Ⅲ-4
Surface,
Interface andThin Films

BL5UⅢ -4. Surface, Interface and Thin Films

BL5U

Polarization-dependent Photoelectron Intensity in Ca-doped Graphene
S. Ichinokura1, K. Tokuda1, K. Tanaka2 and T. Hirahara1

Department of Physics, Tokyo Institute of Technology, Tokyo 152-8551, Japan
2
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan

1

Orbital symmetry strongly influences the interaction
between light and electrons. When polarized light isirradiated on a material, the electronic excitation obeys
the dipole selection rule; electrons in orbitals with oddand even-parity are excited by s- and p-polarized light(described as s- and p-pol. hereafter), respectively.
Therefore, in angle-resolved photoemission spectroscopy(ARPES), complemental intensity maps will be obtained
when the s- and p-linear polarized lights are used.
The remarkable high-carrier mobility in grapheneoriginates from its characteristic π-orbital band called
Dirac cone. The light-matter interaction of graphene
through the π-electron has attracted considerable
attention. For example, the photoelectron intensity of
the Dirac electronic state varies cyclically on the kx-ky
plane for the polarized light [1]. Here, chirality plays
an essential role in polarization dependence. In Liintercalated bilayer graphene (C6LiC6), two Diraccones with different chirality overlap around the Γpoint of the Brillouin zone (BZ). The chiral symmetryis broken due to the lattice distortion by Li, leading to
the gap opening at the Dirac point. These properties
were clarified by laser-ARPES measurements [2].
Ca-intercalated graphite and graphene becomesuperconducting at relatively high temperatures inlayered and two-dimensional materials [3-5]. In
addition to the Dirac cones, a free-electron-like state
called interlayer band (ILB) exists as an occupied statein those systems. Since ILB has different symmetry
from π-band, dipole selection rule and chirality effects
are expected to coexist in C6CaC6.
To resolve the coexistence of the two effects, we
performed high-resolution polarization-dependent
ARPES measurements on Ca-intercalated bilayer
graphene, C6CaC6 at BL5U and BL7U. As shown in
Figure 1(a), C6CaC6 was prepared on a Ca-terminated
SiC substrate. Figure 1(b) shows the ARPES spectrum
obtained by s-pol. A double Dirac cone was seen. The
Dirac cones are folded into Γ point from K point of thegraphene’s BZ due to the √3×√3 periodicity of Ca. The
doubling is caused by the interlayer interaction
between two graphene layers.
On the other hand, a parabolic band (stressed bydashed line) was much more prominently observed
than the double Dirac cones when p-pol. is used, as
shown in Figure 1(c). The free-electron-like characteris consistent with the ILB. Since the spectrum by p-pol.
and s-pol. are complementary, dipole selection rulemainly determines the intensity distribution; odd- andeven-parity components are excited by s- and ppolarization, respectively.

Figures 1(d) and 1(e) show the photoelectron
intensity maps on the Fermi energy obtained for s- andp-polarized light. In Fig. 1(d), the photoelectron
intensity has an anisotropy; intensity map along Γ-Kand Γ-K’ direction (shown by dashed lines) is not
identical. On the other hand, in Fig. 1(e), the intensity
distribution is almost isotropic. Since the Dirac state ismainly excited by s-pol., the anisotropy is estimated tobe caused by chirality effect.
In conclusion, it was revealed that the dipole
selection rule has a stronger effect on the intensity
distribution of photoelectron in C6CaC6 than thechirality effect. Reflecting the different symmetry of πbands and ILB, complementary distribution wasobserved in the Fermi contour for the s- and p-polarized
light. The chirality effect appears as the anisotropy in
the Fermi contour of the Dirac cone component.

Ⅲ- 4Fig. 1. (a) Schematic atomic model of Ca-intercalated
bilayer graphene (C6CaC6) on Ca-terminated SiC
substrate. (b)-(c) Band structure of C6CaC6 around Γpoint, obtained by (b) s- and (c) p-polarized light.
Parabolic band is stressed by the dashed guideline. (d),(e) Intensity mapping at Fermi level using (d) s- and(e) p-polarized light. Γ-K and Γ-K’ direction are shownby dashed lines in (d). ARPES measurements were
performed with hν = 33 or 58 eV under T = 6 - 13 K.
[1] Y. Liu et al., Phys. Rev. Lett. 107 (2011) 166803.
[2] C. Bao et al., Phys. Rev. Lett. 126 (2021) 206804.
[3] T. E. Weller et al., Nat. Phys. 1 (2005) 39.
[4] S. Ichinokura et al., ACS Nano 10 (2016) 2761.
[5] H. Toyama et al., ACS Nano 16 (2022) 3582.

127 1 Ⅲ04-

BL3U
Ⅲ -4. Surface,
Interface and Thin Films

BL3U

Elucidation of the Function of Adsorbed Anions
on the Surface of Cobalt Catalysts by Operando Observation
K. Harada1, S. Tsunekawa1, A. Sakai1, M. Nagasaka2 and M. Yoshida1,3
Yamaguchi University, Ube 755-8611, Japan
Institute for Molecular Science, Okazaki 444-8585, Japan
3
Blue Energy Center for SGE Technology (BEST), Ube 755-8611, Japan
1

2

Ⅲ- 4

Recently, hydrogen production by electrolysis ofwater has been attracting attention. In this system,
cobalt catalysts are known to be one of the efficient
oxygen production catalysts [1]. Thus, various
spectroscopic analyses have applied to the catalysts inorder to investigate the physical properties andfunctions. However, the role of anions in the electrolyte
solution is still not fully understood. From thisbackground, in this study, the role of adsorbed anions
on cobalt catalysts was investigated by attenuated totalreflection infrared spectroscopy (ATR-IR) and X-ray
absorption fine structure (XAFS) measurements underoperando conditions.
The electrochemical cell was used with a Pt counterand an Ag/AgCl reference electrode. The cobalt catalyst
was prepared by electrodeposition on Au thin film in asolution containing Co2+ and carbonate anion (Co-Ci
catalyst). Under electrochemical control, the operando
Co K-edge XAFS were measured by fluorescence modein the PF BL-9A, and the operando O K-edge and C Kedge XAFS were measured by transmission mode at
BL3U in the UVSOR synchrotron.
First, we checked the OER activity and found that
Co-Ci functioned as highly efficient water splitting
catalyst. Next, SEM, EDX, and XPS measurements
were also performed to confirm that the catalyst waselectrodeposited on the substrate surface. Furthermore,
the electrolyte solution was exchanged from potassium
carbonate solution (K-Ci) to potassium sulfate solution(K-Si) during monitoring the OER activity, indicatingthat the water splitting activity of the Co-Ci catalyst was
improved in the K-Ci electrolyte solution.
To investigate the electronic state and local structure,
the operando Co K-edge XAFS measurements were
performed with the cobalt carbonate catalyst. EXAFS
analysis showed that the peaks of Co-O and Co-Co
bonds were observed at similar positions compared to
the CoOOH reference sample, suggesting that the
local structure of Co in the catalyst was consistent withthat of CoOOH.
Then, operando O K-edge XAFS was measured, andthe peak of Co(IV) as an active species [2-4] wasobserved at the electrode potential of water splitting
reaction. This indicates the occurrence of high oxidation
number Co in the Co-Ci catalyst at the catalytic active
potential.
Finally, the operando C K-edge XAFS measurements
under the catalytic reaction (Fig. 1) showed thatcarbonate ions were adsorbed on the catalyst surface.

The adsorbed peak was remained even after exchanging
the electrolyte solution from K-Ci to K-Si. In addition,
the same result was obtained in the operando ATR-IR
measurement. Therefore, these results suggest that the
carbonate ions are strongly adsorbed on the Co-Ci
catalyst to maintain the high oxidation number Co as
active site.

Fig. 1. Operando C-K edge XAFS spectra.

[1] W. Kanan, and D. G. Nocera, Science 321 (2008)
1072.
[2] A. M, Ullman, C. N. Brodsky, N. Li, S. L. Zheng,
and D. G. Nocera, J. Am. Chem. Soc. 138 (2016) 4229.
[3] L. P. Wang, and T. Van Voorhis, J. Phys. Chem. Lett.
2 (2011) 2200.
[4] X. Li, and P. E. M. Siegbahn, J. Am. Chem. Soc. 135(2013) 1380.

128 2 Ⅲ04-

BL3B

Ⅲ -4. Surface, Interface and Thin Films

BL3B

Evaluation of Interface Between Sapphire Substrate and UV Emitting Zinc
Aluminate Phosphor Thin Films
H. Kominami1, M. Endo2, T. Kawashima2, N. Sonoda2, K. Inoue2, N. Uesugi2,
K. Nie2, A. Adachi1, R. Ishihara1, Y. Kamoi1, A. Dorokhina3 and S.Kurosawa4,5

Graduate School of Integrated Science and Technology, Shizuoka University, Hamamatsu 432-8651, Japan
2
Faculty of Engineering, Shizuoka University, Hamamatsu 432-8651, Japan
3
Graduate School of Science and Technology, Shizuoka University, Hamamatsu 432-8651, Japan
4
New Industry Creation Hatchery Center (NICHe), Tohoku University, Sendai 980-8579, Japan
5
Faculty of science, Yamagata University, Yamagata 990-8560, Japan

1

The UV light is used for various applications
depending on the wavelength as well as the sterilization
described above. Recently, from the viewpoint ofconsideration to the environment, the mercury free UVemission devices have been demanded for theapplication of catalyst and medical situations. In ourprevious work, it was clarified that ZnAl2O4 phosphor
was suitable for the UV field emission lamp because of
its stability and luminescent property. It shows strong
UV emission peaked around 250 nm which suitable forsterilization.
In this research, ZnAl2O4 thin film layer wereprepared by thermal diffusion of ZnO and sapphire
substrate for new UV devices. To obtain ZnAl2O4 thinfilm with high quality, we explore optimum conditionof thermal annealing.
As a result of XRD of ZnAl2O4 annealed at 970 to1050 °C, it was found that the peaks of (220), (311)
and (333) appeared prominently, and polycrystalline
ZnAl2O4 was formed. Figure 1 shows the full width ofhalf maximum of diffraction peaks and these peakintensity ratio of each phase of ZnAl2O4 annealed at
970 to 1050 °C. Regarding the intensity ratio, theintensity ratio of each phase increased uniformly up to990 °C, but at 1050 °C, the intensity ratio increased
only in (333) and the intensity ratios of (220) and (311)decreased. From this result, it is considered that thegrowth is likely to occur in the orientation of (333)from a temperature exceeding a certain threshold valueof 990 °C or higher.
Next, for ZnAl2O4 (333) that selectively grows on thec-plane sapphire substrate, the orientation of the c-planesapphire substrate and the growth of ZnAl2O4 were
investigated by evaluating the in-plane orientation by Φ
scan measurement. Figure 2 shows a Φ scan of ZnAl2O4(333) annealed at 970 to 1050 °C. Diffraction of (333)with the c-plane sapphire substrate was observed at 60°
intervals. It is considered that both the c-plane sapphire
substrate and (333) have the atomic arrangement of
Aluminum atoms six-fold symmetric, and (333) has
grown to inherit the six-fold symmetry of Aluminum of
the c-plane sapphire substrate.
ZnAl2O4 was prepared at 970 to 1050 °C andevaluated by CL, XRD, SEM and the like. From the
XRD results, it was found that the orientation of

ZnAl2O4 (333) facilitates growth from temperatures
above a certain threshold of 990 °C or higher. From
the results of the Φ scan measurement, it is consideredthat (333) grows so as to inherit the six-fold symmetryof the atomic arrangement of Aluminum in the c-planesapphire substrate.

Ⅲ- 4

Fig. 1 ependence of FWHM and XRD Peak intensityof ZnAl2O4 thin films on annealing temperature.

Fig. 2 Φ-scan of ZnAl2O4 (333) on c-plane sapphire
substrate.

129 3 Ⅲ04-

BL4U
Ⅲ -4. Surface,
Interface and Thin Films

BL4U

Application of Atomically-thin Graphene to X-ray Astronomy:
Soft X-ray Transmission Measurements
I. Mitsuishi1, K. Kashiwakura1, Y. Niwa1, T. Ogawa1, M. Hirota1, Y. Tawara1, R. Kitaura2,
P. Solís-Fernández3, K. Kawahara3, H. Ago3, T. Taniguchi4, K. Nomoto4, H. Kodaka4,
T. Ohigashi5, H. Yuzawa5 and K. Tanaka5
Graduate School of Science, Division of Particle and Astrophysical Science, Nagoya University,
Nagoya 464-8602, Japan2
Department of Chemistry, Nagoya University, Nagoya 464-8602, Japan3
Global Innovation Center, Kyushu University, Kasuga 816-8580, Japan
4
Optical Measurement Technology Development Department, R&D Division, USHIO INC.,
Yokohama 225-0004, Japan
5
UVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan

1>89% corresponding to >97% for single-layer graphene
although the transmission goes down to ~80 % in the C
K-edge structure corresponding to ~95% for singlelayer graphene as shown in Fig. 1 (Mitsuishi et al., in
prep.). To investigate the impact of residual of thecoated material, PMMA, on the free-standing graphene
structure used in our fabrication process, we obtainedtransmission around the O K-edge structure even though
the coated material was removed by using acetone. The
observed transmission in 520—564 eV ranges from 95
to 98% and thus no strong contamination was found. To
estimate the transmission more accurately, a systematic
error such as a variation in the beam intensity should betaken into account in the near future.
Experimental setup

SEM imagefor free-standing 5-layer graphene

X - ray1

20mm

Transmission for 5-layer graphene(Mitsuishi et al., in prep.)
1-layer graphene (estimated)

Transmission

Ⅲ- 4Thin films have been used in a variety of academic
fields including astronomy. In X-ray astronomy,
because X-rays are absorbed by the atmosphere of the
Earth, balloons, rockets, and satellites are often used toobserve X-rays from astronomical objects such as black
holes, neutron stars, clusters of galaxies, and so on. Thinfilm devices have often been used in payloads ofprevious missions and playing a key role as, e.g., opticaland contamination blocking filters and thermal shields[e.g., 1,2]. For such thin film devices, tolerance forsevere launch and space environments and hightransmission for more efficient use of limited observing
time are required at the same time. Polyimide films haveoften been adopted because of relatively higher
mechanical strength and heat tolerance in plastic
materials. However, there is still room for improvement
especially in transmission of a soft energy band below
1 keV. Thus, we have proposed to make use of graphene
which is an atomically-thin material but has excellent
mechanical and thermal properties at the same time. Ouridea is to apply graphene to thin film devices in X-ray
astronomy for the first time.
As a first step, we need to conduct X-ray transmission
measurements to verify whether the transmission ofgraphene films especially in a soft energy band isactually high or not as expected because, as far as weknow, no observed data is available except around 300
eV corresponding to the C K-edge structure. We
prepared 5-layer free-standing graphene on a quartz
substrate with a thickness of 200 µm with through holes
with a diameter of 10 µm. To measure the number of Xray photons with/without the 5-layer free-standing
graphene collected by the Fresnel zone plate correctly,
a taper structure with a taper angle of 30 degrees was
prepared for each free-standing structure. The sample inthe vacuum chamber and a close-up SEM image of thefree-standing 5-layer graphene are shown in Fig. 1.
Consequently, we obtained the transmission in 100, 140,
180, 220, 260, 340, 380, 420, 460, 500 eV, and the C Kedge structure between 280 and 320 eV in details
successfully and confirmed that the observed
transmission is very high as expected on the order of

0.9

5-layer graphene
0.8

Quartz wafer with free- 280
standing 5-layer graphene

300

Energy [eV]320

Fig. 1. Experimental setup with our sample and an
example of the observed soft X-ray transmission curve.

[1] P.J. Serlemitos et al., Publ. Astron. Soc. Japan 47(1995) 105-114.
[2] P.J. Serlemitos et al., Publ. Astron. Soc. Japan 59(2007) S9-S21.

130 4 Ⅲ04-

BL4B

Ⅲ -4. Surface, Interface and Thin Films

BL4B

Annealing Effect on the Vacuum Ultraviolet Transmission Spectrum of
Amorphous Selenium
K. Hayashi

Department of Electrical, Electronic and Computer Engineering, Gifu University, Gifu 501-1193, JapanThe decrease in the photoconductivity and the dark
conductivity by long exposure to bandgap light havebeen observed in hydrogenated amorphous silicon [1]and amorphous chalcogenide materials [2]. This effectis usually called photodegradation and is explained in
the creation of light-induced metastable defects (LIMD).
Many models have been proposed for LIMD creation,
but details of the mechanism for LIMD creation in thesematerials are still not clear. Recently, we have observedchanges in photoconductivity in amorphous chalcogenide
materials that cannot be explained by the creation of
LIMD. The x-ray diffraction and the volume change ofthe films before and after irradiation of bandgap lightsuggest that the photoinduced phenomena is due to achange of the local structure of the amorphous network.
Understanding the physical mechanism underlying
metastability is one of the important fundamental
problems related to these materials. In the previous
reports, we reported the photoinduced effects on thevacuum ultraviolet (VUV) transmission spectrum ofamorphous arsenic triselenide by the irradiation of the
bandgap light. In this report, we study the annealing
effect on the VUV transmission spectrum of amorphousselenium.
Sample used for the measurement of the VUVtransmission spectra was amorphous Se (a-Se) thin film
prepared onto thin aluminum film by conventional
evaporation technique. The sample thickness was about
180nm. The aluminum film of the thickness of 200 nm
was used to eliminate the higher order light from themonochromator in the VUV region. These measurements
were carried out at room temperature on the BL4B
beam line of UVSOR. The spectrum was measured byusing the silicon photodiode as a detector. Two pinholesof 1.5mm in a diameter were inserted between the
monochromator and sample to remove stray light. The
intensity of the VUV light was monitored by measuring
the TPEY of a gold mesh. The positions of the corelevels for the samples were calibrated by referencing to
the 2p core level absorption of the aluminum film.
Figure 1 shows annealing effect on the VUVtransmission spectra of amorphous Se thin film. The
VUV transmission spectrum of amorphous As2Se3 isalso shown on the figure for reference. Annealing effecton the VUV transmission spectrum was investigated byannealing the amorphous Se with 353 K for 1 hour.
Amorphous Se is thought to crystallize (polycrystalline)
at this annealing temperature. As shown in the figure,each spectrum is very broad and multiple shoulders areobserved. The absorption spectrum observed in theamorphous Se is roughly consistent with the previous

report [3]. Main absorption peaks around 22nm
corresponds to the 3d core level of Se atom. Although
the wavelength resolutions in the spectral
measurements are all the same, the spin-orbit splittingof the 3d5/2 and 3d3/2 level of Se atom is clearly resolvedin amorphous As2Se3, while they are not clearly
resolved in as-deposited amorphous Se and annealed
amorphous Se. When amorphous Se crystallizes byannealing, it can be seen that the broad peak around 20
nm was composed of about three absorption peaks. It is
not clear about the origin of broad spectra and several
peaks. I think that these origins are related to the local
structures of the amorphous network. The detailed
experiments and analysis will be done in the next step.
More detailed experiments are necessary to clarify theorigin of the VUV transmission spectra.

Ⅲ- 4Fig. 1. Annealing effect on the VUV transmission
spectra of a-Se thin film.

[1] D. L. Staebler and C. R. Wronski, Appl. Phys. Lett.
31 (1977) 292.
[2]K. Shimakawa, S. Inami, and S. R. Elliott, Phys. Rev.
B 42 (1990) 11857.
[3] J. Bordas and J. B. West, Phil. Mag. 34 (1976) 501.

131 5 Ⅲ04-

BL4BInterface and Thin Films
Ⅲ -4. Surface,

BL4B

Magnetic Properties of CoPc/γ’-Fe4N Organic-inorganic Hybrid Interface
T. Miyamachi1,2, H. Ono1, Y. Umeda1, K. Yamamoto3,4, O. Ishiyama3,4, T. Yokoyama3,4and M. Mizuguchi1,2Department of Materials Science and Engineering, Nagoya University, Nagoya 464-8603, Japan.
Institute of Materials and Systems for Sustainability (IMaSS), Nagoya University, Nagoya 464-8601, Japan.
3
Institute for Molecular Science, Okazaki 444-8585, Japan
4
The Graduate University for Advanced Studies (SOKENDAI), Okazaki 444-8585, Japan
1

2

Ⅲ- 4

Organic materials are expected to be useful to
spintronics devices due to their low spin current
dissipation derived from weak spin-orbit interaction.
In particular, an organic-inorganic hybrid interface has
attracted much attention because its interface spin state
can be controlled via the proximity effect. Spindependent electron transport properties of organicinorganic hybrid system strongly depend on thedomain size of organic molecular films, defect density
and adsorption geometry of organic molecules. Thus,
understanding structural, electronic and magnetic
properties of the organic-inorganic interface on thelevel of single molecules is essential for realizing
molecular spintronics devices. However, microscopic
details of the hybrid interface have not been clarified
so far.
In this study, we focus on fabricating organicinorganic hybrid films with structurally controlledinterface on the level of single molecules andinvestigating their intrinsic electronic and magnetic
properties. For this purpose, ferromagnetic iron nitride
atomic layers with γ’-Fe4N stoichiometry were chosen
as an inorganic material, which uniformly grow andshow high surface quality on the atomic scale [1,2].
Molecular layers composed of planer cobalt
phthalocyanine (CoPc) were chosen as an organic
material. Structural, electronic and magnetic propertiesof the hybrid interface composed of CoPc with the
thickness of 1, 2 and 3 molecular layers and a bilayer γ’Fe4N were investigated by scanning tunneling microscopy(STM), low energy electron diffraction (LEED) and xray absorption spectroscopy/magnetic circular dichroism(XAS/XMCD).
A bilayer γ’-Fe4N was prepared by iron deposition on
Cu (001) with N+ ion bombardment and subsequentannealing at 620 K. Then, CoPc/γ’-Fe4N hybrid thinfilms were fabricated by depositing CoPc on the γ’Fe4N at room temperature. In combination with resultsof STM and LEED, the impact of the thickness of CoPc
layers on the interfacial magnetic state was investigated
by XAS/XMCD.
XAS/XMCD measurements were performed at
BL4B in UVSOR by total electron yield mode at B = 0- ± 5 T and T = 7.3 K. The XMCD spectra are obtainedat the normal (NI: θ = 0°) and the grazing (GI: θ = 55°)
geometries by detecting μ+ – μ–, where μ+ (μ–) denotes
the XAS recorded at Fe and Co L adsorption edges withthe photon helicity parallel (antiparallel) to the sample
magnetization. Note that θ is the angle between thesample normal and the incident x-ray [3].
We find that the Fe orbital magnetic moment of thebilayer γ’-Fe4N evaluated by XMCD sum rule analysis
changes with increasing thickness of the CoPc layer.
The difference between the out-of-plane and in-plane Fe
orbital magnetic moment, which is proportional to themagnetic anisotropy [4], is the largest when about one
CoPc layer is deposited on the γ’-Fe4N and it decreases
with further increasing thickness of the CoPc layer. The
results suggest the perpendicular magnetic anisotropyof the γ’-Fe4N is enhanced by the magnetic couplingwith CoPc molecules at the interface. STM and LEED
observations reveal that the presence of the CoPc
overlayers increases the surface roughness, which mightin turn decrease the perpendicular magnetic anisotropyof the γ’-Fe4N arising from the formation of the CoPc/γ’Fe4N hybrid interface through the intermolecularinteraction between CoPc layers.

[1] Y. Takahashi et al., Phys. Rev. Lett. 116 (2016)056802.
[2] Y. Takahashi et al., Phys. Rev. B 95 (2017) 224417.
[3] S. Nakashima et al., Adv. Funct. Mater. 29 (2019)1804594.
[4] P. Bruno, Phys. Rev. B 39 (1989) 865.

132 6 Ⅲ04-

BL4B

Ⅲ -4. Surface, Interface and Thin Films

BL4B

Enhancement of the Perpendicular Magnetic Anisotropyin N-surfactant Assisted FeCo Ordered Alloy Thin Films
T. Miyamachi1,2, Y. Umeda1, H. Ono1, K. Yamamoto3,4, O. Ishiyama3,4, T. Yokoyama3,4and M. Mizuguchi1,22

1Department of Materials Science and Engineering, Nagoya University, Nagoya 464-8603, Japan.
Institute of Materials and Systems for Sustainability (IMaSS), Nagoya University, Nagoya 464-8601, Japan.
3
Institute for Molecular Science, Okazaki 444-8585, Japan
4
The Graduate University for Advanced Studies (SOKENDAI), Okazaki 444-8585, Japan

Skyrmions are nano-scale magnetic vortex structures,
attracting great attention as a promising candidate ofnext-generation information storage devices due to their
expected high magnetic stability and low critical current
density for motion. Skyrmions can emerge in magnetic
thin film hetero structures with the ferromagnetic/heavy
metal interface. Since Dzyaloshinsky–Moriya interaction
induced by 3d-5d hybridization effects is the driving
force of the emergence of skyrmions in this system, thestrict control of structural, electronic and magnetic
properties of the interface in magnetic thin film hetero
structures is quite important. Recently, we haverevealed that large-area and atomically uniform ironnitride atomic layers with γ’-Fe4N stoichiometry can begrown on Cu(001) [1]. Thus, in this work, we intend togrow 5d heavy metal thin films on γ’-Fe4N atomic
layers and fabricate the high quality 3d-5d heterointerface
towards developing skyrmions-based novel magnetic
structures. For this purpose, we first grow a monatomic
layer of Co onto bilayer γ’-Fe4N and investigate theimpact of the quality of 3d-3d heterointerface onelectronic and magnetic properties of the system by low
energy electron diffraction (LEED) and x-ray
absorption spectroscopy/magnetic circular dichroism(XAS/XMCD).
To grow a bilayer γ’-Fe4N, N+ ion bombardment was
first conducted with an incident energy of 500 eV onto
Cu substrate and iron was additionally deposited atroom temperature in ultra-high vacuum. The bilayer γ’Fe4N was obtained by subsequent annealing at ~620 K.
Appropriate growth conditions about the deposition
amount of iron and annealing temperature wereprechecked by atomically resolved surface
characterizations using scanning tunneling microscopy(STM) [2]. Then, the low temperature deposition of amonatomic layer of Co at - 170 K was performed tofabricate Co-γ’-Fe4N magnetic thin film hetero
structures. The sample was post-annealed at 300, 570
and 670 K and the annealing temperature dependenceof electronic and magnetic properties was investigated
by XAS/XMCD. XAS/XMCD measurements were
performed at BL4B in UVSOR by total electron yieldmode at B = 0 - ± 5 T and T = 7.9 K. The XMCD spectra
are obtained at the normal (NI: θ = 0°) and the grazing(GI: θ = 55°) geometries. Note that θ is the angle
between the sample normal and the incident x-ray.

Element specific magnetization curves were also
recorded by plotting the L3/L2 Fe and Co XAS
intensities as a function of the magnetic field.
The XMCD signal of the bilayer γ’-Fe4N is greater in
the GI geometry than NI geometry, which reveals its
strong in-plane magnetic anisotropy as previously
reported [1]. Adding one monolayer of Co activates thenitrogen surfactant effect [3,4], which leads to theformation of CoN in the topmost layer. Accordingly, we
find from Fe magnetization curves that the out-of-planemagnetization of the Fe layer is relatively increased.
The perpendicular magnetic anisotropy of the Fe layer
is further enhanced by annealing at 570 K. However, atannealing temperature of 670 K, the decrease in thecoercivity of the Fe layer is overserved. Taking theannealing temperature dependence of the LEED pattern
into consideration, the enhancement of the out-of-planemagnetization could be caused by the improvedordering of the Co/Fe interface up to annealing
temperatures of 570 K. At 670 K, surface N atoms start
to desorb, which induces the interdiffusion of interfacial
Co and Fe atoms and consequently lowers the coercivity.

[1] Y. Takahashi et al., Phys. Rev. B 95 (2017) 224417.
[2] Y. Takahashi et al., Phys. Rev. Lett. 116 (2016)056802.
[3] K. Kawaguchi et al., Phys. Rev. Materials 4 (2020)
054403.
[4] K. Kawaguchi et al., Jpn. J. Appl. Phys. (accepted).

133 7 Ⅲ04-

Ⅲ- 4

BL5U
Ⅲ -4. Surface,
Interface and Thin Films

BL5U

ARPES from Si{111} Facet Surfaces on Three-dimensional Lined
Structures on Si(001) Substrates
K. Hattori1, L. N. Pamasi1, Y. Sakai1, H. Yang1, T. Shimizu1, Y. Ida3, W. Imayama3,
S. Tanaka2, A. N. Hattori2, S. Suga2 and K. Tanaka3
Nara Institute of Science and Technology, Ikoma 630-0192, Japan
2
SANKEN, Osaka University, Ibaraki, 567-0047, Japan
3
UVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan1

Ⅲ- 4

Our information society has required highly
densitized devices like 3D FET, which can break the
restriction of miniaturizing 2D planar-type devices. To
improve the specification (e.g., carrier mobility) of 3D
devices, it is indispensable the control of 3D structuresurfaces which are carrier passing region.
So far, our group have successfully created 3D Si
surfaces by the combination of lithography and surface
treatment techniques [1-7]: SEM, RHEED, LEED, or
STM evaluations for lined or pyramidal structureswith {111}, {110}, or {100} side/facet surfaces on(111), (110), or (001) substrates. In the beam time in
2021 FY, we focused electronic band investigations for
3D-Si surfaces, which promise side/facet-wall bandengineering.
Figure 1 shows brief results for a 3D-Si lined
structure (4 μm period) with {111} facet surfaces on a(001) substrate: (a) SEM image and (c) LEED pattern
after the flash annealing in UHV. The LEED patterns
clearly indicated 7� 7 reconstruction on �111� and�1� 1� 1� facet surfaces; the 7�7 spots move in right orleft directions.
ARPES from the area including �13 �1� 1� 1� facetsurfaces in geometry A (Fig. 1(d), note �111� isinvisible) showed clear bulk-projected band dispersion
and 7�7 surface bands: S1-S3, which guarantees wellcontrolled electronic states on the facet surfaces.
ARPES from �111� mainly in geometry B (𝜃𝜃�� = 30°
and 𝜃𝜃� = 27.5 ° ) showed band dispersions at 𝜃𝜃� ≲35.3° assigned from �111� and also dispersions
below the �111� horizontal at 𝜃𝜃� ≳ 35.3° which
could be assigned from glancingly radiated �1� 1� 1� orthe edge regions.
[1] A.N. Hattori, K. Hattori et al., Surf. Sci. 644 (2016)
86.
[2] A.N. Hattori, K. Hattori et al., Appl. Phys. Express
9 (2016) 085501.
[3]H. Yang, A.N. Hattori, K. Hattori et al., Jpn. J. Appl.
Phys. 56 (2017) 111301.
[4] S. Takemoto, A.N. Hattori, K. Hattori et al., Jpn. J.
Appl. Phys. 57 (2018) 090303.
[5] A.N. Hattori and K. Hattori, 21st Century Surface
Science (IntechOpen, London, 2020).
[6] A. Irmikimov, A.N. Hattori, K. Hattori, et al., ACS
Cryst. Growth Des. 21 (2021) 946.
[7] S. Nakatsuka, T. Abukawa, A.N. Hattori, K. Hattori
et al., e-J. Surf. Sci. NanoTechnol. 19 (2021) 13.

Fig. 1. (a) SEM image, (b) sample schematics on
holder, (c) LEED pattern (𝐸𝐸� = 80 eV), (d) geometry ofincident light (pink arrow) and electron emission(green line and fan-shaped purple) to sample, and (e)ARPES ( ℎ𝜈𝜈 = 60 eV, p-polarization; 𝜙𝜙 = 50 μm ,acceptance angle� �15°, light-analyzer angle= 57.5°)
in geometry A at 𝜃𝜃�� = 55° (𝜃𝜃� = 2.5°), for 3D facetlined structures with Si{111} facet surfaces on Si(001)substrates.

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BL5U

Electronic Structure of K Adsorbed SmS Surface
T. Nakamura1,2, T. Nakaya2, H. Sugihara2, K. Tanaka3,
K. Imura4, H. S. Suzuki5, N. K. Sato4 and S. Kimura1,2,3

Graduate School of Frontier Biosciences, Osaka University, Suita 565-0871, Japan
Department of Physics, Graduate School of Science, Osaka University, Toyonaka 560-0043, Japan
3
Institute for Molecular Science, Okazaki 444-8585, Japan
4
Department of Physics, Graduate School of Science, Nagoya University, Nagoya 464-8602, Japan
5
Institute for Solid State Physics, The University of Tokyo, Kashiwa 277-8581, Japan
1

2

Samarium mono-sulfide (SmS) is a typical valencefluctuation material [1]. At ambient pressure, SmS is asemiconductor with an indirect bandgap of about 0.1
eV, and its color is black [2]. The electrical properties
change to metallic above a critical pressure of 0.65
GPa. Although the pressure-induced phase transition
was discovered over 50 years ago [1], the origin of thephase transition is still under debate. Recently, a phasetransition like the pressure-induced one has beenreported due to two different types of perturbations:light irradiation and current injection [3,4]. These
perturbations are commonly expected to increasecarriers, but the detailed electronic states after carrier
doping have not been clarified yet.
Alkali metal adsorption on crystal surfaces is widelyused as a typical method to investigate the effect ofcarrier injection into a material. Due to the chargetransfer of the free-electron-like outermost electrons in
the alkali metal to SmS, a carrier-doped SmS surface
can be realized. In this work, we have studied thechange of the electronic structure by potassium (K)doping on a SmS surface by synchrotron-based ARPES.
A high-quality single-crystalline SmS was grown by
the vertical Bridgman method in a high-frequency

induction furnace. The clean SmS surface wasobtained by cleaving in-situ in an ultra-high vacuum
chamber. K atoms were evaporated from the welldegassed alkali metal dispenser (SAES-Getters) atroom temperature (RT).
Figure 1(a) shows the ARPES intensity plot of thepristine-SmS along the Γ� - �
X line of the surface
Brillouin zone taken with 60-eV photons. Flat Sm2+ 4f 5
multiplet structure and dispersive S 3p bands wereobserved. After the K deposition as shown in Fig. 1(b),the band dispersion of the Sm 4f states was changed
without a higher binding energy shift due to the naturalelectron doping. These results suggest that the Kadsorption on SmS caused a deformation of the band
structure, which cannot be explained as a simple rigid
band shift model due to electron doping.
[1] A. Jayaraman et al., Phys. Rev. Lett. 25 (1970) 1430.
[2] K. Matsubayashi et al., J. Phys. Soc. Jpn. 76 (2007)
064601.
[3] R. Kitagawa et al., Appl. Phys. Lett. 82 (2003) 3641.
[4] H. Ando et al., JPS Conf. Proc. 30 (2020) 011132.

� with 60-eV photons at
Fig. 1. ARPES intensity plots of (a) pristine SmS and (b) K-adsorbed SmS along Γ�-X
room temperature.

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Interface and Thin Films

BL5U

Explorations for Spontaneously Formed Excitons in Narrow-gap
Semiconductors and Semimetals
K. Fukutani1,2, M. Murakami3, C.I. Kwon4,5, J. S. Kim4,5, K. Tanaka1,2, S. Kera1,2,3

Institute for Molecular Science, Okazaki 444-8585, JapanThe Graduate University for Advanced Studies (SOKENDAI), Okazaki 444-8585, Japan
3
Graduate School of Science and Engineering, Chiba University, Chiba 263-8522, Japan
4
Center for Artificial Low-Dimensional Electronic Systems, Institute for Basic Science, Pohang, Korea
5
Pohang University of Science and Technology, Pohang, Korea
1

2

Ⅲ- 4

Excitons are bound pair of an electron and a hole,conventionally produced transiently by irradiation oflight on semiconductors, and is one of the mostfundamental quasiparticles in solids and molecularmaterials that play central roles in various quantum
devices, such as photovoltaic cells, light emitting diodes
and photodetectors.
In recent years, a new exotic phase of matter called
an excitonic insulator has garnered much attentions. In
the excitonic insulator phase, at sufficiently low
temperature, the electrons and holes are spontaneously
bound to form an excitons and undergo quantum
condensation.
Among the various candidate materials for excitonic
insulator, Ta2NiSe5 is particularly suitable for theexperimental investigations as it exhibits a direct band
gap and the excitonic insulator transition accompanies
only a minor structural distortion, which preserves theperiodicity of the material. For this relative simplicity,
Ta2NiSe5 has been investigated extensively in the past
decade by various experimental methods [1] and it is
widely conceived to be a Bose-Einstein condensation(BEC)-type excitonic insulator.
Of particular interest in the BEC-type excitonic
insulator is the theoretical prediction of the intermediatephase called “preformed exciton phase”, which isbelieved to appear between the excitonic insulator andthe normal phases (see Fig. 1) [2]. In the preformed
exciton phase, the magnitude of the bandgap is smallenough (i.e., the free carrier screening is small enough)to allow for the bound state for the electrons and holes,
yet the temperature is too high for these spontaneously
formed excitons to undergo the Bose-Einsteincondensation. Therefore, this particular region of thephase diagram supports the existence of finite numberof excitons in equilibrium. In our recent study [3], thedirect photoemission signal from these spontaneously
formed excitons have been detected and long-standing
theoretical prediction has been confirmed. However, thedetailed formation mechanism of such excitons is still
elusive due to the lack of experimental data for thisparticular phase of excitonic insulator materials.
Thus, in order to pin down the origin of these
spontaneously formed excitons, we are performing aseries of angle-resolved photoemission spectroscopy(ARPES) experiments at BL5U for the chalcogensubstituted compounds Ta2Ni(Se1-xSx)5 for various
compositions x. In the experiments, the freshly cleaved

samples of Ta2Ni(Se1-xSx)5 have been measured toreveal their band structures as well as to explore forthe photoemission signals from the spontaneously
formed excitons as a function of temperature, photon
energy as well as the light polarizations.
A representative result of the ARPES intensity plot isshown in Fig. 2. It can be seen that the photoemission
signal from excitons, observed in Ta2NiSe5 [3] is also
observed for the S-substituted compounds.

Fig. 1. Theoretical phase diagram of excitonic insulators.

Fig. 2. ARPES intensity plot for chalcogen-substituted
excitonic insulator Ta2Ni(Se1-xSx)5.

[1] Y. Wakisaka et al., Phys. Rev. Lett. 102 (2009)026402; Y.F. Lu et al., Nat. Commun. 8 (2017) 14408.
[2] F.X. Bronold et al., Phys. Rev. B 74 (2006) 165107.
[3] K. Fukutani et al., Nat. Phys. 17 (2021) 1024.

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BL5B

X-ray Absorption Spectroscopy Measurements of Au/Fe/MgO Sandwich
Structure Sample for Study of Soft X-ray Second Harmonic Generation
T. Sumi1, M. Horio1, X. Zhang1, T. Kato2 and I. Matsuda1,3

2

1Institute for Solid State Physics, The University of Tokyo, Kashiwa 277-8581, Japan
Institute of Materials and Systems for Sustainability, Nagoya University, Nagoya 464-8603, Japan
3
Trans-scale Quantum Science Institute, The University of Tokyo, Tokyo 113-0033, Japan

Second harmonic generation (SHG), which is aphenomenon that occurs by the interaction between
light and a system where the inversion symmetry is
broken, has been used not only to convert light tohigher frequencies but also to investigate electronic
states of molecules at the systems in the visible region.
After the construction of X-ray Free Electron Laser(XFEL) such as Pring-8 Angstrom Compact freeelectron LAser (SACLA), we have been developing
SHG methods in the range of soft X ray, and applied
to GaFeO3 [1], LiNbO3 [2], LiOsO3 [3], and GaAs [4].
By setting the incident energy to the inner-shell corelevel, SHG acquires element selectivity by inner-coreexcitation resonance. Although this technique is usefulto reveal the electronic states of the targeted atoms at
surfaces/interfaces, there is no report for the interface
SHG.
In this research, at UVSOR BL5B, we conducted Xray absorption spectroscopy for a Fe film sandwichedby films of Au and MgO to grasp the possibility of theoccurrence of soft X-ray SHG before observing it. We
synthesized the sample by ultrahigh vacuum molecularbeam epitaxy method. The sandwich structure of
Au/Fe/MgO was repeated 4 times. The structure of thesample is [Au (2 nm)/Fe (2 nm)/MgO (2 nm)]4/MgO(001,substrate) (Fig. 1). The sample was placed perpendicular
to the incident beam, and the drain current was measured.
Figure 2 shows a XAS spectrum around the Fe Medge. The drain current, I, was normalized by incident
intensity, I0, measured by the Au mesh. The result shows
Fe M-edge (53 eV) absorption peak appears. This meansthat the Fe M-edge dipole transition is allowed. To
investigate the transition around the SHG energy (106eV), the drain current was measured around that energy
without the Au mesh to prevent the effect of the mesh(Fig. 3). The peak appears around 106 eV. These results
suggest that the dipole transitions in the SHG process
starting from Fe M-shell are allowed.
In conclusion, we investigated the electric dipole
transition for the Au/Fe/MgO sandwich structuresample by XAS and found the possibility of the SHG
process starting from the Fe M shell (hν = 53 eV). It is
expected that SHG originating from the interfaces isavailable. Furthermore, it is possible to achieve soft Xray magnetization-induced SHG (MSHG) by applying
a magnetic field to this sample because it hasperpendicular magnetization anisotropy (PMA).

Fig. 1. Structure of the [Au/Fe/MgO]4 / MgO(001)sandwich structure sample.

Fig. 2. XAS spectrum for the sandwich structuresample around Fe M-edge.

Fig. 3. Drain current of the sandwich structure sample
without (blue) and with (red) the Au mesh.
[1] Sh. Yamamoto et al., Phys. Rev. Lett. 120 (2018)
223902.
[2] E. Berger et al., Nano Lett. 21 (2021) 6095.
[3] C. B. Uzundal et al., Phys. Rev. Lett. 127 (2021)
237402.
[4] T. Sumi et al., e-J. Surf. Sci. Nanotech. (2022)(accepted).

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Interface and Thin Films

BL6U

Bromine Doping to Perylene Monolayer on Au(110): Photoelectron
Momentum Microscopy
O. Endo1,3, F, Matsui2, S. Kera2, W. -J. Chun3, M. Nakamura4, K. Amemiya5 and H. Ozaki1

Department of Organic and Polymer Materials Chemistry, Faculty of Engineering, Tokyo University ofAgriculture and Technology, Koganei 184-8588, Japan
2
UVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
3
Graduate School of Arts and Sciences, International Christian University, Mitaka 181-8585, Japan
4
Department of Applied Chemistry and Biotechnology, Faculty of Engineering, Chiba University,
Chiba 263-8522, Japan
5
Photon Factory, High Energy Accelerator Research Organization (KEK-PF), Institute of Materials Structure
Science (IMSS), Tsukuba 305-0801, Japan1

Ⅲ- 4

Energy level alignment at organic-metal interface is
one of the important topics in the field of organic
electronics [1]. The HOMO and LUMO levels oforganic molecules shift upon adsorption as a result of
the work function change due to the formation of aninterfacial dipole. This causes the change of the charge
injection barrier from the metal electrode, which
affects the efficiency of the organic devices. Recently,
doping of organic semiconductors is re-focused to
improve the conductivity [2]. The doping process inorganic semiconductors is the charge transfer between
the molecules, and two representative mechanisms areproposed: one is the integer charge transfer, or
ionization, and the other is the formation of chargetransfer complex [2]. In either case, the energy levelsof the doped molecule are altered from those of theoriginal HOMO or LUMO, because of the electrostatic
effect derived from the doped charge, or the orbital rehybridization. Therefore, the energy level alignment of
the doped molecules at the metal interface is necessary
to be elucidated. In this study, we have observed theelectronic structure of perylene molecules on theAu(110) surface and the effect of bromine doping byangle resolved photoelectron spectroscopy (ARPES)
and X-ray photoelectron spectroscopy (XPS) using
momentum microscope, which has recently been
introduced at BL6U.
Figure 1(a) shows the ARPES results of the perylene
monolayer on the Au(110)-(1x2) surface, which was
obtained at Eb = 1.5 eV at the surface normal direction.
The photoelectron pattern simulated for the HOMO ofthe perylene molecule at the normal direction withrespect to the molecular plane is shown in Fig. 1(c),right panel, which was obtained by the plane wave
approximation. This four-fold pattern is changed to a
two-fold one for the ±18° off-nomral direction, as
shown in Fig. 1(b). The pattern resemblance for Fig.
1(a) and 1(b) indicates that the molecular plane is tilted±18° with respect to the surface normal. The tilted
molecular orientation is in accordance with the resultsof X-ray absorption spectroscopy (XAS), and thescanning tunneling microscopy [3]. Figure 1(d) depicts
the structural model of perylene on Au(110)-(1x2).
Bromine molecules doped to the perylene monolayer

penetrate into the monolayer and adsorbed dissociatively
on the Au(110) surface. This was confirmed by the Br3d XPS spectra. Upon bromine penetration, theorientation of the perylene molecules become random.
Therefore, the characteristic ARPES pattern of the
HOMO electrons disappears. The XAS results indicatesthat the perylene molecules are cationized uponbromine doping, because of the charge transfer from theperylene to the Au surface mediated by the bromine
layer. The HOMO level exceeds the Fermi level as aresult of the upward energy shift of the perylene MOs
induced by the bromine layer, and hence, part of the
HOMO electron is transferred. The energy shift was
confirmed by the C-1s XPS spectra.

Fig. 1. (a) Momentum map of perylene/Au(110) at Eb= 1.5 eV. (b) Simulated photoelectron distribution for
perylene molecule tilted ±18° along the short axis. (c)Orbital distribution of perylene HOMO and thesimulated photoelectron distribution at the normal
direction with respect to the molecular plane. (d)Structural model of perylene on Au(110).
[1] H. Ishii, et al., Adv. Mater. 11 (1999) 605.
[2] I. Salzmann, et al., J Electron Spectros Relat
Phenomena 204 (2015) 208.
[3] L. Gross, et al., Org. Electron. 3 (2002) 1.

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BL6U

High-resolution Photoelectron Momentum Microscope Study on theElectronic Structure of Charge-density-wave Material
K. Fukutani1,2, S. Tanaka3, F. Matsui1,2 and S. Kera1,2,4

Institute for Molecular Science, Okazaki 444-8585, JapanThe Graduate University for Advanced Studies (SOKENDAI), Okazaki 444-8585, Japan
3
Sanken, Osaka University, Ibaraki 567-0047, Japan.
4
Graduate School of Science and Engineering, Chiba University, Chiba 263-8522, Japan1

2

Among various critical phenomena in solids, charge
density wave (CDW) is one of the widely observed
phase transitions, which induces deformation of lattice
periodicity as well as of the electronic density. The
prototypical examples of such CDW are found in manyof the transition metal dichalcogenides (TMDCs),
which exhibit the wide range of periodicities upon thephase transitions, including commensurate andincommensurate CDWs [1].
On the other hand, despite the ubiquity of CDWs
and the decades-long intensive research efforts, aimed
for revealing their microscopic mechanisms, there isno clear consensus on their driving forces.
Recently, the roles of dimensionalities on theproperties of TMDC materials and their CDWs haveattracted much attentions. In particular, in the twodimensional limit (i.e., a single monolayer), some
TMDC materials are found to behave in drasticallydifferent manners, as can be seen in two-dimensional
ferromagnetism of VSe2 [2], the suppression of CDW
in TaS2 [3], and the enhancement of CDW in NbSe2[4], to name a few. These recent observations showthat the careful studies of the dimensionality effects
can provide key insights in resolving the long-standing
mysteries of the origin of CDW transitions.
Among such TMDC materials, the series of titanium
dichalcogenides, TiX2 (X = S, Se, Te) present particularlyinteresting trends in CDW properties. While in the bulk
form, only TiSe2 exhibits CDW, in the two-dimensional
limit, CDW with the same periodicity emerges for TiTe2[5], suggesting the role of dimensionality in theemergence of CDW.
However, it has been reported that the choice of
substrate affects significantly the CDW order [6]. Thisis most naturally attributed to the interactions between
the monolayer TiTe2 and the substrate. In other words,
while the dimensionality is a critical factor for CDW
formation, the degree to which the monolayer-substrateinteraction breaks the “pure” two-dimensionality of TiTe2
is a critical issue that must be systematically investigated.
In this project, we attempt to tune the dimensionality
quasi-continuously by inserting the intercalation layer
with various atomic thicknesses near the surface of bulk
TiTe2, whereby gradually “lifting up” the two-dimensional
layer to investigate the respective electronic structures.
For this purpose, photoelectron momentum microscope(PMM) is an ideal instrument, which can efficiently
identify the periodicity and the topology of the Fermi
surface structure in wide momentum range. In the firstphase of this project, we have performed the highresolution PMM measurements on pristine TiTe2.
Combined with the use of space-resolved mode, thesurface of high crystallinity can be readily found andthe example of the obtained spectra is shown in Fig. 1.
The experiments were performed with photon energy
as well as polarization dependence, and the obtained
set of data are expected to yield detailed informationon the three-dimensional (kx, ky, kz) electronic structures
as well as their orbital textures.

Ⅲ- 4Fig. 1. (a) Fermi surface intensity image and (b) band
structure mapping of TiTe2 obtained at hv = 52 eV and
T = 50 K with PMM at BL6U.

[1] K. Rossnagel, J. Phys.: Condens. Matter 23 (2011)
213001.
[2] M. Bonilla et al., Nat. Nanotechnol. 13 (2018) 289.
[3]C. E. Sanders et al., Phys. Rev. B 94 (2016) 081404(R).
[4] X. Xi et al., Nat. Nanotechnol. 10 (2015) 765.
[5] P. Chen et al., Nat. Commun. 8 (2017) 516.
[6] M.-K. Lin et al., Phys. Rev. Lett. 125 (2020) 176405.

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Interface and Thin Films

BL6U

Twin-domain Boundary and Monoatomic Step of Graphite Surface
Imaged by Photoelectron Momentum Microscopy
F. Matsui1,2, Y. Okano1, H. Matsuda1, T. Yano1, E. Nakamura1, S. Kera1,2 and S. Suga3,4
1

UVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, JapanThe Graduate University for Advanced Studies (SOKENDAI), Okazaki 444-8585, Japan
3
SANKEN, Osaka University, Suita, Osaka 567-0047, Japan
4
Forschungszentrum Jülich, Germany

2

The photoelectron momentum microscope is an
instrument that combines a photoelectron microscopewith a projection-type electron energy analyzer toenable both μm-scale valence band mapping andmomentum-selective photoelectron microscopy [1-3].
Using these methods, we measured the local electronic
structure of graphite crystal surfaces.

Ⅲ- 4Fig. 1. μm-scale valence band mapping and momentum
selective photoelectron microscopy of graphite surface.

The cleaved graphite surface is found to have facets
a few μm wide that share a twin-domain boundary in thearmchair edge direction. This “armchair facet” wascharacterized by μm-scale VB mapping. The normal
direction of the “armchair facet” differed from that of
the terrace region by about 20°. The π-band splitting due
to interlayer interaction was the same in the “armchair
facet” and the terrace region, indicating that the interlayer
distance between the two regions was identical. By
transforming the photoelectron distribution of theselected momentum direction in reciprocal space to real
space, a momentum-selective microscopic image can beobtained. By detecting photoelectrons of the “armchair
facet” at the M symmetry point, a microscopic image inwhich the “armchair facet” is selectively enhanced was
successfully obtained [4].
Furthermore, the kz dispersion of graphite from thefew mm region was measured using photoelectron
momentum microscope (Fig. 1). The π band dispersion
over the entire Brillouin zone was investigated. Notethat graphite crystals with an ABAB…-type stacking
structure are six-fold symmetric around the z axis,
whereas a surface with one type of termination isthree-fold symmetric. The microscope function of the
PMM has a detection area sufficiently small to select
only one type of graphite termination structure on thecleavage plane. We found that the π band was nolonger degenerate in the ALH plane and its symmetry
was reduced from C6v to C3v. This phenomenon is
attributed to the coupling of the single-domain threefold graphite surface π-band with the six-fold bulk kz
dispersion, which has been neglected up to now. Thissymmetry breaking was used to image the monatomic
steps on the graphite surface [5].
[1] F. Matsui S. Makita, H. Matsuda, T. Yano, E.
Nakamura, K. Tanaka, S. Suga, and S. Kera, Jpn. J.
Appl. Phys. 59 (2020) 067001.
[2] S. Makita, H. Matsuda, Y. Okano, T. Yano, E.
Nakamura, Y. Hasegawa, S. Kera, S. Suga, and F.
Matsui, e-J. Surf. Sci. Nanotech. 19 (2021) 42.
[3] F. Matsui, S. Makita, H. Matsuda, E. Nakamura, Y.
Okano, T. Yano, S. Kera, and S. Suga, J. Phys. Soc.
Jpn. 90 (2021) 124710.
[4] F. Matui, Y. Okano, H. Matsuda, T. Yano, E.
Nakamura, S. Kera, and S. Suga, submitted (2022).
"Domain-resolved Photoelectron Microscopy and μmscale Momentum-resolved Photoelectron Spectroscopy of Graphite Armchair Edge Facet".
[5] F. Matui and S. Suga, submitted (2022) "Couplingof graphite surface π band with kz dispersion"

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BL6U

Development of the Fabrication System for the μm-scale Ultra-thin Filmat BL6U
T. Nakamura1,2, F. Matsui3 and S. Kimura1,2,4

Graduate School of Frontier Biosciences, Osaka University, Suita 565-0871, Japan
Department of Physics, Graduate School of Science, Osaka University, Toyonaka 560-0043, Japan
3
UVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
4
Institute for Molecular Science, Okazaki 444-8585, Japan1

2

Photoelectron spectroscopy (PES) is a powerful
technique to investigate the electronic structures ofmaterials. Recently developed at UVSOR-III BL6U,
synchrotron-based photoelectron momentum microscopy(PMM) is one of the state-of-the-art PES systems [1]. On
the other hand, research on unique electronic states in the
microscopic region, such as edge states in topologicalmaterials and domains in inhomogeneous samples, hasbeen intensively explored [2-4]. The combination of
PMM and small-sized samples with the unique electronic
state leads to fertile physics. In this work, we havedeveloped a new thin-film deposition system in the
preparation chamber at the BL6U end station.
The basic concept of this system is the selective
deposition of the materials passes through the spatial
mask filter from the evaporator. Figure 1(a) shows thephoto of the flagship-type sample holder with two M2
holes to attach the additional filter component. Spotwelded Ta foils are used to fix a substrate. Figure 1(b)shows the mask filter. The main material is a flat Ta foil
(10 × 10 mm2) with a φ2 mm hole at the center. A
honeycomb-type TEM grid (The hole and bar sizes on
the TEM grid are 290 μm and 59 μm, respectively) wasused to make a pattern in the current system. A
commercially available square clip (4 × 4 mm2) is used
as a handle to fix the mask on the sample. The opposite
side of the clip is an M2 screw. Figure 1(c) shows thephoto of the sample holder with the mask filter on aheating stage in the preparation chamber of the BL6U
end station. The distance between the holder and mask
filter is about 1.5 mm. When cleaning the substrate byannealing and Ar sputtering, the mask filter is removed
and set to other sample holders on the sample bank.
We used the InSb(111)B substrate as a test sample.
The substrate was cleaned by the cycle of Ar-ion
sputtering (acceleration energy of 1 kV) and annealing
up to 600 K. After checking the sharp (3 × 3) diffraction
pattern, the 1-nm Sb layer was evaporated on the
InSn(111)B substrate with the mask filter at room
temperature.
Figure 2 shows a spatial-resolved In 4d core level
intensity map. One pixel indicates the sum of thephotoelectron intensity measured by the microscopymode of PMM. The domain scale of the bright area isalmost consistent with the size of the bar of the TEM
grid.
As the next step, we quantitively evaluate the spatial

resolution of selective deposition with mask filters andobserve the band structure from a single micro-scaledomain.

Fig. 1. Photos of the spatially selective deposition
system. (a) sample holder. (b) mask filter. (c) sample
holder with mask filter on a heating stage in the
preparation chamber of BL6U.

Ⅲ- 4

Fig. 2. Real-space image of the In 4d photoelectron
intensity plot. The incident photon energy is 80 eV.

[1] F. Matsui et al., Jpn. J.Appl. Phys. 59 (2020) 067001.
[2] K. Nakayama et al., Nano Lett. 19 (2019) 3737.
[3] R. Noguchi et al., Nature 566 (2019) 518.
[4] H. Iwasawa, Electron. Struct. 2 (2020) 043001.

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Ⅲ -4. Surface,
Interface and Thin Films

BL7U

High-resolution Angle-resolved Photoemission Study on
MnBi2Se4/Bi2Se3/MnBi2Se4 Sandwich Structure
2

Ⅲ- 4

R. Fukushima1, S. Ichinokura1, K. Tanaka2 and T. Hirahara1

Department of Physics, Tokyo Institute of Technology, Tokyo 152-8551, JapanUVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
1

Topological insulators (TI) are extensively studied
recently due to its peculiar properties [1]. The Diraccone surface states of TI are protected by time-reversal
symmetry (TRS) and backscattering among thesesurface states is prohibited. But when TRS is broken byapplication of a magnetic field or incorporating
magnetic materials, a gap opening in the Dirac cone is
expected and an intriguing phase called the quantum
anomalous Hall state can be realized [2]. This phase is
expected to show even more exotic phenomena such as
the topological magnetoelectic effect. To realize suchstate, two types of sample fabrication techniques havebeen employed up to now: (1) magnetic doping while
growing the single crystal or thin film of TI [3], and (2)magnetic impurity deposition on the surface of TI [4].
While method (1) was successful and showed evidenceof the TRS violation, no one has succeeded using
method (2), which should be a more direct way to
examine the interaction between the topological surface
states and magnetism. We have previously foundanother novel technique to induce magnetism into TI,
namely the magnetic extension effect [5]. By depositing
Mn and Se on Bi2Se3, we found that Mn and Se areincorporated in the topmost Bi2Se3 layer and a novel
heterostructure MnBi2Se4/Bi2Se3 is formed [5]. This
heterostructure with an ordered magnetic Mn single
layer showed a clear Dirac cone gap of 85 meV. Frommagnetic measurements utilizing high-resolution X-ray
magnetic circular dichroism (XMCD) at the Mn L
adsorption edge, it was revealed that the Curie
temperature Tc of the system is 15-20K. However, when
we fabricated a sandwich structure of MnBi2Se4/n
quintuple layer (QL) Bi2Se3/MnBi2Se4, which includes
two magnetic Mn layers, we found that the Tc wasenhanced to 20-25 K for n = 1-7. Thus it is important tomeasure the electronic structure of the sandwich
structure and investigate the origin of the enhancementof Tc.
Therefore in this study, we have measured the band
dispersion of MnBi2Se4/7 QL Bi2Se3/MnBi2Se4 sandwich
structure by angle-resolved photoemission spectroscopy(ARPES). The band dispersion measured at 10 K isshown in Fig. 1 system. It shows a band structure similar
to the heterostructure with a linear dispersion [5] and aquantitative analysis of the energy dispersion curve(EDC) at the Γ point revealed that the gap size was 100
meV. This result showed that there is practically little
difference between the hetero and sandwich structures.
Further magnetic characterization with XMCD including
measurements for nonmagnetic elements (Se or Bi)

have given new insights into the magnetic interaction of
the two Mn magnetic layers for the sandwich structure.
Namely it was revealed that the bulk carriers of the
Bi2Se3 near the Fermi level mediate the magnetic
interaction between the two Mn layers [6].

Fig. 1. Band dispersion image of the MnBi2Se4/7 QL
Bi2Se3/MnBi2Se4 sandwich structure measured at 10 K.

[1] M. Hasan and C. Kane, Reviews of Modern Physics
82 (2010) 3045.
[2] X.-L. Qi and S.-C. Zhang, Reviews of Modern
Physics 83 (2011) 1057.
[3] For example, C. Z. Chang et al., Science 340 (2013)
167.
[4] For example, M. Ye et al., Physical Review B 85
(2012) 205317.
[5] T. Hirahara et al., Nano Letters 17 (2017) 3493.
[6] R. Fukushima et al., to be published.

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Ⅲ -4. Surface, Interface and Thin Films

BL7U

Observation of Electronic Structure of YbCu2/Cu(111) Surface Alloy
H. Sugihara1, T. Nakamura2,1, Y. Chen1, K. Tanaka3 and S. Kimura2,1,4

Department of Physics, Graduate School of Science, Osaka University, Toyonaka 560-0043, Japan
2
Graduate School of Frontier Biosciences, Osaka University, Suita, 565-0871, Japan
3
UVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
4
Department of Materials Molecular Science, Institute for Molecular Science, Okazaki 444-8585, Japan
1

The Kondo coupling between localized f-electronsand carriers leads to exotic physical phenomena such as
the formation of the heavy-fermion (HF), theemergence of a magnetic quantum critical point, andunconventional superconductivity [1]. Among them, theHF system, in which massive effective carriers appear
due to the Kondo effect, has fascinated many
researchers [2,3]. On the other hand, the combination of
HF system and low-dimensionality strongly modulate
the hybridization strength because an order parameterof these systems is much sensitive to dimensionality. Ina typical bulk HF compound, CeIn3, for instance, thesuppression of the antiferromagnetism and the increaseof the carrier’s effective mass appear due to the
reduction of the dimensionality [4]. In addition, a HF
quasicrystal, which has higher dimensionality, has an
unconventional quantum criticality [5]. To clarify the
relation of the dimensionality to the HF character, weinvestigate electronic structure of low-dimensional HF
materials. Here, we have studied the surface electronic
structure of a HF surface alloy, YbCu2/Cu(111), which
is a new candidate for the two-dimensional HF system,measured by angle-resolved photoelectron spectroscopy(ARPES).
The clean Cu (111) substrate was prepared by thecycle of Ar+ sputtering and annealing up to 800 K. Afterchecking a sharp and low-background streak electron
diffraction pattern, Yb-metal was evaporated by ahomemade Knudsen cell, resulting in the observation of
fractional order originated from the YbCu2 layer.
ARPES measurement was carried out at UVSOR BL7U(hν = 21 eV) at temperature of 6 K.
Figure 1 shows the ARPES intensity plot of
� on a surface
YbCu2/Cu(111) surface along Γ� - K
Brillouin zone of Cu(111). To see the band dispersion
above the Fermi level, the ARPES spectra were divided
by the Fermi-Dirac distribution function convolved
with the instrumental resolution. The flat bands with thebinding energy of around 0.2 eV are attributed to theYb2+ 4f7/2 final state after the photoexcitation process.
Several hole bands centered on the Γ� point wereobserved. The hybridizations between the hole bands
and the Yb 4f state appears as the modulation of the
shapes and intensities. In addition to the hybridization,
as shown in Fig. 2, a steep peak, which seems to be a
Kondo resonance peak usually observed in HF
materials [6], appears near the Fermi level. These results
suggest the HF formation in YbCu2/Cu(111).
Further analysis to understand the hybridization
between the Yb 4f orbital and conductive hole bands

and the relation to the dimensionality are in progress.

Fig. 1. ARPES band dispersion of YbCu2/Cu(111)
� taken at hν = 21 eV (T = 6 K). The
surface along Γ�-Kphotoelectron intensities were normalized by FermiDirac distribution function convoluted with the
instrumental resolution.

Fig. 2. Angle-integrated photoelectron spectra of
YbCu2/Cu(111). The allow indicates the Kondo
resonance peak.
[1] C. Pfleiderer, Rev. Mod. Phys. 81 (2009) 1551.
[2] A. C. Hewson, The Kondo Problem to Heavy
Fermions (Cambridge Univ. Press, Cambridge, 1993).
[3] P. Coleman et al, J. Phys.: Condens. Matter 13 (2001)
R723.
[4] H. Shishido et al., Science 327 (2010) 980.
[5] K. Deguchi et al., Nat. Mater. 11 (2012) 1013.
[6] S. Chatterjee et al., Nat. Commun. 8 (2017) 852.

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BL7BInterface and Thin Films
Ⅲ -4. Surface,

BL7B

Electrochemical Attenuated Total Reflectance Ultraviolet (EC-ATR-UV)
Spectroscopy Applied for Organic Semiconductor / Ionic Liquids Interface
I. Tanabe, Y. Hanamori and K. Fukui

Department of Materials Engineering Science, Graduate School of Engineering Science, Osaka University,
Toyonaka 560-8531, Japan

Ⅲ- 4

Electric double-layer organic field-effect transistors(EDL-OFETs) have attracted much attention because of
their significantly low operation voltage (<1 V)compared to conventional SiO2-gated OFETs (>10 V).
In EDL-OFETs, a high electric field is generated in the
EDL that accumulates in the interfacial region between
the organic semiconductor and electrolyte, resulting ina low operation voltage. Therefore, the organic
semiconductor/electrolyte interface is especially important.
Recently, we developed a new spectroscopic system,
namely electrochemical- attenuated total reflectance(EC-ATR) ultraviolet-visible spectroscopy, which canaccess the interfacial area [1,2].
In this study, ionic liquid gated organic field-effecttransistors (IL-gated OFETs) were fabricated on the
ATR prism (Fig. 1). Two-layer single crystalline film of
C9-DNBDT-NW was used as an organic semiconductor,
and two kinds of ionic liquids ([EMIM][FSA] and[TMPA][TFSA]) were cast on the film. Au films were
evaporated to a thickness as the source and drainelectrodes (working electrodes) on both sides of the
ATR prism, and a Pt coil and a Pt wire were placed in
the ionic liquids as pseudo counter and reference (gate)electrodes, respectively. In our previous study [2], in
response to the applied gate voltage, the spectral peaksof the organic semiconductor shifted and bleached. Thiswas correlated with the drain current.
The fabricated IL-gated OFETs on the ATR prism
was put on the sample chamber in BL7B at UVSOR.
The light from UVSOR had one important advantage;
polarization direction control. That is to say, by changing
the placing direction of the ATR prism to the incident
light, the polarized direction to the sample can becontrolled. While our previous study used a halogen
lamp as the light source, which was unpolarized, thesynchrotron radiation is innately polarized. in the UV
region, especially in the deep-UV (<300 nm) region, thepreparation of a polarizer is difficult, and thus, thepolarized light generated from the synchrotron is highly
useful.
Figure 2 shows the ATR spectra of C9-DNBDT-NW
on the sapphire prism measured in BL7B at UVSOR.
While the s-polarized incident light gave distinct peaksin the 200-500 nm range (Fig. 2 (a)), p-polarized incident
light did not (Fig. 2 (b)). This is because the C9-DNBDTNW film on the ATR prism was well packed, and shows
strong polarized dependence.
These peaks could be assigned by quantum chemical
calculations, and they verified depending on the applied
voltage [2]. In addition, EC-ATR-UV spectroscopy

could measure the absorbance due to the ionic liquids
near the surface of the C9-DNBDT-NW film because of
the short penetration depth (< 50 nm) and the strong
ionic liquids’ absorbance of the light in the UV region,
which was a unique point of the new technique.
Therefore, we are trying spectral measurements of bothorganic films and ionic liquids during device operations
using the polarized light from BL7B. It will reveal
orientations of interfacial ionic liquids and their behaviors
under electrochemical environment. Additionally, theinteractions between the organic semiconductor film
and ionic liquids will be investigated, leading to themechanism research and improvement of the highperformance EDL-OFETs.

Fig. 1. Schematics of EDL-OFET fabricated on ATR
prism.

Fig. 2. Polarization dependence of ATR spectra of C9DNBDT-NW on a sapphire prism.

[1] I. Tanabe, A. Suyama, T. Sato and K. Fukui, Anal.
Chem. 91 (2019) 3436.
[2] I. Tanabe, I. Imoto, D. Okaue, M. Imai, S. Kumagai,
T. Makita, M. Mitani, T. Okamoto, J. Takeya and K.
Fukui, Commun. Chem. 4 (2021) 88.

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