Ⅲ-4
Surface,
Interface andThin Films

BL2A

Ⅲ -4. Surface, Interface and Thin Films

BL2A

Zn L3-edge XANES of ZnO Powder
E. Kobayashi1, S. Yoshioka 2 and K. K.Okudaira3

Kyushu Synchrotron Light Research Center, Tosu 841-0005, Japan
Gradiate School of Engineering, Kyushu University, Fukuoka 819-0395 Japan
3
Graduate School of Science and Engineering, Chiba University, Chiba 263-8522, Japan
1

2

Zinc oxide (ZnO) is an important material in devise[1] because of its wide band gap 3.37 eV and has arelatively large exciton binding energy of 60 meV. In
recent years, organic photovoltaic (OPV) has been
attracting attention as a low-cost, lightweight battery
that replaces conventional solar cells. ZnO plays anplay an essential role as an electron transporting layer(ETL) material. In order to further improve thecharacteristics of ETL, it is necessary to understandthe electronic states. Near-edge X-ray absorption finestructure (NEXAFS) spectroscopy is a powerful toolfor investigating the electronic structures of materials.
In this report, we investigated the electronic
structure of ZnO powder by means of XANES using
fluorescence yield method.
Zn L3-edge XANES measurements were performedat the BL2A beamline of UVSOR Okazaki, Japan,
using the partial fluorescence yield method (PFY). A
Beryl double crystal monochromator defined Zn L
absorption edges in the energy region from 1000 to1090 eV. Fluorescence X-rays were collected using anenergy dispersible silicon drift detector (SDD). All
measurements of XANES spectra were carried out atroom temperature.
Figure 1 shows the Zn L-edge NEXAFS spectra ofZnO powder and ZnO/Si film obtained from TEY.
The peak A provides information both about theforbidden electron transitions, which does not obey
dipole selection rules and disorder in the crystal
geometry [2]. The peak B and C are related to thetransition of 2p core electrons to the Zn4p levels [2].
The spectral future marked as A in Zn L-edge
NEXAFS spectra of ZnO powder is almost the sameas that of ZnO / Si film, while the peaks B and C in Zn
L-edge NEXAFS of ZnO powder are difference fromthose of ZnO / Si film. This suggests that the surface
state of ZnO powder is different from that of ZnO / Sifilm since TEY is sensitive to the surface electronic
states.
Figure 2 shows the Zn L-edge NEXAFS spectra ofZnO powder obtained from PFY. PFY (Zn L) is almost
the same as the result of TEY, but PFY (O K) is
different. This suggests that the surface and bulk of
ZnO particles may have different electronic states ofoxygen.
Next, we will clarify how this electronic statechanges when an organic layer is placed on ZnO.

Fig. 1. Zn L-edge XANES spectra of ZnO obtained
from TEY. ZnO powder (black) and ZnO/Si film (red)spectrum.

Fig. 2. ZnO L-edge XANES spectra of ZnO powder
obtained from PFY. PFY (Zn L) (black) and PFY (OKα) (blue) spectrum of ZnO.
[1] F. Quaranta, A. Valentini, F. R. Rizzi, and G.
Gasamassima, J. Appl. Phys. 74 (1993) 224.
[2]O. M. Ozkendir, S. Yildirimcan, A. Yuzer, K. Ocakoglu,
Progress in NaturalScience:Materials International 26(2016) 347.

107

Ⅲ04- 1 -Ⅲ- 4

BL2BInterface and Thin Films
Ⅲ -4. Surface,

BL2B

Electronic Structure of ZnO Nanoparticles as an Electron Extraction Layer
for Organic Solar Cells
K. K. Okudaira and T. Kikuchi

Association of Graduate Schools of Science and Technology, Chiba Univererity, Chiba 263-8522, Japan
groups at the surface of nanoparticles. Furthermore,
the work-function of as-grown ZnO NPs can be
estimated to 3.92 eV, which is lower than that of ITO(about 4.6 eV). This value is closer to the electron
affinity of PCBM (3.82 eV) [6], which is a typicalelectron accepter material in BHJ. It is expected that
the ZnO NP is good electron extraction layer forpolymer solar cells.

Intensity (arb. unit)

Ⅲ- 4

Organic devices such as organic photovoltaic cells
have been attracting interest concerning both
fundamental research and practical application for lowcost, large-area, lightweight and exible devices.
Conjugated polymer solar cells are attractive as a sourceof renewable energy due to the low cost by using rollto-roll-printing processes. The most polymer solar cells
have bulk heterojunction (BHJ) morphology. At thismorphology, one of materials consisting of BHJ
contacts directly the undesired electrode. To fabricate
inverted polymer solar cells, one widely used approachis to deposit a thin film of zinc oxide (ZnO)
nanoparticles as an electron extraction layer and a holebroking layer on top of a transparent indium tin oxidecoated substrate [2].
For nanoparticles, the contribution of surface totheir electronic and optical properties is expected to besignicant, because of their large surface area-tovolume ratio.
In this work we deposited ZnO nanoparticles (NPs)using spin-casting method on indium tin oxide (ITO)
substrate and estimated the electronic structure of ZnO
NPs by ultraviolet photoelectron spectroscopy (UPS)
measurements with different exciting energies due tothe photoionization cross-section.
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
and 40 eV. ZnO NPs with uniform shape and highly
dispersed were synthesized using zinc acetate
dihydrate (Zn(CH3COO)2·2H2O) and potassiumhydroxide (KOH) as a precursor and absolute ethanol
as solvent via solvothermal method [3]. The thin filmsof ZnO NPs were deposited on ITO by spin casting(as-grown ZnO NP). The films were annealed at
140 °C in the atmosphere for 10 minutes (annealed
ZnO NPs). The mean size of synthesized ZnO NPs was
about 7 nm using TEM measurements.
We observed UPS of as-grown ZnO NPs andannealed ZnO NPs at hν of 28 eV and 40 eV (Fig. 1).
The peak at binding energy (Eb) of about 10 eV at hν
of 40 eV appears more clearly than that at hν of 28 eV.
The calculated photoionization cross-section of Zn 3d
at hν of 40.8 eV is much larger than that at hν of 26.8
eV, while that of O 2p at hν of 40.8 eV is smaller thanthat of 26.8 eV [4]. The peak at Eb of about 10 eV canbe assigned to Zn-3d. The broad feature at Eb about 7 eVand 4 ~ 5 eV are attributed to mainly Zn-4s electrons andO-2p electrons, respectively [5]. The UPS structure at Eb
about 5 eV changes by annealing. The O-2p states
would be affected by annealing, due to disappearanceof oxygen vacancies and/or formation of hydroxyl

(d)
(c)
(b)
(a)
10

5

Binding Energy relative to E f (eV)Fig. 1. UPS of (a) as-grown ZnO NPs at hν = 28 eV,(b) annealed ZnO NPs at hν = 28 eV (c) as-grown Zn
NPs at hν = 40 eV, (d) annealed ZnO NPs at hν = 40 eV.

[1] X. Gu et al. Adv. Energy Mater. 7 (2017) 1602742.
[2] S. Kim et al. Chem. Commun. 49 (2013) 6033.
[3] N. M. Shamhari et al. Acta Chim. Slov. 65 (2018)578.
[4] Atomic Calculation of Photoionization CrossSections and Asymmetry Parameters, J. -J. YEH, 1993,
AT & T.
[5] W. Ranke, Solid state commun. 19 (1976) 685.
[6] H. Yoshida, J .Phys, Chem, C, 118 (2014) 24377.

108

Ⅲ04- 2 -BL3U

Ⅲ -4. Surface, Interface and Thin Films

BL3U

Layered Manganese Oxide Electrocatalyst Containing K+ Cation
for Water Oxidation Studied by Operando XAFS Observations
S. Tsunekawa1, M. Nagasaka2, H. Yuzawa2 and M. Yoshida1
Yamaguchi University, Tokiwadai, Ube 755-8611, Japan
Institute for Molecular Science, Okazaki 444-8585, Japan1

2

also suggest that the Mn3+ in the δ-MnO2 layers function
as the active sites for OER process [5].
In conclusion, we investigated the electronic stateand local structure of K:MnOx electrocatalyst byoperando O K-edge, Mn K-edge and K K-edge XAFS
measurements. The result elucidates that the catalyst
composed of δ-MnO2 with layered structures containing
hydrated alkali metal ion, and suggested that the water
splitting reaction efficiently proceeded at the active sitesof Mn3+.

Energy consumption is increasing in proportion to theworld’s population. This large energy consumption isleading to serious problems such as depletion of fossil
fuels and increase in carbon dioxide emissions. In recent
years, hydrogen production has been attracting attention
as a CO2-free energy source that does not rely on fossil
fuels, and a hydrogen production process by waterelectrolysis using renewable energy sources has been
proposed. However, the insufficient efficiency ofoxygen evolution reaction (OER) restricts the efficiencyof overall water splitting. In this situation, a potassiumincluding manganese oxide (K:MnOx) was developedby Nocera group [1], and they reported that K:MnOx
could decompose water to oxygen gas efficiently. Thus,
we have investigated the structure and function of the
K:MnOx catalysts during water splitting by operando
soft, tender, and hard X-ray XAFS measurements.
The electrochemical cell was used with a Pt counterand an Ag/AgCl reference electrode. The K:MnOx
catalyst was prepared by electrodeposition on Au thinfilm in a solution containing MnCl2 and K+ cation.
Under electrochemical control, the operando Mn Kedge and K K-edge XAFS were measured byfluorescence mode in the PF BL-9A, and the operando
O K-edge XAFS was measured by transmission modeat BL3U in the UVSOR Synchrotron.
First, we checked the OER activity and found that
K:MnOx function as highly efficient water splitting
catalyst. The surface morphology and chemicalcomposition were investigated by SEM, EDX and XPS.
The Faraday efficiency for catalyst was estimated as
about 100 % for production of oxygen and hydrogengasses by quadrupole mass spectrometry.
Next, operando O K-edge XAFS was measured
under electrochemical control, and the peak top positionand shape of the spectra for the K:MnOx suggested thatthe electronic state of Mn species in the catalyst was
similar with δ-MnO2 (Fig. 1.). Then, operando Mn Kedge XAFS measurements showed that most of the Mn
species were oxidized from Mn3+ to Mn4+ at 1.0V,
although small amount of Mn3+ remained. Furthermore,
the curve fitting of the Fourier transform of k3 weighted
EXAFS oscillation exhibited that the local structure ofMn species in the catalyst composed of δ-MnO2
structure, which was similar to the conclusion of theoperando O K-edge XAFS. On the other hand,operando K K-edge XAFS measurements showed thatthe hydrated K+ intercalated between the δ-MnO2 layers.
It is reported that the water splitting reaction proceeds
at a Mn3+ sites in the δ-MnO2 structure [2-4]. Thus, we

Ⅲ- 4Fig. 1. Operando O K-edge XAFS spectra for
K:MnOx and references.

[1] M. Huynh, D. Bediako and D. Nocera, J. Am. Chem.
Soc. 136 (2014) 6002.
[2] T. Takashima, K. Hashimoto and R. Nakamura, J.
Am. Chem. Soc. 134 (2012) 1519.
[3]M. Huynh, C. Shi, S. Billinge and D. Nocera, J. Am.
Chem. Soc. 137 (2015) 14887.
[4] Y. Gorlin, B. Kaiser, J. Benck, S. Gul, S.Webb, V.
Yachandra, J. Yano and T. Jaramillo, J. Am. Chem. Soc.
135 (2013) 8525.
[5] S. Tsunekawa, F. Yamamoto, K. Wang, M. Nagasaka,
H. Yuzawa, S. Takakusagi, H. Kondoh, K. Asakura, T.
Kawai and M. Yoshida, J. Phys. Chem. C. 124 (2020)
23611.

109

Ⅲ04- 3 -BL3BInterface and Thin Films
Ⅲ -4. Surface,

BL3B

Control of Growth Orientation and Evaluation of Film Quality of UVEmitting Zinc Aluminate Phosphor Thin Films
H. Kominami1, M. Endo2, T. Kawashima2, N. Sonoda2, A. Fujii1, K. Inoue1,
N. Uesugi1, K. Nie1, 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, Japan1

nm was caused from slightly residual ZnO phase. In
order to suppress the residual zinc oxide, it is necessary
to carefully examine the film thickness of ZnO.

PLE Intensity [a.u.]

0.015

em = 237 nm
Annealed at 990 oC

0.01

one-side
both-side

0.005

0

100

150
Wavelength [nm]200Fig. 1. PLE spectra of ZnAl2O4 thin films prepared on
sapphire substrate of one-side polished and both-side
polished.
100
Transmittance [%]Ⅲ- 4

The global pandemic of COVID-19 has led tofrequent disinfection of hands and everywhere they cantouch, and the pharmaceutical industry is rapidly
developing vaccines. A “new normal” has been
advocated, and it has become necessary not only to wear
face masks and secure social distance, but also lifestyle
habits including dietary habits that improve immune
function are emphasized, and how to protect ourselvesfrom viruses is important. It has become a re-concern inpeople's lives.
The UV light is used for various applications
depending on the wavelength as well as the sterilization
described above. The lights of 200-280nm (UV-C)
region as for the sterilization, 280-320nm (UV-B)
region as the treatment of the skin disease, 320-400nm(UV-A) region as application of purification of waterand air, and photocatalysts. Recently, from theviewpoint of consideration to the environment, themercury free UV emission devices have been demanded
for the application of catalyst and medical situations. In
our previous work, it was clarified that ZnAl2O4
phosphor was suitable for the UV field emission lamp
because of its stability and luminescent property. Itshows strong UV emission peaked around 250 nm
which suitable for sterilization.
In this research, ZnAl2O4 layer were prepared bythermal diffusion of ZnO and sapphire substrate for new
UV devices. To obtain ZnAl2O4 thin film with highquality, we explore optimum condition of thermal
annealing, such as annealing temperature, atmosphere,
and annealing time. From the experiment, optimum
annealing conditions were obtained 990 oC for 50 hours.
Figure 1 shows PLE spectra of ZnAl2O4 thin films
prepared on 2 types of sapphire substrate, one-side
polished and both-side polished. PL intensity of oneside polished substrate was higher than the both-side
polished. It is thought that the possibility of totalinternal reflection occurs inside the board of thesubstrate. Therefore, it is necessary to determine thefilm thickness by fully considering the light extraction
efficiency.
Figure 2 shows transmittance spectra of ZnAl2O4 thinfilm, compared with sapphire substrate. Excitationedges were observed around 180 nm and 380 nm. Theedge of 180 nm was caused from ZnAl2O4, it consistent
with the transmittance results. However, the edge of 380

80

substrate

60
ZnAl 2O4o990 C
both-side polished

40
20
0

200

400
Wavelength [nm]600Fig. 2. Transmittance spectra of ZnAl2O4 thin film.

110

Ⅲ04- 4 -BL4B

Ⅲ -4. Surface, Interface and Thin Films

BL4B

Characterization of Amorphous Arsenic, Selenium and Arsenic Triselenide
by Vacuum Ultraviolet Transmission Spectroscopy
K. Hayashi

Department of Electrical, Electronic and Computer Engineering, Gifu University, Gifu 501-1193, Japan
Amorphous chalcogenide semiconductor materials
are very expected as a potential material for
optoelectronic devices. Because, in these materials arevery sensitive to the light, and show a variety ofphotoinduced phenomena [1-3]. Although manystudies have been done on the photoinduced
phenomena of these materials, little is known about thedetails of these mechanisms. These phenomena werestudied by exciting outer core electrons with theirradiation of light with the energy corresponding tothe 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 areinteresting for the changes of the optical properties in
the higher energy region. To obtain a wide knowledgeof the photoinduced phenomena, it is necessary toinvestigate to the photoinduced and annealing effects
on wide energy region. In this report, we report the
VUV transmission spectra of amorphous compound
semiconductors and their constituent elements.
Samples used for the measurement of the VUVtransmission spectra were amorphous arsenic,
selenium and arsenic triselenide thin films preparedonto thin aluminum films by conventional evaporation
technique. The sample thicknesses ranged between
100 and 200 nm. The aluminum film of the thicknessof 200 nm was used to eliminate the higher order lightfrom the monochromator in the VUV region. These
measurements were carried out at room temperature at
the BL4B beam line of the UVSOR facility of theInstitute for Molecular Science. The spectrum wasmeasured by using the silicon photodiode as a detector.
Two pinholes of 1.5 mm in a diameter were inserted
between the monochromator and sample to remove
stray light. The intensity of the VUV light wasmonitored by measuring the TPEY of a gold mesh. The
positions of the core levels for the samples were
calibrated by referencing to the 2p core levelabsorption peak of the aluminum film.
Figure 1 shows the VUV transmission spectra ofamorphous arsenic (a-As), selenium (a-Se) and arsenic
triselenide (a-As2Se3) thin films. Two main absorption
peaks were observed in this wavelength region foramorphous As2Se3. One absorption peak around 22nm
corresponds to the 3d core level of Se atom. Anotherabsorption peak around 28 nm corresponds to the 3dcore level of As atom. As shown in the figure, each
spectrum is very broad and multiple shoulders areobserved. The absorption spectrum observed in theamorphous As2Se3 is roughly consistent with theprevious report [4]. On the other hand, VUVtransmission spectra of amorphous As and Se aredifferent from the previous report. Although thewavelength resolutions in the spectral measurements
are all the same, the spin-orbit splitting of the 3d5/2 and3d3/2 level of each atom is clearly resolved inamorphous As2Se3, while in amorphous As and Se are
not clearly resolved. It is not clear about the origin ofbroad spectra and shoulders. I think that these origins
are related to the local structures of the amorphous
network. Therefore, it seems that it depends on the
preparation method and the presence or absence of
annealing. The detailed experiments and analysis will
be done in the next step. More detailed experiments
are necessary to clarify the origin of the VUVtransmission spectra.

Ⅲ- 4Fig. 1. VUV transmission spectra of a-As, a-Se, anda-As2Se3 thin films.

[1] K. Tanaka, Rev. Solid State Sci. 4 (1990) 641.
[2] K. Shimakawa, A. Kolobov and S. R. Elliott, Adv.
Phys. 44 (1995) 475.
[3] K. Tanaka, Encyclopedia of Nanoscience andNanotechnology 7 (2004) 629.
[4] J. Bordas and J. B. West, Phil. Mag. 34 (1976) 501.

111

Ⅲ04- 5 -BL4BInterface and Thin Films
Ⅲ -4. Surface,

BL4B

Structural and Magnetic Properties of FeCo Alloy Multilayer Thin Films
Grown by Nitrogen Surfactant Epitaxy on Cu(001)
T. Miyamachi1, K. Yamamoto2,3, T. Koitaya2,3 and T. Yokoyama2,3

The University of Electro-Communications, Chofu 182-8585, Japan
2
Institute for Molecular Science, Okazaki 444-8585, Japan
3
The Graduate University for Advanced Studies, SOKENDAI, Okazaki 444-8585, Japan1

Ⅲ- 4

An L10-type FeCo ordered alloy attracts muchattention as a rare-earth free magnetic material due to
its large magnetic anisotropy, large magnetic moment,
and high Curie temperature. Intensive works has been
carried out to fabricate L10-FeCo phase with uniaxial
anisotropy. Using pulsed laser deposition, the growthof FeCo thin films with alternating Fe and Co atomic
layers was investigated [1]. However, the L10 structure
is a non-equilibrium state of FeCo phase and hence its
fabrication method has not been established yet. The
main problem could be caused by the atomic-scaledisorder at the Fe/Co interface during growth
processes, which suggests the importance of
microscopic characterizations of structural, electronic
and magnetic properties of L10-FeCo.
To improve the quality of FeCo alloy thin films, we
intend to incorporate nitrogen surfactant effects ofmonatomic layer magnetic nitrides into the alternate
atomic-layer Fe and Co deposition. In this method, thenitrogen surfactant epitaxy of monatomic layer magnetic
nitride with high lateral lattice stability can suppress
the interdiffusion at the Fe/Co interface during thedeposition and annealing processes, which results inatomically flat surface/interface. The important role ofthe nitrogen surfactant effect on the fabrication of highquality L10-type alloy thin films has been
demonstrated for FeNi alloy thin films [2].
In this study, we here performed combined study ofscanning tunneling microscopy (STM) and x-ray
absorption spectroscopy/x-ray magnetic circulardichroism (XAS/XMCD) to investigate structural,electronic and magnetic properties of FeCo alloy
multilayer thin films by the nitrogen surfactant epitaxy.
This complementary experimental approach enables tolink macroscopic observations of element specific andquantitative electronic and magnetic properties by
XAS/XMCD with microscopic origins of the Fe/Co
interface characteristics revealed by STM [3]. FeCo
alloy multilayer thin films was grown on Cu(001) in thefollowing processes: (1) the monatomic layer ironnitride (Fe2N) was firt grown on Cu(001) [4], (2) 1 ML
Co was deposited at a low temperature (~ 150 K) andannealed at room temperature, (3) alternating layer
deposition of Fe and Co was repeated to fabricate
multilayers.
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 obtained at
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
with the photon helicity parallel (antiparallel) to thesample magnetization. Note that θ is the angle between
the sample normal and the incident x-ray.
Magnetization curves were recorded by plotting the L3
XAS intensity normalized by the L2 one as a functionof the magnetic field.
We first confirmed from XMCD measurements thestrong in-plane magnetic anisotropy of bare Fe2N aspreviously reported [4]. STM measurements revealed
that adding Co 1 ML on Fe2N results in the formation of
Co2N/Fe/Cu (001) via nitrogen surfactant effect.
Accordingly, relative increase in the out-of-planemagnetization of Fe to the in-plane magnetization wasobserved. We found from thickness dependence of Fe
magnetization
curvesthattheout-of-planemagnetization of Fe was further increased by repeating
alternative depositions of Fe and Co. The results
possibly reflect the intrinsic out-of-plane magnetizationof L10 FeCo and indicate that the nitrogen surfactant
effect efficiently suppress the interdiffusion at the Fe/Co
interface and keep atomically flat surface/interface in
FeCo atomic layers.

[1] H. Ito et al., AIP Advances 9 (2019) 045307.
[2] K. Kawaguchi et al., Phys. Rev. Materials, 4 (2020)
054403.
[3] S. Nakashima et al., Adv. Funct. Mater. 29 (2019)1804594.
[4] Y. Takahashi et al., Phys. Rev. B 95 (2017) 224417.

112

Ⅲ04- 6 -BL4B

Ⅲ -4. Surface, Interface and Thin Films

BL4B

Ground State and Magnetic Properties of Iron Phthalocyanine Thin Films
Grown on a Monolayer Graphene Sheet
S. Ohno1, I. Sakaida1, K. Yamamoto2,3, T. Koitaya2,3 and T. Yokoyama2,3College of Engineering Science, Yokohama National University, Yokohama 240-8501, Japan
2
Institute for Molecular Science, Okazaki 444-8585, Japan
3
The Graduate University for Advanced Studies, SOKENDAI, Okazaki 444-8585, Japan

1

Iron phthalocyanine (FePc) is one of the prototype
molecules to study magnetic properties of molecularthin films. It is a planner molecule which has an Fe2+
iron at the center. The ground state of an FePc
molecule has been a controversial issue. Density
functional theory (DFT) calculations showed that thecalculated density of states (DOS) at the valence band
region agree well with the experimental data [1].
However, it was found to be quite difficult todetermine the ground state symmetry unambiguously
because of the similarity of the calculated DOS evenfor the ground states with different symmetries. X-ray
absorption spectroscopy study suggested that the 3Eg
ground state with the half-filled eg state at the Fermi
level is plausible for FePc thin films grown on gold
surfaces [2]. In the present work, we focused on the
ground state and magnetic properties of FePc thinfilms grown on a monolayer graphene sheet, which is
produced by chemical vapor deposition (CVD) andtransported onto the silicon oxide substrate (Gr/SiO2).
BL4B soft X-ray beamline was used for X-ray
Absorption Near Edge Structure (XANES) spectroscopy
measurements in N K-edge and Fe L-edge regions, and
X-ray Magnetic Circular Dichroism (XMCD)
measurements in Fe L-edge region.
We have reported on our previous results for FePc
thin films grown on passivated silicon surfaces as well
as a graphene sheet [3]. Here, we report on our new
results on the high-resolution XANES spectra, andsome further analysis on the magnetic properties.
Figures 1 (a) and (b) show XANES spectra taken at
the incident angle of Ө = 0o and 65o, respectively.
These results agree well with the previous assignmentof the spectral components based on the 3Eg groundstate [2].
Tilt angle of the molecular plane of FePc can beevaluated based on the conventional analysis
method[4]. The obtained value is ~24o in the present
case. The applicability of the full analysis using thesum rules is based on the assumption that the FePc
molecule takes the adsorption configuration of the flatlying orientation and has D4h symmetry in the point
group representation [2]. Present XANES spectra
shown in Fig. 1 is quite similar to those in the otherreports[2,5], suggesting that the sum rules can beapplied approximately.
Thus, we could have obtained a series of physicalquantities related to the magnetic properties of FePc.
For example, the ratio of the orbital moment in themolecular plane (mLxy) and the spin moment (ms) isevaluated to be ~1.0, even larger than the reported
value of ~0.8 [2]. This indicates that the enhancementof the orbital moment is promoted by the contact withthe graphene sheet.

XAS Intensity (arb. unit)

1.6

(a)
e g↑

1.4
1.3

FePc/Gr/SiO2

b1g↓

1.5

 = 0ob1g↑

eg↑ a1g↑

1.2
1.1
1.0
706

708

710

712

714

Photon Energy (eV)XAS Intensity (arb. unit)

1.8

(b)

FePc/Gr/SiO2

a1g↑

1.7

 = 65o

1.6
1.5

eg↑

1.4

b1g↓

1.3

eg↑

1.2
1.1
1.0
706

708

710

712

714

Photon Energy (eV)Fig. 1. Angle-dependent linearly polarized XANES
spectra for FePc/Gr/SiO2.

[1] N. Marom et al., Appl. Phys. A 95 (2009) 165.
[2] J. Bartolomé et al., Phys. Rev. B 81 (2010) 195405.
[3] S. Ohno et al., UVSOR Activity Report 2019 47(2020) 133.
[4] J. Stӧhr, “NEXAFS Spectroscopy” (Springer).
[5] S. Lisi et al., J. Phys. Chem. Lett. 6 (2015) 1690.

113

Ⅲ04- 7 -Ⅲ- 4

BL5UInterface and Thin Films
Ⅲ -4. Surface,

BL5U

Observation of Electronic Band Structure in Two-dimensional WSe2 Flake
M. Sakano1, Y. Tanaka1, S. Masubuchi2, S. Okazaki3, K. Watanabe4, T. Taniguchi5,
T. Sasagawa3, T. Machida2 and K. Ishizaka1

Quantum-Phase Electronics Center and Department of Applied Physics, The University of Tokyo,
Tokyo 113-8656, Japan
2
Institute of Industrial Science, The University of Tokyo, Tokyo 153-8505, Japan
3
Materials and Structures Laboratory, Tokyo Institute of Technology, Yokohama 226-8503, Japan
4
Research Center for Functional Materials, National Institute for Materials Science, Tsukuba 305-0044, Japan
5
International Center for Materials Nanoarchitectonics, National Institute for Materials Science,
Tsukuba 305-0044, Japan1

Ⅲ- 4

Development of fabrication techniques for exfoliatedtwo-dimensional (2D) flakes enables us to investigate
the physical properties of the 2D materials. In 2D
materials, peculiar physical phenomena that do notappear in bulk crystals are realized because theelectronic band dispersion discretely changes as thelayers decrease to the monolayer limit. However, due
to the limited size of the flake samples (typically ~10μm), it is a challenging task to precisely determine theelectronic structures of various two-dimensional
materials.
In our study, we have developed a procedure tofabricate flake samples that can be adapted to various
2D materials and investigated the electronic band
dispersions of monolayer WSe2 by performing microfocused angle-resolved photoelectron spectroscopy(micro-ARPES).
The samples were fabricated by an all-dry pick-up
and flip method (see ref. [1] for details). As shown in
Fig. 1 (a), the monolayer WSe2 is encapsulated withgraphene to prevent oxidation of the WSe2, andelectrically contacts to an Au electrode fabricated on a
SiO2/Si substrate though graphite to prevent charging
up. The fabricated sample is pumped and sealed in an
ICF-70 nipple with a gate valve, and transported to theultrahigh vacuum chamber. Before the micro-ARPES
measurement, the sample is annealed around 200 °C
for ~10 hours in the ultrahigh vacuum.
Figure 1 (b) shows an obtained ARPES image.
Unfortunately, although we could observe thephotoelectron intensities of the graphene and/orgraphite, but not observe those of the monolayer WSe2.
After the measurement, the spot size of the synchrotron
light was evaluated and found to be much larger than
the size of the WSe2 flake (~20 μm) in the setup at thattime. For future measurements, it is necessary to makethe spot size of the synchrotron light comparable to thesize of the fabricated sample before performing the
ARPES measurement.

Fig. 1. (a) A schematic of a fabricated monolayer
WSe2 flake (typical size ~20 μm) sample for microARPES measurement. The monolayer WSe2 electricallyconnects to an Au electrode fabricated on a SiO2/Si
substrate through graphite. To prevent oxidation of the
WSe2 flake, the topmost is covered by graphene (typicalsize ~100 μm). The detailed fabrication process iswritten in ref. [1]. (b) Obtained ARPES image. The
photoelectron intensities from the graphite and/orgraphene can be observed, but not clearly from themonolayer WSe2.

[1] M. Sakano et al., arXiv:2103.11885 (2021).

114

Ⅲ04- 8 -BL5U

Ⅲ -4. Surface, Interface and Thin Films

BL5U

Electronic Structures of Transition Metal Phosphide (TMP) Thin Films on
TMP Substrates
N. Maejima1,2, T. Yoshida1, Y. Shimato1 and K. Edamoto1,2

Coll. Sci., Rikkyo Univ., Tokyo 171-8501, Japan
Research Center for Smart Molecules, Rikkyo Univ.,Tokyio 171-8501, Japan
1

2

Transition metal phosphides (TMPs) have attracted
much attention because of their high catalytic
activities for hydrodesulfurization (HDS). Among
TMPs studied thus far, Ni2P shows the highest
catalytic activity while that of Fe2P is extremely low[1]. Recently it has been found that, when some of Ni
atoms in Ni2P are substituted by Fe atoms (denoted as
NiFeP, hereafter), the reaction path is changed from ahydrogenation path to a direct desulfurization path [2].
Such a change in selectivity should be closely related
to the change in the electronic structure of active Ni
sites due to the charge transfer between Ni, Fe and P
atoms. In this study, we investigate the electronic
structures of NixP/Fe2P and FexP/Ni2P, which can beviewed as model systems to reveal the charge transfer
in NiFeP.
Experiments were performed at BL5U of the
UVSOR facility. Ni2P(10-10) and Fe2P(10-10) werecleaned by cycles of Ar+ ion spattering (0.5 keV) andannealing (600 °C and 750 °C, respectively). The cleaned
surfaces showed c(2x4) and c(2x2) LEED patterns,
respectively. Fe (Ni) atoms were deposited on the Ni2P
(Fe2P) clean surface at room temperature and the films
were post annealed at 350 °C (550 °C), which induces
phosphorization of the film owing to surface
segregation of P atoms from the bulk [3,4]. The
prepared FexP/Ni2P and NixP/Fe2P samples showed 1x2
and c(2x2) LEED patterns, respectively. Ni 3p, P 2p, Fe
3p and valence band photoelectron spectroscopy (PES)
measurements were performed by an MBS A-1 analyzer.
The Fe 3p spectra of Fe2P, NixP/Fe2P and FexP/Ni2P
are shown in Fig.1 (a). The analyses of angle resolved
Fe 3p spectra revealed that the 3p level of Fe atoms in
the interface region of NixP/Fe2P located at 54.5 eV.
This is slightly higher than that observed for a Fe2P
substrate. The Ni 3p spectra of Ni2P, NixP/Fe2P and
FexP/Ni2P are shown in Fig.1 (b). Ni 3p peak of
NixP/Fe2P was shifted to the lower binding energy sidefrom that of the Ni2P substrate. The results showed that
Fe 3p and Ni 3p peaks were shifted due to theinteraction between the Ni2P thin film and the Fe2P
substrate. On the other hand, these peaks showed little
shifts in the case of FexP/Ni2P. These results suggestthat the NixP film is chemically bound to the Fe2P
substrate while the interaction between the film andthe substrate is weak in the case of FexP/Ni2P.

Ⅲ- 4

Fig. 1. (a) Fe 3p and (b) Ni 3p photoelectron spectraof Fe2P, Ni2P, FexP/Ni2P and NixP/Fe2P[1] S. T. Oyama et al., J.Catal. 216 (2003) 343.
[2] S. T. Oyama et al., J.Catal. 285 (2012) 1.
[3] S. Imanishi et al., e-J. Surf. Sci. Nanotech. 10 (2012)45.
[4] Y. Sugizaki et al., Jpn. J. Appl. Phys. 57 (2018)
115701.

115

Ⅲ04- 9 -BL5UInterface and Thin Films
Ⅲ -4. Surface,

BL5U

Electronic Band Structure of Novel Se-containing Phases on SrTiO3
B. Lin1,2, C. Y. Hong1,2, Z. Song1,2, P. X. Ran1,2 and R.-H. He2

Department of Physics, Fudan University, Shanghai 200433, China
School of Science, Westlake Institute for Advanced Study, Westlake University,
Hangzhou 310064, China
1

2

Ⅲ- 4

Searching for novel quantum materials andunderstanding their properties have been a major
theme in condensed matter physics. Se substitution in
SrTiO3 has revealed multiple electronic phases withpeculiar band structures that were initially observed
using our home-based ARPES with Helium lamp.
To further study the electronic band structure of oneof the phases (Phase #1), we performed systematic
ARPES measurements at the BL5U of UVSOR. A
series of Fermi surface maps and cuts along highsymmetry directions were measured with photons oflinearly horizontal (LH) and linearly vertical (LV)polarization and energy (hν) from 42 eV to 180 eV at
T=5.8 K. Figures 1(a) and (b) are, respectively, an isoenergy contour and the band dispersion along Cut#1
through Γ point obtained with hν = 160 eV (LH). Figure
2 are Cut#1 taken with a series of photon energies
between 57 eV and 67 eV with LH & LV polarization,
which suggests a negligible kz dependence.
We also studied another phase (Phase #2) in Sesubstituted SrTiO3 that is different from the one above.
Figure 3 compare the cuts measured near Γ point
between Phase #1 and Phase #2 with hν = 60 eV at T
= 5.8 K. Our measurements of Phase #2 show thephoton energy dependence from 110 eV to 125 eV(See Fig. 4).

Fig. 2. Cut #1 in Fig. 1(a) measured with a series ofphoton energies between 57 eV and 67 eV with LH &LV polarization at T = 5.8 K.

Fig. 3. Band dispersion image measured with hν = 60
eV at T = 5.8 K for (a) Phase #1 and (b) Phase #2 along
Cut #2 as marked in Fig. 3(c).

Fig. 1. Iso-energy contour and momentum cut
obtained with hν = 160 eV at T = 5.8 K. (a) Integrated
spectral intensity in the momentum space of Phase 1
over a small energy window [-0.21 eV, -0.19 eV]. (b)Band dispersion image along Cut #1 as marked in Fig.
1(a).

Fig. 4. kz dependence of Phase #2. (a) Iso-energy map
in the k//-kz plane and (b) stacked momentum distribution
curves (MDCs) at energy -3.5eV. (c) Band dispersion
image along Cut #2 as marked in Fig. 3(c) with hν =110 eV & 125 eV.

116

Ⅲ04- 10 -BL5B

Ⅲ -4. Surface, Interface and Thin Films

BL5B

Reflectance Measurements of Al/TiO2 Bilayers in the 10–30 eV Region at
BL5B, UVSOR
2

T. Hatano1, Y. Matsuda2 and T. Ejima1

IMRAM, Tohoku University, Sendai 980-8577, Japan
Department of Chemistry, Graduate School of Science, Tohoku Universuty, Sendai 980-8578, Japan1

VUV of a photon energy of 12.4 eV from Ar excitedby laser pulse is a high potential source when it isfocused by a suitable condenser optics. Al is known as
the best material for normal incidence mirror if its
surface is not covered by oxide layer. As a capping layermaterial to prevent the surface oxidization of Al, we
have chosen TiO2 considering its low refractive index at
12.4 eV, 0.63 [1]. By bilayer model of 2 or 4 nm thick
TiO2 on a thick Al, normal incidence reflectance can be
expected as 68 % or 52 %, respectively. We havefabricated Al/TiO2 bilayer on SiO2 substrates by threemethods: (1) Al (100 nm)/TiO2 (2 and 4 nm) byconsecutive thermal evaporation deposition, (2) Al (200nm) thermal evaporation deposition, transfer to anothervacuum chamber, Al surface oxide layer milling andTiO2 (2 and 4 nm) magnetron sputtering deposition, and(3) Al (200 nm)/TiO2 (0–14 nm gradient) consecutive
ion beam sputtering deposition.
Reflectance measurements were performed at BL5B,
UVSOR. The grating and mirror combination was
G3M5. The angle of incidence was 11.6°.
Figure 1 shows the measured spectral reflectance ofevaporated Al (100 nm)/TiO2 (2 and 4 nm) bilayers.
Oscillation structure appeared through 9–31 eV. The
period did not depend on the thickness of TiO2, whichmeans the oscillation was caused by interference of
substrate-Al interface reflection and Al-TiO2 interface
reflection. The spectral shape in 9–15 eV looks like a
reduced-size copy of that in18–30 eV. It is because of
the second order diffraction of the monochromator [2].
As a result, reflectances at 12.4 eV were quite low.
Figure 2 shows the measured spectral reflectance ofevaporated Al (200 nm)/sputtered TiO2 (2 and 4 nm)
bilayers. The thickness of Al layer is uncertain becauseof the oxide layer removal before TiO2 deposition. The
result that the periods of the oscillation structure wereshorter than those of Fig. 1 means the Al layer was
thicker than 100 nm.
Figure 3 shows the measured spectral reflectance of
sputtered Al (200 nm)/TiO2 (0–14 nm) bilayer.
Measurement points was shifted by 8 mm to change
TiO2 thickness by 2 nm. The plot raveled by 0 nm
shows an Al with surface oxide layer. The reflectancein low energy region was unexpectedly low [3]. The
reason could be attributed to the second and higher
order diffraction or low energy scattering of the gating
could be attributed.

Fig. 1. Spectral reflectances of evaporated Al (100nm)/TiO2 (2 and 4 nm) bilayers.

Ⅲ- 4Fig. 2. Spectral reflectances of evaporated Al (200nm)/sputtered TiO2 (2 and 4 nm) bilayers.

Fig. 3. Spectral reflectances of sputtered Al (200nm)/TiO2 (0–14 nm) bilayer.
[1] Handbook of Optical Constants of Solids (Ed. by
Edward D. Palik, Academic Press, Inc., 1985).
[2] T. Hatano et al., UVSOR Activity Report 2019 47(2020) 41[3] G. Hass and R. Tousey, J. Opt. Soc. Am. 49 (1959)
539.

117

Ⅲ04- 11 -BL5BInterface and Thin Films
Ⅲ -4. Surface,

BL5B

Measurement of Soft X-Ray Resonant Magneto-Optical Kerr Effect for
GdFe(Co) and TbFe
T. Sumi1, M. Horio1, S. E. Moussaoui1, E. Nakamura2, S. Makita2, K. Tanaka2,3,
A. Tsukamoto4 and I. Matsuda1
The Institute for Solid States Physics, The University of Tokyo, Kashiwa 277-8581, Japan
2
Institute for Molecular Science, Okazaki 444-8585, Japan3
the Graduate University for Advanced Studies, SOUKENDAI, Okazaki 444-8585, Japan
4
College of Science and Technique, Nihon University, Funabashi 274-8501, Japan

1

Ⅲ- 4

In the advanced information society today, spintronic
devices have attracted great interests due to the fastprocessing speed [1]. The material is complicated andcomposed of multi-element, it has been demanded to
track their spin dynamics at individual magnetic
elements. Recently, we have developed an experimental
technique of the resonant magneto-optical Kerr effect(RMOKE) in soft X-ray region and succeeded inelement-selectively tracing spin-states of d-electrons attransition metal atoms, e.g. Fe [1-5]. In the present
research, we extended our spintronics research to the felectronic system, such as in rare-earth elements, by the
RMOKE experiment.
We prepared two ferrimagnetic samples: Gd23Fe67Co10
crystal and Tb20Fe80 crystal. The direction of spontaneous
magnetization was perpendicular to the surface. The
experiments were carried out at soft X-ray beamline
BL5B. The beam is irradiated on the sample with anangle of 67.5 degrees with respect to the surface normal.
The specular beam after the reflection was led to a unit of
the rotating analyzer ellipsometry (RAE) for analyses ofthe light polarization, i.e. the Kerr rotation angle. The
RAE system was composed of a multilayer mirror and a
detector of microchannel plate. By rotating the unit withrespect to the beam direction, the Kerr rotation angle θk
was determined by θΚ = – (χ+ – χ–) / 2, where χ+ and χ–
are the rotation angle which is the measured at theintensity maximum of the ellipsometry curves under the
positive and negative magnetic field, respectively.
Figure 1 shows photon energy spectra of the Kerr
rotation angle for crystals ofGd23Fe67Co10 and Tb20Fe80.
The degree of Kerr rotation angle corresponds tomagnetizations at each element. Therefore, we foundthat the spin directions of f-electrons system areopposite to those of d-electrons system in both
GdFe(Co) and TbFe. This result is consistent to the spin
configuration in a ferrimagnetic material and it
demonstrates that our RMOKE can be applied to the felectronic systems.

Fig. 1. Photon energy dependence of Kerr rotation
angle for crystals of (top) Gd23Fe67Co10 and (bottom)
Tb20Fe80 crystal. The solid squares correspond to theabsorption edge of each elements.

[1] C. D. Stanciu et. al., Phys. Rev. Lett. 99 (2007)
047601.
[2] Sh. Yamamoto et. al., Phys. Rev. B 89 (2014)064423.
[3] Sh. Yamamoto and I. Matsuda, Appl. Sci. 7 (2017) 662.
[4] Sh. Yamamoto et. al. Rev. Sci. Instrum. 86 (2015)
083901.
[5] K. Yamamoto et. al. Appl. Phys. Lett. 116 (2020)
172406.

118

Ⅲ04- 12 -BL6U

Ⅲ -4. Surface, Interface and Thin Films

BL6U

Domain Distribution in the Monolayer CVD Graphene Sheet Observedwith Photoelectron Momentum Microscope
1

Y. Aoyagi1, S. Ohno1 and F. Matsui2

Graduate School of Engineerig Science,Yokohama National University, Yokohama 240-8501, Japan
2
UVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan

Photoelectron Momentum Microscope (MM) is
considered as a promising means to explore orbital
tomography of organic molecules as well as various
nanostructures such as a graphene nanolayer [1]. In thepresent work, we focused on the graphene monolayer
produced by chemical vapor deposition (CVD) andsubsequently transferred to the silicon oxide substrate.
Experiments were performed at BL6U of UVSOR III.
Band dispersion data of CVD monolayer graphene wereobtained over a wide reciprocal range. Figure 1 shows
the typical result obtained near Fermi level. This
indicates that a single-domain structure is formed within
the accuracy of the spatial resolution of the present
measurements. Based on this type of the data, we caneasily recognize the orientation of the monolayer
graphene sheet. In contrast, we observed ring-likepattern at some part of the sample. We deduce thatseveral domains coexist at such a position. In otherwords, density of the domain boundary is larger,
resulting in the isotropic electronic states within themonolayer graphene sheet at such a location. In order toclarify further the two-dimensional distribution of thesingle-domain
structure,
weconducted
themeasurements of the two-dimensional mapping as
shown in Fig. 2. We found that single-domain withseveral equivalent directions coexist within themeasured area (70 x 500 μm2). This indicates that there
should be a preferred direction of the domain boundaryline between the single-domain structures. Our atomic
force microscopy (AFM) study showed that manyboundary lines should exist inside of the single-domain
region, although the band dispersion is well retained asshown in Fig. 1. Our present results indicate that themacroscopic self-organization process should exist
during the growth of CVD monolayer graphene sheet sothat the three single-domain structures preferentially
coexist in a macroscopic range. We deduce that not only
the local electronic structure at the atomic scale but alsothat at the submicron scale should be assessed more
carefully to grasp the spatial distribution of the domains
with a typical band dispersion or isotropic electronic
state.
In the study of two-dimensional materials, it is wellrecognized that the effect related to the domainboundary should be carefully assessed [2]. Here, we
propose that MM will become a useful means to relate
the microscopic knowledge with macroscopictransport property and other physical properties.

119

Fig. 1. Isoenergy cross section of the valence band
dispersion of CVD graphene monolayer near Fermi
level. Photoelectron peaks appeared at the K points.

Fig 2. The Fermi surface patterns from twodimensionally scanned positions.
[1] F. Matsui et al., Jpn. J. Appl. Phys. 59 (2020) 067001.
[2] S. M. Hus et al., Prog. Surf. Sci. 92 (2017) 176.

Ⅲ04- 13 -Ⅲ- 4

BL6UInterface and Thin Films
Ⅲ -4. Surface,

BL6U

Electronic Structures of 1T-TaS2 Studied by a Momentum Microscope
S. Suga1, T. Kobayashi2, E. Iwamoto2, K.Sakamoto2 and F. Matsui3

ISIR, Osaka University, Ibaraki 567-0047, Japan
Graduate School of Engineering, Osaka University, Suita 565-0871, Japan
3
UVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
1

2

Ⅲ- 4

Among various transition metal dichalcogenides, 1TTaS2 shows the richest phase diagram including apronounced metal to insulator phase transition (MIT) anda sequence of different charge density wave (CDW)
transformation.
Withlowering
temperatures,incommensurate CDW (ICCDW) is observed below
550K and then nearly commensurate phase (NC- CDW)
is seen below 350 K. Further a commensurate CDW(CCDW) is realized below 180 K.
This material is cleaved in UHV and the angle resolve
photoemission spectra in a wide wave vector space were
measured at various EB by use of synchrotron radiation(SR) by a newly installed momentum microscope (MM)at BL6U of UVSOR.
The advantage of MM is that without any rotation of
the sample, photoemission intensity at more than several
thousand multichannels of wide (kx,ky) can be
simultaneously recorded by a 2D detector in the form ofEB(kx,ky). Therefore the sample-rotation dependent
intensity normalization, slight shift of the measured areaon the sample surface as well as the consideration of thechange of the measurement configurations are not at all
required for analyses.
As soon as a flat and clean sample surface is obtained,
one should locate the sample just in front of the PEEM
objective lens by use of delicate sample manipulator.
Then one can obtain huge amount of data set within ashort time. Partial results are shown in Figs. 1 (a)-(d).
These results are obtained at T=50 K in the CCDW phaseby use of monochromatized synchrotron radiation light at
h=66 eV. The binding energies EB correspond to (a) 0 eV,(b) 0.5 eV, (c) 1.0 eV and (d) 1.5 eV. Each data is
integrated within ± 0.15 eV for realizing enough statistics.
The detailed behavior of the Ta 5d orbitals is clearlyrecognized around the kx=0, ky=0 point in the data (a)-(c).
Since even the 2nd Brillouin zone is imaged, the hole
pocket resulting from the S 3p orbital can be recognizedin Fig(d) near kx=0, ky=2Å-1.
The band dispersions can be then easily revealed not
only along the ky axis but also any kx-ky axes bycomparing the data selected from a huge data set
integrated at different temperatures.
Thus high potential of MM for studying detailed
I(EB(kx,ky)) is clarified [1]. I(EB(kx,ky,kz)) measurement is also possible by use of SR.
[1] S. Suga, A. Sekiyama and C. Tusche, Photo-electron
Spectroscopy, Springer Series in Surface Sciences 72(2021), in press.

Fig. 1. (kx,ky) images of 1T-TaS2

120

Ⅲ04- 14 -BL6U

Ⅲ -4. Surface, Interface and Thin Films

BL6U

Momentum Microscopy of Highly Oriented Dph-BTBT Film on Ag(110)
M. Iwasawa1, Y. Hasegawa2, F. Matsui3, S. Kera3 and Y. Yamada1

Faculty of Pure and Applied Sciences, University of Tsukuba, Tsukuba 305-8573, Japan
2
Institute for Molecular Science, Okazaki 444-8585, Japan
3
UVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
1

While devices based on [1]benzothieno[3,2-b] [1]benzothiophene (BTBT) derivatives, which exhibit
strong intermolecular interactions and atmosphericstability, have achieved mobility in excess of 30
cm2/Vs, the origin of their efficient conduction is still
not fully understood. Although the mobility of manyorganic semiconductors has been understood by theenergy and spatial distribution of HOMO, a recent
study has shown that the contribution of HOMO-1 issignificant in BTBT derivatives [1]. In this study, we
focused on Dph-BTBT, one of the BTBT derivatives,and analyzed the energy states and the photoelectron
angular distribution (PAD) of HOMO and HOMO-1.
For the detailed measurement and the analysis of
PAD, a molecular layer with single domain structure isrequired. We have recently shown that well-ordered
Dph-BTBT film can be realized on metal(111) surface[2]. However, Dph-BTBT film on metal(111) has multidomain structure, which is not suitable for the PAD
measurement. Therefore, we have further demonstrate
that, by using anisotropic Ag(110) surface, a nearly onedimensionally oriented film of Dph-BTBT can be
fabricated. Here, we tried to measure the photoelectron
momentum map of the single-domain, multilayer filmof Dph-BTBT on Ag(110).
The one-dimensionally oriented Dph-BTBT film
were fabricated by supplying 10 nm of Dph-BTBT on
clean Ag(110). The molecular structure of the DphBTBT film was examined using a scanning tunnelingmicroscope (STM) and low energy electron diffraction(LEED). The PAD measurements were performed using
momentum microscope at BL6U of UVSOR.
Figure 1 shows the STM image and LEED pattern of
Dph-BTBT film on Ag(110). It is seen that themolecular long axis is almost along with the [1-10]
direction of the substrate, indicating the formation ofnearly one-dimensional structure. Although it was not acompletely single-domain structure, it is a suitablesample for the measurement of PAD.
Figure 2(a) shows the energy distribution curve(EDC) of Dph-BTBT film on Ag(110). It is found thatboth HOMO and HOMO-1 are energetically broadened.
Here, each orbital can be fitted with two Gaussianfunctions, suggesting that orbital splitting due to theoverlap of neighboring (upper and lower) molecules.
Then, we examined PAD patterns of each orbital as
shown in Fig. 2(b, c). It is recognized that both PAD
patterns of HOMO and HOMO-1 have strong intensity
in kx direction, which is in general agreement with thesimulation by means of FFT of molecular orbital. For
the detail analysis, we focus on the energy dependanceof the peak location and the width at half maximum(FWHM) of the intensity at around kx = 1.5 ~ 1.7 Å–1 asillustrated with arrows in Fig. 2(b). As for the peaklocation (blue dots in Fig. 2(a)), there is no change in the
HOMO region, but a gradual shift to the lowermomentum side is seen in the HOMO-1 region. On theother hand, the FWHM shows little change in the kx
direction (orange dots), but a significant change in the
ky direction (green dots) in the HOMO region.
Thus, by means of PAD using the momentum
microscope at BL6U, we were able to experimentally
detect the subtle changes in the wavefunction of DphBTBT in the condensed state, which was difficult by
the conventional techniques.

Ⅲ- 4

Fig. 1. STM image and LEED pattern of Dph-BTBT/Ag(110).

Fig. 2. (a) EDC plotted with peak location and
FWHM of PAD. (b, c) PAD patterns of HOMO and
HOMO-1 of Dph-BTBT.
[1] Y. Kuroda et al., Jpn. J. Appl. Phys. 58 (2019).
[2] Y. Yamada et al., UVSOR Activity Report 2019 47(2020) 137.

121

Ⅲ04- 15 -BL6UInterface and Thin Films
Ⅲ -4. Surface,

BL6U

PEEM-mode Magnification Parameters
for Photoelectron Momentum Microscopy
F. Matsui1, S. Makita1, H. Matsuda1, Y. Okano1, T. Yano1, E. Nakamura1 and S. Kera1,2
1

UVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, JapanThe Graduate University for Advanced Studies, SOKENDAI, Okazaki 444-8585, Japan

2

Ⅲ- 4

As reported in the previous activity report, newexperimental station for momentum microscopy wasconstructed and is currently operating at the BL6U, an
undulator-based soft X-ray beamline [1,2]. The
photoelectron momentum microscope is a uniquemultifunctional system for characterizing the electronic
properties of μm- and nm-scale structures. A spectromicroscopy (PEEM) mode in real space and microspectroscopy (momentum) mode in reciprocal space areavailable.
Calibration and lens parameter optimization areimportant issues for high quality data acquisition, so
we use checkered-patterned samples for this purpose.
The spatial distribution of elements can be mappedusing photoelectrons from the core level. On the other
hand, the contrast in valence photoelectron images
varies from case to case. In a recent paper [3], we
reported on a detailed study of contrast formation. The
photoelectron intensity of the gold region near the
Fermi level was higher than that of the silicon
substrate region, while the inverted contrast images
were obtained at lower kinetic energies. The contrast
inversion in the photoelectron images by mercury (Hg)lamp excitation is due to the differences in work
functions specific to materials and surface conditions,and that of synchrotron radiation excitation is due tothe difference in the density of states between gold andsilicon substrate.
The following is an overview of the magnification
modes available in PEEM mode. Figure 1 shows anexample of observing a checkerboard pattern invarious magnification modes. Hg lamp excitation
was used. The largest field of view (φ 140 μm) is
achieved by Mag.1 mode. Note that the irradiation
spot on the sample is smaller than the field of view inthe present case. The intensity ratios of different
magnifications are indicated together. In higher
magnification modes, the flux density per pixel isreduced, resulting in lower photoelectron intensity.
Since the momentum of photoelectrons excited by
the Hg lamp is smaller than the acceptance cone of
the PEEM lens, all photoelectrons are detected. In thecase of synchrotron radiation excitation, it is needed
to considered that the acceptance cone in the
momentum space limits the photoelectrons in low
magnification mode.

Fig. 1. A checkered pattern observed by thephotoelectron momentum microscope in various
magnification modes. The Hg lamp was used for
excitation.

[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] F. Matsui, S. Makita, Y. Okano, H. Matsuda, and S.
Kera, Vacuum and Surface Science accepted (2021).
[3] S. Makita, H. Matsuda, Y. Okano, T. Yano, E.
Nakamura, Y. Hasegawa, S. Kera, S. Suga, and F.
Matsui: e-J. Surf. Sci. Nanotech. accepted (2021).

122

Ⅲ04- 16 -BL7U

Ⅲ -4. Surface, Interface and Thin Films

BL7U

Study of Electronic Band Structure of Li- and Ca-Intercalated Graphene
S. Ichinokura1, M. Hashizume1, K. Horii1, R. Fukushima1, M. Toyoda1, S. Ideta2,
K. Tanaka2, R. Shimizu3, T. Hitosugi3, S. Saito1 and T. Hirahara1
Department of Physics, Tokyo Institute of Technology, Tokyo 152-8551, JapanUVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan3
Department of Applied Chemistry, Tokyo Institute of Technology, Tokyo 152-8550, Japan
1

2

Graphene is known as the most promisingnanomaterial for the post-silicon electrical industry.
The remarkable high-carrier mobility in grapheneoriginates from its characteristic band structure called
the Dirac cone. When the Fermi energy in graphene
locates near the Dirac cone crossing (Dirac point),
graphene has a massless carrier due to its linear andsteep band dispersion.
Many-body interaction in graphene materials is also atarget of intensive research. The band structure ofmonolayer graphene has a saddle point at the M point of
the Brillouin zone. The dispersion near this point is flat,
leading to the heavy effective mass and divergent densityof states. This is called Van Hove singularity (VHS),
expected to drive unconventional superconductivity. It is
known that deposition of alkali- and alkaline earth-metals
tunes the Fermi energy to the VHS point upon electron
doping [1,2]. Recently, this VHS filling has attracted
renewed interest due to the emergence ofsuperconductivity in twisted bilayer graphene, which also
originated from the VHS at the Fermi level [3].
In our group, a comprehensive study on alkali- andalkaline earth-doped graphene is carried out by a
combination of in situ angle-resolved photoemission
spectroscopy (ARPES) and electrical transportmeasurements in ultrahigh vacuum (UHV). By
comparing band structures and the transport properties,
we are investigating the many-body interaction ingraphene.
In the present study, we prepared monolayer grapheneon SiC(0001) substrates. Li and Ca were doped byvapor deposition and annealing in UHV, followed by insitu ARPES measurements. In Fig. 1, we show the band
structure of (a) as-grown, (b) Li- and (c) Ca-doped
graphene. The Brillouin zone (BZ) of the graphene isdrawn in Fig. 1(d). Fig. 1(a) was collected around K
point, parallel to the direction shown as the solid green
line in Fig. 1(d). The slightly n-doped single Dirac cone
centered at the K point is seen, typical for the monolayer
graphene. On SiC, such high-quality epitaxial growth ofgraphene is possible because of the underlying buffer
layer, which terminates the dangling bonds of the
SiC(0001) surface.
Figures 1(b) and (c) were taken at the Γ point alongthe Γ-K line, shown as the solid magenta line in Fig.
1(d). In both spectra, steep band dispersions are seen.
We conclude that these bands are two pairs of Dirac
bands (denoted as π1* and π2*). In Ref. [4], it wasreported that Li intercalates into both sides of thebuffer layer. Consequently, the atomic structure of thesystem is changed into a layered one shown in Fig.
1(e); Li terminates the substrate dangling bonds anddecouples the buffer layer from the substrate. Further
deposited Li intercalates between the lifted grapheneand the top one, forming the √3×√3 periodicity. The
heavily-doped two Dirac bands observed around Γ in
Fig. 1(b) perfectly match this picture. Besides, the π2*band reaches the Fermi level at its flat part at the M
point of √3×√3 BZ, which satisfies the VHS.
We newly found that similar structural change takes
place in Ca-doped graphene, with further chargetransfer to π1* and π2* bands. In Fig. 1(c), another bandwith a parabolic shape can be seen. This free-electron(FE) like characteristic corresponds to the interlayerband of superconducting Ca-intercalated graphite [5].

Ⅲ- 4Fig. 1. (a)-(c) Band structure of (a)As-grown, (b) Lidoped and (c) Ca-doped graphene. ARPES
measurements were performed with hν= 20-40 eV ppolarized light under T = 11-13 K. (d) Schematic of
1×1 and √3×√3 BZ. Measurement directions of (a)-(c)are drawn as solid green and magenta lines. (e)Schematic atomic model of Li- and Ca-doped
graphene.

[1] J. L. McChesney et al., Phys. Rev. Lett. 104 (2010)
136803.
[2] P. Rosenzweig et al., Phys. Rev. Lett. 125 (2020)
176403.
[3] Y. Cao et al., Nature 556 (2018) 43.
[4] S. Fiori et al., Phys. Rev. B 96 (2017) 125429.
[5] K. Sugawara et al., Nat. Phys. 5 (2009) 40.

123

Ⅲ04- 17 -BL7UInterface and Thin Films
Ⅲ -4. Surface,

BL7U

Low-kinetic Energy and Low-temperature Measurements to Unveil
the Impact of Weak Interaction: a Machine Status of the BL7U
Y. Hasegawa1, S. Ideta1, K. Tanaka1,2 and S. Kera1,2

Department of Photo-molecular science, Institute for Molecular Science, Okazaki 444-8585, Japan
School of Physical Sciences, The Graduate University for Advanced Studies, SOKENDAI, Okazaki 444-8585, Japan
1

2

Ⅲ- 4

The purpose of this study is to clarify the impacts on
the electronic state of the organic/inorganic interface
stabilized by weak interaction such as van der Waals
force. We have studied the oriented-monolayer film of
pentacene on graphite so far and realized the emergenceof a dispersive band utilizing low-energy excitation
angle-resolved photoelectron spectroscopy (LE-ARPES).
The dispersive band appears at the kinetic energy of 1 to
2 eV where the secondary electron is a non-negligible
and constant final state (CFS) feature is overlappingwith the non-dispersive molecular orbital states. The
CFS band could be originated from a newly-formed
conduction band at the weakly bounded interface
visualized by high-resolution angle-resolved secondary
electron emission [1], demonstrating that the impact of
weak interaction would appear much stronger inunoccupied states by a larger spread of an electron cloud.
During the experiment at BL7U, however, we
encountered technical issues to measure this system at
low-kinetic energy and low temperature this time.
A single crystalline graphite (SCG) as the substrate
was cleaned by annealing at 600 K for 2 h. A pentacene
film of 4.1 Å was deposited onto the SCG at room
temperature in a custom UHV chamber designed fororganic layer deposition. After the deposition, a rapidly
cooled sample below the phase transition temperature[2] was measured.
Figure 1 shows LE-ARPES image of the SCG taken
at hν of 7.4 eV on the same day. In the image, the signal
lacks at the lower right, and the energy and angle
positions are different from each other. There was no
choice to optimize the image distortion properly byarranging the experimental setup, a measurement
position, a sample preparation, and so on. This curve
appears nearly the same position at a different excitationenergy of 7.2 eV and 8.0 eV because the photoemission
is mainly from a secondary electron. This kind of timedependent phenomenon has never been found at BL7U,
therefore, the artifact was caused by changes of thepresent analyzer condition, unfortunately.
Figure 2 shows ARPES of pentacene/SCG taken at hv= 40 eV with decreasing the temperature from 50 K to
10 K. Upon the cooling, a new feature appears at aroundbinding energy of -11 eV at 10 K. According to theprevious report, it is caused by adsorbing Ar atoms on
the surfaces [3]. Evolution of the Ar 3p peak with thecooling is observed and the feature is completely
recovered at 50 K by annealing (not shown). The
molecular film structure (packing or orientation) is
easily affected by adding such a weak perturbation of
the gas adsorption [4]. To discuss the modification of the124electronic state of the molecular interfaces by the weakinteraction, the low-temperature experiments aremandatory to monitor the effects of decreasing the
distance between a molecule and the surface. We will
improve the present machine status at BL7U for
standing a severe experiment.

Fig. 1. (a) and (b) are LE-ARPES images of the same
SCG taken at hν = 7.4 eV which show different lacked
areas indicated by blue ovals.

Fig. 2. ARPES spectra of pentacene/SCG measured
with decreasing the temperature.

[1] T. Yamaguchi et. al., UVSOR Activity Report 201846 (2019) 148.
[2] Y. Hasegawa et. al., UVSOR Activity Report 201947 (2020) 140.
[3] F. Carnovale et. al., J. Chem. Phys. 90 (1989) 1452.
[4] F. Bussolotti et. al., Phys. Rev. Lett. 110 (2013)
267602.

Ⅲ04- 18 -BL7U

Ⅲ -4. Surface, Interface and Thin Films

BL7U

Hybridization between π Band of Graphene and 6sp Band of Hex-Au(001)
Reconstructed Structure
T. Terasawa1,2, S. Tanaka3, K. Matsunaga4, T. Ito4,5, S. Yasuda1, S. Machida1,
M. Yano1 and H. Asaoka1

Advanced Science Research Center, Japan Atomic Energy Agency, Tokai 319-1195, Japan
2
Institute of Industrial Science, The University of Tokyo, Tokyo 153-8505, Japan3
The institute of Scientific and Industrial Research, Osaka Univ., Ibaraki 567-0047, Japan
4
Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan
5
Nagoya University Synchrotron radiation Research center (NUSR), Nagoya University, Nagoya 464-8603, Japan1

at the Fermi energy. While this value does not matchthe graphene K point, k = 1.7 Å-1, k = 1.47 - 0.44 =1.03 Å-1 is reasonable for the Au 6sp band. Such thereplicated Au 6sp band was observed for Hex-Au(001)in the previous report [4]. We concluded that the Au
6sp band hybridized with the graphene π band to form
the mini-gap in the graphene π band. We expect thishybridization changes the electronic structure and thespin characteristics of graphene, similar to thehybridization between graphene and Au in thegraphene/Au/Ni system reported in 2012 [1].

The interface between graphene and Au has
attracted much attention since the large Rashba
splitting of 100 meV in the π band of graphene/Au/Nistructure was discovered in 2012 [1]. As one of thegraphene and Au interfaces, graphene on Hex-Au(001)
reconstructed surface has also been studied. The quasione-dimensional periodic potential in this structure isconsidered to replicate graphene π band to open a new
bandgap at the Brillouin zone boundary [2]. However,
the electronic structure of this system has not beenreported yet. In this study, we have performed angleresolved photoemission spectroscopy (ARPES) on
graphene grown on the Hex-Au(001) surface todirectly investigate this system's electronic structure.
Graphene was prepared on Hex-Au(001) substrateusing chemical vapor deposition in Japan atomic energy
agency [3]. Hex-Au(001) spontaneously formed during
the graphene growth. Low energy electron diffraction
measurements indicated that the sample surface and theinterface were unchanged during the transport underambient conditions. ARPES measurements were
performed at the UVSOR-III BL7U after the sample
annealing in the pre-chamber by an IR-heater. Data
were acquired at room temperature with hν = 9 – 40 eV.
We changed the photon energy and polarization tovisualize graphene and Au bands and their replicas.
Figure 1 shows the ARPES image on a Γ-X(Au)-K(graphene) line. Two sharp bands and one faint band
were observed. The linear band dispersion from k =1.7 Å-1 (K point of graphene) was assigned to thegraphene π band. This band shows a mini-gap at thebinding energy of about 0.9 eV. The other linear bandcrossing the Fermi energy at k = 1.2 Å-1 close to the X
point of Au was assigned to the Au 6sp band,
according to the previous report about the electronic
structure of Hex-Au(001) [4]. An electron pocket
around the X point was also consistent with theprevious report [4].
The faint linear band comes from k = 1.47 Å-1 at the
Fermi energy and crosses the top edge of the mini-gap.
This band crossing suggests that this linear band is theorigin of the mini-gap formation in the graphene πband. Accounting for the periodicity of the HexAu(001) surface of 1.44 nm, the reciprocal vector ofthis structure is 0.44 Å-1 [2,4]. Thus the original bandof this band should begin from k = 1.47 ± n×0.44 Å-1

Ⅲ- 4

Fig. 1. Band structure of graphene grown on hexAu(001) substrate. An energy gap of 150 meV wasobserved in the graphene π band.

[1]D. Marchenko, et al., Nat. Commun. 3 (2012) 1232.
[2] X. Zhou, et al., ACS Nano 10 (2016) 7550.
[3] T. Terasawa, et al., Jpn. J. Appl. Phys. 58 (2019)
SIIB17.
[4] S. Bengió, et al., Phys. Rev. B 86 (2012) 045426.

125

Ⅲ04- 19 -BL7U,
Ⅲ -4. Surface,
Interface and Thin Films

BL7U, BL5U

Topological Electronic Structure of the Interface
between α-Sn and InSb
T. Nakaya1, Y. Ohtsubo2,1, T. Nakamura1 and S. Kimura2,1,3

Department of Physics, Graduate School of Science, Osaka University, Toyonaka 560-0043, Japan
2
Graduate School of Frontier Biosciences, Osaka University, Suita 565-0871, Japan3
Department of Materials Molecular Science, Institute for Molecular Science, Okazaki 444-8585, Japan

Ⅲ- 4

-1

-0.2

kx(Å )
0.0

_
M

_
Γ

0.2

0.0
0.2

Among the topological materials [1], α-Sn [2,3] isgathering much attention because of its possible
spintronic application, as reported to exhibit spin tocharge conversion due to the inverse Edelstein effecteven at room temperature [4]. The next barrier for the
new-generation spintronic devices is to realize theinterface between TIs and normal semiconductors inorder to make the spin-polarized topological electronic
states available for them. Along this line, to make thejunction between TI and normal semiconductor hosting
the topological “interface” state is awaited. In this study,
we have tried to grow normal semiconductor InSb,
which has a small lattice mismatch to a topologicalmaterial α-Sn (0.14%), on α-Sn(111) ultrathin films andobserved its surface and interface electronic structure byangle-resolved photoelectron spectroscopy (ARPES).
The InSb(111) substrates were cleaned by repeatedcycles of Ar+ sputtering (0.5 keV) and annealing up to600 K in an ultra-high vacuum chamber. Then, homoepitaxial growth of InSb was performed to obtain theclean surface of the InSb(111) substrates. α-Sn films
with the thickness of 8 bi-atomic layers (BL) wereobtained by evaporating Sn from a home-madeevaporator. The evaporation rates of In, Sb, and Sn weremonitored in-situ from the intensity oscillation of theelectron diffraction patterns. After the growth, (1×1)
periodic structure of α-Sn was observed, consistent withthe earlier report [6]. On such α-Sn(111) films, In andSb were deposited and the InSb layer with the thicknessof ~1BL was grown there. The surface periodicity
remained after the growth of InSb without in-planelattice distortion.
Figure 1 shows the band dispersion of the InSb(~1BL)/α-Sn(8BL)/InSb(111)B observed by ARPES. A linear
Dirac cone like dispersion (guided by dashed whitelines), which is a typical behavior of the topologicalelectronic states, was observed around the center of thesurface Brillouin zone (kχ = 0.0Å–1 ) after the depositionof the InSb layer. This result suggests that the topologicalsurface state of α-Sn is transplanted to the interface with
InSb, a normal semiconductor. Further analysis tounderstand the spin texture of the interface electronic
states between α-Sn and InSb is in progress.

Binding Energy(eV)1_MFig. 1. Band dispersion of InSb/α-Sn/InSb(111)B by
observed by ARPES (hν = 16eV). The measurement
was taken at room temperature and normalized by the
Fermi distribution function.

[1] M. Z. Hasan and C. L. Kane, Rev. Mod. Phys. 82(2010) 3045.
[2] Y. Ohtsubo et al., Phys. Rev. Lett. 111 (2013) 216401.
[3] A. Barfuss et al., Phys. Rev. Lett. 111 (2013) 157205.
[4] J-C Rojas-Sanchez et al., Phys. Rev. Lett. 116 (2016)
09602.
[5] Q. Barbedienne et al., Phys. Rev. B 98 (2018) 195445.
[6] H. Omi et al., Phys. Rev. Lett. 72 (1994) 2596.

126

Ⅲ04- 20 -