissociation. In the range 0.01 &lt; RH &lt; 0.1% there is an abrupt onset of dissociative adsorption at terrace sites which saturates at 1 ML at 0.1% RH, and is accompanied by an increase in molecular water adsorption. At 20% RH there is similar to 1 ML of molecularly adsorbed water interacting with a fully hydroxylated interface on MgO(100). The observed onset of hydroxylation near 0.01% RH is suggested to be due to water molecules aggregating at the surface, leading to an autocatalytic dissociation of water at MgO(100) terrace sites.

  75. Formation of hydroxyl and water layers on MgO films studied with ambient pressure XPS 査読有り

    John T. Newberg, David E. Starr, Susumu Yamamoto, Sarp Kaya, Tom Kendelewicz, Erin R. Mysak, Soeren Porsgaard, Miquel B. Salmeron, Gordon E. Brown, Anders Nilsson, Hendrik Bluhm

    SURFACE SCIENCE 605 (1-2) 89-94 2011年1月

    出版者・発行元:ELSEVIER SCIENCE BV

    DOI: 10.1016/j.susc.2010.10.004  

    ISSN:0039-6028

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    To understand the interaction of water with MgO(100), a detailed quantitative assessment of the interfacial chemistry is necessary. We have used ambient pressure X-ray photoelectron spectroscopy (XPS) to measure molecular (H2O) and dissociative (OH) water adsorption on a 4 monolayer (ML) thick MgO(100)/Ag(100) film under ambient conditions. Since the entire 4 ML metal oxide (Ox) film is probed by XPS, the reaction of the MgO film with water can be quantitatively studied. Using a multilayer model (Model 1) that measures changes in Ox thickness from O is (film) and Ag 3d (substrate) spectra, it is shown that the oxide portion of the MgO film becomes thinner upon hydroxylation. A reaction mechanism is postulated in which the topmost layer of MgO converts to Mg(OH)(2) upon dissociation of water. Based on this mechanism a second model (Model 2) is developed to calculate Ox and OH thickness changes based on OH/Ox intensity ratios from O is spectra measured in situ, with the known initial Ox thickness prior to hydroxylation. Models 1 and 2 are applied to a 0.15 Torr isobar experiment, yielding similar results for H2O. OH and Ox thickness changes as a function of relative humidity. Published by Elsevier B.V.

  76. Structural Inhomogeneity of Interfacial Water at Lipid Monolayers Revealed by Surface-Specific Vibrational Pump-Probe Spectroscopy 査読有り

    Mischa Bonn, Huib J. Bakker, Avishek Ghosh, Susumu Yamamoto, Maria Sovago, R. Kramer Campen

    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 132 (42) 14971-14978 2010年10月

    出版者・発行元:AMER CHEMICAL SOC

    DOI: 10.1021/ja106194u  

    ISSN:0002-7863

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    We report vibrational lifetime measurements of the OH stretch vibration of interfacial water in contact with lipid monolayers, using time-resolved vibrational sum frequency (VSF) spectroscopy. The dynamics of water in contact with four different lipids are reported and are characterized by vibrational relaxation rates measured at 3200, 3300, 3400, and 3500 cm(-1). We observe that the water molecules with an OH frequency ranging from 3300 to 3500 cm(-1) all show vibrational relaxation with a time constant of T(1) = 180 +/- 35 fs, similar to what is found for bulk water. Water molecules with OH groups near 3200 cm(-1) show distinctly faster relaxation dynamics, with T(1) &lt; 80 fs. We successfully model the data by describing the interfacial water containing two distinct subensembles in which spectral diffusion is, respectively, rapid (3300-3500 cm(-1)) and absent (3200 cm(-1)). We discuss the potential biological implications of the presence of the strongly hydrogen-bonded, rapidly relaxing water molecules at 3200 cm(-1) that are decoupled from the bulk water system.

  77. Water Adsorption on alpha-Fe2O3(0001) at near Ambient Conditions 査読有り

    Susumu Yamamoto, Tom Kendelewicz, John T. Newberg, Guido Ketteler, David E. Starr, Erin R. Mysak, Klas J. Andersson, Hirohito Ogasawara, Hendrik Bluhm, Miquel Salmeron, Gordon E. Brown, Anders Nilsson

    JOURNAL OF PHYSICAL CHEMISTRY C 114 (5) 2256-2266 2010年2月

    出版者・発行元:AMER CHEMICAL SOC

    DOI: 10.1021/jp909876t  

    ISSN:1932-7447

    詳細を見る 詳細を閉じる

    We have investigated hydroxylation and water adsorption on alpha-Fe2O3(0001) at water vapor pressures up to 2 Torr and temperatures ranging from 277 to 647 K (relative humidity (RH) &lt;= 34%) using ambient-pressure X-ray photoelectron spectroscopy (XPS). Hydroxylation occurs at the very low RH of 1 x 10(-7) % and precedes the adsorption of molecular water. With increasing RH, the OH coverage increases up to one monolayer (ML) without any distinct threshold pressure. Depth profiling measurements showed that hydroxylation occurs only at the topmost Surface under our experimental conditions. The onset of molecular water adsorption varies from similar to 2 x 10(-5) to similar to 4 x 10(-2) % RH depending on sample temperature and water vapor pressure. The coverage of water reaches 1 ML at similar to 15% RH and increases to 1.5 ML at 34% RH.

  78. Ultrafast inter- and intramolecular vibrational energy transfer between molecules at interfaces studied by time- and polarization-resolved SFG spectroscopy 査読有り

    Susumu Yamamoto, Avishek Ghosh, Han-Kwang Nienhuys, Mischa Bonn

    PHYSICAL CHEMISTRY CHEMICAL PHYSICS 12 (40) 12909-12918 2010年

    出版者・発行元:ROYAL SOC CHEMISTRY

    DOI: 10.1039/c0cp00538j  

    ISSN:1463-9076

    詳細を見る 詳細を閉じる

    We present experimental results on femtosecond time-resolved surface vibrational spectroscopy aimed at elucidating the sub-picosecond reorientational dynamics of surface molecules. The approach, which relies on polarization- and time-resolved surface sum frequency generation (SFG), provides a general means to monitor interfacial reorientational dynamics through vibrations inherent in surface molecules in their electronic ground state. The technique requires an anisotropic vibrational excitation of surface molecules using orthogonally polarized infrared excitation light. The decay of the resulting anisotropy is followed in real-time. We employ the technique to reveal the reorientational dynamics of vibrational transition dipoles of long-chain primary alcohols on the water surface, and of water molecules at the water-air interface. The results demonstrate that, in addition to reorientational motion of specific molecules or molecular groups at the interface, inter- and intramolecular energy transfer processes can serve to scramble the initial anisotropy very efficiently. In the two exemplary cases demonstrated here, energy transfer occurs much faster than reorientational motion of interfacial molecules. This has important implications for the interpretation of static SFG spectra. Finally, we suggest experimental schemes and strategies to decouple effects resulting from energy transfer from those associated with surface molecular motion.

  79. NO2 Adsorption on Ag(100) Supported MgO(100) Thin Films: Controlling the Adsorption State with Film Thickness 査読有り

    David E. Starr, Christoph Weis, Susumu Yamamoto, Anders Nilsson, Hendrik Bluhm

    JOURNAL OF PHYSICAL CHEMISTRY C 113 (17) 7355-7363 2009年4月

    出版者・発行元:AMER CHEMICAL SOC

    DOI: 10.1021/jp900410v  

    ISSN:1932-7447

    詳細を見る 詳細を閉じる

    Using photoemission and X-ray absorption spectroscopy, we compare the adsorption properties of NO2 at 300 K on MgO(100)/Ag(100) films with thicknesses varying from 2 to 8 ML and NO2 exposures ranging from 0 L to over 25 000 L. We find that NO2 is stable on 2 ML MgO(100) films, where it is the most abundant adsorbate on the surface (similar to 0.35 ML) for exposures up to at least similar to 25 000 L. At high exposures, NO3 also forms on the surface of 2 ML thick films but is a minority species. In contrast, films thicker than similar to 5 ML show conversion to NO3 beginning already at low exposures. At high exposure to NO2, NO3 is the only species present on the surface. Shifts to lower binding energy of the O 1s spectra with adsorbed species indicate that the NO2 adsorbed on the thin MgO(100) films is likely negatively charged and forms NO2-. A more gradual binding energy shift is observed on thicker films and is likely associated with the slower formation of NO3- Measurements on MgO(1.00) films of various thicknesses indicate that for films thicker than 5 ML, the NO2 adsorption properties are similar and most likely correspond to surfaces of bulk MgO(100). We discuss potential mechanisms for NO2 charging and stabilization on the thin MgO(100) films in the context of recent literature.

  80. Water growth on metals and oxides: binding, dissociation and role of hydroxyl groups 査読有り

    M. Salmeron, H. Bluhm, N. Tatarkhanov, G. Ketteler, T. K. Shimizu, A. Mugarza, Xingyi Deng, T. Herranz, S. Yamamoto, A. Nilsson

    FARADAY DISCUSSIONS 141 221-229 2009年

    出版者・発行元:ROYAL SOC CHEMISTRY

    DOI: 10.1039/b806516k  

    ISSN:1364-5498

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    We discuss the role of the presence of dangling H-bonds from water or form surface hydroxyl species on the wetting behaviour of surfaces. Using scanning tunneling and atomic force microscopes and photoelectron spectroscopy, we have examined a variety of surfaces, including mica, oxides and pure metals. We find that in all cases, the availability of free, dangling H-bonds at the surface is crucial for the subsequent growth of wetting water films. In the case of mica, electrostatic forces and H-bonding to surface O atoms determine the water orientation in the first layer and also in subsequent layers with a strong influence ill its wetting characteristics. In the case or Oxides like TiO2, Cu2O, SiO2 and Al2O3. Surface hydroxyls form readily on defects upon exposure to water vapour and help nucleate the subsequent growth of molecular water films. On pure metals, such as Pt, Pd and Ru, the structure of the first water layer and whether or not it exhibits dangling H-bonds is again crucial. Dangling H-bonds are provided by molecules with their plane oriented vertically. or by OH groups formed by the partial dissociation of water. By tying the two H atoms of the water molecules into strong H-bonds with pre-adsorbed O on Ru can also quench the wettability of the surface.

  81. Direct observation of valence and conduction states near the SiO 2/Si(100) interface 査読有り

    Yoshiyuki Yamashita, Susumu Yamamoto, Kozo Mukai, Jun Yoshinobu, Yoshihisa Harada, Takashi Tokushima, Shik Shin

    e-Journal of Surface Science and Nanotechnology 6 209-212 2008年9月25日

    DOI: 10.1380/ejssnt.2008.209  

    ISSN:1348-0391

    詳細を見る 詳細を閉じる

    Valence and conduction states near the SiO2/Si(100) interface were directly observed using soft x-ray absorption and emission spectroscopy. For the O K-edge absorption spectra, the step-like structures were observed at 531, 533 and 534.5 eV. These step-like structures observed at 531, 533 and 534.5 eV were assigned to an oxygen atom bonding to Si1+ , Si 2+, and Si3+ of the interface, respectively. In the case of O K-edge emission spectra, with decreasing incident photon energy from 535 to 531 eV so as to shift the conduction band minimum of the interface towards Fermi energy, the corresponding valence band maximum was shifted to Fermi energy direction. Thus, the local band gap became narrower with the decrease of the oxidation number of the suboxide species. Further the interface structure was also discussed from the spectrum features. © 2008 The Surface Science Society of Japan.

  82. In situ x-ray photoelectron spectroscopy studies of water on metals and oxides at ambient conditions 査読有り

    S. Yamamoto, H. Bluhm, K. Andersson, G. Ketteler, H. Ogasawara, M. Salmeron, A. Nilsson

    JOURNAL OF PHYSICS-CONDENSED MATTER 20 (18) 2008年5月

    出版者・発行元:IOP PUBLISHING LTD

    DOI: 10.1088/0953-8984/20/18/184025  

    ISSN:0953-8984

    eISSN:1361-648X

    詳細を見る 詳細を閉じる

    X-ray photoelectron spectroscopy (XPS) is a powerful tool for surface and interface analysis, providing the elemental composition of surfaces and the local chemical environment of adsorbed species. Conventional XPS experiments have been limited to ultrahigh vacuum (UHV) conditions due to a short mean free path of electrons in a gas phase. The recent advances in instrumentation coupled with third-generation synchrotron radiation sources enables in situ XPS measurements at pressures above 5 Torr. In this paper, we describe the basic design of the ambient pressure XPS setup that combines differential pumping with an electrostatic focusing. We present examples of the application of in situ XPS to studies of water adsorption on the surface of metals and oxides including Cu(110), Cu(111), TiO2(110) under environmental conditions of water vapor pressure. On all these surfaces we observe a general trend where hydroxyl groups form first, followed by molecular water adsorption. The importance of surface OH groups and their hydrogen bonding to water molecules in water adsorption on surfaces is discussed in detail.

  83. Autocatalytic water dissociation on Cu(110) at near ambient conditions 査読有り

    Klas Andersson, Guido Ketteler, Hendrik Bluhm, Susumu Yamamoto, Hirohito Ogasawara, Lars G. M. Pettersson, Miquel Salmeron, Anders Nilsson

    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 130 (9) 2793-2797 2008年3月

    出版者・発行元:AMER CHEMICAL SOC

    DOI: 10.1021/ja073727x  

    ISSN:0002-7863

    詳細を見る 詳細を閉じる

    Autocatalytic dissociation of water on the Cu(110) metal surface is demonstrated on the basis of X-ray photoelectron spectroscopy studies carried out in situ under near ambient conditions of water vapor pressure (1 Torr) and temperature (275-520 K). The autocatalytic reaction is explained as the result of the strong hydrogen-bond in the H2O-OH complex of the dissociated final state, which lowers the water dissociation barrier according to the Bronsted-Evans-Polanyi relations. A simple chemical bonding picture is presented which predicts autocatalytic water dissociation to be a general phenomenon on metal surfaces.

  84. Ultrafast energy flow in model biological membranes 査読有り

    Marc Smits, Avishek Ghosh, Jens Bredenbeck, Susumu Yamamoto, Michiel Muller, Mischa Bonn

    NEW JOURNAL OF PHYSICS 9 2007年10月

    出版者・発行元:IOP PUBLISHING LTD

    DOI: 10.1088/1367-2630/9/10/390  

    ISSN:1367-2630

    詳細を見る 詳細を閉じる

    We report on the energy flow dynamics in model membranes, investigated by surface-specific time-resolved (femtosecond) sum frequency generation spectroscopy. This recently developed technique allows us to probe energy dynamics selectively at the water/lipid interface. We report vibrational relaxation dynamics of C-H stretch modes in the lipid alkyl chains, and reveal that incoherent energy transfer occurs from the excited CH2 groups to the terminal CH3 groups. We also find evidence for strong anharmonic coupling between different CH2 and CH3 modes. Relaxation and the energy transfer processes within the lipid alkyl chain occur on (sub-)picosecond timescales. Studies of the dynamics on different lipid phases (gel or liquid crystalline phase) reveal a marked independence of the dynamics on the precise molecular conformation of the lipids. In addition, we report the energy transfer dynamics between membrane- bound water and lipids, and find that the transfer of heat between water and lipids occurs remarkably fast: heat is transferred across the monolayer, from the polar head group region of the lipid to the end of the alkyl chain, within 1 ps. These results demonstrate the potential of using ultrafast surface-specific spectroscopies to elucidate biomolecular dynamics at membrane surfaces.

  85. Bridging the pressure gap in water and hydroxyl chemistry on metal surfaces: The Cu(110) case 査読有り

    Klas Andersson, Guido Ketteler, Hendrik Bluhm, Susumu Yamamoto, Hirohito Ogasawara, Lars G. M. Pettersson, Miquel Salmeron, Anders Nilsson

    JOURNAL OF PHYSICAL CHEMISTRY C 111 (39) 14493-14499 2007年10月

    出版者・発行元:AMER CHEMICAL SOC

    DOI: 10.1021/jp073681u  

    ISSN:1932-7447

    詳細を見る 詳細を閉じる

    We report the first measurements on the,quantitative partitioning of water between its molecular and dissociated forms at a gas-metal interface under elevated water pressures and temperatures. By means of synchrotron-based in situ photoelectron spectroscopy, mixed H2O and OH phases on Cu(110) at H2O pressures up to 1 Torr in the 275-520 K temperature range are studied. In increasing order of stability, three phases with H2O/OH ratios of 2:11 1:1, and 0:1 were observed. It was found that surprisingly large quantities of molecular water are present on the surface up to 428 K in 1 Torr H2O. A detailed comparison with previous ultrahigh vacuum (UHV) studies shows that the observed species, phases, and chemical kinetics under UHV compare very well with our results at elevated pressures and temperatures. The stability of the hydrogen-bonded H2O-OH complex at the surface, and its influence on the adsorption -desorption and dissociation kinetics, constitutes the essential link between our results and those obtained under UHV conditions.

  86. The nature of water nucleation sites on TiO2(110) surfaces revealed by ambient pressure X-ray photoelectron spectroscopy 査読有り

    Guido Ketteler, Susumu Yamamoto, Hendrik Bluhm, Klas Andersson, David E. Starr, D. Frank Ogletree, Hirohito Ogasawara, Anders Nilsson, Miquel Salmeron

    JOURNAL OF PHYSICAL CHEMISTRY C 111 (23) 8278-8282 2007年6月

    出版者・発行元:AMER CHEMICAL SOC

    DOI: 10.1021/jp068606i  

    ISSN:1932-7447

    詳細を見る 詳細を閉じる

    X-ray photoelectron spectroscopy at ambient conditions of pressure (up to 1.5 Torr) and temperature (265 K &lt; T &lt; 800 K) was used to study the adsorption of water on rutile TiO2(110) under conditions of thermodynamic equilibrium. It was found that OH groups in bridging positions, normally present in small amounts due to residual O-vacancies, act as nucleation sites for subsequent water adsorption. The adsorption enthalpy of water binding to these sites is similar to 70 kJ/mol, much stronger than that in the bulk liquid (45 kJ/mol). A model is proposed that relates the structure of the oxide surface to its hydrophilic character.

  87. Hydroxyl-induced wetting of metals by water at near-ambient conditions 査読有り

    Susumu Yamamoto, Klas Andersson, Hendrik Bluhm, Guido Ketteler, David E. Starr, Theanne Schiros, Hirohito Ogasawara, Lars G. M. Pettersson, Miquel Salmeron, Anders Nilsson

    JOURNAL OF PHYSICAL CHEMISTRY C 111 (22) 7848-7850 2007年6月

    出版者・発行元:AMER CHEMICAL SOC

    DOI: 10.1021/jp0731654  

    ISSN:1932-7447

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    We report different wetting properties of Cu(110) and Cu(111) at near-ambient conditions using in situ photoemission spectroscopy. At near-ambient conditions of pressure (1 Torr) and temperature (295 K), the Cu(110) surface is covered with a mixed OH and H2O layer, whereas the Cu(111) surface remains clean and adsorbate-free. We show that wetting is controlled by the presence of OH groups on the surface, acting as anchors for water adsorption. Hydroxylation of the Cu(110) surface is facilitated by a lower activation barrier for water dissociation compared to Cu(111).

  88. The first layer of water on Rh(111): Microscopic structure and desorption kinetics 査読有り

    Atsushi Beniya, Susumu Yamamoto, Kozo Mukai, Yoshiyuki Yamashita, Jun Yoshinobu

    JOURNAL OF CHEMICAL PHYSICS 125 (5) 2006年8月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.2227393  

    ISSN:0021-9606

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    The adsorption states and growth process of the first water (D2O) layer on Rh(111) were investigated using infrared reflection absorption spectroscopy, temperature programed desorption, and spot-profile-analysis low energy electron diffraction. Water molecules wet the Rh(111) surface intact. At the early stage of first layer growth, a (root 3x root 3)R30 degrees commensurate water layer grows where "up" and "down" species coexist; the up and down species represent water molecules which have free OD, pointing to a vacuum and the substrate, respectively. The up domain was a flatter structure than an icelike bilayer. Water desorption from Rh(111) was a half-order process. The activation energy and the preexponential factor of desorption are estimated to be 60 kJ/mol and 4.8x10(16) ML1/2/s at submonolayer coverage, respectively. With an increase in water coverage, the flat up domain becomes a zigzag layer, like an ice bilayer. At the saturation coverage, the amount of down species is 1.3 times larger than that of the up species. In addition, the activation energy and the preexponential factor of desorption decrease to 51 kJ/mol and 1.3x10(14) ML1/2/s, respectively. (c) 2006 American Institute of Physics.

  89. Effects of interface roughness on the local valence electronic structure at the SiO2/Si interface: Soft X-ray absorption and emission study 査読有り

    Y Yamashita, S Yamamoto, K Mukai, J Yoshinobu, Y Harada, T Tokushima, Y Takata, S Shin

    JOURNAL DE PHYSIQUE IV 132 259-262 2006年3月

    出版者・発行元:EDP SCIENCES S A

    DOI: 10.1051/jp4:2006132049  

    ISSN:1155-4339

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    We investigated effects of interface roughness oil the local valence electronic structures at SiO2/Si interface in order to clarify the relation between interface structures and interface electronic properties, by using soft X-ray absorption and emission spectroscopy. For atomically smooth interface, the local valence structures depend on intermediate oxidation states at the interface. For atomically rough interface. on the other hand, the local valence structures at the interface show amorphous-like electronic states irrespective of the intermediated oxidation states.

  90. Direct observation of the site-specific valence electronic structure at SiO2/Si(111) interface

    Yamashita Y., Yamamoto S., Mukai K., Yoshinobu J., Harada Y., Tokushima T., Takeuchi T., Takata Y., Shin S., Akagi K., Tsuneyuki S.

    e-Journal of Surface Science and Nanotechnology 4 280-284 2006年

    出版者・発行元:The Surface Science Society of Japan

    DOI: 10.1380/ejssnt.2006.280  

    ISSN:1348-0391

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    For today's silicon based devices, understanding the SiO<sub>2</sub>/Si(111) interface on atomic level is an important subject for fabricating superior devices. However, despite of many studies on the SiO<sub>2</sub>/Si(111) interface, the interfacial valence electronic states have been typically evaluated as the average and not as individual states. In the present study, we successfully observed valence electronic states of particular atoms at the SiO<sub>2</sub>/Si(111) interface for the first time using soft x-ray absorption and emission spectroscopy. In addition, comparing the experimental results to first-principles calculations revealed local interfacial properties. [DOI: 10.1380/ejssnt.2006.280]

  91. Direct observation of site-specific valence electronic structure at the SiO2/Si interface 査読有り

    Y Yamashita, S Yamamoto, K Mukai, J Yoshinobu, Y Harada, T Tokushima, T Takeuchi, Y Takata, S Shin, K Akagi, S Tsuneyuki

    PHYSICAL REVIEW B 73 (4) 280-284 2006年1月

    出版者・発行元:AMERICAN PHYSICAL SOC

    DOI: 10.1103/PhysRevB.73.045336  

    ISSN:1098-0121

    詳細を見る 詳細を閉じる

    Atom specific valence electronic structures at the solid-solid interface are elucidated successfully using soft x-ray absorption and emission spectroscopy. In order to demonstrate the versatility of this method, we investigated the SiO2/Si interface as a prototype and directly observed valence electronic states projected at the particular atoms of the SiO2/Si interface; the local electronic structure strongly depends on the chemical states of each atom. In addition, we compared the experimental results with first-principles calculations, which quantitatively revealed the interface properties in atomic scale.

  92. Water adsorption on Rh(111) at 20 K: From monomer to bulk amorphous ice 査読有り

    S Yamamoto, A Beniya, K Mukai, Y Yamashita, J Yoshinobu

    JOURNAL OF PHYSICAL CHEMISTRY B 109 (12) 5816-5823 2005年3月

    出版者・発行元:AMER CHEMICAL SOC

    DOI: 10.1021/jp044379d  

    ISSN:1520-6106

    詳細を見る 詳細を閉じる

    The adsorption of water (D2O) molecules on Rh(I 11) at 20 K was investigated using infrared reflection absorption spectroscopy (IRAS). At the initial stage of adsorption, water molecules exist as monomers on Rh(l 11). With increasing water coverage, monomers aggregate into dimers, larger clusters (n = 3-6), and two-dimensional (2D) islands. Further exposure of water molecules leads to the formation of three-dimensional (3D) water islands and finally to a bulk amorphous ice layer. Upon heating, the monomer and dimer species thermally migrate on the surface and aggregate to form larger clusters and 2D islands. Based on the temperature dependence of OD stretching peaks, we succeeded in distinguishing water molecules inside 2D islands from those at the edge of 2D islands. From the comparison with the previous vibrational spectra of water clusters on other metal surfaces, we conclude that the number of water molecules at the edge of 2D islands is comparable with that of water molecules inside 2D islands on the Rh(I 11) surface at 20 K. This indicates that the surface migration of water molecules on Rh(111) is hindered as compared with the cases on Pt(111) and Ni(111) and thus the size of 2D islands on Rh(111) is relatively small.

  93. Low-energy electron-stimulated chemical reactions of CO in water ice 査読有り

    S Yamamoto, A Beniya, K Mukai, Y Yamashita, J Yoshinobu

    CHEMICAL PHYSICS LETTERS 388 (4-6) 384-388 2004年4月

    出版者・発行元:ELSEVIER SCIENCE BV

    DOI: 10.1016/j.cplett.2004.03.030  

    ISSN:0009-2614

    詳細を見る 詳細を閉じる

    We investigated low-energy electron-stimulated chemical reactions between CO and water molecules in low-temperature ice using infrared reflection absorption spectroscopy. Carbon dioxide, the formyl radical, formaldehyde, and methanol were produced by electron irradiation of the water/CO/water layered ice. The electron energy threshold and temperature dependence for the chemical reactions were investigated to elucidate the reaction mechanisms. (C) 2004 Elsevier B.V. All rights reserved.

  94. Vibrational structure in C 1s photoelectron spectra of ethylene on the Si(100)(2 x 1) surface 査読有り

    Y Yamashita, S Machida, M Nagao, S Yamamoto, K Mukai, J Yoshinobu

    CHEMICAL PHYSICS LETTERS 374 (5-6) 476-481 2003年6月

    出版者・発行元:ELSEVIER SCIENCE BV

    DOI: 10.1016/S0009-2614(03)00732-2  

    ISSN:0009-2614

    詳細を見る 詳細を閉じる

    We have investigated the C Is photoelectron spectra of ethylene on the Si(l 0 0)(2 x 1) surface, using high resolution photoelectron spectroscopy. The vibrational structure has been observed in the C Is spectra where the C-H stretching mode is dominant. The vibrational splittings of C Is ionized state are very similar to those in the ground state. It is found that linear coupling model is applicable in this system and this excitation process is a Frank Condon process. The curvature of potential energy surface of C-H and C-D bond is almost unchanged upon core ionization. (C) 2003 Elsevier Science B.V. All rights reserved.

  95. Electronic states and chemical reactivity of Si(100)c(4 x 2) surface at low temperature studied by high resolution Si 2p core level photoelectron spectroscopy 査読有り

    S Machida, M Nagao, S Yamamoto, Y Kakefuda, K Mukai, Y Yamashita, J Yoshinobu

    SURFACE SCIENCE 532 716-720 2003年6月

    出版者・発行元:ELSEVIER SCIENCE BV

    DOI: 10.1016/S0039-6028(03)00177-8  

    ISSN:0039-6028

    eISSN:1879-2758

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    We have investigated the electronic states of clean and BF3 adsorbed Si(l 0 0) surfaces at low temperature by means of high resolution Si 2p photoelectron spectroscopy. The peak intensities of upper atom and lower atom of the asymmetric dimer in Si 2p spectra do not change even at 30 K compared with those at higher temperature up to 300 K, indicating that the dimer is asymmetric in the ground state. In order to investigate chemical reactivity of asymmetric dimer on Si(I 0 0), a typical Lewis acid molecule BF3 is adsorbed on Si(I 0 0). We have found that BF3 molecules are dissociated into BF2 and F on Si(I 0 0) and dissociated species (BF2 and F) are adsorbed predominantly on the up dimer atoms of the asymmetric dimers. (C) 2003 Elsevier Science B.V. All rights reserved.

  96. Direct evidence for asymmetric dimer on Si(100) at low temperature by means of high-resolution Si 2p photoelectron spectroscopy 査読有り

    Y Yamashita, S Machida, M Nagao, S Yamamoto, Y Kakefuda, K Mukai, J Yoshinobu

    JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS 41 (3A) L272-L274 2002年3月

    出版者・発行元:JAPAN SOC APPLIED PHYSICS

    DOI: 10.1143/JJAP.41.L272  

    ISSN:0021-4922

    詳細を見る 詳細を閉じる

    We have investigated the electronic states of the Si(100) surface at low temperature by means of high-resolution Si 2p photoelectron Spectroscopy. The peak intensities of up and down atoms of the asymmetric dimer in Si 2p spectra do not change from 140 K to 55 K, showing that the number of asymmetric dimers is preserved. Therefore, we can conclude that the ground state of the dimer is asymmetric and the symmetric dimer images observed by scanning tunneling microscopy at this temperature range are due to extrinsic or dynamical intrinsic effects on the buckled dinner.

︎全件表示 ︎最初の5件までを表示

MISC 7

  1. Materials Science Research by Ambient Pressure X-Ray Photoelectron Spectroscopy Systems at Synchrotron Radiation Facilities in Japan: Applications in Energy, Catalysis, and Sensors 招待有り

    Susumu Yamamoto, Yasumasa Takagi, Takanori Koitaya, Ryo Toyoshima, Masafumi Horio, Iwao Matsuda, Hiroshi Kondoh, Toshihiko Yokoyama, Jun Yoshinobu

    Synchrotron Radiation News 35 (3) 19-25 2022年6月23日

    出版者・発行元:Informa UK Limited

    DOI: 10.1080/08940886.2022.2082168  

    ISSN:0894-0886

    eISSN:1931-7344

  2. 雰囲気軟X線光電子分光を用いた触媒表面反応のオペランド計測 招待有り 査読有り

    山本達, 小板谷貴典, 松田巌, 吉信淳

    日本放射光学会誌「放射光」 35 (3) 182-190 2022年5月

  3. SACLAを用いた時間分解透過型X線回折による1T′‐MoTe<sub>2</sub>の格子ダイナミクス観測

    下志万貴博, 中村飛鳥, 石坂香子, 田中良和, 田久保耕, 平田靖透, 和達大樹, 山本達, 松田巌, 池浦晃至, 高橋英史, 酒井英明, 石渡晋太郎, 富樫格, 大和田成起, 片山哲夫, 登野健介, 矢橋牧名, SHIN Shik

    X線分析の進歩 49 163‐168 2018年3月31日

    ISSN:0911-7806

  4. 時間分解軟X線光電子分光法:半導体表面における光励起キャリアの実時間観測

    山本達, 松田巌

    表面科学 37 (1) 9-13 2016年

    DOI: 10.1380/jsssj.37.9  

  5. フェムト秒時間分解光電子分光法によるグラフェンの超高速キャリアダイナミクスの追跡

    染谷隆史, 吹留博一, 石田行章, 吉田力矢, 山本達, 板谷治郎, 小森文夫, 辛埴, 松田巌

    表面科学 36 (8) 418-423 2015年

    DOI: 10.1380/jsssj.36.418  

  6. 時間分解軟X線光電子分光法による表面キャリアダイナミクス研究の進展 招待有り 査読有り

    山本達, 松田巌

    日本放射光学会誌「放射光」 27 (5) 241-252 2014年

  7. 氷表面の物性と化学反応:振動分光をプローブとして

    吉信淳, 山本達, 奥山弘

    応用物理 73 (10) 1307-1311 2004年

︎全件表示 ︎最初の5件までを表示

書籍等出版物 2

  1. 現代表面科学シリーズ「6.問題と解説で学ぶ表面科学」

    山本達

    共立出版 2013年

    ISBN: 9784320033740

  2. 第5版実験化学講座:第24巻 表面・界面 「放射光、 XAS、XES」

    小笠原寛人, 山本達

    丸善 2007年

    ISBN: 9784621073230

講演・口頭発表等 20

  1. 飛行時間型電子分析器を利用したピコ秒時間分解X線吸収分光法の開発

    山本達, 小澤健一, 保原麗, 松田巌

    第37回放射光学会年会・放射光科学合同シンポジウム 2024年1月11日

  2. 次世代放射光施設ナノテラスの挿入光源とビームライン 招待有り

    山本達

    日本物理学会第78回年次大会 2023年9月16日

  3. Development of time-resolved ambient pressure X-ray photoelectron spectroscopy system at SPring-8 BL07LSU

    S. Yamamoto, T. Koitaya, T. Wada, T. Sumi, M. Miyamoto, M. Horio, J. Yoshinobu, I. Matsuda

    IMS PES symposium "Seeds and needs for tomorrow's synchrotron radiation photoelectron spectroscopy research" 2023年7月29日

  4. Development of time-resolved ambient pressure X-ray photoelectron spectroscopy system at SPring-8 BL07LSU

    S. Yamamoto, T. Koitaya, T. Wada, T. Sumi, M. Miyamoto, M. Horio, J. Yoshinobu, I. Matsuda

    International Workshop on Photoionization (IWP) Resonant Inelastic X-ray Scattering (RIXS) 2022 (IWP-RIXS 2022) 2022年11月16日

  5. Hard X-ray Photoelectron Spectroscopy at NanoTerasu BL09U: Design and Applications

    Susumu Yamamoto

    Asia Oceania International Conference on Synchrotron Radiation Instruments 2022 (AO-SRI 2022) 2022年11月11日

  6. BL09U 硬X線光電子分光 (HAXPES)

    山本達

    第1回コアリションBLエンドステーション利用技術説明会 2022年6月9日

  7. BL09U (BL-I): X線オペランド分光による材料内部電子状態の可視化

    山本達

    第2回東北大学学内ビームライン説明会 2021年12月16日

  8. Operando observation of photo-excited carriers and molecules at solid surfaces using time-resolved XPS 招待有り

    Susumu Yamamoto

    8th Annual Ambient Pressure X-ray Photoelectron Spectroscopy Virtual Workshop (APXPS 2021) 2021年12月10日

  9. Catalytic surface reactions studied by operando soft X-ray spectroscopy 招待有り

    Susumu Yamamoto

    MIRAI 2.0 Materials Science TEG Workshop 2021年11月30日

  10. BL09U (BL-I): X線オペランド分光ビームラインの概要と触媒・材料分野での利用

    山本達

    第4回触媒学会次世代放射光勉強会 2021年11月26日

  11. Development of soft X-ray photoelectron spectroscopy systems at SPring-8 BL07LSU

    Susumu Yamamoto

    The first European-Japanese workshop on SX beamline automation and experimental optimization 2021年6月24日

  12. 軟X線~テンダーX線オペランド計測で拓く触媒表面科学 招待有り

    山本達

    日本物理学会第76回年次大会 シンポジウム講演 2021年3月15日

  13. プラズモンナノ材料における光励起キャリアの実時間観測:光触媒反応のオペランド観測に向けた取り組み 招待有り

    山本達

    SPring-8ユーザー協同体顕微ナノ材料科学研究会・日本表面科学会放射光表面科学研究部会・日本表面科学会プローブ顕微鏡研究部会 合同シンポジウム (Nanospec 2021) 2021年3月11日

  14. 放射光X線オペランド計測が拓く触媒表面科学:SPring-8 BL07LSUから次世代放射光施設へ 招待有り

    山本達

    ISSP workshop「先端軟X線科学への基幹技術」 2021年3月4日

  15. Catalytic surface reactions studied by operando soft X-ray spectroscopy 招待有り

    Susumu Yamamoto

    The 3rd Workshop of the Reaction Infography (R-ing) Unit 2020年12月10日

  16. 雰囲気X線光電子分光法が拓く触媒研究の現状と将来展望 招待有り

    山本達

    化学反応経路探索のニューフロンティア2020 (SRPS2020) 2020年9月13日

  17. Operando observation of photo-excited carriers and molecules at solid surfaces using soft X-ray spectroscopies 招待有り

    S. Yamamoto

    The 81st Okazaki Conference "Forefront of measurement technologies for surface chemistry and physics in real-space, k-space, and real-time" 2019年12月4日

  18. 放射光を利用した表面分析

    山本達

    第68回 表面科学基礎講座「表面・界面分析の基礎と応用」 2019年10月18日

  19. 軟X線オペランド観測で拓く次世代の表面界面科学

    山本達

    東京大学物性研究所 第19回機能物性セミナー 2019年10月16日

  20. シリカ担持ニッケル触媒表面におけるサバティエ反応の軟X線オペランド観測

    山本達, 宮脇淳, 唐佳藝, 小板谷貴典, 徳永拓馬, 柴田悠宇, 小瀬川友香, 山添康介, 向井孝三, 吉本真也, 吉信淳, 松田巌

    第32回放射光学会年会・放射光科学合同シンポジウム 2019年1月11日

︎全件表示 ︎最初の5件までを表示

共同研究・競争的資金等の研究課題 7

  1. 新規時間分解X線吸収・光電子分光法の開発と光励起キャリアダイナミクスへの展開 競争的資金

    山本 達

    2019年4月 ~ 2022年3月

  2. 新規太陽エネルギー変換材料における光励起キャリア物理の探求 競争的資金

    小澤 健一

    2016年4月 ~ 2020年3月

  3. 時間分解雰囲気X線光電子分光法によるプラズモニック化学反応の実時間オペランド観測 競争的資金

    山本 達

    2016年4月 ~ 2019年3月

  4. 軟X線共鳴カー効果による希薄磁性物質のスピンダイナミクス研究 競争的資金

    松田 巌

    2014年4月 ~ 2017年3月

  5. 酸化物半導体・金属界面におけるキャリアダイナミクスの実時間観察 競争的資金

    山本 達

    2013年4月 ~ 2016年3月

  6. 酸化物半導体表面の光誘起電子輸送現象の研究 競争的資金

    松田 巌

    2011年4月 ~ 2013年3月

  7. フェムト秒時間分解振動分光法を用いた生体膜における超高速ダイナミクスの研究 競争的資金

    山本 達

    2008年6月 ~ 2009年10月

︎全件表示 ︎最初の5件までを表示