Ⅲ-4
Surface,
Interface andThin Films

BL6UⅢ -4. Surface, Interface and Thin Films

BL6U

The Photoelectron Momentum Microscope
F. Matsui1, S. Makita1, H. Matsuda1, T. Yano1, E. Nakamura1, K. Tanaka1,2, T. Ohigashi1,2,
H. Horigome1, S. Ideta1,2, Y. Hasegawa2, S. Suga3 and S. Kera1,2
UVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, JapanThe Graduate University for Advanced Studies, SOKENDAI, Okazaki 444-8585, Japan
3
The Institute of Scientific and Industrial Research, Osaka University, Ibaraki 567-0047, Japan
1

2

The importance of characterizing microstructure
electronic properties cannot be overemphasized. The
demand for photoelectron micro-spectroscopy andspectro-microscopy is growing rapidly. Photoelectron
spectroscopy resolved in three-dimensional momentum
space with a microscopic field of view is realized by
combining a so-called Momentum Microscope with asoft X-ray synchrotron radiation source. This method
opens the door to direct observation of the Fermi surfaceof μm-sized crystals, which was difficult withconventional ARPES-type hemispherical analyzers. A
new experimental station for Momentum Microscopy
has been built at BL6U, an undulator-based soft X-ray
beamline. In fact, this successful combination of asingle HDA-type Momentum Microscope at thesynchrotron facility is the first case in the world. As
shown in Fig.1, the system consists of a photoemission
electron microscope (PEEM) lens, a hemisphericaldeflection analyzer (HDA) for imaging-type energy
filter, and a 2D detector with a CMOS camera. This
experimental station specializes in characterizing theelectronic structure of surface atomic sites, thin films,
molecular adsorbates, and bulk crystals.
The details of the specification evaluation result aredescribed elsewhere [1]. In brief, the energy resolutionof the analyzer was estimated to be 22.74 meV at passenergy of 20 eV. The spatial resolution in the
microscopy mode was evaluated to be about 50 nm.
The momentum resolution of 0.012 Å-1 has beenachieved. The position of sample stage facing to theanalyzer is precisely controlled by a hexapod. Samples
can be cooled down to 10 K and heated up to 400 K.
Figure 2 shows the optical and PEEM images of apiece of micro channel plate (MCP) fragment. The
pore size was 10 μm and the interval of each pore was
11.6 μm. The top surface of the MCP is clearly imaged,
despite the nearby deep holes and useful for the lateral
length calibration. It is interesting to note that excited
photoelectrons are detected from one side of the holewall. Figure 3 shows the preliminary results of valenceband photoelectron 2D angular patterns excited by Helamp and synchrotron radiation. The six bright spots
correspond to the π band at the vicinity of Dirac cone.
The center double ring structure originates from thesubstrate Ru 4d band.
We greatly acknowledge Dr. Markus Breusing, Dr.
Marko Wietstruk, and Dr. Mirko Weidner (SPECS)
and Dr. Dai Yamaguchi (Tokyo Instruments Inc.) for
their contribution in the construction of the BL6U
Momentum Microscope experimental station.

Fig. 1. Photograph of the Momentum Microscopy
station at BL6U.

Ⅲ- 4

Fig. 2. (a) Optical photograph and (b) PEEM imageof a honeycomb pattern.

Fig. 3. Photoelectron angular distribution of valenceband from graphene grown on the Ru(111) surface
excited by (a) He lamp and (b) synchrotron radiation.
[1] F. Matsui et al., Jpn. J. Appl. Phys. 59 (2020) 067001.

123

Ⅲ04- 1 -BL2AInterface and Thin Films
Ⅲ -4. Surface,

BL2A

NEXAFS Spectroscopy of Magnesium Oxide Powder
E. Kobayashi1, K. K. Okudaira2, T. Kikuchi2, M. Imamura3, K. K. Bando3, S. Yoshioka4
and O. Takahashi5
Kyushu Synchrotron Light Research Center, Tosu 841-0005, Japan
2
Chiba University, Chiba 263-8522, Japan
3
National Institute of Advanced Industrial Science and Technology, Tsukuba 305-8565, Japan
4
Graduate School of Engineering, Kyushu University, Fukuoka 819-0395 Japan
5
Graduate School of Science, Hiroshima University, Higashi-Hiroshima, 739-8526, Japan1

Ⅲ- 4

Magnesium oxide (MgO) has been widely used as
catalytic, optical and electrical applications [1]. In
recent years, the performance of not only organic
photovoltaics but also perovskite solar cells has beensuccessfully improved by employing MgO nanolayers
as electrodes [2,3].
In order to further improve the characteristics ofsuch solar cells, it is necessary to understand thesurface and bulk electronic states. Near-edge X-ray
absorption fine structure (NEXAFS) spectroscopy is a
powerful tool for investigating the electronic
structures of materials. The NEXAFS spectra can beobtained by electron yield (EY) mode or fluorescence
yield (FY) mode. The former is sensitive to the surface
and the latter is sensitive to the bulk.
In this study, we measured Mg K-edge NEXAFS
spectra of MgO using both total electron yield (TEY)and partial fluorescence yield (PFY) modes in order toinvestigate the change in surface and bulk states withparticle size.
Two MgO powders with different particle size wereprepared. One is the size of 50 nm or less (MgO_A).
The other is 50 nm average (MgO_B). NEXAFS
spectra of the MgO powders were measured at thebeamline 2A of the UVSOR in the Institute of
Molecular Science. For TEY, the drain current fromthe sample was measured. For PFY fluorescence Xrays were collected using an energy dispersible silicon
drift detector (SDD). All experiments were performedat room temperature.
Figure 1 shows the Mg K-edge NEXAFS spectra of
MgO powder obtained from TEY and PFY. In the
spectrum measured in the TFY mode, the spectra of
MgO_A and MgO_B showed almost the same shape.
Their spectra were different from the Mg(OH)2 spectra
measured as a reference. On the other hand, in the
spectrum measured in the TEY mode, the spectra of
MgO_A and MgO_B were different. The spectrum of
MgO_A was almost similar to the spectrum of
Mg(OH)2 measured as a reference. These results
indicate that the bulk of MgO_A is MgO, but thesurface is Mg(OH)2. Since MgO_A has a smaller
particle size than MgO_B, the surface has high activity.
Therefore, Mg(OH)2 formed on the surface of MgO_A
with water in the atmosphere.
As a next step we will clarify the electronic structureof the interface between organic semiconductors andMgO nanolayers.

Fig. 1. Mg K-edge NEXAFS spectra of MgO powder.

[1] E. A. Colbourn, Surf. Sci. Rep.15 (1992) 281.
[2]H. J. Bolink, H. Brine, E. Coronado and M. Sessolo,
J. Mater. Chem. 20 (2010) 4047.
[3] J. Ma, G. Yang, M. Qin, X. Zheng, H. Lei, C. Chen,
Z. Chen, Y. Guo, H. Han, X. Zhao and G. Fang, Adv.
Sci. 4 (2017) 1700031.

124

Ⅲ04- 2 -BL2BⅢ -4. Surface, Interface and Thin Films

BL2B

Electronic Structure of ZnO Nanoparticles Deposited on ITO
K. K. Okudaira and T. Kikuchi

Association of Graduate Schools of Science and Technology, Chiba University, Chiba 263-8522, Japan

Intensity (arb. units)

Organic photovoltaic cells (OPV) have been
attracting interest concerning both fundamental
research and practical application for low-cost, largearea, lightweight and exible devices. In recent years,
varioussolution-processedbulk-heterojunction
photovoltaic devices have been reported using p-type
conjugated polymers, either in combination with ntype inorganic semiconductor nanoparticles. Thesehybrid polymers: inorganic - nanoparticle bulk
heterojunctions can take advantage of the beneficial
properties of both types of materials: solution
processing of polymer semiconductors and highelectron mobility of inorganic semiconductors.
The characteristics of OPV such as efficiency andfilling factor are considered to be dependence on theelectronic structure of not only organic semiconductor
but also n-type inorganic semiconductor nanoparticles.
In this work we deposited ZnO nanoparticles (NPs)thin films on ITO and clarify the electronic structureof ZnO NPs using hν-dependence of ultraviolet
photoelectron spectroscopy (UPS) measurements.
We synthesized ZnO NPs with different particle size.
The size of nanoparticles synthesized by ref [1] isabout 5 nm. On the other hand, the size of ZnO
nanoparticle synthesized by ref [2] is about 80 nm,
which is ten times larger than that synthesized by the
first methods. Here after we refer the ZnO
nanoparticles by the first method and the second
method to ZnOs and ZnO200, respectively. UPS
measurements were performed at the beam line BL2B
of the UVSOR storage ring at the Institute for
Molecular Science. UPS were measured with thephoton energy (hν) of 28 eV and 40 eV. The ZnO NP
thin films were prepared by spin-cast on ITO. The ZnO
NP thin films were annealed at 120 °C.
We observed hν)dependence of UPS of ZnO NPs
with different particle size (ZnOs and ZnO200) on ITO(Fig. 1). In the UPS three broad peaks appear about Eb(binding energy) of about 5 eV, 7.5 eV, and 10 eV.
These peaks around 5 eV and 7.5 eV are assigned tothe states which are hybridized Zn 4s and O 2p orbitals.
By considering the photoionization cross section of O
2p and Zn 4s of hν of 28 eV and 40 eV, the peak atlower binding energy and that at higher binding energy
is made of mainly by O 2p and Zn-4s, respectively.
The peak at Eb of about 10 eV is the emission of theZn 3d band. These assignments are good agreementwith ref [3]. In Fig. 2 the annealing processes do notaffect the UPS of ZnOs as well as ZnO200. On theother hand, the relative peak intensity of the peak
about 10 eV to that about 5 eV of ZnOs is larger thanthat of ZnO200. It is considered that the two synthetic
methods provide the different surface structures suchas the introduction of hydroxyl group.

40eV

28eV

10

5

Binding Energy relative to E f (eV)Fig. 1 UPS of ZnO NPs (ZnOs) at hν of 28 eV and
40 eV.

h=28eV
Intensity (arb. units)

ZnO200annealed
ZnO200ZnOs
anneale
ZnOs
ITO

10

5

Binding Energy relative to Ef (eV)Fig. 2 UPS of ZnO nanoparticles (ZnOs and ZnO200)
at hν of 28 eV.

[1] N. M. Shamhari, B. S. Wee, S.F. Chin and K. Y.
Kok, Acta Chim. Slov. 65 (2018) 578.
[2] H. Du, F. Yuan, S. Huang, J. Li and Y. Zhu, Chem.
Lett. 33 (2004) 770.
[3] W. Ranke, Solid State Commun. 19 (1976) 685.

125

Ⅲ04- 3 -Ⅲ- 4

BL2BInterface and Thin Films
Ⅲ -4. Surface,

BL3U

Cobalt Oxide Catalyst in Carbonate Aqueous Solution
Studied by Operando C K-edge XAFS Measurement
T. Moriyama1, M. Nagasaka2, H. Yuzawa2 and M. Yoshida1,3

Faculty of Engineering, Yamaguchi University, Ube 755-8611, Japan
2
Institute for Molecular Science, Okazaki 444-8585, Japan
3
Blue energy center for SGE technology (BEST), Yamaguchi University, Ube 755-8611, Japan1

Ⅲ- 4

existence of γ-NiOOH with highly active reaction sites.
In conclusion, we revealed the function of Ni-Ci
electrocatalyst by operando O K-edge and C K-edge
XAFS measurements. It was exhibited that the
carbonate species was adsorbed on the γ-NiOOH
structure to stabilize the active reaction sites, and theinterface of γ-NiOOH and adsorbed carbonate ion is
likely to function as efficient OER site.

Electrochemical water splitting with renewableenergies is attracting attention as a sustainablehydrogen production technique. In the electrolysis ofwater, overvoltage of the oxygen evolution reaction(OER) is a problem, and the development of a highly
active OER electrocatalyst is strongly required. In thissituation, a nickel carbonate (Ni-Ci) was reported
recently as an OER catalyst with high activity [1].
Meanwhile, we revealed the function of similar cobalt
OER catalysts by operando X-ray absorption finestructure (XAFS) observation [2]. Therefore, we
attempted to clarify the structure and reaction
mechanism of the Ni-Ci catalyst by performing
operando soft X-ray XAFS measurements.
A electrochemical cell was equipped with a Pt
counter electrode and an Ag/AgCl reference electrodefor all electrochemical experiments. The Ni-Ci thinfilms were electrodeposited on Au thin film in
potassium carbonate aqueous solution containing
Ni(NO3)2 at 1.7 V vs. RHE. The operando O K-edge
and C K-edge XAFS spectra for Ni-Ci were taken
under electrochemical control with transmission modeat BL3U in the UVSOR Synchrotron, according to theprevious works [3].
First, we checked the electrochemical OER activity
for Ni-Ci catalyst and confirmed that the catalyst candecompose water efficiently. The surface states andchemical composition were also measured by SEM,
EDX, stylus profilometer.
Next, operando O-K edge XAFS spectra were
measured for Ni-Ci catalyst under electrochemical
condition. In this spectra, a peak coincided with that of
γ-NiOOH of the reference sample was observed ataround 528.6 eV, indicating that the Ni-Ci catalystchanged its structure to γ-NiOOH during the OER
process.
Finally, operando C-K edge XAFS measurements
were performed, as shown in Figure 1. At the nonactive potential of 1.2 V, a peak was observed ataround 290.3 eV near the peak position of carbonate
ion, suggesting that the carbonate ion was adsorbed on
the Ni-Ci catalyst. Furthermore, when the electrodepotential changed from 1.2 V to 1.7 V, the carbonate
peak shifted to a higher energy side. This phenomenon
is presumed to be due to the direct adsorption ofcarbonate ion on the γ-NiOOH as active species. Thus,
we suggest that the adsorption of carbonate ion is
likely to contribute the stabilization of γ-NiOOH andthat the Ni-Ci catalyst has high OER activity by theFig. 1. Operando C K-edge XAFS spectra for Ni-Ci at
1.2 V (non-active state) and 1.7 V (active state) vs.
RHE, together with the saturated K2CO3 aqueous
solution.

[1] (a) M. Ma, Y. Liu, X. Ma, R. Ge, F. Qu, Z. Liu, G.
Du, A. M. Asiri, Y. Yao and X. Sun, Sustainable Energy
Fuels 1 (2017) 1287.
(b) K. S. Joya, Y. F. Joya and H. J. M. de Groot,
Advanced Energy Materials 4 (2014) 1301929.
[2] K. Yamada, T. Hiue, T. Ina, K. Wang, H. Kondoh,
Y. Sakata, Y. L. Lee, T. Kawai and M. Yoshida, Anal.
Sci. 36 (2020) 35.
[3] (a) M. Nagasaka, H. Yuzawa, T. Horigome and N.
Kosugi, Rev. Sci. Instrum. 85 (2014) 104105.
(b) M. Yoshida, Y. Mitsutomi, T. Mineo, M. Nagasaka,
H. Yuzawa, N. Kosugi and H. Kondoh, J. Phys. Chem.
C 119 (2015) 19279.

126

Ⅲ04- 4 -BL2B

Ⅲ -4. Surface, Interface and Thin Films

BL3U

In Situ XAFS Study of Pt Subnanoparticles on the Oxygen Reduction Reaction
A. Kuzume1, M. Nagasaka2 and K. Yamamoto1

JST-ERATO, Yamamoto Atom Hybrid Project, Institute of Innovative Research, Tokyo Institute of Technology,
Yokohama 226-8503 Japan
2
Institute for Molecular Science, Okazaki 444-8585, Japan

1

Subnanoparticles (SNPs) is a new-generationmaterial with a particle diameter of about 1 nm,
composing only several tens of atoms. Due to its small
number of constituent atoms (atomicity), it exhibits
unique properties not commonly found in bulk andnanomaterials. However, it was difficult to understandthe detailed characteristics and chemical activity of
SNPs because of its difficulty in synthesis and analysis.
In our laboratory, we have established a liquidphase SNPs synthetic method using a dendritic
polymer called 4th generation Tetraphenylmethanecore, phenylazomethine dendrimer (TPM-DPA-G4) asa template macromolecule, which can control theatomicity precisely [1-3]. With this technique, scalable
synthesis of SNPs is possible, and thus detailed
analyses of physical, chemical and electric properties,
as well as chemical activities, of SNPs is expected [4].
Pt SNPs have been synthesized using the method
described above and were found to exhibit unique
catalytic activities on electrochemical oxygen
reduction reaction (ORR), which is the key cathodic
reaction for the fuel cell development. Pt SNPs were
found to exhibit discrete catalytic activity on ORR,
depending on the atomicity [5-7]. To evaluate its
specificity, it is necessary to monitor changes in theelectron state of SNPs during the electrochemical
reaction. In this study, in situ XAFS measurements ofPt SNPs on O K-edge were performed at BL3U in
UVSOR facility to elucidate precise atomicitydependent ORR activity by monitoring the state of Pt
oxide on the surface of SNPs under electrochemical
condition.
The home-made in situ XAFS cell with theelectrochemical setup was used [8], where Pt SNPs
were cast on a carbon-film modified on the silicon
nitride substrate (10 mm x 10 mm). A Pt wire and
Ag/AgCl electrode were used as a counter andreference electrode. Air-saturated 0.1M HClO4
solution (prepared with MERCK Suprapur HClO4 andultrapure water from the Milli-Q system) wereconstantly supplied during the in situ measurement by
the peristaltic pump.
Figure 1 shows the potential dependent in situ
XAFS spectra of O K-edge on Pt12 SNPs. It was noteasy to identify the potential dependence in the seriesof spectra due to significantly low signal intensity ofO species adsorbed on Pt surface. Difficulty in thecharacterization of SNPs is mainly originated fromtheir size. In general, the signal intensity of SNPs in
the vibration spectroscopic study, such as infrared andRaman spectroscopy, is far below the detection limit
with the conventional technique and requires

E / V vs. Ag/AgCl

improvement in sensitivity to detect SNPs [9]. To
increase the signal intensity of XAFS spectra, one
needs to increase the amount/surface coverage of Pt
SNPs in our electrochemical XAFS setup. However,
due to the principle of the measurement, one needs tokeep the thickness of the sample as low as possible toincrease the transmission rate. This trade-off situation
makes it difficult to detect O species on Pt SNPs.
In conclusion, our preliminary results indicated thatthe transmission detection configuration needs to bechanged to the fluorescence mode, where one cansimply increase the amount of Pt SNPs to improve thedetection sensitivity.

-0.06 V
0.04 V
0.14 V
0.24 V
0.34 VⅢ- 4

0.44 V
0.54 V
0.74 V
0.94 V

526

528

530

532

Energy / eV

534

536

Fig. 1. Potential dependent in situ O K-edge XAFS
spectra of Pt12 SNPs in 0.1M HClO4 versus Ag/AgCl.
[1] A. Kimoto, K. Masachika, J.S. Cho, M. Higuchi
and K. Yamaomto, Org. Lett. 6 (2004) 1179.
[2] O. Enoki, H. Katoh and K. Yamamoto, Org. Lett. 8(2006) 569.
[3] K. Yamamoto, M. Higuchi, S. Shiki, M. Tsuruta
and H. Chiba, Nature 415 (2002) 509.
[4] K. Yamamoto and T. Imaoka, Acc. Chem. Res. 47(2014) 1127.
[5] K. Yamamoto, T. Imaoka, W.J. Chun, O. Enoki, H.
Katoh, M. Takenaga and A. Sonoi, Nat. Chem. 1(2009) 397.
[6] T. Imaoka, H. Kitazawa, W.J. Chun and K.
Yamamoto, Angew. Chem. Int. Ed. 54 (2015) 9810.
[7] T. Imaoka, Y. Akanuma, N. Haruta, S. Tsuchiya, K.
Ishihara, T. Okayasu, W.J. Chun, M. Takahashi andK .Yamamoto, Nat. Commun. 8 (2017) 688.
[8] M. Yoshida, Y. Mitsutomi, T. Mineo, M. Nagasaka,
H. Yuzawa, N. Kosugi and H. Kondoh, J. Phys. Chem.
C 119 (2015) 19279.
[9] A. Kuzume, M. Ozawa, Y. Tang, Y. Yamada, N.
Haruta and K. Yamamoto, Sci. Adv. 5 (2019) eaax6455.

127

Ⅲ04- 5 -BL2BInterface and Thin Films
Ⅲ -4. Surface,

BL3B

Clarify of Formation Process and Optical Properties Evaluation of UltraViolet Emitting Zinc Aluminate Phosphor Thin Films
H. Kominami1, M. Arimura1, K. Imagawa1, K.Warita2, S. Nishibori2, M. Endo2,
T. Kawashima2, N. Sonoda2, S. Kodama3 and S. Kurosawa3,4

Graduate School of Integrated Science and Technology, Shizuoka University, Hamamatsu 432-8651, Japan
2
Faculty of Engineering, Shizuoka University, Hamamatsu 432-8651, Japan3
New Industry Creation Hatchery Center (NICHe), Tohoku University, Sendai 980-8579, Japan
4
Faculty of science, Yamagata University, Yamagata 990-8560, Japanthermal annealing is necessary for obtain the goodquality ZnAl2O4 thin film preparation.

XRD Intensity [log10 a.u.]

50 hrs
25 hrs
5 hrs
As-depo30

40

ZnO(002)50

2 [deg.]

(440)

(333)

(422)

(331)

(400)

ZnAl2O4(311)

sapphire substrate

60

70

Fig. 1 XRD patterns of films on a-plane sapphire
substrate before and after annealing for several hours.

Annealed for 50 hours
ex=165 nm

PL Intensity [a.u.]

Ⅲ- 4

The UV light is used for various applications
depending on the wavelength as well as the sterilization
described above. The lights of 200-280 nm (UV-C)
region as for the sterilization, 280-320 nm (UV-B)
region as the treatment of the skin disease, 320-400 nm(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.
Conventionally, powder samples have been
prepared and evaluated, but it was difficult to analyzetransmittance and refractive index due to the
influences of surface scattering, so it would bepossible to evaluate these basic physical properties by
preparing thin film samples. In this research, ZnO
films were deposited on sapphire substrates by
sputtering and ZnAl2O4 thin films were prepared bythermal diffusion. These films were evaluated theorientation and crystallinity. Quality of thin films were
evaluated by relationships between UV emission
intensity and penetration depth of electron beam, andalso the distribution of Zn and Al was studied using
cross sectional FE-EPMA to analyze the emitting layer.
Figure 1 shows the XRD patterns of thin films
prepared on a-plane sapphire substrate. Before
annealing, any diffraction peaks of ZnAl2O4 were notobserved, however ZnO (002) peak was confirmed
near 34o. After annealing, diffraction peak of ZnAl2O4(333) appeared, and selective growth was confirmed.
FWHM of diffraction peaks of ZnAl2O4 (333)decrease according to inarticulate interface of eachlayer, the multilayer film containing constituent
elements was formed by sputtering on quartz substrate,
and tried to prepare the ZnAl2O4 thin film by thermal
diffusion.
Figure 2 shows PL spectra of ZnAl2O4 thin film
annealed for 15 hours excited by VUV. From thespectra, ZnO emission around 380 nm and 520 nm(caused from exiton and oxygen vacancy,
respectively) were not observed. It indicates that ZnOlayer were diffused to substrate completely and reevaporated. It is thought that the 50 hours or more

(220)

1

200

300

400

500

600

700

Wavelength [nm]Fig. 2 PL spectra of ZnAl2O4 thin film.

128

Ⅲ04- 6 -

800

BL4U

Ⅲ -4. Surface, Interface and Thin Films

BL4U

Microscopic Electronic Structure of Vanadium Nitride/Oxide Supercapacitors
H. W. Shiu1, L. C. Yu1, Y. L. Lai1, T. Ohigashi2, Y.-G. Lin1 and Y. J. Hsu1
1

National Synchrotron Radiation Research Center, Hsinchu 300, Taiwan
2
Institute for Molecular Science, Okazaki 444-8585, Japan

How to provide an environmentally friendly energy
system with high performance and low cost has
become an important issue due to the rapid growth ofelectric vehicles and portable electronic devices.
Supercapacitors (SCs), also called electrochemicalcapacitors, have attracted a lot of attentions due to their
specific advantages of fast power release and long
cycle-life [1]. However, the existing commercialized
carbon electrode has the bad traits of low specificcapacitance. Accordantly, the main research targets of
SCs mainly focused on the development of pseudocapacitive electrode materials. Transition metal oxide,
nitride, sulfide and conducting polymers have been
experimentally demonstrated as a promising electrodematerial for the next generation SCs [2].
Recently, the earth-abundant and inexpensive
materials i.e. vanadium oxides (VOx), have been
intensely investigated as cathode materials for SCs.
The multiple stable oxidation states and layered
structure enable it to have a higher storage capability.
A similar material named Vanadium nitride (VN)
holds great promise as an advanced electrode forasymmetric super capacitors due to its large speciccapacitance (1340 F/g) and superb electricalconductivity (106/Ωm). In our previous studies wealso observed that the capacitance retention isenhanced as high as 90% at high current density. Only
5.9% decay was observed at 1000 cycles.
In order to understand the mechanism of theenhancement of the specific capacitance and thecapacitance retention, we synthesized a set of VON
and VN through the electrochemical deposition in anelectrolyte solution containing Na2SO4 and NH4VO3
for 6 hours and post-treatment at 500 to 700 degree
Celsius under NH3 condition. A systematically study
for the set of materials was made by scanningtransmission X-ray microscopy (STXM) and Nearedge X-ray absorption fine structure (NEXAFS) at
UVSOR BL4U and TLS 09A2, respectively.
Figure 1 shows the XAS spectra of VON and VN
powders transferred onto Si substrate measured at TLS
BL 09A2 with the photon beamsize of 100 μm. The“average” spectrum of VN has no oxygen feature andthe characteristic peaks of V L-edge shifted to lower
photon energy which clearly indicated that the valence
state is altered to the lower oxidation state.
To investigate the chemical distribution of the VON
powders, multiple sets of STXM images at different
photon energy have been measured. The results display
the STXM element mapping as shown in Fig. 2 (a). Allof the VON samples exhibit nano-rod structure with thedimension of ~ 150 nm in diameter and ~ 1 μm in length.

Figure 2 (b) shows the XAS spectra near the V L-edge
and O K-edge extracted from Fig. 2 (a). The two major
peaks at ~ 518 and 525 eV are the V LIII and LII peaks,
respectively. Different from the broadened peak of V
LII-edge, the three considerable peaks were observed at
V LIII-edge correspond to the transition from V 2p3/2 tot2g (π*), t2g (d*) and eg (σ*), respectively. The two clear
features between 527 to 534 eV are the transition from
O 1s to the hybridized O 2p/V 3d, i.e. t2g and eg orbitals.
Significant intensity changes between those two peaks(O K-edge, t2g and eg) may result from the ununiform
valence state of N-V-O bound and polarization effect [3].
Further experiments are needed to confirm thisobservation.

Ⅲ- 4

Fig. 1. V L-edges and O K-edge XAS spect
ra of VON and VN measured at Taiwan Light Source(TLS).

Fig. 2 (a) Color-coded composite mapping of VON
powder identified by the O K-edge spectra (eg/t2g) and (b)the corresponding micro-spectra of red and green areas.
[1] Y. Yang, G. Ruan, C. Xiang, G. Wang and J. M. Tour,J. Am. Chem. Soc. 136 (2014) 6187.
[2] H. Pang, C. Wei, X. Li, G. Li, Y. Ma, S. Li, J. Chen
and J. Zhang, Sci. Rep. 4 (2014) 3577.
[3] D. Maganas, M. Roemelt, M. Hävecker, A.
Trunschke, A. Knop-Gericke, R. Schlögl and F. Neese,
Phys. Chem. Chem. Phys. 15 (2013) 7260.

129

Ⅲ04- 7 -BL4BInterface and Thin Films
Ⅲ -4. Surface,

BL4B

Absorption Spectra of Amorphous Chalcogenide Thin Films in the Vacuum
Ultraviolet Region
K. Hayashi

Department of Electrical, Electronic and Computer Engineering, Gifu University, Gifu 501-1193, JapanⅢ- 4

Amorphous chalcogenide semiconductor materials
are very photosensitive materials and show a variety ofphoto-induced phenomena. Therefore, these materials
are expected as materials for optoelectronic devices. A
lot of work have been done on the photo-induced
phenomena of these amorphous semiconductormaterials and various mechanisms have been proposed
for these photo-induced phenomena [1-3]. However, thedetails of the mechanisms are still unknown. For device
applications, it is necessary to sufficiently understandthe fundamental properties of these materials. Thesephenomena have been studied by exciting outer coreelectrons by irradiating 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 ourknowledge, little attention has been given to photoinduced changes at the vacuum ultra-violet (VUV)
absorption spectrum. In this report, we report the VUVabsorption spectra of as-deposited evaporated
amorphous Se and As2Se3 thin films.
Samples used for the VUV absorption spectrum
were amorphous Se and As2Se3 thin films preparedonto aluminum thin films by conventional evaporation
technique. Typical thickness of the amorphous film
and the aluminum film were around 200 nm and 100
nm, respectively. The aluminum film of the thicknessof 200 nm was also used in order to eliminate thehigher order light from the monochromator in the
VUV region. The measurements were carried out atroom temperature at the BL4B beam line of the
UVSOR facility of the Institute for Molecular Science.
And the spectrum was measured by using the silicon
photodiode as a detector. A pinhole of 1.5 mm in adiameter was inserted between the monochromatorand sample to remove stray light. The intensity of the
VUV light was monitored by measuring the total
photoelectron yield of a gold mesh. The positions of
the core levels for the samples were calibrated byreferencing to the 2p core level absorption peak of thealuminum film.
Figure 1 shows the VUV absorption spectra of asdeposited amorphous Se and As2Se3 thin films at room
temperature. The structure observed in this energy
region from 40 to 55 eV is due to the transitions fromthe As 3d core level. On the other hand, the structure
observed in this energy region from 55 to 70 eV is dueto the transitions from the Se 3d core level. As shownin the figure, each spectrum is very broad and multiple

shoulders are observed. The structure in the spectrumof amorphous As2Se3 is good agreement with previous
report [4]. On the other hand, the spectrum shape ofthe main peak of amorphous Se is slightly different
from the previous report. It can be attributed to thespin-orbit splitting of the 3d core level of each atom as
observed by XPS. 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. The detailed experiments and analysis will bedone in the next step.

Fig. 1. VUV absorption spectra of as-deposited
amorphous Se and As2Se3 thin films at room temperature.

[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, Phil. Mag. 34 (1976) 501.

130

Ⅲ04- 8 -BL4B

Ⅲ -4. Surface, Interface and Thin Films

BL4B

Tuning Surfaces and Interfaces of FeNi Alloy Thin Films
by Nitrogen Surfactant Effects
T. Miyamachi1, K. Kawaguchi1, Y. Takahashi1,2, T. Iimori1, T. Hattori1, T. Koitaya3,4,
K. Yamamoto3,4, M. Kotsugi2, T. Yokoyama3,4 and F. Komori1

1
Institute for Solid State Physics (ISSP), The University of Tokyo, Kashiwa 277-8581, Japan
Faculty of Industrial Science and Technology, Tokyo University of Science, Tokyo 125-8588, Japan3
Department of Materials Molecular Science, Institute for Molecular Science, Okazaki 444-8585, Japan
4
Department of Structural Molecular Science, The Graduate University for Advanced Studies, SOKENDAI,
Okazaki 444-8585, Japan2

A rare-metal-free ferromagnetic L10-type FeNiordered alloy attracts much attention due to its
expected strong uniaxial magnetic anisotropy.
Previous studies reported the preparation of L10 FeNi
films by several thin film growth techniques such as
layer-by layer molecular beam epitaxy (MBE) andpulse laser deposition (PLD). However, theperpendicular magnetic anisotropy of L10 FeNi has notbeen achieved so far possibly due to an imperfectlayer-by-layer stacking and intermixing at the Fe/Niinterface during growth processes, which results in the
low structural ordering.
To realize high-quality FeNi alloy thin films, weincorporate nitrogen surfactant effects of monatomic
layer magnetic nitrides into the alternate Fe and Ni
deposition. The nitrogen surfactant epitaxy intends tosuppress the interdiffusion at the Fe/Ni interface
during the deposition and annealing processes andkeeps atomically flat surface/interface. The validity ofthis approach on structural and magnetic properties of
FeNi alloy thin films were confirmed for 1 monolayer(ML) Fe on Ni2N/Cu (001), which is the initialfabrication step, by scanning tunneling microscopy(STM) and x-ray absorption spectroscopy/x-ray
magnetic circular dichroism (XAS/XMCD). We
observed structural changes of the system from
Fe/Ni2N/Cu(001) to FeN/Ni/Cu(001) induced by thenitrogen surfactant effect while keeping the highquality Fe/Ni interface even after annealing process at
420 K, and resultingly the enhancement of theperpendicular anisotropy [1,2].
In this work, we grow thicker FeNi alloy thin films
up to tri- and quadruple-layers (NiN/Fe/Ni and
FeN/Ni/Fe/Ni) and investigate the impact of
surface/interface modifications with increasing thefilm thickness on their electronic and magnetic
properties by STM and XAS/XMCD [3].
The Ni2N was grown on Cu(001) by following
fabrication processes of a monatomic layer iron nitride(Fe2N) [4]. The quality of the Ni2N was prechecked by
STM and LEED before XAS/XMCD measurements.
Then, 1 ML Fe and Ni were alternatingly deposited at~ 150 K to grow tri- and quadruple-layers.
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 the grazing (GI: θ = 55°)
geometries. Magnetization curves were recorded byplotting the L3/L2 XAS intensity as a function of themagnetic field.
We find from the magnetization curve that themagnetization easy axis of the trilayer is toward theout-of-plane direction. This indicates that the out-ofplane magnetocrystalline anisotropy of the trilayer islarge enough for overcoming the in-plane film shapeanisotropy. On the other hand, the quadruple layershows the strong in-plane magnetic anisotropy. The
results could be interpreted from the modification of
the topmost surface layer from NiN (trilayer) to FeN(quadruple layer), which presumably prefers the inplane magnetization [5].

Ⅲ- 4[1] T. Miyamachi et al., UVSOR Activity Report 201846 (2019) 138.
[2] T. Miyamachi et al., UVSOR Activity Report 201846 (2019) 139.
[3] K. Kawaguchi et al., Phys. Rev. Materials accepted.
[4] Y. Takahashi et al., Phys. Rev. Lett. 116 (2016)056802.
[5]Y. Takahashi et al., Phys. Rev. B 95 (2017) 224417.

131

Ⅲ04- 9 -BL4BInterface and Thin Films
Ⅲ -4. Surface,

BL4B

Magnetic Properties of FeCo Alloy Thin Films Grown
by Nitrogen Surfactant Epitaxy
T. Miyamachi1,2, Y. Takahashi1,3, T. Hattori1, T. Koitaya4,5, K. Yamamoto4,5, M. Kotsugi3,
T. Yokoyama4,5 and F. Komori1
Institute for Solid State Physics, The University of Tokyo, Kashiwa277-8581, Japan
2
The University of Electro- Communications, Chofu 182-8585, Japan
3
Tokyo University of Science, Tokyo 125-8588, Japan
4
Institute for Molecular Science, Okazaki 444-8585, Japan
5
The Graduate University for Advanced Studies, SOKENDAI, Okazaki 444-8585, Japan1

Ⅲ- 4

An L10-type FeCo ordered alloy is theoretically
predicted to show an extraordinary large perpendicularmagnetic anisotropy among transition metal alloys,
attracting great attention as a rare earth-free permanent
magnet. The precisely controlled thin film growth ofalternating Fe and Co atomic layers using pulsed laser
deposition have been used for the preparation of L10
FeCo thin films [1]. However, the degree of order ofthe L10 structure is still low due to atomic-scale
structural and magnetic disorder at the Fe/Co interface
and resultingly the perpendicular magnetization has
not yet been achieved.
Toward realizing high quality FeCo alloy thin films,
we here focus on the fabrication method utilizing
nitrogen surfactant effects of monatomic layer ironand cobalt nitrides (Fe2N and Co2N). The validity of
the nitrogen surface epitaxy on the growth of L10-type
alloy thin films has been demonstrated for FeNi alloy
thin films [2]. High lateral lattice stability of magnetic
nitrides [3], and the surfactant nitrogen during thedeposition of Fe and Co atomic layers can effectively
suppress the interdiffusion at the Fe/Co interface,leading to atomically flat and homogeneous surface
and interface in FeCo alloy thin films.
We here performed combined study of scanningtunneling microscopy (STM) and x-ray absorption
spectroscopy/x-ray magnetic circular dichroism(XAS/XMCD) to investigate structural and magnetic
properties of 1 monolayer (ML) Co on Fe2N/Cu (001),
the initial step for the fabrication of FeCo alloy thinfilms grown by the nitrogen surfactant epitaxy. The
advantage of this complementary experimental
approach is that macroscopic observations of element
specific and quantitative electronic and magnetic
properties by XAS/XMCD can be linked withmicroscopic origins of the Fe/Co interface
characteristics revealed by STM [4].
The monatomic layer of Fe2N was grown on
Cu(001) in the following processes: (1) N+
bombardment onto a clean Cu(001) surface with abeam energy of 500 eV, (2) Fe deposition onto
N/Cu(001) at room temperature, and (3) subsequentannealing up to ~ 670 K [3]. 1 ML Co was thereafter
deposited at a low temperature (~ 150 K).
XAS/XMCD measurements were performed at
BL4B in UVSOR by total electron yield mode at B =0 - ± 5 T and T = 6.6 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
the sample 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 [3]. STM measurements revealed
the formation of Co2N/Fe/Cu (001) via nitrogensurfactant effect by adding 1 ML Co. Accordingly,
relative increase in the out-of-plane magnetization of
Fe to the in-plane magnetization was observed. These
results indicate that the nitrogen surfactant effectefficiently suppresses the interdiffusion at the Fe/Co
interface and keeps atomically flat surface/interface in
FeCo atomic layers, presumably reflecting the
intrinsic out-of-plane magnetization of L10 FeCo.

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

132

Ⅲ04- 10 -BL4B

Ⅲ -4. Surface, Interface and Thin Films

BL4B

Molecular Orientation and Magnetic Properties of Iron Phthalocyanine
Thin Films Grown on Passivated Silicon Surfaces
S. Ohno1, K. Yamamoto2, T. Koitaya2 and T. Yokoyama2

Fuclty of Engineering, Yokohama National University, Yokohama 240-8501, Japan
2
Institute for Molecular Science, 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. It has been shown that the first
Hund’s rule is violated in FePc, resulting in the groundstate of S=1 rather than S=2 [1]. It has been reported
that highly unquenched orbital moment is caused by
the 3Eg ground state with the half-filled eg state at the
Fermi level for FePc thin films grown on gold surfaces[2].
In the present work, we studied both molecularorientation and magnetic properties of FePc thin films
grown on passivated silicon surfaces, such as wateradsorbed Si(001) (H2O/Si(001)), oxidized Si(001)(SiO2/Si(001)) and oxidized silicon wafer covered
with monolayer graphene (Gr/SiO2).
BL4B soft X-ray beamline was used for X-ray
Absorption Near Edge Structure (XANES) spectroscopy
measurements in N K-edge region and X-ray Magnetic
Circular Dichroism (XMCD) measurements in Fe Ledge region.
Figure 1 shows angle-dependent linearly polarized
XANES spectra at the N K-edge. The peaks A, B, andC are assigned to π* resonances and D, E, and F are
assigned to σ* resonances [2]. In the present cases, thetilted angles of the molecular plane are estimated to be~35-65° on average. These suggest that the FePc
molecules are not perfectly aligned parallel to thesurface nor perpendicular to the surface.
Figure 2 shows MCD spectra of FePc/Gr/SiO2 at the
Fe L-edge. We have evaluated the orbital magnetic
moment (mL) and the spin magnetic moment (mS) using
the sum rules. The values of mL are estimated to be ~0.10.8 μB, depending on the thickness and substrate. In
several cases, the values are even larger than thereported values ( ~0.2-0.5 μB) obtained for FePc/Au [2].
The present results indicate that the properties of
FePc thin films grown on H2O/Si(001) and SiO2/Si(001)are similar in the molecular orientation as well as themagnetic moment. In contrast, the MCD spectra exhibit
quite different features in the case of FePc thin films
grown on Gr/SiO2. For instance, the two distinct peaks
are observed in the LIII region, as shown in Fig. 2. Thesemay correspond to the a1g and eg states observed for thewell-ordered films [2]. The role of monolayer graphene
is found to be substantial to modify both molecularorientation and magnetic properties.

Fig. 1. Angle-dependent linearly polarized XANES
spectra of FePc/H2O/Si(001) at the N K-edge.

Fig. 2. MCD spectra of FePc/Gr/SiO2 at the Fe L-edge.
[1] M.D. Kuz’min et al., Phys. Rev. B 79 (2009) 024413.
[2] J. Bartolomé et al., Phys. Rev. B 81 (2010) 195405.

133

Ⅲ04- 11 -Ⅲ- 4

BL4BInterface and Thin Films
Ⅲ -4. Surface,

BL5U

Polarization Dependent Interfacial Electronic Structure of
Ultra-thin Fe Layers on Rashba-splitted Au (111) Surfaces
J. Okabayashi1, K. Tanaka2 and S. Mitani3

Research Center for Spectrochemistry, The University of Tokyo, Tokyo 113-0033, JapanUVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
3
National Institute for Materials Science, Tsukuba 305-0047, Japan

1
2

Ⅲ- 4

When ferromagnetic transition metals (TMs) aredeposited on the Rashba-type spin-orbit coupled surface,novel properties such as perpendicular magnetic
anisotropy (PMA) are emerged at the interfaces, which
are derived from the symmetry broken spin-orbit effects.
The gold Au (111) surfaces have been investigatedextensively by means of scanning tunneling microscopy
and angle-resolved photoemission spectroscopy(ARPES) because this surface exhibits the large
Rashba-type spin-orbit splitting of 110 meV [1]. It
provides the wide varieties for the topological physics
and spin-orbit coupled sciences at the surfaces andinterfaces. Recently, the interfaces between Au(111) andother heavy elements such as Bi or Ag have been
extensively investigated [2,3]. Here, we focus on theinterfaces between ferromagnetic materials andAu(111) interfaces because the thin Fe layers on theheavy elements are expected to exhibit the PMA
induced by the Rashba-type spin-orbit interaction.
The spin-orbit coupling between the ferromagnetic
3d TMs Fe or Co and 5d, 6sp heavy metal elements of
non-ferromagnetic materials such as Pt and Au has beenutilized for the PMA through the proximity at theinterfaces. It is believed that the future researches
concerning not only spins but also orbitals arerecognized as the spin-orbitornics. Therefore, to clarify
the origin of the PMA at these interfaces is a crucial role.
The relationship between Au (111) Rashba-type spinorbit interaction and PMA in 3d TMs has not beenclarified explicitly. In order to investigate the orbitalresolved states in the Fe films showing the PMA,
ARPES at the interfaces becomes powerful techniquesthrough the photon-energy and polarization
dependences in each 3d orbital. By using ARPES, we
aim to understand the orbital-resolved electronic
structures at the magnetic interfaces on the Rashba-type
Au (111) surface in order to develop the researches ofnovel PMA using spin-orbit coupled interfaces.
We prepared the clean Au (111) surface for the Fe
deposition. The commercialized single-crystalline 100nm-thick Au (111) films on sapphire substrate wereused. At the beamline BL5U in UVSOR, we repeated
the Ar-ion sputtering at 1 kV accelerating voltage andsubsequent annealing at 400 °C under the high vacuum
conditions. After the sample preparation, the Fe layer
was deposited at room temperature and then annealed.
By in-situ transferring the samples into the ARPES
chamber, we performed ARPES at 10 K using thephoton energies of 60 and 120 eV because of the large
cross-section of Au (111) surface states and detectionsof Fe 3s and Au 4f intensity ratios, respectively.

134

Figures 1 (a) and (b) display the photoemission spectrain Fe layers on Au (111) with horizontally and verticallypolarized beams at 60 eV. As shown in Fig. 1a, theintensity ratio changes due to the difference of orbital
symmetry. The Au (111) surface clearly exhibits the
Rashba-type surface states. The Fe 3d states appear near
the Fermi level (EF) and the surface states disappear. As
shown in Fig. 1 (c), band dispersion image plots taken
by horizontal and vertical polarized beams exhibit
asymmetric feature, which can be explained by the Fe
3d orbital-resolved states through the overlap between
Fe and Au. Horizontal and vertical cases detect
preferentially out-of-plane and in-plane orbitals,
respectively. Furthermore, we confirmed the PMA at
Fe/Au interface by x-ray magnetic circular dichroism
and Mössbauer spectroscopies. Therefore, theinterfacial chemical reaction between Fe and Au brings
the novel properties on the ultrathin Fe electronic
structures.
We acknowledge Dr. S. Ideta in IMS for technicalsupports of data analyses. This work was in part
supported by KAKENHI Kiban(S) project.

Fig. 1. Polarization dependence in Fe valence-band
photoemission spectra taken at 60 eV for (a) 6 ML and(b) 9 ML. (c) Band-dispersion mapping of Fe 6 ML
case for horizontal and vertical beams taken at 60 eV.
[1] S. LaShell et al., Phys. Rev. Lett. 77 (1996) 3419.
[2] C. Tusche et al., Ultramicroscopy 159 (2015) 620.
[3] B. Yan et al., Nature Commun. 6 (2015) 10167.

Ⅲ04- 12 -BL4B

Ⅲ -4. Surface, Interface and Thin Films

BL5U

Electronic Structure of Ultrathin Bismuth Films Fabricated on InSb(111)
Y. Ohtsubo1,2, J. K. Modak2, T. Nakamura2 and S. Kimura1,2

Gradudate School of Frontier Biosciences, Osaka University, Suita 565-0871, Japan
Department of Physics, Graduate School of Science, Osaka University, Toyonaka 560-0043, Japan1

2

The electronic structure of elemental bismuth (Bi)has been studied extensively in this decade because of
its ambiguous three-dimensional topological order
driven by the large size of spin-orbit interaction invalence bands [1]. Moreover, ultrathin Bi film down to
few monatomic layers is also predicted as a twodimensional topological insulator [2] and hence isgathering much attention. Although growth of Bi
ultrathin films with several layers has been achieved
on various substrates [3-5], most of them are strongly
influenced from substrates, such as the significant
structural deformation on SiC [3] and intermixing withthe metallic states of the Bi2Te3 substrate [4]. In thisproject, we tried to grow ultrathin Bi films with a few
layers on InSb(111), which has the lattice constantvery close to the Bi crystal and no electronic statesaround the Fermi level. These characteristics of InSb
suggest that it is a suitable substrate to realize freestanding Bi ultrathin films down to 1-2 bilayers (BL).
The InSb(111) substrates were cleaned in an ultrahigh vacuum chamber by repeated cycles of Ar ion
sputtering with the ion energy of 1 keV and annealing
with the temperature of 550 K until a sharp RHEED
pattern was observed. Subsequent evaporation of Bi
was performed on the substrate at room temperatureusing a home-made Knudsen cell, resulting in sharp
and low-background patterns as shown in Fig. 1 (a). It
suggests that high-quality Bi(111) films were obtainedby this method. The Bi evaporation rate was checkedin-situ by monitoring the intensity oscillation of the
RHEED diffraction rods. Accordingly, we could
fabricate the ultrathin Bi(111) films with the
thicknesses from 1 to 5 BLs. The film thicknesses werecross-checked by core-level photoelectron peak areasof Bi, In, and Sb, showing a consistent behavior to the
RHEED oscillation.
Figure 1 (b) shows the Fermi contour of the 5-BL
Bi(111) film grown on InSb(111) obtained by ARPES.
The six-fold tear-drop like contours and nearly circular
one at the center of the surface Brillouin zone areconsistent with the earlier results [1,5]: the lattershould be hexagonal, but it is difficult to distinguishhexagon and circle with the current angular resolution.
This agreement suggests that the obtained Bi(111) film,
especially its electronic structure around the Fermi
level, is free from any modulations by substrates. At
the lower thicknesses, the shape of the Fermi contour
as well as the surface-band dispersions changed
according to the thicknesses. Detailed analysis of suchchanges, especially a comparison with theoretical
calculations are ongoing in order to examine whether
the fabrication of the free-standing Bi(111) films with
1-2 BLs, a promising playground to study the
topological edge states of two-dimensional topologicalinsulators, could be achieved or not.

Ⅲ- 4Fig. 1. (a) RHEED pattern of the Bi(111) film (5 BL)
on InSb(111). (b) Fermi contour of the same sample
taken by ARPES (hν= 60 eV, 7 K).
[1] L. Fu and C. L. Kane, Phys. Rev. B 76 (2007) 045302.
S. Ito et al., Phys. Rev. Lett. 117 (2016) 236402. Y.
Ohtsubo and S. Kimura, New J. Phys. 18 (2016) 123015
and references therein.
[2] S. Murakami, Phys. Rev. Lett. 97 (2006) 236805.
[3] F. Reis et al., Science 357 (2017) 287.
[4] T. Hirahara et al., Phys. Rev. Lett. 107 (2011) 166801.
[5] T. Hirahara et al., Phys. Rev. Lett. 97 (2006) 146803.

135

Ⅲ04- 13 -BL5U,Interface
BL7U
Ⅲ -4. Surface,
and Thin Films

BL5U, BL7U

Thermal Effect of the Surface Reconstruction of the Topological Kondo
Insulator SmB6
Y. Ohtsubo1,2, T. Nakamura2, T. Nakaya2, F. Iga3 and S. Kimura1,2

Graduate School of Frontier Biosciences, Osaka University, Suita 565-0871, Japan
Department of Physics, Graduate School of Science, Osaka University, Toyonaka 560-0043, Japan
3
College of Science, Ibaraki University, Mito 310-8512, Japan
1

2

Ⅲ- 4

Topological Kondo Insulators (TKI) are gatheringmuch attention in these days as an interesting
playground to study the concert effect of the spinpolarized topological surface states and strong electron
correlation resulting in the metal-insulator transition of
Kondo insulators [1]. Samarium hexaboride (SmB6) is
the first and the most extensively studied candidate of
TKI. It has been revealed that the (001) surface of acleaved SmB6 single crystal hosts the metallic and spinpolarized surface states as expected from topologicalclassification [1,2]. However, the topological order of
SmB6 itself is still under debate because of the multiple
possible interpretations of the metallic surface bands[3,4] as well as the various surface atomic structures
randomly appear on the cleaved surfaces [5].
In this project, we have revisited the surface atomic
and electronic structures of SmB6(001) by using the insitu cleaning method in an ultra-high vacuum (UHV)
chamber. The (001) faces of SmB6 single crystals were
polished under air atmosphere and then cleaned in the
UHV chamber by repeated cycles of Ar+ sputtering (ionenergy: 1 keV) and annealing. The annealing temperature
was set at several temperatures from 600 to 1400 °C andthe surface atomic and electronic structures were checkedat each temperature by LEED and ARPES measurements,
respectively.
As shown in Fig. 1 (a), we found the (2×1) surface
reconstruction with the annealing temperature of 800 °C.
The fractional order spots became weak and diffusedwith the elevated annealing temperature up to 1000 °C.
Afterward, at the highest annealing temperature(1400 °C), the fractional-order spots appeared again
with the sharper shape than those after 800 °C annealing,(see Fig. 1 (b)). These (2×1) surface reconstructions are
consistent with the known surface structures [3,5-7].
Figure 1 (c) shows the B-1s core-level photoelectron
spectra corresponding to the LEED patterns shown in
Figs. 1 (a, b). At 800 °C (the lower spectrum), a satellite
peak around 16.7 eV is shown, suggesting the surface
reconstruction by boron, which would originate fromdisplacements of B6 clusters. In contrast, at 1400 °C (theupper), no such satellite observed in the spectrum. It
suggests that the latter (2×1) surface reconstruction does
not originate from the surface boron but from the otherreasons such as periodic desorption of Sm atoms fromthe surface atomic layers.
These two different (2×1) surfaces on SmB6(001)
could reconcile the wide variety of surface preparation
conditions reported so far [6,7]. Further analysis on the136

surface electronic structure around the Fermi level,
especially the influence from the newly distinguishedsurface reconstructions, is ongoing.

Fig. 1. (a, b) LEED patterns (The pass energy: EP = 44eV) of the SmB6(001)-(2×1) surfaces annealed at (a)800 °C and (b) 1400 °C. (c) B-1s core-level spectra takenfrom the SmB6(001)-(2×1) surfaces; the lower (upper)
one is from the surface annealed at 800 (1400) °C.

[1] M. Dzero et al., Phys. Rev. Lett. 104 (2010) 106408.
[2] N. Xu et al., J. Phys.: Condens. Matt. 28 (2016)
363001 and references therein.
[3] P. Hlawenka et al., Nat. Commun. 9 (2018) 517.
[4] Y. Ohtsubo et al., Nat. Commun. 10 (2019) 2298.
[5] S. Rößler et al., PNAS 111 (2014) 4798.
[6] H. Miyazaki et al., Phys. Rev. B 86 (2012) 075105.
[7] M. Ellguth et al., Philos. Mag. 96 (2016) 3284.

Ⅲ04- 14 -BL6U

Ⅲ -4. Surface, Interface and Thin Films

BL6U

Photoemission Tomography Utilizing
One-dimensionally Ordered Film of High-mobility Organic Semiconductors
M. Iwasawa1, S. Kobayashi1, Y. Hasegawa2, M. Nozaki3, S. Kurihara3, S. Otaki3, K. Niki3,
M. Sasaki1, F. Matsui2, S. Kera2 and Y. Yamada1
1
Institute of Applied Physics, University of Tsukuba, Tsukuba 305-8573, Japan
Institute for Molecular Science, Department of Photo-Molecular Science, Okazaki 444-8585, Japan
3
Institute of Applied Physics, Chiba University, Tsukuba 305-8573, Japan

2

Recently, the researches of the photoelectron
tomography (PT) of the organic semiconductor films
have rapidly been increased with many successes toobtain the information of the character of the initialstate wavefunction. However, the researches have still
been limited to the model molecules with simple
molecular shape. In this work, we tried to apply PT torather practical organic semiconductor molecules withhigh mobility, in order to clarify the mechanism of
their charier transport.
In the present study, we especially focused on thepractical molecules with rather simple structure, such as
picene and Dph-BTBT. The single crystals and films ofthese molecules are known to show lather high mobility
up to the range of 101 cm2/Vs. Recent theoretical
calculation have shown that, while the hole mobility inthe case of picene can be rather fairly explained
considering the HOMO, that in the case of BTBT
cannot be understood only by HOMO. In the case of
BTBT, HOMO-1 must be taken into account, despite
the energy difference between HOMO and HOMO-1 of
BTBT is much larger than that of picene. The PT
analysis can shied the light on the nature of themolecular orbital which is responsible in the carriertransport.
We utilized well-defined thin film of picene and DphBTBT film utilizing anisotropic Ag(110) substrate. The
molecular arrangements in these films were directly
determined LEED and STM. PT of these system weredone at BL6U of UVSOR. In the PT measurements, we
utilized mesh electrode in front of the sample which was
at +500 V with respect to the sample, in order toincrease the acceptance angle of the photoelectron toprobe wider area in the reciprocal space.
Figure 1 (a) shows the one-dimensional structure of
the picene films on Ag(110) substrate, where themolecular axis of picene is aligned [1-10] direction of
the substrate. Figure 1 (b) is corresponding photoelectron
angular distribution (PAD) mapping patterns for
HOMO and HOMO-1. The obtained patterns wellcorrespond to the Fourier transform (FT) of the eachmolecular orbitals as shown in the inset. We then extractthe energy distribution curve (EDC) from the portion of
the rectangles in the PAD mapping, as shown in Fig. 1(c) Although the area averaged EDC showed
overlapped spectrum, selected-area accumulation
clearly shows the EDC of HOMO and HOMO-1.
Figure 2 shows the results of Dph-BTBT. In contrast

to the case of picene, the molecular long axis of DphBTBT/Ag(110) was not in the [1-10] direction and two
different domains were found. In this case, the energyof the HOMO and HOMO-1 levels are well separated
and their PAD are rather similar, in contrast to the caseof picene. However, we can clearly separate thephotoelectrons from these levels in PAD mapping,which will be useful in the discussion of the overlappingof these orbitals.

(a)(b) HOMO

(c)

3.0nm

[1-10]

HOMO-1

10nm

Ⅲ- 4Fig. 1 (a) STM image of several layer of Picene/Ag(110). (b) PAD images of HOMO and HOMO-1 (c)selectred-area EDC of HOMO and HOMO-1.

(a)

(b)

HOMO

HOMO−1

Fig. 2 (a) STM image of monolayer of Dph-BTBT/Ag(110). (b) PAD images of HOMO and HOMO-1.

137

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

BL6U

ARPES and RAES Study of Nanographene on Pt(111)
O. Endo1,3, F. Matsui2, W.-J. Chun3, M. Nakamura4, K. Amemiya5 and H. Ozaki1

Department of Applied Chemistry, Faculty of Engineering, Tokyo University of Agriculture and Technology,
Koganei 184-8588, Japan
2
UVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
3
Graduate School of Arts and Sciences, International Christian University, Mitaka 181-8585, Japan
4
Department of Applied Chemistry and Biotechnology, Faculty of Engineering, Chiba University, Chiba 2638522, Japan
5
Photon Factory, High Energy Accelerator Research Organization (KEK-PF), Institute of Materials Structure
Science (IMSS), Tsukuba 305-0801, Japan1

Ⅲ- 4

Graphene, a single sheet of carbon, is one of typical
2D materials which exhibits a peculiar band structure.
Nanographene (NG), which is cut from graphene into
nano-size, is expected as a material for next generation
devices due to the confined electronic structure and an
open band gap. In this study, Angular Resolved Photo
Emission Spectroscopy (ARPES) and Resonant Auger
Electron Spectroscopy (RAES) were performed toinvestigate the electronic structure of NG.
NG was obtained by the thermal decomposition ofbenzene on the Pt(111) surface at the substratetemperature of either 1100 K (HT) or 800 K (LT). All
the spectra were measured at BL6U of UVSOR.
Figure 1 shows the band dispersion along the Γ-K
direction of the NGs on Pt(111). Both the NGs
obtained at HT(a) and LT(b) exhibit the π band, andtherefore, the π band is formed for the NG obtained at
LT with the size of as small as 10 nm diameter, which
was confirmed by scanning tunneling microscopy. The
size of NG obtained at HT is estimated > 100 nm
diameter. The NG lattice is rotated ca. 30° with respect
to the Pt lattice. The bottom of the π band is located at
7.8 eV from EF, which is shallower than that ofgraphite (8.16 eV) [1]. This indicates the electrontransfer to the Pt substrate [2,3]. Figures 2 (a) and (b)show the C1s XPS spectra. In addition to the principal
peaks at BE = 283.9 eV (sp2 carbon of graphene), a
shoulder at 284.2 eV is enhanced for the NG obtainedat LT. This shoulder suggests the existence of the sp3
carbon, which forms the C-Pt bond [4]. This isconsistent with the Pt4f XPS spectra shown in Figs.
2(c) and (d), which exhibit a smaller surface-relatedband at 70.7 eV for the NG obtained at LT. Figure 3
shows the RAE spectra excited at the photon energy of
1s→π* transition. Although the angular dispersion isobserved for the NG obtained at HT, which is similar
to graphite [5], the auger electrons are focused at the Γpoint for the NG obtained at LT. Similar dispersion
patterns are observed for all the excitation energies in
the C K-edge region.

Fig. 1. π band of NG obtained at (a)HT and (b)LT.

Fig. 2. C1s XPS of NG obtained at (a)HT and (b)LT.
Pt 4f XPS of NG obtained at (c)HT and (d)LT.

Fig. 3. RAES at C K-edge of NG obtained at (a)HTand(b)LT.

[1] F. Matsui et al., Phys. Rev. B 97 (2018) 045430.
[2] G. Giovannetti et al., Phys. Rev. Lett. 101 (2008)026803.
[3] P. Sutter et al., Phys. Rev. B 80 (2009) 245411.
[4] S. Rajasekaran et al., Phys. Rev. B 86 (2012) 075417.
[5] F. Matsui et al., JPS 2019 Autumn meeting.

138

Ⅲ04- 16 -BL7U

Ⅲ -4. Surface, Interface and Thin Films

BL7U

High-resolution Angle-resolved Photoemission Study on MnBi2Te4/Bi2Te3
S. Kusaka1, K. Sumida1, T. Fukasawa1, S. Ichinokura1, S. Ideta2, K. Tanaka2 and T. Hirahara1
Department of Physics, Tokyo Institute of Technology, Tokyo 152-8551, JapanUVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
1

2

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
by application 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 suchas the topological magnetoelectic effect. To realize
such state, two types of sample fabrication techniques
have been 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 ofTI [4]. While method (1) was successful and showed
evidence of the TRS violation, no one has succeededusing method (2), which should be a more direct way
to examine the interaction between the topologicalsurface states and magnetism. We have previously
found another 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 are incorporated in the topmost Bi2Se3 layer and anovel 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 temperaturein this system. Taking all these facts into account, it
can be said 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.
Therefore in this study, we have employed Bi2Te3 as
the parent TI and have deposited Mn and Te on Bi2Te3
to see if magnetic extension can also occur for thissystem. Our structural analysis based on LEED-IV
measurements ensured that the heterostructure we
fabricated was MnBi2Te4/Bi2Te3. The band dispersion
measured at 10 K is shown in Fig. 1. In contrast to the
MnBi2Se4/Bi2Se3 sample, there was no gap opening inthe surface Dirac cone of MnBi2Te4/Bi2Te3 even at 10
K. We have also performed X-ray magnetic circulardichroism measurements on this heterostructure andfound that it is paramagnetic down to 5.6 K, the lowest
temperature we can reach in the experimental system.
Thus the absence of the Dirac cone gap and its
correspondence with the magnetic properties is clearcut in this system. The remaining questions are: (1)why is this structure paramagnetic down to 5.6 K incontrast to the theoretical calculations that predict a
Curie temperature of 12 K [6] with a 77 meV Diraccone gap [7]? (2) why is the magnetic property of thissystem so different from that of MnBi2Se4/Bi2Se3? Wehope to resolve these questions in the near future fromfurther investigation.

Ⅲ- 4

Fig. 1. Band dispersion image of the MnBi2Te4/Bi2Te3
heterostructure measured at 10 K.

[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] M. Otrokov et al., Phys. Rev. Lett. 122 (2019)107202.
[7] M. Otrokov et al., 2D Materials 4 (2017) 025082.

139

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

BL7U

Evolution of Electronic Structure of Pentacene Monolayer on Graphite
Probed by Low-Energy ARUPS
Y. Hasegawa1, T. Nakamura2, M. Meissner1, T. Yamaguchi1, S. Ideta1, K. Tanaka1 and S. Kera1
1

Department of Photo-Molecular Science, Institute for Molecular Science, Okazaki 444-8585, Japan
Department of Physics, Graduate School of Science, Osaka University, Toyonaka 560-0043, Japan

2

Ⅲ- 4

Thin films of small organic semiconductor moleculeson layered substrates have been widely studied to
explore new electronic property and application. The
electronic state of the organic thin film can be modified
by the subtle change of intermolecular and moleculesubstrate interaction which is dominated by weak van
der Waals forces. Although impacts of such weakinteraction on the electronic state are important to study
the mechanism, it has been hardly investigated due tocomplex and inhomogeneous organic molecular structure.
We have revealed the precise growth of well-orderedthin film of small organic semiconductor molecules on
the graphite substrate and investigated the system bymeans of angle-resolved ultraviolet photoelectron
spectroscopy (ARPES) using low-photon energy (hv)
excitation (LE-ARUPS). Utilizing the system, we havefound modification of the wavefunction despite the weakinteraction between the molecule and the substrate [1].
Here, the impact of the structural transition of twodimensional molecular arrangement in the monolayer ofthe pentacene/graphite on the electronic structure isinvestigated by changing the sample temperature. The
sample was prepared in a custom UHV chamber. A single
crystal graphite (SCG) substrate was cleaned byannealing at 900 K for several hours. Pentacene film of 3
Å was deposited onto the substrate at room temperature.
Low-energy electron diffraction (LEED) measurement
was performed separately as independent experiments.
First, the structural transition of pentacene monolayer
was investigated by taking LEED pattern as shown in
Fig. 1. Transition of the LEED pattern from sharp spot
to filled hexagon-like pattern with increasing thetemperature indicates that the pentacene monolayer
with densely packed molecule is formed below thetransition temperature (135 K), whereas the monolayer
consisting both of molecules which is aligned with amean distance from adjacent molecules and densely
packed molecules with relatively small grains areformed above the transition temperature.
Energy and momentum (E-k) maps of both phases
observed by LE-ARPES are shown in Fig. 2. In the Ek maps, flat bands originated from highest occupied
molecular orbital (HOMO) of pentacene, consisting ofa main peak (00) with the vibrational progressing ofsatellite peaks toward higher binding energy, (01) and(02), is observed as in the previous works [2]. Below
the transition temperature, in addition to the energy
shift toward higher energy side, dispersed band ataround Γ-point marked by dashed line which is notderibed from a clean graphite is observed (Fig. 2 (a)).

This feature is detected only in a certain hv energy
region from 7.4 eV to 7.8 eV [1] and shifts withincreasing the kinetic energy, indicating that it ispossibly originated from resonant excitation of anunoccupied band newly formed for the pentacenemolecule and the SCG substrate. This band disappears
above the transition temperature, indicating that theelectronic state is sensitive to the interfacial structure.
These observations suggest that the electronic wave
function of pentacene monolayer is connected to thatof graphite coherently which causes strong
modification of their unoccupied state. The method
realizes that the possibility to probe a tailoring ofelectronic state via weak interaction.

Fig. 1. LEED pattern of pentacene/SCG taken at (a) 72
K and (b) 170 K with electron beam energy of 18 eV.

Fig. 2. Second derivative of E-k map taken from
pentacene/SCG at (a) 85 K and (b) 165 K with hv = 7.4
eV.
[1] T. Yamaguchi et al., UVSOR Activity Report 201846 (2019) 148.
[2] H. Yamane et. al., Phys. Rev. B 72 (2005) 153412.

140

Ⅲ04- 18 -