HiSOR
ACTIVITY REPORT
20 0 7

Hiroshima Synchrotron Radiation Center, HSRC
Hiroshima University

HiSORACTIVITY REPORT2007

Hiroshima Synchrotron Radiation Center, HSRC
Hiroshima University

Edited by
T. Hori, M. Nakatake
The annual report is available from
Hiroshima Synchrotron Radiation Center
Hiroshima University
2-313 Kagamiyama, Higashi-Hiroshima 739-0046
JAPAN
Phone: +81-82-424-6293
Fax: +81-82-424-6294
e-mail: hisor@hiroshima-u.ac.jp
URL: http://www.hsrc.hiroshima-u.ac.jp/

Preface
Hiroshima Synchrotron Radiation Center is a common facility opened for outside users. The
light source operated at 700 MeV with a critical energy of 873 eV has 14 photon beam ports on thebending sections and two on the straight sections with a linear and a helical undulators. In 2007,
the light source has been operated for 1950 hours, and used for 1550 hours for user experimentswith the beam lifetime of about 8 hours at 300 mA accumulation curret under the operation of two
undulators.
A total of 13 beamlines has been constructed so far; three normal-incidence monochromators,
seven grazing-incidence monochromators, two double crystal monochromators and an apparatus
for white beam irradiation. In particular, resolutions of energy and momentum in angle-resolved
photoemission spectroscopy experiments have been significantly improved to 600-700 μeV and
4×10–3 Å–1, respectively, at excitation photon energy of hν~8 eV on helical undulator beamline.
The low-energy tunable excitation-photons have enabled us to resolve a very small nodal
bilayer splitting, unmasking the intrinsic quasi-particle scattering rate, and to observe precisely
a small electronic structure change due to an oxygen isotope effect, in nearly optimally doped
Bi2Sr2CaCu2O8+δ. A part of the research has been presented at The 9th International Conference on
Synchrotron Radiation Instrumentation as a plenary talk.
In 2007, new end station for polarization-dependent angle-resolved photoemission
spectroscopy (ARPES) has been designed. ARPES with s- or p-polarization geometry, which
determines symmetry of the initial-state wave function, will soon be possible. On the soft x-ray
beamline, an in situ system for fabrication of magnetic ultrathin films with monatomic layer control
by means of MBE technique and their characterization by Auger electron spectroscopy, low energy
electron diffraction and reflection high-energy electron diffraction, has been introduced. Afterthe fabrication and characterization of magnetic films, the soft x-ray magnetic circular dichroism
experiments are available on the grown films.
In addition to electronic and spin structures of solids above, activities are going up in thefield of photochemistry such as photo-fragmentation, analysis on chemical states of catalyst
for automobile emission, secondary-structual analysis of denatured protein, electronic structure
determination by inverse-photoemission and direct observation of nano-structure by STM.
We will continue to develop the performance of HiSOR facility and utilize the environment of
HiSOR for training of students and young scientists.
June 2008
Masaki Taniguchi

Director of Hiroshima Synchrotron Radiation Center—i—

— ii —

Table of Contents
Preface
Current Status of HiSOR
Status of the HiSOR storage ring and future plan of HSRC .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 1A. Miyamoto, K. Goto, H. Tsutsui, T. Hori

Beamlines.  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 11

Research Activities
New end station for the linear undulator beamline BL-1 .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 17
K. Shimada, M. Higashiguchi, N. Tobita, S. Fukuda, K. Tanaka, J. Jiang, H. Hayashi, H. Namatame,
M. Taniguchi

Angle-resolved photoemission study of the Shockley state in Au(110).  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 18
M. Higashiguchi, K. Shimada, Y. Miura, N. Tobita, Y. Aiura, H. Namatame, M. Taniguchi

Angle-resolved photoemission study of Pt (111) .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 22
N. Tobita, S. Fukuda, N. Nakajima, N. Ishimatsu, H. Maruyama, H. Hayashi, K. Tanaka, J. Jyan,
M. Higashiguchi, K. Shimada, H. Namatame, M. Taniguchi

Angle-resolved photoemission study of Cr (110) .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 24
S. Fukuda, N. Tobita, N. Nakajima, N. Ishimatsu, H. Maruyama, H. Hayashi, K. Tanaka, J. Jyan,
M. Higashiguchi, K. Shimada, H. Namatame, M. Taniguchi

High-resolution angle-resolved photoemission study of the surface-derived statein Al(100) single crystal .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 25
J. Jiang, K. Shimada, M. Higashiguchi, N. Tobida, K. Tanaka, S. Fukuda, H. Hayashi, Y. Aiura,
H. Namatame, M. Taniguchi

High-resolution angle-resolved photoemission spectroscopy of Rh(100) .  .  .  .  .  .  .  .  .  .  .  .  .  . 30
H. Hayashi, K. Shimada, K. Tanaka, M. Higasiguchi, N. Tobita, J. Jing, S. Fukuda, H. Namatame,
M. Taniguchi

High-resolution angle-resolved photoemission spectroscopy of Rh(111). . . . . . . . . . . . . . 32
K. Tanaka, K. Shimada, N. Tobita, S. Fukuda, H. Hayashi, J. Jiang, Y. Aiura, H. Namatame, M. Taniguchi

Angle resolved photoemission spectroscopy measurements of VO2 thin films .  .  .  .  .  .  .  .  .  .  .  . 34
K. Saeki, Y. Muraoka, T. Wakita, M. Hirai, T. Yokoya, R. Eguchi, S. Shin, K. Shimada— iii —

Carrier-doping effects on Cr-doped perovskite-type titanates Sr1–(x+y)Lax+yTi1–xCrxO3 studied
by photoemission spectroscopy.  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 36
H. Iwasawa, S. Kaneyoshi, K. Kurahashi, T. Saitoh, T. Katsufuji, Y. Miura, M. Higashiguchi,
K. Shimada, H. Namatame, M. Taniguchi

ARPES study of Fermi surface of T*-phase high-Tc cuprate SmLa0.8Sr0.2CuO4 .  .  .  .  .  .  .  .  .  .  . 39

Y. Nakashima, H. Anzai, T. Fujita, A. Ino, M. Higashiguchi, N. Tobita, J. Jiang, K. Tanaka, S. Fukuda,
K. Shimada, M. Arita, H. Namatame, M. Taniguchi, T. Kakeshita, S. Adachi, S. Tajima

Annealing effect on the chemical structure of diamondlike carbon (DLC) by C 1s
photoelectron spectroscopy.  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  40
S. Takabayashi, K. Shimada, K. Okamoto, T. Nakatani, H. Sakaue, T. Takahagi

NEXAFS, XPS and AFM studies of Rh deposited on Al2O3 thin film/NiAl(100).  .  .  .  .  .  .  .  .  .  . 42
T. Nomoto, S. Yagi, K. Soda, H. Namatame, M. Taniguchi

Adsorption and oxidation reaction of sulfur on Rh/Al2O3/NiAl(100) studied
by XPS and NEXAFS .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 46
T. Nomoto, S. Yagi, K. Soda, H. Namatame, M. Taniguchi

Cl K-edge NEXAFS and AFM study of Pd(PVP) nanoparticle by means of He path system.  .  .  .  . 50
S. Yagi, T. Kodera, T. Nomoto, G. Kutluk, H. Namatame, M. Taniguchi

Pd L3-edge NEXAFS study of Pd(PVP) nanoparticle by means of He path system.  .  .  .  .  .  .  .  .  . 54
S. Yagi, T. Kodera, T. Nomoto, G. Kutluk, H. Namatame, M. Taniguchi

Reaction study of L-cysteine on Rh(PVP) nanoparticle surface in the aqueous
solution environment.  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 56
S. Gohd, T. Ashid, S. Yagi, H. Namatame, M. Taniguchi

Dissociation reaction of (CH3)2S adsorbed on Pd nanoparticles fabricated by gas
evaporation method using NEXAFS and in-situ XPS.  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  60
M. Morihara, K. Miura, T. Nomoto, S. Yagi, G. Kutluk, H. Namatame, M. Taniguchi

Site- and state-selective dissociation of core-excited organic molecules: Deuterium-labeled
methyl acetate.  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 63
R. Kawasaki, T. Yamanaka, H. Yoshida, K. Tabayashi

Hydrogen-bond interactions of small ammonia clusters observed with inner-shell excitation
spectroscopy at the nitrogen K-edge.  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 65
T. Yamanaka, T. Maruyama, H. Yoshida, K. Tabayashi

Dissociation dynamics of multiply-charged CF4 and CHF3 by momentum imaging
spectroscopy.  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 66
Y. Kimura, I. Miyagami, Y. Kawakami, H. Kawabata, H. Yoshida, A. Hiraya

Study on symmetries of core-excited states in CF4 and CHF3 .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 67
I. Miyagami, Y. Kimura, Y. Kawakami, H. Kawabata, H. Yoshida, A. Hiraya— iv —Dissociation dynamics of multiply-charged CH2F2 by momentum imaging spectroscopy .  .  .  .  .  . 68
Y. Kawakami, Y. Kimura, I. Miyagami, H. Kawabata, H. Yoshida, A. Hiraya

Dissociation dynamics of multiply-charged SF6 by momentum imaging spectroscopy.  .  .  .  .  .  .  . 69
H. Kawabata, Y. Kimura, I. Miyagami, Y. Kawakami, H. Yoshida, A. Hiraya

Photoemission study of fluorescein isothiocyanate isomer 1 (FITC) monolayer on platinum .  .  .  . 70
T. Maeda, M. Nakatake, H. Namatame, M. Taniguchi, T. Ishibashi

Core-level photoemission spectra and glass-forming ability in Pd42.5Ni7.5Cu30P20
bulk metallic glass.  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 72
S. Hosokawa, M. Nakatake, H. Sato, N. Happo, T. Ichitsubo, E. Matsubara, N. Nishiyama

Electronic states in Zr70Ni20Al10 Bulk Metallic Glass.  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 76
T. Nasu, S. Hosokawa, M. Nakatake, H. Sato, W. Zhang, A. Inoue

Angle-resolved photoemission spectroscopy of SrSi2/Si(111) .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 80
H. Maso, H. Kurihara, Y. Tatsukawa, H. Sato, M. Nakatake, H. Namatame, M. Taniguchi

The constant volume dilution effect of Eu site in EuPd2Si2: Eu 4d-4f resonant
photoemission study.  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 82

K. Mimura, D. Okumura, T. Ishizu, M. Nakatake, T. Kuwai, H. Namatame, M. Taniguchi,
Y. Taguchi, K. Ichikawa

Temperature-dependent angle-resolved photoemission spectra of TlInSe2:
specification of incommensurate and commensurate phases.  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 84
K. Mimura, T. Nogami, K. Abe, K. Wakita, M. Arita, N. Mamedov, G. Orudzhev, J. Takasu,
Y. Yonehira, H. Namatame, M. Taniguchi, Y. Taguchi, K. Ichikawa

Fermi surface and CDW gap of 2H-TaS2 studied by angle resolved photoemission
spectroscopy.  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 87
M. Arita, H. Sato, Y. Utsumi, H. Namatame, M. Taniguchi, M. Sasaki

Primary role of the barely occupied states in the charge density wave formation of NbSe2.  .  .  .  . 88
D. W. Shen, Y. Zhang, L. X. Yang, J. Wei, H. W. Ou, J. K. Dong, B. P. Xie, C. He, J. F. Zhao,
B. Zhou, M. Arita, K. Shimada, H. Namatame, M. Taniguchi, J. Shi, D. L. Feng

Superconducting coherence peak in the electronic excitations of a single layer cuprate
superconductor Bi2Sr1.6La0.4CuO6+d .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 90
J. Wei, Y. Zhang, H. W. Ou, B. P. Xie, D. W. Shen, J. F. Zhao, L. X. Yang, M. Arita, K. Shimada,H. Namatame, M. Taniguchi, Y. Yoshida, H. Eisaki, D. L. Feng

Novel electronic structure induced by a highly strained oxide interface with incommensurate
crystal fields.  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 92
H.W. Ou, J.F. Zhao, Y. Zhang, B.P. Xie, D.W. Shen, Y. Zhu, Z.Q. Yang, J.G. Che, X.G. Luo, X.H. Chen,
M. Arita, K. Shimada, H. Namatame, M. Taniguchi, C.M. Cheng, K.D. Tsuei, D.L. Feng—v—

Observation of the multibands and superconducting gaps in the trilayer high-Tc cuprate
superconductor Bi2Sr2Ca2Cu3O10+d.  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 94
S. Ideta, K. Takashima, M. Hashimoto, T. Yoshida, A. Fujimori, A. Ino, H. Anzai, T. Fujita,
Y. Nakashima, M. Arita, H. Namatame, M. Taniguchi, K. M. Kojima, S. Uchida

Impurity effect of nodal fine quasiparticle structure of Bi2Sr1.6(La,Gd)0.4CuO6+d studied
by low-energy synchrotron-radiation ARPES.  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 98

T. Fujita, T. Kamo, H. Anzai, A. Ino, M. Arita, H. Namatame, M. Taniguchi, A. Fujimori,
Z.-X. Shen, K. Fujita, S. Uchida

Doping- dependence of gap anisotropy of Bi2Sr2CaCu2O8+d studied by low-energy ARPES .  .  .  . 99
H. Anzai, T. Kamo, T. Fujita, A. Ino, M. Arita, H. Namatame, M. Taniguchi, M. Ishikado,
A. Fujimori, S. Uchida, Z. -X. Shen

ARPES study of the quantum size effects in atomically uniform Pb films on Si(111)-7×7 .  .  .  .  .  101S. He, Z. Zeng, M. Arita, M. Sawada, K. Shimada, S. Qiao, G. Li, X. Liu, W.-X. Li, Y.-F. Zhang,
J. Jia, Q.-K. Xue, H. Namatame, M. Taniguchi

Optimization of fluorescence XAFS spectroscopy for L edge measurements of Pd nanoparticles supported onto ZrOx. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .105
S. Hayakawa, H. Koga, H. Sumida, H. Namatame, T. Hirokawa

Molecular chain effect in photon stimulated ion desorption of self-assembled monolayers
induced by carbon core excitation .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 106
A. Hirano, I. Ohyama, Y. Tanikawa, S. Wada, K. Tanaka

Adsorption of HS(CH2)2COOCH3 on Cu(111) surface studied by XPS and NEXAFS
spectroscopy.  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 108
K. Yufu, K. Watanabe, K. Matsushita, S. Wada, K. Tanaka

Site-selective ion desorption of fluorine substituted self-assembled monolayers by coreelectron excitations .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  111S. Wada, N. Kushima, T. Yamamoto, K. Tanaka

In-situ XMCD measurement system for magnetic ultrathin films at BL14 .  .  .  .  .  .  .  .  .  .  .  .  .  114M. Sawada

Structural and magnetic properties of Cr/Fe/Cu(001).  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 117
S. Tohoda, M. Sawada, M. Nagira, T. Ueno, T. Tagashira, A. Kimura, H. Namatame, M. Taniguchi

Fabrication and in-situ XMCD study of Fe/Pd multilayers on Pd(001) .  .  .  .  .  .  .  .  .  .  .  .  .  . 119
T. Ueno, M. Sawada, M. Nagira, S. Tohoda, T. Tagashira, A. Kimura, H. Namatame, M. Taniguchi

XMCD study of orbital contribution to perpendicular magnetization in Co80Pt20 Thin-Films.  .  . 123
N. Ishimatsu, R. Ogasawara, T. Sone, Y. Tsutsui, H. Maruyama, N. Nakajima, M. Sawada, H. Namatame— vi —

L2,3 XAFS spectroscopy as a probe for the local symmetry of dopants (Nb, Ti)
in LiNi1–xCoxO2.  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 124
S. Hayakawa, R. Hasuno, T. Hayashi, T. Sako, M. Sawada, H. Namatame, T. Hirokawa

Improved sequence-based prediction of protein secondary structures by combining
vacuum-ultraviolet circular dichroism spectroscopy with neural network.  .  .  .  .  .  .  .  .  .  .  .  . 125
K. Matsuo, H. Watanabe, K. Gekko

Secondary-structure analysis of intermediate states of apo-myoglobin and pepsin using
a vacuum-ultraviolet circular dichroism spectroscopy.  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 129
H. Watanabe, K. Matsuo, H. Namatame, M. Taniguchi, K. Gekko

Secondary-structure analysis of disulfide variants of lysozyme by vacuum-ultraviolet
circular dichroism spectroscopy .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 131
K. Matsuo, H. Watanabe, S. Tate, H. Tachibana, K. Gekko

Vacuum-ultraviolet circular dichroism analysis of glycosaminoglycans by synchrotron-radiation
spectroscopy.  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 133
K. Matsuo, H. Namatame, M. Taniguchi, K. Gekko

Secondary-structure analysis of human serum albumin and a-chymotrypsinogen at
trifluoroethanol-denatured state using a vacuum-ultraviolet circular dichroism spectroscopy .  . 136
K. Matsuo, S. Yoshie, H. Namatame, M. Taniguchi, K. Gekko

Structural analysis of g-polyglutamic acids by vacuum-ultraviolet circular dichroism
spectroscopy.  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 138
K. Gekko, K. Matsuo, Y. Nogusa

Spin- and angle-resolved photoemission study of ultrathin Bi films on a silicon substrate .  .  .  . 139
T. Hirahara, K. Miyamoto, A. Kimura, Y. Niinuma, G. Bihlmayer, E. V. Chulkov, T. Nagao,
I. Matsuda, S. Qiao, K. Shimada, H. Namatame, M. Taniguchi, S. Hasegawa

Spin polarization of spin-orbit induced electronic structures of Bi(111).  .  .  .  .  .  .  .  .  .  .  .  .  .  143

R. Nishimura, K. Miyamoto, T. Kadono, K. Kanomaru, A. Kimura, K. Shimada, S. Qiao,
H. Namatame, T. Taniguchi

Unveiling spin characters of spin-orbit induced surface states.  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 144
K. MiyamotoA R. Nishimura, T. Kadono, K. Kanomaru, K. Iori, AKimura, S. Qiao, K. Shimada,H. Namatame, M. Taniguchi

Spin-resolved ARPES of Sb(111) single crystal surface .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 146
T. Kadono, K. Miyamoto, R. Nishimura, K. Kanomaru, M. Nagano, T. Shishidou, T. Oguchi,
S. Qiao, K. Shimada, H. Namatame, A. Kimura, M. Taniguchi– –Spin- and angle- resolved photoemission spectroscopy of a Si(111)√ 3×√ 3-Sb surface .  .  .  .  .  .  147K. Kanomaru, K. Miyamoto, T. Kadono, R. Nishimura, A. Kimura, S. Qiao, K. Shimada,H. Namatame, M. Taniguchi— vii —

Unoccupied band structure of 1T-TaS2 investigated by angle-resolved inverse-photoemission
spectroscopy.  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 148
Y. Utsumi, Y. Mukaegawa, M. Arita, H. Sato, M. Sasaki, A. Ohnishi, H. Namatame, M. Taniguchi

Surface electronic structures of ferromagnetic Ni(111) studied by scanning tunnelingmicroscopy and spectroscopy.  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 150
Y. Nishimura, H. Narita, M. Kakeya, M. Higashiguchia Y. Miura, M. Nakatake, A. Kimura,
K. Shimada, H. Namatame, M. Taniguchi

Atomic and local electronic structure of Co and CoSi2 clusters .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  151H. Narita, K. He, T. Okuda, A. Kakizaki, I. Matsuda, Y. Cui, A. Kimura, M. Nakatake,
H. Namatame, M. Taniguchi

Co-induced nano-structures on Si (111) surface .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 153
Y. T. Cuia, T. Xieb, M. Yea, A. Kimura, S. Qiao, H. Namatame, M. Taniguchi

Graphene epitaxially grown on the step with unit-cell height of 4H-SiC(0001) substrate.  .  .  .  . 157
M. Ye, Y. T. Cui, S. Qiao, A. Kimura, M. Sawada, H. Namatame, M. Taniguchi

Appendicies
Organization.  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 161
List of Publications.   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .  166Symposium.   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .  172Plan of the Building .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 173
Location .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .  174— viii —Current Status of HiSOR

Status of the HiSOR storage ring and future plan of HSRC
A. Miyamoto, K. Goto, H. Tsutsui†, T. Hori
Hiroshima Synchrotron Radiation Center, Hiroshima University
2-313 Kagamiyama, Higashi-Hiroshima, 739-0046 Japan†
Sumitomo Heavy Industries, Ltd.
1-1, Yato-cho 2-chome, Tanashi, Tokyo 188-8585, Japan

1. Introduction
HiSOR is a synchrotron radiation (SR) source of Hiroshima Synchrotron Radiation Center,
Hiroshima University, established in 1996[1]. HiSOR is a compact racetrack-type storage ring
having 21.95 m circumference, therefore its natural emittance 400π nmrad is not so small
compared with the other medium~large storage rings. The most outstanding advantage of the
facility lies in good combination with beamlines (BL’s) for high-resolution photoelectron
spectroscopy in energy range of VUV ~ soft X-ray. The principal parameters are shown in
Table 1.
Table 1: Main parameters of the HiSOR Storage ring.
CircumferenceType
Bending radiusBeam energy at Injection
at Storage
Magnetic field at Injection
at Storage
Injector
Betatron tune (νx, νy)RF frequency
Harmonic number
RF voltage
Stored current (nominal)
Natural emittanceBeam life time
Critical wavelength
Photon intensity (5 keV)

21.95 mRacetrack
0.87 m
150 MeV
700 MeV
0.6 T
2.7 T
150 MeV Racetrack Microtron(1.72, 1.84)
191.244 MHz
14
200 kV
350 mA
400 π nmrad~10 hours@200 mA
1.42 nm1.2×1011 /sec/mr2/0.1%b.w./300mA

The designed current of HiSOR is 300 mA, however, after the completion of both upgradeof the control system and improvement of the RF system in 2003, HiSOR has been in—1—

operation with 350 mA stored current since then. Fig. 1 shows an example of recent one-day
operation. Beam injection for HiSOR is operated twice a day, at about 9:00 and 14:30.
400

600
500
400

200

300
200

100

Beam life time [min]Ring current [mA]

300

100
0
09:00

0
12:00

15:00

18:00

Time

Fig. 1: Typical daily operation status.
HiSOR has two 180-deg. bending magnets which generate 2.7 T magnetic fields withnormal conductivity. This storage ring has two undulators, linear and helical, in each straightsection. The fundamental parameters of these undulators are shown in Table 2. The photon
energy spectra of the SR from HiSOR are shown in Fig. 2.
Table 2: Main parameters of the undulators.
Linear undulator (BL-1)
Total length
2354.2 mm
Periodic length λu
57 mmPeriodic number
41
Pole gap
30-200 mm
Maximum magnetic field
0.41 T
Magnetic material
Nd-Fe-B (NEOMAX-44H)
Helical undulator (BL-9A,B)
Total length
1828.6 mm
Periodic length λu
100 mmPeriodic number
18
Pole gap
30-200 mm
Maximum magnetic field
0.347 T (helical mode)
0.597 T (linear mode)
Magnetic material
Nd-Fe-B (NEOMAX-44H)—2—

Wavelength [nm]2

Photon flux density [photons/sec/mrad /0.1 % band width]

1000
10

16

10

15

10

14

10

13

10

12

10

11

10

10

100

Helical undulator
1st peak (helical mode)

10

1

Linear undulator
1st, 3rd, 5th, 7th peak

Ring current = 300 mA(linear mode)

Bending magnet

1

10

100

1000

10000

Photon energy [eV]Fig. 2: Photon energy spectra of the SR from HiSOR.

2. Operation status in FY 2007
Fig. 3 shows operation time of HiSOR storage ring in FY 2007. HiSOR is stopped for along term to have routine inspection every year in summer. In 2007, the serious trouble did
not occur and was able to digest a schedule on schedule. Therefore the user time achieved
1546 hours and it exceeded one of last year more than 100 hours, though we did not extend
the machine time after 20:00.
User time (1546hr)
Machine study (388hr)
Others (17hr)

Operation time [hours]

250

200

150

100

50

0

04

05

06

07

08

09

10

11

12

01

02

03

Month in FY2007

Fig. 3: Monthly operation time in FY 2007.
Further because there was not serious trouble, the storage time of HiSOR increased and—3—

recorded the longest time in last year. A change of operation time of storage ring andMicrotron from FY 2002 to FY 2007 is shown in Fig. 4.

2000

Operation time [hours]

HiSOR Storage ring
Storage time
150 MeV Microtron
Injection to REFER
Injection to HiSOR
1500

1000

500

0

2002

2003

2004

2005

2006

2007

Fiscal year

Fig. 4: Annually operation time of Storage ring and Microtron.

3. Future plan of HSRC, ‘HiSOR-II’
The emittance of the existing ring is not small because HiSOR is a compact synchrotron
light source when we compare it with the third generation light sources. In addition, there are
14 BL’s available in the bending section, but only two straight lines for undulators which are
obviously not enough as a current SR facility. Therefore, we are planning a compact storage
ring, ‘HiSOR-II’2,3, where undulators are dominant light sources as a next plan in HSRC.

3.1 Outline of HiSOR-II

We refer to electron storage ring MAX-III4 (in Lund, Sweden) as the outstanding models
with same scale to design of HiSOR-II. This storage ring is designed that the circumference isequal to or less than 50m so that it can be build in the site of HSRC, it has several straightsections for undulators, and its emittance is about 14nmrad. The main parameters of HiSOR-II
are shown in Table 3, and the schematic view is shown in Fig. 5.
A booster ring to have top-up injection is built the inside of HiSOR-II. This ring accelerates
the electron beam to 700 MeV for full energy injection to HiSOR-II storage ring. The detailsof the injector to the booster ring are considering, but we plan either 150MeV Microtron
which is operating as injector to HiSOR now or 15MeV linac (this detail is described later).
This booster has to be smaller than storage ring because it is arranged in the inside ofcompact storage ring. Further, it is placed in sublevel lower than the storage ring, this isconvenient that we can thin radiation shield walls.

—4—

Fig. 5: Schematic draw of HiSOR-II storage ring and booster ring.
Table 3: Main parameters of HiSOR-II.
Beam energy

700 [MeV],

Circumference [m]Bρ=2.335 [Tm]40.079Betatron tune

3.761, 2.846

Natural emittance [nmrad]

13.57

Momentum spread

5.79e-04

Momentum compaction factor

0.0319Bunch length [mm]37.0Harmonic number

7

RF Frequency [MHz]52.4

Radiation dumping time [msec]
Touschek lifetime [hour]
Straight sections

L:11.44

H: 8.57

V:14.70

2.7
3.4 m×4

2.0 m×4

The quadrupole magnets of HiSOR-II are combined magnets that occurring quadrupole andsextupole field as well as MAX-III. Further the bending magnets have focusing force, andsextupole component occurs by curved surface of edge of magnetic pole. Fortunately, we
could reduce the number of magnet and were able to plan ring miniaturization. The design of—5—

these magnets that complicated shapes is calculated with 2D and 3D electromagnetic code.
Fig. 6 shows optical functions of the unit cell of HiSOR-II.

βx
βy
ηx

1.5

10

1.0

5

0.5

0

0.0

0

2

4

6

8

Eta function [m]Beta function [m]1510Pathlength [m]Fig. 6: Beta and dispersion functions of HiSOR-II.

3.2 Spectra of synchrotron radiation
Fig. 7 shows radiation spectra from bending magnets, linear and helical undulators of
HiSOR-II at 300mA stored current. For comparison, the spectra of HiSOR are carried by finelines. It was assumed that the linear and helical undulators are the same that are used in
HiSOR now.
Wavelength [nm]2

Photon flux density [photons/sec/mrad /0.1 % band width]

1000

100

10

1

16

10

HiSOR2 (MAX-III Oct)

Ring current = 300 mA

15

10

Linear undulator
1st, 3rd, 5th, 7th peak

Helical undulator
1st peak (helical mode)

14

10

13

10

Bending magnet

12

10

11

10

10

10

1

10

100

1000

10000

Photon energy [eV]Fig. 7: Spectra of radiation from HiSOR and HiSOR-II at 300 mA current. Bold lines show
spectra from HiSOR-II, and fine lines from HiSOR.

—6—

3.3 Layout of accelerator complex of HSRC
A layout plan of accelerator complex of HSRC including HiSOR-II is shown in Fig. 8. But
the layout which is different from this may be adopted because this plan is not yet decision.
The building installing HiSOR-II storage ring and booster ring is built newly in this plan. The
arrangement of the ring is considered to be able to lengthen a straight section as much as
possible, and the beam is injected from the inside of the ring not to reduce beam line.

Microtron
Experimental hall
NEW experimental hall
HiSOR
HSRC Office building

HiSOR-II
Storage/Booster ring

Fig. 8: Layout plan of accelerator complex of HSRC.

3.4 Conversion to booster ring from NAR
We are planning that converts the second generation synchrotron radiation ring into booster
ring of HiSOR-II to save a construction cost of new accelerators. This ring is NAR5 of the
NTT synchrotron radiation facility, and middle class SR ring in about 53m circumference.
The magnets of NAR are separate function type, but we expect that it is necessary to convert
it into the combined function type on converting it into very compact booster ring. The outlineof the 700 MeV booster ring that is converted from NAR is shown in Fig. 9, and Fig. 10shows the optical functions of the booster ring. Circumference of this ring is 29.23 m,
betatron tune (νx, νy) is (2.31, 1.20).
About injector to the booster ring, it is considered two plans. One is 150 MeV Microtron
operating as injector to HiSOR now. However, we cannot have injection to HiSOR if we
install Microtron in the inside of the booster. Still, it is expected that that the construction oflong beam transport line by way of the underground tunnels from Microtron to the booster
ring is difficult. The other is a plan to transfer 15 MeV Linac which was injector to NAR. In
this case, the electron will be accelerated from 15 MeV to 700 MeV at the booster ring, the—7—conquest of many problems such as the injection to the ring by the low energy becomesrequired. Even if either plan is put into execution, enough studies are necessary.

Grid size 1.5000 [m]Fig. 9: Outline of the 700 MeV booster ring for HiSOR-II.

βx
βy
ηx

Booster from NAR

1.5

10

1.0

5

0.5

0

0.0

0

2

4

6

8

10

12

Eta function [m]Beta function [m]1514Pathlength [m]Fig. 10: Optical functions of 700 MeV booster ring.

3.5 REFER-II to study of injection / extraction of booster ring
The booster ring installed inward of the storage rings has short straight section for beam
injection or extraction. Therefore it is expected that the ordinary beam injection which we—8—

used septum for is difficult. Thus we proceed with plan using pulse sextupole magnet for
beam injection, we want to have the testing at the place where REFER is installed in.
REFER (Relativistic Electron Facility for Education and Research) is a very compact
multipurpose electron ring using the 150MeV electron beam from Microtron, and it is used
for experiments using electron stored in the ring with internal target and extracted beam fromthe ring. It is necessary to give ability same as REFER in REFER-II which is the test ring of
the booster to maintain these activity. Therefore we decided to find space to arrange theinstrument which was necessary for beam injection or extractions by extending two straightsection of the booster ring. Fig. 11 shows the overview of REFER-II, for comparison of thesize, the booster ring is drawn in the figure in a watermark, too. The circumference of thisring is 35.23 m, and 6 m are longer than it of the booster ring.

Grid size

1.500

Fig. 11: Outline of REFER-II.
Because the study of the magnets is performed in REFER-II, this ring consist of themagnets totally same as the booster ring. Furthermore, the lattice of this ring is assembled
with magnetic field strength same as the magnets of the booster ring. The optical functions of
the completed lattice in that way are shown in Fig. 12. The betatron tune (νx, νy) in this
Lattice is (2.31, 1.20).
Because the design of REFER-II still began, there will be many parts which you must
consider. Problems such as the injector of the booster ring will solve it in future byconsidering about the injection using pulse sextupole magnets enough.

—9—

βx
βy
ηx

REFER-II from NAR

1.5

10

1.0

5

0.5

0

0.0

0

5

10

Eta function [m]Beta function [m]1515Pathlength [m]Fig. 12: Optical functions of REFER-II

1

K. Yoshida, et al., “Commissioning of a Compact Synchrotron Radiation Source at
Hiroshima University”, APAC’98, KEK (1998) pp.653-657.
2
Sumitomo Heavy Industries, Ltd., “MAX-III/UVSOR-II type ring basic design examinationfor HiSOR-II”, (2006). (in Japanese)3
A. Miyamoto, et al., “Status of the HiSOR storage ring and future plan of HSRC”, HiSOR
activity report 2007.
4
G. LeBlanc et al., “MAX-III, a 700 MeV Storage Ring for Synchrotron Radiation”,
EPAC2000, Vienna (2000).
5
S. Shibayama, et al., “NTT normal-conducting accelerating ring”, Rev. Sci. Instrum. 60(1989) pp.1779-1782.

— 10 —

Beamlines
A total of 13 beamlines has been constructed so far; three normal-incidence monochromators,
seven grazing-incidence monochromators, two double crystal monochromators and an apparatus forwhite beam irradiation. Table 1 lists the beamlines at present together with the main subject, energy
range and monochromators.
At present, nine beamlines BL1, BL3, BL6, BL7, BL9(A), BL11, BL13, BL14 and BL15 havebeen opened for users. Furthermore, two off-line systems, spin- and angle-resolved photoemission(SARPES) spectrometer and inverse-photoemission spectrometers have also opened for users.
Research proposals are regularly submitted in the beginning of every year or additionally any timeon demand of users not only in Japan but also in worldwide countries. In 2007, 66 research proposals
and 7 improvement proposals were approved. At the undulator beamlines BL1 and BL9A dedicatedto the photoemission and angle-resolved photoemission spectroscopies, the experiments with a totalenergy resolution of 0.66-15 meV at 6-100 eV are now possible.
In 2007, new end station at BL1 for polarization-dependent angle-resolved photoemission
spectroscopy (ARPES) has been designed. ARPES with s- or p-polarization geometry, which
determines symmetry of the initial-state wave function, will soon be possible. At the soft x-ray
beamline BL14, in situ system for fabrication of magnetic ultrathin films in monatomic layer
control by MB and their characterization by means of Auger electron spectroscopy, low energy
electron diffraction and high energy electron diffraction, has been introduced. After the fabricationand characterization of magnetic films, the soft x-ray magnetic circular dichroism experiments on
the grown films are available. The similar fabrication system has been introduced for the SARPES
spectrometer and several in situ SARPES data have been obtained on magnetic atoms on simple
metals.

— 11 —

SRPES

Surfacephoto-chemistry

13
BL
-

- 9A
BL

BL-11

VUV-CDBL12

BL-9B

diffraction

-14

BL

5

BL-1

HRPES

VUV-CD(bio-materials)
BL16
Beam monitor

Helical undulator
Beam monitor

Linear undulator

BL-8

BL-7
BL

Gas-phasephotochemistry

4
BL-3

-5

BL

-1

-6

BL

BL-

PES/IPES

MCD/LD

irradiation
Surface XAFSARPES/PEEM

Fig. 1. Schematical view of the experimental hole.

— 12 —HRPES

Table I. List of Beamlines
beam
line

monochsource romator

subject

energy range(eV)

status

BL1

LU

GIM

High-resolution PES and ARPES

26-300in use

BL3

BM

DCM

Surface XAFS

1800-3200

in use

BL4

BM

BL5

BM

GIM

ARPES and PEEM

40-220in use

BL6

BM

GIM

Gas-phase photochemistry200-1200in use

BL7

BM

GIM

PES and IPES

20-380in use

BL8

BM

BL9A

HU/LU

NIM

High-resolution PES and ARPES

5-35

in use

BL9B

HU/LU

GIM

Spin-resolved PES (in future)

16-300testing

BL11

BM

DCM

X-ray diffraction

2000-5000

in use

BL12

BM

NIM

VUV-CD of biomaterials

2-10

testing

BL13

BM

GIM

Surface photochemistry60-1200

in use

BL14

BM

GIM

Soft x-ray MCD

400-1200in use

BL15

BM

NIM

VUV-CD of biomaterials

4-40

in use

BL16

BM

White beam irradiationin useBeam monitor

Beam monitor— 13 —

Wavelength (Å)
1000
100

Photon Flux Density (photon/sec/mrad2/0.1%b.w)

10000

1016

Helical Undulator
1st peak

1st

3rd

helical mode

1015

10

5th

7th peakplanar mode

1014

Linear Undulator

1013

Bending Magnet

1012
BL1

1011

BL12

BL9A
BL15

1

10

BL5
BL7
BL9B

BL6
BL13

100
Photon Energy (eV)Fig. 2. Energy ranges of beamlines with spectra of HiSOR.

— 14 —

BL14

1000

BL3

BL11

Research Activities

New end station for the linear undulator beamline BL-1
K. Shimadaa, M. Higashiguchib, N. Tobitab,
S. Fukudab, K. Tanakab, J. Jiangb, H. Hayashib, H. Namatamea, M. Taniguchia,baHiroshima Synchrotron Radiation Center, Hiroshima Universityb
Graduate School of Science, Hiroshima University

In year 2007, we have designed new end station for BL-1 in order to perform
polarization-dependent angle-resolved photoemission spectroscopy (ARPES). In the new
system, the electron analyzer can be rotated around the light axis, which enables us to
examine ARPES spectra with s- or p-polarization geometry. It is indispensable to determine
symmetry of the initial-state wave function.
Figure 1 shows the final design of the rotatable frame. High-resolution angle-resolved
photoemission spectrometer (VG-SCIENTA, R4000), main chamber with a μ-metal chamber
inside, and multi-axes low-temperature goniometer (i-GONIO) will be rotated with the frame.
Differentially pumped rotary feedthroughs will be installed between the main chamber andthe beamline, and the main chamber and the preparation chamber. We will use a highprecision goniometer with in-plane motion for Fermi surface mapping. New system will be
installed in year 2008.


Fig. 1. Final design of the rotatable frame for new BL-1 end station.

— 17 —

06-A-50

BL-1

Angle-resolved photoemission study of the Shockley state in Au(110)
Mitsuharu Higashiguchi1, Kenya Shimada2, Yuichi Miura1, Naohisa Tobita1, Yoshihiro Aiura3,
Hirofumi Namatame2, Masaki Taniguchi1,2123Graduate School of Science, Hiroshima University

Hiroshima Synchrotron Radiation Center, Hiroshima University

National Institute of Advanced Industrial Science and Technology

In the present study, we have examined the electronic states of the Shockley state (SS) in
Au(110) by means of high-resolution angle-resolved photoemission spectroscopy (ARPES).
Although Au(110) surface is known to have the “(2×1) missing-row” reconstructed structureas Fig. 1(b) shows [1-3], we have obtained the (1×1) unreconstructed structure (Fig. 1(a))
judging from the Fermi surface (FS) mapping. Figure 1(c) shows the relation between thebulk Brillouin zone (BBZ) and surface Brillouin zone (SBZ) of the (110) plane without
reconstruction. If the (2×1) surface reconstruction occurs, a new zone boundary is formed
midway between the Γ and Y points as Fig. 1(d) shows. In this case, the Γ and Y points
become essentially identical.

(c)

(d)

Figure 1. Schematic view of the (1×1) unreconstructed surface of (110) plane (a), and the (2×1) reconstructedsurface of (110) plane (missing-row structure) (b). (c) The relation between BBZ and SBZ of (110) plane. (d)The SBZ with and without reconstruction.

High-resolution ARPES measurements were carried out using an angular mode of ahemispherical electron-energy analyzer (ESCA200, SCIENTA) installed at the linear— 18 —

undulator beamline BL-1. The total energy resolution was set at ∆E=10-17 meV, and theangular resolution at ∆θ= ±0.15° (∆k//=0.016-0.02 Å-1). A single crystal of Au(110)(99.999%) was cleaned by repeated cycles of Ar+ ion sputtering (the beam energy, 1-2kV)
and subsequent annealing at 400 °C. The amounts of impurities such as C, O on the surface
were found to be below the detection limit of Auger electron spectroscopy and ultraviolet
photoemission spectroscopy. The sample was mounted on a liquid-He-flow-type 5-axis
goniometer (i-GONIO LT, R-DEC Co.). The sample temperature was set at 13 and 150 K.
The pressure of the main chamber was lower than 2×10-10 Torr. The angle between the lensaxis of the detector and incident synchrotron radiation was 45°. The polarization vector of theundulator radiation was parallel to the [11 0] direction (p-polarized geometry).
Figure 2 shows FS images for Au(110) taken at incident photon energies of hν = 40.5-59.9
eV at the sample temperature of 13 K. We could observe half of the elliptic FS centered at theYpoint of SBZ. Since the FS at the Γ and Y points are not identical, the surface of thepresent sample was not reconstructed. Since the size and shape of the FS does not depend on
the incident photon energy, we can confirm that the Au(110) SS forming FS are indeed
localized at surface.

Figure 2. The photon energy dependence FS image for Au(110) taken at hν=40.5-59.9 eV.

— 19 —

Figures 3(a) and (b) show intensity plots of the FS of the Au(110) SS around the Y pointat 13K and 150K, respectively. In order to evaluate the shape and size of FS, we fitted themomentum distribution curves (MDCs) with Lorentzians at the Fermi level. The evaluatedpeak positions are indicated by circles in Figs. 3(a) and (b). The contour of FS is well
reproduced by the elliptic fit. The size and shape of FS are almost the same at 13K and 150K.
The area of the Fermi surface was determined to be SEF = 0.088 Å-2, which corresponds to thecarrier density of 2.2×1013 cm-1.
(a)

(b)

Figure 3. The intensity plots of the FS of the Au(110) Shockley state at 13K (a) and 150K (b).

Figures 4 and 5 exhibit the intensity plots of the band dispersion and energy distribution
curves (EDCs) along the YS

and ΓY directions, respectively. One can see almost

free-electron-like band dispersion. By the fitting of EDCs with a Lorentzian, we evaluatedpeak positions (circles in Figs. 4(a) and 5(a)). The observed energy band dispersions are
explained well by a parabolic function (solid lines in Fig. 4(a) and 5(a)). Along the ΓYdirection, half of the spectral intensity was suppressed. We assume that the suppression of thespectral intensity is derived from the matrix element effect. The Fermi energy was evaluatedas ε Y0 S = 590±5 meV along the YS direction. The Fermi wave number along the YS

direction, kFY S = 0.195 Å-1, is larger than that along the ΓY direction, kFΓY = 0.167 Å-1.
Accordingly, the effective mass with respect to the free electron mass (me) along the YS

direction, m* = 0.25 me, is heavier than that along the ΓY direction, m* = 0.13 me.
In conclusion, we have performed a high-resolution ARPES of Au(110) SS using tunable
photons. We observed elliptic FS centered at the Y point of SBZ. We found that half of thespectral intensity of FS was suppressed. We estimated the shape and size of FS, as well as— 20 —

band parameters such as kF and m*. These parameters did not depend on the photon energy,
confirming highly two dimensional nature of Au(110) SS.

Figure 4. The intensity plot of the band dispersion (a), EDC spectra (b) along the Y S direction. (c) SBZ
of Au(110) and measured direction (red arrows).

Figure 5. The intensity plot of the band dispersion (a), EDC spectra (b) along the ΓY direction. (c) SBZ
of Au(110) and measured direction (red arrows).

References[1] K. –M. Ho, K. P. Bohnen, Phys. Rev. Lett. 19, 1833 (1987).
[2] Y. Uehara, F. Fujita, S. Ushioda, Phys. Rev. Lett. 83, 2445 (1999).
[3] Y. Uehara, S. Ushioda, Phys. Rev. B 66, 165420 (2002).

— 21 —

07-A-39    

BL-1

Angle-resolved photoemission study of Pt (111)
N. Tobita1, S. Fukuda1, N. Nakajima1, N. Ishimatsu1, H. Maruyama1,
H. Hayashi2, K. Tanaka1, J. Jyan1, M. Higashiguchi1, K. Shimada3,
H. Namatame3 and M. Taniguchi1, 3
1Grad. Sch. of Sci., Hiroshima Univ., 2Fac. of Sci. Hiroshima. Univ.,
3
Hiroshima Synchrotron Radiation Center, Hiroshima. Univ.
Platinum is known as one of the most important catalytic materials for long. Its catalytic
effect is thought to be caused by a relativistic effect which is also related to surface reconstruction of clean surfaces. In noble metals with an fcc structure such as Cu, Ag and Au, a bit
wider band-gaps exist at the Fermi level around an L point and also Shockley surface-states
derived from an sp-like bulk bands are observed in between the gaps. Among them, a splittingof the surface-state bands caused by strong spin-orbit interaction was observed in Au. Recently, it is observed that the intensity of the splitting depends on crystal orientation [1]. Pt
also shows strong spin-orbit interaction and is therefore expected to be a basic material for
spintronics devices or a good testground for spin Hall effect in metals.
The lowered dimensionality of intrinsic electron states favors the production of screening
singularities and phonon anomalies, and is thus responsible for the surface reconstruction [2].
Therefore, it is important to clarify the surface state of Pt. In this study, we have performed anangle-resolved photoemission study (ARPES) of a Pt (111) clean surface.
The ARPES spectra were measured on the undulator beamline BL1 at HiSOR. All theexperiments were performed at low temperature (~30K). The base pressure of the chamber
was an order of 10-10 Torr. A clean (111) surface was simply prepared by Ar+ ion sputteringand annealing. Once a clean surface was obtained, the sample surface was almost free fromcontaminations.
Figure 1 shows photoemission spectra of a Pt (111) surface at several
points. Solid(dashed) lines are the spectra for positive (negative) polar angle () which origin ( = 0°) is
set to a normal emission configuration. At each photon energy, the spectra show strong dependence on the polarity of , which is directly due to the difference in the components ofpolarization and may be influenced by an sp-like nature of the corresponding bands. The
binding energies (EB) of several peaks for EB below 3.8 eV strongly depend on the polarity of
, however, those of the peaks for 0 eV < EB < 2 eV remain the same except the peak S labeled by solid triangles (). Compared to a theoretical prediction of the band structure [3], all
the peaks except the peak S locate in the projection of bulk bands at the
point. The peak S
shows strong dependence on the polarity of . Besides, the binding energy for positive  isalmost constant. It is therefore safely concluded that the peak S is a surface state derived fromthe sp-like bulk bands.

— 22 —

Fig. 1: ARPES spectra of a Pt (111) clean surface.
Solid (dashed) lines are the spectra for positive (negative) polar angles ().
At BL-1, new energy analyzer (Scienta R4000)
will be installed on a bland-new chamber which enables
the polarization dependence measurement without
breaking the vacuum. A complete understanding of thespectra will be achieved soon.
[1] M. Higashiguchi, Doctoral thesis, Hiroshima Univ. (2008).
[2] H. H. Ernst et al., Phys. Rev. Lett. 58, 1941 (1987); W.
Kohn, ibid. 2, 393 (1959).
[3] D. A. Papaconstantopoulos, Handbook of the Band Structure of Elemental Solids (Plenum, New York, 1986); W. Di
et al., Phys. Rev. B 45, 3652 (1992).

— 23 —

07-A-34

BL-1

   Angle-resolved photoemission study of Cr (110)
S. Fukuda1, N. Tobita1, N. Nakajima1, N. Ishimatsu1, H. Maruyama1,
H. Hayashi2, K. Tanaka1, J. Jyan1, M. Higashiguchi1, K. Shimada3,
H. Namatame3 and M. Taniguchi1, 3
1Grad. Sch. of Sci., Hiroshima Univ., 2Fac. of Sci. Hiroshima. Univ.,
3
Hiroshima Synchrotron Radiation Center, Hiroshima. Univ.
Chromium (Cr) is one of the key elements for the recent study on the spintronics mainly
because its antiferromagnetic nature can be utilized to manipulate the spin state of materials.
Among the wide variety of 3d transition metals, antiferromagnetism of Cr is the most challenging problem to tackle with. Especially, a spin-density wave (SDW) and a charge-density
wave which result in modulation of electronic states are still under debates together with surface ferromagnetism caused by lattice expansion. These fascinating features are still difficult
to examine partly due to difficulties in preparing a clean (contamination-free) surface. The
recent progress of evaporation techniques for preparing ultrathin films has made it possible toeasily obtain clean Cr surfaces and intensive studies such as photoemission and scanning tunneling spectroscopy are performed using these films. However, the above-mentioned nature of
Cr is very delicate and faint to see depending on the film conditions such as lattice parameters
and/or surface morphology.
In order to eliminate the uncertainty arising from the film condition, we have used a bulk
sample with an (110) surface. A clean surface was carefully prepared by repeated cycles of
Ar+ ion sputtering (< 3 kV) and annealing (< 800 K) followed by a thermal flash at 1100 K.
Special care was paid to the initial cleaning process in order not to create an oxidized surface
which is hard to remove in a vacuum. The angle-resolved photoemission spectra were measured on the undulator beamline BL1 at HiSOR. Throughout the course of experiments, thebase pressure of the chamber was an order of 10-10 Torr.
Figure 1 shows a Femi surface mappingof Cr (110) in a HPN plane of a bcc Brillouin zone taken at 77K with photon energyof 139 eV. Two pantographs around  and H
points correspond to electron and hole pockets, respectively. A momentum distribution
curve along a white dashed line reveals aback-folding band caused by an antiferromagnetic order. Details of multifolding bands
due to the SDW will be examined in a forthcoming experiment.

Fig. 1: A Fermi surface mapping of a Cr(110) clean surface taken at 77K withphoton energy of 139 eV.

— 24 —

07-A-41

BL-1

High-resolution angle-resolved photoemission study of the surface-derived
state in Al(100) single crystal
J. Jianga, K. Shimadab, M. Higashiguchia, N. Tobidaa, K. Tanakaa,
S. Fukudaa, H. Hayashia, Y. Aiurac, H. Namatameb, M. Taniguchia,baGrad. Sch. of Sci., Hiroshima Univ.,b
HSRC, Hiroshima Univ.,c
AIST

Recently, energy and momentum resolutions of angle-resolved photoemission
spectroscopy (ARPES) have been improved drastically. Now one can examine fine electronic
structures of solids that are directly related to the physical properties of solids. Using photon
energies in the vacuum ultraviolet and soft X-ray region, ARPES spectra are sensitive to theelectronic states at surface. Based on the quantitative analyses of photoemission spectralfeatures, one can evaluate the magnitudes of the electron-phonon and electron-electroninteractions at a specific point on the Fermi surface.
Aluminum is the textbook example of a trivalent nearly-free electron metal and a weakcoupling superconductor. It has been well known that there exists a free-electron-likesurface-derived state around the Γ point of the surface Brillouin zone in the (100) surface[1-4]. So far, there has been no report on the quasi-particle properties near Fermi level (EF) of
aluminum by means of ARPES. In this study, we have done high-resolution ARPES of
Al(100) to evaluate the many-body interactions on the quasi-particles near EF in thesurface-derived state. A kink structure has been clearly observed in the energy band dispersionof the surface-derived state. The magnitudes of the electron-phonon and electron-electron
coupling parameters at low temperature have been successfully evaluated. The obtained
electron-phonon coupling parameter showed reasonable agreement with the calculated one[4].
ARPES experiments were performed on the linear undulator beamline (BL-1) of acompact electron-storage ring (HiSOR) at Hiroshima University [5]. High-resolution ARPES
measurements were carried out using an angular mode of hemispherical electron-energy
analyzer (ESCA200, GAMMADATA-SCIENTA at BL-1). Linearly polarized undulator
radiation (hν=43 eV) was used. We set the total energy resolution at ∆E =15 meV and∆θ =0.3°. The clean surface of Al(100) single crystal (purity 99.9999%) was obtained byrepeated cycles of Ar+ sputtering (5 keV) over 10 hours and annealing at 400°C for 30
minutes to minimize surface roughness introduced by Ar+ sputtering. The amount of
impurities such as C, O, and S on the surface was evaluated below the detection limit ofAuger electron spectroscopy. The sample was mounted on the liquid-He-flow-type 5-axis— 25 —

goniometer (i-GONIO LT, R-DEC Co.). The sample temperature was set at 30 K. The
pressure of the main chamber was 1 × 10 −8 Pa.

Fig. 1. The ARPES results of Al(100) surface-derived state at hν = 43 eV and at 30 K.

Fig. 2. Experimentally determined band points near EF. A kink structure exists at -37 meV.

Figure 1 shows the energy-band dispersion of the surface-derived state centered at the Γpoint. It has a sharp spectral feature and a parabolic dispersion, which is suitable for thedetailed line shape analyses to elucidate many-body interactions. In order to quantitatively
analyze the spectral shape, we used Lorentzian on a linear background to fit the momentum
distribution curves (MDCs). The blue points and red lines in Fig. 1 indicate evaluated peak
positions, and assumed non-interaction band. Figure 2 shows the area surrounded by the green
square in Fig. 1. One can recognize a clear kink structure at -37 meV below EF. Since themagnitude of the energy of the kink coincides well with the energy scale of the Debye
temperature of Al (ΘD=426 K, kBΘD=37 meV), it is reasonable to assume that the structure isderived from the electron-phonon interaction [6,7].
Next we examine the strength of many-body interactions on the quasi-particles near EF,
by evaluating the self-energy, Σ(k, ω ) . The ARPES spectral features are given by thesingle-particle spectral function A(k,ω ) , which is related to the imaginary part of the— 26 —

single-particle Green’s function, G(k,ω ) :A( k , ω ) = −1πG (k, ω ) = −Im Σ(k, ω )π [ω − ε − Re Σ(k, ω )] 2 + [Im Σ(k, ω )] 2
1

0
k

(1)

where ε k0 represents the energy of non-interacting band. In the present analyses, we haveassumed that ε k0 is linear near EF as shown by a solid line in Fig. 2. Re Σ (k, ω ) gives anenergy shift from the energy of non-interaction band. The Im Σ(k, ω ) is related to thespectral width, Γ = 2Im Σ (k, ω ) [6,7]. In the present analyses, we used the MDC width, δk,to estimate the ImΣ(k ,ω ) , namely, | 2ImΣ(k , ω ) |= δ E = (dE / dk ) δ k , where dE / dk is thegradient of the energy band.
In the case that electron-scattering processes such as the electron-phonon,
electron-electron, and electron-impurity interactions can be regarded as independent, thelifetime broadening ( Γ = | 2Im Σ (k, ω ) | ) of the quasi-particles is expressed by the sum of eachcontribution: Γ = Γel − ph + Γel −el + Γ0 .
Figure 3(a) and 3(b) respectively show obtained Γ = | 2Im Σ (k, ω ) | and Re Σ (k, ω ) .
Solid and dashed lines in Fig. 3(a) exhibit theoretical Γel − ph and Γel− el , respectively. One cansee observed Γ = | 2Im Σ (k, ω ) | is explained well by the theoretical curve Γel − ph + Γel −el .
Solid line in Fig. 3(b) indicates the theoretical Re Σ el− ph , which agrees well with theexperimental one. These results confirm that the kink structure originates fromelectron-phonon interaction.
One can evaluate the dimensionless coupling parameter of the electron-phonon
interaction as follows.

λel− ph = −∂Re Σ el− ph
∂ω

(2)
ω= 0

Using the observed gradient of Re Σ el− ph at EF (dashed line in Fig. 3(b)), we haveobtained λel − ph = 0.67. Recently, Sklyadneva et al. have reported an ab initio study of theelectron-phonon interaction in the surface electronic states of Al(100), on the basis of thedensity-functional theory using a linear response approach in the plane-wave pseudopotential
representation [4]. The calculated electron-phonon coupling parameter is λel − ph = 0.51 at theΓ point. However, the coupling parameter increases with energy [4]. Although the coupling
parameter at EF was not provided, calculated Re Σ el− ph (solid line in Fig. 3(b)) using
theoretical α 2 F coincides well with the experimental one near EF. It clearly indicatesexperimental coupling parameter is in good agreement with the theoretical value.
In order to evaluate the magnitude of the electron-electron interaction, on the other hand,
we fit the observed 2Im Σ assuming 2βω 2 [1/4 + ln2 − 1/2 ln ω /ω 0 ] + C for the energy
region of −800 meV ≤ ω ≤ −50 meV . Here C is a constant, and the Fermi energy was set atω0 = 2.63 eV. We have obtained 2β = 0.03 eV-1. Using the Kramers-Kronig relation, one canevaluate the coupling parameter of the electron-electron interaction as— 27 —

λel − el = 4βω 0ζ π = 0.060 [8].
In summary, we have performed a high-resolution ARPES study of the surface-derived
state centered at the Γ point in Al(100). We have observed a clear kink structure in theenergy-band dispersion at ω = -37 meV, which corresponds well to the energy scale of the
Debye temperature. We have evaluated the electron-phonon and electron-electron coupling
parameters as λel − ph = 0.67 and λel −el = 0.060, respectively. We have found that λel −el ismuch smaller than λel − ph .

Fig. 3 Imaginary part (a) and real part (b) of self-energy of the surface-derived state in Al(100) .

We thank the N-BARD, Hiroshima University for supplying liquid helium.
References[1] H. J. Levinson, F. Greuter and E. W. Plummer, Phys. Rev. B 27, 727 (1983).
[2] Ph. Hofmann, S. V. Hoffmann et al., Phys. Rev. B. 66, 245422 (2002).
[3] E. E. Krasovskii and W. Schattke, Phys. Rev. Lett. 93, 027601 (2004).
[4] I. Y. Sklyadneva, E. V. Chulkov and P. M. Echenique, J. Phys.: Condens. Matter 20,
165203 (2008).
[5] K. Shimada, M. Arita, Y. Takeda, H. Fujino, K. Kobayashi, T. Narimura, H. Namatame, M.
Taniguchi, Surf. Rev. Lett. 9, 529 (2002).
[6] T. Valla, A. V. Fedorov, P. D. Johnson, S. L. Hulbert, Phys. Rev. Lett. 83, 2085 (1999).
[7] M. Higashiguchi, K. Shimada, K. Nishiura, X. Y. Cui, H. Namatame, M. Taniguchi, Phys.

— 28 —

Rev. B 72, 214438 (2005).
[8] In the present analyses, we have assumed the imaginary part of the self-energy as
⎡1
⎡1
⎤
ω ⎤
1
ImΣ el−el (ω ) = −βω 2 ⎢ + ln2 − ln
⎥ for ω ≤ ω 0 , and ImΣ el−el = −β ω 02 ⎢ + ln2⎥
⎦
⎣4
ω0 ⎦
2
⎣4

for ω > ω 0 . Here ω 0 is the Fermi energy. On the basis of the Kramers-Kronig relation,
one can calculate the real part of the self-energy as follows.
+ω 0 ImΣ1el−el (ω ′)Re Σ el−el (ω ) = P ∫dω ′(ω ≤ ω0)−ω 0πω′ − ω
Then, the coupling parameter can be calculated as follows.

λel−el = −+∞ ImΣ
∂Re Σ el−el (ω )1el−el (ω ′)= − P ∫−∞
dω ′
∂ω
π
ω ′2
ω= 0

∴ λel−el =⎤ 4 βω 0
4βω 0 ⎡ 1
+ ln2 ⎥ =
ζ,
⎢
⎦
π ⎣2
π

⎡1
⎤
+ ln2 ⎥ ~ 1.193
⎣2
⎦

ζ ≡⎢

— 29 —

06-A-48

BL-1

High-resolution angle-resolved photoemission spectroscopy of Rh(100)
Hirokazu Hayashia, Kenya Shimadab, Katsunori Tanakac, Mitsuharu Higasiguchic,
Naohisa Tobitac, Jan Jingc, Shugo Fukudac, Hirofumi Namatameb, Masaki Taniguchia,baFac. of Sci. Hiroshima Univ.,b
HSRC, Hiroshima Univ.,cGrad. Sci. of Sci. Hiroshima Univ.
Rhodium is one of the most important
and widely used metals as a catalyst
cleaning exhaust gas from automobiles. So
far, the electronic band structures of Rh
clean surface together with molecule
adsorbed surface have been studied bymeans of angle-resolved photoemission
spectroscopy (ARPES). However, the detailof the electronic band structures and the
Fermi surface of Rh clean surface have notbeen elucidated yet. In this study, by meansof high-resolution ARPES with tunable
synchrotron radiation, we have examined
Figure 1. Fermi surface mapping of Rh (100) taken
three-dimensional Fermi surface of Rh. In
at h = 155.7 eV, at 150 K. White portion
the vacuum ultraviolet region, one can corresponds to the highest spectral intensity. Solidobserve both surface- and bulk-derived lines show Fermi surfaces calculated by theelectronic structures. It is noted that the band-structure calculation [1]. Broken lines trace
structures that cannot be explained by thesurface electronic state is closely related to bulk-derived Fermi surfaces.
catalysis. We also elucidate quasi-particles
in the bulk-derived electronic states.
Experiments were done on the linear undulator beamline (HiSOR BL-1) of Hiroshima
Synchrotron Radiation Center. By repeated Ar+ sputtering and high temperature anneal at
1200 K, we obtained clean surface of Rh(100). Cleanliness of the sample surface was checkedby Auger spectroscopy. The sample was mounted on the 5-axes low-temperature goniometer(iGONIO) for the Fermi surface mapping. A high-resolution hemispherical electron-energy
analyzer (ESCA200) was used for the ARPES measurements. The overall energy andmomentum resolutions were respectively set at E = 13.4 - 89.7 meV and k = 0.011 0.027Å-1, depending on the incident photon energy range h = 63.5 - 155.7 eV.
Figure 1 shows an image plot of the observed Fermi surface in the KWX plane of theBrillouin zone (Fig. 2) taken at photon energy of h=155.7 eV and at sample temperature of— 30 —

150 K. White portion corresponds to the highest spectral intensity. Solid lines exhibit
theoretical Fermi surfaces given by the band-structure calculation [1]. One can see good
agreements between experiment and theory. However, Broken lines trace structures thatcannot be explained by the bulk-derived Fermi surfaces.
We also measured energy-band dispersions along the X and XW high symmetry lines.
The energy band positions at the high symmetry points were found to coincide well with thosegiven by the calculation [1]. We could identify the bulk-derived electronic states
unambiguously. Near the M point of the surface Brillouin zone (Fig. 2), on the other hand,
we found structures S, S1 and S2 which were not predicted by the bulk band-structure
calculation (Fig. 3). In order to confirm the origin of the structure, we measured ARPES ath=63.9 eV, 115.2 eV and 135.9 eV. The spectral feature at the M point showed no h
dependence. It clearly indicates that the structure is derived from the surface electronic states.

Figure 2. Surface Brillouin zone andBrillouin zone.

bulk

Figure 3. Band dispersion of Rh (100) taken at h = 63.9 eV
and at 31K. White portion corresponds to the highest spectral
intensity. Solid line (B) shows the bulk-derived band. Brokenlines (S, S1, S2) show the structures that are derived from thesurface electronic states.

Reference[1] G.S. Tripathi et al., Phys. Rev. B 38 (1988) 10454.

— 31 —

07-A-48

BL-1

High-resolution angle-resolved photoemission spectroscopy of Rh(111)
K. Tanakaa, K. Shimadab, N. Tobitaa, S. Fukudaa, H. Hayashia,
J. Jianga, Y. Aiurac, H. Namatameb, M. Taniguchia,baGrad. of Sci. Hiroshima Univ.
b
HSRC, Hiroshima Univ.
c
AIST
Rhodium is one of the most important andwidely used metals as a catalyst cleaning exhaustgas from automobiles. In this study, by means ofhigh-resolution angle-resolved photoemission
spectroscopy (ARPES) with tunable synchrotron
radiation, we have clarified the Fermi surfaces
and the bulk-derived electronic states of Rh(111).
By means of quantitative analyses of the ARPES
spectra, we have evaluated the coupling parameterof the electron-phonon interaction.
Experiments have been performed on thelinear undulator beamline BL-1. By repeated Ar+
sputtering and high temperature annealing at 1200
K, we obtained clean surface of Rh(111) single
crystal. We used a high-resolution hemisphericalelectron energy analyzer (SCIENTA SES200).
The overall energy and momentum resolutions
were respectively set at E = 11-170 meV and k= 0.011-0.027 Å-1, depending on the incident
photon energy h = 21.2-172.5 eV.
Figure 1 shows an image plot of the observed
Fermi surface located around the L point in the
KUX plane at the photon energy of h = 35.4 eV
and sample temperature of T = 20 K. The black
portion indicates strong spectral intensity at EF.
We examined the energy band along the red line
in Fig. 1.
In order to evaluate peak position of theenergy band, we fit momentum distribution curves
with a Lorentzian. If the electron-phonon coupling— 32 —

Figure 1. Fermi surface mapping of Rh(111) taken at h = 35.4 eV and T = 20 K.

Figure 2. Experimental and theoreticalimaginary and real parts of the self-energy.

is strong enough, one can see a kink structure at the energy scale of the Debye temperature(kBD) [1]. In the case of Rh, the energy scale is expected to be kBD = 41 meV (D = 480 K)[2]. Although the kink structure in the observed energy-band dispersion was very weak, we
could discern a kink structure at energy of -30 ~ -40 meV.
Figure 2 shows evaluated real and imaginary parts of the self-energy () deduced from thelineshape analyses [2]. We have evaluated a dimensionless coupling parameter of theelectron-phonon interaction as  = 0.10, based on the gradient of Re  at EF. On the other
hand, by the fit of the lower energy part of |2Im | with a function 22, we obtained 2 =0.25 eV-1 which gives a measure of the electron-electron interaction. The 2 value iscomparable with that for the Cu 1 band (2 = 0.2 eV-1)[3], but smaller than that for the Ni
1 band (2 = 0.6-1.4 eV-1) [1]. Present results indicate that the effective mass enhancement is
negligible for the energy band we examined, confirming that electrons in Rh have itinerant
nature.
References[1] M. Higashiguchi, K. Shimada, K. Nishiura, X. Y. Cui, H. Namatame, M. Taniguchi, Phys.
Rev. B 72, 214438 (2005), and references therein.
[2] C. Kittel, Introduction to Solid State Physics 8th ed. (John Wiley & Sons Inc. New York,
2005).
[3] M. Higashiguchi, Ph.D. thesis, Hiroshima University (March 2008).

— 33 —

07-A-40

BL-1

Angle resolved photoemission spectroscopy measurementsof VO2 thin films
K. Saeki1, Y. Muraoka1, 4, T. Wakita2, M. Hirai1, T. Yokoya1, 4, R. Eguchi3,
S. Shin3, K. Shimada5
1

Graduate School of Nature Science and Technology, Okayama University,
Faculty of Science, Okayama University, 3RIKEN/SPring-8, 4JST-CREST,
5
Hiroshima Synchrotron Radiation Center, Hiroshima University

2

Vanadium dioxide, VO2, exhibits a sharp metal-insulator transition (MIT) at 341K, which isa first-order phase transition accompanied by a structural change from a high-temperature
rutile-type tetragonal form to a low-temperature monoclinic form. Even though many
scientists have tried to clarify the MIT mechanism, it is under debate that this MIT is caused
by whether electronic correlation (Mott-Hubberd-type) or electron-lattice interaction(Peierls-type). Angle-resolved photoemission spectroscopy (ARPES) study is important toelucidate the electronic structure of VO2 which helps to understand the underlying physics ofthe MIT. However, few ARPES measurements of VO2 have been carried out because VO2single crystals do not have chemically stable cleaved surface and crack easily due to thechange of unit cell volume when they undergo the MIT. Recent our work reveals that byusing the thin films of VO2 we have obtained the PES spectra without any difficulties as seenin the case of single crystals. In this work, we perform the ARPES measurements using VO2thin films and demonstrate for the first time the energy dispersion of V3d band in VO2.
We fabricated epitaxial thin films of VO2 grown on TiO2 (001) single crystal substrates using
a pulsed laser deposition technique. The prepared thin films were found to exhibit a MIT at
300K from resistivity measurements. The ARPES measurements with various photon energy
for VO2 (001) surface was carried out on the beamline BL-1 at Hiroshima synchrotron
radiation center (HiSOR) in Hiroshima University.
Fig.1 (a) shows the photon energy dependence of ARPES spectra near EF for the VO2 (001)surface at 350K. Broad peak around binding energy of 0.2eV is attributed to the V3d state.
We can see that this broad peak moves with photon energy, indicating that the V3d bandshows the energy dispersion along a - Z direction in the rutile-type tetragonal Brillouin zone.
Fig. 1 (b) shows intensity at EF plotted against the k which represents the wave number alongthe - Z direction. Two sets of peaks labeled A - A’ and B - B’ are observed, and each set ofpeaks is symmetrical to k = 6.6 Å-1 (- points. inner potential of 16 meV). This means thatthese two kinds of V3d bands are crossing the Fermi level and form electron pockets in theband structure of the metallic VO2 thin films.

— 34 —



Fig. 1 (a) ARPES spectra near EF of (001)surface of VO2 thin films measured at 350K.
Photon energy of the spectra labeled A,A’, B,B’corresponds nearly to the Fermi wave number(see Fig. 1(b)).

— 35 —(b) Intensity at EF as a function of
the wave number k along the -Z
direction.

07-A-18

BL-1

Carrier-doping effects on Cr-doped perovskite-type titanates
Sr1-(x+y)Lax+yTi1-xCrxO3 studied by photoemission spectroscopy
H. Iwasawaa,b, S. Kaneyoshia, K. Kurahashia, T. Saitoha, T. Katsufujic, Y. Miurad, M.
Higashiguchid, and K. Shimadae, H. Namatamee, and M. Taniguchid,eaDepartment of Applied Physics, Tokyo University of Science, Shinjuku-ku, Tokyo 162-8601,
Japanb
National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki
305-8568, Japanc
Department of Physics, Waseda University, Tokyo 169-8555, Japand
Graduate School of Science, Hiroshima University, Higashi-Hiroshima 739-8526, Japane
Hiroshima Synchrotron Radiation Center, Hiroshima University, Higashi-Hiroshima
739-0046, Japan

Recent developments on semiconductor devices are directed towards two or morefunctionalities by utilizing the charge and spin degrees of freedom of electrons. Magnetic
semiconductors are one of such devices, called spintronics devices, many of the recent studies
on which have been done on oxide semiconductors doped with magnetic ions with very highferromagnetic transition temperatures (TC), such as Ti1-xCoxO2 (TC ~ 400 K).[1-3] However, it
is still unknown why and how the room temperature ferromagnetism appears in spite of thevery small amount of transition-metal (TM) doping. In this context, it is necessary to performa systematic as well as detailed investigation on the electronic structure of a system including
local-spins coupled by (itinerant) conduction electrons.
A Cr-doped perovskite-type titanate Sr1-(x+y)Lax+yTi1-xCrxO3 is suitable to perform such asystematic study. Starting from the d0 band insulator SrTiO3, we can control the electric andmagnetic properties independently by two TM elements Ti and Cr. Carrier doping can berealized by La3+ substitution for Sr2+, which introduces electrons (y) into Ti 3d conduction
band. A further manipulation of the resulting Sr1-yLayTiO3 is to introduce Cr3+ by replacing
SrTiO3 with LaCrO3 by the amount of x. Because Cr3+ (3d3) ions are usually magnetic inoxides, the above substitution of Cr3+ for Ti4+ would realize a “spin doping” of S=3/2 local
moment at the Ti sites. According to the previous magnetic and transport measurements, x andy actually represent the spin and carrier concentration, respectively.[4] Our recent
photoemission study also found that the spectral weight of the Cr 3d state is completely
proportional to x irrespective of y. However, the near Fermi-level (EF) spectral weight due tothe Ti 3d states can not be controlled solely by y.[5] In this report, we investigate they-dependence of the electronic structure of this system in detail using high-resolution
photoemission spectroscopy, to examine how independently we can control the charge andspin degrees of freedom.
Polycrystalline samples of Sr1-(x+y)Lax+yTi1-xCrxO3 were prepared by solid-state reaction. To
identify the y-dependence of this system, we fixed the spin concentration at x=0.2, and varied
y from 0.05 to 0.2. Photoemission measurements were done at BL-1 of Hiroshima
Synchrotron Radiation Center (HSRC). The beamline is equipped with a high-resolution,
hemispherical electron analyzer (SCIENTA ESCA200). The clean surface of the samples was
obtained by fracturing in situ in ultrahigh vacuum (better than 110-10 Torr) at 50 K. All the
spectra were taken with the photon energy of 150 eV at 50 K, being the overall experimental— 36 —

energy resolution better than 40 meV, which was confirmed by Fermi edge spectra ofevaporated Au. The backgrounds due to the unscattered electrons were removed from all the
spectra.

D

C

B
y=
0.2

A

0.15
0.1
0.08
0.05

-10

-8 -6 -4 -2 0
Binding energy (eV)Peak area of A (arb.units)

Intensity (arb. units)(a)Peak area of B (arb.units)

Figure 1 (a) shows the valence-band photoemission spectra of Sr0.8-yLa0.2+yTi0.8Cr0.2O3 forseveral carrier concentrations. The four spectral features can be clearly observed as denoted A
to D, consistent with our previous study.[5] From the Ti 3p 3d and Cr 3p 3d resonant
photoemission measurements, the leading feature A (-0.7 eV) and the subsequent featutre B(-2.7 eV) can be assigned to the Ti 3d and Cr 3d states, respectively.[5] The following features
C (-5.1 eV) and D (-6.9 eV) are the O 2p non-bonding band and Ti and Cr 3d O 2p bonding
bands, respectively.
Figures 1 (b) and (c) demonstrate the carrier-depedence (y-dependence) of the features B
and A, where an integrated intensity of the features B and A are plotted as functions of y. The
integration windows are from -3.5 to -2.0 eV (B) and from -0.4 to 0.1 eV (A). As is seen in Fig.
1 (b) and (c), the Cr 3d states have an almost constant intensity for all y, whereas the coherent
spectral weight of the Ti 3d states shows a proportional relationship to y. It is, therefore, thecarrier density can be controlled by y when x is fixed, which is in perfect agreement with theelectrical resistivity data.
2.0
1.5

(b)

1.0
0.5
0
2.5
2.0

0
0.10
0.20
Carrier concentration (y)

(c)

1.5
1.0
0.5
0

0
0.10
0.20
Carrier concentration (y)FIG. 1 (a) y-dependence of valence-band photoemission spectra of Sr0.8-yLa0.2+yTi0.8Cr0.2O3 taken with150 eV at 50 K. (b) and (c) Integrated intensity of the features B and A as functions of y, respectively.
The intensity is normalized by the averaged intensity of B [Fig. 1 (b)] and the intensity at (0.2, 0.1)
[Fig. 1 (c)]. Each integration window is shown by dotted rectangles.

In conclusion, we have investigated the detailed y-dependence of the electronic structure of
Sr1-(x+y)Lax+yTi1-xCrxO3 by high-resolution photoemission spectroscopy. We found that the Cr
3d peak intensity were not affected by changing y, and the near-EF intensity composed of the— 37 —

Ti 3d states showed a very proportional relationship with y at a fixed x, demonstrating that thecarrier-density control is realized on the condition that x is fixed.
This work was partly supported by a Grant-in-Aid for COE Research (13CE2002) by
MExT of Japan, and also was performed under the Cooperative Research Program of HiSOR,
Hiroshima Synchrotron Radiation Center, Hiroshima University. (Accept No. 06-A-39 and07-A-18).
References[1] S. A. Wolf et al., Science 294, 1488 (2001).
[2] J. W. Quilty et al., Phys. Rev. Lett. 96, 027202 (2006).
[3] K. Mamiya et al., Appl. Phys. Lett. 89, 062506 (2006).
[4] J. Inaba and T. Katsufuji, Phys. Rev. B 72, 052408 (2005).
[5] H. Iwasawa et al., Phys. Rev. Lett. 96, 067203 (2006).

— 38 —

07-A-45

BL-1

ARPES study of Fermi surface of T*-phase high-Tc cuprate SmLa0.8Sr0.2CuO4
Y. Nakashimaa, H. Anzaia, T. Fujitaa, A. Inoa, M. Higashiguchia, N. Tobitaa, J. Jianga,
K. Tanakaa, S. Fukudaa, K. Shimadab, M. Aritab, H. Namatameb, M. Taniguchia,b,T. Kakeshitac, S. Adachid, S. Tajimad,eaGraduate School of Science, Hiroshima Universityb
Hiroshima Synchrotron Radiation Center, Hiroshima UniversitycNational Institute for Materials SciencedSuperconductivity Research Laboratory of the International Superconductivity Technology Centere
Deptertment of Physics, Osaka University
Two-dimensional CuO2 planes are widely considered as the stage of high-Tc
superconductivity in cuprates. However, the effect of apical oxygens adjacent to the CuO2
plane has also been discussed for long. Here, SmLa1-xSrxCuO4 crystallizes in a uniquestructure called T*-phase, where the apical oxygen is located only on one side of the single
CuO2 plane, but the low-energy electronic structure of SmLa1-xSrxCuO4 has still been unclear.
In order to clarify the effect of the apical oxygens, we performed an high-resolution
angle-resolved photoemission spectroscopy and determined the Fermi surface and pseudogap
structure of T*-phase SmLa1-xSrxCuO4 system.
Figure 1 shows the result of Fermi-surface mapping
for the sample of relatively high Sr-substitution x =0.20 and of Tc = 20 K. The momentum-space
distribution has been obtained by integrating thephotoemission spectral intensity in an energy range of0 > ω > -20 meV. In the nodal direction along(0,0)-(π,π) line, the band dispersion crossing Fermi
level has clearly been observed. In the antinodal
region around (π,0), the spectral peak is appreciably
broadened and shifted in energy away from Fermi
level, and the leading-edge midpoint of the spectralfeature is lower than -30 meV. These observations
indicate the formation of a pseudogap in the antinodal
region, and thus that Fermi surface is not closed as
so-called “Fermi arc” even at the high Sr-substitution
level of x = 0.20. The result of SmLa0.8Sr0.2CuO4 isin sharp contrast to that of overdoped La1.8Sr0.2CuO4.,
Fig. 1 Fermi-surface mapping
suggesting that the pseudogap formation is affectedof SmLa0.8Sr0.2CuO4 (Tc = 20 K).
by the apical site.

— 39 —

07-A-3

BL-1

Annealing effect on the chemical structure of diamondlike carbon (DLC)
by C 1s photoelectron spectroscopy
Susumu Takabayashia, Kenya Shimadab, Keishi Okamotoa,c, Tatsuyuki Nakatanic,
Hiroyuki Sakauea, and Takayuki TakahagiaaGraduate School of Advanced Sciences of Matter (AdSM), Hiroshima Universityb
Hiroshima Synchrotron Radiation Center (HSRC), Hiroshima UniversitycToyo Advanced Technologies Co., Ltd., 5-3-38 Ujina-Higashi, Minami-ku,
Hiroshima 734-8501, Japan

Normalized Intensity / a.u.

Diamond-like carbon (DLC) is an amorphous carbonaceous material, which iscomposed of sp2 carbon, sp3 carbon, and hydrogen.1 So far, the analysis varies by authors.
Recently, we have analyzed a DLC film prepared by the ionized deposition method withbenzene gas by angle-resolved C 1s XPS with the Doniach-Šunjić function.2 Sequentially weanalyzed other DLC films with different electrical resistivities prepared by the unbalanced
magnetron sputtering (UBMS) method with using the same procedures3, and concluded that
the C 1s spectrum for DLC is divided into four curves for, in the order of the binding energy,
sp3 carbon in the carbon-carbon bonds (C-C sp3, 283.8 eV), sp2 carbon in the carbon-carbon
bonds (C-C sp2, 284.3 eV), sp2 carbon in the hydrogen-carbon bonds (H-C sp2, 284.8 eV), andsp3 carbon in the hydrogen-carbon bonds (H-C sp3, 285.3 eV).
The characteristics of DLC are subject to vary by heat treatment. In this report, weanalyzed the influence of heat on the characteristics of DLC by C 1s photoelectron
spectroscopy.
All experiments were performed at BL-1. The DLC films were prepared by theionized deposition method with benzene gas. Before the photoelectron measurements, thefilms were annealed in UHV at fixed
temperatures for 30 min. The photoelectron
1.0
measurements were conducted with the incident
0.8
600℃
As-prep.
energy of 408 eV, and the total resolution of
900℃
450℃
0.6
0.22 eV. The binding energy was calibrated byKish Graphite(reference)
0.4
the Au 4f7/2 spectrum of a clean Au (110) single
0.2
crystal.
0.0
Figure 1 shows the C 1s spectra of the
286.0
285.0
284.0
283.0
DLC films after annealing. The spectrum of a
Binding Energy / eVclean kish graphite was also shown. The C 1s
Fig. 1 C 1s photoelectron spectra of thespectrum of the DLC film shifted a little
DLC films after annealing in UHV atpositively in binding energy with increasing thedifferent temperatures.

— 40 —

References
1

J. Robertson, Mater. Sci. Eng., R 37, 129(2002).
2
S. Takabayashi, K. Motomitsu, T. Takahagi, A.
Terayama, K. Okamoto, and T. Nakatani, J.

As-prep.

1.0
0.8
0.6
0.4
0.2
0.0
1.0

450℃

0.8
0.6
0.4
0.2
0.0
1.0

600℃

0.8
0.6
0.4
0.2
0.0

286

285

284

283

Binding Energy / eV

Fig. 2 C 1s photoelectron spectra of the
DLC films with fitting-curves for thecomponents after the UHV-annealing atdifferent temperatures.

0.8

C 1s

0.7

Fraction Intensity / a.u.

annealing temperature until 450°C. However, at
600°C, the spectrum drastically negative-shifted
and showed a different lineshape. Over 600°C,
the spectrum was almost no shifted, but the
FWHM decreased.
Figure 2 shows the C 1s spectra withthefitting-curves
analyzedbytheDoniach-Šunjić function according to theprocedures in our previous report.2,3 Figure 3
shows the fraction intensities of the components
as a function of temperature. These results
demonstrate that the H-C components are
decreased suddenly during 450-600°C. Thus inthis region, hydrogen (or CHx species) in the
DLC film are emitted to the outside. Over
600°C, the C-C sp2 component is enhanced
gradually. thus in this region, the graphization
proceeds.
We concluded that the variation of
DLC by heat treatment in UHV is analyzed by
its C 1s photoelectron analysis with considering
the difference between H-C and C-C bonds.
The authors gratefully acknowledge
Mr. Yuichi Miura, Dr. Mitsuharu Higashiguchi,
and Dr. Naohisa Tobita, Graduate School of
Science, Hiroshima University for kindly
support.

Appl. Phys. 101, 103542 (2007).
3
S. Takabayashi, K. Okamoto, K. Shimada, K.
Motomitsu, H. Motoyama, T. Nakatani, H.
Sakaue, H. Suzuki, and T. Takahagi, Jpn. J.
Appl. Phys. 47, 3376 (2008).

2

0.6������

0.5
0.4

3������

0.3
0.2

������

0.1
0.0

0

200

3

400

600

Temp. / ℃

800

1000

Fig. 3 Correlation between the fraction
intensities of the components of the C 1s
spectra of the DLC films and the annealed
temperature.

— 41 —

������

2

06-A-20, 06-A-21                       

BL-3

NEXAFS, XPS and AFM studies of Rh deposited on Al2O3 thin film/NiAl(100)T. Nomotoa, S. Yagia, K. Sodaa, H. Namatameb and M. TaniguchibaDepartment of Quantum Engineering, School of Engineering, Nagoya University; Chikusa-ku,
Nagoya, 464-8603 Japanb
Synchrotron Radiation Center, Hiroshima University; 2-313 Kagamiyama, Higashi-Hiroshima,739-8526 Japan
1. Introduction
In the field of automotive catalyst, the nano-particles of platinum group metals aresupported on Al2O3. These catalysts play an important role in the reduction of NOx and theoxidation of CO. Those performances are frequently degraded by some deactivation factors
because of the use in the severe environment. The high temperature causes a diffuse of catalyst
metals and it leads to an aggregation of metals or dissolution into support materials [1, 2].
Therefore, it is important to understand the thermal change in the chemical state and themorphology of the catalyst surface.
The aim of this work is to investigate the structural and chemical changes of Rh on
Al2O3/NiAl(100) depending upon heat treatment by means of Near Edge X-ray Absorption Fine
Structure (NEXAFS), X-ray Photoelectron Spectroscopy (XPS) and Atomic Force Microscopy(AFM) techniques.
2. Experimental
A well-ordered ultrathin Al2O3 layer was grown on exposing the cleaned NiAl(100) to O2(~1000 L) at 500 K and subsequently annealing at 1000 K for 5 min [3]. 1.0 ML of rhodium wasdeposited on the Al2O3 thin layer at room temperature. After deposition, the sample was heated at
600 K or 1000 K for 5 min. Four types of samples were prepared in this work, which were
Al2O3/NiAl(100), Rh/Al2O3/NiAl(100) as Rh deposited, Rh/Al2O3/NiAl(100) heated at 600 K or1000 K. The AFM images of each surface were measured by NanoScope III-a (Veeco
Instruments). The XPS measurements were recorded by use of the concentric hemisphericalelectron energy analyzer (PHOIBOS 100-5ch, SPECS) with MgKα X-ray (1253.6 eV). The
NEXAFS spectra were recorded at the soft X-ray double crystal monochromator beamline BL-3.
3. Results and Discussion
3. 1. Surface morphology
Figures 1(a)-(d) show the obtained AFM images. A lot of stripe structures are observed on
the Al2O3/NiAl(100) surface in Figure 1-(a). These structures are thought to grow preferentially— 42 —

along the crystal directions. The stripes disappear when the surface covered with Rh layer. The
deposited Rh on Al2O3/NiAl(100) forms a protruded structures with the height of 0.3-0.7 nm.
Thereby, it can be speculated that nanoclusters with 1-3 Rh layers formed on the
Al2O3/NiAl(100) surface. These structures become higher and spherical shape after theheat-treatment at 600 K. This means the aggregation of Rh atoms on the Al2O3 layer caused by
the thermal migration. After heating at 1000 K, the surface morphology drastically changes into
the surface with a lot of nano-hole structures as shown in Figure 1-(d). With NEXAFS and XPS
results, this outmost surface seems to be composed with the Al2O3 layer
2. 2. Chemical change in Rh/Al2O3/NiAl(100)Figure 2 shows the Rh 3d5/2 peaks (with deconvolution results) for the
Rh/Al2O3/NiAl(100) systems. Rh on Al2O3/NiAl(100) has two chemical states after thedeposition at room temperature. The lower binding energy peak (307.2 eV) is assigned to the Rh
atom in second layer or more, because the peak position corresponds to that of the metallic Rh
such as Rh(111) bulk [4]. The second peak locating at 307.7 eV shifts from the metallic Rh state
to the higher energy side, indicating the first layer Rh atoms on the Al2O3 layer which interact
with each other. In contrast, the peak shape of the Rh/Al2O3/NiAl(100) heated at 1000 K can be
described with a single state at 307.4 eV. The state extremely stabilizes against various
treatments, such as the DMS adsorption, the heating and the O2 exposure. These integral
intensities decay in comparison with that of the Rh as-deposited sample. Therefore, we canspeculate the dissolution of Rh atom into the substrate.
Figure 3 shows the Rh 3d XPS spectra for the Rh/Al2O3/NiAl(100) systems after different
thermal treatments. In order to compare these peak shapes, the main peak positions are matchedeach other. The area colored with green signifies the difference between each spectrum and thatof bulk Rh. One can find that the peak width of as-deposited surface becomes broader than thatof bulk Rh. Therefore, Rh atoms seem to form clusters with at least two layers on
Al2O3/NiAl(100) surface. The peak width becomes narrower when the sample is heated at 600 K.
Then the spectral shape is considerably corresponding to that of bulk Rh. This change indicatesthe aggregation of Rh atoms on the Al2O3 layer. In contrast to the former two spectra, thespectrum of the Rh/Al2O3/NiAl(100) heated at 1000 K can be seen with a sharper and symmetricpeak shape. Furthermore, the peak undergoes a higher shift in comparison with bulk Rh, and thesatellite structure locating at higher biding energy side disappears. Similar change in a XPS
spectral shape was observed on nickel aluminides [5]. They have reported that the positive shiftsof Ni 2p3/2 energy level increases, the satellite structure disappears, and further, the peak shape of
Ni 2p3/2 becomes symmetric with the decrease of nickel concentration in the alloys. Suchchanges can be well understood with the charge-transfer satellite. Therefore, the Rh atoms arelikely to form the alloy like state at 1000 K. Then, we can confirm that the Rh atoms dissolve
into the NiAl(100) substrate through the Al2O3 layer, occurred by the heat-treatment at 1000 K.

— 43 —

Rh L3-edge NEXAFS are shown in Figure 4. The spectral shape, such as the peak height
and the width, is quite similar between the bulk Rh and the Rh/Al2O3/NiAl(100) heat-treated at1000 K. Thus, one can also verify the aggregation of Rh atoms at 600 K by Rh L3-edge
NEXAFS analysis. When the sample is heated at 1000 K, the peak intensity of the main peak at
3007.0 eV decrease, and another structure appears at the higher energy side. We can speculatethat the new structure shows the bonds between Rh-Al or Rh-Ni. These Rh atoms are assumed toexist as single atom and/or small cluster, because the spectrum has two peaks assigned to alloyand metallic states. The schematic model for the Rh state on Al2O3/NiAl(100) with elevatedtemperatures is shown in Figure 5.
References[1] K. Dohmae Y. Hirose, M. Kimura, TOYOTA Central Laboratory R&D review. 32, 75 (1997).
[2] T. Nomoto, S. Yagi, K. Soda, H. Namatame, M. Taniguchi, submitted to e-J. Surf. Sci. Nanotech.
[3] M. Ozawa, M. Kimura, H. Sobukawa, K. Yokota, TOYOTA Central Laboratory R&D review. 27, 43(1992).
[3] M. S. Zei, C. S. Lin, W. H. Wen, C. I. Chiang, M. F. Luo, Surf. Sci. 600, 1942 (2006).
[4] T. L. Barr, J. Phys. Chem. 82, 1801 (1978).

[5] N. Ohtsu, M. Oku, T. Shishido, K. Wagatsuma, Appl. Surf. Sci. 253, 8713 (2007).

5

0.8

5

1.0

Rh 3d5/2 XPS
0 nm

0 nm

0.4

0μm

0.4

(a) Al2O3 layer

1.0

5

1.0

5

0 nm

0.5

1.0

0 nm

0.5

0.5

1.0

0μm

0.5

(b) Rh/Al2O3 as-deposited

0μm(c) Rh/Al2O3 heated at 600 K

1.0

0.5

Rh bulk

Intensity (Arb. units)

0.8

0.5

as-deposited(1.0 ML)

1st layer

2nd layer or moreheated at 1000 K(1.0 ML)0μm(d) Rh/Al2O3 heated at 1000 K

Figure 1. AFM images for the surfaces of (a) Al2O3/NiAl(100),(b) Rh/Al2O3/NiAl(100) as-deposited, (c) Rh/Al2O3/NiAl(100)heated at 600 K, and (d) Rh/Al2O3/NiAl(100) heated at 1000 K.

disolved Rh

312

310

308

306

304

Binding Energy (eV)Figure 2. Thermal dependence of Rh 3d5/2 XPS
spectra for Rh/Al2O3/NiAl(100) as-deposited, andRh/Al2O3/NiAl(100) heated at 1000 K surfaces.

— 44 —

Rh 3d XPS

Rh L3-edge NEXAFS
Rh/Al 2O3/NAl(100): Difference with bulk Rh spectrumhν

Rh/Al2O3/NiAl(100)E

as-deposited

Fluorescence Yield (Arb. units)

Intensity (Arb. units)

detectorheated at 600 K

heated at 1000 K

bulk Rh

30

25

20

15

10

5

Relative Binding Energy (eV)heated at 600 K

heated at 1000 K

0bulk Rh

Figure 3. Rh 3d XPS spectra for the Rh/Al2O3/NiAl(100)systems after different thermal treatments. The main peak
positions are matched each other, and the area colored withgreen signifies the difference between each spectrum andthat of bulk Rh.

2995 3000 3005 3010 3015 3020 3025

Photon Energy (eV)Figure 4. Rh L3-edge NEXAFS spectra for thebulk Rh and the Rh/Al2O3/NiAl(100) systems
after heat-treatment at 600 K or 1000 K.

nano-clusters

aggregation

diffusion

dissolution

600 - 1000 K

1000 K

Al2O3
NiAl(100)

600 K

Figure 5. Schematic model for the Rh chemical states on Al2O3/NiAl(100) with elevated temperatures.

— 45 —

06-A-20, 06-A-21                       

BL-3

Adsorption and oxidation reaction of sulfur on Rh/Al2O3/NiAl(100)studied by XPS and NEXAFS
T. Nomotoa, S. Yagia, K. Sodaa, H. Namatameb and M. TaniguchibaDepartment of Quantum Engineering, School of Engineering, Nagoya University; Chikusa-ku,
Nagoya, 464-8603 Japanb
Synchrotron Radiation Center, Hiroshima University; 2-313 Kagamiyama, Higashi-Hiroshima,739-8526 Japan
1. Introduction
Platinum group metals supported on oxides, such as Al2O3, CeO2 and ZrO2, are widelyused as the typical catalysts in the purification process of the automobile exhaust gas. For
example, Rh/Al2O3 catalyst is noticeable in the reduction of NOx. Those performances are
frequently degraded by some deactivation factors because of the use in the severe environment.
Especially, the poisoning of catalyst surface is regarded as the main problems [1]. The residual
sulfur in fuel causes a sulfur adsorption on the catalyst surface, so-called “Sulfur-Poisoning” [2].
In order to remove such sulfur contaminations, the oxidation reaction of sulfur on the catalyst
surface is of great interest in the field of an automotive catalyst.
The aim of this work is to reveal the oxidation reaction of atomic sulfur on
Rh/Al2O3/NiAl(100) surface by means of Near Edge X-ray Absorption Fine Structure(NEXAFS), X-ray Photoelectron Spectroscopy (XPS) and Atomic Force Microscopy (AFM)
techniques.
2. Experimental
A well-ordered ultrathin Al2O3 layer was grown on exposing the cleaned NiAl(100) to O2(~1000 L) at 500 K and subsequently annealing at 1000 K for 5 min [3]. 1.0 ML of rhodium wasdeposited on the Al2O3 thin layer at room temperature. After deposition, the sample was heated at1000 K for 5 min. Three types of samples were prepared in this work, which were
Al2O3/NiAl(100), Rh/Al2O3/NiAl(100) as Rh deposited, Rh/Al2O3/NiAl(100) heated at 1000 K.
(CH3)2S : DMS gas was admitted via the variable leak valve into the UHV chamber as the
sample was cooled down to 90 K. The atomic sulfur was obtained by the adsorption of DMS,
and subsequently the thermal dissociation with annealing up to 300 K. The sulfur oxidation
reaction was promoted under O2 environment (2.7×10-5 Pa for 1h) at 523 K or in air (for 3 days,
at 300 K). The XPS measurements were recorded by use of the concentric hemispherical electronenergy analyzer (PHOIBOS 100-5ch, SPECS) with MgKα X-ray (1253.6 eV). The NEXAFS
spectra were recorded at the soft X-ray double crystal monochromator beamline BL-3.

— 46 —

3. Results and Discussion
3. 1. Adsorption reaction of DMS on Rh/Al2O3/NiAl(100)Figure 1 shows the temperature dependent S 2p XPS spectra for DMS on Rh(1.0ML)/Al2O3/NiAl(100) as-deposited, Rh(1.0 ML)/Al2O3/NiAl(100) heated at 1000 K, andAl2O3/NiAl(100) surfaces. On the Al2O3/NiAl(100) surface, most of DMS adsorb on Al2O3 layer
without dissociation into CH3S- and atomic S at 90 K. It is found that the sulfur in DMS has aninteraction with the substrate and is picked some electrons up by the Al2O3 layer, because themain peak position located at 164.3 eV undergoes a higher energy shift from that of themultilayer DMS at 163.8 eV [4]. Almost all of the adsorbates desorb from the Al2O3/NiAl(100)surface at 200 K, indicating no catalytic performance for DMS dissociative reaction.
Dissociation of DMS also hardly occurs on the Rh/Al2O3/NiAl(100) as-deposited surface at 90 K.
More than half the molecules (0.18 ML) remain on the surface at 200 K without desorption.
Some of those molecules undergo the scission in the S-C bonds. The dissociation is promoted as
the temperature rises, and most of the S-C bonds are cleaved at 300 K. Thus the Rh over-layer
possesses a catalytic performance for the dissociative reaction of DMS. In the case of the
Rh/Al2O3/NiAl(100) heated at 1000 K, the dissociative reaction and the desorption behavior arequite equivalent to that on the Al2O3/NiAl(100) surface, meaning inert against the dissociation
process of DMS.
The sulfur-poisoned Rh/Al2O3/NiAl(100) as-deposited surface was heated under O2
environment to remove the sulfur atoms. The main peak is located at 162.0 eV showing theadsorption of the atomic sulfur. One can find the broad peak at 166 eV to 169 eV, when thesample is annealed at 423 K and 473 K. This chemical state is assigned to SOx species [1]. The
broad peak disappears at 523 K, and simultaneously the total coverage of sulfur decreases. Thosechanges indicate the oxidation of sulfur and the desorption of SOx from the Rh/Al2O3/NiAl(100)as-deposited surface. The desorption onset temperature is higher than that reported withpolycrystalline Rh and Rh(100) surfaces, on which the sulfur atoms desorb at 423 K [1, 5].
Therefore, the performance of Rh in the sulfur removal reaction is weakened on the Al2O3 layer.
3. 3. Oxidation of sulfur on Rh/Al2O3/NiAl(100)Figure 2 shows the S 2p XPS spectra for atomic sulfur on Rh/Al2O3/NiAl(100)as-deposited surface, which were measured after O2 treatment at 523 K and after exposing to air.
The initial coverage of atomic sulfur is estimated to be about 0.1 ML. The S 2p XPS feature of
S/Rh(100) shows a single state of atomic sulfur. In previous study [6], we have revealed thedesorption of atomic sulfur from the Rh/Al2O3/NiAl(100) surface caused by oxidation (2.7×10-5
Pa of O2 at 523 K). However, most of the atomic sulfur is not oxidized and remains on thesurface. Therefore, a similar feature to S/Rh(100) is obtained for the sulfur on— 47 —

Rh/Al2O3/NiAl(100) after O2 treatment. After the exposure to air, the intensity of the main peakat 162 eV decreases and a broad peak appears from 165 eV to 171 eV. These chemical states are
assigned to atomic S and SOx species (x = 1-4) [1]. The Sulfur K-edge NEXAFS spectrum forthis sample, shown in Figure 3, also has both peaks for the atomic sulfur at 2470.7 eV and theoxidized sulfur state at 2479.1 eV. The chemical state of the oxidized sulfur atom on the
Rh/Al2O3/NiAl(100) can be assigned to SO2 or SO3, because the peak lies at the middle position
between SO and SO4 states. Noticeable oxidation of the atomic sulfur occurs under atmosphericenvironment even at 300 K. From these results, it is found that not only the reaction temperature
but also the degree of the O2 partial pressure significantly affects the oxidation reaction of theatomic sulfur on the Rh/Al2O3/NiAl(100) surface. This oxidation reaction is important in theremoval reaction of sulfur from catalyst surfaces, because it is known that such sulfur
contaminations desorb from catalyst surfaces as SO2.
References[1] K. Dohmae, TOYOTA Central Laboratory R&D review. 35, 43 (2000).
[2] M. Ozawa, M. Kimura, H. Sobukawa, K. Yokota, TOYOTA Central Laboratory R&D review.
27, 43 (1992).
[3] M. S. Zei, C. S. Lin, W. H. Wen, C. I. Chiang, M. F. Luo, Surf. Sci. 600, 1942 (2006).
[4] T. Nomoto, S. Yagi, G. Kutluk, K. Soda, E. Hashimoto, M. Taniguchi, J. Surf. Anal. 12, 238(2005).
[5] T. Nomoto, K. Miura, S. Yagi, G. Kutluk, H. Sumida, K. Soda, E. Hashimoto, H. Namatame,
M. Taniguchi. Surf. Sci. 601, 3784 (2007).
[6] T. Nomoto, S. Yagi, K. Soda, H. Namatame, M. Taniguchi, submitted to e-J. Surf. Sci.
Nanotech.

— 48 —

Figure 1. Thermal dependence of S 2p XPS spectra for DMS on Rh/Al2O3/NiAl(100) as-deposited,
Rh/Al2O3/NiAl(100) heated at 1000 K, and Al2O3/NiAl(100). Rh coverage is 1.0 ML. The samples were treatedwith O2 gas above 423 K.

S 2p XPS

Atomic S

×5

Sulfur K-edge NEXAFS

S/Rh/Al2O3(atomospheric environment)

×5
S/Rh/Al2O3(heated at 523 K
under O2 environment)

S/Rh(100)

S/Rh/Al 2O 3

(atomospheric environment)

Absorbance (Arb. units)

Intensity (arb. units)

SOx species

SOx

SR
E

(x=2, 3)detector

S/Rh(100)

Atomic S

K 2SO 4

SO4

176

172

168

164

160

Binding Energy (eV)156

Figure 2. S 2p XPS spectra for atomic sulfur on
Rh/Al2O3/NiAl(100) as-deposited surface, whichwere measured after O2 treatment at 523 K and after
exposing to air.

2460

2465

2470

2475

2480

2485

Photon Energy (eV)

2490

2495

Figure 3. S K-edge NEXAFS spectra for atomic sulfur on
Rh/Al2O3/NiAl(100) under atmospheric environment,
S/Rh(100), and K2SO4.

— 49 —

06-A-26, 07-A-27

Cl K-edge NEXAFS and AFM study of Pd(PVP) nanoparticle
by means of He path system

a

BL-3

S. Yagia, T. Koderaa, T. Nomotoa, G. Kutlukb, H. Namatameb, M. Taniguchib
Department of Quantum Engineering, Graduate School of Engineering, Nagoya University;
Chikusa-ku, Nagoya, 464-8603 Japanb
Synchrotron Radiation Center, Hiroshima University; 2-313 Kagamiyama,
Higashi-Hiroshima, 739-8526 Japan

Metal nanoparticles have a good property for the purification effects. In these years,
the regulation value for the emission gas has become severe. Moreover the reduction of theamount of precious metals has been demanded in the world. Therefore, the catalyst with
nanoparticle having a large effect for the purification is much desired. Especially, Pd and Pt
nanoparticles have been used as a DPF (diesel particulate filter) and are much in demand inresent years. Thus there are many reports about the applications of the nanoparticle focusedon the DPF [1-3]. We have revealed that the changes of the particle size and the chemical state
about the Rh(PVP) nanoparticles, which are fabricated by means of the reflux-flow method at
353 K [4,5]. In those studies, we have used the AFM and NEXAFS measurements. Because
both measurements are nondestructive, the same sample can be used for other experiments. It
suggests that both two measurements are suitable for doing the combined measurement to thesame sample. In this study, our purposes are to fabricate the Pd nanoparticle by means ofsimilar method of our previous way for Rh(PVP), and to characterize the nanoparticle by the
combined measurements of both AFM and NEXAFS techniques.
We have fabricated the Pd(PVP) nanoparticles with one kind of PVP (K-15,
molecular weight of 10000) received by KISHIDA CHEMICAL CO., Ltd. The 5.0x10-2 mmol
palladium chloride received from Mitsuwa Chemicals Co., Ltd and 0.5 mmol PVP weredissolved into a mixture solvent of ethanol and distilled water (total volume: 70 ml). The
Pd(PVP) nanoparticle colloidal solution was fabricated by the reflux-flow system at 353 K for
2 hours. We have prepared the nanoparticle thin film by the spin-coating method for thePd(PVP) nanoparticles on the Ni (for NEXAFS) and Si (for AFM) substrates (10×10 mm2, 0.5
mm thickness) at 4000 rpm and heated at several temperatures in the air. The AFM images foreach Pd(PVP)/Si specimens were measured by NanoScope IIIa (Veeco Instruments) with
non-contact tapping mode at Innovation Plaza Hiroshima JST. The Near-edge XAFS(NEXAFS) spectra were carried out by yielding fluorescence X-rays with the atmospheric
XAFS measurement system using He gas at the soft X-ray double crystal monochromator
beamline BL-3.
AFM Results
We have used AMF for the estimation of the particle size of Pd(PVP) nanoparticles.
In general, a vertical value of AFM image has a little error bar in comparison with ahorizontal one. Therefore, the particle size can be evaluated by the height value of the AFM
analysis. Figures 1(a)-(d) show the AFM images with inset of the size distribution of thePd(PVP) nanoparticles, which are as-prepared, heating up to 723 K, 873 K and 1073 K. As
reported about the Rh(PVP) nanoparticle by Ashida and Yagi et al., since the nanoparticles
with using PVP polymer are covered with the capping molecule, we can not obtain an exact
particle size [4,5]. Because the PVP polymer decomposes at temperature higher than 673 K,
reported by Ashida et al. [4], we have prepared the samples by heating at temperatures higher
than 723 K.
— 50 —

Judging from each AFM measurements, the average particle sizes with standard
deviation are estimated to be (a) 0.8±0.2, (b) 2.0±0.6, (c) 2.4±1.1 and (d) 3.3±1.1 nm,
respectively. The estimated particle size about the as-prepared sample is very small, itsuggests that the average particle size is underestimated. It is found that the average particle
size is gradually growing along with the rise of annealing temperature. It is necessary to notethat there are some nanoparticles, which have a large particle size of 5-6 nm, as annealing
temperature of the substrate rises. This result is not obtained by our previous study about
Rh(PVP) nanoparticles. It might depend upon the element kind, whether the nanoparticles
grew up largely or not by heating the specimens.
Cl K-edge NEXAFS Results
Figure 2 shows the Cl K-edge NEXAFS spectra of (a) PdCl2 powder, (b) PdCl2
aqueous solution, and (c)-(f) Pd(PVP) with annealing at several temperatures. All spectra
were normalized to the edge-jump. There are four peaks (A), (B), (C) and (D), which are
shown in Figure 2. The peak (A) can observe in spectra (a), (b) and (c) and is associated withthe transition from the Cl- 1s level to the lowest antibonding molecular orbital ag(σ*) of the[PdCl4]2- state [6,7]. The peak at 2822.1 eV in the spectrum (b) is observed accurately at
different peak position of (A). Because the chemical state of Cl in (b) is ionic state in the
aqueous solution, this peak shows the Cl- state. It is found that the chemical state of Cl in (c)is almost same as (a), since the peak positions are almost correspond to (a). Therefore, the Pd
atoms of the nanoparticle have a chemical bonding with the Cl atom before annealing. Peak(A) disappears after annealing Pd(PVP) nanoparticles. This result suggests that there is no Clstate in the annealed samples of (d)-(f). On the other hand, peaks (C) and (D) can be seen in
all NEXAFS spectra though there is a difference of the peak intensity. Sugiura et al. hasreported that the origin of those peaks are the square-planar complex ions of [MCl4]2- [6].
Here, M is the palladium. Hence, it is found that there are same structures of [MCl4]2- about
Pd-Cl bonding in the Pd(PVP) nanoparticles. After annealing up to 1073 K, two peaks of (C)and (D) are still observed. It seems that the structure of [MCl4]2- is a very stable structure.
Peak B can be seen only in the spectrum of (f), annealed up to 1073 K. The origin of this peakis unknown. However, we think that peak (B) appears, if the chlorine atom receives one
electron or less. A more detailed experiment is necessary in the future.
Figure 3 shows the Cl K-edge NEXAFS spectra for Pd(PVP) specimens which are(c) RT, and annealed at (d) 723 K, (e) 823 K and (f) 1073 K. All NEXAFS spectra are plottedby the agreement with each base line. The difference value between the post-edge at 2845 eV
and the pre-edge at 2810 eV is the edge-jump value and means a total amount of Cl atoms.
Therefore we can estimate the Cl amount of decrease in comparison with the edge-jumpvalues. The edge-jump values decrease with raising the annealing temperature. Those results
indicate that some of chlorine atoms desorb from the sample. But the chlorine atom for 1073
K specimen remains about 25 %, (edge-jump value (1073 K)/edge-jump value (RT) %), incomparison with the start specimen of RT. In our previous study for Rh(PVP) nanoparticle,
the residual chlorine atoms have decreased to less than 10 % [5]. There is a big difference
about the amount of the residual chlorine atoms between Pd(PVP) and Rh(PVP). It is thoughtthat this difference depends upon a stability of chlorine atom in the nanoparticles. Actually,
the NEXAFS spectrum for Rh(PVP) has no peak such as (C) and (D) shown in Figure 2. This
result seems to show the chlorine atom has no structure of [RhCl4]2- state in Rh(PVP)
nanoparticle— 51 —

References[1] A. Güthenke et al., Chem. Eng. Sci. 62, 5357 (2007).
[2] Ulrich G. Alkemade et al., Solid State Ionics 177, 2291 (2006).
[3] S. Yagi et al., to be submitted.
[4] T. Ashida et al., Surf. Sci. 601, 3898 (2007).
[5] S. Yagi et al., submitted to Surf. Interface Anal.
[6] CHIKARA SUGIURA and SHINJI MURAMATSU, J. Phys. Chem. Solids 46, 1215
(1985).
[7] P. BEHRENS et al., Synthetic Metals 34, 199 (1989).

(b) 723 K

20

10

10

0

2.0

15

Distribution (%)

2.0

30

Distribution (%)(a) as prepared

0

1

2

3

Size (nm)

4

5

5

0

6

0

1

2

3

Size (nm)

4

5

6

1.0

1.0

15

Distribution (%)(c) 873 K(d) 1073 K

10

15

10

5

0

0

1

2

3

Size (nm)

4

5

5

0
0

6

1.0

0

0
2.0
2.0

1.0
Distribution (%)

0
0
2.0
2.0

1.0

0

1.0

0
2.0

1

2

3

Size (nm)

4

5

6

1.0

0

1.0

0
2.0

Figures 1(a)-(d). The AFM images with inset of the size distribution of the Pd(PVP)
nanoparticles, which are (a) as-prepared, heating up to (b) 723 K, (c) 873 K and (d)1073 K. Each scan size is 2×2 µm2.

— 52 —

Cl K-edge NEXAFS

Fluorescence Yield (arb. units)(f)1073 K(e)873 K(d)723 K(c)RT(b)PdCl2 aqueous
solution
(B)
(A)

2810

(D)

(a)PdCl2 powder

(C)

2820
2830
2840
Photon Energy (eV)2850

Figure 2. The Cl K-edge NEXAFS spectra of (a) PdCl2 powder, (b) PdCl2 aqueous

Fluorescence Yield (arb. units)

solution, and (c)-(f) Pd(PVP) with annealing at several temperatures.

Cl-K NEXAFS(c)RT(d)723 K(e)873 K(f)1073 K

2810

2820
2830
2840
Photon Energy (eV)2850

Figure 3. The Cl K-edge NEXAFS spectra for Pd(PVP) specimens which are (c) RT,
and annealed at (d) 723 K, (e) 823 K and (f) 1073 K.

— 53 —

06-A-26, 07-A-27

BL-3

Pd L3-edge NEXAFS study of Pd(PVP) nanoparticle
by means of He path system
S. Yagia, T. Koderaa, T. Nomotoa, G. Kutlukb, H. Namatameb, M. TaniguchibaDepartment of Quantum Engineering, Graduate School of Engineering, Nagoya University;
Chikusa-ku, Nagoya, 464-8603 Japanb
Synchrotron Radiation Center, Hiroshima University; 2-313 Kagamiyama,
Higashi-Hiroshima, 739-8526 Japan
Metal nanoparticles have a good property for the purification effects. In these years,
the regulation value for the emission gas has become severe. Moreover the reduction of theamount of precious metals has been demanded in the world. Therefore, the catalyst with
nanoparticle having a large effect for the purification is much desired. Especially, Pd and Pt
nanoparticles have been used as a DPF (diesel particulate filter) and are much in demand inresent years. Thus there are many reports about the applications of the nanoparticle focusedon the DPF [1-3]. We have revealed that the changes of the particle size and the chemical state
about the Rh(PVP) nanoparticles, which are fabricated by means of the reflux-flow method at
353 K [4,5]. In those studies, we have used the AFM and NEXAFS measurements. Because
both measurements are nondestructive, the same sample can be used for other experiments. It
suggests that both two measurements are suitable for doing the combined measurement to thesame sample. In this study, our purposes are to fabricate the Pd nanoparticle by means ofsimilar method of our previous way for Rh(PVP), and to characterize the chemical state of thenanoparticle by Pd L3-edge NEXAFS technique.
We have fabricated the Pd(PVP) nanoparticles with one kind of PVP (K-15,
molecular weight of 10000) received by KISHIDA CHEMICAL CO., Ltd. The 5.0x10-2 mmol
palladium chloride received from Mitsuwa Chemicals Co., Ltd and 0.5 mmol PVP weredissolved into a mixture solvent of ethanol and distilled water (total volume: 70 ml). The
Pd(PVP) nanoparticle colloidal solution was fabricated by the reflux-flow system at 353 K for
2 hours. We have prepared the nanoparticle thin film by the spin-coating method for thePd(PVP) nanoparticles on the Ni (for NEXAFS) substrate (10×10 mm2, 0.5 mm thickness) at
4000 rpm and heated at several temperatures in the air. The Near-edge XAFS (NEXAFS)
spectra were carried out by yielding fluorescence X-rays with the atmospheric XAFS
measurement system using He gas at the soft X-ray double crystal monochromator beamline
BL-3.
Figure 1 shows the Pd L3-edge NEXAFS spectra of (a) PdCl2 powder, (b) Pd bulk,(c) Pd nanoparticle on Ni substrate (by dry process), (d) PdCl2 aqueous solution, and (e)-(h)— 54 —

Pd(PVP) annealed at several temperatures. All spectra were normalized to the edge-jump.
There are two peaks (A) and (B), which are shown in Figure 1. Since the peak (A) iscorresponding to (b)Pd bulk peak, the peak (A) can be assigned to the metal Pd(0) state. On theother hand, the peak (B) is same as the peak position of (c) Pd nanoparticle, which isfabricated by the gas evaporation method with He gas [6]. Yagi et al. [6] and Miura et al. [7]have reported that the surface of the Pd nanoparticle is easily oxidized by the exposure to the
air at room temperature. Therefore, the peak (B) shows that there is the oxidized state inPd(PVP) nanoparticle. However, the peak of (d) Pd aqueous solution has a same position of(B). In the aqueous solution, the Pd atom can exist in the state of the Pd2+. In other words, thePd2+ state is equal to the same state of the oxidized state. Thus, it is found that most of Pd
atoms in Pd(PVP) nanoparticle take the Pd2+ state, regardless of the substrate temperature.
Such results was not seen for Rh(PVP) nanoparticle [4,5]. The Rh L3-edge NEXAFS spectra
show that the peak position shifts to the lower energy side with annealing in the air. When
Pd(PVP) nanoparticle is compared with the result of Rh(PVP), it has been understood that Pd
can not easily reduce with annealing in the air.
References[1] A. Güthenke et al., Chem. Eng. Sci. 62, 5357 (2007).
[2] Ulrich G. Alkemade et al., Solid State Ionics 177, 2291 (2006).
[3] S. Yagi et al., to be submitted.
[4] T. Ashida et al., Surf. Sci. 601, 3898 (2007).
[5] S. Yagi et al., submitted to Surf. Interface Anal.
[6] S. Yagi et al., e-J. Surf. Sci. Nanotech. 4, 258 (2006).
[7] K. Miura et al., submitted to J. Surf. Anal.
Pd L3-edge NEXAFS(h)1073 K

Fluorescence Yield (arb. units)(g)873 K(f)723 K(e)RT(d)PdCl2 aqueous
solution(c)Pd nanoparticle(dry process)(b)bulk Pd

Figure 1. The Pd L3-edge NEXAFS spectra of(a) PdCl2 powder, (b) Pd bulk, (c) Pd
nanoparticle on Ni substrate (by dry process),(d) PdCl2 aqueous solution, and (e)-(h) Pd(PVP)
at several temperatures.

(A) (a)PdCl2 powder
(B)

3165

3170

3175 3180 3185
Photon Energy (eV)3190

— 55 —

06-A-22, 07-A-27

BL-3

Reaction study of L-cysteine on Rh(PVP) nanoparticle surface
in the aqueous solution environment
S. Gohdaa, T. Ashidaa, S. Yagia, H. Namatameb and M. TaniguchibaDepartment of Quantum Engineering, School of Engineering, Nagoya University; Japanb
Synchrotron Radiation Center, Hiroshima University; Japan
The platinum group elements show a high reactivity for halogen and chalcogen.
Especially, the nanoparticle made of the platinum group metal is expected to remove thehalogen and chalcogen efficiently because the ratio of the surface atom to internal atom
increases on a nanoparticle phase. Therefore, this nanoparticle has been used in the cosmetic
and medical products in these years.
In our previous study, we have investigated the reaction of L-cysteine on Rh(PVP)
nanoparticle surface in the nanocolloidal solution [1]. It indicates that L-cysteine molecule
decomposes to cysteine thiolate, the thiolate adsorbs on Rh nanoparticle surface through thesulfur and cystine molecule is produced by making the S-S bond from two cysteine thiolates.
However, existence state of the cystine in the aqueous solution environment has not beencleared yet. Besides, chlorine ions which remain in the nanocolliodal solution may influence
the reaction between L-cysteine and Rh(PVP) nanoparticle. In this work we have clarified thereaction of L-cysteine on Rh(PVP) nanoparticle surface under the aqueous solution
environment by near edge X-ray absorption fine structure (NEXAFS) of S-K and Cl-K edges.
Rh(PVP) nanocolloidal solution were prepared by the liquid reduction method [2].
The rhodium chloride tri-hydrate (RhCl3(3H2O)) and PVP were dissolved into a mixed
solvent of distilled water and ethanol, and refluxed at 353 K. The sample was prepared bydissolving L-cysteine powder into Rh(PVP) nanocolloidal solution and keeping reaction for
the appropriate time at room temperature. The S-K and Cl-K edges NEXAFS measurementsof the liquid samples were surveyed by the yielding fluorescence X-ray using the atmosphericpressure XAFS measurement system with He gas at the beamline BL-3 [3].
Figure 1 shows S K-edge NEXAFS spectra for L-cysteine aqueous solution,
L-cystine aqueous solution and the mixed samples that passed each time after dissolving
L-cysteine powder (5 hours, 1, 30, 180 days). The spectra after 30 and 180 days have theshoulder structure at 2473.9 eV and this position is assigned to the peak position of σ*(S-C)
for L-cystine. Figure 2 shows the relation between the reaction time and the relative peakintensity at 2473.9 eV. As seen in this figure, the amount of the cystine increases in proportion
to the reaction time. The amount of the produced cystine gradually increases and keeps
constant after 30 days. It is suggested that L-cysteine dissolved into the nanocolloidal solution— 56 —

is used by cystine synthesis reaction and the reaction is finished for saturation of cystine after
30 days.
Figures 3 and 4 show Cl K-edge NEXAFS spectra for Rh(PVP) nanocolloidal
solution and the mixed samples. In Figure 3, two peaks of Rh(PVP) nanocolloidal solution arelocated at 2822.4 eV and 2828.8 eV. These peaks are attributed to chlorine ion state and thebonding between chlorine and rhodium, respectively [2]. The main peak at 2828.8 eV shifts to2827.4 eV after dissolving L-cysteine into Rh(PVP) nanocolloidal solution and the peakintensity at 2827.4 eV increases with the reaction time. The previous researches have reported
that the peak at around 2827.4 eV can be observed in the Cl K-edge NEXAFS spectra for the
specimen of ammonium hexachlororhodate(Ⅲ) [(NH4)3[RhCl6]] [4, 5]. In Figure 4, it isobserved that the peak intensity at 2827.4 eV increases for the reaction time within 2 hours. In
addition, the peak intensity of chlorine ion state observed at 2822.4 eV decreases with thereaction time. Therefore, this indicates that the similar structure to (NH4)3[RhCl6] is madefrom the surface Rh atom of Rh(PVP) nanoparticle, chlorine ion and amino group of cysteine(cystine). Moreover, it is supposed that chlorine ions contribute to form the complex structure
on Rh(PVP) nanoparticle surface.

[1] S. Gohda, T. Ashida, S. Yagi, H. Namatame, M. Taniguchi, J. Surf. Anal. in press.
[2] T. Ashida, T. Miura, T. Nomoto, S. Yagi, H. Sumida, G. Kutluk, K. Soda, H. Namatame, M.
Taniguchi, Surf. Sci. 601, 3898 (2007).
[3] S. Yagi, Y. Matsumura, K. Soda, E. Hashimoto, M. Taniguchi, Surf. Interface Anal. 36,
1064 (2004).
[4] H. Rumpf, H. Modrow, J. Hormes, P. Amann, A. Möller, G. Meyer, J. Synchrotron Rad. 8,707 (2001).
[5] C. Sugiura, M. Kitamura, S. Muramatsu, J. Chem. Phys. 84, 4824 (1986).

— 57 —

Fluorescence Yield (arb. units)

Fluorescence Yield (arb. units)

S K-edge NEXAFS

2465

2470

2475

Photon Energy (eV)L-cysteineaqueous solution

L-cystine
aqueous solution
180 days later
30 days later
1 day later
5 hours later

2473.9 eV
cystine σ*(S-C)

2460

2465

2470

2475

2480

2485

2490

Photon Energy (eV)Figure 1. S K-edge NEXAFS spectra for L-cysteine aqueous solution, L-cystine aqueous
solution and the mixed samples that have left for arbitrary time. The inset shows the detailed
NEXAFS spectra of the mixed samples.

Relative Peak Intensity

1.50

1.25

1.00

0.75
1

10

100

Reaction Time (hours)

1000

10000

Figure 2. Relation between the reaction time and the relative peak intensity of σ*(S-C) forL-cystine.

— 58 —

Fluorescence Yield (arb. units)

Cl K-edge NEXAFS

2828.8 eV

2822.4 eV
Cl

Rh(PVP)nanocolloidal solution

3 hours later

180 days later
2827.4 eV2805 2810 2815 2820 2825 2830 2835 2840 2845 2850

Photon Energy (eV)Figure 3. Cl K-edge NEXAFS spectra for Rh(PVP) nanocolloidal solution and the mixed
samples after 3 hours and 180 days.

Cl K-edge NEXAFS

114 minutes later
101 minutes later
88 minutes later
39 minutes later
31 minutes later
23 minutes later
15 minutes later

Fluorescence Yield (arb. units)2827.4eV2822.4eV

2815

2820

2825

2830

2835

Photon Energy (eV)

2840

2845

Figure 4. Cl K-edge NEXAFS spectra for the mixed samples that have left for arbitrary time.

— 59 —

06-A-22, 07-A-27             

BL-3

Dissociation reaction of (CH3)2S adsorbed on Pd nanoparticles fabricatedby gas evaporation method using NEXAFS and in-situ XPS
M. Moriharaa, K. Miuraa, T. Nomotoa and S. Yagia
G. Kutlukb, H. Namatameb and M. TaniguchibaDepartment of Quantum Engineering, School of Engineering, Nagoya University, Japanb
Synchrotron Radiation Center, Hiroshima University, Japan
Automobile catalyst is composed of the platinum group metals (Pd, Rh and Pt) sincethese metals indicate the superior property of the purification of the automobile exhaust gas[1-3]. The platinum-group metals are used as nanoparticle since it is effective to enhance its
catalytic performance. However, there are two problems of decreasing the catalytic property:(1) surfactant molecules remain on the active sites of nanoparticle surface, which arefabricated by chemical reduction method [1] and (2) the performance of automobile catalyst is
decreased by sulfur-containing molecules in gasoline fuel, known as “Sulfur Poisoning” [2].
In previous study, we have fabricated the Pd nanopartilcles (Pd NPs) with clean surface by thegas evaporation method, and we expose dimethyl sulfide (DMS: (CH3)2S) to the Pd NPs
surface [3]. This result shows that the activity of Pd NP surface is higher than that of bulk Pd
surface. However, it is not found the relation between dissociation reaction of DMS and theamount of deposited Pd NPs. Thus, we have investigated the dissociation reaction of DMS
depending on amount of deposited Pd NPs using Near Edge X-ray Absorption Fine Structure(NEXAFS) and in-situ X-ray Photoelectron Spectroscopy (XPS).
Pd NPs with clean surface were fabricated by the gas evaporation method using He
gas and deposited on Ni(111) substrate. The amount of Pd NPs on Ni(111) was controlled as
an aggregated phase or a dispersed one. Pd substrate sample was prepared as a reference. The
samples were transferred to the ultra high vacuum chamber without breaking the vacuum
condition. After cooling these substrates down to 90 K, they were exposed to DMS. XPS
measurement was carried out by using Mg K X-ray. NEXAFS measurements (ex-situ
condition) were carried out by the fluorescence yielding method under the atmosphericcondition of He gas at BL-3.
Figure 1 shows a summary of S 2p XPS spectra for multilayer, DMS adsorbed onNi(111), bulk Pd and different amount of deposited Pd NPs (0.26, 0.40, 0.58 and 0.90 layer of
Pd NPs). DMS adsorbed on Ni(111) and bulk Pd does not decompose. However, DMS
dissociates into methanethiolate (MT: CH3S-) and atomic S on Pd NPs/Ni(111). Therefore, it
indicates that the activity of Pd NPs surface is higher than that of the bulk Pd surface. This
result is corresponding to previous our study [3]. In addition, it is found that the dissociation— 60 —

reactions of DMS adsorbed on different amount of deposited Pd NPs are different. When theamount of deposited Pd NPs increases, the area of Pd NP surface becomes large and theexistence ratio of MT increases. Thus, DMS dissociates into MT on Pd NPs surface. On theother hand, the area of Pd-Ni interface becomes large on dispersed phase and decreases onaggregated phase. This behavior is similar to that of atomic S as shown in Figure 2. Therefore,
it is supposed that DMS dissociates into atomic S at Pd-Ni interface. Figure 3 shows theresults of Pd L3-edge NEXAFS spectra of bulk Pd and Pd NPs (ex-situ). The chemical statesof Pd NPs (ex-situ) have three phases, such as metal Pd, Pd oxidized 1 and Pd oxidized 2. To reveal
the interaction of Pd NPs surface and DMS, we have a plan to measure in-situ NEXAFS.
References[1] T. Ashida, K. Miura, T. Nomoto, S. Yagi, H. Sumida, G. Kutluk, K. Soda, H. Namatameand M. Taniguchi, Surf. Sci. 601, 3898 (2007).
[2] T. Nomoto, S. Yagi, K. Soda, G. Kutluk, H. Sumida, E. Hashimoto and M. Taniguchi, e-J.
Surf. Sci. Nanotech. 4, 39 (2006).
[3] M. Morihara, K. Miura, T. Nomoto, S. Yagi in press.

Figure 1. S 2p in-situ XPS spectra for multilayer, DMS/Ni(111), DMS/Pd and
DMS/Pd NPs/Ni(111).

— 61 —

Figure 2. The existence ratio of adsorbed species depending on the amount of deposited Pd
NPs.

Figure 3. The Pd L3-edge NEXAFS spectra for bulk Pd and Pd NPs (ex-situ).

— 62 —

06-A-12                              BL-6

Site- and state-selective dissociation of core-excited organic
molecules: Deuterium-labeled methyl acetate
R. Kawasakia, T. Yamanakaa, H. Yoshidab,c, and K. Tabayashia,cabDepartment of Chemistry, Graduate School of Science, Hiroshima University

Department of Physical Science, Graduate School of Science, Hiroshima Universityc
Hiroshima Synchrotron Radiation Center (HSRC), Hiroshima University

Core-electrons are localized closely to a nucleus and their binding energies are sensitive toelectronic and structural properties of the local surroundings of the absorbing atom. If thesame element atoms in a molecule have nonequivalent structural environments, the differencesin their core-electron binding energies are generally significant so that selective core-electron
excitation of the atoms can be made. For example, acetone molecule ((CH3)2CO) has two
types of nonequivalent C atoms available for different C1s core-electron excitation, and simple
esters (RC(O)OR’) have two different O atoms for O1s site-selective excitation, etc. Usingtunable soft X-rays from synchrotron radiation sources, the excitation site- and state-selective
photoreactions following core-electron excitation have so far been examined as fundamental
subjects, in the last two decades, for isolated molecules in the gas phase and condensed
molecules on the surfaces.
The excitation site-specific fragmentation was firstly reported by Eberhardt et al. [1] fromthe observation of partial ion-yields (PIYs) of gaseous acetone at the C1s electron transitions
to antibonding CO and Rydberg orbitals. Tinone et al. [2] observed photon-stimulated ion
desorption (PSID) of poly-(methyl-methacrylate) (PMMA, –[CH2C(CH3)C(O)-OCH3]n–) thinfilm in the oxygen K-edge region and found efficient desorption of excitation state-specificcations (CH3+, CHO+) that strongly depended on the antibonding character of resonant coreexcited states. In order to elucidate the changes in fragmentation mechanisms between theisolated molecules and macromolecules on the surfaces upon O1s excitation, the stateselective fragmentation of methyl-isobutyrate (MIB, (CH3)2CHC(O)OCH3), i.e. a monomer
methyl-ester unit of PMMA, has been lately examined in the isolated condition [3]. In the PIY
measurement of MIB, enhancement of CHO+ production was observed at the 1s(O-CH3)
(C-OCH3) band, however, the state-selective CH3+ production at the 1s(O-CH3)(OCH3) could not be identified, as opposed to the efficient production of CHn+ cations found in
PMMA. For the absence of the state-selectivity, possible interfering production of the CHn+
cations from the isopropyl site of MIB has been proposed on the ground of large excessenergy transfer within the isolated molecules. In order to eliminate such CHn+ contaminationand determine the level of site- and state-selective dissociation for the isolated esters, it is ofparticular importance to distinguish either CpHq functional group by labeling hydrogen with
deuterium atoms.

— 63 —

Fig. 1 Comparison of the branching ratios between CD3+ and CDO+
production at the core-to-valence excitation bands.


Here, we studied inner-shell excitation and fragmentation of methyl acetate molecule (MA,
CH3C(O)OCH3), i.e. a prototype of methyl-ester, in the gas phase using time-of-flight (TOF)
fragment-mass spectroscopy. Total-ion-yield (TIY) spectrum of MA was measured in theoxygen K-edge region, and O1s core-to-valence excitation bands were properly assigned. In
the PIY measurements for the site- and state-selective dissociation analysis, specificallylabeled methyl-d3 acetate (Md3A, CH3C(O)OCD3) was used in place of normal MA to
examine the influence of different methyl sites on the photo-induced processes. Deuterium
labeled experiments showed that the site-selective bond scission takes place between the(O1sCO-1CO) and (O1sOMe-1CO) transitions, whereas the state-selective excitation at the(O1sOMe-1O-Me) does not lead to predominant CD3+ production. The lack of the stateselectivity for both MA and MIB observed was interpreted as being due to the small core-tovalence cross sections buried into the congestion of Rydberg transitions.

References[1] W. Eberhardt, T. K. Sham, R. Carr et al., Phys. Rev. Lett., 50, 1038 (1983).
[2] M. C. K. Tinone, K. Tanaka, J. Maruyama et al., J. Chem. Phys., 100, 5988 (1994).
[3] K. Tanaka ed., Report of the Grant-in-Aid on Research for Future ‘Photoscience’ (JSPS-RFTF98P01202), (2003), p. 53— 64 —

07-A-58                              BL-6

Hydrogen-bond interactions of small ammonia clusters observedwith inner-shell excitation spectroscopy at the nitrogen K-edge
T. Yamanakaa, T. Maruyamaa, H. Yoshidab,c, and K. Tabayashia,cabDepartment of Chemistry, Graduate School of Science, Hiroshima University
Department of Physical Science, Graduate School of Science, Hiroshima Universityc
Hiroshima Synchrotron Radiation Center (HSRC), Hiroshima University

In order to obtain new spectroscopic insight into the local hydrogen bond (HB) interaction
within molecular clusters, we previously observed inner-shell excitation spectra of small formic
acid clusters [1], where constituent acid molecules interact strongly through the HBs (C=O···H-O).
By monitoring partial-ion-yields (PIYs) of cluster-origin products, cluster-specific core-excitation
spectra with no contribution from molecular excitation could be studied. Comparison of the cluster
bands with those of molecular formic acid showed that the first and second core-to-valence bands
shift in energy by ca. +0.2 and ca. –0.6 eV upon clusterization. The band shifts of the resonancetransitions have been interpreted as being due to the changes in core electron binding energy(CEBE) of the oxygen atoms upon HB formation. Here, we studied inner-shell excitation
spectroscopy of small ammonia (AM) clusters at the nitrogen K-edge and examined thecontribution of (N···H-N) HB interaction on the core-excited AM clusters.
The experiments were carried out using a cluster beam-photoreactive scattering apparatus(CBPRSA) [2] where AM cluster beam was generated by supersonic expansion of 9.9% AM/He
mixture at P0 = 0.15 MPa through a 50 μm nozzle. Time-of-flight (TOF) spectra of the clusters
were compared with those of isolated molecules recorded under the effusive beam condition.
Besides the molecular cation, we found a single series ofprotonated clusters, (AM)n·H+ in the TOF spectra.
Fig. 1 shows the PIY spectra at the first/second
resonances (N1s-13sa1/3pe) obtained in the cluster beam.
Although free AM molecules are still involved in thecluster beam, “cluster-origin” excitation spectra can berecorded without contribution of free molecules bymonitoring PIYs of the fragments originating from AM
clusters [1]. Comparison of the “cluster-origin” bands
with the “monomer-origin” bands showed that bothcluster resonance bands are considerably broadened andthat the second N1s-13pe band clearly shifts to a lower
energy. The changes in the band structures can beunderstood by the non-equivalent N sites generated uponclusterization through the HBs. The core-to-valenceband behavior of AM clusters will be discussed on thebasis of density functional theory calculations.
References[1] K. Tabayashi et al., J. Chem. Phys. 125, 194307 (2006).    Fig.1 PIY spectra of AM clusters[2] K. Tabayashi et al., AIP Conf. Proceedings, 879, 1788 (2007).

— 65 —

07-A-54

BL6

Dissociation dynamics of multiply-charged CF4 and CHF3
by momentum imaging spectroscopy
Y. Kimura1, I. Miyagami1, Y. Kawakami1, H. Kawabata1, H. Yoshida1,2, A. Hiraya1,21Department of Physical Science, Hiroshima University
2
Hiroshima Synchrotron Radiation Center, Hiroshima University
Multiply-charged ion is often produced by inner-shell ionization through Auger decay,
and it generally dissociates into some fragment ions by Coulomb explosion. We haveinvestigated the dissociation processes of inner-shell ionized CHF3 and CF4 with a time-offlight mass spectrometer and a two-dimensional position-sensitive detector at the BL6 of
HiSOR. Angular distributions of ejected ions are obtained by measuring the three-dimensional
initial momenta derived from the detected position (X, Y) and flight time (T) of fragment
ions.
In Fig.1, we show the obtained distributions of correlation angles for 1 (F+(First hit),
F+(Second hit)), 2 (F+(First hit), CF+), and 3 (F+(Second hit), CF+) in the (F+, F+,CF+) formation process
after C1s ionization of CF4. Both 2 and 3 distribute 120. The F-C-F angle in the stablestructure of the neutral ground state is 109.5  with Td symmetry. The experimental values of120 are larger than it. On the other hand, 1 distributes 113, which is relatively close to109.5 . We consider the 4-body dissociation process as
CF4+++ F + + F+ + CF+ + F .
The calculated correlation angles for (F, F+ ) and (F, CF+) using the experimental results are
100  and 97 , respectively. Dissociation dynamics to produce (F+, F+, CF+) ion trio aresummarized in Fig.2.

Fig.1 Correlation angles in the (F+, F+, CF+)
formation after C1s ionization of CF4.

— 66 —

Fig.2 Dissociation dynamics toproduce (F+, F+, CF+) ion trio.

07-A-55

BL6

Study on symmetries of core-excited states in CF4 and CHF3
I. Miyagami1, Y. Kimura1, Y. Kawakami1, H. Kawabata1, H. Yoshida1,2, A. Hiraya1,21Department of Physical Science, Hiroshima University
2
Hiroshima Synchrotron Radiation Center, Hiroshima University
We have investigated dissociation processes of CF4 and CHF3 in the F1s excitation
region with a time-of-flight mass spectrometer (TOF-mass) and a two-dimensional
position-sensitive detector at the BL-6 of HiSOR. Total-ion yield spectrum of CHF3 at the F1s
excitation region is shown in Fig.1. The peak at 690.8 eV was already assigned to F1s 
excitation. However, there are two possible symmetries of electronic state,  a1 and  e,since CHF3 molecule belongs to C3v point group. In the present study, we measured theejected angle of F+ against the electric vector () of synchrotron radiation at 688.9 eV( -low) and 693.6 eV ( -high), which are lower and higher energies of the   peak,
respectively. The three-dimensional initial momenta of fragment ions arise from core-excited
CHF3 were obtained by analyzing the detected position (X, Y) and the flight-time (T) of them.
The detection axis of the TOF-mass coincides with the direction of .
In order to remove the contribution of isotropic F+ distribution by successive
dissociation, we selected F+ measured in coincidence with CF+. Ion-pair dissociation isconsidered to occur immediately by Coulomb explosion after Auger decay of core-excitedmolecules. Therefore, the ejected angle of F+ in (F+, CF+) would reflect the initialconfiguration of CHF3 in space. The obtained angular distributions at  -low and  -highare shown in Fig.2. The upper spectrum shows a peak 30, while the lower one shows almost
constant. As shown in Figs. 3(a) and 3(b), the C-H bond of CHF3 is perpendicular to  in  eexcitation, while that is parallel in  a1 excitation. F+ should be ejected 20 in  e, while70 in  a1 if the ion-pair dissociation is much faster than molecular rotation anddeformation. At the  -low spectrum, the observed peak of 30 is in good agreement with
20 in  e. Thus, we concluded that  e state exists at around “ -low” position. On theother hand, the almost isotropic distribution at “ -high” indicates that some of Rydberg
states with both e and a1 symmetries would overlap complexly.

H
C


20

F

Fig.3(a)  e70

Fig.1 Total ion yield spectra

Fig.2 Angular distribution of F+— 67 —

Fig.3(b)  a1

07-A-56

BL6

Dissociation dynamics of multiply-charged CH2F2
by momentum imaging spectroscopy
Y. Kawakami1, Y. Kimura1, I. Miyagami1, H. Kawabata1, H. Yoshida1,2, A. Hiraya1,21Department of Physical Science, Hiroshima University
2
Hiroshima Synchrotron Radiation Center, Hiroshima University
Multiply-charged ion is often produced by inner-shell ionization through Auger decay,
and it generally dissociates into some fragment ions by Coulomb explosion. We haveinvestigated the dissociation processes of inner-shell ionized CHF3 and CF4 with a time-offlight mass spectrometer and a two-dimensional position-sensitive detector at the BL6 of
HiSOR. In the present study, we discuss on dissociation dynamics of CH2F2. Angular
distributions of ejected ions are obtained by measuring the three-dimensional initial momenta
derived from the detected position (X, Y) and flight time (T) of fragment ions.
In Fig.1, we show the obtained distributions of correlation angles for (H+, F+(First hit)),(H+, F+(Second hit)), and (F+, F+) in the (H+, F+, F+) formation process after F1s ionization of
CH2F2. Both (H+, F+) and (F+, F+) distribute 110. The H-C-F and F-C-F angles in the stablestructure of the neutral ground state are 108.9  and 108.5 , respectively. The experimental
values of 110 are in good agreement with them. Supposing that all the simultaneous
dissociation occur along the direction of the respective bond axis, the momentum of
undetected particle can be estimated by synthesizing the all momenta of detected particles.
Now, we consider the 4-body dissociation process as
CH2F2+++  H+ + F+ + F+ + CH .
The calculated correlation angles for (H+, CH ) and (F+, CH) are 72  and 124 , respectively.
Dissociation dynamics to produce (H+, F+, F+) ion trio is summarized in Fig.2.
H+,F+(First hit)

F+,F+
H
H
C
H+,F+(Second hit)F

Fig.1 Correlation angles (deg) in the (H+, F+, F+)
formation after F1s ionization of CH2F2.

— 68 —

F

Fig.2 Dissociation dynamics toproduce (H+, F+, F+) ion trio.

07-A-57

BL6

Dissociation dynamics of multiply-charged SF6
by momentum imaging spectroscopy
H. Kawabata1, Y. Kimura1, I. Miyagami1, Y. Kawakami1, H. Yoshida1,2, A. Hiraya1,21Department of Physical Science, Hiroshima University
2
Hiroshima Synchrotron Radiation Center, Hiroshima University
Multiply-charged ion is often produced by inner-shell ionization through Auger decay,
and it generally dissociates into some fragment ions by Coulomb explosion. We haveinvestigated the dissociation processes of inner-shell ionized SF6 with a time-of- flight mass
spectrometer and a two-dimensional position-sensitive detector at the BL6 of HiSOR. Angular
distributions of ejected ions are obtained by measuring the three-dimensional initial momenta
derived from the detected position (X, Y) and flight time (T) of fragment ions.
In Fig.1, we show the obtained distributions of correlation angles for 1 (F+(First hit),
F+(Second hit)), 2 (F+(Second hit), F+(Third hit)), and 3 (F+(First hit), F+(Third hit)) in the (F+, F+, F+)
formation process after F1s ionization of SF6. Both 1 and 2 distribute 100. The F-S-F
angle in the stable structure of the neutral ground state is 90  with Oh symmetry. The
experimental values of 100 are larger than it. On the other hand, 3 has two peaks at 100
and 165. This is ascribed to the difference of spatial distributions of three F+ ions and will
be discussed in detail.

SF6

Fig.1 Correlation angles in the (F+, F+, F+) formation after F1s ionization of SF6.

— 69 —





H


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


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
        
 
            
            


  
  
  
               


               
  
  

  
  

— 70 —



              
              

                          
                                        


             




— 71 —

07-A-36

BL-7

Core-level photoemission spectra and glass-forming ability in
Pd42.5Ni7.5Cu30P20 bulk metallic glass
S. Hosokawa,a M. Nakatake,b H. Sato,b N. Happo,c T. Ichitsubo,d E. Matsubara,d and N.
NishiyamaeaCenter for Materials Research Using Third-Generation Synchrotron Radiation Facilities,
Hiroshima Institute of Technology, Hiroshima 731-5193, Japanb
Hiroshima Synchrotron Radiation Center, Hiroshima University, Higashi-Hiroshima 7390046, Japanc
Graduate School of Information Sciences, Hiroshima City University, Hiroshima 731-3194,
JapandDepartment of Materials Science and Engineering, Graduate School of Engineering, Kyoto
University, Kyoto 606-8501, Japane
R&D Institute of Metals and Composites for Future Industries, Sendai 980-8577, Japan
Bulk metallic glasses of Pd-Ni-Cu-P alloys, discovered by Nishiyama and Inoue [1],have intensively been investigated due to their good glass-forming abilities (GFA). They have
optimized the concentration dependence of the critical-cooling-rate, and found that
Pd42.5Ni7.5Cu30P20 has at present the slowest critical-cooling-rate (CCR) of 0.067 K/s and canform a massive bulk glass with a diameter of more than 40 mm by simple water-quenching[2]. Although several thermodynamic and mechanical properties have been investigated for
the Pd-Ni-Cu-P glassy alloys in detail [2], only a few fundamental attempts have been madefrom the viewpoints of its structural and electronic properties to understand why it has suchan excellent GFA. Electrical conductivity, σ, measurements for the Pd42.5Ni7.5Cu30P20 metallic
glass [3] showed that σ decreases by exchanging the Ni with Cu atoms from the reference
Pd40Ni40P20 glass [4], which has a bad CCR of 1.6 K/s [5], suggesting a decrease of electronic
density of states (DOS) at the Fermi energy, N(EF). With the further replace of Ni by Cu, thePd40Cu40P20 glass has a worse CCR of more than 103 K/s, and a smaller σ value [6].
In order to clarify the role of the electronic structure in this excellent glass-former
Pd42.5Ni7.5Cu30P20 by comparing to the Pd40Ni40P20 reference glass, a series of electronic
spectroscopic measurements were recently performed [7], such as in-house photoemission
spectroscopy (PES) and inverse-photoemission spectroscopy (IPES), incident photon energy
dependence of PES using synchrotron radiation. Since the knowledge of the partial DOS isessential for the detailed study of the electronic DOS, we have also measured the Ni and Cu
3d partial DOS in the valence band using soft X-ray emission spectroscopy (SXES), and thePd 4d, Ni and Cu 3d partial DOS in the conduction band using X-ray absorption spectroscopy(XAS). From these data, partial DOS of Pd 4d, Ni 3d, and Cu 3d electrons were estimated,
and it was found that the Pd 4d partial DOS largely decreases near the E F, and its feature
seems to become localized by replacing the Ni atoms with the Cu atoms, while the Ni partial
DOS remains almost unchanged. Therefore, these electronic data demonstrate that theseresults are closely related to the excellent GFA of the Pd42.5Ni7.5Cu30P20 bulk metallic glass
through a selective formation of Pd-P covalent bonds. This was also supported by a recent
study of local atomic structure around the Pd atoms using an anomalous X-ray scattering [8].
Due to an extremely small value of the photoionization crosssection of the P element[9], information on the electronic structure of the P atoms has been completely lack.
Subsequently to the above works, we have recently measured Pd 3d, Ni 3p, Cu 3p, and P 2p
core-level spectra of the Pd42.5Ni7.5Cu30P20 glass, and compared them to those of the
Pd40Ni40P20 and Pd40Cu40P20 reference glasses. In this report, we present the obtained data, and— 72 —

discuss changes of the chemical nature of the whole elements by replacing the Ni atoms with
the Cu atoms, and the relation to the excellent GFA of the Pd42.5Ni7.5Cu30P20 glass.
The procedure of the sample preparation was given elsewhere [2]. The absence of
crystallinity in the samples was confirmed by X-ray diffraction and calorimetry. The
composition of the samples was examined to be within 1 % by an electron-probe microanalysis method before and after the experiments. The core spectra were measured using a
PES spectrometer at the beamline BL7 of Hiroshima Synchrotron Radiation Center.
Ultraviolet photons generated from the storage ring HiSOR with the ring energy of 700 MeV
and the ring current of 160-300 mA were monochromatized with a Dragon-type
monochromator, covering the incident photon-energy h ν from 20 to 600 eV. A PES
spectrometer with a hemispherical photoelectron energy-analyzer (GAMMA-DATASCIENTA SES100) attached to the analyzer chamber at the end-station of BL7, was used for
the PES experiment. The overall energy resolution of the PES spectrometer was about 0.1 eV
at hν = 220 eV for the Ni 3p, Cu 3p, and P 2p spectra, and about 0.5 eV at hν = 450 eV for
the Pd 3d spectra. All the core spectra were collected at room temperature. Clean surfaces
were in situ obtained by Ar ion sputtering in a sample preparation chamber attached with theanalyzer ones, which were kept under ultrahigh vacuum with a basic pressure below 1×10-10
mbar. Any core spectra due to oxygen or carbon contamination were not visible within 24 hafter the sample cleaning, and the measurements were performed within 12 h. The energy ofall spectra was defined with respect to the E F determined from the spectra of a freshly
evaporated Au film.
Figure 1 shows the P 2p core spectra of Pd42.5Ni7.5Cu30P20, Pd40Ni40P20 and Pd40Cu40P20
glasses measured at h ν = 220 eV observed at a binding energy of about –130 eV, theintensities of which are reduced to be unity at the peak position with respect to thebackground at the higher energies. By replacing the Ni atoms by the Cu atoms, the P 2p3/2
core spectrum shows a slight shift towards a smaller binding-energy by 0.04 eV in
Pd42.5Ni7.5Cu30P20, and much larger shift in Pd40Cu40P20 towards a smaller binding-energy by
0.29 eV. It should be noted that the spectral shapes change with adding the Cu atoms, and the
new P 2p3/2 core level appears at about –129.8 eV in Pd42.5Ni7.5Cu30P20 glass. Thus, the centerof gravity of the P 2p3/2 core level shifts towards the larger binding-energy in Pd42.5Ni7.5Cu30P20
glass.

Fig. 1. The P 2p core spectra of Pd42.5Ni7.5Cu30P20 and Pd40Ni40P20 glasses measured at h ν =220 eV.
Figure 2 shows the reduced Pd 3d5/2 core spectra of Pd42.5Ni7.5Cu30P20, Pd40Ni40P20 and
Pd40Cu40P20 glasses measured at hν = 400 eV observed at a binding energy of about –336 eV.

— 73 —

By replacing the Ni atoms by the Cu atoms, the P 3d5/2 spectrum shows a large shift in
Pd42.5Ni7.5Cu30P20 towards a larger binding-energy from by –0.38 eV. With the further replaceby the Cu atoms, however, the P 3d5/2 spectrum shows a large shift towards smaller bindingenergy from by –0.28 eV The same shifts are also observed in the Pd 3d3/2 core spectra.

Fig. 2. The Pd 3d5/2 core spectra of Pd42.5Ni7.5Cu30P20 and Pd40Ni40P20 glasses measured at hν =400 eV.
Figure 3 shows the reduced Ni 3p core spectra of Pd42.5Ni7.5Cu30P20 and Pd40Ni40P20
glasses measured at hν = 220 eV observed at a binding energy of about –67 eV. Although theNi 3p spectrum is rather scattered due to the small concentration of the Ni element, a shift
towards a larger binding-energy is observed by 0.28 eV in the Ni 3p3/2 spectra by replacing theNi atoms by the Cu atoms. Although the Ni 3d partial valence-band DOS measured by SXES
seems not to be changed [7], the core level shifts can be seen.

Fig. 3. The Ni 3p core spectra of Pd42.5Ni7.5Cu30P20 and Pd40Ni40P20 glasses measured at hν =220 eV.
Figure 4 shows the reduced Cu 3p core spectra of Pd42.5Ni7.5Cu30P20 and Pd40Cu40P20
glasses measured at hν = 220 eV observed at a binding energy of about –75 eV. A slight shift
towards a smaller binding-energy is observed by 0.11 eV in the Cu 3p3/2 spectra by replacing
the Ni atoms by the Cu atoms.

— 74 —

Fig. 4. The Cu 3p core spectra of Pd42.5Ni7.5Cu30P20 and Pd40Cu40P20 glasses measured at hν =220 eV.
It should be noted that the core spectra in all the elements, Pd 3d5/2, Ni 3p3/2, Cu3/2, andP 2p3/2 always show the larger values in Pd42.5Ni7.5Cu30P20 glass compared to the reference
Pd40Ni40P20 and Pd40Cu40P20 glasses. The shifts of the binding energies in every core-level areobserved, indicating changes of the chemical nature of these elements by replacing the Ni
atoms with the Cu atoms. A similar change in the core spectra was already discussed by
Alamgir et al. [10] for Pd40Ni40P20 alloys from crystal and glassy states, and such shifts
indicate a charge transfer. The present finding of the shifts in the core levels revealed that all
the elements in the Pd42.5Ni7.5Cu30P20 have the smallest electron charges among three metallic
glasses, which may closely related to the excellent GFA in the Pd42.5Ni7.5Cu30P20 glass.
In conclusion, the Pd 3d, Ni 3p, Cu 3p, and P 2p core-level spectra of thePd42.5Ni7.5Cu30P20 were measured by PES together with those of the reference Pd40Ni40P20 and
Pd40Ni40P20 glasses. By replacing the Ni atoms with the Cu atoms, a shift towards a larger
binding-energy is observed in the core spectra of all the elements, Pd 3d5/2, Ni 3p3/2, Cu3/2, andP 2p3/2, by which it can be concluded that all the elements in the Pd42.5Ni7.5Cu30P20 have thesmallest electron charges among three metallic glasses, which may closely related to theexcellent GFA in the Pd42.5Ni7.5Cu30P20 glass.
[1] N. Nishiyama and A. Inoue, Mater. Trans. JIM 37 (1996) 1531.
[2] N. Nishiyama and A. Inoue, Appl. Phys. Lett. 80 (2002) 568.
[3] O. Haruyama et al., J. Non-Cryst. Solids 312-314 (2002) 552.
[4] O. Haruyama et al., Mater. Sci. Eng. A 375-377 (2004) 288.
[5] N. Nishiyama and A. Inoue, Mater. Trans. JIM 38 (1997) 464.
[6] G. L. Tangonan, Phys. Lett. 54A, 307 (1975).
[7] S. Hosokawa et al., Acta Mater. 55 (2007) 3413.
[8] S. Hosokawa et al., Mater. Trans. 48, 2358 (2007).
[9] J. J. Yeh and I. Lindau, At. Data Nucl. Data Table 4s 32 (1985) 1.
[10] F. M. Alamgir FM et al., in ed. by T. B. Massalski and P. E. A. Turchi, The Science ofComplex Alloy Phases, Warrensdale (PA), The Minerals, Metals and Materials Society, 2005.

— 75 —

07-A-38

Electronic States in Zr70Ni20Al10 Bulk Metallic Glass

BL7

T.Nasua, S.Hosokawab, M.Nakatakec, H.Sato c, W.Zhang d and A.Inoue daFaculty of Education, Art and Science, Yamagata University, Yamagata 990-8560 Japanb
Hiroshima Institute of Technology, Hiroshima 731-5193 Japanc
Hiroshima Synchrotron Radiation Research Center, Hiroshima University, HigashiHiroshima 739-0046 Japand
Institute of Materials Research, Tohoku University, Sendai 980-8577 Japan
Abstract. A Zr-based bulk metallic glass of Zr70Ni20Al10 has an excellent glass-forming
ability (GFA), and can form a massive bulk glass by simple water-quenching. In order toclarify the role of electronic structure in this excellent GFA of Zr70Ni20Al10 glass bycomparing to the Zr70Ni30 reference, having a worse GFA, valence-band photoemission
spectra were measured with changing the incident photon energy using synchrotron radiation
at BL7 of HiSOR. We have also measured Ni3P, Zr 3d and Zr 4p core-level photoemission
spectra of the Zr70Ni20Al10 glass, and compared them to those of the Zr70Ni30 reference glass.
The shifts of the binding energies in every core-level are observed, indicating changes of thechemical nature by replacing the Ni atoms with Al atoms.
1. Introduction
Bulk metallic glass of Zr-Ni-Al alloys was discovered by Inoue et al [1]. It is well known that theglass forming ability (GFA) in the Zr-Ni-based binary metallic glass can be improved by the additionof Al [1]. Nagel and Tauc suggested that good GFA is closely related to the decrease of N(EF), or
Mott’s preudogap, under a free-electron model [2]. Electronic structural studies on GFA of bulk
metallic glass were done by Suzuki et al.[3] and Hosokawa et al.[4]. These results showed good
agreements with the prediction of correlation of GFA with electronic structure. Short range structurechange of Zr-Ni-based metallic glass induced by addition of Al was studied by Sato et al by means of
X-ray diffraction and EXAFS [5]. The main purpose of this research is to investigate electronic
structural change of Ni-Zr alloy by Al addition in terms of GFA.

2. Experimental procedure
The samples were prepared as follows [1]. The master ingots were prepared by arc-melting
mixtures of pure Zr, Ni and Al in an argon atmosphere. Rapid quenching was done by using
single-roller technique for obtaining metallic glass sample from the master ingot pieces. The hdependent photoemission spectra (PES) experiments were carried out at beamline BL7 of theHiroshima Synchrotron Radiation Centre. Ultraviolet photons generated from the storage ring
HiSOR with a ring energy of 700 MeV and a ring current of 160-300 mA weremonochromatized with a Dragon-type monochromater, ranging hν values from 20 to 380 eV.
A PES spectrometer with a hemispherical photoelectron energy analyzer (SCIENTA SES100)
equipped with the analyzer chamber at the end-station of BL7, was used for the PES
experiment. The overall energy resolution of the PES spectrometer was set to be 0.1 eV athν =100 eV. All the PES spectra were collected at room temperature. Clean surfaces were insitu obtained by Ar sputtering in a sample preparation chamber attached to the analyzer
chambers, which were kept under ultrahigh vacuum below 1x10-10 mbar. Any changes in the
spectral features due to oxygen or carbon contamination were not observed within 12 h after
the sample cleaning and the measurements were performed within 6 h. The energy of each of
the spectra was defined with respect to the EF determined from the spectra of a freshly
evaporated Au film.

— 76 —

3. Results
Figure 1 shows the PES spectra from hν=30-150 eV of Zr70Ni20Al10 as a function of thebinding energy, EB. Figure 2 shows the PES spectra from hν=30-150 eV of Zr70Ni30 glasses asa function of EB.
Zr70Ni20Al10

Zr70Ni30hν (eV) =

100
70
30

-8

-6

-4
-2
Binding Energy (eV)

150
100
70
30

-8

0

Fig.1. The hν dependent PES spectra
between hν=30 and 150 eV of
Zr70Ni20Al10 metallic glass.

-6

-4

-2

0

Binding Energy (eV)Fig.2. The hν dependent PES spectra
between hν=30 and 150 eV of Zr70Ni30
metallic glass.

Zr70Ni20Al10

Zr 4p

Zr70Ni20Al10
Intensity (Arb. Units)

Intensity (Arb. Units)Zr 3dhν (eV) =Intensity (Arb. Units)

Intensity (Arb. Units)

150

Zr70Ni30

Zr70Ni30
-184

-182
-180
Binding Energy (eV)

-34

-178

Fig.3. Zr 3d core-level PES spectra with hν=320eV of Zr70Ni20Al10 metallic glass (solidline) and Zr70Ni30 metallic glass (dashed line)..

-32

-30

-28

Binding Energy (eV)

-26

-24

Fig.4. Zr 4p valence-band PES spectra withhν=240eV of Zr70Ni20Al10 metallic glass (solidline) and Zr70Ni30 metallic glass (dashed line).

— 77 —

Zr70Ni20Al10

Intensity (Arb. Units)

Ni 3p

Zr70Ni30
-71

-70

-69

-68

-67

-66

Binding Energy (eV)

-65

-64

Fig.5 Ni 3p core-band PES spectra with hν=
240 eV of Zr70Ni20Al10 metallic glass (solidline) and Zr70Ni30 metallic glass (dotted line).

Figure 3 shows Zr 3d core-level PES spectra of Zr70Ni20Al10 metallic glass (solid line) andZr70Ni30 metallic glass (dotted line). The peak position does not seem to shift by replacing Ni
atom to Al atom as shown in Fig.3. Figure 4 shows Zr 4p valence-band PES spectra of
Zr70Ni20Al10 metallic glass (solid line) and Zr70Ni30 metallic glass (dotted line). In this case,the peak position of Zr 4p shifts 0.15 eV to smaller binding energy side by replacing Ni atom
to Al atom as shown in Fig.4. Figure 5 shows Ni 3p core-level PES spectra of Zr70Ni20Al10
metallic glass (solid line) and Zr70Ni30 metallic glass (dotted line). The peak position of Ni 3p
shifts 0.1 eV to larger binding energy side by replacing Ni atom to Al atom.
4. Discussion
Nagel and Tauc suggested that good GFA is closely related to the decrease of N(EF), or
Mott’s pseudogap, under a free-electron model. Electronic structural studies on GFA of bulk
metallic glass were done by Suzuki et al. [3] and Hosokawa et al. [4]. Their results showed
good agreements with the prediction of correlation of GFA with electronic structure by Nagel
and Tauc. From the results of measurements on the hν dependent PES spectra of Zr70Ni20Al10
and Zr70Ni20 metallic glasses as shown in Fig.1 and Fig.2, it was not so clear that if thedensity of state near the Fermi energy decreases or not by replacing Ni atoms to Al atoms. In
Fig.1, the peak at around 6 eV corresponds to Zr, the peak at 2 eV corresponds to Ni, and theweak shoulder beside the peak at 2 eV corresponds to Al atom. Comparing Fig.1 with Fig.2, itis clear that the peak around 2 eV shifts to larger binding energy side and makes a shoulder by
replacing Ni atoms to Al atoms. As shown in Fig.5, the peak position of Ni 3p shifts 0.1 eV tolarger binding energy side, and the peak position of Zr 4p shifts 0.15 eV to smaller binding
energy side by replacing Ni atom to Al atom as shown in Fig.4. This means that electronstransferred from Ni atoms to Zr atoms. By the way, the short range structure change of Zr-Nibased metallic glass induced by addition of Al was studied by Sato et al. by means of X-ray
diffraction and EXAFS [5]. According to Sato’s structural research, the Al-induced
disordered local environment accompanying with the formation of novel local structure of ZrAl and decomposition of that of Zr-Ni would improve effectively thermal stability of the ZrNi-Al metallic glass [5]. The formation of novel local structure of Zr-Al made a shift of Zr 4plevel as shown in Fig.4. The decomposition of local structure of Zr-Ni made a shift of Ni 3p
as shown in Fig.5. Totally, electron transfer occurs from Ni atom to Zr atom by replacing the— 78 —

Ni atoms to Al atoms. The electrons, which transferred to Zr atoms from Ni atoms,
presumably play an important role for the formation of novel local structure of Zr-Al.

Fig.6 The photo ionization crosssection σpvalues of Zr 4d and 5s, Ni 3d and 4s and Al
3s, 3p electrons as a function of hν.
5. Summary
The PES spectra of Zr70Ni20Al10 metallic glass were measured to examine the excellent glass
forming ability (GFA) compared with those of Zr70Ni30 glass. By replacing Ni atoms to Al
atoms, the peak position of Ni 3p shifts 0.1 eV to larger binding energy side and the peak
position of Zr 4p shifts 0.15 eV to smaller binding energy side. This means the electronstransfer occur from Ni atoms to Zr atoms. It suggests that Zr-Al strong correlation formed bythis electron transfer which occurs by addition of Al atoms to Zr-Ni glass, and increases GFA.
References[1]Inoue A, Zhang T and Masumoto T 1990 Mater. Trans. JIM 31 177[2]Nagel SR and Tauc J 1975 Phys. Rev.Lett.35 380[3]Suzuki K, Miyazaki K, Soda K, Takeuchi K, Hasegawa T, Sato Y and Mizutani U 2006 J.
Jpn. Soc. Powder and Powder Metallurgy 53 107[4]Hosokawa S, Sato H, Happo N, Mimura K, Tezuka Y, Ichitubo T, Matsubara E andNishiyama N 2007 Acta Mater. 55 3413
[5]Sato S, Sanada T, Saida J, Imafuku M, Matsubara E and Inoue A 2005 Mater. Trans. 46
2893— 79 —

07-A-47

BL-7

Angle-resolved photoemission spectroscopy of SrSi2/Si(111)
H. Masoa, H. Kuriharaa, Y. Tatsukawaa, H. Satob, M. Nakatakeb, H. Namatameb and M. Taniguchia,baGraduate School of Science, Hiroshima University, bHiSOR, Hiroshima University

In recent years, epitaxial silicides on silicon have been a subject to intense investigations
as well as increasing technological application. Evaporation of the alkali earth metal or therare earth metal such as M=Ca, Sr, Ce and so on, on the Si substrate forms MSi2 epitaxial filmwith a various Si network. Recently, we have grown tr6-type CaSi2 epitaxial film by Ca
evaporation on the Si (111) substrate and have successfully derived the experimental band
dispersion for the grown CaSi2 films by means of angle-resolved photoemission spectroscopy(ARPES) [1]. The results exhibit that the CaSi2 epitaxial film shows the metallic behavior anda band crosses the Fermi level (EF) near the Γ point forming “hole pocket” with the Fermi
wavenumber of kF=0.22 Å-1. The whole feature of band structures of CaSi2 epitaxial film is ingood agreement with the calculated result [2]. We have also observed the Fermi surface with asix-fold symmetry, which reflects the ty6-type CaSi2(111) surface symmetry and is similar tothat of YSi2 [3].
In this study, we have tried to grow SrSi2 epitaxial film on the Si(111) substrate byevaporating the Sr element and have carried out ARPES for the grown films. Recently,
Yamanaka et al. have been revealed that the Sr evaporation onto the Si(111) substrate leads tothe EuGe2-type (h1-type) SrSi2(111) epitaxial films, which is very similar to tr6-type one,with a low lattice mismatch with the Si(111) substrate [4]. It is noted that the EuGe2-type(h1-type) SrSi2 is not naturally grown. The electronic structure of SrSi2 is not known atpresent.
The SrSi2 epitaxial film was prepared by evaporating the Sr element with a purity of
99.9 % onto the Si(111) substrate at 800 ˚C with 0.05 Å/sec. After the evaporation, thesubstrate temperature is kept at 800 ˚C for 1 hour to proceed the reaction between Sr and Si.
For the grown films, the 2×2 RHEED (reflection high energy electron diffraction) pattern was
successfully obtained, which was also observed for CaSi2 [1], and AES (Auger electron
spectroscopy) analysis showed no contamination just after the growth. For the grown samples,
we have in situ measured the ARPES spectra o beamline BL7 of HiSOR.
Figure 1 shows the intensity plot of the ARPES spectra of SrSi2 (θSr=100 Å) taken athν=27 K along Γ-Σ-M direction. Since it is somewhat difficult to direct see the band
dispersion from the plot, we indicate those by dashed lines for guide. The upper right panel— 80 —

exhibits the expanded intensity plot aroundEF with the second-order derivative of the
ARPES spectra. We find characteristic threebands A, B and C. Of these bands, the A andB bands originate from Si(111). The C bandnewly appears by evaporating Sr and crosses
EF near the Γ point forming “hole pocket”.
An existence of the C band indicates thatSrSi2 epitaxial film shows the metallic
behavior, though the density of states is
extremely low at EF.
The whole feature of the band structureof SrSi2 is very similar to that of CaSi2,

Fig. 1. Experimentally derived band dispersionof SrSi2/Si(111) epitaxial film.

reflecting their similar crystal structure (h1-type for SrSi2 and tr6-type for CaSi2). In case of
CaSi2, its C band is derived from the hybridization between the Ca 3d and Si 3p orbitals
normal to (111) layers, in comparison with the results of the band-structure calculation [2].
Accordingly, also for SrSi2, the C band is derived from the Sr 4d – Si 3p hybridization bands.
Although h1-type SrSi2 and tr6-type CaSi2 show the similar band dispersion, we findslight differences in the C band; its binding energy of SrSi2 is deeper than that of CaSi2 andkF=0.10 Å-1 for SrSi2 is also smaller than kF=0.22 Å-1. These differences are qualitatively
explained by the band-structure calculations for h1-type CaSi2 and tr6-type CaSi2 [1]. The Sr
4d states more strongly hybridize with the Si 3p states compared with the Ca 3d and Si 3p
states and the energy gap between Sr 4d – Si 3p bonding and anti-bonding bands becomeslarger, leading to the deeper binding-energy and the small kF of SrSi2.
The difference of the h1-type and tr6-type crystal structure is also reflected in the Si 2p
spectra as the difference of the number of the Si site; the Si 2p spectrum of h1-type SrSi2 with
one Si site is composed of one component, while that of tr6-type CaSi2 with two Si sites iscomposed of two components.
References[1] S. Nishimoto, Master Thesis, Graduate School of Science, Hiroshima University 2006; S.
Nishimoto et al., the 10th Hiroshima International Symposium on Synchrotron Radiation, P-28,
2006.
[2] S. Fahy and D. R. Hamann, Phys. Rev. B 41, 7587 (1990).
[3] C. Rogero et al., Phys. Rev. B 69, 045312 (2004).
[4] Y. Tokinaga, Master Thesis, Graduate School of Engineering, Hiroshima University 2001.

— 81 —

07-A-4

BL-7

The Constant Volume Dilution Effect of Eu Site in EuPd2Si2 :Eu 4d-4f Resonant Photoemission Study
K. Mimura, D. Okumura, T. Ishizu, M. Nakatake A, T. Kuwai B,
H. Namatame A, M. Taniguchi A, Y. Taguchi, and K. Ichikawa
Graduate School of Engineering, Osaka Prefecture University, Sakai 599-8531, Japan
A
HSRC, Hiroshima University, Higashi-Hiroshima 739-0046, JapanB
Faculty of Science, Toyama University, Toyama 930-8555, Japan

Intensity (arb. units)

EuPd2Si2 undergoes an abrupt but continuous valence transition at around 160 K: the Eumean valence changes from 2.8 below 130 K to 2.3 above 180 K [1-3]. Recently, in the
Eu-diluted system substituted by nonmagnetic (La0.67Y0.33) with constant lattice volume,
electrical and magnetic anomalies at dilution concentration (x) higher than 0.25 have been
discussed from the standpoint of the Kondo effect [4]. In this study we have investigated the x
dependence of Eu 4f states in (Eu1–x(La0.67Y0.33)x)Pd2Si2 by means of Eu 4d-4f resonant
photoemission spectroscopy (RPES)
We used polycrystalline (Eu1–x(La0.67Y0.33)x)Pd2Si2 samples (x = 0, 0.12, 0.85) grown byarc melting and by annealing at 900 °C for one week. Eu 4d-4f RPES measurements at thetemperature lower than 20 K were performed at BL-7 with the excitation photon energies(hν’s) between 120 and 170 eV. The sample was in situ fractured under the base pressure of
4×10–8 Pa. The overall energy resolution around the Eu 4d-4f threshold was set at 150 meV.
Figure 1 shows Eu 4f spectra of (Eu1–x(La0.67Y0.33)x)Pd2Si2 (x = 0, 0.12 and 0.85). The Eu
4f spectrum has been evaluated by subtracting
the spectrum measured at the resonancesurface(Eu1– (La0.67Y0.33) )Pd2Si2
minimum (hν = 136 eV) from that at the Eu3+
Eu 4 spectra
4f resonance maximum (hν = 150.5 eV). In
bulk( = 150.5 eV) – ( = 136 eV)each spectrum, multiplet structures from ~EF
to 3 eV and from 5.5 to 11 eV ascribed to theEu2+ and Eu3+ 4f states, respectively.
= 0.85Furthermore, the component around 0.7 eV isascribed to the bulk Eu2+ 4f states, while thataround 2 eV to the surface Eu2+ 4f states,= 0.12
respectively. A noteworthy point is that theEu3+ 4f component is observed even in the=0spectrum of x = 0.85, even though the( EuPd2Si2 )suppression of Eu intersite interaction has
3+
2+
been suggested at the diluted concentrationEu
Euhigher than x = 0.25 [4]. Then, we extracted
15
10
5
0
bulk Eu2+ and Eu3+ components from theBinding Energy (eV)spectrum of x = 0.85 and found that its
integrated intensity ratio (I3+/I2+) is nearly the Fig. 1. The Eu site dilution dependence ofsame as that of x = 0.12. This probably Eu 4f spectra of (Eu1–x(La0.67Y0.33)x)Pd2Si2.
suggests that the valence fluctuation of Eu in All the spectra were normalized by peak2+
(Eu1–x(La0.67Y0.33)x)Pd2Si2 occurs across the intensity of the Eu 4f state at around 2 eV.

— 82 —

Intensity (arb. units)

extremely long range.
Figure 2 shows the Eu2+ 4f spectra of (Eu1–x(La0.67Y0.33)x)Pd2Si2 measured in detail. The
detailed Eu 4f spectrum has been evaluated bysubtracting the resonance minimum spectrum(Eu1– (La0.67Y0.33) )Pd2Si2(hν = 136 eV) from the Eu2+ 4f resonanceEu 4 spectra
maximum spectrum (hν = 141 eV). We can( = 141 eV)– ( = 136 eV)
find that a weak shoulder structure is observed
at 0.15 eV in the spectrum of x = 0.85. The
feature of its shoulder may be a quasi-particle
peak due to the Kondo effect that in Eu= 0.85compounds has not been discussed so far
except for a few examples [5, 6]. We cannot,
however, declare whether the shoulder is a
= 0.12surfacequasi-particle peak or not at this moment,bulk
because of the difficulties of the accuracy for=0
the Eu 4f spectral subtraction (The spectral( EuPd2Si2 )intensity of conduction electrons for x = 0.85
is much larger than those for x = 0 and 0.12)
5
4
3
2
1
0
and the energy resolution. We are planning to
Binding Energy (eV)measure the spectra by Eu 3d-4f RPES andhard X-ray photoemission spectroscopy with Fig. 2. The detailed Eu2+ 4f spectra ofhighly bulk sensitivity and discuss the Kondo (Eu (La Y ) )Pd Si .
1–x
0.67 0.33 x
2 2effect for the sample with low concentrationof Eu.
[1] E.V. Sampathkumaran et al., J. Phys. C: Solid State Phys. 14, L237 (1981).
[2] E. Kemly et al., J. Magn. Magn. Mater. 47&48, 403 (1985).
[3] G. Wortmann et al., J. Mang. Mang. Mater. 49, 325 (1985).
[4] T. Kuwai, et al., J. Magn. Magn. Mater. 310, e68 (2007).
[5] S. Fukuda, et al., J. Phys. Soc. Jpn. 72, 3189 (2003).
[6] Z. Hossain, et al., Phys. Rev. B 69, 014422 (2004).

— 83 —

07-A-6

BL-9A

Temperature-Dependent Angle-Resolved Photoemission Spectra of TlInSe2:
Specification of Incommensurate and Commensurate Phases
K. Mimura, T. Nogami, K. Abe, K. WakitaA, M. AritaB, N. MamedovC, G. OrudzhevC,
J. Takasu, Y. Yonehira, H. NamatameB, M. TaniguchiB, Y. Taguchi, and K. Ichikawa
Graduate School of Engineering, Osaka Prefecture University, Sakai 599-8531, JapanA
Faculty of Engineering, Chiba Institute of Technology, Narashino, Chiba 275-0016, Japan
B
HSRC, Hiroshima University, Higashi-Hiroshima 739-0046, JapanC
Azerbaijan National Academy of Science, Baku, AZ-1143, Azerbaijan
TlInSe2 has attracted much interest because of the structural low-dimensionality, and theinteresting electric and thermoelectric properties [1, 2]. TlInSe2 crystallizes in a quasi
one-dimensional chain structure with a body-centered tetragonal unit cell of D18
4 h space group[3]. The structure is built-up of the edge-sharing InSe4 tetrahedron along the crystallographic
c axis, and of the Tl atoms positioned between the chains. Recently, the Seebeck coefficient of
TlInSe2 has then been found to be positive only below 473 K, reaching very high values of�
more than 106 µV/K below 413 K [2]. The record-breaking thermoelectric
power of TlInSe2
has then been ascribed to the inhomogeneous charge distribution inherent in modulated
structures, particularly, incommensurate phases.
Normal–incommensurate–commensurate (N–I–C) phase transition with decreasing
temperature was observed in many materials of the TlMeX2 (Me = Ga, In; X = S, Se, Te)family. In particular, temperature-dependent X-ray diffraction studies [4] disclosed the N–I–C
transition in TlGaTe2 [4]. In a similar way, the I phase might have taken place in TlInSe2.
However, neither extended X-ray nor neutron scattering examination has been undertaken so
far to come to unambiguous conclusions in this regard.
Very recently, our temperature-dependent angle-resolved photoemission spectroscopy(ARPES) studies at low temperature on TlInSe2 have revealed splitting of some bands, related
to the phase transition of this material [5]. In this study, we focus on the temperaturedependent experimental bands including the valence-band maximum (VBM) at the T point of
the Brillouin zone (BZ), and discuss the observed peculiar temperature changes in terms of
the N–I–C phase transition of TlInSe2.
The sample used was single crystalline TlInSe2. The ARPES spectra at 50 and 280 K were
measured at the circular undulator beam line BL-9A. Clean (110) surfaces were obtained byin situ cleaving of the sample under the pressure lower than 8 × 10–11 Torr. We selected theexcitation photon energy (hν) of 11.4 eV to observe the ARPES spectra along the Γ-H-T(N-P-N) direction of BZ of TlInSe2. This direction is parallel to the chains. The overall energy
resolution was set at 5 meV and angular resolution was better than 0.3°.
Figure 1 shows the experimental bands that form VBM in the Γ-H-T (N-P-N) direction
parallel to the chains. The plots for 280 and 50 K correspond to Figs. 1(a) and 1(b),respectively. The blue solid circles in Fig. 1 indicate the peak positions determined from the
ARPES spectrum at each wave number. According to the theoretical results [5], the observed
band of this area originates from Se 4p states. Interesting enough, VBM includes not only Se
4p states but also some admixture of Tl 6s states, as calculated partial density-of-states [5] andLCAO (linear combination of atomic orbitals) analyses [6] show.
One can see from Fig. 1 that the largest energy shift of 423 meV is observed for the bandthat forms VBM at the T point after lowering the temperature. A strong downward shift of the
Fermi level (EF), which is known to depend very much on temperature especially in the I— 84 —

Fig. 1. The experimental band structure (ARPES intensity plot) near the valenceband maximum along the Γ-H-T (N-P-N) direction of TlInSe2 at 280 K (a) and 50
K (b). White solid and broken lines represent the results of the fit. Vertical arrows
indicate the position of the kink or gap structure. Red dot-dashed lines are the
LAPW-based results for TlInSe2 [5]. The details are given in the text.
phases due to formation of the new electronic levels inside the band gap [7], is considered tobe responsible for the observed ARPES spectral shift with temperature.
As it has already been mentioned, the I phase of TlInSe2 is very likely to occupy sometemperature region below 473 K [2]. The splitting with further formation of the multi-gap
structure in the energy bands at 50 K is an unambiguous evidence of a phase transition in
TlInSe2 [5]. Note, however, that the temperature region of the I phase is a very peculiar region
where phase transition occurs continuously throughout the phase until the modulation vector
is locked in some (commensurate) point of the BZ. The temperature at which this happens is
the temperature of the I–C transition. Therefore, the question regarding whether the observed
energy band transformations reflect the evolution of the I phase or the terminal I–C transition
remains open. In fact, the temperature-dependent photoluminescence measurements on
TlInSe2 have disclosed a very unusual temperature behavior of the 0.97-eV peak intensity,
related to a phase transition at 55 K [8]. All these make us believe that the I–C transition
occurs above 50 K and below this temperature TlInSe2 is already in the C phase.
From the above reasoning, the following picture of the N–I–C transition in TlInSe2 comesin sight. The phase transition from the N to the I phase that causes unusual behavior of thethermoelectric power of TlnSe2 occurs between 413 K and 473 K [2]. The terminaal I–C
transition takes place at around 55 K [8]. Then, the temperature 280 K at which the ARPES
spectra were taken is well below (by at least 133 K) the N–I transition point, remaining well
above (by 225 K) the I–C transition point. In other words, the accessed temperature is close to
the middle of the I phase.
Then, in order to check the ARPES spectral shape between 280 and 50 K, all experimental
data were fitted by a parabolic arch with the maximum at the T point. The results of the fit are
shown in Fig. 1 by a white solid curve. One can see that the data points for the wave numbers
smaller than approximately 0.65 Å–1 are not reproduced well by this fit. Fitting (white broken
curve in Fig. 1) performed in this region with the aid of other polynomials has revealed a kinkstructure at 0.67 Å–1 in the plot for 280 K and a gap-like structure at practically the same point(0.66 Å–1) in the plot for 50 K. Furthermore, by superimposing the calculated results for— 85 —

relevant bands of normal phase onto the corresponding experimental bands, we have found
the following. The experimental band at 280 K corresponds well to the calculated band (Fig.
1(a), red dash-dotted curve) from the kink to the T point, while at 50 K, the correspondence
between the experimental and calculated data becomes much worse (Fig. 1(b), reddash-dotted curve).
Thus, the above detailed analysis has definitely given a valuable insight into the structureof the topmost valence band of TlInSe2 and the revealed kink structure is definitely a room
temperature manifestation of the I phase of this material. If we add here that the wave vector
position of the kink structure in the BZ coincides not only with the position of the gap
structure but also with the position of the wave vector at which intersection between the
acoustic and low-frequency optical modes occurs [9], the self-consistence of the drawn
picture of the phase transition in TlInSe2 causes no doubts. What still remains unclear iswhether this picture is complete. The point is that the I phase may also appear due to thesoftening of the low-frequency optical mode along the Δ direction of the BZ [9]. The Δ
direction is perpendicular to the chains whereas the above-mentioned the A direction isparallel. Since low- temperature gap structures in the valence bands have been observed by
ARPES for both directions, the incommensurability linked to two independent wave vectors
in the BZ might also be considered as plausible. But, by any account, further studies arenecessary for drawing a more precise and complete picture of the N–I–C phase transition in
TlInSe2.
Acknowledgement
This work was partly supported by the grants from the Japan Society for the Promotion of
Science (Grant-in-Aid for Scientific Research (C), No. 18560014).
References[1] M. Hanias, A. N. Anagnostopoulos, K. Kambas, and J. Spyridelis, Phys. Rev. B 43 (1991)
4135.
[2] N. Mamedov, K. Wakita, A. Ashida, T. Matsui, and K. Morii, Thin Solid Films 499(2006) 275.
[3] D. Müller, G. Eulenberger, and H. Hahn, Z. Anorg. Allg. Chem. 398 (1973) 207.
[4] V. A. Aliev, M. A. Aldzhanov, and S. N. Aliev, JETP Lett. 45 (1987) 534.
[5] K. Mimura, K. Wakita, M. Arita, N. Mamedov, G. Orudzhev, Y. Taguchi, K. Ichikawa, H.
Namatame, and M. Taniguchi, J. Electron Spectrosc. Relat. Phenom. 156-158 (2007) 379.
[6] N. Mamedov, K. Wakita, S. Akita, and Y. Nakayama, Jpn. J. Appl. Phys. 44 (2005) 709.
[7] J. B. Sokoloff: Phys. Rev. B 25 (1982) 5901.
[8] K. Abe, K. Wakita, Y. Shim, and N. Mamedov, Ext. Abstr. 15th Int. Conf. Ternary andMultinary Compounds, Kyoto, 2006, Tue-P-35B.
[9] G. Orudzhev, V. Jafarova, S. Schorr, K. Mimura, K. Wakita, Y. Shim, N. Mamedov, F.
Hashimzade, Jpn. J. Appl. Phys., in press.

— 86 —

07-A-67

BL-9

Fermi surface and CDW gap of 2H-TaS2 studied
by angle resolved photoemission spectroscopy
M. Aritaa, H. Satoa, Y. Utsumia, H. Namatamea, M. Taniguchia,b, M. Sasakica
Hiroshima Synchrotron Radiation Center, bGraduate School of Science,
Hiroshima University, Kagamiyama , Higashi-Hiroshima 739-8526, Japanc
Department of Physics, Faculty of Science, Yamagata University, Kojirakawa, Yamagata
990-8560, Japan
Layered transition-metal dichalcogenides have various charge density wave (CDW)
phases. Especially, 2H-polytype materials are very interesting, because some of them
becomes superconductor at low temperature. Thus the competition and/or coexistence of
CDW and superconductivity take place in the system. In the stoichiometric 2H-TaS2,
incommensurate CDW order is observed below TCDW~75 K and the system is not into thecommensurate CDW at low temperature. Upon the intercalation of Na into one, the CDW
transition is suppressed and the transition temperature decreases. On the other hand, thesuperconducting phase appears and Tc increases up to 4.4 K. There are a few reports about the
Fermi surface (FS) and CDW gap of 2H-TaS2 with the angle resolve photoemission
spectroscopy [1]. As the clear FS and gap structures have not observed yet, the CDW
mechanism of the system is not clear.
In this report, we performed ARPES in non-intercalated 2H-TaS2, TCDWs of which are ~ 75
K, to clarify the FS structures and the CDW gaps. ARPES measurements were performed atundulator beam line BL-9A.
Figure shows the image of the photoemission intensity around Fermi energy (EF) with h= 19.2 eV at 100 K, that is, in the normal phase. The solid lines indicate the hexagonal
Brillouin Zone. A hole-type hexagonal FS is found around  point and there are two nearlycircular FS around K points. The obtained FS's are similar to the FS of 2H-TaSe2 and2H-NbSe2 in ARPES[1,2]. In respect of the FS's around K, the FS's near the K and M arecalled "inner FS" and "outer FS", respectively.
In order to find the FS nesting parts,
the temperature dependences of thespectra are measured at somemomentums where the CDW gap is
expected to opens. As a result, in the
spectrum along the KM line, the clear
gap structure is observed in inner FS
below 50 K. In other loci of the inner andouter FS's, the spectral intensities aroundEF decrease with decreasing temperature.
On the other hand, the gap is not foundin the FS around . Therefore it isconsidered that FS nesting occurs aroundK. That is similar to the case of
2H-TaSe2 [3].
[1]W. C. Tonjes. et al., Phys. Rev. B 63, 235101
Map of ARPES spectral intensity around EF in 2H-TaS2 at 100 K(2001).
withh = 19.2 eV. The solid lines indicate the hexagonal Brillouin[2]R. Liu, et al., Phys. Rev. B 61, 5212 (2000).
Zone.
[3]K. Rossnagel, et al., Phys. Rev. B 72, 121103(2005).

— 87 —

07-A-33

BL- 9

Primary role of the barely occupied states in the charge density wave
formation of NbSe2
D. W. Shena, Y. Zhanga, L. X. Yanga, J. Weia, H. W. Oua, J. K. Donga, B. P. Xiea, C. Hea, J. F.
Zhaoa, B. Zhoua, M. Aritab, K. Shimadab, H. Namatameb, M. Taniguchib, J. Shic and D. L.
Fengaa
Department of Physics, Surface Physics Laboratory(National Key Laboratory) and
Advanced Materials Laboratory, Fudan University, Shanghai 200433, P. R. Chinab
Hiroshima Synchrotron Radiation Center and Graduate School of Science, Hiroshima
University, Hiroshima 739-8526, Japanc
School of Physics, Wuhan University, Wuhan, 430072, P. R. China
2H-NbSe2 is one of the most studied materials for its prototypical superconductivity (SC) andtwo dimensional charge density wave (CDW). Based on experiments conducted on NbSe2,
understanding on some of the most basic properties of SC and CDW was reached.
Nevertheless, the very mechanism of the CDW in NbSe2 itself has been mysterious andcontroversial for over three decades. In the typical picture of CDW, the scattering of electrons
between the parallel Fermi surface (FS) sections would give the so called nesting condition
for CDW. Similarly, saddle band points, where the singularities of density of states (DOS) arelocated, were proposed to cause CDW as well [1]. Recently, the authors discussed anotherFermi-patch CDW mechanism for some polaronic systems, where large DOS at EF hovers
over an extended area of the Brillouin zone (BZ) and work collectively to favor certain CDW
order [2]. However, the CDW in NbSe2 cannot be explained by any of these scenarios.
We have performed the high resolution ARPES experiment at BL-9 on NbSe2, where the
CDW related weight-suppressed momenta were precisely revealed for the first time and thus
the aforementioned long-standing controversies are naturally solved [3]. In this experiment,
the used photo energy was 21.2eV and the total energy resolution was tuned to be better than
10meV.

  (a) The illustration of the CDW induced weight-suppressed regions (b) The spectral weight suppression map
and its corresponding ratio map are false color plotted, where the dashed lines contour the obviously suppressedregions.

— 88 —

Through careful examination, the delicate spectral weight suppression upon CDW is observed.
Therefore, the weight-suppressed regions in the BZ can be determined accurately, as marked
in Fig. 1(a) by bars. Moreover, both the maps of the spectral weight suppression and its
corresponding suppressing ratio confirm the result as well (Fig.1(b)). This distribution makes
a broken-honeycomb-shaped structure in the BZ, as shown in Fig. 2(a). Obviously, theseregions can be well connected by the CDW wavevector Qi's (represented by the
double-headed arrows). In this way, the long-lost nesting condition is naturally satisfied.
In addition, we note that the distribution includes some regions where the DOS at EF is very
weak. However, the spectral weight suppression over these regions accounts for around 60%of the total one. In other words, although the DOS is low, the barely occupied states indeed
play the primary role in the CDW formation due to their relatively extensive momentum
space. This result will be more clearly illustrated through the so-called weighted joint DOS
analysis, which can effectively estimate the contribution of the states to the final CDW
instability. It is found that the saddle band points (high DOS) only contribute about 17% of
the total weighted joint DOS computed over the entire broken-honeycomb region, as shown in
Fig.2(b). Therefore, the nesting of states with low DOS at EF indeed dominates the charge
instability at Qi's here.

  (a) The distribution of CDW related weight suppression over the entire BZ sketched from the spectral
weight suppression map, which are marked by the orange broken-honeycomb-shaped structure. (b) Comparison of thecorresponding joint DOS results along -M.

Our findings not only recover the long-lost nesting condition for this classic CDW material,
but also show that collective contribution of the weakly occupied states can play the primaryrole in CDW formation in some cases, which may amend the conventional wisdom of CDW.
References
1
2
3

T. M.Rice and G. K. Scott, Phys. Rev. Lett. 35, 120 (1975).
D. W. Shen et al, Phys. Rev. Lett. 99, 216404 (2007).
D. W. Shen et al, Phys. Rev. Lett. (in press).

— 89 —

07-A-33

BL-9Superconducting coherence peak in the electronic excitations of asingle layer cuprate superconductor Bi2Sr1.6La0.4CuO6+
J. Wei1, Y. Zhang1, H. W. Ou1, B. P. Xie1, D. W. Shen1, J. F. Zhao1, L. X. Yang1, M. Arita2,
K. Shimada2, H. Namatame2, M. Taniguchi2, Y. Yoshida3, H. Eisaki3, and D. L. Feng1*
1
Department of Physics, Surface Physics Laboratory (National Key Laboratory) and
Advanced Materials Laboratory, Fudan University, Shanghai 200433, P. R. China
2

Hiroshima Synchrotron Radiation Center and Graduate School of Science, Hiroshima
University, Hiroshima 739-8526, Japan
3
National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki,
3058568, JapanFor investigation of the mechanism of high temperature superconductivity, one central
issue is whether there are certain bosons that play the critical mediating role of phonons in aconventional BCS superconductor. So far, signatures of electron-boson interactions have been
identified in single particle excitations measured by angle resolved photoemission
spectroscopy (ARPES).
We have performed ARPES on optimally doped Bi2Sr1.6La0.4CuO6+ (La-Bi2201) (TC=
34K) using BL 9 [1].The photon energy was 22.5eV, and energy resolution was 7 meV. The
samples were cleaved in ultra-high vacuum (510-11 mbar).
Figure.1 shows photoemission data in the superconducting state of La-Bi2201. The data
were taken in the -Y quadrant of the Brillouin zone. In the vicinity of (, 0), a feature near
the Fermi energy (EF) gradually becomes quite prominent as indicated by the diamonds in
Figs.1a(5-8), b(5-8). Though weak, the appearance of such two-component structure over abroad momentum area clearly proves its robustness against the experimental uncertainties. It
is the first time to observe the superconducting coherence peak (SCP) or two-component
spectrum in the antinodal region of single layer compounds. We attribute it to the minimized
disorder effects in the current sample. As comparison, for another optimally doped La-Bi2201
sample (TC = 32K) with finite residual resistivity (Fig.1c), its spectrum in the antinodal region
is much broader than that of the current sample (Fig.1d).
Figure.2 shows the temperature dependences and compares the spectra below and above
Tc after removing the temperature broadening effects in Fig.2b. The data evidence that the
sharp peak in the antinodal region is the SCP as observed in multi-layered cuprates before.
Fig.2c shows the associated “peak-dip-hump” (PDH) structures for three momenta near (, 0).
Through a phenomenological fitting, one could precisely determine the peak position and theseparation between the peak and dip, which is about 19 meV at all three momenta. Follow thesame analyses as in many previous ARPES studies that the peak-dip separation corresponds
to the energy of a bosonic mode. We consider this low energy mode could have an intriguing
correlation with the energy scale of spin excitations near (, ). The weaker dip structure, in
Bi2201 is consistent with the weaker intensity of the spin excitations observed in low-TC
systems.

— 90 —

In summary, we have discovered the PDH in the antinodal region of the single layer
La-Bi2201, found the peak-dip distance to be about 19 meV, suggesting the possibility of abosonic mode in Bi2201 with a much lower energy than that in Bi2212 [2]. It will face serious
challenges to consistently explain the PDH's in different systems [3, 4]. The temperaturedependence of the PDH in the antinodal region and the 19 meV peak-dip separation of
La-Bi2201 intriguingly correlate with the behaviors of spin fluctuations. Our data provides a
critical piece to the global picture, which would help to eventually resolve controversial issues
and uncover the glue of high-Tc superconductivity.

Fig. 1: Photoemission data of La-Bi2201. (a1-a8) Photoemission
intensity map along cuts 1–8 across the Fermi surface in the
superconducting state. Thick lines in a1-a4 are the dispersions
fitted from momentum distribute curves. (b1-b8) display thecorresponding spectra in panel a1-a8. (c) The resistivity of two
La-Bi2201 samples, (d) their corresponding spectrum at kF8, and (e)the momentum dependence of their gaps.
Fig. 2: (a) Detailed temperature dependence of photoemission data
at kF7, as indicated in the inset, (b) compare the spectra below andabove TC at kF7 after removing the temperature broadening effects,(c) the SCP in the vicinity of (, 0),Peak and dip positions areillustrated by the arrows.

[1] J. Wei et al., Phys. Rev. Lett. 101, 097005 (2008).
[2] D. L. Feng et al., Science 289, 277 (2000)[3] Z. X. Shen and J. R. Schrieffer, Phys. Rev. Lett. 78, 1771(1997)[4] A. A. Kordyuk et al., Phys. Rev. Lett. 89, 077003 (2002).

— 91 —

07-A-21

BL-9A

Novel electronic structure induced by a highly strained oxide interface
with incommensurate crystal fields
H. W. Oua,b, J. F. Zhaoa,b, Y. Zhanga,b, B. P. Xiea,b, D. W. Shena,b, Y. Zhua, Z. Q. Yanga, J. G.
Chea, X. G. Luoc, X. H. Chenc, M. Aritad, K. Shimadad, H. Namatamed, M. Taniguchid, C. M.
Chenge, K. D. Tsueie, and D. L. Fenga,b*aSurface Physics Laboratory (National key laboratory) and Physics Department,
Fudan University, Shanghai 200433, P. R. Chinab
Advanced Materials Laboratory, Fudan University, Shanghai 200433, P. R. Chinac
Hefei National Laboratory for Physical Sciences at Microscale and Department of Physics,
University of Science and Technology of China, Hefei, Anhui 230026, P. R. Chinad
Hiroshima Synchrotron Radiation Center and Graduate School of Science,
Hiroshima University, Hiroshima 739-8526, Japane
National Synchrotron Radiation Research Center, and Department of Physics,
National Tsing-Hua University, Hsinchu 30077, Taiwan, Republic of China
Novel phenomena emerging from the oxide interfaces have attracted enormous attention,
which provide opportunities for promising applications: one may be able to make oxide
heterostructure devices with desired physical properties. A thorough understanding of the
microscopic processes at the oxide interface is the first step toward designing functional
heterostructures. Particularly, it is crucial to find out the electronic behavior at oxideinterfaces, e.g., how the electron bands behave on both sides of the interface; and how they
react to strain and peculiar phonon structures at the interface. The answers to these questions
would lead to the understanding of the charge transfer process, the insulator-metal transitions,and anomalous transport behavior of the interfaces.
Angle-Resolved Photoemission Spectroscopy (ARPES) is proven to be a powerful tool toinvestigate the electronic structure of solids and thin films. However, due to the short mean
free path of photoelectrons, photoemission signals from the interface of pulsed-laser depositedoxides are very weak, which forbids high resolution and momentum resolved measurements.
The misfit oxide single crystal, which is made of alternating rocksalt-structured [MO] layers(M=Ca, Bi, Ba, Sr) and CdI2-type hexagonal CoO2 layers, provides an alternative solution. It
resembles a very clean artificial oxide heterostructure and is suitable for photoemission
experiments.
Misfit Cobaltate Bi2Ba1.3K0.6Co2.13O7.94 (BBKCO) was studied by ARPES at HiSOR
BL-9A beam line. Detailed electronic structure of such a highly strained oxide interface isrevealed for the first time. As illustrated in Fig.1, we found that under the two
incommensurate crystal fields, electrons are confined within individual sides of the interface,and scattered by umklapp scattering of the crystal field from the other side. In addition, thehigh strain on the rocksalt layer raises its chemical potential and induces large charge transfer
to the CoO2 layer.

— 92 —

  Fermi surfaces (FS) measured at 20K with (a) 12.5 eV and (b) 21.2 eV photons respectively, which are
obtained by integration of the spectral weight in a 20meV window around EF. The dash-dotted and dashed thickcurves are [CoO2]-derived and [BiO/BaO]-derived Fermi pockets respectively. Their umklapp FS’s are indicatedby thinner curves.

Furthermore, a novel interface effect, the interfacial enhancement of electron-phonon
interactions, is discovered. As shown in Fig.2, the Na0.7CoO2 dispersion is a smooth curve[Fig.2 (c)], however there are strong kinks on the dispersions of the BBKCO bands [Fig.2(a-b)]. These kinks are suggesting an intrinsic effect due to interactions with some bosonicmodes, most likely phonons induced by the interface here. This strong coupling is also
reflected in its scattering rate [Fig. 2(d)], where a clear turning point around 60meV appears
for both the bands of BBKCO.

   Photoemission intensity along -K (cut #1 in Fig. 1) taken at 20K, for (a) BBKCO’s CoO2 layer(h=15eV), (b) BBKCO’s [BiO/BaO] layers (h=21.2eV), and (c) Na0.7CoO2 (h=21.2eV). The red thick curves
are fitted dispersions. (d) The width of the momentum distribution curve vs. binding energy for data presented inpanel a-c, which is an estimate of the quasiparticle scattering rate.

In conclusion, we have studied various interfacial electronic properties by ARPES, andthe relation between strain and charge transfer across oxide interface is illustrated from a
microscopic level. Our results suggest that interfacial strain might cause large charge transfer
without severely changing the properties of participating layers. The enhancement of electron
phonon coupling and interfacial umklapp scattering are discovered, which affect the low
energy electronic behavior. Our findings provide an electronic structure foundation forunderstanding oxide interfaces, and some important guidelines for designing oxide devices.
Note: the manuscript on this work has been submitted to Phys. Rev. Lett.

— 93 —

07-A-10

BL 9A

Observation of the multibands and superconducting gaps in the trilayer
high-Tc cuprate superconductor Bi2Sr2Ca2Cu3O10+δ�
S. Ideta1, K. Takashima1, M. Hashimoto1, T. Yoshida1, A. Fujimori1, A. Ino2, H. Anzai2,
T. Fujita2, Y. Nakashima2, M. Arita3, H. Namatame3, M. Taniguchi2, 3,
K. M. Kojima1 & S. Uchida11Department of Physics, University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan.
2
Graduate School of Science, Hiroshima University, Higashi-Hiroshima 739-8526, Japan.
3
Hiroshima Synchrotron Center, Hiroshima University, Higashi-Hiroshima 739-0046, Japan
It has been empirically known that the superconducting transition temperature (Tc) of
optimally doped high-Tc cuprate superconductors (HTSCs) increases with the number ofadjacent CuO2 planes (n) from single-layer (n = 1) to trilayer (n = 3) and then decreases withmore layer number (n > 3). In the case of Bi-based HTSCs, the optimum Tc increases fromsingle-layer Bi2Sr2CuO6+δ (Bi2201, Tc max = 35 K), bilayer Bi2Sr2CaCu2O8+δ (Bi2212, Tc max =95 K) to trilayer Bi2Sr2Ca2Cu3O10+δ (Bi2223, Tc max = 110 K). According to a theory withtunneling of Cooper pairs between the CuO2 planes, Tc continues to increase with increasing n
1. However, when the charge imbalance and a competing order parameter are taken into
account, Tc becomes maximum at n = 32. Tc tends to be large when the value of next nearestneighbor hopping parameter t’/t is large3 and the CuO2 plane is the ideally flat4. However, themicroscopic origin of the correlation between the n and Tc has been unclear so far because of
the lack of detailed knowledge about the multi-layer effects in the electronic structure.
Angle-resolved photoemission spectroscopy (ARPES) is one of the most powerful tools toinvestigate the electronic structure of HTSCs. In previous ARPES results on the double-layer
Bi2212 and the four-layer Ba2Ca3Cu4O8F2 (F0234), splitting of the band dispersions and two
Fermi surfaces (FSs) have been observed. In the case of Bi2212, hybridization between
orbitals on the two CuO2 planes causes band splitting into the anti-bonding and bonding bands
5. Recently, band splitting in the nodal direction has also been observed in high resolution
experiment9. F0234 has indicated band splitting due to the differences in the holeconcentrations for the inner CuO2 planes (IPs) and outer CuO2 planes (OPs), and two FS
sheets corresponding to IPs and OPs have been observed 10. The gap magnitude of the IP bandis approximately twice as large as that of the OP. However, previous ARPES results on
Bi2223, which has three CuO2 planes, have not shown band splitting corresponding to the IP
and OP bands 6-8. In the present work, we have observed the band splitting for Bi2223 andshown that the electronic structures of the IP and OP have different doping levels and the gap
magnitudes. Single crystals of optimally doped Bi2223 (Tc = 110 K) were grown by thetravelling solvent floating zone (TSFZ) method11. ARPES experiments were carried out using— 94 —

at BL-9A (hν = 6.6-12.9 eV, circularly polarized light) at Hiroshima Synchrotron Radiation
Center, and the total energy resolution (∆E) was set at 5 meV. The samples were cleaved insitu under an ultrahigh vacuum of ~1×10-11 Torr and all experiments were measured at T = 10K.
In Fig. 1(a), we show spectral weight mapping around 40 meV below the Fermi level (EF)integrated with a window 10 meV. Two FS sheets corresponding to the IP and OP are clearlyobserved. Particularly, as shown in Fig. 1(b), the intensity of IP is enhanced for hν = 11.95 eV.
In the NMR study of trilayer HTSCs, the hole concentration of OPs and IP are found to be in
the overdoped and underdoped regions, respectively 12. Thus, we assign the FS sheets close to
the Γ point is the OPs, and the other FS to IP. The dispersions in the nodal direction
corresponding to Fig. 1(a) and (b) are shown in Fig. 1(d) and (e), respectively. Since there arethree neighbouring CuO2 planes, one would expect to observe three bands which come fromone IP and two OP bands. Although theoretical calculation shows the three bands clearly 13,
we have observed only two bands, implying that the two OP bands, i.e., the bonding andanti-bonding OP bands, are degenerate. In fact, the full width at half maximum (FWHM) of
the momentum distribution curve (MDC) for the OP band at EF, ~0.011 Å-1, is significantly
larger than that of the IP band ~0.0074 Å-1, indicating the presence of two unresolved bands.
The FWHM of IP's is almost the same as that of Bi2212, 0.0065 Å-1 9. The kF positions of theFSs for OP and IP have been determined by the minimum-gap-locus. The result oftight-binding (TB) fit is shown in Fig. 1(c). The hole concentrations for IP and OP deduced
from the FS areas are 6 ± 3 and 25 ± 2 %, respectively, indicating that IP and OP areunderdoped and overdoped region, respectively. The values of the TB parameter –t’/t are~0.29 (IP) and ~0.26 (OP) similar to the theoretically predicted values for multi-layermaterials such as HgBa2Ca2Cu3O1+δ, Tl2Ba2Ca2Cu3O10 (n = 3)3.

Figure 1 Intensity plots of ARPES spectra integrated within E = - 40 ± 5 meV (a, b). Two-FSs havebeen observed, and correspond to the inner CuO2 plane (IP) and outer CuO2 planes (OPs). The holeconcentration of the OP is higher than that of IP, therefore the FS for OP locate near the Γ point (c).
(d) and (e) show the band dispersion taken by hν = 7.65 and 11.95 eV. In using excitation energy of
7.65 eV, OP band-spectra are enhanced mainly, while in 11.95 eV, IP band is enhanced.

— 95 —

In Fig.2 (a) and (b), we show band dispersions in the superconducting state for OP and IP,
respectively, from the nodal to off-nodal regions. Due to matrix-element effects, theintensities of the OP and IP bands' are enhanced at photon energies hν = 9 and 11.95 eV,

Figure 3: Intensity plots for OP band from the nodal to the off-nodal region (a1 - a3) and for IP band(b1 - b3) observed in the superconducting state (T = 10 K) corresponding to the cuts (red lines) for theright panels. The photon energies, hν = 9 eV and 11.95 eV, enhance the OP and IP bands,
respectively. We can clearly see the difference of the gap amplitudes for the IP and OP bands in theoff-nodal region.

Figure 2: The Energy distribution curve (EDC) spectra for OP and IP bands’ are shown in panels(a1) and (a2), respectively. (b) The gap anisotropies for the IP and OP bands have different
characters. The OP’s SC gap shows the simple d-wave, while the IP’s deviates from the d-wave (c).
The gap size of Bi2223 is compared with that of Bi2212 and one can see the gap sizes between
Bi2212 and Bi2223 have a large difference (c). Red filled square indicates the average of ∆0 for IP
and OP bands.

respectively. The gap energies for both bands are very different, as in the case of the other— 96 —

multi-layer cuprate F0234 (n = 4). In Fig. 3(a1) and (a2), the symmetrised EDCs at kF are
shown. The momentum dependence of the gap anisotropy for OP is almost simple d-wave
like ∆0OP|cos (kxa) - cos (kya)|/2 with ∆0OP ~40 meV as shown in Fig. 3(b). On the other hand,
the SC gap for IP band deviates from the simple d-wave, and the gap size is ∆0IP ~60 meV and∆*IP ~80 meV, where ∆0 and ∆* are defined by the extrapolation of nodal and anti-nodal gaps
to |cos (kxa)-cos (kya)|/2 = 1, respectively, as shown in Fig. 3(b) 14, 15. Since the deviation fromthe simple d-wave is prominent in the underdoped region, the observed gap and anisotropy is
consistent with the doping levels estimated from the FS area. Judging from the present resultof the OP gap ∆0 ~40 meV, one can conclude that the previous ARPES result ∆0 ~40 meV for
Bi2223 represents the OP band 6, 7. In Fig.3 (c), compared with Bi2212, Fig. 3(c), the gap sizeof OP band is almost the same as that of optimally doped Bi2212 in spite of heavily
overdoping 14-17. Now, let us discuss the origin of the large ∆0 in Bi2223 compared with theother cuprates. In Bi2223, there are three possible factors for large ∆0: (1) the value of
hopping parameter, t´/t, which has a correlation with Tc, is larger than those of single andbilayer cuprates3, (2) disorder effect is small because the inner CuO2 plane is ideally flat
among various cuprates4, (3) the interlayer tunneling of Cooper pairs between CuO2 planes
enhances superconducting order parameter1, 2.
In conclusion, we have measured the band splitting of Bi2223 by ARPES using low photon
energy. The Fermi surfaces corresponding to the IP and OP bands have been observed and thesuperconducting gaps of OP and IP’s show the different values between them.

References
1. J. M.Wheatley et al., Nature 333, 121 (1988).
2. S. Chakravarty et al., Nature 428, 53 (2004).
3. E. Pavarini et al., Phys. Rev. Lett. 87, 047003 (2001).
4. H. Eisaki et al., Phys. Rev. B 69, 064512 (2004).
5. D. L. Feng et al., Phys. Rev. Lett. 86, 5550 (2001).
6. T. Sato et al., Phys. Rev. Lett. 91, 157003 (2003).
7. H. Matsui et al., Phys. Rev. B 67, 060501 (2003).
8. D. L. Feng et al., Phys. Rev. Lett. 88, 107001 (2002).
9. K. Yamasak et al., Phys. Rev. B 75, 140513(R) (2007).
10. Y. Chen et al., Phys. Rev. Lett. 97, 236401 (2006).
11. T. Fujita et al., J. Phys. Chem. Solids 62, 171 (2001).
12. K. Kotegawa et al., J. Phys. Chem. Solids 62, 171 (2001).
13. M. Mori et al., Phys. Rev. B 66, 064502 (2002).
14. K. Tanaka et al., Science 314 (2006).
15. W. S. Lee et al., Nature 450, 81 (2007).
16. J. Mesot et al., Phys. Rev. Lett. 83, 840 (1999).
17. H. Ding et al., Phys. Rev. Lett. 87, 227001 (2001).

— 97 —

07-A-1

BL-9

Impurity effect of nodal fine quasiparticle structure of
Bi2Sr1.6(La,Gd)0.4CuO6+δ studied by low-energy synchrotron-radiation ARPES
T. Fujitaa, T. Kamoa, H. Anzaia, A. Inoa, M. Aritab, H. Namatameb, M. Taniguchia,b,A. Fujimoric, Z.-X. Shend, K. Fujitac, S. UchidacaGraduate School of Science, Hiroshima Universityb
Hiroshima Synchrotron Radiation Center, Hiroshima Universityc
Deptertment of Physics, University of Tokyod
Deptertment of Physics and Stanford Synchrotron Radiation Laboratory, Stanford University
The structural unit common to all the high-Tc cuprate spuperconductors is the CuO2 planes,
which is considered as the main stage of the superconductivity. However, in order tounderstand the diversity of the cuprates such as the difference in superconducting criticaltemperatures Tc, we have to clarify the effect of the part outside CuO2 plane. For
Bi2Sr1.6Ln0.4CuO6+δ (Ln = La, Gd), the degree of out-of-plane disorder may be systematicallycontrolled with Ln site, and Tc decreases with increasing
the out-of-plane disorder.
So far, angle-resolved
photoemission (ARPES) studies are concentrated on theantinodal region, while it is required for extremely highresolution to observe the small gap near a node.
In the present study, we performed an ARPES
experiment with high energy and momentum resolution
by using low-energy synchrotron radiation (hν = 7.8 eV),and determined the directional-dependence of the gap
magnitude around the nodal direction. Figure 1 shows
the ARPES spectra of Bi2Sr1.6La0.4CuO6+δ (Tc = 33 K)
collected along the Fermi surface. The near-nodal gap
is well consistent to the directional dependence ofd-wave symmetry, 2Δ / kBTc = 9.1 kBTc. Substituting
50% of La with Gd, the out-of-plane disorder increases
and thus Tc reduces to 27 K. However, while thequasiparticle peak is appreciably broadened, thedecrease in the gap magnitude is smaller than that in Tc,
Fig. 1
ARPES spectra ofsuggesting that the out-of-plane disorder mainly affects
Bi2Sr1.6La0.4CuO6+δ (Tc = 33 K)
the quasiparticle coherence.
collected along the Fermi surface,indicating that the near-nodal gap isconsistent to d-wave symmetry.

— 98 —

07-A-2BL-9Doping dependence of gap anisotropy of Bi2Sr2CaCu2O8+ studied by
low-energy ARPES
H. Anzai a, T. Kamo a, T. Fujita a, A. Ino a, M. Arita b, H. Namatame b, M. Taniguchi a,b,
M. Ishikado c, A. Fujimori c, S. Uchida c, and Z.-X. Shen daGraduate School of Science, Hiroshima University, Higashi-Hiroshima 739-8526, Japanb

Hiroshima Synchrotron Radiation Center, Hiroshima University, Higashi-Hiroshima 739-0046, Japanc

Department of Physics, University of Tokyo, Tokyo 113-0033, Japand

Department of Applied Physics and SSRL, Stanford University, Stanford, CA94305, USA

High-Tc cuprates show diverse phases depending on the concentration of doped holes.
Hence, the doping evolution of electronic structure may be the key to the understanding of thethe mechanism of the high-Tc superconductivity. It has been established that thesuperconducting gap of the cuprates has nodes like in d-wave superconductors, but the detailof the directional dependence of the gap magnitude is still unclear. Here, we havesystematically studied the hole-concentration dependence of the superconducting gap of
bilayer cuprate Bi2Sr2CaCu2O8+ (Bi2212) by angle-resolved photoemission spectroscopy(ARPES). Experiments were performed at BL-9 of HiSOR.
With the photon-energy tunability and the high momentum and energy resolution, we havedetermined the shape of two Fermi surfaces split due to intra-bilayer interaction for all overthe brillouin zone, and revealed the fine detail of the directional dependence of gap magnitude
for each of the bonding and andtibonding bands. Figure 1 (a) shows the ARPES spectra ofunderdoped Bi2212, taken along the Fermi surface of the bonding band. The open circles

Fig.1 (a) The ARPES spectra of underdoped Bi2212 (Tc = 66 K), taken along the Fermi surface of thebonding band. (b) Directional dependence of the gap magnitude for underdoped (UD66),
optimally-doped (Opt91) and overdoped (OD80) samples. (c) Schematic diagram of momentum space.
The spectra are cut along Fermi surface.

— 99 —

denote the energy of the spectral peak, indicating the directional dependence of the gap
magnitude as a function of dx2-y2 wave-gap magnitude, cos2. Near the node, the result is
consistent with dx2-y2-symmetry, whereas in the antinodal region it is appreciably deviatedfrom the dx2-y2-symmetry. Figure 1 (b) shows the directional dependence of the gap magnitude
for various hole concentration. The magnitude of antinodal gap rapidly increases as holeconcentration decreases, suggesting that the antinodal gap is related to antiferromagnetic
fluctuation. We have found that the near-nodal d-gap region rapidly shrinks as holeconcentration decreases, and that 2() / kBTc cos2~ 8 in the near-nodal region for all thedoping levels. This value is larger than the value ~ 4.12, which is predicted by BCS
weak-coupling model for d-wave gap within mean-field approximation. It has also been
observed for underdoped samples that the quasiparticle group velocity gradually decelerates
in going from || ~ -20 meV to Fermi level in (0,0) – (,) direction. The Fermi velocity of
the underdoped samples is suppressed to 75% of that of the optimally-doped samples,indicating that the renormalization effect increases with decreasing hole concentration. Theseobservations imply that excessively strong interaction may lead to the shrinkage of thenear-nodal d-gap region.

— 100 —

BL-9A

ARPES study of the quantum size eﬀects in atomically uniform Pb ﬁlms on
Si(111)-7x7
Shaolong He 1, , Zhenhua Zeng 2 , Masashi Arita1 , Masahiro Sawada 1 ,Kenya Shimada 1 , Shan Qiao 3, , Guoling Li 2 ,Xin Liu 2 , Wei-Xue Li 2 , Yan-feng
Zhang4 , Jinfeng Jia5 , Qi-kun Xue5 , Hirofumi Namatame 1 , and Masaki Taniguchi 1
1

Hiroshima Synchrotron Radiation Center, and Graduate School of Science,
Hiroshima University, Higashi-Hiroshima 739-8526, Japan
2
State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics,
Chinese Academy of Sciences, Dalian 116023, China
3
Advanced Materials Laboratory, Fudan University, Shanghai 200433, China
4
Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Japan and5
Department of Physics, Tsinghua University, Beijing 100084, China(Dated: October 8, 2008)
The electronic structures and the Fermi surface (FS) topology of atomically uniform Pb(111)ﬁlms are investigated by high resolution angle resolved photoemission spectroscopy (ARPES). Our
results reveal a well-deﬁned FS topology of the atomically uniform Pb ﬁlms on Si(111) surface.
First principle calculations can reproduce the main FS features and further clarify that FS features
centered at the Γ point are composed of a well-shaped hexagonal hole pocket and a snowﬂake-shapedhole pocket. In addition, we clearly demonstrate that the quantum well states induced oscillations
in density of state near EF are directly related to the numbers of the subbands which survive toenclose hole pockets at the Fermi level.

The electronic structures of thin metallic ﬁlms
are of great research interests due to that thesequasi two-dimensional electron systems exhibit novel
properties quite diﬀerent from their bulk counterparts.
Many important properties such as thesuperconductivity,1–5 electron-phonon coupling,6 andsurface chemical reactivities,7 can be modulated by thequantum well states (QWS)8 formed in these metallic
ﬁlms. Such modulation in physical transport properties
and chemical reactivity by quantum size eﬀects (QSE)
has been convincingly demonstrated to relate closely withthe oscillations in density of states(DOS) near EF induced by the formation of the QWS in the ﬁlms.9 However, the interesting issue about how QWS modulate
the DOS near EF has remained elusive. The recent advances in manufacturing atomical-layer-resolved Pb ﬁlms
on Si(111)9 provide us an unique opportunity to explore
this fundamental issue by using high resolution angle resolved photoemission spectroscopy (ARPES).
In addition, the convincingly demonstrations of Tc oscillations in Pb ﬁlms1 is of particular interests. While Tc
is strongly inﬂuenced by zone-averaged electronic structure especially by the Fermi-level DOS, the Fermi surface(FS) topology also play a signiﬁcant role. On the other
hand, the FS topology may be also shaped or distorted
by dimensional conﬁnement in thin ﬁlms and therefore
aﬀect Tc . Hence investigations on the electronic structures and the FS topology of atomically-layer-resolved
Pb ﬁlms are of fundamental interests and importance.
In this letter, we present a systematic electronic structures study of the atomically uniform Pb(111) ﬁlms overa wide range of thickness. It is found that Pb(111) ﬁlms
have a well-deﬁned FS which diﬀers signiﬁcantly fromthat of bulk Pb(111) crystals. The FS topology featuresof Pb ﬁlms are further clariﬁed by density functional the-ory (DFT) calculations. Detailed theoretical and experimental studies show that the QWS induced oscillationsin DOS near EF are directly related to the numbers of
the subbands which survive to enclose hole pockets at
EF .
The experiment was performed at Hiroshima Synchrotron Radiation Center (HSRC), Hiroshima University. The clean and defect free Si(111) − (7 × 7) reconstructed surfaces were prepared and checked by STM and
LEED. The Pb(111) ﬁlms were then prepared by evaporating lead from a Mo crucible on Si(111) − (7 × 7)
surfaces. The evaporating rate was carefully adjusted
to favor the layer-by-layer growth mode at 100 K, whichwere veriﬁed by STM and reﬂection high energy electron
diﬀraction pattern. The prepared ﬁlms were graduallyannealing to room temperature and then transferred tothe analysis chamber with base pressure of 1×10−11 Torr
for in situ ARPES measurements. The ARPES spectra
were taken by a Scienta-R4000 electron analyzer at beamline BL-9A10 with resolution of about 12 meV at photon
energy around 21 eV.
The Vienna ab initio simulation package (VASP)11
was used to solve the Kohn-Sham equations with projector augmented wave (PAW) potentials12 and GGAPBE functional for exchange-correlation interaction.13
Pb 6s and 6p electrons were treated as valence electrons, and plane wave cutoﬀ (100 eV) for PAW potentials were used. The spin-orbit coupling were found to
be important to describe band structure properly, andincluded in all our calculations. Calculated lattice constant (5.03 Å) was used to build the supercell separated
by 20 Åvacuum. The Brillouin zone was sampled by
Monkhorst-Pack (12×12×1) grid, and Methfessel-Paxton
approach with parameter of 0.20 for accelerating the electronic relaxation.14 The top ﬁve metal layers on both

— 101 —

2
(a)

(b)

1.0

(b)

17ML
K

ky(Å-1)

0.5
0.0

Γ

S

M

1.0

E-EF (eV)

E-EF (eV)

0.0
-0.5

-1.0

(c)

-1.0
-0.5

0.0
kx(Å-1)

0.5

1.0

-1.0

(d)

24ML

ky(Å-1)ky(Å-1)-0.5

FIG. 1: (a)ARPES intensity image of a 21 ML Pb(111) ﬁlm
taken, at a temperature of 12 K, along ΓM direction with aphoton energy of 21 eV. (b)The calculated band structureson the 21 ML Pb(111) slabs. The black and blue lines represent the two diﬀerent group subbands. The ARPES intensity
image in (a) is also included for comparison.

sides of the slab were relaxed until the forces less than
0.0X eV/Å.
Fig. 1 shows ARPES intensity images along ΓM obtained on a Pb(111) ﬁlm with thickness of 21 monolayers(ML). For a 21 ML Pb(111) ﬁlm, the bulk bands
are split into 21 two-dimensional subbands as indicatedby the results from DFT calculations (solid lines) in
Fig. 1(b), where the same ARPES intensity image in
Fig. 1(a) is also included for comparison. The dispersions of the QWS in the 21 ML Pb(111) ﬁlm is very similar to a previous ARPES study on thin Pb(111) ﬁlms.15
Near the zone center, a sharp QWS peak, which locatedabove binding energy of 0.2 eV, can be resolved indicating the high quality of the Pb ﬁlms. However, around−1k ∼ 0.7 Å , there are four subbands crossing EF andenclosed hole pockets around the M point which can be
reproduced by the calculations presented in Fig. 1(b)and Fig. 2(d)(blue lines). These band features have notbeen reported in previous ARPES results on Pb(111)ﬁlms15–17 since it needs high quality ﬁlms and high resolution ARPES.
The FS evolution in the Pb(111) ﬁlms over a wide
range of thickness is summarized in Fig. 2. For comparison, we also include calculated FS of the Pb(111)crystal in (a) (dotted red line, only the FS feature nearzone center is shown) and that of the 21 ML Pb(111)slabs in (d). The experimental FS mapping was obtained
from high-resolution ARPES data and integrated overthe energy window EF ±5 meV with photon energy of
21 eV. The main features of the experimental FS can be
reproduced by this calculation. While the bulk FS fea-

0.5

0.0

0.5

1.0

0.0

-0.5

-1.0
-1.0

0.0

kx(Å-1)0.5

0.0

k-k0 (Å-1)

-0.5

1.0

0.5

k-k0 (Å-1)

21ML

0.5

-0.5

-1.0

1.0

ky(Å-1)

(a)

-1.0
-0.5

0.0
kx(Å-1)

0.5

1.0

-1.0

-0.5

kx(Å-1)

1.0

FIG. 2: ARPES intensity mapping integrated over the energy
window EF ±5 meV taken on Pb(111) ﬁlms over a wide rangeof thickness at a temperature of 10 K with a photon energyof 21 eV. Bright regions correspond to bands crossing EF ,and thus to sections of the FS. (a) FS mapping of a 17 ML
Pb(111) ﬁlm. The surface Brillouin zone (SBZ) of a Pb(111)
surface is indicated by solid red line. Also included is thecalculated bulk FS contour center at the Γ point (dotted redline) obtained on the (111) surface of Pb(111) crystal. (b)FS
mapping of 21 and (c) 24 ML Pb ﬁlms. (d)The calculated FSof the 21 ML Pb(111) slabs.

ture has three-fold symmetry, the ﬁlm FS are clearly six
fold symmetric indicating a two-dimensional origination.
Near the zone center, the ﬁlm FS is composed of twocrossing triangular bulk FS, which are both center at Γ
and are rotated 60◦ apart from each other. To further
clarify the two-dimensional character of the ﬁlm FS, we
measured the ARPES spectra on the ﬁlms by varying
the incident photon energy from 15 to 35 eV, which cancover ∼ 60% of the Brillouin zone. The band dispersions
associated with the inner hexagonal FS features indeed
remain the same regardless of the incident photon energies. Hence, the Pb(111) ﬁlm FS shown in Fig. 2 is oftrue two-dimensional nature.
Here we are interested in FS features around the zone
center. As can be seen in Fig. 2, at the crossing pointsof the two isotropic triangular features, there are noncrossing gaps open. Their details are further examined
in Fig. 3 showing the band dispersions close to a crossing
point. Fig. 3(a) is a band mapping close to one of thecrossing point along the red line drew in the FS sketch
in Fig. 3(c), where the dotted red and green lines represent the Pb bulk FS after rotated 60◦ apart from each— 102 —

3
(b)

-0.2

(a)

-1

-0.6
-0.8
-1.0
-0.10

0.00

-1

0.10

k-k0(Å )(c)

E-EF(eV)

E-EF(eV)∆≈ 270 meV

-0.4

0.11Å

Intensity(arb. units)

(a)

Γ

Μ

Κ

Γ

(b)

ky(Å-1)

K
B

A

Γ

M

-1

-0.13Å
kx(Å-1)

-1.2

-0.8

-0.4

E-EF(eV)

0.0

FIG. 3: (a)The band mapping close to the crossing point
along the red line drew in the FS sketch in (c). The ﬁlled
black circles are band positions extracted from the same data
but displayed as EDCs in (b). (c) A sketch of the ﬁlm FS
features centered at the Γ point. The dotted red and green
lines represent the Pb bulk FS after rotated 60◦ from eachother. The FS feature contains a hexagonal hole pocket (solid
black line A) and a snowﬂake-shaped hole pocket (solid blackline B).

other. The gap can be directly resolved in Fig. 3(a) andfurther determined in Fig. 3(b), where the energy distribution curves (EDCs) clearly exhibit two well separated
peaks indicating a noncrossing gap opens when the twobands, which are associated with the right and left triangular bulk FS respectively, intersect. To determine thegap size, we ﬁt the EDCs in Fig. 3(b) after subtracted
a suitable background and obtained the band position
depicted as solid circles in Fig. 3(a). The determined
gap size is about 270 meV. The origination of this gap isdue to strong spin-orbit interaction since the calculatedband structures without spin-orbit coupling show no gap
opens. As a result of the interaction between the rightand left triangular FS features, the ﬁlm FS (near zone
center) contains two closed contours, namely, a hexagonal hole pocket (A) and a snowﬂake-shaped hole pocket(B) both centered at the Γ point. The snowﬂake-shapedhole pocket and the hexagonal pocket are derived, respectively, from two diﬀerent group of subbands indicated as
black and blue lines in Fig. 2(d) and 4(a). These twogroup of subbands separated from each other in energy
due to strong spin-orbit interaction, which also plays adominant role in forming the noncrossing band gap discussed in Fig. 3. It is interesting to clarify the originationof the observed six-fold symmetric ﬁlm FS. The ﬁrst possibility is that we may have observed the bulk-derived

FIG. 4: First principle calculated results on the 21 ML freestanding Pb(111) slabs. (a) The calculated band structures of
the Pb(111) slabs. (b) The calculated DOS at EF as a function of Pb(111) ﬁlms thickness (open circles). Also plotted vs
the thickness is the number of the subbands which cross EF
and enclose hole pockets at EF (ﬁlled black circles.) and theelectron density determined by the volume of hole pockets associated with the FS feature A (ﬁlled red squares). The lines
between markers are to guide the eyes.

FS features, which are averaged along the kz direction
due to the ambiguity along the kz direction. However,for a 21 ML Pb ﬁlms, the estimated kz uncertainty is
about ∆kz ∼ 1% of the Brillouin zone. On the other
hand, features originating from lack of kz -resolution areusually more broad and accompanied by a diﬀuse background. Therefore, our observations do not favor theabove explanation. Noting that the surface plane might
be approximately six-fold symmetric then it is possible
we are seeing the electronic states localized at surface.
This is indeed consistent with the photon energy dependent measurements results which reveal that the ﬁlm FS
is of two-dimensional nature.
To examine the FS topology transition induced by ﬁlm
thickness, we will compare the sizes of the FS featurefor diﬀerent thickness since the FS shape in Fig. 2 arealmost identical regardless of their thickness. Here, forexample, we compare the sizes of the FS feature A fordiﬀerent thickness. Since the FS feature A has a goodhexagonal shape with parallel FS edges, the size of the FS−→
feature A can be characterized by a vector S as shown−→in Fig. 2(a). The magnitude of S is estimated to be−1−1∼ 0.44, 0.43, 0.44, and 0.43 Å (±0.01 Å ) for thicknessof 17, 21, 24, and 25 ML(data not shown in Fig. 2) and canbe considered to be the same within the error level. The
fact of no or weak thickness dependence on the shape and— 103 —

4
size of the ﬁlms FS comes from the weak QSE of FS edge,
which is far from Γ point. Our DFT calculations showthat QSE is not only size but also wavevector dependent:
being maximum at Γ due to strong interlayer coupling
between p z orbitals, but could be vanishingly small atother symmetry points due to weak interlayer coupling
between p x,y orbitals.18
As was already discussed in Fig. 1, for a given ﬁlm withthickness of t ML, the bulk bands of Pb are split into t
two-dimensional subbands. Some of the subbands, which
are associated with the FS feature A, sink below EF due
to the formation of the QWS in the ﬁlm normal direction. In order to determine the number of the subbands
that are survived to crossing EF , we check the calculated
results for thickness of 21 ML as presented in Fig. 2 (d)and Fig. 4(a). For the hexagonal FS feature A, 10 of 21
subbands sink below EF due to QWS and thus only 11
subbands survive to enclose hole pockets at EF . With
increasing the thickness of Pb layers, one subband moves
down to cross EF and becomes occupied for every two
added layer. This produces a 2 − ML step increase in thenumber of the survived subbands crossing EF as shownin Fig. 4(b) as ﬁlled black circles.
So far we have clariﬁed that the ﬁlm FS features A
and B are two-dimensional hole pockets and determined
the number of subbands which enclosed hole pockets associated with the FS features A. It is therefore straightforward to determine the carrier density by calculating
the volume of these pockets for a given thickness. For
simplicity, we only calculate the Luttinger volume of FS
features A and the consequent results should represent
the true oscillatory trend induced by QSE eﬀects, since
the QWS are totaly derived from the subbands associated with the FS feature A. The thus determined electron density is plotted as a function of the ﬁlms’ thick-1

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7
X. Ma, P. Jiang, Y. Qi, J. Jia, Y. Yang, W. Duan, W.-X.
Li, X. Bao, S. B. Zhang, and Q.-K. Xue, Proc. Natl. Acad.
Sci. U.S.A. 104, 9204 (2007).
8
For a review, see T.-C. Chiang, Surf. Sci. Rep. 39, 181(2000).
9
J.F. Jia, S.C. Li, Y.F. Zhang, and Q.K. Xue, J. Phys. Soc.

ness in Fig. 4(b) as ﬁlled red squares. Also displayed inFig. 4(b)(open circles) is the calculated DOS at EF . Interestingly, the calculated electron density according to
the Luttinger volume of the FS feature A also exhibits a2−ML oscillations with a beating node showing at 17 ML
and can exactly match the oscillatory trend of the DOS
at EF . Our results, therefore, indicate convincingly thatthe formation of QWS in the Pb(111) ﬁlms determines
the number of the subbands, which survive to cross the
Fermi level and enclose hole pockets at EF , and thus determine the oscillatory behavior of electron density of thePb(111) ﬁlms. For the ﬁrst time, we are able to explain
quantitatively how the QWS formed in the ﬁlm normal
direction modulates the DOS at EF .
In conclusion, the high-resolution ARPES data presented in this paper clearly revealed a well-deﬁned FSwith sixfold symmetry for the atomical-layer-resolved
Pb(111) ﬁlms. By varying the incident photon energy, weestablished convincingly that the ﬁlm Fermi surface features centered at the Γ point are of true two-dimensional
nature. The details of ﬁlm FS features centered at theΓ point are further clariﬁed to be composed of a wellshaped hexagonal hole pocket and a snowﬂake-shapedhole pocket. In addition, we, for the ﬁrst time, revealthat the QWS modulate the DOS at the Fermi level by
aﬀecting the number of the subbands enclosed the hexagonal hole pockets at EF .

Acknowledgments

The synchrotron radiation experiments were performed under the approval of HSRC (Proposal No. 07A-66).

Jpn. 76, 082001 (2007).
M. Arita, K. Shimada, H. Namatame, and M. Taniguchi,
Surf. Rev. Lett. 9, 535 (2002).
11
G. Kresse and J.Furthmüller, Phys. Rev. B 54,
11169(1996).
12
G. Kresse and D. Joubert, Phys. Rev. B 59, 1758 (1999).
13
J. Perdew, K. Burke, and M. Ernzerhof, Phys. Rev. Lett.
77, 3865 (1996)
14
H. J. Monkhorst and J. D. Pack, Phys. Rev. B 13, 5188
(1976).
15
M.H. Upton, T. Miller, and T.-C. Chiang, Phys. Rev. B
71, 033403 (2005).
16
J.H. Dil, T.U. Kampen, B. Hülsen, T. Seyller, and K.
Horn, Phys. Rev. B 75, 161401 (R) (2007).
17
P. S. Kirchmann, M. Wolf, J. H. Dil, K. Horn, and U.
Bovensiepen, Phys. Rev. B 76, 075406 (2007).
18
X. Liu, S. B. Zhang, X. C. Ma, J. F. Jia, Q. K. Xue, X. H.
Bao and W. X Li, Appl. Phys. Lett. 93, 093105 (2008).
10— 104 —

07-A-11

BL-11

Optimization of fluorescence XAFS spectroscopy for L edge measurements of Pd nanoparticles supported onto ZrOx
Shinjiro Hayakawaa, Hiroyuki Kogaa, Hirosuke Sumidab, Hirofumi Namatamec and Takeshi
Hirokawaa
aDepartment of Applied Chemistry, Hiroshima University, Hiroshima, Japanb
Technical Research Center, Mazda Motor Co., Hiroshima, Japanc
Hiroshima Synchrotron Radiation Center, Hiroshima University, Hiroshima, Japan
X-ray absorption fine structure (XAFS) measurements are widely utilized for characterizationof noble metal catalysis. However, characterization of modern Pd catalysis for vehicle
exhausts requires trace sensitivity because the size and the amount of the Pd particles are
getting smaller while maintaining their functions.
We have investigated the reduction of the detection limit (DL) with the fluorescence yield
method. The improvements in the signal to background ration (S/B) can be achieved withthe use of a Si detector compared to the conventional gas counter. However, the advantage ofthe intense SR beam may be lost when the upper counting rate is determined by the signals
from supporting materials. We have investigated the use of a poly-ethylene (PE) filter torealize higher S/B for Pd catalysis supported onto ZrOx.
Fig.1 shows x-ray fluorescence spectra of Pd catalysis supported onto ZrOx with andwithout a PE filter. Without the PE filter Pd L peak could be rarely recognized owing to thehigher energy tail of the strong Zr peak. The DL is inversely proportional to the square root of
S2/B, and the DL for Pd was reduced from 86 ppm to 13 ppm (wt) with the filter of 120 μm.
Fig.2 shows a comparison of Pd L3 XAFS spectra, and the reduction of the backgroundsuccessfully improved signal to noise ratio of XAFS spectra.

Fig. 1 (left) XRF spectra from Pd/ZrOx (0.129%) with and without a PE filter (120 μm).
Fig. 2 (right) Pd L3 XAFS spectra of Pd/ZrOx with and without the PE filter.
[1] S. Hayakawa et al., Anal. Sci. 24, 835(2008).

— 105 —

07-A-22,26

BL-13

Molecular chain effect in photon stimulated ion desorption ofself-assembled monolayers induced by carbon core excitation
A. Hiranoa, I. Ohyamaa, Y. Tanikawaa, S. Wadaa,b, and K. Tanakaa,baDepartment of Physical Science, Hiroshima University,
Higashi-Hiroshima 739-8526, Japanb

Hiroshima Synchrotron Radiation Center,Hiroshima University,
Higashi-Hiroshima 739-0046,Japan

Introduction
Possibility of site-selective ionic dissociation induced by core excitation has been focused on
research in soft X-ray induced chemical reaction. Recently, remarkable site-selective ion desorption
was observedin methyl

ester terminated self-assembled

monolayer(MHDA SAM:

Au-S(CH2)15COOCH3) [1]. This finding revealed the more selective reaction in MHDA-DSAM thanthat of PMMA (-[CH2C(CH3)COOCH3]n-) thin film due to its higher orientation. In the following
study, the ion desorption yield of MHDA SAM was compared with that of methyl mercaptoacetate(MA SAM: Ag-SCH2OCOCH3), because it can be considered that such selectivity in ion desorption
depends on molecular environment, especially interaction between reaction moiety (methyl-ester
group) and metal surface. In fact, site-selective ion desorption is different between MA and MHDA,
namely less desorption yield in MA [2]. From these previous studies, thus, photon simulated ion
desorption (PSID) reaction depends on molecular environment. In this study, PSID of methyl
mercaptopropionate (MP SAM: Ag-S(CH2)2OCOCH3), 4-methoxy benzyl mercaptan (MeOPh SAM:
Au-SCH2(C6H4)OCH3), and 4-methylbenzyl mercaptan (MePh SAM: Au-SCH2(C6H4)CH3) were
investigated in order to clarify molecular chain effect in PSID (Fig. 1).
Experiment
Experiments were performed at the beamline

(a)

(b)

(c)

(d)

BL-13 of HiSOR. The experimental chamber was
equipped with a conventional ion detector and its
pressure was 5×10-10 torr at room temperature. Total
ion yield (TIY) was obtained by the ion detector.
Near

edge

X-ray

absorption

finestructure(NEXAFS) was recorded in total electron yield(TEY) mode by measuring a sample drain current.
All spectra measured were normalized to the incident
photon flux monitored with a gold-coated W mesh.

— 106 —

Fig. 1 Molecular structures of (a) MA, (b) MP,(c) MeOPh, and (d) MePh SAMs.

MePh and MeOPh SAMs were prepared by immersing Au coated Si substrates into 1.0 mM
ethanol (Kanto Chemical) solutions during 24 h. Similarly, MA and MP monolayers were also
prepared by the same manner for Ag coated Si substrates. SAMs were rinsed in ethanol immediately
after removal from solutions and quickly inserted into the UHV chamber for analysis. Chemicals usedin this study are illustrated in Fig. 1.
1.8

Results and Discussion

1.6

spectra in the C K-edge region,

1.4

where
pre-edgeionyields
are

in

the

subtracted.

Comparing MP with MA
SAMs, the desorbing ion yieldof MP become higher than thatof MA. Difference between

Relative intensity / arb. units

Fig. 2 shows relative TIY

MP
MA
MeOPh
MePh

1.2
1.0
0.8
0.6
0.4
0.2

MP and MA is the length of

0.0

methylene chain, namely MA

280

285

290

295

300

305

has one methylene group,

Photon energy / eV

while MP has two. In previous

Fig. 2 TIY spectra for MP, MA, MeOPh, and MePh SAMs in
the C K-edge region.

study, ion yield of MHDA310

SAM was compared with that of MA SAM, and it was concluded that ion desorption from thecore-excited MA is strongly suppressed due to its thinness and therefore occurrence of reneutralization[2]. Methyl ester group where ionic dissociation induced core excitation occurs abundantly exists apartfrom the metal surface by a methylene group in the MP monolayer compared with that of MA. Basedon the result, it can be considered that variation of desorbing ion yield is attributed to different strengthof interaction between ionic moieties and the metal surface in desorbing.
On the other hand, TIY spectra of MeOPh and MePh SAMs indicate less desorption comparedwith those of MP and MA SAMs. This result contradicts the above result because molecular lengths of
MeOPh (~8 Å) and MePh (~7 Å) are longer than those of MP (~4 Å) and MA (~3 Å). This result isvery interesting. MP and MA SAMs are composed of methylene group, while MeOPh and MePh
SAMs are composed of phenyl group. As PSID is strongly inhibited by rapid delocalization of excessenergy including a charge, p conjugated systems of MeOPh and MePh SAMs would induce
delocalization of excess energy. In conclusion, it can be considered that chemical property of main
chain which compose SAM greatly influence PSID.
References [1] S. Wada et al., J. Phys.: Condens. Matter 18 (2006) S1629. [2] H.Kizaki et al.,Surf.Sci. 601 (2007) 3956.

— 107 —

07-A-25

BL-13

Adsorption of HS(CH2)2COOCH3 on Cu(111) surface studied by
XPS and NEXAFS spectroscopy
Kei Yufua, Katsumi Watanabea, Kazuhiro Matsushitaa,
Shin-ichi Wadaa,b and Kenichiro Tanakaa,baDepartment of Physical Science, Hiroshima University,
Higashi-Hiroshima 739-8526, Japanb
Hiroshima Synchrotron Radiation Center, Hiroshima University,
Higashi-Hiroshima 739-0046, Japan
Introduction
It is well-known that thiol molecules chemisorb on metal surfaces by strong S-metalbonding via experiencing deprotonation of thiol groups (thiolate formation). Such detailed
investigation about bonding with metal surfaces can be applied to technological application ofmolecular electronics. Therefore, the understanding of the adsorption structure and theinteraction of organic thiol molecules with metal surfaces are very useful to clarify chemicaland physical surface processes.
In the previous study, we revealed the adsorption structure of methyl mercaptoacetate(HSCH2COOCH3 : MA) on the clean Cu(111) surface at room temperature, which has tworeactive functional groups, thiol and carbonyl groups [1]. MA adsorbs on the surface via
thiolate formation and weak interaction of the carbonyl group with the surface. Moreover, twodifferent adsorption states were confirmed besides atomic sulfur. It is interesting how theadsorption structure and the interaction with metal surfaces vary by an elongation of
methylene chain. In this study, we investigated the adsorption structure of methyl
mercaptopropionate (HS(CH2)2COOCH3 : MP) on the Cu(111) surface at room temperatureusing synchrotron radiation (SR) spectroscopy.
Experiment
Experiments were carried out in a surface photochemistry chamber equipped with aconcentric hemispherical electron analyzer (CHA) and a low energy electron diffraction(LEED) apparatus at the soft X-ray beamline BL13 in HiSOR. The clean surface was obtainedby repetitive cycles of annealing at 800K and argon ion irradiation. The cleanliness of thesurface was checked by LEED and X-ray photoelectron spectroscopy (XPS) using Mg-Kα
source. Multilayer of MP was obtained by dosing with a few tens of Langmuirs at low
temperature with liquid N2. And monolayer of MP was obtained by annealing the multilayer
up to room temperature. Polarization-dependent near edge X-ray absorption fine structure(NEXAFS) spectra and XPS spectra were measured to estimate adsorption structure andsurface-functional group interaction. The NEXAFS spectra, which were obtained by drain— 108 —

current of the sample as total electron yield (TEY), were measured by changing an incidence
light angle to the surface between 20° and 90°. XPS spectra were measured by changing an
exposure of MP.
Results and Discussion
Carbon and oxygen 1s, and sulfur 2p XPS spectra indicate the discriminative peak shifts bydifferent adsorption conditions from the multilayer to the monolayer, in other words, from thephysisorbed to chemisorbed states. Typical example measured for C1s is shown in Fig. 1. The
XPS analysis reveals that MP is chemisorbed on the Cu(111) surface with the strong Cu-S
bonding, and has week interaction between the C=O group and the Cu surface. Moreover,results of S2p XPS spectra reveal that the atomic sulfide coexists on the Cu(111) surface.
C1s and O1s NEXAFS spectra depicted in Fig. 2 show the presence of sharp andpolarization-dependent resonances. The C, O1s(C=O) → p*(C=O) resonances located at thephoton energy of 288.5eV and 531.8eV, respectively, indicate clear polarization dependence.
From the E-vector polarization analysis of C and O 1s NEXAFS spectra, p*(C=O) transition
dipole moment is tilted by 64±8°from the surface normal. In the same way, orientations of theother transition dipole moments (s*(O-CH3), s*(C=O) etc.) were also determined.

π*(C=O)

4

3

0

+1.0L

284

288

292

296

300

304

308

Photon Energy / eV

O1s

294

292

290

288

286

284

*

σ (O-CH3)

0.5

*

1.0

σ*(C=O)O-CH3 S-C -CH 2

1.5

σ*(C-O)

C=O

2.0

90deg
70deg
50deg
30deg
20deg

π*(C=O)

monolayer

2.5

π*(C=O)

3.0

σ (C-OCH3)

3.5

Intensity / arb. units

Intensity / arb. units1

σ*(C=O)2

σ*(C-O)

monolayer element
multilayer element

90deg
70deg
50deg
30deg
20deg

σ*(C-C)hv = 554 eV
T = 100 K

C1s

σ*(C-S)+2.0L

Intensity / arb. units

5

0.0

282

Binding Energy / eV

525

530

535

540

545

550

555

Photon Energy / eV

Fig. 1. C1s XPS spectra of MP in
different exposure conditions.

— 109 —

Fig. 2. C1s and O1s NEXAFS spectraof MP measured for various SR
incident angles.

560

From the results of NEXAFS and XPS measurements, the carbonyl oxygen faces thesubstrate side and -C-(C=O)-O plane skeleton tilts by 26±8° from the surface normal. Suchadsorption structure of MP resembles that of MA in the -C-(C=O)-O plane skeleton, eventhough the methylene chain of MP is elongated. The proposed adsorption structure of MP on
Cu(111) is illustrated in Fig. 3.
References[1] S. Wada et. al., Surf. Sci. 601, 3833 (2007).

Fig. 3. Schematic structure proposed for MP
adsorbed on Cu(111).

— 110 —

07-A-26

BL-13

Site-selective ion desorption of fluorine substituted self-assembled
monolayers by core electron excitations
Shin-ichi Wada1,2, Noriyuki Kushima1, Takahiro Yamamoto1, and Kenichiro Tanaka1,2
1
Department of Physical Science, Hiroshima University,
Higashi-Hiroshima 739-8526, Japan
2
Hiroshima Synchrotron Radiation Center, Hiroshima University,
Higashi-Hiroshima 739-0046, Japan
Introduction
Core-electron excitations have quite unique nature differently from valence excitations
because of special localization of core electrons. So, ionic dissociation induced by resonant
core excitations also reveals characteristic phenomena. In particular, site-selective ionicdissociation is one of noteworthy characteristics. So far, we have found that such selective
bond breaking can occur on organic surfaces, especially for ester compounds likepoly-methylmethacrylate (PMMA) thin films and ester-terminated self-assembled monolayers(SAMs) [1].
In this study, near-edge X-ray absorption fine structure (NEXAFS) and the following ionicdissociation were spectroscopically investigated for fluorine substituted SAMs, alkane type
SAM (CF3(CF2)7(CH2)2S/Au; FD SAM) and benzyl type one (p-FC6H4CH2S/Au； pFPhSAM), in which strong C-F bond scission is expected under the equivalent core model (Z+1approximation).
Experiment
Experiments were carried out on the soft X-ray beamline BL13. NEXAFS spectra in the C
1s and F 1s edges were recorded in total electron yield (PEY) and total ion yield (TIY) modes.
In polarization-dependent TEY measurements, incident angle of X-ray was changed by(a) FD

B

B'

C'

q

D

3

2

E

1.4

F

A

F

A

1.2
1.0

D

E

A' B

0.8

q

0.6
0.4

1

B' C

0.2
0.0

0
280

(b) pFPh1.6/ degree
20°
35°
45°
55°
75°
90°

Intensity / arb. units

Intensity / arb. units

4

1.8

C

285

290

295

300

305

310

315

320

275

Photon Energy / eV

280

285

290

295

300

305

/ degree
20°
35°
45°
55°
75°
90°
310

315

320

Photon Energy / eV

Fig. 1. TEY spectra of core-excited (a) FD and (b) pFPh SAMs in the C1s regions measured at the
SR incident angle of 20° (grazing incidence) - 90° (normal incidence).

— 111 —

rotating a sample holder. During measurements, the experimental chamber was kept at 2x10-10
Torr. Photon energy was calibrated by PMMA thin film for the C 1s edge and gaseous SF6 forthe F 1s. Monolayer films were prepared by immersing Au coated Si substrates into 1.0 mM
ethanol solutions during 24 hours.
Results and Discussion
Fig. 1 shows the incident-angle dependent TEY spectra measured for (a) FD and (b) pFPh
SAMs in the C 1s region. The spectra were measured at 20° - 90° incident angles (q) fromsample surfaces. Assignment of each peak labeled in the figure is listed in Table 1 based on
refs. 2-5. Clear dependence are seen in the spectra for peaks mainly attributed to the s*(C-F)(peak B) and s*(C-C) (peak C) excitations for FD, and 1p*(C-H) (peak A) excitation for
pFPh. Net intensities for the resonances derived from curve fitting procedure are plotted as afunction of incident angle of SR as shown in Fig. 2. From the polarization (incident) angle
dependence, angles of transition dipole moments from surface normal for the excitations canbe derived. It should be noted here that the angle a of the transition moment of the s*(C-C)
excitation for FD SAM corresponds to the average tilting angle of C-C skeleton and the angleof the s*(C-F) corresponds to the angle perpendicular to the C-C skeleton (90 - a). The
derived angle b of the transition moment of 1p*(C-H) for pFPh SAM also corresponds to theangle perpendicular to the tilting phenyl ring from the surface normal. From the dependence,
tilting angles of FD and pFPh SAMs were derived to be ~44° and ~33° using the formula
between the angles of the electric field vector (incident angle of SR, q) and the transition
dipole moment [6].
TIY spectra measured for both SAMs in the C and F 1s regions are shown in Fig. 2 together
with the corresponding TEY. All of TIY
4.6
4.0
4.4
FD
spectra indicate different spectral
3.8
4.2

noteworthy that the s*(C-F) excitationsof both SAMs cause strong ion
desorption as expected by the equivalentcore model (Z+1 approximation).

s*(C-F)s*(C-C)

4.0
3.8

3.6
3.4

3.6

a

3.2

3.4

Intensity / arb.units

features, indicating specific ionicdissociation promoted by resonant core
excitations. Moreover, it is noted thatsuch specific ion desorption makes
obscure peaks buried in the TEY spectra
visible in the TIY, like peaks B' and C' in
the C 1s of FD, and peak C in the C1s
and peak A in the F 1s of pFPh.
Especially in the F 1s edge, it is

3.0

3.2

2.8

3.0
2.8

2.6

2.6

2.4

5.8

FD

p-FPh

5.6
5.4

ß

1p*(C-H)

5.2
5.0
4.8
4.6

pFPh

4.4
4.2

10

20

30

40

50

60

70

80

Incident Angle / degree

90

100

Fig. 2. Incident angle dependence of integrated
intensities of the net s*(C-C) and s*(C-C) excitations
for FD and the 1p*(C-H) for pFPh.

— 112 —

(a) FD C1s(b) pFPh C1s(c) FD F1s
A BCIntensity / arb. units

TEY(d) pFPh F1s
AB
TEY

E

D

D
C

TEY

TEY

TIY
TIY
TIY
TIY

280

285 290295 300 305 310

315

320 280

285 290

Photon Energy / eV295

300 305 310

315 320 680

690

Photon Energy / eV

700

710

720

730

740 680

Photon Energy / eV

690

700

710

720

730

Photon Energy / eV

Fig. 3. TEY and TIY spectra measured for C 1s spectra of (a) FD and (b) pFPh SAMs, and F 1sof (c) FD and (d) pFPh.

Table 1: Assignments of FD and pFPh SAMs in the C 1s and F 1s edges.
Peak

Energy / eV

Assignment

Peak

FD

Energy / eV

Assignment

pFPh

A

~289

s (C-H) / Rydberg

A

285.3

1p* : C-H

B

292.5

s*(C-F) : -CF2-

A'

287.6

1p* : C-F

B'

295.0

s*(C-F) : -CF3

B

288.6

2p* : C-H

C

295.7

s*(C-C) : -CF2-

B', C

289.5

2p* : C-F, s*(C-F)

C'

296.4

s*(C-C) : -CF3

D

293.8

s*(Ph)

D

299.0

s*(C-F) : -CF2-

E

297.0

s*(Ph)

E

300.2

s*(C-C)F

304.0

s*(Ph)

F

308.4

s*(C-F)A

689.5

s*(C-F)A

688.5

p*(Ph) → s*(C-F)

B

694.3

s*(C-C)B

690.0

s*(C-F)C

696.3

s*(C-F)C

695

s*(Ph) ?

D

704.0

s*(C-C)

D

~708

s*

720

multi-ex.

724

s*(C-F)E*

References[1] S. Wada et. al., J. Phys.: Condens. Matter 18, S1629 (2006).
[2] H. Setoyama et al., Nucl. Instr. Meth. Phys. Res. B 199, 275 (2003).
[3] A. Fujimori et al., Bull. Chem. Soc. Jpn. 76, 663 (2003).
[4] K.K. Okudaira et al., Nucl. Instr. Meth. Phys. Res. B 199, 265 (2003).
[5] A.P. Hitchcock et al., J. Phys. Chem. 91, 531 (1987).
[6] J. Stöhr, NEXAFS Spectroscopy, Surface Sciences vol.25 (Springer, Berlin, 1992).

— 113 —

740

BL-14In-situ XMCD measurement system for magnetic ultrathin films at BL14
M. Sawada
Hiroshima Synchrotron Radiation Center, Hiroshima University
Magnetic properties of thinfilm and multilayer have been attracted great interest
from viewpoints of both fundamental science and technological applications for the few
decades. With the technological progress of ultra high vacuum (UHV) and molecular beam
epitaxy (MBE), well-defined structures of magnetic monolayer have been obtained on single
crystal surfaces of metals and semiconductors. The microscopic magnetic property of themonatomically layered magnetic ultrathin films is a critical issue to understand interface
magnetism, origin of perpendicular magnetic anisotropy (PMA) and spin-dependent transportof tunneling magnetic resistance (TMR) junctions. X-ray magnetic circular dichroism(XMCD) spectroscopy is a very powerful tool to study the local magnetic moment in theatomic sites of the magnetic ultrathin films element-specifically. So far, many XMCD studies
on the thickness-dependent spin moment and the enhanced orbital moment at the interface
have been carried out for various magnetic thinfilms and multilayers. However, most of them
are ex-situ experiments where the samples are fabricated in separate apparatus and covered
with antioxidant layers like Au cap layers. Because the crystal and magnetic structures of themonolayer films are sensitive to overlayers or adsorbates, it has been recognized that in orderto determine the inner nature of magnetism in the monolayer films, in-situ experiments in
UHV are desirable. To promote the research project on the monolayer magnetism including
the interface magnetism, we have constructed an XMCD measurement system connected tothe soft X-ray beamline in the synchrotron radiation facility, where various types of themagnetic ultrathin films are fabricated in monatomic layer control and their structures andmagnetic properties are analyzed in-situ.
Our in-situ XMCD measurement system has been constructed at the soft X-ray
beamline BL-14. The beamline is designed to provide the monochromatic polarized light
whose energy ranges from 400eV to 1200eV, aimed at X-ray absorption spectroscopy (XAS)
and photoelectron spectroscopy with linearly and circularly polarized light. The XMCD
station is directly connected into the beamline in the first focal section behind the exit silt of
the monochromator. The XMCD station consists of two UHV chambers for the measurement
and the sample fabrication, whose base pressures are below 410-10 Torr. The measurement
apparatus is composed of a sample stage connected to a 4-axis manipulator and a— 114 —

permanent-magnet array joined to a motorized liner stage. The permanent-magnet array
supplies magnetic field to the samples along the surface normal direction, whose magnetic
flux density is 1.3 Tesla. The XMCD spectra can be measured in the total electron yield mode
and in conventional transmission mode by flipping the magnetic field direction with respect tothe fixed photon helicity at each energy step of the photon energy scan. In the fabricationchamber, we can conduct the sample fabrication in monatomic layer control and the structuraland chemical analysis of the as-grown samples. The fabrication chamber is equipped with an
ion gun with differential pumping (ULVAC-PHI FIG-5) for sample cleaning, two UHV
evaporators (Omicron EFM3) for MBE deposition, a cylindrical mirror analyzer with anelectron gun (ULVAC-PHI 10-155) for Auger electron spectroscopy (AES), a low energy
electron diffraction (LEED) optics (Omicron SPECTALEED), an electron gun (EVC
RDA-002G) and a fluorescence screen for reflection high energy electron diffraction(RHEED). The sample is mounted on a heating stage for annealing or a cryo stage cooledwith liquid nitrogen, which is connected to a 4-axis manipulator. The film growth during theMBE deposition can be monitored in real time by the RHEED intensity oscillation observedwith a CCD camera linked to a PC. We have achieved accurate control of film thickness
within a few 0.1 ML in layer-by-layer growth mode, using the RHEED monitoring and thecrosscheck on AES.

FIG. 1

Schematic diagram of the in-situ XMCD measurement system installed at BL-14.

— 115 —

FIG. 2

Photograph of the in-situ XMCD measurement system.

— 116 —

BL-14Structural and magnetic properties of Cr/Fe/Cu(001)
S. Tohoda a, M. Sawada b, M. Nagira a, T. Ueno a, T. Tagashira a,A. Kimura a, H. Namatame b and M. Taniguchi a, b
ab

Graduate school of science, Hiroshima University, Higashi-Hiroshima 739-8526, Japan.

Hiroshima synchrotron radiation center, Hiroshima University, Higashi-Hiroshima 739-0046, Japan
Fe/Cr multilayers are very interesting system from viewpoints of the Giant Magnetic

Resistance (GMR) effect, well known as prize-winning subject, and the junction of ferromagnetic
and anti-ferromagnetic layers. The crystal structure of the conventional Fe/Cr multilayers is body
centered cubic (bcc). On the other hand, Fe films with face centered cubic (fcc) like structure are
realized in the ultrathin film regime, in case the films are grown on a substrate of Cu(001). The
structural and magnetic properties of the Fe/Cu(001) films are classified into three phase regions
depending on the Fe thickness. In the region I below 4 ML, the Fe films have face centered
tetragonal (fct) structure and shows ferromagnetic and perpendicular magnetic anisotropy (PMA)
behavior. In the region II between 5 ML and 11 ML, the films are obtained as fcc Fe films where theonly top two layers are tetragonally distorted and ferromagnetic with PMA. In the region III above
12 ML, the Fe films become bcc structure and shows in-plane magnetic anisotropy. Since thefilm structure of Fe is sensitive to the film thickness and overlayers, the structural andmagnetic properties of Cr/Fe/Cu(001) are unobvious and expected quite different properties
from the conventional Cr/Fe multilayers.

Fig.1 RHEED intensity of (00) spot during the Cr deposition on the Fe films.

— 117 —

We have investigated the structure and growth mode of Cr/Fe/ Cu(001) for the three
region of Fe thickness by means of Low Energy Electron Diffraction (LEED) and Reflection
High Energy Electron Diffraction (RHEED) . Figure1 shows the RHEED (00) spot intensity
during Fe and Cr deposition. The intensity oscillation of RHEED for region I and II are
clearly observed at 1 ML Cr deposition. We conclude that the 1 ML Cr grows epitaxially on
the Fe ultrathin films and we have succeeded to create the ultrathin multilayer of Fe and 1 ML
Cr with a sharp interface.
We have also examined the magnetism of the Cr/Fe/Cu(001) system by means of
X-ray absorption magnetic circular dichroism (XMCD). All the processes of sample
preparation and XMCD experiment were performed in-situ. Figure 2 show the XMCD
spectrum of Cr/ 3ML-Fe/Cu(001) at L2,3 edge of Fe. It is obvious that the amplitude of the
XMCD signal becomes smaller with increasing Cr thickness. The intensity of the XMCD
spectra at the L3 edge reaches into a certain value at the 1 ML Cr deposition. It is consideredthat the depression of the XMCD signals is caused by the interface formation of the Cr/Fe.

Fig.2 Cr thickness dependence of XMCD spectra for Cr/3ML-Fe/Cu(001).

— 118 —

BL-14Fabrication and in-situ XMCD study of Fe/Pd multilayers on Pd(001)
T. Uenoa, M. Sawadab, M. Nagiraa, S. Tohodaa, T. Tagashiraa, A. Kimuraa,
H. Namatameb, and M. Taniguchia,baGraduate School of Science, Hiroshima Universityb

Hiroshima Synchrotron Radiation Center, Hiroshima University

Magnetic metal multilayers with perpendicular magnetic anisotropy (PMA) havebeen studied for long years, because of importance of its application to high-density magnetic
recording media. Ultra-thin films or multilayers of Fe/Pd are well known as a PMA system.
Previous studies using XMCD spectroscopy revealed that the orbital magnetic moment of Fe
films are enhanced in Fe/Pd(001) [1]. In Fe/Pd multilayers, it is reported that Pd layers
become ferromagnetic up to four monolayers (ML) from the Fe-Pd interface [2]. L10-typeordered FePd alloy is known to have strong uniaxial magnetic anisotropy perpendicular to Fe
and Pd layers [3]. Some experiments and calculations about FePd alloy thinfilms have beenreported. However, most of them focus on the chemical ordering of the alloy [4, 5]. We focus
on the thinnest limit of the layered PMA structures in the L10 FePd alloy films, fabricating themonatomic Fe/Pd multilayers. We have fabricated the Fe/Pd multilayers on the Pd(001)substrate and investigated the magnetic anisotropy using X-ray magnetic circular dichroism(XMCD) spectroscopy.

Fig. 1: RHEED [00] streak oscillation during the

Fig. 2: Fe LMM/Pd MVV AES intensity ratio of t

Fe/Pd multilayers growth. Red and blue curves

ML Pd/3 ML Fe/Pd(001) (t = 0-5). Blue diamonds

correspond to the Fe and Pd layer growth,

are experimental data, and the red curve is therespectively.

fitting curve based on the model that theexponential decay of Auger electrons.

— 119 —

Our experiments were performedat the soft X-ray beamline BL-14, which
provides linearly and circularly polarized
photons for dichroic spectroscopy. The
XMCD experimental system and the sample
fabrication system are directly connected tothe beamline under an ultra high vacuum.
Single crystalline Pd(001) surface wasprepared by repeated cycles of argon ion
bombardment and annealing at 970 K.
Several types of Fe/Pd multilayers were

Fig.3: Schematic diagram of XMCD experimental
configuration, showing sample magnetization andincident photon direction in the case of detecting (a)out-of-plane

and

(b)

in-planemagnetization,

respectively.

fabricated by alternate thermal deposition of Fe and Pd. During the sample fabrication, we
observed the reflection high-energy electron diffraction (RHEED) pattern. The thickness
control of Fe and Pd was achieved by the real-time observation of the intensity oscillations of
the [00] RHEED streak (Figure 1). We also observed Auger spectra of Pd/3ML-Fe/Pd(001) andconfirmed that the inter layer mixing between Fe and Pd layer is negligible (Figure 2). The
XMCD spectra were obtained at the Fe L2,3 absorption edge (2p-3d transition) for the fabricatedfilms with remanent magnetization, which was magnetized by the pulsed magnetic field
generated by the Helmholtz coil. The sample magnetization was switched in parallel andanti-parallel directions to the incident photon spin. During the XMCD measurement, thesample was cooled by liquid nitrogen. Absorption signal was obtained in total electron yield
method of measuring the sample drain current. We employed two different configurations in the
XMCD experiments to investigate the magnetic anisotropy (Figure 3).
Figure 4 shows the Fe L2,3 XMCD spectra for the monatomic Fe/Pd multilayers withseveral stacking patterns. It is probed that the XMCD signals appear only in the grazing
incidence configuration shown in Fig. 3. It means that the monatomic Fe/Pd multilayers withregular alternate stacking have the in-plane magnetic anisotropy. The XMCD intensity of theremanently magnetized samples increases with the Fe layer stacking, and close to the intensity
measured under the magnetic field. Figure 5 shows the Fe L2,3 XMCD spectra for the different
samples, whose stacking patterns are different in the thickness of the second Fe layer from thatof the samples presented in Fig. 4. In contrast to the case of the regular alternate stacking,out-of-plane magnetic anisotropy was found in the particular stacking patterns as shown in
Fig.5 (c). It seems that the out-of-plane magnetic anisotropy is attributed to the thickness of the
topmost Fe layer. We also found that the out-of-plane anisotropy disappears when the topmost— 120 —

Fig. 4: Fe L2,3 XMCD spectra for monatomic
Fe/Pd multilayer. Green and orange lines
represent XMCD spectra for grazing andnormal incidence, respectively. XMCD spectra
taken under the magnetic field (1.3 T) are also
shown for comparison (blue line).

Fig.5 : Fe L2,3 XMCD spectra for Fe/Pd multilayerof which the second Fe layer is 1.5 ML. Green andorange lines represent XMCD spectra for grazing
and normal incidence, respectively. XMCD spectra
taken under the magnetic field (1.3 T) are also
shown for comparison (blue line).

Fe layer is covered with the additional Pd overlayer, as shown in Fig. 5 (d). It is suggested thata part of the Fe atoms on the topmost Fe layer forms island structure, and the peculiar electronic
state of Fe atoms on the island edge contribute to the out-of-plane spin reorientation.
In summary, we have fabricated several types of Fe/Pd multilayers and investigatedthe magnetic anisotropy using XMCD spectroscopy. We observed the in-plane magnetic
anisotropy in the monatomic Fe/Pd multilayers with regular alternate stacking. On the other— 121 —

hand, we observed the out-of-plane magnetic anisotropy in the Fe/Pd multilayers of particular
stacking patterns, and the out-of-plane anisotropy seems to be attributed to the Fe thickness ofthe topmost Fe layer.

References[1] X. Le Cann, C. Boeglin, B. Carrière, and K. Hricovini, Phys. Rev. B 54, 373 (1996).
[2] J. Vogel, A. Fontaine, V. Cros, F. Petroff, J.-P. Kappler, G. Krill, A. Rogalev, and J.
Goulon, Phys. Rev. B 55, 3663 (1997).
[3] N. Miyata, H. Asami, T. Misushima, and K. Sato, J. Phys. Soc. Jpn. 59, 1817 (1990).
[4] P. Kamp, A. Marty, B. Gilles, R. Hoffmann, S. Marchesini, M. Belakhovsky, C. Boeglin,
H. A. Dürr, S. S. Dhesi, G. van der Laan, and A. Rogalev, Phys. Rev. B 59, 1105 (1999).
[5] L. Szunyogh, J. Zabloudil, A. Vernes, P. Weinberger, B. Üjfalussy, and C. Sommers,
Phys. Rev. B 63, 184408 (2001).

— 122 —

07-A-35

BL-14

XMCD Study of Orbital Contribution to Perpendicular Magnetization in
Co80Pt20 Thin-Films
N. Ishimatsu A), R. Ogasawara B), T. Sone B), Y. Tsutsui A), H. Maruyama A), N. Nakajima A)
M. Sawada C), H. Namatame C)
A)
Grad. Sch. of Sci., Hiroshima Univ., B) Faculty of Sci. Hiroshima Univ.
C)
HSRC, Hiroshima Univ.
Co-Pt films deposited on a Ru seed layer are one of the candidates for perpendicular
recording media. It has been recently reported that uniaxial magnetic anisotropy constant Ku
of the Co-Pt film exceeds 1107 erg/cm3 and Ku significantly increases as the film thickness
 decreases to less than =20 nm.1,2)
We measured X-ray magnetic circular dichrosim (XMCD) at the Co L2,3-edges of Co80Pt20
films and determined  dependence of Co 3d spin (mSCo) and orbital (mLCo) magnetic
moments using the magneto-optical sum rules. In order to investigate the relationship of Ku
with anisotropy of the orbital moment (AOM), defined as a difference of mLCo between
out-of-plane and in-plane magnetization, two experimental geometries were adapted3): one forthe normal incidence (=0º) and the other for glancing incidence to the sample surface (=60º).
For this purpose, the films with different , =3, 10, 20, and 60 nm, were prepared.
Furthermore, we separately measured XMCD at the Pt L2,3-edges on BL39XU of SPring-8,
and  dependence of the Pt 5d magnetic moment (mSPt and mLPt) has been studied.
Figure 1 shows X-ray absorption spectrum(XAS) and XMCD spectra at the Co L2,3-edges. It
is found regardless of  that XMCD at =0ºgeometry is larger than that at =60º geometry, sothat the magnitude of the Co magnetic moment
depends on .  for =60 nm is small
compared with those for the thinner films.
However, a monotonous increase in the  isnot observed in a range from =20 to 3 nm. On
the other hand, AOM for mLPt is almost constantas a function of . It is found that the AOM forboth Co 3d and Pt 5d are much smaller thanmagnitudes expected from the large Ku. The result
reveals that contribution of the AOM to the large
Ku is weak for the present films.
References:
1) T. Shimatsu et al., J. Appl. Phys. 99 (2006)
08G908.
2) T. Shimatsu et al., IEEE Trans. Magn., 43 (2007)
2995.
3) W. Grange et al., Phys. Rev. B58 (1998) 6298.

— 123 —

Figure 1: XAS and film thickness ()dependence of XMCD spectrum at
the Co L2,3-edges. Solid and brokenlines correspond to out-of-plane(=0º) and in-plane magnetization(=60º), respectively.

07-A-49

BL-14

L2,3 XAFS spectroscopy as a probe for the local symmetry of dopants (Nb, Ti) in
LiNi1-xCoxO2
Shinjiro Hayakawaa, Ryuta Hasunoa, Tetsutaro Hayashib, Takefumi Sakob,
Masahiro Sawadac, Hirofumi Namatamec and Takeshi Hirokawaaab

Department of Applied Chemistry, Hiroshima University, Hiroshima, Japan
Niihama Center Analytical Technology Dep., Sumitomo Metal Mining Co. LTD, Niihama,Ehime, Japanc
Hiroshima Synchrotron Radiation Center, Hiroshima University, Hiroshima, Japan

LiNi1-xCoxO2 (LNO) is widely used as a positive electrode material for secondary lithium cells,
and the large capacity of LNO is related to its layered structure that can intercalate Li ionsreversibly. It is known that charged LNO has the intrinsic thermal instabilities, and one of thesolutions is the addition of Ti or Nb to substitute some of Ni sites in LNO. Though thestructural change of LNO during the charging has been studied with the x-ray diffraction(XRD) and the extended x-ray absorption fine structure (EXAFS) spectroscopy, themechanism of the thermal stabilization is still unknown.
To investigate the local structural changes of Ni and doped Ti, L23 edge XAFS spectra were
measured on BL14. Two types of charged LNO were prepared for XAFS measurements. One
was charged in the test cell, and the disk of LNO was removed just before the measurements.
Another one was prepared with hydrochloric acid to extract Li ions chemically from LNO.
The fraction of Li desorption was evaluated from the ICP-AES method in the case ofchemical charging.
Figs. 1 and 2 show Ni and Ti L23 XAFS spectra of Ti doped LNO. The marked peak showedsignificant decrease after the Li desorption, and the resultant spectrum was quite similar tothat of NiO. The result indicates the local structure of Ni has changed close to Oh symmetry.

Fig.1 L23 XAFS spectra of Ti doped LNO as a function of Li desorption.

— 124 —

BL-15

Improved sequence-based prediction of protein secondary structuresby combining vacuum-ultraviolet circular dichroism spectroscopy
with neural network
Koichi Matsuo1, Hidenori Watanabe2, and Kunihiko Gekko2(1Synchrotron Radiation Center, 2Graduate School of Science, Hiroshima University)— 125 —CD (%)CD (%)CD

CD

Synchrotron-radiation vacuum-ultraviolet circular dichroism (VUVCD) spectroscopy cansignificantly improve the predictive accuracy of the contents and segment numbers of protein
secondary structures by extending the short wavelength limit of CD spectra (1, 2). However,
VUVCD spectroscopy itself in principle yields no information on the sequence of thesecondary structures, which limits the applicability of this technique to the structure analysis
of proteins. In the present study, we combined the VUVCD data with neural-network (NN)method to improve the sequence-based prediction of protein secondary structures.
The 30 proteins were used as the target
Content of β-Strands
Content of α-Helices
proteins for the sequence-based prediction of
60
80
(b)
(a)
secondary structures. The VUVCD spectra of60
40
40
target proteins were previously measured
20
20
down to 160 nm (1, 2). The secondaryr = 0.82
r = 0.93
00structures of these proteins were assigned into
0
20
40
60
0 20 40 60 80
X-ray (%)
X-ray (%)
α-helices, β-strands, and others using the
Number of α-Helices
Number of β-Strands
30
DSSP program from their PDB codes. The
30
(c)
(d)
20
secondary-structure contents and segments of20
the target proteins were estimated from their1010
r = 0.94
r = 0.83
VUVCD spectra using the SELCON3 program
0
0
0
10
20
30
0
10
20
30
X-ray
X-ray
(3). The contents and segment numbers of
α-helix and β-strand obtained are plotted Fig. 1. Plots of the secondary-structure contents
against those determined from X-ray structures and segment numbers of 30 target proteins(Fig. 1). Evidently, there is good agreement predicted from the VUVCD spectra versus the
X-ray estimates: (a) α-helix content, (b)between the CD and X-ray estimates for the
β-strand content, (c) number of α-helix
contents and segment numbers of α-helices segments, and (d) number of β-strand segments.
and β-strands. The RMSD (δ) and the Pearson
correlation coefficient (r) between the X-ray
and CD estimates for the overall secondary-structure contents were 0.058 and 0.85,
respectively.
Two NN methods were used in this study for computational convenience (4). The first was
the Holley and Karplus (NNHK) algorithm, in which the weights (output) and biases of 20
amino acids for α-helices and β-strands were calculated using the secondary-structure
information and amino-acid sequences of 48 known proteins as a training set. The second wasthe Jones (NNJ) algorithm, which predicts the protein secondary structures using theevolutional sequence information based on the Position Specific Scoring Matrices generated
by the PSI-BLAST algorithm. In our VUVCD-NNJ method, a data set of 607 proteins was
obtained as a training set for NNJ algorithm. The secondary structures of these training
proteins and their amino-acid sequence information were used to calculate the weights andbiases of 20 amino acids for α-helices and β-strands using the public free simulation package
Stuttgart Neural Network Simulator (version 4.2).
The VUVCD data were combined with the
NNHK and NNJ algorithms using thecomputational protocol shown in Fig. 1. First,
the α-helix and β-strand weights (Wα and Wβ)of 20 amino-acids were calculated by NNHK or
NNJ methods as described above (Step 1).
Second, the positions of α-helices and β-strands
were assigned on the amino-acid sequence indescending order of their weights until thedetermined numbers of α-helix and β-strand
residues converged to those estimated fromVUVCD analysis. The residues assigned asneither α-helices nor β-strands were considered
to be other (Step 2). Overlapping regions(residues) were assigned to α-helices for thetarget protein which had more than twice as
Fig. 2. Computational protocol for combining
many α-helix residues as β-strand residues, and VUVCD data with the NN algorithm
they were assigned to β-strands for the target
protein which had more than twice as many β-strand residues as α-helix residues. For othertarget proteins, overlapping regions were assigned to either α-helices or β-strands by directlycomparing the weights of overlapped residues. Furthermore, short stretches comprising lessthan four α-helix residues and less than two β-strand residues were classified as other (Step 3).
The procedures from Step 2 to Step3 were repeated until the predicted numbers of α-helix and
β-strand residues agreed with those estimated from VUVCD analysis (Step 4). The
assignment was complete if the two estimates were consistent, but in other cases the sequencealignment that minimized the difference between the two estimates was taken as the final
solution (Step 5). The results thus predicted by combining the NN (NNHK and NNJ) algorithm
and the number of residues estimated from VUVCD spectroscopy (CD1) were designated as
NN+CD1 (NNHK+CD1 and NNJ+CD1).
Next, the numbers of α-helix and β-strand segments estimated from VUVCD analysis
were introduced into the NN calculation (Step 6). If the predicted numbers of α-helix and
β-strand segments did not agree with those estimated from VUVCD analysis, the weights(Wα) of 20 amino acids for α-helices were multiplied by factors from 0.1 to 2.0 until thepredicted numbers of segments converged to those obtained from the VUVCD estimation— 126 —

(Step 7). The assignment was complete when the two estimates were consistent. If thepredicted numbers of segments did not converge to the VUVCD estimates, the sequencealignment that minimized the difference between the two estimates was taken as the final
solution. The predictions obtained by combining the numbers of both residues and segments(CD2) for α-helices and β-strands were designated as NNHK+CD2 and NNJ+CD2 (Step 8).
The improvement in sequence-based prediction by using VUVCD data was examined for
NNHK and NNJ algorithms using three performance indices: success rate (Q3), correlation
coefficient (C), and segment overlap value (SOV). The obtained results are listed in Table 1.
The total Q3 value of NNHK increased from 59.5 to 60.7% by combining the α-helix and
β-strand contents estimated from VUVCD data (NNHK+CD1). Further combining thenumbers of α-helix and β-strand segments (NNHK+CD2) slightly decreased Q3 to 60.3%, but
greatly increased the C and SOV scores from 0.39 to 0.51 and from 43.8 to 51.9%,
respectively, by introducing the contents and segment numbers step by step. The improvementin predictive accuracy was also
Table 1. Accuracy (Q3, C, and SOV) of predicting
observed when VUVCD datasecondary-structure sequences of target proteins determined
were combined with the NNJ by the NNHK and NNJ methods combined with VUVCD data
algorithm. The Q3 value of NNJ
MethodQ3
C
SOV
increased from 70.9 to 72.1% by
NNHK
59.5
0.39
43.8
NNHK+CD1
60.7
0.43
50.7
introducing the α-helix and
NN
+CD2
60.3
0.51
51.9
HK
β-strand contents (NNJ+CD1),
and further to 72.5% by adding
NNJ
70.9
0.56
59.9
the numbers of α-helix and
NNJ+CD1
72.1
0.59
63.6
β-strand segments (NNJ+CD2).
NNJ+CD2
72.5
0.61
63.7
NNJ+CD3
73.3
0.63
65.6
Improvements were also evident
NN
+CD4
74.9
0.62
69.8
J
in the C and SOV scores.
To facilitate comparison of the predictive accuracy of the various methods, the Q3, C, andSOV values in Table 1 are depicted as proportional histograms in Fig. 3. This figure indicatesthat the predictive accuracy of NNHK and NNJ can be improved by utilizing VUVCD data.
The increases in Q3, C, and SOV imply that the improvement is due to not only the improved
prediction of the average number of residues but also those of the positions and lengths of
α-helix and β-strand segments. Thus, the VUVCD data are valuable for improving thesequence-based prediction of NN algorithm.
The results described above indicate that utilizing VUVCD data can significantly improve
the secondary-structure prediction of NNJ. However, further improvements in accuracy would
be required for practical application of this combination method to unknown proteins. Such
improvement would be possible from both the VUVCD data and the sequence-based
prediction algorithm. We have previously shown that the prediction could be improved bygrouping the reference VUVCD data into α-helix-rich and β-strand-rich proteins (2). We
therefore examined whether such grouping improved the predictive accuracy of the NNJ+CD2
method. The training set of 607 proteins was divided into two groups: 379 proteins with alarger α-helix content than β-strand content were classified as α-helix-rich proteins (α-group),— 127 —

and the remaining 228 proteins were classified
as β-strand-rich proteins (β-group). The 30
target proteins were also divided with the same
criterion into 17 α-helix-rich proteins (α-group)and 13 β-strand-rich proteins (β-group). The
secondary-structure weights (output) of 20
amino acids obtained from the training set ofthe α-group (or β-group) were used in NNJ
calculations for predicting the secondary
structures of the α-group (or β-group) of target
proteins (NNJ+CD3 method). The values of Q3,
C, and SOV thus obtained are listed in Table 1
and depicted in Fig. 3, from which it is evident
that classification of proteins improves theoverall predictive accuracy in any scoresFig. 3. Comparison of three performancecompared with NNJ+CD2 method. Because we indices (Q3, C, and SOV) for the NNHK and NNJ
could judge the extent to which an unknown methods combined with VUVCD data: CD1,
protein was rich in α-helix or β-strand from its number of residues; CD2, numbers of residues
VUVCD spectrum, classification of VUVCD and segments; CD3, proteins classified as richin α-helices and β-strands; and CD4, 16 target
data would be useful for improving theproteins of high quality.
secondary-structure
predictionofthe
VUVCD-NN method. Furthermore, we examined the effects of quality of VUVCD data using
16 proteins whose δ values were smaller than the average value (0.058) for the 30 target
proteins. Relative to the NNJ+CD3 method, the predictive accuracy as calculated with the 16
proteins (NNJ+CD4 method: Table 1 and Fig. 3) improved to 74.9% for Q3 and to 69.8% for
SOV, but there was no improvement in C. These results suggest that the predictive accuracy of
the VUVCD-NN method could be improved by raising the quality of VUVCD data, in termsof the types and numbers of target proteins.
The sequence-based prediction of protein secondary structures using the NN algorithm
can be significantly improved by utilizing data obtained from VUVCD spectroscopy. The
VUVCD-NN method developed here should be further improved to more accurately predict
the secondary structures for the many proteins for which X-ray and NMR structures areunobtainable. The use of VUVCD data could enhance the predictive accuracy to over 80%
when combined with the currently best sequence-prediction algorithm. Accumulation of
VUVCD data would expand the applicability of VUVCD spectroscopy both to structural
biology and computational biology.
1.
2.
3.
4.

K. Matsuo, R. Yonehara, and K. Gekko, J. Biochem., 135, 405–411 (2004).
K. Matsuo, R. Yonehara, and K. Gekko, J. Biochem., 138, 79–88 (2005).
N. Sreerama and R. W. Woody, Anal. Biochem., 287, 252–260 (2000).
K. Matsuo, H. Watanabe, and K. Gekko, Proteins, 73, 104–112 (2008).
— 128 —

07-A-12

BL-15

Secondary-Structure Analysis of Intermediate States of Apo-Myoglobin andPepsin using a Vacuum-Ultraviolet Circular Dichroism Spectroscopy
Hidenori Watanabe1, Koichi Matsuo2, Hirofumi Namatame2, Masaki Taniguchi2,
and Kunihiko Gekko1
1

Graduate School of Science, 2Synchrotron Radiation Center, Hiroshima University

The structures of the intermediates in denaturation process of proteins remain controversial
although they give important information for understanding the folding mechanism andstability of proteins. A synchrotron-radiation vacuum-ultraviolet circular dichroism (VUVCD)
spectroscopy is a powerful technique for the structural analysis of denatured proteins (1) as
well as native ones (2, 3) because it is available for various solvent conditions and can predict
accurately the secondary-structure contents and segment numbers. In the present study, wemeasured the VUVCD spectra of apo-myoglobin (apo-myo) and pepsin down to 170 nm at
various pHs and 25oC in order to characterize the intermediate states of the proteins.
Figure 1 shows the VUVCD spectra of apo-myo at pHs 7.5, 4.2, and 2.0. From the pH
dependence of the molar ellipticities at 222 nm (inset), the spectra at pHs 7.5 and 2.0 are
ascribed to the native and acid-denatured states, respectively. However, the transition curve
has a shoulder at around pH 4.2, suggesting the existence of an intermediate state between thenative and acid-denatured states. Then, the pH 4.2 spectrum would be close to the VUVCD
spectrum of the intermediate of apo-myo. Figure 2 shows the VUVCD spectra of pepsin at
pHs 9.0, 4.9, and 2.0, and the pH dependence of the molar ellipticities at 215 nm (inset). The
molar ellpticity at pH 2.0 is larger (more negative) than that at pH 9.0, indicating that the
spectra at pHs 2.0 and 9.0 correspond to the native and alkaline-denatured states, respectively.
However, the transition curve has a minimum ellipticity at around pH 4.9, suggesting theexistence of an intermediate state between the native and alkaline-denatured states. Then, thepH 4.9 spectrum would be close to the VUVCD spectrum of the intermediate of this protein.
Evidently, the intermediates of two proteins exhibit some characteristic CD peaks, suggesting
their different secondary structures from the native and denatured states. However, these
VUVCD spectra of the intermediates would involve the contributions of the coexisting nativeand denatured components. Therefore, we cannot directly calculate the secondary-structure
contents and segment numbers of the intermediates from the observed VUVCD spectra.
Detailed secondary-structure analysis of the intermediates with the SELCON3 program must
await the determination of the native, intermediate, and denatured fractions, which is inprogress by fitting the pH profiles of molar ellipticities (inset of each figure) to the three-statetransition model.
1. K. Matsuo, Y. Sakurada, R. Yonehara, M. Kataoka, and K. Gekko, Biophys. J., 92,
4088–4096 (2007).

— 129 —

10

-10
-5
2

3

4

5 6
pH

200
220
Wavelength / nm

240

8

-3

0

7

-10
-20
-30

180

260

-1

-6.5

-2
-3

-15

12
10
8
6
4
2
0
-2
-4
-6
-8
-10
-12

[θ ]×10 /deg cm dmol

-2
-3

20

-20

2

-1

30

[θ ] × 10 / deg ・ cm ・ dmol40[θ ]×10 /deg cm dmol

2

-3

-1

50

[θ ] × 10 / deg ・ cm ・ dmol

-12. K. Matsuo, R. Yonehara, R., and K. Gekko, J. Biochem. 135, 405–411 (2004).
3. K. Matsuo, R. Yonehara, and K. Gekko, J. Biochem., 138, 79–88 (2005).
4. N. Sreerama and R. W. Woody, Anal. Biochem., 287, 252–260 (2000).

180

200

-7.0
-7.5
-8.0
1 2 3 4 5 6 7 8 9 10pH220

Wavelength / nm

240

260

Fig. 1 VUVCD spectra of apo-myo at native

Fig. 2 VUVCD spectra of pepsin at native(pH 7.5, solid line), intermediate (pH 4.2,

(pH 2.0, solid line), intermediate (pH 4.9,

dotted line), and denatured states (pH 2.0,

dotted line), and denatured states (pH 9.0,

broken line). Inset shows the plots of molar

broken line). Inset shows the plots of molar

ellipticity at 222 nm against pH.

ellipticity at 215 nm against pH.

— 130 —

07-A-29

BL-15

Secondary-Structure Analysis of Disulfide Variants of Lysozyme by
Vacuum-Ultraviolet Circular Dichroism Spectroscopy
Koichi Matsuo1, Hidenori Watanabe2, Shin-ichi Tate2, Hideki Tachibana3,and Kunihiko Gekko2

1

Synchrotron Radiation Center, 2Graduate School of Science, Hiroshima University,
3
Kinki University

Disulfide bridges play an important role in the construction of the tertiary structure ofproteins. However, it is unknown whether disulfide bridges force the protein into its folded
form or whether other forces guide the protein into a conformation in which the disulfide

3SS∆2
3SS∆3
3SS∆4

contents of α-helices, β-strands, turns, andunordered structures were estimated with the
SELCON3 program using the VUVCD spectra
and PDB data of 31 reference proteins (1, 2).
The numbers of α-helix and β-strand segments
were also estimated from the VUVCD data. In
general, the secondary structures were more
effectively stabilized through entropic forces as
the number of disulfide bridge increased and as— 131 —

-32

[θ ] × 10 / deg � cm � dmol

-1bridges can form easily. Hen lysozyme contains four disulfide bridges, Cys6−Cys127 (SS1),
Cys30−Cys115 (SS2), Cys64−Cys80 (SS3), and Cys76−Cys94 (SS4) (Fig. 1). In this study, toelucidate the effects of a specific disulfide bridge of Cys6−Cys127, Cys30−Cys115,
Cys64−Cys80, and Cys76−Cys94 on the
SS4secondary structures of this protein, the76 94
vacuum-ultraviolet
circulardichroism
SS2
115
64
(VUVCD) spectra of 13 species of30
disulfide-deficient variants, in which Cys
12780
residues were replaced with Ala or Ser residues,
SS3
SS1
were measured down to 170 nm at pH 2.9 and25oC using a synchrotron-radiation VUVCD
spectrophotometer.
Fig. 1. X-ray structure of hen lysozyme.
As shown typically in Fig. 2, each variant
exhibited a characteristic VUVCD spectrum
that reflected a considerable amount of residual
20
native2SS1+2
secondary structures depending on the position
15
2SS3+43SS∆1
and number of deleted disulfide bridges. The
10
5
0
-5
-10
-15

180

200

220

Wavelength / nm

240

260

Fig. 2. VUVCD spectra of 3SS and 2SS
variants of hen lysozyme at pH 2.9 and25oC.

it was formed over a larger distance in the primary structure. The structures of three-disulfide
variants were similar to that of the wild-type, but other variants diminished α-helices with aborder between the ordered and disordered structures around two-disulfide variants. Thereexisted many β-strands in the disordered structures of one-disulfide and no-disulfide variants
as well as in other denatured proteins (3). The amino-acid sequences of the secondary
structures were successfully predicted for all the variants by combining the VUVCD data andthe neural network algorism, this method being recently developed in our laboratory (4).
These results demonstrate that a VUVCD spectroscopy is a powerful technique for predicting
comprehensively not only the contents and segment numbers of the secondary structures but
also their positions in the primary structure over the native to denatured states of proteins.
This study is in preparation for publication.
1. K. Matsuo, R. Yonehara, and K. Gekko, J. Biochem. 135, 405–411 (2004).
2. K. Matsuo, R. Yonehara, and K. Gekko, J. Biochem. 138, 79–88 (2005).
3. K. Matsuo, Y. Sakurada, R. Yonehara, M. Kataoka, and K. Gekko, Biophys. J. 92,
4088–4096 (2007).
4. K. Matsuo, H. Watanabe, and K. Gekko, Proteins 73, 104–112 (2008).

— 132 —

07-A-50

BL-15

Vacuum-Ultraviolet Circular Dichroism Analysis of Glycosaminoglycans by
Synchrotron-Radiation Spectroscopy
Koichi Matsuo1, Hirofumi Namatame1, Masaki Taniguchi1, and Kunihiko Gekko2
1
Synchrotron Radiation Center, 2Graduate School of Science, Hiroshima University
Glycosaminoglycans (GAGs) areunbranched chain polymers composed of
repeating a disaccharide unit containing
an N-acetylglycosamine and a uronic acid
(Fig. 1). We recently constructed a
vacuum-ultraviolet circular dichroism(VUVCD) spectrophotometer at theHiroshima Synchrotron Radiation Center(HiSOR) (1, 2), to obtain the structural
information of saccharides based on thehigher energy transitions such as Fig. 1. Chemical structures of the repeating disaccharidehydroxyl and acetal groups (3). In the units of the GAGs used in this study.
present study, this spectrophotometer
was used to measure the VUVCD spectra of five GAGs [chondroitin (CH), chondroitin sulfate
A (CS-A), chondroitin sulfate B (CS-B), chondroitin sulfate C (CS-C), and heparin (HP) ] down
to 160 nm and one GAG [hyaluronic acid (HA)] down to around 185 nm in aqueous solutions
at 25oC (4). The VUVCD spectra of their component sugars [N-acetylglucosamine (GlcNAc),
N-acetylgalactosamine (GalNAc), N-acetylgalactosamine 4-sulfate (GalNAc4Sul), glucuronic
acid (GlcU), and N-acetyllactosamine (LacNAc)] were also measured to clarify the influencesof the constituent sugar residues of GAGs (4). The contributions of the constituent
chromophores to the CD spectra are discussed by comparing the VUVCD spectra of GAGs andcomponent sugars.
Figs. 2 and 3 show the VUVCD spectra of six GAGs (CH, CS-A, CS-B, CS-C, HP, andHA) and five N-acetylaminosugars (GlcNAc, GalNAc, GalNAc4Sul, LacNAc, GluU),
respectively. For comparison, the spectra of glucose and galactose are also shown in Fig. 3. As
shown in these figures, the VUVCD spectra of GAGs and their component sugars sensitively
reflect the differences in their structures, although they are highly self-similar (Fig. 1). The
differences in the CD spectra are larger in the VUV region than in the far-UV region,
indicating that VUVCD spectroscopy provides considerably more information on the
structures of GAGs in solution. The optical properties of GAGs are complicatedly affected byseveral factors: the number, position, and configuration of chromophores (e.g., acetamido,
sulfate, carboxyl, and hydroxyl groups); the type of intersaccharide linkages (1→3 and 1→4);— 133 —

-1
-32

[θ ] × 10 / deg cm dmol

180

200

220

Wavelength / nm

240Fig. 2. VUVCD spectra of CH (black), CS-A
(brown), CS-B (pink), CS-C (blue), HA (violet),and HP (red) in aqueous solutions at 30 mg/ml-1

and 25oC.

2-3

the n-π* transitions of N-acetyl and carboxylgroups appears to be additive. The CS-A (Fig.
2) shows the negative CD spectrum below 205
nm compared to the CH. The difference
between both CD spectra is clearly
attributable to the sulfate group at position
C-4 of the GalNAc residue, because CS-A
and CH have the same backbone structure(Fig. 1). The CS-C (Fig. 2) shows more

24
20
16
12
8
4
0
-4
-8
-12
-16
-20
160

20
16
12
8
4
0
-4
-8
-12

[θ ]× 10 / deg cm dmol

the anomeric form (α and β) of the hydroxyl
group at C-1; and the staggered orientations[gauche-gauche (GG), gauche-trans (GT),and trans-gauche (TG)] of the hydroxymethylgroup at C-5.
The CH spectrum (Fig. 2) markedly
differs from the sum of the spectra for
GalNAc and GlcU (pH 6.7) below 200 nm,
although a negative peak at 210 nm due tonegative CD spectrum than CS-A at 190−210
nm, and shows less negative one than CH(Fig. 2). These differences are mainly
160
180
200
220
240
260
attributable to the transfer of the sulfate group
Wavelength / nmfrom the C-4 to the C-6 position in theFig. 3. VUVCD spectra of GalNAc (black),
GalNAc residue, because the backbone
GlcNAc (blue), GalNAc4Sul (green), GlcU at pH
structure of CS-C is the same as those of CS-A
6.7 (red) and pH 2.4 (pink), LacNAc (light blue),
and CH. The VUVCD spectrum of CS-B
Galactose (red dotted), and Glucose (black
differs markedly from those of CH, CS-A, anddotted) in aqueous solutions at 25oC.
CS-C (Fig. 2). Because CS-B has the sameamino sugar (GalNAc) as CH, CS-A, and CS-C,
such a large difference in VUVCD spectra is mainly attributable to the different uronic acidresidue: the configuration of the carboxyl group is equatorial (β-D-GlcU) and axial [α-L-IdoU(iduronic acid)] in CS-A and CS-B, respectively. The VUVCD spectrum of HP is more
complicatedly affected by many factors that are not present in other GAGs. HP involves the
IdoU unit as well as CS-B, but a striking difference is observed in the spectra of both GAGs:
the positive band near 190 nm and the negative one near 173 nm in HP have the opposite signin CS-B. However, this difference in the two spectra cannot be simply attributed to the different
constituent amino sugars (GalNAc in CS-B and GlcNAc in HP), because GalNAc and GlcNAc
have negative and positive CD spectra at 173 nm, respectively, and both amino sugars have apositive CD spectrum at 190 nm (Fig. 3). The overall CD spectra of HA and CH are similar— 134 —

above 185 nm, but the intensity of the spectrum at 210 nm of HA is about twice that of CH (Fig.
2). HA and CH differ only in the configuration of the hydroxyl group at C-4 of the amino
sugars (axial in CH and equatorial in HA). The configuration of the hydroxyl group at C-4
affects the staggered conformations of the hydroxymethyl group at C-5 (3). The comparable
difference in the CD-spectrum intensities between GalNAc and GlcNAc (Fig. 3) suggests thatthe difference in the CD spectrum at 210 nm between CH and HA is mainly due to electronic
perturbation of the acetamido chromophore directly induced by the hydroxyl group at C-4 or
via a modified conformational change in the hydroxymethyl group at C-5. The latter
contribution would predominate since the CD spectra below 190 nm differ among GalNAc,
GlcNAc, and LacNAc, and glucose (equatorial) and galactose (axial) have VUVCD spectra ofdifferent signs (Fig. 3).
As shown above, the comprehensive VUVCD spectra of GAGs and their component sugars
down to 160 nm revealed the characteristic contributions of constituent chromphores to thehigher energy transitions of oxygen lone-pair electrons, which are not detectable by aconventional CD spectrophotometer. Further accumulation of VUVCD data and their
theoretical assignments would give important basis for understanding the detailed
conformations and biological functions of GAGs.
1.

Ojima, N., Sakai, K., Matsuo, K., Matsui, T., Fukazawa, T., Namatame, H., Taniguchi, M., and2.

Gekko, K. (2001) Chem. Lett. 30, 522–523.
Matsuo, K., Sakai, K., Matsushima, Y., Fukuyama, T., and Gekko, K. (2003) Anal. Sci. 19,
129–132.

3.

Matsuo, K. and Gekko, K. (2004) Carbohydr. Res. 339, 591–597.

4.

Matsuo, K.,. Namatame, H., Taniguchi, M., and Gekko, K. Biosci. Biotech. Biochem. (in press).

— 135 —

07-A-51

BL-15

Secondary-Structure Analysis of Human Serum Albumin and
α-Chymotrypsinogen at Trifluoroethanol-Denatured State using a
Vacuum-Ultraviolet Circular Dichroism Spectroscopy

Koichi Matsuo1, Sakurada Yoshie2, Hirofumi Namatame1, Masaki Taniguchi1,
and Kunihiko Gekko2
1
Synchrotron Radiation Center, 2Graduate School of Science, Hiroshima University— 136 —

-32

[θ ] × 10 / deg ・ cm ・ dmol

-1
-3

2

[θ ] × 10 / deg ・ cm ・ dmol

-32[θ ] × 10 / deg ・ cm ・ dmol

-1

-1

A synchrotron-radiation vacuum-ultraviolet circular dichroism (VUVCD) spectroscopy is a
powerful technique for the secondary-structure analysis of denatured proteins (1) as well as
native ones (2, 3), because it is available under various solvent conditions and can accurately
predict the contents and segment numbers of secondary structures compared with aconventional CD spectroscopy. In the present study, this technique was applied to characterize
the secondary structures of human serum albumin (HSA) and α-chymotrypsinogen (α-CGN)
denatured by trifluoroethanol (TFE).
Figure 1 shows the VUVCD spectra of HSA and α-CGN down to 170 nm in TFE aqueous
solutions of various concentrations (0 ~50%) at pH 2.0 and 25oC. As shown in the60-14insets of the figure, the molar ellipticity at
a
-16
40
-18
222 nm decreases with increasing the TFE-20-22
concentration and saturates in 50 % TFE,
20
-24
0 10 20 30 40 50
indicating that the two proteins are almost
TFE conc. / %0completely denatured in 50 % TFE. The
TFE-denatured states have typical VUVCD-20
spectra of α-helix proteins. HSA shows an-4
40
isoellipticity point at around 200 nm, whileb-8-12
α-CGN shows two isoellipticity points at
-16
20
-20
around 208 and 202 nm. Further, α-CGN
0 10 20 30 40 50
TFE conc. / %shows characteristic VUVCD spectrum of0β-strand proteins in 20 % TFE (Figure 1b).
These results suggest that TFE induces the-20
α-helix-rich structure in HSA by the
180 200 220 240 260
two-state transition mechanism from acid- to
Wavelength / nm
TFE-denatured states, but TFE denaturation
Fig. 1 VUVCD spectra of HSA (a) and α-CGN (b)of α-CGN has the three-state transition
in TFE solutions at pH 2.0 and 25oC. Native state at
involving a β-strand-rich intermediate stateneutral pH (black), TFE 0% (brown), 10% (red),
between acid- and TFE-denatured states.
20% (green), 30% (blue), 40% (sky-blue), and 50%
The secondary structures (α-helix,
β-strand, turn, PPII, and unordered structure) (pink). Insets show the plots of molar ellipticity atof these TFE-denatured proteins were 222 nm against TFE concentration.

analyzed with the SELCON 3 program (5) using the PDB data and VUVCD spectra of 31
reference proteins (2, 3). The TFE-denatured structure of HSA was composed of α-helix(85.6%), β-strand (0%), turn (11.8%), PPII (1.8%), and unordered structure (9.8%). The
TFE-denatured α-CGN showed similar secondary-structure contents although the α-helix
content (69.3%) was less than that of HSA. The number of α-helix segment was estimated tobe 39 and 12 for HSA and α-CGN, respectively. From these results, it is speculated that theTFE-denatured states of HSA and α-CGN are an ensemble of several long α-helix segments
connected by turns and unordered structure, as well as those of met-myoglobin andthioredoxin (4).
1. K. Matsuo, Y. Sakurada, R. Yonehara, M. Kataoka, and K. Gekko, Biophys. J., 92,
4088–4096 (2007).
2. K. Matsuo, R. Yonehara, and K. Gekko, J. Biochem. 135, 405–411 (2004).
3. K. Matsuo, R. Yonehara, and K. Gekko, J. Biochem., 138, 79–88 (2005).
4. K. Matsuo, Y. Sakurada, H. Namatame, M. Taniguchi, and K. Gekko, HiSOR Activity
Report, 97–98 (2006).
5. N. Sreerama and R. W. Woody, Anal. Biochem., 287, 252–260 (2000).

— 137 —

07-A-15

BL-15

Structural analysis of γ-polyglutamic acids by vacuum-ultraviolet circulardichroism spectroscopy
Kunihiko Gekko,1 Koichi Matsuo,2 and Yoshihito Nogusa3(1Graduate School of Science, 2Synchrotron Radiation Center, Hiroshima University,
3
Ajinomoto Co., INC.)-32[θ ] × 10 / deg ・ cm ・ dmol

-1γ-Polyglutamic acid (γ-PGA) produced in Bacillus natto is a natural polypeptide which is
linked at γ-position of the side chains of glutamic acids with the mixed composition of D- andL-isomers. This polymer is widely used in food industries for various functional properties
such as water retentivity, high viscosity, and biodegradability. However, the conformation ofthis polymer remains unknown although α-polyglutamic acid (α-PGA) linked at α-position
forms helix structure in acidic solution. In this study, we measured the vacuum-ultraviolet
circular dichroism (VUVCD) and far-UV CD spectra of γ-PGA under various solvent
conditions to examine the helix-forming ability of this polymer.
Fig. 1 shows the VUVCD spectra of L-isomer-rich γ-PGA (L-PGA, L:D = 7.5:2.5) andD-isomer-rich γ-PGA (D-PGA, L:D = 2.5:7.5) with low and high molecular weights. L-PGA
showed no negative peak around 220 nm and positive peak around 190 nm characteristic tohelix structure and its spectra were rather similar to that of random coil form independent of
its molecular weight. No significant changes in the far-UV CD spectra were observed at any
polymer concentrations by changing pH and adding Ca2+ ion, lipids, and sugars in the solvent,although Ca2+ ion decreased the peak intensity at 215 nm probably due to its binding with
α-carboxyl group of the side-chain of γ-PGA.
These results indicate that γ-PGA does not form
4
Mw=26,000
helix structure under any solvent conditions
3
L-PGA
2
examined probably because the neighboring
D-PGA
1
0
peptide groups are too far to make peptide bonds-1-2
with each other in γ-PGA different from α-PGA.
-3-4Interestingly, L-PGA and D-PGA showed-5
asymmetric VUVCD spectra about the X-axis with
4
Mw=300,000
3
L-PGA
different intensities although they had the opposite
2
D-PGA
1
sign as expected. This result suggests that both
0-1γ-PGAs have the different arrangement of L- and-2-3
D-glutamic acids although L-PGA and D-PGA-4-5
consist of the mutually same composition of L-and
-6
180
200
220
240
260
D-isomers with the symmetrical CD. Further
Wavelength / nm
detailed VUVCD studies coupled with thepolyelectrolyte solution theory will be necessary
Fig. 1. VUVCD spectra of γ-PGAs
for elucidating the conformation of γ-PGA .
— 138 —

Spin-ARPES

Spin- and angle-resolved photoemission study ofultrathin Bi films on a silicon substrate
T. Hirahara1, K. Miyamoto2, A. Kimura2, Y. Niinuma1, G. Bihlmayer3, E. V. Chulkov4,5, T.
Nagao6, I. Matsuda7, S. Qiao8, K. Shimada8, H. Namatame8, M. Taniguchi2,8, S. Hasegawa1
1
Department of Physics, University of Tokyo, Japan
2
Graduate School of Science, Hiroshima University, Japan
3
Forschngszentrum Jülich, Germany
4
Donastia International Physics Center, Spain
5
Departmento de Física de Materiales, UPV/EHU, Spain
6
National Institute for Materials Science, Japan
7
Institute for Solid State Physics, Japan
8
Hiroshima Synchrotron Radiation Center, Japan
1. Introduction
Spintronics, which aims at the utilization of the spin degree of freedom in addition to thecharge, has attracted wide interest due to their promising potentials in realizing new
functionalities in electronic devices [1]. Spin manipulation is the key factor in spintronics, andthe conventional style was to develop novel ferromagnetic materials [2]. Recently, on theother hand, it was shown that by applying gate voltage (electric field), spin-split
two-dimensional electron gases (2DEG) can be formed in asymmetric quantum wells of
non-magnetic materials [3]. This is called the Rashba effect, due to the spin-orbit interaction
and the structure inversion asymmetry (SIA) [4].
At the crystal surface, the same effect occurs due to the SIA in the surface-normal direction
and spin-orbit split band structures have been found for Au(111) [5,6] and W(110)-H [7]surfaces. This splitting is caused by the spin-orbit coupling Hamiltonian, whereis the spin of electrons, V is the one-electron potential,andis the momentum [8]. Usually in the bulk, the time-reversal symmetry (E(k, ↑) = E(-k,↓)) and space inversion symmetry (E(k, ↑) = E(-k, ↑)) lead to the Kramers degeneracy.
However, at the crystal surface, due to the loss of the space-inversion symmetry thedegeneracy will be lifted.
Bismuth (Bi) is a very heavy element and its electronic structure is highly influenced by the
spin-orbit interaction [9]. It was reported that the surface states of single crystal Bi surfaces
are highly metallic [10] and show large Rashba-type spin-orbit splitting [11]. Furthermore,using ultrathin Bi films on a Si substrate, we have previously shown from angle-resolved
photoemission spectroscopy (ARPES) and relativistic ab initio calculations that as these
Rashba-split surface-state bands overlap with the bulk projection and become quantum-well— 139 —

states (QWSs), the spin-polarization will be lost [12]. However, direct experimental evidence
is still lacking. Therefore in the present study, we have performed spin-resolved ARPES(SARPES) to experimentally confirm if the above fact is true or not.
2. Experimental
The measurements were performed in the SARPES system at Hiroshima Synchrotron
Radiation Center. The spectra were recorded at ~120 K using unpolarized HeIα radiation(21.2 eV) with a compact Mott detector operating at 25 keV [13]. In our measurement
geometry, we can obtain the in-plane spin polarization of the spin component perpendicular tothe plane spanned by the two vectors directed along the light incidence and electron emission.
We define the spin direction as "up" and "down" with respect to this plane, which can also bethought as "left" and "right" with respect to k (Fig. 1).
Epitaxial Bi(001) films (for our filmorientation we use hexagonal notation
Bi(001) which is Bi(111) in rhombohedral
notation) were grown on the Si(111)-7x7
surface at room temperature and annealed at~380 K to improve the film quality [14].
The film thickness in the present
measurement was 7 BL (bilayers, 1 BL = 1.14 Fig 1: Schematic illustration of thex
152
10 atoms/cm , 0.39 nm thick).
spin orientation.
3. Results and Discussion
Figures 2 (a) and (b) show the SARPES spectra around normal emission. The red (blue)
curves represent the spin-up (-down) spectra. We can obviously see that the surface states near
the Fermi level are spin-split (for example, we only see a peak for the spin-up spectra at
4.75°). Figure 2 (c) shows the spin-polarization map deduced from the spin-polarization
curves obtained from the spectra of Figs. 2 (a) and (b). Red (blue) represents positive(negative) spin polarization. The overlapped points are the results of the first principles
calculations [11,12]. Figure 2 (d) shows the band dispersion image obtained by usual ARPES
measurements. Comparing Figs. 2 (c) and (d), we can say that although the features in (c) area bit blurred due to the limited energy and angular resolutions of the SARPES instrument, thespin-split property is unequivocally observed and also consistent with the theoreticalprediction; an antisymmetric spin structure with respect to Γ.
Figure 3 (a) shows the SARPES spectra at larger emission angles. We notice that at 8°, asharp spin-up peak is present just below EF shown by the red filled circle. As this peak
disperses downwards approaching the M point, the peak width becomes broad. Furthermore,
we can recognize that the spin-down spectra start to show peak features at the same energy as
the spin-up spectra. This indicates that the spin-polarization is decreasing. Another spin-down
peak emerges at 14° indicated by the blue open circle, and this state shows very small
negative polarization, probably due to the effect of the Fermi-Dirac function and the limited— 140 —

(a)

(b)

(a)

0.25°
-0.25°

0.75°

29°-0.75°

1.25°
1.75°

-1.25°

26°-1.75°

23°
M-2.25°

20°

2.25°
2.75°

-2.75°

3.25°
3.75°

-0.6

(c)

EF

0

-3.25°

14°-3.75°

12°

4.75°-4.75°

5.75°-5.75°

Binding Energy (eV)
0.6

20
40
60
80
Γ
100
-0.2 -0.1 0 0.1 0.2kΓM (Å-1)

17°

10°

8°
Binding Energy (eV)Binding Energy (eV)

(b)

(d)

EF
20
40
60
80
100

M

←Γ

SS with higher EB
SS closer to EFΓ-0.1 0 0.1 0.2kΓM (Å-1)

Fig 2: (a,b) SARPES spectra around normal emission

Wavenumber (Å-1)

Fig 3: (a) SARPES spectra around the
M point for the 6 BL Bi(001)for the 6 BL Bi(001) film on Si(111). (c) The

film on Si(111). (b) The change

spin-polarization map deduced from the spectraof the spin-polarization withof (a) and (b). The overlap points represent thewavenumber deduced from theresults of ab initio calculations. (d) The band

spectra of (a).

dispersion image of the usual ARPES.

— 141 —

resolution in our measurement. At the M point (23° spectra), the spin-up and -down spectra
overlap almost completely, meaning that there is practically no spin polarization for any stateat this angle. As we pass M, the shallow state near EF now shows a peak for the spin-up
spectra, while the surface state with higher binding energy is negatively polarized. The changeof the spin-polarization value with wavenumber is explicitly shown in Fig. 3 (b). This showsthat the spin structure is basically antisymmetric with respect to the M point. Thus we haveobtained experimental evidence of our previous expectation that the spin polarization willdiminish where the surface-state bands overlap with the bulk projection and become QWSs.
Referenes[1] S. A. Wolf et al., Science 294, 1488 (2001).
[2] H. Ohno, Science 281, 951 (1998).
[3] T. Koga et al., Phys. Rev. Lett. 89, 046801 (2002).
[4] E. I. Rashba, Sov. Phys. Solid State 2, 1109 (1960).
[5] S. Lashell et al., Phys. Rev. Lett. 77, 3419 (1996).
[6] M. Hoesch et al., Phys. Rev. B 69, 241401(R) (2004).
[7] M. Hochstrasser et al., Phys. Rev. Lett. 89, 216802 (2002).
[8] R. Winkler, Spin-Orbit Coupling Effects in Two-Dimensional Electron and Hole Systems,(Springer-Verlag, Berlin, 2003)[9] X. Gonze et al., Phys. Rev. B 41, 11827 (1990).
[10] C. R. Ast and H. Höchst, Phys. Rev. Lett. 87, 177602 (2002).
[11] Yu. Koroteev et al., Phys. Rev. Lett. 93, 046403 (2004).
[12] T. Hirahara et al., Phys. Rev. Lett. 97, 146803 (2006).
[13] K. Iori et al., J. Elec. Spec. Rel. Phen. 144-147, 997 (2005); Rev. Sci. Inst. 77, 013101(2005).
[14] T. Nagao et al., Phys. Rev. Lett. 93, 105501 (2004).

— 142 —



Spin polarization of spin-orbit induced electronic structures of Bi(111)
R. Nishimura1, K. Miyamoto2, T. Kadono1, K. Kanomaru1, A. Kimura1
K. Shimada2, S. Qiao3, H. Namatame2, T. Taniguchi1, 2
1
Graduate School of Science, Hiroshima University, Higashi-Hiroshima,
Hiroshima, 739-8526, Japan.
2
Hiroshima Synchrotron Radiation Center, Hiroshima University, Higashi-Hiroshima,
Hiroshima, 739-0046, Japan.
3Advanced Materials Laboratory and Department of Physics, Fudan University,
Shanghai 200433, China.
Recently, spintronics has received broad attention for the possibility as next-generation
technology, where control of both spin and charge is considered as fundamental concept. Oneof the most striking ideas is to manipulate spin of free electron gas only by an electric field as
proposed for spin- field effect transistor (spin-FET) [1], which is related to an appearance ofspin-split energy band structure due to a broken space inversion symmetry. In analogy, crystal
surface is expected to exhibit spin split feature of energy band structure due also to a broken
space inversion asymmetry. Recently, spin-split metallic surface states of Bi(111) has beenclearly observed by an angle resolved photoelectron spectroscopy [2].
In order to determine a detailed spin electronic state, we have performed spin- and angleresolved photoemisson spectroscopy of Bi(111) surface along -M in Hirosima Synchrotron
Radiation Center. In the present study, we have observed new spin-split bands in the larger
binding energy (EB) region above 1 eV. Fig.1 shows energy band dispersion curves of up-spinand down-spin states, separately. As one of the most intense features, we observe a downward
energy dispersion starting from EB=2.6 eV. It is noticed that the spin-up (spin-down)
photoemission intensity is strong at negative (positive) wave number. For a shallower state,
one finds a broad and steep energy dispersion curves from EB=1.2 eV. This also shows astrong spin dependence, which will be discussed with the one-step model photoemission
calculation.

Fig.1 Experimental energy dispersion curves of up-spin (left) and down-spin (right) components.
References[1] S. Datta and B. Das, Appl. Phys. Lett. 56, 665 (1990).
[2] Yu. M. Koroteev et al., Phys. Rev. Lett. 93. 046403 (2004).
— 143 —


 

Unveiling spin characters of spin-orbit induced surface states

K. MiyamotoA, R. NishimuraB, T. KadonoB, K. KanomaruB, K. IoriB, A KimuraB, S. QiaoC,
K. ShimadaA, H. NamatameA and M. TaniguchiA,B
A

Hiroshima Syncrotron Radiation Center, Hiroshima University
B
Graduate. School. of Science, Hiroshima University
3
Laboratory of advanced Material and Department of Physics, Fudan University

kmiyamoto@hiroshima-u.ac.jp

Recently, “spintronics”, which manipulates a spin degree of freedom as well as charge, has
attracted a great attention as a new technology in next generation. In particular, spin field
effect transistor (SFET) controlled with gate voltage without external magnetic field is one of
the most striking ideas as firstly proposed by Datta and Das [1]. The efficiency of SFET isdominated by spin-polarized free electrons traveling in an asymmetric spin-orbit potential
induced by the external gate voltage, which is so called “Rashba effect”. A crystal surface
with a broken spatial symmetry would also form a spin-split band electronic structure in aspin-orbit potential as suggested for Bi(111) and Sb(111) surfaces without spin resolution [1].
Spin-resolved ARPES is a powerful tool to enable a quantitative evaluation of spinpolarizations of spin-split bands in order to see how the surface states are localized from abulk projection and a symmetry of constituent wave functions In the present study, we have
tried to clarify the spin characters of spin-orbit induced surface state bands of Bi(111) andSb(111) by means of spin-resolved ARPES in Hiroshima University.
Figures.1 (a) and (b) show spin resolved energy distribution curves (EDC’s) as a functionof binding energy (EB) of Bi(111) surface near EF for positive and negative emission angles(a) Bi(111) SARPES(b) Bi(111) SARPES = +3.5
+3.0

+2.5

+2.0
+1.5
+1.0
+0.5
0
0.20

0.10

0.00

spin
spin

Spin Resolved Photoemission Intensity (Arb. Units)

Spin Resolved Photoemission Intensity (Arb. Units)

spin
spin

-0.10

 = -3.5

-3.0
-2.5
-2.0
-1.5
-1.0
-0.5
0

0.20

0.10

0.00

-0.10

Binding Energy (eV)Binding Energy (eV)Fig. 1 Spin-resolved EDCs of Bi(111) surface near EF for (a) positive and (b) negative emission angles.
— 144 —

(), respectively. At =0º, the peak structures are found at the same EB=50meV in bothspin-up and spin-down components, that is, the spins of the relevant state are degenerate justat k = 0. The peak position of spin-down spectra shifts from slightly below to above EF withincreasing  from +0.5º to +1.5º as marked with vertical bars and is finally crossing EF around+2.5º. In contrast to the spin-down spectra, the spectral weight of spin-up component moves
to a little higher EB from 0º to +1.5º and shift back to EF from +2º to +3.5º. If one takes a lookat the spin-resolved EDCs for negative emission angles of Fig.1(b), the behavior of peak shift
in spin-up (spin-down) states is similar to that in spin-down (spin-up) along positive emission
angle. This result means that the spin dependent band structures originate in spin-orbit
interaction.
[1] Yu. M. Koroteev et al. 2004 Phys. Rev. Lett. 93. 046403. /T. Hirahara et al. 2006 Phys. Rev. Lett. 97. 146803.
/K. Sugawara et al. 2007 Phys. Rev. Lett. 96. 046411.

— 145 —




Spin-resolved ARPES of Sb(111) single crystal surface
A

T. Kadono, BK. Miyamoto, AR. Nishimura, K. AKanomaru, CM. Nagano, CT. Shishidou,C
T. Oguchi, DS. Qiao, BK. Shimada, BH. Namatame, AA. Kimura, A,BM. Taniguchi
Grad. Sch. Sci., Hiroshima Univ.A, Hiroshima Univ. , HSRCB,
ADSM, Hiroshima Univ.C, Dept. Phys., Fudan Univ.D

Crystal surfaces with a strong spin-orbit coupling have attracted a great
attention because it would cause a spin splitting despite of non-magnetic
property. At surfaces, spin degeneracy could be lifted due to a space inversion
asymmetry. Recently, energy splittings are observed in the surface states ofAu(111) and Sb(111) [1,2]. Surprisingly, the size of splitting for Sb(111) iscomparable to that for Au(111) although the spin-orbit coupling strength ofouter p shell is much weaker for Sb [1]. In order to clarify the origin of suchthe marked spin-split feature, spin- and angle- resolved photoelectron
spectroscopy (spin-ARPES) has been applied to Sb(111) surface.
Figure 1 shows the E-k// plot of spin-up component in the binding energy(EB) range of 0 – 0.45 eV along -M of surface Brillouin zone. The intensity
maxima of photoemission spectra in the lower
EB region are traced with open triangles. Theband shows an upward energy dispersion with abottom (EB = 0.2 eV) at  and crosses Fermi
level (EF) just at +0.15 Å-1 (-0.05 Å-1) in thepositive (negative) k// region. It can be noticed
that this energy dispersion is asymmetric withrespect to , which clearly indicates the
Rashba-type spin splitting due to a broken
space inversion symmetry. Combined withthe ab-initio slab calculation, the large
spin-splitting is caused by the strong
asymmetry of constituent wave function.
References[1] S. LaShell et al., Phys. Rev. Lett. 77, 3419
(1996).
[2] K. Sugawara et al., Phys. Rev. Lett. 96,
046411 (2006).

— 146 —

Fig. 1: Experimental E-k// relation ofSb(111) surface in spin-up channel.
The peak maxima are traced as denotedby open triangles.

07-A-9Spin- and angle- resolved photoemission spectroscopy
of a Si(111)33-Sb surface
K. Kanomaru1, K. Miyamoto1, T. Kadono1, R. Nishimura1, A. Kimura1
S. Qiao3, K. Shimada2, H. Namatame2, M. Taniguchi1, 2
1

Grad. Sch. Sci., Hiroshima Univ., Higashi-Hiroshima, 739-8526, Japan
2
HSRC, Hiroshima Univ., Higashi-Hiroshima, 739-0046, Japan
3
Dept. Phys., Fudan Univ., Shanghai 200433, China

Spin-split band structure at surfaces is paid a lot of
attention since it leads, for instance, to application of the spin
field effect transistor with high performance. The spin-splitting
is brought about by an asymmetric spin-orbit potential that
surface state electrons feel. Since the spin-orbit potential
depends on a structural property of surface, various types ofsuperstructure would cause different spin-split bands[1]. It is
known that Sb/Si(111) surface exhibits eight different surface
phases obtained by a fine tuning of temperature and coverage[2].
For the purpose of investigating the adsorbate induced spin-split
band structures, we have carried out a spin- and angle- resolved
photoemission spectroscopy of 33-Sb/Si(111) surface.
Figure 1 shows spin-ARPES spectra at emission angles() of ±9° for parallel and perpendicular spin components withrespect to   M direction of 33 surface Brillouin zone
(SBZ). These spectra correspond to the electronic states near the
middle of   M of 33 SBZ (upper part of Fig.1). As
indicated with arrows in Fig. 1, the fine spin-split features areobserved above the binding energy (EB) of 4 eV at  = ±9° forthe parallel spin component, whereas negligible spinpolarization is found for the perpendicular spin component.
Since the turns of the spin components change between Fig.1(c)and (d), it can be assigned to spin-split band induced by abroken spatial symmetry. Here, the relevant band structure
comes mainly from a Si bulk-derived band. Thus, it isFig.1 Spin-ARPES spectra at ±9
considered that the observed spin-split feature is derived for the   M direction of 33
by the interaction of Sb 5p and the Si 3s,p states.
SBZ for perpendicular(a,b) and
References[1] C. R. Ast et al., Phys. Rev. Lett. 98, 186807 (2007)[2] V. K. Paliwal et al., Surf. Sci. Lett 513, L397 (2002)— 147 —

parallel(c,d) spin components.
Spin-up (spin-right) and spin-down(spin-left) are denoted by open andsolid symbols for perpendicular(parallel) spin components with respect
to kx (   M ).

07-A-47

IPES

Unoccupied band structure of 1T-TaS2 investigated by angle-resolved
inverse-photoemission spectroscopy
Y. Utsumia, Y. Mukaegawaa, M. Aritab, H. Satob, M. Sasakic,
A. Ohnishic, H. Namatameb and M. Taniguchia,baGraduate School of Science, Hiroshima University, Higashi-Hiroshima 739-8526, JapanbHiSOR, Hiroshima University, Higashi-Hiroshima 739-0046, JapancFaculty of Science, Yamagata University, Yamagata 990-8560, Japan

Quasi-2D material, 1T-TaS2, has been studied for long time, because of its interesting
charge density waves (CDW) phenomenon. 1T-TaS2 has three CDW phases depending on
temperature; incommensurate (IC) phase in the temperature range between 600 and 350 K,
nearly commensurate (NC) phase with a hexagonal array of commensurate domains withtypical size of 70 Å [1] between 350 and 180 K, and commensurate (C) phase with a √13 ×√13 superlattice below 180 K. The NC to C phase transition is accompanied by ametal-insulator transition. There are many researches on valence bands of 1T-TaS2 by meansof photoemission spectroscopy (PES), and the band reconstruction due to the √13 × √13
superlattice and an energy gap of ~100 meV in the C phase have been revealed [2]. However,there are few researches on unoccupied band of this material, because of experimental
difficulty.
In this study, we have observed unoccupied band structures in ΓM and ΓK directions for
the IC phase (380K) and C phase (100K) of 1T-TaS2 single crystal, by means ofangle-resolved inverse photoemission spectroscopy (ARIPES). ARIPES spectrometer used inthis work consists of Erdman-Zipf electron gun with a BaO cathode, and ultraviolet emission
spectrometer with non-periodic spherical gratings and CsI-coated multichannel plates [3]. The
total energy resolution is 540 meV at an incidence electron kinetic energy of EK=44 eV,
which is determined by Fermi edge fit of spectra for evaporated Au film measured underidentical conditions as the samples. The clean surface was obtained by cleavage in theanalysis chamber below 2 × 10-10 Torr.
We have successfully observed the clear unoccupied band dispersion in both IC and C
phases of 1T-TaS2. Figure 1 shows the experimental unoccupied bands in ΓM direction for IC
and C phase of 1T-TaS2 measured at EK=44 eV. In order to compare the experimental resultswith band-structure calculation, theoretical bands for undistorted 1T structure in ΓM and AL
directions calculated by Mattheiss [4] are also plotted in the IC result. In the IC phase, a— 148 —

continual band near the Fermi level (EF), which can be attributed to the Ta dxy and dx2-y2
bands, is in very good agreement with the band-structure calculation. In contrast, in the Cphase, the continual band of the IC phase splits into two manifolds around M point, and theupper and lower bands exist about 3.8 and 1.5 eV, respectively. This band splitting is anevidence of band folding in the reconstructed Brillouin zone due to the √13 × √13 superlattice.
Band folding occurs at the boundary between the √13 × √13 Brillouin zone. Since threeboundaries are found around M point, the effect of the band folding is easy to be observed as
the flat bands around 1.5 eV.
In comparison with the intensity near the Γ point of the IC and C phases, we find that
intensity decreases in the C phase. We also find about 100 meV gap at EF in the C phase, stillin the unoccupied states, from the comparison of ARIPES spectrum of the Γ point between
the IC and C phases. Together with the PES results of ~100 meV gap in the occupied states[2], the gap is considered to be the Mott-type.
References[1] F. Clerc, C. Battaglia, M. Bovet, L. Despont, C. Monney, H. Cercellier, M. G. Garnier, H.
Berger, L. Forro and P. Aebi, Phys. Rev. B 74 (2006) 155144.
[2] M. Arita, H. Negishi, K. Shimada, F. Xu, A. Ino, Y. Tkeda, K. Yamasaki, A. Kimura, S.
Qiao, S. Negishi, M. Sasaki, H. Namatame and M. Taniguchi, Physica 351 (2004) 265.
[3] H. Sato, T. Kotugi, S. Senba, H. Namatame and M. Tanigushi, J. Syn. Rad. 5 (1998) 772.
[4] L. F. Mattheiss, Phys. Rev. B 8 (1973) 3719.
10

1T-TaS2 ARIPES IC phase (380K)

8Energy above EF (eV)Energy above EF (eV)

10

6
4
2
0

1T-TaS2 ARIPES C phase (100K)

8
6
4

high

2
0

Γ
(A)

M
(L)

low

Γ

M

Fig.1. Experimental unoccupied band structures in ΓM direction for the IC and C phases of 1T-TaS2.
Left side is the IC phase band structure with band-structure calculation [4]. The dashed line and solidline indicate the results of AL and ΓM directions, respectively. Right side is the C phase band
structure. The band near EF splits into two manifolds at M point.

— 149 —



Surface electronic structures of ferromagnetic Ni(111)
studied by scanning tunneling microscopy and spectroscopy
Yosuke Nishimura a, Hisashi Narita c, Mitsuru Kakeya a, Mitsuharu Higashiguchi a, Yuichi
Miura a, Masashi Nakatake b, Akio Kimura a, Kenya Shimada b, Hirofumi Namatame b
Masaki Taniguchi a, b
aGraduate School of Science, Hiroshima University, Higashi-Hiroshima 739-8526, Japanb
Hiroshima Synchrotron Radiation Center, Hiroshima University, Higashi-Hiroshima
739-0046, Japanc
Institute for Solid State Physics, Tokyo University, Kashiwa 277-8581, Japan
It is well known that free electron surface states, so called Shockley-type surface states,
are present at (111) surface of noble metals with face centered cubic (fcc) structure like Au,
Ag and Cu [1]. The Shockley-type surface state likewise exists at Ni, Pd, and Pt single
crystalline surfaces. Particularly, a ferromagnetic Ni surface has attracted a considerable
attention because a spin-polarized two-dimensional electron gas (2DEG) could emerge on
this surface. In fact, the Shockley surface state of Ni(111) was approached using several
experimental techniques, such as ARPES, STM, spin and angle resolved inverse
photoemission spectroscopy [2-4]. However, the contradictory results were obtained so far.
In order to resolve these discrepancies, the Shockley surface state of the Ni(111) has been
investigated carefully with STM and STS.
Figure 1 shows the STM image of Ni(111) at the sample bias (Vs)=+0.35V. This image
clearly shows a standing wave that is spread isotropically around point defects, whichclearly indicates the existence of 2DEG on the surface. The STS spectrum shows two “risingedges” attributed to an exchange split pair of Shockley states at around -130meV and+60meV. From this spectrum, we concluded that the exchange splitting energy is 193meV.

Fig. 1: The STM image of Ni(111)Fig. 2: STS spectrum of Ni(111) surface.

surface (Vs=+0.35V, T=77K)

References
1) M. F. Crommie et al., Nature 363 (1993) 524.

3) S. Pons et al., Europhys. Lett 61 (2003) 375.

2) M. Higashiguchi et al., Surf. Sci. 601 (2007) 4005.

4) M. Donath et al., Phys. Rev. Lett 70 (1993) 28.

— 150 —Atomic and local electronic structure of Co and CoSi2 clusters

LT-STM

H. Narita, K. He, T. Okuda, A. Kakizaki, I. Matsuda
Y. Cui, 2A. Kimura, 1M. Nakatake, 1H. Namatame, 1M. Taniguchi
Synchrotron Radiation Laboratory, The Institute for Solid State Physics, University of Tokyo
1
Hiroshima Synchrotron Radiation Center, Hiroshima University,
2
Graduate School of Science, Hiroshima University
1

The formation mechanism of fabricated structure on a nano-scale is an important subject inthe study of the development and spread of nano technology. Especially, the nano-scale
clusters attract a great deal of interest in industry and surface science as the most advanced
technique, such as ultrahigh density storage media, nanocatalysis and single electrontransistor [1-3].
Over the past few decades, the observation of Co/Si (111) system was carried out by
scanning tunneling microscopy (STM), photoemission spectroscopy (PES) and
Pseudopotantial DFT calculations methods [4-6], and it was well known that the system has
the flat-topped and 2×2 reconstructed triangular clusters for deposition at 320°C as shown in
FIG. 1 (a) and (b). It was also suggested in some reports that these clusters show CoSi2
structure with seven-fold Co coordination (interface) and so-called B-type geometry. Whilethe clusters (Co cluster) on Al nanocluster fabricated on Si (111) 7×7 surface also have theflat-topped cluster at the same temperature, and they are seldom observed with 2×2
reconstruction as shown in FIG. 1 (c). He et al.[7] did not assume in detail if Co and Si atoms
constitute these clusters or not. However, the interesting thing is that this Co clusters have thehigh perpendicular magnetic anisotropy (PMA) under 40K (Here, the cluster fabricated on Al
nanocluster is described as “Co cluster” in order to differentiate the two clusters). Our
final-purpose is to clarify the difference of the atomic structure between Co and CoSi2 clusters
and the template effect of Al nanocluster phase using
photoelectron experiment [core-level photoemission
spectroscopy (CL-PES), photoelectron diffraction (PED)and X-ray photoelectron diffraction (XPD)] andscanning tunneling spectroscopy (STS). In this report,
we will discuss STM/STS data of CoSi2 clusters
fabricated on Si (111) 7×7 surface.
The experiment were carried out in an
ultrahigh-vacuum (UHV) chamber with a base pressureof 1.0×10-10 mbar, using Omicron LT-STM. We usedhighly B-doped Si (111) wafers (p-type), and the surface
was chemically treated by a modified RCA cleaning
method [8]. A clean Si (111) 7×7 reconstructed surface
was obtained by a standard flashing procedure up
1250 °C after outgassing at about 500 °C for several
hours, and checked by LEED system. Al atoms were
carefully deposited using a well-outgassed homemade
evaporator, and the periodic array of Al nanocluster has
been prepared by 0.24-0.3 ML-Al deposition at substratetemperature 500°C. While Co atoms were deposited at
FIG. 1 Empty state STM images of (a)320°C by using commercial evaporator (Omicron: flat-topped CoSi (Vs=+1.8V), (b) 2×2
2
EFM-3). All of STS spectra were obtained at 78K.
CoSi2 (Vs= +1.5V) clusters on Si (111)
Figure 1 (a) shows two flat-top CoSi2 clusters 7×7 surface and (c) flat-topped Co cluster
fabricated on Al nanocluster template.

— 151 —

fabricated on Si (111) 7×7 reconstruction surface. Here,higher CoSi2 cluster is described as HF-CoSi2 andlower one is “LF-CoSi2.” While Fig. 1 (b)-(c) show the
2×2 periodical structure on cluster, and the flat area on
2×2 phase is partially formed at the corner of cluster.
All of clusters is fabricated in the form of triangle
shape depended on 7×7 periodicity, and the areaaround cluster often change from the 7×7 phase to thedepressed area. According to the line-profile (notshown here), the depth of the depressed area is0.23-0.30 nm, and this value says one monolayer of
7×7 DAS structure is broken. Accordingly, it should beconsidered that the related Si atoms diffuse toward anearby cluster or somewhere. Actually, the depressedarea is often appeared around the HF-CoSi2 cluster,
this phenomenon tells us that CoSi2 cluster need more
Si atoms to be higher cluster.
Figure 2 shows the experimental density of state(DOS) of CoSi2 cluster formed on Si (111) andtheoretical DOS of bulk CoSi2 [9]. Upper five spectra(two brown, gray, yellow and orange lines) show the FIG. 2 Experimental and theoretical DOS
STS spectra of 2×2 phase and HF/LH-CoSi2 clusters, of CoSi2. STS spectra were obtained atand undermost spectrum shows the theoretical DOS of each atomic site in FIG. 1 (a)-(c).
bulk CoSi2. Probing points are described in FIG.1 (a)-(c). These spectra show the different
feature, and this result shows the site-resolved probing technique should be reliable. Here, we
focus the difference between HF- and LF-clusters. LF-cluster has several broadened peaks in
the region of -4 < sample bias (Vs) < 0. But, comparing to HF-CoSi2, these peaks become
more clear, especially at Vs = -3.0, -1.8, -0.8V. While the strong peak of LF cluster at +0.5 V
is suppressed. Additionally, the STS spectra of HF/LF-CoSi2 clusters have a double peakaround Vs = -1.8V, those peak shapes and energy positions are consistent with that of
calculation results. Besides, it is interesting to note, as growing from LF to HF, thecharacteristics of electronic structure at Vs = +0.5 V gradually becomes similar to thecalculated DOS. Confirming the reliability of STS spectra, the photoemission spectra of CoSi2
cluster and Si (111) 7×7 surfaces is shown in the middle of FIG. 2. The “difference” spectrum
is gotten by subtracting between those spectra, and we can find the subtracted spectrum has
the double peak at around -1.7 V below Fermi level as the STS spectra and theoretical DOS
do. Besides, the strong peak of subtracted spectra at -0.7 V is consistent with that of 2×2
phase STS spectra at the same energy, therefore, it is expected that strong peak arises from the
2×2 electronic structure. As described above, we can understand that CoSi2 cluster has thesame electronic state as bulk CoSi2 in spite of low dimensional structure.
For the future, we will do more accurate STM/STS experiment for CoSi2 and Co clusters.

References[1] K Bromann et al., Science 274 (1996) 956.
[2] H. Brune et al., Nature (London) 394 (1998) 451.
[3] S. Sun et al., Science 287 (2000) 1989.
[4] P. A. Bennett et al., J. Vac. Sci. Technol. A 11(4) (1993) 1680.
[5] C. Pirri et al., Phys. Rev. B 29 (1984) 3391.
[6] M. A. K. Zilani et al., J. Phys.: Condens. Matter 18 (2006) 6987, Phys. Rev. B 72 (2005) 193402.
[7] Ke. He et al., Surf. Interface Anal. 38 (2006) 1028.
[8] W. Kem et al., PCA Rev. 31 (1970) 187.
[9] L. F. Mattheiss et al., Phys. Rev. B 37 (1988) 10623.

— 152 —

Co-induced nano-structures on Si(111) surface
Y. T. Cui a T. Xie b M. Ye a A. Kimura a S. Qiao b,c H. Namatame b M. Taniguchi a,b
a Graduate School of Science, Hiroshima University Higashi-Hiroshima, 739-8526 Japanb Hiroshima Synchrotron Radiation Center, Hiroshima University, Higashi-Hiroshima 739-0046, Japanc Advanced Materials Laboratory, Fudan University, Shanghai 200433, China.

Abstract
The interaction of cobalt atoms with silicon (111) surface has been investigated by means of scanning tunnelingmicroscopy (STM) and low-energy electron√diﬀraction√ (LEED). Besides the Co silicide islands, we have successfully
distinguished two inequivalent Co-induced 13 × 13 reconstructionson√√ Si (111) surface. Our high-resolution STM
images provide some structural properties of the two diﬀerent 13 × 13 derived phases. Both of the two phases
seem to form islands with single domain. The new ﬁndings will help us to understand the early stage of Co silicide
formations.
Key words: Co silicide; Si(111) surface; Scanning tunneling microscopy; LEED; reconstructions
PACS: 61.14.Hg, 61.30.Hn, 61.46.Bc, 68.35.-p, 73.20.At

1. Introduction
Transition-metal silicides have been widely investigated in recent years in terms of microelectronic industry and fundamental science. Besides
the applications of transition-metal silicides (suchas CoSi2 , NiSi2 ) in integrated-circuits, the eﬀects
of adsorbed atoms on a reconstructed Si surface
and the mechanisms and coeﬃcients of surface
diﬀusion are also fundamental subjects of surface
science. Although there have been extensive studies on the growth and properties of CoSi2 epitaxial
ﬁlms, knowledge about the structural details of Co
adatoms and the initial stages of cobalt disilicide
are insuﬃcient partly due to an appearance√ √ of veryrich reconstructed√phases. Si(111)- 7× 7R19.1◦ Co (hereafter as 7) structure has been studied
by means of LEED, XPS (X-ray Photoemission
Spectroscopy), ARPES (Angle-Resolved Photoelectron Spectroscopy), STM and LDA (Local Density
Email address: yitaocui@gmail.com (Y. T. Cui).

Approximation) based √calculations(1; 2; 3). Two
√
◦
types
of
domainswith
13×
13R13.9(hereafter√√
13)
reconstructions
and
both
the
13 andas√√√
19× 19R23.4◦ (hereafter as 19) reconstructions were found by LEED and STM (4; 5), but
the detailed structural information is still lacking.
In order to investigate the detailed surface structures, STM experiment was carried out. In thispaper,
we will show two inequivalent Co-induced√
13 structural phases through several real space
STM images together with their FFT (fast Fouriertransformation) and LEED patterns.
2. Experimental
The Co induced surface structures were fabricatedand studied with a commercial room-temperaturescanning tunneling microscope (STM, RHK UHV400) mounted in an ultrahigh-vacuum (UHV) chamber combined with a sample-preparation chamber. The base pressures of the two chambers werearound 1.0×10−10 Torr. Clean Si(111) (p type, ≥Preprint submitted to Elsevier

26 September 2008

— 153 —

Fig. 1. LEED pattern with electron√energy of√63.4 eV. The reciprocal unit cells of Si(111)-1×1, 13 and 7 reconstructedsurfaces are marked.

1000 Ω·cm) surfaces were obtained by the following
process. After degassed for several hours at 800 K,
the sample was ﬂashed several times to 1470 K for 5
seconds, then the sample temperature was rapidly
reduced to about 1170 K, and slowly decreased toroom temperature at a pace of 1∼2 K/s with apressure below 1.0×10−9 Torr. The sample temperature was controlled by direct-current-heating anda nearly perfect 7×7 reconstruction was obtainedby this method. Co was deposited from a watercooled electron-beam evaporator (Omicron EFM 3)
to clean 7×7-Si(111) surface with a rate of ∼0.08
ML/min (where 1 ML = 7.83×1014 atoms/cm2 ).
The temperature of silicon substrate was kept at
800 K during the Co deposition. Auger electron
spectroscopy (AES) and LEED observations wereroutinely carried out to check the surface cleanliness and reconstruction. All of the STM images
were taken at room temperature.

Fig. 2. Typical occupied-state STM images (V S = -2.5 V, I S= 0.51 nA) of Si (111) surface after deposition of 0.5 ML Co
at a temperature of 800 K; (a) Typical topographic image inthe wide area (600nm×600nm); (b) The cross section proﬁlesalong the lines shown in (a); Close view of typical Co islandsin three dimensional form: (c) atomically ﬂat top island with
2×2 structure and (d) pyramid-like island.

√
induced√ 19 twinned atomic structures(6), Si(111)√
21× 21-Ag surface with diﬀerent orientations of◦at OPB3 (out-of-phase-boundary of[112̄]±10.89√
the 3-Ag phase)(7) and so on. The present√LEED
pattern also indicates two domains for the 7 surface phase as shown in Fig. 1.
Fig. 2 (a) shows the typical occupied-state STM
image in the wide area (600nm×600nm, V S = -2.5
V, I S = 0.51 nA). Here, one can ﬁnd some islands
with larger height (brighter image). The cross sections along two lines marked on Fig. 2 (a) are shownin Fig. 2 (b). The lateral size of islands is in theorder of tens nanometers, and mostly in the range
between 20 to 50 nm with the height of about 2∼5
nm. These islands can be classiﬁed into two typicaltypes. The major one shows approximately triangular, trapezoidal or hexagonal shape with atomicallyﬂat top that shows well-known CoSi2 (111)-(2×2)
structure (8; 9). A typical image of this kind of island is shown in Fig. 2 (c) in three dimensional form.
The minority one as marked by ellipses in Fig. 2 (a)shows pyramid-like feature without any CoSi2 (111)(2×2) structure on the triangular ﬂat top as seen

3. Results and discussion
The LEED patten of 0.5 ML Co on Si(111) surface√ 7×7 and√ is presented in Fig. 1. Besides 1×1,
7 patterns, one can ﬁnd the spots of 13 derived
structure, which are the same as those in the published results(4). It should be mentioned here thatthese additional spots were
√ formerly attributed to
two types of domains with 13 phase by Dolbak et al(4), which were deﬁned as A and B domains in theirpaper. The two kinds of domains are separated withrespect to Si (11̄0) mirror-image
symmetry plane√
and they widely exist in n structures such as Ni2— 154 —

ture in Fig. 3 (a) and magniﬁed in Fig. 3 (b) has notbeen observed before. In order to know the structural property, we have analyzed the occupied-state
STM image carefully. It is found that the unit cellsize is around 1.38 nm and the unit cell is rotatedby an angle of 13.9◦ in clockwise direction relative
to [112̄] direction (illustrated√ in Fig. 3 (e)) indicating the same periodicity of 13√ in this new surface
phase. To distinguish with α- 13 phase, this newphase is denoted as β phase with A type domain.
The fast Fourier transformation (FFT) images ofFigs. 3 (a) and (b) using WSXM software(10) are
shown in Figs. 3 (c)√and (d), respectively. The sharp
FFT patterns of 13 surface phases can be seen
well (11), and both of them show the same orientation, which together with their corresponding
STM images √gives the strong evidences of the two
inequivalent 13 surface phases.
√
It has been mentioned above that most n surface
phases on Si (111) surface have two domains with a
misﬁt angle owing to Si (11̄0) mirror-image symmetry planes shown in LEED pattern. For easily understood the diﬀerent domains the schematic diagramsof the relationship of√the diﬀerent
domains (here, A√
and B domains) for 13 and 7 reconstructions areshown in Figs. 3 (e) and (f). So, √it is reasonable toobserve both domains of the two 13 phases on thesurface (not shown here). It should be mentionedthat both α and β phases seem
√ islands with√ to form
one domain, which is not like 7 and 19 structuresthat form twined structures with defects. The defect structures will restrain themselves from forming
large islands. This feature
indicates that the defect√
free, single-domain 13 island-like structures may
be one kind of early-stage formation of Co silicide
islands on Si (111) surface.
From this point of view,√the investigation of 13 structures will help us tounderstand the early stage of Co silicide formations.
√
In order to study the detailed structures of 13
surface phases, high-resolution STM observations
have been performed. The empty- and occupied√state STM images of α- (upper) and β- (lower) 13
phases are presented in Fig. 4 with the unit cell indicatedin the ﬁgures. The prominent feature of both√
13 surface phases is the centered hexagonal arrayof threefold symmetric protrusions as is evident in
Fig. 4. Note that the α phase seems to comprise twolayers of triangular clusters on the top and anothertriangle with six protrusions below them as shownin the occupied-state STM image (Fig. 4 (b)). Bothof them just occupies half of the unit cell (here after as HUC), the other half is a dark hole at nega-√
Fig. 3. (a) Occupied-state√ STM images of α- 13 phase with
A type domain and β- 13 phase with both√A and B domains(80 nm×80 nm). (b) Close-up view of β- 13 phase with B
type domain (35.5nm×18nm, V S = -2.1 V, I S = 0.3 nA). (c)FFTpattern of Fig. (a). (d) FFT pattern of Fig. 3 (b) (The√7 FFT spot is marked with an arrowhead (11)). Schematic
diagramsof the relationshipsof two (A and B) domains for√√(e) 13 and (f) 7 surface phases.

in Fig. 2 (d). It is a little higher than the former
type. The edges of both two types of islands arealigned parallel to those of the 7×7 unit cell, andthe lengths are integer times as large as that of 7×7
unit cell as have been discussed elsewhere(8). Due tothe small percentage of island relative to the wholesurface, the structures of the island surface did not
reﬂect clear corresponding spots in LEED pattern.
It means that the surface structures shown in LEED
pattern mainly come from the contribution of interisland.
In the√ inter-island
regions, besides 7×7, Co√
induced 7 and 19 phases, one can ﬁnd irregular
ﬂat areas with a height of about 0.3 nm (some typical regions were marked by black arrowheads in
Fig. 2 (a)). More details of the occupied-state STM
images in this region are shown in Figs. 3 (a) and(b). Here,√two diﬀerent structures are found. One
shows a 13 surface phase, which has been observed by Löﬄer et al (5) (denoted as α phase with
A type domain). It is found that the length of unit
cell is 1.38 nm and its orientation is rotated by anangle of 13.9◦ relative to [112̄] direction in clockwise
direction as illustrated in Fig. 3 (e). Another struc3— 155 —

4. Conclusion
In summary, self-assembled Co silicide have been
fabricated on Si(111) and investigated by meansof scanning tunneling microscopy (STM) and lowenergy diﬀraction (LEED).
√ The LEED pattern has
veriﬁed the existence of 13 phases on Si(111) surface. Our high resolution STM images show that besides√the Co silicide island, there are two inequivalent 13 surface phases in the inter-island regions.
Both of the two phases seem to form islands withsingle domain. From this point of view, the new ﬁndings will help us to understand the early stage of Co
silicide formations.
This work was supported by the Ministry of Education, Culture, Sports, Sciences and Technology.
References

Fig. 4. High-resolution empty-(left) and occupied-(right)√
state STM images of α- (up case) and β- (lower case) 13
phases (10 nm×10 nm) V S = ±1.5 V, I S = 0.3 nA for (a)and (b); V S = ±2.0 V, I S = 0.8 nA for (c) and (d). The
crossehairs are located in identical positions in both of theoccupied- and empty-state images.

[1]

C. Pirri, J. C. Peruchetti, G. Gewinner and J.
Derrien, Phys. Rev. B 29 (1984) 3391; B 30
(1984) 6227.
[2] P. A. Bennett, M. Copel, D. Cahill, J. Falta andR. M. Tromp, Phys. Rev. lett. 69 (1992) 1224.
[3] M. -H. Tsai, J. D. Dow, P. A. Bennett, D. G.
Cahill, Phys. Rev. B 48 (1993) 2486.
[4] A. E. Dolbak, B. Z. Olshanetsky, S. A. Teys,
Surf. Sci. 373 (1997) 43.
[5] M. Löﬄer, J. Cordón, M. Weinelt, J. E. Ortega,
T. Fauster, Appl. Phys. A 81 (2005) 1651.
[6] G. Kinoda, K. Ogawa, Surf. Sci. 461 (2000) 67.
[7] Xiao Tong, Satoru Ohuchi, Norio Sato, Takehiro Tanikawa, Tadaaki Nagao, Iwao Matsuda,
Yoshinobu Aoyagi, and Shuji Hasegawa, Phys.
Rev. B 64 (2001) 205316[8] P. A. Bennett, S. A. Parikh, D. G. Cahill, J.
Vac. Sci. Technol. A 11 (1993) 1680.
[9] M. A. K. Zilani, Lei Liu, H. Xu, Y. P. Feng, X.
-S. Wang and A. T. S. Wee, J. Phys.: Condens.
Matter 18 (2006) 6987
[10] I. Horcas, R. Fermández, J. M. GómezRodrı́guez, J. Colchero, J. Gómez-Herrero, A.
M. Baro, Rev. Sci. Instrum. 78 √(2007) 013705.
[11] One can see a large number of 7 reconstructions from the STM images (See Figs.
√3 (a) and(b)). Since there are many defects in 7 phases,√
one can not get very sharp FFT spots with 7
structure. The irregular lattices just contributeto a dark background as shown in Figs. 3 (c)and (d).

tive sample bias( shown in Fig. 4 (b)). For the lower
layer, at a negative sample bias, the triangle with
six protrusions and the other dark HUC can be observed, while at positive sample bias the dark HUC
becomes brighter and the number of protrusions is
reduced to three at the corner with a dark hole inthe center. For the upper layer, it is noticed that thebright triangle always occupies the same HUC – on
the top of six-protrusion triangle in occupied-states– and the positions of the bright triangle are notchanged at various sample bias, which means thatthe protrusions of the bright triangle give the sites
information of real atoms.
The expanded high-resolution β phase images
show four protrusions (tetramers) and a dark HUC
in both empty- and occupied-states. In contrast to
the α phase, the β phase exhibits a little diﬀerence inspatial distribution between empty- and occupiedstate, except the protrusions in occupied-state STM
images seem fatter than that in empty-state STM
images. It should be mentioned that we still can notgive the√information of Co atoms contribution in αand β- 13 surface phases just from STM image.
For more information, deeper investigation and a
atomic structural model need to be made and some
calculated results should be helpful.
4— 156 —

RT-STM

Graphene epitaxially grown on the step with unit-cell height of
4H-SiC(0001) substrate
M. Ye 1, Y. T. Cui2, S. Qiao3, A. Kimura1, M. Sawada2, H. Namatame2, M. Taniguchi1, 2
1

Grad. Sch. Sci., Hiroshima Univ.
2
HSRC, Hiroshima Univ.
3
Laboratory of advanced materials, epartment of physics, and urface physics Laboratory,
Fudan Univ.
As a novel member of carbon-based materials, graphene holds promising potential for the
next-geneation nano-devices[1]. Epecially, graphene nano-ribbons (GNRs) are highly expected
for the novel spintronics[2].
Being the substrate that allows epitaxial
growth of high quality graphene film [3]and the self-assembling of periodicallyordered one-dimensional system, vicinal
surface of SiC(0001) has been chosen to
epitaxially grow GNRs films in ourpresent research.
4H-SiC(0001) with off-axis angle of 4°
towards [1,-1,0,0] has been annealed inultra-high vacuum (UHV) above 1100°C.
The surface is characterized by scanningtunneling microscopy (STM) and low
energy electron diffraction (LEED) afterFig.1 STM image of graphene on the stepped surface ofeach different annealing temperature.
SiC(0001), 13nm13nm. Sample bias voltage: -0.5V,
The result shows that, prior to the tunneling current 0.18nA. Region G (inside of the brokenline): graphene phase on the step Region I and I’:
thermal decomposition of SiC(0001), theC-rich phase.
height of the micro-steps on the vicinal
surface bunched from single atomic layer height to one unit-cell height of 4H-SiC(0001) after
being annealed at 950°C. After the decomposition started at 1130°C, the vicinal surface wasgraphitized from the edge of the bunched steps (Fig. 1), forming well separated narrowgraphene domains, which indicated a growth mode that Si atoms diffused into the vacuum
through the step edges, and the carbon atoms that remained on the steps formed graphene
phase from the edge regions through the surface reconstruction.
Reference:[1]. K. S. Novoselov, et al., Nature 438, 197 (2005)[3]. C. Berger, et al., J. Phys. Chem. B 108, 19912[2]. Y. W. Son, et al., Nature 444, 347 (2006).

(2004).

— 157 —

Appendices

Organization		Adviser		

Steering Committee		

Faculty Meeting		

Advisory Committee					Program Advisory
Evaluations Committee			Basic Science Division

Director		

SR Light Source Division			

SR Instrumentation Division			

Visiting Professors

			

Cooperative Research Staffs (Faculty Members)			

Visiting Scientists (University, Industry)		Administration Department

Fig. 1. Organization chart of HSRC

Director
TANIGUCHI, Masaki

Hiroshima Synchrotron Radiation Center, HSRC,
Graduate School of Science, Hiroshima University

Adviser
OHTA, Toshiaki
SATO, Shigeru
IWAMI, Motohiro

Ritsumeikan University Emeritus Professor, University of Tokyo
Emeritus Professor, Tohoku University
Emeritus Professor, Okayama University— 161 —

Staff Members
TANIGUCHI, Masaki
NAMATAME, Hirofumi
HORI, Toshitada
SHIMADA, Kenya
SATO, Hitoshi
KUTLUK, Galif
SAWADA, Masahiro
NAKATAKE, Masashi
MIYAMOTO, Atsushi
GOTO, Kiminori
ARITA, Masashi
KASUGA, Toshio
TSUTSUI, Hiroshi
MIZOKAWA, Takashi
NEGISHI, SaikoHE, Shaolong
HONG, Cai Hau
MORIMOTO, Osamu
CUI, Yitao
MATSUO, Koichi
KANEKO, Miyoko
SHINNO, Naoko
SHIMOKUBO, Harumi

Director, Prof.
Co-director, Prof.
Prof.
Assoc. Prof.
Assoc. Prof.
Visiting Assoc. Prof.
Assist. Prof.
Assist. Prof.
Assist. Prof.
EngineerEngineer
Visiting Prof.
Visiting Assoc. Prof.
Visiting Assoc. Prof.
Pos. Doc. Fellow
Pos. Doc. Fellow
Pos. Doc. Fellow
Pos. Doc. Fellow
Pos. Doc. Fellow
Pos. Doc. Fellow, Japan Society for the Promotion of Science
Technical Staff
Secretary
Secretary

Steering Committee
TANIGUCHI, Masaki*
NAMATAME, Hirofumi
HORI, Toshitada
SHIMADA, Kenya
SATO, Hitoshi
INUI, Masanori
MARUYAMA, Hiroshi
KIKKAWA, Takamaro
HARIMA, Yutaka
UENO, Satoshi
HOSHI, Seiji*Chair Person

HSRC
HSRC
HSRC
HSRC
HSRC
Graduate School of Integrated Arts and Sciences
Graduate School of Science
Research Center for Nanodevices and Systems
Graduate School of Engineering
Graduate School of Biosphere Science
Research Institute for Radiation Biology and Medicine— 162 —

Advisory Committee
TANIGUCHI, Masaki*
NAMATAME, Hirofumi
HORI, Toshitada
SHIMADA, Kenya
SATO, Hitoshi
MARUYAMA, Hiroshi
KUROIWA, Yoshihiro
TANAKA, Kenichiro
HIRAYA, Atsunari
HAYAKAWA, Shinjiro
FUJIMORI, Atsushi
SODA, Kazuo
ISHII, Hiroyoshi
SAITOH, Tomohiko
YOKOYA, Takayoshi
KASUGA, Toshio
AIURA, Yoshihiro*Chair Person

HSRC
HRSC
HSRC
HSRC
HSRC
Graduate School of Science
Graduate School of Science
Graduate School of Science
Graduate School of Science
Graduate School of Engineering
University of Tokyo
Nagoya University
Tokyo Metropolitan University
Tokyo University of Science
Okayama University
High Energy Accelerator Research Organization
Advanced Industrial Science and Technology

Program Advisory Committee
NAMATAME, Hirofumi*
HORI, Toshitada
SHIMADA, Kenya
SATO, Hitoshi
SAWADA, Masahiro
NAKATAKE, Masashi
MIYAMOTO, Atsushi
ARITA, Masashi
KUTLUK, Galif
MATSUO, Koichi
KIMURA, Akio
YOSHIDA, Hiroaki
WADA, Shin-ichi
HAYAKAWA, Shinjiro*Chair Person

HSRC
HSRC
HSRC
HSRC
HSRC
HSRC
HSRC
HSRC
HSRC
HSRC
Graduate School of Science
Graduate School of Science
Graduate School of Science
Graduate School of Engineering— 163 —

Evaluations Committee
HORI, Toshitada*
NAMATAME, Hirofumi
SHIMADA, Kenya
SATO, Hitoshi
MARUYAMA, Hiroshi
TSUTSUI, Hiroshi
NAKA, Yoshio
KANDA, Michiaki*Chair Person

HSRC
HSRC
HSRC
HSRC
Graduate School of Science
Sumitomo Heavy Industries, Ltd.
Academic Affairs Office
Academic Affairs Office

Cooperative Research Staffs (Faculty Members)
HOSHINO, Kozo
KOJIMA, Kenichi
INUI, Masanori
TANAKA, Kenichiro
HIRAYA, Atsunari
MARUYAMA, Hiroshi
KUROIWA, Yoshihiro
TABAYASHI, Kiyohiko
SEKITANI, Tetsuji
KIMURA, Akio
OKADA, Masakazu
NAKAJIMA, Nobuo
TAKAHASHI, Yoshio
YOSHIDA, Hiroaki
WADA, Shin-ichi
ISHIMATSU, Naoki
MORIYOSHI, Chikako
INO, Akihiro
TAKAHAGI, Takayuki
TAKABATAKE, Toshiro
JO, Takeo
MIYAZAKI, Seiichi
OGUCHI, Tamio
TAKAHASHI, Toru
IGA, Toshifumi
TANAKA, Arata

Faculty of Integrated Arts and Sciences
Faculty of Integrated Arts and Sciences
Faculty of Integrated Arts and Sciences
Graduate School of Science
Graduate School of Science
Graduate School of Science
Graduate School of Science
Graduate School of Science
Graduate School of Science
Graduate School of Science
Graduate School of Science
Graduate School of Science
Graduate School of Science
Graduate School of Science
Graduate School of Science
Graduate School of Science
Graduate School of Science
Graduate School of Science
Graduate School of Advanced Sciences of Matter
Graduate School of Advanced Sciences of Matter
Graduate School of Advanced Sciences of Matter
Graduate School of Advanced Sciences of Matter
Graduate School of Advanced Sciences of Matter
Graduate School of Advanced Sciences of Matter
Graduate School of Advanced Sciences of Matter
Graduate School of Advanced Sciences of Matter— 164 —

YAMANAKA, Shoji
HIROKAWA, Takeshi
SHIZUMA, Kiyoshi
SASAKI, Gen
HAYAKAWA, Shinjiro
SATO, Kiyotaka
UENO, Satoshi
HOSHI, Seiji
KAMIYA, Kenji
YOKOYAMA, Shin

Graduate School of Engineering
Graduate School of Engineering
Graduate School of Engineering
Graduate School of Engineering
Graduate School of Engineering
Faculty of Applied Biological Science
Faculty of Applied Biological Science
Research Institute for Radiation Biology and Medicine
Research Institute for Radiation Biology and Medicine
Research Center for Nanodevices and System

Visiting Scientists
SUMIDA, Hirosuke
MIYADE, Hiroki
SENBA, Shinya
YAMAMOTO, Yasukazu
YOKOYA, Takayoshi
HIRAI, Masaaki
MURAOKA, Yuji
YAGI, Shinya
AOKI, Kenichi
AIURA, Yoshihiro
SASABE, Jun
OBA, Akira
SATOZONO, Hiroshi
SHAN, Qiao
DONGLAI, Feng

Technical Research Center, Mazda Motor Co.
Sumitomo Heavy Industries, Ltd.
Ube National College of Technology
Ritsumeikan University SR Center
Graduate School of Nature Science and Technology, Okayama University
Graduate School of Nature Science and Technology, Okayama University
Graduate School of Nature Science and Technology, Okayama University
Graduate School of Engineering, Nagoya University
Sumitomo Heavy Industries, Ltd.
Advanced Industrial Science and Technology
Hamamatsu Photonics Central Research Laboratory
Hamamatsu Photonics Central Research Laboratory
Hamamatsu Photonics Central Research Laboratory
Loawrence Berkeley National Laboratory, USA
Fudan University, China— 165 —

List of Publications
S. He, M. Arita, H. Namatame, M. Taniguchi, H.‑N. Li, H.‑Y. Li

Angle-dependent oscillations in valence-band photoemission intensity of C-60
JOURNAL OF PHYSICS-CONDENSED MATTAB 19(2) 26202 (2007)

S. Nagaoka, G. Prumper, H. Fukuzawa, M. Hino, M. Takemoto, Y. Tamenori, J. Harries, I.H. Suzuki,
O. Takahashi, K. Okada, K. Tabayashi, X.‑J. Liu, T. Lischke, K. Ueda

Electron-ion-ion triple-coincidence spectroscopic study of site-specific fragmentation caused by Si :2p core-level photoionization of F3SiCH2CH2Si(CH3)3 vapor

PHYSICAL REVIEW A 75(2) 020502 (2007)

J. Chaboy, Laguna-MA. Marco, C. Piquer, H. Maruyama, N. Kawamura, N. Ishimatsu, M. Suzuki,
M. Takagaki
Relationship between the magnetic moment of Lu and the magnetic behavior of (YyLu1–y)(Co1–xAlx)2
from x-ray absorption spectroscopy and x-ray magnetic circular dichroism
PHYSICAL REVIEW B 75(6) 064410 (2007)

J.F. Douglas, H. Iwasawa, Z. Sun, A.V. Fedorov, M. Ishikado, T. Saitoh, H. Eisaki, H. Bando,
T. Iwase, A. Ino, M. Arita, K. Shimada, H. Namatame, M. Taniguchi, T. Masui, S. Tajima, K. Fujita,
S.‑I. Uchida, Y. Aiura, D.S. Dessau
Superconductors - Unusual oxygen isotope effects in cuprates?
NATURE 446 E5 (2007)

B.‑P. Xie, K. Yang, D.‑W. Shen, J.F. Zhao, H.‑W. Ou, J. Wei, S.Y. Gu, M. Arita, S. Qiao, H. Namatame,
M. Taniguchi, N. Kaneko, H. Eisaki, K.‑D. Tsuei, C.‑M. Cheng, I. Vobornik, J. Fujii, G. Rossi,
Z.‑Q. Yang, D.‑L. Feng
High-energy scale revival and giant kink in the dispersion of a cuprate superconductor
PHYSICAL REVIEW LETTERS 98(14) 147001 (2007)

T. Yamasaki, K. Yamazaki, A. Ino, M. Arita, H. Namatame, M. Taniguchi, A. Fujimori, Z.‑X. Shen,
M. Ishikado, S. Uchida
Unmasking the nodal quasiparticle dynamics in cuprate superconductors using low-energy
photoemission
PHYSICAL REVIEW B 75(14) 140513 (2007)

J. Chaboy, M.A. Laguna-Marco, H. Maruyama, N. Ishimatsu, Y. Isohama, N. Kawamura

X-ray magnetic circular dichroism study of the decoupling of the magnetic ordering of the Er andCo sublattices in Er1–xYxCo2 systems

PHYSICAL REVIEW B 75(14) 144405 (2007)

O. Takahashi, T. Matsui, A. Kawano, K. Tabayashi, K. Yamasaki
Systematics of the gradient on the resonant core-hole state

JOURNAL OF MOLECULAR STRUCTURE-THEOCHEM 808 35–40 (2007)— 166 —

K. Matsuo, Y. Sakurada, R. Yonehara, M. Kataoka, K. Gekko

Secondary-structure analysis of denatured proteins by vacuum-ultraviolet circular dichroism
spectroscopy
BIOPHYSICAL JOURNAL 92(11) 4088–4096 (2007)

K. Mimura, M. Arita, K. Wakita, N. Mamedov, G. Orudzhev, Y. Taguchi, K. Ichikawa, H. Namatame
Angle-resolved photoemission study of quasi-one-dimensional TIInSe2

JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA 156–158 379–
382 (2007)
K. Yoshikawa, H. Sato, M. Arita, M. Higashi, K. Hiraoka, K. Kojima, H. Namatame, M. Taniguchi
Low-energy excited photoemission spectroscopy of YxYb1–xInCu4

JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA 156–158 361–364(2007)
H. Sato, K. Tsuji, K. Yoshikawa, Y. Tezuka, S. Nishimoto, M. Higashi, F. Iga, M. Tsubota,
M. Takemura, T. Takabatake, M. TaniguchiTi 2p soft X-ray emission spectroscopy of Ti2O3

JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA 156–158 365–368 (2007)
S. Hosokawa, H. Sato, K. Mimura, N. Happo, Y. Tezuka, T. Ichitsubo, E. Matsubara, N. Nishiyama
Soft X-ray emission study of Pd-Ni-Cu-P bulk metallic glass

JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA 156–158 426–
429 (2007)
N. Ishimatsu, S. Miyamoto, H. Maruyama, J. Chaboy, M.A. Laguna-Marco, N. Kawamura

Experimental evidence of pressure-induced suppression of the cobalt magnetic moment in ErCo2
PHYSICAL REVIEW B 75(18) 180402 (2007)

M. Arita, H. Sato, M. Higashi, K. Yoshikawa, K. Shimada, M. Nakatake, Y. Ueda, H. Namatame,
M. Taniguchi, M. Tsubota, F. Iga, T. Takabatake
Unoccupied electronic structure of Y1–xCa xTiO3 investigated by inverse photoemission spectroscopy

PHYSICAL REVIEW B 75(20) 205124 (2007)

S. Hosokawa, H. Sato, N. Happo, K. Mimura, Y. Tezuka, T. Ichitsubo, E. Matsubara, N. Nishiyama

Electronic structure of N42.5N7.5Cu30P20, an excellent bulk metallic glass former: Comparison to the
Pd40Ni40P20 reference glass

ACTA MATERIALIA 55(10) 3413–3419 (2007)

N. Ishimatsu, H. Maruyama, N. Kawamura, M. Suzuki, Y. Ohishi, O. Shimomura
Stability of ferromagnetism in Fe, Co, and Ni metals under high pressure

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 76(6) 64703 (2007)— 167 —

S. Kaneyoshi, H. Iwasawa, T. Saitoh, Y. Aiura, D. Satoh, T. Katsufuji, I. Hase, M. Higashiguchi,
K. Shimada, H. Namatame, M. Taniguchi, M. Kubota, K. Ono

Independent control of charge and spin density in Sr1–(x+y)La x+yTi1–xCrxO3 probed by photoemission
spectroscopy
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 310(2) Part 2 E278–E280 (2007)

T. Saitoh, D. Ishii, A. Hachimura, M. Hirose, TS. Naing, Y. Kobayashi, K. Asai, M. Nakatake,
M. Higashiguchi, K. Shimada, H. Naniataine, M. Taniguchi
Electronic structure of La1–xPrxCoO3 and NdCoO3 studied by photoemission spectroscopy

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 310(2) Part 2 981–983 (2007)
K. Terai, K. Yoshii, Y. Takeda, S. Fujimori, Y. Saitoh, K. Ohwada, T. Inami, T. Okane, M. Arita,
K. Shimada, H. Namatame, M. Taniguchi, K. Kobayashi, M. Kobayashi, A. Fujimori
Electronic structure and magnetism of CaMn1–xRuxO3 thin films

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 310(2) Part 2 1070–1072 (2007)

Y. Miura, K. Shimada, M. Hoesch, M. Higashiguchi, N. Tobita, XY. Cui, Y. Aiura, H. Namatame,
M. Taniguchi
High-resolution angle-resolved photoemission study of the spin-polarized Fermi surface of Ni(100)JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 310(2) Part 2 1082–1083 (2007)

XY. Cui, K. Shimada, M. Hoeschc, Y. Sakisaka, H. Kato, Y. Aiura, S. Negishi, M. Higashiguchi,
Y. Miura, H. Namatame, M. Taniguchi
High-resolution angle-resolved photoemission spectroscopy of iron: A study of the self-energy

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 310(2) Part 2 1617–1619 (2007)
N. Tobita, K. Emi, N. Nakajima, H. Maruyama, Y. Miura, M. Higashiguchi, K. Shimada,H. Namatame, M. Taniguchi
Valence-band photoemission spectroscopy of a single-crystal FePt3

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 310(2) Part 2 1642–1644 (2007)
K. Shimada, M. Higashiguchi, M. Arita, H. Namatame, M. Taniguchi, S. Fujimori, Y. Saitoh,
A. Fujimori, Y. Takata, S. Shin, K. Kobayashi, E. Ikenaga, M. Yabashi, K. Tamasaku, Y. Nishino,
D. Miwa, T. Ishikawa, T. Sasakawa, T. Takabatake
High-resolution photoemission study of the hybridization gap in the Kondo semiconductor CeRhAs
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 310(2) Part 1 E57–E58 (2007)

M. Higashiguchi, K. Shimada, M. Arita, Y. Miura, N. Tobita, XY. Cui, Y. Aiura, H. Namatame,
M. Taniguchi
High-resolution photoemission study of electron-electron interaction in the Ni(111) surface state

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 310(2) Part 3 E743–E744 (2007)— 168 —

M. Arita, H. Sato, M. Higashi, K. Yoshikawa, K. Shimada, M. Sawada, Y. Ueda, H. Namatame,
M. Taniguchi, SI. Fujiomori, Y. Saitoh, M. Tsubota, F. Iga, T. Takabatake
X-ray absorption and inverse photoemission study of Y1–xCa xTiO3JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 76(7) 74720 (2007)

H. Kato, S. Takemura, Y. Watanabe, A. Ishii, I. Tsuchida, Y. Akai, T. Sugiyama, T. Hiramatsu,
N. Nanba, O. Nishikawa, M. Taniguchi
X-ray photoemission spectroscopy and Fourier transform infrared studies of electrochemical dopingof copper phthalocyanine molecule in conducting polymer
JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A 25(4) 1147–1151 (2007)
H. Narita, A. Kimura, M. Taniguchi, M. Nakatake, T. Xie, S. Qiao, H. Namatame

Intermediate surface structure of Al nanoclusters restricted to Si(111) half-unit cells observed via
scanning tunneling microscopy
PHYSICAL REVIEW B 76(11) 115405 (2007)

A. Kimura, S. Asanao, T. Kambe, T. Xie, S. Watanabe, M. Taniguchi, S. Qiao, E. Hashimoto,
H. Namatame, T. Muro, S. Imada, S. Suga
Electron correlation and magnetic properties of c(2×2)CuMn/Cu(001) two-dimensional surface
alloysPHYSICAL REVIEW B 76(11) 115416 (2007)

T. Hirahara, K. Miyamoto, I. Matsuda, T. Kadono, A. Kimura, T. Nagao, G. Bihlmayer, E.V. Chulkov,
S. Qiao, K. Shimada, H. Namatame, M. Taniguchi, S. Hasegawa
Direct Observation of Spin Splitting in Bismuth Surface States
PHYSICAL REVIEW B 76, 153305 (2007)

SI. Fujimori, Y. Saitoh, T. Okane, H. Yamagami, A. Fujimori, K. Shimada, H. Namatame,
M. Taniguchi, H. Shishido, D. Aoki, S. Ikeda, Y. Haga, E. Yamamoto, Y. Onuki
Photoemission study on heavy fermion superconductors

PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 460 Part 1 657–658 (2007)
JF. Zhao, HW. Ou, G. Wu, BP. Xie, Y. Zhang, DW. Shen, J. Wei, LX. Yang, JK. Dong, M. Arita,
H. Namatame, M. Taniguchi, XH. Chen, DL. Feng
Evolution of the electronic structure of 1T-Cu xTiSe2

PHYSICAL REVIEW LETTERS 99(14) 146401 (2007)
S. He, M. Nakatake, M. Arita, X. Cui, S. Qiao, H. Namatame, M. Taniguchi, H. Li, H. Li

Temperature-dependent photoemission spectroscopy study of RExC60 (RE=Yb and Sm) films
APPLIED PHYSICS LETTERS 91(14) 143103 (2007)— 169 —

H. Iwasawa, Y. Aiura, T. Saitoh, H. Eisaki, H. Bando, A. Ino, M. Arita, K. Shimada, H. Namatame,
M. Taniguchi, T. Masui, S. Tajima, M. Ishikado, K. Fujita, S. Uchida, JF. Douglas, Z. Sun, DS. Dessau
A re-examination of the oxygen isotope effect in ARPES spectra of Bi2212

PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 463–465 52–55 (2007)
T. Nomoto, K. Miura, S. Yagi, G. Kutluk, H. Sumida, K. Soda, E. Hashimoto, H. Namatame,
M. Taniguchi
Spectroscopic study on thermal reaction and desorption of sulfur/Rh(100) induced by oxygencontaining molecules
SURFACE SCIENCE 601(18) 3784–3787 (2007)

S. Wada, M. Takigawa, K. Matsushita, H. Kizaki, K. Tanaka

Adsorption and structure of methyl mercaptoacetate on Cu(111) surface by XPS and NEXAFS
spectroscopy
SURFACE SCIENCE 601(18) 3833–3837 (2007)

T. Ashida, K. Miura, T. Nomoto, S. Yagi, H. Sumida, G. Kutluk, K. Soda, H. Namatame, M. Taniguchi
Synthesis and characterization of Rh(PVP) nanoparticles studied by XPS and NEXAFSSURFACE SCIENCE 601(18) 3898–3901 (2007)

H. Kizaki, Y. Matsumoto, H. Ban, K. Morishita, SI. Wada, K. Tanaka

Configuration dependence of photon stimulated ion desorption from methyl ester compounds
induced by core excitation
SURFACE SCIENCE 601(18) 3956–3960 (2007)

M. Higashiguchi, K. Shimada, M. Arita, Y. Miura, N. Tobita, X. Cui, Y. Aiura, H. Namatame,
M. Taniguchi
High-resolution angle-resolved photoemission study of Ni(111) surface state

SURFACE SCIENCE 601(18) 4005–4009 (2007)

XY. Cui, K. Shimada, M. Hoesch, Y. Sakisaka, H. Kato, Y. Aiura, M. Higashiguchi, Y. Miura,
H. Namatame, M. Taniguchi
Angle-resolved photoemission spectroscopy study of Fe(110) single crystal: Many-body interactions
between quasi-particles at the Fermi level
SURFACE SCIENCE 601(18) 4010–4012 (2007)

M. Nagira, M. Sawada, M. Higashiguchi, K. Yaji, T. Mao, T. Ueno, U. Miura, K. Shimada, A. Kimura,
H. Namatame, M. Taniguchi
Surface quantum well state at the striped Cu(110)(2×1)O surface studied by angle resolved
photoemission spectroscopy
SURFACE SCIENCE 601(18) 4041–4044 (2007)— 170 —

S. Yagi, Y. Matsumura, T. Nomoto, K. Soda, E. Hashimoto, H. Namatame, M. Taniguchi

Liquid-solid interface of L-cysteine/TM (TM = Ni and Cu) in aqueous solution by means of sulfur
K-edge NEXAFSSURFACE SCIENCE 601(18) 4154–4157 (2007)

M. Kotsugi, FZ. Guo, M. Taniguchi, N. Ishimatsu, H. Maruyama

Easy-axis rotation in meteoritic iron probed by photoelectron emission microscope (PEEM)
SURFACE SCIENCE 601(18) 4326–4328 (2007)

T. Kinoshita, E. Ikenaga, J. Kim, S. Ueda, M. Kobata, JR. Harries, K. Shimada, A. Ino, K. Tamasaku,
Y. Nishino, T. Ishikawa, K. Kobayashi, W. Drube, C. Kunz
How is it possible to obtain buried interface information through very thick films using a hard-X-ray
PEEM?
SURFACE SCIENCE 601(20) 4754–4757 (2007)

M. Kotsugi, T. Wakita, N. Kawamura, T. Taniuchi, K. Ono, M. Suzuki, M. Oshima, N. Ishimatsu,
M. Taniguchi, H. Maruyama
Application of photoelectron emission microscopy (PEEM) to extraterrestrial materials
SURFACE SCIENCE 601(20) 4764—4767 (2007)

M. Nagira, M. Sawada, M. Higashiguchi, K. Yaji, T. Moko, T. Ueno, Y. Miura, K. Shimada,A. Kimura, H. Namatame, M. Taniguchi

Temperature dependent quantum well state on Cu(110)(2×1)O striped surface studied by angle
resolved photoelectron spectroscopy
SURFACE SCIENCE 601(22), 5254–5257 (2007)

K. Shimada, Edited by S. Huefner

High-resolution Photoemission Spectroscopy of Solids Using Synchrotron Radiation, in Very High
Resolution Photoelectron Spectroscopy
Lecture Notes in Physics 715, Chap. 4, pp. 85-112. (Springer-Verlag, Belin-Heidelberg, 2007)— 171 —

Symposium
The 12th Hiroshima International Symposium on Synchrotron Radiation
March 13–14, 2007

— 172 —

liq H2

Preparation Laboratory— 173 —
2

1

oﬃce oﬃce

ユーザー室

BL5

HelicalUndulator

BL14

BL15

BL1

LinearUndulator

BL13

Surface
Photochemistry

BL4 BL3

BL9A BL11 BL12User Room

BL6

BL7

BL9A

Experimental Hall

Control RoomMicrotron

Injection Room

Plan of the BuildingLocation

SapporoSendai

Higashi-Hiroshima
HiroshimaTokyo
Kyoto Nagoya

Osaka

Fukuoka

Hiroshima

Nishi-Takaya
Hachihonmatsu
Shiraichi
SaijyoSanyo-Shinkansen
Osaka

Higashi-Hiroshima Station

Hiroshima University
SaijyoLetters

Hiroshima

0

2

4

6

8 km

Law Science
Economics

Education

Hiroshima Synchrotron Radiation Center
Engineering
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Hiroshima Synchrotron Radiation Center
Hiroshima University
2-313 Kagamiyama,
Higashi-Hiroshima 739-0046
TEL+81-82-424-6293
FAX+81-82-424-6294
URL
http://www.hsrc.hiroshima-u.ac.jp/— 174 —