რ

Surface,
Interface andThin Films

Ⅲ-4 Surface, Interface and Thin Films

BL6U

Fermiology of a Kagome Superconductor Cs(V1-xNbx)3Sb5 Revealed by
Momentum Microscope
T. Kato1, K. Nakayama1, Y. Li2,3,4, Z. Wang2,3,4, S. Souma5,6, F. Matsui7,
T. Takahashi1, Y. Yao2,3 and T. Sato1,5,6,8
1

Department of Physics, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan
Centre for Quantum Physics, Key Laboratory of Advanced Optoelectronic Quantum Architecture andMeasurement (MOE), School of Physics, Beijing Institute of Technology, Beijing 100081, P. R. China
3
Beijing Key Lab of Nanophotonics and Ultrafine Optoelectronic Systems, Beijing Institute of Technology,
Beijing 100081, P. R. China
4
Material Science Center, Yangtze Delta Region Academy of Beijing Institute of Technology,
Jiaxing, 314011, P. R. China
5
Advanced Institute for Materials Research (WPI-AIMR), Tohoku University, Sendai 980-8577, Japan
6
Center for Science and Innovation in Spintronics (CSIS), Tohoku University, Sendai 980-8577, Japan
7
UVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
8
International Center for Synchrotron Radiation Innovation Smart (SRIS), Tohoku University,
Sendai 980-8577, Japan
2

Recently, AV3Sb5 compounds (where A represents analkali metal K, Rb, or Cs) have been discovered to hostan ideal two-dimensional kagome lattice formed by Vatoms [Fig. 1(a)]. These materials undergo a charge
density wave (CDW) transition below the criticaltemperature (TCDW) of 78-103 K. The CDW transition ischaracterized by lattice distortions with the star-ofDavid or inverse star-of-David patterns. Notably, theCDW phase exhibits intriguing properties, including
the coexistence with superconductivity, time-reversal
symmetry breaking, and nematicity. Understanding theorigin of the CDW in AV3Sb5 and its interplay withother properties is currently a hot topic in condensed
matter physics. One useful approach to study this issue
is to perturb the CDW phase by varying key physicalparameters such as pressure and carrier concentrations.
In this regard, chemical substitution in the crystal,
which can adjust chemical pressure and/or carrier
concentrations, is a promising strategy.
In this study, we performed an angle-resolved
photoemission spectroscopy (ARPES) study on Nbsubstituted CsV3Sb5, Cs(V1-xNbx)3Sb5, with x = 0, 0.03,
and 0.07 [1]. The substitution of V with isovalent Nb
results in a reduction of TCDW, while simultaneously
enhancing the superconducting transition temperature(Tc) [Fig. 1(b)].
High-quality single crystals of Cs(V1-xNbx)3Sb5 weresynthesized by the self-flux method. ARPES
measurements were carried out by using momentum
microscope KREIOS 150 MM (SPECS) at BL6U [2].
In Fig. 1(c), we present the experimentally determined
Fermi surface in the normal state at T = 120 K (above
TCDW) for the highest Nb concentration (x = 0.07). The
use of a momentum microscope allowed to collectphotoelectrons over a wide momentum space, enablinga comprehensive observation of multiple Fermi
surfaces. Specifically, we observed a circular pocket
centered at Γ, which is derived from the p orbital of Sb
atoms embedded in the kagome lattice plane, and alarge hexagonal pocket at Γ and triangular pockets at K,
both of which originate from the 3d orbitals of the V
kagome lattice. A comparison of the Fermi surface at
x = 0.07 with that at x = 0 reveals intriguing trends: thecircular pocket expands with increasing x, while thetriangular pocket shrinks. The significant impact of theobserved band shift is a lifting of the saddle point near
the M point away from the Fermi level. Since TCDW
becomes higher when the saddle point is located atcloser to the Fermi level, a large density of states of thesaddle point plays a key role in stabilizing CDW.
Additionally, our findings suggest that the enhancementof Tc through Nb substitution is partly attributed to the
expansion of the circular pocket.

Fig. 1. (a) Crystal structure and (b) phase diagram ofCs(V1-xNbx)3Sb5. (c) ARPES intensity at the Fermi levelplotted as a function of two-dimensional wave vector.
Red, purple, and blue dashed lines are guides for theeyes to trace the experimental Fermi surfaces.
[1] T. Kato et al., Phys. Rev. Lett. 129 (2022) 206402.
[2] F. Matsui et al., Jpn. J. Appl. Phys. 59 (2020)
067001.

− 141 −BL2A

Mg K-edge NEXAFS of MgO, Mg(OH)2 and MgCO3
E. Kobayashi 1, S. Yoshioka 2 and K. K. Okudaira 3
1
Kyushu Synchrotron Light Research Center, 8-7 Yayoigaoka, Tosu, Saga 841-0005, Japan
Gradiate School of Engineering, Kyushu University, 744 Motooka Nishi-ku Fukuoka 819-0395 Japan
3
Graduate School of Science and Engineering, Chiba University,
1-33 Yayoi-cho Inage-ku, Chiba 263-8522, Japan

2

In recent years, organic photovoltaic (OPV) has been
attracting attention as a low-cost, lightweight battery
that replaces conventional solar cells. Metal oxides
plays an essential role as an electron and a hole transportlayer (ETL and HTL) material. [1,2] In order to further
improve the characteristics of these charge transportlayers, it is necessary to understand the band structure.
Near-edge x-ray absorption fine structure (NEXAFS)
spectroscopy is a powerful tool for investigating theunoccupied state of band structure of materials. When
discussing the band structure, information on theposition of the unoccupied bottom is important. It isnecessary to know the eﬀects on the bottom of theunoccupied band when metal oxides are contaminatedby atmospheric component such as OH and CO2.
Therefore, we measured the unoccupied state of MgO,
Mg(OH)2 and MgCO3・xH2O generated by theadsorption of OH and CO2 on the MgO surface.
NEXAFS spectra of the MgO, Mg(OH)2 and MgCO3・
xH2O powders using both total electron yield (TEY)and partial fluorescence yield (PFY) modes were
measured at the beamline 2A of the UVSOR in theInstitute of Molecular Science. For TEY, the draincurrent from the sample was measured. For PFY,
fluorescence X-rays were collected using an energy
dispersible silicon drift detector (SDD). All experiments
were performed at room temperature.
Figure 1 shows the Mg K-edge NEXAFS spectra of
MgO, Mg(OH)2 and MgCO3・xH2O powder obtained
from TEY mode. The peak positions of MgO, Mg(OH)2and MgCO3・xH2O spectra are diﬀerent. This suggeststhat their structures are diﬀerent. On the other hand, therising positions of the spectra of MgO, Mg(OH)2 andMgCO3・xH2O are very similar. This suggests that thebottom of the unoccupied band is the same. Figure 2
shows the Mg K-edge NEXAFS spectra of MgO,
Mg(OH)2 and MgCO3・xH2O powder obtained from
PFY mode. The rising positions of the spectra of MgO,
Mg(OH)2 and MgCO3・xH2O are very similar. It was

found that the bottom of the unoccupied state of MgO
was not aﬀected by contamination by atmosphericcomponent such as OH and CO2.

Fig. 1. Mg K-edge NEXAFS spectra of MgO, Mg(OH)2and MgCO3・xH2O powder obtained from TEY mode.

Fig. 2. Mg K-edge NEXAFS spectra of MgO, Mg(OH)2and MgCO3・xH2O powder obtained from PFY mode.
[1] I. Ierides et al., J. Mater. Chem. C 9 (2021) 3901.
[2] Y. –J. Lee et al., Adv. Energy Mater. 2 (2012) 1193.

− 142 −

Ⅲ-4 Surface, Interface and Thin Films

BL2A

Structural Analyses of Silicon Atoms in a Zero-dimensional Metal-atom
Encapsulating Silicon Cage Clusters by X-ray Absorption Spectroscopy
A. Nakajima and T. Inoue
Department of Chemistry, Faculty of Science and Technology, Keio University, 3-14-1 Hiyoshi, Kohoku-ku,
Yokohama 223-8522, Japanbetween the obtained spectra and the theoreticallycalculated FEFF spectra of structural isomers to obtainthe structural information.

Fig. 1. Photo of the connected chamber transported
from Keio University.

ROI / Photon (a. u.)

Since silicon (Si) element belongs to the same groupas carbon, it has been highly expected to create novel
low-dimensional compounds as fullerene and carbon
nanotube. In zero-dimensional silicon nanoclusters, it
has been found that metal-atom encapsulating siliconcage, M@Si16 superatom (SA), can be generated in a
gas-phase synthesis [1, 2]. In this study, the X-ray
absorption fine structure analysis (XAFS), especiallythe extensive X-ray absorption fine structure analysis(EXAFS), has been applied to thin films of M@Si16 SA
deposited on a solid surface to reveal the structural
information, compared with the structure obtained byquantum chemical calculations.
The Ta@Si16 SA, composed of tantalum (Ta) and Si,
was generated using a pulsed magnetron sputteringsystem, and Ta@Si16 SA cations were deposited on ahighly oriented pyrolytic graphite (HOPG) substratethat was set on a wobble stick, as ten layers with a spotof 6-8 mm in diameter. The deposited substrate was
kept in vacuum with an ion pump and transported from
Keio University to UVSOR, where an ion pump wasused with a nickel hydride battery (pumping speed
20L/s). The battery (24 V, 2000 mA h) can work in 10
hours, which covers the transportation time, and XAFS
measurements of the Si K-edge were performed at theBL2A beamline (Fig. 1). Absorption of Si atoms wasmeasured by the fluorescence method. The structure
was identified by comparing the obtained EXAFS
spectrum with the theoretically calculated FEFF
spectrum of three structural isomers (Td, D4d, and C3v).
For the deposited Ta@Si16 SA samples, XANES and
EXAFS measurements were performed for the Si
K-edge at 1800 to 2400 eV in the soft X-ray region(Fig. 2). For monitoring the incident light intensity, thescattered intensity of the copper mesh was used insteadof gold mesh, because there is no XAFS of copper inthe measurement energy region. However, the optics inthe beamline inevitably contain gold-coated ones, andthen X-ray absorption based on gold appears above
2000 eV; the light intensity decreases, where Si K-edge
signals should be observed from the thin Ta@Si16 SA
films. Although proper normalization of the incident
light intensity had been tried with the scatteredfluorescence from the measurement sample itself, theincident light intensity could not be accurately
evaluated, and then the measurement energy range wassqueezed to 1800-2000 eV (k = 3 - 7 Å-1). The EXAFS
vibrations in the soft X-ray region were compared

Background subtracted
spectrumRaw spectrum

Background signal
1800

2000

2200

2400

Photon energy (eV)Fig. 2. Si K-edge XAFS Spectra for the deposited Ta@
Si16 SA samples. The spectrum in blue was obtained bysubtracting background signal in red from raw spectrumin black. The spectrum in 1800-2000 eV was used forthe structural analyses.
[1] H. Tsunoyama, H. Akatsuka, M. Shibuta, T. Iwasa,
Y. Mizuhata, N. Tokitoh and A. Nakajima, J. Phys.
Chem. C 121 (2017) 20507.
[2] H. Tsunoyama, M. Shibuta, M. Nakaya, T. Eguchi
and A. Nakajima, Acc. Chem. Res., 51 (2018) 1735.

− 143 −

BL2B

Annealing Eﬀects on Surface Electronic Structure of MoO3
Nanoparticles by UPS
K. K. Okudaira1 and S. Ishii2,
1

Graduate School of Engineering, Chiba University, 1-33 Yahoi-cho, Inage-ku Chiba 263-8522, Japan
2
Graduate School of Science and Engineering, Chiba University,
1-33 Yahoi-cho, Inage-ku Chiba 263-8522, Japan

Organic photovoltaic (PV) cells have been the hot
research topic in recent years due to their advantages of
low-cost manufacturing, light weight and good
flexibility. Among these PV cells, solution-processedbulk heterojunction PV cells with donor–acceptor (D–A) blends sandwiched between the anode and cathodeare the most promising alternative to realize large-scale
production. In bulk heterojunction PV cells, the charges
generated in the active layer upon light absorption aretransported via D–A networks and collected by theelectrodes to realize light-electricity conversion.
Recently, the transition metal oxides (TMOs) wereinserted between the electrodes and organic active layer
to prevent the leakage of undesired charged carrier toelectrode as well as to promote the charged carriertransfer. [1] The eﬃciency of these electron transfer
layer (ETL) and hole transfer layer (HTL) largely
depend on the surface electronic structure of the TMO
layer.
In this work we prepared MoO3 nanoparticles (NPs)films with diﬀerent annealing atmosphere and estimatedthe electronic structure of MoO3 NPs by ultraviolet
photoelectron spectroscopy (UPS) measurements toestimate the eﬀect of annealing on the surface electronic
structure and the work function.
UPS measurements were performed at the beam line
BL2B of the UVSOR storage ring at the Institute for
Molecular Science at the photon energy (hν) of 28 eV.
MoO3 NPs were synthesized via solvothermal method.
[2] The thin films of MoO3 NPs were deposited on ITO
by spin casting (denoted as “non”). The films wereannealed at 500℃ in air and hydrogen atmosphere(denoted as “in air” and “in H2”, respectively). The
mean size of synthesized MoO3 NPs was about 10 ~ 30
nm using TEM measurements.
The whole spectral structure of MoO3 thin films byannealing in H2 atmosphere is almost same as that of
non annealing as shown in Fig. 1 (a). On the contrary,by annealing in air, the position of valence band top(VBT) is shifted to higher binding energy by about
0.3 ~ 0.4 eV. It is expected that the Fermi level leaves
from VBT due to the formation of defect states justabove the Fermi level by annealing in air. Furthermore,
the work function of MoO3 films by annealing in air islarger than that of non annealing MoO3 films by about
0.2 eV. This vacuum level shift is considered by theinterfacial dipole formation due to the introducing thehydroxyl group to the surface of the MoO3 film byannealing in air.

a

b

c

Fig. 1. UPS of MoO3 NPs at hν = 28eV (a) in thevalence band region (b) in the secondary cut-oﬀ and (c)in the valence top region.
[1] F. Liu et al., Sol. Energy Mater. Sol. Cells 94 (2010)842.
[2] W.-S. Kim et al., J. Nanopart. Res. 12 (2010) 1889.

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Ⅲ-4 Surface, Interface and Thin Films

BL3U

X-ray Absorption Spectroscopy Study of 4-MBA and Cysteine
on Gold Surfaces
F. Sato1, I. Sakaida1, S. Ohno1 and M. Nagasaka2
Graduate School of Engineering Science, Yokohama National University, Yokohama 240-8501, Japan
2
Institute for Molecular Science, Okazaki 444-8585, Japan

It is important to understand the behavior of
biomolecules on solid surfaces for the application to
medical device, biosensor and biocompatible material.
It is essential to study the adsorption and desorption
behavior of biomolecules and their response to theapplied electric fields. It is of particular importance toanalyze the dynamic behavior of biomolecules on asurface in electrolyte solutions, which is close to therealistic condition in the body of living creatures [1,2].
In the present study, potential-dependent adsorption/
desorption behavior of 4-mercaptobenzoic acid (4MBA) and cysteine on Au membrane surfaces havebeen investigated using soft X-ray absorption
spectroscopy (XAS) in the transmission mode. The
experiments were performed on the soft X-ray undulator
beam line at UVSOR-III, BL3U. We used H2SO4 and
KOH as the electrolyte solution. For the adsorption of
4-MBA molecules, the samples were immersed in
1mM 4-MBA/ethanol solution for more than 30 min.
For the adsorption of cysteine molecules, the samples
were immersed in 1mM cysteine/K-OH solution for
more than 1 hour.
In our previous study, we have studied the adsorption/
desorption behavior of 4-MBA on Au films using
surface diﬀerential reflectance spectroscopy (SDRS)
combined with cyclic voltammetry (CV) [3]. The key
issue was the interaction between functional group(-COOH) and Au films through Coulomb interaction
depending on the applied biases and pH conditions.
Redox processes involving charge transfer were clearlyobserved with CV and the relation between the change
in the reflectance spectra and the peaks in CV wasinvestigated in detail. Interestingly, we found some
precursor phenomena to cause significant changes in
the reflectance spectra with no corresponding signal in
CV. This indicates that such changes in the reflectancespectra are not due to the charge-transfer-type reactions
but rather to the subtle change in the orientation/
conformation of 4-MBA molecules. We also observed
similar eﬀects for cysteine.
To our knowledge, there has been no serious eﬀort tostudy the 4-MBA/Au and cysteine/Au systems using
XAS in terms of the aforementioned precursor
phenomena. At the initial stage, we have tried toobserved the eﬀects on Au(111). However, we could
not obtain the clear data showing the adsorption/
desorption behavior of 4-MBA, though they are

confirmed with CV measurements.
Here, we used an Au membrane as the substrate
which has polycrystalline structure. Our CV data revealthat there should be Au(111) part on the surface, andthat clear feature for adsorption/desorption for both
4-MBA and cysteine are confirmed.
In our previous XAS measurements, we havesucceeded in obtaining the absorption peak of calbonylgroup (-COOH) for 4-MBA. In this case, we observed
two distinct features at 532 and 535 eV in the O K-edge
region. These are assigned as due to the transition to theπ* orbital in the C=O double bond. Here, we observed
a rather weak feature at 533 and 536 eV for cysteine, as
shown in Fig. 1. We expect that these are the slightly
shifted components, similarly assigned to the C=O
double bond.
As a result, we could have established themeasurement set up for the transmission mode for both
4-MBA and cysteine. We now plan to investigate aseries of alkanethiol molecules to form self-assembled
monolayer (SAM), and compared their behavior with
4-MBA and cysteine.
The next step should be the observation of the change
in the orientation/conformation depending on theapplied bias to the electrode (Au membrane). We expectthat the precursor phenomena be proved more clearly.
0.5

Cysteine
Absorbance (x102)

1

0.0
-0.5
-1.0
-1.5
-2.0
530

535

540

545

Photon Energy (eV)Fig. 1. O K-edge XAS spectrum for cysteine.
[1] R. LeParc et al., Langmuir 22 (2006) 3413.
[2] C. I. Smith et al., J. Electrochem. Soc. 150 (2003) 1.
[3] N. Ikeda et al., ALC’19 (2019) 22.

− 145 −

BL3B

Evaluation of Growth Orientation and Crystallinity of Deep UV Emitting
Zinc Aluminate Thin Films
H. Kominami1,2,3, K. Inoue1, N. Uesugi1, K. Nie1, A. Adachi1, R. Isihara1, K. Yabe1,
J. Kamikawa2, T. Sadamori2, D. Takeya2, N. Miyazaki2, A. Dorokhina3 and S. Kurosawa4,51

Graduate School of Integrated Science and Technology, Shizuoka University,
2
Faculty of Engineering, Shizuoka University,
3
Graduate School of Science and Technology, Shizuoka University,
1~3
3-5-1 Johoku, Naka-ku, Hamamatsu, 432-8651 Japan
4
New Industry Creation Hatchery Center (NICHe), Tohoku University
6-6-10 Aza-Aoba, Aramaki, Aoba-ku, Sendai, Miyagi, 980-8579, Japan
5
Faculty of science, Yamagata University, 1-4-12, Kojirakawa-machi, Yamagata, 990-8560, JapanThe 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. In order to evaluate theinside of the film, an etching treatment was performed
using hydrochloric acid.
XRD measurement was performed on the preparedsample. As a result, diﬀraction peaks of (220)(311)(400)(333) were observed. XRD measurement was
performed on the prepared sample. As a result,diﬀraction peaks of (220)(311)(400)(333) wereobserved.
φ scan results of ZnAl2O4(220)(422)(533) andc-Al2O3 (110)(300) where diﬀraction peaks wereobserved in 2θχ/φ scans around the a- and m-planes, a
total of six diﬀraction peaks were observed every 60°.
The results are shown in Fig.1. This is a diﬀraction
peak with six-fold symmetry derived from α-Al2O3,
which is a hexagonal system. ZnAl2O4 is a cubic
substance, and ZnAl2O4 (220)(422)(533) also had atotal of six diﬀraction peaks at intervals of 60°.
In ZnAl2O4{220}{422}, there are 6 planes
perpendicular to ZnAl2O4 (333) every 60°. There is aface. From this, the diﬀraction peaks of ZnAl2O4 (220)(422)(533) with six-fold symmetry in the φ scan are
considered to be the diﬀraction peaks of a crystal inwhich ZnAl2O4 (333) is oriented on the c-plane ofc-Al2O3.
The six planes of ZnAl2O4{220} and {422} eachform an angle of 30°, and the m-plane and a-plane ofc-Al2O3 also form an angle of 30°. ZnAl2O4(220) and(422) are oriented along the m-plane and a-plane ofc-Al2O3, respectively, from the measurement results of2θχ/φ scans around the m-plane and a-plane of c-Al2O3,
so ZnAl2O4{422} and the a-plane of c-Al2O3, and them-plane of ZnAl2O4{220} and c-Al2O3 are parallel toeach other.
From Fig.1, there is a large peak of 6-fold symmetry
and a small peak of 6-fold symmetry at 30° shift (▼).
In addition, ZnAl2O4(220) is also oriented on thea-plane of c-Al2O3 from the measurement result of2θχ/φ scan around the a-plane of c-Al2O3. Thesediﬀraction peaks are thought to be due to crystals
formed by a phase relationship in which ZnAl2O4 isrotated 30° about ZnAl2O4[333], where the planes of
ZnAl2O4 and c-Al2O3 are parallel to each other. Sincealmost no diﬀraction peaks other than the above twomodels are observed, it is considered that the sample isformed by the relationship between the phases ofc-Al2O3 and ZnAl2O4 in these two models.
φ scans of ZnAl2O4(220) samples whose thin film
surface was etched by hydrochloric acid showed thatthe sample etched about 400 nm lost some of its internalorientation, while the sample etched about 450 nm lostits orientation largely. lost part.
From the CL measurement results of this sample, thesample etched about 400 nm maintained the UVemission intensity, but then the emission intensity
dropped sharply, and the sample etched about 450 nm
did not obtain UV emission. From these results, it isconsidered that a uniform ZnAl2O4 thin film is formed
from the sample surface to about 400 nm, but theformation of ZnAl2O4 is insuﬃcient inside.

Fig. 1. φ - scan XRD spectra of ZnAl2O4 and c-Al2O3.

− 146 −

Ⅲ-4 Surface, Interface and Thin Films

BL4U

Application of atomically-thin Graphene to X-ray Astronomy:
Soft X-ray Transmission Measurements
I. Mitsuishi 1, K. Kashiwakura1, Y. Niwa1, T. Ogawa1, M. Hirota1, Y. Tawara1, R. Kitaura2,
H. Yuzawa3, T. Ohigashi 3 and K. Tanaka3
1

Graduate School of Science, Division of Particle and Astrophysical Science, Nagoya University, Furo-cho,
Chikusa-ku, Nagoya, Aichi 464-8602, Japan2
Department of Chemistry, Nagoya University, Nagoya 464-8602, Japan
3
UVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan

20 mm

X-ray

Sample chamber

Graphene sample
on a quartz substrate

Fig. 1. Sample chamber and a close-up view of thegraphene sample on the quartz substrate with a taper
structure.
Single-layer
Five-layer

Transmission

Thin-film devices have been used in a large variety offields including astronomy. In X-ray astronomy, thinfilm devices have been prepared for payloads such asdetectors and telescopes and playing a key role as, e.g.,
optical and contamination blocking filters and thermal
shields [e.g., 1, 2]. For such thin film devices, severe
launch and space environmental tolerance and hightransmission are essential at the same time for highsensitivity space observations in the limited observing
time. Plastic films such as polyimide have often been
adopted as thin films. However, there is still room for
improvement especially in transmission of a soft energy
range below 1 keV. Thus, we have proposed to makeuse of graphene which is an atomically-thin material
but has excellent mechanical strength. Our idea is to
apply graphene to thin film devices in X-ray astronomy[3].
As a first step, we conducted rough X-ray transmission
measurements from 100 to 500 eV and confirmed very
high transmission for both single- and five-layer
graphene sample [3]. As a next step, we performed
detailed X-ray transmission measurements tounderstand systematic errors for the observed values inthis experimental setup and aging degradation as shownin Fig. 1. We used the same quartz substrates with large
tapers with an angle of 30 degrees to avoid the
shadowing eﬀect by the substrate for focused X-ray
photons by the Fresnel zone plate. Consequently, very
high transmission, specifically 94-99% and 95-101%
for single- and five-layer graphene samples in nominal
values except the C K-edge structure, was obtained.
The systematic errors are estimated to be 3% for oursample in this experimental setup considering shortand long-term time variability and spatial dependence
and thus, there is no significant diﬀerences in thetransmission between the samples within the systematic
errors in our current experimental setup. This suggeststhat very high transmission is expected even for fivelayer graphene films with much stronger mechanicalstrength which allows us to fabricate free-standing
structures with larger diameter much easier. The results
are shown in Fig. 2. We confirmed that there is no
significant aging degradation at least for the singlelayer graphene sample for 9 months. The paper
including these results is being prepared (Kashiwakura,
Mitsuishi et al., in prep.).

Energy [eV]Fig. 2. Resultant transmission from 100 to 500 eV forsingle- (filled circle) and five-layer (triangle) graphenesamples (Kashiwakura, Mitsuishi et al., in prep.).
Systematic errors are +/-3%.
[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.
[3] I. Mitsuishi et al., UVSOR Activity Report 2021 49(2022) 45.

− 147 −

BL4B(XMCD)

Tuning Magnetic Properties of Atomic Layer Materials
by organic-inorganic Interfacial Magnetic Coupling
H. Ono1, Y. Umeda1, K. Yamamoto3,4, O. Ishiyama3,4,
T. Yokoyama3,4, M. Mizuguchi1,2 and T. Miyamachi1,21Department of Materials Science and Engineering, Nagoya University, Aichi, 464-8603, Japan.
Institute of Materials and Systems for Sustainability (IMaSS), Nagoya University, Aichi, 464-8601, Japan.
3
Institute for Molecular Science, Myodaiji-cho, Okazaki 444-8585, Japan
4
The Graduate University for Advanced Studies, Myodaiji-cho, Okazaki 444-8585, Japan

2

Organic materials are expected to be useful to
spintronics devices due to their low spin current
dissipation derived from weak spin-orbit interaction.
Organic-inorganic hybrid interface has been studied
because of its controllable interfacial spin state via theproximity eﬀect. Spin-dependent electron transport
properties depend on the electronic interaction between
organic and inorganic materials and local interface
structures. Thus, understanding structural, electronic
and magnetic properties of the organic-inorganicinterface on the level of single molecules is important
for realizing molecular spintronics devices. However,microscopic details of the hybrid interface have notbeen clarified so far.
In this study, we fabricate organic-inorganic hybrid
films and investigate their intrinsic electronic andmagnetic properties on the level of single molecules.
For this purpose, ferromagnetic iron nitride atomic
layers with γ’-Fe4N stoichiometry were chosen as aninorganic material, which uniformly grow and showhigh surface quality on the atomic scale [1,2]. Molecularlayers composed of planer cobalt phthalocyanine(CoPc) were chosen as an organic material. Structural,electronic and magnetic properties of the hybridinterface 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 x-ray
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 thickness-dependent
structural properties of CoPc layers on the interfacial
Fe and Co spin states were investigated by 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 confirm the magnetic coupling for
CoPc(1ML)/γ’-Fe4N from the finite of Co XMCD
signal. The perpendicular magnetic anisotropy of γ’Fe4N, which is proportional to the diﬀerence between
out-of-plane and in-plane Fe orbital magnetic moment
obtained by XMCD sum rule, becomes larger after thedeposition of CoPc molecules on the γ’-Fe4N. This
result indicates the magnetic coupling with CoPc
enhances the perpendicular magnetic anisotropy of γ’Fe4N. As for magnetic properties of CoPc, we find that
Co out-of-plane and in-plane XMCD signals show
diﬀerent behaviors with increasing the amount of CoPc.
While the out-of-plane Co XMCD signal gradually
decreases with increasing CoPc thickness, the strong
Co XMCD is maintained in the in-plane direction.
Taking the random stacking of CoPc layers revealed by
STM and LEED, these results indicate that the orbital
dependent magnetic coupling between CoPc layers,i.e., the magnetic coupling via the in-plane Co 3d
orbitals is weak, but that via the out-of-plane Co 3d
orbitals relatively robust.
[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.

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Ⅲ-4 Surface, Interface and Thin Films

BL4B (XMCD)

X-ray Magnetic Circular Dichroism Study of Chiral Antiferromagnetic
Co2-xPdxMo3N Thin Films
B. Qiang1,2, M. Togashi3, T. Fukasawa1, T. Hajiri1, M. Kuwahara3,4, H. Asano1,5 and T. Ito61
Department of Materials Physics, Nagoya University, Nagoya, Japan, 464-8603
Department of Materials Design Innovation Engineering, Nagoya University, Nagoya, Japan, 464-8603,
3
Department of Applied Physics, Nagoya University, Nagoya, Japan, 464-8603
4
Institute of Materials and Systems for Sustainability, Nagoya University, Nagoya, Japan, 464-8603
5
Research Department, Nagoya Industrial Science Research Institute, Nagoya, Japan, 464-0819
6
Synchrotron Radiation Research Center, Nagoya University, Nagoya, Japan, 464-8603

2

Dzyaloshinskii-Moriya (DM) interaction-induced
magnetic skyrmions [1,2] have been observed in manychiral magnets with broken space reversal symmetry[3,4]. Recently, filled β-Mn-type Fe2-xPdxMo3N [5] andCo2-xPdxMo3N (CPMN) [6,7] have been reported tohost small size skyrmions at room-temperature, which
are a good playground for skyrmion device applications.
X-ray magnetic circular dichroism (XMCD) is known
as a very powerful tool to detect the element-specificspin and orbital states in each site. In this study, we
have applied XMCD on filled β-Mn-type CPMN toelucidate the relation between its magnetism, especiallyferromagnetic skyrmions at the low-temperature(Spiral-II) phase [6], and spin and orbital magnetic
moment of Co.
CPMN (x=1.01) thin film (30 nm in thickness,without capping layer) was prepared using magnetron
sputtering technique grown on C-sapphire substrates.
Measurements of XAS/XMCD were performed at theBL4B in UVSOR by total electron yield mode at T = 4
K (Spiral-II phase). The external magnetic fields H up
to ±1 T were applied in parallel to the surface normal
axis. The circularly polarized x-ray beam was induced
nearly parallel to H. It should be noted that each Co L2,3
XAS spectra at H = +0.5 ~ +0.1 T (-0.5 ~ -0.1 T) wereobtained after the magnetization due to canted
antiferromagnetism being saturated at H = - 1 T (+ 1 T),
since the magnetic skirmions in this system is expected
to be generated around H = ±0.2 T asymmetrically withrespect to the zero field (see inset of Fig. 1(b))[6].
Figures 1(a) and 1(b) show the magnetic fielddependence of the Co L2,3 edge-XAS spectra of CPMN
(x = 1.01) and the XMCD spectrum obtained bysubtracting XAS spectra between H = +1 T (~ +0.1 T)
and H = -1 T (~ -0.1 T), respectively. It can be seen thata clear XMCD is observed at H = ±1 T, where the spinstate associated with the formation of canted
antiferromagnetism is expected from the magnetic andtransport measurements at the low temperature region.
With decreasing magnetic field, the observed XMCD
intensity gradually decreases, and a opposite sign of the
XMCD intensity near the L3 edge at 778 eV appears in
the region of H < ±0.25 T, where magnetic skirmion

formation is expected from the topological Hall eﬀect
measurement (Fig. 1(b), inset). We expect that theobserved magnetic field dependence of XMCD near the
low-energy edge might suggest the change in themagnetic structure associated with the formation ofmagnetic skirmions on CPMN.

Fig. 1. (a) XAS spectrum at the Co L2,3 edge obtainedby using the photon helicity parallel (μ+, red) andantiparallel (μ-, blue) to the external magnetic field H,
respectively. (b) External magnetic field dependence of
XMCD spectra (μ+−μ-) for CPMN (x=1.01) at T = 4 K.
Inset shows the field dependence of topological Halleﬀect [6].
[1]T. Jo, J. Phys. Soc. Jpn. 62 (1993) 1814.
[2]Y. Teramura, A. Tanaka, and T. Jo, J. Phys. Soc. Jpn.
65 (1996) 1053.
[3]C. Papas et al., Phys. Rev. Lett. 102 (2009) 197202.
[4]V. Kumar et al., Phys Rev B 101 (2020) 014424.
[5]B. W. Qiang et al., Appl. Phys. Lett. 117 (2021)
142401.
[6]B. W. Qiang et al., Jpn. J. Appl. Phys. 61 (2022)
120901.
[7]B. W. Qiang et al., AIP Advances 13 (2023) 025138.

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BL4B(XMCD)Controlling Magnetic Anisotropy of Magnetic Thin Film Heterostructures
Y. Umeda1, H. Ono1, K. Yamamoto3,4, O. Ishiyama3,4,
T. Yokoyama3,4, M. Mizuguchi1,2 and T. Miyamachi1,21Department of Materials Science and Engineering, Nagoya University, Aichi, 464-8603, Japan.
Institute of Materials and Systems for Sustainability (IMaSS), Nagoya University, Aichi, 464-8601, Japan.
3
Institute for Molecular Science, Myodaiji-cho, Okazaki 444-8585, Japan
4
The Graduate University for Advanced Studies, Myodaiji-cho, Okazaki 444-8585, Japan2

3d transition metal ordered alloy thin films with L10
crystal structure are attracting attention as rare-earth
free magnetic materials due to their large perpendicularmagnetic anisotropy, large magnetic moment, and highCurie temperature. Using pulsed laser deposition, thegrowth of FeCo thin films with alternating Fe and Co
atomic layers was investigated [1]. Although mucheﬀort has been made to realize uniaxial anisotropy in
the L10-FeCo phase, the L10 structure is a nonequilibrium state of the FeCo phase and hence themethod for achieving the out-of-plane magnetization
has not been established. The main problem could becaused by atomic-scale disorder at the Fe/Co interface
during growth processes, which highlights theimportance of microscopic characterizations of thestructural, electronic, and magnetic properties of L10FeCo. Therefore, we intend to fabricate high-quality
FeCo alloy thin films on Cu(001) substrates by utilizing
the nitrogen surfactant eﬀect of a monatomic layer
nitride. The high surface lattice stability of a monatomic
layer nitride and the nitrogen surfactant eﬀect thateﬀectively suppresses the interdiﬀusion at theheterointerface could lead to the growth of FeCo alloy
thin films with atomically flat and uniform interfaces[2,3]. The important role of the nitrogen surfactant
eﬀect in the preparation of high-quality L10-type alloy
thin films has been demonstrated for FeNi alloy thinfilms [2].
In this study, FeCo ordered alloy thin films in theinitial growth stage were prepared using the nitrogensurfactant eﬀect. The correlation between the structuralchanges at the FeCo interface and magnetic properties
upon sample heat treatment was investigated using
low-energy electron diﬀraction (LEED) and X-ray
absorption spectroscopy/X-ray magnetic circulardichroism (XAS/XMCD). FeCo alloy multilayer thinfilms were grown on Cu(001) using the following
process: (1) a bilayer iron nitride (Fe2N/Fe) was firstgrown on Cu(001), (2) 1 monolayer (ML) of Co was
deposited at a low temperature (~150 K), (3) annealing
was carried out at 300, 570, and 670 K, and (4)additional 1 ML of Fe was deposited at a lowtemperature (~150 K) for samples heated at 570 K(FeN/Co/Fe/Fe).
The
annealing
temperaturedependence of electronic and magnetic properties wasinvestigated by XAS/XMCD.XAS/XMCD measurements
were performed at BL4B in UVSOR by total electron
yield mode at B = 0 - ± 5 T and T = 7.9 K. The XMCD
spectra are obtained at the normal (NI: θ = 0°) and thegrazing (GI: θ = 55°) geometries. Note that θ is theangle 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 iron nitride is greaterin the GI geometry than in the NI geometry, revealing
its strong in-plane magnetic anisotropy as previously
reported [3]. Adding 1 ML Co activates the nitrogensurfactant eﬀect [2], which leads to the formation of
CoN in the topmost layer (CoN/Fe/Fe). Accordingly,
we observed an increase in the out-of-planemagnetization of the Fe layer from Fe magnetization
curves. The perpendicular magnetic anisotropy of the
Fe layer is further enhanced by annealing at 570 K.
However, at an annealing temperature of 670 K, adecrease in the coercivity of the Fe layer is observed.
Taking into consideration the annealing temperaturedependence of the LEED pattern, the enhancement of
the out-of-plane magnetization could be due toimproved ordering of the Co/Fe interface up toannealing temperatures of 570 K. At 670 K, surface N
atoms start to desorb, which induces the interdiﬀusionof interfacial Co and Fe atoms and consequently lowers
the coercivity. In the sample with additional Fe
layers (FeN/Co/Fe/Fe), the perpendicular magnetic
anisotropy of Fe is further enhanced.
[1] H. Ito et al., AIP Adv. 9 (2019) 045307.
[2] K. Kawaguchi et al., Phys. Rev. Mater. 4 (2020)
054403.
[3] Y. Takahashi et al., Phys. Rev. B 95 (2017) 224417.

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Ⅲ-4 Surface, Interface and Thin Films

BL4B

X-ray Photoemission Spectroscopy and X-ray Absorption Spectroscopy
Measurement of the Chiral Molecule on the Metal Substrate
F. Nishino1,2, K. Fukutani 1,2, P. I. Jaseela1,2, H. Iwayama1,3, S. Makita3 and S. Kera1,2,3,4
1
Institute for Molecular Science, Okazaki 444-8585, JapanThe Graduate University for Advanced Studies (SOKENDAI), Okazaki 444-8585, Japan
3
UVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
4
Graduate School of Science and Engineering, Chiba University, Chiba 263-8522, Japan
2

Chirality-induced spin selectivity (CISS) is aphenomenon in which the spin of an electron ispolarized/filtered in the process of electron transfer(transmission) in a system with broken mirror
symmetry. The spin polarization by chiral molecular
CISS in the gas phase was studied from 1980’s. Since it
was reported that the spin polarization was less than
0.5%, CISS has not attracted wide attention at this time.
However, in 1999, R. Naaman et al. reported that spinunpolarized electrons that transmitted through thechiral molecular film on solids exhibited spinpolarization as high as 60% at room temperature [1].
While the CISS does not require magnetic materials or
external magnetic fields, it exhibits higher spinpolarization than the spin filters using magnetic metals.
These features are expected to be applied to magnetic
storage media with high storage density. Therefore,
CISS by organic chiral molecules has been actively
studied both theoretically and experimentally toelucidate its mechanism and for the purpose of device
applications. Presently, however, the details of
mechanism why chiral molecular film on solid exhibits
spin polarization larger than 1000 times that of gasphase molecules remains unsolved. For this reason, thegap between the theory and the application research is
growing. In order to elucidate the mechanism, it isnecessary to rigorously observe the interaction between
the travelling electrons and the chiral molecules. In
order to understand the CISS processes in chiralmolecules, it is important to investigate how CISSeﬀect depends on the relative orientations among thechiral molecules, the substrate, and the direction ofelectron transmission. Also, the diﬀerence of electronic
structure and structure between the gas phase and thechiral molecular film on substrate.
In this study, the chiral molecule 2,2’-Bis(diphenylphosphino)-1,1’-binaphthyl (BINAP hereafter) shownin Fig. 1(a) were deposited on a clean Au(111) substrate,and in-situ X-ray photoemission spectroscopy (XPS)
measurements were performed to investigate theinteractions between BINAP molecules and Au(111)substrate.
Figure 1(b) shows the results of XPS from thephosphorus (P) 2p core orbital of BINAP molecules,acquired at the nominal coverages of 0.4 monolayer(ML) and 2 ML of (R)-BINAP on Au(111).
Interestingly, while the molecules at the sub-monolayer coverage (0.4 ML) are expected to interact
more strongly with the substrate than the multi-layer
coverage (2 ML), we find that the P2p core peaks
appear very similar, as can be seen from the peak fitting
results for the two peaks [labelled A and B in Fig. 1(b)].
This likely signifies that the intermolecular interactions
are much stronger (which determines the chemical shiftof the atomic orbitals) than the molecule-substrateinteractions. This view is indeed consistent with thelater measurements in our project using the low-energy
electron diﬀraction (LEED) and scanning tunnelling
microscopy (STM), which clearly reveals the weaklyinteracting incommensurate molecular overlayer
structures.

Fig. 1. (a) Molecular structures of (R)- and (S)BINAPs. (b) P2p core level peaks of (R)-BINAP on
Au(111) measured by XPS at the nominal coverages of
0.4 ML (bottom) and 2 ML (top). The spectra at eachcoverage are fitted with the two spin-orbit doublets[labelled A (green) and B (blue)] with Doniach-Sanjiclineshape.
[1] K. Ray, S. P. Ananthavel, D. H. Waldeck and R.
Naaman, Science 283 (1999) 814.

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BL4B

Observation of Heat Treatment Eﬀects of Amorphous Selenium Thin Filmby Vacuum Ultraviolet Transmission Spectrum
K. Hayashi
Department of Electrical, Electronic and Computer Engineering, Gifu University, Gifu 501-1193, Japan

It is well-known that various photoinduced
phenomena [1,2] such as changes in optical band gap,
conductivity, and volume occur in chalcogenide
amorphous semiconductors by light irradiation.
Although many studies have been done on thephotoinduced phenomena of these materials, little is
known about the details of these mechanisms. Thesephenomena were studied by exciting outer coreelectrons with the irradiation of light with the energy
corresponding to the optical bandgap or sub-bandgap.
The interest has been attracted for the change of the
optical properties in the energy region of the visible
light. We are interesting for the changes of the opticalproperties in the higher energy region. To obtain a wide
knowledge of the photoinduced phenomena, it isnecessary to investigate to the photoinduced and heat
treatment eﬀects on wide energy region. In this report,
we report heat treatment eﬀects on the vacuum
ultraviolet (VUV) transmission spectra of amorphousselenium thin film.
Sample used for the measurement of the VUVtransmission spectra was amorphous selenium 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 wasmeasured by using the silicon photodiode as a detector.
Two pinholes of 1.5mm 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 level absorptionof the aluminum film. Observation of the heat treatmenteﬀect in the VUV transmission spectrum was carriedout by performing heat treatment for one hour at eachtemperature up to 363K.
Figure 1 shows heat treatment eﬀects on the VUVtransmission spectrum of an amorphous selenium thinfilm. Main absorption peaks around 22nm corresponds
to the 3d core level of Se atom. The absorption spectrum
observed in the amorphous selenium thin film isroughly consistent with the previous report [3].
Although the spin-orbit splitting of the 3d5/2 and 3d3/2
level of Se atom is not clearly resolved in thisamorphous selenium thin film. I don’t know the cause,
but there may be diﬀerences in the preparation

conditions of the film. As can be seen from the figure, asignificant change in the VUV transmission spectrum isobserved by heat treatment at temperatures above
343K. We are also studying the eﬀect of heat treatment
on the photoconductivity of amorphous selenium thinfilms in our laboratory. There is a correlation between
the heat treatment eﬀect on photoconductivity andVUV transmission spectrum, and it is thought that thischange is due to the crystallization of the amorphousselenium thin film. From the VUV transmission
spectrum change of selenium thin films by heat
treatment, it can be seen that the broad peak around
20nm in the VUV transmission spectrum of amorphousselenium thin films is composed of about threeabsorption peaks. It is not clear about the origin ofbroad spectra and several peaks. I think that these
origins are related to the local structures of theamorphous network. The detailed experiments andanalysis will be done in the next step. More detailed
experiments are necessary to clarify the origin of the
VUV transmission spectra.

Fig. 1. Heat treatment eﬀects on the VUV transmission
spectrum of amorphous selenium film.
[1] K. Tanaka, Rev. Solid State Sci. 4 (1990) 641.
[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.

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Ⅲ-4 Surface, Interface and Thin Films

BL4B

UV-X-ray Transmission Measurements of Atomically Thin Graphene
Astronomical Applications
I. Mitsuishi 1, K. Kashiwakura1, Y. Niwa1, T. Ogawa1, R. Kitaura2, E. Nakamura3,
M. Nagasaka3 and K. Tanaka3
1

Graduate School of Science, Division of Particle and Astrophysical Science, Nagoya University, Furo-cho,
Chikusa-ku, Nagoya, Aichi 464-8602, Japan2
Department of Chemistry, Nagoya University, Nagoya 464-8602, Japan
3
UVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan

Thin-film devices have been utilized in a great variety
of uses as not only ground-based but also space-based
applications such as optical and contamination blocking
filters and thermal shields [e.g., 1, 2]. Recently,
polyimide films have often been used as thin films
considering relatively stronger mechanical strength inplastic films. However, there is still room of
improvement in sensitivity of the thin films (=transmission) below 1 keV including UV region
although such energy ranges are very informative forunderstanding, e.g., stellar coronae and large-scale
structure of the Universe [e.g., 3, 4]. Thus, we haveproposed to make use of graphene which is anatomically-thin material but has excellent mechanicalstrength. Our idea is to apply graphene to thin film
devices in X-ray astronomy [5].
As a first step, we measured reflectivity at a soft
X-ray range between 100 and 500 eV successfully forsingle- and five-layer graphene samples at BL4U andconfirmed very high transmission above 90% except C
K-edge structure [5]. Thus, as a next step, we tried tomeasure transmission in UV region below 100 eV andconstruct our original experimental setup at BL4B. Our
experimental setup is shown in Fig. 1 and we prepareda five-layer graphene sample with a diameter of 300
μm on a quartz substrate to obtain larger photon
statistics. To check the consistency of transmission
between the beamlines of BL4U and BL4B, we used
the same sample and measured transmission from 100
to 250 eV as well. Consequently, we measured
transmission from 30 to 100 eV successfully andconfirmed very high transmission from 91 to 101% in
nominal values with systematic errors of 5% due toshort- and long-term time variability. We confirmedthat there are no significant diﬀerences in 100-250 eV
between the results obtained from BL4B and BL4U.
The results are summarized in Fig. 2. A slight decreasing
trend can be seen toward 30 eV even though thesystematic errors are high (5%). This trend is the sameas the expected from a database for bulk carbon. In
order to verify the trend, we need additional
measurements with smaller measurement accuracyof <2% down to 10 eV. The paper including theseresults is being prepared (Kashiwakura, Mitsuishi etal., in prep.).

Fig. 1. Sample chamber and a close-up view of thegraphene sample on the quartz substrate.

Fig. 2. Resultant transmission from 30 to 250 and from100 to 250 eV for five-layer graphene samples measured
at BL4B (filled triangle) and BL4U (filled circle)(Kashiwakura, Mitsuishi et al., in prep.). Systematic
errors are 5% / 3% at BL4B / BL4U.
[1] P.J. Serlemitos et al., Publ. Astron. Soc. Japan 47(1995) 105.
[2] P.J. Serlemitos et al., Publ. Astron. Soc. Japan 59(2007) S9.
[3] I. Mitsuishi et al., Publ. Astron. Soc. Japan 64(2012) 18-1.
[4] S. Takasao, I. Mitsuishi et al., The Astrophys. J. 901(2020) 70.
[5] I. Mitsuishi et al., UVSOR Activity Report 2021 49(2022) 45.

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BL4B

Si L-edge NEXAFS Spectra of Native Oxide Si Wafer
with Diﬀerent Crystal Surface
K. K. Okudaira1, S. Yoshioka 2 and E. Kobayashi3
1

Graduate School of Engineering, Chiba University, 1-33 Yahoi-cho, Inage-ku Chiba 263-8522, Japan
Gradiate School of Engineering, Kyushu University, 744 Motooka Nishi-ku Fukuoka 819-0395 Japan
3
Kyushu Synchrotron Light Research Center, 8-7 Yayoigaoka, Tosu, Saga 841-0005, Japan

2

Silicon dioxide is one of the most popular substrate
for inorganic semiconductor devices as well as organic
devices such as self-assembled monolayers, which isuseful for organic field eﬀect transistors. [1] One
important advantage of the silicon substrate over the
metal substrate is that conductive currents are
eliminated. The leakage current is relatively large byusing native oxide Si wafer as dielectric layer due to thethinness and inhomogeneous of oxide layer of nativeoxide Si wafer. The application of self-assembled
monolayer to SiO2/Si substrate depress the leakage
current. [2] The electrical properties such as insulation
characteristics depends on the structure of surface
silicon dioxides layer, which is considered amorphous.
It is expected that the properties of native oxide layer
on Si substrates would be aﬀected by the underlying
crystalline Si.
In this report, we investigate the eﬀect of crystal
structure of underlying crystalline Si on the surface
structure of silicon dioxide by means of NEXAFS ofnative oxide Si(001) and Si(111) wafers.
NEXAFS spectra of the native oxide Si(001) andSi(111) wafers were measured at the beamline 4B of
the UVSOR in the Institute of Molecular Science. In
the total electron yield (TEY), the drain current of thesample was measured. All experiments were performedat room temperature.
Figure 1 shows the TEY Si L-2,3 edge NEXAFS
spectra of native oxide of Si(111) and Si(001) wafers.
In the observed fine structure two region are identified.
The absorption features observed from 100 to 104 eV
are attributable to Si0 (crystalline Si under native oxide
layer) and those from 104 to 110 eV are associated with
Si4+ (SiO2) [3]
In the hν range from 100 eV to 104 eV due to the Si
crystalline layer, the spectral structure of Si(001) is
identical with the one of Si(111). On the contrary, thespectral feature of native SiO2/SI(001) is diﬀerent fromthat of SiO2/Si(111) in the hν range from 104 to 110 eV,

which is attributed to native oxide layer (SiO2). By
closed comparison the relative intensity of the peak a1
at hv of 106 eV to that of the peak a2 at hν of 106.8 eV
for the SiO2/Si(001) is diﬀerent from that of SiO2/
Si(111). The peak a1 disappears in the observed Si
L-edge NEXAFS of native oxides Si(111) wafer. The
peaks a1 and a2 can be assigned to 2p3/2 and 2p1/2 → theantibonding orbital of Si 3s character. [4] Harp et al.
shows the peak positions of a1 and a2 depend on not
only the oxidation state but also the thickness of nativeoxide layer [5]. These diﬀerences indicate that theproperties of surface native oxide layer such as bonding
structure as well as oxidation states are aﬀected byunderlying crystalline Si layer.

a1 a2Fig. 1. Si L-edge NEXAFS of native oxide Si(001) andSi(111) wafers in TEY mode
[1] M. McDowell et al., Appl. Phys. Lett. 88 (2006)
073505.
[2] M. -H. Yoon et al., PNAS 102 (2005) 4678.
[3] M. Kasrai et al., Appl. Surf. Sci, 99 (1996) 303[4] M. Kasrai et al., J. Vac. Sci, Tech. A11 (1993) 2694.
[5] G. R. Harp et al.,. J. Vac. Sci, Tech. A8 (1990) 2566.

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Ⅲ-4 Surface, Interface and Thin Films

BL5U

ARPES from Si{111} ξ૜ × ξ૜-Ag ultra-thin Film on Artificially Designed
three-dimensional Si facet-line Structure with {111} Facet Surfaces
on Si(001) Substrates
K. Hattori1, Ni’matil Mabarroh1, Juharni1, Y. Ida1, W. Imayama1, Y. Kimoto1, Y. Kitagawa1,
S. Tanaka2, A. N. Hattori2, S. Suga2 and K. Tanaka3
1

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, Japan

Highly densified device like 3D FET has beenrequired by information society to break the limitationof miniaturizing 2D planar-type devices. Control of 3D
structure device is indispensable to improve thespecification, such as carrier mobilities on any direction
surfaces of the 3D structures.
Recently, our group has successfully created 3D-Si
surfaces by combining lithography and surface
treatment techniques [1-4], and reported a successful
creation of Si{111} 7×7 clean facet surfaces showing
surface and bulk electronic bands on Si(110) substrates
using laboratory based angle-resolved photoelectron
spectroscopy (ARPES) [5], aiming for a future
3D-surface band-engineering. Here, we first
demonstrated the creation of ultra-thin film on 3D Si
clean facet surfaces indicating characteristic film band
structures, essential for the 3D surface control.
In our experiment, 3D Si facet-lined structures with
(111) and (1ത 1ത 1) facet surfaces and [1ത 10]-direction faceedges on (001) substrates with the facet pitch of 4 μm
period, were prepared by using a photo-lithography andwet etching (Fig. 1). After degassing and flashing thesample in ultra-high vacuum, {111} 7×7 reconstruction
was confirmed by low-energy electron diﬀraction(LEED). Subsequently Ag was deposited on the sample
at ~770 K, showing ξ3 × ξ3 reconstruction in bothFig. 1. SEM image of 3D
Si facet-lined structure.

Fig. 2. LEED pattern of{111} ξ3 × ξ3 -Ag facet
surfaces (120 eV).

Fig. 3. ARPES geometry. 60
eV photons (pink) result inelectron emission (purple)
from (111) facet surfaces.

(111) and (1ത 1ത 1) facet surfaces. Note that thesuperposition of the LEED patterns from the two facet
surfaces are seen in Fig. 2.
ARPES was also performed in UVSOR at BL5U.
Valence band dispersion was measured mainly at 70 eV
photons with the (111) facet surface normal to theanalyzer at 6 K, by optimizing the sample orientation(Fig. 3). We obtained the specific band structurescaused by ξ3 × ξ3 -Ag ultra-thin film on the (111)facet surface (Figs. 4a and 4c), which was almost thesame as those of the ξ3 × ξ3 -Ag on a 2D planar
surface (Figs. 4b and 4d) measured under the same
condition.
We confirmed that ARPES under optimizing 3D
geometries informs us band structures of artificiallydesigned 3D structure surfaces and “created films”.
This will shed the light on future band engineering of
3D devices.

Fig. 4. E-k along [1ത 1ത 2] (a, b) and kx-ky near Fermi level(dashed lines in a and b) (c, d) for facet (a, c) and planar(b, d) (111) ξ3 × ξ3 -Ag surfaces.

[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] A.N. Hattori and K. Hattori, 21st Century Surface
Science (IntechOpen, London, 2020).
[4] S. Nakatsuka, T. Abukawa, A.N. Hattori, K. Hattori,
et al., e-J. Surf. Sci. NanoTechnol. 19 (2021) 13.
[5] K. Hattori, A. N. Hattori, et al., e-J. Surf. Sci.
Nanotechnol. 30 (2022) 214.

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BL5U

Sizable Rigid Shift of the Valence Band of h-BN by Cs-doping
S. Ichinokura1, A. Hemmi2, H. Cun2, K. Tanaka3, T. Greber2 and T. Hirahara1
1
Department of Physics, Tokyo Institute of Technology, Tokyo 152-8551, Japan
Physik-Institut, Universität Zürich, Winterthurerstrasse, 190, Zürich CH-8057, Switzerland
3
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan

2

Hexagonal boron nitride (h-BN) is a two-dimensional
semiconductor with a wide bandgap. Its gap size ofaround 5.9 eV corresponds to deep ultraviolet light,
making h-BN a promising material for the developmentof energy-eﬃcient optical disinfection devices. To
reduce the working voltage of electroluminescencethrough tunneling carrier injection, it is required todevelop p- and n-doping near the electrodes. However,
the wide gap in h-BN poses a challenge for carrier
doping through conventional substitution methods,
which limits its use in electroluminescence devices.
To address this challenge, we are exploring analternative approach known as chemical gating, which
involves surface adsorption or intercalation of alkali
metals (AMs) to the substrate interface. This creates anelectrical dipole by facilitating charge transfer from theAMs to the substrate. Cs-doping has been shown to
induce the largest electron doping in h-BN/Ir, where thevalence band maximum (VBM), specifically the top of
the π band at the K point, was indirectly estimated to be
at 5.9 eV from the shift of the σ band at the Γ point,
assuming a rigid band shift [1]. However, the limits ofdoping remain unclear until the direct observation of
the band structure in a wide wavenumber range from Γ
to K point.
In the present study [2], we conducted an analysis of
the complete valence band structure of monolayerh-BN on Rh substrate before and after Cs doping via
angle-resolved photoemission spectroscopy (ARPES)
utilizing synchrotron radiation as a light source. The
h-BN/Rh was grown by means of chemical vapor
deposition. The doping of Cs was carried out via
vacuum deposition at room temperature in the
preparation chamber of the BL5U end station, followed
by in-situ measurements of ARPES utilizing linear
polarized light with hν = 72 eV at 200 K. Figures 1(a)and (b) depict the valence band spectra before and afterCs doping obtained by horizontally polarized (H-pol.)light, respectively, whereas Figures 1(c) and (d) show
the same as Figs. 1(a) and (b), respectively, obtained byvertically polarized (V-pol.) light. The uppermost
portion of the π band is located at the K point with ahigher binding energy than the top of the σ band at theΓ point, making it possible for us to evaluate the VBM.
EVBM and E’VBM are defined as the binding energy of the
VBM before and after doping, as denoted by dashedblack lines. The shift of the VBM, ΔE = E’VBM - EVBM is

observable to be 2.5 eV, identical to the σ band at the Γpoint (refer to Figs. 1(c) and (d)). This clearly suggests
a rigid shift of both the π and σ bands. Notably, Cs
doping lowers the VBM to 5.7 eV. Considering the
bandgap of h-BN is known to be 5.9 eV, the conduction
band should lie only 0.2 eV above the Fermi surface.
Thus, h-BN experiences significant electron doping.
As a concluding remark, for both Rh and Ir substrates,
the VBM attained binding energy nearly equated to theband gap. This can be elucidated by the vacuum levelalignment model when Cs is adsorbed on both sides ofh-BN. This indicates that Cs with the lowest work
function is the most eﬃcacious, and this method can be
implemented on an electroluminescence device usingh-BN with any electrode.

Fig. 1. ARPES spectrum of hBN along Γ-K-M line in
the Brillouin zone. Panels (a) and (c) display thespectrum before Cs-deposition, while and (b) and (d)show the spectrum after Cs-deposition. The spectra
were obtained with hν = 72 eV at a temperature of 200
K. Panels (a) and (b) were obtained wiht hollizontallypolarized light, while panels (c) and (d) were obtainedwith vertically-polarized light. In panels (a) and (b), theshift of VBM is indicated by black dashed line andarrow. In panels (c) and (d), the shift of σ band isdenoted by black dashed line and arrow.
[1] J. Cai et al., Phys. Rev. B 98 (2018) 195443.
[2] S. Ichinokura et al., Appl. Phys. Lett. 122 (2023)
071601.

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Ⅲ-4 Surface, Interface and Thin Films

BL5U

Growth of Transition Metal Phosphide Thin Film on Au(111)
N. Maejima 1, 2 K. Inaoka 1 and K. Edamoto1, 2
1Coll. Sci., Rikkyo Univ., Tokyo 171-8501, Japan
Research Center for Smart Molecules, Rikkyo Univ.,Tokyio 171-8501, Japan

2

The Ni12P5@Au core-shell catalyst has attracted
attention because of its high catalytic activity foroxygen evolution reactions [1]. Novel functions ofcore-shell catalysts arise from the interaction between
the core and the shell at the interface [2]. Direct
observation of the electronic states formed through theinteractions between core and shell is diﬃcult, and thus
the fabrication of the Ni phosphide thin film on an Au
substrate is desirable as a model system that allows theinvestigation using photoelectron spectroscopy. In thisreport, we will show that a nickel phosphide thin film
can be grown on Au(111) by Ni deposition on a
P-covered Au(111).
Experiments were performed at BL5U of the UVSOR
facility. The Au(111) surface was cleaned by cycles of
Ar+ ion spattering (0.5 keV) and annealing (750 °C) . P
atoms were deposited on the Au(111) surface at 400℃
(AuP/Au(111)). The prepared Au(111) and AuP/
Au(111) samples showed 1x1 and 5x5 LEED patterns,
respectively. Ni was subsequently evaporated onto
AuP/Au(111) at 400℃ to form a NixP thin film on
Au(111)(NixP/Au(111)). This LEED pattern of thissample consisted of 1x1 spots arising from the Au(111)substrate and the additional 12 spots which are assigned
as the spots from the NixP crystal thin film. Au 4f, P 2p,
Ni 3p and valence band photoelectron spectroscopy(PES) measurements were performed by an MBS A-1
analyzer. The ratio of the amount of Ni and P atoms on
the Au substrate were determined by the ratios of thepeak areas of Ni 3p and P 2p photoelectron spectra to
be Ni : P = 2:1.
Au 4f 7/2 spectra obtained from Au(111) clean surface,
AuP/Au(111), and NiP/Au(111) samples are shown in
Fig. 1. In the Au 4f7/2 spectra of Au(111) clean surface,
two bulk and surface components were observed atbinding energies of 84.0 and 83.7 eV, respectively.[3]The spectrum obtained from P deposited sample containthe bulk and surface Au-P component at 84.0 eV and
84.4 eV, respectively.[4] The surface component
observed in the spectra of Au(111) clean surface hasdisappeared, indicating that the whole surface iscovered with P. In the spectrum of the Ni deposited
sample, peaks of bulk and surface components wereobserved at 84.0 eV and 83.7 eV, respectively. The
disappearance of the peak at 84.4 eV corresponding to
Au-P bonds indicates the cleavage of all Au-P bonds.

Though the P 2p spectrum obtained from NixP/Au(111)contains multiple peak components, the component
that is ascribed to P atoms bonded to Au wasdisappeared. In addition, the surface component
observed in the spectrum of the Au(111) clean surface
reappears in the spectrum of NixP/Au(111). These
results imply that the interaction between the thin film
and the substrate is weak or the nickel phosphide film
congregates to form islands. The Ni 3p peak position in
the spectrum of NixP/Au(111) was higher than thatobtained from Ni2P(10-10) single crystal by 0.3 eV [5],whereas the spectral shape was almost the same. These
results suggested that a Ni phosphide whose
composition was Ni : P = 2:1 can be formed on Au(111).

Fig. 1. Au 47/2 photoelectron spectra of clean Au(111),
AuP/Au(111) and NiP/Au(111) samples.
[1]Lee. Jong-Soo et al., JACS 130 (2008) 9673.
[2]Xu. Yingying et al., Nano research 10 (2017) 3103.
[3]Citrin. Ph. H. et al., Phys. Rev. Lett. 41 (1978) 1425.
[4]Zhang. Wei et al., Small 14 (2018) 1804066.
[5]N. Maejima et al., UVSOR Activity Report 48(2020) 115.

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BL5U, 7U

Heavy-Fermion in a Mono-Atomic Layer YbCu2/Cu(111)
H. Sugihara1, T. Nakamura2,1, Y. Chen1, K. Nishihara1
M. F. Lubis1, K. Tanaka3 and S. Kimura2,1,4
1

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, JapanThe Kondo eﬀect leads to exotic physical phenomena
due to hybridization between localized f-electrons andconductive carriers at low temperatures. Especially,
heavy-fermion (HF) systems, in which massive
eﬀective carriers appear due to the Kondo eﬀect, havefascinated many researchers [1,2]. Recently, twodimensional (2D) HF systems have been realized using
a molecular beam epitaxy method and it was shownthat dimensionality is also important for the characterof the HF system [3,4]. However, two-dimensionalmono-atomic layer HF material has never beenreported. Here, we have studied the electronic structureof a mono-atomic layer HF material, YbCu2/Cu(111),
which is a novel perfect two-dimensional HF system,measured by angle-resolved photoelectron spectroscopy(ARPES).
Clean Cu(111) substrates were prepared by the cycleof Ar+ sputtering with an acceleration of 0.5 eV andannealing at a temperature up to 800 K. After checking
the sharp peaks and low background of the streakelectron diﬀraction pattern appearing in the reflection
high-energy electron diﬀraction (RHEED), Yb-metal
was evaporated with a homemade Knudsen cell. The
fabricated YbCu2 mono-atomic layer has a fractional
pattern suggesting a small lattice mismatch of YbCu2
from the Cu(111) substrate. VUV-ARPES measurement
was carried out at BL7U (hν = 37 eV) at temperaturesof 7 – 130 K.
Figure 1 shows the ARPES intensity plot of YbCu2/
ഥ of the surface BrillouinCu(111) surface along Ȟത - Kzone of YbCu2/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. A flat band near the
Fermi level and several highly dispersive bands arevisible. The flat band is attributed to the Yb2+ 4f7/2 final
state after the photoexcitation process. The highly
dispersive conduction bands are hybridized with theflat Yb 4f band near the Ȟത point suggesting theappearance of the c-f hybridization, which is the
spectral evidence of the appearance of HF. Furthermore,angle-integrated photoelectron spectra of YbCu2/
Cu(111) taken at hν = 37 eV (T = 10 – 130 K) are shownin Fig. 2. The appearing steep peak, pointed by anarrow, is grown and moves to the low energy withdecreasing temperature. The peak can be attributed to a
Kondo resonance peak usually observed in HF materials[5], therefore, the results suggest the HF formation in

the mono-atomic layer YbCu2/Cu(111).

Fig. 1. ARPES band dispersion of YbCu2/Cu(111)
ഥ taken at hν = 37 eV (T = 7 K). The
surface along Ȟത-Kphotoelectron intensities were normalized by the
Fermi-Dirac distribution function convoluted with the
instrumental resolution.

Fig. 2. Angle-integrated photoelectron spectra of
YbCu2/Cu(111) taken at hν = 37 eV (T = 10~130 K).
The allow indicates the Kondo resonance peak.
[1] A. C. Hewson, The Kondo Problem to Heavy
Fermions (Cambridge Univ. Press, Cambridge, 1993).
[2] P. Coleman, et al., J. Phys.: Condens. Matter 13(2001) R723.
[3] L. Fernandez et al., Nanoscale 12 (2020) 22258.
[4] M. Ormaza et al., PRB 88 (2013) 125405.
[5] S. Chatterjee et al., Nat. Commun. 8 (2017) 852.

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Ⅲ-4 Surface, Interface and Thin Films

BL6U

Region and Element-specific Surface Observation of CVD Graphene on
Ir(111)/α-Al2O3(0001) by Photoelectron Momentum Microscopy
E. Hashimoto 1, Y. Onuma1, F. Matsui2 and S. Koh1
1

Aoyama Gakuin University, 5-10-1, Fuchinobe, Chuo-ku, Sagamihara, 252-5258, JapanUVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki, 444-8585, Japan2

A photoelectron momentum microscopy (PMM) is acomplementary characterization tool to conventional
methods, e.g. Raman spectroscopy and atomic force
microscopy (AFM), for comprehensive and elementspecific characterization of 2D materials owing to its
multifunctionality. We have demonstrated by valenceband photoelectron spectroscopy (VB-PES) using
PMM that graphene grown by low-pressure chemical
vapor deposition (LP-CVD) on Ir(111)/α-Al2O3(0001)
had high single-crystallinity for several 100 μm2 [1]. In
this study, we performed region and-specific surface
observation for graphene by photoemission electron
microscopy (PEEM).
Graphene was grown on Ir(111)/α-Al2O3(0001)
substrates by LP-CVD using H2 and CH4 gases. Fig.
1(a) shows an AFM image (1.0 μm2) of the graphenesurface on Ir(111). Continuous step terraces of theIr(111), which were the nucleation sites of graphene,
were observed. The average step height corresponded
to the one-atomic step height of the Ir(111) surface.
Wrinkles, which were formed due to the mismatch of
the thermal expansion coeﬃcients between grapheneand Ir(111), were formed across the step terraces,indicating that graphene domains coalesced andcontinuous graphene films were formed.
Real space images for graphene/Ir(111) were obtainedby PEEM at the linearly polarized soft X-ray beamline
BL6U of the UVSOR-Ⅲ synchrotron [2]. The electronic
structure for graphene/Ir(111) were determined by VBPES. The PEEM images of graphene/Ir(111), whichhave non-uniformity, are shown in Figs. 1(b) and 1(c).
In Fig. 1(b), the photon energy was 85 eV andphotoelectron corresponding to the binding energy
from 2.0 to 3.5 eV was integrated. Intensity of graphene
M points contributes the most. Thus, the bright areas inFig. 1(b) correspond to the areas where graphene exists.
The iso-energy cross section of the 2D band dispersion
for the bright area in Fig.1(b) by VB-PES is shown in
Fig. 1(d). The 6-fold symmetry pattern is attributed tothe π band dispersion of graphene connecting the M
points. Fig. 1(c) shows the PEEM image at the sameobservation area as Fig.1(b). The photon energy was set
to 100 eV. Photoelectron corresponding to the binding
energy from 0 to 0.2 eV was integrated. The density ofstates at the Fermi level of Ir dominates in this condition.
Therefore, the bright areas correspond to the area where
the Ir surface was exposed. The iso-energy cross sectionof the 2D band dispersion for the bright areas in Fig.1(c)is shown in Fig.1(e). The pattern with 6-fold symmetry,
which corresponds to the energy dispersion of Ir(111),

was observed. The pattern of graphene was notobserved, which confirmed that the Ir surface was
exposed. We identified areas where covered bygraphene and where Ir(111) is exposed, by region andelement-specific PEEM for Gr/Ir(111) samples withlow single-crystallinity.
In this study, we observed surface irregularities of
Gr/Ir(111) samples that were not captured byconventional measurement methods such as Raman
spectroscopy and AFM observation, by performing
region and element-specific PEEM using PMM.
Element-specific measurements using PMM on
practical samples are very promising, and thecharacterization of detailed properties for high-quality
Gr/Ir(111) samples is expected.

Fig. 1. (a) AFM image and (b)-(c) PEEM images ofgraphene/Ir(111). Iso-energy cross sections of 2D band
dispersion of graphene/Ir(111), with photon energy of(d) 85 eV and (e) 100 eV.
[1] E. Hashimoto et al., Jpn. J. Appl. Phys. 61 (2022)
SD1015.
[2] F. Matsui et al., Jpn. J. Appl. Phys. 59 (2020)
067001.

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BL7U

High-resolution angle-resolved Photoemission Study on
MnBi2Te4/MnBi2Te4/Bi2Te3 Heterostructure
K. Ishihara1, H. Nishimichi1, K. Ide1, S. Ichinokura1, K. Tanaka2 and T. Hirahara1
1

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

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 w ay 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 showed a clear Dirac cone gap of 85
meV and the gap persisted up to room temperature.
From magnetic measurements it was revealed thatferromagnetism also persists up to room temperature inthis system. Taking all these facts into account, it can besaid that this system is promising to observe thequantum anomalous Hall eﬀect at room temperature.
However, the Dirac cone gap is not at the Fermi level
and there is no systematic method to control the Fermi
level position in Bi2Se3. Thus, we employed Bi2Te3 as
the parent TI and have deposited Mn and Te on Bi2Te3
to see if magnetic extension can also occur for thissystem. However, it was revealed that the Dirac cone
gap is absent in this MnB i2Te4/Bi2Te3 system [6], in
contrast to the theoretical prediction [7].
Therefore, in the present study, we have measured
the band structure of the MnBi2Te4/MnBi2Te4/Bi2Te3
system to verify whether an addition of another
MnBi2Te4 layer would influence the magnetic property

as well as the Dirac Cone gap opening. The experiments
were performed at BL 7U of UVSOR with the photon
energy of 19 eV. Figure 1 shows the measured band
dispersion at diﬀerent temperatures.
We found that in addition to the Dirac cone gap
opening which was observed from 6.6 K up to room
temperature, the lower Dirac cone showed somesplitting at 6.6 K. Furthermore, this splitting disappeared
once at 160 K, but revived at 250 K. Since the state at
higher binding energy showed photon energy
dependence, it can be regarded as a bulk state, although
our preliminary ab initio calculation suggested that it
can also be a surface state. This puzzling behavior is
unexpected from theory and calls for a comprehensive
study on the atomic structure as well as magnetism of
the system, which we hope to clarify in the future.

Fig. 1. Band dispersion image of the MnBi2Te4/
MnBi2Te4/Bi2Te3/MnBi2Se4 hetero structure measured
at 6.6 K, 160 K, and 250 K, respectively.
[1] M. Hasan and C. Kane, Rev. Mod. Phys. 82 (2010)3045.
[2] X.-L. Qi and S.-C. Zhang, Rev. Mod. Phys. 83(2011) 1057.
[3] For example, C. Z. Chang et al., Science 340 (2013)
167.
[4] For example, M. Ye et al., Phys. Rev. B 85 (2012)205317.
[5] T. Hirahara et al., Nano Lett. 17 (2017) 3493.
[6] T. Fukasawa et al., Phys. Rev. B 103 (2021) 205405.
[7] M. Otrokov et al., Phys. Rev. Lett. 122 (2019)107202; 2D Mate. 4 (2017) 025082.

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Ⅲ-4 Surface, Interface and Thin Films

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, 1-3,
Machikaneyama, Toyonaka, Osaka 560-8531, Japan

Electric double-layer organic field-eﬀect transistors(EDL-OFETs) have attracted much attention due totheir significantly low operating 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 of particularimportance. Recently, we developed a newspectroscopic system, namely electrochemicalattenuated total reflectance (EC-ATR) ultravioletvisible spectroscopy, which can access the interfacial
area [1, 2].
In this study, we fabricated ionic liquid gated organic
field-eﬀect transistors (IL-gated OFETs) on the ATR
prism. A two-layer single crystalline film of C9DNBDT-NW was used as an organic semiconductor,
and two kinds of ionic liquids (EMIM-TFSI and
HMIM-TFSI) were cast on the film. The only diﬀerence
between EMIM-TFSI and HMIM-TFSI is the length ofthe carbon chain: two for EMIM and six for HMIM. Au
films were evaporated to a thickness as the source anddrain electrodes (working electrodes) on both sides of
the ATR prism, and a Pt coil and a Pt wire were placedin the ionic liquids as pseudo counter and reference(gate) electrodes, respectively. In our previous study[2], we found that in response to the applied gate
voltage, the spectral peaks of the organic semiconductor
shifted and bleached, which was correlated with thedrain current.
The IL-gated OFETs fabricated on the ATR prism
were placed in the sample chamber in BL7B at UVSOR.
Figure 1 shows the diﬀerence spectra of C9-DNBDTNW films with EMIM-TFSI or HMIM-TFSI as afunction of the applied voltage. Despite the very slight
diﬀerence in the carbon chain length between EMIMTFSI and HMIM-TFSI, their spectral behaviors weresignificantly diﬀerent.
In the case of HMIM-TFSI (Fig. 1b), spectral
bleachings at ~300, 220, 210, 190, and 170 nm wereobserved. According to TD-DFT calculations, theseabsorbances are mainly due to electronic excitations in
the C9-DNBDT-NW molecule for ~300 nm and in
HMIM-TFSI for ~220, 210, 190, and 170 nm. There isa positive relationship between the amount of spectralchanges and applied voltage. On the other hand, in thecase of EMIM-TFSI (Fig. 1a), no obvious spectralchanges were detected. These results indicate adiﬀerence in the interaction between the organic

semiconductor and ionic liquid species underelectrochemical environments.
The development of the EC-ATR spectroscopic
system has the potential to greatly impact the field ofelectrochemical devices by enabling researchers toaccess and study the interfacial area between films andILs, leading to improved understanding of device
performance and the development of new, highperformance materials.

Fig. 1. Diﬀerence spectra of C9-DNBDT-NW films
with (a) EMIM-TFSI and (b) HMIM-TFSI as a functionof the applied voltage.
[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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