Ⅲ-4
Surface,
Interface andThin Films

781_Ⅳ_BL4B_2015_江口敬太郎.docx

Ⅲ -4. Surface, Interface and Thin Films

BL4B

Soft X-Ray Absorption Spectroscopy
opy of 1,3,5-Trithia-2,4,6Triazapentalenyl Thin Film on Ag(111)K. Eguchi1, K. Awaga1, 2, Y. Takagi3,4 and T. Yokoyama3,4

Graduate school of Science, Nagoya University, Nagoya 464-8602, Japan
2
CREST, JST, Kawaguchi 332-0012, Japan
3
Institute for Molecular Science, Okazaki 444-8585, Japan
4
School of Physical Sciences, The Graduate University for Advanced Studies (SOKENDAI), Okazaki 444-8585,
Japan
1

Organic radicals, which are open-shell molecules,
have been attracting significant attention because of
their potential applications in organic electronics andspintronics. Because of its magnetic bistability at room
temperature,
1,3,5-trithia-2,4,6-triazapentalenyl(TTTA; Fig. 1(a)) is a candidate for such applications[1]. Although its crystal structures as well as thethermally induced and photo-induced magnetic phasetransitions in single crystals have been widely studied,few studies have investigated the structures andelectronic and magnetic states of TTTA in thin films.
In this study, we measure the angular dependence of
X-ray absorption spectra (XAS) of a TTTA thin film
prepared on Ag(111) using linearly polarized X-rays.
The sample was prepared on Ag(111) by exposureof gaseous TTTA under ultra-high vacuum condition(~6 × 10−8 Pa) at room temperature and subsequentannealing at 500 K. XAS were measured at the end
station of the bending magnet beamline 4B using an Xray
magnetic
circulardichroism(XMCD)
measurement chamber in total electron yield detection
mode. Linearly polarized X-rays were irradiated to thesample at incident angles between 0° (normal) and 60°(grazing) in increments of 10° with respect to thesubstrate normal. Energy resolutions were set to E/ΔE
= 2000 and 4000 at N K- and S L-edge, respectively.
Figure 1(b) shows angle-dependent N K-edge XASof the TTTA thin film on Ag(111). Four peaks labeled
A–D were mainly observed in this region, and they
increased with the X-ray incidence angle, indicatingthat molecules adsorbed with a relatively flat-lying
orientation because of the π* bonding characters of thesingly occupied molecular orbit (SOMO) and lowest
unoccupied molecular orbit (LUMO) of TTTA.
Judging from the peak intensities and energy levels,
peaks A and B can be assigned to SOMO and LUMO,
respectively, indicating that the radical in TTTA cansurvive in the thin film.
Figure 1(c) shows angle-dependent S L-edge XASof the TTTA thin film. Five peaks, labeled A–E, wereobserved. Although the intensity of peaks B–E
decreased with increasing X-ray incidence angle, peak
A showed an opposite polarization dependence.
Therefore, peak A can be attributed to the transition
from the 2p3/2 to the σ* orbital, as observed inthiophene [2], suggesting less contribution of the S 3d
orbitals to the SOMO of TTTA.

Ⅲ- 4

Fig. 1. (a) Chemical structure of TTTA. (b) N K-edge
and (c) S L-edge XAS of the TTTA thin film on
Ag(111) taken at 220 K.
[1] W. Fujita and K. Awaga, Science 286 (1999) 261.
[2] A. P. Hitchcock, J. A. Horsley and J. Stöhr, J. Chem.
Phys. 85 (1986) 4835.

113701_Ⅳ_BL2B_507_細貝拓也.docx
Ⅲ -4. Surface,
Interface and Thin Films

BL2B

Potassium Doping into Single Crystalline Organic Monolayer
T. Hosokai1, Y. Hasegawa2, M. Yano2, K. R. Koswattage3 amd Y. Yamada2

National Institute of Advanced Industrial Technology and Science, Tsukuba 305-8568, Japan
2
Institute of Applied Physics, University of Tsukuba, Tsukuba 305-8573, Japan
3
Institute for Molecular Science, Department of Photo-Molecular Science, Okazaki 444-8585, Japan1

Ⅲ- 4

Metal doping into organic semiconducting thinfilms (OTFs) is practically relevant technology in
Organic Electronics. Potassium (K) is known as a very
low workfunction (WF) metal showing around 2.3 eV
and is often used as the dopant. K-doped OTF systems
often show new electronic states within the band gapof the bare OTFs [1]. This is usually interpreted byfilling the lowest unoccupied molecular orbital(LUMO) of OTFs by electron-transfer from the doped
K atoms. For such experiments bulk OTFs have been
often employed. Owing to this, the discussion on theelectronic structure of the doped-OTFs with respect tothe doped structure in a molecular level was hindered.
To overcome this issue, we will study the single
crystalline K-doped organic monolayers fabricated on
Au(111) surface by using angle-resolved ultraviolet
photoelectron spectroscopy (UPS). Previously, we
found a well-ordered monolayer is formed bydepositing K atoms onto two kind of organicmonolayer of picene (C22H14, Fig. 1(a)) and coronene(C24H12, Fig. 1(b)) [2]. For these doped monolayer
systems, here we applied ARUPS to reveal the physics
behind the K-doped OTFs.
All the experiments were conducted at BL2B. After
preparing a clean Au(111) with conventional Ar
sputtering and annealing process, picene, coronene, orK was thermally grown on the substrate. The
deposition amount is controlled by a quartz
microbalance and is confirmed by a change in WF of
the systems. For the well-ordered doped monolayers,
K was deposited step-by-step onto the picene orcoronene monolayer. ARUPS was measured with aphotoelectron emission angle θ= -5~15o, hv = 28 eV.
All the depositions and measurements were performedat room temperature.
Figures 1(a) and 1(b) show the ARUP spectra ofbare Au(111), picene or coronene monolayer, K-doped
picene or coronene monolayer, K/Au(111),
respectively. The surface state (SS) near the Fermi
level in the substrate (top) spectra is vanished by themolecular monolayer formation (second top spectra).
The highest occupied MO (HOMO: H) is located at
1.36 eV for picene and 1.57 eV for coronene. The K
doping into the films results in the appearance of newstates at 0.31 eV for picene and 0.52 eV for coronene.
As seen in the K/Au(111) spectra (bottom ones), the
new states observed by the K doping are differed to
one originating from pure K atoms, which is located at
0.92 eV.
The new states formed in the K/picene andK/coronene systems near the Fermi level can be
ascribed to the former LUMO (L’) bands. X-ray

photoelectron spectroscopy showed a large chemical
shift of C1s in the systems towards higher binding
energy side due to electron transfer from K atoms [2].
The resemble features have been observed for otherorganic/metal systems, such as PTCDA and DIP [3].
The position of L’ state is depending on filling amountof the LUMO by electrons. It can be considered that
LUMO of picene thin films is partially filled since the
L’ feature is partly cut at the Fermi level. On the other
hand, the L’ feature for the K/coronene system islocated at higher binding energy side, implying more
electrons are transferred to LUMO of coronene.
However, the question arises why the doping amountof the electrons are differed between picene andcoronene. In previous, a complete filling of LUMO
level was reported for the K doped-thick picene andcoronene films (thickness is 5 nm) [4]. In this sense,
presence of the Au(111) substrate as well as the low
dimensional organic monolayer may play the role. To
understand this, theoretical investigations based on theordering model as determined by STM [2] is required.

Fig. 1. (a)ARUPS
of
Au(111),
picenemonolayer/Au(111), K-doped/picene, and K/Au(111).
(b) ARUPS of Au(111), coronene monolayer/Au(111),
K-doped/coronene, and K/Au(111).
[1] C.-P. Cheng et al., Org. Electron. 14 (2013) 942.
[2] M. Yano et al., J. Chem. Phys. 141 (2014) 034708.
[3] T. Hosokai et al., MRS proceedings 1647 (2013)
mrsf13-1647-gg01-03.
[4] M. Benjamin et al., J. Chem. Phys. 136 (2012)
134503.

114

Ⅲ -4. Surface, Interface and Thin Films

711_Ⅳ_BL2B_530_中山泰生.docx

BL2B

Electronic Structures of Thienyl-Porphyrin Derivatives
Y. Nakayama1, A. Nakagawa1, K. R. Koswattage2, T. Aikawa1, T. Kondo1 and M. Yuasa1
1

Department of Pure and Applied Chemistry, Graduate School of Science and Technology,
Tokyo University of Science, Noda 278-8510, Japan
2
Center for Frontier Science, Chiba University, Chiba 263-8522, Japan

Porphyrin is a representative bio-functional unit ofa large π-conjugated ring and has been attracting muchattention of both physico-chemical and bio-medical
points of view. Porphyrins functionalized by
thiophenes, typical organic semiconductors, aretherefore of particular interests for bio-electronics
applications [1]. In the present study, we elucidated theelectronic structures of two thienyl-porphyrinderivatives, 5,10,15,20-tetra(2-thienyl)porphyrin (2T)and 5,10,15,20-tetra(3-thienyl)porphyrin (3T) (Fig. 1),
by means of photoelectron spectroscopy (PES).
Procedures for synthesizing 2T and 3T are foundelsewhere [2]. Thin films of 2T and 3T were preparedby vacuum evaporation onto Au-coated Si substrates,
where their thicknesses were monitored with a quartz
microbalance. PES measurements were conducted at
BL2B of UVSOR. The work function of the present
electron analyzer (VG-Scienta, R3000) was
determined to be 4.40 eV after accurate calibration of
the photon energy by using second-order light.
Figure 2 shows wide range PES spectra of bulk (16nm-thick) films of 2T and 3T. The spectral profiles arerespectively well reproduced by density-of-states
curves which are simulated from each orbital energy
distribution. The electronic structures in the highest
occupied regions evolve on step-by-step deposition of
2T and 3T as shown in Fig. 3. For both cases, peaks
derived from the highest occupied orbitals movetoward the Fermi level as the films become thinner.
This trend to reduce substantial hole injection barrier(HIB) heights may be attributed to a common
screening effect at metal-organic interfaces.
Changes in the work function (WF), HIB, and theionization potential (IP) values are summarized in Figs.
3(a), (b), and (c), respectively, plotted as a function of
the 2T or 3T thickness. These results imply thatorientation of the side groups merely gives minor
impacts, if any, to the charge carrier conduction
characteristics of these thienyl-porphyrin derivatives.

Fig. 2. (Top panel) Quantum chemical calculation
results of 2T (blue) and 3T (red) molecules. (Bottom)
PES spectra of 16 nm-thick films of 2T and 3T.

Ⅲ- 4

Fig. 3. Evolution of the PES spectra of 2T (left) and3T (right) thin films grown on Au substrates.

Fig. 4. (a) Work functions (WF), (b) HIB, and (c)ionization potentials (IP) of the 2T (blue) and 3T (red)thin films plotted as a function of the thickness.
[1] K. Oyaizu et al., J. Polym. Sci. A: Polym. Chem.
44 (2006) 5403.
[2] M. Yuasa et al., Polym. Adv. Tech. 16 (2006) 616.

Fig. 1. Molecular structures of (a) 2T and (b) 3T.

115

721_Ⅳ_BL2B_550_奥平幸司.docx
Ⅲ -4. Surface,
Interface and Thin Films

BL2B

Molecular Orientation of Pentacene Thin Film on Silane-SAM withDifferent Growth Condition
K. K. Okudaira and Y. Tuboi

Association of Graduate Schools of Science and Technology, Chiba Univererity, Chiba 263-8522, Japan
SAM(60%) show intense peaks at normal take-off
angle (θ = 0°), and at grazing angle these intensities
become small. At grazing angle (θ = 60°) the intensityof HOMO peak of pentacene on OTS-SAM (10%)
remains, while the pentacene HOMO peak on OTSSAM(60%) almost disappears. Take-off angle
dependence of HOMO peak on OTS-SAM(10%) isdifferent from that on OTS-SAM (60%). It indicatesthat the molecular orientation of pentacene on OTSSAM(10%) is different from that on OTS-SAM(60%).
The surface conditions of OTS-SAM due to the growth
condition of SAM such as humidity affect themolecular orientation of organic semiconductor layer,
which would have an effect on the characteristics of
OTFT such as mobility.

(a)

(b)
=60°
=50°
=40°
=30°
=20°
=10°
=0°

4 3 2 1 0
Binding Energy (eV)Intensity (normalized)

Intensity (normalized)

Ⅲ- 4

Recently, organic thin-lm transistors (OTFT’s)
with eld-effect mobility and on/off current ratio
comparable to hydrogenated amorphous silicon thinlm transistors. OTFT’s have been fabricated using
pentacene as the active material.
Since the interface between the organic active
material and the gate dielectric material is a criticalpart of the eld-effect device, control of this interface
is important. The characteristics of pentacene TFT’s
can be improved by using a self-organizing material
like octadecyltrichlorosilane (OTS) between the SiO2
gate dielectric and the pentacene active layer [1].
To achieve optimum control over SAM growth, anew, efficient, and humidity controlled method of
growing highly ordered OTS SAMs has been reported.
OTFT eld-eﬀect mobility and contact angle of thesurface of the SAM show strong dependence of thegrowth condition such as humidity [2].
Thecharacteristics of OTFT such as mobility are
considered to be dependence on not only the electronic
structure but also the molecular orientation of organic
molecule.
In this work we used OTS SAMs for substrate andexamined the molecular orientation of pentacene thinfilms thermally deposited on these SAM surfaces byangle-resolved ultraviolet photoelectron spectroscopy(ARUPS) measurements. In the ARUPS take-off
angle dependence of HOMO peak for π-conjugatedorganic molecule provides an important informationon the molecular orientation [3].
ARUPS measurements were performed at the beamline BL2B of the UVSOR storage ring at the Institutefor Molecular Science. The take-off angle (θ)
dependencies of photoelectron spectra were measured
with the photon energy (hν) of 28 eV. We use
octadecyltrichlorosilane (OTS) as coupling agent for
SAM. The SAMs were prepared using a dipping
method at room temperatures. To fabricate humiditycontrolled SAM growth was performed under ambientconditions in a controlled atmosphere glovebox at
varied relative humidity levels with 10%, 60%, and80%. Pentacene thin film was deposited on theseSAMs.
We observed take-off angle (θ) dependence of
HOMO peak in UPS of pentacene thin film (thicknessof about 1.5 nm on OTS-SAMs with different growth
condition, expressed by humidity (10%) and (60%)(Figs.1(a) and (b)). The HOMO peaks of pentacene on
OTS-SAM(with humidity 10%) and 60%) appear atbinding energy of about 2 eV. The HOMO peaks ofpentacene on both OTS-SAM (10%) and on OTS-

=60°
=50°
=40°
=30°
=20°
=10°
=0°
4 3 2 1 0
Binding Energy (eV)Fig. 1. Take-off angle (θ) dependences of ultraviolet
photoelectron spectra with HOMO region of pentacene(1.5nm)/OTS-SAM (with humidity of 10%) (a) andpentacene(1.5nm)/OTS-SAM (with humidity of 60% )(b).
[1] J. -M. Kim et al., Appl. Phys. Lett. 85 (2004) 6368.
[2] S. R. Walter et al., J. Am. Chem. Soc. 134 (2012)
11726.
[3] N. Ueno et al., J. Chem. Phys. 99 (1993) 7169.

116

731_Ⅳ_BL2B_556-804_栗木雅夫.docx

Ⅲ -4. Surface, Interface and Thin Films

BL2B

A Surface Study of CsK2Sb Multi-Alkali Photocathode by UPS
1

M. Urano1, M. Kuriki1, K. Negishi1, A. Yokota1, T. Konomi2 and Y. Seimiya2

Graduate school of Advanced Science of Matter, Hiroshima University, Higashi-hiroshima 739-8530, Japan
2
Hight Energy Accelerator Research Organization, Tsukuba 305-0801, Japan

Linear accelerator based facilities such as X-FEL,
ERL, Linear colliders break the limitations of thecircular accelerators such as 3rd generation light source,
ring colliders, etc. In the linear accelerator, highquality and high average current beam has to beprovided because of no circulation. Laser photocathode can provide such beam, but conventional
cathode material such as metal, GaAs, Cs2Te are notideal. CsK2Sb multi-alkali photocathode is thecandidate of the ideal cathode due to the high quantum
efficiency (QE), and high robustness, and green laser
driver for photo-electron effect. Many experimental
efforts has been made to obtain the CsK2Sb
photocathode optimized for the photo-cathode purpose,but it is on the way. In this study, we perform UPS
analysis of the CsK2Sb cathode to reveal the cathode
performance and the surface states.
Figure 1 shows QE (405nm) evolution during thecathode activation (Sb, K, and Cs evaporation on Si
substrate (Si 100) in this order). Typical pressure was
1.0×10-7 Pa.
Amount of Sb, K, and Cs are shown as thickness
measured by quartz monitor. The sample is in situ andis transferred to UPS chamber by transfer rod.
Amplitude (cross section) ratio of Cs 5s and Cs 5p as
a function of QE with laser (405nm) are shown in Fig.
2. Different color shows different samples. QE
variation is due to the degradation in time for eachsample. According to the results, the small ratio givesa large QE for each sample, but the sample dependenceis large. According to a similar measurement for Cs3Sb[1], the low ratio is interpreted as that Cs is bound to
Sb as Cs+ ion. From this observation, the bound stateof Sb and Cs is a good index to examine the photocathode performance. This is the first observation for
the relation between the cathode performance and theCs-Sb bound state.

117

Fig. 1. QE evolution during CsK2Sb activation.

Ⅲ- 4

Fig. 2. Cs 5s/5p ratio as a function of QE.
[1] Clayton W. Bates Basic studies of highperformance multi-alkali photo-cathodes (1979).

741_Ⅳ_BL3U_218_吉田真明.docx
Ⅲ -4. Surface,
Interface and Thin Films

BL3U

Operando Observation of Cobalt Catalyst for Oxygen Evolution Reaction
by Soft X-Ray Absorption Spectroscopy
M. Yoshida1,2,*, Y. Mitsutomi1, S. Onishi1, F. Yamamoto1, M. Nagasaka3, H. Yuzawa3,
N. Kosugi3 and H. Kondoh1
Department of Chemistry, Keio University, Yokohama 223-8522, Japan
Cooperative Research Fellow, Institute for Catalysis, Hokkaido University, Japan
3
Institute for Molecular Science, Okazaki 444-8585, Japan
1

2

Ⅲ- 4

Recently, hydrogen production by electrochemical
water splitting using renewable energy sources such as
solar, wind, and hydroelectric powers attracts attention
from the viewpoint of the realization of a sustainable
society that does not depend on fossil fuels. For
practical applications, the improvement of overallwater splitting efficiency has been required by thedevelopment of highly active oxygen evolution
electrocatalyst. In this situation, Nocera et al. reported
that cobalt oxides electrodeposited from a dilute Co2+
solution in phosphate or borate buffered electrolyte(Co-Pi or Co-Bi, respectively) are efficientelectrocatalysts for oxygen evolution reaction (OER)[1]. The local structures of Co species in the Co-Pi and
Co-Bi catalysts were investigated by X-ray absorption
fine structure (XAFS) spectroscopy and pair
distribution function (PDF) analysis, and it was foundthat the Co-Pi and Co-Bi thin films form a nano-sizedcluster (ca. 2-3 nm and 3-4 nm, respectively) with anedge-sharing CoO6 octahedral structure [2]. However,the detailed information about oxygen species in theseelectrocatalysts under working condition is not yet
obtained. Thus, we have investigated the reaction
mechanism by measuring operando O K-edge XAFS
spectra for Co-Pi and Co-Bi under electrochemical
potential control.
Electrochemical O K-edge XAFS measurementswith transmission mode using soft X-rays were
performed at BL3U in the UVSOR Synchrotron,
according to the previous work [3]. A home-madeelectrochemical cell was used with Au/Cr/SiC thinfilm substrates as working electrodes, a Pt counterelectrode, and a Ag/AgCl reference electrode. Co-Pi or
Co-Bi electrocatalyst was electrodeposited on the
Au/Cr/SiC working electrode at 1.0 V in 0.1 M
phosphate or borate buffered electrolyte containing 0.5
mM Co(NO3)2.
The OER activities of Co-Pi and Co-Bi were testedby the linear sweep voltammograms in phosphate andborate buffered electrolytes, respectively. The result
exhibited that the OER current for Co-Pi electrode washigher than that for Co-Bi, which means that Co-Pi is amore efficient OER electrocatalyst compared with CoBi. Next, the operando O K-edge XAFS spectra for CoPi catalyst were taken under electrode potential control
in a phosphate buffered electrolyte, as shown in Fig. 1.
At 0.0 V, an absorption peak derived from oxygen
species of CoOOH was observed around 531 eV. Whenthe electrode potential was changed from 0.0 to 1.1 V,
a new absorption peak attributed to oxygen species of
CoO2 was observed around 529 eV, meaning that thepart of CoOOH cluster was oxidized to CoO2 with thehigh-valent cobalt species (Co4+) (Fig. 2). Meanwhile,when the similar measurements were tested for Co-Bi,
the fraction of generated CoO2 against CoOOH for CoBi was slightly smaller than that for Co-Pi. Therefore,
we found that Co-Pi can function as a highly active
OER electrocatalyst due to the presence of many CoO2
species.

Fig. 1. Operando O K-edge XAFS spectra of Co-Pi
electrocatalyst at various electrode potentials in 0.1 M
phosphate buffered electrolyte.

Fig. 2. Proposed reaction mechanism for Co-Pi and
Co-Bi OER electrocatalysts.
[1] D. G. Nocera et al., J. Am. Chem. Soc. 131 (2009)2615.
[2] (a) D. G. Nocera et al., J. Am. Chem. Soc. 132(2010) 13692. (b) J. Am. Chem. Soc. 135 (2013) 6403.
[3] (a) M. Nagasaka et al., J. Phys. Chem. C 117 (2013)
16343. (b) M. Yoshida et al., J. Phys. Chem. C 119(2015) 19279.

118751_Ⅳ_BL3B_512_大木義路 new.docx

Ⅲ -4. Surface, Interface and Thin Films

BL3B

Effects of Ion Implantation and Thermal Annealingon PL due to Cr3+ in LaAlO3
M. Harima, T. Morimoto and Y. Ohki
Waseda University, Tokyo 169-8555, Japan

High permittivity (high-k) dielectrics such as
LaAlO3 are expected as a gate insulator in advanced
MOS devices. In the manufacturing process ofsemiconductors, ion implantation and thermal
annealing are often used [1]. However, few reports
have been published on the influences of suchprocessing procedures on point defects in LaAlO3.
In the present study, single crystal LaAlO3 was
implanted with B+ ions and then annealed in O2 at
900°C. The effects of such treatments were examinedby measuring optical absorption, X-ray diffraction(XRD), and photoluminescence (PL).
Figure 1 shows optical absorption spectra. The sharp
increase in the absorption from around 5.0 eV iscaused by the bandgap absorption [2]. This absorption
becomes weak by the ion implantation, whereas thefollowing thermal annealing increases the absorption
in nearly the whole energy range.
Figure 2 shows in-plane XRD spectra. A sharp peakis seen at 2θχ= 23.5°, which corresponds to thediffraction on (012) planes of crystalline LaAlO3 [3].
The XRD intensity decreases by about 40 percent after
the ion implantation. The annealing given following
the implantation increases the intensity to almost thesame level as the untreated sample. This indicates thatthe crystallinity of single crystal LaAlO3 is degradedby the ion implantation and is recovered by the thermal
annealing after the ion implantation.
Figure 3 shows PL spectra excited by 6.0-eV
photons. A PL, which has three sharp components at
1.62, 1.65, and 1.69 eV, is observable. This PL is due
to Cr3+ present in LaAlO3 as an impurity [4]. After theion implantation, the total intensity of this PL

decreases by about 79% compared with the untreatedsample. When the sample was implanted with B+ ionsand then annealed at 900°C, the intensity of this PL
increases to almost the same level as the untreatedsample. Since this PL is sensitive to the crystallinity of
LaAlO3 [5], the decrease of the PL intensity is due todegradation of crystallinity.
These results indicate that the crystallinity of
LaAlO3 is collapsed by the ion implantation and isrecovered by the thermal annealing after the ion
implantation.

Ⅲ- 4

Fig. 2. In-plane XRD pattern. The notations ofsymbols and curves are the same as those in Fig. 1.

Fig. 3. PL spectra induced by the irradiation ofphotons with energies of 6.0 eV. The notations ofsymbols and curves are the same as those in Fig. 1.

Fig. 1. Optical absorption spectra observed for
LaAlO3 samples with a thickness of about 0.5 mm at
room temperature before any treatment (1), after
implantation of B+ ions at a fluence of 1015 cm-2 (2),and after thermal annealing in O2 at 900 °C given
following the B+ implantation (3).

119

[1] Q. Zhang et al., Proc. Int. Symp. Power Semiconductor Devices and ICs (ISPSD) (2005) 211.
[2] J. Robertson, Rep. Prog. Phys. 69 (2006) 327.
[3] C. J. Lu et al., Appl. Phys. A 67 (1998) 253.
[4] J. Heber et al., Z. Phys. 246 (1971) 261.
[5] T. Morimoto et al., J. Inst. Eng. Elec. Discharges
Japan 57 (2014) 3.

761_Ⅳ_BL4U_2001-2017_佐野雄一.docx
Ⅲ -4. Surface,
Interface and Thin Films

BL4U

STXM Analysis of Adsorbent for Effective Recovery of Radioactive
Elements
Y. Sano, S. Watanabe and S. Kibe

Japan Atomic Energy Agency (JAEA), Tokai 319-1194, Japan
behavior, and to optimize the distributions of SDB
polymer, i.e. polymer thickness, and extractants.

50μm
Fig. 1. Photo of the SiO2 supports.
CDP:15%+CMPO
CDP: 15%
CDP: 10%
CDP: 5%

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 be quite
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 (SDB) copolymer (SiO2-P)
and extractants on its surface. 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 thecondition of its surface in which polymer andextractants are impregnated [1]. In this study, some
information about the adsorbent surface, such as
thickness of polymer and uniformity of extractants,
were investigated by scanning transmission 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. [2]. The average
diameter and pore size of the SiO2 supports were 50μm
and 600nm, respectively (Fig.1). These adsorbents
were sliced to 300nm in thickness by focused ion beam
(FIB), and were supplied to STXM analysis.
Figure 2 shows the change of C-NEXAFS spectra(C-K edge) with CDP, which were obtained near thepore surface on the cross section of the sliced
adsorbents. The intensity of the peak at 285 eV (whichmust be attributed to C 1s→π* transition of aromatic
C=C) changed with CDP and the impregnation of
CMPO. Figure 3 show the colorized composition mapson the cross section of sliced SiO2-P (CDP=10%) andSiO2-P (CDP=15%) with 20wt% CMPO, which were
calculated by fitting C-NEXAFS spectra with those of
SDB polymer and CMPO. The SDB polymer and
CMPO were distributed within several hundred
nanometers from the pore surface, and theirdistributions were spread by the increase of CDP and
CMPO.
The excess increase of the region with SDB polymer
and CMPO in the pore may disturb the fluid flow
through the pore, and this will give some interpretationof our previous experiment, in which it was moredifficult to elute adsorbed metal ions from theadsorbent with higher CDP [1]. It should be required
for effective recovery of radioactive elements tocompare the STXM data and adsorption/elution

280

285

290
295
Photon Energy (eV)300

Fig. 2. Change of C-NEXAFS spectra (C-K edge).

1μm

1μm

(b) 20wt%CMPO/SiO2-P(a) SiO2-P(CDP=15%)(CDP=10%)
Fig. 3. Colorized composition maps (light green;
SiO2, red; SDB, blue; CMPO (purple; mixture of red
and blue) ).
[1] S. Watanabe et al., Procedia Chemistry 7 (2012)411.
[2] Y. Wei, M. Kumagai and Y. Takashima, Nucl.
Technol. 132 (2000) 413.

120

Ⅲ -4. Surface, Interface and Thin Films

771_Ⅳ_BL4B_2014-2033_岡林潤.docx

BL4B

Pd M-Edge X-Ray Magnetic Circular Dichroism
in Perpendicularly Magnetized Co/Pd Multilayers
J. Okabayashi1* and H. Munekata2

Research Center for Spectrochemistry, University of Tokyo, Tokyo 113-0033, Japan
Imaging Science and Engineering Laboratory, Tokyo Institute of Technology, Yokohama 226-8503
1

2

CoPd is a candidate for the spintronics materials
possessing perpendicular magnetic anisotropy (PMA)
which can be utilized for the low power operation
devices [1]. The 4d transition metal (TM) system of Pd
is well recognized as the sustainable elements of 5d
TM system in Pt toward the PMA materials combinedwith the magnetic 3d TMs. In order to understand themechanism of PMA in CoPd, the contributions oforbital magnetic moments of each element have to beclarified explicitly. Bruno theoretically proposed theorbital moment anisotropy in transition-metal
multilayers as a second perturbation of spin-orbit
interaction [2]. However, even in the strong spin-orbit
coupled cases using 4d or 5d TMs, the applicability ofthis formula has been still debated [3].
We reveal the anisotropic orbital magnetic moments
in Co/Pd multilayers using angular-dependent x-ray
magnetic circular dichroism (XMCD) and theirspectral analysis. Core-level X-ray absorption spectra(XAS) of Pd M-edge appears at around 530 eV which
overlaps with the O K-edge absorption. In order todetect the Pd M-edge absorption signals, the surface
oxide components have to be removed, which enables
to measure both Pd M-edge and Co L-edge absorption
at the same experimental condition. Our aim in thisstudy is to discuss both orbital and spin moments of Co
and Pd for PMA and in-plane anisotropy samples.
We prepared two kinds of samples of Co/Pd
multilayered structures: Co (0.69 nm)/Pd (1.62 nm) for
PMA and Co (1.03 nm)/Pd (1.62 nm) for in-planeanisotropy with stacking five periods on the Si
substrates [4]. Sample surfaces were sputtered by Ar
ions before the XMCD measurements in order toremove the oxygen contamination. We performed
XMCD experiments at BL4B, UVSOR, Institute of
Molecular Science. Total electron yield mode bydirectly detecting the sample current was adopted. A
magnetic field of ±5 T was applied along the directionof the incident polarized soft x-ray.
We successfully observed clear XMCD signals in
Pd M-edges after the removal of surface contamination
as shown in Fig. 1. Although the XAS line shapes
overlap with those of O K-edge absorption, clear
XMCD signals induced by the proximity with Co
layers are observed. The Pd M-edge XMCD line
shapes in both PMA and in-plane samples almost
remain unchanged. Unfortunately, conventional
magneto-optical sum rule analysis, which is defined in
the TM L-edge absorption, cannot be applicable for Medge XMCD [5]. Precise XAS line shapes in Pd Medges are necessary for the determination of absolutevalues of spin and orbital moments. On the other hand,clear Co L-edge XAS and XMCD with angulardependence reveal the enhancement of orbital
moments in the surface normal direction because of
PMA.
Considering these results, we discuss the PMA in
Co/Pd multilayers. The Co atoms possess large spin
moments and the Pd atoms possess large spin-orbit
interaction. The orbital moments in Co is enhanced
through the proximity with Pd which induces the spinorbit coupling. On the other hand, magnetic moments
are induced in Pd through the proximity with Co.
These collaborate at the interfaces, which enhances the
PMA in Co/Pd multilayers. In case of thick Co, theshape anisotropy in Co governs the in- planeanisotropy. Therefore, we propose that the origin of the
PMA in Co/Pd interface can be explained by theorbital moment transfer at the interface, which opens
up new research fields of 'Spin-Orbitronics'.
We acknowledge to Prof. T. Yokoyama, Dr. Y.
Takagi, and Ms. M. Uozumi for the technical supports
at BL4B.
1.08
1.06

Co/Pd
Pd M-edge XAS
10 K, 5 T

M5

M4

1.02

Co/Pd
Co L-edge XAS
10 K, 5 T

L3

1.5
1.4
1.3

1.00

1.2

0.98

1.1
1.0

4

0.05

2

0.00

-3

0.96

x10

Intensity (arb. units)

1.04

1.6

0

-0.05

-2

-0.10

-4

-0.15

-6

-0.20

-8

L2

-0.25
520

540

560

580

760

770

780

790

800

810

820

Photon Energy (eV)Fig. 1. XAS and XMCD of Pd M-edge and Co L-edge
in perpendicularly magnetized Co (0.69 nm)/Pd (1.62nm) multilayer.
[1] M.T. Johnson et al., Rep. Prog. Phys. 59 (1996)
1409.
[2] P. Bruno, Phys. Rev. B 39 (1989) 865.
[3] C. Andersson et al., Phys. Rev. Lett. 99 (2007)
177207.
[4] K. Yamamoto et al., IEEE TRANSACTIONS ON
MAGNETICS 49 (2013) 3155.
[5] T. Ueno et al., Phys. Rev. B 85 (2012) 224406.
*e-mail: jun@chem.s.u-tokyo.ac.jp

121

Ⅲ- 4

791_Ⅳ_BL4B_2016-2030_宮町俊生.docx
Ⅲ -4. Surface,
Interface and Thin Films

BL4B

A Monatomic Layer Iron Nitride
Magnetically Coupled with Chromium Nano-Clusters
T. Miyamachi1, Y. Takahashi1, S. Nakashima1, Y. Takagi2,3, M. Uozumi2,3,
T. Yokoyama2,3 and F. Komori1

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, Japan
1

2

Ⅲ- 4

An iron nitride compound, Fe4N, in the
ferromagnetic phase is a promising candidate for rareearth free permanent magnets for their large magnetic
anisotropy and high coercivity. The crystal structure of
the Fe4N is composed of so called Fe-plane and Fe2N
plane in the fcc Fe sublattice with a N atom centeredin the cubic cell [1].
We have previously investigated atomic scale
structural and electronic properties of a monatomic
Fe4N layer grown on a Cu(001) using scanningtunneling microscopy (STM). The surface of themonatomic Fe4N is composed of the Fe2N plane with
p4gm(2×2) surface reconstructed structure, but its
appearance alters between p4gm(2×2) and c(2×2) onesin the STM image due to an orbital selective tunnelingprocess [2]Magnetic properties of the monatomic Fe4N layer(Fe2N layer) have been clarified by x-ray adsorption
spectroscopy and x-ray magnetic circular dichroism(XAS/XMCD) conducted at BL4B in UVSOR [3]. We
find that the fundamental magnetic properties, such as
magnetic moments, magnetic anisotropy and the Curie
temperature, rely on the surface quality, being
considerably lowered by atomic defects on the surface[4]. In this work, we have further grown Cr nanoclusters on the Fe2N layer and investigated theirinfluence on the magnetism of the Fe2N layer.
To grow the Fe2N layer on Cu(001), N+ ions with anenergy of 0.5 keV were firstly bombarded to the cleanCu surface and Fe was additionally deposited at room
temperature. By subsequent annealing at 570 K, wellordered Fe2N layer can be obtained on the surface. The
high-quality Fe2N layer on Cu(001) is achieved by thestrict control of the growth condition especially for theamount of deposited Fe and annealing temperature.
Thereafter, the Cr deposition is done at room
temperature, resulting in the formation of bilayer Cr
nano-clusters with an almost identical lateral size of ~3 nm, which is confirmed by STM in advance of
XAS/XMCD measurements.
The measurements were performed at BL4B in
UVSOR by total electron yield mode at B = ± 5 T and
T = 7.2 K. In the in-plane (θ = 55°) and the out-of-plane(θ = 0°) geometries, the XMCD spectra are obtainedby detecting μ+ – μ–, where μ+ (μ–) denotes the XAS at
Fe and Cr L-adsorption edges with the photon helicity
parallel (antiparallel) to the sample magnetization.

Note that θ is the angle between the sample normal andthe incident x-ray.
We find no significant difference in the Cr μ+ and μ–,
and thus the minute XMCD signal from the bilayer Cr
nano-cluster. Combined with the structuralcharacterization by STM, the results suggest that theantiferromagnetic coupling between the first andsecond layers in the Cr nano-cluster. The XMCD
spectrum at Fe L-adsorption edges reveals themodification of magnetic properties of the Fe2N layer.
While the magnetic easy axis of the Fe2N layer with Cr
nano-clusters is towards in-plane direction as in thecase of the bare Fe2N layer [3, 4], the reduction of the
XMCD signal is observed, indicating the influence of
the antiferromagnetic Cr nano-clusters through themagnetic coupling.
Quantitative analyses of the XMCD spectra giving
magnetic moments, magnetic anisotropy and the Curie
temperature of the system will unravel the details of
the magnetic coupling between the Cr nano-clusters
and Fe2N layer.
[1] Y. Takagi et al., Phys. Rev. B 81 (2010) 035422.
[2] Y. Takahashi et al., Phys. Rev. Lett. 116 (2016)056802.
[3] T. Miyamachi et al., UVSOR Activity Report 42(2015) 132.
[4] Y. Takahashi et al., submitted.

122

Ⅲ -4. Surface, Interface and Thin Films

801_Ⅳ_BL4B_2031_中川剛志.docx

BL4B

Magnetism of Single and Double Layer Co Films on W(112)
Y. Takamura1, S. Mizuno1, T. Nakagawa1, Y. Takagi2 and T. Yokoyama2

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

1

Magnetic thin films on heavy metal surfaces show
large anisotropy and coercivity due to their strong spin
orbit coupling in the heavy metals [1,2]. Magnetic
anisotropy and coercivity can also be enhanced on
anisotropic surface structures. bcc(112) surfaces, suchas W(112), are good candidates for the highly
anisotropic structure since they has ridge and furrow(Fig.1(a)), which would exhibit high magnetic
anisotropy. Few investigations of magnetic overlayers
on bcc(112) have been examined so far [3]. We have
prepared Co nano structures on W(112) surface andinvestigated their magnetic properties.
X-ray magnetic circular dichroism (XMCD)
measurements were done at BL4B using high field andlow temperature end station (Ts ~ 5 K, H~6 T). All thesample preparation and measurements were performedin situ under the vacuum of 1×10-10 Torr.
Figure 1 shows single and double layer Co on
W(112) observed by scanning tunneling microscope(STM). We observed Co atomic wires along [11-1],
and found no evidences for W-Co alloy formation. The
1st Co layer as well as the 2nd Co layer keep the same
surface structure as W(112), 1×1 structure, irrespectiveof the large size mismatch between Co and W (~10%).
Figure 2(a) shows Co L edge XAS for 0.6 ML
Co/W(112) and its XMCD, which does not show any
dichroic signal even at Ts = 6 K and the magnetic fieldof ±5 T. The absence of the XMCD signal means thatthe surface is not ferromagnetic. As in Fig. 2(b),increasing the Co thickness above 1 ML exhibits
dichroic signal, corresponding to magnetic moment of
0.4 μB, which is rather small compared with that ofbulk Co (1.6μB). The second layer Co is ferromagnetic,
which is not ferromagnetically coupled with the 1st
layer Co.
Figure 3 shows a magnetization curve (M-H curve)for 1.5 ML Co/W(112), which was measured bymonitoring Co L3 edge XAS intensity as a function of
the magnetic field. The M-H curve along the [11-1]
direction shows hysteresis with large coercivity of 3 T.
The absence of ferromagnetism in the first Co layeron W(112) is attributed to strong electronic
hybridization between Co and W, caused by the
reduced bond length. The bond length between Co and
W is 0.239 nm, as determined by low energy electron
diffraction, which is 8% shorter than that for the hardshare model (0.260 nm).

123

Fig. 1. STM images for (a) Co(0.6 ML)/W(112) and(b) Co/(1.2 ML). The inset in (a) shows a structure
model.

Ⅲ- 4
Fig. 2. Co L2,3-edge XAS and XMCD spectra for (a)Co(0.6 ML)/W(112) and (b) Co(1.5 ML). The spectra
are taken at H = ± 5 T.

Fig. 3. In-plane magnetization curve for Co(1.5ML)/W(112) taken along the [11-1] direction.
[1] P. Gambardella et al., Nature, 416 (2002) 301.
[2] T. Nakagawa et al., Phys. Rev. B 86 (2012) 144418.
[3] J. Kołaczkiewicz and E. Bauer, Surf. Sci., 144(1984) 495.

811_Ⅳ_BL4B_2034_吉澤俊介.docx
Ⅲ -4. Surface,
Interface and Thin Films

BL4B

X-Ray Magnetic Circular Dichroism of a Copper-Phthalocyanine
Monolayer on Si(111)-(√7×√3)-In
S. Yoshizawa and T. Uchihashi

International Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science(NIMS), Tsukuba 305-0044, JapanⅢ- 4

The reconstruction surface Si(111)-(√7×√3)-In[hereafter (√7×√3)-In] exhibits superconductivity
below about 3 K [1]. The Cooper pairs of thissuperconductor reside in the surface atomic layer ofindium and are sensitive to the surface environment [2].
Our electrical transport measurements have shown thatthe superconducting characteristics of (√7×√3)-In canbe modified by covering the surface with selfassembly layers of various transition-metal
phthalocyanines (Pcs). To clarify the mechanism weneed to determine the magnetic moments of the Pcs on(√7×√3)-In, because both the electrostatic andmagnetic interactions are expected to be involved. We
have already performed X-ray magnetic circulardichroism (XMCD) experiments on MnPc and FePc [3,4], and this time we focus on CuPc to complete the data
sets.
The experiments were carried out at the BL4B
XMCD system. (√7×√3)-In samples were prepared insitu by depositing indium onto a clean Si(111) surface
followed by an annealing at about 400°C. The growthof the √7×√3 phase was confirmed with low-energy
electron diffraction. CuPc was thermally depositedfrom a Knudsen cell onto the (√7×√3)-In surface heldat room temperature. The molecular coverage wasadjusted to be less than 1 monolayer (ML) for avoiding
a second-layer formation. Then, the samples werecooled down to ~7 K and X-ray absorption spectra(XAS) were measured by using a circularly polarized
light with ~60% polarization. XMCD signals wereobtained from the difference of XAS measured inmagnetic fields of B = ±5 T applied in the direction
parallel to the incoming light.
Before going to the XMCD measurement, theadsorption geometry of CuPc was checked from XAS
at the K edge of nitrogen (Fig. 1). The sharp peaks ataround 400 eV in the XAS curve at θ = 55° are
assigned to transitions from the nitrogen 1s orbital toπ* molecular orbitals [5]. Their disappearance at θ = 0°
(normal incidence) demonstrates that the molecular
framework of CuPc is nearly parallel to the surface.
Figure 2 shows the XAS and the XMCD at the L2,3
edges of copper. By using XMCD sum rules, weestimated the effective spin moments as <Seff> =0.7±0.2μB for θ = 0° and <Seff> = 0.5±0.2μB for θ = 55°.
Here, <Seff> is a sum the spin moment and the intraatomic magnetic dipolar moment. Since the latter
contribution goes to zero at θ ~ 55° for molecularorbitals with C4 symmetry [6], the non-zero <Seff> at θ
= 55° obtained here clearly indicates the presence of124

spins in CuPc molecules adsorbed on the (√7×√3)-In
surface. The present results give important clues forunderstanding the function of a CuPc monolayer onsuperconducting (√7×√3)-In.

Fig. 1. XAS at the N K edge. The coverage of CuPc
is about 0.7 ML.

Fig. 2. XAS and XMCD at the Cu L2,3 edges. The
coverage of CuPc is about 0.7 ML.
[1] T. Uchihashi et al., Phys. Rev. Lett. 107 (2011)
207001.
[2] S. Yoshizawa et al., Phys. Rev. Lett. 113 (2014)
247004.
[3] T. Uchihashi and S. Yoshizawa, UVSOR Activity
Report 41 (2014) 133.
[4] T. Uchihashi and S. Yoshizawa, UVSOR Activity
Report 42 (2015) 131.
[5] K. Eguchi et al., J. Phys. Chem. C 117 (2013)
22843.
[6] S. Stepanow et al., Phys. Rev. B 82 (2010) 014405.

Ⅲ -4. Surface, Interface and Thin Films

821_Ⅳ_BL5B_523_林浩司.docx

BL5B

Vacuum Ultraviolet Transmission Spectra of Amorphous Arsenic
Chalcogenide Thin Films
K. Hayashi

Department of Electrical, Electronic and Computer Engineering, Gifu University, Gifu 501-1193, Japan
It is well-known that amorphous chalcogenide
materials exhibit a variety of photoinduced phenomena
by irradiation of light with energy corresponding to theoptical band gap [1]. Photoinduced changes observedin amorphous chalcogenide materials are classified
into two types, irreversible and reversible changes.
Reversible changes can be induced optically inamorphous bulk materials and well-annealed
evaporated thin films, in which the changes can beremoved by annealing to the glass-transition
temperature. The reversible photodarkening arisingfrom the red-shift of the optical absorption edge is atypical reversible photoinduced phenomenon.
Irreversible changes are induced in as-deposited
evaporated thin films. The irreversible photodarkening
in as-deposited amorphous films is an irreversible
change, it is believed that it occurred by photopolymerization. The irreversible change observed in
EXAFS [2] and IR [3] is interpreted by rearrangementof bonding configurations of molecular species within
as-deposited evaporated films.
To our knowledge, little attention has been given to
photoinduced changes at the vacuum ultra-violet(VUV) absorption spectrum. In this report, wemeasure the VUV transmission spectra on asdeposited evaporated amorphous arsenic chalcogenide
films.
Samples used for the measurement of the VUVtransmission spectra were amorphous arsenic
chalcogenide (a-AsxSe1-x) thin films prepared onto
aluminum thin films by conventional evaporation
technique. Using different bulk glass of thecomposition as a source material, different amorphousfilm of the compositions was prepared. Typical
thickness of the amorphous film and the aluminum
film were around 200 nm and 100 nm, respectively.
The aluminum film of the thickness of 100 nm wasalso used in order to eliminate the higher order lightfrom the monochromator 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 wasmeasured by using the silicon photodiode as a detector.
Two pinholes of 1.5 mm in a diameter were inserted
between the monochromator and sample to remove
stray light. The intensity of the VUV light wasmonitored 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 of as-

deposited a-As0.3Se0.7, a-As0.4Se0.6, and a-As0.5Se0.5
films. Two main absorption peaks were observed inthis wavelength region. One absorption peak around
22 nm corresponds to the 3d core level of selenium
atom. Another absorption peak around 28 nm
corresponds to the 3d core level of arsenic atom. As
shown in the figure, the ratio of the two main
absorption peaks changes depending on composition.
The spectrum shape also changes depending on
composition. We think that those changes are related
to the local structures of the amorphous network. We
will observe the composition dependence of thechange in the spectrum before and after irradiation oflight in future. And we are going to investigate therelations between those changes.

Ⅲ- 4Fig. 1. The VUV transmission spectra ofasdeposited a-As0.3Se0.7, a-As0.4Se0.6, and a-As0.5Se0.5
films.
[1] K. Tanaka, Rev. Solid State Sci. 4 (1990) 641.
[2] A. J. Lowe, S. R. Elliot and G. N. Greaves, Philos.
Mag. B 54 (1986) 483.
[3] S. Onari, K. Asai and T. Arai, J. Non-Cryst. Solids
77&78 (1985) 1215.

125831_Ⅳ_BL5B_829_松田巌.docx
Ⅲ -4. Surface,
Interface and Thin Films

BL5B

Study of M-Edge Resonant Magneto Optical Effect of Fe Ultrathin Films
with Large Perpendicular Magnetic Anisotropy Induced by Rashba-Type
Spin-Orbit Interaction
Sh. Yamamoto1, K. Yamamoto1, K. Takubo1, K. Fukuta2, D. Oshima3, T. Kato2, S. Iwata3,
H. Wadati1 and I. Matsuda1
1

Ⅲ- 4

Institute for Solid State Physics, The University of Tokyo, Kashiwa 277-8581, Japan2
Department of Electrical Engineering and Computer Science, Nagoya University,
Nagoya 464-8603, Japan
3
Nagoya University, IMaSS, Nagoya 464-8603, JapanIn Fig. 1, RMOKE spectrum around Fe M-edge isshown with error bars ± 0.5 degrees. There are mainly
two structures in the spectrum. One is around theregion in 54 – 55 eV that corresponds to Fe M
absorption edge, 3p → 3d transition. The other appears
to be broader compared to the former, which can beobserved around the region in 60 – 65 eV. This
corresponds to Au O3 edge.
It is shown that this method has sensitivity even for
the ultrathin ferromagnetic systems. Furthermore thismeasurement has been preliminary experiment for
time-resolved measurement [3]. It was found thatenergy around 54 - 55 eV was suitable for tracing
dynamics of Fe of this system. Ultrafast spin dynamics
of this system has been attracting because this system
can be used for investigating effects of spin-orbit
interaction at interfaces on its dynamics in subpicoseconds timescale.

Magneto-optical Kerr effect (MOKE) in visible
region has been widely utilized in condensed matterphysics, especially in the field of magnetism. We havebeen developing a measurement scheme for resonant
MOKE (RMOKE), in which an energy for incident
light is tuned to particular absorption edge of target
element composed of samples [1], and applied to thin
ferromagnetic metals, ferrimagnetic alloys, andartificial multilayers, for examples. For exploring theapplicability in terms of its sensitivity of this method,
we focus on ultrathin ferromagnetic films here. In such
systems, interfacial properties contribute toperpendicular magnetic anisotropy (PMA) of ultrathin
films. PMA has been one of the important features in
spintronics field due to its potential for developing a
non-volatile device with higher density. However, its
mechanism has not been understood from microscopic
point of view. Therefore in order to access such
systems, it is essential to probe the ultrathin magnetic
systems in methodological point of view. Recently, anovel scheme considering Rashba-type spin-orbit
interaction has been shown to explain the existence of
PMA and its electric-field dependence as a result ofcompetition with exchange interaction of magnetic
systems as an analogy of Dzyaloshinskii-Moriya
interaction [2]. The Rashba effect has been known toemerge in the system without inversion symmetry suchas surface or interface. In the new scheme, effective
Rashba field acts at an interface between a noble metalor an insulator and ultrathin ferromagnetic films.
In this research, at UVSOR BL5B, we conducted Fe
M-edge RMOKE measurement of the Fe film that was
sandwiched by films of noble metal, Au, and insulator,
MgO. We synthesized the sample using molecularbeam epitaxy method. The structure of the sample isAu (2 nm)/MgO (2 nm)/Fe (0.29 nm)/Au (25 nm)/Cr(5 nm)/MgO(001, substrate). Fe thickness of 0.29 nm
corresponds to ~ 2 monolayer assuming that this layer
takes body-centered cubic structure. In measuring
RMOKE, rotating-analyzer ellipsometry has beenutilized for obtaining Kerr rotation angle at eachenergy point [1]. The measurement has been conductedat room temperature and external magnetic field (±0.47 T) that was in perpendicular to sample surface
was applied using permanent magnet. The incident
light angle was set to 45 degrees.

Fig. 1. Fe (0.29 nm) M-edge resonant magneto optical
Kerr effect spectrum.
[1] Sh. Yamamoto. et al., Phys. Rev. B 89 (2014)064423.
[2] S. E. Barnes et al., Sci. Rep. 4 (2014) 4105.
[3] Sh. Yamamoto et al., Rev. Sci. Instrum. 86 (2015)
083901.

126

Ⅲ -4. Surface, Interface and Thin Films

841_Ⅳ_BL6U_228-602_米澤恵一郎.docx

BL6U

Various Electronic Structures of SnCl2Pc Film on Graphite
1

K. Yonezawa1, T. Ueba2, R. Shiraishi2, H. Yamane2, N. Kosugi2 and S. Kera1,2

Department of Nanomaterial Science, Graduate School of Advanced Integration Science, Chiba University,
Chiba 263-8522, Japan2
Department of Photomolecular Science, Institute of Molecular Science, Okazaki 444-8585, Japan,

Organic π-conjugated molecular solid is consisted
by a weak intermolecular interaction. Thus, the film
structure could be easily modified by a thermal impact,
leading a wide variety in the electronic property of themolecular solid. Tin phthalocyanine dichloride(SnCl2Pc) is a π-conjugated molecule which has beenreported as an n-type semiconductor property [Fig.
1(a)]. Since SnCl2Pc is non-planer molecule, the film
structure is considered to be variable depending on the
preparation conditions. In this work, we studied
impacts of the thermal annealing on the electronic
structure of the SnCl2Pc film prepared on graphite byangle-resolved UPS (ARUPS) and XPS.
The clean surface of graphite was obtained bycleaving a HOPG under the air and subsequentannealing in the UHV chamber. SnCl2Pc is purified bysublimation method twice. After preparing themonolayer film (0.5 nm) on the graphite at room
temperature, valence-band and secondary electron cutoff were measured at 45 eV, and Sn 4d, C 1s, Cl 2p andN 1s core levels were measured at 60 eV, 335 eV, 335
eV and 500 eV, respectively.
In Fig. 1(b), the intense peak at 1.8 eV (label a) andthe weak peak at 1.4 eV (label a’) are observed for asdeposited film. The peak a is assigned to HOMO. The
peak a’ must be originated from the electronic structureof SnCl2Pc, not from that of impurities nor surface
contaminations. Upon annealing the film at 343 K for
9h, the spectrum changes drastically from the asdeposited one. New features at 1.6 eV (label b) and 1.2
eV (label b’) are observed in addition to the peaks a
and a’ found for the as-deposited film. Furthermore,
weaker features (labels α’ and β’) at around 0.3 eV are
observed after the annealing. From the intensity
analysis of ARUPS, the angular dependences of thepeaks b, b’ and β’ are very similar one another, while itis different from those of the peaks a, a’ and α’(notshown), indicating two kinds of molecular orientation
exist in the film.
It has been reported that dissociation of the Cl atomof SnCl2Pc has occurred for the monolayer film on
Ag(111) after the annealing [1], thus one may consider
the peaks b, b’ and β’ might be ascribed to HOMO of
SnPc or SnClPc (radical) etc, which may be formed
after the surface chemical reaction upon the annealing.
However, the XPS spectra of Cl 2p are nearly identicalbefore/after the annealing (Fig. 1 (c)), indicating
almost all the Cl atoms have remained in the film.
Therefore, peaks b, b’ and β’ should be originated fromthe electronic states of SnCl2Pc with another molecularorientation or aggregation.

Figure 1 (d) shows Sn 4d states. In contrast to Cl 2p,
new features are observed at low-binding energy sideof the main peaks of the as-deposited film by 0.33 eV.
The spectra of C 1s and N 1s indicate the same trend
to Sn 4d, while the energy differences of new features
are not equal (not shown). The results indicate theenergy shift found in Sn 4d, C 1s, and N 1s could becaused by the charge redistribution at the Pc ring.
The electronic structure of the SnCl2Pc film ongraphite is clearly modified by the annealing, namely
rearrangement of the molecular orientation andaggregation. Finally we would assume the origin ofvarious peaks, though further experiments arerequested to conclude. The peaks a’ and α’ (b’ and β’)
are possible to be originated from HOMO and LUMO
of anion states of SnCl2Pc. The wave-function
localization in the film would be a key to understandthe non-trivial features because adsorption distance of
Pc ring could be longer by Cl as a spacer.

Ⅲ- 4Fig. 1. (a) Chemical structure of SnCl2Pc. (b)Valence-band spectra for the as-deposited (black) andthe annealed at 343 K for 9 h (magenta). (c) Cl 2p XPS
spectra. (d) Sn 4d XPS spectra. In (c) and (d), asdeposited spectra (pale gray) are shown with theannealed one for comparison.
[1] S. Kera et al., UVSOR Activity Report 42 (2015)
138.

127

851_Ⅳ_BL6U_228-602_米澤恵一郎.docx
Ⅲ -4. Surface,
Interface and Thin Films

BL6U

Orbital Energy Rearrangement by the Organic–Metal Interaction:
Perfluoropentacene on Ag(111)

PFP adsorbs on Ag(111) with the flat-lying geometry.
Hence, such core-level shift cannot be explained onlywith the photohole screening by the substrate or withthe surface potential. The result can be taking into
account the intramolecular charge redistribution, most
likely arising from the change in molecular structure
upon the weak molecule- substrate interaction. Indeed,
our high-resolution electron energy loss spectroscopy(HREELS) for PFP/Ag(111) resolved the change invibrational energies as compared with PFP/HOPG (notshown). The result clearly indicates the very slight
modification in the molecular structure uponadsorption on Ag(111), which probably causes
intramolecular charge redistribution and consequently
the orbital energy rearrangement.
Binding Energy (eV)
2.5
1.5
3
2

.5

Intensity (a.u.)1

on Ag(111)

15 K
RT

on HOPG
50 K
3

2.5
2
1.5
Binding Energy (eV)1Fig. 1. Valence-band spectra of PFP/Ag(111) (top)and PFP/HOPG (bottom) measured at 45 eV.
C1sIntensity (a.u.)

Ⅲ- 4

Understanding the weak interaction at organicmetal interface, including intermolecular interaction
and molecule-metal interaction, is of great importance.
Even such weak interaction can cause the rearrangement of molecular orbitals both in energy andspace, which defines the electronic properties atinterfaces.
Perfluoropentacene (PFP), an organic semiconductor, gives us an interesting example. The energy gap
between the HOMO and HOMO–1 of PFP monolayer
adsorbed on highly oriented pyrolytic graphite(HOPG), observed by ultraviolet photoelectron
spectroscopy (UPS), is identical to gaseous PFP (2.42eV), while it is 70-meV narrower for PFP on Ag(111)[1]. Because PFP adsorbs on both surfaces in a“physisorptive” manner, namely, without chemicalbonding nor charge transfer, the orbital energy
rearrangement is a consequence of the weakinteraction at the interface. In this work, we performed
photoemission spectroscopy to examine the origin of
the orbital energy rearrangement of PFP/Ag(111), bycomparing with PFP/HOPG.
The Ag(111) surface was purified by repeated cycles
of Ar+ sputtering and subsequent annealing. The
cleanliness was confirmed by the low-energy electron
diffraction (LEED) and the appearance of the Shockleystate in angle-resolved UPS. After multilayer
deposition on Ag(111), the sample was annealed at 130
K for 5 minutes for obtaining the monolayer [2]. The
clean HOPG surface was obtained by cleaving in air
and by annealing in the UHV chamber. Valence bandand secondary cut-off was measured at a photon
energy (hv) of 45 eV, and the C1s and F1s core levels
at hv = 335 eV and 730 eV, respectively.
Figure 1 shows the valence-band spectra. For
PFP/Ag(111), the ordered/disordered phase transition
at Tc ~145 K is reported [2]. However, our results
detected no temperature dependence in the HOMOHOMO–1 gap energy, indicating that the narrower gap
arises from the molecule-metal interaction, not theintermolecular interaction.
Figure 2 shows the core-level spectra. The binding
energy of the C1s peaks (C-C and C-F) for PFP/
Ag(111) are higher than those for PFP/HOPG, as foundin the valence band. However, the C-F peak appears at
rather similar energy for both films, as compared with
the C-C peak. The energy difference of the F1s peak
between PFP/Ag(111) and PFP/HOPG is also
reasonably less than the C-C peak.
According to the X-ray standing wave analysis [3],

@77 K

@77 K

on HOPG@77 K

on Ag(111)on Ag(111)

PFP
C-F

PFP
C-C

HOPG

Intensity (a.u.)

2

T. Ueba1, K. Yonezawa2, H. Yamane1, N. Kosugi1 and S. Kera1,2

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, Japan1

F1s

on HOPG@130 K(x5)

289 288 287 286 285 284
Binding Energy (eV)690 689 688 687 686
Binding Energy (eV)Fig. 2. A comparison of the C1s (left) and F1s (right)
core level energies.
[1] S. Kera et al., J. Electron Spec. Relat. Phenom. 204(2015) 2.
[2] M. Marks et al., J. Phys. Chem. C 116 (2012) 1904.
[3] S. Duhm et al., Phys. Rev. B 81 (2010) 045418.

128

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861_Ⅳ_BL6U_9001_山根宏之.docx

BL6U

Lateral Intermolecular π-Band Dispersion in the Superstructure of
Perylene Monolayer Physisorbed on Au(111)2

H. Yamane1,2 and N. Kosugi1,2

Institute for Molecular Science, Okazaki 444-8585, JapanThe Graduate University for Advanced Studies (SOKENDAI), Okazaki 444-8585, Japan
1

Using angle-resolved photoemission spectroscopy(ARPES), we have recently investigated the lateralintermolecular π-band dispersion in superstructuremonolayers of polycyclic aromatic hydrocarbons(PAHs) physisorbed on Au(111), e.g., coronene(4×4)/Au(111), hexa-peri-hexabenzocoronene (HBC)(5×5)
R0°/Au(111), and HBC(3√3×3√3)R30°/Au(111) [1].
This systematic investigation has revealed that theobserved lateral π-band dispersion is dependent on themonolayer’s surface Brillouin zone (SBZ) but not on
the substrate’s SBZ [1]. This finding suggests that theobserved π-band dispersion at the PAHs/Au(111)interface is introduced not by a substrate-mediatedintermolecular interaction [2,3] but by a genuine
lateral intermolecular interaction. In the present work,in order to investigate the impact of the intermolecular space on the lateral intermolecular π-band
dispersion, we study the electronic structure of thesmaller PAHs of perylene, which also forms the (4×4)
superstructure on Au(111) depending on the film
growth condition in the monolayer coverage [4].
The experiment was performed at the in-vacuum
undulator beamline BL6U. The clean Au(111) surface
was obtained by the repeated cycles of the Ar+
sputtering and the subsequent annealing at 700 K, asconfirmed by the low-energy electron diffraction(LEED) and the Shockley state in ARPES.
Figure 1 shows (a) a LEED image at 20 K and (b)the corresponding SBZ of the perylene monolayer on
Au(111). The LEED image shows the (4×4) super-

structure with respect to the Au(111) hexagonal lattice,
as reported in Ref. [4]. The ARPES spectra were
measured by considering the high symmetric point of
Γ’, K’, and M’ in the monolayer’s SBZ [blue hexagon
in Fig. 1(b)].
The E-k map of perylene(4×4)/Au(111) along the
Γ’-K’ and Γ’-M’ (kΓK and kΓM) directions, obtained
from ARPES, is shown in Fig. 1(c) and 1(d),respectively. The π-type highest occupied molecularorbital (HOMO)-derived peak of perylene is observedat the binding energy of ca. 1.15 eV. Although no directintermolecular π-π overlap exist in the flat- lying
monolayer, the HOMO peak shows a very weak lateral
π-band dispersion by 20 meV at Γ’-K’ and by <10 meV
at Γ’-M’. The observed π-band dispersion at
perylene(4×4)/Au(111) is narrower than that at thecomparable interface of coronene(4×4)/Au(111) [1].
This difference can be explained by the larger intermolecular space in the perylene monolayer than that in
the coronene monolayer due to the molecular size. The
observed π-band dispersion is ascribed to the longrange lateral intermolecular interaction through theintermolecular space.
[1] H. Yamane et al., UVSOR Activity Report 2014.
[2] H. Yamane et al., Phys. Rev. B 76 (2007) 165436;
J. Electron Spectrosc. Rel. Phenom. 174 (2009) 28.
[3] M. Wieβner et al., Nat. Commun. 4 (2013) 1514;
Phys. Rev. B 88 (2013) 075437.
[4] C. Seidel et al., Phys. Rev. B 64 (2001) 195418.

Fig. 1. (a) LEED of the perylene(4×4)/Au(111) at 20 K, wherein the red dot indicates the substrate’s spot. The
molecular structure of perylene is also shown. (b) SBZ of the Au(111) (black) and the perylene(4×4)/ Au(111)(blue). The red line indicates the scanned region in ARPES. (c,d) The E-k maps of the perylene(4×4)/Au(111) at
20 K along the kΓK and kΓM directions and the energy distribution curves.

129

Ⅲ- 4

871_Ⅳ_BL6U_9001_山根宏之.docx
Ⅲ -4. Surface,
Interface and Thin Films

BL6U

A High Hole-Mobility Molecular Layer Formed byStrong Electron Acceptor F4TCNQ on Gold Electrode2

Ⅲ- 4

H. Yamane1,2 and N. Kosugi1,2

Institute for Molecular Science, Okazaki 444-8585, JapanThe Graduate University for Advanced Studies (SOKENDAI), Okazaki 444-8585, Japan1

orbital (HOMO) as considered in the neutral F4TCNQ
molecule, respectively, show the large dispersion by
the 0.3-eV bandwidth for LUMO and by the 0.4-eVbandwidth for HOMO with the same k periodicity.
These band dispersions are observable even at 300 K,
and can be ascribed to the adatom(Au)-mediatedintermolecular interaction, which is not observable atthe physisorbed TCNQ/Au(111) interface.

Because of the large electron affinity, 2,3,5,6-tetra
fluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ)
is well known as a strong electron-accepting molecule,and has been applied for the p-type doping of organic
semiconductors [1] and for the work-function controlof metal electrodes [2]. It is understood that the cyanogroup in the molecule plays a crucial role in the chargetransfer (CT) interaction. In particular, at the
F4TCNQ/Au(111) interface, the F4TCNQ molecule
forms a two-dimensional network via the cyano groupand the segregated Au atom from the substrate [3]. In
the present work, in order to investigate the electronic
structure of the F4TCNQ-Au network, we studied the
TCNQ/Au(111) and F4TCNQ/Au(111) interfaces byangle-resolved photoemission spectroscopy (ARPES)
and low-energy electron diffraction (LEED).
The experiment was performed at the in-vacuum
undulator beamline BL6U. The clean Au(111) surface
was obtained by the repeated cycles of the Ar+
sputtering and the subsequent annealing at 700 K, asconfirmed by LEED and the Shockley state in ARPES.
In order to obtain the ordered monolayer film, thesample was heated at the multilayer desorption
temperature of ca. 380–390 K, which is slightly lower
than the desorption temperature of the TCNQ and
F4TCNQ monolayers on Au(111), as confirmed by thetemperature-dependent ARPES.
Figure 1 shows the normal-emission ARPES andLEED data of TCNQ/Au(111) and F4TCNQ/Au(111).
Upon the TCNQ monolayer formation, the Shockleystate of Au(111) just below EF (labeled S) is survived
with the lower-energy shift. The LEED image of
TCNQ/Au(111) shows the 22×√3 herringbone patternof Au(111) just around the 0,0 spot. These ARPES andLEED characteristics of TCNQ/Au(111) indicate theweak physisorption at the interface. On the other hand,both the Shockley state in ARPES and the 22×√3
herringbone pattern in LEED are quenched at
F4TCNQ/Au(111). These evidences in ARPES andLEED of F4TCNQ/Au(111) can be explained by the
Au-atom segregation from the Au(111) surface by thestrong chemisorption at the interface, which induces
the formation of the F4TCNQ-Au network and theresultant CT-derived peak in ARPES (CT1 and CT2).
The different interfacial interaction between TCNQ
/Au(111) and F4TCNQ /Au(111) is supported by the N
1s photoemission spectra (not shown here).
Figure 2 shows the E-k map of the F4TCNQ-Au
network on Au(111) at 20 K. Peaks CT1 and CT2,
originating from the lowest-unoccupied molecularorbital (LUMO) and highest-occupied molecularFig. 1. Normal-emission ARPES and LEED data of
TCNQ/Au(111) and F4TCNQ/Au(111).

Fig. 2. The E-k map and the selected energy
distribution curves of the F4TCNQ-Au network on
Au(111) at 20 K along the Γ-K direction.
[1] W. Y. Gao and A. Kahn, J. Appl. Phys. 94 (2003)
359, and references therein.
[2] N. Koch et al., Phys. Rev. Lett. 95 (2005) 237601.
[3] M. N. Faraggi et al., J. Phys. Chem. C 116 (2012)
24558.

130881_Ⅳ_BL6U_9001_山根宏之.docx

Ⅲ -4. Surface, Interface and Thin Films

BL6U

Site-Specific Organic/Metal Interactions Revealed from the Analysis of
Shockley-Type Interface State
2

H. Yamane1,2 and N. Kosugi1,2

Institute for Molecular Science, Okazaki 444-8585, JapanThe Graduate University for Advanced Studies (SOKENDAI), Okazaki 444-8585, Japan
1

The Shockley state is a well-known surface state
associated with the breakdown of the periodic crystal
potential at the surface, and can be observed as aparabolic dispersion for normal metals and semiconductors by using angle-resolved photoemission
spectroscopy (ARPES). The origin of the Shockleystate is also valid for adsorbed-surface systems. Indeed,
the Shockley state has been reported for metal surfaces
adsorbed with metals, rare gases, and molecules withmodified band dispersions, and has recently been
applied to the determination of the interfacial bonding
strength [1]. In the present work, we have applied theShockley-state measurement to the well-orderedmonolayer of cobalt phthalocyanine (CoPc) on
Au(111), for the quantitative study of the site-specificinterfacial interaction.
The experiment was performed at the in-vacuum
undulator beamline BL6U. The clean Au(111) surface
was obtained by the repeated cycles of the Ar+
sputtering and the subsequent annealing at 700 K, asconfirmed by the low-energy electron diffraction(LEED) and the Shockley state in ARPES.
In Fig. 1, the Shockley state of CoPc/Au(111) iscompared with that of H2Pc/Au(111) and that of theclean Au(111) at 23 K. The Shockley state of both
CoPc/Au(111) and H2Pc/Au(111), labeled S’, shows
the lower-energy shift from that of the clean Au(111).
The upshift of the Shockley state originates from thePauli repulsion (exchange interaction) of surface
electrons by adsorbates. Furthermore, one moredispersive band just below the Fermi level (EF) isobserved for CoPc/Au(111), labeled X, which cannot
be observed for H2Pc/Au(111).
As shown in the inset of Fig. 2, the CoPc/Au(111)interface forms an interface state of the Co 3d character(labeled H’), just above the original highest- occupied
molecular orbital of the C 2p character (HOMO,
labeled H), due to the strong interaction between the
Co atom in the molecule and the Au surface, and is notobserved for H2Pc/Au(111). The observed dispersive
band X in Fig. 1 might thus originate from the sitespecific Co-Au interaction at the CoPc/Au(111)interface. On the other hand, band S’ mainly originatesfrom the interfacial interaction between the Pc-ringsite and the Au surface.
In order to examine the site-specific interfacialinteraction, we measured the temperature dependenceof the Shockley state of CoPc/Au(111) at the Γ point(kΓM = 0 Å−1). The Shockley state of the clean Au(111),
labeled S, shows the higher-energy shift with131

decreasing the temperature due to the contraction of
the bulk-crystal lattice constant. A similar behavior isobserved for peak S’ of CoPc /Au(111). However, theamounts of the energy shift is different; ΔE(S) = 60
meV for the clean Au(111) and ΔE(S’) = 42 meV for
CoPc/Au(111) at 299→23 K. The energy difference byΔE(S’)−ΔE(S) = −18 meV is ascribed to the differencein the Pauli repulsion at the interface due to thenarrowing of the bonding distance between the Pc ringand the Au surface with decreasing the temperature.
Peak X shows the lower- energy shift with decreasing
the temperature by ΔE(X) = −25 meV, indicating thestronger interaction at the Co site than the Pc-ring sitewith the Au surface. From the present observation andRef. [1], the interfacial bonding strength of
CoPc/Au(111) at 23 K is determined as 13.0 meV/Å2
at the Pc-ring site and 45.9 meV/Å2 at the Co site.

Ⅲ- 4Fig. 1. The E-k map around the Shockley state for
CoPc/Au(111) and H2Pc/Au(111) at 23 K, together
with the best-fit curve of the Shockley state for theclean Au(111) at 23 K (black dashed curve).

Fig. 2. Temperature dependence of the Shockley stateof CoPc /Au(111) and Au(111) at the Γ point. The
ARPES near the HOMO are shown in the inset.
[1] J. Ziroff et al., Surf. Sci. 603 (2009) 354.

891_Ⅳ_BL6U_9001_山根宏之.docx
Ⅲ -4. Surface,
Interface and Thin Films

BL6U

Band Structure Modification of Graphene by Bi Intercalation
1

Ⅲ- 4

Y. Sohn1,2, S. W. Jung1,2, M. Huh1,2, K. Kwon1, H. Yamane3, N. Kosugi3 and K. S. Kim1,2

Department of Physics, Pohang University of Science and Technology (POSTECH), Pohang 37673, Republic of
Korea
2
Center for Artificial Low Dimensional Electronic Systems, Institute for Basic Science (IBS), Pohang 37673,
Republic of Korea
3
Department of Photo-Molecular Science, Institute for Molecular Science, Okazaki 444-8585, Japan

Graphene, a two-dimensional atomic crystal with
the Dirac band structure, can be grown on the surfaceof SiC(0001) [1]. It has been well known thatintercalating atoms between the epitaxial graphene
layer and SiC(0001) can not only decouple graphenefrom the substrate, but also modify the low-energy
band structure such as doping level, band gap, and spin
splitting [2-4]. In this report, we have investigated theband structure of graphene modified by theintercalation of heavy-Z atoms with angle- resolved
photoemission spectroscopy (ARPES).
We first prepared zero-layer graphene samples,
where a single graphitic layer is strongly bonded to thesurface atoms of SiC(0001) and lacks the well-known
linear π bands. The zero-layer sample was fabricatedby thermal sublimation of surface Si atoms out of the
SiC(0001) substrate at high temperature. Bismuth (Bi)was then deposited on the zero-layer sample at room
temperature followed by mild annealing at elevatedtemperatures. ARPES and core-level spectroscopy
measurement were performed at the in-vacuum
undulator beamline BL6U, UVSOR, equipped with ahigh-performance hemispherical electron analyzer.
The overall energy and momentum resolutions were
better than 0.02 eV and 0.002 Å−1, respectively. Data
were collected at 60 K with the photon energy of 100
eV.
We checked the intercalation of Bi by using lowenergy electron diffraction (LEED) and core-level
spectroscopy. After intercalation we observed that
(1×1) spot of SiC(0001) is suppressed, while that ofgraphene layer remains unchanged. (6√3×6√3)R30°
spot, which originates from the lattice mismatch
between SiC(0001) and the graphene layer is also
suppressed. Bi 5d5/2 core-level spectra is observed to
be shifted by 0.18 eV after intercalation, and the peak
position does not change with the sample annealed up
to 1200°C. Figure 1 shows a wide-scale ARPES dataof Bi-intercalated graphene, taken near the Fermi
energy along the ΓK direction of the hexagonal
Brillouin zone. Graphene π bands clearly appear after
intercalation, demonstrating that graphene iseffectively decoupled from the SiC(0001) substrate.
From the above facts, we concluded that Bi is
successfully intercalated beneath the graphene layer.
Further ARPES studies are underway to observe thesystematic evolution of the band structure.

Fig. 1. Band dispersion along the ΓK direction of Biintercalated graphene.
[1] K. V. Emtsev et al., Nat. Mater. 8 (2009) 203.
[2] I. Gierz et al., Phys. Rev. B 81 (2010) 235408.
[3] D. Marchenko et al., Nature comm. 3 (2012) 1232.
[4] A. Varykhalov et al., Nature comm. 6 (2015) 7610.

132901_Ⅳ_BL7U_530_中山泰生.docx

Ⅲ -4. Surface, Interface and Thin Films

BL7U

Angle Resolved Photoelectron Spectroscopyon the Clean Surface of the Pentacene Single Crystal
M. Hikasa1, Y. Mizuno2, S. Ideta3, K. Tanaka3, H. Ishii2,4 and Y. Nakayama1

Department of Pure and Applied Chemistry, Faculty of Science and Technology, Tokyo University of Science,
Noda 278-8510, Japan
2
Graduate School of Advanced Integration Science, Chiba University, Chiba 263-8522, Japan
3
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
4
Center for Frontier Science, Chiba University, Chiba 263-8522, Japan1

Pentacene (C22H14) single crystal (Pn-SC) is a
representative p-type organic field effect transistor
material, which indicating a high charge carrier
mobility larger than 30 cm2V-1s-1 at room temperature[1]. Therefore, its valence band structures are ofparticular interest. As reported previously [2], ourgroup succeeded in valence band dispersion
measurements of the Pn-SC by angle-resolved
photoelectron spectroscopy (ARPES). However,previous ARPES results were obtained on Pn-SC
samples which had exposed to ambient air and thus are
known to be contaminated by several percent of oxide
at their surfaces [3]. On the other hand, in the case of
the single crystal of tetracene, a sister molecule ofpentacene, existence of the “surface band” waspredicted because of surface relaxation [4]. Therefore,
ARPES measurements on the clean surface are
required in order to clarify the true valence band
structures of Pn-SC.
In the present study, photoconductivity-assisted
ARPES measurements [5] were performed on the PnSC clean surface prepared by vacuum cleavage.
Extraction of a spectral contribution of the surface
bands was attempted through excitation energy
dependent measurements.
Plate-shaped (typically several mm2 wide and a few
μm thick) Pn-SCs were produced by a physical vapor
transport technique, which were selected and posted
onto conductive carbon tape individually. Ag glue wasadditionally pasted at the rim of each crystal to ensure
good electric conductivity. A strip of adhesive tape wascarefully attached onto the top side of the Pn-SC
sample prior to introduction into the ultra-high vacuum
condition. The Pn-SC clean surface was obtained bycleaving that top side off together with the adhesive
tape in vacuum. ARPES measurements were carriedout at BL7U of UVSOR. The excitation photon energy(hν) was set at 8.0 eV and 21.2 eV in this study. In
order to cancel sample charging, the sample wasshined by continuous wave laser light (405 nm) during
the measurements [2-4, 6]. All ARPES measurements
were performed at room temperature.
Figures 1(a) and (b) show the ARPES spectra of PnSC (measured with the excitation energy of 8.0 eV and
21.2 eV respectively. The former spectra transform bychanging emission angle as seen in Fig. 1(a). The
probing depth at the valence band region in thiscondition is known to be several nanometer [7]. In
other words, energy dispersion of the valence bands of
the Pn-SC clean surface was observed in a bulk
sensitive condition.
In contrast, the ARPES spectra taken at hν = 21.2 eV
do not exhibit apparent dependence on the emission
angle. Note that the probing depth in this condition isin the order of sub-nm, namely shallower than one
molecular layer of Pn-SC. This implies a shrinkage ofthe surface valence bands with respect to the bulk ones
as predicted in the literature [4]. More precise
excitation energy dependence is anticipated in order toclarify the detailed structures of the surface valencebands.

Ⅲ- 4

Fig. 1. (a) Bulk-sensitive (hν = 8.0 eV) and (b)surface-sensitive (21.2 eV) ARPES spectra of Pn-SC.
[1] O. D. Jurchescu et al., Appl. Phys. Lett. 84 (2004)
3061.
[2] Y. Nakayama et al., UVSOR Activity Reports 42(2015) 88.
[3] Y. Nakayama et al., J. Phys.: Cond. Matter 28(2016) 094001.
[4] H. Morisaki et al., Nat. Commun. 5 (2014) 5400.
[5] S. Machida et al., Phys. Rev. Lett. 104 (2010)
156401.
[6] Y. Nakayama et al., Jpn. J. Appl. Phys. 53 (2014)
01AD03.
[7] Y. Ozawa, et al., J. Electron Spectrosc. Relat.
Phenom. 197 (2014) 17.

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Ⅲ -4. Surface,
Interface and Thin Films

BL7U

Electronic Structure of a Monolayer h-BN
1

Y. Sugiyama , Y. Okuyama1, C. Bernard2, S. Ideta3, K. Tanaka3, T. Greber2 and T. Hirahara1
Department of Physics, Tokyo Institute of Technology, Tokyo 152-8551, Japan2
Physik-Institut, Universit ̈at Zu ̈rich, CH 8057 Zu ̈rich, Switzerland
3
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan

1

Ⅲ- 4

Silicene is a monolayer sheet of silicon and believed
to host Dirac electrons similar to graphene [1,2].
Experimental studies have been extensively performed
recently to reveal the presence of the Dirac-cone-type
bands and associated intriguing properties. However,the strong substrate-silicene interaction hinders theexotic properties related to the Dirac physics. For
example, we have previously shown that when we try
to grown silicene on Ag(111), the Ag atoms from thesubstrate segregate to the surface of the deposited Si
film and the well-known Si(111)3x3-Ag structure isformed [3].
One way to get around this problem is to use asubstrate that weakly interacts with Si. Usually an
insulating material is the right choice. In this respect,hexagonal boron-nitride (h-BN), which is a large gap
insulator, should be an ideal substrate. It has beenutilized as a substrate for graphene and thisgraphene/h-BN system was shown to host fascinating
physical properties [4]. Furthermore, silicene formedon h-BN was shown by first-principles calculations tomaintain the Dirac-like dispersion [5].
In the present study, we have measured theelectronic structure of a monolayer h-BN formed onRh(111)withhigh-resolution
angle-resolved
photoemission spectroscopy (ARPES). The samples
were prepared in an ultrahigh vacuum (UHV) system
in Switzerland and taken out into air. After they weretransported to Japan, they were installed in an UHVchamber and annealed at ~500C for 30 minutes. Lowenergy electron diffraction (LEED) measurements
showed sharp spots corresponding to h-BN, Rh(111),
as well as the superstructure. Then the h-BN/Rh(111)
samples were hydrogenated to flatten the h-BN since
the original h-BN/Rh(111) system is buckled due to theinteraction among h-BN and Rh(111) [6]. Figure 1
shows the band dispersion of the flattened h-BN
measure with ARPES. One can find states near the
Fermi level that correspond to the substrate Rh. Below
the binding energy of 5eV, one can find σ and π statesthat originate from the h-BN. Thus we have succeededin preparing an atomically flat h-BN, and thus hope toactually grow silicene and other group IV and V
monolayer systems.

Fig. 1. The band dispersion of h-Bn/Rh(111) systemmeasured at hν = 21 eV with p-polarization.
[1] K. Takeda and K. Shiraishi, Phys. Rev. B 50 (1994)
14916.
[2] S. Cahangirov et al., Phys. Rev. Lett. 102 (2009)
236804.
[3] T. Shirai et al., Phys. Rev. B 89 (2014) 241403.
[4] C. R. Dean et al., Nature Nanotech. 5 (2010) 722.
[5] Z.-X. Guo et al., Phys. Rev. B 87 (2013) 235435.
[6] T. Brugger et al., Angew. Chem. Int. Ed. 49 (2010)
6120.

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921_Ⅳ_BL7U_534-811_解良聡.docx

Ⅲ -4. Surface, Interface and Thin Films

BL7U

Scattering of Photoelectrons from Graphite via Organic Molecular
Monolayer
T. Yamaguchi1, 2, F. Bussolotti2, K. Kimura3, M. Matsunami2,3, S. Ideta2,3, K. Tanaka2,3,
T. Ueba2,3 and S. Kera1, 2, 3
1

Graduate School of Advanced Integration Science, Chiba University, Chiba 263-8522, Japan
2
Institute for Molecular Science, Okazaki 444-8585, Japan3
School of Physical Sciences, SOKENDAI, Okazaki 444-8585, Japan
kera@ims.ac.jp

Electron scattering governs fundamental properties
in solids, such as thermal and electron conductivity.
Recently, photoelectron scattering by phonons ofgraphite was discovered by low-energy angle resolved
ultraviolet photoelectron spectroscopy (LE-ARUPS)[1]. In this work, we observed scattering phenomenaof the photoelectron from graphite via organicmonolayer interfaces using LE-ARUPS at beam line
BL7U.
Figure 1 (a) shows LE-ARUPS intensity maps along
Γ-K axis for a clean single crystal graphite (SCG).
Fig.1 (b-h) depict pentacene (PEN), zincphthalocyanine (ZnPc) and tin phthalocyanine
dichloride (SnCl2Pc) monolayers prepared either on
SCG or highly oriented pyrolytic graphite (HOPG)
substrates. Several linearly dispersive bands with thesame slope parameter to the clean SCG band areobserved in Fig.1 (b-h), indicating that the origin of

these features is photoelectron scattering of graphite πbands by molecular film. The scattering vector
depends on the molecule and the measured
temperature. We suggest that the features reflect
reciprocal vectors of molecular unit cell of monolayer
films. However, there are 6 domains for PEN andgeneral Pc-type molecules on the graphite, whichmeans reciprocal vectors do not match to the graphite
ones [2, 3], leading to complicated scattering process.
To understand a pure nature of these features, acommensurate superstructure of molecular systemshould be measured.
[1] S. Tanaka et. al., Sci. Rep. 3 (2013) 3031.
[2] T. G. Gopakumar et. al., J. Phys. Chem. B 108(2004) 7839.
[3] J. Götzen et. al., Phys. Rev. B 81 (2010) 085440.

Fig. 1. E(k) intensity maps taken at hν=40eV for (a)bare SCG at room temperature (RT) and at 11eV for themonolayers; (b)ZnPc/SCG at 166K, SnCl2Pc/SCG at (c)11K and (d)164K, ZnPc/HOPG at (e)11K and (f)142K,
and PEN/HOPG at (g)14K and (h)145K. The image was obtained along Γ-K direction for (a-d). Inset spectra show
momentum distribution curves at Fermi energy (EF) integrated EF±25meV. Dashed lines represent the linearly
dispersive band with the same slope to the SCG band. The numbers in the maps indicate the momentum (Å-1)
where the linearly dispersive band crosses the EF.

135

Ⅲ- 4

931_Ⅳ_BL7U_542-816_木村真一.docx
Ⅲ -4. Surface,
Interface and Thin Films

BL7U

ARPES of a Kondo Insulator YbB12(001) Surface
K. Hagiwara1, Y. Ohtsubo1, 2, J. Kishi1, M. Matunami3, S. Ideta3, K. Tanaka3, T. Ito4,
H. Miyazaki5, F. Iga6 and S. Kimura1, 2
Graduate School of Science, Osaka University, Toyonaka 565-0043, Japan
Graduate School of Frontier Biosciences, Osaka University, Suita 565-0871, Japan
3
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
4
Department of Materials Engineering, Nagoya University, Nagoya 464-8603, Japan
5
Department of Frontier Materials, Nagoya Institute of Technology, Nagoya 466-8555, Japan
6
Department of Physics, Ibaraki University, Mito 310-8512, Japan
1

2

Ⅲ- 4

Recently, non-trivial topology of the electronic
states on Kondo insulator (KI), so-called topological
Kondo insulator (TKI) [1], is one of hot topics in solidstate physics as a synergy effect between strong
electron correlation and spin-orbit interaction. SmB6, awell-known KI, is firstly argued as a candidate of TKI.
Earlier angle-resolved photoelectron spectroscopy(ARPES) experiments revealed metallic surface states
on SmB6 [2], but its origin and the topological order of
SmB6 is still under debate [3]. Therefore, a survey ofanother material is desirable to provide further insight
into the origin of metallic surface states on KIs.
In this work, we performed high-resolution ARPES
experiments of the surface electronic structure ofanother Kondo insulator, YbB12(001) [4] at BL7U of
UVSOR-III. We prepared the well-ordered surfaces of
YbB12 (001) by heating the sample up to 1600 K in a
preparation chamber at the BL7U end station. The
quality of the clean surface was checked by lowenergy electron diffraction (LEED) as well as ARPES.
Figure 1 is the band dispersions along [100]. A bandwith steep dispersion below 100 meV would be a
conduction band. This band becomes less dispersive
around 35 meV, probably due to the hybridization withlocalized Yb2+ 4f bands. Such hybridization between
conduction and 4f bands would be driven by the Kondo
effect.
In addition to these states, we observed another stateclearly crossing EF at k//[100] ~ 0.18 Å-1, as shown by the
momentum distribution curve in Fig. 1. Since the bulk
electronic structure of YbB12 has a bandgap at thistemperature (~20 K), this metallic band originatesfrom surface electronic structure. This metallic surface
state can be a cause of the remnant conduction path of
YbB12 observed at low temperature.
Figure 2 is the constant energy contour at EF (10meV).
It shows closed Fermi contour surrounding the＿, a time-reversal-invariant momentum. This behaviorof the metallic surface state suggests its origin from the
topological order.
These results at low temperatures agree with what is
expected for a surface state on a theory of the
topological Kondo insulator [1].

Fig. 1. ARPES intensity plots along [100] near EF
taken with 16.5 eV photons (bottom) and momentum
distribution curves at EF (±10 meV) (top). Lines in thebottom figure are guides the eyes. Each data are
divided by the Fermi distribution function at the
sample temperature (20 K) convolved with the
instrumental resolution.

Fig. 2. Constant energy contour at EF (10 meV)taken with 16.5 eV photons at 14 K.
[1] M. Dzero et al., Phys. Rev. Lett. 104 (2010) 106408.
[2] H. Miyazaki et al., Phys. Rev. B 86 (2012) 075105.
[3] P. Hlawenka et al., arXiv:1502.01542.
[4] F. Iga et al., JMMM 177-181 (1998) 377.

136

Ⅲ -4. Surface, Interface and Thin Films

941_Ⅳ_BL7U_819_横谷尚睦.docx

BL7U

Surface Electronic Structure Studies of High Quality CrO2(001) Films
1

H. Fujiwara1, M. Sunagawa1, K. Terashima1,2, T. Nagayama1, T. Kittaka1, M. Ogata1,
S. Ideta3, K. Tanaka3, T. Wakita1,2, Y. Muraoka1,2 and T. Yokoya1,2

Research Laboratory for Surface Science and Graduate School of Natural Science and Technology, Okayama
University, Okayama 700-8530, Japan
2
Research Center of New Functional Materials for Energy Production, Storage, and Transport, Okayama
University, Okayama 700-8530, Japan
3
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan

Chromium dioxide, CrO2, is a half-metallic
ferromagnet whose spin polarization at Fermi energy
is 100% [1]. Previous studies of spin-resolved
photoemission spectroscopy (spin-resolved PES) on
CrO2 films reported insulating-like photoemission
spectra [2], while the temperature-dependence ofresistivity of CrO2 is metallic. As the reason of theinsulating-like Fermi edge, reconstructions of
CrO2(001) surface has been theoretically suggested.
However, it is also known that the surface of CrO2
easily transforms into antiferromagnetic insulator
Cr2O3 [3]. Due to the existence of Cr2O3, it has beendifficult to discuss the intrinsic electronic states ofRecently, our group has
CrO2(001) surface.
succeeded in preparing high quality CrO2(100) films
by the closed system chemical vapor deposition(CVD) method using Cr8O21 as a precursor [4]. The
photoemission spectrum of our CrO2(100) film showsa peak at 1 eV with a clear Fermi edge, indicating that
there are few contaminants of Cr2O3 on the surface of
our sample. In this study, we prepared CrO2(001)epitaxial films on TiO2 substrates with the closed
system CVD method and investigated the electronic
structure of the CrO2(001) surface by PES withsynchrotron radiation. In this report, we show photon
energy dependence of PES spectra and discuss thesurface-metallicity of CrO2(001) films.
The PES measurements were carried out at BL-7U
in UVSOR. The photon energies between 15 eV and
33 eV were used in our measurement. The energy
resolution was approximately 15 meV when photon
energy of 21 eV.
Figure 1(a) shows the near-EF valence band PES
spectra taken at hν = 15 eV and 33 eV. Both spectra
show clear Fermi edge. In the spectrum taken at hν =33 eV, the intensity is higher than one of spectrum
taken at hν = 15 eV because of the difference in crosssection of Cr 3d and O 2p bands, indicating that the Cr
3d and O 2p bands are hybridized at least in the energy
region between EB = 0.7 eV and EF.
Figure 1(b) shows difference spectrum of hν = 33
eV with hν = 15 eV in order to emphasize the surface
components of the CrO2(001) film. As seen in Fig.
1(b), two peaks at EB = 0.5 eV and at EF were observed,
indicating that these structures are surface derived
bands. It should be noted that the observation of clear
Fermi edge indicates existence of metallic (001)surface states, which has not been predicted in band

Difference intensity(arb. units)

Intensity (arb. units)

calculations [5] assuming that oxygen atoms in
CrO2(001) surface is reconstructed into tetrahedral
arrangement. On the other hand, the observed surface
states are consistent with band calculations [6]assuming that the oxygen atoms remain in octahedral
arrangement, which indicates that the surface
reconstruction does not occur.
In summary, we investigated the photon energy
dependence of photoemission spectra of CrO2(001)film in order to clarify the surface electronic states.
The metallic surface states were observed, consistent
with the band calculations not considering surface
reconstruction.
(a)

(b)

hv =
15 eV
33 eV

0.5
E0F
Binding energy (eV)(hv = 33 eV) - (hv = 15 eV)
0.5
E0F
Binding energy (eV)Fig. 1. (a) Near-EF valence band PES spectra of the
CrO2(001) film at 15 K taken at hν = 15 eV and 33 eV.
These spectra are normalized at EB = 0.7 eV. (b) The
surface states of the CrO2(001) film determined fromthe difference between spectra taken at 33 eV and 15
eV.
[1] H. Fujiwara et al., Appl. Phys. Lett. 106 (2015)
202404.
[2] K. P. Kämper et al., Phys. Rev. Lett. 59 (1987) 2788.
[3] R. Cheng et al., Appl. Phys. Lett. 79 (2001) 3122.
[4] K. Iwai et al., J. Appl. Phys. 108 (2010) 043916.
[5] F. Hong et al., Phys. Rev. Lett. 96 (2006) 167206.
[6] H. van Leuken et al., Phys. Rev. B 51 (1995) 7176.

137

Ⅲ- 4

951_Ⅳ_BL7B_824_小野晋吾.docx
Ⅲ -4. Surface,
Interface and Thin Films

BL7B

Development of Photoconductive Detector Based on LaF3 Thin Film
S. Otani, R. Yamazaki, S. Kokuryu, K. Toyama and S. Ono
Nagoya Institute of Technology, Nagoya 466-8555, JapanⅢ- 4

According to increase in application of vacuum
ultraviolet (VUV) light source, the detector formonitoring the light source is required. Consequently,
the spectral response of the detector is demanded to
optimize for each light source. The spectral responseof the detector varies according to band gap of thematerial. Therefore, our group is proceeding todevelopment of the VUV detectors by using fluorides
which have extremely wide band gap [1, 2]. In our past
study, the detectors based on BaF2 and YF3 show
response below 147 nm and 170 nm, respectively. Here,
we report on the development of filterless VUVphotoconductive detector by using LaF3 thin film.
LaF3 thin film was deposited by pulsed laser
deposition (PLD) on the MgF2 single crystal substrate.
LaF3 ceramic target was irradiated with the
femtosecond laser pulses (wavelength: 790 nm, laser
fluence: 16.1 mJ/cm2). The deposition was carried out
4 h under high vacuum condition (2×10-4 Pa). The
temperature of the substrate was controlled at 670 K.
Figure 1 is scanning electron microscope (SEM)
images of YbF3 thin film. A sub-micron-sizedparticulates make up the majority of the deposition
layer.
To evaluate these thin films as photoconductive
detectors, a pair of interdigitated aluminum electrodes
was fabricated onto the thin film by vacuum deposition.
Photoconductivity of the detector was evaluated bymeasuring variation of the amperage by VUVirradiation. The amperage increased 1-digit by VUVirradiation as showan in Fig. 2. Additionally,transmission spectrum and spectral response of thedetector were measured. The transmission edge wasaround 115 nm in wavelength. The detector showedphotoconductivity below 161 nm in wavelength andthe response signal increased as the radiation
wavelength decreases (Fig. 3). Furthermore, response
speed of the detector was evaluated by measuring
temporal response of a VUV pulse by a flash lamp
(pulse duration: 10.1 μs). As a result, the temporal
waveform by the detector was equivalent to that of acommercially available detector based on diamond.
In summary, we achieved filterless VUVphotoconductive
detector
meetingpractical
performance by applying LaF3 thin film grown by PLD.

Fig. 1. SEM images of the surface and section of LaF3
thin films.

Fig. 2. I-V characteristic of LaF3 thin film.

Fig. 3. Transmission spectrum and spectral responseof the detector.
[1] M. Ieda, T. Ishimaru, S. Ono, K. Yamanoi, M.
Cadatal, T. Shimizu, N. Sarukura, K. Fukuda, T.
Suyama, Y. Yokota, T. Yanagida and A. Yoshikawa,
Jpn. J. Appl. Phys. 51 (2012) 022603.
[2] T. Ishimaru, M. Ieda, S. Ono, Y. Yokota, T.
Yanagida and A. Yoshikawa, Thin Solid Films 534(2013) 12.

138