BL1A, BL8B1

Electronic Structure Change of LiNi1/2Mn1/2O2 Cathode Materials for
Lithium-Ion Secondary Batteries from Metal L-Edge and Oxygen K-Edge
Spectroscopy
Y. Arachi1, H. Kobayashi2, H. Maeda1, T. Asai1
Faculty of Engineering, Kansai University, Osaka 564-8680, Japan
2
Research Institute for Ubiquitous Energy Devices, AIST, Ikeda, Osaka, 563-8577 Japan1

lattice parameters are a = 2.8922(0) Å and c =14.31(5) Å and Ni occupancy at Li site, gNi is 0.028.
The chemical composition can be expressed as[Li0.97Ni0.03]3a[Li0.03Ni0.47Ni0.50]3bO2, referring to the
Wyckoff positions 3a and 3b with space group R3m.
The structure depended on the ion-exchange reaction
temperature and time. As increased the reaction
temperature and time, the Li/Ni disorder became
remarkable. The irreversible capacity was improvedby the ion-exchange. Figure 1 shows the selected
XANES spectra of O K-edge for chemically oxidized
Li1-xNi0.5Mn0.5O2. The notation from deLi1 to deLi4
corresponds to the reaction time of 0.1 to 1.0 h atvarious steps.
These peaks indicate transition
metals 4sp. A peak of A slightly shifted towards
lower energy, while maintaining the peak position of
B. As the sample oxidized, the orbital of O 2p
introduced a hole. On the other hands, the results of
Ni L-edge showed a slightly higher shift and that of
Mn L-edges showed no chemical shifts for all thesamples. On the basis of these results, we areconstructing the band structure and investigating thecharging mechanism for this material.

In order to establish the materials design for the
Lithium ion batteries, we have employed the variety
of measurement techniques and specifically,
examined the crystal structure and electronic structureusing X-ray, neutron diffraction and XAFS
measurements. The absorption peaks of transition
metal L2,3 edges can directly obtain the information ofunoccupied 3d states.
Because the quadrupoletransitions from 1s to 3d (K edge) are much weaker
than dipole from 2p to 3d. In addition, O K edge
spectra provide bonding interactions between metaland oxygen due to the overlapping between 3d ofmetal and 2p orbital of oxygen. In our field, thealternatives to conventional LiCoO2 cathode material
have been extensively searched due to small naturaldeposits of Co and its toxicity. LiNi0.5Mn0.5O2 withlayered-NaCl type structure proposed as one of apromising material manifests fascinated charactersuch as a good cycleability and reversible capacity of
150 mAh/g within the voltage range of 3.0 to 4.3 V,
which corresponds to one-half of theoretical capacity(280mAh/g). Recently, we have synthesized thematerial by using ion exchange reaction, whichshowed the suppression of Li/Ni disordering in thelayered structure.
In this study, the electronic
structural changes were observed by XANES spectraof Ni, Mn L-edges and O K-edge respectively and thecharging behavior was examined.
LiNi1/2Mn1/2O2 was prepared by ion exchange
reaction of NaNi1/2Mn1/2O2 as a precoursor. NaNO3
and precipitates of Ni, Mn hydroxides were mixed
and then calcinated at 600°C for 12h. The obtained
powders were pressed and sintered at 900°C for 12h
in air. The ion exchange reaction was carried out in
Li molten salt(LiCl: LiNO3=1:1 (mol), eutectic point= 244°C) at 280-450°C for 0.1 to 10 h. andde-lithiated samples were electrochemically andchemically prepared. The former was used bycoin-type
cells
with
Li/1M
LiPF6
in
EC:DEC(1:1)/samples and the latter was by thechemical oxidants, ammonium persulfate as thefollowing reaction:
S2O82- + 2e-  2 SO42LiNi1/2Mn1/2O2  Li1-x Ni1/2Mn1/2O2 + xLi+ + xe-.
X-ray absorption measurements at the Ni, Mn
L-edges and O K-edge by total electron yield were
performed on BL1A, BL8B1 and occasionally BL4B.
LiNi1/2Mn1/2O2 showed a single phase adopted thea-NaFeO2 structure like as LiCoO2. Neutron
diffraction measurements demonstrated that theFig. 1. O K-edge XANES spectra of chemicallyoxidized Li1-xNi1/2Mn1/2O2.

105

BL1A

Mo LIII-Edge XANES Study of Catalytically Active Mo Sites on
H-MFI for Methane Dehydriaromatization with Hydrogen

H. Aritani1, H. Shibasaki1, N. Naijo1, K. Takanashi1, K. Nagashima1, A. Nakahira2
1
Faculty of Engineering, Saitama Institute of Technology, Fukaya 369-0293, Japan
2
Graduate School of Engineering, Osaka Prefecture University, Sakai 599-8531, Japan
Introduction

wt%

Mo-modified H-MFI catalysts show high activity
for dehydroaromatization of methane in absence ofoxygen. In this reaction, reduction of Mo species isbrought about in contact with methane in initial step,and reduced Mo ions react methane to form carbide
and/or oxycarbide species in next step. It has been
accepted that the carbide and/or oxycarbide species
are the active center for dehydroaromatization of
methane. However, deactivation cannot be avoided
by carbon deposition. Hydrogen co-feed withmethane is effective for suppression of coking. On
the other hand, excess hydrogen may affect a
reduction of Mo species during the reaction, anddecrease of active Mo-oxycarbide species may give
low reactivity. Thus the effect of hydrogen withmethane is very important to give an effect on Mo
states. This study addresses the effects of hydrogenco-feed on methane dehydroaromatization over
Mo/H-MFI catalysts. Mo LIII-edge XANES studies
were introduced to characterize the active Mo species
on
H-MFI
before/afterthemethanedehydroaromatization in the absence/presence ofhydrogen.
Fig. 1. Mo LIII-edge XANES of Mo/H-MFI
before/after methane dehydroaromatization.

Experimental
Catalysts were prepared by impregnation of H-MFI
support with MoO2(acac)2CHCl3 solution, andfollowed by drying overnight and calcination at 773
K. H-MFI supports were synthesized hydrothermallyat 413 K for a week, and followed by ion-exchange
and calcination at 873 K. Mo LIII-edge XANES
spectra were measured in BL1A of UVSOR-IMS in a
total-electron yield mode. Photon energy wascalibrated by using Mo metal-foil at Mo LIII-edge,
and normalized XANES spectra and their second
derivatives were obtained. Catalytic activity wasevaluated in a fixed bed flow reactor. Each catalyst(0.25 g) was placed in a quartz-tube reactor, andpretreated in HeH2(0-1%) flow (30 mL min-1) at 973
K for 1 h. Then CH4(20%)H2(0-3%)He reactant
gas was fed at 973 K (30 mL min-1: SV = 7.2 L g-1
h-1). Products were analyzed by online GC. Amountofcokingcarbonwasevaluatedbythermogravimetry.

Mo-loading on H-MFI (Si/Al2 =72) showed amaximum C6H6 yield under no additives with
CH4(20%) reactant. H2(1%) co-feed with CH4 gave
low deactivation, indicating the suppression of
coking. But excess H2 (in 1.5 %) enhanced thedeactivation. H2 pretreatment brought about low
activity in the initial step. These results suggest thatboth inhibition of excessive Mo reduction andsuppression of coking on H-MFI relate to the highly
catalytic activity for methane dehydroaromatization.
The results of LIII-XANES (Fig. 1) and their 2nd
derivatives suggests the coexistence of Mo2+ andoxidized ions after the reaction with CH4 or
CH4-H2(1%). On the other hand, Mo2+ is dominant
after H2(1%)-He pretreatment. These results indicatethat H2 co-feed with CH4 does not affect the
reduction of active Mo sites, and H2 pretreatment(without CH4) brings about the reduction to form
Mo2+ species in major. And thus, it is concluded that
active Mo species consist of Mo2+-oxycarbide specieson H-MFI support.

Results and Discussion
For the dehydroaromatization in our study, 5.0

106

BL1A

Local Structure Analysis of Composite Oxide Electrodes of Dye-SensitizedSolar Cells by XAFS Method
S. Iwamoto1, Y. Sazanami1, T. Kadata1, H. Ozaki1, W. Hong1, H. Kanai1, M. Inoue1, T. Inoue2,
T. Hoshi2, K. Shigaki2, M. Kaneko2
1
Graduate School of Engineering, Kyoto University, Katsura, Kyoto 615-8510, Japan
2
Nippon Kayaku Co.Ltd., 31-12, Shimo 3-chome, Kita-ku, Tokyo 115-8588, Japan
Dye-sensitized solar cells (DSSCs) attract great
attention because of their high photovoltaic
conversion efficiency, simple fabrication process, andlow material and production costs [1]. In the last two
decades, noticeable improvement in short-current
density (Jsc) and fill factor (ff) has been attained;
however, only a slight increase has beenaccomplished with regard to open-circuit voltage(Voc). In usual DSSCs, titanium oxide andiodide-based solution are used as the electrode andelectrolyte, respectively. As the maximum Voc is
determined by the difference between the Fermi levelof the electrode under illumination and the redox
potential of the electrolyte, using these twocomponents, Voc is definitely limited to ca. 0.9 V.
Recently, we found that a DSSC consisting of a
conjugated acid organic sensitizer and ananocrystalline Mg-containing TiO2 generated quite ahigh Voc of 1 V [2]. In this study, Mg K-edge XANESof various Mg-containing samples were measured toelucidate the local structure of the Mg-modified
titanias.
Mg-modified titanias (Mg(x)-TiO2, where x is
Mg/Ti charged ratio) were prepared by the thermal
reaction of mixtures of titanium tetraisopropoxide andmagnesium acetate tetrahydrate in 1,4-butanediol at
300 ºC (Glycothermal method) [3]. X-ray diffraction(XRD) analysis shows that the obtained products ofx  0.2 were nanocrystals with the anatase structure.
The unit cell parameters of these Mg-modified
titanias were increased with increasing the amount of
the Mg addition, indicating that Mg2+ ions wereincorporated in the anatase structure. In Fig. 1, Mg
K-edge XANES of various samples are shown. The
spectra of Mg-modified TiO2 samples prepared by animpregnation
method(designatedasMg(x)-TiO2(imp)) suggested the presence of MgOphase. On the contrary, the spectra of Mg(x)-TiO2
samples preapered by the glycothermal method show
peaks at 1310 and 1314 eV, which are similar to thatof MgTi2O5, suggesting that of Mg2+ ions areincorporated in octahedral sites in titania matrix. In
the UV-vis absorption spectra of Mg(x)-TiO2, theabsorption edges were gradually shifted to the lower
wavelength side as the amount of Mg modification
increased. This result indicates the shifts of the flatband potentials of the Mg(x)-TiO2, which contributeto the enhancement of the Voc.

Fig. 1. Mg K-edge XANES of various Mg-containing
samples.
[1] M. Grätzel, Nature 414 (2001) 338.
[2] S. Iwamoto et al., ChemSusChem, in press.
[3] M. Inoue, J. Phys.: Condens. Mater 16 (2004)
S1291.

107

BL1A

Local Environment Analysis of Mg Ions in  -Tricalcium Phosphate

1K. Kawabata1, H. Sato1, T. Yamamoto2
Institute for Sports and Health Science, Kwansei Gakuin University, 662-8501 Japan
2
Faculty of Science and Engineering, Waseda University, 169-8555, Japan
Introduction

the first principles calculations must be applied forthe analysis of local environment of other traceelements in the bioceramic materials.

Bioactive ceramic materials, such as hydroxyapatiteand -tricalcium phosphate (-TCP), have been
widely studied and already applied in dentistry andorthopedics to repair bone defects and substitution.
As it is well known that the natural bone contains
many kinds of trace elements, such as Mg, Na, K, Zn,
Fe, Mn etc. To understand the basic properties ofnatural human bone, it is very important to know theeffects of these trace elements. In the present study,
the local environment analysis of Mg ions in -TCP
is carried out by the near-edge X-ray absorption finestructure (NEXAFS) technique, which was
successfully applied for Mn-doped -TCP [1].

Relative intensity (arb. units)(a) MgO

Experiments
-TCP samples
doped
with
Mg
ions,
Ca2.7Mg0.3(PO4)2, are synthesized by the conventional
solid-state reaction method. High purity powders of
CaHPO4, CaCO3 and Mg(OH)2 were mixed andgrinded in an agate mortar for an hour and theresulting powder was calcined in an air at 1273 K for
6 hours. NEXAFS measurements were carried out
at BL1A in UVSOR by the total electron yield
method. Powder samples were put on the carbon
adhesive tape. The incident photon beams weremonochromatized using double-crystal of KTP (110).

(b) Mg(OH) 2(c) -TCP:Mg

1310

1320
Energy (eV)1330

Fig. 1. Observed Mg K-edge NEXAFS spectra of (a)MgO, (b) Mg(OH)2 and (c) Mg doped -TCP.
(b) -TCP:Mg

Relative intensity (arb. units)(a) MgO

Results
Prior to the NEXAFS measurements, the sample
powder was examined by using the X-ray diffraction(XRD) technique, in which no extra diffraction peaks
due to the precipitates was seen in the XRD pattern.
Observed NEXAFS spectrum of Mg-doped -TCP iscompared with those of the reference materials (MgO
and Mg(OH)2) in Fig. 1. Significant difference
between these three NEXAFS spectra were clearly
seen, which indicate the local environment of Mg
ions in these three materials is quite different. The
first principles calculations within the density
functional theory (DFT) were also performed for thetheoretical estimation of the NEXAFS spectra withthe all-electron linearized augmented plane wave
package, WIEN2k [2]. Calculated NEXAFS spectraof Mg-doped -TCP and MgO at Mg K-edge arecompared with the experimental ones in Fig. 2. Good
comparison of NEXAFS spectra between observedand calculated ones can be obtained. From the resultsof the XRD, the NEXAFS and the first principles
calculations, we could conclude that Mg ions in
-TCP are substituted on Ca2+ site in -TCP. This
type of combinational analysis with the NEXAFS and

expt.

expt.

calc.

1310 1320 1330

Energy (eV)calc.

1310 1320 1330

Energy (eV)Fig. 2. Comparison between observed and calculated
NEXAFS spectra at Mg K-edge of (a) MgO and (b)Mg-doped -TCP.
[1] K. Kawabata et al., J. Ceram. Soc. Jpn. 116(2008) 108.
[2] P. Blaha et al., http://www.wien2k.at.

108

BL1A, BL8B1

Study on the Surface Structures of the LiNi0.8Co0.15Al0.05O2
Electrode after the Preservation Tests for Li-Ion Battery Cells (II)H. Kobayashi, M. Shikano, D. Mori
Research Institute for Ubiquitous Energy Devices, AIST, Ikeda, Osaka, 563-8577 Japan
Introduction

power after preservation tests. The relative capacityand power decreased on increasing the test
temperature from 40 ºC to 60 ºC. Figure 1 shows
the Li K-edge XANES spectra of 50% SOC samples
before and after preservation tests. In TEY modeon
the BL8B1, Li K-edge XANES spectra provide
information on the surface structure. The spectrum
measured before preservation tests contained peak A,
corresponding to LiF. After the preservation tests,
the intensity of peak A clearly decreased at 60 ºC
after 96 weeks and the shape of peak A was close tothat of the Li2CO3 spectrum (data not shown).
These results indicate that a part of the layered
structure at the surface of the positive electrode wascovered with Li2CO3 at 60 ºCafter 96 weeks. In
TEY modeon the BL1A, P K-edge XANES spectra
also provide information on the surface structure.
The P K-edge spectrum measured before and after
preservation tests showed the existence of
P-containing surface films(data not shown). The
relationship between power fade and the surface stateof the positive electrode will be studiedin detail.

Several of the requirements of rechargeable
batteries for hybrid electric vehicles (HEVs) are quite
different to those of portable electronic devices. In
particular, high specific power and long calendar life
are very important requirements of HEV applications.
Much effort has been applied to understanding themechanisms that limit the calendar life of high power
Li-ion cells. Until now, although the deteriorationin the power performance of currently available
lithium batteries is thought to result from problems
with the positive electrodes, the mechanism ofdeterioration of the electrodes is still poorly
understood. Detailed information on the changes
taking place in both the cathode and anode is essential
in order to determine the origin of the degradation of
power
performance.
In
thisstudy,
LiNi0.8Co0.15Al0.05O2 positive electrodes from cells
that had undergone power fading throughpreservation tests were examined by XANES analysis
to obtain information on their surfaces.
The
relationship between power fade and the surface stateof the positive electrode was studied.

Table 1. Summary of preservation test results.
Temp.
Preservation
Relative
Relative
PeriodCapacityPower(Weeks)
40C˚
96
0.918
0.868
60C˚
96
0.716
0.571

Experimental
We made 18650-type cylindrical battery cells witha capacity of about 400 mAh, which were designed tohave a rate capability of more than 10 C. The
positive and negative electrode was comprised of
LiNi0.8Co0.15Al0.05O2 and hard carbon, respectively.
Each cell was characterized using the standard battery
test procedure given in the partnership for a newgeneration of vehicles (PNGV) Battery Test Manual.
The changes in both capacity and power werechecked every few weeks. After completion of thedegradation test, the SOC of the cell was adjusted to
50% immediately before disassembling it, since thechemical and physical properties of the active
materials are influenced by the SOC.
After
disassembly of the SOC-adjusted cell, the surface ofthe positive electrode was examined by XANES inorder to study the surface film or phase transitions inparticles of the active material. The Li K-edge andP-K edge XANES spectra of the samples were
measured on the BL8B1 and BL1A beamline of the
UVSOR Facility. Data were obtained in the total
electron yield (TEY) modes.

Intensity

A

TEY

LiF

after
96 w
before
test
56

58

60

62

64

66

Energy / eV

68

70

Fig. 1. Li K-edge XANES spectra for the positiveelectrode before and after preservation tests at 60ºC.

Results
Table 1 summarizes the relative capacity and

109

BL1A

Characterization of Aluminum Naphthalocyanine Complexes by X-ray
Absorption Spectra at Cl and Al K-Edges

T. Kurisaki1, D. Tanaka1, Y. Sakogawa1, H. Wakita1,2
1Department of Chemistry, Faculty of Science, Fukuoka University, Nanakuma, Jonan-ku,
Fukuoka 814-0180, Japan
2
Advanced Materials Institute, Fukuoka University, Nanakuma, Jonan-ku, Fukuoka 814-0180,
Japan
Naphthalocycnine (NPC) has p-conjugated systembigger than that of phthalocycnine (PC). Therefore,
the metal complexes of NPC is expected a very
interesting property. However, the electronic structureof naphthalocycnine is not well known. In theprevious work, we studied the electronic structure ofaluminum phtalocycnine by the X-ray absorption
spectroscopy [1, 2]. This result suggested that there iscorrelation between the shape of XANES spectrum
and the local structure
In this work, we applied the x-ray absorption nearedge structure (XANES) spectroscopy to aluminumcompounds combined with oxygen atoms. The resultsof the measurement indicate unoccupied andoccupied electronic structure of aluminumcompounds. The X-ray absorption spectra were
measured at BL1A of the UVSOR in the Institute of
Molecular Science, Okazaki [3]. The ring energy of
the UVSOR storage ring was 750MeV and the stored
current was 110-230 mA. Al K-edge absorption
spectra were recorded in the regions of 1620-1750eV
by use of two KTP(011) crystals. The absorption wasmonitored by the total electron yield using aphotomultiplier. The samples were spread into thecarbon tape on the first photodynode made of CuBeof the photomultiplier.
The Al K-edge XANES spectra for the aluminum
naphthalocycnine and aluminum phthalocycnine areshown in Fig. 1. A change of the spectral patterns was
not clearly observed between the aluminum
naphthalocycnine and aluminum phthalocycnine. This
result showed that the electronic structures of thealuminum ion in these complexes are about the same.
We are going to try to analyze the Cl K edge XANES
spectra.

Fig. 1. Observed Al K-edge XANES spectra ofaluminum
naphthalocycnine
andaluminumphthalocycnine[1] H. Ichihashi et al., Jpn. J. Appl. Phys. 38 (suppl.)(1999) 101.
[2] S. Matsuo et al., Adv. Quan. Chem. 42 (2002)
407.
[3] S. Murata et al., Rev. Sci. Instrum. 63 (1992)
1309.

110

BL1A

Study of Al K-Edge of Local Structure in Mesoporous Alumina Bulk
Prepared by Hydrothermal Hot-Pressing
A. Nakahira, H. Nishimoto, H. Nagata, Y. Hamada, T. Kubo
Osaka Prefecture University, Gakuen-cho, Sakai 599-8531, Japan
Mesoporous alumina has attracted much attention
because of their possible uses as supports for catalysts
and adsorption. However, the application ofmesoporous alumina was restricted because it was
obtained as a powder only. Solidification ofmesoporous alumina will improve handleability andexpand application. Nakahira et al reported thatdensified bulky mesoporous silica was successfully
synthesized using hydrothermal hot-pressing (HHP)
method [1]. Therefore, we attemped to synthesize
mesoporous alumina bulk by this HHP method andexmine the local structure around Al by XANES
spectra.
Mesoporous alumina powder was prepared as astarting material [2]. Mixture of powder and water
was heated at 110 °C with the uniaxial pressing under
40MPa and kept constant for 2 hours. Obtained bulks
were identified by XRD. Al K-edge XANES spectra
were obtained in a total electron yield mode at room
temperature
using
a
KTP
double–crystal
monochrometer at BL01A of the UVSOR. The
spectra were collected in the photon energy range
from 1520 to 1600 eV atintervals of 0.05 eV with adwell time of 1 s.
XRD patterns showed that mesoporous alumina
HHP bulk was also retained the mesoporous structure
after HHP. Figure 1 shows the results of Al K-edge
XANES of mesoporous alumina HHP bulk (a),starting mesoporous alumina powder (b), and-alumina (c) as reference materials of amorphs-like-alumina. The spectrum of HHP bulks was
significantly similar to those of starting mesoporousalumina powder and -alumina. Hence, there is noapparent change in the relative intensity nor the widthof these spectra. These results of XANES revealed
that there is not large difference for local structurearound Al between bulks prepare by HHP and ones
before HHP treatment.

Fig. 1. Al K-edge XANES spectra of mesoporousalumina bulk prepared by HHP.
[1] H. Nagata et al., Materials Transactions 47 (8)(2006) 2103.
[2] F. Vaudry, S. Khodabandeh, M. E. Davis,
American Chemical Society 8 (1996) 1451.

111

BL1A

Structure Charactarization of Poly(vinyl butyral)-Silica
Organic-Inorganic Nano-Hybrid by X-Ray Absorption Spectrum

H. Nameki1, T. Yoshida2, S. Yoshimoto1, K. Yamada1, H. Fukaya1
Indusrial Research Institute, Aichi Prefecture, nishi-shinwari, Kariya 448-0003, Japan2
Department of Materials, Physics and Energy Engineering, Nagoya University, Furo-cho,
Chikusaku, Nagoya 464-8603, Japan
1

Introduction
The organic-inorganic nano hybrids are expected asa new material that has the properties of both the
inorganic materials and the organic materials. In
general, flexibility and hardness are the trade-off
relation, and then materials which have both theflexibility and the hardness have been difficult toprepare in past technology. By nano-levelhybridization of poly(vinyl butyral) as the organic
material and silica(SiO2) as the inorganic material, wedeveloped a novel material that has both
flexibility(impact
resistance)
andhardnesssimultaneously[1]. To consider the appearance
mechanism of this peculiar property, we examined
the structure of the hybrid by X-ray absorption
spectroscopy.

In the sample #1 or #3, alkoxides was mainly
reacted with hydroxyl group of PVB, not with eachother, because of no addition of H2O. Then in sample#1 and #3, silica was dispersed as SiO2 mono unit in
the hybrid. This means the arrangement of
atoms(oxygen) around Si is irregular in bond distancein sample #1 or #3. Especially, spectrum of thesample #1 was quite similar to the silica glass, which
has amorphous structure.
The sample #1 is superior in the properties oftransparency, flexibility and impact resistance to thesample #2,#3,#4. The structural difference showed in
X-ray absorption spectra is considered to beconcerned with the difference in these properties, andthat may contributes the appearance of the peculiar
property of sample #1.

Experimental

Table 1. Sample preparation conditions.

Alkoxides(tetraethoxysilane and 3-glycidoxypropyltrimethoxysilane) were added into 5 %2-propanol solution of PVB, and HCl or NH4OH wasadded into the mixture as catalyst(the amount of thecatalyst is 0.05mol per 1 mol of total alkoxides). In apart of these sample, water(10mol per 1mol of total
alkoxides) was added to reacting solution. Thus,
sample preparation was done by four methods(shownin table1). The reacted solution was stirred for 2
hours further, and then this was coated into a brass
substrate. The coated substrate was preserved in a
desiccator for 16 hours, and then heated first at 333K
for 2h, next at 363K for 2h. Structure characterizationof these sample was done by measuring Si-K edge
X-ray absorption spectra at BL1A in UVSOR.

Results and Discussion
Figure 1 shows X-ray absorption spectra of samples
and a silica glass as standard material. In all spectra,
peak of strong intensity was observed at 1845eV,
which was assigned to Si-K edge absorption. Abovethe energy of the peak, oscillation pattern due to thestructure around Si atom was observed.
The oscillation pattern of sample #2 and that ofsample #4 were quite similar to each other, on theother hand, these were different from that of sample#1 or #3. Sample #2 and 4 were prepared throughH2O addition, then hydrolysis of alkoxides was
occurred and alkoxides was polymerized to form
silica(SiO2 multi-units). The oscillation pattern ofspectra was considered to reflect the structure ofmulti-units silica.

Fig. 1. X-ray absorption spectra of the hybrid
samples.
[1] Japan Patent, 2007-119635.

112

BL1A

In-Situ Measurement of X-Ray Excited Optical Luminescence from a Silica
T. Yoshida1, T. Tanabe2, S. Muto1, H. Yoshida3
1
Department of Materials, Physics and Energy Engineering, Nagoya University, Furo-cho,
Chikusa-ku, Nagoya 464-8603
2
Department of Advanced Energy Engineering Science, Interdisciplinary Graduate School ofEngineering Science,Kyushu University6-10-1, Hakozaki, Higashi-ku, Fukuoka 812-8581
3
EcoTopia Science Institute, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603
Figs. 1(b) shows the time evolutions of the XEOL
intensities at 50 K for the three excitation energies.
The intensity value of each point was evaluated by
the total area of the emission band in Fig. 1(a). The
luminescence intensity is monotonically decreased
with the irradiation time at the excitation energy of1848 eV, whereas at 1834 eV and 1858 eV, theintensities are nearly constant with the irradiation
time. A difference spectrum (not shown) between the
spectra after irradiated for 300 and 5000 seconds at
1848 eV was dominated by the component peaked at
2.6 eV, indicating that the observed intensity
reduction is mainly ascribed to the reduction of thiscomponent. These results above suggest that a
specific type of point defects in the sample ispreferentially decomposed by a specific electronictransition excitation. In other words, a selective
electronic excitation can control formation and/or
annihilation of a specific type of defects.
In the present case, the transition induced by 1848
eV X-ray corresponds to that from the Si 1s occupied
state to the 3p antibonding orbitals relating to the
SiO bonds. The high-density electron excitation will
break the SiO bonds and also excite the electrons
trapped at the luminescent centers of the 2.6 eV band,
which could effectively contribute to thedecomposition of the centers.

Degradation of optical properties of silica glass byionizing radiation is one of the main concerns fortheir use in fusion and fission environments.
Although the radiation damage of silica glass has
been extensively studied, the detailed damaging
processes and/or radiation effects are not yet fully
understood. This is partly because most of thestudies have been done by post-irradiation tests,
which cannot give information on the “processes” butonly “traces” or “results” since the relaxation time of
excited electrons is usually very short.
Recently, we have tried in situ measurement of
X-ray excited optical luminescence (XEOL) from asilica glass. The in situ measurements were very
effective for observing the dynamic changes in theirelectrical properties by ionizing radiations. In thepresent study, we examined the changes in XEOL ofa silica glass with respect to excitation X-ray energy
near the threshold of the Si K-edge, irradiation time
and temperature.
The sample used in this study was a low-OH fusedsilica glass (T-2030) disc produced by Toshiba
Ceramics, Japan. The diameter and thickness of thesample were 13 mm and 2 mm, respectively. XEOLof the silica glass by X-ray energy between 1.8 and1.9 keV was measured between 50 K and 300 K on
the beam line 1A at UVSOR-II, Institute for
Molecular Science. The luminescence was collected
and guided by a lens in a UHV chamber to themonochromator (CP-200, JOBIN YVON) anddetected by a multi-channel analyser (OMAIII,
EG&G PRINCETON APPLIED RESEARCH),
which covers the photon energies from ca. 1.5 eV to 4
eV.
We selected three excitation X-ray energies of1834 eV (just below the Si K-edge), 1848 eV (on thewhite line) and 1858 eV (well above the threshold).
In the measurement of XEOL at room temperature, anintense emission band peaked around 3.1 eV isobserved in each spectrum. The previous studies
assigned the origin of the 3.1 eV band to the intrinsic
B2 center [1,2]. We also measured XEOL at lower
temperatures, and found the broadening of theemission band below 100 K. Fig. 1(a) shows XEOLof the same sample measured at 50 K. A peak
position is shifted to the lower energy side, because
an additional emission band appears around 2.6 eV,
revealed by the peak fit, as shown in Fig.1.

Fig. 1. (a) Optical luminescence spectra of a fusedsilica glass excited by X-rays with the energies of1834, 1848 and 1858 eV at 50K. (b) Irradiation timedependence of XEOL intensities at 50 K.
[1] R. Tohmon et al., Phys. Rev. B 55 (1989) 1337.
[2] S. Agnello et al., J. Non-cryst. Solids 232-234(1998) 323.

113

BL3U

Direct Observation of Electronic States at
Inner Pentacene Thin Films Beneath Au Electrodes

H. S. Kato1, F. Yamaguchi1,2, M. Kawai1,2, T. Hatsui3, M. Nagasaka3, N. Kosugi3
RIKEN (The Institute of Physical and Chemical Research), Wako 351-0198, Japan2
Department of Advanced Materials Science, University of Tokyo, Kashiwa 277-8501, Japan
3
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
1

Introduction
In order to extend new functionality of electronic
devices, the molecular devices have recently been
investigated with great efforts. The organic field
effect transistor (OFET) is a typical molecular device
that controls electric conductivity by injection ofcarriers into the organic thin film under the applied
electric field. The conductive mechanism has
generally been understood with a scheme of band
bending of electronic states, based on the knowledgeof inorganic semiconductor transistors. However, theenergy diagram might be not exactly the same
between organic and inorganic materials, because of
more localized orbitals of the organics. Moreover, it
is also important to elucidate the difference ofelectronic states for future advanced devices utilizing
the noble characters of organic materials. Therefore,
the direct observation of electronic states in theorganic thin films under operation conditions has
been required.
In this study, we aim to establish a newexperimental method that elucidates the electronic
state change in organic thin films of OFET under theelectric field. The fluorescence-yield X-ray
absorption spectroscopy (FY-XAS) should be a
promising method for detection of inner electronic
states of organic devices, because the fluoresced
X-ray has a long mean free path more than several 10
nm in most of materials even for soft X-ray excitation.
In addition, the X-ray is not disturbed by applied
electric field, besides emitted electrons. Thus, wehave attempted to utilize FY-XAS for investigation of
inner electronic states of OFETs.

sample-entry system. The fluorescence intensities
were measured using a retarding field detector
consisting of MCP plates.

Results and Discussion
Figure 1 shows the incidence angle dependence offluorescence-yield C K-edge XA spectra of the Pn
films (t = 20 nm), in which the spectra of a non
Au-covered Pn film and a fully Au-covered Pn film
are compared. In both cases, the relative intensities of* components at photon energies of  285 eV
decrease with increasing incidence angle of excitation
X-ray, while the broad * components above 300 eV
increase with increasing incidence angle. These
results are consistent with the structure of crystallized
Pn thin films on SiO2 substrates; the molecular axis is
towards surface normal with a small tilting angle ineach monolayer. The small difference between the
non Au-covered and fully Au-covered Pn films would
be due to a perturbation at the Au deposition form athermal evaporation source. However, the similarity
in the incidence angle dependence of the spectra
evidences that the perturbation is not significant for
the whole Pn thin film. As above, the FY-XAS
measurements have enough potential to characterize
the inner organic thin films even beneath electrodes.

Experimental
To investigate the electronic states of OFET,
pentacene (Pn) thin films on the SiO2-covered Si
substrates were fabricated using a molecular beam
deposition system at RIKEN. The quality of theirmorphology and crystallinity was high enough incomparison with those in previous reports. The
performance for FETs of the fabricated Pn thin films
was also confirmed with additive deposition of Au
electrodes on the films. By the same preparation, thefully Au-covered Pn thin-film samples were made toevaluate the field effects obtained from uniform
electric fields in the films.
The FY-XAS measurements were performed at theBL3U beamline of UVSOR facility in IMS. The
samples were set in a BL3U end-station throughFig. 1. Incidence angle dependence of fluorescence
yield C K-edge XA spectra of pentacene thin films on
SiO2-covered Si substrate, in which the spectra of anon Au-covered Pn film (red broken lines) and a fully
Au-covered Pn film (blue solid lines) are compared.
The incidence angle is defined from surface normal.

114

BL4B

Study on the Surface Structures of the LiNi0.8Co0.15Al0.05O2
Electrode after the Preservation Tests for Li-Ion Battery Cells (I)H. Kobayashi, M. Shikano
Research Institute for Ubiquitous Energy Devices, AIST, Ikeda, Osaka, 563-8577 Japan
Several of the requirements of rechargeable
batteries for hybrid electric vehicles (HEVs) are quite
different to those of portable electronic devices. In
particular, high specific power and long calendar life
are very important requirements of HEV applications.
Much effort has been applied to understanding themechanisms that limit the calendar life of high power
Li-ion cells. Until now, although the deteriorationin the power performance of currently available
lithium batteries is thought to result from problems
with the positive electrodes, the mechanism ofdeterioration of the electrodes is still poorly
understood. Detailed information on the changes
taking place in both the cathode and anode is essential
in order to determine the origin of the degradation of
power
performance.
In
thisstudy,
LiNi0.8Co0.15Al0.05O2 positive electrodes from cells
that had undergone power fading throughpreservation tests were examined by XANES analysis
to obtain information on their surfaces.
The
relationship between power fade and the surface stateof the positive electrode was studied.

after preservation tests. In TEY mode, O K-edge
XANES spectra provide information on the surface
structure.
The spectrum measured before
preservation tests contained peak A, corresponding tooxygen originating from the layered structure, andpeaks B and C. After the preservation tests, theintensity of peak A clearly decreased at 60 ºC after 96
weeks, while the intensities of peaks B and C
increased. The position of peak B was close to thatof the NiO spectrum, indicating the existence of a
cubic phase on the surface, and the position of peak C
was close to that of Li2 CO3, or to conductive
materials such as AB (data not shown). These
results indicate that a part of the layered structure at
the surface of the positive electrode was transformed
to a cubic structure at 60 ºC after 96 weeks.

Experimental
We made 18650-type cylindrical battery cells witha capacity of about 400 mAh, which were designed tohave a rate capability of more than 10 C. The
positive and negative electrode was comprised of
LiNi0.8Co0.15Al0.05O2 and hard carbon, respectively.
Each cell was characterized using the standard battery
test procedure given in the partnership for a newgeneration of vehicles (PNGV) Battery Test Manual.
The changes in both capacity and power werechecked every few weeks. After completion of thedegradation test, the SOC of the cell was adjusted to
50% immediately before disassembling it, since thechemical and physical properties of the active
materials are influenced by the SOC.
After
disassembly of the SOC-adjusted cell, the surface ofthe positive electrode was examined by XANES inorder to study the surface film or phase transitions inparticles of the active material. The O K-edge
XANES spectra of the samples were measured on the
BL4B beamline of the UVSOR Facility. Data wereobtained in the total electron yield (TEY) mode.

Fig. 1. Preservation period vs. relative capacity andpower.

Results
Figure 1 shows the preservation period vs. relative
capacity and power. The relative capacity andpower decreased on increasing the test temperaturefrom 40 ºC to 60 ºC. Figure 2 shows the O K-edge
XANES spectra of 50% SOC samples before andFig. 2. O K-edge XANES spectra for the positiveelectrode after preservation tests at 40 ºC and 60 ºC.

115

BL4B

Magnetic Properties of C60 and Co Nanocomposite Films

Y. Matsumoto1, S. Sakai1, T. Takagi2, T. Nakagawa2, T. Yokoyama2
Advanced Science Research Center, Japan Atomic Energy Agency (JAEA), Tokai Naka-gun,Ibaraki 319-1195 Japan2
Department of Materials Molecular Science, Institute of Molecular Science (IMS), Okazaki,
Aichi 444-8585, Japan
1

Recently, we have found that fullerene (C60) andcobalt (Co) nanocomposite films show large tunnel
magnetoresistance (TMR) effects at low temperature[1]. As shown schematically in a figure 1, these films
consist of a matrix of C60-Co compounds anddispersed Co nano particles [2]. However, observed
TMR effects cannot be explained only by a spintransport among the Co particles even if they arecompletely spin polarized. Therefore, in the present
work, we have investigated local magnetic propertiesof C60-Co films by X-ray magnetic circular dichroism(XMCD) spectroscopy.
MCD measurements were performed at beam line
4B with a super conducting magnet. The details of
this MCD system are described elsewhere [3].
Different Co content films of C60Cox (x: the numberof Co atoms per a C60 molecule) were prepared by aco-deposition method [1] under the UHV condition(<10-7Pa) and then transferred into the experimental
chamber without breaking the vacuum. The Co
LIII,II-edge MCD spectra were taken with thepolarization factor of a0.85. Total energy resolutionof 0.75eV was applied in the present work.
Figure 2(a) and 2(b) show XAS spectra at the Co
3dm2p excitation, and MCD spectra of different
contents of C60Cox and pure-Co films measured at 5T
and 4.9K, respectively. In the case of Co dense films(x>10), peak profiles of MCD spectra are similar to
those of the pure Co film. This result indicates that
Co particles dispersed into the film have a samemagnetic property as a Co metal. On the other hand,in the case of Co dilute films (x<10), MCD signal aredifferent to pure-Co film (see inset, Fig. 2(b)).
According to our previous works of Raman
spectroscopy [2], the matrix of C60-Co compounds isdominant in this composition domain. In fact, XAS
spectrum of C60Co4.3 has several fine structures asshown in Fig. 2(a) in contrast to the Co film. Though
the derails of such structures which show MCD
responses are not clearly right now, it is expected thatthey are connected to the hybrid molecular orbitals(MOs) of Co 3d band and C60 S orbital from XPS
and C K-edge NEAXFS measurements. In addition, it
has been also observed that MCD signal of Co dilute
films indicate the strongly temperature dependence(not shown in figures here). Especially, MCD signalof C60Co4.3 film was vanished at 77K. These findings
indicate that there are hybrid MOs which show
paramagnetic properties in the C60-Co compounds. It
is speculated that these states act as a spin-filter inspin transport processes.

Co nano particle

C60-Co compound

Intensities / arb.units

Fig. 1. Schematically illustration of the C60 and Co
nanocomposite film.

(a)Co
C60Co4.3(b)
5T, 4.9K
o
T=55 (magic angle)

MCD

0
Co
C60Co4.3
C60Co7.7
C60Co10.7
C60Co13.4

-1

760

780

800

820

Photon Energy / eV

Fig. 2. Co L-edge XAS spectra (a), and MCD spectraof different Co contents of C60Cox and the pure Co-film measured at 5T and 4.9K (b).
[1] S. Sakai, I. Sugai, S. Mitani, K. Takanashi, Y.
Matsumoto, H. Naramoto, P. V. Avramov, S. Okayasu,
Y. Maeda, Appl. Phys. Lett. 91 (2007) 242104.
[2] S. Sakai, H. Naramoto, V. Lavrentiev, K. Narumi,
M. Maekawa, A. Kawasuso, T. Yaita, Y. Baba, Mater.
Trans. 46 (2005) 765.
[3] T. Nakagawa, T. Takagi, Y. Matsumoto, T.
Yokoyama, Jpn. J. Appl. Phys. in press.

116

BL5U

Valence Band Spectra of Fe/Si Interfaces Changing Probing-Depth

T. Ejima, T. Goto, T. Jinno
Institute for Multidisciplinary Research for Advanced Materials, Tohoku University,
Sendai 980-8577 Japan
Node and antinode positions of standing waves caneasily move in uppermost layers of the multilayer,
therefore photoelectrons excited in the uppermost
layers can be effectively scanned through theinterface of the layers[1]. Recently, these positions
can be determined by total electron yield (TEY)
spectra measured simultaneously with reflection
spectra [2].
Magnetic coupling between Fe layers in Fe/Si
multilayers exhibits initially ferromagnetic one, thenantiferromagnetic, and finally ferromagnetic or no
coupling with an increase of the sandwiched Si layer
thickness [3]. When the thickness of the Si layer is
2.0 – 2.5 nm, the coupling changes from
antiferromagnetic
one
toferromagneticor
non-magnetic one. The origin of this inter-layer
coupling is controversial, and is roughly classified
into either a metallic model as Fe-Si compound or asemiconductor model as amorphous Si [4, 5]
In this study, electronic structures of Fe/Si
interfaces of Fe/Si/Fe trilayers deposited on a Mo/Si
reflection multilayer are investigated using
photoelectron spectroscopy changing the probing
depth, which is caused by the phase changes
according to the changes of the thicknesses of theuppermost trilayers and of incident wavelength. The
phase changes are observed in situ by both TEY andreflection spectra.
Nominal layer structure of the Fe/Si/Fe trilayer
estimated from the experimental deposition rates isrepresented in Fig. 1. Magnetic behavior of thistrilayer estimated from the VSM measurement was
ferromagnetic one. The photoelectron spectra were
measured with TEY spectra. Probing depth estimatedfrom the TEY and reflection spectra is represented inFig. 1 concerning with the Ar+ etching time andobtained UPS spectra [2].
Obtained UPS spectra represented in Fig. 2 can beclassified into 3 groups: first is a Fe-Si compound
structure (spectra b – d), second is an amorphous Si
structure (spectra e – f), and the last is a Fe structure(spectra h & i). This classification of the electronic
structures suggests that inter-diffusion layer between
Fe/Si layers is formed when a Fe layer is deposited
onto a Si layer, and not formed when a Si layer isdeposited onto a Fe layer. The second Si-likeelectronic structures observed between the Fe layers
suggest that the origin of the coupling is well
explained by the semiconductor model, if theferromagnetic behavior is caused by the inter-layer
coupling.

Fig. 1. Nominal layer structure of Fe/Si/Fe trilayer
with estimated probing depth.

Fig. 2. Valence band spectra of Fe/Si interfaceschanging the probing depth. Characters represent the
probing depths that are designated in Fig. 1.
[1] S. –H. Yang et al., J. Phys., Condens. Matter 14(2002) L407.
[2] T. Ejima et al., Appl. Phys. Lett. 89 (2006)
021914.
[3] E. E. Fullerton et al., J. Magn. Magn. Mater. 117(1992) L301.
[4] For example, P. Bruno, C. Chappert, Phys. Rev.
Lett. 67 (1991) 1602.
[5] For example, D. M. Edwards et al., Phys. Rev.
Lett. 67 (1991) 493.

117

BL5U

Fermi Surface Mapping of 8 ML Fe/Cu(001) by Angle-Resolved Ultraviolet
Photoemission Spectroscopy
X. Gao1, H. Miyazaki2,3, S. Chen1, A. T. S. Wee1, T. Ito3, S. Kimura3, J. Yuhara2, K. Soda2,3
1
Department of Physics, National University of Singapore, Singapore 117542
2
Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan
3
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
Introduction

Further study of the Fermi surface mapping using
different photon energies at various temperatures tocompare with theoretical calculation should help tounderstand the nature of the fcc Fe films on Cu(001).

Despite many years’ research efforts in Fe/Cu(001)system, it remains one of the most complicatedmagnetic thin film systems. It is generally believedthat there are three thickness range of the Fe film withdifferent magnetic properties and structures [1]:below 3 monolayers (ML), Fe film has so-called facecenter distorted (fct) structure and is ferromagnetic;from 4 ML to about 10 ML, the film has aferromagnetic fct top layer with the rest layers either
anti-ferromagnetic or paramagnetic with fcc structure
depending on the temperature; above 11 ML, thewhole film changes to bcc structure and isferromagnetic. Non-uniform reduced magnetic
response in the second thickness range than in theother two ranges are still full of mysteries and there
are still disputes about its nature. Fermi surface
mapping by ultraviolet photoemission spectroscopy(UPS) is a powerful technique to study electronic
structure in k space. Although there have been Fermi
surface mapping studies of Co and Ni grown on
Cu(001) and many studies of valence band using UPS
for Fe/Cu(001), no Fermi surface mapping has beenreported so far for Fe/Cu(001).

Binding Energy (eV)

0

-2

-4

-6

-4

-2

0

2
o
Angle ( )4

6

8

Fig. 1. Photoemission intensity of 8 ML Fe/Cu(001)around [001] direction (indicated by the dark solidline).

Experimental

Cu(001) surfaces were prepared by cycles of Ar +ion bombardment at 1 keV and annealing at 800 K in
an ultrahigh vacuum system. The (1x1) pattern was
clearly observed on the clean Cu (001) surface by low
energy electron diffraction. 8 ML Fe film was in situ
evaporated onto the Cu(001) surface at room
temperature, which was cooled down to 5 K for UPS.
The thickness was monitored by a quartz oscillator
and calibratedusing XPS.
Angle-resolved
photoelectron spectra were recorded under 2.7 x 10-8
Pa with a high-resolution energy analyzer at BL5U.
The total energy resolution was 14 meV with theexcitation photon energy of 90 eV at 5 K.

Results and Discussion
Figure 1 shows the photoemission intensity of 8
ML Fe/Cu(001) along [001] direction recorded at a
photon energy of 90 eV. Dispersions of both Fe 3d at
the Fermi surface and Cu 3d at the binding energy ofabout 2 eV can be clearly observed.
Figure 2 shows Fermi surface mapping for 8 ML
Fe/Cu(001) at 5 K obtained from angle-resolved UPS
using the photon energy of 90 eV. The energy slice
for the mapping is set at the binding energy of 0.4 eV.

Fig. 2. Fermi surface mapping for 8 ML Fe/Cu(001)
at 5 K using photon energy of 90 eV.
[1] D. Li et al., Phys. Rev. Lett. 72 (1994) 3112; D.
Li et al., Appl. Phys. 76 (1994) 6425.

118

BL5U

Ce and Gd 4d-4f Resonant Photoemission Studies of Ce1-xGdxCoSi3

H.J. Im1,2, H. Miyazaki3,2, T. Ito2,4, S. Kimura2,4, J.B. Hong1, Y.S. Kwon1
1
Department of Physics, Sungkyunkwan University, Suwon 440-746, Korea
2
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
3
Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan
4
School of Physical Sciences, The Graduate University for Advanced Studies, Okazaki444-8585, Japan
We have performed Ce and Ge 4d-4f resonant
photoemission
spectroscopy(RPES)
on
Ce1-xGdxCoSi3 systems in order to understand theorigin of quantum criticality in view of electronic
structure. As Gd is replaced by Ce, the ground statechanges from the antiferromagnetic (x = 1.0, 0.8, 0,6)
to non-magnetic heavy fermion (x = 0, 0.2) via thequantum critical point (QCP, x = 0.4) [1,2]. This isconsidered as a new type of QCP since theantiferro-magnetism and non-magnetism originate
from the different kinds of f-electrons belonging to
Gd and Ce ions, respectively, and seem to competeeach other causing the QCP. Therefore, the studies ofthe electronic structure of both Gd and Ce 4f states
are essential to understand the new QCP [1,2].
RPES measurements for polycrystalline samples
Ce1-xGdxCoSi3 (x = 0, 0.2, 0.4, 0.6, 1) were carriedout at BL5U. The used photon energies are 120 (on)and 113 eV (off) for Ce 4d-4f RPES, and 146.5 (on)and 134.8 eV (off) for Gd 4d-4f RPES. Total energy
resolutions are about 65 and 95 meV for the photon
energies of 120 and 146.5 eV, respectively.
Measurement temperature is 10 K. Sample surfaces
were prepared by in situ fracturing under 210-8 Pa.
Sample cleanliness is checked by the absence ofoxidization peak around 6 and 10 eV.
Figure 1 displays Gd 4d-4f on-RPES spectra for x= 0.2, 0.4, 0.6, and 1. All spectra are subtracted by
Shirley background, and then are normalized to theintensity of Gd 4f6 final-state peaks around -8.4 eV
according to the Gd composition ratio. In the regimeof from -3.5 to -2 eV, the broad peaks, which areoverlap of both Ce 4f0 final state and non-f-states, areobserved. Particularly, the Ce 4f1 final-states, theso-called tail of Kondo resonance, show somevariation. For the meaningful comparison of Kondo
resonance peaks, Ce 4f spectra should be extracted,
precisely.
Figure 2 shows the Ce 4f spectra for x = 0, 0.2, 0.4,
and 0.6, which are obtained by the subtraction ofoff-spectra from on-spectra in Ce 4d-4f RPES. We
clearly observe the well-defined Ce 4f0 and Ce 4f1
final states around -2.5 eV and at the Fermi level,
respectively. It should be noted that the sharp tail of
Kondo resonance (Ce 4f1-state near EF) persists from
non-magnetic (x = 0, 0.2) to magnetic (x = 0.6)
regime via the QCP (x = 0). This indicates that the

new kind of QCP in this system does not come fromthe change of Ce 4f electronic structures unlike a
local quantum critical scenario [5].

Fig. 1. Gd 4d-4f on-RPES spectra of Ce1-xGdxCoSi3.

Fig. 2. Ce 4f spectra of Ce1-xGdxCoSi3 obtained in Ce
4d-4f RPES measurements.
[1] J.B. Hong et al., J. Magn. Magn. Mater. 310(2007) 292.
[2] J.B. Hong et al., Physica B 403 (2008) 911.
[3] D. Eom et al., J. Phys. Soc. Jpn. 67 (1998) 2495.
[4] H.J. Im et al., Phys. Rev. B 72 (2005) 220405.
[5] Q. Si et al., Nature 413 (2001) 804.

119

BL5U

Photoemission Studies on Quantum-Well States of
Pb-Covered Ag Films on Si(111)
H. Ke, H. Narita, I. Matsuda
Institute for Solid State Physics (ISSP), University of Tokyo5-1-5 Kashiwanoha,
Chiba 277-8581, Japan

Spin controls in utrathin metal films have been
important topics in developing (nanometer-scale)spintronics and studying modern solid state physics.
When thickness of metal film reduces to electron
wavelength, electron energy is quantized by quantum
size effect, resulting in formation of quantum-wellstates (QWS’s). In contrast to isolated metal thinfilms, those on solid substrates have shown new
intriguing spin properties through boundary
conditions between films and substrates.[1]Spin-polarization of quantum Ag film has beenreported when the film was grown on Fe substrate(e.g. Fe).[2] The polarization originates fromspin-polarized bulk bands of the ferromagnetic metal
substrate, which induces spin-dependent reflection
phase shift at the film/substrate interface for electrons
confined in the film. While varieties of spin
properties have been reported in nanometer-thickmetal film on metal substrates, there has been little
report for those on the semiconductor substrates.
In the present research, we have challenged torealize spin-split bands in a nonmagnetic metal (Ag)film on a semiconductor (Si) substrate by ultilizing
the strong Rashba effect at a surface atomic layer
induced by heavy metal deposition. Up to now, wehave succeeded in demonstrating spin-splitting of
QWS subbands for Bi-covered quantum Ag film on
Si(111).[3] Then, we move on to Pb-covered Ag filmon Si(111). In contrast to the former case, the latter
one is expected show spin-split Fermi surfaces, which
induce exotic macroscopic properties.
The experiment was performed at the undulator
beamline of BL-5U at UVSOR. With ahigh-resolution analyzer of MBS-Toyama ‘Peter’ A-1,
angle-resolved
photoemission
spectroscopy
measurements were performed at photon energy of 21~ 29 eV.
Figure (a) shows experimental band dispersion ofthin Ag film (~30 ML) deposited on Si(111)7x7. We
observed clear Fermi-edge and a broad spectra featurearound 2 eV. On the other hand, after 1 ML-Pb
adsorption on the Ag film, we detected subbands of
QWS as shown in Fig. (b). This drastic spectralchange is likely due to change of the film morphology.
The Pb adatoms seemed to induce formation ofcontinuous Ag film from rough Ag islands on Si(111).
Analyses of the band parameters are underway.

120

Fig. 1. Experimental band dispersion diagrams for (a)~30 ML-Ag film deposited on Si(111)7x7 and (b)that is subsequently covered with Pb monolayer.
[1](A review paper) I. Matsuda et al., e-J. of Surf. Sci.
and Nanotechnology 2 (2004) 169.
[2] N. V. Smith et al., Phys. Rev. B 49 (1994) 332.
[3] H. Ke et al., submitted to Phys. Rev. Lett.

BL5U

Temperature-Dependent Angle-Resolved Photoemission Spectra on
Ferromagnetic EuO Thin Films

H. Miyazaki1,2, T. Ito2,3, S. Ota1,2, H. J. Im4, S. Yagi1, M. Kato1, K. Soda1,2, S. Kimura2,3
1
Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan
2
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan3
School of Physical Sciences, The Graduate University for Advanced Studies, Okazaki444-8585, Japan
4
Department of Physics, Sungkyunkwan University, Suwon 440-746, Korea
the 4f state mainly hybridizes with the majority spinstate of O 2p. Therefore, the bonding and antibonding
states of the Eu 4f and O 2p states are shifted to thehigher and lower binding energy side, respectively.
This result indicates that the origin of theferromagnetic transition is strong hybridization
between the Eu 4f and O 2p states.

Europium monoxide (EuO) is a ferromagnetic
semiconductor with the Curié temperature (TC) ataround 70 K [1, 2]. In the electron doping case by theEu excess or substitute Gd3+ or La3+ from Eu2+ ion,
the TC increases up to 150 K and the electricalresistivity drops twelve-order of magnitude below theTC originating in a metal-insulator transition (MIT) [2,3]. To reveal the origin of these physical properties of
EuO, it is important to clarify the electronic structure.
Three dimensional angle-resolved photoemission
spectroscopy (3D-ARPES) using a synchrotron
radiation source is the most powerful technique to
directly determine the electronic band structure.
Using this technique we observed the change in theEu 4f and O 2p states across TC.
Single-crystalline EuO thin films with a thicknessof about 50 nm were fabricated by the molecularbeam epitaxy (MBE). Epitaxial growth of thesingle-crystalline EuO thin films with the 1 x 1 EuO(100) patterns was confirmed with low energy
electron diffraction (LEED) and reflection highenergy electron diffraction (RHEED) methods. The
TC measured with a superconducting quantum
interference device (SQUID) magnetometer was 71 K.
The 3D-ARPES measurements were performed at thebeam line 5U of UVSOR-II combined with the MBE
system. The total energy and momentum resolutions
for the ARPES measurement were set 123 meV and
0.020 Å-1 at the  point and 45 meV and 0.014 Å-1 at
the X point, respectively.
Figure 1 shows temperature dependent 3D-ARPES
spectra obtained for EuO (100) at the  (a) and X (b)points. ARPES peaks at binding energies EB of 1.0 –3.0 eV and of 4.0 – 7.0 eV are attributed to the Eu 4f
and O 2p states, respectively, based on a band
structure calculation as well as the photoionization
cross section [4, 5]. In the ferromagnetic phase below
71 K, every peaks shift to the lower binding energy
side by about 0.2 eV than that in the paramagnetic
phase. These energy shifts originate from the band
splitting of the Eu 5d state due to the ferromagnetictransition. In addition, the top of the Eu 4f states atthe  and X points is shifted away from the main 4f
states and also the intensity increases. In contrast, theO 2p state is spitted into two bands below TC. The
bands at the higher and lower binding energies are
attributed to the majority and minority spin states,
respectively. Since the Eu 4f state is fully polarized,

Fig. 1. Temperature dependence of the photoemission
spectra of an EuO (100) thin film at the  (a) and X(b) points. The open circles indicate the peaks
position evaluated from the second-derivative curveof
each spectrum.
[1] N. Tsuda et al., Electronic Conduction in Oxides(Springers College) (1976).
[2] A. Mauger et al., J. Phys. (paris) 39 (1978) 1125.
[3] Y. Shapira, S. Foner, and T. B. Reed, Phys. Rev.
B 8 (1973) 2299; Phys. Rev. B 8 (1973) 2316.
[4] H. Miyazaki et al., Physica B 403 (2008) 917.
[5] J. J. Yeh and I. Lindau, At. Data Nucl. Data
Tables 32 (1985) 1.

121

BL5U

Angle-Resolved Ultra-Violet Photoemission Study of Fe2-xV1+xAl

K. Soda1,2, K. Nakamura3, H. Miyazaki1,2, M. Inukai1, F. Ishikawa4, Y. Yamada4
1
Graduate School of Engineering, Nagoya University, Nagoya 464-8603 Japan
2
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585 Japan3
School of Engineering, Nagoya University, Nagoya 464-8603 Japan
4
Faculty of Science, Niigata University, Niigata 950-2181, Japan
Introduction
Heusler-type intermetallic compound Fe2 VAlshows unusual transport properties, which arereminiscent of the heavy fermion system [1]. The
off-stoichiometric alloys Fe2-xV1+xAl also reveal theremarkable enhancement in the thermoelectric power,
which cannot be explained in terms of a rigid bandmodel [2]. Theoretical studies suggest that theunusual properties may be induced by magnetic
clusters around anti-site defects, whose d states
appear within a sharp pseudogap across the Fermi
energy EF in its semimetallic electronic structure [3,4].
Thus, we have investigated the electronic structuresof Fe2-xV1+xAl using angle-resolved photoemission
spectroscopy (ARUPS) in order to clarify the originsof the unique transport and thermoelectric properties.

Experimental
The ARUPS measurements were performed at
BL-5U using linearly polarized synchrotron light as
an excitation light source. Single crystalline
specimens of Fe2-xV1+xAl were prepared by the
Czochralski pulling method in a tetra-arc furnace [2]and their clean (001) surfaces were obtained by in situ
fracturing them at low temperatures.

Fig. 1. Angle-resolved photoemission spectra of
Fe2.05V0.95Al.

Results and Discussion
Figure 1 shows ARUPS spectra of the Fe2.05V0.95Al(001) surface recorded with the (010)-polarized 65 eV
excitation light at various polar angles  along the(100) axis, which elucidates the electronic structure
along the -X line. There are at least two prominent
bands and three weak bands, whose peak positions
are indicated by black solid circles in Fig.2, the image
plot of the second derivative of the ARUPS spectra
versus the wave vector. The band structure of Fe2 VAlcalculated by a code Wien2k is also shown by whitecurves in the figure. In spite of the expected increasein the valence electron concentration for Fe2.05V0.95Al,
no electron pockets are clearly observed at the X
point. This might be caused by the small enrichmentof Al in the growth of the single crystals and result inthe observed positive thermoelectric power [2].
Detailed analysis near EF around the  and X
points will be reported elsewhere.

Fig. 2. Energy dispersion relation along the -X lineof Fe2.05V0.95Al.
[1] Y. Nishono et al., Phys. Rev. Lett. 79 (1997)
1909.
[2] F. Ishikawa et al., J. Magn. Magn. Mater. 310(2007) e616.
[3] J. Deniszczyk, Acta Phys. Pol. B 32 (2001) 529.
[4] S. Fujii et al., J. Phys. Soc. Jpn. 72 (2003) 698.

122

BL5U

Surface Chemistry of Alkyl-Passivated Si Nanoparticles Studied by
Photoelectron Spectroscopy

A. Tanaka, N. Takashima, M. Imamura, T. Kitagawa, Y. Murase
Department of Mechanical Engineering, Graduate School of Engineering, Kobe University,
Kobe 657-8501, Japan
Introduction

reported the QMC HOMO-LUMO gaps of
surface-passivated Si nanoparticles with and without
oxygen contaminants, and have shown a significant
decrease of HOMO-LUMO gap due to the oxygen
contaminations [2]. Moreover, they have also
calculated the density of states (DOS) in surfacepassivated Si nanoparticles with various contaminantsby means of local density approximation (LDA).
When a double bonded contaminant such as oxygenand sulfur is added to Si nanoparticle, Si sp3 network
is considerably distorted and HOMO and LUMO
change their nature significantly. As a result, HOMO
and LUMO states localized in the vicinity of the
Si=O double bond, and the modified DOS originatedfrom the HOMO and LUMO appears near the Fermi
level as the additional features. From the comparison
with this theoretical LDA DOS, it is considered thatthe additional feature in the present photoemission
spectrum of Si nanoparticles with oxygen
contaminants is ascribed to the modified HOMO
states by oxygen contaminations.

Numerous works focused on the optical propertiesof Si nanoparticles prepared by various methods havebeen reported to date. However, these opticalproperties in the literatures are ascribed to various
sources, and this discrepancy is considered tooriginate that the physical properties of nanoparticles
are greatly influenced by surface chemistry due toincrease of surface area to volume ratio by reducing
the size to the nanometer scale. In this paper, we havecompared the valence-band photoemission spectra offully n-butyl-passivated Si nanoparticles and thosewith oxygen contaminants in order to investigate theirsurface chemistry.

Experiment
Synthesis procedure of n-butyl-passivated Si
nanoparticles used in this work is described elsewhere[1]. Photoemission measurements were performed at
BL-5U of UVSOR II Facility for as-synthesized(fresh) n-butyl-passivated Si nanoparticles with mean
diameter of dc=1.1 nm and those exposed to ambient
air for 10 minutes.

Results and Discussion
Figure 1 shows the valence-band photoemission
spectra of as-prepared n-butyl-passivated Si
nanoparticles with dc=1.1 nm and those exposed toambient air for 10 minutes, on the HOPG substrate atroom temperature with photon energy of 195 eV.
Spectral features in the photoemission spectrum of
as-prepared n-butyl-passivated Si nanoparticles
originate from the C 2sp- and Si 3sp-derived valence
electronic states. The valence-band maximum energy(HOMO) energy is estimated to about 2.2 eV below
the Fermi level as shown by thin arrow on lower
spectrum in Fig. 1. If the Fermi level is considered to
be located in the middle of HOMO-LUMO gap,
HOMO-LUMO gap of the present n-butyl-passivatedSi nanoparticles with dc=1.1 nm can be estimated toabout 4.4 eV. This result agrees with the recent
quantum Monte Carlo (QMC) calculation by Putzer et
al. [2]. On the other hand, it is confirmed from the
FT-IR spectrum that the exposure to ambient air of
the present n-butyl-passivated Si nanoparticles induce
the removal of surface-passivants of alkyl groups andsubsequent passivation of oxygen. As shown in Fig. 1,
the valence-band spectrum of Si nanoparticles withoxygen contaminants exhibits an additional feature
centered around 2.6 eV in binding energy (as shownby thick arrow in Fig. 1). Putzer et al. have also

Fig. 1. Valence-band photoemission spectra ofas-synthesized n-butyl-passivated Si nanoparticles
with dc=1.1 nm (blue) and those exposed to ambient
air for 10 minutes (red).
[1] A. Tanaka et al., Solid State Commun. 140 (2006)
400.
[2] A. Puzder et al., Phys. Rev. Lett. 88 (2002)
097401.

123

BL7U

Momentum-Dependent Kondo Resonance Peaks in a Low-Energy
Angle-Resolved Photoemission Spectroscopy

H.J. Im1,2, T. Ito2,3, H. Miyazaki4,2, S. Kimura2,3, C.I. Lee1, K.E. Lee1, Y.S. Kwon1
1
Department of Physics, Sungkyunkwan University, Suwon 440-746, Korea
2
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan3
School of Physical Sciences, The Graduate University for Advanced Studies, Okazaki444-8585, Japan
4
Graduate School of Engineering, Nagoya University, Nagoya 464-8603, JapanFor investigation of the electronic structure ofstrongly correlated electrons system, bulk-sensitive
high-resolution
angle-resolved
photoemission
spectroscopy (ARPES) with utilizing tunable photons
has been a great challenge issue to physicists. In thecase of cuprate superconductors, for instance, theirelectronic structures have been well surveyed withhigh energy resolution regardless of the bulk- or
surface-states because of the two-dimensional
electronic structure of CuO2 layers which governs
their physical properties [1]. On the other hand, theprecise understanding of heavy-fermion systems
requires the three-dimensional bulk electronic
structure with high resolution [2]. This can berealized in a low energy photoemission using thesynchrotron radiation source. Recently, the highresolution ARPES apparatus has been equipped in
BL7U of UVSOR-II with photon energies from 6 to
40 eV [3].
Therefore, we have performed ARPES on
CeCoGe1.2Si0.8, where the c-f hybridization bands
were firstly observed in Ce 4d-4f resonant ARPES [4],as a target sample. The used photon energy is 15 eV,
where the measured momentum spaces include
-point in normal emission. Total energy resolution isabout 15 meV. Measurement temperature is 20 K
which is very low compared to the Kondo
temperature of CeCoGe1.2Si0.8 (TK ~ 350 K). Sample
surfaces were prepared by in situ cleaving under ultrahigh vacuum. Sample cleanliness is checked by thevariation of spectral shape of valence which becomes
broad due to surface contamination.
Figure 1 is the spectrum of valence band obtainedin angle-integrated mode. We observed the two
prominent spectral weights around -1.2 and -2.5 eV,
and the tail of Kondo resonance peak at the
Fermi-level. This indicates that Kondo resonancepeaks composed of mainly f-state is well observed
although the cross section of f-state is smaller than
one of non-f-states (spd-state) in a low kinetic energyof photoelectrons.
Figure 2(a) is an intensity plot of ARPES spectra
which represents a band dispersion. It is observed thata conduction band crosses the Fermi level at k = 0.2
Å-1, where the evidence of c-f hybridization must
appear as in Ce 4d-4f resonant ARPES [4]. Figure

124

2(b) shows the energy distribution curves at k = 0.07
and 0.2 Å-1. The tail of Kondo resonance peak at the
Fermi-vector (k = 0.2 Å-1), while the corresponding
feature is absent at k = 0.07 Å-1. This indicates that
Kondo resonance peak has the momentum
dependence in agreement with a periodic Andersonmodel [4].

Fig. 1. Angle-integrated PES spectrum
CeCoGe1.2Si0.8 in valence band regime.

ofFig. 2. (a) ARPES intensity plot of CeCoGe1.2Si0.8 at
hv = 15 eV. (b) Energy distribution curves at k = 0.2
and 0.07 Å-1.
[1] A. Damascelli et al., Rev. Mod. Phys. 75 (2003)
473.
[2] D. Malterre et al., Adv. Phys. 45 (1996) 299.
[3] T. Ito et al., AIP Conference Proceedings 879(2007) 587.
[4] H.J. Im et al., Phys. Rev. Lett. 100 (2008)
176402.

BL7U

Evidence of Three-Dimensional CDW Formation on CeTe2:

VUV Three-Dimensional Angle-Resolved Photoemission Study
T. Ito1,2, H. J. Im3, S. Kimura1,2, Y. S. Kwon3
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
2
School of Physical Sciences, the Graduate University for Advanced Studies (SOKENDAI),
Okazaki 444-8585, Japan3
Department of Physics, Sungkyunkwan University, Suwon 440-749, Korea
1

Low-dimensional electronic structure is believed to
be an important essence to understand the anomalous
physical properties, such as a charge/spin density
wave formation, high-Tc superconductivity, etc.,
originating from the anisotropic electronic/magnetic
structure. In turn, the investigation of thethree-dimensional effect in the electronic structure isessentially important to understand the anomalous
physical properties of low-dimensional compounds.
To
demonstratetheimportanceof
three-dimensionality to insight into the anomalous
physicalproperties,
wehave
performed
three-dimensional angle-resolved photoemission
spectroscopy (3D-ARPES) on quasi-two-dimensionalcharge-density-wave (CDW) compound CeTe2 [1]
where the existence of three-dimensional anomaly at
the Fermi surface (FS) has been reported [2].
The 3D-ARPES was performed at the beamline 7U
of UVSOR-II, the Institute for Molecular Science,
which has been developed in 2007 for bulk-sensitive
ARPES on strongly correlated electron systems in the
VUV region [3]. Taking account of the inner potentialof V ~ 16.4 eV [2], we set the measurement axis
along (110) plane of Te 5p hole-like FS (see hatchedblue area in Fig. 1).
Figure 2 shows the evolutions of the hole-pocket
around the MR line as a function of photon energy h ,in other word, of the kz line in the Brillouin zone. We
clearly observe that the Te 5p band (solid line) folds
at the EF crossing point (dashed line) at h = 19 eV(M line), i.e., the Fermi surface of the Te 5p band isnested due to the CDW formation. Furthermore,with decreasing photon energy, the separation
between the Te 5p band and the folded band
gradually increases. This result suggests that thenesting condition becomes imperfect from the M to
ZR lines gradually. The observed change of thefolded band certainly indicates the existence of theunexpected three-dimensional CDW vector inquasi-two-dimensional CeTe2.
The origin of the observed three-dimensional CDW
vector is not clear at present, since there are few
examples of three-dimensional study of electronic
structure so far, especially for the quasi-two
dimensional materials. Present observation of
three-dimensional
interactionsonquasi-twodimensional CeTe2 clearly indicates that 3D-ARPES

will shed light on understanding the effect ofanisotropic interactions originating in the various
functionalities.

Fig. 1. Schematic Fermi surface of CeTe2.

Fig. 2. h-dependent experimental band structure of
CeTe2 The images of h = 19 and 13 eV correspondto the band structure in the M and ZR lines,
respectively. See the text for details.
[1] M. H. Jung et al., J.Phys.Soc.Jpn 69 (2000) 937.
[2] T. Ito et al., J. Mag. Magn. Mater. 310 (2007)
431; Physica B 378-380 (2006) 767.
[3] S. Kimura et al., AIP conf. Proc. 879 (2007) 527.

125

BL7U

Temperature-Dependent Extremely Low-Energy Photoemission
Spectroscopy of a Fe-Based "Kondo Semiconductor"

A. Sekiyama1, G. Funabashi1, S. Komori1, M. Kimura1, M. Tsunekawa1, H. Sugiyama1,
T. Uyama1, H. Nakamura2, T. Ito3, S. Kimura3, S. Imada1, S. Suga1
1
Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531,
Japan
2
Graduate School of Engineering, Kyoto University, Kyoto 606-8501, Japan
3
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585 Japan
Introduction

seen in normal metals, suggesting that the electronic
structure changes intrinsically with temperature. On
the other hand, a clear Fermi cut-off is seen at 20 K.
If it is assumed that the surface contribution in these
ELEPES spectra is negligible, we can conclude thatFeSb2 is semimetallic at low temperatures, in otherwords, a Kondo semiconductor with the negative
indirect gap.
There is a broad peak at the binding energy ofabout 200 meV in all photoemission spectra at h =6.5, 10, 21 and 30 eV (not shown here) which wehave measured at 20 K in the so-called
semiconductong phase. When we normalized thespectra by the intensity of the broad peak, the Fermi
cut-off intensity decreases rather discontinuously
from h = 21 eV to 10 eV whereas it is comparable
between h = 30 eV and 21 eV, and between h = 10
eV and 6.5 eV, respectively. This discontinuous
reduction of the cut-off might be ascribed to thehigher bulk sensitivity of the photoemission at h 
10 eV than that at h > 20 eV.

Kondo semiconductor or Kondo insulator, whichshows nonmagnetic semiconducting behavior at low
temperatures with a formation of the (pesudo-)gap
while it is rather metallic at high-temperature, is oneof intriguing subjects in strongly correlated electron
systems. FeSb2 [1,2] is recognized as a candidate forthe Kondo semiconductor, whose macroscopic
properties are similar to those for already known
4f-based Kondo semiconductors. From previous
photoemission studies [3], it has been known that thesurface of the Kondo semiconductor is often metallic.
Therefore, bulk-sensitive photoemission is very
important to clarify their intrinsic electronic states.
Recently, extremely low-energy photoemission(ELEPES, h < 10 eV) has been thought as anotherpossibletechnique[4]asbulk-sensitive
photoemission, being complementary to highexcitation-energy photoemission. We have performed
ELEPES for FeSb2 in order to examine the bulk
electronic state.

Experimental
ELEPES was performed at BL7U by using aphotoelectron spectrometer of MB Scientific A1
analyzer. In order to obtain clean surfaces, the bulk
FeSb2 samples were fractured in situ. We havemeasured both surface-sensitive and bulk-sensitive
photoemission spectra by controlling excitation
photon energies from 6.5 to 30 eV. The energy
resolution was set to ~5 meV.

Results and Discussions
Figure 1 shows the temperature dependence of the
ELEPES spectra measured at h = 6.5 eV for FeSb2.
The spectra have been normalized by the spectral
weight above the binding energy of 200 meV. At allmeasuring temperatures, the intensity monotonously
decreased from the binding energy of 200 meV
toward the Fermi level (EF). In this energy region, thespectral weight is clearly reduced with lowering
temperature. This indicates that the density of statesnear EF decreases from 200 K in the metallic phase to
20 K in the semiconducting phase in the energy scaleof 200 meV. Such temperature dependence is not

Fig. 1. Temperature-dependent extremely low-energy
photoemission spectra of FeSb2.
[1] C. Petrovic et al., Phys. Rev. B 67 (2003) 155205.
[2] C. Petrovic et al., Phys. Rev. B 72 (2005) 045103.
[3] For example, K. Breuer et al., Phys. Rev. B 56
(1997) R7061.
[4] T. Kiss et al., Phys. Rev. Lett. 94 (2005) 057001.

126

BL7U

Electronic Structure and Thermoelectric Power of La2-xSrxCuO4

T. Takeuchi1,2, H. Komoto2, T. Ito3, S. Kimura3
1
EcoTopia Science Institute, Nagoya University, Nagoya 464-8603 Japan2
Department of Crystalline Materials Science, Nagoya University, Nagoya 464-8603 Japan
3
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585 Japan
samples. The ARPES measurements were performed
at 50K with the incident photon energy of 30.0 eV.
Figure 1 shows a typical example of the observed
ARPES images together with the energy distribution
curves and the momentum distribution curves whichwere cut from the image. The band dispersion isclearly observed, and we safely determined  ( k )with employing the tight-binding function fitting offour different transfer integrals. Once  ( k ) is
determined, spectral conductivity  (  ) can becalculated from  ( k ) under an assumption of
constant mean free path as we assumed in ourprevious analysis on the Bi2201 and Bi2212. Bytaking the effect of the AFZB scattering into account,
we calculated thermoelectric power of LSCO fromthe experimentally determined  (  ) . Figure 2 shows
calculated and measured thermoelectric power. The
calculated thermoelectric power quantitatively
reproduced the measured one even in their carrier
concentration dependence. As a result of thiscalculation, we realized that the LSCO is morestrongly affected by the AFZB scattering than the
Bi2201 and Bi2212. This tendency must be caused by
the smaller carrier concentration of LSCO than that of
Bi2201 and Bi2212.

Thermoelectric
power
of
the
cupratesuperconductors is widely known to possess unusual
behaviors such as the non-linear temperaturedependence and the positive to negative sign-reversal
with increasing hole-concentration. These behaviors
are not generally observable for metallic compounds.
Strong electron correlation is considered as one of thepossible origins inducing such unusual behaviors inthermoelectric power.
By using the angle resolved photoemission
spectroscopy (ARPES) and the semi-classical
Bloch-Boltzmann theory, we revealed for the(Bi2201)
andBi2Sr2CaCu2O8+
Bi2Sr2CuO6+
(Bi2212) superconductors that the unusual behaviorsof the thermoelectric power, especially its large
magnitude with positive sign in underdoped samples,
are caused by the strong scattering of the conduction
electrons at the anti-ferromagnetic zone boundary(AFZB). [1,2] Note here that the AFZB is essentiallycaused by the anti-ferromagnetic ordering of the
conduction electrons, that is not fully observable inthe superconductors but in the Mott-Insulator as aconsequence of the carrier localization caused by thestrong on-site coulomb interaction. Therefore, it issafely argued that the thermoelectric power of thecuprate superconductor is indeed characterized by thestrong electron correlation.
One may wonder that the effects of the electron
correlation on the thermoelectric power, that iscaused strong scattering at the AFZB, could beclosely related with the stability or instability ofsuperconducting phase. To gain deeper insight into
the relation between the strong scattering at the
AFZB and superconducting transition temperature,
we determined the development of the AFZB
scattering of conduction electrons as a function ofcarrier concentration by analyzing thermoelectric
power of the La2-xSrxCuO4 (LSCO) superconductors
as we did for the Bi2201 and Bi2212 in our previous
works. [1,2]The single grained La2-xSrxCuO4 samples of 0.06 x  0.25 were prepared by the floating-zone method.
The superconducting transition temperature wasdetermined by the magnetization measurement with
the SQUID magnetometer. We also measured
electrical resistivity and thermoelectric power with
the Thermal Transport Option of the Physical
Property Measurement System assembled by
Quantum Design Inc. High resolution ARPES was
performed at the BL05U of UVSOR, Okazaki Japan.
The energy resolution employed in this study was~20meV, which was defined by the energy with ofintensity reduction from 90 % to 10 % at the Fermi
level of reference gold electrically contacted with

Thermoelectric power, S / μV K

-1Fig. 1. (a) an ARPES intensity image near the (  , 0)
point of La1.75Sr0.25CuO4 accumulated at 50K. (b)Energy distribution curves and (c) momentum
distribution curves cut from the ARPES image. A
band crossing the Fermi level is clearly observed.
calculated S measured S
x = 0.06
0.08
0.10
0.12
0.15
0.19

150
100
50
0
0

200

400

600

800

1000

Temperature, T/ K

Fig. 2. Calculated and measured thermoelectric powerof La2-xSrxCuO4. The measured value is quantitatively
reproduced by the calculation.
[1] T. Kondo et al., Phys. Rev. B 72 (2005) 024533.
[2] T. Takeuchi et al., J. Elec. Spec. Relat. Phenom.
156-158 (2007) 452-456.

127

BL8B1Graphitization of Thin Films Formed by Focused-Ion-Beam
Chemical-Vapor-Deposition

K. Kanda, J. Igaki, N. Yamada, R. Kometani, S. Matsui
Laboratory of Advanced Science and Technology for Industry, University of Hyogo, Kamigori,
Hyogo, 678-1205 Japan
Focused-ion-beam chemical-vapor deposition(FIB-CVD) method is developed as an effective
technique for producing of three-dimensional
nano-structures, which formed complex shape withoverhung, hollow and bridging structure. In thismethod, scanning of focused Ga ion beam under thephenanthrene gas atmosphere using as a source gas
leads to deposition of carbon material at arbitrarynano-scale area. The fundamental structure of carbon
material formed by FIB–CVD is diamond-like carbon(DLC) from the measurement of Raman spectrum [1].
It was known that pillars grown by FIB–CVD had aGa-rich core and these residual Ga departed from the
FIB–CVD DLC by the annealing at 700°C. In theother hand, the pillar was reported to graphitize by
the transfer of Ga using flash discharge [2].
The coordination of the carbon atoms has been
principally determined by near-edge x-ray absorption
fine structure spectroscopy (NEXAFS). The
movement of Ga in the FIB-CVD DLC thin film byannealing was observed in the NEXAFS study [3],but the graphitization was not obviously confirmed.
In the present study, FIB-CVD DLC films of 200
nm thickness were prepared by annealing at 1 hour inthe temperature range from room temperature to
750°C. Fig. 1 shows the C K-edge NEXAFS spectraof FIB-CVD DLC films, (a) as deposition and (b)after 1 h annealing at 750°C with that of (c) graphite
as a reference. The intensity of a peak at 285.4 eV,corrsponding to 1s* trangition increased by theannealing. This increase indicated that sp2/sp3 ratio
increased in the film. In the 290-320 nm of *
resonance region, the several bands characteristic to
FIB-CVD DLC thin film changed by the annealing to
the strctural bands characteristic to the graphite.
These changes indicated that FIB-CVD DLC films
graphitized by the 1 h annealing at 750°C.

Fig. 1. C K-edge NEXAFS spectra of FIB-CVD DLC
thin films and graphite.
[1] S. Matsui et al., J. Vac. Sci. Tech. B 18 (2000)
3181.
[2] J. Fujita et al., Appl. Phys. Lett. 88 (2006) 83109.
[3]A. Saikubo et al., Jpn J. Appl. Phys. 46 (2007)
7512.

128

BL8B1

Characterization of Various Lithium Compounds by an XAFS Method

T. Kurisaki1, Y. Sakogawa1, D. Tanaka1, H. Wakita1,2
1Department of Chemistry, Faculty of Science, Fukuoka University, Nanakuma, Jonan-ku,
Fukuoka 814-0180, Japan
2
Advanced Materials Institute, Fukuoka University, Nanakuma, Jonan-ku, Fukuoka 814-0180,
Japan
Lithium compounds are used in industrial andcommercial applications such as lithium ion batteries,
lithium glasses, and medicines of a manic-depressive
illness. The XAFS method has not been widely used
to estimation the characteristic of these materials
owing to the low energy (below about 70eV) of Li K
edge. However, there are a few reports about Li-K
XANES spectra [1].
In this work, we applied the X-ray absorption nearedge structure (XANES) spectroscopy to lithiumcompounds. X-ray absorption spectra of near Li K
absorption edges were (XAFS) measured at BL8B1of the UV-SOR in the Institute of Molecular Science,
Okazaki [4]. The energy of the UVSOR storage ringwas 750MeV and the stored current was 110-230 mA.
The absorption was monitored by the total electron
yield using a photomultiplier. We employed thediscrete variational (DV)-X molecular orbital (MO)method to obtain calculated spectra, and compared
observed spectra with the calculated spectra.
The Li K XANES spectra for various lithiumcompounds are shown in Fig. 1. The energy was notcalibrated by standard samples. The energy positionof each first peak should not depend on the charge ofanion. However, the peak shapes are different by theanions. This result showed that the two aluminumcompounds have different electronic state. We aregoing to try to calculate the spectra by DV-X
molecular orbital calculations

Fig. 1. Li K-edge XANES spectra of lithiumcompounds.
[1] J. Tsuji et al., Adv. X-ray Chem. Anal. Jpn. 31(2000) 149.
[2] J. Tsuji et al., J. Synchrotron Radiat. 8 (2001)
554.
[3] J. Tsuji et al., X-Ray Spectrom. 31 (2002) 319.
[4] S. Murata et al., Rev. Sci. Instrum. 63 (1992)
1309.

129

BL8B1N K-Edge XANES Analysis of Nitrogen Implanted in TiO2

T. Yoshida1, S. Muto1, H. Yoshida2
1
Department of Materials, Physics and Energy Engineering, Nagoya University, Furo-cho,
Chikusa-ku, Nagoya 464-8603
2
EcoTopia Science Institute, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603
Fig.1 shows the N K-edge XANES spectra of the
N+-implanted TiO2 samples and a TiN powder.
Similar XANES features for (a) and (b) suggest that
N in the sample implanted by 3 x 1021 m-2 (highest
active photocatalyst) is in a chemical environment
similar to that in TiN. More thorough observationsuggested that double-peak around 400 eV in (b)shifted to the lower energy side compared with that of
TiN, which was well reproduced by the theoreticalprediction using FEFF code [3] when N occupies oneof the O sites of TiO2, as suggested in ref.[1]. On theother hand, the XANES spectrum of the sample
implanted with the N+ fluence of 5 x 1021 m-2
followed by heat-treatment (almost inactive tovisible-light) shows a distinct single peak at around
401 eV (Fig. 1c). This peak was attributed toformation of NO and/or NN bonds near the surface[3], which significantly suppresses the photocatalytic
activity.

Photocatalytic reactions at the surface of titanium
dioxide (TiO2) under UV light irradiation have been
attracting much attention due to their practicalapplications such as environmental cleaning.
Recently, Asahi et al. reported that substitutional
doping of nitrogen into TiO2 contributed to narrowingof the band gap, thus providing a visible-light
response [1]. Furthermore, previous investigations
demonstrated that nitrogen doping generated new
optical absorption bands in the visible-light region
and the absorbance evolved with increasing nitrogen.
On the other hand, absorbance may not be linearly
proportional to the photocatalytic activity, and it isthus important to understand the chemical
In the present
environment of N in TiO2.
investigation, structural analysis was performed for
N+-implanted TiO2 catalysts by means of X-ray
absorption spectroscopy (XAFS).
The samples used in this study were TiO2 (1 0 0)
single crystals (5 x 5 x 0.5 mm3), supplied by
Furuuchi Kagaku, Japan. Mass analyzed 100 keV N2+
ions (50 keV/ N+ ion) were injected into the samples
at room temperature, perpendicular to the sample
surface. The N+ fluence ranged from 1 to 5 x 1021 m-2.
After the ion implantation, parts of the samples were
heat-treated at 573 K for 2 hours in air.
A typical photocatalytic experiment consisted of
placing the N +-implanted sample in 0.5 ml of aqueous
methylene-blue (MB) solution (9.8 μmol/L) andsubsequent exposure to visible-light using a 15 W Xe
lamp with a cut filter for  > 430 nm. The lightabsorbance at  = 664 nm after exposure for 2 hours
was measured to estimate the photocatalytic activityof the samples.
N K-edge XANES spectra of the N+-implanted
TiO2 samples were measured at the BL-8B1 station of
UVSOR-II at the Institute for Molecular Science,
Okazaki, Japan. Data were recorded at room
temperature in total electron yield mode, and the
X-ray energy dependence of the N Auger electron
yield was monitored [2]. Considering the escapedepth of the Auger electrons, the spectra probe thesample from the surface up to a few nanometers in
depth.
The photocatalytic activity reached its maximum ata fluence of 3 x 1021 m-2 and then decreased with thefluence. The sample implanted at a fluence of 5 x 1021
m-2 followed by heat-treatment at 573 K was almost
photocatalytically- inactive under visible-lightirradiation.

Fig. 1. N K-edge XANES spectra of a TiN(a),N+-implanted at 3 x 1021 m-2(b) and 5 x 1021 m-2
followed by heating at 573 K for 2 h(c).
[1] R. Asahi et al., Science 293 (2001) 269.
[2] A. Erbil et al., Phys. Rev. B 37 (1988) 2450.
[3] A. L. Ankudinov et al., Phys. Rev. B 58 (1998)
7565; J. Stöhr, R. Jaeger, Phys. Rev. B 26 (1982)
4111.
[4] J.-H. Wang et al., Anal. Chim. Acta 476 (2003)
93.

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