5
Solid state
spectroscopy
II: XAFS and
PES

93

BL5U

Angle-resolved Photoemission Study of CeCoGe1.2Si0.8 in theThree-dimensional Momentum Space
H.J. Im1,2, T. Ito2,3, S. Kimura2,3, J.B. Hong1, Y.S. Kwon1
1
BK21 Physics Research Division and Institute of Basic Science, 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
Recently, CeTX2 systems (T = transition metals, X= semiconducting elements) have intensively studied
because of several intriguing phenomena such as
heavy fermion behavior with J = 5/2 in CeCoGe2 [1],valence fluctuation in CeNiSi2 [2], and strongly
anisotropic magnetic and transport properties in
CeNiGe2 [3]. Hybridization of localized f-electrons
with conduction electrons (f-d hybridization) plays animportant role to derive the above properties. In orderto understand these interesting physical properties, it
is important to clarify the electronic structure of thissystem. Therefore, we have performed theangle-resolved photoemission spectroscopy (ARPES)
on CeCoGe1.2Si0.8 with large f-d hybridization
strength in the three-dimensional momentum (k-)
space at BL5U.
Figure 1(a) shows the energy distribution curves(EDCs) measured at T = 10 K and θ = 0° (normal
emission) with changing the photon energy (hv) from48 to 88 eV. Peak positions represent the band
dispersion along the ky-direction. We can recognizethat there are two weakly dispersed bands around EB= 0.4 and 1.2 eV with the bottom and top at hv = 66
eV, respectively. This indicates that hv = 66 eV is asymmetry point in the ky-direction, and is found tocorrespond to the Γ-point with inner potential, V0 =15.8 eV.
Figure 2(a) shows the Fermi surface (FS) in the
kzx-ky plane as depicted by the shaded plane in Fig.
1(b), mapped with the energy window from EB = 100
to -100 meV. There are two kinds of FS: One is alarge FS, which is continuously formed along
ky-direction in the range of from kzx ≈ 0.5 to 0.7 Å-1 as
guided by a dashed line. Other FS inside large FS
also seems to open along ky-direction. In comparison
to band dispersions around Γ and Υ-points as shownin Fig. 2(b) and (c), respectively, the opened large FS
consists of bands which cross EF at around kzx = 0.6
Å-1 ,forming hole pockets.
As a result, the large hole FS that opens along the
ky-direction indicates the quasi-two-dimensional
electronic structure. This is consistent with the resultsof transport experiments (large anisotropy ofelectrical resistivity, ρc/ρab ≈ 700 [4]) and suggeststhat the f-d hybridization strength has anisotropy due
to two-dimensionality.

Fig. 1. (a) EDCs of CeCoGe1.75Si1.25 observed by
hv-dependent ARPES. The dashed lines are guides tothe eye. (b) Brillouin zone of the single-faced
orthorhombic structure. The bold arrow and shadeplane stand for the measurement path and plane,
respectively.

Fig. 2. (a) FS mapping of CeCoGe1.75Si1.25 in the
kzx-ky plane as depicted by the shaded plane in Fig
1(b). ARPES intensity plot representing the band
dispersions along kzx-direction at around Υ- (ky = 4.89
Å-1, b) and Γ- (ky = 4.52 Å-1, c) points, respectively.
[1] E.D. Mun et al., Phys. Rev. B 69 (2004) 085113.
[2] E.D. Mun et al., Phys. Rev. B 67 (2003) 033103.
[3] M.H. Jung et al., Phys. Rev. B 66 (2002) 054420.
[4] Y.S. Kwon et al., private communication (2007).

94

BL1A

Local Structure Analysis of Aluminum Compounds by an XAFS Method
T. Kurisaki1, Y. Inoue1, 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
Aluminum compounds collected much interest
because of their ability to act as catalysts, andfunctional materials. The function of aluminumcompound is concerned closely with that coordination
structure. For various aluminum compounds, we havestudied the electronic structure by X-ray absorption
spectroscopy [1, 2]. This result suggested that there iscorrelation in the form 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 and occupied
electronic structure of aluminum compounds. The
X-ray absorption spectra were measured at BL1A of
the UVSOR in the Institute of Molecular Science,
Okazaki [2]. 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 was monitored by the total
electron yield using a photomultiplier. The samples
were spread into the carbon tape on the first
photodynode made of CuBe of the photomultiplier.

The Al K-edge XANES spectra for the aluminum
phosphate and aluminum sulfate are shown in Fig. 1.
A remarkable change of the spectral patterns wasobserved for the aluminum phosphate and aluminum
sulfate. This result showed that the two aluminumcompounds have different electronic state. We aregoing to try to analyzed this change from comparisonof Al K edge XANES and calculated spectra by
DV-Xα molecular orbital calculations.
[1] H. Ichihashi, T. Kurisaki, T. Yamaguchi, T.
Yokoyama, and H. Wakita, Jpn. J. Appl. Phys. Part 1,
38(suppl.) (1999) 101.
S. Matsuo, K. Shirouzu, Y. Tateishi and H. Wakita,Adv. Quan. Chem. 42 (2002) 407.
[3] S. Murata, T. Matsukawa, S. Naoè, T. Horigome,
O. Matsuodo, and M. Watatabe, Rev. Sci. Instrum. 63(1992) 1309.

Intensity/a.u.

AlPO4
Al2(SO4)3

1640

1660

1680
1700
Energy / eV

1720

Fig. 1 Observed Al K-edge XANES spectra ofaluminum phosphate and aluminum sulfate

95

BL1A

Characterization of Aluminum Naphthalocyanine Complexes by an XAFS
MethodT. Kurisaki1, Y. Inoue1, 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
Phtalocyanines (PC) and their derivatives are ofparticular interest due to many possible applications,such as catalyst, medical supply, semiconductor, andhighsensitivity
colorimetricregent.
Naphthalocyanine (NPC) has a largely p-conjugated.
In order to elucidate the effect of the axial ligand, it isnecessary to determine their electronic structure [1].
But the electronic structure of naphthalocyanine is notwell known.
In this work, we applied the x-ray absorption nearedge structure (XANES) spectroscopy to analyze thestructure of AlNPC-Cl. The results of themeasurement indicate unoccupied and occupied
electronic structure of AlNPC-Cl complex. The X-ray
absorption spectra were measured at BL1A of the
UVSOR in the Institute of Molecular Science,
Okazaki [2]. The ring energy of the UVSOR storage
ring was 750MeV and the stored current was 110-230
mA. Cl K-edge absorption spectra were recorded in
the regions of 3000-3285eV by use of two InSb(111)crystals. The absorption was monitored by the total
electron yield using a photomultiplier.

Intensity / a.u.

obs.
Al 3p
Cl 3p

3100 3110 3120 3130 3140 3150
Energy / eV
Fig. 2 Observed and calculated Cl K-edge XANES
spectra of AlNPC-Cl.

AlPC-ClAlNPC-Cl
Intensity / a.u.

The Cl K-edge XANES spectra for AlNPC-Cl and
AlPC-Cl are shown in Figs. 1. A remarkable change ofthe spectral patterns was observed for AlNPC-Cl and
AlPC-Cl. The observed and calculated Cl K XANES
spectra for AlNPC-Cl are shown in Fig. 2.
Comparison of observed and calculated spectra
revealed that aluminum 3p and chloride 3p orbits
contribute to the first peak. However, AlNPC-Cl did
not contain the contribution from the N 2p and Al 3d
orbits.

3050

3100
3150
Energy / eV

[1] J. Simon F. Tournilhaec and J. –J. André, Nouv. J.
Chim. 10 (1986) 295.
[2] S. Murata, T. Matsukawa, S. Naoè, T. Horigome,
O. Matsuodo, and M. Watatabe, Rev. Sci. Instrum. 63,(1992) 1309.

3200

Fig. 1 Observed Cl K-edge XANES spectra of
AlNPC-Cl and AlPC-Cl

96

BL1A

Study of Local Structure of Al-K Edge for Modified Hydrotalcite(Layered Double Hydroxide)1

A. Nakahira1, H. Murase1, H. Nagata1, S. Nakamura1, T. Kubo1, H. Aritani2
Faculty of Engineering, Osaka Prefecture University, Gakuencho, Sakai 599-8531, Japan
2
Saitama Institute of Technology, Fukaya 369-0293, Japan
Figure 1 shows the results of XANES of Al-K edge ofsome mixed oxides. All were different from oxides
like α and γ-Al2O3 and a hydroxide like Al(OH)3. The
spectrum of
mixed oxide obtained at 200°C
corresponded approximately to that of MgAl-LDH. It
was elucidated that Al-K edge XANES spectra of
mixed oxides generated at 300, 400, and 500°C was
similar to that of MgAl-LDH, although peaks wasbroad with temperature.

Introduction

Normalized Intensity/a.u.

Layered double hydroxide (LDH) is a clay mineralwith a layered structure, in which its composition
formula is [M(II)1-x M(III)x(OH)2]x+·[An-x/n·YH2O].
M(II), M(III) and exchangeable anions in LDH areable to substitute to various cations and anions. In thepresent study, we focus on the structure evaluation ofbasic LDH composed of Mg2+ and Al3+, which iscalled hydrotalcite, MgAl-LDH. Furthermore, it is
known that various mixed oxide was generated bycalcination of LDH. Obtained mixed oxide is expected
to be applicable to many fields such as adsorption andion exchange materials, magnetic materials, catalysis,
and environmental purification materials since it has
high specific surface area and unique rehydration
behaviors. However, it is not clarified about hestructure evaluation of basic LDH and the detailed
structure of mixed oxides generated of LDH from 300
to 500°C.
In the present study, the structure evaluation ofbasic LDH composed of Mg2+ and Al3+, which iscalled hydrotalcite, and mixed oxide obtained bycalcination of MgAl-LDH at 300 to 500°C were
performed.

Experiments
Mixing solution was adjusted by mixing 0.2
mol/dm3 MgCl2 aqueous solution and 0.1 mol/dm3
AlCl3 aqueous solution. MgAl-LDH with M2+/M3+ =2
were synthesized by adding mixing solution into 0.05
mol/dm3 NaHCO3 at room temperature. 1 mol/dm3
NaOH was simultaneously added into the aqueous
solution in order to keep pH 10. After precipitation
was finished, products for MgAl-LDH were aged atroom temperature for 2 hours. They were separated
from liquid phase and sufficiently washed bydeionized water and finally air-dried at 110°C for 24hours.
Mixed oxides were obtained by calcination at 200, 300,
400, and 500°C for 2 hours of MgAl-LDH. The local
structures around Al were characterized by measuring
X-ray adsorption near edge structure (XANES) at
BL1A in UVSOR with KTP.

 -Al2O3
 - Al2O3
Al(OH) 3
500 °C
400 °C
300 °C
200 °C

MgAl-LDH
1550 1560 1570 1580
Energy/eV

1590

Fig. 1 Al-K XANES of MgAl-LDH products andsamples obtained by calcination of MgAl-LDH atvarious temperatures. -Al2O3 and -Al2O3 arereference materials.

Results and Discussion
Products prepared by co-precipitation method
identified to be layered double hydroxide consisted of
Mg2+ and Al3+ by powder X-ray diffraction analysis.
Then, it was suggested that mixed oxide generated bycalcination of obtained MgAl-LDH had broad peaks
derived from rock salt structure from XRD results.

97

BL1A

Study of Si K-edge of Local Structure in Mesoporous Silica Bulk
Prepared by Hydrothermal Hot-pressing
1

A. Nakahira , H. Nagata1, M. Takimura2, S. Nakamura1, T. Kubo1, H. Aritani3
1
Faculty of Engineering, Osaka Prefecture University, Gakuencho, Sakai 599-8531, Japan
2
Faculty of Engineering, Kyoto Institute of Tech, Matsugasaki, Kyoto 605-8585, Japan
3
Saitama Institute of Technology, Fukaya 369-0293, Japan
Mesoporous silica MCM-41 have attracted muchattention because of their possible uses as supports forcatalysts, a host for nanosize materials and adsorption.
However, since bulks of mesoporous structure could
not be obtained by conventional solidified methods
such as sintering, the application of mesoporous
materials is limited. Nakahira et al reported thatdensified bulky MCM-41 was successfully
synthesized using hydrothermal hot-pressing (HHP)
method [1]. Therefore, we attemped to exmine thelocal structure around Si of MCM-41 bulk by XANES
spectra.
MCM-41 powder was prepared as a starting material[2]. Mixture of powder and water was heated at 150°C
with uniaxial pressing under 40MPa and kept constantfor 2 hours. Obtained bulks were identified by XRD.
Si 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 1700 to 1925 eV atintervals of 0.05
eV with a dwell time of 1 s.
XRD results showed that MCM-41 bulk was also
retained the mesopores after HHP. Figure 1 shows theresults of Si K-edge XANES of MCM-41 bulk andstarting material powder ((a) and (b)). Silicagel (c) wasused as a reference material of amorphous silica withcoordiation number 4. The spectrum of HHP bulk wassignificantly similar to those of starting powder andsilicagel. Hence, there is no apparent change in therelative intensity nor the width of these spectra. These
results of XANES spectra revealed that the local
structure around Si enviroment was almost unchanged
before or after HHP treatment.

Fig. 1 Si K-edge XANES spectra of MCM-41 bulk
prepared by HHP.

[1] H. Nagata, M. Takimura, Y. Yamasaki and A.
Nakahira, Materials Transactions, 47 (08) (2006)
2103-2105[2] H. P. Lin and C. Y. Mou, Science, 273 (1996)
765-768.

98

BL1A

Measurement of X-ray Excited Optical Luminescence from a Silica Glass
T. Yoshida1, T. Tanabe2, H. Yoshida3
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
1

8Introduction

Radiation effects on silica glasses are one of themain concerns for their application as optical
windows, insulators and optical fibers under fusionand 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.
In the present study, we have utilized soft X-ray
as a radiation source. Since the energy region of thesoft X-ray covers the K- and L-edges of silicon andoxygen, it enables us to study the effects ofpreferential excitations of inner-shell electrons on thedefect production and/or annihilation. We thus
examined the changes in X-ray excited opticalluminescence (XEOL) of a silica glass with respect toexcitation X-ray energy near the threshold of the Si
K-edge, irradiation time and temperature.

ex.1834eV

Intensity (arb. unit)(a)6

ex.1858eV

4
ex.1848eV
20
2.0

Intensity (arb. unit)

6

Experimental
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.

5

3.0

4.0

Photon energy (eV)

(b)

5.0

ex.1858eV
ex.1834eV

4

ex.1848eV

3
2
1
0
2.0

3.0

4.0

5.0

Photon energy (eV)Fig. 1 Optical luminescence spectra of a fusedsilica glass excited by X-rays with the energies of1834, 1848 and 1858 eV at (a) 300 K and (b) 50K.
Solid curves are two Gaussians peaked at 2.6 and3.1 eV, resulting from the peak fit for the profile at1848 eV.
We also measured XEOL at lower temperatures, andfound the broadening of the emission band below 100
K. Fig. 2(b) shows XEOL of the same sample
measured at 50 K. A peak position is shifted to thelower energy side, because an additional emission
band appears around 2.6 eV, revealed by the peak fit,
as shown in Fig.2 (b). This additional emission bandoccurs, presumably because the excited electrons
survive longer at lower temperatures until relaxed tothe corresponding energy level(s).

Results and Discussion

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).
Fig. 1(a) shows observed XEOL spectra from thesample excited by the three different energies,
measured at room temperature. An intense emission
band peaked around 3.1 eV is observed in each
spectrum. The previous studies assigned the origin of
the 3.1 eV band to the intrinsic B2 center [1,2]. We
reported previously that in-reactor or UV irradiation
on silica glasses induced similar emission bands, andthis emission band can be induced also by the soft
X-ray irradiation, presumably by exciting theelectrons trapped at the oxygen-deficient sites.

[1] R. Tohmon, H. Mizuno, Y. Ohki, K. Sasagane, K.
Nagasawa, Y. Hama, Phys. Rev. B 55 (1989) 1337.
[2] S. Agnello, R. Boscaino, M. Cannas, F. M.
Gelardi, J. Non-cryst. Solids 232-234 (1998) 323.

99

BL1A

Atomic Structure of Supersaturated ZnO-Al2O3 Solid Solutions
I. Tanaka, S. Yoshioka, F. Oba, T. Yamamoto
Department of Materials Science and Engineering, Kyoto University, Kyoto 606-8501, Japanapplication to dopant characterization can be foundelsewhere. [1, 3]

X-ray absorption near-edge structure (XANES) is
known to be a powerful tool to probe local electronic
structure because of its sensitivity to change inchemical environment. It allows us to access the local
structure of dopants, utilizing the element selectivity.
In the present study, we investigate the local structureof Al solute atoms in ZnO by XANES. Samples aresupersaturated solid solution synthesized by pulsed
laser deposition (PLD) technique. First-principles
calculations are systematically made to evaluate thelocal atomic structures and energetics. Theoretical
XANES is also obtained by first-principles
calculations to interpret the experimental spectra.

Results and Discussion
X-ray diffraction (XRD) analysis found that
ZnO:Al films with Al concentration of less than 19
cation% are composed of a single crystalline phase. It
can be assigned as a wurtzite phase with an abnormal
expansion in lattice constant c by 1.5%. Experimental
and calculated XANES are shown in Fig 1. The
spectral features of experimental thin film sample aredifferent from those of the reference compound,
ZnAl2O4 having spinel structure. The spectrum iscloser to the theoretical spectrum for AlZn model
where Al is located at the substitutional Zn site ofwurtzite ZnO. However, this model is found to beinconsistent to the XRD results revealing lattice
expansion in the c direction. Systematic evaluation oftheoretical lattice constants and XANES spectra formodels with miscoordinated Al indicates that partial
contribution of such Al can provide a consistent
explanation of the structural and spectral features.

Experimental and Computational
ProceduresThin film samples were prepared by PLD
technique using an excimer KrF* laser source (=248 nm,  = 25 ns, Lambda physik COMPex205).
Laser frequency was kept at 10 Hz. The ceramic
samples were used for targets of PLD. Laser power
was approximately 3 × 104 J/m2. All PLD
experiments were made in oxygen backfill pressure of
pO2=0.3Pa. High purity SiO2 glass plates were used as
substrates. Substrate temperature was 600 ºC.
High-resolution X-ray absorption spectra at the Al
K-edge were measured using the BL1A beamline at
UVSOR. The XANES spectra were collected by the
total electron yield (TEY) method. The incident
photon beam was monochromatized using a KTP(2d011=10.954Å) double-crystal monochromator.
Samples were mounted using adhesive carbon tapes.
No surface coating to avoid charging was found to benecessary.
In order to reproduce XANES by theoretical
calculations, it is necessary to take into account thecorrelation between the core-hole and the excitedelectron. [1] It can be evaluated in a straightforward
way using all-electron methods. Therefore,
first-principles all-electron calculations based onorthogonalized linear combination of atomic orbitals(OLCAO) method [2] were employed in the present
study. Theoretical XANES spectra were obtained
within the electronic-dipole transitions. The core-hole
effects were fully taken into account by removing one
electron on Al 1s orbital and putting one additional
electron at the bottom of the conduction band. Inorder to avoid the artificial interactions amongcore-holes, supercells composed of more than 100
atoms were chosen on the basis of test calculations.
Transition energies were obtained as the difference intotal energy between the ground and core-hole states.
More details of the XANES calculation and its

Fig. 1. Theoretical and experimental Al K-edge
XANES spectra for ZnAl2O4 and Al-doped ZnO.
[1] I. Tanaka, T. Mizoguchi, and T. Yamamoto, J.
Am. Ceram. Soc. 88 (2005) 2013.
[2] W. Y. Ching, J. Am. Ceram. Soc. 73, 3135 (1990).
[3] I. Tanaka et al., Nature Mater. 2 (2003) 541.

100

BL1A

Structural Analysis of Active Mo species on H-MFI for Methane
Dehydroaromatization with Hydrogen

H. Aritani,1 N. Naijo,1 K. Takanashi,1 H. Orihara,1 A. Nakahira2
Faculty of Engineering, Saitama Institute of Technology, Fukaya 369-0293, Japan
2
Graduate School of Engineering, Osaka Prefecture Universitty, Sakai 599-8531, Japan1

Supported Mo catalysts on H-MFI zeolites show
noted high and selective activity to convert methane
to benzene. Because the catalytic process, so-called“GTL (Gas to Liquid)” one, is conventional and quite
selective for liquefaction of natural gases, catalysts
with high and durable activity have been called for.
However, design of the catalysts with durable activity
for methane dehydroaromatization is very difficult
because of carbon deposition and/or grafting during
the reaction. For MoO3/H-MFI, Mo species are
reduced to form several types of carbide species(Mo2+ mainly) in the initial reaction step (at above
973 K), and the carbide species play a role formethane activation to form CHx intermediates. At thesame time, H2 is outgassed. On H-MFI support,oligomerization of CHx intermediates assist to form
benzene. Selectivity of benzene formation is based on
the sieving by microporous structure of H-MFI.
Therefore, relation between the H-MFI support (withsurface acidity) and active Mo species formed in thereaction is thus important to clarify the formation
process and its stability of highly active Mo.1,2 In thisstudy, Mo LIII-edge XANES is applied to characterize
the Mo species on H-MFI with various SiO2/Al2O3
ratios.
All the catalysts were prepared by impregnation ofeach silica-alumina support with ammonium
heptamolybdate solution (7.5wt% loading as MoO3),
and followed by drying and calcination at 773 K for 3
h. H-MFI (Si/Al2=40, 72, 90, and 1880) supports
were synthesized hydrothermally at 443 K for 7 days,
and followed by ion-exchange (NH4+) treatment andcalcination at 773 K. Mo LIII-edge XANES spectra
were measured in BL1A of UVSOR-IMS in
total-electron yield mode at ambient temperature.
For evaluation of catalytic activitty for methane
dehydroaromatization at 973 K, it is concluded that
MoO3/H-MFI(Si/Al2=40) in low Mo contents (2.5-5.0
wt% as MoO3) shows the maximun benzene yield in
an initial streaming range. In this case, deactivation
due to carbon deposition can not be avoided. It isdefinitely that rate of deactivation becomes low bycoexistence of H2 (CH4/H2=20) in the reaction. Figure
1 shows the LIII-edge XANES spectra ofMoO3(5.0wt%)/H-MFI(Si/Al2=40) catalysts after
methane dehydroaromatization with/without H2.
Second derivatives of XANES spectra are also shownin Fig. 2. After the reaction with CH4 (denoted as[A]), Mo2C-like species are formed, indicating a
reduction and carbinding of Mo ions. Because ofpartially oxidized (due to coexistence of Mo4+ orothers), spectral feature is slightly different from thatof Mo2C. 2 It indicates that highly active Mo species
are consist of Mo2C (in major) and partially oxidized

species such as oxycarbide species. After the reaction
with CH4+H2 (denoted as [B]), the spectrum is quite
similar to that of CH4 reaction. Thus H2 coexistencebrings about depression of coaking but be
independent on reduction of active Mo species. In
case of H2 reduced catalysts in a pretreatment, thespectrum (denoted as [C]) is quite similar to bare
Mo2C. In this case, low dehydroaromatization activity
is shown. It is concluded that excess reduction
enhance the formation of Mo2C species, and low
activity is brought about at the same time.
[1] H. Aritani et al., UVSOR Activity Report, 33,(2006) 92.

[2] H. Aritani et al., Chem. Lett. 35 (2006) 416.
[A]
[B]
[C]
Mo2C (ref.)Normalized TEY

4

2

0
2520

2525
2530
Energy / eV2535

Fig.1 Mo LIII-edge XANES of 5wt% MoO3/H-MFI(Si/Al2=40). [A] After reaction with CH4(20%)+He.;[B] After reaction with CH4(20%)-H2(1%)-He.; [C]After pretreatment with H2 and reaction with CH4(20%)-H2(1%)-He.

2nd Derivatives

0

[A]
[B]
[C]
Mo2C (ref.)Mo metal (ref.)

-2

-2x10

2520

2522

2524

2526

2528

2530

2532

2534

2536

Energy / eV

Fig. 2 Mo LIII-edge XANES of 5wt% MoO3/H-MFI(Si/Al2=40). [A] After reaction with CH4(20%)+He.;[B] After reaction with CH4(20%)-H2(1%)-He.; [C]After pretreatment with H2 and reaction with
CH4(20%)-H2(1%)-He.

101

BL3U

Unoccupied Electronic States of Inner Organic Thin Films: Soft X-ray
Absorption Spectra of Pentacene Derivative Films
H.S. Kato1, R. Hirakawa1,2, F. Yamauchi1,2, M. Kawai1,2, T. Hatsui3, N. Kosugi3
1
RIKEN (The Institute of Physical and Chemical Research), Wako 351-0198 Japan
2
Dept. of Advanced Materials Science, Univ. of Tokyo, Kashiwa 277-8651 Japan
3
Dept. of Vacuum UV photoscience, Institute for Molecular Science, Okazaki 444-8585 Japanments, the photon energies of each component arealmost the same, while the relative intensities aredifferent.
One of the obvious differences is the detection of apeak at 398 eV. The intense peak is characteristic in
the Auger electron yield spectra that are surface
sensitive. Since its relative intensity increased withincreasing time of ambient gas exposure, the origin of
the peak would be an attachment of any impurities orsurface oxidation. Thus, we concluded that thefluorescence yield spectra show the intrinsic electronic state of 6,13-dihydrodiazapentacene, which has
also been supported by a molecular orbital calculationof the isolate molecule. In the fluorescence spectra,
the observed * and * peaks have clear incidence
angle dependence. These evidence a good oriented
structure of the molecules in the inner thin film, as thepentacene thin films on flat substrates.

Introduction
In order to extend new functionality of electronic
devices, the molecular devices have recently been
investigated with great efforts. In most of the devices,the properties of organic molecules are controlled by
the applied electric field and charge injection. The
organic field effect transistor (OFET) is the typicalmolecular device that controls of electric conductivity
by injection of carriers into the organic thin film
under the applied electric field. Based on the knowledge of inorganic semiconductor transistors, theconductive mechanism has generally been understoodwith a scheme of band bending of electronic states.
However, the energy diagram may not be the same
between inorganic and organic materials, because of
more localized orbitals of the organic molecules. It isalso important to elucidate the difference of electronic
states for using the noble characters of organic
molecular materials for the future advanced devices.
Therefore, the direct observation of electronic statechanges in the organic thin films under the applied
electric field has been required.
In this study, we aim to establish a new experimental
method that elucidates the electronic state change inorganic molecular thin-films under the electric field,
using model OFET devices. In general, X-ray absorption spectroscopy (XAS) is measured by the detectionof Auger electrons emitted after X-ray absorption.
However, the mean free path of the electrons, typically less than 1 nm, in bulk is too short for detectionof the electronic states of inner organic thin films, ofwhich typical thickness is about 100 nm. Thus, we
attempted the fluorescence yield detection for XAS.

Experimental
The XAS measurements were carried out at BL4B
and BL3U of UVSOR facility in IMS. We fabricated
6,13-dihydrodiazapentacene thin films on the
SiO2-covered Si substrates using a deposition system
in RIKEN. Then, the samples were set in the measurement chamber at BL3U through ambient conditions. The typical base pressure at the XAS measurements was less than 10-5 Pa. Both the Auger electron
yield and the fluorescence yield were observed using
a retarding-field detector equipped with MCP plates.

Fig. 1.
N K-edge XA spectra of a6,13-dihydrodiazapentacene film (t = 100 nm) on
SiO2-covered Si substrate: (a) Auger electron yield
spectra, (b) fluorescence yield spectra. In both measurements, incidence angle dependence was performed
at 70° and 20° from the surface normal, and then theintensity of the spectra was normalized by a height ataround 420 eV in photon energy.

Results and Discussion
The N K-edge XA spectra of the same
6,13-hydrodiazapentacene film (t = 100 nm) on
SiO2-covered Si substrate by detecting both the Auger
electron yield and the fluorescence yield, as shown in
Figs. 1(a) and 1(b), respectively. In both measure-

102

BL4B

Study on the Surface and Bulk Structures of the Positive Electrodefor Li-Ion Battery Cells with High Power-Type
H. Kobayashi, M. Shikano
Research Institute for Ubiquitous Energy Devices, AIST, Ikeda, Osaka, 563-8577 Japan: 0°C: 20°C: 40°C: 60°C: 80°C

1.8
1.6

DC resistance

1.4
1.2
1.0
0

10000

20000

30000

Figure 1 shows the cycle dependence of the DC
resistance. DC resistance increased from 1.08 to 1.74
on increasing the test temperature from 20 ºC to 80 ºC.
Above 80 ºC, an abrupt increase in DC resistance wasobserved. Figure 2 shows the O K-edge XANES
spectra of 0% SOC samples before and after test. In
TEY mode, O K-edge XANES spectra provide
information on the surface structure. The spectrum
measured before cycle testing contained peak A,
corresponding to oxygen originating from the layered

40000

50000

Cycle Number

Fig.1 Cycle dependence of retention of DC resistance.
Surface

O K-edgeCA
B: before: 80ºC
Bulk

Intensity(A.U.) / FY

Results

2.0

Intensity(A.U.) / TEYExperimental
We used cylindrical battery cells of capacity 400
mAh for this study, which were designed to have a ratecapability of more than 10 C. The positive andnegative electrode was comprised of LiNi0.8Co0.2O2-based oxides and hard carbon, respectively. Eachcell was characterized using the standard battery test
procedure given in PNGV Battery Test Manual. Thechange in DC resistance was checked every few cycles.
After completion of the degradation test, the SOC ofthe cell was adjusted to 0% immediately before
disassembling it, since the chemical and physicalproperties of the active materials are influenced by the
SOC. After disassembly of the SOC-adjusted cell,the surface of the positive electrode was examined by
XANES in order to study the surface film or phasetransitions in particles of the active material. The O
K-edge XANES spectra of the samples were measured
on the BL4B beamlines of the UVSOR Facility. Data
were obtained in the total electron yield (TEY) andfluorescence yield (FY) modes.

structure, and peaks B and C. After the cycle tests,
the intensity of peak A clearly decreased at 80 ºC,
while the intensities of peaks B and C showed nosignificant changes. The position of peak B was close
to that of the NiO spectrum, indicating the existence ofa cubic phase on the surface, and the position of peak
C was close to that of Li2CO3, or to conductive
materials such as AB (data not shown). Whenmeasured in FY mode, O K-edge XANES spectra
provide information on the bulk structure. Here,essentially the same spectra were observed before andafter the cycle tests for both samples. The strong
peak A originating from the layered structure of thepositive electrode was observed in FY mode.
However, peak B was absent and peak C was much
lower in intensity. These results indicate that thesurface structure is different to that of the bulk in thissystem. Furthermore, it is clear that part of thelayered structure at the surface of the LiNi0.8Co0.2O2-based positive electrode was transformed to a cubic
structure at 80 ºC, although the layered structure wasretained in the bulk.
Relative DC Resistance (mohm/mohm)

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 deterioration in
the performance of currently available lithium
batteries is thought to result from problems with thepositive electrodes, the mechanism of deterioration of
the electrodes is still poorly understood. Detailed
information on the changes taking place in both thecathode and anode on cycling is essential in order todetermine the origin of the degradation of performance.
In this study, LiNi0.8Co0.2O2-based positive electrodes
from cells that had undergone power fading throughcycling tests were examined by XANES analysis toobtain information on their surfaces. The relationshipbetween power fade and the surface state of thepositive electrode will be studied.

: before: 80ºC
520

530

540

550

560

Energy / eV

Fig.2 O K-edge XANES spectra for the positiveelectorrode after 45000 cycle test at 80 ºC.

103

BL5U

Core-Level Photoemission Study of Alkyl-Passivated Si Nanoparticles
A. Tanaka1,2,3, T. Kamikake2, K. Tomio1, N. Takashima4, M. Imamura3, Y. Murase2
Department of Mechanical Engineering, Faculty of Engineering, Kobe University,
Kobe 657-8501, Japan2
Department of Mechanical Engineering, Graduate School of Science and Technology, Kobe
University, Kobe 657-8501, Japan3
Department of Mechanical and Systems Engineering,
Graduate School of Science and Technology, Kobe University, Kobe 657-8501, Japan
4
Department of Physics, Faculty of Science and Engineering, Konan University,
Kobe 658-8501, Japan
1(C10H21-) terminated bulk-Si(111) surface are 0.27,
0.21, and 0.21 eV, respectively. On the other hand, thechemical shift of n-butyl-bonded Si atoms of thepresent Si nanoparticles is 0.33 eV. An important point
to note is that the chemical shift of the surface
component in the present Si nanoparticle issignificantly larger than those of surface componentsof alkyl-terminated bulk Si surfaces. This indicatesthat the interfacial features between the surface Si
atoms and surface passivants of alkyl groups, andtherefore the bonding natures between thesurface-passivants of alkyl groups and surface Si
atoms, such as a coordination number andconfiguration of surface-passivants, are different
among the bulk Si surface and Si nanoparticle surface.

Introduction
Recently, the various Si nanostructures have a greatinterest, since it has been reported that they show astrong visible photoluminescence and a possibility of
future integrating electronic devices with opticalsensing technique is suggested. However, the interplay
to their optical properties between the intrinsic
quantum confinement effects and extrinsic
surface/interface properties is still controversial. In
order to understand the intrinsic properties of Si
nanostructures, it is indispensable to characterize theirsurface chemical properties. In this work, we havecarried out the core-level photoemission studies ofalkyl-passivated Si nanoparticles synthesized by thesolution routes in order to characterize their surface
electronic structures.

Fig. 1. Si 2p core-level photoemission spectrum of
n-butyl-passivated Si nanoparticle with mean diameter

Experiment
Synthesis procedure of n-butyl-passivated Si
nanoparticles used in this work is described elsewhere[1]. Core-level photoemission measurements were
performed at BL-5U of UVSOR II Facility.

Results and Discussion
Figure 1 shows the Si 2p core-level photoemission
spectrum of n-butyl-passivated Si nanoparticle withmean diameter of 1.4 nm. As shown in Fig. 1, it isfound that the present Si 2p core-level spectrum isreproduced by two components fairly well. From theanalogy with the previous results of alkyl-terminatedbulk-Si(111) surfaces [2], the lower- andhigher-binding-energy features originate from theinner Si atoms of Si nanoparticles (bulk component)and surface Si atoms of Si nanoparticles bonded tosurface-passivants of n-butyl groups (surface
component), respectively. As shown in Fig. 1, thissurface component accompanies with the chemical
shifts to higher binding energies relative to the bulk
components. This indicates the different chemical
states in the surface Si atoms bonded to n-butyl groups
with the inner Si atoms and existence of a chemical
reaction(chemisorption)
betweenthesurface-passivants of n-butyl groups and Si
nanoparticles. It has been reported in the previous
work [2] that the chemical shifts for surface Si atomsof methyl- (CH3-), pentyl- (C5H11-), and decyl-of 1.4 nm measured with h=184 eV. Result ofline-shape analysis is also shown. Observed spectrum
is decomposed into bulk component (blue line) andsurface component bonded to surface n-butyl
molecules (red line).
[1] A. Tanaka et al., Solid State Commun. 140 (2006)
400.
[2] J. Terry et al., J. Appl. Phys. 85 (1999) 213.

104

BL5U(FEL)

Threshold Photoemission Magnetic Circular Dichroism using Free
Electron Laser
T. Nakagawa, T. Yokoyama, M. Hosaka, M. Katoh
Department of Electronic Structure, Institute for Molecular Science, Okazaki 444-8585 JapanUVSOR Facility, Institute for Molecular Science, Okazaki 444-8585 Japanthat the asymmetry drops to 0.1% for photon energy
larger than the work function by 0.6 eV. A theoretical
calculation also shows enhanced dichroism near thephotoemission threshold, in agreement with theexperimental result.
To obtain the high MCD asymmetry we have totune the photon energy a little higher than theworkfunction. We have used tunable free electron
laser from UVSOR-II, which can deliver lower
energy than hν = 6.3 eV, close to typical workfunction
for transition metal surfaces without surface
modification such as alkali metal adsorption. Thus
FEL at UVSOR-II is a suitable source to thresholdphotoemission MCD measurements. Fig. 2 shows amagnetization hysteresis curve on Ni(8 ML)/Cu(001)using hν = 5.37 eV, where the photoemission
threshold for Ni is ~5.3 eV. As is expected from theresult shown in Fig. 1, the asymmetry is high, ~6%.
This result clearly evidences that the clean Ni surface
also shows high asymmetry near the photoemission
threshold.

Introduction
Magnetic circular dichroism (MCD) in the x-ray
regions (XMCD) has widespread over thesynchrotron radiation facilities because of its highsensitivity to the element specific magnetism. On theother hand, MCD in the regions from infrared toultraviolet (UV) is also a useful tool for the study offerromagnetic ultrathin films. The magneto-optical
Kerr effect (MOKE) detects the rotation anddistortion of the polarization of reflected lights frommagnetic materials. The Kerr effect in valence bands
in thin films usually rotates the polarization andchanges the ellipticity only by 10-2-10-6rad. In thevalence band photoemission, nevertheless, extensive
works have been performed using circularly polarizedsynchrotron
radiationandangle-resolved
measurement, showing high (~30%) asymmetry. [1,2]Fig. 1 MCD asymmetry as a function of
maximum kinetic energy(photon energy–work
fuction) on perpendicularly magnetizedNi(12ML)/Cu(001). The photon energies used
are 1.95 eV and 3.81 eV. The inset showsmagnetization hysteresis curves by MCD and
MOKE measurements, which are identical toeach other.

Fig. 2 Magnetization hysteresis curves on aclean eight monolayer Ni film grown on
Cu(001) obtained by FEL-MCD and MOKE.
The photon energy of FEL is 5.37 eV.

[1] C. M. Schneider, et al., Phys. Rev. B 44 (1991)
R12066.
[2] W. Kuch and C.M. Schneider, Rep. Prog. Phys.
64(2001) 147.
[3] T. Nakagawa, and T. Yokoyama, Phys. Rev. Lett.
96(2006) 237402.
[4] T. Nakagawa, T. Yokoyama, M. Hosaka, and M.
Katoh, Rev. Sci. Instrum. 78 (2007) 023907.

We have investigated the observation of enhanced
MCD near the Fermi level using visible andultraviolet lasers in a total yield mode. [3] More than
10% MCD asymmetry is achieved on perpendicularly
magnetized 12 ML Ni film on Cu(001), andmagnetization curves are obtained. By changing thework function with the aid of cesium adsorption, thelaser experiments show that the MCD asymmetry isenhanced only near the photoemission threshold, and

105

BL5U

Adsorpiton of Benzene on Au(111) Surface by Angle-Resolved Ultravoilet
Photoemission Spectroscopy
L. Wang1, D. Qi1, A. T. S. Wee1, T. Mochizuki2, H. Miyazaki2,
T. Ito3, S. Kimura3, J. Yuhara2, K. Soda2
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
Molecules have been shown to operate as Coulomb
blockade structures, diodes, switching devices withhigh negative differential resistance (NRD) andconductance switches, making the nascent field of
molecular electronics very promising[1]. The central
issue in molecular electronics is the characteristics ofthe molecule-metal interface which strongly
influences the transport properties in the moleculardevice[2]. Benzene/Au system is chosen as testbedsince benzene is a typical molecule with delocalized orbitials and gold is one of the most widely used
substrate. In this study, the adsorption of benzene on
Au(111) surface have been investigated byangle-resolved photoemission spectroscopy.

Experimental

Au(111) surfaces were prepared by cycles of Ar+
ion bombardment at 1 KeV and annealing at 800 K in
an ultrahigh vacuum system. The (1x1) reconstruction
was clearly observed on clean Au (111) surface by
low energy electron diffraction. Benzene (99%,company name) was in situ evaporated onto Au(111)
surface which was cooled down to 5 K. One
monolayer of benenze on Au was achieved byintroducing the dosage of 1 Lagmuir assuming the
stick coefficient =1. Angle-resolved photoelectron
spectra were recorded under 2.7x10-8 Pa with ahigh-resolution energy analyzer at BL5U. The totalenergy resolution was 14 meV with the excitation
photon energy of 29.3 eV at 5 K.

Fig.1 Photoemission intensity of Schockely-typesurface state on clean Au(111) along [ 110 ] direction
as a gray scale.

Results and Discussion
Figures 1 show the photoemission intensity ofsurface state on clean Au(111) along [ 110 ] direction.
A dispersion near the Fermi edge with the maximum
binding energy of 430 meV at  point can be clearlyobserved, which is consistent with that for
Shockley-type surface state on Au(111) [3].
Figure 2 shows the angle-integrated valence band
spectra for benzene mononlayer adsorbed on Au(111)
at the various temperatures. After the adsorption,some noticeable features, which are originated frombenzene molecules[4], emerge in the binding energy
range from 8-14 eV. On the other hand, theShockley-type surface state of Au(111) is
immediately extinguished, indicating the presence ofa strong interaction between the benzene molecules
and the gold surface. This interaction can not be
described only as purely physical interaction.

Fig.2 Angle-integrated valence band spectra for clean
Au(111)andbenzene/Au(111)atvarioustemperatures.
[1] M. A. Reed et al., Science 278 (1997) 252; Z. J.
Donhauser et al., Science 292 (2001) 2303.
[2] J. G. Kushmerick et al., Phys. Rev. Lett. 89 (2002)
086802; L. Wang et al., J. Am Chem. Soc. 128(2006) 8003.
[3] S. D. Kevan et al., Phys. Rev. B 36 (1987) 5809;
R. Paniago et al., Surf. Sci. 336 (1995) 113.
[4] Y. K. Kim et al., Phys. Rev. B 71 (2005)
115311.

106

BL5U

Electronic Structure and Stability of the Pd-Ni-P Bulk Metallic Glass
T. Takeuchi1, D. Fukamaki2, H. Miyazaki3, K. Soda3
T. Itoh4, S. Kimura4
1
EcoTopia Science Institute, Nagoya University, Nagoya 464-8603 Japan2
Department of Applied Physics, Nagoya University, Nagoya 464-8603 Japan3
Department of Quantum Mechanics, Nagoya University, Nagoya 464-8603 Japan
4
Institute for Molecular Science, Okazaki 444-8585 Japan
Bulk metallic glasses (BMGs) have attracted a great
deal of interests because of their ability in practicalusage, such as mechanical parts of high strength,surface coating materials with high degree of
hardness, soft-magnetic materials, etc. In order todesign the BMGs suited for each practical usage,
stabilization mechanism of the BMG's has to berevealed from microscopic viewpoints; the local
atomic arrangements and the electronic structure.
Since it is naturally considered that the highly-stable
BMGs possess a low free-energy, the stabilization
mechanism of BMG's should be discussed in terms of
free-energy, which is mostly determined by theelectronic structure.
We investigate, in this study, the electronic structureof the Pd-Ni-P BMG, that is one of the most famous,
stable BMGs obtained in metal-metalloid systems, byemploying the relevant crystals with the first principle
cluster
calculation,
band
calculation,andhigh-resolution photoemission spectroscopy. By
calculating electronic structure of the relevant crystals,
in which the structure units of the BMG (trigonal
prism clusters with a phosphorus atom in the center)are formed, we found that the these units (trigonal
prism clusters) possess covalent nature and highlyD(c) Ni 2P(d) Pd 3P

D

C

F

-16

-14

-12

-8

-6

-4

-2

0

2

Energy, E-EF / eV

(b)

E

-10

E

Pd3P

20

D

C
B

A
0

F

B

A

B

D
C

10

A

E

20

0
40

E

Ni2P

(b)

(a)

30

stable. The formation of the covalent bonds in theclusters (relevant crystals) was further confirmed byobservations of the bonding bands in thehigh-resolution photoemission spectra.
We also calculated the cluster-orbitals of large
clusters consisting of two trigonal clusters withdifferent inter-cluster-connections, and found that theelectronic structure does not significantly altered by
the inter-cluster connection with keeping thebonding-bands far below the Fermi level. This
characteristic leads to flexible connections of theclusters. The trigonal clusters, therefore, are able toconstruct a random network to form the bulk metallic
glass without significantly increasing their internalenergy. The enhanced entropy and the small internalenergy result in the very low free-energy of the BMG.
We conclude, therefore, that the Pd-Ni-P BMG isstable because of the random cluster network of therigid, stable, large structure unit (cluster) of covalentnature. This stabilization mechanism is applicable for
the Zr-based BMG's and even for the silica glasses,
and, therefore, commonly acceptable for highly-stable
amorphous solids.

-15

F

(A)
-10

-5

0

5

B C

Energy, E- / eV

Figure 1 (a)Trigonal prism cluster and (b)tetragonal
dodecahedron cluster (deformed trigonal cluster) exist
in the Pd-Ni-P bulk metallic glass. Electronic density ofstates of the relevant crystals, (c) Ni2P, and (d) Pd3P
calculated by the FLAPW-GGA method (Wien2K). The
density of states of the relevant crystals are commonly
characterized by possession of the narrow bands
marked as A - F. The bands A-C are bonding bands,
while the corresponding anti-bonding bands exist far
above EF. The bands D and E are nearly non-bonding
d-bands. These configurations provide a strong covalentnature.

107

F

-16

-14

-12

-10

-8

-6

-4

-2

0

2

Energy, E-EF / eV

Figure 2 High-resolution photoemission spectraof the (a)Ni2P and (b)Pd3P measured with anincident energy of 40eV. The characteristics ofelectronic
structure
expected
fromband-calculation and cluster-calculation are
qualitatively reproduced in the spectra.

BL5U

Electronic Structure of Pd-Ni-P Bulk Metallic Glass
S. Ota1,2, T. Suzuki1, H. Miyazaki1,2, K. Soda1,2, T. Takeuchi3,
M. Hasegawa4, N. Nishiyama5, H. Sato6, U. Mizutani7, T. Ito2, S. Kimura2
1
Graduate School of Engineering, Nagoya University, Nagoya 464-8603 Japan
2
Institute for Molecular Science, Okazaki 444-8585 Japan
3
EcoTopia Science Institute, Nagoya University, Nagoya 464-8603 Japan
4
Institute for Materials Research, Tohoku University, Sendai 980-8577 Japan
5

R&D Institute of Metals and Composites for Future Industries, Sendai 980-8577 Japan
6

7

Aichi University of Education, Kariya 448-8542 Japan
Toyota Physical and Chemical Research Institute, Nagakute-cho, Aichi-gun 480-1192 Japan
Introduction

the inter-cluster bond direction, as in the silica glass.

Bulk metallic glasses (BMG) possess excellent
mechanical, physical and chemical properties, whichcome from their amorphous structure. In spite of
their thermodynamical metastability, Pd-based BMG
have large glass forming ability (GFA) [1]. In orderto understand the mechanism of their large GFA, wehave studied the electronic structure of PdxNi80-xP20
BMG by photoemission spectroscopy (PES) andtheoretical calculation for local clusters expected in
BMG.

[1] A. Inoue, Acta Mater. 48 (2000) 279.
[2] H. Adachi et al., J. Phys. Soc. Jpn. 45 (1978) 875.
[3] M.Vennstrom et al., J. Sol. Stat. Chem. 177(2004) 1449.
[4] J. J. Yeh and I. Lindau, Atom. Data and Nucl.
Data Tables 32 (1985) 1.

PdxNi80-xP20

INTENSITY / arb.units

1

Experimental
The PES measurement was carried out at 25 K
under 2 × 10-8 Pa. PdxNi80-xP20 specimens wereprepared by a casting method and their clean surfaces
were obtained by in situ scraping with a file.
The theoretical calculation was performed by the
DV-X method with a code SCAT [2] for a Pd3Ni6Pcluster in a form of a capped trigonal prism, which isderived from a crystalline PdNi2P [3].

x = 45x = 40x = 35h/ eV
85

0

50

0

30

0

Results and Discussion

8

Valence-band spectra of PdxNi80-xP20 recorded at
excitation photon energies h are shown in Fig.1.
They were normalized by the integrated intensity up
to the binding energy EB of 10 eV. There are threebands at EB ~ 0.8, 2.2, and 3.9 eV, which are ascribedto the Ni 3d-, Pd 4d-, and Pd 4d-derived states,
respectively, judging from the h-dependence of theirphotoionization cross sections [4]. The spectral
shape for x = 45 is not so much different from one for
x = 40, while the Ni 3d band is relatively large for x =35. There is almost no peak shifts for these bands.
In Fig.2, a spectrum recorded at h = 40 eV iscompared with the density of states calculated for thecluster in the inset, where a black sphere represents P
at the center, green and blue ones for Pd at corners of
the prism and a top of the cap, and yellow and pinkones for Ni at the corners and the tops, respectively.
Taking account of the difference in photoionization
cross sections [4], both results agree very well witheach other. This suggests that the cluster may be adominant form in Pd40Ni40P20. The calculation also
shows a strong P-(Pd, Ni) bonding. In the Pd-Ni-P
BMG, the network of such clusters may be formed bysharing their vertices and sides with large flexibility in

6

4
2
0
BINDING ENERGY / eV

-2

Pd40Ni40P20
DENSITY OF STATES / arb. unitsh / eV = 40

1

1
P 3s
P 3p
Ni 3d cap
Ni 3d prism Pd3Ni6P
Pd 4d cap
Pd 4d prism
total

0

INTENSITY / arb.units

Fig.1 Valence-band spectra of PdxNi80-xP20.

0
x 30

0

8

6
4
2
0
BINDING ENERGY / eV-2

Fig.2 Valence-band spectrum of Pd40Ni40P20 andcalculated density of states for Pd3Ni6P cluster.

108

BL5U

Electronic Structure of (Fe1-xRex)2VAl and Fe2(V1-yTiy)AlK. Yamamoto1, H. Miyazaki2,3, T. Mochizuki2, T. Suzuki2, S. Ota2
M. Kato2, S. Yagi2, Y. Nishino4, K. Soda2,3
1
School of Engineering, Nagoya University, Nagoya 464-8603 Japan
2
Graduate School of Engineering, Nagoya University, Nagoya 464-8603 Japan
3
Institute for Molecular Science, Okazaki 444-8585 Japan
4
Graduate School of Engineering, Nagoya Institute of Technology, Nagoya 466-8555 Japanthe Re 5d states, while the Fe and V 3d-derived band
C shows no shift and the intensity near EF isrelatively increased by the Fe 3d states: the band
width of the Fe 3d states seems to be extended by theinteraction between the Re 5d and Fe 3d states.

Introduction
Heusler-type Fe2VAl and its related alloys haveattracted much attention because Fe2VAl shows
remarkable enhancement of thermoelectric power onpartial substitution by the forth element [1]. In thispaper, we will report results on the Fe and V 3p-3d
resonance photoemission study of p-type alloys(Fe1-xRex)2VAl and Fe2(V1-yTiy)Al in order to clarify
the relation between changes in their thermoelectric
properties and electronic structure on the substitution.

[1] Y. Nishino, The Science of Complex Alloy Phases(Ed. by T. B. Massalski and P. E. Turchi, TMS,
Warrendale, 2005) p.325.
[2] K. Soda et al., Phys. Rev. B 71 (2005) 245112.
[3] G. Y. Guo et al., J. Phys.: Condens. Matter. 10(1998) L 119.

Experimental
Photoelectron spectra were recorded at 20 K
under 1.8 x 10-8 Pa. The origin of the binding
energy EB, the Fermi level EF, and total energy
resolution were determined by measuring the Fermiedge of a gold film. The total energy resolution was
63 meV at the photoexcitation energy h = 80 eV.
Specimens used in this study were polycrystalline
alloys of Fe2VAl, (Fe1-xRex)2VAl and Fe2(V1-yTiy)Al.
Clean surfaces for the measurement were prepared byin situ fracturing the specimens.

INTENSITY / arb.units

1

Results and Discussion

0
0(Fe1-xRex)2VAl
x = 0.05

Fe2(V1-yTiy)Aly = 0.02

Fe2VAl0h = 80 eV0

Figure 1 shows typical valence band spectra
recorded at h = 80 eV together with a bulk-sensitive
one of Fe2VAl at h = 900 eV [2]. In Fe2VAl, there
are a shoulder structure A near EF and four bands B,
C, D and E at EB = 0.4, 0.8, 1.6 and 3.0 eV,
respectively. The overall features agree well withthose in theoretical density of states [3] and the bulksensitive spectrum except for the feature around EF:
the large intensity of the shoulder A observed in thisstudy is attributed to surface states appearing in a
pseudogap across EF in the bulk electronic structure.
On the partial substitution of Ti or Re, the shoulder A
becomes indistinct with increase in the intensity at EF
and the valence band shifts to the low binding energy
side as a whole, as expected in a rigid band model.
This rigid-band-like shift results in the enhancementof their thermoelectric power.
Partial densities of Fe and V 3d states of Fe2VAland (Fe0.95Re0.05)2VAl, which were estimated by the
3p-3d resonance photoemission, are compared in Fig.
2 together with their valence-band spectra. By theRe substitution, the V 3d-derived band D shifts to thelow binding energy side due to the interaction withx = 0.01h = 900 eV

0

C

E

B
A

3
2
1
0
BINDING ENERGY / eV
Fig.1 Valence band photoelectron spectra.

INTENSITY / arb.units

5

D

4

1 (Fe Re ) VAl
0.95
0.05 2
Fe 3d
V 3d

0

0

D

C

-1

B

Fe2VAl
Fe 3d
V 3d

3
2
1
0
BINDING ENERGY / eV
Fig.2 Partial densities of Fe 3d and V 3d states in
Fe2VAl and (Fe0.95Re0.05)2VAl.

109

4

BL5U

Electronic Structure and Glass Forming Ability of
Zr-Cu-Al Bulk Metallic Glasses
T. Suzuki1, H. Miyazaki1,2, S. Ota1,2, M. Inukai1, M. Kato1, S. Yagi1, K. Soda1,2
H. Kato3, M. Hasegawa3, T. Takeuchi4, H. Sato5, U. Mizutani6, T. Ito2, S. Kimura2
1
Graduate School of Engineering, Nagoya University, Nagoya 464-8603 Japan
2
UVSOR, Institute for Molecular Science, Okazaki 444-8585 Japan
3
Institute for Materials Research, Tohoku University, Sendai 980-8577 Japan
4
EcoTopia Science Institute, Nagoya University, Nagoya 464-8603 Japan
5
Aichi University of Education, Kariya 448-8542 Japan
6
Toyota Physical and Chemical Research Institute, Nagakute-cho, Aichi-gun 480-1192 Japancovalent nature of Zr and the increase in the structuraldegree of freedom may lead to the large GFA.

Introduction
Bulk metallic glasses (BMG's) possess the large glass
forming ability (GFA) and show physical, chemical andmechanical properties, which are superior to crystalline
materials [1]. In order to understand the origin of theirlarge GFA from the microscopic point of view, we havesystematically studied electronic structure of Zr-Cu-Al
BMG's using photoelectron spectroscopy.

[1] M. Telford, Mater. Today 7 (2004) 36.
[2] S. Nakano et al., private communication.
Tg / Tl> 0.650.60 - 0.65
0.55 - 0.60
< 0.55

40 60

at%

60

Zr
/

A

80

at%

Photoelectron spectra were recorded under 2 x 10-8 Pa
at 25 K at BL5U. Total energy resolution and the originof the binding energy EB, i.e. the Fermi level EF, were
determined by the Fermi edge of an evaporated Au film.
Specimens were ternary Zr-Cu-Al BMG's in a size of2 mm x 3 mm. These compositions are shown in
Fig.1 by symbols A ~ H with a counter map of their
reduced glass temperatures Tg/Tl (Tg: glass transition
temperature, Tl: liquidus temperature), which is regarded
as one of parameters representing GFA. Clean surfaces
for the photoelectron measurement were prepared by insitu scraping the specimen with a diamond file.

40

G40 H
E F
D
C

/
Cu

Experimental

20

B

0

100
0

20

40

60

Al / at%

Fig.1 Compositional dependence of Tg/Tl

110

A

0

B

0

C

0

D

0

E

0

F

0

G

0

H

0

2

1
0
BINDING ENERGY / eV-1

Fig.2 Typical spectra of Zr 4d band of Zr-Cu-Al BMG's.
0.75
0.70
0.65
0.60

A

B

A

C
E D
B

0.6

F

0.5

G
H

0.55

C

0.50

E D

0.45
0.40
0.52

0.7

Zr4d

0.56

0.60
Tg / Tl

G

0.64

F H

0.4
0.3

0.2
0.68

INTEGRATED INTENSITY / a.u

Figure 2 shows typical Zr 4d spectra of Zr-Cu-Al
recorded at the excitation photon energy of 40.5 eV.
These spectra are normalized with their Cu and Zr
compositions so that the spectral intensity may be
proportional to the density of occupied Zr 4d states per Zr
atom. Arrows indicate peak positions of the Zr 4d bands.
There is a tendency recognized that the peak binding
energy and integrated intensity of the Zr 4d bands are
increased with the Zr composition increasing from H to A.
This may suggest the increase in the covalent interaction
around Zr atoms with increasing the Zr composition.
The peak position (●) and integrated intensity (■) ofthe Zr 4d band are plotted as a function of Tg/Tl in Fig.3.
As seen in the figure, they decrease as Tg/Tl increases: thecovalent nature of Zr is relatively weak for Zr-Cu-Al withthe large GFA. According to Nakano et al. [2], there are
two typical local atomic arrangements appearing in
Zr-Cu-Al: the Zr-centered covalent cluster and the Cu- or
Al-centered metallic clusters, which have relatively low
and high structural degree of freedom, respectively.
Thus, the present results suggest that the weakening of the

PEAK POSITION / eVResults and Discussions

INTENSITY / arb.units1

Fig.3 Peak position and integrated intensity of Zr 4d bandas a function of the reduced glass temperature Tg/Tl.

BL5U

Three-Dimensional Angle-Resolved Photoemission Studyon EuO Thin Films
1,2

H. Miyazaki , T. Ito , S. Ota , 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

2,3

1,2

Department of Physics, Sungkyunkwan University, Suwon 440-746, Korea

EuO is a ferromagnetic (TC ~ 70 K) semiconductor.
In Eu excess case (Eu-rich EuO), it shows a metal
insulator transition (MIT) near the TC ~ 150 K [1, 2].
To clarify the origin of MIT and enhancement TC
mechanism of Eu-rich EuO from the microscopic
electronic structure view, we investigated thefundamental electronic structure of EuO and Eu-rich
EuO. In this report, we have performed in situ
three-dimensional angle-resolved photoemission
spectroscopy (3D-ARPES) on single crystalline EuO
thin films.
EuO thin films have been grown by a molecularbeam epitaxy (MBE) method. To obtain high-quality
single-crystalline films, we evaporated Eu onto BaO
buffered Nb-doped SrTiO3 substrates at 350 °C underoxygen pressure of 8 x 10-6 Pa. Epitaxial growth of
single-crystal EuO thin films has been confirmed 1 x
1 EuO (100) patterns by LEED and RHEED methods.
The sample was transferred to the 3D-ARPES
chamber in situ and then the photoemission spectra
were measured at UVSOR-II BL5U. Sample
temperature was set at 20 K (< TC ~ 70 K).
Figure 1 shows the photon-energy dependence of the
ARPES spectra of EuO at normal emission (k?// = 0
Å-1). Observed spectra mainly show two structure at
the binding energy EB = 1.3 ~ 3.7 eV and 3.7 ~ 8.0 eV.
From the comparison with the calculated photoionization cross section of Eu 4f and O 2p [3], thelower binding energy side is attributed to Eu 4f states
and the other is O 2p states. Eu 4f and O 2p bands
show small dispersion about 0.2 and 0.3 eV,
respectively. Here, we use the dispersion relation( h / 2 )k   2mE K cos 2   V ,where V is the inner potential, EK is the kinetic
energy at the Fermi level EF and  = 0 degree. We
determined the inner potential V = 13 eV from thesymmetry of the dispersive features.
Figure 2 shows the high-resolution ARPES spectraof Eu 4f around  point (a) recorded at h = 76 eV
and X points (b) at h = 38 eV, respectively. Sizableenergy dispersion of the Eu 4f states is observed atthe  and X point. The observed dispersive features
are the direct evidence for the 3D-lattice effect due tothe Eu 4f and O 2p hybridization. However thedispersion around X point is larger than  point. This
indicates that the hybridization between Eu 4f and O

2p states at the X point is stronger. This result is notconsistent with the band calculation [4]. The detailed
analysis and the further study for temperaturedependence ARPES are in progress.

Fig. 1 Photon-energy dependence of the normal
emission photoemission spectra of EuO (100).

Fig. 2 ARPES spectra of Eu 4f around  (a) and X(b) points, respectively. The blue lines indicate thespectra at the  and X points.
[1] A. Mauger et al.,J. Phys. (paris) 39 (1978) 1125..
[2] M. R. Oliver et al., Phys. Rev. B 5 (1972) 1078.
[3] J. J. Yeh and I. Lindau.Atomic Data and Nucl.
Data Tables 32 (1985) 1.
[4] S. J. Cho. Phys. Rev. B 1 (1970) 4589.

111

BL8B1

Characterization of Lithium Compounds by an XAFS Method
T. Kurisaki1, Y. Inoue1, 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
The Li K XANES spectra for four lithium halides areshown in Fig. 1. The energy position of each firstpeak should depend on halide ion. According to theincrease in the atomic number of halide ion, theenergy of the first peak shifts toward low energies.
The observed and calculated Li K XANES spectra
for lithium chloride are shown in Fig. 2. The
calculated transition peaks (bars) are convoluted by
the Gaussian function of 1.0 eV full width at half
maximum (FWHM). The first peak is estimated to theelectron transition (mainly Li 1s to unoccupied mixed
orbital consisting of Li 2s, Li2p and Cl 3d).

Lithium compounds are generally used in industrial
and commercial applications such as lithium batteries,
lithium glasses and other materials. Therefore, it isvery interesting to investigate the chemical bonding
condition of lithium compounds. 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 BL8B1 of
the UV-SOR in the Institute of Molecular Science,
Okazaki [2]. 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)-Xα molecular orbital (MO)method to perform calculated spectra, and compared
observed spectra with calculated spectra.

[1] J. Tsuji, K. Kojima, S. Ikeda, H. Nakamatsu, T.
Mukoyama and K. Taniguchi, J. Synchrotron Rad. 8(2001) 554-556[2] S. Murata, T. Matsukawa, S. Naoè, T. Horigome,
O. Matsuodo, and M. Watanabe, Rev. Sci. Instrum. 63(1992) 1309.

obs.
calc.

LiF
Intensity / a.u.

Intensity / a.u.

LiCl

LiBr
LiI

58

56

58

60 62 64
Energy / eV

66

60
62
Energy / eV

64

Fig. 2 Calculated transition peaks (vertical bars) andcurves (broken line). The solid line is the observed Li
K-XANES spectrum for lithium chloride

Fig. 1 Li K-edge XANES spectra of lithium halides

112

BL8B1

Comprehensive Classification of DLC Films Formed by Various Methods
Using NEXAFS Measurement
A. Saikubo1, N. Yamada1, K. Kanda1, S. Matsui 1, H. Saitoh2
1
Laboratory of Advanced Science and Technology for Industry, University of Hyogo,
Kamigori 678-1205 Japan,
2
Department of Materials Science and Technology, Nagaoka University of Technology,
Nagaoka 940-2188, Japan
0.4. This group consists merely of the sample
formed by PVD method. The DLC thin films in thisgroup can be estimated to have high hardness. GroupB was characterized by low density, 1.3-2.6 g/cm3,and high sp2/(sp2+sp3) ratio, 0.8-0.9. This groupconsists also of the sample formed by PVD method.
Group C was characterized by medium density,
1.8-2.4 g/cm3, and medium sp2/(sp2+sp3) ratio, 0.4-0.6.
Most number of samples includes this group and thisgroup consists of samples formed by both PVD and
CVD methods. For group A-C, density of DLC film
increases with decreasing of sp2/(sp2+sp3) ratio. It isinterpreted that the density of DLC film increases
with the ratio of sp3 component in the film. Group D
was characterized by low sp2/(sp2+sp3) ratio, 0.2-0.6,
in spite of low density, 1.2-2.0 g/cm3. This groupconsists almost of the sample formed by CVD
method. The peak at 288 eV was observed in theseveral NEXAFS spectra of this group. The presenceof this peak indicates the containing hetero-atom,such as nitrogen, and oxygen etc. [3]. These
hetero-atoms were considered to reduce -bonding in
the DLC film. Therefore, DLC films with low density
were formed in spite of low sp2/(sp2+sp3) ratio.

Introduction
Various diamond like carbon (DLC) thin films havebeen applied to a large number of industrial fields
according to the development of nanotechnology.
Recently, classification and standardization of various
DLC films are demanded for the expansion of further
usage and applications of DLC films. Mechanical,
electronic, chemical and optical properties of DLC
films are strongly dependent on the elementarycomposition and the coordination of carbon atoms infilms. Near edge X-ray absorption fine structure(NEXAFS) spectroscopy using synchrotron radiation
was utilized as an efficient method of sp2 content for
DLC films [1,2]. The sp2 content can be extracted
from the NEXAFS spectrum with a highsensitiveness and a high quantitativeness, because theisolated peak corresponding to the resonancetransition from carbon 1s to * orbital can beobserved. In the present study, the 55 kinds of DLC
films, which were provided by the enterprises andacademic organizations, were discussed by themeasurement of NEXAFS spectra.

Experiment
The NEXAFS measurement was performed at theBL8B1 stage of UVSOR in the Institute for
Molecular Science. The C K-edge NEXAFS spectra
were measured in the energy range 275-320 eV. Theenergy resolution is estimated to be less than 0.5 eV
FWHM. The detection of electrons coming fromsample was performed in the total electron yield(TEY) mode. The sp2/(sp2+sp3) ratio in the film canbe extracted by normalizing the area of the resonancetransition to * at 285.3 eV with the area of a large
section of the spectrum. The absolute sp2/(sp2+sp3)
ratio was determined by the comparison with that
estimated from the NEXAFS spectrum of graphite.
Density of DLC film was measured with X-ray
reflectivity method at Nagaoka University ofTechnology.

[1] K. Kanda, T. Kitagawa, Y. Shimizugawa, Y.
Haruyama, S. Matsui, M. Terasawa, H. Tsubakino, I.
Yamada, T. Gejo and M. Kamada, Jpn. J. Appl. Phys.
41 (2002) 4295.
[2] K. Kanda, Y. Shimizugawa, Y. Haruyama, I.
Yamada, S. Matsui, T. Kitagawa, H. Tsubakino and T.
Gejo, Nucl. Inst. Meth. B 206 (2003) 880.
[3] K. Kanda, J. Igaki, Y. Kato, R. Kometani and S.
Matsui, New Diamond Frontier Carbon Tech. 15(2005) 123.

Result and Discussion

Determined sp2/(sp2+sp3) ratio populated in therange of 0.1-0.9. Observed samples could beclassified roughly to 4 kinds of group by sp2/(sp2+sp3)
ratio and density. Group A was characterized by highdensity, 2.7-3.4 g/cm3, and low sp2/(sp2+sp3) ratio,

113

BL8B2The Electronic Structure and the Energy Level Alignment
at PTCDA / Metal Interfaces
1

E. Kawabe , H. Yamane1, K. Koizumi1, R. Sumii2, K. Kanai1, Y. Ouchi1, K. Seki1,3
1Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku,
Nagoya 464-8602 Japan
2
Research Center for Materials Science, Nagoya University,
3
Institute for Advanced Research, Nagoya University
In recent years, extensive research has been carriedout for applying organic materials to electronic
devices such as organic light emitting diodes, organic
solar cells and organic field effect transistors. It is
important to understand how the energy levels align atorganic/metal (O/M) interfaces for understanding themechanism of such devices and for improving theirperformance, since these factors strongly affectvarious phenomena such as charge injection. However,the detailed mechanism of the energy level alignment
at O/M interface is not yet well understood even for
nonpolar molecules. We investigated the electronic
structure and the energy level alignment at theinterfaces formed by vacuum-depositing perylene-3,4,9,10-tetracarboxylic
dianhydride(PTCDA,
molecular structure shown in Fig. 2(a)) on
polycrystalline vacuum-deposited films of metals (Au,Cu and Co) by ultraviolet photoelectron spectroscopy(UPS).
In the case of PTCDA/Au interface, the apparent
interface states or charge transfer (CT) states were notobserved in its UPS spectra (not shown here), whichindicates that the interaction between Au and PTCDA
is very weak, and that PTCDA molecule physicallyadsorbed on Au surface. The vacuum level (VL)
showed sudden shift toward Fermi level (EF) of Au atthe interface, as shown in Fig. 1, indicating theformation of an interface dipole. The possible origins
of such interface dipole have been proposed by Ishii
et al. [1], and we can ascribe the presently observedchange at PTCDA/Au interface to the push-back of
the electron cloud spilled out from the metal surface(push-back effect) by the adsorption of PTCDA
molecules. The interface dipole () for this loweringof the VL was 0.52 eV.
The UPS spectra at PTCDA/Cu interface are shownin Fig. 2(b). The highest occupied molecular orbital(HOMO) of PTCDA is observed at binding energy(EB) of 2.47 eV at the film thickness d = 5 nm. At d =0.4 nm, an additional spectral feature is observed at EB= 0.2 ~ 1.2 eV. This interface specific structure may
be due to the CT from Cu to PTCDA. Actually, theupward VL shift shown in Fig. 1 with  = -0.29 eV isconsistent with the picture that CT from Cu to
PTCDA leading to the rise of VL overwhelmed thepush-back effect which tends to lower the VL.
At PTCDA/Co interface, VL showed upward shift
after the initial abrupt downward shift (Fig. 1).
Although this upward shift indicates the CT from Co
to PTCDA, CT states were not observed in the UPS
spectra (Fig. 2(c)), possibly because the amount of
the transferred charge is too small to appear as a newstate in the spectra. The estimated amount oftransferred charge at PTCDA/Cu and PTCDA/Co
interfaces by the electrostatic theory [2] for
explaining the VL shift are one electron per about two
and five PTCDA molecules, respectively.
The schematic energy diagrams of these interfaces
are summarized in ref. [3]. We found an interesting
behavior at PTCDA/Co interface, so we focus
attention on the effect of the d electrons on the energy
level alignment.

Fig. 2 (a) The molecular structure of PTCDA. (b)and (c) The UPS spectra of PTCDA/Au and
PTCDA/Co interfaces, respectively.
[1] H. Ishii, K. Sugiyama, E. Ito and K. Seki, Adv.
Mater. 11 (1999) 605.
[2] H. Ishii, N. Hayashi, E. Ito, Y. Washizu, K. Sugi,
Y. Kimura, M. Niwano, Y. Ouchi and K. Seki, Phys.
Stat. Sol. (a) 201 (2004) 1075.
[3] E. Kawabe, H. Yamane, K. Koizumi, R. Sumii, K.
Kanai, Y. Ouchi and K. Seki, Mater. Res. Soc. Symp.
Proc. 965 (2006) S09-28.

Fig. 1 The film thickness dependence of VL at
PTCDA/Au, Cu and Co interfaces.

114

BL8B2

Photoelectron Angular Distribution of 3d-orbital Derived Bandsin Mn-Phthalocyanine Monolayer
S. Kera1, H. Fukagawa1, T. Kataoka1, T. Hanatani1,
R. Sumii2, S. Nagamatsu1, N. Ueno1
1
Graduate School of Science and Technology, Chiba University, Chiba 263-8522 Japan#
2
IMS and Graduate School of Science, Nagoya University
Furo-cho, Chikusa-ku, Nagoya 464-8602, Japanintensity shows maximum at  =8o for the HOMO
and  =30o for the HOMO-1. The difference in thedistributions might be related to the different orbital
distribution, that is, 3d-orbital for HOMO and2p-orbital for HOMO-1.
Now we are trying to simulate the patterns bytaking into account the characteristics of 3d-orbitals
with theoretical calculations, multiple-scattering
approximation combined with MO calculation [1].
ARUPS results would be helpful for making
assignments of complex electronic structure such as amixed valence and spin configuration oforganometalic compounds.

Angle-resolved
ultraviolet
photoelectron
spectroscopy (ARUPS) has been known as a powerful
technique to obtain crucial information on electronic
band structure for various kinds of materials.
Moreover, for organic thin films, information on thegeometrical structure of the thin films can be also
discussed in accordance with a quantitative analysisof the ARUPS intensity using photoelectron
scattering theory. However, it is noteworthy that theexperimental results are still limited to describe therelationships between the distribution of themolecular orbital (MO) and the ARUPS intensity due
to a lack of a standard/simple theoretical model andwell-ordered organic thin films [1].
We measured the take-off angle () dependencesof 2p- and 3d-orbital derived bands in ARUPS spectra
for well-ordered Mn-phthalocyanine (Pc) monolayers
to clarify the MO distribution affecting to the angular
distribution.

Experiments
ARUPS spectra were measured at photon incidence
angle =45o, photon energy (h) of 0 eV and 28 eV,
and at a sample temperature T=295 K. The purified
MnPc molecules were carefully evaporated onto thegraphite (HOPG:ZYA) substrate.

Results and Discussion

Figure 1(a) shows the  dependence of ARUPS ofannealed-MnPc monolayer (0.3nm) on HOPG. The
intensity is normalized to the incidence photon flux(IR). A lowest lying feature appeared at 0.65 eV,
where the binding energy is observed lower thanprevious metal-Pc monolayers on HOPG [2], could
be ascribed to HOMO band of MnPc. The next
feature at 1.2 eV is assigned to a single  MO
(HOMO-1) that corresponds to HOMO of other Pc
molecules [2]. DFT-MO calculation suggests that the
HOMO band of the MnPc is related to Mn-3d-derived
state. However, we are in progress to conclude theassignment which character of 3d MOs is responsible
to this state because of a variety in the spin
configuration.
Figure 1(b) shows the observed  dependences of
HOMO and HOMO-1 intensities obtained at hv=20eV. Both patterns show a similar distribution to
give a maximum around  =50o, though the intensity
is slightly different around  =25o. Figure 1(c) showsthe  dependences of HOMO and HOMO-1
intensities at hv =28eV. The patterns are different
significantly between HOMO and HOMO-1. The

Fig. 1.(a)  dependence of ARUPS of 1-ML(0.3nm)
MnPc on HOPG measured at hv=20eV. Observed patterns of the HOMO band (blue circles) and
HOMO-1 band (red circles) obtained by hv=20 eV(b) and hv=28eV (c).
[1] S. Nagamatsu et al, e-J. Surf. Sci. Nanotech. 3(2005) 461.
[2] H. Fukagawa et al, Phys. Rev. B 73 (2005)
041302(R).
#Present add: Graduate School of Advanced
Integration Science, Chiba University

115

BL8B2

Electronic Structure of Lithium Phthalocyanine Thin Film
1

S. Tanaka1, 2, K. Watanabe3, Y. Yoshida3, I. Hiromitsu3, K. Yoshino2
Center of Integrated Research in Science, Shimane University, Matsue 690-8504 Japan
2
Research Project Promotion Institute, Shimane University, Matsue 690-8504 Japan
3
Faculty of Science and Engineering, Shimane University, Matsue 690-8504 Japan
Introduction

Phthalocyanine (Pc) and metal phthalocyanines haveattracted much interest for their semiconducting
properties implying many interesting applications
including photovoltaics, photoconductors and sensors.
Lithium phthalocyanine (LiPc) is known as a stableneutral radical and is one of a few intrinsic
semiconducting molecules [1, 2]. The chemical
structure of LiPc is shown in Fig. 1. It is known that
LiPc has rather high conductivity and a peculiar
UV-VIS absorption spectrum as compared to othermetal phthalocyanines such as ZnPc, CuPc or TiOPc.
Thus, the structures of LiPc and those properties areinteresting, and these have been the subject of manystudies [2-4]. In this work, we investigate theelectronic structures of thin films of LiPc on an Au
substrate. The energy level alignment at the LiPc/Au
interface is revealed from the photoelectron spectra as
a function of the LiPc thickness.

dipole layer with LiPc side positively charged. In the
thick-layer region (10 – 30 nm), no obvious shift wasobserved at the HOMO peak and the secondary
electron cutoff. These results indicate that the thermal
equilibrium condition of the LiPc layer is achieved in
the thin-layer region (~ 10nm).
The HOMO peak of LiPc appears at around 1.1 eV.
The binding energy and the intensity of the LiPc
HOMO peak were smaller than those of the H2Pc
HOMO peak. The ionization potential of the LiPc
thin film and that of the H2Pc thin film were
estimated at about 5.1 eV and 5.2 eV, respectively,from the secondary cutoff and the lower cutoff of the
HOMO peak. The HOMO peak intensity of LiPc wassmaller than that of H2Pc, reflecting a characteristicof the unpaired electron of LiPc.

N

Experimental

Results and Discussion
Figure 2 shows the photoelectron spectra of LiPc
grown on Au as a function of thickness. The abscissais the binding energy relative to the Fermi energy of
Au. The energy difference between the HOMO of
LiPc and Fermi level of Au at the interface is about
0.3 eV. This suggests that the energy barrier height forhole injection from Au to LiPc is relatively small.
From the secondary electron cutoff, it was observedthat the energy of the vacuum level sharply decreases
by about 0.4 eV within the thin-layer region up toaround 1 nm (not shown here). The abrupt loweringof vacuum level at metal/organic interfaces is
ascribed to the formation of the interface dipole [5].
The downward of the vacuum level caused by the
LiPc deposition suggests the formation of interfacial

N

Li

N

N

N
N

N

Fig. 1 Chemical structure of lithium phthalocyanince.

LiPc Thickness

Intensity / arb. units

LiPc was synthesized by electrochemical oxidationof dilithium phthalocyanine (Li2Pc) following thesynthesis procedure described in literatures [1]. The
purification of LiPc was done by vacuum sublimation.
LiPc was deposited on an Au substrate. Evaporationof LiPc was performed using a glass-cell evaporator
after careful outgassing, keeping the pressure of the
preparation chamber at less than 4 × 10-6 Pa. All thephotoelectron measurements were carried out at
photon incident angle of 45°, h = 40 eV, and sample
temperature of about 295 K. Photoelectron spectra ofmetal-free phthalocyanine (H2Pc) were also measured
for comparison.

N

50 nm
30 nm
10 nm
5 nm
3 nm
1 nm

h = 40 eV
10

Au

8
6
4
2
0
Binding Energy / eV

Fig. 2 Photoelectron spectra
incrementally deposited on Au.

of

-2
LiPc

film

[1] P. Turek et al., Chem. Phys. Lett. 134 (1987) 471.
[2] M. Brinkmann et al., Thin Solid FIlms 324 (1998)
68.
[3] T. Kimura et al., Chem. Phys. 253 (2000) 125.
[4] N. Sato et al., Appl. Surf. Sci. 212-213 (2003) 438.
[5] H. Ishii et al., Adv. Mat. 11 (1999) 605.

116

BL8B2

Structural Change in Lithium Phthalocyanine/Poly(3-hexylthiopehne)Interface Caused by Annealing
1

S. Tanaka1, 2, K. Watanabe3, Y. Yoshida3, I. Hiromitsu3, K. Yoshino2
Center of Integrated Research in Science, Shimane University, Matsue 690-8504 Japan
2
Research Project Promotion Institute, Shimane University, Matsue 690-8504 Japan
3
Faculty of Science and Engineering, Shimane University, Matsue 690-8504 Japan
spectrum of fig. 2 (c) is the photoelectron spectrum
after the annealing. As seen in fig. 2 (c), the spectrum
showed not the LiPc electronic structures but the
P3HT electronic structures. Because of the surface
sensitivity of the photoelectron spectroscopy, theseresults indicate that there were few LiPc molecules on
the sample surface after annealing. A possible reasonof the drastic change caused by annealing is that the
LiPc molecules were diffused into the P3HT layer
with the conformation change by the annealing. The
Li 1s spectra showed peak shift and the splitting
caused by annealing (not shown). To investigate therelations between the doping mechanism and thevariations of the photoelectron spectra, further studies
are now in progress.

Introduction
The conjugated polymers are promising material fororganic semiconductor devices. Poly (3-hexyl-thiophene) (P3HT) is one of conjugated polymers.
P3HT is used widely in polymer field-effecttransistors, photovoltaic cells, and light-emitting
diodes because of its characteristic properties such assolubility for various organic solvents, fusibility at
relatively low temperature, and relatively high carrier
mobilities. [1] The control of electrical properties in
the conjugated polymers is a major issue for further
device applications. Doping is the one way to control
the electric property of the conjugated polymers.
We have recently studied an effective moleculardoping for the P3HT film. Lithium phthalocyanine(LiPc) molecule is a candidate of the moleculardopant for P3HT. In this work we measured thevariation of the photoelectron spectra of the P3HT
films caused by annealing following a deposition of
LiPc molecules.

C6H13

N
N
N

N

Li
N

S

Experimental
The molecular structure of P3HT and LiPc are
shown in Fig. 1. The P3HT sample was prepared witha chloroform solution of P3HT casting on a clean Au
foil. The sample was immediately introduced into thevacuum chamber. The annealing of the sample wasdone in the preparation chamber in situ.

N
N

N

n

(b)
(a)
Fig. 1 Chemical structures of (a) poly(3-hexyl-thiophene) and (b) lithium phthalocyanince.
(c) LiPc(3nm) /P3HT(annealed)

Intensity / arb. units

Results and Discussion
Figure 2 shows the photoelectron spectra of (a)P3HT, (b) LiPc (3nm) on P3HT, and (c) LiPc (3nm)
on P3HT after annealing at 373 K. The abscissa is thebinding energy relative to the Fermi energy of Au. It
is expected from the shape of the spectrum that the
P3HT sample was slightly charging because of the
thickness of the P3HT film. In the P3HT spectrum,
the intense feature extending from 12 to 5 eVcontains the levels associated to the alkyl groups andthe -electrons of the thiophene rings contributes tothe region below 5 eV [3]. The LiPc layer with 3 nm
thickness was deposited on to the P3HT layer byvacuum evaporation, and the photoelectron spectrum(Fig. 2. (b)) was measured in situ. The feature of thephotoelectron spectrum showed the electronic
structure almost only of LiPc; hence, the surface of
the P3HT layer was fully covered with the LiPc
molecules. After the measurement of thephotoelectron spectrum, the sample of LiPc (3 nm) on
P3HT was annealed at 373 K (100 min) in situ. The(b) LiPc(3nm) /P3HT(a) P3HTh  = 40 eV
20

15

10

5

0

-5

Binding Energy / eV

Fig. 2. The photoemission spectra of (a) P3HT, (b)LiPc (3 nm) on P3HT, and (c) LiPc (3 nm) on P3HT
after annealing at 373 K.
[1] K. Yoshino, M. Onoda, Polymer Electronics,
Corona, Tokyo, (1996) (in Japanese).
[2] M. Brinkmann et al., Thin Solid Films 324 (1998)
68.
[3] R. Lazzaroni et al., J. Chem. Phys. 93 (1990)
4433.

117

BL8B2

Electronic Structure of Singlet Biradical Hydrocarbon Ph2-IDPL Thin Film
K. Kaname, T. Kubo1, H. Yamane2, R. Sumii, K. Nakasuji3, Y. Morita1, K. Seki2,4
Research Center for Materials Science, Nagoya University, Furo-cho, Chikusaku Nagoya
464-8602 Japan1
Department of Chemistry, Graduate School of Science, Osaka University, Machikaneyama 1-1,
Toyonaka, Osaka 560-0043, Japan2
Department of Chemistry, Graduate School of Science, Nagoya University, Furo-cho,
Chikusa-ku, Nagoya 464-8602, Japan
3
Fukui University of Technology, Gakuen 3-6-1, Fukui-shi, Fukui 910-0028, Japan
4
Institute for Advanced Research, Nagoya University, Furo-cho, Chikusa-ku, Nagoya
464-8602, Japanthe framework of extended Hueckel (EH) theory [1].
Especially, the behaviors of A and B are qualitatively
well explained by the energy band calculation byusing EH theory. However, observed energy widthof the dispersion (e.g. about 0.1 eV and 0.5 eV for A
and B, respectively) is smaller than that estimated byenergy band calculation [1].

Realization of the columnar stackings of planarmolecule on the substrate by intermolecularinteraction between extended -systems is widelyinterested matter in surface physics and organic
device technology.
Diphenyl derivative ofs-indacenodiphenalene (Ph2-IDPL) was isolated andcharacterized as a singlet biradical hydrocarbon by T.
Kubo et al [1]. Ph2-IDPL was reported to havestrong intra- and intermolecular interaction leading to- stacking distance (3.137 Å) for the crystal, which
is substantially shorter than the van der Waals contactof carbon atoms (3.4 Å). In Ph2-IDPL crystal,staggered stacking of the molecules forms ideal
one-dimensional molecular chain.
Such strong
intermolecular interaction in the ground state of
Ph2-IDPL molecule is caused from the interaction
between unpaired electrons characteristic of biradical
molecule. It is expected that tendency of Ph2-IDPL
molecules to undergo facile self-association on thesubstrate and form highly oriented film with - 
stacking originated form the strong intermolecularinteraction.
In this report, the electronic structure of Ph2-IDPL
film deposited on single crystal GeS(100) surgface
were investigated by angle-resolved ultraviolet
photoemission spectroscopy (ARUPS).
ARUPS measurements were performed in UVSOR
BL-8B2.
Base pressure of the experimental
chamber was under 5×10-8 Pa. Clean surface of GeS
substrate was obtained by cleaving the surface invacuum. Thickness of the Ph2-IDPL film wasmonitored by quartz microbalance.
Figure 1 shows UPS spectra of Ph2-IDPL film withthe thickness of 0.4 nm on GeS(100) surface. stands for take-off angle of photoelectron.
Dependence of the spectral shape on  was clearlyobserved.
Based on ARUPS measurements asshown in Fig. 1 the momentum k// dependences of theenergy of each spectral features labeled A, B, C, D
and E are presented in Fig. 2. Those features show
clear
energydispersion
characteristicof
one-dimensional system, which indicates theformation of well-ordered Ph2-IDPL film withanisotropy on GeS(100) surface.
Such
one-dimensional energy dispersion was predicted inFig. 1 UPS spectra of Ph2-IDPL film on GeS(100) surface.
The normal emission is origin of .

A
B
C
D

E

Fig. 2 Momentum dependence of the energy of thespectral features labeled in Fig. 1. Dotted verticalbars represents the boundary of Brillouin zone
calculated by lattice constant along the molecular
stacking in crystal.
[1] T. Kubo, K. Nakasuji et al., Angew. Chem. Int.
Ed., 44 6564 (2005).

118

BL8B2Ultraviolet Photoelectron Spectra of (YC)2@C82 and Y2@C82*
S. Hino 1†, N. Wanita1, K. Iwasaki1, D. Yoshimura2,3, T. Akachi4,
T. Inoue4, Y. Ito4, T. Sugai4, H. Shinohara4
1

Chiba University, Inage-ku, Chiba 263-8522 Japan
Institute for Molecular Science, Okazaki 444-8585 Japan
3 Research Center of Material Science, Nagoya University, Nagoya 464-8602 Japan
4
Faculty of Science, Nagoya University, Nagoya 464-8602 Japan
2

Recently, encapsulation of multiple atoms, such as
metal clusters [1, 2], metal nitrides [3] and metal–carbon clusters [4] inside the cage has been reported.
These metallofullerenes are considered a different
class from mono-metal atom encapsulated
metallofullerenes from the view point of electrontransfer from the encapsulated atoms to the fullerene
cage. This is thought to be because encapsulated
atoms may form chemical bonds among them as wellas they may form bonds to the carbon atoms that
constitute the cage.
Recently, numerous yttrium and carbon
atoms encapsulated metallofullerenes ((YC)2@C82)
have been reported, and three isomers were isolated[4]. Yttrium atoms have also been reported to be
encapsulated into the fullerene cage, and three
Y2@C82 isomers were identified [4]. NMR spectraof a (YC)2@C82 (III) isomer [4] and Y2@C82(III)revealed that their cage structures are exactly thesame and, their absorption spectra resemble eachother, suggesting their analogous electronic
structures.
Figure 2 shows the UPS of (YC)2@C82 (III). The
intensity of each structure in the UPS of Y2@C82 (III)labeled A – I changes upon tuning the incident photon
energy, which is typical spectroscopic behavior offullerenes. The USP of (YC)2@C82 (III) resemble
those of Y2@C82 (III). To clarify the difference
between these two metallofullerenes, their UPS
obtained with 30 eV photon are shown in Fig.2

4

3

E n e rg y ( e V )1
0 -1 -2

2

-3

-4

-5

C 3 v -C 8 2 (N o .8 )c h a rg e = - 4h = 30 eV

Y 2C 2@ C 82

Y 2@ C 82

Y 2@ C 82 - Y 2C 2@ C 82

0
8

6

4

2

0 =EF

B in d in g E n e rg y ( e V )Fig.2 Comparison of the UPS of (YC)2@C82 andY2@C82 isomers. Difference spectrum between
them (bottom) and simulation spectra (top)obtained by MO calculation.

The first three structures of (YC)2@C82 (III) can be
deconvoluted into three components with intensity
ratio of 4 : 5 : 9. This is well reproduced by asimulation spectrum (top in Fig. 2) calculated using
geometry of C3v-C82 (No.5) [5] with additional 4
electrons on the cage.
This finding indicates(YC)2+2@C824- is the plausible oxidation state.
Onset energy of Y2@C82 (III) is slightly smaller thanthat of (YC)2@C82 (III).
Difference spectrum
between them (bottom in Fig. 2) reveals two
additional electrons on Y2@C82 (III). Thus, theoxidation state of this metallofullerene might be
Y3+2@C826-. Since the oxidation state of Y must be+ 3, probably two electrons in (YC)2@C82 (III) might
be used either to form the bonds between Y and C or
to donate electrons to acetylide.

Y 2C 2@ C 82

55eV
50eV

* This work was published in Phys. Rev. B 72 (2005)
195424.
† present address, Ehime University, Matsuyama,
Ehime 790-8577.
[1] M. Takata et al., Phys. Rev Lett. 83 (1999) 2214.
[2] C.-R. Wang et al., Nature 408 (2000) 426.
[3] S. Stevenson et al. ibid. (1999) 55.
[4] T. Inoue et al., Chem. Phys. Lett. 382 (2003) 226
and J. Phys. Chem. B 108 (2004) 7573.
[5] P. W. Fowler, “An atlas of Fullerenes”, Oxford
Press, Oxford, 1995.

45eV
40eV

I

35eV
30eV

H

G

F E

25eV

D
C B

14

12

10

8

6

4

A

20eV

2

0

B in d in g E n e rg y ( e V )Fig. 1 Incident photon energy dependence of the
UPS of (YC)2@C82 (I).

119

BL8B2Ultraviolet Photoelectron Spectra of Three Tm@C82 Isomers*
S.Hino 1†, N. Wanita1, K. Iwsaki 1, D. Yoshimura2,3, N. Ozawa4,T. Kodama4, K. Sakaguchi4, H. Nishikawa4, I. Ikemoto4, K. Kikuchi4
1

Chiba University, Inage-ku, Chiba 263-8522 Japan
Institute for Molecular Science, Okazaki 444-8585 Japan
3Research Center of Material Science, Nagoya University, Nagoya 464-8602 Japan
4
Faculty of Science, Tokyo Metropolitan University, Hachioji, Tokyo 192-0397 Japan2

Up to now a lot of metallofullerenes have beensynthesized [1] and among them the most abundantly
obtainable metallofullerene seem to have C82 cage.
There are nine isolated pentagon rule (IPR) satisfying
cage structures for C82. While it seems that trivalent
metal atom accommodates only in C2v and Cs cages,
divalent metal atoms prefer more cages. Tm atom is
entrapped inside the C82 cage and three Tm@C82
isomers have been reported [2, 3]. We present the
UPS of three Tm@C82 isomers and compare them withpreviously reported one [4] and those of two Ca@C82
isomers [5] and discuss the correspondence among
these metallofullerenes. Cage structures of three
Tm@C82 isomers are also proposed with an aid ofmolecular orbital calculation.
Figure 1 shows the valence band UPS one of three
Tm@C82 isomers, isomer (I) obtained with h = 20 –55 eV photon energy. Spectral onsets of threeisomers are 0.85 eV (I), 0.75 eV (II) and 0.9 eV (III).
The onset energies of Tm@C82 isomers are relatively
large compared with those of La@C82 and Gd@C82
but almost the same as those of Ca@C82 isomers [4].
Figure 2 shows the UPS of three Tm@C82 isomers
and two Ca@C82 isomers. The UPS of Tm@C82 (II)and Ca@C82 (III) are essentially the same whichindicates that these two metallofullerenes have thesame electronic structure derived from the same cage
structure. The UPS and MO calculation proposed
C2(c) cage structure for the geometry of Ca@C82 (III)[6] and this deduction was later supported by the NMR
measurements [7]. Further the NMR on Tm@C82 (II)predicts the same C2 symmetry. On the other hand,

G

F

E

D

h  = 40 eV
Ca@ C 82(IV)photoelectron counts

Ca@ C 82 (III)Tm @ C 82 (II)Tm @ C 82(I)14photoelectron counts

55 eV

45 eV
40 eV
35 eV
30 eV

25 eV
20 eV

10

15 eV

8

6

4

2

6

4

2

0 = EF* This work was published in Chem. Phys. Lett. 402,
217 (2005).
†
present address : Ehime University, Matsuyama,
Ehime 790-8577 Japan[1] for example, H. Shinohara, Rep. Prog. Phys. 63(2000) 843.
[2] U. Kirbachet al., Chem. Int. Ed. Engl. 35 (1996)
2380.
[3] T. Kodama et al., J. Ame. Chem. Soc. 124 (2002)
1452.
[4] T. Pichler et al., Appl. Phys. A66 (1998) 281[5] S. Hino et al., Chem. Phys. Lett. 230 (1994) 165.
[6] S. Hino et al., Chem. Phys. Letts. 227 (2001) 65.
[7] T. Kodama et al., Chem. Phys. Letts. 377 (2003)
197.

50 eV

12

8

these spectra correspond with the HeI and HeII excitedspectra reported by Pichler’s group who claimed thatThat is, thethey measured C3v-Tm@C82 [4].
metallofullerenes that we and Pichler’s group havemeasured are the identically the same species andPichler’s claim of symmetry definition was wrong.
The UPS of three Tm@C82 isomers were comparedwith MO calculation and it was found that their cage
structures are Cs(c) cage structure for Tm@C82 (I),C2(c) for Tm@C82 (II) and C2v for Tm@C82 (III)

A

14

10

Fig.2 Comparison of the UPS of two Ca@C82
isomers and three Tm@C82 isomers.

B

Tm@C82(I)12Binding Energy ( eV )C

H

T m@ C 82 (III)0 =EF

Binding Energy ( eV )Fig. 1 Incident photon energy dependence of the
UPS of Tm@C82 (I).

120

BL8B2

Electronic Structure at Highly Ordered Pentacene/Cu(110) Interface:
Energy-Level Splitting and Energy-Band Dispersion
H. Yamane 1, E. Kawabe 1, R. Sumii 2, K. Kanai 2, Y. Ouchi 1, K. Seki 1,2
Department of Chemistry, Nagoya University, Nagoya 464-8402 Japan
2
Research Center for Materials Science, Nagoya University, Nagoya 464-8602 Japan1

pentacene monolayer on the substrate, the intensity ofthis substrate peak S decreases, and the new peaks A,
B, and C appear with the continuous change in thepeak positions with . We note that the separation
between A and B is about 0.7 eV, while the Eb
difference between the HOMO and HOMO-1 peaksin the gas-phase spectrum is much larger (1.4 eV) [1].
This discrepancy is in contrast to the case of thephysisorbed pentacene monolayer on highly oriented
pyrolytic graphite, where the relative energies of thepeaks correspond well with those in the gas phase [2].
Thus we can consider that the peaks A and B are
formed by the strong molecule-substrate interaction.
From the consideration of symmetry selection rules
and the  dependences of the ARUPS spectra [3], we
can deduce that (i) the peaks A and B originate fromthe energy-level splitting of the original HOMO level
and that (ii) the continuous change in the peak
position with  originates from the intermolecularenergy-band dispersion. In this system, theintermolecular interaction via direct contact isconsiderably weak, and these findings may originate
from the intermolecular interaction via the substrate
due to the significant hybridization of the MOs andthe substrate.

Introduction
The electronic structure at organic/metal interfaces,in particular the energy positions of the highestoccupied and lowest-unoccupied molecular orbital(HOMO and LUMO) levels relative to the Fermi
level (EF) of metal electrodes, plays a crucial role indetermining the charge injection barrier in (opto)
electronic devices using organic semiconductors.
Therefore it is natural that many research groups havebeen investigating the energy-level alignment atorganic-related interfaces in order to elucidate theenergetics at the interfaces. For deeper understandingof the energetics at organic/metal interfaces, a more
pertinent experimental approach to this issue would
be the use a well-characterized system in quantitativeelectron spectroscopic measurements. In this work,
we studied the electronic structure of highly-orderedmonolayer of pentacene prepared on Cu(110) surface
by angle-resolved UV photoemission spectroscopy(ARUPS) using synchrotron radiation. We observed adistinctive electronic structure at the interface, whichis completely different from those of the gas- andbulk-phase pentacene.

Experimental
The purified pentacene was carefully evaporated
onto the clean Cu(110) surfaces, which was kept at
500 K during the deposition.
The azimuthal angle () dependence of ARUPS
spectra was measured at the photon energy (h) of
20 eV, the photon incidence angle () of 60°, take-off
angle () of 58° from the surface normal, and thetemperature of 300 K. The origin of the azimuthal
angle  = 0° was defined so that the electric-field
vector of the incident photon is on the incident plane
containing the substrate [1-10] direction and thesurface normal.

hv = 20eV,  = 60°,  = 58°
Cu(110)Pentacene(1ML)/Cu(110)=

Intensity / normalized

90°

121

90°

75°

75°

B
60°

60°

A
45°

45°

30°

30°

Results and Discussion

The  dependences of the ARUPS spectra with astep of 3° for the clean Cu(110) substrate and thepentacene monolayer on the Cu(110) substrate areshown in Fig. 1. The abscissa is binding energy (Eb)relative to the substrate EF, and the spectra arenormalized to the incident photon flux. As a reference,
we also show the UPS spectrum of the gas-phasepentacene [1], which is shifted to align the lowest-Eb
peak to that of the pentacene monolayer on Cu(110)at = 0°. For the Cu(110) substrate, the peak S due tothe direct s,p-band transition appears at 1.9 eVwhen = 0° and gradually shifts toward the low-Eb
side until  reaches 30°. Upon formation of the

=

15°

C

15°

gas
S
2

0°

1

0

0°

2

1

0

Binding Energy (vs. EF) / eV

Fig. 1 Azimuthal angle () dependence of the
ARUPS spectra for the Cu(110) substrate (left) andthe pentacene monolayer on Cu(110) (right).
[1] V. Coropceanu et al., Phys. Rev. Lett. 89, (2002)
275503.
[2] H. Yamane et al., Phys. Rev. B 72 (2005) 153412.
[3] H. Yamane et al., UVSOR Activity Report 2005
(2006) 113.