რ
Material SciencesⅢ-2 Material Sciences

BL4U

Observation of Charge Separation Reaction in a Ti-Mn Electrolyte forRedox Flow Batteries by STXM
E. Hosono1,2,3, D. Asakura1,2,3, A. Ohira1,2, H. Yuzawa4 and T. Ohigashi4,51

Global Zero Emission Research Center, National Institute of Advanced Industrial Science (AIST),
Tsukuba, Ibaraki 305-8569, Japan
2
Research Institute for Energy Conservation, AIST, Tsukuba, Ibaraki 305-8565, Japan
3
AIST-UTokyo Advanced Operando Measurement Technology Open Innovation Laboratory (Operando-OIL),
Kashiwa, Chiba 277-8565, Japan
4
UVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
5
School of Physical Sciences, The Graduate University for Advanced Studies (SOKENDAI),
Okazaki 444-8585, Japan

Redox flow battery (RFB) is one of the candidates oflarge-scale energy storage device to utilize renewableenergy. RFBs use the redox reaction of electrolytes [1],which is diﬀerent from lithium-ion batteries using theredox reaction of the solid-state electrodes. To enhance
the performances of RFBs such as cyclability, chargedischarge capacity, and cost, understanding the redox
reaction is of particular importance. Electronicstructure analysis by synchrotron X-ray spectroscopy isessential to reveal the redox reaction.
In this study we focus on Ti-Mn RFB which involves
sulfuric acid aqueous solution electrolyte with Ti and
Mn ions [2]. The same Ti-Mn electrolyte is used forboth positive and negative electrodes. The redox
reaction has been thought to be
Mn2+ ⇔ Mn3+ + e- (1)in the Ti-Mn electrolyte of the positive electrode and(TiO)2+ + 2H+ + e- ⇔ Ti3+ + H2O (2)in the Ti-Mn electrolyte of the negative electrode [2].
Besides, it has been reported that the Mn3+ ions in the
charged electrolyte of the positive electrode (Eq. (1))
exhibits charge separation reaction as
2Mn3+ → Mn2+ + Mn4+ (3)during the charge process [2]. Moreover, the Mn4+ ionsare changed to MnO2 which precipitates in theelectrolyte of the positive electrode.
Mn4+ + 2H2O → MnO2 + 4H+ (4)This reaction is less reversible that is problematic forthe cyclability. To further understand those reactions in
Ti-Mn RFB, we demonstrate STXM measurements ofthe electrolytes [3]. The high spatial resolution of
STXM is helpful to clarify the formation of precipitation.
To conduct soft X-ray spectroscopic measurementsof liquid samples, we have developed a special cell asshown in Fig. 1 [3]. The Si3N4 thin-film window (100nm) and UV curable resin bond separate liquid sample
from the vacuum. A Ti-Mn electrolyte of the positiveelectrode was investigated by STXM at BL4U of
UVSOR. The electrolyte had been charged up to 50 %of state of charge. The spatial resolution was around
100 nm.
Figure 2(a) shows the STXM image at the Mn L3edge. The bright area corresponds to a precipitate

whose size is approximately 4 μm × 4 μm. The Mn L3edge absorption spectrum of the white area (I) shown in
Fig. 2(b) is mostly attributed to Mn4+ state as comparedwith spectra of reference materials [4]. The surroundingarea in Fig. 2(a) corresponds to the solution whose
spectrum (area (II)) is attributed to Mn2+ state (Fig.
2(b)). Therefore, the charge separation reaction of Eq.
(3) was successfully confirmed by STXM. Similar
STXM experiments of diﬀerent electrolytes will be
performed to obtain strategies to suppress the formationof precipitations.

Fig. 1. A schematic image of the cell for the STXM
measurements [3].

Fig. 2. (a) Mn L3-edge STXM image and (b) spectra of
selected area in the charged Ti-Mn electrolyte of thepositive electrode [3].
[1] For example, T. Shigematsu, Curr. Opin.
Electrochem. 18 (2019) 55.
[2] Y. R. Dong et al., ECS Trans. 69 (2015) 59.
[3] D. Asakura et al., Chem. Asian J. 18 (2023)
e202201047.
[4] For example, R. Qiao et al., Nano Energy 16 (2015)
186.

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BL7U

Temperature-dependent Electronic Band Structure ofOrganic Molecular Semiconductor
K. Fukutani 1, 2, F. Nishino2, P. I. Jaseela2, D. Okaue3, K. Fukui1,3, S. Makita1,
K. Tanaka1,2 and S. Kera1,2
1

Institute for Molecular Science, Okazaki 444-8585, JapanThe Graduate University for Advanced Studies (SOKENDAI), Okazaki 444-8585, Japan
3
Graduate School of Engineering Science, Osaka University, Osaka 560-8531, Japan2

The organic molecular semiconductors are among
the very promising materials in shaping the future of
our electronic device applications in various aspects,
including their physical flexibility, low cost of
fabrication, high biodegradability in the environment,
and the abundance of the constituent elements (mostly
carbon and hydrogen) that are, in principle, inexhaustive.
In fact, the organic molecular semiconductor crystals
already play indispensable roles in our industry, and thecontinuing extensive researches have been ceaselessly
improving their performances.
However, despite the success of organic molecular
semiconductor devices, the knowledge of theirelectronic structure, one of the most fundamentalbuilding blocks for understanding and controlling theirproperties, is far from complete. Among such organic
molecular semiconductors, single crystalline rubrene(C42H28) is known to exhibit exceptionally high carrier
mobility (40 cm2/Vs [1]) and is considered one of themost promising organic semiconductor materials forthe next-generation electronics.
In this regard, we have been extensively investigating
the electronic band structure of rubrene for the purposesof not only elucidating their band structures, but also
for understanding the vibrational eﬀects, arising fromthe intra-molecular and inter-molecular (phonon)
degrees of freedom.
It is well known that many organic semiconductors
exhibit a dual nature in their electronic transport
properties, namely the (coherent) band transport and(polaronic) hopping transport, assisted by the electronic
coupling to the aforementioned vibrations. Rubrene
indeed falls into this category and its transport
properties are believed to originate from the ‘mixture’of both the band and the hopping transports. Since therespective contributions from each mechanism are
believed to depend on temperature, it is clear that thedirect experimental elucidations of the temperaturedependent band structure are essential for the fullunderstanding of the origin of carrier transport inorganic semiconductors.
However, there are very limited number of suchdirect measurements as with angle-resolved
photoemission spectroscopy (ARPES) [2], most likely
due to the numerous experimental diﬃculties, including
the fabrication of large single crystals, removing of thesample charge-up eﬀects and molecular damages
caused by light irradiations.

In our experiments, we have successfully overcome
these obstacles by utilizing BL7U at UVSOR andrevealed the high-resolution temperature-dependent
band structure of rubrene by ARPES. Figure 1 shows
the band structure of rubrene observed at T = 300, 180,
and 80 K along the π-stacking (Γ-Y) direction. Our dataclearly shows the change in the band dispersion width
as the temperature decreases. These data points towards
the discernable change in the carrier eﬀective masses,
which play an important role in the determining thecarrier mobilities. Furthermore, the band dispersion
width appears to be ‘locked’ above T ~ 200 K, which is
the temperature at which the structural anomaly [3] isobserved. Our researches with these experimental
results are expected to provide a key insight into thetransport mechanisms of organic semiconductors.

Fig. 1. Temperature-dependent ARPES data (second
derivative plots) obtained along the Γ-Y direction at (a)T = 300 K, (b) 180 K and (c) 80 K. (d) shows the band
dispersion widths as a function of temperature extracted
from our measurements.
[1] J. Takeya et al., Appl. Phys. Lett. 90 (2007) 102120.
[2] F. Bussolotti et al., Nat. Commun. 8 (2017) 173.
[3] A. van der Lee et al., J. Phys. Chem. Lett. 13 (2022)
406 .

− 64 −

Ⅲ-2 Material Sciences

BL1U

Gamma-induced Positron Annihilation Lifetime Spectroscopy of
β-SiAlON:Eu Phosphor
M. Kitaura1, S. Watanabe2, H. Masai3, Y. Taira4,5, K. Takahashi6, T. Takeda6, N. Hirosaki6,
M. Tansho7, K. Deguchi7, S. Ohki7 and A. Ohnishi1
1

Faculty of Science, Yamagata University, Yamagata 990-8560, Japan
Institute of Innovative Research, Tokyo Institute of Technology, Tokyo 152-8550, Japan3
Department of Materials and Chemistry, National Institute of Advanced Industrial Science and Technology,
Ikeda 563-8577, Japan
4
UVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
5
School of Physical Sciences, The Graduate University for Advanced Studies, Okazaki 444-8585, Japan
6
Research Center for Functional Materials, National Institute for Materials Science, Tsukuba,
Ibaraki 305-0044, Japan
7
High field NMR group, National Institute for Materials Science, Tsukuba, Ibaraki 305-0003, Japan2

Eu-doped β-SiAlON (Si6-zAlzOzN8-z; 0 ≤ z ≤ 4.2) iswell-known to be a green-emitting phosphor with highbrightness, narrow line width, and excellent resistanceto thermal quenching [1]. These features areindispensable for the development of next-generation
phosphors to fabricate advanced wide gamut
backlighting device. For this purpose, it is important toinvestigate the nature of lattice imperfections such asvacancies, interstitials, and unexpected impurities,
because they aﬀect adversely as so-called “killer” or“trap” responsible for luminescence quenching andafterglow.
Positron annihilation lifetime spectroscopy (PALS)
is a unique experimental method that can probevacancy-type defects with negative charge. In thepresent study, we investigated such vacancy-type
defects in β-SiAlON:Eu phosphors by gamma-ray
induced PALS (GiPALS) experiment [2]. GiPALS
experiment was performed at the BL1U of UVSOR
synchrotron facility. Positron annihilation lifetimes andrelative intensities were analyzed using the software
LT10 [3]. Positron annihilation lifetimes at the bulk anddefect states were calculated by two-component
density-functional-theory (TCDFT) calculations [4,5].
Figure 1 shows the GiPALS spectrum of aβ-SiAlON:Eu phosphor. The composition was
Si5.97Al0.03O0.03N7.97Eu0.01. The data were obtained atroom temperature. The GiPALS spectrum reproduced
three exponential decay components indicated bybroken lines. The first and second component withshort and middle lifetime are attributed to the positronannihilation at the bulk and defect states in β-SiAlON,
respectively. The third component with long lifetime
originates in the formation of positroniums, which may
arise from amorphous layer covering phosphor particles[6]. The relative intensity of the third component was
negligibly small compared to other two. To estimate
bulk lifetimes using experimental lifetimes and relative
intensities, we adopted two-state trapping model, where
the long lifetime component was not considered. The
experimental bulk lifetime was estimated to be 265±18

ps. This value agreed with the bulk lifetime (= 271 ps)
calculated for the relaxed lattice of a β-SiAlON(Si95Al1O1N127). This fact indicates the validation of ourexperiment and calculation. On the other hand, thelifetime of the middle lifetime component was not
reproduced by DFT calculations for monovacancies atsilicon and nitrogen sites. We suppose that the second
component originates in defect complexes of multiple
vacancies. The origin of the second component is now
in investigation.

Fig. 1. (Upper) GiPALS spectrum of a β-SiALON:Eu
phosphor. (Lower) Residual between the results ofexperiment and curve fit analysis.
[1] X. Zhang et al. Chem. Mater. 29 (2017) 6781.
[2] Y. Taira et al., Rev. Sci. Instrum. 84 (2013) 053305.
[3] D. Giebal and J. Kansy, Phys. Procedia 35 (2012)
122.
[4] P. Giannozzi et al. J. Phys.: Condens. Matter 21(2009) 395502.
[5] X. Gonze et al., Comput. Phys. Commum. 248(2020) 107042.
[6] N. Hirosaki et al., Appl. Phys. Lett. 86 (2005)
211905.

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BL1U

In-situ Measurement of Defects Dynamics in Stress Applied Bulk Iron by
Means of Gamma Ray Induced Positron Annihilation Spectroscopy
F. Hori 1, S. Araki1, S. Hirayama1 and Y. Taira2
Dept. of Quantum and Radiation Eng., Osaka Metropolitan University, Sakai, Osaka 599-8570, Japan
2
UVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan

hydrogen introduced sample slightly higher than that ofpure Fe. This indicates the formation of vacancy
clusters, such as di-vacancy, and the presence ofhydrogen may facilitate the aggregation of vacancies.
However, this is considered that the τ2 slightly decreases
taking long time afterwards indicates that these initiallyformed di-vacancies dissociate. Also, it found that therelative intensity I2 corresponds to the defectconcentration of τ2 component, and the concentration
change after stress addition also shows a slight decrease
with relaxation time.
㻥㻜㻲㼑㻲㼑 㻨㻙 㻴㻲㼑㻔㼑㻙 㼕㼞㼞㼍㼐㻚㻕 㻨㻙 㻴㻯㼔㼍㼚㼓㼑 㼕㼚 㼟㼠㼞㼑㼟㼟㻘䃢㻔㻹㻼㼍㻕㻵㼚㼕㼠㼕㼍㼘 㼍㼜㼜㼘㼕㼑㼐 㼟㼠㼞㼑㼟㼟 㻦 㻤㻤 㻹㻼㼍
㻤㻡

㻤㻜

㻣㻡

㻣㻜

㻢㻡

㻜

㻝

㻞

㻟

㻠

㻡

㻢

㻣

㼀㼕㼙㼑㻘 㼠 㻔㼔㻕

Fig. 1. Stress change after initial stress applied.
㻡㻜

㻠㻝㻜

㻟㻜
㻟㻢㻜

㻟㻝㻜

㻵㼚㼠㼑㼚㼟㼕㼠㼥㻘 㻵㻞 㻔㻑㻕

The behavior of hydrogen atoms is attracting
attention in a wide range of research fields such as
high-strength structural materials and hydrogen storage
materials. In such materials, hydrogen atom diﬀuses
and has various interaction with defects, consequently
it makes serious characteristic change. In particular, inthe corrosion of metallic materials, it is known that thepresence or absence of lattice defects in the materialaﬀects mechanical and physical properties of materials.
On the point of view, positron annihilation techniques
are useful to detect and estimate the behavior of
vacancy type micro defects in materials. However, inorder to investigate the dynamics of the internal defectbehavior without destructing materials, more thanmega electron volts positron is needed. Recently, thedevelopment of high-energy Gamma-ray induced
positron spectroscopy (GiPS) has developed at somephoton factories. Especially, direct incidence of highenergy gamma rays with the energy more than 1.022
MeV into the target material produces positrons in it
and annihilated there. High-energy gamma rays fromlaser Compton scattering at synchrotron radiation
facilities enables positron experiments to detect defects
in bulk materials without sample destruction. In thisstudy, in-situ positron annihilation lifetime measurement
while applying stress to a bulk specimen have performedon the beam line BL1U at UVSOR.
Positron lifetime measurement has performed onpure iron bulk specimens processed into JIS standard
tensile specimens, irradiated with 8 MeV electron, andirradiated with electron and then hydrogen introduced.
Electron irradiation have done by linear accelerator at
Kyoto University Reactor Research. Hydrogen was
introduced into the sample by immersion in a 20%
ammonium thiocyanate solution at 318 K for 14 days.
Figure 1 shows the results of the stress change after
applying a stress of 88 MPa, corresponding to 90% of
the yield stress, for all samples. It is clear that stressrelaxation is suppressed by the presence of hydrogenand vacancies. In addition, the sample without defects
relaxes greatly in a short period of time and almost nochange can be confirmed after that, but the sample withvacancy and hydrogen shows a small amount ofrelaxation, but it relaxes slowly over a long period oftime. Figure 2 shows the change of positron lifetimes
and their relative intensities during relaxation after
initial stress applied. The long lifetime of positron τ2
increase to more than 170 ps after stress application inall samples, indicating that vacancies were formed
even at stresses below the yield point. Also, τ2 for㻜
W㻞 㻔㻲㼑㻕
W㻞 㻔㻲㼑 㻨㻙 㻴㻕W㻞 㻔㻲㼑 㻔㼑㻙 㼕㼞㼞㼍㼐㻚㻕 㻨㻙 㻴㻕W 㻔㻲㼑㻕
W 㻔㻲㼑 㻨㻙 㻴㻕W㻝 㻔㻲㼑 㻔㼑㻙 㼕㼞㼞㼍㼐㻚㻕 㻨㻙 㻴㻕㻞㻢㻜㻼㼛㼟㼕㼠㼞㼛㼚 㼘㼕㼒㼑㼠㼕㼙㼑㻘 W 㻔㼜㼟㻕

1

㻞㻝㻜

㻙㻝㻜

㻙㻟㻜

W㻞

㻙㻡㻜

㻝㻢㻜
㻙㻣㻜

W㻝

㻝㻝㻜

㻙㻥㻜
㻢㻜
㻜

㻝

㻞

㻟

㻠

㻡

㻢

㻣

㻙㻝㻝㻜

㼀㼕㼙㼑㻘 㼠 㻔㼔㻕

Fig. 2. Positron lifetimes and relative intensity I2change after initial stress applied.

− 66 −

Ⅲ-2 Material Sciences

BL1U

Gamma-ray Induced Positron Annihilation Lifetime Measurementof CeO2 Catalyst Placed in a Quartz Tube
S. Dohshi1, K. Maeda1, Y. Taira2 and T. Hirade3
1

Osaka Research Institute of Industrial Science and Technology
2-7-1, Ayumino, Izumi, Osaka 594-1157, Japan
2
UVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
3
Japan Atomic Energy Agency, Ibaraki 319-1195, Japan

In situ observation of the catalyst during catalytic
reactions is very important for elucidating the reaction
mechanism and preparing the highly active catalyst.
Recently, it has been reported that the presence ofoxygen vacancies in CeO2 catalysts aﬀect their catalytic
activity [1]. Therefore, it becomes more and more
important to analyze the behavior of oxygen vacancies
of CeO2 with high sensitivity during catalytic reactions.
Positron annihilation lifetime measurement is a
powerful tool for the detection of lattice defects such as
oxygen vacancies with high sensitivity. However, there
have been no examples of positron annihilation lifetime
measurements with controlling gas atmosphere andtemperature. Typically, the catalytic reaction is
performed in a quartz or alumina tube with controlling
gas atmosphere and temperature. When gamma-ray
induced positron annihilation lifetime measurement isperformed under the same conditions as the catalytic
reaction, positrons generated in the sample can be
annihilated not only in the sample but also in the quartz
tube, because of the presence of the quartz tube between
the sample and the detector.
In this study, the eﬀect of quartz tube on the positronannihilation lifetime of CeO2 was investigated.
The pellet sample with 20 mm in diameter and 10
mm in thickness were prepared using CeO2 nanoparticles
with a primary particle size of ca. 2 nm.
We have set up a gamma-ray spectroscopy system atthe laser-Compton scattering (LCS) beamline of BL1U
at UVSOR-III [2], and measured the lifetime of theannihilation gamma-rays at room temperature using
BaF2 scintillation detector. We used the software
Lifetime9 (LT9) to analyze the spectra.
Table 1 shows the positron annihilation lifetimes andrelative intensities of CeO2 catalyst with various
measurement conditions. In case of the measurement
without quartz tube, the positron annihilation lifetime
was composed of two components (τ1 and τ2). These
lifetimes were attributed to the positron annihilation in
CeO2 bulk and surface. On the other hand, in case of themeasurement with quartz tube, the positron annihilation
lifetime was composed of three components (τ1, τ2 andτ3). The longest lifetime component (τ3) can be attributed
to the annihilation in the quartz tube, with a relative
intensity (I3) of about 1%, regardless of the gamma-ray
beam diameter. Furthermore, the lifetimes and relative
intensities of the other two components derived fromCeO2 (τ1 and τ2) did not change significantly whenmeasured using quartz tubes. These results suggest that
positron annihilation lifetime measurements can be
performed in a quartz tube while controlling the gas
atmosphere and temperature.
Next fiscal year, gamma-ray induced positronannihilation lifetime measurement will be performed
with controlling the gas atmosphere and temperature toclarify the behavior of oxygen vacancies in CeO2.
[1] X. Liu et al., J. Am. Chem. Soc. 131 (2009) 3140.
[2] Y. Taira et al., Rev. Sci. Instr. 84 (2013) 053305.

Table 1 Positron annihilation lifetimes and relative intensities of CeO2 catalyst with various measurement conditions.
measurement
conditions

(ps)

I1
(%)

(ps)

I2
(%)

(ps)

I3
(%)
-

without quartz tube

155

6.5

388.2

93.5

-

with quartz tube
( -ray beam: 2 mm)

159

3.8

367.8

95.0

1386

1.2

with quartz tube
( -ray beam: 3 mm)

142

4.2

362.5

94.4

1290

1.4

− 67 −

BL1U

Formation of the stress-induced Vacancies in Iron
by in situ Positron Annihilation Lifetime Spectroscopy
M. Fujinami1, R. Awaji1, A. Yabuuchi2, T. Hirade3, N. Oshima4 and Y. Taira5
1
Department of Applied Chemistry and Biotechnology, Chiba University, Chiba 263-8522, Japan
Institute for Integrated Radiation and Nuclear Science, Kyoto University, Kumatori 590-0494, Japan
3
Nuclear Science and Engineering Center, Japan Atomic Energy Agency, Tokai 319-1195, Japan
4
National Institute of Advanced Industrial Science and Technology, Tsukuba 305-8568, Japan
5
UVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan

2

Investigating the formation process of atomic
vacancies by mutual cutting of dislocations is essential
to understand the role of vacancies in the mechanicalproperties of metals. However, such vacancies have yet
to be directly observed. The reason is that vacancies
have a significant diﬀusion coeﬃcient and are unstable.
Positron annihilation lifetime spectroscopy is the
only method that allows direct observation of atomic
vacancies. However, the conventional method using aradioactive isotope such as 22Na as a positron source isdiﬃcult to measure in situ under various conditions dueto the risk of radioactive contamination. If it becomes
possible to measure the vacancies while applying
stress, it will be possible to detect transient vacancies,
which leads to the first detection of transient vacancy
formation. It also provides essential fundamental
knowledge for discussing the behavior of vacancy
stabilization by impurities, including hydrogen. In thisstudy, we attempted to directly detect vacancies formedin pure iron during tensile deformation in situ using theBL1U beamline, where positrons are created in thesample directly.
A 3-mm-thick tensile sample was mounted on a small
tensile tester. The sample was subjected to tensile
deformation up to a nominal strain of over 7% with astrain rate of 2.2×10−5 s−1. Ten samples were measured
under the same tensile deformation conditions to obtainenough counts of positron lifetime spectra.
Figure 1 shows the positron lifetime spectra of pureiron before and after tensile deformation. A longer
lifetime component is observed in the positron lifetime
spectrum when the sample is elongated to a nominal
strain of ~7.3%. Figure 2 shows the change in mean
positron lifetime during tensile deformation. The mean
positron lifetime increases with increasing nominal
strain. However, the change in mean positron lifetime
obtained in this study diﬀers significantly from thetrend reported in an earlier study using the conventional
method [1]. One possible reason for this diﬀerence isthe diﬀerence between the conventional method, whichobserves a depth of about 0.1 mm from the sample
surface, and this method, which observes the entire
sample, including the deeper region. Further detailed
analysis is currently underway.

Fig. 1. Positron lifetime spectra of pure iron before andafter tensile deformation with a nominal strain of~7.3%.

Fig. 2. Change in mean positron lifetime during tensile
deformation.
[1] B. Somieski et al., NDT & E Int. 27 (1994) 235.

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Ⅲ-2 Material Sciences

BL1U

In-situ Measurements of Vacancies Formed in Pure Ironby Electrolytic Hydrogen Charging using gamma-ray-induced
Positron Annihilation Lifetime Spectroscopy
A. Yabuuchi1, T. Hirade2, M. Fujinami3, R. Awaji3, N. Oshima4, K. Takai5 and Y. Taira6
1Institute for Integrated Radiation and Nuclear Science, Kyoto University, Kumatori 590-0494, Japan
2
Nuclear Science and Engineering Center, Japan Atomic Energy Agency, Tokai 319-1195, Japan3
Department of Applied Chemistry and Biotechnology, Chiba University, Chiba 263-8522, Japan
4
National Institute of Advanced Industrial Science and Technology, Tsukuba 305-8568, Japan
5
Department of Engineering and Applied Sciences, Sophia University, Tokyo 102-8554, Japan
6
UVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan

Recently, a fracture mechanism involving vacancies
has been proposed as a new model to explain thehydrogen embrittlement of steels [1]. Therefore, manystudies on hydrogen embrittlement have been performed
using positron annihilation spectroscopy, a vacancy
detection technique. However, the conventional
positron annihilation technique is challenging tomeasure during hydrogen dosing in a liquid. The highenergy pulsed gamma-rays obtained at UVSOR make itpossible to produce positrons directly inside a sample
placed in a fluid and perform positron annihilation
measurements. In this study, we attempted in-situ
positron annihilation lifetime measurements duringhydrogen charging in liquid to investigate hydrogeninduced vacancies in pure iron.
Six well-annealed pure iron plates with a purity of
99.99% and a thickness of 2 mm were arranged in the
beam axis direction with a gap of 2 mm between them.
This measurement geometry was chosen to achieve
suﬃcient hydrogen introduction throughout the sample
and still obtain a suﬃcient count rate of annihilation
gamma-rays. For electrolytic hydrogen charging, thesample was immersed in 0.1 N NaOH solution
containing 5 g/L NH4SCN. A pulsed gamma-ray beamwith a maximum energy of 6.6 MeV was injected tomeasure the positron lifetime.
Figure 1 shows the positron lifetime spectra of pureiron plate samples placed in air and the electrolyte
solution. The spectrum obtained from the in-air
measurement shows almost no lifetime component of
positrons annihilated outside the sample. In contrast, alonger lifetime component originating from positronannihilation in the electrolyte solution appears in the
spectrum obtained from the sample placed in theelectrolyte solution. The change in positron lifetime iniron during hydrogen charging was investigated byanalyzing such spectra. However, it was concluded thateliminating the electrolyte solution component fromthe spectra is essential for a detailed analysis of the ironsample components.
Figure 2 shows the calculated positron flux
distribution when a gamma-ray beam is injected into aniron plate in water. Positrons are mainly produced iniron, which has a high specific gravity, but they are also
produced to some extent in water. In addition, some ofthe positrons produced in iron are emitted out of ironand annihilated in water. Therefore, we consider
improving the measurement geometry for the next
beamtime.

i 1. Positron
i lifetime
lif i spectra of well-annealed
f
ll
l d
Fig.
pure
iron measured in air or an electrolyte solution.

Fig. 2. (a) Geometry of the simulation model.
(b) Calculated positron flux distribution.
[1] M. Nagumo, Mater. Sci. Technol. 20 (2004) 940.

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BL2A

Formation of Catalytically Active Mo2C Species on H-MFI for Methane
Aromatization Studied by Mo L-edge XANES
K. Kuramochi1, Y. Sonobe2, H. Shimura2, Y. Kinoshiro2, R. Yamazaki1, Y. Uchimura2
and H. Aritani2
Advanced Science Research Laboratory, Saitama Institute of Technology, Fukaya 369-0293 Japan
2
Graduate School of Engineering, Saitama Institute of Technology, Fukaya 369-0293 Japanenergy side after the reaction for 10 minutes, indicatingthat further reduction of Mo proceeds to form β-Mo2C
like species with low crystallinity. Since the edgeenergy is kept on after 90 minutes (in the maximum
activity) is exhibited, β-Mo2C like species are possibly
act as a highly active one for methane dehydrogenation.
As the reaction time progresses, only a slight shift ofthe edge to the lower energy side can be seen. Therefore,
it is presumed that the deactivation of reactivity after 30
minutes is caused mainly by carbon deposition on
H-MFI support rather than excess reduction of Mo
species.
1.0

TEY (Normalized Intensity)

As a typical GTL (Gas-To-Liquid) catalyst, supported
molybdenum on H-MFI zeolites show catalyticallyhigh and selective activity to convert methane tobenzene directly. Although the GTL process isextremely innovative, it is an important subject tosuppress deactivation as well as increase the yield ofaromatics. For the Mo/H-MFI catalysts, definite
deactivation due to coke deposition has been a major
problem for enhancement of MTB reactivity. A causeof the deactivation strongly depends on both coke
deposition onto strong acid sites over H-MFI andstructural deactivation of carbonized Mo species. Oneof the most important subjects for catalytically highand durable activity is the elucidation of active Mo
carbide (MoCx) species and their structural stability. In
this study, Mo LIII-edge XANES is applied tocharacterize the active MoCx species on Mo/H-MFI
during the methane aromatization.[1] The change ofactive Mo species during the reaction was investigatedas a time course of XANES spectra.
Mo/H-MFI (Si/Al2=23-30 in H-MFI, 5.0 wt% as
MoO3-loading) catalysts were prepared as described in
the previous paper.[2] The methane dehydroaromatization reactivity was evaluated at 1023 K. Mo
LIII-edge XANES spectra were obtained in BL2A of
UVSOR-IMS in a total-electron yield mode using the
InSb double-crystal monochromator. A REX-2000(Rigaku) software was used for normalization of each
XANES spectra. The edge energy was obtained fromthe maximum of the first derivative of XANES.
Figure 1 shows the LIII-edge XANES of reference
Mo compounds. The energy of the absorption edge
becomes higher according to the higher oxidation stateof molybdenum. For Mo-carbides, the edge energy in
α-Mo2C (fcc: 2526.55 eV) is significantly larger thanthat in β-Mo2C (orthorhombic: 2524.45 eV). Since thediﬀerence of energy value should be due to thecoordination number in Mo-C shells, the edge energy
of XANES can be applied to characterize the local
structure of Mo2C species.
For evaluation of catalytic activity for methane
aromatization at 973 K, it is concluded that Mo/HMFI(Si/Al2=30) shows the maximum benzene yield in
30 minutes as an initial streaming range. On the Mo/HMFI catalysts, time course of L-edge XANES spectra
are shown in Figure 2. Before the reaction (at 0 min.),the Mo/H-MFI catalyst has been pre-reduced with
CO(2%)-He at 1023 K. At this time, Mo species havealready reduced to form Mo4+ (due to MoO2) and/or
Mo2+ (α-Mo2C). The edge of XANES shifts to the low

Mo metal
D-Mo2CE-Mo2C
MoO2
MoO3

0.5

0.0
2515

2520

2525

2530
2535
Energy /eV

2540

2545

Fig. 1. Mo LIII-edge XANES spectra of reference Mo
compounds.
Mo/H-MFI(30)
0 min.
10 min.
30 min.
90 min.
180 min.
D-Mo2CE-Mo2C

1.0

TEY (Normalized Intensity)

1

1.0

0.8

0.6
2525

2526

2527

0.5

0.0
2515

2520

2525
Energy / eV

2530

2535

Fig. 2. Mo LIII-edge XANES spectra of Mo/H-MFI (Si/Al2=30) catalyst after the reaction for each time (0 –180 minutes).
[1] H. Aritani et al., UVSOR Activity Report 2021 49(2022) 58.
[2] H. Aritani et al., J. Environm. Sci., 21 (2009) 736.

− 70 −

Ⅲ-2 Material Sciences

BL2A

Local Environment of Dopants in (M, Nb) co-doped TiO2 (M=Fe, Ni)
H. Murata 1, 2, T. Nishio2, Y. Nagatomo2 and A. Nakahira1, 2
1

Department of Materials Science, Osaka Metropolitan University, Sakai 599-8531, Japan2
Department of Materials Science, Osaka Prefecture University, Sakai 599-8531, Japan

Both of the co-doped TiO2 samples exhibited visible
light absorption. Based on the spin and valence statesof dopants, the visible light absorptions are induced at
diﬀerent origins. The (Fe, Nb) co-doped TiO2 has anarrowed band gap and weak spin forbidden d-dtransitions. On the other hand, the (Ni, Nb) co-doped
TiO2 has a strong spin-allowed d-d transition. These
diﬀerent origins of visible light absorption
fundamentally influence behaviors of excited careersand chromaticity. These results lead to a comprehensive
understanding of the visible light applications such as
photocatalyst and pigments.

Nb-L3
Ti0.50Ni0.33Nb0.17O2
Ti0.60Ni0.13Nb0.27O2

Intensity / arb. units

Titanium dioxide (TiO2) is a typical fine ceramicmaterial used in a wide range of applications, such as
photocatalysts, pigments and transparent conductors.
TiO2 has a several polymorphs with wide band gaps
and absorb only UV light. Numerous studies have been
carried out on cation and anion doping into TiO2 toutilize visible light. However, most of them induce
weak visible light absorption due to their small solid
solubility limits. Co-doping into TiO2 has been
investigated [1] and combinations of dopants such as(Fe, Nb) and (Ni, Nb) significantly increase solid
solubility limits [2-4]. However, local environments ofthe co-doped dopants int TiO2 and their light absorption
mechanism have not been clarified. In this study, local
environments and electronic structures of (Fe, Nb) and(Ni, Nb) co-doped TiO2 were investigated.
(Fe, Nb) and (Ni, Nb) co-doped TiO2 samples wereprepared by a conventional solid-state reaction method
using TiO2, Fe2O3, NiO and Nb2O5 as starting materials.
The stating materials were ground and mixed by analumina mortar and pestle. They were calcined in analumina crucible at 1200 °C for 6 h. The samples wereground and mixed by the mortar and pestle again. Then,they were calcined in an alumina crucible at 1200 °C
for 6 h.
Samples were characterized using X-ray diﬀraction(XRD), UV-Vis, 57Fe Mössbauer spectroscopy, and
X-ray absorption near edge structure (XANES). Ni-L3
and Nb-L3 XANES spectra were collected using thetotal electron yield method with a sample current at
BL2A in UVSOR (Okazaki, Japan). The X-ray beam
was monochromated using beryl and InSb double
crystals for Ni-L3 and Nb-L3, respectively. NiO andNb2O5 was used as reference materials.
XRD patterns of the samples can be assigned torutile-type TiO2 with peak shifts. They confirmed that
(Fe, Nb) and (Ni, Nb) co-doped TiO2 has large solubility
limit over 50 cation%, where the dopants ratios are 1:1
and 1:2 for (Fe, Nb) and (Ni, Nb), respectively. Notethat their lattice parameters increased linearly with theconcentration of dopants.
57
Fe Mössbauer spectroscopy and Ni-L3 XANES
show that Fe and Ni in the samples are high-spin Fe3+
and Ni2+ in octahedral coordination, respectively. Nb-L3
XANES of the samples have typical features of Nb5+ inoctahedral coordination [5], as shown in fig. 1. These
results indicate that large solid solubility limit of theco-doped TiO2 is due to charge compensation between
dopants.

Ti0.80Ni0.07Nb0.13O2
Ti0.50Fe0.25Nb0.25O2

Ti0.60Fe0.20Nb0.20O2
Ti0.80Fe0.10Nb0.10O2
Nb2O5

2360

2370
2380
2390
Photon energy / eV

2400

Fig. 1. Nb-L3 XANES spectra of (Fe, Nb) and (Ni, Nb)
co-doped TiO2.
[1] A. S. M. Nur et al., J. Water Process. Eng. 47 (2022)
102728.
[2] M. A. Tena et al., Mater. Res. Bull. 27 (1992) 1301.
[3] B. Balzer and H. Langbein, Cryst. Res. Technol. 31(1996) 93.
[4] M. Wenger and T. Armbruster, Neues Jahrb.
Mineral. Monatsh. 5 (1993) 225.
[5] Y. Kubouchi et al., X-ray Spectrom. 41 (2012) 259.

− 71 −BL2A

XAFS Study of MgAl2O4 - MgGa2O4 Solid Solutions
S. Yoshioka 1, K. Yasuda1, E. Kobayashi2 and K. Okudaira3
1

Department of Applied Quantum Physics and Nuclear Engineering, Kyushu University,
Fukuoka, 819-0395, Japan
2
Kyushu Synchrotron Light Research Center, Saga 841-0005, Japan
3
Graduate school of Advanced Integration Science, Chiba University, Chiba, 263-8522, Japanenergy of 1330 eV after the removal of the background
intensity. The Mg K-edge XANES of MgGa2O4 wereclearly diﬀerent from that of MgAl2O4. The spectrum
diﬀerence between MgAl2O4 and MgGa2O4 suggests
local structure diﬀerence between two specimens.
Previous study using diﬀraction technique reported
octahedral location of Mg in MgGa2O4 as an inverse
spinel, whereas tetrahedral location of Mg in normal
spinel of MgAl2O4. Detailed analyses on the local
environment of Mg and Al in the MgAl2-xGaxO4 are in
progress by combined use of the XANES and the firstprinciples band structure calculations.
Mg K-edge
MgAl2O4

Intensity (arb. units)

Spinel oxides with the general formula AB2O4 can beformed with various kinds of divalent A and trivalent B
cations. Owing to their unique mechanical, electronic,
and magnetic properties, the spinel oxides have gained
considerable attention not only from the fundamental
research fields but also from the industrial application
point of view. Some spinel compounds accommodate alarge degree of cationic disorder. The cationicdisordering naturally aﬀects the structural properties ofthe spinels. For example, magnesium aluminate(MgAl2O4) and magnesium gallate (MgGa2O4) are
generally known as normal and inverse spinel
structures, respectively. However, their inversion
degrees for synthetic specimens were also reported to
be fluctuating between 0 and 1, respectively, due to the
cationic disordering. Recently, the structure of
MgAl2-xGaxO4 was reported using first principles
calculations and X-ray diﬀraction [1]. X-ray absorption
spectroscopy (XAS) is a powerful structure
characterization method that uses an X-ray probe toreveal local atomic coordination and electronic
structures. In this study, we focus on the local structuresin MgAl2O4 – MgGa2O4 solid solutions, particularly
cationic-disordered structures.
The polycrystalline samples of MgAl2-xGaxO4 (x = 0,0.5, 1.0, 1.5, and 2.0) were synthesized by a solid-state
reaction. They were sintered in air at 1500 ºC for 10 hfollowed by furnace. Mg and Al K-edge XANES
measurements were performed on BL2A beamline at
UVSOR Synchrotron Facility, Okazaki, Japan, using
the partial fluorescence yield method. A KTiOPO4
double-crystal monochromator gives Mg and Al
K-absorption edges in the energy regions 1290–1340
eV and 1540–1610 eV, respectively. The measurementsof Mg and Al K-edge XANES spectra were carried out
in vacuum at a pressure and temperature of 1×10−4 Pa
and 20 ºC, respectively. Fluorescence X-rays of Mg Kα
and Al Kα were collected utilizing an energy-dispersible
silicon drift detector.
The Mg K-edge XANES spectra for MgAl2O4 and
MgGa2O4 are shown in Fig. 1. The intensity of each
spectrum was normalized to a value of 1 at the photon

1310

MgGa2O4

1320

1330

1340

1350

Photon energy (eV)Fig. 1. Mg K-edge XANES spectra of MgAl2O4 and
MgGa2O4[1] G. Pilania, V. Kocekski, J. A. Valdez, C. R. Keller
and B. P. Uberuaga, Commun. Mater. 1, Article number:
84 (2020).

− 72 −

Ⅲ-2 Material Sciences

BL2A

NEXAFS Spectroscopy of Battery Materials Using a Transfer Vessel
A, Inoishi1 and E. Kobayashi 2
1

Institute for Materials Chemistry and Engineering, Kyushu University
6-1 Kasuga-koen, Kasuga-Shi 816-8580, Japan
2
Kyushu Synchrotron Light Research Center, 8-7 Yayoigaoka, Tosu, Saga 841-0005, Japan

To increase capacity in all solid-state lithium-ion
batteries, it is better to remove as much of the solid
electrolyte and conductive carbon contained in theelectrode as possible. Recently, we reported the allsolid-state lithium batteries using electrochemicallithium insertion in some anode materials. We reported
Mg(BH4)2, and MgH2 anode materials.[1,2] In theseconversion-type electrodes, LiBH4 and LiH are
generated as lithium salt during lithiation and ionic
conduction paths are formed during the electrochemical
reaction. Solid electrolyte is not required in theseelectrode mixture and reasonable battery performanceswere observed with the electrode composed of active
material (Mg(BH4)2 or MgH2) and acetylene black,
without electrolyte powder. We call this new concept as“in-situ forming of solid electrolyte”. Recently, we
newly focused on MgCl2 as a new anode active material.
For the case of MgCl2, it is assumed that LiCl is formed
after lithiation as “in-situ formed electrolyte”. In thisstudy, we evaluated the mechanism of electrochemical
reaction of MgCl2 anode by X-ray adsorption
spectroscopy.
Composite powder containing MgCl2 was preparedby mechanical milling of MgCl2 with acetylene black(AB) in a 70:30 mass ratio at 400 rpm for 30 min. Each
all-solid-state cell (Li/LiBH4/MgCl2, AB) was
assembled using an insulating cell die (Poly Ether Ether
Ketone) sandwiched between two stainless steel rods
under Ar. Discharge/charge measurements wereconducted in a vacuum at a current density of 0.05
mAcm-2 and at 120 °C. Ex-situ X-ray absorption
spectroscopy (XAS) data for Mg K-edge and Cl K-edge
were acquired at the BL2A of UVSOR Synchrotron
Facility, Institute for Molecular Science. For thetransportation to XAS, a sample transfer vessel wasused.[3,4]Initial lithiation capacity and delithiation capacity of
the Li/LiBH4/MgCl2 cell were 465 mAhg-1 and 321
mAhg-1, respectively. The initial lithiation capacity was
82 % of the theoretical capacity of MgCl2. In thiselectrode, solid electrolyte is not required in theelectrode mixture. This indicates that lithium
conduction path is formed from MgCl2 by theelectrochemical reaction. Mg K-edge X-ray adsorption
spectroscopy for the MgCl2 electrode before and after
the discharge-charge were measured. MgCl2 showedsharp peaks at 1310 eV. “Initial state” just after cellfabrication was similar spectrum with MgCl2 chemical,

indicating that “initial state” is still MgCl2. After the
initial lithiation, adsorption at 1302 eV was newly
observed. This is also observed in Mg metal.[5]Therefore, MgCl2 is reduced to form Mg metal duringlithiation process. After the following delithiation,
similar spectrum with initial state was observed,
indicating that MgCl2 is reversibly formed after thedelithiation process. Cl K-edge X-ray adsorption
spectroscopy for the MgCl2 electrode before and after
the discharge-charge were also measured. Initial stateand delithiated state were similar spectra with that of
MgCl2. After lithiation, the main intense peak wasslightly shifted to higher energy. This corresponds tothe adsorption observed in LiCl.[6] From these results,
it was confirmed that following reaction is occurred in
the MgCl2 anode as shown in Fig. 1.
MgCl2 + 2Li+ + 2e-→ 2LiCl + Mg (1)Fig. 1. Schematic view of “in-situ forming of solid
electrolyte” in MgCl2 electrode using Li/LiBH4/MgCl2
cell.
[1] H. Sato, R. Sakamoto, H. Minami, H. Izumi, K.
Ideta, A. Inoishi, S. Okada, Chem. Commun, 57 (2021)
2605.
[2] A. Inoishi, H. Sato, Y. Chen, H. Saito, R. Sakamoto,
H. Sakaebe, S. Okada, RSC Advances, 12 (2022) 10749.
[3] E. Kobayashi, J. Meikaku, T. Okajima, and H.
Setoyama, Japanese Patent No. 5234994.
[4] E. Kobayashi, J. Meikaku, H. Setoyama, T. Okajima,
J. Surf. Anal., 19 (2012) 2.
[5] J. W. Chiou, H. M. Tsai, C. W. Pao, K. P. Krishna
Kumar, S. C. Ray, F. Z. Chien, W. F. Pong, App. Phys.
Lett. 89 (2006) 043121.
[6] H. S. Lee, X. Q. Yang, J. McBreen, L. S. Choi, Y.
Okamoto, J. Electrochem. Soc. 143 (1996) 3825.

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BL3U

Direct Observation of Electrochemically Generated High Valent Iron-Oxo
Species of μ-Nitrido-Bridged Iron Phthalocyanine Dimer Deposited on
Graphite Surface by Soft X-ray Absorption Spectroscopy
Y. Yamada 1, 2 and M. Nagasaka3
1

Department of Chemistry, Graduate School of Science, Nagoya University,
Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan
2
Research Center for Materials Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan
3
Institute for Molecular Science, Myodaiji, Okazaki 444-8585, Japan

CH4 is expected as a next generation carbon resource
because it is abundant in nature as natural gas ormethane hydrate. Therefore, development of novel
catalysts that convert CH4 into valuable raw chemicals
eﬃciently is strongly desired. However, high chemical
stability of CH4 makes it highly challenging. We
recently reported that a μ-nitrido-bridged ironphthalocyanine dimer closely stacked on a graphite
surface 1/G (Fig. 1a) eﬃciently convert CH4 intomethanol, formaldehyde, and formic acid in an acidic
aqueous solution containing excess H2O2 at atemperature below than 100 °C. It was demonstrated
that 1/G showed especially potent CH4 oxidation
catalyst among a variety of molecule-based CH4oxidation catalysts and its catalytic activity was almost
comparable to that of a natural particulate methane
monooxgenase (pMMO)[1].
In order to advance the chemistry of 1/G, we next
attempted to develop the method for electrochemical
generation of 1oxo/G. It is expected that 1oxo/G could be
generated by oxidation of coordinating H2O on the ironcenter of 1(H2O)/G in an aqueous solution (Fig. 1b).
This method is expected to provide a more economicallyfavored approach for CH4 oxidation.
We first prepared a SiN membrane tip modified by
1/G. A SiN membrane tip modified with 20 nm
thickness of carbon membrane (cmSiN) was treatedwith a pyridine solution of 1, followed by washing withtrifluoroacetic acid and H2O to give a SiN membrane
tip modified by 1/G (1/cmSiN). It was confirmed that 1
was successfully deposited on the carbon surface of
cmSiN (Fig. 2a) by using cyclic voltammogram in an
CH3CN solution containing 100 mM nBu4N+·PF6–.
Electrochemical generation of the high-valent ironoxo species from 1(H2O)/cmSiN (Fig. 2b) wasmonitored by O K-edge XAS spectra in a 100 mM
phosphate buﬀer (pH = 7.0) by using a beamline
equipped with a transmission-type liquid flow cell in
BL3U of UVSOR [2]. The measurements were
performed by changing the applied voltage to 1(H2O)/
cmSiN. The spectra were obtained by the LambertBeer law, ln(I0/I), where I0 is the transmission signals of
the cmSiN in buﬀer and I is those of 1(H2O)/cmSiN at
diﬀerent applied voltage in buﬀer.
It was found that the broad peak around 532 eV wasapparently appeared when applying the voltage of 1.8

V vs. Ag/AgCl (Fig. 2c). Taking that DFT calculation
indicated that the peak of O1s – π* of Fe=O for 1oxoshould appear at around 529 eV, whereas the peaks for
1 having a coordinating H2O should be observed at
higher energy than 534 eV, it is considered that the peak
appeared at around 532 eV is assignable to the excitationof O1s – π* of Fe=O of electrochemically generated
high-valent iron-oxo species of 1(H2O)/cmSiN (1oxo/
cmSiN). We are going to check the CH4 oxidation
activity of electrochemically generated 1oxo/cmSiN.
(a)
O
N
N

N

N

N
N

N

N
N

N

CH4

N

N

N
N

H2O2

FeN4+ NN

N

FeN4+ N
N

N
N

N

0

N
N

FeN3+ N

N

N

N

FeN4+ N
N

CH3OH
HCHO
HCOOH

Graphite

1oxo/G

1/G
(b)
OH2
N
N
N

N

N

N
Fe3+
N

Electrochemical
Oxidation

O
N
N

N

N

N

N
N

N

FeN4+ N
N

N
N

0

N
N

N

–2H+–2e–N

FeN4+ N

N

N
N

N

FeN4+ NN

N

Graphite1(H2O)/G

1oxo/G

Fig. 1. Generation of 1oxo/G from 1/G (a) by using H2O2or (b) by electrochemical oxidation.
(a)

(c)

N
N

N
N

N

FeN3+ N
N

N

N
N

N
N

N

FeN4+ N

1.8 V vs. Ag/AgClN

C membrane~ 20 nmRest potential
SiN membrane

1/cmSiN

(b)

OH2
N
N

N
N

N

FeN3+ N
N

N

N
N

N
N

N

FeN4+ NN

C membrane
SiN membrane

1(H2O)/cmSiN

Fig. 2. Structures of (a) 1/cmSiN and (b) 1(H2O)/
cmSiN. (c) Comparison of O K-edge XAS spectra of1(H2O)/cmSiN at rest potential (blue) and 1(H2O)/
cmSiN at the applied potential of 1.8 V vs. Ag/AgCl.
[1] Y. Yamada, M. Nagasaka et al., JACS Au. DOI :10.1021/jacsau.2c00618.
[2] M. Nagasaka and N, Kosugi, Chem. Lett. 50 (2021)
956.

− 74 −

Ⅲ-2 Material Sciences

BL3U

Structural Analysis of fluoro-polymers Using Resonant Soft x-ray Scattering
K. Yamanoi 1, 2, M. Yamashita1, Y. Yamamoto1, H. Iwayama3 and M. Noumi2
1Institute of Laser Engineering, Osaka university, Suita, Osaka, 565-0871, Japan2
DAIKIN Industries Ltd, Settsu, Osaka, 566-8585, Japan
3
UVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan

Fluoropolymers or sometimes referred to as
fluororesins have been widely used for chemical,
electrical, and medical applications because of theirhigh chemical resistance, mechanical strength,hydrophobicity, heat resistance, low surface energies,
low coeﬃcients of friction, and low dielectric constants[1-3]. These favorable properties stem from theelectronic structure of the fluorine (F) atom, the stablecarbon-fluorine (C-F) covalent bond, and the uniqueintramolecular and intermolecular interactions between
the polymers’ fluorinated segments and main chains[4]. Based on their structure and composition,
fluoropolymers can be classified as partially fluorinatedpolymers or perfluoropolymers. Partially fluorinatedpolymers contain F and hydrogen (H) atoms in theirstructures, while perfluoropolymers only contain F
atoms, i.e., the H atoms are replaced with F atoms. For
example, polyvinylidene fluoride (PVdF) is a very
processable and mechanically strong partiallyfluorinated polymer, whereas polytetrafluoroethylene(PTFE) is a chemically strong and heat-resistant
perfluoropolymer.
Among their diﬀerent applications, modified PTFE
which includes oxygen component in the polymer isused to fuel injectors and as packing and linings ofhigh-pressure vessels. Consequently, the ability todirectly observe the oxygen related microscopic
morphology is very important in revealing polymer
function. As PTFE is known to have semi-crystalline,
lamellar structures consisting of both amorphous andcrystal phases [5], small-angle x-ray scattering (SAXS)
technique is the most appropriate method to study theinternal morphologies of these fluoropolymers within
the 10 to 100-nm range. Additionally, the Resonant
Soft X-ray Scattering (RSoXS) is attractive method toobserve the structure related with specific chemicalbond in mesoscopic region.
Previously, SAXS has been used to investigate themorphology of PTFE and their co-polymers under
supercritical carbon dioxide condition [6]. In thisresearch the RSoXS method was used in BL3U,UVSOR facility on the modified PTFE sample.
The sample was sliced to 1 μm thickness andsandwiched with Si3N4 membrane. Soft x-ray isirradiated on the sample through the Si3N4 membrane
and the scattered soft x-ray is monitored by camera at
the position of 2θ=7.5 and 30°. The x-ray energy istuned at 540 eV which is resonant with oxygen bonging
in polymer.
Figure 1 shows the results of scattering patterns of
540 eV comparing with the 528 eV which is notresonant with oxygen bonding.
We could observe the diﬀerence around the higher
angle corresponding to smaller structure between
resonant and non-resonant x-rays. This result shows theoxygen bonding related structure has the smaller crystal
structure compared with others, however the scattered
x-ray signal was weak since the sample was muchthick. For the detailed discussion of oxygen bonding
related structure, more thinner sample is required.

Fig. 1. Scattering patterns of RSoXS with 540 eV and
528 eV[1] S. Ebnesajjad, P. R. Khaladkar, Fluoropolymer
applications in the chemical processing industries(Second Edition), William Andrew Publishing (2017).
[2] Z. Cui, E. Drioli, Y. M. Lee, Prog. Polym. Sci. 39(2014) 164.
[3] G. Eberle, H. Schmidt, W. Eisenmenger, IEEE
Trans. Dielectr. Electr. Insul. 3 (1996) 624.
[4] H. Teng, Appl. Sci 2 (2012) 496.
[5] A. Marigo, C. Marega, R. Zannetti, G. Ajroldi,
Macromolecules 29 (1996) 2197.
[6] K. Yamanoi, S. Shibuta, A. Shiro, M. Noumi, M. J.
F. Empizo, M. Cadatal-Raduban, N. Sarukura, K.
Nishikawa, and T. Morita, J. Supercrit. Fluids, May
2022 vol. 184 (2022) 105555.

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BL3U

Structure Analysis on Chiral Dark Conglomerate of Achiral Liquid Crystal
Trimers by Resonant Soft X-ray Scattering (RSoXS) at UVSOR
Y. Takanishi1, F. Araoka2 and H. Iwayama3,4
1

Faculty of Science, Kyoto University, Kitashirakawa-oiwake, Sakyo, Kyoto, 606-8502, JapanRIKEN Center for Emergent Matter Science, Hirosawa 2-1, Wako, Saitama 351-0198, Japan
3
UVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
4
School of Physical Sciences, The Graduate University for Advanced Studies (SOKENDAI),
Okazaki 444-8585, Japan

2

Spontaneous chiral symmetry breaking in soft matteris one of most attractive topics. Liquid crystal (LC) isa typical one of soft matter, and bent-core molecules
show unique LC phases. The B4 phase is the lowest
temperature phase observed in the bent-core liquid
crystals, and it shows spontaneously chiral separated
domains despite of achiral molecules. Recently it isreported that some kinds of rod-like LC trimers also
show similar DC phase caused by unique molecular
packing by designing intermolecular interactions.
Yoshizawa’s group studied intensively achiral LC
trimers exhibiting DC phase. They systematicallysynthesized LC trimers, and reported that the DC phaseis stabilized in (a) equimolecular mixture of nematicand smectic trimers, (b) binary mixtures of a nematic
trimer with biphenyl units at the center and cyanobiphenyl compound and (c) a single asymmetric trimer.
In resonant X-ray scattering, using X-ray whoseenergy is coincident with a certain atom absorption
edge, the structure factor becomes a tensor instead of
the scalar in conventional X-ray diﬀraction. Carbon
K-edge resonant soft x-ray scattering (RSoXS) has
been applied to study, and successful in obtaining the
precise structures of polymer blends, block copolymer,
and LCs. Recently one of authors (YT) studied thebinary system between a rod-like cholesteric LC
mixture and a bent-core LC showing B4, and found a
new smectic structure that does not appear in only
constituent molecules with wide temperature range was
unexpectedly discovered. Last year, the structure ofhelical nano-filament of B4 phase in the nano phaseseparation of cholesteric liquid crystal mixture and abent-core molecule was analyzed using RSoXS to
study the eﬀect on the nano-helical filament in thismixture. We summarized that the pitch of helicalfilament decreases and coherence of helical structure
increases, which would be caused by the interaction
between bent-core and rod-like molecules.[1]In this study, we report the local nano-structure
analysis of DC conglomerate phase in achiral LC trimer
using resonant soft-X-ray scattering (RSoXS)
technique. Small angle and wide angle scattering were
measured and alkyl chain length dependence of rodlike molecules was discussed.
The experiment was performed at BL3U of UVSOR.
Used achiral liquid crystal trimers are I-(m,n), as shownin Fig. 1. In this study, m is fixed to 9, and n changes

from 7~11. Samples used were filled in the isotropic
phase between two pieces of 100 nm-thick Si3N4
membranes (Norcada). The scattering was detected by
CCD (ANDOR DO940P-BN). Incident X-ray beam
was tuned between 270~300eV. In these compounds,
carbon K-edge energy was 284.5 eV.
Figure 2 shows 2D small-angle RSoXS images of (a)I-(9,7), (b)I-(9,9) and (c)I-(9,11). Resonant scatteringpeaks are clearly observed, and with the increase of
spacer chain length n, the long-range periodicity
corresponding to the peak increases from ca. 900~1300
nm. In I-(9,9), tubercle structures a are seen by STEM
observation, but its diameter was about 200 nm, andhence our results suggest the existence of the longerrange periodic structure.
Figure 3 shows 2D wide-angle RSoXS images of (a)I-(9,7), (b)I-(9,9) and (c)I-(9,11). Even in these images,
clear sharp peaks are observed, and the corresponding
periodicity are ca. 70~80Å, which increases with theincrease in the spacer chain length n. Since the layer
thickness by conventional X-ray scattering are ca.40Å,these results indicate that LC trimers form intercalated
bilayer structure.

Fig. 1. Chemical structure of I-(m,n).
(a)

(b)

(c)

Fig. 2. 2D small-angle RSoXS images of (a)I-(9,7), (b)I-(9,9) and (c)I-(9,11).
(a)

(b)

(c)

Fig. 3. 2D wide-angle RSoXS images of (a)I-(9,7), (b)I-(9,9) and (c)I-(9,11).
[1] Y. Takanishi, Soft Matter, 17 (2021) 563.

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Ⅲ-2 Material Sciences

BL3B

Measurements of Fluorescence Lifetimes of Scintillators Adopted for a New
in-beam Detector of the ࡷ૙ࡸ Rare Decay Experiment at J-PARC
K. Shintate, R. Abe, Y. Hayashi, T. Naito, S. Sakano, J. Ohashi, Y. Tajima and H.Y. Yoshida
Department of Physics, Yamagata University, 990-8560, Japan

J-PARC E-14 KOTO [1] is the experiment ofsearching for the direct CP violating decay‫ܭ‬௅ ՜ ߨ ଴ ߥߥҧ . This decay mode is considered to besensitive to new physics beyond the Standard Model(SM), and its branching ratio is predicted to be 3.0×10-11
in the SM with about 2% theoretical uncertainly.
The cross-sectional view of the KOTO detector isshown in Fig.1. The upper limit currently obtained on
the branching fraction of ‫ܭ‬௅ ՜ ߨ ଴ ߥߥҧ decay is 3.0×10-9
at the 90% confidence level [2].
One of the main backgrounds is caused by ‫ ܭ‬± decays
in the beam. To reduce this background by detecting‫ ܭ‬± , we are planning to install an in-beam charged
particle detector with a scintillator of 0.2 mm thickness
named UCV (Upstream Charged Veto, Fig.2). The
scintillator used for UCV is required to have suﬃcient
light yield and short fluorescence lifetime. We measured
fluorescence spectra and decay curves of the scintillator
to evaluate the performance of UCV as a particle
detector.

Fig. 1. Cross-sectional view of the KOTO detector.
The beam enters from the left. Detector components
with their abbreviated names written in blue (in green
and underlined) are photon (charged-particle) vetocounters. The UCV detector is installed at the upstream(left) end of the KOTO detector.

Fig. 3 shows the 2D fluorescence spectra of the UCV
scintillator. Fig. 4 shows the decay curve for the 432
nm band under excitation at 284 nm. The blue line
indicates experimental data. The red line is the fitting
curve consists of two fluorescence lifetimes andreproduces the experimental data. The fitting results
analyzed by using the data analysis framework named“ROOT” [3] are summarized in Table 1.

Fig. 3. 2D fluorescence spectra of the UCV scintillator.
Y-axis is excitation wave length (nm), and x-axis isemission wave length (nm).

Fig. 4. Decay curve of the UCV scintillator for the 432
nm band under excitation at 284 nm.
Table 1. Fluorescence lifetimes of the UCV scintillator,
determined from our data analysis.

SampleUCV

Fig. 2. The UCV detector. To install in the beam line,
the scintillators are made as thin as 0.2mm thick andscintillating lights are detected by photomultipliertubes (PMTs) using reflector sheets.

ȜEX
[nm]
284

ȜEM
[nm]
432

Ĳ1[ns](Ratio)1.9(91.4%)

Ĳ2[ns](Ratio)20.3(8.6%)[1] J. Comfort et al., Proposal for ‫ܭ‬௅ ՜ ߨ ଴ ߥߥҧExperiment at J-PARC (2006).
[2] J. Ahn et al. (KOTO Collaboration), Phys. Rev.
Lett. 122 (2019) 021802.
[3] R. Brun and F. Rademakers, Nucl. Instrum. Methods
Phys. Res. A 389 (1997) 81.

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BL3B

Material Search of Li-Containing Halide Scintillators for Neutron Detection
C. Fujiwara1,2, S. Kurosawa2,3,4 and A. Yamaji2,31

Department of Materials Science, Graduate School of Engineering, Tohoku University, Sendai, Japan
2
Institute for Materials Research (IMR), Tohoku University, Sendai, Japan3
New Industry Creation Hatchery Center (NICHe), Tohoku University, Sendai, Japan
4
Institute of Laser Engineering, Osaka University, Osaka, Japan

A remote real-time radiation detector consisting of ascintillator and optical fiber is required to achieve thedecommissioning of the Fukushima Daiichi Nuclear
Power Plant[1]. The scintillator for this application isrequired to have an emission wavelength of 550 nm or
longer and high light output from the viewpoint oftransmission eﬃciency in the optical fiber and reductionof optical fiber-derived noise[2][3]. In addition,neutrons-emitting debris is expected to be present
inside the reactor, and neutron-sensitive scintillationmaterials are needed. Due to the above reason, we havedeveloped Li2HfI6 as a candidate material [4], while
Li2HfI6 contains a heavy element, Hf with a highdetection eﬃciency for gamma rays. Therefore, in thisstudy, Li2ZrX6 (X=Cl, Br, I) was prepared by replacing
Hf with Zr, and its luminescence properties were
investigated.
Li2ZrX6 crystal specimen was synthesized by thevertical Bridgman growth method in our laboratory
using 99.9%-pure LiCl, LiBr and LiI powders, and
99%-pure ZrCl4, ZrBr4 and ZrI4 powders were used. We
measured the photoluminescence excitation andemission spectrum from 50 to 300K at UVSOR BL3B
beam line.
As shown in Fig.1(a), Li2ZrCl6 showed broad
luminescence with a peak at 570 nm at an excitation
wavelength of 300 nm at 50K. Although theluminescence intensity decreased as the temperature
increased, no significant change in both the excitationand emission wavelengths were observed. The emission
wavelength was 580 nm at the excitation wavelength of
300 nm at room temperature. This wavelength range
satisfies the above requirement, and Li2ZrCl6 can be a
candidate material for neutron detection with opticalfiber.
Fig.1(b) showed the emission spectrum of Li2ZrBr6
as a function of temperatures. Li2ZrBr6 shows a broad
emission with a peak at 580 nm at an excitation
wavelength of 305 nm at 50 K. When the temperature
is increased, the emission intensity decreases, and theemission wavelength became shorter.
Fig. 1(c) shows the emission spectrum of Li2ZrI6, and
Li2ZrI6 had red and near-infrared emission with theemission wavelength of 670 nm at an excitation
wavelength of 430 nm at 50 K. However, the emission
intensity decreases significantly as the temperature
increases, and no emission is observed at room
temperature.
From these results, LiZrCl6 was found to be a

candidate material for neutron detection using an
optical fiber. In the future, we plan to investigate thelight output by neutron excitation and conduct a
detection test by connecting the optical fiber.

Fig. 1. Photoluminescence spectrum at each temperaturefor (a) Li2ZrCl6, (b)Li2ZrBr6, (c)Li2ZrI6[1] I. Wakaida, Topic. Fukushima 70 (2015) 1.
[2] C. and H. Ltd, Opt. Quantum Electron 13 (1981) 85.
[3] H. Liu et al., Rev. Sci. Instrum. 89 (2018) 083302.
[4] C. Fujiwara, K. Shunsuke, and Y. Akihiro, UVSOR
Activity Report 49 (2021) 84.

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Ⅲ-2 Material Sciences

BL3B

Optical Properties of Cs2IrCl6-CsCl Composite Phosphor
S. Kodama, S. Omiya, N. Shimoyama, T. Saito, I. Yanase and H. Takeda
Saitama University, Saitama 338-8570, Japan

Cs2HfCl6 was reported as the novel single-crystalline
inorganic scintillator with a high light output and agood energy resolution [1]. Cs2HfCl6 exhibits the strong
intrinsic luminescence at the blue region. Several
luminescence origins were suggested for Cs2HfCl6 [23], however, the detailed mechanism was still unclear.
In this study, we focused on the charge transitiontransfer (CT) phenomena. Inorganic crystals which
consist an isolated anion complex show the CT
luminescence. In order to occur the CT luminescence,the peripheral electron orbital of the center metal ion in
the anion complex should be empty. The crystal
structure of Cs2HfCl6 consists Cs+ ions and isolated[HfCl6]2- anion complexes. In addition, the electron
orbital of Hf 4+ of [HfCl6]2- anion complex is empty, thus
we assumed that the intrinsic luminescence of Cs2HfCl6
can be attributed to be CT luminescence.
To distinguish the CT luminescence from otherluminescence origins such as the self-trappedluminescence or the defect luminescence, therefore inthis study, we synthesized Cs2IrCl6 and compared theoptical properties with Cs2HfCl6. Although Cs2IrCl6 has
the same crystal structure as Cs2HfCl6, the peripheral
electron orbital of Ir4+ of [IrCl6]2- is not empty, therefore,
Cs2IrCl6 must not exhibit the CT luminescence. If someluminescence was observed in Cs2IrCl6, the CT
luminescence should not occur in Cs2HfCl6.
Cs2IrCl6 was synthesized from the starting powdersof CsCl and IrCl4. The melted specimen included
Cs2IrCl6 and CsCl phases, thus we represent theobtained specimen to be Cs2IrCl6-CsCl composite.
Additionally, in order to compare the optical properties,
non-doped CsCl and Ir:CsCl crystals were grown.
Figure 1 shows the photoluminescence spectra ofCs2IrCl6-CsCl composite, CsCl and Ir:CsCl. At 300K,
all specimens showed the single emission peak at ~310
nm excited by 254 nm. In addition to ~310 nm band, allspecimens showed another emission peak at ~420 nm
at 300K. The emission peaks of Cs2IrCl6-CsClcomposite and Ir:CsCl well corresponded to that of
CsCl, therefore, Cs2IrCl6 was concluded to show noluminescence originated from the self-trapped excitons
or defects. Based on the obtained results, theluminescence origin of Cs2HfCl6 might be assumed tobe the CT luminescence.

Fig. 1. Photoluminescence spectra of Cs2IrCl6-CsClcomposite (represented as CIC+CsCl), CsCl and
Ir:CsCl at (a) 300K and (b) 10K.
[1] A Burger et al., Appl. Phys. Lett 107 (2015) 34.
[2] B. Kang and K. Biswas, J. Phys. Chem. C 120(2016) 12187.
[3] R. Král et al., J. Phys. Chem. C 121 (2017) 12375.

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BL3B, 6B

Visible-to-Ultraviolet Spectral Change with the Current-Induced Local-toNonlocal Transition of SmS
H. Watanabe1,2, S. Tatsukawa2, K. Imura3, H. S. Suzuki4, N. K. Sato5 and S. Kimura1,2,6
1
Graduate School of Frontier Biosciences, Osaka University, Suita 565-0871, Japan
Department of Physics, Graduate School of Science, Osaka University, Toyonaka 560-0043, Japan
3
Institute of Liberal Arts and Sciences, Nagoya University, Nagoya 464-8602, Japan
4
Institute for Solid State Physics, The University of Tokyo, Kashiwa 277-8581, Japan
5
Center for General Education, Aichi Institute of Technology, Toyota, 470-0392 Japan
6
Institute for Molecular Science, Okazaki 444-8585, Japan

2

Samarium monosulfide SmS exhibits the phasetransition from a black-colored semiconductor to agolden-colored metal (BGT) by applying pressure
above 0.7 GPa [1,2]. The origin of the BGT is now still
under debate. Among the possible origins, the transition
between Bose-Einstein condensation and BCS state of
excitons is currently being discussed [3,4], but nodefinitive evidence has been obtained. Recently, Andoet al. reported the nonlinear relation between thevoltage (V) and electric current (I) with increasing
current at lower temperatures than 100 K, whichsuggests a drastic change in the electrical resistivity [5].
It is unclear whether the nonlinear V/I relation is related
to pressure-induced BGT. To clarify the origin of thenonlinear V/I curve and its relation to the BGT, we haveinvestigated the current and temperature dependenciesof the reflectivity spectrum in the THz and IR regions.
We have already reported the carrier character change
from the high increasing rate (dN/dI) and the highrelaxation time (τ) of carriers at the region of low
temperature and low current to low dN/dI and low τ athigh temperature or high current regions [6,7].
The origin of the character change of carriers can be
attributed to an electron delocalization, in which thelocalized electrons trapped at Sm sites start moving by
the applied current. In this case, the electronic structure
is modified, and finally, the band gap is expected to beclosed, but it has not been revealed. In the visibleultraviolet region, there are excitations from occupied
4f states to the unoccupied 5d states. It is expected to beable to observe changes in the reflectivity spectrum dueto the modification in the electronic structure, such as aband gap narrowing. To observe the current-induced
spectral change in SmS, we measured the current
dependence of the visible-ultraviolet reflectance at
BL3B.
Single crystalline SmS with a typical sample size of
1×1×1 mm3 was sandwiched by the electrodesconnected to the current source. The sample was cooled
down to 30 K during the experiment.
Figure 1 shows the applied current dependence of thevisible-ultraviolet reflectivity spectrum. With increasing
applied current, the intensity of a peak at 3 eV decreases,
and a shoulder at about 6 eV shifts to low energy. In

addition to the spectral change, an oscillation inreflectivity appeared between 4 to 6 eV, which is
expected to be due to a change in the surface condition,
but the exact origin is not clarified. From these results,
although we observed a slight change in the reflectivity
spectrum in the visible-ultraviolet region due to thecurrent application, these could not suggest a drasticchange in the electronic structure, such as a shift in theoverall band structure due to a change of the band gap.
In summary, the application of electric current gives
energy to the electrons, causing delocalization.
However, the results suggest that the applied current
does not influence the electronic structure far from theFermi level.

Fig. 1. Current dependence of the visible-to-ultraviolet
reflectivity spectrum of SmS at 30 K.
[1] A. Jayaraman et al., PRL 25 (1970) 1430.
[2] T. Mizuno et al., JPSJ 77 (2008) 113704.
[3] B. I. Halperin and T. M. Rice, RMP 40 (1968) 755.
[4] S. Watanabe, JPSJ 90 (2021) 023706.
[5] H. Ando et al., JPS Conf. Proc. 30 (2020) 011132.
[6] H. Watanabe et al, UVSOR Activity Report 2021
(2022) 92.
[7] S. Kimura et al., arXiv: 2302.12998 (2023).

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Ⅲ-2 Material Sciences

BL3B

Exciton States of Cesium Silver Iodide Crystals
S. Ibuki and T. Kawai
Graduate School of science, Osaka Metropolitan University, Sakai 599-8531, Japanߝሺ߱ሻ ൌ ߝ௥ ൅ ݅ߝ௜ൌ ߝ௕ ൅

݂ଵଶ߱௘௫ଵ െ ߱ ଶ െ ݅߱ߛଵ
൅350

where |ε | = (εr2 + εi2)1/2. From the best-fitting analysis,

Wavelength (nm)
250

200

Reflection (arb. units)

CsAg2I3
12 K

4.0

4.5
5.0
5.5
Photon Energy (eV)

6.0

6.5

Fig. 1. Reflection spectrum of the CsAg2I3 crystal at
12K.
340

Wavelength (nm)
330
320

310

CsAg2I3
12 K

3.6

1 ൅ |ߝ| െ ඥ2ሺ|ߝ| ൅ ߝ௥ ሻ
1 ൅ |ߝ| ൅ ඥ2ሺ|ߝ| ൅ ߝ௥ ሻ

300

3.5

݂ଶ
ଶ
߱௘௫ଶ
െ ߱ ଶ െ ݅߱ߛଶwhere εr and εi are the real and imaginary parts of thedielectric constant, respectively, ωex1,2 is the resonancefrequency of the excitons, εb the background dielectric
constant, f1,2 oscillator strength, and γ the damping
constant. The reflectance R is given byܴൌ

which is shown by the broken curve in Fig.2, theresonance energies of the excitons were estimated to be
3.78 and 3.87 eV.
As future works, we are planning to investigate theoptical properties of ternary sliver iodides such as
Cs2AgI3.

Reflection (arb. units)

In the past decade, ternary lead halides have attracted
wide interest in the field of applications, including
scintillator materials, photodetectors, and solar cells[1]. However, the environmental toxicity of the lead isamong the significant concerns in this field. Therefore,
considerable eﬀorts have been devoted to developing
alternative eco-friendly lead-free ternary metal halide.
In this study, we focused on ternary sliver iodides suchas CsAg2I3.
CsAg2I3 compounds were obtained by the Bridgman
method from high purity CsI and AgI powders, whichwere mixed in a stoichiometric ratio. The thin crystals
of CsAg2I3 were prepared by a cell method [2]. The
quartz-cells with the narrow gap are made of a pair of
two quartz plates. The melt of CsAg2I3 compounds was
percolated into the gap of the quartz-cells throughcapillary action and the thin crystals were grown in the
gap by natural cooling.
Figure 1 shows the reflection spectrum of the CsAg2I3
crystal at 12 K in the energy region of 3.5 ~ 6.5 eV. The
sharp dispersion-like structures due to band-edge
excitons are observed around 3.8 eV. Furthermore, thebroad reflection peaks are observed around 4.6 and 5.1
eV. The energy values are consistent with those of theabsorption bands reported in a previous paper [3].
Now, we confine one’s attention to the dispersionlike structures due to the band-edge excitons around 3.8
eV. The reflection spectrum magnified around thedispersion-like structures is shown in Fig.2. Two
dispersion-like structures are confirmed. We attempted
to fit the reflection structures by using the simple
oscillators model with two close-lying resonances.
Then, the dielectric function is represented by thefollowing expression:

3.7
3.8
3.9
Photon Energy (eV)

4.0

4.1

Fig. 2. Reflection spectrum of the CsAg2I3 crystals inthe band-edge exciton region at 12 K. Broken curve isthe fitting result calculated with the two-oscillator
model.
[1] J. Yuan, et. al, Joule 4 (2020)1160.
[2] S. Hashimoto and M. Itoh, Jpn. J. Appl. Phys. 27(1988) 726.
[3] V. K. Miloslavskii, et. al, Solid State Spectro. 80(1996) 577.

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BL3B

Temperature Dependence of Excitation Spectra in Er-doped La2Zr2O7
M. Yoshino and M. Ito
Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan

Based on our first-principles calculations, Er
substituted for La in pyrochlore-type oxide, La2Zr2O7(LZO) has multiple stable positions with significant
displacements from the original La position, and is
expected to spread in a disc shape at room temperature.
This combination of static and dynamic disorderproduces diversity in the Er coordination environment,
and the transition spectrum of Er3+ is expected to havea broad shape due to the overlap of each environment
case. At low temperatures, the transition spectra
become sharper due to the decrease in the dynamic
disorder. Therefore, we measured the excitation spectraof Er-doped LZO from low temperature to room
temperature. For comparison, we also measured Erdoped Y2Ti2O7 (YTO) with pyrochlore-type structure,
Y0.5Zr0.5O1.75 (YZO) with defect fluorite structure, andY3Ga5O12 (YGG) with garnet-type structure. Er in YTO
and YGG have small displacements, and Er in YZO has
static disorder but less dynamic disorder, so thetemperature dependence of their spectral shapes is
expected to be small. Fig. 1 shows the excitation
spectrum of LZO with emission wavelength of 560 nm.
Results from 20 K to 100 K are shown here, but
measurements were also performed up to 300 K. To
examine the temperature dependence of the spectral
shape, we normalized the spectra using the peak withthe maximum intensity at 20 K. Fig. 2 and Fig. 3 show
the results for YZO and YTO, respectively. In eachcase, the spectral shape becomes broader withincreasing temperature. To compare their temperaturedependences, we estimated the change in the height ofthe valley between peaks around 380 nm with respect
to the 20 K case as shown in Fig. 4. It was found that
LZO tends to have a larger change in the height of thevalley than the other samples, resulting in broad spectra.
This indicates that the temperature dependence is larger
for LZO.

Fig. 1. Excitation spectra of La2Zr2O7 : Er( λem = 560 nm ).

Fig. 2. Excitation spectra of Y2Zr2O7 : Er( λem = 560 nm ).

Fig. 3. Excitation spectra of Y2Ti2O7 : Er( λem = 560 nm ).

Fig. 4. Change in the height of the valley between
peaks around 380 nm.

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Ⅲ-2 Material Sciences

BL4U

Analysis of Cathode Materials for Li-Ion Batteries by STXM
E. Hosono1,2,3, D. Asakura1,2,3, H. Yuzawa4, T. Ohigashi4,5, W. Zhang6, M. Kobayashi7,8,
H. Kiuchi6 and Y. Harada3,6,9
1

Global Zero Emission Research Center, National Institute of Advanced Industrial Science and Technology (AIST),
Tsukuba, Ibaraki 305-8569, Japan
2
Research Institute for Energy Conservation, AIST, Tsukuba, Ibaraki 305-8565, Japan
3
AIST-UTokyo Advanced Operando Measurement Technology Open Innovation Laboratory (Operando-OIL),
Kashiwa, Chiba 277-8565, Japan
4
UVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
5
School of Physical Sciences, The Graduate University for Advanced Studies (SOKENDAI),
Okazaki 444-8585, Japan
6
Institute for Solid State Physics (ISSP), The University of Tokyo,
5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8581, Japan
7
Department of Electrical Engineering and Information Systems, The University of Tokyo,
7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
8
Center for Spintronic Research Network, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo
9
Synchrotron Radiation Research Organization, The University of Tokyo,
7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8656, JapanThe development of clean energy devices is attracting
attention toward the realization of a low-carbon society
for preventing global warming. Since lithium ion
batteries (LIBs) are expected to be broadly used forsuch as electric vehicles and stationary types for homeuse, their devices are the most actively investigated inboth industry and academia fields. However, the market
demand for improved performance of LIBs is still
extremely high, and the development of innovative
materials for LIBs is essential to exceed significantly
the current performance. To solve this diﬃcult problem,
characterization of component materials for LIBs is
crucially important.
We have been analyzing electrode active materials byabsorption and emission spectroscopy usingsynchrotron soft X-rays in order to clarify the detailed
electronic states of the materials. In addition, we havealso been analyzing them by microscopic photoelectron
spectroscopy using synchrotron soft X-rays. The LIBs
are devices that stores energy by the insertion anddiﬀusion of Li into the host crystal, which is strongly
dependent on the local environment of the active
materials. Therefore, local analysis can provide
important information for understanding the chargedischarge mechanism. Photoelectron spectroscopy is asurface-sensitive method, while scanning transmission
X-ray microscopy (STXM) is a bulk-sensitive method
because of its transmission.
In this study, we applied STXM analysis to most
famous LIB cathode material, LiCoO2 (LCO). Figure 1
shows the Co L3-edge X-ray absorption spectra (XAS)of the initial (dotted line) and charged (solid line)
conditions of LCO. By using STXM, we were able toobtain XAS spectra of selected areas and visualize the
distribution of the oxidation state of LCO. The details
were reported in ref. [1].

Fig. 1. Co L3-edge XAS of the initial (dotted line) andcharged (solid line) conditions of LCO. Panel (a) shows
average spectra of selected particles including area 1-5(circle areas: 300 nm diameter). Panel (b) shows
extracted spectra from area 1-5, which exhibit diﬀerent
charging states (oxidation states) from each other.
[1] W.X. Zhang et al., Sci. Rep. 13 (2023) 4639.

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BL4U

Unraveling the Origin of Irreversibility between the First and Second
Charging Process in Primary Conversion Anode Particle
J. Kim 1, J. Chung1, T. Ohigashi2, H. Yuzawa2 and J. Lim1
Department of Chemistry, Seoul National University; 1 Gwanak-ro, Gwanak-gu, Seoul 08826, Republic of Korea
2
UVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan

Among the various candidates for rechargeable
lithium-ion battery anode, alpha-hematite (α-Fe2O3)
has been actively investigated due to its high theoretical
capacity (1007 mA∙h/g), low processing cost, abundantremaining source, and nontoxicity. Despite theseadvantages, commercialization of α-Fe2O3 anode ischallenging due to the fast capacity fading, particularly
occurring in first and second charging process. A
previous report proposed the three reaction pathways inthe first charging process of α-Fe2O3 [1]. First step:
monophasic insertion reaction; (1) Fe2O3 + xLi+ →LixFe2O3. Subsequent second and third steps: biphasic
conversion reaction; (2) LixFe2O3 + (2-x) Li+ → 2FeO +Li2O and (3) 2FeO + 4Li+ → 2Fe + 2Li2O. From ourelectrochemistry data (Fig. 1), it shows that the voltage
plateau in the first charging is attributed to (2) and (3)distinct conversion reactions. Since this conversion
reaction produces an (ir)reversible reaction product(i.e., Li2O), we hypothesize that the local reaction
pathway of subsequent electrochemical cycles could be
influenced by the site-specific Li2O formation in firstcycle. The Li2O, well-known insulating material,
increases reaction overpotential which allows the
sluggish reaction kinetics of the host material.
To reveal this degradation mechanism, we note thatthe nanoscale chemical distribution of α-Fe2O3 single
particle at first charged/discharged states should be
identified. The compositional heterogeneity within theintraparticle in first charging process allows us toinvestigate non-uniform intraparticle distribution of
Li2O, which insulates the subsequent electrochemical
reaction. Furthermore, to unravel reaction hysteresis in
first battery cycle in Fig. 1, it is essential for capturing
the chemical distribution of α-Fe2O3 at first discharged
state which are entangled with the first charging
process. Thus, we conducted ex-situ STXM
measurement of first charged/discharged states of
α-Fe2O3 at UVSOR BL4U.
Fig. 2 shows chemical composition maps at pristine,
first charged state, and first discharged state, revealingthat chemical distribution of Fe phases is inhomogeneous
within the single particle. In Fig 2b, fully charged Fephase (Fe0) was partially formed and randomly
distributed, suggesting that insulating Li2O species was
generated in the first charge regardless of any specificlocation. In Fig. 2c, the discharging end phase was not

fully recovered to the pristine state (Fe3+). Thisobservation correlates with some previous reports [2,3], claiming that existence of various discharging
reaction pathways; (4) 2Fe + 3Li2O → Fe2O3 + 6Li+, (5)Fe + Li2O → FeO + 2Li+ and (6) 3Li2O + 2Fe →1.5LiFeO2 + 0.5Fe. From our results, we conclude that
intraparticle heterogeneity evolves in first charging
process (conversion reaction) and this inhomogeneity
could be aﬀected by the distribution of the reaction
product (Li2O), resulting in irreversibility of (dis)charging process.
3.0
2.5
2.0

Voltage (V)1

1.5

Reaction hysteresis
1.0

Capacity loss

0.5
0.0
0

200

400

600

800

1000

1200

Specific Capacity (mAh g-1)

Fig. 1. Charge/discharge profiles of the synthesized α-Fe2O3 at 0.1 C current rate. (Unpublished)ab
Pristine(Fe2O3)cFirrst charging(at 0.05 V)

Fe0

First discharging(at 3.0 V)

Fe3+

Fig. 2. Chemical composition maps at a. pristine, b.
first charged state (0.05 V vs. Li/Li+), and c. firstdischarged state (3.0 V vs. Li/Li+). Scale bars below
each image are 1 um.
[1] A. Banerjee, et al., Nano Energy 2 (2013) 890.
[2] T. C. Christie, et al., Journal of Materials Chemistry22 (2012) 12198.
[3] Su. Qingmei, et al., ACS Nano 7 (2013) 9115.

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BL4U

Chemical Bonding Structures of SBR/BR Interfaces
T. Ejima1 and Y. Tamura2
1
SRIS, Tohoku University, Sendai 980-8577, JapanENEOS Materials Corp., Yokkaichi 510-0871, Japan

2

Rubber materials used in tires often have multiple
elastomers to achieve desired properties. Combining
styrene-butadiene rubber (SBR) and butadiene rubber(BR) can enhance skid and rolling resistance, but
increasing styrene content can reduce low-temperature
performance. By using high cis-1,4 BR instead of BR
and adding it to SBR, the glass transition temperature(Tg) can be controlled, and low-temperature
performance can improve [1-3]. The study used SBR
and BR to fabricate interface structures with NEXAFS
spectra, clarifying chemical bonding states.
Understanding these states can clarify complex
elastomer properties.
The preparation of the samples involved compounding
SBR-A, SBR-B, and BR with a 75 ml plast mill (ToyoSeiki). The diﬀerence of the types of SBR is thediﬀerence of the crosslink density: The A type SBR(SBR-A) is normal one and the B type has a highcrosslink density (SBR-B). The prepared samples werethen cut into sheet shapes, and these sheets were
subsequently laminated together to form a SBR-A/BR
interface sheet and a SBR-B/BR interface sheet.
Furthermore, a sample SBR-B/BR was kneaded bycompounding SBR-B and BR at a ratio of 70:30. The
resulting SBR-A/BR and SBR-B/BR interface sheets
and kneaded SBR-B/BR sheet were sliced using an
ultramicrotome, placed on an electron microscope grid,
fixed to a dedicated STXM sample holder. The thicknessof the sample was fixed at 100 nm.
The soft X-ray image of the SBR-B/BR interface
sample shows the existence of a region near theinterface that exhibits a spectral structure diﬀerent fromthat of the SBR-B and BR used to prepare the sample
The two-dimensional (2D) soft X-ray absorption
distributions of the SBR-B phase, the BR phase, andthe residual phase are shown in Fig. 1(a). In the figure,the absorption intensity of the BR phase is shown inred, the SBR-B phase in blue, and the residual phase ingreen. The respective absorption intensities are
represented by the respective color gradations. The
simultaneously obtained spectra of the BR phase, the
SBR-B phase, and the residual phase are shown in Fig.
1 (b). The color of the spectra corresponds to the color
in the soft X-ray image of Fig. 1(a). The spectral
intensities are normalized by the background before
and after the absorption edge.

5HVLGXDO

6%5%

%5

D

Fig. 1. (a) Material separation image of S-SBR-B/BR
interface sample, (b) NEXAFS spectra of each material
obtained in (a).
[1] A. J. Marzocca, et al., Polym. Int. 49 (2000) 216.
[2] J. M. Massie, et al., Rubber Chem. Technol. 66(1993) 276.
[3]H. H. Le, et al., Macromol. Mater. Eng. 298 (2013)1085.

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Observation of Distribution of Sulfur and cross-linking Reagent in
Vulcanized Rubber by Using STXM
T. Ohigashi1, 2, 3, F. Kaneko4, H. Yuzawa2 and H. Kishimoto4
1

Institute of Material Structure Science, High Energy Accelerator Research Organization,
Tsukuba 305-0801, Japan
2
UVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan3
School of Physical Sciences, The Graduate University for Advanced Studies (SOKENDAI),
Tsukuba 305-0801, Japan
4
Sumitomo Rubber Industries Ltd., Kobe 651-0072, Japan

In recent years, SDGs (Sustainable Development
Goals) is a keyword to represent attitude of our daily
life. Especially, reduction of mass consumption is a
critical issue. Rubber is one of the important resources
and its demand is assumed to increase especiallyaccording to growth of car industries. To reduce its
consumption, establish of LCA (Life Cycle Assessment)of rubber industrialization and further improvement offunctionality of rubbers, such as wear- and destructionresistant, are essential.
Rubber is generally heterogeneous network structure,
which is produced by rubber polymer and cross-linking
agent (vulcanization). Since the remained cross-linking
reagent in this structure is heterogeneously distributed,
it gathers internal stress of rubber deformation to cause
the destruction. Therefore, dispersion of a cross-linking
reagent in the rubber is an important parameter todetermine mechanical character of rubber. However, it
is not easy to observe the dispersion because the crosslinking reagent in rubber is so small amount and isconsisted of light elements.
We have been characterized rubber by using scanningtransmission X-ray microscopy (STXM) at BL4U
[1,2]. STXM is a powerful tool to obtain 2-dimensional
X-ray absorption spectroscopy by near edge X-ray
absorption fine structure (NEXAFS) with high spatial
resolution around 30 nm. Moreover, STXM gives muchless radiation damage to the sample than by electron
microscopy. Therefore, STXM is the best approach forthis study. In this report, the distribution of crosslinking reagent in vulcanized rubber is investigated by
STXM.
The sample is styrene-butadiene rubber with zincoxide, sulfur, N-cyclohexyl-2-Benzothiazolylsulfenamide(CBS), 3-diphenylguanidine (DPG) as cross-linking
reagents. The rubber was cut as 200 nm-thick by
ultramicrotome and was placed on a TEM grid. As
reference
samples,
CBS,
DPG
and
2-mercaptobenzothiazole (MBT) were dispersed in
acetone and were drop-casted onto TEM grids withsupport membrane. X-ray absorption images ofunvulcanized and vulcanized rubbers taken at 400 eV
are shown in Fig. 1. In these images, dark spots show
higher absorption than matrix and are considered as
distribution of cross-linking reagents. By comparing
Figs. 1(a) and 1(b), dark spots decrease in size andbecome more dispersive through a vulcanization
process. Normalized N K-edge NEXAFS spectra ofreference samples of CBS (blue), DPG (green), MBT(red) and the dark spot (black; shown by an arrow in
Fig. 1(b)) are shown in Fig. 2. Although the signal ofthe dark spot is quite low, the dark spot seems to beconsisted of mixture of CBS, DPG and MBT. Especially,
the sharp peak of MBT at 400.8 eV contributes to thatof the dark spot. MBT was produced by vulcanization
process and contributed to the distribution of crosslinking reagent.

(a)

(b)

Fig. 1. X-ray absorption image of (a) unvulcanized and(b) vulcanized rubbers taken at 400 eV. Scale bars are 5
μm.

Fig. 2. N K-edge NEXAFS spectra of CBS (blue),
DPG (green), MBT (red) and a dark spot (shown in Fig.
1 by an arrow). The spectra are normalized by max andminimum.
[1] T. Ohigashi, F. Kaneko, H. Yuzawa and H.
Kishimoto, UVSOR Activity Report 2021, 49 (2022) 73.
[2] T. Ohigashi, et al., J. Electron Spectrosc. Relat.
Phenom. 266 (2023) 147356.

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BL4U

Scanning Transmission X-ray Microscopy of Hydrogen Evolution
Electrocatalysts on Graphene Oxide Membranes
C. O. M. Marianoa, J. S. D. Rodrigueza,b, R. H. Clementea,
T. Ohigashic,d, H. Yuzawac, W. H. Hsue, J. Shiuef and C. H. Chuanga,*a

Department of Physics, Tamkang University, Tamsui, New Taipei City 251301, TaiwanbInstitute of Chemistry, Leiden University, Leiden, 2300 RA, The NetherlandscInstitute for Molecular Science, Okazaki 444-8585, Japand
Photon Factory, Institute of Materials Structure Sciences, High Energy Accelerator Research Organization,
Tsukuba 305-0801, Japane
Institute of Physics, Academia Sinica, Nankang, Taipei 11529, TaiwanfInstitute of Atomic and Molecular Sciences, Academia Sinica, Daan, Taipei 106319, Taiwan
The oxygen functional groups present in GO haveeﬀects on the HER activity of cobalt catalyst (CoxOy)
and should be studied for its specific role thoroughly.
GO has several oxygen functional groups, i.e., carboxyl(-COOH), carbonyl (C=O), hydroxyl (-OH), andepoxide groups (C-O-C). These functional groups areimportant because they can interact with the cobalt
ions, which increases the catalytic activity for the HER.
The oxygen functional groups of GO can be identified
using such as fourier-transform infrared spectroscopy,
raman spectroscopy, and X-ray photoelectron
spectroscopy, but to acquire additional information
about the spatial distribution of these functional groups,
scanning transmission X-ray microscopy (STXM)
must be used [1].
This study aims to understand the relationshipbetween the oxidation state of CoxOy supported on GO
membranes (called as Co/GO), for their catalytic
activities. Fig. 1(a) shows the surface morphology ofthe dropcast GO membranes measured using thetapping mode of AFM. The vertical diﬀerence along
the line profile (red arrow) was noted as 46 nm because
a random flake stacking of the GO on the Au meshbehaves like a rough surface after drying. Fig. 1(b)exhibits a SEM image for the CoxOy grown on GO
membranes, and Fig. 1(c) shows a high magnification
image of Co/GO to display the 3D wrinkle flower
structure of electrodeposited (ED) Co.
To identify the nanoscale distribution of theseheterogeneous materials, STXM was measured in theenergy regions of C K-edge, O K-edge, and Co L-edge
XANES. The area-selected spectra are marked as “1”,“2”, and “3” owing to the prominent contrast in the OD
image at C/O K-edges and Co L-edge, as for the total
absorbance amount of Co/GO membranes. From the C
K-edge XANES of Fig.1(d), the oxygen functionalgroups (C-O-C, C=O of COOH, and C=O) in the GO
membranes were assigned based on our previous result[1]. The feature at 284.9 eV was assigned to theformation of doubly coordinated carbon, because of thering opening and modifying π* bond [2]. The intensive
feature at 288.4 eV is known as HO-C=O (π*)/defectstate and its low-energy shoulder nearby at 287.4 eV is
assigned to C-O-C (π*) state; furthermore, the mostintensive feature and its shoulder are identified as
O-C(O)-O/C=O (π*) of the GO edge at 290.2 eV and
HO-C=O (σ*) state at 289.5 eV [1,2,3]. C-OH (π*) at
286.5 eV appears in the raw GO membranes [1] but isabsent in Co/GO membranes.
Fig. 1(e) exhibits the area-selected O K-edge XANES
spectra of Co/GO and GO. Compared the spectrum Co/
GO with that of GO, the signal of O 2p-Co 3d (π*) andCo-4s (σ*) newly centered at PEs of 531.5 eV and 539.5
eV [3,4]. The surface oxidation (i.e., C=O and C-O-C)of the GO membranes also emerges among the feature
centered at 531.5 eV [1]. Furthermore, it is critical tosee one shoulder at the 534.4 eV, mainly considered awater signal[5]. Fig. 1(f) shows Co L-edge XANES
spectra, which are composed of spectral components of
Co0, Co2+, and Co3+ states. The octahedral (Oct.)symmetrical Co2+ state composes of two features at
775.0 and 776.2 eV. The metal species of cobalt has one
primary absorption at 776.2 eV because its energy
levels are continuous. The Oct. symmetrical Co3+ stateoﬀers two additional features at 777.3 and 779.6 eV,with a higher energy range than the other cobalt
species[3]. The rising shoulder shows the gains ofmetal cobalt and Oct. Co3+ states due to the chemical
reduction and growth along the continuous
electrodeposition process, consistent with the result on
the G membranes (Co/G) in Fig. 1(f) [3].
The Co/GO membranes became a great variety in theoxidation state and lattice structure at the interface,compared to the raw GO surface. The mapping andspectroscopic information at diﬀerent positions helps
us to understand the chances of ED CoxOy growth on
the confirmed GO membranes.

Fig. 1. (a) AFM image of GO membranes and certain
curve of its height line profile along the red dottedarrow. (b)(c) SEM image of electrodeposited Co-GO
membranes. (d)-(f) XANES spectra of selected areas at
C K-edge, O K-edge, and Co K-edge.
[1] J.S.D. Rodriguez et al., Carbon N Y. 185 (2021) 410.
[2] J.J. Vélez et al., Electrochem. Soc. 160 (2013) C445.
[3] J.-J.V. Vélez et al,. Chin. J. Phys. 76 (2022) 135.
[4] J. Wang et al., Energy Environ. Sci. 6 (2013) 926.
[5] J.W. Smith et al., Chem. Rev. 117 (2017) 13909.

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BL4B

Examination of Methods for Inner Structures of Magnetic Thin Films at
UVSOR BL4B by Reflection XMCD Measurement Setup
K. Yamamoto, H. Iwayama, O. Ishiyama and T. Yokoyama
Institute for Molecular Science, Okazaki 444-8585, Japan

Complex depth-structured magnetic thin films/
multilayers exhibit a wide range of magnetic phenomena
due to interlayer interactions[1]. In addition, multilayer
structures are used to achieve useful properties inrecording media, an application area of great importancefor magnetic materials. It has been possible to elucidate
the evolution mechanism of the magnetic structure ofthin films by directly observing the magnetic
distribution in the depth direction of these magnetic
multilayers.
We have installed an experimental setup for thereflection X-ray magnetic circular dichroism (XMCD)
method [2] in the soft X-ray region at BL4B, andexperiments have been performed on test samples. The
sample and detector can be rotated independently toobtain the reflectivity. The magnetic field was about
0.35T and the measurements were performed at room
temperature. The magnetic field was applied by twopairs of opposing Nd magnets. The magnets can berotated and the relative position between the magnetic
field and the sample was kept constant. The setup is
shown schematically in Fig. 1. We used a photodiode(AXUV100G, Optodiode inc.) for our measurements
last year. In order to measure the lower signals in thehigher angle regions and to eliminate the fluorescenceof oxygen from the substrates, we introduced a silicon
drift detector (FASTSDD, Amptek). The detector
temperature was controlled by water cooling and thenoise level was kept constant at lower levels and thedetector and samples can be rotated arbitrary in thevacuum chamber shown in Fig. 2.
We used oﬀ-axis components of X-rays from thebending magnet to obtain circularly polarised light. The
X-rays are elliptically polarised. The intensity of the
XMCD was measured by changing the direction of themagnetic field.
When measurements were performed on a reference
sample, a vibrational structure was observed due tointerference between the cap layer and the underlying
layer. By changing the direction of the magnetic field,
diﬀerences corresponding to XMCD were observed.
The same measurements were also made near theabsorption edge and spectroscopic information was
extracted. However, structural information is not wellobtained compared to hard x-rays. Using an X-ray tube
light source, we also performed hard x-ray reflectometry.

Both soft and hard X-ray results could be reproducedby simulations based on a full-matrix algorithm, taking
into account the magneto-optical eﬀects of ellipticallypolarized X-rays. Although there have been previous
studies using XMCD of reflectance, few have extended
this method to obtain spectroscopic information. In
order to analyze depth-resolved magnetization
information, spectroscopic measurements were
performed to obtain the photon energy dependence andthe reflection angle dependence.
Combining this study with a light source that canarbitrarily modulate polarization would provide amethod to reveal more detailed properties.
Magnetic
Polarized
thin films
X-rays2䃗
䃗

Silicon drift
detector

Fig. 1. The illustration for the XMCD reflectivity
measurements.

Fig. 2. The vacuum chamber for the maeasurements in
UVSOR BL4B.
[1] F. Hellman et al., Rev. Mod. Phys. 89 (2017)025006.
[2] S. Macke and E. Goering, J. Phys. Condens. Matter.
26 (2014) 363201.

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Ⅲ-2 Material Sciences

BL4B

L2,3-edge X-ray Absorption Spectra of Transition Metal in Wurtzite-AlN
S. Imada
Faculty of Electrical Engineering and Electronics, Kyoto Institute of Technology, Kyoto 606-8585, Japan

3d-TM doped AlN (Al1-xTMxN) is promising forlight-emitting, spintronic, and photoelectric conversion
materials [1,2]. For these applications, it is indispensable
to reveal the electric structure, including ligand fieldand charge transfer multiplets. For this purpose, TM
L2,3-edge X-ray absorption structure (XAS) andresonant X-ray emission scattering (RIXS)
spectroscopies are powerful tools. So far, however, acomprehensive and systematic study of these importantsystems still needs to be included.
We synthesised and investigated the band structuresof Al1-xTMxN using Al and N K-edge XAS [2-4]. This
study investigated TM L2,3-edge XAS structures of
Al1-xTMxN films with various TM concentrations(0.02<x<0.08), focusing on Ti, V and Mn for the firsttime. For example, with low concentrations x<0.05, theaverage distance between TMs is larger than 7.5Å; we
expect to observe a well-localised electronic structure.
Looking ahead, we can even prepare films including
other TMs with concentrations well above 0.1 (<6Å) toreveal interactions between TMs, which are necessary
to understand for spintronic and photoelectric
conversion use.
Here we show an example of the TM concentration
dependence of the XAS structure for Al1-xTixN. Our
previous study [2] revealed that the Al1-xTixN films with
x≧0.083 showed photoconductivity under blue-green
light irradiation, while the film with x<0.083 did not.
The Ti L2,3-edge XAS spectra of Al1-xTixN films showed
structural change at x=0.083 (Fig.1). Our previous
study on Ti K-edge extended X-ray absorption finestructure (EXAFS) did not show any evidence of local
crystallographic structure change at the concentration.
Thus, we tentatively conclude that the observed change

in L2,3-edge XAS implies delocalisation of Ti 3delectrons starts at around x=0.083. To reveal the originsof the spectral change in detail, we will conduct L-edge
RIXS measurements and partial RIXS yield (PRIXSY)
analyses, which will give us new insights into XAS
structure interpretation.

Fig. 1. Ti L2,3-edge X-ray absorption spectra of Al1-xTixN
films (x= 0.083, 0.064, and 0.045) These spectra were
measured in partial fluorescence yield (PFY) mode.
[1] S. S. Khludkov et al., Russian Physics Journal 63(2020) 2013.
[2] N. Tatemizo et al., J. Mater. Chem. A 5 (2017)
20824.
[3] N. Tatemizo et al., Sci. Rep. 10 (2020) 1819.
[4] S. Imada et al., Matr. Adv. 2 (2021) 4075.

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BL4B

C K-edge XAFS Measurement of Carbon Containing Porous Silica
S. Dohshi
Osaka Research Institute of Industrial Science and Technology
2-7-1, Ayumino, Izumi, Osaka 594-1157, Japan

Porous silica with only micropores of less than 1 nm
in diameter has been successfully synthesized by using
collagen fibers or denatured collagen as a template [1].
As a result of a detailed study of the process of removing
collagen as a template by calcination, we found that theporous silica with a small amount of carbon (hereafter
denoted as carbon containing porous silica) showed
white luminescence under UV light irradiation [2]. The
emission spectrum of the prepared carbon containing
porous silica under UV excitation shows a continuous
spectrum over the visible light region, and this carbon
containing porous silica is expected to be used as awhite light source material with high color rendering
property. The author investigated the mechanism ofwhite luminescence of carbon-containing porous silica.
Since porous silica without carbon does not show whitelight luminescence property under UV light irradiation,
it is clear that carbon in porous silica contributes toluminescence property. However, the local structure ofcarbon in porous silica has not yet been elucidated
because the carbon content is very low, about 0.1%.
Therefore, in this study, we attempted to elucidate thelocal structure of carbon in porous silica by C K-edge
XAFS measurement using BL4B of UVSOR III. We
optimized the sample preparation method andmeasurement conditions.
Fig. 1 shows the experimental setup at BL4B and thesample holder for C K-edge XAFS measurement. The
powder sample was fitted onto carbon tape or indium
foil. The measurement was performed by fluorescencemode (using SDD detector).
When the sample was fixed on the carbon tape, thespectra derived from the carbon tape were observed,
and almost no spectra derived from the sample wereobserved. On the other hand, when the sample was
fixed on indium foil, the spectra derived sample wasobtained. It was also found that the X-ray irradiation
angle to the sample had a significant eﬀect on theintensity of the spectra.
In the next fiscal year, we will measure the C K-edge
XAFS measurement using pelletized sample under the
optimized conditions.

Fig. 1. The experimental setup at BL4B and the sample
holder for C K-edge XAFS mesurement.
[1] S. Dohshi, J. Soc. Leather Technol. Chem, 95 (2011)
200.
[2] S. Dohshi et al., J. Soc. Mater. Sci., Jpn., 68 (2019)549.

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Ⅲ-2 Material Sciences

BL5U

Evolution of the Electronic States by Electron Doping in a Kagome
Superconductor KV3Sb5
T. Kato1, K. Nakayama1, Y. Li2,3,4, Z. Wang2,3,4, S. Souma5,6, K. Tanaka7,8, T. Takahashi1,
Y. Yao2,3 and T. Sato1,5,6,9
1

Department of Physics, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan
Centre for Quantum Physics, Key Laboratory of Advanced Optoelectronic Quantum Architecture andMeasurement (MOE), School of Physics, Beijing Institute of Technology, Beijing 100081, P. R. China
3
Beijing Key Lab of Nanophotonics and Ultrafine Optoelectronic Systems, Beijing Institute of Technology,
Beijing 100081, P. R. China
4
Material Science Center, Yangtze Delta Region Academy of Beijing Institute of Technology,
Jiaxing, 314011, P. R. China
5
Advanced Institute for Materials Research (WPI-AIMR), Tohoku University, Sendai 980-8577, Japan
6
Center for Science and Innovation in Spintronics (CSIS), Tohoku University, Sendai 980-8577, Japan
7
UVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
8
School of Physical Sciences, The Graduate University for Advanced Studies (SOKENDAI),
Okazaki 444-8585, Japan
9International Center for Synchrotron Radiation Innovation Smart (SRIS), Tohoku University,
Sendai 980-8577, Japan
2

Recent discovery of a new kagome-lattice material
AV3Sb5 (A = K, Rb, and Cs) is attracting great attention.
While most of the kagome-lattice materials studied so
far have been magnetic, AV3Sb5 is unique in that it isparamagnetic and shows superconductivity with Tc of
0.93-2.5 K. AV3Sb5 also undergoes a charge-density
wave (CDW) transition below TCDW = 78-103 K,
accompanied by the unit-cell doubling with the 2×2×2
periodicity. This CDW state shows an intriguinginterplay with the superconductivity and hosts exotic
properties such as strong anomalous Hall eﬀect,
possible time-reversal symmetry breaking, andnematicity. From the electronic structure point of view,
AV3Sb5 is a multiband/multi-orbital superconductor
characterized by the formation of multiple Fermi
surfaces originating from Dirac-cone, saddle-point, andfree-electron-like bands. Given the multiband character,
it is essential to understand which bands/orbitals are
responsible for the CDW and superconductivity. A
useful means to clarify this point is to control the energy
position of bands relative to the Fermi level (EF) by
carrier doping [1] because the CDW andsuperconductivity would be sensitive to the band filling.
In this study, we have performed an angle-resolved
photoemission spectroscopy (ARPES) study on
K-dosed KV3Sb5. We have successfully controlled
electron doping level by K dosing and determined thedoping-induced evolution of the band structure.
High-quality single crystals of KV3Sb5 were grownby the self-flux method. K dosing was carried out by
using K dispenser (SAES Getters) in an ultrahighvacuum. High-resolution ARPES measurements were
performed by using a MBS-A1 spectrometer at BL5U
with linearly-polarized energy-tunable photons.
A comparison of Fermi surfaces in pristine [2] andK-dosed KV3Sb5 [Figs. 1(a) and 1(b), respectively]
shows that a circular-shaped electron pocket at the Γpoint expands with the K dosing, indicative of theelectron doping. We have estimated the amount ofenergy shift for each band and found band/orbitaldependent electron doping eﬀect. In addition, we
determined the evolution of CDW gap size withelectron doping. Our results suggest an important roleof the saddle-point band for the occurrence of CDW.

Fig. 1. (a), (b) ARPES intensity plots at EF in freshly
cleaved and K-dosed KV3Sb5, respectively[1] K. Nakayama et al., Phys. Rev. X 12 (2022) 011001.
[2] T. Kato et al., Commun. Mater. 3 (2022) 30.

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BL5U

Evolution of Electronic Correlations and Excitonic Properties Near
semiconductor-excitonic Insulator Transition
K. Fukutani1, 2, K. Kiyosawa3, C.I. Kwon4,5, J.S. Kim4,5, K. Tanaka1,2 and S. Kera1,2,3
1
Institute for Molecular Science, Okazaki 444-8585, JapanThe Graduate University for Advanced Studies (SOKENDAI), Okazaki 444-8585, Japan
3
Graduate School of Science and Engineering, Chiba University, Chiba 263-8522, Japan
4
Center for Artificial Low-Dimensional Electronic Systems, Institute for Basic Science, Pohang, Korea
5
Pohang University of Science and Technology, Pohang, Korea
2

In semiconductors, external stimuli, such as lightirradiations are known to create bound pair of anelectron and a hole. This quasi-particle is known as
excitons, and are known to play principal roles invarious quantum devices, including solar cells, lightemitting diode (LED), and excitonic lasers etc. The
eﬃcient creation of excitons and the manipulations of
their properties are among the central interest in thecurrent semiconductor industry.
Recently, what is called an excitonic insulator has
been experimentally identified. This new class ofmaterials is either a narrow-gap semiconductor or ashallow-overlap semimetal in their normal phase and,at suﬃciently low temperature, the electrons and holes
are spontaneously paired into excitons via quantum
condensation process.
Ta2NiSe5 is one of the most extensively studied
excitonic insulators [1], along with 1T-TiSe2. Whatdiﬀerentiates Ta2NiSe5 from 1T-TiSe2 is the fact that theformer exhibits a direct band gap and does notaccompany the change in the structural periodicities(charge density wave transition). Thus, from the pointof view of excitonic instability, Ta2NiSe5 is ideal
platform to study the nature of excitonic insulator andthe transition to/from the normal phase.
The recent extensive researches have revealed that
Ta2NiSe5 is classified into Bose-Einstein condensate(BEC)-type excitonic insulator, while it is near the
crossover regime between BEC and BCS transitions.
Theoretically, in the BEC-type excitonic insulator,
the excitons are created above the transition temperature(Tc) and as they cool down below Tc, those “preformed
excitons” undergo the condensation and acquire themacroscopic coherence [2]. The temperature (and bandgap) regime where such steady-state excitons exist
without forming a condensate is called “preformed
exciton phase” and its existence has been recently
verified [3].
Such phase of steady-state excitons represents theinverted ground state from the normal semiconductors(i.e., the excitons are formed in the ground state, while
the external stimuli are required to dissociate them into
free carriers) and provides a particularly uniqueplayground for future electronics applications.
The purpose of this research project is to explore theexcitonic insulator phase diagram both in terms oftemperature and the bandgap to evaluate the propertiesof the steady-state excitons, including its binding

energy, Bohr radius and their relative density (comparedto the free carriers), in order to understand the formation
process of this new ground state.
With these goals, we have performed high-resolution
angle-resolved photoemission spectroscopy (ARPES)
at BL5U for the chalcogen-substituted compounds
Ta2Ni(Se1-xSx)5 with particular focus at the compositionx ~ 0.6, where the material is believed to be very close
to the transition between a BEC-type excitonic insulator
and a normal semiconductor. Figure 1 shows thetemperature-dependent ARPES spectra for thiscomposition. It can be seen that at T ~ 120 K, thematerial exhibits a flat-top valence band, characteristicof excitonic insulator phase. As the temperature rises,
at T ~ 200 K, the clear signature of exciton appears near
the valence band maximum and at T ~ 350 K, thevalence band maximum is no longer flat, reminiscent of
the normal semiconductor Ta2NiS5, and the weakened
exciton signal moves towards the Fermi level with thevalence band. These observations possibly indicatesthat as the temperature increases, the electronic
correlations, which are keeping the excitons bound, areweakening at the same time as the exciton binding
energy decreases. The experimental results obtained
here are expected to give new insights into the formation
path of excitons.

Fig. 1. Temperature-dependent ARPES data from
Ta2Ni(Se1-xSx)5 at x ~ 0.6 measured at (a) T ~ 120 K, (b)200 K and (c) 350 K. The second derivative plots from
Γ01 are shown on the bottom panel (d-f).
[1] Y. Wakisaka et al., Phys. Rev. Lett. 102 (2009)026402.
[2] Y.F. Lu et al., Nat. Commun. 8 (2017) 14408.
[3] F.X. Bronold et al., Phys. Rev. B 74 (2006) 165107.
[4] K. Fukutani et al., Nat. Phys. 17 (2021) 1024.

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BL5U

Polarization-dependent Angle-resolved Photoemission Study of
MAX Phase Compound Zr3SnC2
M. Mita1, D. Pinek2, M. Nakatake3, K. Tanaka4,5, T. Ouisse2 and T. Ito1,6
1

Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan
2
Grenoble Alpes, CNRS, Grenoble INP, LMGP, F-38000 Grenoble, France
3
Aichi Synchrotron Radiation Center, Seto, 489-0965, Japan
4
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
5
The Graduate University for Advanced Studies, Okazaki 444-8585, Japan
6
Synchrotron radiation Research center, Nagoya University, Nagoya 464-8603, JapanMAX phase compounds, i.e., Mn+1AXn where M is atransition metal, A belongs to groups 13-16 and X is the
C or N element, have recently been attracted muchattention due to their possible application for new classof two-dimensional systems called MXenes byremoving A atoms [1]. On the other hand, the bulk
electronic structure of MAX phase has been studied
mostly by calculations, mainly because of lack of wellestablished single crystalline samples. In this study, we
have performed angle-resolved photoemission
spectroscopy (ARPES) on MAX phase compound
Zr3SnC2, in which relatively higher two-dimensionality
than 211 phase due to the thicker MX layer as well as
the strong spin-orbit coupling eﬀect due to the 4dtransition metal Zr were expected.
ARPES measurements were performed at the
UVSOR-Ⅲ BL5U. Data were acquired at T = 30 K
with hν = 76 eV which enables us to trace around theΓKM plane with inner potential of V0=17.7 eVestimated from the photon energy dependentmeasurement (not shown). With using linear
horizontally (LH), vertically (LV) and circularly right(CR), left (CL) polarized photons, we have obtained
the orbital and orbital-angular-momentum (OAM)
dependent ARPES images. It should be noted that each
ARPES images were obtained without changing thephoton incident angle relative to the sample surface byutilizing two-dimensional mapping lens mode of MBS
A-1 analyzer.
Figure 1 shows the obtained Fermi surface (FS)image on the ΓKM plane. The band structure along theΓM line is shown in Fig. 2 (a) together with the DFT
calculation of Sn-terminated surface. Six-folded
symmetry of hole-pockets α and β has clearly been
observed in consistent with the DFT calculation. In
addition, three-fold symmetry around the K point of thesmall triangular-shape FS γ formed by so-called saddlelike surface state (SS) at the M point also has been
elucidated in Fig.1. With respect to this SS, even orbital
symmetry has been recognized with almost the same
circular dichroism (Fig. 2(b) and (c)). On the other
hand, opposite OAM sign without changing orbital
symmetry with respect to the MK line has been

observed at the high-binding energy region. The results
might suggest the change of chirality of OAM at thehigh-energy bound states at the Sn-terminated surfaceof Zr3SnC2. To elucidate the relation between theobserved anomalies and the spin-orbit coupling eﬀect,
further studies are intended.

Fig. 1. (a) Fermi surface (FS) image on ΓKM plane of
Zr3SnC2.

Fig. 2. (a) Band structure along the ΓM line of Zr3SnC2
obtained by LH polarized photons. Solid lines are DFT
calculation for Sn-terminated surface. (b,c) orbital (b)and OAM (c) dependent ARPES image of Zr3SnC2
along the ΓM line, which is obtained by subtracting the
ARPES results of linearly (LH−LV) and circularly(CR−CL) polarized photons, respectively.
[1] M. Basoum, MAX phases (Wiley, Weinheim 2013).

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Electronic Structure of a Layered Magnetic Semiconductor CeTe1.83Sb0.17
T. Nakamura1,2, H. Murakawa2, Y. Chen2, H. Sugihara2, K. Tanaka3,
N. Hanasaki2 and S. Kimura1,2,3
1

Graduate School of Frontier Biosciences, Osaka University, Suita 565-0871, Japan
Department of Physics, Graduate School of Science, Osaka University, Toyonaka 560-0043, Japan
3
Institute for Molecular Science, Okazaki 444-8585, Japan2

The metal-insulator transition through charge density
wave (CDW) formation has been a central topic ofsolid-state physics. While many materials have beenreported to exhibit CDW, CeTe2, a family of rare-earth
dichalcogenide, has attracted considerable interest due
to its high transition temperature that reaches 1000 K[1,2] as well as magnetic ordering below 4 K [3].
Recently, CeTe1.83Sb0.17, which shows a huge anisotropic
magnetoresistance ratio as high as 7500 thanks to theextremely low carrier density, has been synthesized bya chemical vapor transport technique [4]. Due to thepartial substitution of Te with Sb, an extra charge
carrier removes by hole doping. However, the detail ofthe electronic band structure of this sample has notbeen observed yet. In this study, we have measured theangle-resolved photoelectron spectroscopy (ARPES)of the CeTe1.83Sb0.17 to investigate the electronic
structure.
The single-crystalline CeTe1.83Sb0.17 was cleaved
under ultra-high vacuum conditions. Due to thediﬃculty of cleavage, the ARPES measurable domain
size was less than 100×100 μm2. However, the microfocused beam from UVSOR-III BL5U made it possible
to observe the electronic structure in a piece of domains.
Figure 1 shows the resonant angle-integrated
photoelectron spectra of CeTe1.83Sb0.17, taken with theenergy of 122 eV, corresponding to the resonant energyof the Ce 4d-4f absorption. In contrast to the nonresonant condition (hv = 110 eV), the sharp peak at abinding energy of 1.7 eV originates from the Ce 4f 0
final states after photoexcitation was observed in theresonant condition, indicating that the Ce 4f states are
fully localized.
Figure 2 shows the ARPES intensity plot along Γ-M
at 15 K. Several hole bands near the Γ point are
observed. Among them, the apex of band H1, which isat the outermost part of the measurement range, seems
to be in an unoccupied state, indicating that it exhibits
metallic properties even though extremely low carrier
densities are confirmed in the transport measurements.
Further experimental studies such as polarization
dependence and bulk sensitive measurement using
higher energy photons would help to elucidate theorbital character of bands in the electronic structure of
CeTe1.83Sb0.17.

Fig. 1. Resonant angle-integrated photoelectron spectraof CeTe1.83Sb0.17 at 15 K. The excitation energies of 110
and 122 eV correspond to the oﬀ- and on-resonanceconditions at the Ce 4d-4f absorption edge.

Fig. 2. ARPES intensity plot of CeTe1.83Sb0.17 along
Γ-M taken with 103 eV at 15 K.
[1] J. G. Park et al., Physica B 241-243 (1998) 684.
[2] M. H. Jung et al., J. Phys. Soc. Jpn. 69 (2000) 937.
[3] M. H. Jung et al., Phys. Rev. B 67 (2003) 212504.
[4] H. Murakawa et al., Phys. Rev. Mater. 6 (2022)
054604.

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BL5U

Synchrotron ARPES Study of Nodal Dirac Semimetal Candidate LaTeBi
R. Saitou1, N. Kataoka1, H. Kageyama1, R. Kondo1 and T. Yokoya1,21Graduate School of Natural Science and Technology, Okayama University, Okayama 700-8530, Japan
2
Research Institute for Interdisciplinary Science, Okayama University, Okayama 700-8530, Japan

point with respect to EF is found to be calculation
dependent. However, an implication from this study isthat the electron concentration is not enough. To
achieve the interesting physical properties originatingfrom the topological electronic structure in the sample,
further electron doping is necessary.

Binding Energy (eV)

E0F

-1
1

-2
2

-3
3

-4
4

-5
5

-1.0

-0.5

0

-1

0.5

1.0

kx (‫) ڣ‬

Fig. 1. ARPES intensity map of LaTe1+xBi1-x measured
with 94 eV photons and at 20 K.

Binding Energy (eV)

LnTe1+xSb1-x (Ln: lanthanides) is a layered material
consisting of alternative stack of a layer of LnTe and alayer of a single Sb square lattice. It is theoretically
predicted as a nodal line semimetal [1]. In addition, by
selecting a magnetic element as Ln, it is possible tobreak the time-reversal symmetry. Therefore, it is amaterial that has the potential to access novel
topological phases [2-5]. Our research group are
making an eﬀort to control the physical properties ofrelated materials by introducing magnetic elements,
substituting Sb with Bi, and changing carrier
concentration [6] for the purpose of observing theexotic transport properties peculiar to Dirac electrons.
In the present study, we have performed synchrotron
angle-resolved photoemission spectroscopy (ARPES)
to clarifying the electronic structure of the nonmagnetic phase and check the relative energy
relationship between the Fermi energy (EF) and Dirac
nodes in a related material, LaTe1+xBi1-x, which
possesses single square lattices composed of Bi atoms,
having a stronger spin-orbit interaction than Sb.
LaTe1+xBi1-x single crystal samples (x = 0.025) wereprepared by a self-flux method. ARPES measurements
were performed at BL5U of UVSOR III. Linear
polarized light of 32-124 eV energies were used. Theenergy resolution was set to ~ 40 meV. All samples
were cleaved in situ on the (001) plane in an ultrahigh4vacuum of less than 5.0 x 10-9 Pa and were measured
at 20 K.
Figure 1 shows the valence band dispersion of
LaTe1+xBi1-x along the Γ-X direction in the Brillouinzone (BZ), measured with the photon energy of 94 eV.
White regions, which are the higher-intensity regions,correspond to band dispersions. The band dispersions
are symmetric with respect to the high symmetry
points: Γ and X of the bulk BZ of LaTe1+xBi1-x. This
indicates that the band dispersions reflect intrinsic
electronic structure of the sample. Importantly, one canobserve weak structures near EF on both sides of the X
points, where Dirac nodal lines are expected to belocated theoretically. To look at the electronic structures
more in detail, an energy and momentum enlarged
intensity map is shown in Fig. 2. We now clearlyobserve two electron-pockets-like structures. Theseband dispersions are consistent with the calculatedband dispersions. However, at the X point, the intensity
at EF is very small, indicating that the starting point of
the theoretically expected Dirac nodal line at the X
point is not located below EF for the measured sample.
The energy position of the Dirac nodal line at the X

EF0
-0.1
0.1
-0.2
0.2
-0.3
0.3
-0.4
0.4
-0.5
0.5

0.4

0.6

0.8

-1

1.0

kx (‫) ڣ‬
Fig. 2. Enlargement of Fig.1 for the region near EF and
the X point.
[1] A. Weiland et al., APL Mater. 7 (2019) 101113.
[2] Y. Wang et al., Phys. Rev. B 103 (2021) 125131.
[3] S. Yue et al., Phys. Rev. B 102 (2020) 155109.
[4] P. Gebauer et al., Chem. Mater. 33 (2021) 2420.
[5] L. M. Schoop et al., Sci. Adv. 4 (2018) eaar2317.
[6] R. Kondo, in preparation.

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Re-examination of the Phase Diagram of the high-Tc Cuprate
Superconductor Bi2Sr2CaCu2O8+δ Studied by ARPES
Y. Tsubota1, Y. Miyai2, S. Nakagawa5, S. Ishida4, S. Kumar2, K. Tanaka3, H. Eisaki4,
T. Kashiwagi5, M. Arita2, K. Shimada1,2 and S. Ideta1,21Graduate School of Advanced Science and Engineering, Hiroshima Univ., Japan
2
Hiroshima Synchrotron Radiation Center (HiSOR), Hiroshima Univ., Japan
3
UVSOR-Ⅲ Synchrotron, Institute for Molecular Science, Japan
4
National Institute of Advanced Industrial Science and Technology (AIST), Japan
5
Graduate School of Science and Technology, Tsukuba Univ., Japan

It has been known that the cuprate superconductors
show a high superconducting (SC) transition
temperature (Tc) and exotic physical properties.
However, the SC mechanism has been unclear yet. In
order to understand the mechanism of high-Tc cuprates,
Bi2Sr2CaCu2O8+δ (Bi2212) is one of the promising
candidates to study the electronic structure and reveal
the physical properties. Bi2212 has two CuO2 planes in
the unit cell and shows the high Tc around 95 K at the
optimally doped sample. Superconductivity occurs
upon hole doping into the CuO2 plane and the amountof hole doping can control Tc, and therefore, carrier
doping (hole/electron concentration) plays an important
key parameter in cuprates [1, 2]. The electronic phase
diagram of hole-doped high-Tc cuprate superconductors
plotted as a function of temperature and carrier
concentration has been reported as an empirical anduniversal phase diagram which is a dome-like shapecentered at ~0.16 of hole concentration [1]. However,previous ARPES experiments suggest that its empiricalphase diagram is not universal and shifted toward
overdoped region [2-4]. Therefore, in the present study,
we have performed an angle-resolved photoemission
spectroscopy (ARPES) measurements to study whether
the phase diagram changes depending on sample
compositions and hole concentration or not.
In this study, we have performed ARPES
measurements systematically to directly investigate theelectronic structure of the underdoped, optimally
doped, and overdoped Bi2212. ARPES experiments
were carried out at BL5U and BL7U. We measured
overdoped sample: Bi2.1- xPbxSr2CaCu2O8+δ (x = 0.66, Tc~ 70 K) in the SC and the normal states at BL7U and
5U. We measured underdoped, optimally doped, andoverdoped samples: underdoped Bi2Sr2CaCu2O8+δ (Tc ~75 K ), optimally doped Bi2Sr2CaCu2O8+δ (Tc ~ 92 K ),overdoped Bi2Sr2CaCu2O8+δ (Tc ~ 74 K ) and optimally
doped Bi2.1- xPbxSr2CaCu2O8+δ (x = 0.66, Tc ~ 97 K) in
the SC and the normal states. High quality single
crystals of Bi2212 were cleaved in-situ in the ultrahighvacuum ~5×10-9 Pa.
Figure 1 (a) shows the Fermi surface taken at hν =17.8 eV and T = 30 K in the SC state for optimally
doped Bi2Sr2CaCu2O8+δ. Fermi surface is clearlyobserved in wide momentum space.

We have analyzed the ARPES spectra from the nodal
to the antinodal region for each sample and determined
the Fermi momentum (kF) for each Fermi surface byfitting of momentum-distribution curves (MDCs) withsingle Lorentzian or double Lorentzian. Around thenodal region, kF is defined at Fermi level (EF) by single
Lorentzian. In the oﬀnodal to the antinodal region, kF is
defined at the momentum which shows the gap
minimum by double Lorentzian. The kF points areplotted as shown by red dots (Fig. 1. (a)). We have fitted
Fermi surface shape (red dots) by tight binding model(white curve) and estimated the hole concentration ofeach sample from the Fermi surface area and comparedthem quantitatively. Figure 1 (b) shows the new phase
diagram re-examined by the present ARPES study. As aresult, the phase diagram (Fig. 1. (b)) is diﬀerent fromthe previous one which was reported by Tallon et al [1].
We have figured out that the phase diagram changes
depending on sample compositions and holeconcentration. As a future work, we continue to study
the electric structure of underdoped and overdoped
samples to make an entire phase diagram of Bi2212.

Fig. 1.
(a) Fermi surface of optimally doped
Bi2Sr2CaCu2O8+δ in the superconducting state (30 K).
(b) The new phase diagram of Bi2212 in the present
ARPES study.
[1] J. L. Tallon et al., Phys. Rev. B 51 (1995) 12911.
[2] I. M. Vishik et al, Proc. Nat. Acd. Sci. 6 (2012)1833218337.
[3] R. Sobota et al, J. Phys. Soc. Jpn. 88 (2019) 064711.
[4] H. Sakamoto et al, J. Phys. Soc. Jpn. 85 (2016)
104710.

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BL5U

Alkaline-metal-dependent Electronic States in V-based Kagome Metals
T. Kato1, K. Nakayama1, Y. Li2,3,4, Z. Wang2,3,4, S. Souma5,6, K. Tanaka7,8, T. Takahashi1,
Y. Yao2,3 and T. Sato1,5,6,9
1

Department of Physics, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan
Centre for Quantum Physics, Key Laboratory of Advanced Optoelectronic Quantum Architecture andMeasurement (MOE), School of Physics, Beijing Institute of Technology, Beijing 100081, P. R. China
3
Beijing Key Lab of Nanophotonics and Ultrafine Optoelectronic Systems, Beijing Institute of Technology,
Beijing 100081, P. R. China
4
Material Science Center, Yangtze Delta Region Academy of Beijing Institute of Technology,
Jiaxing, 314011, P. R. China
5
Advanced Institute for Materials Research (WPI-AIMR), Tohoku University, Sendai 980-8577, Japan
6
Center for Science and Innovation in Spintronics (CSIS), Tohoku University, Sendai 980-8577, Japan
7
UVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
8
School of Physical Sciences, The Graduate University for Advanced Studies (SOKENDAI),
Okazaki 444-8585, Japan
9International Center for Synchrotron Radiation Innovation Smart (SRIS), Tohoku University,
Sendai 980-8577, Japan
2

Kagome lattice oﬀers a fertile playground to explore
exotic quantum phases such as Weyl semimetals,
density-wave orders, fractional charge, andsuperconductivity, owing to the interplay between
electron correlation eﬀects and unique band structures
such as flat bands, Dirac cone bands, and van Hove
singularities. Recently-discovered AV3Sb5 (A = alkali
metal), in which V atoms form an ideal two-dimensional
kagome lattice, provides an excellent opportunity toinvestigate charge-density wave (CDW) in the kagome
lattice. The CDW state of AV3Sb5 is characterized bythree-dimensional lattice distortions with 2×2×2 or
2×2×4 periodicity depending on the A element. The
transition temperature TCDW varies with the A elementfrom 78 K to 103 K. AV3Sb5 also exhibits
superconductivity in the CDW phase (Tc = 0.92–2.5 K).
Besides the CDW and superconductivity in the bulk,
AV3Sb5 shows an A-element-dependent charge order at
the surface. To clarify the origin of these A-element
dependent physical properties, elucidation of the bulk
and surface band structures is urgently required.
In this study, we have performed high-resolution
angle-resolved photoemission spectroscopy (ARPES)
measurements of a series of AV3Sb5 (A = K, Rb, andCs). High-quality single crystals of KV3Sb5, RbV3Sb5,
and CsV3Sb5 were grown by the self-flux method.
High-resolution ARPES measurements were performedby using a MBS-A1 spectrometer at BL5U withlinearly-polarized energy-tunable photons of 90-150
eV.
Figures 1(a) and 1(b) show the ARPES intensity plotsmeasured along the high-symmetry line of the bulk
Brillouin zone in KV3Sb5 [1] and CsV3Sb5, respectively.
While the band dispersions show overall similarity
between the two compounds, a closer look reveals
A-element dependence in the energy positions of theelectron-like band at the Γ point and the Dirac point at

the K point. High-resolution measurements at low
temperatures show doubling of some energy bands,
indicative of CDW-induced electronic reconstruction.
We performed first-principles band calculations tounderstand the origin of A-element-dependent band
structures and their relationship with physical properties
in AV3Sb5.

Fig. 1. (a) ARPES intensity along the ΓK cut in KV3Sb5
plotted as a function of binding energy and wave vector.
(b) Same as (a) but for CsV3Sb5.
[1] T. Kato et al., Commun. Mater. 3 (2022) 30.

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Verification of the Intrinsic Electron Doping Eﬀect in T’-type Cuprate hightemperature Superconductors
M. Miyamoto1, M. Horio1, K. Moriya2, A. Takahashi3, K. Tanaka4,
Y. Koike3, T. Adachi2 and I. Matsuda1
12Institute for Solid State Physics, The University of Tokyo, Kashiwa, Chiba 277-8581, Japan.
Department of Engineering and Applied Sciences, Sophia University, Tokyo 102-8554, Japan.
3
Department of Applied Physics, Tohoku University, Sendai 980-8579, Japan.
4
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan.

It is believed that in cuprate high-temperature
superconductors, superconductivity appears when the
carrier is doped by elemental substitution. However, inthe electron-doped cuprates R2-xCexCuO4 (R: rare earth)with a T’-type structure, As-grown samples don’t showsuperconductivity and reduction annealing is essential
for it, regardless of Ce doping level [1,2]. This isprobably due to the presence of excess oxygen on theapical site from the CuO2 plane in As-grown samples. A
crucial role of this reduction annealing has been thought
to remove the apical oxygen [3]. In thin-film samples
with large surface area relative to volume, the apicaloxygen was reduced more eﬃciently, resulting in a
non-doped superconductor [4]. On the other hand,
ARPES measurement performed on Pr2CuO4 thin films
reviled that the carrier concentration was comparable tothat of Ce-doped superconductor samples [5].
Therefore, the nature of the electronic structure in T’type cuprates remains elusive. And it is important toinvestigate the carrier concentration dependence inisolation from the actual crystal structure degrees of
freedom.
In recent years, several studies have shown that thecarrier concentration in cuprate high-temperature
superconductors can be controlled by alkali metal
adsorption [6,7,8]. And our group has previously used asimilar technique for a Mott insulator Ca3Ru2O7 withsuccessful carrier dosing [9]. This method can dope
electrons on the sample’s surface without changing its
crystal structure, Ce concentration, and oxygen amount.
That is, if this method is eﬀective enough, we candistinguish the eﬀects of apical oxygens from that ofcarrier concentration.
We have carried out the ARPES measurement on
Pr1.22La0.7Ce0.08CuO4 As-grown samples at BL5U at 8 K
and dosed K on them. To verify the K deposition, werecorded the core level peaks of K 3p and O 2s (Fig.1).
The figure shows K was dosed eﬀectively. Fig.2 showsthe energy distribution curves at the nodal cut before
and after dosing of K. After 10 minutes of dosing, thequasi-particle spectrum around the Fermi level
enhanced, and the nodal gap looks closing. After
experimenting with various deposition times anddeposition counts, we currently concluded that fewer

and longer depositions lead to more electron electrons
being doped.

Fig. 1. Energy distribution curves around the K corelevel

Fig. 2. Energy distribution curves at nodal cut[1] Y. Tokura, et al. Nature 337 (1989) 345.
[2] H. Takagi et al. Phys. Rev. Lett. 62 (1989) 10.
[3] M. Horio et al. Nat. Commun. 7 (2016) 10567.
[4] O. Matsumoto et al. Physica C 469 (2009) 924.
[5] M. Horio et al. Phys. Rev. B 98 (2018) 020505(R)[6] Q. Gao et al. Chinese Phys. Lett. 37 (2020) 087402.
[7] S. Kunisada et al. Science 369 (2020) 833.
[8] C. Hu et al. Nat. Commun. 12 (2021) 1356.
[9] M. Horio et al. UVSOR activity report 2021 49(2021) 79.

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BL5U

Polarization Dependent Orbital States in Mn3-xGa Studied by angle-resolved
Photoemission Spectroscopy
J. Okabayashi1, Y. Miura2, K. Tanaka3, K. Z. Suzuki4 and S. Mizukami4
1

Research Center for Spectrochemistry, The University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan
2
National Institute for Materials Science (NIMS), Tsukuba, 305-0047, Japan
3
UVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585
4
WPI Advanced Institute for Materials Research, Tohoku University, Sendai 980-8579, Japan

Magnetic ordered alloys have attracted significant
attention for use as spintronics materials because they
are highly likely to exhibit perpendicular magnetic
anisotropy (PMA). Tetragonal Mn3-xGa alloys arewidely recognized as hard magnets which exhibit
highly anisotropic, ferrimagnetic, and metallic
properties [1]. We have investigated the mechanism of
PMA and large coercive fields in Mn3-xGa by x-ray
magnetic circular and linear dichroisms (XMCD /XMLD) [2]. The origin of PMA in Mn3-xGa alloys canbe explained by the quadrupole contribution along thez-axis by the charge distribution. The specific crystalline
structures provide the elongated c-axis direction, which
induces the anisotropic chemical bonding, resulting in
the anisotropy of electron occupancies in 3d states.
However, orbital magnetic moments in the Mn sites arealmost quenched because of the half-filled occupation.
Although the site-specific charge distributions can beaccessed by x-ray absorption spectroscopies, the originof quadrupole-induced PMA from the viewpoint of theband structures in Mn3-xGa alloys is not fully understood.
Here, we employ the angle-resolved photoemission
spectroscopy (ARPES) to unveil the anisotropic band
structures in Mn3-xGa by the comparison with thedensity-functional
theory(DFT)
calculations.
Especially, in order to clarify the anisotropic electronic
structures, the polarization dependent APRES arenecessary.
30-nm-thick Mn3-xGa samples were prepared on
MgO (001) substrate using sputtering technique. On
the surface of Mn3-xGa layer, the Mg and MgO capping
layers were deposited. The MgO layer was removed by
Ar-ion sputtering and the Mg layer was removed byannealing just before the ARPES measurements. We
construct the method to remove the Mg layer which
does not react chemically with Mn atoms at theinterface. Clear low-energy electron diﬀraction (LEED)
patterns were also obtained.
ARPES was performed at BL5U, UVSOR, where thephotoemission chamber is connected to the sample
preparation chamber. The measurement conditions
were set at 15 meV energy resolution and 10 K. Linear
polarized beams of s- and p-polarization were used todetect the orbital symmetry. We employ the photon
energy ranges of 60 – 80 eV to enhance the Fe 3d

photo-ionization cross section, where the Γ-X(M) line
is scanned by the angular mode of ±15°.
Figure 1 shows the Fermi surface mapping taken at
photon energy of 70 eV. Assuming the inner potentialof 10 eV and the work function of 5 eV with the lattice
constant along c-axis as 3.90 Å, Γ point can be accessed
at 70 eV photon energy. Figures 1(a) and 1(b) show thevertical (s-polarized) and horizontal (p-polarized) casesin Mn3Ga. Four-hold symmetric lines are detected.
High intensity spots appear at the Γ point and they havea character of yz orbital because it can be detected by
the s-polarized beam in vertical geometry andreproduced by the density-functional-theory (DFT)
calculations.
We discuss the quadrupole formation. In the DFT
calculations, the virtual spin-flip transitions fromoccupied up-spin yz to down-spin z2 orbitals correspondto the finite matrix element to the PMA in theperturbation. Therefore, occupied yz orbitals detectedby ARPES contribute to spin-flipped yz-z2 oblate
quadrupole charge distribution, resulting in the PMA.
Our finding explains the origin of PMA in Mn3-xGa
comes from not orbital moment anisotropy but
elongated charge distribution through the spin-flipped
transition in specific orbitals [3], whose results are also
supported by XMCD and XMLD [2].

Fig. 1. ARPES images of Mn3Ga taken at hv=70 eV
using (a) s-polarized beam and (b) p-polarized beam.
[1] S. Mizukami et al., Scr. Mater. 118 (2016) 70.
[2] J. Okabayashi et al., Sci. Rep. 10 (2020) 9744.
[3] Y. Miura and J. Okabayashi, J. Phys.: Cond. Mater
34 (2022) 473001.

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Impact of Electron Scattering on Seebeck CoeﬃcientK. Kandai1, K. Kuga1, 3, M. Matsunami1, 2, 3, 4 and T. Takeuchi1, 2, 3, 4
1
Toyota Technological Institute, Nagoya 468-8511, Japan
Research Center for Smart Energy Technology, Toyota Technological Institute, Nagoya 468-8511, Japan
3
CREST, Japan Science and Technology Agency, Tokyo 102-0076, Japan
4
MIRAI, Japan Science and Technology Agency, Tokyo 102-0076, Japan2

The thermoelectric power generation has been
considered as one of the most important technologies
for constructing a sustainable society. The thermoelectric
devices can directly convert heat and electricity using
Seebeck and Peltier eﬀects. The maximum eﬃciency ofthermoelectric generator at an absolute temperature T isexpressed as an increasing function of the dimensionlessfigure of merit ZT = S2T/ρκ, where S, ρ, and κ are theSeebeck coeﬃcient, electrical resistivity, and thermal
conductivity, respectively, of constituent materials [1].
In the research field of thermoelectric materials, thethermoelectric properties, particularly for Seebeck
coeﬃcient, are frequently interpreted and predicted on
the basis of electronic structure calculated with density
function theory (DFT). However, the Seebeck
coeﬃcient of the materials with unconventional
electronic structures, such as strongly correlated
electron systems (SCES), cannot be accurately
described in terms of only the electronic density ofstates obtained with first-principles DFT calculations.
In the theoretical point of view, the main reason is thatthe energy dependence of relaxation time in the
scattering process of conduction electrons is notconsidered [2, 3]. Although the first principles
calculations incorporating dynamical eﬀects are now inprogress, it is still diﬃcult to accurately treat an electron
correlation eﬀect. In any case, it is necessary toexperimentally evaluate the energy dependence of therelaxation time to verify how it aﬀects the Seebeck
coeﬃcient. The strong electron correlation is considered
as one of the key concepts for developing nextgeneration thermoelectric materials because some
SCES materials possess superior thermoelectricperformance. Therefore, for constructing the guiding
principle to develop high-performance thermoelectricmaterials using SCES, it is very important to identify
the origin of the preferable thermoelectric properties.
The main purpose of this research is to establish amethodology for experimentally evaluating the energy
dependence of the relaxation time of conduction
electrons using angle-resolved photoemission
spectroscopy (ARPES). As a first step toward achieving
this purpose, we select the elemental Cu metal as asample because the Cu can be expected to show no
significant energy dependence of relaxation time of
conduction electrons based on its simple electronic

structure and band dispersion.
Clean (110) surface of single crystalline Cu was
prepared by in-situ Ar sputtering and subsequentannealing under ultra-high vacuum condition. The
ARPES measurements were performed in the energy
range of 32-160 eV at the undulator beamline BL5U of
UVSOR facility.
Figure 1 shows the ARPES image of Cu (110) surface
at 9 K measured with the photon energy of 100 eV. The
free electron-like parabolic dispersion of the (bulk)
conduction band is clearly observed in the energy range
down to -3 eV below the Fermi level. The energy
dependent relaxation time of conduction electrons canbe estimated from the peak width both of energy
distribution curves and momentum distribution curves.
As expected, we confirmed that the energy dependenceof the relaxation time shows less significant variation
across the Fermi level.

Fig. 1. ARPES image of Cu (110) surface at 9 K
measured with 100 eV.
[1] T. Takeuchi, J. Thermoelectrics Soc. Jpn. 9 (2012)
1.
[2] Y. Xia et al., Phys. Rev. Applied 11 (2019) 024017.
[3] B. Xu et al., Phys. Rev. B 102 (2020) 155128.

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Temperature Dependence of the Band Folding in TiSe2
S. Tanaka1, K. Ueno2, K. Fukutani3 and K. Tanaka3
2

1
Sanken, Osaka University, Ibaraki 567-0047, Japan.
Graduate School of Science and Engineering Saitama University, Saitama 338-8570, Japan.
3
UVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan.

Layered material TiSe2 is one of the TransitionMetal-Dichalcogenide (TMDC) and has extensively
studied for decays as a typical system of ChargeDensity-Wave (CDW) transition. Although excitonic
condensation is considered to be the most importantfactor in the CDW transition in TiSe2 thanks to many
experimental and theoretical studies, there are still
many unanswered concerns regarding the electrical andatomic structure upon the CDW transition at ~200K. In
this article, we use angle-resolved photoelectron
spectroscopy (ARPES) to examine how TiSe2’s
electronic structures change with temperature. We
focus on the specifics of the band folding brought on by
the reconstruction of the (2x2x2) superstructure as aresult of the CDW transition.
Figs.1 displays the ARPES spectra at 190K (a) and8K (b) with photon energies of 46eV. The electron
pocket at M-points (commonly referred to as the
conduction band) and the hole pocket at Γ points(commonly referred to as the valence band) combine toform bands close to the Fermi level in TiSe2. As a resultof the CDW transition, where the M point of the originallattice is folded to the Γ point in the rebuilt lattice, ourmeasurements show that the replica of the valence bandat the Γ point is clearly visible at the M point at 8K.
This is in agreement with how the Brillouin zone wasrecreated when the CDW transition created the (2x2x2)
superlattice. The replica of the conduction band at the
M point, on the other hand, is faintly visible even at 8K.
We discovered that this replica’s intensity greatly
fluctuates with photon energy and is quite low athν=46eV. Moreover, the intensity distribution at the M
point significantly changes at two temperatures (see thethird panel from the top). This can be explained by the
Fermi surface modulation along the kz line due to the
CDW transition.
Together with the production of replicas and changes
in the intensity distribution, the energetic profile of theband changes with temperature. At low temperatures,the valence band’s energy location is visibly moved
downward (see the second panel from the top). This isa defining trait of the bigger gap development broughton by the CDW transition’s associated excitonic
condensation. The replica located at M at 9K is alsoenergetically displaced to the original valence band at
the same temperature. Although the specifics are still

being examined, it might also be linked to themodulation of the band along the kz line.
It should be noted that the replica at M can be dimly
detected at 190K, which is considerably lower than thereference’s CDW transition temperature. We looked
more closely at how the ARPES spectra change withtemperature and discovered that the reported
temperature of the CDW transition is around thetransition temperature determined by energetic profile,which is substantially higher than that determined byreplica intensity. Investigations are currently ongoing
to determine the physical cause of this behavior.

Fig. 1. ARPES spectra of TiSe2 taken at 190K (a) and8K (b). Upper two panels for (a) and (b) show theintensity maps along the energy-angle axes. Lower twoshow the iso-energy intensity maps along the x- andy-angles at the binding energies of 0eV and 0.4eV.

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Doping-Dependent ARPES Study of Nodal Dirac Semimetal Candidate
LaTeSb and LaTeBi
R. Saitou1, N. Kataoka1, T. Wakita1, H. Kageyama1, R. Kondo1 and T. Yokoya1,21Graduate School of Natural Science and Technology, Okayama University, Okayama 700-8530, Japan
2
Research Institute for Interdisciplinary Science, Okayama University, Okayama 700-8530, Japan

LnTe1+xSb1-x (Ln: lanthanides) is a layered material
consisting of alternative stack of a layer of LnTe and alayer of a single Sb square lattice. It is theoretically
predicted as a nodal line semimetal [1]. In addition, by
selecting a magnetic element as Ln, it is possible tobreak the time-reversal symmetry. Therefore, it is amaterial that has the potential to access novel
topological phases [2-5]. Our research group are
making an eﬀort to control the physical properties ofrelated materials by introducing magnetic elements,
substituting Sb with Bi, and changing carrier
concentration [6] for the purpose of observing theexotic transport properties peculiar to Dirac electrons.
In the present study, we have performed synchrotron
angle-resolved photoemission spectroscopy (ARPES)
to experimentally observe the electronic structure of
the non-magnetic phase and check whether the carrier
concentration can be controlled by changing the Teconcentration.
LaTe1+xSb1-x (x = -0.1 and 0.2) and LaTe1+xBi1-x (x =0.2) single crystal samples were prepared by a self-flux
method. ARPES measurements were performed at
BL5U of UVSOR III. Linear polarized light of 70-110
eV energies were used. The energy resolution was set
to ~ 40 meV. All samples were cleaved in situ on the(001) plane in an ultrahigh vacuum of less than 5.0 x
10-9 Pa and were measured at 20 K.
Figure 1(a) shows the valence band dispersion of
LaTe1.2Bi0.8 along the Γ-M direction in the Brillouinzone (BZ), measured with the photon energy of 94 eV.
White regions, which are the higher-intensity regions,correspond to band dispersions. The band dispersionsof the two samples are symmetric with respect to thehigh symmetry points: Γ and M of the bulk BZ of
LaTe1+xBi1-x. This indicates that the band dispersions
reflect intrinsic electronic structure of the sample.
Figure 1(b) is the valence band dispersion of
LaTe1.025Bi0.975 measured with the same experimental
condition. Although there are small diﬀerences in theintensity distribution between the two ARPES maps,
which may originate from the diﬀerence in the conditionof the measured surface, the band dispersions of thetwo maps look very similar with each other. On theother hand, from a careful comparison, it was foundthat the energy positions of the structures in the x = 0.2

sample shift to the higher biding energy side by ~ 100
meV. Two guidelines to demonstrate the energy shift ofstructures at the Γ point were shown with orange dottedlines. This indicates that increasing Te concentration
works as electron doping and one can control the
relative energy between the Dirac nodal line and the
Fermi level (EF) by changing the relative concentration
between Te and Bi. Since the energy position of the
Dirac nodal line in the x = 0.025 sample was found tobe located above EF, the Dirac nodal line in the x = 0.2
sample may be located closer to EF or just at EF. Further
ARPES studies along the X-R line in the Brillouinzone, where the Dirac nodal line is expected to islocated by band structure calculations, is planned toconfirm this anticipation.

Fig. 1. Comparison of ARPES intensity maps along theΓ-M direction of LnTe1+xBi1-x between (a) x = 0.2 and(b) x = 0.025, measured with 94 eV photons and at 20
K.
[1] A. Weiland et al., APL Mater. 7 (2019) 101113.
[2] Y. Wang et al., Phys. Rev. B 103 (2021) 125131.
[3] S. Yue et al., Phys. Rev. B 102 (2020) 155109.
[4] P. Gebauer et al., Chem. Mater. 33 (2021) 2420.
[5] L. M. Schoop et al., Sci. Adv. 4 (2018) eaar2317.
[6] R. Kondo, in preparation.

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Symmetry Reduction of the Electronic Structure in Heavily Overdoped PbBi2201 Observed by Angle-resolved Photoemission Spectroscopy
Y. Miyai1, T. Kurosawa2, M. Oda3, M. Arita4, K. Tanaka5, S. Ideta4 and K. Shimada4
1
Graduate School of Science, Hiroshima University, Higashi-Hiroshima 739-8526, Japan
Fuculty of Science and Engineearing, Muroran Institute of Technology, Muroran, 050-8585, Japan3
Department of Physics, Hokkaido University, Sapporo 060-0809, Japan
4
Hiroshima Synchrotron Radiation Center, Hiroshima University, Higashi-Hiroshima 739-8526, Japan
5
UVSOR-III Synchrotron, Institute for Molecular Science, Okazaki, 444-8585, Japan2

cuprateHightransition-temperature(TC)superconductors have attracted much interest since
their discovery in 1986 for their high superconducting
transition temperature as well as unusual physicalproperties such as a pseudogap state and a nematic
phase [1, 2]. Superconductivity occurs in the CuO2
plane and the Cu 3dx2-y2 state forms the Fermi surface(FS). One can expect a four-fold symmetry of the FS
because the CuO2 plane is tetragonal. However,symmetry reduction of the electronic structure has beenreported in Bi-based cuprate superconductors recently[2, 3]. Similar symmetry reduction or nematicity was
found in iron-based superconductors, the electronic
states break the four-fold rotational symmetry of thelattice [4, 5]. Although nematicity in electron liquids
has attracted much interest, the rotational symmetry
breaking in the electronic states for high-TC cuprate
superconductors has not been clarified yet.
Here, we have examined the symmetry of theelectronic
structureofheavily
overdoped(Bi,Pb)2Sr2CuO6+δ (Pb-Bi2201) (TC < 2.5 K) using highresolution angle-resolved photoemission spectroscopy(ARPES). We selected Bi2201 because it has a single
CuO2 plane and one can exclude the complexity of theelectronic structure such as bilayer splitting derived
from two CuO2 planes. Furthermore, the pseudogap
disappears in the heavily overdoped sample and one
can clearly see the entire FS in the normal state without
Fermi arc.
Figures. 1(a) and 1(b) show the FS obtained byrotating the sample around the two nodal directions
taken at hν = 60 eV and T = 20 K with the s-polarizationgeometry. We have found that the value of 2kF (kF:
Fermi momentum) for the two nodal directions are
diﬀerent; 2kF(1) = (7.996 ± 0.003) × 10-1 Å-1 (Fig. 1(a))
and 2kF(2) = (8.572 ± 0.003) × 10-1 Å-1 (Fig. 1(b)). Thisdiﬀerence independents of temperature from T = 20 K
to 260 K. In addition, we reveal that the energy
dependence of the quasiparticle lifetime broadening is
also diﬀerent for these two nodal directions. The
situation is similar for the samples with TC = 4, 6, and
10 K. Our results indicate C4 symmetry breaking of theelectronic structure in the CuO2 plane in the heavily

overdoped Pb-Bi2201, which might be related to acharge order formation in the heavily overdoped PbBi2201 as observed by resonant inelastic X-ray
scattering [6], and/or the nematic phase associated with
the Pomeranchuk instability as suggested by Raman
scattering measurements on Bi2212 [7].

Fig. 1. (a), (b) Fermi surface mapping obtained byrotating around the two nodal directions taken at hν =60 eV and T = 20 K with the s-polarization geometry.
Red and blue markers indicate the Fermi surface points
determined from the peaks of the momentum
distribution curves. We determine 2kF values (2kF(1) and2kF(2)) for the two nodal directions as shown in the inset
of panel (b).
[1] M. Hashimoto et al., Nat. Phys. 10 (2014) 483.
[2] S. Nakata et al., npj Quantum Mater. 6 (2021) 86.
[3] Y. Zheng et al., Sci. Rep. 7 (2017) 8059.
[4] H. C. Xu et al., Phys. Rev. Lett. 117 (2016) 157003.
[5] J-H. Chu et al., Science 329 (2010) 824.
[6] Y. Y. Peng et al., Nat. Mater. 17 (2018) 697.
[7] N. Auvray et al., Nat. Commun. 10 (2019) 5209.

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Far- and Mid-infrared Absorption on the Single-crystal Pentacene
Y. Nakayama1, 2, K. Yamauchi1, Y. Baba1 and J. Miyamoto1
1

Department of Pure and Applied Chemistry, Tokyo University of Science, Noda 278-8510, Japan
2
Institute for Molecular Science, Okazaki 444-8585, Japan

Electronic coupling with molecular vibrations and/or
lattice phonons is one of the key issues for theconsideration of charge carrier transport in organic
semiconductor solids. In the present work, we
conducted infrared absorption measurements on the
pentacene single-crystal (PnSC) samples as a modelcase of high-mobility organic semiconductors for the
elucidation of the electron-vibration coupling in welldefined solid-state molecules.
Infrared absorption measurements were carried out at
BL6B. A Si bolometer or a HgCdTe detector was used
for the signal detection in a wave number range of
100 – 700 cm−1 (FIR) or 700 – 7000 cm−1 (MIR),
respectively. Details of the PnSC samples andmeasurement geometry were the same as reported
previously [1]. The data were collected by changing thesample azimuthal angle by 180° in 15° and 45° intervals
for the FIR and MIR measurements, respectively. In
this report, angularly averaged spectra were used forthe analyses. Spectra measured through a diamondplate were adopted as blank spectra (I0) to derive theabsorbance of PnSCs.
Figure 1 shows a typical FIR spectrum of PnSC in aregion where prominent peaks were observed. A
persistent background modulation of a “frequency” at(5.9 ± 0.2) cm−1 is filtered out for further analyses. The
spectral feature can be attributed to two vibration
modes predicted to be at 476.9 cm−1 and 491.7 cm−1. In
the present measurements, twenty vibration modes
were assignable in the spectra. Energy deviations of theexperimental vibration peaks with respect to thetheoretical values calculated in the B3-LYP/6-31g(d)level are plotted in Fig. 2, where a recommended “scale
factor” for the calculated wavenumbers [2] is indicatedas a standard. As the vibration mode #88 (in-planescissoring of the backbone) exhibited the best match,
the relative intensity for each spectral peak is derived
with respect to the mode #88 intensity and plotted as afunction of the corresponding calculated relative
intensity in Fig. 3. Further discussion on the results is
yet under consideration.

Fig. 2. Energy deviation of the experimental peak
positions with respect to the calculated values. The sizeof the symbols indicates the peak intensity.

Fig. 3. Experimental relative peak intensity plotted asa function of the calculated magnitudes. The color of
the symbols corresponds to the mode number indicatedin Fig. 2. The inset image shows the mode #88 vibrationof the pentacene molecule.
[1] Y. Nakayama and J. Miyamoto, UVSOR Activity
Report 2020 (2021) 83.
[2] J. P. Merrick, D. Moran and L. Radom., J. Phys.
Chem. A 111 (2007) 11683.

Fig. 1. FIR absorption spectrum on the PnSC.

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BL7U

ARPES Study of a chalcopyrite-type Topological Insulator Candidate
T. Iwaya1,, A. Honma1, K. Nakayama1, K. Sugawara1,2, S. Souma2,3, K. Tanaka4,5,
T. Takahashi1, K. Segawa6 and T. Sato1,2,3,7
1

Department of Physics, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan
Advanced Institute for Materials Research (WPI-AIMR), Tohoku University, Sendai 980-8577, Japan
3
Center for Science and Innovation in Spintronics (CSIS), Tohoku University, Sendai 980-8577, Japan
4
UVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
5
School of Physical Sciences, The Graduate University for Advanced Studies (SOKENDAI),
Okazaki 444-8585, Japan
6
Department of Physics, Kyoto Sangyo University, Kyoto 603-8555, Japan
7
International Center for Synchrotron Radiation Innovation Smart (SRIS), Tohoku University,
Sendai 980-8577, Japan
2

Three-dimensional topological insulators (3D TIs)
are a novel quantum state of matter where the bulk
band gap induced by a strong spin-orbit coupling leads
to the appearance of gapless Dirac-cone surface states
protected by time-reversal symmetry. The discovery of
3D TIs has further stimulated the search for novel
topological materials. From the viewpoint of the crystal
symmetry, most of the 3D TIs so far discovered, e.g.,
Bi2Se3, Bi2Te3, and TlBiSe2, have the spatial inversion
symmetry in the crystal. On the other hand, there areseveral theoretical proposals of TI candidates withbroken inversion symmetry. There is a demand to
experimentally discov such symmetry-broken phasebecause a peculiar phenomenon which cannot berealized in inversion-symmetric TIs is predicted toemerge.
Here we focus on CdGeAs2 which crystalizes in achalcopyrite structure with I̅ 42d space group. As seenfrom Fig. 1(a), the crystal consists of a stack of zinc
blend structure and hence breaks the inversion
symmetry. Recent theoretical study predicted CdGeAs2
to be a topological insulator [1]. Owing to the inversion
symmetry breaking, CdGeAs2 can have nontrivial
Fermi arc surface states and lead to a giant
magnetoelectric eﬀect. To establish a material platformof such exotic phenomena, experimental elucidation of
the topological properties in CdGeAs2 is highly desired.
In this study, we have performed high-resolution
angle-resolved photoemission spectroscopy (ARPES)
of CdGeAs2 at BL7U. Single crystals of CdGeAs2 weregrown by the vapor-phase growth method. Clean
surfaces for ARPES were obtained by in situ cleavingof the crystals. By x-ray laue diﬀraction, the cleaved
surface was determined to be (101) plane. ARPES
measurements were performed by using a MBS-A1
spectrometer at BL7U with linearly-polarized energytunable photons.
Figure 1(b) shows the ARPES intensity plot along a
momentum cut crossing the Γ point of the bulk Brillouinzone. We observed several highly dispersive hole-likebands centered at the Γ point. These bands are
reproduced by the band calculations shown by red

curves and attributed to the bulk valence bands withdominant As 4p orbital character. We further performed
detailed measurements over the entire Brillouin zone
with tuning photon energies to find a signature of the
topological surface states.

Fig. 1. (a) Three-dimensional view of the crystal
structure of CdGeAs2. (b) ARPES intensity plotted as afunction of binding energy and wave vector measured
in CdGeAs2. Red curves are the result of first-principles
band structure calculations.
[1] K. Osumi et al., Commun. Phys. 4 (2021) 211.

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Electronic Structure of the five-fold oxygen-coordinated Cuprate
Superconductor
M. Horio 1, M. Miyamoto1, X. Peiao2, K. Tanaka3, T. Taniguchi2, M. Fujita2 and I. Matsuda1
1Institute for Solid State Physics, The University of Tokyo, Kashiwa, Chiba 277-8581, Japan
2
Institute for Materials Research, Tohoku University, Katahira, Sendai 980-8577, Japan
3
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan

Structural isomers of so-called 214-type cuprates
provide a unique platform for studying the eﬀect ofoxygen coordination on the electronic structure ofcuprate superconductors. The local oxygen coordination
around copper can be varied from a six-fold octahedron(T-type) to a four-fold square plane (T’-type). It is
known that a decrease in the oxygen coordination
number leads to a decrease in the charger-transfer gap
and hence electron correlation [1]. However, while theT-type cuprates can be doped only with holes, the T’type cuprates do not usually accept hole doping [2],preventing direct comparisons. On the other hand, T*type cuprates with five-fold pyramidal oxygen
coordination can be hole-doped and are directlycomparable to the T-type one [3]. Optical conductivity
studies of the parent compound suggest that T*-type
cuprates have a smaller charge transfer gap than T-type[1]. As-grown samples of the T*-type cuprates are
known to have oxygen defects in the apical site, and inorder to induce superconductivity, post-growth highpressure oxygen annealing is required [3,4]. Recent
oxygen K-edge x-ray absorption spectroscopy (XAS)
studies [5] found a dramatic increase in doped holes
upon oxygen annealing, consistent with compensationof oxygen defects. The Tc of O2-annealed T*-SmLa1xSrxCuO4 (SLSCO) monotonically increases withdecreasing Sr concentration [6], in contrast to thedome-like behavior of the T-type La2-xSrxCuO4 (LSCO).
The diﬀerent superconducting properties between T*and T-type cuprates suggest a significant diﬀerence inthe electronic structure associated with a change in thecoordination number of oxygen. However, theelectronic structure of T*-type cuprates, including its
evolution by annealing, is still largely unknown [7],even 35 years after its discovery. In this work, we
performed angle-resolved photoemission spectroscopy(ARPES) measurements on the T*-type cuprates T*SLSCO.
Single crystals of T*-SLSCO (x = 0.25) were grownby the travelling-solvent floating-zone method. After
post-growth O2 annealing at 500 ℃ and 45 MPa for 72
hours, the sample showed superconductivity below Tc= 17 K. ARPES measurements were performed at
BL7U of UVSOR at T = 7 K and hν = 18 eV.
Fig. 1 presents ARPES spectra obtained from T*SLSCO. While the spectral weight becomesdiminishingly small as approaching the Fermi level,
Fermi crossing is observed for the nodal spectrum (#1).
As moving away from the nodal region, the band
become gapped with a strong suppression of thespectral weight, signifying the opening of a pseudogap.
According to a previously reported phase diagram for
T*-SLSCO, x = 0.25 corresponds to deep in theoverdoped region. This is apparently incompatible withthe present observation of the robust pseudogap, which
is typical of underdoped or optimally doped samples.
The result suggests a potentially unique phase diagramof T*-type cuprates, which deserves further systematicinvestigations with varying hole concentrations.

Fig. 1. ARPES spectra of O2-annealed T*-SLSCO (x =0.25). (a)-(f) Energy-momentum maps from the nodal
to antinodal regions. Cut positions are indicated in (g).
(h) Energy distribution curves at each kF point.
[1] Y. Tokura et al., Phys. Rev. B 41 (1990) 11657.
[2] N. P. Armitage et al., Rev. Mod. Phys. 82 (2010)2421.
[3] J. Akimitsu et al., Jpn. J. Appl. Phys. 27 (1988)
L1859.
[4] F. Izumi et al., Physica C 158 (1989) 440.
[5] S. Asano et al., J. Phys. Soc. Jpn. 89 (2020) 075002.
[6] T. Kakeshita et al., J. Phys.: Conf. Ser. 150 (2009)052089.
[7] A. Ino et al., Physica B 351 (2004) 274.

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Angle-Resolved Photoemission Study of Solid Electrolytes Li3xLa2/3-xTiO3
Bulk Single Crystal
S. Koyama1, M. Nakatake2, S. Takakura3, K. Tanaka4,5,
Y. Fujiwara6, T. Taishi6, H. Moriwake7, Y. Iriyama1 and T. Ito1,3
1

Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan
2
Aichi Synchrotron Radiation Center, Seto, 489-0965, Japan
3
Synchrotron radiation Research center, Nagoya University, Nagoya 464-8603, Japan
4
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
5
The Graduate University for Advanced Studies, Okazaki 444-8585, Japan
6
Faculty of Engineering, Shinshu University, Nagano 380-8553, Japan
7
Nanostructures Research Laboratory, Japan Fine Ceramics Center, Nagoya 456-8587, Japan

With the recent expansion of the use of lithium-ion
secondary batteries, development of all-solid-statebatteries using lithium-ion conductive inorganic solid
electrolytes has been progressing to realize further
safety, high energy density, and high output, etc. On theother hand, the valence-band electronic structure,
which is essential to understand the relation between
lithium-ion and electron conductivity in inorganic solid
electrolytes, has not been well elucidated yet, though
the chemical analysis using operand X-ray
photoemission has intensively been applied on thesystem [1,2]. In this study, we have performed angleresolved photoemission spectroscopy (ARPES)
measurements on Li3xLa2/3-xTiO3 (LLTO) bulk single
crystals to clarify the eﬀect of lithium on the electronic
structure of solid electrolytes. The results werecompared with the ARPES study on LixLa(1-x)/3NbO3(LLNbO) in which relatively lower Li ion conductivity
has been reported [3].
ARPES measurements were performed at the
UVSOR-Ⅲ BL7U. Data were acquired with hν = 18 eVat room temperature. To minimize spectral modification
due to photo-irradiation, photon flux was suﬃciently
reduced (<3E+10 photons/s) during all measurements.
Single crystals were cleaved in situ along (100) plane,
where La/Li rich (A1) and La/Li poor layers (A2)appear alternately (inset: Fig.2 (a)).
Figure 1 (a) and (b) show ARPES spectra and band
structure along the ΓX line of LLTO, respectively. The
observed band structure mainly consists of two peaks
around 4 and 7 eV with the band gap about 3 eV. Fromthe comparison with DFT calculation (Fig. 2(a)) [4], wefound that the valence band width (~5 eV) seems to be
similar between the ARPES and calculation.
When we compare the ARPES band structure
between LLTO and LLNbO bulk single crystals [3], wefound that the valence band width of LLTO becomes
about 1 eV narrower than LLNbO, while the band gap
size observed as almost the same. In Fig. 2(a) and (b),the observed diﬀerences of band width as well as the
spectral features between LLTO and LLNbO are
qualitatively reproduced by the DFT calculations. The
results indicate the applicability of ARPES to study theelectronic structure of solid electrolytes single-crystal.

Fig. 1. ARPES spectra (a,c) and band structures (b,d)
along the ΓX line of Li3xLa2/3-xTiO3 (a,b) andLixLa(1-x)/3NbO3 (c,d), respectively. Solid and dashedlines are guides for eyes.

Fig. 2. The partial density of states of Li0.2375La0.5875TiO3[4] (a) and La1/3NbO3 (b), respectively. Inset of eachpanel shows average crystal structures of LLTO andLLNbO, respectively.
[1]K. Hikima et al., Commn. Chem. 5 (2022) 52.
[2]K. N. Wood et al., Nature Commun. 9 (2018) 2490.
[3]Y. Fujiwara et al., J. Cryst. Growth 433, 48-53(2016); Y. Fujiwara et al., Jpn. J. Appl. Phys. 55,
090306 (2016).
[4]K. Dai et al., J. Mater. Sci. 57 (2022) 2825.

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BL7U

Electronic Structure of Layered Nitride Chloride ZrNCl by ARPES
N. Kataoka1, R. Saitou1, M. Tanaka2 and T. Yokoya1,31Graduate School of Natural Science and Technology, Okayama University, Okayama 700-8530, Japan
2
Graduate School of Engineering, Kyushu Institute of Technology, Kitakyushu 804-8550, Japan
3
Research Institute for Interdisciplinary Science, Okayama University, Okayama 700-8530, Japan

spectrum near EF shows a small structure, whose energy
position and spectral shape are similar to the structure
before K deposition (Figure 2), although the intensity
increases after K deposition. Based on previous studies,
the structure before evaporation may be a state causedby hydrogen impurities[5]. Further studies, including
comparison with theoretical studies that also take thesurface state into account, are necessary to understandthese observations.

Fig. 1. 2nd-derivative ARPES intensity maps along
Γ-M of ZrNCl before (a) and after (b) K deposition.

Normalized intensity(arb. units)

Electron-doped layered nitride chloride ZrNCl shows
superconductivity of Tc ~ 16 K by intercalating alkali
metals between the layers[1]. Observed exotic
properties have suggested that its superconducting
properties are diﬃcult to be explained by the BCS
theory[2]. Theoretical studies have proposed a model
mediated by spin fluctuations[2] and a superconducting
mechanism with a BCS-BEC crossover[3]. However,there are no experimental observations of the electronic
structure by ARPES measurements, and thesuperconducting
mechanismhasremainedundetermined. This is due to the fact that alkali metalinserted ZrNCl is easily oxidized in the atmosphere andthat it is diﬃcult to obtain large single-crystal samples.
In this study, we prepare electron-doped ZrNCl bydepositing alkali metals in vacuum on a relatively large
parent material. The electronic structure of ZrNCl
before and after alkali metal deposition is studied by
ARPES.
Samples were prepared by vacuum evaporation oncleaved ZrNCl single crystals at room temperature inultrahigh vacuum using a Potassium(K) deposition
source. The samples were transferred from theevaporation chamber to the measurement chamber.
ARPES measurements were performed at BL7U of
UVSOR III with 28–40 eV photons and an energy
resolution of 15~20 meV. The measurement temperature
was 40 K.
Figures 1(a) and 1(b) show the band dispersion of
Γ-M line in ZrNCl before and after K deposition.
Before deposition, the top of the valence band was
located at ~ 3.0 eV at the Γ point and the bottom of thevalence band was located at ~ 8.3 eV at the M point.
After K deposition, the band near the Γ point, the top of
the valence band, is shifted to the higher binding energy
side by about 100 meV. The energy position of thebottom of the valence band at the M point did notchange significantly. A theoretical study predicted abandwidth of 6.1 eV[4] for ZrNCl and significant
expansion of the valence band width by alkali metalintercalation. This is diﬀerent from nearly the sameband width between before and after K deposition.
Regarding the change of the bandwidth by K
evaporation, it is possible that the result is not an
intrinsic change in electronic structure, but rather
reflect an eﬀect of the surface state formed by thedeposition. For near the Fermi energy (EF), after
deposition, a clear dispersive band was not observed at
the K point, where electron pockets are expected toappear theoretically. On the other hand, angle integrated

1.0

ZrNCl
K deposited ZrNCl
Au

0.8

0.6
0.4
0.2
0
Binding energy (eV)-0.2

Fig. 2. Angle-integrated spectra near EF of ZrNCl
before and after K deposition, compared with Au.
[1] Y. Kasahara et al., Physica C 514 (2015) 354.
[2] K. Kuroki, Phys. Rev. B 81 (2010) 104502.
[3] Y. Nakagawa et al., Science 372 (2021) 190.
[4] Z. P. Yin et al., Phys. Rev. X 3 (2013) 021011.
[5] T. Yokoya et al., Phys. Rev. B 70 (2004) 193103.

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Ⅲ-2 Material Sciences

BL7U

Low-Energy ARPES Study on the Electronic Structure of Cr2Se3
C.-W. Chuang1,, T. Kawakami1, T. Kato1, K. Sugawara1,2, K. Nakayama1, S. Souma2,3,
K. Tanaka4,5, A. Chainani6, T. Takahashi1, K. Segawa7 and T. Sato1,2,3,8
1

Department of Physics, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan
Advanced Institute for Materials Research (WPI-AIMR), Tohoku University, Sendai 980-8577, Japan
3
Center for Science and Innovation in Spintronics (CSIS), Tohoku University, Sendai 980-8577, Japan
4
UVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
5
School of Physical Sciences, The Graduate University for Advanced Studies (SOKENDAI),
Okazaki 444-8585, Japan
6
National Synchrotron Radiation Research Center, Hshinchu, 30077, Taiwan ROC
7
Department of Physics, Kyoto Sangyo University, Kyoto 603-8555, Japan
8
International Center for Synchrotron Radiation Innovation Smart (SRIS), Tohoku University,
Sendai 980-8577, Japan
2

Transition metal chalcogenides (TMCs) are a groupof materials that have been intensively studied for longtime because of a wide variety of physical properties
depending on their crystal structure and composition,
including superconductivity, metal-insulator transition,and three-dimensional topological insulators. Recently,
TMCs have attracted even more attention because their
atomic layer films show dramatically diﬀerent
properties from those of bulk counterparts, such as
Ising superconductivity, spin-valley Hall eﬀect, twodimensional topological insulators. To understand andcontrol these exotic properties, an experimental study
on the electronic structure of TMCs is of crucial
importance.
Here we focus on a chromium-based TMC, Cr2Se3
with the two-dimensional rhombohedral crystal
structure (NiAs type; P63/mmc). Bulk Cr2Se3 is known
as a thermoelectric material with a large figure of merit.
This material is attracting attention because of
intriguing magnetic properties; bulk Cr2Se3 exhibits acollinear antiferromagnetic order with TN ~ 45 K,
followed by a successive transition to a non-collinear
antiferromagnetic phase [1], whereas monolayer Cr2Se3
was predicted to be a ferromagnet which potentiallyhosts a half metallic ground state [2]. To clarify theinterplay between these magnetic orders and theelectronic structure, we have performed angle-resolved
photoemission spectroscopy (ARPES) measurementsof bulk and monolayer Cr2Se3.
High-quality bulk Cr2Se3 was grown by flux method.
Monolayer Cr2Se3 was grown on graphene/SiC bymolecular-beam epitaxy method. High-resolution
ARPES measurements were performed by using a
MBS-A1 spectrometer at BL7U with linearly-polarizedenergy-tunable photons.
Figure 1 shows representative ARPES results in theantiferromagnetic state of bulk Cr2Se3, i.e. ARPES
spectra measured along a momentum cut crossing the Γpoint [Fig. 1(a)] and the corresponding intensity plot
[Fig. 1(b)]. We observed several band dispersions in theenergy range of the Fermi level (EF) to 5 eV, such as arelatively flat hole-like band near EF and a highly
dispersive hole-like band topped at 2 eV below EF at theΓ point. Upon increasing the temperature, we found afinite change in spectral intensity across TN, indicativeof magnetism-induced electronic reconstructions. We
also measured the photon-energy dependence of theband dispersion and determined the three-dimensionalbulk band structure. In addition, we found a clear
diﬀerence in the band structure and its temperaturedependence between bulk and monolayer Cr2Se3. The
obtained ARPES results were compared with firstprinciples band structure calculations to understand thetemperature- and thickness-dependent changes in theband structure.

Fig. 1. (a) ARPES spectra in the valence band region of
bulk Cr2Se3 measured at T = 30 K with 21-eV photons,and (b) corresponding intensity plot as a function ofbinding energy and wave vector.
[1] Y. Adachi et al., J. Phys. Soc. Jpn. 63 (1994) 1548.
[2] J.-Y. Chen et al., Adv. Electron. Mater. 6 (2020)
2070001.

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BL7U

Polarization-Dependent Photoemission from the Folded Band of TiSe2
S. Tanaka1, K. Ueno2, K. Fukutani3 and K. Tanaka3
2

1
Sanken, Osaka University, Ibaraki 567-0047, Japan.
Graduate School of Science and Engineering Saitama University, Saitama 338-8570, Japan.
3
UVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan.

It is crucial for the creation of symmetry-broken
collective phases, such as charge density waves andtopological and superconducting states of matter, thatcrystalline solids have a momentum-dependent orbital
structure. Measurements with the polarizationdependent angle-resolved photoelectron spectroscopy(ARPES) can provide important details on the material’s
orbital texture. Layered material TiSe2, one of thetransition-metal-dichalcogenide (TMDC) and known
as a model system of the charge-density wave (CDW)
transition, is a good candidate to make such a study,
since TiTe2, which has a similar electronic structure to
TiSe2 but does not exhibit the CDW transition, has been
recently well studied by similar method[1].
Fig. 1 shows ARPES spectra near the Γ point at 10K
taken using the vertically polarized photon of 7eV. The
cutting plane along the kx (at ky=0) and ky (at kx=0)
axes is shown in the lower panels, while the upper
panel displays the photoelectron intensity map along
the kx-ky plane at the Fermi level. The band below theBE~0.07eV is the Se4p/Ti3d valence band, and theband near the Fermi level is the replica of the Ti3dderived conduction band originally located at the M
point, which is caused by the formation of the (2x2x2)
superlattice as a result of the CDW transition. The
assignment can be confirmed by the observation of theextinction of this feature at higher temperatures. The
photoelectron intensity distribution, however, isdiﬀerent from the original Ti3d conduction band at M.
White dot lines represent the replica’s anticipatedtraces, which originate from the six nearby M points,
and only a portion of them have photoelectrons visible.
This must be due to the matrix element eﬀect, which
relates to the orbital texture and also discerning
structural and collective phases of the material in the
CDW transition.
We measure the polarization-dependent ARPES byrotating the sample along the surface normal to provide
information about the matrix element eﬀect (azimuthal
rotation). The vertically-polarized photon was used,
and the polarization vector is always parallel to thesample surface. The variation in the photoelectron
distribution as a result of azimuthal angle is depicted in
Figure 2. Shiny branches shift as the polarization
vector’s angle with the sample axis changes. It makes it
evident that the matrix element is crucial, and the indepth research, currently underway, will yield
information regarding the orbital texture of the replicaband formed by the CDW transition.

Fig. 1. ARPES spectra of TiSe2 at 10K. The photon
energy taken was 7eV of vertical polarization.

Fig. 2. ARPES intensity maps near the Fermi level as afunction of the azimuth rotation. The photon of 7eV
with a vertical polarization is used.
[1] S. Beaulieu et.al., npj Quantum Materials 6 (2021)
93.

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Ⅲ-2 Material Sciences

BL7U

Momentum Dependence of the Spectral Weight in the Single Layer HighTc Cuprate Bi2Sr2CuO6+δ Studied by ARPES
Y. Onishi1, Y. Miyai1, Y. Tsubota1, S. Kuma2, M. Atira2, K. Tanaka3, H. Eisaki4, S. Ishida4,
K. Shimda1,2 and S. Ideta1,21Graduate School of Advanced Science and Engineering, Hiroshima Univ., Japan
2
Hiroshima Synchrotron Radiation Center (HiSOR), Hiroshima Univ., Japan
3
UVSOR-III Synchrotron, Institute for Molecular Science (IMS), Japan.
4
National Institute of Advanced Industrial Science and Technology (AIST), Japan

Spectral weight (SW) directly observed by angleresolved photoemission spectroscopy (ARPES) has theinformation of the electronic structure which is related
to the mechanism of high-transition temperature (Tc)
cuprate superconductivity [1-3]. Nonetheless extensive
experimental and theoretical studies have been reported,the mechanism of high-Tc cuprates have not been clear
yet, why their Tc exceeds above ~40 K which cannot be
explained by the BCS theory [4]. To understand themechanism of high Tc in cuprate superconductivity, oneof the essential physical parameters is superfluid
density (ρs) which plays an important role in determining
Tc and might be proportional to SW observed by
ARPES [1,2,5,6]. In this study, we have performed an
ARPES study to investigate the relationship between
coherent spectral weights (SW) on the Fermi surface
directly and Tc in cuprates, which seem to correspondto the magnitude of ρs and Tc [5].
We measure the electronic structure of the singlelayer Bi-based high-Tc cuprate superconductor,
Bi2Sr2CuO6+d (Bi2201), which has one CuO2 layer inthe unit cell and shows a high Tc of 35-40 K at optimal
doping [7]. We have performed ARPES measurements
systematically to directly investigate the electronic
structure of the optimally doped (Tc ~ 35 K) andoverdoped (Tc ~ 30 K) Bi2201. ARPES were carriedout at BL7U, and temperature was set at ~10 K (< Tc)
and 1.5Tc to measure the electronic structure in the
superconducting and normal states, respectively. The
photon energy was hν = 17 eV. High-quality single
crystals of Bi2201 were cleaved in-situ in the ultrahighvacuum ~5×10-9 Pa.
In this study, We have clearly observed Fermi surface(FS) on Bi2201 in the s polarization above and below

Tc. Energy distribution curves (EDCs) are symmetrized
and we have estimated the Fermi momentum (kF) on theentire FS, where the kF is determined by minimum gap
locus method.
Compared with EDC in the
supercondcuting and normal states, we have successfully
observed diﬀerence of the spectral weight even though
the nodal region in contrast with the previous study [6].
We will systematically measured doping dependence of
SW in the nodal direction. From the present study, we
found that the even in the nodal region which shows thezero sueprconducting gap, the nodal region should
contirbute to the supercondcutivity in cuprates. As anext step ,we will measure the momentum dependence
on the entire FS and discuss the distribution of SW on
FS. We will also study the relationship between
pseudogap and the distribution of SW.

Fig. 1. Symmetrized EDC of OPT35K (a) and OD30K(b).
[1] D. L. Feng et al., Science 289 (2000) 277.
[2] H. Ding et al., Phys. Rev. Lett. 87 (2001) 227001.
[3] K. M. Shen et al., Science 307 (2005) 901.
[4] W. L. McMillan, Phys. Rev. 167 (1968) 331.
[5] Y. J. Uemura et al., Phys. Rev. Lett. 66 (1991) 2665.
[6] T. Kondo et al., Nature 457 (2009) 296.
[7] A. Iyo et al., J. Phys. Soc. Jpn. 76 (2007) 094711.

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BL7B

Excitation Spectra of Plastic Scintillators in the Vacuum Ultraviolet Region
M. Koshimizu1, Y. Fujimoto2 and K. Asai3
2

1
Research Institute of Electronics, Shizuoka University, Hamamatsu 432-8011, Japan
Department of Applied Chemistry, Graduate School of Engineering, Tohoku University, Sendai 980-8579, Japan

Plastic scintillators consist of host polymer andorganic phosphor molecules and are widely used owing
to their fast response and easy fabrication at large scale.
The scintillation process in the plastic scintillators isroughly described as initial formation of ionization andelectronic excitation and subsequent transfer of theexcitation energy to the phosphor molecules. In theconsideration of the scintillation process, we have toconsider two kinds of electronic excitations: singlet andtriplet states. The triplet states are formed in two
processes: one is the intersystem crossing from thesinglet to the triplet states, and the other is the direct
formation of the triplet states upon recombination ofionization. To analyze the contribution of the latterprocess, we consider that the excitation in the vacuum
ultraviolet (VUV) light may be a convenient tool,
because the excitation by the VUV light produces
ionization at higher probability with the excitation
photon energy. In this study, we measured the excitation
spectra of the plastic scintillators at 50–200 nm.
Plastic scintillators were fabricated using polystyrene
as the host polymer and DPO and POPOP as theprimary and secondary phosphors, respectively. The
samples having diﬀerent phosphor concentrations were
fabricated. The photoluminescence spectra of thesamples were obtained with VUV excitation at BL7B,
UVSOR. The excitation spectra were obtained as theemission intensity in the photoluminescence spectra asfunctions of the excitation wavelength.
The photoluminescence spectra of the samples arepresented in Figure 1. The emission bands are derived
from the singlet excitation of POPOP. The spectra weresimilar at diﬀerent excitation wavelengths. The
excitation spectra of the samples with diﬀerent DPOPOPOP concentrations are presented in Figures 2 and3. The photoluminescence intensity increased andsubsequently decreased as the excitation wavelength
became shorter. The increase in the intensity down to
150 nm can be attributed to production of secondary
excitation. The decrease in the intensity can be
attributed to the enhanced probability of the triplet
formation.

Fig. 1. Photoluminescence spectra of the plastic
scintillators with excitation at 150 nm.

Fig. 2. Excitation spectrum of the plastic scintillators
having DPO-POPOP concentration of 0.5 wt%.

Fig. 3. Excitation spectrum of the plastic scintillators
having DPO-POPOP concentration of 2 wt%.

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Ⅲ-2 Material Sciences

BL7B

Mineral Analysis for Resource Exploration by Deep Ultraviolet Spectroscopy
T. Shimizu, K. Shinohara, K. Yamanoi and N. SarukuraInstitute of Laser Engineering, Osaka University, 2-6 Yamadaoka Suita, Osaka 565-0875 Japan

Vacuum ultraviolet (VUV) light has important
technological applications in photochemical processing,surface treatment, optical cleaning of semiconductor
substrates, and sterilization. In particular, it has beensuggested that non-contact sterilization, treatment, andprocessing may be advanced by using VUV in thecurrent coronavirus pandemic. To keep pace with therapid progress in VUV research and application, it isessential to develop detectors in the short wavelength
range. Conventional detectors are mainly sensitive only
to visible light, and therefore VUV scintillators basedon rare-earth ions and wide bandgap materials havebeen investigated for the detection of VUV. In our
research group, we have developed scintillators withrare-earth ions doped in fluoride materials using widebandgap materials and have achieved good results.
Currently, there is a need to develop a spectrometerfor two-dimensional analysis of broadband light, whichis required in the fields of industrial technology, energy,
and the environment. Imaging spectroscopy is widelyused for the identification of molecular species of gases
and nondestructive analysis of liquids and solids, and is
beginning to be applied to environmental measurements
and resource surveys. In addition to the sorting by
visible light imaging called color sorting, multiwavelength imaging measurement is becoming a key tosolving social problems in the future. In addition, thenon-destructive nature of the measurement reduces theenvironmental burden, and research that integrates thehumanities and sciences, such as the non-contact
analysis of cultural assets, is also expected. If thisimaging spectroscopic measurement can be performed
in a large space, it is expected to make it possible toestimate the location of buried resources without
digging, and to analyze tiles and paints on the walls ofvaluable old temples and shrines.
In the case of resource survey as one of the goals, thedeep ultraviolet region, such as VUV, is compatible
with the absorption and emission of quartz, the mostcommon mineral on earth, for observation, and its
characteristics are well represented. On the other hand,the practical application of imaging spectroscopy
systems, for which technology has been accumulated in
the visible light region, has not progressed due to thelack of optical elements that are compatible with nonvisible light. The applicant has focused on theapplicability of imaging spectroscopy measurement
and has so far succeeded in developing a lens that canbe applied up to deep UV, also using UVSOR [1][2].

Since the preparation of the elements around themeasurement device has progressed significantly up to
this point, the next step is to start evaluating the VUVproperties of the actual minerals.
Typical minerals are known to exhibit fluorescence.
Minerals contain a variety of impurities, which are theactive factors that give rise to fluorescence. In otherwords, by observing fluorescence, it is possible toevaluate the quality of a mineral, making it a powerfultool for resource exploration and environmental
measurement. However, fluorescence observation
requires excitation in the deep ultraviolet. In this study,
we used UVSOR-BL7B to demonstrate whether typicalmineral impurities can be evaluated by PL (photo
luminescence) spectra and PLE (photo luminescence
excitation) spectra.
Fig. 1 shows the measurement results of fluorite. It isconventionally believed that europium is contained influorite as an impurity. The measurement data this timeshows a peak that is certainly derived from europium.
Although the data shown here are for general fluorite,other minerals were also analyzed in the same way, andimpurities were confirmed. It was found that the deep
ultraviolet analysis technique is eﬀective for mineralevaluation. In the future, we will combine this techniquewith our spectroscopic technology and put it to practicaluse as a new technology for resource exploration andenvironmental measurement.

Fig. 1. PL spectra and PLE spectra of fluorite.
[1] T. Shimizu et al., UVSOR Activity Report 2019, 47(2020) 100.
[2] Y. Minami et al., Phys. Status Solidi B, 257(2020)
1900480.

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BL7B

Optical Reflectivity Study of Au-Al-Yb Quasicrystals
H. Okamura 1, A. Kamiki1 , K. Namba2, S. Hirokawa2 and K. Deguchi2
Department of Applied Chemistry, Tokushima University, Tokushima 770-8506, Japan
2
Graduate School of Science, Nagoya University, Nagoya 464-8602, Japan

Since its discovery, quasicrystals (QCs) haveattracted a lot of interest for their unique properties [1].
For example, they do not have a translational symmetry
in the crystal structure but show a clear rotational orderin the measured diﬀraction pattern. Recently, Ybcontaining QCs have been studied in detail [2,3], andthey have revealed a singular behavior of the average
Yb valence as a function of a6D, a six-dimensionallattice parameter of the QC [3]. Namely, the average
Yb valence of a series of Au-Al-Yb QC samples showeda sudden and steep drop, from 2.82 to 2.31, when a6D of
the sample was increased through a critical value of0.74 nm by about 0.01 nm. Valence transitions or
crossovers have been observed in many Yb-containing
crystalline materials such as heavy fermion andintermediate-valence compounds. It is quite interestingwhether or not the singular behavior of the Yb valence
in QCs shares any common feature with the Yb-based
heavy fermion compounds.
To investigate the interesting electronic structures of
Yb-containing QCs, we have been measuring theoptical reflectivity spectra [ܴ(߱)] of Au-Al-Yb QCs
that show the above-mentioned valence-transition-likebehavior. In our experimental method, ܴ(߱) of asample is measured over a wide spectral range between
infrared and vacuum UV, and the Kramers-Kronig(KK) analysis is used to obtain the dielectric function
߳(߱) or the optical conductivity ߪ(߱) from themeasured ܴ(߱). At BL7B of UVSOR, we havemeasured ܴ(߱) between 40 and 600 nm on the six
samples indicated in Table 1. Note that Sample C has
the critical value of a6D, and that the average Yb valence
rapidly decreases from Sample C to F.
Figure 1 indicates the ܴ(߱) spectra of Samples A-F
measured at room temperature. All the samples show
increase of ܴ(߱) toward longer wavelength, with an
onset at around 150-200 nm. Samples C, D and E also
show a clear minimum of ܴ(߱) at 160-200 nm range.
Samples A, B and F, on the other hand, do not show aclear minimum. Namely, there seems to be somequalitative diﬀerence between the two groups ofsamples. The diﬀerence in the onset wavelength
between Samples B and C is particularly clear, although
they are next to each other in Table 1. An onset of highreflectivity in a metallic compound is usually associatedwith the plasma frequency, and is related with thedensity of free electrons. However, to make a detailed
analysis on the electronic structures, we need to obtain
߳(߱) and ߪ(߱) via the KK analysis of ܴ(߱). To do so,
we are currently extending the measurement to theinfrared range, since a wide spectral range of ܴ(߱) is
required to perform a reliable KK analysis. The spectrain Fig. 1 will be connected to those in the infrared range
to obtain ܴ(߱) in a wide spectral range, and will be
used for the KK analysis.
Table 1. Measured QC samples.

Sample
label
A
B
C
D
E
F

Chemical formula

Average Ybvalence
2.90
2.83
2.82
2.73
2.66
2.31

(Au0.5Cu0.5)49Al34Yb17(Au0.9Cu0.1)49Al34Yb17
Au49Al34Yb17
Au49(Al0.9Ga0.1)34Yb17
Au49(Al0.7Ga0.3)34Yb17
Au56Ga28Yb16

0.6(Au-Al-Yb) quasicrystals

Reflectivity

1

A
B
C
D
E
F

0.4

0.2

297 K
0

0

100

200

300

400

500

600

Wavelength (nm)Fig. 1. Optical reflectivity spectra of Au-Cu-Yb
quasicrystal samples A to F at room temperature
measured at BL7B.
[1] D. Shechtman et al., Phys. Rev. Lett. 53 (1984)
1951.
[2] K. Deguchi et al., Nat. Mater. 11 (2012) 1013.
[3] K. Imura et al., Sci. Rep. 10 (2020) 17116.

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UVSOR User 5