Ⅲ-4
Surface,
Interface andThin Films

Ⅲ -4. Surface, Interface and Thin Films

BL2B

An Optimization Study for Multi-Alkali Photocathode as the Ultimate
Electron Source
1

M. Kuriki1, Y. Seimiya1, T. Konomi2, M. Katoh2 and R. Inagaki3

Graduate school of Advanced Science of Matter, Hiroshima University, Higashi-hiroshima, 739-8530, Japan
2
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
3
Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan

Multi-alkali photocathode, CsK2Sb is the strongest
candidate as the ultimate photocathode forhigh-brightness electron accelerator. Recently,
advanced accelerator projects based on the linear
accelerator (Linac) have been proposed and some ofthem, e.g. X-ray FEL, are already in operation. To
realize a high brightness beam with Linac, theelectron source is one of the key components, because
the beam brightness normalized with its energy is
kept during the acceleration over Linac. From theview point of electron source, a small emittance andlarge current beam from a small spot size has to begenerated. As the cathode requirements, not only thesmall emittance, but also high quantum efficiency(QE) and high robustness are required. In addition, if
the visible light laser instead of UV laser which iscommonly used for metal cathode is applicable, it
relaxes the technical requirements for the laser.
CsK2Sb cathode fulfills these requirements; high QE
as high as more than 10%, driven by a green laser,and high robustness [1]. CsK2Sb is then suitable forthe high brightness Linac application. On the other
hand, CsK2Sb cathode is made with evaporation in a
vacuum chamber as a thin film in order of several 10s
nm. The cathode activity is lost by air exposure. The
evaporation condition to maximize the cathode
performance is not established and material property
is not well understood. The aim of our study is tounderstand the cathode performance from thematerial science point of view.
We made the multi-alkali evaporation chamber
which is capable to form the thin film in an extreme
vacuum environment. The thin-film cathode is madeon a substrate fixed on a sample holder. The pressureof the chamber was 5.0×10-8 Pa.
Figure 1 shows an example of CsK2Sb evaporation.
The horizontal axis shows time in minutes and t=0
gives the start of the evaporation. On boron doped
p-type Si substrate (100), Sb, K, and Cs were
evaporated in this order. The thickness was measured
with a quartz monitor. QE was measured with 405 nm
laser. It was more than 8%.
Figure 2 shows UPS spectrum for CsK2Sb. By
comparing Sb peaks[2][3], Sb 4d peaks split into 5.
The valence band peaks are enhanced. Peak at 18 and
10 eV are consistent with K 3p[4] and Cs 5p[5],respectively, but need more careful investigation for
the identification.
As the summary, we successfully took UPS spectrafor (multi) alkali cathode evaporated on Si substrate.

To identify the optimized evaporation condition for
the thin film cathode, UPS spectra of the cathodeevaporated with various different conditions should
be taken. UPS spectral change during the cathodedegradation should give curious information about
the process.

Ⅲ- 4Fig. 1. An example of evaporation of CsK 2Sb. The
right and left vertical axes show thickness (Angstrom)and QE (405nm) in %.

Fig. 2. CsK2Sb UPS spectrum as a function ofbinding energy.
[1] B. Dunham et al., Appl. Phy. Lett. 102 (2013)
034105.
[2] M. Scrocco et al., J. Electron Spectrosc. Relat.
Phenom. 50 (1990) 171.
[3] G. E. Franklin et al., Phys. Rev. B 45 (1992)
3426.
[4] H. H. Weitering et al., Phys. Rev. B 48 (1993)
8119.
[5] A. N. Belsky et al., J. Electron Spectrosc. Relat.
Phenom. 80 (1996) 109.

125

Ⅲ -4. Surface, Interface and Thin Films

BL2B

Electronic Structure of Chlorophyll-a Investigatedby Photoelectron Spectroscopy and Photoelectron Yield Spectroscopy
Y. Takeda1, H. Ezawa2, T. Miyauchi1, H. Kinjo1, K. R. Koswattage3,
Y. Nakayama1 and H. Ishi1,31Advanced Integration Science, Chiba University, Chiba 263-8522, Japan2
Department of Engineering, Chiba University, Chiba 263-8522, Japan
3
Center for Frontier Science, Chiba University, Chiba 263-8522, Japan

Fig. 1. UPS spectrum of the Chl-a filma)UPS by Synchrotron radiation, b)Low Energy UPS.

/ arb. units

Dried film
Solution

1/3

4.93eV
4.95eVY

Ⅲ- 4

estimated to be 1.2 eV by the formula: P+ = Ig - Il.
Interestingly this value is 0.5 eV smaller than aliterature value of P+ (=1.7eV [3]) for a watermolecule induced by adjacent H2O molecules. Thissuggest that large molecules like Chl-a reducepolarization energy by water.

Observingtheelectronic
structuresofbio-molecules in their living environment is
indispensable to elucidate their functionalities.
Especially understanding how photosystem of plants
realizes energy conversion in high efficiency is an
important factor for the development of artificial
photosynthesis. In photosystem, photon energy isconverted to electron energy by photoexcitation
reaction of Chlorophyll-a (Chl-a) aggregation. In
addition, in actual systems, Chl-a is surrounded bysolvent. In water-rich acetone-water binary solvent,
Chl-a exists predominantly as oligomer, which havebeen utilized as artificial model of Chl-a in vivo [1].
For general materials, photoelectron spectroscopy(PES) is a powerful and widely used technique toexamine their electronic structures. However, PES
needs vacuum environment and its application tobio-related systems has been much limited. In thisstudy, we tried to observe the electronic structure of
Chlorophyll-a (Chl-a) with the techniques.
Chl-a powder was bought from Wako Pure
Chemical Industries and was used as purchased.
Sample of UPS was spin-coated film which was
deposited acetone solution of chlorophyll a on ITO.
For PYS, Chl-a powder was dissolved in water-rich(83.3 vol%) acetone-water binary solution (0.7 mM),
in which almost all Chl-a molecules are known toexist as oligomers, which have been utilized as an
artificial in vivo model of RC [1]Figure 1 a) shows UPS results by Synchrotron
radiation at BL2B. Blue line is estimated DOS and
red line is the observed spectra. The observed spectralfeature is consistent with calculated DOS. Weaksample-charge-up seems to slightly induce thespectral broadening. Moreover, we measured Low
Energy UPS and the determined that the ionizationenergy of Chl-a film was 5.0eV. In addition, gap state
was observed above HOMO as shown in Fig. 1 b).
The spectra HOMO state may spread due to thevariation of molecular packing. Figure 2 shows PYS
spectra of Chl-a solution and a film which wasmeasured after drying up of the solution. The
ionization energies of Chl-a in the solution and solid
phase were determined to be Il = 4.95 eV and Is = 4.93
eV, respectively. Its ionization energy in the gas phase
had been reported to be Ig = 6.1eV [2] which wascollaborated by DFT calculation. Hence thepolarization energies P+ of Chl-a in the solvent is

4.0

4.5

5.0

5.5

Photon energy / eV

6.0

Fig. 2. PYS spectra of Chl-a in the solution and solid
phases.
[1] Agostiano et al., BBA BIOENER. 936 (1988)
171.
[2] Y. Nakato et al., Chem. Soc. Jpn. 47 (1974) 3001.
[3] M. Faubel et al., J. Chem. Phys. 106 (1997) 9013.

126

Ⅲ -4. Surface, Interface and Thin Films

BL3U

Cobalt-Borate Oxygen Evolution Catalyst Studied by Electrochemical
XAFS Technique Using Soft X-Ray
Y. Mitsutomi1, M. Yoshida1,2, T. Mineo1, M. Kawamura1, M. Nagasaka3, H. Yuzawa3,
N. Kosugi3 and H. Kondoh1
1

Department of Chemistry, Keio University, Yokohama 223-8522, Japan
Cooperative Research Fellow, Catalysis Research Center, Hokkaido University, Sapporo 001-0021, Japan
3
Institute for Molecular Science, Okazaki 444-8585, Japan2

Photoelectrochemical water splitting using solar
energy is an attractive candidate to produce hydrogengas from water. This system consists of two half
reactions of hydrogen and oxygen evolutions. Amongof them, the rate of oxygen evolution is generally
slower than that of hydrogen evolution. Thus, thedevelopment of efficient oxygen evolution catalyst
has been required toward highly active energy
conversion system. Recently, a cobalt-borate
electrodeposited from a dilute Co2+ solution in aborate-buffered electrolyte (Co-Bi) was reported tofunction as an efficient electrocatalyst for oxygen
evolution reaction [1]. The structural information wasinvestigated by X-ray pair distribution function (PDF),
which indicates that Co-Bi catalyst is formed bycoherent domains consisting of 3−4 nm cobaltate
clusters with up to three layers [1]. However, thecorrelation between structure and activity is still
unclear. Therefore, in this study, the Co-Bi catalyst
was investigated by in-situ O K-edge XAFS
measurements under potential control conditions.
Electrochemical XAFS measurements withtransmission mode using soft X-rays were performed
at BL3U in the UVSOR Synchrotron, according to
the previous work [2]. A home-made electrochemicalcell was used with Au/Cr/SiC thin film substrates asworking electrodes, a Pt mesh counter electrode, anda Ag/AgCl (saturated KCl) reference electrode. Co-Bi
catalyst was prepared on the Au/Cr/SiC working
electrode at 1.0 V in 0.1 M K-Bi electrolyte
containing 0.5 mM Co(NO3)2.
Figure 1 shows the linear sweep voltammogramsof bare and Co-Bi-modified Au electrodes in 0.1 M
K-Bi electrolyte. The current density of oxygen
evolution reaction for Co-Bi-modified electrode washigher than that for bare Au electrode, which exhibitsthat Co-Bi can function as an efficient oxygen
evolution catalyst. Figure 2 shows the O K-edge
XAFS spectra for Co-Bi catalyst at 1.0 V in a 0.1 M
K-Bi. Two absorption peaks were observed at ca.
529.3 eV and 530.9 eV for Co-Bi sample. Empirically,
the O K-edge absorption peak position shifts to lower
energies with increasing the formal oxidation state.
Thus, the absorption peak at ca. 529.3 eV is likely to
be attributed to a high-valent cobalt species. Further
investigation is in progress in order to reveal the
relationship between production of high-valent cobalt
species and oxygen evolution activity.

127

Fig. 1. Linear sweep voltammograms of the bare and
Co-Bi-modified Au electrodes in 0.1 M K-Bi (pH 9.2)
electrolyte at 100 mV/s.

Ⅲ- 4

Fig. 2. O K-edge XAFS spectra of Co-Bi catalyst on
the Au/Cr/SiC electrode at 1.0 V in 0.1 M K-Bi. The
spectra of Co3O4, CoO, K-Bi, O2, and H2O are shown
as reference samples.
[1] D. G. Nocera et al., J. Am. Chem. Soc. 135 (2013)6403.
[2] M. Nagasaka et al., J. Electron. Spectrosc. Relat.
Phenom. 177 (2010) 130., J. Phys. Chem. C 117(2013) 16343., Rev. Sci. Instrum. 85 (2014) 104105.

Ⅲ -4. Surface, Interface and Thin Films

BL4U

STXM Analysis of Adsorbent for Effective Recovery of Radioactive
Elements
1

Y. Sano1, S. Watanabe1, H. Matsuura2 and A. Nezu2

Japan Atomic Energy Agency (JAEA), Tokai-mura 319-1194, Japan
Research Laboratory for Nuclear Reactors, Tokyo Institute of Technology, Tokyo 152-8550, Japan

2

50μm

Fig. 1. Photo of the SiO2-P adsorbents (CDP: 10%).
CDP: 10%
4
3
μm
2
1

0

1

2

μm

3

4

Fig. 2. STXM image of the surface of the SiO2-P
adsorbent at 530eV (O-K edge).
3
CDP: 15%（0.4‐0.6um*）
CDP: 15%（0.2‐0.4um*）

2.5

CDP: 15%（0‐0.2um*）
CDP: 10%（0‐0.2um*）

Optical density

Ⅲ- 4Spent nuclear fuels generated from nuclear power
plants contain U and Pu which can be reused, andseveral long-lived radioactive elements. It will bequite important for effective utilization of energy andenvironmental loading reduction to process the spent
fuel adequately. JAEA has been developing theselective recovery process of radioactive elements,
which uses adsorbents of SiO2 supports coated withstyrene-divinylbenzene copolymer (SiO2-P) andextractants on its surface [1]. Our recent work showsthat the separation and recovery abilities of adsorbent,
i.e. adsorption/elution behavior of radioactive
elements, in this process are strongly dependent on
the condition of its surface in which polymer andextractants are impregnated [2]. In this study, some
information about the adsorbent surface, such as
uniformity of extractants and SiO2/polymer/
extractants interaction, were investigated by scanningtransmission X-ray microscope (STXM).
Some adsorbents with different crosslinking degreeof polymer (CDP) were synthesized and octyl(phenyl)-N, N-diisobutylcarbonoylmethylphosphineoxide (CMPO) was impregnated as an extractant by
the flowsheet reported by Wei et al. [3]. The average
diameter and pore size of the synthesized adsorbents
were 50μm and 50nm, respectively (Fig.1). These
adsorbents were sliced to 1~3μm in thickness byfocused ion beam (FIB), and were supplied to STXM
analysis.
Figures 2 and 3 show the STXM image ofadsorbent surface and the change of O-NEXAFS
spectra with CDP at 530eV (O-K edge), respectively.
The intensity of pre-edge peak at 532eV increased
with CDP at any positions in the adsorbent. The
impregnation of CMPO into the adsorbent showed nosignificant effect on these results.
The appearance of pre-edge peak at 530eV in
O-NEXAFS spectra with increasing CDP indicatesthe some interactions between SiO2 and the polymer
or/and the capture of some kinds of molecules, suchas H2O, by the polymer. These will give someinterpretation of our previous experiment, in which it
was more difficult to elute adsorbed metal ions fromthe adsorbent with higher CDP [2]. To obtain moredetailed information about the adsorbent surface,
STXM analyses at 300eV (C-K edge) and 189eV(P-K edge) will be carried out. It should be further
required for effective recovery of radioactive
elements to evaluate and compare the STXM data andadsorption/elution behavior using several kinds ofadsorbents with different pore sizes and extractants.

2

SiO2（0‐0.2um*)

pre‐edge*scanning lengthfrom the surface

1.5
1
0.5
0
520

530

540
550
560
570
Photon energy (eV)580

Fig. 3. Change of O-NEXAFS spectra with CDP at
530eV (O-K edge)[1] Y. Koma et al., Proc. OECD Nuclear Energy
Agency 11th Information Exchange Meeting on
Actinide and Fission Product Partitioning andTransmutation, San Francisco, USA, November 1-4,
(2010) IV-4.
[2] S. Watanabe et al., Procedia Chemistry 7 (2012)411.
[3] Y. Wei, M. Kumagai and Y. Takashima, Nucl.
Technol. 132 (2000) 413.

128

Ⅲ -4. Surface, Interface and Thin Films

BL4B

XMCD Study on Magnetic Multilayer of CoNi2 on W(110)
T. Yasue1, M. Suzuki1, T. Nakagawa2, K. Takagi3, T. Yokoyama3 and T. Koshikawa1
1

Fundamental Electronics Research Institute, Osaka Electro-Communication University,
Neyagawa 572-8530, Japan2
Department of Molecular and Material Sciences, Kyusyu University, Fukuoka 816-8580, Japan
3
Institute for Molecular Science, Okazaki 444-8585, Japan

Co/Ni2 multilayer shows the perpendicularmagnetic anisotropy (PMA) and hence is attracted
much attention as a candidate for the spintronics
device based on the current induced domain wallmotion. We have investigated the dynamic behaviorof emerging PMA during the multilayer growth
process on W(110) by a high-brightness and highly
spin polarized low energy electron microscopy(SPLEEM) [1]. In the beginning of the growth below
3 Co/Ni2 pairs, the perpendicular magnetization
appears during Ni deposition, while the magnetization
becomes in-plane by Co deposition. PMA becomesstable after 4 pairs even after Co deposition. In orderto understand the behavior, XMCD measurements
were performed at BL4B in the present work.
Ni L2,3 and Co L2,3 XMCD spectra were taken at
the incident angle of X-ray of 60 (GI) and 0 (NI)with applying the external high magnetic field enoughto saturate the magnetization. The magnetic field wasparallel to the X-ray direction. The spin magnetic
moments ms and the orbital magnetic moments mo of
Ni and Co were derived from the measured XMCD
spectra using the sum rules.
The white line intensities of Ni and Co L2,3
absorption spectra were almost constant overdifferent multilayer repetitions examined. The whiteline intensity is proportional to the number of 3dholes, so that the charge transfer between Ni, Co andthe substrate W could be negligible. On the contrary,
XMCD spectra strongly depend on the multilayer
repetition. This indicates that the spin and orbital
moments vary in the multilayer stacking sequence.
Figure 1 shows mo/ms ratio of Ni taken at NI (red) andGI (blue). At NI configuration, the mo/ms ratio
increases with coverage, and decreases at GI. This
result clearly indicates that the orbital moment of Ni
plays an important role for the perpendicularmagnetization at higher coverage. Figure 2 shows thespin (squares) and orbital moments (circles) of Ni(top) and Co (bottom). The parallel (blue) andperpendicular (red) components are separated for theorbital moment. Both spin and orbital moments of Co
do not show clear coverage dependence, while thoseof Ni increase with coverage up to 3 pairs and reachto the constant value above 4 pairs. The perpendicularorbital moment of Ni becomes more dominant withincreasing coverage. Therefore it is concluded that
PMA of the Co/Ni2 multilayer is mainly induced by
the perpendicular orbital moment of Ni.

Fig. 1. Ratio of the orbital moment to the spin
moment of Ni. Red circles are taken at NI and blue
squares at GI.

Ⅲ- 4

Fig. 2. Spin and orbital magnetic moments of Ni(top) and Co (bottom) obtained by XMCD
measurements.
[1] M. Suzuki, K. Kudo, K. Kojima, T. Yasue, N.
Akutsu, W. A. Diño, H. Kasai, E. Bauer and T.
Koshikawa, J. Phys.: Condens. Matter 25 (2013)
406001.

129

Ⅲ -4. Surface, Interface and Thin Films

BL4B

XMCD Study of Anisotropic Magnetism of Fe/W(112)
K. Yamaguchi, T. Kawashima, S. Mizuno and T. Nakagawa

Department of Molecular and Material Sciences, Kyushu University, Kasuga 816-8580, JapanⅢ- 4

Ordered atoms on surfaces have highly anisotropic
structures which is not available for the bulk
materials. Such strained or low dimensional structures
bring anisotropic electronic structures, resulting ininteresting magnetic properties. One-dimensional
structures are successfully prepared on steppedsurfaces and shows intrigue magnetic properties,
which has attracted much attentions [1,2]. On theother hand, other works on bcc(112), highly
anisotropic surfaces, are also interesting due to its
furrow structure (Fig.1), which would exhibit highmagnetic anisotropy. However few investigation ofmagnetic overlayers on bcc(112) have been examinedso far [3], and its magnetic properties are unknown.
We have prepared Fe quasi-chain structure on W(112)
surface and investigated its magnetic properties.
X-ray magnetic circular dichroism (XMCD)
measurements were done at BL4B using high field
and low temperature end station. All themeasurements were performed in situ under thevacuum of 1×10-10 Torr.
Figure 1 shows anisotropic Fe quasi chain structureon W(112), as determined by tensor low energy
diffraction (LEED) analysis (Fig.1 (a)), andvisualized by STM (Fig.1(b)). Fe atoms occupy the
furrow of W(112), and forms 1×1 structure,irrespective of the large size mismatch between Fe
and W (~10%), in accordance with other Fe
monolayer structures on W(111), W(110), andW(100) surfaces.
Figure 2 shows Fe-L XAS for 0.6 ML Fe/W(112)and its XMCD. Figure 3 shows magnetization curves(M-H curves) for 0.6 ML Fe/W(112), which wasmeasured by monitoring Fe L3 XAS intensity. The
M-H curve along the [11-1] direction shows
hysteresis with the large coercivity of 3.7 T, while theM-H curves along the [112], surface normal, and the[1-10] directions do not show hysteresis and do notsaturate even at H = 5 T. This M-H curvemeasurement reveals that the magnetization easy axis
is along the [11-1] direction, parallel to the quasi Fe
chains and that the magnetic anisotropy energy is 0.6
meV/Fe atom.
In summary, XMCD study reveals that Fe/W(112)
exhibits the large magnetic anisotropy and coercivity
as expected from its anisotropic structure.

Fig. 1. A structure model of Fe(1 ML)/W(112)
determined by tensor LEED and its atomicallyresolved STM image.

Fig. 2. XAS and XMCD spectra for Fe(0.6ML)/W(112) for H = ± 5 T along the [11-1] direction
with the background contribution from W(112) cleansurface.

Fig. 3. Magnetization curves for Fe(0.6 ML)/W(112)
taken along three different directions.
[1] M. Pratzer et al., Phys. Rev. Lett. 87 (2001)
127201.
[2] P. Gambardella et al., Nature 416 (2002) 301.
[3] J. Kołaczkiewicz and E. Bauer, Surf. Sci. 144(1984) 495.
[4] T. Nakagawa et al., Phys. Rev. B 86 (2012)
144418.

130

Ⅲ -4. Surface, Interface and Thin Films

BL4B

X-Ray Magnetic Circular Dichroism Study of Mn- and Fe-Phthalocyanine
Molecules Self-Assembled on the Si(111)-(73)-In Surface
T. Uchihashi and S. Yoshizawa

International Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science,
Tsukuba 305-0044, Japan
Recently, atomic-layer superconductors on siliconsurface (surface reconstructions) were investigated byelectron transport measurement and scanningtunneling microscopy. The superconductivity of thisclass of atomically thin materials can be tuned byadsorption of molecules due to its high surface
sensitivity. In this work, we studied the magnetic
properties of Mn-Phthalocyanine (Pc) and FePc
self-assembled on the Si(111)-(73)-In surface
reconstruction [referred to as (73)-In], which ismade of atomic indium layers on a clean siliconsurface [1,2]. Since the (73)-In surface exhibits
superconducting phase transition at 3 K, interesting
competition effects between superconductivity andmagnetism are expected to occur in this system.
X-ray absorption spectroscopy (XAS) and X-ray
magnetic circular dichroism (XMCD) measurements[3,4] were taken to detect the magnetic properties ofthe MnPc and FePc. The experiment was performedin the ultrahigh vacuum XMCD system with asuperconducting magnet, which was set at the
UVSOR beam line BL4B in the Institute for
Molecular Science. First, preparation of the(73)-In surface was confirmed by low energy
electron diffraction (LEED) (Fig. 1). MnPc was thenevaporated to a monolayer level. Parallel molecularadsorption geometry on the surface was confirmed
from the XAS measurement of N K-edge. Similar
results were obtained for or FePc on the (73)-In
surface. XMCD spectra were determined from thedifference between the XAS spectra taken at T=5K
and B = 5 T.
We found clear XMCD signal for both MnPc and
FePc molecules, which showed that the spins of Mn
and Fe atoms coordinated at the Pc molecules wereretained even when they are adsorbed onto the(73)-In surface (Fig. 2). Detailed analysis of the
XMCD data using the sum rule gives the following
results. MnPc (1ML, θ=55): <Seff> = 0.940.18μB,<L> = 0.610.08μB, FePc (1ML, θ=55): <Seff> =0.500.23μB, <L> = 0.310.12μB. Therefore, it isconcluded that MnPc and FePc have about one andhalf spins, respectively, on adsorption. The observed
orbital magnetic moments were also found to berelatively large in both cases. These magnetic
moments should influence the superconductivity ofthe (73)-In surface at low㻌 temperatures.

Fig. 1. LEED patterns of the (73)-In sample
before evaporation of Pc molecules.

Ⅲ- 4

Fig. 2. XAS and XMCD spectra taken for Mn-Ledge (MnPc) and Fe-L dege (FePc) at T = 5K, B= 5
T, and θ=55. The coverage of the molecule is 1ML
for both cases.
[1] T. Uchihashi et al., Phys. Rev. Lett. 107 (2011)
207001.
[2] S. Yoshizawa et al., Phys. Rev. Lett. 113 (2014)
247004.
[3] S. Stepanow et al., Phys. Rev. B 82 (2010)
014405.
[4] K. Eguchi et al., J. Phys. Chem. C 118 (2014)
17633.

 Å131

Ⅲ -4. Surface, Interface and Thin Films

BL4B

Magnetic Properties of Ordered Iron Nitride Monatomic Layer
T. Miyamachi1, Y. Takahashi1, Y. Takagi2,3, M. Uozumi2,3, T. Yokoyama2,3 and F. Komori1
1

Institute for Solid State Physics, University of Tokyo, Kashiwa 277-8581, Japan
Department of Materials Molecular Science, Institute for Molecular Science, Okazaki 444-8585, Japan3
Department of Structural Molecular Science, The Graduate University for Advanced Studies (SOKENDAI),
Okazaki 444-8585, Japan2

Ⅲ- 4

agreement with a recent study [3].
Detailed analyses of the XMCD spectra and thetemperature dependence of the remanent XMCD
signal give further information on the magnetic
moments and the Curie temperature of the Fe2N layer.
In future work, combined XMCD with surface
analysis techniques, the correlation between
magnetism and surface quality of the Fe2N layer willbe also discussed.

Iron nitrides, especially in iron-rich phases asrepresented by Fe16N2 [1], or F4N [2], are of greatinterest for the field of materials science due to their
extraordinarily large magnetic anisotropy androom-temperature ferromagnetism. Towards practicalapplications, deep understanding of their magnetic
properties in the form of thin films and extremely of amonatomic layer is required. For this purpose, wefabricated well-ordered iron nitride monatomic layer(Fe2N layer) on a Cu(001) substrate and performed
x-ray magnetic circular dichroism (XMCD)
measurements at BL4B in UVSOR by total electron
yield mode.
The Fe2N layer was fabricated by three processes,
i.e., (1) ionic bombardment of N+ onto a clean
Cu(001) surface with a beam energy of 500 eV, (2) Fe
deposition onto N+-bombarded Cu(001) at room
temperature, and (3) subsequent annealing up to ~700 K. The high-quality surface of the Fe2N layer
with a p4gm(2×2) reconstruction was confirmed
before XMCD measurements by scanning tunnelingmicroscopy and low energy electron diffraction.
Figure 1(a) displays XMCD spectra obtained at B
= 5 T and T = 7.2 K in the in-plane (θ = 55°) and theout-of-plane (θ = 0°) geometries by detecting μ + – μ–,where μ+ (μ–) denote the x-ray adsorption spectrum(XAS) with the photon helicity parallel (antiparallel)to the sample magnetization. θ is defined as the angle
between the sample normal and the incident x-ray. We
find that the XMCD intensity in the in-planegeometry is greater than that in the out-of-planegeometry, which indicates the magnetic easy axis of
the Fe2N layer is towards in-plane direction.
The easy magnetization direction of the Fe2N layer
is clearly recognized by the magnetization curves.
Figure 1(b) displays the magnetization curves
obtained in the in-plane and out-of-plane geometries.
The data points represent the Fe L3 intensity as afunction of applied magnetic field. A steplikemagnetization curve with a clear hysteresis loop nearB = 0 T [see inset of Fig. 1(b)] is observed in thein-plane geometry, while the magnetization curve inthe out-of-plane geometry can be fit rather well by asimple Langevin function. Furthermore, the intensityof the in-plane remanent XMCD signal in Fig. 1 (c)monotonously decreases with increasing temperature,
but the reduction was only by ~ 20 % whentemperature is increased from 7.2 to 41 K. These facts
would reveal that the Fe2N layer is ferromagnetic
with a strong in-plane magnetic anisotropy, in goodFig. 1. (a) XAS and XMCD spectra obtained at B =5 T and T = 7.2 K in the in-plane and out-of-planegeometries. (b) Magnetization curves obtained at T =7.2 K in the in-plane and out-of-plane geometries. (c)Remanent XMCD spectra obtained at T = 7.2, 10, and
41 K.
[1] K. H. Jack, Proc. R. Sot. London, Ser. A 208(1951) 200.
[2] J. M. Gallego et al., Phys. Rev. B 70 (2004)
115417.
[3] Y. Takagi et al., Phys. Rev. B 81 (2010) 035422.

132

Ⅲ -4. Surface, Interface and Thin Films

BL4B

Magnetism of Oxygen Covered Fe Monolayer on Mo(110)
T. Nakagawa1, Y. Higuchi1, K. Yamaguchi1, S. Mizuno1, Y. Takagi2 and T. Yokoyama2
1

Department of Molecular and Material Sciences, Kyushu University, Kasuga 816-8580, Japan
2
Institute for Molecular Science, Okazaki 444-8585, Japan

Iron oxides have a variety of structures, whichshow intriguing magnetic ordering such as
antiferromagnetism in FeO, ferrimagntism in Fe3O4.
Thin film iron oxides have been studied since they areimportant for basic research and solid devices, but
few studies have been devoted to understand theirmagnetic properties of the single layer unit [1].
Experiments were done at x-ray magnetic circulardichroism(XMCD) endstation with a superconducting
magnet (H ~ 6 T). Fe was deposited on Mo(110)which was cleaned by repeated cycles of oxidation at
1500 K and high temperature annealing up to 2200 K.
Subsequently the monolayer Fe film was exposed tooxygen with the crystal temperature kept at room
temperature. We found three Fe oxide structures,
namely p(3×2), p(5×1), and quasi-FeO(111), which isin good agreement with the previously reported
structures for O/Fe/W(110)[1]. The structuralconsistency is plausible since both of W and Mo
substrates have similar crystal and electronic
structures.
Figure 1(a) shows Fe L edge XAS spectra for
Fe/Mo(110) with different exposures to oxygen. Here
1 L corresponds to 1×10-6 Torr s. With increasing theexposure, the white line intensity gradually increases,
indicating the increase of Fe 3d hole. The L2 peakaround hv = 720 eV shows clear difference due to theoxidation. The spectrum with the exposure of 150 L
shows a splitting at L2 with 718 and 721 eV, while thespectra for the Fe films exposed upto 17 L does notshow the splitting. According to the previous XAS
result [2], the oxygen covered Fe at 150 L is FeO.
Oxygen adsorption on Fe/Mo(110) drasticallymodifies the magnetization. Figure 1(b) shows
XMCD spectra for various oxygen adsorption. The
application of the conventional sum rule gives theeffective magnetic moment of 2.0 μB for the clean Fe
monolayer, which is the sum of the orbital andeffective spin moment including the dipole term.
When Fe is exposed to 0.2 L oxygen, corresponding
to the appearance of the first super structure, p(3×2),
the XMCD intensity decreases, resulting in 0.3 μB ofthe magnetic moments. When the p(3×2) iscompleted, the magnetic moment is suppressed to 0.2
μB. With further expose to oxygen, the magnetic
moment slightly increases to 0.4 μB at 17 L, but it isalmost zero at 150 L.
In conclusion, the oxygen adsorption on monolayer
Fe drastically deactivates ferromagnetism, and theresulting structures are antiferromagnetic orparamagnetic structures.

Ⅲ- 4Fig. 1. (a) XAS spectra for Fe films exposed to 0, 0.2,
2.5, 17, and 150 L oxygen taken at Ts = 5 K with thelight incidence normal to the surface. The inset is the
Fe L edge white line intensity. (b) The same as (a),but XMCD spectra taken at H = ±5 T. (c) Magnetic
moment obtained from the sum rule analysis.
[1] K. Feindl et al., Surf. Sci. 617 (2013) 183.
[2] P. S. Miedema and F. M. F. de Groot, J. Electron
Spectrosc. Relat. Phenom. 187 (2013) 32.

133

Ⅲ -4. Surface, Interface and Thin Films

BL5B

Characterization of Amorphous Chalcogenide Thin Films by Vacuum
Ultraviolet Transmission Spectroscopy
K. Hayashi

Department of Electrical, Electronic and Computer Engineering, Gifu University, Gifu 501-1193, JapanⅢ- 4core level of Se atom. Another absorption peakaround 28nm corresponds to the 3d core level of As
atom. As shown in the figure, the photoinducedchanges are observed on the transmission spectra
before and after the irradiation of the bandgap (BG)
light. We think that those changes are related to the
local structures of the amorphous network. The
annealing effect on the film after the irradiation by
the BG light did not appear clearly as a change inspectrum shape. More detailed experiments arenecessary to clarify the origin of the photoinducedchanges of the VUV transmission spectra.

Amorphous chalcogenide semiconductor materials
are very expected as a potential material for
optoelectronic devices. Because, in these materials
are very sensitive to the light, and show a variety ofphotoinduced phenomena [1-3]. For device
applications, it is necessary to sufficiently understandthe fundamental properties of these materials.
Although a large number of studies have been doneon the photoinduced phenomena of these materials,
little is known about the details of these mechanisms.
These phenomena were studied by exciting outer coreelectrons with the irradiation of light with the energy
corresponding to the optical bandgap or sub-bandgap.
The interest has been attracted for the change of the
optical properties in the energy region of the visible
light. We are interesting for the changes of the opticalproperties in the higher energy region. To obtain awide knowledge of the photoinduced phenomena, it isnecessary to investigate to the photoinduced effects
on wide energy region. In previous reports, wereported the photoinduced change at the VUVtransmission spectra of amorphous thin films [4]. In
this report, we investigated the photoinduced effects
on the as-deposited film by VUV transmission
spectroscopy. We also report on the annealing effects
at glass transition temperature.
Samples used for the measurement of the VUVtransmission spectra were amorphous chalcogenide(a-As2Se3 and a-As2S3) semiconductor thin films
prepared onto aluminum thin films by conventional
evaporation technique. Typical thickness of thesamples and the aluminum films were around 180nm
and 100nm respectively. The aluminum film of the
thickness of 100 nm was also used in order toeliminate the higher order light from themonochromator in the VUV region. The
measurements were carried out at room temperature
at the BL5B beam line of the UVSOR facility of theInstitute for Molecular Science. And the spectrum
was measured by using the silicon photodiode as adetector. Two pinholes of 1.5mm in a diameter wereinserted between the monochromator and sample toremove stray light. The intensity of the VUV light
was monitored by measuring the TPEY of a gold
mesh. The positions of the core levels for the samples
were calibrated by referencing to the 2p core levelabsorption peak of the aluminum film.
Figure 1 shows the VUV transmission spectra ofa-As2Se3 film in each state. Two main absorption
peaks were observed in this wavelength region. One
absorption peak around 22nm corresponds to the 3d

Fig. 1. VUV transmission spectra of a-As2Se3 thinfilm in each state.
[1] K. Tanaka, Rev. Solid State Sci. 4 (1990) 641.
[2] K. Shimakawa, A.Kolobov and S. R. Elliott, Adv.
Phys. 44 (1995) 475.
[3] K. Tanaka, Encyclopedia of Nanoscience andNanotechnology 7 (2004) 629.
[4] K. Hayashi, UVSOR Activity Report 2013 41(2014) 140.

134

Ⅲ -4. Surface, Interface and Thin Films

BL6U

Phase-Dependent Electronic Structure of Superstructure Monolayer of
Hexa-peri-Hexabenzocoronene on Au(111)
H. Yamane and N. Kosugi__(5x5)R0º

0,0

1,0

0

1

1

H0

2

k= 0
kΓK
kΓM
(√27x√27)R30º

0,0

1,0

k= 0
kΓK
kΓM

H0

H1

2

1.2 1.4 1.6 1.8

0H1

1.2 1.4 1.6 1.8kΓK / Å−1kΓM / Å−1

0

1

1

H0

2

H0

H1

2

H1

Ⅲ- 4
1.2 1.4 1.6 1.8kΓK / Å−1

1.2 1.4 1.6 1.8kΓM / Å−1

EDC

,
kΓK

R0

_

of Γ', K', and M' in SBZ of the HBC superstructure;
therefore, the observed π-band dispersion rationallyarises from the intermolecular interaction.
The lateral intermolecular π-band dispersion inorganic monolayers has been reported for strongly
chemisorbed interfaces with the 0.2-0.3 eV dispersion
width [3,4], which is 10 times larger than the present
dispersion. Such large dispersions are caused by thesubstrate-mediated intermolecular interaction due tothe strong orbital hybridization and the highly orderedstructure at the interface [3,4]. In the present case, theinterfacial electronic coupling is weak because of theobservation of the vibrationally-resolved HOMO line
shape, as indicated by the downed arrow. In addition,
we observed no evidence for the interfacial chargetransfer. These evidences are the indication of the
weak interaction at the interface. Furthermore, thesubstrate-mediated π-band dispersion should beobserved along the underlying metal-atom array [3,4].
Since the present π-band dispersion is dependent noton the substrate SBZ but on the molecular SBZ, theobserved π-band dispersion might be introduced by alateral intermolecular interaction.

0

Binging Energy (vs. EF) / eV

The intermolecular interaction is a key issue inmolecular electronic properties. It has been reported
that hexa-peri-hexabenzocoronene (HBC) on Au(111)forms various ordering phases in the monolayer, e.g.,(5×5)R0° “R0 phase”, (√27×√27)R30° “R30 phase”,
and their mixed phase, depending on the preparation
condition [1,2]. In the present work at BL6U, in order
to examine the lateral intermolecular interaction inflat-lying molecular layers, we investigated theelectronic structure of the R0 and R30 phases of HBC
on Au(111), which was realized by controlling thesubstrate temperature during the thin-film growth.
Figure 1 shows the low-energy electron diffraction(LEED) image, the surface Brillouin zone (SBZ), andthe energy-versus-momentum [E(k)] map of the R0
and R30 phases of the HBC monolayer on Au(111) at
15 K, obtained from angle-resolved photoemission
spectroscopy (ARPES). In the R0 phase, the highest
occupied molecular orbital (HOMO, H0) disperses ina narrow width by 20 meV only along the kΓKdirection, and the HOMO-1 (H1) disperses by 25 meV
only along the kΓM direction, which is more evident in
the selected energy distribution curve (EDC) in Fig. 1.
The opposite trend was observed in the R30 phase;that is, the HOMO disperses by 20 meV along the kΓMdirection, and the HOMO-1 disperses by 25 meValong the kΓK direction. The observed dispersion
periodicity is dependent on the high symmetric points

Binging Energy (vs. EF) / eV

Department of Photo-Molecular Science, Institute for Molecular Science, Okazaki 444-8585, Japan

HOMO (H0)

H1 H0

kΓM

R30

kΓK
kΓM

HOMO-1 (H1)

2

1

0

Binging Energy (vs. EF) / eV

Fig. 1. LEED, SBZ [thick-black hexagon for
Au(111) and thin-blue hexagon for HBC], wherein
the red line indicates the scanned region in ARPES,
the E(k) map, and the EDCs at the high symmetricpoint of the superstructure monolayer of
HBC/Au(111) with the (5×5)R0° and (√27×√27)R30°
phases at 15 K. The LCAO patterns of the HOMO
and HOMO-1 of HBC are also shown.
[1] D. Kasemann et al., Langmuir 25 (2009) 12569.
[2] C. Wagner et al., Phys. Rev. B 81 (2010) 035423,
and references therein.
[3] H. Yamane et al., Phys. Rev. B 76 (2007) 165436;
J. Electron Spectrosc. Rel. Phenom. 174 (2009) 28.
[4] M. Wieβner et al., Nat. Commun. 4 (2013) 1514;
Phys. Rev. B 88 (2013) 075437.

135

Ⅲ -4. Surface, Interface and Thin Films

BL6U

Formation of Delocalized π Band and Interface State inSuperstructure Monolayer of Coronene on Au(111)
H. Yamane and N. Kosugi

Department of Photo-Molecular Science, Institute for Molecular Science, Okazaki 444-8585, Japan

(c)

0,0

1,0

Clean Au(111)

0

1

(c)

HOMO

(d)

kΓK
kΓM

IS2

2

Au 5d
3

0.8

1

1.2

1.4

Momentum kΓK / Å−1

IS1

HOMO
IS2

2

IS3

3

0

1

sp

2

(b)

(d)

0

IS1

1

_

[1] C. Seidel et al., Phys. Rev. B 64 (2001) 195418.
[2] H. Yamane et al., a separate page in this volume,
UVSOR Activity Report 2014.

Binding Energy (vs. EF) / eV(a)Binding Energy (vs. EF) / eV

Ⅲ- 4

_

lateral band
dispersion by 30 meV at Γ'-K' and by 15__
meV at Γ'-M'. The observed dispersion is larger thanthat for the (5×5) hexa-peri- hexabenzocoronene(HBC) superstructure monolayer on Au(111) [2]. Thisdifference is explained by the smaller molecular unit
cell and the shorter inter- molecular spacing of thecoronene monolayer than those of the HBC
monolayer. The observed π-band dispersion is
ascribed to the lateral intermolecular interaction inflat-lying aromatic hydrocarbons.
On the other hand, the interface-specificelectronic_
states are observed around the Γ' point as labeled IS1,
IS2, and IS3 in Figs. 1(c) and 1(d), which show the
relatively large dispersion with the evidence for the
spin-orbit splitting. These interface states may
originate from the backfolded Shockley- and Tamm-_
type electronic
states of the Au(111) surface at the Γ_and M points, respectivery, induced by the superstructure. Note that, the observed dispersions are
modified from the original Shockley and Tamm statesin terms of the effective mass, the Rashba parameter,and so on. Such modifications might be introduced by
the Pauli repulsion of surface electrons due toadsorbates and by the scattering due to the superstructure lattice.

Polycyclic aromatic hydrocarbons have attracted
attention again as a fragment of graphene. In thepresent work, by using angle-resolved photo emission
spectroscopy (ARPES), we have studied theelectronic structure of a (4×4) superstructure monolayer of coronene on Au(111).
The experiment was performed at the in-vacuum
undulator beamline BL6U. The cleanliness of theAu(111) surface was confirmed by the low-energy
electron diffraction (LEED) and the Shockley state in
ARPES, as obtained from the repeated cycles of theAr+ sputtering and the subsequent annealing at 700 K.
The total energy resolution in ARPES was 13 meV.
Figures 1 shows (a) a LEED image at 15 K and (b)the corresponding surface Brillouin zone (SBZ) of thecoronene monolayer on Au(111). The LEED image
shows the (4×4) superstructure with respect to theAu(111) hexagonal lattice, as reported in Ref. [1].
The ARPES spectra were measured
by considering___
the high symmetric points of Γ', K', and M' in themolecular SBZ [blue hexagon in Fig. 1(b)].
The energy-vs-momentum E(k) relation
map ofthe____coronene(4×4)/Au(111) along the Γ '-K ' and Γ '-M '(kΓK and kΓM) directions, obtained from ARPES, isshown in Figs. 1(c) and 1(d), respectively. The
highest occupied molecular orbital (HOMO, π)derived peak of coronene is observed at the binding
energy (Eb) of 1.6 eV. Although no directintermolecular π-π overlap exist in the coronene
monolayer, the HOMO peak shows a quite weak

IS3

3

0.8

1

1.2

1.4

Momentum kΓK / Å−1

1.2

1.4

1.6

1.8

Momentum kΓM / Å−1Fig. 1. (a) LEED of the coronene(4×4)/Au(111) at 15 K, wherein the red dot indicates the substrate’s spot. The
molecular structure of coronene is also shown. (b) SBZ of the Au(111) (black) and the coronene(4×4)/ Au(111)(blue). The red line indicates the scanned region in ARPES. (c,d) The E(k) maps of the clean Au(111) and thecoronene(4×4)/Au(111)
at 15 K along the k_ ΓK and kΓM directions.
The energy distribution curves at kΓK = 1.08___
Å−1 (Γ'), 1.44 Å−1 (K') and kΓM = 1.25 Å−1 (Γ'), 1.56 Å−1 (M') are also shown.

136

Ⅲ -4. Surface, Interface and Thin Films

BL6U

Manybody Interactions in Rb-Doped Graphene
1,2

1

W. J. Shin , S. H. Ryu1,2, H. Yamane3, N. Kosugi3, K. S. Kim1,2 and H. W. Yeom1,2Center for Artificial Low Dimensional Electronic Systems, Institute for Basic Science (IBS), 77 Cheongam-Ro,
Pohang 790-784, Korea
2
Department of Physics, Pohang University of Science and Technology, 77 Cheongam-Ro, Pohang 790-784, Korea
3
Department of Photo-Molecular Science, Institute for Molecular Science, Okazaki 444-8585, Japan
Graphene has served as a prototypical model
system for study of various low-dimensional physics[1]. It has rather simple lattice and electronic
structures, and the energy scale of phonons, collective
excitations of periodic atoms, is relatively large (up to~200 meV), making it ideal to investigate theelectron-phonon interaction and its interplay withelectron correlations [2]. Angle-resolved photo
emission spectroscopy (ARPES) is an ideal techniquethat can directly observe energy band dispersion ofelectrons. Also, ARPES is capable of probing not
only a signature of electron-phonon interactions thatappear as an abrupt slope change in band dispersion(kink) [2,3], but also electron correlations that lead tothe multiple Dirac points. Indeed, high-resolution
ARPES spectra from heavily doped graphene have
shown
such
kink
structures
andband
renormalizations [4,5].
In this work, we have measured a systematic
evolution of graphene π bands as increasing the Rb
density (Fig. 1). We found the phase separation of Rb
dopants that the two distinct doping levels coexist at
the moderate Rb density. This can be understood by
the different degree of charge transfer between the
scatter Rb atoms and Rb islands. From the kinked
dispersion we could compare electron-phonon andelectron-electron coupling constants, which turn out
to be different from those for K atoms as dopants.
This shows a different degree of screening (ordielectric constant of dopant islands) between Rb and
K. We anticipate that this work would provide ameaningful step forward to understanding manybody
correlations in heavily-doped graphene as well as tosearching for superconductivity in graphene with arelatively high transition temperature.

(a)

(b)

(c)

(d)

Ⅲ- 4

Fig.1. Doping dependence of band dispersions ofrubidium doped graphene.
[1] H. Castro Neto et al., Review of Modern Physics
81 (2009) 109.
[2] C. S. Leem et al., Physical Review Letters 100(2008) 016802.
[3] A. Damascelli et al., Review of Modern Physics
75 (2003) 473.
[4] A. Bostwick et al., Nature Physics 3 (2007) 36.
[5] S. Y. Zhou et al., Physical Review B 78 (2008)
193404.

137

Ⅲ -4. Surface, Interface and Thin Films

BL6U

Surface Coordination Chemistry to Control the Charge Transfer at
Organic/Metal Interface: SnCl2Pc on Ag(111)1

S. Kera1,2, K. Yonezawa2, T. Tago2, F. Bussolotti1, H. Yamane1,
N. Kosugi1 and K. K. Okudaira2

Department of Photomolecular Science, Institute of Molecular Science, Okazaki, 444-8585, Japan
Department of Nanomaterial Science, Graduate School of Advanced Integration Science, Chiba University,
Chiba 263-8522, Japan

2

Ⅲ- 4

For more than two decades molecular adsorbates
on metal surfaces represent a very active field of
research in surface and interface science.
Fundamental understanding the basic physicalproperties is a key issue for tuning the geometric andelectronic structure at the interfaces, hence toimprove and control the organic device performance.
To understand the mechanism of charge transfer (CT)at organic/metal interfaces, the binding energy offrontier orbitals (HOMO and LUMO) and theadsorption height of the molecules on the metal are
critical parameters.
Using coordination chemistry we introduce“spacers” which change the contact distance to thesurface, and investigate the consequences forgeometric (adsorption height, molecular bending,etc.) and electronic structure (amount of CT). In
contrast to planer phthalocyanines (Pc), dichlorotin
Pc (SnCl2Pc) is an n-type semiconductor and its
conductivity is 1–3 orders larger than most of theother Pcs. In this study, we performed ARUPS and
XPS for SnCl2Pc films prepared on Ag(111). Since
the size of the SnCl2 group is large, the molecule isconsidered to be non-planar, but there is nopermanent dipole.
The experiments were conducted at BL6U. The
clean surface was obtained by the repeated cycles of
Ar+ sputtering and annealing. After preparing themonolayer film (0.4nm) on the Ag(111) at room
temperature, valence band (VB) and secondary
cut-off (SECO) was measured at 45eV, then each corelevels are scanned for C1s, N1s, Cl2p, and Sn4d. The
same measurements are repeated for the annealedmonolayer film (633K for 3h). We evaluated thephotoelectron angular distribution of HOMO andconcluded the flat-lying orientation both for as-grown
and annealed films (not shown).
Figure 1 shows the Cl2p XPS spectra of
SnCl2Pc/Ag(111) before and after the annealing. For
the as-grown film, spin-orbit splitting of Cl2p is
detected in different binding energies for upper(towards the vacuum) and lower-side (to thesubstrate) of Cl atoms. However the peaks disappear
totally for the annealed film. Considering energy
shifts in other core levels, the chemical structure may
change to SnPc by removing the Cl atoms.
Figure 2 shows the angle-integrated UPS for VB
and SECO regions. Regardless of Cl atoms, clearly

the gap state due to the CT from the metal to the
LUMO state is observed as for other metal-Pcs onAg(111) [1]. By detaching the Cl atoms, HOMO
shifts to high energy side to show a very similar
spectrum to SnPc/Ag(111) [1]. The work function is
reduced by 0.2eV upon annealing, which might becaused by differences in total CT amount and/or
push-back effects induced by rearrangement of theadsorption height.
It is an open question if this chemisorption with CT
involves the anchored Cl atom via an expanded
LUMO orbital, or whether basically the indole groups
bond to the surface due to a strongly distorted ortilted geometry. A geometrical study including aprecise determination of adsorption height will give aclear answer for these.

Fig. 1. Cl2p XPS spectra for SnCl2Pc/Ag(111) taken
at 297K for as-grown and annealed film.

Fig. 2. a) SECO and b) VB for SnCl2Pc/Ag(111)
taken at 297K for as-grown and annealed film. The
spectra for the clean substrate are also shown.
[1] M. Häming et al., Phys. Rev. B 82 (2010) 235432.

138

Ⅲ -4. Surface, Interface and Thin Films

BL7U

Electronic Structure of a MnSe/Bi2Se3 Ultrathin Film Heterostructure
T. Hirahara1, T. Kubo2, A. Takayama2, T. Hajiri3, M. Matsunami3,
K. Tanaka3 and S. Hasegawa2

1

Department of Physics, Tokyo Institute of Technology, Tokyo 152-8551, Japan2
Department of Physics, University of Tokyo, Tokyo 113-0033, Japan
3
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan

Topological insulators (TI) are extensively studied
recently due to its peculiar properties [1]. The
Dirac-cone surface states of TI are protected bytime-reversal symmetry (TRS) and backscattering
among these surface states is prohibited. But when
TRS is broken by application of a magnetic field orincorporating magnetic materials, a gap opening in
the Dirac cone is expected and an intriguing phasecalled the quantum anomalous Hall state can berealized [2]. This phase is expected to show evenmore exotic phenomena such as the topologicalmagnetoelectic effect. To realize such state, two typesof sample fabrication techniques have been employed
up to now: (1) magnetic doping while growing thesingle crystal or thin film of TI [3], and (2) magnetic
impurity deposition on the surface of TI [4]. Whilemethod (1) was successful and showed evidence of
the TRS violation, no one has succeeded using
method (2), which should be a more direct way to
examine the interaction between the topologicalsurface states and magnetism.
In the present work, we have attempted analternative approach to break the TRS in TI: making aheterostructure of TI and magnetic insulators (MI)and making use of the magnetic proximity effect at
the interface. For this purpose, we have fabricated aheterostructure of MnSe (MI) and Bi2Se3 (TI) since
the lattice mismatch between the two materials is
relatively small (~6%). MnSe is a layered structure
and is antiferromagnetic as a whole, but in each Mn
layer, the spin is oriented in one direction(ferromagnetic within the layer and antiferromagnetic
among the adjacent layers) [5]. Thus one can expectthat the ferromagnetic Mn layer will break TRS of TI.
Figures 1 (a) and (b) show the band dispersion of thesurface states of Bi2Se3 and the 2BL MnSe/Bi2Se3
heterostructure. While the Dirac-cone surface states
are massless in (a), one can find a clear gap of ~ 80
meV at the Dirac point in (b), meaning that it has
turned into in a massive Dirac cone. This result showsthat our method is indeed a successful way to induce
TRS breaking in TI surface states. Spin- andangle-resolved photoemission measurements will be
performed to see the change of the spin-polarizationof the Dirac cone upon the gap opening.

Ⅲ- 4

Fig. 1 The band dispersion of Bi2Se3 (a), and arespectively
heterostructureofMnSe/Bi2Se3,
measured at hν = 21 eV with p-polarization.
[1] M. Hasan and C. Kane, Reviews of Modern
Physics 82 (2010) 3045.
[2] X.-L. Qi and S.-C. Zhang, Reviews of Modern
Physics 83 (2011) 1057.
[3] For example, C. Z. Chang et al., Science 340(2013) 167.
[4] For example, M. Ye et al., Physical Review B 85
(2012) 205317.
[5] R. J. Pollard et al., J. Phys. C: Solid State Phys. 16(1983) 345.

139

Ⅲ -4. Surface, Interface and Thin Films

BL7U

Angle-Resolved Photoelectron Spectroscopy Study of One-Dimensional
Electronic States on Bi/InSb(001)
Y. Ohtsubo1,2, J. Kishi2, K. Hagiwara2, M. Matsunami3, K. Tanaka3 and S. Kimura1,2
1

Graduate School of Frontier Biosciences, Osaka University, Suita 565-0871, Japan
Department of Physics, Graduate School of Science, Osaka University, Toyonaka 560-0043, Japan
3
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan

2

Ⅲ- 4

One-dimensional (1D) metals behave in completely
different ways from ordinal 3D metals [1]. Tomonaga
Luttinger liquid (TLL) is one of the most extensively
studied phases as an example of the exotic 1D metals.
It is theoretically predicted that TLL should exhibit
exotic power-law scaling and spin-charge separation[2]. So far, various 1D systems with 1D structure
were studied as candidates of TLL and only a few ofthem showed metallic states with power-law spectralfeatures e.g. carbon nanotube [3] and Lithium purple
bronze (LiPB) [4, 5].
On the surface of semiconductor, various
self-assembled 1D atomic structures are known andthey have been regarded as suitable systems to study
1D metallic states [1]. However, most of them do not
behave as TLL at low temperature, because of 2D
undulation of the surface states and/or metal-insulatortransition driven by strong nesting. Up to now, theonly system claimed as a surface TLL is the Au
nanowire assembled on Ge(001) [6]. However, evenon Au/Ge(001), the direction of conduction path andeven the nature of TLL itself is still under debate.
In this project, we have performed angle-resolved
photoelectron spectroscopy (ARPES) study on thesurface 1D system Bi/InSb(001). Bi/InSb(001) isreported to form an 1D atomic structure with metallic
electronic states [7] and hence the encouraging
candidate of surface TLL. ARPES measurements
were performed at the beamline BL7U of UVSOR-III.
The InSb(001) substrate is cleaned by repeated cyclesof sputtering and annealing and then Bi is evaporated
from a home-made Knudsen cell. The sample
preparation process was performed in situ.
Figure 1 (a) shows the Fermi surface of
Bi/InSb(001) taken at room temperature. The Fermi
surface clearly shows the 1D and metallic features ofthe surface electronic states of Bi/InSb(001). No kz
dispersion of the metallic state was observed withdifferent photon energies (not shown here), indicatingthat it is the 1D surface state. The 1D state disperses
along the 1D chain direction (the relationshipbetween the surface periodicity and 1D atomic-chain
direction has been already reported in Ref. [7]).
We examined the polarization dependence of themetallic 1D state. As shown in Fig. 1 (b) and (c), thesurface state is observed only with P-polarized
photons. Broad features below 0.6 eV come frombulk bands. The clear polarization dependence on thesurface state indicates the even symmetry of the 1D

140

state with respect to the photon-incident plane.
Further analysis based on temperature dependence
and spectral shape around the Fermi level is inprogress in order to examine whether the 1D surface
state on Bi/InSb(001) behaves as TLL or not.

Fig. 1. The Fermi surface (a) and band dispersion(b, c) of the Bi/InSb(001) surface taken at hν = 15 eV.
(b) and (c) are measured with P- and S- linearlypolarized photons, respectively.
[1] M. Grioni et al., J. Phys.: Condens. Matt. 21(2009) 023201.
[2] S. Tomonaga, Prog. Theor. Phys. 5 (1950) 544.
[3] H. Ishii et al., Nature 426 (2003) 540.
[4] F. Wang et al., Phys Rev. Lett. 96 (2006) 196493.
[5] L. Dudy et al., J. Phys.: Condens. Matt. 25 (2013)
014007.
[6] C. Blumenstein et al., Nat. Phys. 7 (2011) 776.
[7] P. Laukkanen et al., Phys. Rev. B 81 (2010)035310.

Ⅲ -4. Surface, Interface and Thin Films

BL7U

Formation of the Dirac Cone at the Γ-Point on the Epitaxial Graphene
Sheet Observed by the Angle-Resolved Photoelectron Spectroscopy with the
Low Energy Photon
1

Institute of Scientific and Industrial Research, Osaka University, Ibaraki 567-004, Japan
Department of Materials Science and Engineering, Meijo University, Nagoya 468-8502, Japan
3
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan

Graphene, a single-atomic-layer consisting of acarbon sp2-orbital-network, is one of the materials
that have been most extensively studied these years.
Here, for the first time, we report a peculiar behaviorof the epitaxial single-layer graphene formed on the
SiC crystal; a backfolding of the Brillouin zone whichenables an observation of the characteristic Diraccone at the Γ-point, which is located at the K-point in
the normal Brillouin zone of the graphene.
The experiments were made at the BL-7U,
UVSOR-III. The sample used was provided by the“Graphene Platform” inc, and cleaned by heating at
700Co in UHV. The sample was then moved to theexperimental chamber and slowly cooled down to
13K for measuring the angle-resolved photoelectron
spectra (ARPES) near the surface-normal direction as
a function of the photon energy. Figure 1 shows
volume and plane (ky=0) maps of the ARPES
intensity taken at hν=10.8eV as functions of the
momentum parallel to the graphene sheet and theelectron binding energy. The feature in the ARPES
spectra is absolutely agreed with the so called “Diraccone”, which is consisting of linearly  dispersed
π-bands and most prominent characteristics of thegraphene. The Dirac point is located 0.4 eV below theFermi level, which indicates that a single-layer of thegraphene is formed. This behavior is very surprising,since the Dirac cone of the graphene exists not at theΓ-point but at the K-point of the Brillouin zone,(separated by 1.7 Å-1 from the Γ-point) which cannot
be accessed with the ARPES technique below thephoton energy of 15.4eV if the work function of
4.5eV is assumed. Since the defects orelectron-phonon scattering cannot be a candidate
considering the momentum and energy conservation
rule, the most probable interpretation is the surface
Umklapp process, in which the electron is diffracted
from K to Γ due to the formation of the superstructure(e.g., ( 3  3 ) R30 ) formed on the graphene layer.
As shown in Fig.2, this Dirac cone is only observed
when the photon energy is near 11eV. This clearly
indicates that the final state located 11eV above theFermi level plays a key role for this observation. Thus,
it seems reasonable the scattering occurs among theunoccupied bands located this energy region.
We found that the surface normal photoelectron
emission due to the Dirac cone is extinguished when
the sample is warmed to 50K. This behavior is similar141

to the superstructure formation on the graphite
surface, where the CDW transition was proposed[1],and similar transition may occur on the graphenesurface and/or the step edge. However, thissuperstructure on the graphene surface is less stable
than the graphite surface, and we could not find adefinite condition for the observation of the Diraccone, and more work is needed for a deeper
understanding the physical nature of this surprisingphenomenon.
ky

ky=0

G
EF

kx

EB

Ⅲ- 4

Fig. 1. ARPES results of epitaxial graphene on SiC(13K) near Fermi level at the Γ-point (surface
normal) taken at hν=10.8eV.

㻼㼔㼛㼠㼛㼠㼑㼘㼑㼏㼠㼞㼛㼚㻌㻵㼚㼠㼑㼚㼟㼕㼠㼥㻌㻌㻌㻌㻌㼍㼠㻌㻱㻲㻌㻔㻭㼞㼎㻚㻌㼁㼚㼕㼠㼟㻕

2

S. Tanaka1, T. Maruyama2, M. Matsunami3 and K. Tanaka3㻝㻜㻝㻞㻼㼔㼛㼠㼛㼚㻌㻱㼚㼑㼞㼓㼥㻌㻔㼑㼂㻕㻝㻠

Fig. 2. Photoelectron intensity near the Fermi levelin the ARPES spectra of graphene as a function of theexcitation photon energy.The line is a Lorentzian
curve centered at 11.1eV.
[1] S. Tanaka, M. Matsunami and S. Kimura, Phys.
Rev. B 84 (2011) 121411(R) .

Ⅲ -4. Surface, Interface and Thin Films

BL7U

Inelastic Scattering of Photoelectrons at Organic/Graphite Interface
T. Yamaguchi1, F. Bussolotti2, J. Yang1, K. Kimura1, M. Matsunami2, N. Ueno1 and S. Kera1,2
1

Graduate School of Advanced Integration Science, Chiba University, Chiba 263-8522, Japan
2
Institute for Molecular Science, Okazaki 444-8585, JapanⅢ- 4

Understanding electron-phonon coupling as well as
weak intermolecular interaction is required to discuss
the mechanism of charge transport in functional
molecular materials. The experimental study ofelectron-phonon coupling of the highest occupied
molecular orbital (HOMO) state in the orderedmonolayer film is essential to comprehend holehopping transport and small-polaron related transport[1]. In this work, we succeeded to observe a
modulation of energy loss of photoelectron fromgraphite by exiting intramolecular vibration ofadsorbed organic molecule at the substrate surface.
Low-energy excited angle-resolved ultraviolet
photoelectron spectroscopy (ARUPS) was performedat beamline BL7U. A highly oriented pyrolytic
graphite (HOPG) substrate was cleaned by heating at
900K for 2h. Pentacene (PEN) and zincphthalocyanine (ZnPc) were deposited on the HOPG
at < 0.1nm/min at room temperature, then the film
was annealed to obtain the well-ordered monolayer.
First derivative of ARUPS intensity maps for
PEN/HOPG and ZnPc/HOPG are shown in Fig.1 (a)and (b), respectively. Strong peaks beneath the Fermi
level due to scattering from k-point of graphite (redarrows) are observed similarly to the previous report[2]. To exclud the impact of intensity background by
the strong peaks, energy distribution curve, I(E) was
integrated for = 0±3o. In Fig. 2, photon energy
dependence of I(E) (top panel) and their derivatives,-dI(E)/dE (bottom) taken for photon energies of
7~11eV are shown for PEN/HOPG.
Clearly one can find peaks observed strongly at
Eb=170 meV for higher energy excitation and weakly
at Eb=90 meV for lower energy excitation in Fig. 2(b).
Tanaka et al., reported ARUPS result of a bare HOPG
where features of energy loss of photoelectron (60~70
and 154~175 meV) due to inelastic scattering bygraphite phonon are observed with phonon dispersion[3]. Comparing to the bare surface, the loss energy
increases from 154 meV to 170 meV and 67 meV to
90 meV at  point, respectively with no energy
dispersion. Similar results are observed for ZnPc (notshown). The energy loss of 170 meV may correspondto the effective vibronic coupling mode of 167 meVfor PEN/HOPG and 170 meV for ZnPc/HOPG
detected for HOMO in high-resolution UPS [1]. We
observed that the energy dependences of the intensityof both peaks are similar to that of the bare surface,indicating that the process of the inelastic scattering
would be bounded by the resonance excitation
channels of the graphite [3], however the frequency

142

of emitted phonon is arranged by exciting
intramolecular vibrations. Obviously, the observed
intensity is too large for extrinsic energy loss inpropagation process to the surface as found for
HREELS (on the order of 10-3), indicating that theinelastic scattering could be dominated by intrinsic
loss of photoelectron at molecule/graphite interface
where the wavefunction of electron couples strongly
to that of intramolecular vibrations.

Fig. 1. First derivative of ARUPS intensity map
taken at hν=11 eV for PEN/HOPG at 11 K (a) and
ZnPc/HOPG at 14 K (b).

Fig. 2. Photon-energy dependence of I(E) anddI(E)/dE for PEN/HOPG (=0±3o).
[1] S. Kera et. al., Prog. Surf. Sci. 84 (2009) 135.
[2] H. Yamane et al., UVSOR Activity Report 201341 (2014) 144.
[3] S. Tanaka et al., Sci. Rep. 3 (2013) 3031.

Ⅲ -4. Surface, Interface and Thin Films

BL8B

Direct Observation of Electronic Structure of Nylon-6,6
to Clarify the Contact Electrification Mechanism
1

T. Sato1, K. R. Koswattage 2, Y. Nakayama1 and H. Ishii1,2

Graduate School of Advanced Integration Science, Chiba University, Chiba 263-8522, Japan
2
Center for Frontier Science, Chiba University, Chiba 263-8522, Japan

Contact electrification of insulating polymers has
been widely used in several technologies such as laser
printing and photocopying. But the fundamental
mechanism of this phenomenon is still controversial,and several models have been discussed [1]. In mostmodels such as surface state model [2] andmolecular-ion-state model [3], the existence of thesome gap states is often assumed between highest
occupied molecular orbital (HOMO) and lowest
unoccupied molecular orbital (LUMO). These states
can work as charge reservoir for the charge transfer
upon the contact electrification. However, the direct
observation of the electronic structure including gap
states was examined only for very limited insulating
polymers. Therefore, the investigation of theelectronic structure of insulating polymers isimportant to clarify the contact electrification
mechanism. In this study, the electronic structure of
Nylon-6,6 including gap states was observed by not
only ultraviolet photoemission spectroscopy (UPS) at
BL8B of UVSOR but also high sensitivity UPS andphotoelectron yield spectroscopy (PYS) at handmade
apparatus of our laboratory [4].
Figure 1 shows the UPS spectrum of Nylon-6,6thin film, which was made by spin coating on
indium-tin oxide (ITO) substrate. The ionizationenergy (I) of Nylon-6,6 is determined as 7.49 eVfrom the onset of the photoemission from the HOMO.
Moreover, the photoemission was detected from thevicinity of 4.3 eV by high sensitivity PYS. This result
suggests that the gap states of Nylon-6,6 exist fromthe HOMO to at least 3.2 eV above, and the existenceof such gap states was also confirmed by highsensitivity UPS by using pure deep UV light withextremely low stray light. These gap states are related
to the charge transfer upon the contact electrification.
In PYS measurement, the information on thedensity of states (DOS) of the sample can be obtainedin principle by differentiating the PYS spectrum withrespect to photon energy [5]. Accordingly, we
determined the DOS distribution of nylon-6,6including gap states by combining the UPS at BL8B,
high sensitivity UPS, and high sensitivity PYS results(Fig. 2). As a result, the density of states of gap statesnear the Fermi level of the substrate was about 10-5
times smaller than that of HOMO. Besides, using thisobserved DOS distribution, we estimated the charge
density during the contact electrification if the chargetransfer occurs via only gap states. Consequently, theorder of estimated charge density was consistent withthat of the literature data observed by Kelvin Probe.
This result suggests that contact electrification of
insulating polymers can be explained by chargetransfer via only gap states.

Fig. 1. (a) UPS spectrum of Nylon-6,6 thin film anda simulated density of states curve of Nylon-6,6 basedon quantum chemical calculation (Gaussian09 with
B3LYP/6-31g basis set). (b) UPS spectrum of the
SECO region. (c) UPS spectrum of the top valence
region.

Fig. 2. The density of states of Nylon-6,6 estimatedfrom UPS and PYS spectra.
[1] S. Matsusaka et al., Chem. Eng. Sci. 65 (2010)
5781.
[2] J. Lowell, Adv. In Phys. 29 (1980) 947.
[3] C. B. Duke et al., J. Appl. Phys. 49 (1978) 315[4)]S. Machida et al., Appl. Phys. Express 6 (2013)
025801.
[5] J. Szuber, Vacuum 57 (2000) 209.

143

Ⅲ- 4

Ⅲ -4. Surface, Interface and Thin Films

BL8B/BL2B

Investigation of Charge-Transfer Interaction by Metal Deposition on
Organic Semiconducting Thin Films
T. Hosokai1, K. Yonezawa2, R. Makino2, K. R. Koswattage2, K. K. Okudaira2 and S. Kera2,3
1

National Institute of Advanced Industrial Technology and Science, Tsukuba 305-8568, Japan
2
Graduate School of Advanced Integration Science, Chiba 263-8522, Japan3
Department of Photo-Molecular Science, Institute for Molecular Science, Okazaki 444-8585, Japan

144

(a)

Intensity (arb. units)

DIP/Ag(poly)

CT stateAg(poly)

Ag (nm)
6.4
3.2
1.2
HL

0.6

Lying DIP

2
1
0
Binding energy (eV)

0.0

(b)
DIP/Cu(poly)
CT state

Intensity (arb. units)

Ⅲ- 4Understanding the impact of the electronic
structure on the charge-transfer (CT) interaction
between organic semiconductors and noble metals ishighly important for Organic Electronics, because
their interfacial energy-level alignment determines anefficiency of charge-carrier injection. Previously, we
have proposed that such a CT can happen for organicon-metal systems (as seen in Figs. 1(a) and 1(b) top)
due to surface-induced aromatic stabilization (SIAS),
and the SIAS takes place owing to a specific chemical
structure of the adsorbates [1,2,3]. However, it is still
not clear whether the SIAS can also occur for
metal-on-organic systems, which is usually used inorganic devices as a top-contact fabrication. Here, weinvestigated the electronic structure of a prototypicalorganic semiconductor, diindenoperylene (DIP:
C32H16, Fig. 1(b)), thin films by using angle-resolved
ultraviolet photoelectron spectroscopy (ARUPS).
All the experiments were conducted at BL8B in
UVSOR. After preparing a clean SiO2/Si wafer or
Au-coated Si wafer, DIP films were thermally grownon the surfaces in situ with a nominal film thicknessof 20 nm. There, DIP molecules orient with up-rightstanding on SiO2 surface or lying-down on Au surface,which exhibit a large difference in energy ofmolecular features relative to the Fermi level (see thebottom spectrum in Figs. 1(a) and 1(b)). Then, Ag or
Cu was thermally deposited step-by-step on those
DIP films. ARUPS was measured at each deposition
amount of the metals, with a photoelectron emission
angle θ=40o at hv=28 eV. All the depositions andmeasurements were performed at room temperature.
Figures 1(a) and 1(b) show the ARUPS results ofAg or Cu/DIP systems as a function of the metal
deposition amount, where spectra of DIP
monolayer/Ag or Cu polycrystalline (poly) surface
systems are also depicted. The bottom spectrum ofeach DIP film clearly shows no gap states. As metals
are deposited on the DIP films, abundant gap states
immediately appear and grow together with a distinct
feature colored by green, which is resembled to the
DIP/Ag or DIP/Cu systems. These results imply thatthe observed distinct feature in the metal/DIP systems
is caused by CT interaction between the deposited
metals and DIP. Thus, it can be concluded that SIAS
can occur even for a top-contact condition as thesame as a bottom-contact condition, which should bea key to realize Ohmic contacts in various organic
devices. Furthermore, the molecular orientations do
not effect formation of the CT state.

Cu(poly)Cu (nm)
5.0
2.0
1.0
HS

2

Standing DIP

1

0

0.5
0.0

Binding energy (eV)Fig. 1. ARUPS of Ag (a) and Cu (b) deposited on
DIP (inset in (b)) thick films, where spectra of DIP
monolayer on Ag(poly) or on Cu(poly) systems arealso depicted. Hs and HL indicates the highest
occupied molecular orbital band of standing and lying
DIP films.
[1] G. Heimel et al., Nature Chem. 5 (2013) 187.
[2] T. Hosokai et al., MRS proceedings 2013, 1647,
mrsf13-1647-gg01-03.
[3] T. Hosokai et al., UVSOR Activity Report 201341 (2014) 152.