2021

Activity Report 2021
TABLE OF CONTENTS
Yoshihisa Harada
Preface :Status of Beamline BL07LSU at the SPring-8
Status of spin-and angle-resolved photoelectron spectroscopy with laser light at LASOR
Seminar
Activities

1
2
3
4

Synchrotron Radiation Experiments (SPring-8)
1)Operando measurement of ethanol steam reforming reaction on Ni(111)
using ambient pressure X-ray photoelectron spectroscopy
Susumu Yamamoto, Kota Moriyama

2)

DEVELOPMENT OF SOFT X-RAY MICROSCOPY SYSTEM WITH CYLINDRICAL-SHAPEWOLTER MIRROR
Takashi KIMURA, Yoko TAKEO, Kai SAKURAI, Noboru FURUYA, Satoru EGAWA, Gota YAMAGUCHI,
Yusuke MATSUZAWA, Takehiro KUME, Hidekazu MIMURA, Mari SHIMURA, Haruhiko OHASHI, Iwao
MATSUDA, and Yoshihisa HARADA

3)A NOVEL MEASUREMENT METHOD OF NEAR-EDGE X-RAY ABSORPTION FINESTRUCTURE USING CONTNIOUS ROTATION OF LINEAR POLARIZATION ANGLES
Masafumi HORIO, Yoshiki KUDO, Yasuyuki HIRATA, Masahito NIIBE, Masato KOTSUGI, Iwao MATSUDA

4) Coherence Effect of Intermediate State in Resonant Inelastic Soft X-ray Diffraction
J. Miyawaki, T. Yachi, S. Maki, K. Kanie and Y. Harada

5)

ANALYSIS OF ELECTRONIC STATES OF PARTICULATE PHOTOCATALYSTS BY 3D
NANO-ESCA
Takashi HISATOMI, Naoka NAGAMURA, Wenxiong ZHANG, Kenta OHISHI, Asako YOSHINARI,
Shingo TAKEZAWA, Masaharu OSHIMA, Yoshihisa HARADA

6) SPECTRAL IMAGING ANALYSIS OF EDGE-CONTROLLED 2D MATERIALS
Naoka NAGAMURA, Mitsuhiro OKADA, Ryo NOUCHI, Tarojiro MATSUMURA, Yasunobu ANDO,
Asako YOSHINARI, Shingo TAKEZAWA, Kenta OHISHI, Kentaro FUKU, Wenxiong ZHANG,
and Masaharu OSHIMA

7) RIXS-MCD Study of Chromium Trihalides CrX3 (X = Cl, Br, I)
C. S. Pathiraja, J. N. Ranhili, Y. C. Shao, Y. -D. Chyang, B. Freelon

8)

INVESTIGATION OF ELECTRONIC STRUCTURE OF FE-CO SPINELS BY 2P3D RIXS AND
L-EDGE XAS
Olaf Rüdiger, Minmin Chen, Derek Rice, Hisao Kiuchi, Wenxiong Zhang, Ralph J. Ugalino, Naoya Kurahashi,
Yoshihisa Harada, Serena DeBeer

9)

STUDY ON THE ELECTRONIC STATE OF WATER MOLECULES IN POLYMERELECTROLYTE MEMBRANES
Naoya Kurahashi, Ugalino Ralph John and Yoshihisa Harada

ELECTRONIC STATES OF FUNCTIONAL MATERIALS IN HYDROGEN
10) ADSORPTION/DESORPTION STUDIED BY AMBIENT PRESSURE SOFT X-RAY
PHOTOELECTRON SPECTROSCOPY
Takanori Koitaya, Susumu Yamamoto, Iwao Matsuda, Jun Yoshinobu and Toshihiko Yokoyama

11)

O K-edge soft X-ray emission spectroscopy of the solvents in electrolyte solutions for redox flow
batteries
Eiji Hosono, Daisuke Asakura, Akihiro Ohira, Wenxiong Zhang, Naoya Kurahashi, Ralph J. Ugalino, Hisao Kiuchi,
and Yoshihisa Harada

12) Co L3-edge Soft X-ray Emission spectroscopy of LiCoO2 for Li-ion batteries
Daisuke Asakura, Eiji Hosono, Kosuke Yamazoe, Naoya Kurahashi, Ralph J. Ugalino, Hisao Kiuchi,
and Yoshihisa Harada

13)

REAL-TIME OBSERVATION OF HYDROGEN-ABSORPTION PROCESS IN PD-AU ALLOYS
BY OPERANDO AP-XPS
Takanori KOITAYA, Susumu YAMAMOTO, Masafumi HORIO, Iwao MATSUDA, Jun YOSHINOBU, andToshihiko YOKOYAMA

HALF-METALLIC ELECTRONIC STATES OF BULK-SINGLE CRYSTAL Co2MnZ (Z = Ge
14) AND Ga) HEUSLER ALLOYS PROBED BY RESONANT INELASTIC SOFT X-RAY
SCATTERING (SX-RIXS) IN A MAGNETIC FIELD
Rie Y. Umetsu, Hidenori Fujiwara, Jun Miyawaki, Rika Kasahara, Takuma Nishioka, Akane Ose, Akira Sekiyama,
Yoshihisa Harada and Shigemasa Suga

15) KINETIC SQUARE SCHEME IN OXYGEN-REDOX BATTERY ELECTRODES
Masashi OKUBO

16)

ORBITAL TORQUE IN COFE/CU/AL2O3: INVESTIGATION ON THE LARGE TORQUEWITHOUT HEAVY ELEMENT
Junyeon KIM

17)

MAGNETIC STATE OF VNB3S6 DETERMINED BY X-RAY MAGNETIC CIRCULARDICHROISM
Masafumi HORIO, Tomoaki SENOO, Tetsuya WADA, Yasuyuki HIRATA, Shota OKAZAKI,
Takao SASAGAWA, Iwao MATSUDA

MEASUREMENT OF X-RAY MAGNETIC LINEAR DICHROISM BY
18) ROTATING POLARIZATION ANGLE OF SOFT X-RAY GENERATEDBY A SEGMENTED CROSS UNDULATOR
Masafumi HORIO, Yoshiki KUDO, Toshihide SUMI, Tetsuya WADA, Yasuyuki HIRATA, Kohei YAMAMOTO,
Takuo OHKOCHI, Toyohiko KINOSHITA, Iwao MATSUDA

19) DEVELOPMENT OF ANGLE-RESOLVED SOFT X-RAY EMISSION SPECTROSCOPY
Naoya Kurahashi, Jun Miyawaki, Kosuke Yamazoe and Yoshihisa Harada

20)

CHARGE EXCITATION RESEARCH ON THE T* PHASE HOLEDOPEDCUPRATES BY RESONANT SOFT X-RAY SCATTERING
Xie PEIAO, Shinnosuke KITAYAMA, Takanori TANIGUCHI, Hisao KIUCHI, Kenji ISHII, and Masaki FUJITA21) Co L3-edge Soft X-ray Emission spectroscopy of La0.6Sr0.4CoO3- for solid oxide fuel cells

Daisuke Asakura, Eiji Hosono, Tomohiro Ishiyama, Riyan Achmad Budiman, Haruo Kishimoto, Kosuke Yamazoe,
Naoya Kurahashi, Ralph J. Ugalino, Hisao Kiuchi, and Yoshihisa Harada

22)

POSSIBLE ANAPOLE ORDER IN THE ANTIFERROMAGNETIC PHASE OF
MULTIFERROIC CUO
Ryusuke MISAWA, Keito ARAKAWA, Hiroki UEDA, Jun MIYAWAKI, Hisao KIUCHI, Yoshihisa HARADA,
Yoshikazu TANAKA, and Tsuyoshi KIMURA

23)

ELECTRONIC STRUCTURE ANALYSIS OF OXYFLUORIDE CATHODE OF ALL-SOLIDSTATE FLUORIDE BATTERY USING RESONANT INELASTIC X-RAY SCATTERING
Kentaro YAMAMOTO, Datong ZHANG, Hisao KIUCHI, Jun MIYAWAKI, Tomoki UCHIYAMA,
Toshiki WATANABE, Tsuyoshi TAKAMI, Toshiyuki MATSUNAGA, Yoshihisa HARADA,
Yoshiharu UCHIMOTO

24)

OPERANDO AMBIENT PRESSURE PHOTOELECTRON SPECTROSCOPY OF CHEMICALREACTION ON THE FUNCTIONALIZED BASAL AND EDGE SURFACES OF MoS₂
F. OZAKI, Y. CHOI, H. Li, Y. SAWAGUCHI, S. TANAKA, K. MUKAI, M. HORIO,
I. MATSUDA and J. YOSHINOBU

25)

ELECTRONIC STATE ANALYSIS OF EARTH-ABUNDANT FE–AL–SI THERMOELECTRIC(FAST) MATERIALS USING SCANNING PHOTOELECTRON MICROSCOPY
Yoshiki TAKAGIWA, Shunsuke TSUDA, Naoka NAGAMURA, Asako YOSHINARI, Shingo TAKEZAWA,
Kenta OISHI, Kentaro FUKU, Wenxiong ZHANG

26)

ANALYSIS OF WATER STRUCTURE OF THERMORESPONSIVE POLYMER MODIFIEDINTERFACE
Kenichi NAGASE, Naoya KURAHASHI, Hisao KIUCHI, Yoshihisa HARADA27) RESONANT INELASTIC X-RAY SCATTERING SPECTROSCOPY OF CU-PROTEINS
Kentaro FUJII, Jun MIYAWAKI, Naoya KURAHASHI, Hisao, KIUCHI, Yoshihisa HARADA,
Motoyasu ADACHI, Akinari YOKOYA

Experiments at E-Labo
1)

STUDY ON THE HELICAL SPIN TEXTURE OF TOPOLOGICAL SURFACE STATE IN
SUPERCONDUCTOR 2M-WS2
Soonsang Huh, Soohyun Cho, Hua Bai, Yuqiang Fang, Fuqiang Huang, Yuto Fukushima, Ayumi Harasawa,
Yunhao Lu, Gang Mu and Dawei Shen and Takeshi Kondo

2)

ENHANCED RASHBA-SPLITTING OF AU(111) SURFACE STATES BY
THE MELAMINE HONEYCOMB LAYERS
Rena MOUE, Yuta KOKUBO, Kozo MUKAI, Hirotaka MIZUSHIMA, Yuto FUKUSHIMA,
Kaishu KAWAGUCHI, Takeshi KONDO, Ayumi HARASAWA, Jun YOSHINOBU, Shik SHIN, Kaname KANA

3)

ELECTRONIC STATES OF TOPOLOGICAL SEMIMETALSSTUDIED BY SPIN- AND ANGLE-RESOLVED PHOTOEMISSION
Y.X. Wan, K. Kuroda, C. Bareille, Y. Ishida, A. H. Mayo, H. Takahashi , M. S. Bahramy, C. Lin, Y. Arai,
H. Tanaka, Y.Y. Dong, M. Hashimoto, D.H. Lu, T. Muro, S. Ishiwata, T. Kondo

4)

LASER-SARPES STUDY OF SPIN-POLARIZED ELECTRONIC STATES FORPB(BI1-XSBX)2TE4

Koichiro YAJI, Yuya HATTORI, Shunsuke YOSHIZAWA, Shunsuke TSUDA, Youhei YAMAJI,
Yuto FUKUSHIMA, Kaishu KAWAGUCHI, Takeshi KONDO, Yuki TOKUMOTO, Keiichi EDAGAWA,
and Taichi TERASHIMA

5)ELECTRONIC STRUCTURES OF HALF-METALLIC FERROMAGNET La1-xSrxMnO3 BY
HIGH-RESOLUTION SPINRESOLVED PHOTOEMISSION SPECTROSCOPY
T. Setoguchi, N. Kataoka, K. Kawaguchi, Y. Fukushima, A. Harasawa, K. Kuroda, T. Kondo, S. Shin, T. Wakita,
Y. Muraoka, and T. Yokoya

5

Staff

6

Publication List

Preface
The Synchrotron Radiation Laboratory (SRL) of the Institute for Solid State Physics (ISSP)
has been cooperating with the Synchrotron Radiation Research Organization of the
University of Tokyo to operate the BL07LSU soft X-ray beamline and its experimental end
stations at SPring-8 since 2006. The beamline has a 27-m-long polarization-controlled
undulator and monochromator covering the photon energy range from 250 eV to 2 keV, withan average photon flux of 1012 photons/s. Since 2009, the SRL staff has been playing anessential role in promoting the ISSP’s joint research program for domestic and international
users of the BL07LSU. The three end stations—ambient pressure X-ray photoemission
spectroscopy, three dimensional nanoESCA, and the high-resolution soft X-ray emission
spectroscopy stations—have excellent ability to operate under high pressure (~20 mbar), highspatial resolution (~70 nm), and high energy resolution (E/E≈10,000), respectively. During
FY2021, as the COVID-19 pandemic persisted, we conducted joint research experiments
while applying infection control measures in accordance with the SPring-8 facility policy. Allof the experiments were carried out as scheduled, except for those involving the internationaluser groups, who could not come to Japan. We thus conducted the experiments on their behalf
via remote connection.
To utilize the characteristics of BL07LSU, new challenges were undertaken, including thefirst observation of rotational X-ray magnetic linear dichroism (XMLD), which is a soft X-ray
magneto-optical measurement during rotation of the angle of the linearly polarized beam andthe X-ray magneto-optical Kerr effect when utilizing polarization switching. A soft X-ray
XAFS imaging experiment has been launched using a 50 nm focused beam produced by aWalter-type soft X-ray focusing mirror system. This experiment serves as both research anddevelopment for the next-generation synchrotron radiation facility in Sendai and a way to takeadvantage of the characteristics of BL07LSU. A high-resolution soft X-ray charge-coupleddevice detector has been introduced for soft X-ray emission spectroscopy to obtain aresolution of E/E > 10000. The ambient-pressure photoemission spectroscopy system has
also been improved to increase the measurement pressure to 100 Torr. All of these
improvements were made as part of research and development for the upcoming synchrotron
radiation facility. We have also expanded our activities to include the time-resolved soft X-ray
magneto-optical effect and nonlinear spectroscopy experiments using a focused beam ofseveral hundred nanometers at the X-ray free electron laser facility SACLA.
The SRL will terminate the joint research program at SPring-8 in the first half of 2022 andtransfer most of the instruments to the new facility. In addition, SRL will continue to develop
a novel soft X-ray imaging system that can most effectively make use of the new light source.
In addition to the cutting-edge activities using synchrotron radiation and SACLA, the SRL
has promoted the scientific use of laser-based high-harmonic generation in the vacuum
ultraviolet and soft X-ray regions at the Kashiwa campus. Since 2015, the SRL has operated ajoint research program of the high-resolution laser spin- and angle-resolved photoelectronspectroscopy (SARPES) system, which is designed to provide high-energy (1.7 meV) and angular resolutions with high-efficiency spin detectors for various types of solids, such as spinorbit coupled materials and ferromagnetic materials.
Our goal is to provide users with a platform that uses both synchrotron radiation and highharmonic laser generation through strong collaboration with other LASOR group members.

June 30, 2022
Yoshihisa Harada
Director of SRL-ISSP

1. Status of Beamline BL07LSU at SPring-8
The University-of-Tokyo high-brilliance synchrotron soft X-ray outstation beamline
BL07LSU at SPring-8 has been maintained by the permanent staff members with adjuncts
for user operations. The scientific aim of the beamline is to promote advanced
spectroscopy for solid state and soft (including bio-) materials. There are three regular
endstations for ambient pressure X-ray photoelectron spectroscopy, 3D-scanningphotoelectron microscope (3D nano-ESCA) and high-resolution soft X-ray emission
spectroscopy (HORNET) that are open for users. There is also a free port station for users
who bring in their own experimental apparatus.
The beamline BL07LSU is equipped with a segmented cross-type undulator. Circularly
and linearly polarized soft X-rays can be used in user experiments at full energy range(250 – 2000 eV). By using phase shifters between the neighboring undulator segments,
polarization of the soft X-ray beam is regulated continuously and the switching frequency
can be tuned up to 13 Hz. At the end-stations, various scientific experiments were carriedout by both the laboratory staffs and users with applications of G-type (general), S-type(special), or P-type (priority). A user group of the S-type spends the long-term beamtime
to pursue the challenging issues in synchrotron radiation research. A user team of the Ptype proceeds an experiment mainly for developing technologies of beamline and endstation for the next generation light source.
It should be mentioned that the coronavirus (COVID-19) pandemic has continuously
been a serious issue in 2021. Safety and health of users at the beamline have been takencare during their beamtime experiment at the end-station.
Status of the individual end-stations are briefly described below.
(1) Ambient-pressure X-ray photoelectron spectroscopy (AP-XPS)
AP-XPS station is aimed mainly for operando observations of catalytic reactions at
the gas/solid interface. The AP-XPS system is equipped with a differentially pumped
electron analyzer (SPECS, PHOIBOS 150 NAP) and an ambient pressure gas cell. XPS
measurements can be performed both under ultrahigh vacuum and in near-ambient gas
pressure up to 100 mbar. Reactant and product molecules of a catalytic reaction aremonitored by mass spectrometer and, simultaneously, chemical states of the reaction
intermediates at a surface can be examined by AP-XPS.
In 2021, a variety of research projects was conducted at the AP-XPS station, forexample, operando observations of hydrogen permeations at metal alloys and of catalytic
reactions at model surfaces.

(2) 3D-scanning photoelectron microscope (3D-nanoESCA)
3D-nanoESCA can be used for sub-100 nm range microscopic 2D mapping and depth
profile of the chemical structure of functional materials and devices. In 2021, visible light
responsive Al-doped SrTiO3 photocatalytic particles and BaTaO2N photocatalytic
particles, developed by Prof. Hisatomi group at Shinshu University, were measured tocapture changes in band alignment by single-particle measurements. A core-level shiftreflecting the Fermi energy shift caused by a change in catalytic efficiency was
successfully monitored. As a demonstration study of the next-generation operando
spectromicroscopy system with a piezoelectric four-tip unit, the potential distribution of
single-layer CVD graphene on a p+-Si/SiO2 substrate was measured under an electric field
applied to the probe, where the probe was fixed to a sample holder. As a result, a clear
peak shift was detected only in the vicinity of the tip contact, suggesting a potential dropat the domain boundary.
(3) Ultra high-resolution soft X-ray emission spectroscopy (HORNET)
The station is dedicated for soft X-ray emission (or resonant inelastic X-ray scattering:
RIXS) spectroscopy measurements with high-resolution (E/ΔE > 10,000) and undervarious environmental conditions (gas, liquid, and solid).
In the beginning of this term, new soft X-ray CCD detector with ultra-high spatial
resolution (< 5mm) for next-generation synchrotron radiation (NanoTerasu) was
introduced. Although the total resolution was only slightly improved due to the limited
beam size on the sample, it is expected that the resolution at NanoTerasu will beapproximately three times higher than the current improvement.
HORNET station was used for studies on temperature-dependent water hydrogen-bondbehavior in electrolyte membranes, spin polarization in half metals by RIXS-MCD,
demonstration of soft x-ray inelastic diffraction, CO2 sorption process in PDMS for
silicon materials. Two abroad applications (RIXS-MCD of CrX3 and dd excitation
observation of Fe-Co spinel materials) were conducted remotely. As part of the New
Academic Field Research, outstanding results were obtained in the study of a watermolecule confined in C60, and ionization of ultrafine water upon adsorption to hydrophilic
and hydrophobic surfaces.
(4) Soft X-ray imaging (Free-port station)
This year, we developed a new soft X-ray ptychography system at the free-port station.
The reflecting surface of the Wolter mirror, which was covered with Au, enables seamlessptychographic measurements in a wide energy range of soft X-rays at BL07LSU.
A soft X-ray ptychographic system with a total-reflection Wolter mirror achieved aresolution of approximately 50 nm in a test chart evaluation. We have also shown that it
is possible to visualize the microstructure of a mammalian cell over a wide photon energy
range without chromatic aberration. Furthermore, taking advantage of the long working
distance of the optical system, stereo imaging with a large rotation angle was also
attempted to measure the cell sample. Ptychographic imaging with a pink beam from theundulator was also possible.
The soft X-ray ptychography system based on the Wolter mirror optics is expected to behighly effective for investigating thick samples with complex three-dimensional
structures and chemical compositions.

２．Status of SARPES
Spin and angle-resolved photoemission spectroscopy (SARPES) is a powerful experimental
technique to reveal various information about the occupied electronic states in solids, including theirenergy, momentum, and spin. In recent years, the demand for spin-resolved measurements has beengetting high because of much interest in Rashba surface states and topological materials with spinpolarized electronic structures derived from strong spin-orbit interactions. These experiments require
high energy resolution and enough photoelectron yield rates to detect their small energy scales(~several meV). Following these demands and requirements, we have developed a high-energy
resolution SARPES apparatus using a vacuum-ultraviolet (6.994-eV) laser and very-low-energyelectron-diffraction (VLEED) type spin detectors at the Laser and Synchrotron Research Center(LASOR) in the Institute for Solid State Physics (ISSP) [1]. Our SARPES apparatus is currently
utilized to obtain precise information on fine distributed spin-dependent electronic structures near the
Fermi level in solids. We started the project to construct the laser-SARPES apparatus in FY 2014 andjoint research at this station started in FY2015.
Our laser-SARPES apparatus consists of an analysis chamber, a carousel sample-bank chamberconnected to a load-lock chamber, and a molecular beam epitaxy (MBE) chamber. All of thesechambers are connected via UHV gate valves. Figure 1 represents the hemispherical electron analyzer,
which is a custom-made ScientaOmicron DA30-L, modified to attach the VLEED type spin detectors.
The electrons are currently excited by 6.994-eV photons, yielded by the 6th harmonic of a high-power
Nd:YVO4 quasi-continuous wave laser. A helium discharge lamp (VG Scienta, VUV5000) is alsoavailable as a photon source. At the MBE chamber, samples can be heated by a direct current heating
or electron bombardment. The surface evaluating and preparing instruments, such as evaporators, lowenergy electron diffraction, sputter-gun, and quartz microbalance can be installed. At the carouselchamber, 16-samples can be stocked in the UHV environment. Spin-polarized states were investigatedin both bulk and surface of various topological materials including magnetic and superconducting ones,
atomic layers, and ferromagnetic compounds.
Spin-resolved technique with highly efficient photoelectron yield rates has advantages not only inhigh-resolution measurements but also in time-resolved

Figure 1: The laser-SARPES apparatus at LASOR
in ISSP [1]. The double VLEED spin detectors areattached to a hemispherical analyzer (DA30-L,
ScientaOmicron). Currently, 7-eV laser for highenergy resolution measurement and 10.7eV pulsed
laser for pump- probe measurements are available.

measurements based on pump-probe methods. A combination of SARPES with pump-probe laser
techniques makes it possible to image the optically excited spin-polarized electron population in theunoccupied bands in energy-momentum space and track the dynamics of charge and spin in theultrafast time-domain, which is useful for studying novel optical responses of many materials such as
topological and spin-valley materials. Since FY2018, we have started to upgrade our laser-SAPRES
apparatus by combining a pomp-probe laser, setting up the system named time-resolved SARPES (trSARPES). This project requires a short pulse laser, and thus we newly installed a pulsed 10.7-eV laser
system [2,3] developed by the Kobayashi group at ISSP’s LASOR. This fundamental laser system isytterbium fiber-based, achieving a 270-fs, 1-MHz repetition rate, and high power by a chirped pulse
amplification technique, which allows the pump-probe measurements with high photoelectron yieldrates. In addition to a great capability of the time-resolution, our 10.7-eV laser gives more wide
momentum information in contrast to the low photon energy sources such as 7-eV.
The development progressed, and now tr-SARPES measurements have been realized. The 10.7-eVlaser as the probe photon is obtained as the third harmonic generation in Xe gas, and a unique Xe gaschamber has been developed for the system up to the monochromatization and the focusing system.
In addition, the light polarization of the 10.7-eV laser can be selectively controlled by MgF2 half-wave
plate. The pump photon is selectable from 1.19-eV or 2.38-eV for a wide variety of band-gap materials.
The beamline is designed as a vacuum chamber after 10.7-eV generation, and it is connected to the
UHV analyzer chamber through a differential pumping system without a vacuum window.
Furthermore, some mirror and lens in the vacuum beamline are movable, allowing the system to switch
between 7-eV and 10.7-eV beamlines. In this way, this system has made tr-SARPES possible, which
is demonstrated in Fig. 2. This state-of-the-art tr-SARPES apparatus can be widely used for studying
unoccupied electronic states in spintronics materials and their ultrafast carrier/spin dynamics.

Figure 2: Time-resolved ARPES (a) andtr-SARPES mapping (b) of unoccupied
topological surface state in Sb2Te3,
observed by 10.7-eV laser after 1.19-eVlaser pumping.

References:[1] K. Yaji, A. Harasawa, K. Kuroda, S. Toyohisa, M. Nakayama, Y. Ishida, A. Fukushima, S.
Watanabe, C.-T. Chen, F. Komori and S. Shin, Rev. Sci. Instrum. 87, 053111 (2016).
[2] Z. Zhao and Y. Kobayashi, Opt. Exp. 25, 13517 (2017).
[3] Z. Zhao, K. Kuroda, A. Harasawa, T. Kondo, S. Shin and Y. Kobayashi, Chin. Opt. Lett. 17,051406 (2019).

3. Seminar(ISSP Lectures by Visiting Professors)
Date: May 13, 2021
Title: Surface hydration and biocompatibility
Speaker: Dr. Tomohiro Hayashi (Tokyo Institute of Technology)(ISSP Colloquiums)
Date: December 20, 2021
Title: A new approach of X-ray microscopy using high-precision optical devices
Speaker: Dr. Takashi Kimura (ISSP, The University of Tokyo)(LASOR Seminar)
Date: January 19, 2022
Title: Study of strongly correlated systems by complementary use of vacuum-ultra-violet andsoft x-ray photoemission spectroscopy
Speaker: Dr. Masafumi Horio (ISSP, The University of Tokyo)

Operando measurement of ethanol steam reforming reaction on Ni(111)
using ambient pressure X-ray photoelectron spectroscopy
Susumu Yamamoto1,2, Kota Moriyama3
1

International Center for Synchrotron Radiation Innovation Smart (SRIS), Tohoku University
2

Institute of Multidisciplinary Research for Advanced Materials (IMRAM),
Tohoku University

3

Department of Electrical, Information and Physics Engineering, School of Engineering,Tohoku University

Ethanol steam reforming (ESR) reaction, which produces hydrogen from ethanol(CH3CH2OH (EtOH) + 3H2O → 2CO2 + 6H2), has attracted much attention toward therealization of a hydrogen society. However, the reaction mechanism of the ESR reaction is
not fully understood. This is mainly because there are many side reactions in the ESR reaction,
which produce various molecules such as CH4, C2H4, CO. To elucidate the reaction path andreaction mechanism of the ESR reaction, we performed operando measurements of the ESR
reaction using ambient pressure X-ray photoelectron spectroscopy (AP-XPS).
The experiments were performed using the AP-XPS system installed at SPring-8 BL07LSU[1-4]. The Ni(111) surface was cleaned by a cycle of Ar+ ion sputtering and annealing, andused as a catalyst for the ESR reaction. The Ni(111) catalyst was placed in the mixed gas
atmosphere of 3 mbar EtOH and 9 mbar H2O, and was heated from 300 K to 700 K. For
comparison, the Ni(111) catalyst was heated in the pure gas atmosphere of 3 mbar EtOH (or 9mbar H2O). The catalytic activity was monitored by mass spectrometry (MS), and the surface
chemical states and surface adsorbed molecules of the Ni catalyst were measured by AP-XPS.
Figure 1 shows the catalytic activity of Ni(111) in the mixed gas of EtOH and H2O as afunction of temperature. At 600-700 K, the formation of H2 and CO2 is confirmed. The MS
and AP-XPS results for EtOH + H2O and pure EtOH were almost identical. This indicatedthat EtOH decomposition, one of the elementary processes of the ESR reaction, was thedominant process in the current reaction conditions. Furthermore, in the Ni 2p AP-XPS
spectra, the Ni surface was oxidized only when EtOH was introduced, and the surface
oxidation/reduction coincided with EtOH introduction/decomposition, indicating that EtOH
acts as an oxidant on the Ni surface.

Figure 1. Catalytic activity measurements of Ni(111) for an ESR reaction. Gas composition
was monitored with mass spectrometer, while the Ni catalyst was heated in a stepwise mannerfrom 300 K to 400 K, 500 K, 600 K and 700 K in the mixed gas of 3 mbar EtOH and 9 mbar
H2O.

REFERENCES
[1]
[2]
[3]
[4]

T. Koitaya, S. Yamamoto et al., Topics in Catalysis 59, 526-531 (2016).
T. Koitaya, S. Yamamoto et al., e-J. Surf. Sci. Nanotechnol. 17, 169-178 (2019).
S. Yamamoto et al., Synchrotron Radiat. News, in press (2022).
S. Yamamoto et al., Journal of the Japanese Society for Synchrotron Radiation
Research 35, 182-190 (2022). (in Japanese)

DEVELOPMENT OF SOFT X-RAY MICROSCOPY SYSTEM
WITH CYLINDRICAL-SHAPE WOLTER MIRROR
Takashi KIMURA,1 Yoko TAKEO,1,2 Kai SAKURAI,3 Noboru FURUYA,3Satoru EGAWA,4 Gota YAMAGUCHI,5 Yusuke MATSUZAWA,6 Takehiro KUME,6
Hidekazu MIMURA,7 Mari SHIMURA,8 Haruhiko OHASHI,2,5
Iwao MATSUDA,1 and Yoshihisa HARADA1
1

The Institute for Solid State Physics, The University of Tokyo
2

Japan Synchrotron Radiation Research Institute3

Department of Applied Physics, School of Engineering, The University of Tokyo
4

RIKEN Center for Advanced Photonics
5

RIKEN, SPring-8 Center, 1-1-1

6Technology Center, Natsume Optical Corporation

7

Department of Precision Engineering, School of Engineering, The University of Tokyo
8

Research Institute, National Center for Global Health and Medicine

X-ray microscopy has a wide range of applications in science due to its high spatial
resolution and variety of analytical techniques. Ptychography provides a particularly highspatial resolution by reconstructing the sample image using phase recovery calculations[1, 2].
The combination of ptychography and spectroscopy in the soft X-ray region is promising forinvestigating samples with light-element-rich heterogeneous structures. For example, in the
combination of soft X-ray ptychography with X-ray absorption spectroscopy, mapping thechemical state of magnetic nanoparticles in bacteria[3] and the visualization of the cathodedegradation mechanism of the lithium-ion batteries[4] have been demonstrated.
For ptychography at multiple X-ray wavelengths, total reflection mirror optics have theoptimal character of achromatic aberration and high focusing efficiency. The current
achievable focusing size of total reflection mirrors in soft X-rays is around a few hundred
nanometers[5], much larger than that of zone plates. However, the spatial resolution obtainedin ptychography is independent of the focusing beam size, which makes the total reflection
mirrors a potential candidate. In addition, the long working distance of the mirror optics also
makes it suitable for applications in tomographic and in-situ/operand measurements.
In this work, we developed a new total-reflection Wolter mirror optics for soft X-ray
ptychography and demonstrated that it can be used to measure cellular samples[6]. The
total-reflection Wolter mirror was fabricated by modifying our previous precisionelectroforming process. The reflecting surface of the Wolter mirror, which was covered with
Au, enables seamless ptychographic measurements in a wide energy range of soft X-rays.
Figure 1 shows the schematic illustration of the system
A soft X-ray ptychographic system with a total-reflection Wolter mirror achieved aresolution of approximately 50 nm in a test chart evaluation. We have also shown that it ispossible to visualize the microstructure of a mammalian cell over a wide photon energy range
without chromatic aberration. Figure 2 shows the retrieved image of the mammalian cell from
250 eV to 1.2 keV. Furthermore, taking advantage of the long working distance of the opticalsystem, stereo imaging with a large rotation angle was also attempted to measure the cellsample. Ptychographic imaging with a pink beam from the undulator was also possible. The
soft X-ray typography system based on the Wolter mirror optics developed in this study is
expected to be highly effective for investigating thick samples with complex
three-dimensional structures and chemical compositions.

Figure 1. Schematic illustration for the soft X-ray ptychography system
at BL07LSU of SPring-8.

Figure 2. Soft X-ray ptychography measurement of a mammalian cell. (a) Visible lightdifferential interference contrast image. (b-k) Reconstructed absorption (b,d,f,h,j) and phase(c,e,g,i,k) images at 250 eV, 350 eV, 450 eV, 600 eV, and 1200 eV. The magnified images tothe right of the main images are taken from areas corresponding to the dotted rectangles
shown in (b).
REFERENCES[1] A. M. Maiden, J. M. Rodenburg, Ultramicroscopy, 109 (10), 1256 (2009).
[2] P. Thibault, et al., Science, 321, 379 (2008).
[3] X. Zhu, et al. Proc. Natl. Acad. Sci. , 113 (51) E8219 (2016).
[4] T. Sun, et al., ACS Nano, 15, 1475 (2021).
[5] Y. Takeo, et al., Appl. Phys. Lett. 117, 151104 (2020)[6] T. Kimura, et al., Opt. Express, accepted.

A NOVEL MEASUREMENT METHOD OF NEAR-EDGE X-RAY
ABSORPTION FINE STRUCTURE USING CONTNIOUS ROTATION
OF LINEAR POLARIZATION ANGLES
Masafumi HORIO1, Yoshiki KUDO1, Yasuyuki HIRATA2, Masahito NIIBE3,
Masato KOTSUGI4, Iwao MATSUDA1
1

The Institute for Solid State Physics, The University of Tokyo

2

Department of Applied Physics, National Defence Academy

3

Laboratory of Advanced Science and Technology for industry, University of Hyogo
4

Department of Materials Science and Technology, Tokyo University of Science

Near-edge X-ray absorption fine structure (NEXAFS) is one of the X-ray spectroscopy
methods employed to analyze the electronic state [1]. In recent years, NEXAFS
measurements have evolved into nano-spatial imaging and openrando experiments, allowing,for example, to identify orbital types and determine molecular configurations by use of linear
polarization. In such measurements, NEXAFS spectra are acquired by changing the angle
between the molecule and the linear polarization. Typically, at a synchrotron radiation facility,
the linear polarization of the beam is fixed, and a series of angle-resolved data is collected
while the sample is rotated. This experimental method is simple, but at the same time, it limits
the conditions of the sample environment. For example, the sample must be uniform to cover
the misalignment between the beam spot and the sample rotation axis. On the other hand, inthe case of nano-beam NEXAFS and operando experiments, it is technically difficult toensure the exact beam position after sample rotation on a non-uniform and complex
nanodevice. Therefore, it is now required to rotate the linear polarization of the X-ray beaminstead of rotating the sample. In the present research, we designed a novel control method of
linear polarization angles by the segmented undulator of SPring-8 BL07LSU.
The light source of SPring-8 BL07LSU consists of an 8-segment insertion device (ID) and a
7-segment phase shifter (PS), as shown in Fig. 1 [2]. The ID segments are either horizontal orvertical figure-8 undulators. The horizontal (H) and vertical (V) ID segments are alternately
placed between the PS, which is used to adjust the relative phase of the radiation. To achieve
linear polarization at arbitrary angles, two waves of left and right circular polarization
produced by sets A and B of ID segments were combined, as shown in Fig. 1 (b). Set A
consists of H1, V2, H3, and V4 segments, while set B is assembled with H5, V6, H7, and V8
segments. If set A generates right (left) circular polarization, set B generates left (right)
circular polarization. The rotation angle  of the linearly polarized light could then becontrolled by changing the phase difference between the left and right circular polarizations
with PS #4. As a demonstration of NEXAFS using this new polarization control, experiments
were performed in the ultrahigh vacuum chamber of the SPring-8 BL07LSU. Hexagonalboron nitride (h-BN) films were prepared as samples. h-BN microcrystals have a flat shape,
and the films were found to be oriented in two dimensions when mechanically pressurized.
NEXAFS spectra were recorded by total electron yield at room temperature.
Figure 2(a) shows a collection of N K-edge NEXAFS spectra of oriented h-BN films,
measured at the incident angle of 80° with linearly polarized light in the horizontal andvertical direction. The horizontal direction and the rotation axis of the sample were set
perpendicular to each other. As shown in the figure, two prominent peaks were found at h =401.5 and 408.0 eV corresponding to * and * orbitals of h-BN. In the horizontal
polarization experiment, the intensity of the * peak is found to be larger while the * peak isenhanced by vertical polarization. This spectral behavior is explained in terms of a dipole

transition in optical absorption. Since the * (*) orbitals are oriented out-of-plane (in-plane),the peak intensity is enhanced when the linearly polarized light is parallel to the out-of-plane(in-plane) direction.
We focus on the * and * peaks and track their intensity changes with the angle of linear
polarization  [Fig. 2(b)] Since this NEXAFS technique differs from the conventional one, it
is hereafter referred to as a rotational NEXAFS measurement. The intensity at h = 401.5 eV(*, plotted in green) is maximum at  = 0, , 2 (horizontal) and minimum at  =/2, 3/2(vertical) while at h = 408.0 eV (*, plotted in yellow) the opposite trend is seen. This result
is consistent with the conventional NEXAFS results shown in Fig. 2(a). However, therotational NEXAFS data contain angle-dependent data, which increases the reliability of theexperiment and thus allows more precise determination of orbital configuration. In future, thistechnique could be combined with nano-focusing and/or fast polarization switching byelectromagnetic PSs. This will allow quick and sensitive detection of NEXAFS signals from
non-uniform functional materials and enhance the potential of NEXAFS in modern science.

Fig. 1: Segmented cross undulator. (a) The light source composed of eight segments of theinsertion device (ID) and seven phase shifters (PS’s). Horizontal (H) and vertical (V) IDs
are positioned alternately. (b) The setup for producing linear polarization at arbitrary
azimuthal angles. Circularly polarized light with opposite helicities is produced byundulator sets A and B, and interfere with a relative phase difference controlled by PS #4.

Fig. 2: NEXAFS spectra of h-BN recorded with a grazing incidence of 80°. (a) NEXAS
measured by using the horizontal (top) and vertical (bottom) polarization. (a) Absorption
intensity of the selected transition as indicated, plotted versus linear-polarization angle.

REFERENCES[1] J. Stöhr, NEXAFS Spectroscopy (Springer, Berlin, Heidelberg, 1992).
[2] S. Yamamoto et al., J. Synchrotron Rad. 21, 352 (2014).

Coherence Effect of Intermediate Statein Resonant Inelastic Soft X-ray Diffraction
J. Miyawaki1,3, T. Yachi2, S. Maki2, K. Kanie2 and Y. Harada3
1

Institute for Advanced Synchrotron Light Source,
National Institutes for Quantum and Radiological Science and Technology
2Institute of Multidisciplinary Research for Advanced Materials, Tohoku University
3
Institute for Solid State Physics, The University of Tokyo
The fundamental determinants of the physical properties of materials (external field response)are elementary excitations such as phonons, magnons, and crystal field excitations. Theseelementary excitations are very sensitive to structural changes in materials, suggesting theimportance to identify both the structure and these excitations simultaneously. Resonant
inelastic X-ray scattering (RIXS) is the most direct method to observe these elementary
excitations. Since elastic scattering contains information related to diffraction, RIXS also
contains diffraction-derived structural information. Therefore, RIXS originally has thepotential to correlate the structural information with the electronic state, i.e., to observe theelectronic state in a structure-selective manner.
We have been conducting angle-resolved RIXS experiments with several
Fe-containing nanoparticles to demonstrate the diffraction-assisted enhancement of the RIXS
intensity using small angle X-ray scattering (SAXS), which is caused by diffraction
phenomena from nanoparticles. The combined method of RIXS and SAXS is the inelastic
version of SAXS and can be called small angle inelastic X-ray scattering (SAIXS). SAXS andSAIXS were measured at the Fe L-edge for two types of nanoparticles, Fe3O4 (insulator) and
FePt (metal), and the angle dependence of the elastic scattering was clearly observed for bothtypes of nanoparticles: SAXS in the soft X-ray region was successfully observed. On theother hand, we have reported that SAIXS was observed in FePt, but not in Fe3O4; theobservation of SAIXS in FePt demonstrated that diffraction-assisted inelastic scattering canbe realized when the conditions are met, but the results that SAIXS was not observed in Fe3O4
nanoparticle were not fully interpreted.
In order for angular (momentum) dependence of RIXS to be observed, the absorption
and core-hole decay processes must be undisturbed by other relaxation effects such as
electron-electron and electron-phonon interactions, and temporally coherent so that they canbe regarded as RIXS processes. In addition, for the core-hole of the final state to be
momentum-dependent, it must be delocalized so that it has well-defined crystal momentum inthe crystal. This corresponds to spatial coherence, and both temporal and spatial coherence areconsidered to be necessary for SAIXS to be observed [1]. In this study, SAIXS was measured
at near the threshold of the absorption edge, where the temporal coherence was enhanced [2],and the effects of temporal and spatial coherence were investigated.
Fig. 1(a) shows the SAXS results of Fe3O4 nanoparticles. The average particle size ofthe nanoparticles was 5.9 nm, and the incident energy was set to 707.5 eV, which was thethreshold of the L3 absorption edge. Linear vertical polarization was used to focus on theintensity of the elastic scattering. The SAXS profile obtained was slightly ambiguous thanwhen measured at the top of the L3 peak because of the weak resonance effect at the thresholdof the absorption edge, but the similar SAXS profile were obtained. The profile was good
agreement with the simulation, suggesting that the SAXS profiles were successfully observed.
Next, RIXS measurements were performed at the same diffraction condition as SAXS, using
linear horizontal polarization to focus on inelastic scattering. The SAIXS profile which was
obtained by integrating the intensity of the inelastic component in RIXS spectra from ~1 to~8 eV is shown in Fig. 1(b) together with the SAXS profile. No clear SAIXS profile wasobserved at the threshold of XAS, as was the case for measurements at the L3 peak top.
Since the incident energy in this experiment was set at the threshold of the absorption
edge, we believe that temporal coherence is >50%, which is sufficiently high to observe
SAIXS. Therefore, it is difficult to conclude that SAIXS was not observed due to the
influence of temporal coherence. On the other hand, as for spatial coherence, since Fe3O4 is
the insulator and valence orbitals are well localized, the observed inelastic components suchas dd and charge-transfer excitations are mainly due to relaxation from the localized orbitals.
Thus, the lack of SAIXS observed in Fe3O4 nanoparticles would be attributed to the lack ofspatial coherence rather than temporal coherence. These results are consistent with the resultsof SAIXS observed for the metal FePt, in which the valence state is well delocalized in the
crystal and the spatial coherence is high enough for SAIXS.

Fig. 1 SAXS and SAIXS of Fe3O4 nanoparticle measured at hv=707.5 eV. (a) Experimental (red) and simulated(blue) SAXS profile measured by σ polarization. (b) SAIXS spectra (blue) measured by π polarization comparedwith SAXS profile (red).

REFERENCES[1] Y. Ma, Phys. Rev. B 49, 5799 (1994).
[2] L. Zhang et al., Fuller. Nanotub. Carbon Nanostructures 23, 471 (2014).

ANALYSIS OF ELECTRONIC STATES OF
PARTICULATE PHOTOCATALYSTS BY 3D NANO-ESCA
Takashi HISATOMI,1,2 Naoka NAGAMURA,2,3,4 Wenxiong ZHANG,5 Kenta OHISHI,2,3,4
Asako YOSHINARI,3,4 Shingo TAKEZAWA,3,4 Masaharu OSHIMA,5 Yoshihisa HARADA5
1

Research Initiative for Supra-Materials, Shinshu University2

Precursory Research for Embryonic Science and Technology, Japan Science and Technology Agency

3

Research Center for Advanced Measurement and Characterization National Institute for Materials Science
4

Department of Materials Science and Technology, Tokyo University of Science
5

The Institute for Solid State Physics, The University of Tokyo

The water splitting reaction using particulate semiconductor photocatalysts is studied as ameans of renewable solar hydrogen production on a large scale. BaTaO2N is an oxynitride
photocatalyst material having a band gap energy of 1.9 eV and band edge potentials suitablefor both hydrogen and oxygen evolution from water [1,2]. The photocatalytic activity of thismaterial is dependent strongly on the preparation methods. In many cases, the activity forthe hydrogen evolution reaction utilizing excited electrons is low. This is probably because
BaTaO2N is an n-type semiconductor and has a large Schottky-type barrier that prevents thetransfer of excited electrons at the interface with cocatalyst nanoparticles serving as an activesite. In fact, it is known that doping Al3+ into the Ti4+ site of the SrTiO3 photocatalyst tocancel the n-type semiconducting properties drastically improves the photocatalytic water
splitting activity [3]. These facts suggests that there is a certain correlation between thesemiconducting characters such as the Fermi level and the hydrogen evolution activity ofsemiconductor photocatalysts.
In this work, the electronic states of BaTaO2N and SrTiO3 photocatalysts were analysed bythree-dimensional nano-electron spectroscopy for chemical analysis (3D-nano ESCA). Withhigh spatial resolution reaching less than 100 nm, it is expected that the valence band
spectrum of individual photocatalyst particles without signals originating from the conductive
sample stage can be obtained [4]. This will allow us to determine the Fermi level ofparticulate photocatalyst materials and the investigate the correlation between the Fermi leveland photocatalytic activity.
Two kinds of BaTaO2N and SrTiO3 were prepared according to literature. BaTaO2N
nitrided from BaCO3 and Ta2O5 in the presence of RbCl flux, denoted as BaTaO2N (RbCl),
showed high hydrogen evolution activity [1]. The other BaTaO2N nitrided from nominally(a)(b)
Na1/4Ba3/4Zn1/4Ta3/4O3 and BaCO
3 in the presence of
NaCl flux, denoted as BaTaO2N (NBZTO), showed highoxygen evolution activity [2]. Commercial SrTiO3 asreceived, denoted as SrTiO3, was hardly active in overallwater splitting, while SrTiO3 doped with Al in thepresence of SrCl2 flux, denoted as SrTiO3:Al, was highly
active in overall water splitting and showed an external
quantum efficiency exceeding 90% in the near
ultraviolet region [3]. These particulate photocatalysts
had particle sizes of 200–500 nm and were immobilizedon Au thin film by using the particle transfer method [5].
Figure 1 shows a scanning electron microscope image ofa representative BaTaO2N sample embedded on Au film.
100 μm
1 μm
The core level and valence band X-ray photoelectron
spectroscopy (XPS) data were acquired using the Figure 1. A scanning electron
microscope image of BaTaO N
3D-nanoESCA at BL07LSU of SPring-8. The incident (NBZTO) embedded on Au film. 2

photon energy was set to 1200 eV. The(A)
spectral data were acquired with energy andAu 5d
spatial resolutions of 100 meV and 200 nm,
respectively.
(a)
It was possible to acquire a valence band
Efspectrum of a particulate photocatalyst free(b)from the signal of the underlying Au thin filmby choosing the measurement spot carefully(Figure 2Ab).
However, at almost allmeasurement points, the signal of Au 5d(B)orbitals derived from Au fragments exposedfrom the gap among photocatalyst particles
overlapped in the valence band region (Figure(a)(b)2Aa), and spectra that could be used for thedetermination of the Fermi level was not
obtained in a reasonable time. Therefore,
the Fermi level shift was estimated from thechange in the binding energy of core levels.
(C)
Figures 2B and 2C show Ta 4f and Ba 3d
spectra of the BaTaO2N materials,
respectively. BaTaO2N (RbCl) had binding
energies smaller than BaTaO2N (NBZTO) by(b) (a)0.2 eV. The binding energy reflects theenergy gap between the Fermi level and thecore level. Given that the binding energy
shift was attributable solely to the Fermi level
shift, BaTaO2N (RbCl) should have a Fermi Figure 2. (A) Valence band, (B) Ta 4f, and (C) Ba
level at a 0.2 eV more positive potential than 3d spectra of (a) BaTaO2N (RbCl) and (b)BaTaO2N (NBZTO). The valence band spectrum of
BaTaO2N (NBZTO). As a result, BaTaO2N BaTaO2N (RbCl) was overwhelmed by the signal(RbCl) was closer to the intrinsic from Au fragments.
semiconductor
and
had
a
weakerSchottky-type barrier at the interface with the cocatalyst. This may account for the higherhydrogen evolution activity of BaTaO2N (RbCl). However, the energy shift was relatively
small. More comprehensive analysis of the materials properties will be needed to make adecisive conclusion. On the other hand, SrTiO3:Al had binding energies smaller than SrTiO3
by 0.4 eV for both Sr 3d and Ti 2p orbitals and thus was closer to the intrinsic semiconductor.
This clear Fermi level shift confirms the corelation of the semiconducting properties andwater splitting activity of the SrTiO3 photocatalyst.
In summary, the Fermi level shift could be estimated from the core level shifts, althoughmeasurement results that took advantage of the high spatial resolution were not obtained.
Considering that the observed signal is given by the weighted average of the signals from theparticulate sample and Au, it may be possible to extract the signal of the sample by statisticalanalysis of a large number of spectra.
REFERENCES[1] Wang et al. Nat. Commun. 2021, 12, 1005.
[2] Jadhav et al. J. Mater. Chem. A 2020, 8, 1127.
[3] Takata et al. Nature 2020, 581, 411.
[4] Sakai et al., Nanoscale 2016, 8, 18893.
[5] Minegishi et al. Chem. Sci. 2013, 4, 1120.

SPECTRAL IMAGING ANALYSIS OF
EDGE-CONTROLLED 2D MATERIALS
Naoka NAGAMURA1,2,3, Mitsuhiro OKADA4, Ryo NOUCHI3,5, Tarojiro MATSUMURA4,
Yasunobu ANDO4, Asako YOSHINARI1,2, Shingo TAKEZAWA1,2, Kenta OHISHI1,2,3,Kentaro FUKU6, Wenxiong ZHANG7, and Masaharu OSHIMA7
1

National Institute for Materials Science (NIMS), Tsukuba, Ibaraki, Japan.
2
Tokyo University of Science, Katsushika, Tokyo, Japan
3
PRESTO, Japan Science and Technology Agency, Honcho, Saitama, Japan.
4
National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki, Japan
5
Osaka Metropolitan University, Sakai, Osaka, Japan
6
Tohoku University, Sendai, Miyagi, Japan
7
The University of Tokyo, Kashiwa, Chiba, Japan

In atomic layer semiconductor sheets, edge states are remarkably effective to the transport
properties. Highly reactive dangling bonds exist at the edges of finite-size two-dimensional(2D) materials. Structures and chemical bonding states of the edges are easily modulated, so
direct observation of edge states is important to discuss the characteristics of 2D materials.
Here we have investigated the spatial distribution of electronic states and chemical bonding
states of the edge-controlled functional 2D materials, the monolayer MoS2–Nb-doped MoS2
lateral homojunctions and the gate-controlled UV photo-oxidized graphene field effecttransistors, using the 3D nano-ESCA[1] system at BL07LSU of SPring-8.
1. MoS2–Nb-doped MoS2 lateral homojunctions
Monolayer transition metal dichalcogenides (TMDs) are promising materials for various
next-generation semiconductor devices. However, carrier doping techniques for TMDs havenot been completely established yet. We synthesized monolayer MoS2–Nb-doped MoS2
lateral homojunctions using chemical vapor deposition (CVD).
To analyse the spatial elemental
composition and the carrier distributionof MoS2–MoS2:Nb, we performed 3D
nano-ESCA
measurements.
Peakfitting of X-ray photoemission
spectroscopy (XPS) spectra was
performed using the spectrum- adapted
expectation-conditional maximization(ECM) algorithm[2,3].
The Mo 3d and S 2s core levels of
the MoS2:Nb region had smaller
binding energies than those of the pure
MoS2 region (Δ ∼0.3 eV) as shown in
Fig. 1(a). This difference wasattributed to the Fermi-level (EF) Figure 1 (a) Mo 3d and S 2s core level spectra measured
downshift by hole doping[4]. Fig. 1(b) at points indicated in the inserted image. Right picture
MoS2–MoS2:Nb growth strategy. (b) peak intensitypresents the intensity mapping of Nb4+ is
mapping image of Nb4+ 3d5/2 and (c) peak position
3d5/2
core
level
peak
in
a mapping image of Mo4+ 3d5/2 measured on
MoS2–MoS2:Nb sheet. Signals from MoS2–MoS2:Nb sheet.
Nb4+ were observed only in the edge
regions. Moreover, in the peak position mapping of Mo4+ 3d5/2 (Fig. 1(c)), low-binding energy
shift were observed also only at the edge region. Therefore, the grown MoS2–MoS2:Nb isrevealed to have a built-in p–n lateral homojunction[5].

2. Gate-controlled UV photo-oxidized graphene field effect transistor
Photo-oxidation is one of the means for surface modifications to control the electronic andchemical properties. Recently, the gate controllability of photo-oxidation reaction in graphene
has been verified using a field-effect-transistor (FET) configuration[6,7]. However, thechemical structure of photo-oxidized graphene surface has not yet been experimentallymeasured. Then we performed an XPS analysis with a high spatial resolution using the 3D
nano-ESCA.
Fig. 2(a) shows pin-point XPS
spectra of C 1s taken at the edge
region and the center region of thephoto-oxidized graphene FET.
The binding energy of the main
peak at the edge is 0.12 eV lower
than that at the center. This energy
shift is considered to be caused by
the Fermi-level (EF) shift inducedbychargedoping[4].
Theconcentration of the doped holes
in graphene at the edge isestimated to be 1.1×1012 cm-2,
which is consistent with theprevious studies on thermal
annealing[8].
As oxidation reactions progress, theFigure 2 Pin-point C 1s and core level spectra measured atshape of the spectrum changes. Fig. (a) the mildly photo-oxidized graphene FET and (b) the2(b) shows pin-point XPS spectra of heavily photo-oxidized graphene FET.
C 1s at several locations in the heavily
photo-oxidized graphene FET. Peak components at higher binding energies, derived from sp3
bonding and carbon-oxygen chemical bonding, seems to increase as oxidation progress.
Therefore, we revealed that the gate-controlled UV photo-oxidation reaction proceed asfollows: hole doping via adsorbed molecules at the edge region → defect introduction bychemical reactions with adsorbed molecules → decomposition and disappearance[9].
REFERENCES[1] K. Horiba, Y. Nakamura, N. Nagamura, S. Toyoda, H. Kumigashira, M. Oshima, K. Amemiya, Y.
Senba, and H. Ohashi, Rev. Sci. Instrum. 82, 113701 (2011).
[2] T. Matsumura, N. Nagamura, S. Akaho, K. Nagata, and Y. Ando, Sci. Technol. Adv. Mater. 20,
733 (2019).
[3] T. Matsumura, N. Nagamura, S. Akaho, K. Nagata, and Y. Ando, Sci. Technol. Adv. Mater.:
Methods 1, 45 (2021).
[4] N. Nagamura, H. Fukidome, K. Nagashio, K. Horiba, T. Ide, K. Funakubo, K. Tashima, A.
Toriumi, M. Suemitsu, K. Horn, and M. Oshima, Carbon 152, 680 (2019).
[5] M. Okada, N. Nagamura, T. Matsumura, Y. Ando, A. Lu, N. Okada, W. Chang, T. Nakanishi, T.
Shimizu, T. Kubo, T. Irisawa, and T. Yamada, APL Mater. 9, 121115 (2021).
[6] N. Mitoma, and R. Nouchi, Appl. Phys. Lett. 103, 201605 (2013).
[7] R. Nouchi, M. Matsumoto, and N. Mitoma, J. Mater. Chem. C 7, 1904 (2019).
[8] S. Ryu, L. Liu, S. Berciaud, Y. Yu, H. Liu, P. Kim, G. W. Flynn, and L. E. Brus, Nano Lett. 10,4944 (2010).
[9] N. Nagamura, S. Konno, M. Matsumoto, W. Zhang, M. Kotsugi, M. Oshima and R. Nouchi, in
preparation.

RIXS-MCD Study of Chromium Trihalides CrX3 (X = Cl, Br, I)
C. S. Pathiraja, J. N. Ranhili, Y. C. Shao, Y. -D. Chyang, B. Freelon
In the recently discovered 2D magnets formed by chromium trihalides CrX3 (X = Cl, Br, I), a richinterplay between stacking and interlayer exchange has eventually led to a range of applications in
spintronics, heterostructures, and twisted-layer devices. However, one of the most important open
questions in this new field is what is the nature of the magnetic anisotropic interactions? Magnetic
circular dichroism (MCD) in Resonant Inelastic X-ray Scattering (RIXS-MCD) is well-suited to address
this issue because the technique allows the determination of d-orbitals that are associated withmagnetic (dichroic) signals. The purpose of this beamtime was to use high-resolution RIXS-MCD anddetermine the detailed excitations that are relevant for the magnetic interaction in the CrX3. Magnetic
dichroic effect was studied for each d-d excitation to track their evolution.
During the beamtime, the data were taken for three samples CrCl3, CrCl0.8Br0.2 and CrI3. Samples werealigned with the c- axis along antiparallel to the incident beam and the magnetic field was parallel tothe incident beam. With the incident angle 450 at Room temperature, L-edge Cr RIXS-MCD werecollected for both RCP and LCP at ~ 6 excitation energies with the incident wave vector directed along
the direction of magnetization of the given 3 samples. Then the incident angle was changed to 900 andthe measurements was repeated. Finally, the temperature was cooled down to liquid nitrogentemperature(~73.9K). At 74K, we could collect RIXS-MCD data only for CrCl3 and CrCl0.8Br0.2 because
the limited time.
The experiment was successful, and we could observe some dichroism in the materials under given
circumstances. In CrCl3, the dichroism could be observed in the XAS, and it was almost vanished in the
RIXS-MCD spectra (Figure 1). For the mix halide RIXS-MCD spectra, lots of the loss features had no
noticeable dichroic dependence; however, there was some small circular polarization difference d-dregion of 576.5 eV spectrum. Moreover, 3-5 eV loss region was rich with some features. Even though
there was not much dichroic dependence in that region, the spectral evolution was interesting. (Figure2) When comparing the XAS spectra for different materials, there was a shift in the peak position for
CrI3 nearly around 576.1 eV (Figure 3). As a summary, dichroism could observe in the XAS spectra andfor the RIXS-MCD as we expected and further data analysis is still on the process. In the upcoming
future, we are planning to work with theorists and obtain a theoretical point of view for our
experimental results.

Figure 1: XAS and RIXS-MCD comparison of CrCl3 for different excitation energies

Figure 2: RIXS-MCD comparison of mix halide for different excitation energies

Figure 3: XAS comparison of different materials

INVESTIGATION OF ELECTRONIC STRUCTURE OF FE-COSPINELS BY 2P3D RIXS AND L-EDGE XAS
Olaf Rüdiger,1 Minmin Chen,1 Derek Rice,1 Hisao Kiuchi2, Wenxiong Zhang2, Ralph J. Ugalino3,
Naoya Kurahashi2, Yoshihisa Harada2,3, Serena DeBeer1
1. Max Planck Institute for Chemical Energy Conversion, Mülheim an der Ruhr, Germany
2. Synchrotron Radiation Laboratory, The Institute for Solid State Physics, The University of Tokyo
3. Graduate School of Frontier Sciences, The University of Tokyo

We collected cobalt L2,3 X-ray absorption spectra and 2p3d RIXS spectra of a series of
Fe-loaded Co-based spinels relevant for water and alcohol oxidation reactions.[1] Fe loading ina Co spinel is known to induce spinel inversion, but the degree of inversion cannot be easily
obtained by XRD. Spinels have a general formula A2+B3+2O4, with A occupying a tetrahedral
site (Td) and B an octahedral one (Oh). For an inverse spinel, the +3 ions are equallydistributed among the Td and Oh sites,
while the +2 ion sits at a Oh site. In
order to obtain the spectral signaturesof the different sites, we collected
spectra from the inverse spinel
CoFe2O4, containing only Co2+Oh, andfrom the spinels CoAl2O4 (containing
only Co2+Td), and ZnCo2O4 (Co3+Oh).
Figure 1 shows the 2p3d RIXS spectraof Al2CoO4, Co2ZnO4, Co3O4, andCoFe2O4.The spectra show significant
differences that can be assigned to the
distinct spinel sites (Figure 1). At low
incident energy we are primarily
exciting the Co2+ ions, and we canclearly observe the differences between
the Td and Oh sites comparing theAl2CoO4 and CoFe2O4 samples, where
the former has an emission signature atvery low energy loss (0.5 eV). In
contrast, the ZnCo2O4 sample has atransition at 0.7 eV, while the firstinelastic peak for the inverse spinel
appears at slightly higher energy.
To fully understand the different
transitions, we are currently running
Figure 1. 2p3dRIXS of (a) CoAl2O4, (b) ZnCo2O4, (c)multiplet calculations within the ORCA
Co3O4, and (d) CoFe2O4 at incident energy 777.3eV,
code.[2] In Figure 2, we show
778.4eV, 779.1eV, and 780.5eV respectively.
preliminary calculations for the CoO
and CoAl2O4 samples. The best fit to
the spectra gave a 10 Dq value of 0.97 eV in a Oh geometry and a reduction of the atomic
Slater-Condom parameters by 65% to account for covalency. For the Td geometry we obtained
a 10 Dq value of 0.52 eV and a reduction of the atomic Slater-Condom parameters of 70% for
Fk and 63% for Gk have been used to reproduce CoAl2O4 spectra, although we found aninconsistency for the spectra at 779.1eV that we are still trying to refine. Similar calculations
are being carried on for the Co3+Oh using the measured Co2ZnO4 as references.

Figure 2. (a) L3-edge XAS calculation of Co2+Oh and (b) Co2+Td used the same parameter as their 2p3d RIXS
calculation. (c) 2p3d RIXS calculation of Co2+Oh and (d) Co2+Td at incident energy 777.3eV, 778.4eV, 779.1eV,
and 780.5eV with ORCA-LFT.

Figure 3 shows the 2p3d RIXS spectra of a series of Co-spinels with increasing amounts of
Fe-loading at an incident excitation energy of 779.1 eV. The first conclusion that can beextracted is that the intensity at 0.5 eV, as well as the position of the peak between 0.6 and 1
eV energy transfer, appears to correlate withthe degree of spinel inversion. This way wecan easily assign the Co2FeO4 as a spinel,
while the Co1.5Fe1.5O4 resembles much more
the inverse spinel. Another interesting
conclusion is that the position of the peaks for
the Co2FeO4 is shifted with respect to the pure
Co3O4 spinel. This is indicative of amodulation of the crystal field parameters of
the Co ions by Fe substitution. Fe loading is
known to improve the catalytic properties ofCo spinel for water oxidation.[1b] In thepresent work, we show evidence of how the
Figure 3. 2p3d RIXS spectra for a series of
Fe loading influences the Co electronic
Fe-substituted Co spinels at 779.1 eV incident
structure, as well as a technique to identify
energy. The data has been smoothed by applying aspinel inversion in these materials.
5-point moving average.
REFERENCES
[1]

[2]

a) D. Waffel, E. Budiyanto, T. Porske, J. Büker, T. Falk, Q. Fu, S. Schmidt, H. Tüysüz, M. Muhler, B.
Peng, Molecular Catalysis 2020, 498, 111251; b) E. Budiyanto, M. Q. Yu, M. M. Chen, S. DeBeer, O.
Rudiger, H. Tuysuz, Acs Applied Energy Materials 2020, 3, 8583-8594.
F. Neese, Wiley Interdisciplinary Reviews: Computational Molecular Science 2012, 2, 73-78.

STUDY ON THE ELECTRONIC STATE OF WATER MOLECULES INPOLYMER ELECTROLYTE MEMBRANES
Naoya Kurahashi1, Ugalino Ralph John2 and Yoshihisa Harada1

1

Synchrotron Radiation Laboratory, The Institute for Solid State Physics, The University of Tokyo
2

Graduate School of Frontier Sciences, The University of Tokyo

A fuel cell is a power generation device that directly converts chemical energy such ashydrogen into electrical energy. Fuel cells are highly energy efficient and do not generate carbon
dioxide during power generation, so they are expected to contribute to the reduction ofgreenhouse gas emissions. In Japan, stationary fuel cells for home use were put on the market
in 2009, and fuel cell vehicles were put on the market in 2014, but further spread and expansion
are required. In particular, polymer electrolyte fuel cells (PEFCs) are being installed in
automobiles because they are small and can generate electricity at low temperatures.
In PEFCs, when hydrogen gas is supplied to the anode, hydrogen ions (H+) are generated on
the electrodes. The generated hydrogen ions pass through the polymer electrolyte membrane(PEM) and move to the cathode, where hydrogen ions react with oxygen gas on the electrodes
to generate energy and water molecules. Therefore, the polymer electrolyte membrane musthave high gas barrier properties, water resistance, and mechanical strength, while allowing onlyhydrogen ions to permeate with high efficiency. Most of the polymers used in PEMs have astructure in which a strong acid group such as a sulfo group is introduced at the end of ahydrophobic skeleton. When these macromolecules aggregate, they take an inverted micellestructure and form nanometer-order channel structures1. When the PEM is humidified, water istaken into the channel and hydrogen ions are released from the superacid group, which isthought to be a conduction path for hydrogen ions2. Therefore, it is necessary to evaluate thehydrogen-bond property of water molecules in the PEM in order to understand the proton
permeability. However, experimental research was lacking because it was difficult to directly
observe the water molecules incorporated inside the membrane. The authors have previously
attempted to evaluate the diffusion of water molecules incorporated into the Nafion membraneusing nuclear magnetic resonance spectroscopy. As a result, it was clarified that the motility ofwater molecules changes significantly around a temperature of around 15 oC. The authors
predicted that the cause of the change in motility was the change in the size of the proton
channel, but we could not reach a conclusion only by NMR measurement. Therefore, we
considered searching for the cause of the change in motility by investigating the electronic stateof water molecules in the proton channel by soft X-ray emission spectroscopy. The sample wasprepared by casting commercially available Nafion suspension onto a SiC plate and evaporate
the solvent. By controlling both the temperature and humidity of the atmosphere control cell,the temperature dependence of the electronic state can be measured.
We evaluated the damage to Nafion because it was reported that soft X-rays would damage
the fluorinated material. In the emission spectroscopy, the sample was moved at regularintervals to prevent damage to the SiC window and the sample, so that the same place is notcontinuously irradiated with synchrotron radiation. As a result of measuring the soft X-ray
emission spectrum from Nafion by changing the X-ray irradiation time per point, it was
concluded that damage to Nafion can be avoided if the X-ray irradiation is 5 seconds per point
or less. Subsequently, the soft X-ray emission spectra from Nafion in a dry state with circulating
nitrogen gas and in a humidified state at 80 % relative humidity were measured, and thedifference spectrum between the two was calculated. As a result, only the emission spectrum
derived from water molecules incorporated into the Nafion membrane could be extracted.

The soft X-ray emission spectra measured
with photon energy of 550 eV and energy
resolution of 150 meV is shown in Fig. 1.
The spectra of water molecules confined in
Nafion are quite different from that of bulk
watermeasured
under
the
same
temperatures, with a largest peak that isthought to be 1b1" at all temperatures. Thissuggests that water molecules confined in
Nafion and in the bulk form differenthydrogen bonding networks. On the other
hand, since the emission spectrum has four
overlapping peaks, it was difficult toevaluate the temperature dependence of thespectra. Therefore, in order to quantitatively Fig. 1 Soft X-ray emission spectrum of bulk water andwater molecules in Nafion at 80% relative humidity
evaluate the temperature dependence, we
performed a peak-fitting of the emission spectrum with four Gaussians and evaluate thetemperature dependence of the fitting parameters. Fitting of the spectra was performed using
the following function,(

𝐼(𝑥) = 𝐼 + ∑𝑒)(𝑖 = 1𝑏 , 3𝑎 , 1𝑏 , 1𝑏" )(1)where I0, Ai, Xi, and i are the baseline, peak area, peak position, and standard deviation of thepeak, respectively. As a result, the peak area of 1b1' and 1b1" show an interesting temperaturedependence (Fig. 2). The 1b1' emission intensity of water molecules confined into Nafion
reached a maximum at 18 °C, while the 1b1" emission intensity reached a minimum at 18 °C.
The 1b1' and 1b1" intensities of bulk water showed monotonic changes in the range from 1 to
50 °C. This suggests that the water molecules confined into Nafion reach a maximum rate ofhydrogen bondingintetrahedral
coordination
around 18 °C.
Combined with theresults of previous
NMR studies, thissuggests that thesize of proton
channels in Nafion
maychangeFig. 2 Temperature dependence of 1b1’ (a) and 1b1” (b) peak areas by fitting. Filled andopen circles are the results for water in Nafion and for bulk water, respectively. The
around 18 °C.
result of Nafion was that the area of 1b1’ was the largest and the area of 1b1” was thesmallest at 18 °C.

REFERENCES[1] M. Rikukawa, Journal of Synthetic Organic Chemistry, 66, 488 (2008).
[2] M. Yoshida-Hirahara et al., RSC Adv., 10, 12810 (2020).

ELECTRONIC STATES OF FUNCTIONAL MATERIALS IN
HYDROGEN ADSORPTION/DESORPTION STUDIED BY AMBIENT
PRESSURE SOFT X-RAY PHOTOELECTRON SPECTROSCOPY
F. OZAKI, W. OSADA, Y. CHOI, H. YOSHIOKA, S. TANAKA, K. MUKAI, M. HORIO,
I. MATSUDA and J. YOSHINOBUThe Institute for Solid State Physics, The University of Tokyo

Introduction
In this research, we have studied the electronic and chemical states of functional materials
whose electronic and chemical properties are changed by the interaction with hydrogen, by theuse of ambient-pressure photoelectron spectroscopy (AP-XPS) at BL07LSU, SPring-8.
Molybdenum disulfide (MoS2) is a layered material and it has been used as a hydrogenation
catalyst [1]. For example, MoS2 has long been used as a hydrodesulfurization catalyst to
selectively remove sulfur from petroleum to produce clean fuels [2]. MoS2 has also attracted
attention for its high activity as a hydrogen evolution electrocatalyst [3]. Thus, understanding
the interactions between MoS2 surfaces and hydrogen is an important issue. Here, we report theinteraction of the MoS2 basal surface and the Pd-deposited MoS2 basal surface with hydrogen,because it is known that the basal plane of MoS2 is inert for the dissociation of molecularhydrogen at room temperature.
Experimental
A natural MoS2 crystal was used as a sample. After the sample was mounted on metal plates,
scotch tape was used to peel the surface layers off. The sample was transferred to a load lockchamber within 10 min after the exfoliation and annealed at approximately 550 K for 30 min
in an ultrahigh vacuum (UHV) chamber. To prepare a Pd-deposited MoS2 surface, Pd atoms
were deposited on a MoS2 basal surface at 300 K by resistive heating of a Pd wire. The deposited
Pd atoms were considered to aggregate to form islands on the MoS2 surface at 300 K [4].
AP-XPS measurements were performed in a chamber equipped with a hemispherical electronenergy analyzer (SPECS, PHOIBOS150 NAP) at BL07LSU of SPring-8, Japan [5]. All XPS
spectra were obtained at room temperature using the photon energy of 680 eV. The binding
energies of the measured spectra were calibrated by the Fermi energy of a gold foil on thesample holder. The high-purity H2 gas was introduced into an ambient-pressure gas cell, where
the base pressure was below 5 × 10-10 mbar.
Results and discussion
In the Mo 3d, S 2p, and valence-band photoelectron spectra of a bare MoS2 surface, littlechange was observed in the energy shift before and after exposure to hydrogen gas (not shown
here; please refer to Ref. 6). At the Pd-deposited MoS2 surface under hydrogen gas exposure,the Mo 3d, S 2p, valence-band and Pd 3d XPS spectra were measured by AP-XPS [Figure 1(a)–(d)]. The peak energy of Pd 3d gradually shifted to a higher binding energy as a function ofhydrogen exposure, which can be ascribed to the dissociative adsorption of molecular hydrogen.
We performed fitting of the Pd 3d5/2 XPS spectra before and after the exposure to hydrogen gas.
The fitting result before hydrogen exposure is shown in the lower part of Fig. 1(e), where thelow energy component (334.9 eV, green) and high energy component (335.6 eV, blue) can be
assigned to the surface and bulk Pd components in the Pd island, respectively Note that eachpeak in the photoelectron spectra (Mo 3d, S 2p, and valence-band) shifted to a lower binding
energy with 0.1 eV [Figure 1(f)]. These results indicate that the dissociation of molecularhydrogen and the adsorption of atomic hydrogen occur on the Pd-deposited sites on the MoS2
surface, and thereafter hydrogen atoms spillover onto the MoS2 surface.

The present study shows that the active site for the dissociation of molecular hydrogen iscreated on an inert MoS2 basal surface by Pd deposition. In addition, the electronic state of the
MoS2 substrate is modulated by hydrogen atoms spilled over onto the MoS2 surface. The detailsof this study have been published elsewhere [6].

Figure 1 (a) Mo 3d5/2, (b) S 2p, (c) valence-band, and (d) Pd 3d5/2 spectra of the Pd/MoS2 as a functionof H2 gas pressure at 300 K. The amount of deposited Pd was estimated to be 2.0 % for the amount of
Mo atoms on the outermost MoS2 layer. (e) The upper and lower figures show the fitting results for thePd 3d5/2 AP-XPS spectra before and after the hydrogen exposure, respectively. The green component
and blue component in the lower figure are assigned to be surface and bulk components of the Pd
islands, while the pink component consists of both the bulk component and hydrogen atoms-adsorbed
surface component. (f) The relative binding energies for the Mo 3d5/2, S 2p3/2 and valence band
maximum (VBM) as a function gas exposure process. © 2022 Elsevier B.V [6].

ACKNOWLEDGMENTS
The AP-XPS measurements using synchrotron radiation were performed at SPring-8
BL07LSU as joint research in the Synchrotron Radiation Research Organization, The Institutefor Solid State Physics, The University of Tokyo (Proposal No. 2020A7481, 2021A7426). We
thank Mr. Yu Tsuchihara at the initial stage of this research.
REFERENCES[1] J. Mao et al., Front. Phys. 13 (2018) 138118.
[2] H. Topsøe et al., Ind. Eng. Chem. Fundamen. 25 (1986) 25.
[3] Y. Yan et al., ACS Catal. 4 (2014) 1693.
[4] H. Dong et al., ACS Appl. Mater. Interfaces 9 (2017) 38977.
[5] T. Koitaya et al., Top. Catal. 59 (2016) 526.
[6] F. Ozaki et al., Appl. Surf. Sci. 593 (2022)153313.

O K-edge soft X-ray emission spectroscopy of the solvents in electrolyte
solutions for redox flow batteries
Eiji Hosono1,2, Daisuke Asakura2,3, Akihiro Ohira3, Wenxiong Zhang4, Naoya Kurahashi4,
Ralph J. Ugalino4, Hisao Kiuchi4, and Yoshihisa Harada2,4
1

Global Zero Emission Research Center, National Institute of Advanced Industrial Science andTechnology (AIST)2

AIST-UTokyo Advanced Operando-Measurement Technology Open Innovation Laboratory, AIST
3

Research Institute for Energy Conservation, AIST

4

Synchrotron Radiation Laboratory, The Institute for Solid State Physics, The University of Tokyo

Redox flow battery (RFB) is a rechargeable battery which is attractive for application tolarge-scale energy storage system. RFBs consist of electrolyte solutions containing the active
materials, positive and negative electrodes soaked in the electrolyte solutions, and anelectrolyte membrane that separates the two electrodes. It is characteristic for RFBs that theelectrolyte solutions are mainly responsible for the redox reactions unlike Li-ion batteries
where the solid-state electrodes are redox active. For example, vanadium RFB is mostpromising for practical use. The redox reaction is vanadium’s V4+ ⇆ V5+ in the electrolyte forcathode and V3+ ⇆ V2+ in that for anode. Thus, the battery capacity depends on the vanadium
ion concentration in the electrolyte solutions.3
To increase the capacity of RFBs, it is important to understand the redox reaction at theinterface between the active material and the electrode in the electrolyte solution, which is
directly connected with the concentration. Thus, the electronic structure analysis is ofparticular importance. Especially, it is necessary to clarify the solvation and de-solvation
behavior of the active material due to the redox reaction. X-ray emission spectroscopy (XES)
is one of the promising techniques to understand those properties. For aqueous electrolyte
solutions, O K-edge XES is highly useful to investigate the coordination mechanisms of H2O
molecules. In this study, we apply O K-edge XES to aqueous electrolyte solutions includingorganic active materials.1
The O K-edge XES measurements were carried out by using HORNET spectrometer at
BL07LSU, SPring-8. The energy resolution was set to 170 meV at 540 eV. The aqueous
electrolyte solutions including organic active materials and reference solution samples were
put in a flow-type liquid cell with a 150-nm-thick Si3N4 membrane window to separate theliquid samples from vacuum. The samples were flowed with a flow rate of 1 ml/min by aperistaltic pump (Fig. 1) during the XES measurements.
Figure 2 shows the O K-edge XES spectra for pure H2O (25 ℃) and 1 M NaCl/H2O (roomtemperature) that is used as the solvent of the electrolyte solutions. The excitation energy was
550 eV in the post-edge region at the O K edge. The peaks around 521.2, 524.6, 525.8 and527.7 eV are attributed to 1b2, 3a1, 1b1’ and 1b1” as reported in previous papers.2,3 The 1b1’
and 1b1” peaks are of ice-like tetrahedral coordination of H2O molecules and distorted
coordination environment, respectively. For 1 M NaCl/H2O, the 1b1’ peak is slightly lower
than the 1b1” peak in contrast to the spectrum for pure H2O, suggesting that the H2O
molecules in 1 M NaCl/H2O should be less coordinated than those in pure H2O. Moreover, thehigher 3a1 peak, which is dipole-forbidden transition in tetrahedral symmetry, for 1 M
NaCl/H2O indicates that the H2O tetrahedron is relatively distorted. The electrolyte solutions
including organic active materials showed similar tendencies, while slight differences in the O
K-edge XES spectra were observed among the solution samples. In the near future, the XES

spectra will be analyzed in detail. Then, we will try the operando XES with charge-discharge
measurement.

Fig. 1. A picture of the liquid flow system with a peristaltic pump for the in situ XES
measurements.

Fig. 2. O K-edge XES spectra for NaCl/H2O and H2O. The excitation energy was set to 550
eV.

REFERENCES[1] A. Ohira et al., ACS Appl. Energy Mater. 3, 4377 (2020).
[2] T. Tokushima et al., Chem. Phys. Lett. 460, 387 (2008).
[3] K. Yamazoe et al., Langmuir 33, 3954 (2017).

Co L3-edge Soft X-ray Emission spectroscopy of LiCoO2 for Li-ion batteries
Daisuke Asakura1,2, Eiji Hosono2,3, Kosuke Yamazoe4, Naoya Kurahashi4, Ralph J. Ugalino4,
Hisao Kiuchi4, and Yoshihisa Harada2,4
1

Research Institute for Energy Conservation, National Institute of Advanced Industrial Science andTechnology (AIST)2

AIST-UTokyo Advanced Operando-Measurement Technology Open Innovation Laboratory, AIST
3

Global Zero Emission Research Center, AIST

4

Synchrotron Radiation Laboratory, The Institute for Solid State Physics, The University of Tokyo

Li-ion battery (LIB) is one of the key energy-storage devices for CO2 reduction. To further
enhance the performances of LIBs for applications to electric vehicles and large-scalestationary energy storage systems, increasing the charge-discharge capacity of the cathode ishighly demanded. Electronic-structure analysis using X-ray spectroscopy has been playing animportant role on the clarification of the redox mechanism of cathode materials, which willlead to increase of the charge-discharge capacity. By clarifying the redox mechanism oftypical cathode materials, strategies for designing novel cathode materials could be obtained.
We have been studying the electronic structure of several cathode materials using soft X-ray
absorption (XAS) and emission spectroscopy (XES). For example, the Mn L-edge XAS andXES studies for LiMn2O4 revealed the redox reaction of Mn3+ ⇔ Mn4+ at the Mn3+ site in
the initial state. The Mn4+ state has very strong charge-transfer effect between the O 2p andMn 3d orbitals, resulting in the important role of O 2p orbital on the redox reaction.1,2 For
LiFePO4, the redox reaction of Fe was confirmed by Fe L-edge XAS and XES, which was
attributed to simple ionic redox of Fe2+ ⇔ Fe3+.3 Then, LiCoO2 (LCO) is a prototypicalcathode material for practical use like LiMn2O4 and LiFePO4. While the electronic structureof LCO has been studied by XAS,4 we demonstrate the Co L-edge XES to further understandthe Co 3d and O 2p orbitals.
Powdered LCO sample was pasted with acetylene black and PTFE. The pasted LCO
electrode was assembled as a three-electrode beaker cell with Li-metal counter and referenceelectrodes and an organic electrolyte solution. We prepared two cells to make charged-stateand discharged-state samples with different modes by cyclic voltammetry. The
charged/discharged cells were disassembled in an Ar-filled glovebox. The LCO samples weretransferred from the glovebox to a transfer vessel without exposure to the air. Ex situ Co
L-edge XAS and XES measurements for the pristine and the two charged samples werecarried out by HORNET spectrometer at BL07LSU, SPring-8. The energy resolution for the
XES measurement was set to 330 meV at 785 eV.
Figure 1 shows the Co L3-edge XES spectra measured with an excitation energy of 780.4
eV. Considering the Co L3,2-edge XAS results (not shown), the XES spectrum for the initialstate should be of Co3+ low-spin state as with the XAS spectrum. On the other hand, the XESline shape is relatively different from that for LaCoO3 having a Co3+ low-spin electron
configuration.5 One of the reasons should be the lower symmetry of the CoO6 octahedron in
LCO, which should reflect the different structures for the dd excitation around 779 eVcompared to the XES results for LaCoO3.5 These differences could be obtained by thehigh-resolution XES while the XAS line shapes of both LCO and LaCoO3 are quite similar.
For the charged state, the XES line shape is greatly changed, indicating that the oxidation
reaction of Co due to charge (Li-extraction) reaction. For the discharged state, the line shapeis almost the same as the initial state. Therefore, the redox reaction of Co is highly reversible.

The XES spectra will be analyzed by using charge-transfer multiplet calculations in detail.
We will focus on the charge-transfer effect between the O 2p and Co 3d orbitals likeLiMn2O4.1,2 Then, the relation between the electronic structure and the electrode performance
will be further investigated. Also, we will try the operando measurement with anall-solid-state-type operando cell for LIB (under construction), because LCO works inall-solid-state LIB6 which is highly attractive for application to electric vehicles.

Fig. 1. Co L3-edge XES spectra for LiCoO2. The excitation energy was set to 780.4 eV.

REFERENCES[1] D. Asakura et al., Electrochem. Commun. 50, 93 (2015).
[2] D. Asakura et al., Phys. Chem. Chem. Phys. 21, 18363 (2019).
[3] D. Asakura et al., ChemPhysChem 19, 988 (2018).
[4] For example, W.-S. Yoon et al., J. Phys. Chem. B 106, 2526 (2002) and T. Mizokawa et al., Phys.
Rev. Lett. 111, 056404 (2013).
[5] Y. Yokoyama et al., Phys. Rev. Lett. 120, 206402 (2018).
[6] For example, Y. Kato et al., J. Phys. Chem. Lett. 9, 607 (2018).

REAL-TIME OBSERVATION OF HYDROGEN-ABSORPTIONPROCESS IN PD-AU ALLOYS BY OPERANDO AP-XPS
Takanori KOITAYA,1, 2 Susumu YAMAMOTO,3, 4 Masafumi HORIO,5 Iwao MATSUDA,5
Jun YOSHINOBU,5 and Toshihiko YOKOYAMA1
1 Department of Materials Molecular Science, Institute for Molecular Science
2 Precursory Research for Embryonic Science and Technology (PRESTO), Japan Science andTechnology Agency (JST)3 International Center for Synchrotron Radiation Innovation Smart (SRIS), Tohoku University
4 Institute of Multidisciplinary Research for Advanced Materials (IMRAM), Tohoku University
5 The Institute for Solid State Physics, The University of Tokyo

Palladium-based alloys are widely known as hydrogen storage materials, and hydrogen
absorption/desorption processes on the sample surfaces have been extensively studied.
Palladium-gold (Pd-Au) alloy is expected to be used in various fields such as a hydrogensensor [1] and a heterogeneous catalyst [2]. It has been also revealed that the adding gold topalladium promotes hydrogen absorption compared with pure palladium, which is caused bydestabilization of chemisorbed surface hydrogen and decrease of a hydrogen penetration
barrier from the surface into the subsurface [3].
In order to clarify the effects of the alloying with gold in the hydrogen absorption process, it
is very important to perform operando spectroscopy under the conditions in which theabsorption of hydrogen occurs. In this study, we measured the electronic states of the Pd-Au
alloys during the hydrogen adsorption/desorption processes by soft X-ray nearambient-pressure photoelectron spectroscopy (AP-XPS), to reveal the nature of the interaction
between the palladium alloy and absorbed hydrogen.
The experiments were performed using the AP-XPS system installed at the SPring-8
BL07LSU. Recently, the AP-XPS apparatus was improved, which enables AP-XPS
measurements at higher gas-phase pressures up to 100 mbar. As a result, real-time AP-XPS
measurements of the hydrogen adsorption/desorption processes have become possible withenough signal intensity and energy resolution to detect change in the chemical states of the
Pd-Au alloys by the interaction with absorbed hydrogen. Before the AP-XPS experiments, thePd-Au samples were cleaned by a cycle of Ar+ ion sputtering and annealing.
A series of AP-XPS spectra were measured while controlling the hydrogen pressure with aconstant ramp rate ( = 0.01 mbar/s) at a sample temperature of 297.2 K. Figures 1(a) and (b)show the Pd 3d and Au 4f AP-XPS spectra of the Pd-Au alloy sample during the absorption
and desorption processes as a function of hydrogen pressure. When the hydrogen pressure
rises to about 15 mbar, hydrogen absorption occurs and the core-level peaks of the substratechange accordingly (Fig. 1(a)). In Fig. 1 (b), the spectral change in the hydrogen desorption
process is observed at hydrogen pressure of 5 mbar. The transition pressure is clearly different
between the absorption process and the desorption process (pressure hysteresis). This result
indicates that the observed change in the chemical states of the alloy is caused by ametal-hydride phase transition.

Figure 1. A series of Au 4f and Pd 3d AP-XPS spectra of the Pd-Au alloy (Au: 12 at%) in (a) absorption and (b)desorption processes as a function of hydrogen pressure. The gas-phase pressure was linearly changed at aconstant rate of 0.01 mbar/s, whereas sample temperature was kept at 297.2 K. All the spectra were measured at
photon energy of 1600 eV.

REFERENCES[1] C. Wadell et al., Nano Lett. 15, 3563 (2015).
[2] Y. He et al., Catal. Today 339, 48 (2020).
[3] K. Namba et al., Proc. Natl. Acad. Sci. 115, 7896 (2018).

HALF-METALLIC ELECTRONIC STATES OF BULK-SINGLECRYSTAL Co2MnZ (Z = Ge AND Ga) HEUSLER ALLOYS PROBED BYRESONANT INELASTIC SOFT X-RAY SCATTERING (SX-RIXS) IN A
MAGNETIC FIELD
Rie Y. Umetsu1, Hidenori Fujiwara2, Jun Miyawaki3, Rika Kasahara2, Takuma Nishioka2,
Akane Ose2, Akira Sekiyama2, Yoshihisa Harada4,5 and Shigemasa Suga6
1

Institute for Materials Research (IMR), Tohoku University, Miyagi, Japan
Graduate School of Engineering Science, Osaka University, Osaka, Japan
3
National Institutes for Quantum and Radiological Science and Technology (QST), Miyagi, Japan
4
The Institute for Solid State Physics (ISSP), The University of Tokyo, Tokyo, Japan
5
Synchrotron Radiation Research Organization, The University of Tokyo, Hyogo, Japan
6
SANKEN, Osaka University, Osaka, Japan
2

Introduction
In our research group, several kinds of Heusler alloys have been investigated by soft x-ray
resonant inelastic x-ray scattering (SX-RIXS) measurements in magnetic field to reveal theirhalf-metallic electronic structures [1-3]. The RIXS is a bulk sensitive photon-in andphoton-out spectroscopy, and very powerful to investigate such as d-d excitations for open
shell 3d orbitals and magnetic excitations for spin systems as well as 2p-3d transitions inelement- and symmetry-specific ways. From comparison between the experimental andtheoretical spectra, it was found that the quantitative analyses of the spin-polarized valenceband electronic structures related to the half-metallicity would be possible, including such as
the Zeeman splitting energy and the spin dependent band gap width across the Fermi level.
RIXS experiments for single crystal of bulk Co2FeSi Heusler alloy was performed in aprevious study. This material has been controversial as a half-metallic ferromagnet, because
the given spin polarization is different depending on the theoretical calculation method [4].
The weak structure in the RIXS-MCD spectra between the elastic component and strong
fluorescence component suggested the existence of the density of states of Fe-3d orbitals at
the Fermi level, suggesting that the obtained results follow the electronic structures given by
the generalized gradient approximation (GGA) but not by the local density approximation
with considering the electron-electron correlation (LDA+U) [4].
In the present study, we focus on the Co2MnGa Heusler alloy, which is predicted as one of
the Weyl semimetals. It would be very useful to discuss the difference of the electronic
structures between such a Weyl semimetal and typical half-metallic materials as Co2MnSi and
Co2MnGe.
Experimentsa) Sample preparation
Single crystals of bulk Co2MnGe and Co2MnGa was prepared by Bridgman method after
preparing a master alloy by induction furnace melting in Ar gas atmosphere, and annealed at1273 and 1323 K, respectively. The sample compositions identified by scanning electron
microscope-energy dispersive x-ray spectrometry were Co: 49.3, Mn: 24.9, Ge: 25.8 at.%,and Co: 49.4, Mn: 25.2, Ga: 25.4 at.%. Crystal orientations were checked by the Laue method
and the specimens were cut in the stripe form with the length of 5 mm along the <100> with
about 1 × 1 mm2 cross section. Magnetic properties were investigated with SQUID
magnetometer and the magnetic moments converted from the spontaneous magnetizations at
5 K for Co2MnGe and Co2MnGa were 4.96 and 4.07 μB/f.u., respectively, and the Curie
temperatures measured by differential scanning calorimetry were 913 and 697 K, respectively.
b)

RIXS experiment
RIXS experiments were performed using a high-resolution soft x-ray emission

spectrometer installed at the end of the BL07LSU of SPring-8. The specimens were fractured
in a VUV chamber. The RIXS spectra for Mn 2p core excitation were measured with use of
the right and left helicity circularly polarized light at room temperature. A permanent magnet
with the field of 0.25 T was installed in the chamber and arranged as the x-ray incidence
direction and the magnetic field direction become parallel.
Results
Figures (a) and (b) show the intensity maps of RIXS-MCD spectra obtained by parallel+(μ ) and antiparallel (μ−) configurations between the photon helicity and the magnetic field at
incoming photon energy, for Mn L3 edge in Co2MnGe and Co2MnGa, respectively. Strong
RIXS-MCD signals are recognized in both the elastic and fluorescence components. The
former is observed at the zero-energy loss and the latter shifts linearly with the excitation
photon energy. The fluorescence MCD signals contain both negative (blue) and positive (red)signs. The blue area is dominant in lower incoming photon energy regions, and the red area
dominates in higher energy regions.
Figures (c) and (d) are intensity maps obtained by calculated spectra of RIXS-MCD for
Mn L3 edge in Co2MnGe and Co2MnGa, respectively. The features pointed out above are
qualitatively reproduced. In details, the distributions of the RIXS-MCD of the fluorescencecomponents for Co2MnGa are slightly shifted to lower energy loss regions, reflecting thedifferent number of the electrons in the valence band between Co2MnGa and Co2MnGe.
REFERENCES[1] K. Nagai, H. Fujiwara et al., Phys. Rev. B 97 (2018) 035143.
[2] R.Y. Umetsu et al., Phys. Rev. B 99 (2019) 134414.
[3] H. Fujiwara et al., Sci. Rep., 11 (2021) 18654.
[4] K. Nishimoto, H. Fujiwara, R.Y. Umetsu et al., in preparation.

Figs. Intensity maps of RIXS-MCD spectra for L3 edge in Co2MnGe (a) and Co2MnGa (b). The RIXS
spectra recorded for parallel (μ+) and antiparallel (μ−) configurations of the photon helicity. Calculated
spectra by Kramers-Heisenberg formula based on the GGA for Co2MnGe (c) and Co2MnGa (d).

KINETIC SQUARE SCHEME IN OXYGEN-REDOX BATTERYELECTRODES
Masashi OKUBO
Department of Electrical Engineering and Bioscience, School of Advanced Science and Engineering,
Waseda University

The rapid market growth of electric vehicles (EVs) has significantly increased the industrial
demands for their improved performance, such as longer driving distance, longer calendar life,and lower cost. For example, the driving distance of an EV is determined by the energy
density of in-vehicle lithium-ion batteries (LIBs). However, current LIBs possess anunsatisfactory gravimetric energy density of 200‒250 Wh/kg, powering typical EVs for300‒400 km per charge, which is below most consumers’ requirements. Thus, increasing theenergy density of LIBs is crucial for the widespread use of EVs. The energy density of LIBs
is limited in part by the specific capacity of the positive electrode (cathode) material.
Conventional cathode materials, i.e., layered transition-metal oxides LiMO2 (M = transition
metal), deliver a modest capacity of approximately 160 mAh/g, where the dominantmechanism of charge compensation for lithium-ion (de)intercalation is the valence change ofthe transition metal. Further increase in the cathode capacity requires an additional redox
center. To activate redox reactions of oxide ions (oxygen redox), lithium-rich transition-metaloxides have been extensively studied for over a decade as they deliver much larger reversible
capacities (> 200 mAh/g).
This work focuses on O2-type lithium-rich layered transition-metal oxides as cathodematerials with structural integrity (O2: lithium ions occupy octahedral sites between the MO2layers and the packing arrangement of the oxide ions is ABCBA), which is an emerging classof oxygen-redox electrode materials. In the O2-type oxides, the structural degradation upon
cycling is suppressed because migration of M to the Li+ layers is unfavorable: M in a Li+ layer

Figure 1. Redox couples in O2-Li1.12‒yNi0.17Mn0.71O2. dQ/dV plot during the second cycle at acharge/discharge rate of C/20. (a–d) Ex situ Mn and Ni K-edge X-ray absorption spectra upon charge
and discharge. (e) Ex situ O K-edge resonant inelastic X-ray scattering (RIXS) spectra excited by an
incident photon energy of 531 eV.

suffers from strong Coulombic repulsion from face-sharing Mn+ in an adjacent MO2 layer.
Moreover, O2-type Li-rich layered oxides exhibit negligible O2 gas release. As aconsequence, O2-Li1.12‒yNi0.17Mn0.71O2 provides a large reversible capacity greater than 200
mAh/g with minimal voltage decay and capacity fading upon cycling.
O2-Li1.12‒yNi0.17Mn0.71O2 was synthesized by the Na+/Li+ ion-exchange method using
P2-Na0.71[Li0.12Ni0.17Mn0.71]O2 as a precursor. The powder X-ray diffraction pattern of
O2-Li1.12‒yNi0.17Mn0.71O2 shows Bragg peaks indexed to a hexagonal system (space group:
P62mc, typical of the O2 phase), indicating the successful transformation of the P2-type
sodium layered oxide to the O2-type lithium layered oxide. Indeed, a high-angle annulardark-field scanning transmission electron microscopy image confirms the O2-type stacking of
the transition-metal layers. Galvanostatic charge/discharge measurements show that
O2-Li1.12‒yNi0.17Mn0.71O2 delivers a large discharge capacity of approximately 210 mAh/g,
exceeding the M-redox capacity (193 mAh/g). After 80 cycles, 98% of the discharge capacity
in the second cycle is retained, while the decay of the average discharge voltage is negligibly
small (< 5 mV). Typically, conventional O3-type oxygen-redox layered oxides exhibit
structural degradation initiated by the migration of M to Li+ layers. In contrast, in O2-typelayered oxides, Mn+ ions migrated to Li+ layers would be subjected to strong Coulombic
repulsion from face-sharing Mn+ ions in the adjacent MO2 layers, such that the migration of M
would be energetically unfavorable to mitigate both capacity fading and voltage decay during
the charge/discharge cycles.
To identify the redox center, ex situ X-ray absorption/emission spectroscopy measurements
were conducted. Mn and Ni K-edge X-ray absorption near-edge structure (XANES) spectra
during the second cycle show that the redox reaction at 2.8 V vs. Li/Li+ corresponds to theoxidation and reduction of Mn while that at 3.9 V vs. Li/Li+ can be attributed to the oxidation
and reduction of Ni (Figure 1a-d). These attributions (Mn and Ni redox reactions at 2.8 and
3.9 V vs. Li/Li+, respectively) are double-confirmed by Mn and Ni L-edge absorption spectra.
After charging to 4.8 V vs. Li/Li+, O K-edge X-ray absorption spectroscopy shows the
emergence of new absorption at approximately 531 eV, while resonant inelastic X-ray
scattering (RIXS) spectra with the incident photon energy of 531 eV show intense emission at
524 eV (Figure 1e), both of which are characteristic features of charged oxygen-redox
electrode materials. Thus, the anodic dQ/dV peak at 4.5 V vs. Li/Li+ corresponds to theoxidation of oxide ions. These signals for oxidized oxygen do not completely disappear evenafter discharging to 3.6 V vs. Li/Li+. Instead, the disappearance is confirmed after discharging
to 3.1 V vs. Li/Li+. Considering the similar emission peaks observed for Li2O2, CaO2, and O2
molecule, dimerized oxygen species O2n– (n = 0 or 2) exists in charged
O2-Li1.12‒yNi0.17Mn0.71O2 at 4.5 V. It is noteworthy that an enhancement in the elastic peakregion was observed after charge (spectrum C and D in Figure 1e). A possible explanation is
the Raman scattering arising from the vibrational transition of O‒O bond although its origin isstill under debates.
Overall, the O–O dimerization in O2-Li1.12‒yNi0.17Mn0.71O2 can be summarized by thesquare scheme. Upon charge, O2‒ with non-bonding 2p states is oxidized to O‒ above 4.2 V vs.
Li/Li+. At the early stage of oxygen oxidation, O‒ is thermodynamically more favorable than
O22‒. However, with further oxygen oxidation, the over-oxidized oxide ions dimerize to form
O22‒.
REFERENCES[1] K. Kawai, X. M. Shi, N. Takenaka, J. Jang, B. Mortemard de Boisse, A. Tsuchimoto, D. Asakura,
J. Kikkawa, M. Nakayama, M. Okubo, A. Yamada, Energy Environ. Sci. 2022, 15, 2591-2600

ORBITAL TORQUE IN COFE/CU/AL2O3: INVESTIGATION ON THE
LARGE TORQUE WITHOUT HEAVY ELEMENT
Junyeon KIM
Center for Emergent Matter Science, RIKENIntroduction
Recently, sizeable orbital torque is experimentally observed in CoFe/Cu/Al2O3 stacks [1].
This orbital torque is indeed caused by the generation of nonzero orbital angular momentum(OAM) at the Cu/Al2O3 interface (Fig. 1). Nowadays, the orbital torque greatly draws interestfor the spin accumulation since there is no clear restrictions on materials for the nonzero
OAM generation. It is apparently contrast to the spin angular momentum generation which ismainly shown in material systems consisted of heavy elements.
A recent theoretical study reports that the orbital hybridization between the p-orbital ofoxygen atom and the d-orbital atom serves the formation of a chiral orbital texture by orbital
Rashba effect (Fig. 1(a)) [2]. For further understand on the nonzero OAM generation at the
Cu/Al2O3 interface, we require detailed material characterization. Also observation of amodulation of the energy spectrum by a generation of nonzero OAM is also desired.

Fig. 1(a)Excess OAM generation at a chiral orbital texture. Here the chiral orbital texture is formed byorbital Rashba effect. (b) Orbital torque in FM/Cu/Oxide system.

Experimental method
For the observation of the Cu/Al2O3 interface, L-edge X-ray magnetic circular dichroism(XMCD) was utilized. Nominally, the 3d orbital state of Cu is known to be fully occupied.
However Grioni et al. claimed that there is still unoccupied 3d orbital state for Cu due to a
hybridization between s state and d states [3]. And the number of unoccupied 3d orbital state
can be promoted by formations of compounds such as CuOx. Thus we could expect the L2, 3
edge X-ray absorption.
As a first, we attempt to obtain the energy spectrum nearby the Cu/Al 2O3 interface. Next,
we also attempt to obtain a clue of the nonzero OAM generation by turning on/off the charge
current.
The observation was performed in superconducting magnet magneto-optical observation
system in the free board. The CoFe/Cu/Al2O3 and the Cu/Al2O3 stacks are electronicallyconnected by the silver paste. And the observation was carried out by high speed switching of
the circularly polarized light and total electron yield (TEY) technique. To optimize the sample
condition, 2, 5, 7, 10 nm of Al2O3 was tested considering with the detection length of the TEY
technique (~10 nm).

Experimental results and discussion
As shown in Fig. 2, the energy spectrum is successfully obtained by the TEY technique for
the CoFe/Cu/Al2O3 and the Cu/Al2O3 stacks. Here the Cu peak is clearly found for all thestacks, but the CuO or Cu2O peak is not shown. It asserts that formation of Cu oxide mostly
does not occur, although temperature would drastically increase during the Al2O3 layer
deposition. We think the Al2O3 is extremely stable as showing large Gibbs free energy, thus it
is not easily decomposed even in extreme conditions. We think this result is quite helpful forfurther analysis of the interfacial condition. We also attempt to observe the nonzero OAM
generation by the XMCD, but it is not successful due to a drastic Joule heating during theobservation..

Fig. 2 Energy spectrum for the several CoFe/Cu/Al2O3 and the Cu/Al2O3 stacks observed by the TEY
technique.

REFERENCES[1] J. Kim et al. Phys. Rev. B 103, L020407 (2021).
[2] D. Go et al., Phys. Rev. B 103, L121113 (2021).
[3]M. Grioni et al., Phys. Rev. B 39, 1541 (1989).

MAGNETIC STATE OF VNB3S6 DETERMINED BY X-RAY
MAGNETIC CIRCULAR DICHROISM

Masafumi HORIO1, Tomoaki SENOO1, Tetsuya WADA1, Yasuyuki HIRATA2,
Shota OKAZAKI3, Takao SASAGAWA3, Iwao MATSUDA1
1

The Institute for Solid State Physics, The University of Tokyo

2

Department of Applied Physics, National Defence Academy

3

Materials and Structures Laboratory, Tokyo Institute of Technology

Transition metal dichalcogenides TX2 (T = Mo, Nb, W, X = S, Se, Te) are model
semiconductors with various intriguing aspects such as charge ordering, Weyl semimetalicity,
valleytronics, Mottness, and superconductivity, and have established themselves as a major
research field in condensed matter physics. In the 1970s and 1980s, there has been a trend toextend the physical properties of TX2 by intercalating 3d metal M into TX2. It wasdemonstrated that magnetic ordering appears with a strong dependence on the inserted 3dtransition metal [1]. One of the reasons why the MT3X6 system attracted much attention isthat the intercalation of Cr into NbS2 results in a helical magnetic structure called chiralsoliton lattice. Recently, due to the coexistence of the space-inversion and time-reversal
symmetry breaking, the MT3X6 system has attracted a renewed attention from a topologicalpoint of view. In particular, VNb3S6, which is known to be ferromagnetic below Tc~50 K, hasbeen predicted by first-principles calculations to host a Weyl point in the ferromagnetic phaseand exhibit an anomalous Hall effect [2]. The prediction has triggered intense efforts tosynthesize high-quality MT3X6 single-crystal samples and to evaluate their physical properties.
Surprisingly, a recent neutron scattering study [3] reported that VNb3S6 is not ferromagnetic
but in a canted antiferromagnetic state, contrary to the understanding accepted for 40 years [1].
Under these circumstances, it is required to precisely determine the intrinsic magnetic state of
VNb3S6, excluding the possibility of impurities, in order to elucidate the origin of theanomalous Hall conductivity of VNb3S6.
We have therefore performed x-ray absorption spectroscopy (XAS) and x-ray magnetic
circular dichroism (XMCD) measurements of VNb3S6 single crystals. The samples werecleaved in air and immediately introduced into an ultra-high vacuum chamber equipped witha superconducting magnet at SPring-8 BL07LSU. The measurements were conducted in the
total electron yield mode at T = 30 K, below the magnetic transition temperature, under amagnetic field of 3 T. Both normal and grazing (20 degree) incidence conditions were
employed.
Figure 1 shows the XAS and XMCD spectra of VNb3S6 measured with the grazing
incidence condition. Whereas transition-metal ions intercalated into NbS2 have been usuallyassumed to be trivalent, the broad absorption spectrum without well-defined pre-edge does
not seem compatible with V3+ [4-6]. Instead, it is more consistent with intermediate valence
state lower than 3+, as seen in systems like V0.1(Bi0.32Sb0.68)1.9Te3 [7]. This deviation suggests
strong hybridization of V orbitals with surrounding NbS6 layers. The spectral shape ofobtained XMCD spectrum is also close to that of V0.1(Bi0.32Sb0.68)1.9Te3 [7] rather than thoseof the V3+ compounds [4-6], further supporting this conclusion. Due to the overlap of L2 andL3 absorption edges, the sum rule cannot be applied for V L-edge XMCD and hence it is notstraightforward to quantitatively evaluate the magnetic moment. Nevertheless, a naive
comparison with a cluster calculation [6] yields an approximate value of ~0.4 B which is oneorder of magnitude smaller than the values from previous magnetization measurements which
reported ferromagnetism [1]. The magnitude of the XMCD signal did not substantially change
under the normal incidence setup (not shown). The obtained results are therefore in favor ofIntensity (a.u.)canted antiferromagnetism rather than the ferromagnetism. Combined with our ongoing
photoemission measurements, the present work will establish the electronic structure of
VNb3S6 and set a starting point to discuss the origin of anomalous Hall conductivity.

Fig. 1: XAS and XMCD spectra of VNb3S6 measured at the incidence angle of 20 degree
and at T = 30 K under the magnetic field of 3 T.

REFERENCES[1] S.S.P. Parkin et al, Philos. Mag. B 41, 65 (1980).
[2] T. Inoshita et al., Phys. Rev. B 100, 121112(R) (2019).
[3] K. Lu et al., Phys. Rev. Mater. 4, 054416 (2020).
[4] M. Abbate et al., J. Electron Spectrosc. Relat. Phenom. 62, 185 (1993).
[5] M. Horio et al., J. Phys. Spc. Jpn. 87, 105001 (2018).
[6] Y. Nonaka et al., Phys. Rev. B 97, 205126 (2018).
[7] T. R. F. Peixoto et al., npj Quantum Materials 5, 87 (2020).

MEASUREMENT OF X-RAY MAGNETIC LINEAR DICHROISM BY
ROTATING POLARIZATION ANGLE OF SOFT X-RAY GENERATEDBY A SEGMENTED CROSS UNDULATOR
Masafumi HORIO1, Yoshiki KUDO1, Toshihide SUMI1, Tetsuya WADA1,
Yasuyuki HIRATA2, Kohei YAMAMOTO3, Takuo OHKOCHI4,5, Toyohiko KINOSHITA4,
Iwao MATSUDA1
1

The Institute for Solid State Physics, The University of Tokyo

2

Department of Applied Physics, National Defence Academy

3

Department of Materials Molecular Science, Institute for Molecular Science
4

Japan Synchrotron Radiation Research Institute (JASRI)
5

RIKEN SPring-8 Center

X-ray magnetic linear dichroism (XMLD) is a widely used technique for studying magnetic
anisotropy. By measuring the absorption of soft X-rays while changing the relative angle
between the linear polarization of the soft X-rays and the crystal axis, information about theorientation of the spin of the magnet can be obtained. Because of the limitation in controlling
the polarization of soft X-rays, the sample is conventionally rotated around a certain axis toperform XMLD measurements. Therefore, the measurement conditions were limited,
especially when measuring non-uniform samples under operando conditions. In the present
study, we report a novel method for XMLD measurements operated by continuously rotating
the linear polarization angles while samples are fixed.
At BL07LSU at SPring-8, continuous polarization modulation of a soft X-ray beam wasachieved using a segmented cross undulator [1]. The source consists of eight insertion devices(IDs) and seven phase shifters; the ID segments are a horizontal figure-8 undulator and a
vertical figure-8 undulator, which generate horizontal and vertical linear polarization,
respectively. To generate linear polarization at arbitrary angles, we first prepared two sets, set
A and set B, consisting of two sets of horizontal and vertical figure-8 undulators, as shown in
Fig. 1. By adjusting phase shifters #1-3 and #5-7, each set can generate right or left circularpolarization. For example, the four undulators in the front (set A) generate right circularpolarization, while the four undulators in the rear (set B) generate left circular polarization.
The roles of Set A and Set B can be interchanged. The two waves of right and left circularpolarization are then combined to produce linear polarization. There, the rotation angle of thelinearly polarized light was controlled by changing the phase between Set A and Set B using aphase shifter (PS#4 in Fig. 1). As a sample, we prepared a single crystal of NiO (Néeltemperature TN = 523 K). The crystal was cleaved with a knife to expose the (001) plane andfixed on a copper plate with carbon tape. The sample was then introduced into an ultra-highvacuum chamber. Here, in addition to the conventional XAS/XMLD measurements, a novel"rotational" XMLD measurement was performed. All spectra were recorded at room
temperature in the total electron yield mode.
Figure 2(a) shows the Ni L absorption edge XAS spectrum of a NiO crystal, measured withhorizontal and vertical polarization with an incident angle of 80° from the (001) surface [seeFig. 1]. The XAS spectrum was normalized by the integrated intensity in the range 878-881
eV. The XMLD spectrum of the NiO crystal was obtained by taking the difference between
the XAS spectra recorded with horizontal and vertical linear polarization [Fig. 2(b)]. Linear
dichroism is clearly found. Focusing on the L2a and L2b peaks in the figure, we see that theL2a peak is enhanced by horizontal polarization and the L2b peak by vertical polarization.
This contrasting response to light polarization gives rise to the XMLD signal plotted in Fig.

2(b). These results are consistent with previous L-absorption edge XMLD experiments on
NiO [2] and suggest that the in-plane spin component is dominant on the cleaved NiO (001)surface.
After confirming the performance of the conventional method, we present the results of
XMLD measurements while rotating the linear polarization angle. Here, we focus on the Ni
L2 absorption edge peaks, L2a and L2b. The photon energy incident on these peaks was fixed,
and the XAS intensity was detected while continuously changing the angle of linear
polarization during the measurement. Figures 2(c) and (d) show the results. The intensity
varies with a period of π, indicating a clear contrast in XMLD. The inversion of the order of
the ID section (red and blue curves in the figure) also confirms that the signal is dichroic.
Figures 2(c) and (d) also show that the dependence is opposite between L2a and L2b, as
expected for the XMLD signal displayed in Fig. 2(b).
The advantage of this rotation method is that the linear dichroism signal is more reliablebecause the linear polarization angle dependence is tracked while the sample position is fixed.
This method is useful for detecting the small electronic and magnetic anisotropies often foundin quantum materials. Fixing the sample position also allows operando XMLD experiments,
where sample size and rotational motion are severely restricted.

Fig. 1: A schematic of the segmented cross undulator and the measurement configuration. H
and V denote IDs for horizontal and vertical polarization, respectively. Linearly polarized
soft X rays travel along the Y axis and the polarization angle  is varied within the X-Z
plane.

Fig. 2: Ni L-edge XMLD of NiO taken at an incident angle of 80 degree. (a) XAS measured
with horizontal and vertical polarization. (b) XMLD obtained by taking the difference of two
curves in (a). (c), (d) Rotational XMLD measured at L2a and L2b peaks [see (b)], respectively,plotted against linear polarization angle . For the red (blue) curve, undulator set A
produces right (left) polarization while set B produces left (right) polarization.

REFERENCES[1] S. Yamamoto et al., J. Synchrotron Rad. 21, 352 (2014).
[2] G. van der Laan et al., Phys. Rev. B 83, 064409 (2011).
[3] H. Ohldag et al., Phys. Rev. Lett. 86, 2878 (2001).

DEVELOPMENT OF ANGLE-RESOLVED SOFT X-RAY EMISSION
SPECTROSCOPY
Naoya Kurahashi1, Jun Miyawaki1, Kosuke Yamazoe2 and Yoshihisa Harada1
1

Synchrotron Radiation Laboratory, The Institute for Solid State Physics, The University of Tokyo
2

Japan Synchrotron Radiation Research InstituteSoft X-ray emission spectroscopy is a powerful technique to observe the valence electronic
state of occupied orbitals, as it involves emission of excess energy as light when a valence
electron relaxes into a core hole generated by the soft X-ray excitation. The measurement underambient pressure including wet condition is realized by using X-ray transmission windows suchas silicon nitride. Photoelectron spectroscopy is another method for directly observing occupied
electronic states, and it is possible that photoelectron spectroscopy and emission spectroscopy
provide complementary information, as exemplified by the results of bulk water measurements[1]. While soft X-ray emission spectroscopy can approach samples in a variety of environments,
it tends to have a broad natural width of the spectrum, due to the short lifetime of the core hole.
Because of this, it may not be possible to completely separate the electronic states only by theemission energy but a method utilizing other physical parameters for assigning electronic states
is required.
Since photoelectron spectroscopy for atoms and molecules has long been used to study
photo-excitation dynamics, there has been a need for a method to understand the electronic
excitation states. To solve this problem, a photoelectron velocity mapping method[2] has beendeveloped that enables simultaneous observation of the kinetic energy and emission angle ofphotoelectrons. In the process of photoelectron emission, the orbital angular momentum ofelectrons changes by ±1 according to the law of conservation of angular momentum (l = ±1).
For example, electrons from the s-orbital are emitted in the form of p-orbitals, while those in
the p-orbital are emitted as a superposition of s- and d-orbitals. As a result, by measuring the
kinetic energy and emission angle distributions of photoelectrons, information on the energy
levels and angular momenta of the original orbitals can be obtained, which enables precise
assignment of electron orbitals.
As in X-ray emission spectroscopy, l = ±1 should
hold and the angular momentum change of theelectron orbitals is expected to be emitted in theform of light. Therefore, the soft X-ray emission is
expected to be anisotropic, reflecting the symmetryof the electron orbitals. Therefore, we planned toobserve the angular anisotropy of soft X-ray
emission from a gaseous sample.
In emission spectroscopy, a portion of the lightemitted from a sample is cut off and dispersed by aspectrometer. In a soft X-ray emission angularanisotropy experiment, the angular anisotropy ofsoft X-ray emission from a sample can be observedbyperforming
emission
spectroscopy
measurements with linearly polarized light incident
on the sample and the entire grating and detector
Fig. 1 Schematic of soft X-ray emission angularrotated around the sample (Fig. 1). By using a gasanisotropy measurement. The incident light andemission points were fixed and the spectrometer phase sample, the angular emission anisotropy is
considered to depend only on the angle between thewas rotated in the horizontal plane.

molecular axis and the electric field plane of light and the symmetry between the core-excitedintermediate and final states of the molecule, making it easy to compare with theoretical
calculations. Due to the trade-off between energy resolution and detection efficiency inemission spectroscopy, and the low efficiency of X-ray fluorescence for light elements, soft Xray emission spectroscopy for gaseous samples has been considered difficult. To solve thisproblem, we have developed a method to increase the density of a target gaseous element at the
sample position. In this method, X-ray is introduced very close to the sample introduction
nozzle (within a few-m) by devising the shape of the sample introduction nozzle, allowing
emission measurement in a high-density region before the sample diffuses. This method
achieves a signal intensity 100 times higher than that of conventional gas nozzles, while
maintaining a high vacuum in the chamber by reducing the absolute amount of sample. We
performed soft X-ray emission observation of oxygen gas and succeeded in the first soft X-ray
emission angle anisotropy measurement of gaseous molecules (Fig. 2). The pressure in thevacuum chamber remained at around 10-4 Pa even though 100 kPa pure-oxygen gas wasintroduced, and no influence on the light source or other devices was observed.
When the excitation energy was 530.8 eV, which is the 1s-u to 2p-1g* excitation (3g→ 3u), and the polarization was horizontal, the 3g- signal intensity was dependent on theangle of the spectrometer. The 3g- emission from 3u is stronger in the direction perpendicular
to the polarization direction of the incident light. On the other hand, no clear angular anisotropy
was observed for 3g emission; both 3g- and 3g emission angular anisotropies differed fromtheoretical predictions and from the results of photoelectron angular anisotropy. The presenceof a relatively long-lived
component in 3g- may have
weakened the information
on angular anisotropy due tomolecular rotation[3]. The
results of the present study
were compared with thetheoretical calculations.
No angular anisotropy wasobserved in any of the peaks
when the polarization was
set to vertical. This indicatesthat the measurement system
maintains
cylindricalFig. 2 Soft X-ray emission angle anisotropy measurements of oxygen excited
symmetryinverticalat 530.8 eV. The angle in the figure indicates the angle between the opticalpolarization. This means thataxis of the incident light and the monochromator.
thesampleemission
occurred at the center of rotation of the spectrometer.
With this research, we succeeded in a windowless experiment of soft X-ray emission
spectroscopy, and also succeeded in measuring the soft X-ray emission angular anisotropy. We
would like to compare our understanding of the measurement results with theoretical
calculations.
REFERENCES[1] T. Fransson et al., Chem. Rev., 116, 7551 (2016).
[2] T. Suzuki, Annu. Rev. Phys. Chem., 57, 555 (2006).
[3] J.-E. Rubensson et al., J. Electron Spectros. Relat. Phenomena, 185, 294 (2012).

CHARGE EXCITATION RESEARCH ON THE T* PHASE HOLEDOPED CUPRATES BY RESONANT SOFT X-RAY SCATTERING
Xie PEIAO1, Shinnosuke KITAYAMA1, Takanori TANIGUCHI1, Hisao KIUCHI2, Kenji
ISHII3, and Masaki FUJITA1
1

Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
Institute for Solid State Physics, University of Tokyo, Kashiwa 277-8581, Japan
3
Synchrotron Radiation Research Center, National Institutes for Quantum and Radiological Scienceand Technology, Hyogo 679-5148, Japan
2

Recently, the momentum-dependent charge excitations have been found to exist on the holedoping La2-x(Br, Sr)xCuO4 from the O K-edge resonant inelastic x-ray scattering (RIXS)
experiment [1]. The results showed the outwardly dispersive mode which contains the same
behaviors as the NCCO L3-edge RIXS spectrum [2,3]. The authors ascribed it’s come from thecharge excitations. However, the existence of the dispersive mode originating from charge
excitations in all cuprate families is still under debate [4,5]. In this experiment, we first
performed the charge excitations study for another 214-type cuprate — the T* phase family,
which contained CuO5 pyramid coordination formed by alternate stacks of rock-salt layers (Tphase) and fluorite layers (T' phase). The SC state of T* phase cuprates emerged after oxidation
annealing (O-AN) under high pressure to repair the oxygen deficiency around the apical site.
Due to such a unique crystal structure, this research may inspire us further understand thephysical nature of charge excitations.
The measurement was performed on the beamline BL07LSU at SPring-8. The
SmLa0.75Sr0.25CuO4 (SLSCO) of the as-sintered (AS) samples were grown by the travelingsolvent floating zone (TSFZ) method with 2.5 atoms of oxygen. The quality of the crystal waschecked by the x-ray back-scattering Laue method. The representative Laue pattern taken withthe x-ray beam parallel to [0, 0, 1] crystalline axis is shown in Fig. 1 (a). The oxygenized (OAN) samples were prepared by annealing the AS samples in oxygen gas under ~ 46MPa at
500 °C for 80 h. Fig. 1 (b) shows the magnetic susceptibility of the O-AN sample. We tuned
the incident photon energy for the RIXS measurements to the hole peak value at ~528.3eV byscanning the total fluorescence yield. In this measurement, we set the c axis of AS and O-AN
samples kept parallel to the horizontal scattering plane. The samples were cleaved in the air justbefore the measurements.
Figures 2 (a) – (d) show the O K-edge RIXS
spectra and image plot for both AS and O-AN
samples with the whole q range in our
measurement. We observed the RIXS signal(grey line) of T*-type cuprates and theoxidation annealing effect on the charge
excitations for the first time. The signal was
obtained by subtracting the elastic andfluorescence peak, and all the data werenormalized by the integrated intensity offluorescence at q = (0.1, 0) of the O-AN sample.
Because it was difficult to fit the RIXS signal
systematically, the spectral intensity over 90%of the maximum has been chosen as the peak’s
region. Notably, the elastic peak of O-AN
samples contained an obvious additional peak ataround 0.2 - 0.3 eV. We fitted only elastic peakFig. 1 (a) Laue pattern and (b)magnetic
by Gaussian function to extract such a peak. For susceptibility of O-AN SmLa0.75Sr0.25CuO4.

Fig 2. RIXS spectra and image
plots of (a), (c) AS and (b), (d) O(e)AN
SmLa0.75Sr0.25CuO4.
Doping dependence of the ratio
value from the integral intensity ofhole and upper Hubbard band
peaks, the LSCO results plotted in
the black line as a reference.

both O-AN and AS samples, the RIXS signal was much weaker than the LSCO in the previous
report with faintly momentum-dependent charge excitations. O-AN sample contained an
additional peak near the elastic peak independent of q, and the intensity of the elastic peak in
the O-AN sample changed non-successive with the momentum. In contrast, the AS sample
showed relatively higher intensity than the O-AN sample. Furthermore, by comparing theimage plot results of AS and O-AN samples, the spectra weight of RIXS in AS sample is moreconcentrated.
In Fig. 2 (e), we plotted the ratio value of the integrated intensity of peaks corresponding to
the hole-induced state and a hybridized state of the Cu upper Hubbard band with the O 2p states.
Comparing them with the standard value of La2-xSrxCuO4 (LSCO) from the published report,
it’s clearly shown that the actual doping amount of strontium in both AS and O-AN samples ismuch lower than the chemometric value [6]. Meanwhile, the RIXS spectrum of La2-x(Sr,Ba)xCuO4 in a lightly doped region showed a momentum-independent behavior with a relativity
weaker signal than the higher doping region, which would be one of the explanations for our
results. However, from the theoretical part, the effect of apical oxygen is strongly correlatedwith the hopping parameter t, which may play an important role but is not taken into account.
For the next step, the doping dependence of RIXS for the T* phase cuprates is important [7].
REFERENCES[1] K. Ishii, et al. Phys. Rev. B 96, 115148 (2017).
[2] C. Jia, et al. Phys. Rev. X 6, 021020 (2016).
[3] K. Tsutsui and T. Tohyama, Phys. Rev. B 94, 085144 (2016).
[4] W. S. Lee, et al. Nature Phys. 10, 883 (2014).
[5] A. Greco, et al. Phys. Rev. B 94, 075139 (2016).
[6] C. T Chen, et al. Phys. Rev. Letter 66, 104 (1991).
[7] Y. Ohta, et al. Phys. Rev. B 43, 2968 (1991).

Co L3-edge Soft X-ray Emission spectroscopy of La0.6Sr0.4CoO3- for solidoxide fuel cells
Daisuke Asakura1,2, Eiji Hosono2,3, Tomohiro Ishiyama1, Riyan Achmad Budiman1, Haruo
Kishimoto3, Kosuke Yamazoe4, Naoya Kurahashi4, Ralph J. Ugalino4, Hisao Kiuchi4, andYoshihisa Harada2,4
1

Research Institute for Energy Conservation, National Institute of Advanced Industrial Science andTechnology (AIST)2

AIST-UTokyo Advanced Operando-Measurement Technology Open Innovation Laboratory, AIST
3

Global Zero Emission Research Center, AIST

4

Synchrotron Radiation Laboratory, The Institute for Solid State Physics, The University of Tokyo

Solid oxide energy devices including oxide-based all-solid-state Li-ion battery (LIB) arecharacteristic of the stability compared to energy devices with liquid systems. For example,
solid oxide fuel cell (SOFC) is a well-known solid oxide energy device. SOFC is a fuel cellworking at a high temperature (around 800 ℃) with oxygen ion conduction. Oxygen in the air
is supplied to the cathode (air electrode) and converted to O2- ion with electrons from thecircuit. The O2- ions are transferred through a solid-state electrolyte and reach at the anode(fuel electrode). In the anode, the O2- ions react with H2 and are converted to H2O withgenerating electrons, resulting in electricity generation. This is the operating principle ofSOFC.
For the cathode of SOFC, 3d transition-metal oxides with the Perovskite structure arewidely used. La1-xSrxCoO3- (LSC) is one of the prototypical cathode materials for SOFC
while LSC has also been studied in the research field of strongly correlated electron systems.
To further enhance the performance of LSC as the SOFC cathode, the electronic structure
analysis for the Co 3d and O 2p orbitals is particularly important to understand the redox
reaction and O2- ion conduction mechanisms. Here, we employ the Co L-edge X-ray
absorption spectroscopy (XAS) and X-ray emission spectroscopy (XES) for LSC utilizing
experiences for LiCoO2 which is a Co-oxide cathode material for LIB.
We conducted the Co L3,2-edge XAS and L3-edge XES measurements for a bulk LSC(La0.6Sr0.4CoO3-, made in AIST)
by using HORNET spectrometer at
BL07LSU, SPring-8. For XAS,
total-electron-yield (TEY) andpartial-fluorescence-yield (PFY)
detection modes were employed.
The energy resolution for the XES
measurement was set to 240 meV
at 780 eV.
Figure 1 shows the Co L3,2-edge
TEY and PFY XAS spectra for the
LSC. According to previous
studies for LaCoO3 and LiCoO2,1,2
the XAS line shape for the TEY
spectrum is assigned to be mainly
Co3+ state while the peaks for Fig. 1. Surface-sensitive TEY and bulk-sensitive
777-779 eV suggests a small PFY Co L3,2-edge XAS spectra for La0.6Sr0.4CoO3-.

amount of Co2+ should
coexist. For the PFY
spectrum, the highest pointof Co L3 edge shifted by +1
eV and the structure around783 eV was enhanced,
indicating that the oxidation
state of the bulk region ishigher than that near thesurface.2 Most likely, the Srcontent and/or oxygen defectcontributing to hole dopingon the Co cite should be
suppressed near the surface.
We selected three points
characteristic of the Co
L3-edge PFY spectrum (thedotted lines in Fig. 1) as theexcitation energies for XES.
The XES results are shownin Fig. 2. For the 780.9-eV Fig. 2. Co L3-edge XES spectra for La0.6Sr0.4CoO3-. The
excitation,thebroad allows indicate the elastic scattering peaks.
structure around 775 eVshould be of charge-transfer excitation. The structures from 776 to 780 eV should be of dd
excitation, while the strong peak at 778 eV is ascribed to the fluorescence peak because thepeak position is independent of the excitation energy. On the other hand, for a previous studyof LaCoO3 thin film, the peak position of fluorescence is lower in emission energy scale.1
This difference between the LaCoO3 thin film and LSC should correspond to that theoxidation state of Co is higher observed from the PFY XAS result. Similar energy shift of thefluorescence depending on the oxidation state has been also reported for the Co L3-edge XES
for LiNi0.65Co0.25Mn0.1O2 (a cathode material for LIB).3 Thus, the XES spectra for LSC
should include the component of Co4+ state in addition to that of the Co3+ state. The XAS andXES spectra will be analyzed with multiplet calculation. The relation between the electronic
structure and the performance as a cathode for SOFC will be further investigated. Also, wewill try the operando measurement with developing an all-solid-state-type operando cell for
SOFC.

REFERENCES[1] Y. Yokoyama et al., Phys. Rev. Lett. 120, 206402 (2018).
[2] For example, W.-S. Yoon et al., J. Phys. Chem. B 106, 2526 (2002) and T. Mizokawa et al., Phys.
Rev. Lett. 111, 056404 (2013).
[3] H. M. Hollmark et al., J. Electrochem. Soc. 157, A962 (2010).

POSSIBLE ANAPOLE ORDER IN THE ANTIFERROMAGNETIC
PHASE OF MULTIFERROIC CUO
1Ryusuke MISAWA1, Keito ARAKAWA1, Hiroki UEDA2, Jun MIYAWAKI3, Hisao
KIUCHI4, Yoshihisa HARADA4, Yoshikazu TANAKA5, and Tsuyoshi KIMURA1

Dept. of Adv. Mater. Sci., The University of Tokyo, 2Paul Scherrer Institut, 3National Institutes for
Quantum and Radiological Science and Technology, 4Synchrotron Radiation Laboratory, The Institutefor Solid State Physics, The University of Tokyo,5RIKEN SPring-8 Center

The orbital current is characterized by a time-odd polar
vector that corresponds to an anapole or toroidal moment [1]. It is
proposed as the order parameter in the pseudo-gap phase of high-Tc
cuprate superconductors and in the hidden ordered phase in some 5dtransition-metal systems such as Sr2(Ir,Rh)O4. Anapoles are formedby orbital currents between metal ions and ligands and between
ligands as shown in Fig. 1. Symmetry breakings due to the orbital
currents have been examined so far by several experimental
techniques such as magneto-optical effects [2] and second harmonic
generation [3]. Though some of the experimental results suggest
the formation of anapole order, others do not support it [4]. In this Fig.1. Schematic drawing
anapolemomentstudy, we examined the presence of anapole order in oforbitalcurrents.
inducedbyantiferromagnetic CuO by using resonant x-ray diffraction (RXD)
and resonant inelastic x-ray scattering (RIXS).
CuO (space group: C2/c) exhibits successive magnetic transitions at TN1 =213 K andTN2 =230 K. At TN1 < T < TN2, it shows an incommensurate (ICM) spiral magnetic order withthe wavevector of qICM = (0.507, 0, -0.486). The spiral magnetic order induces spin-driven
ferroelectricity [5]. The ferroelectricity disappears below TN1 where the magnetic structuretransforms into a commensurate (CM) colinear antiferromagnetic one with the wavevector of
qCM = (0.5, 0, -0.5). Based on experimental results of circularly polarized resonant x-ray
diffraction on CuO, the existence of anapole order induced by the orbital currents between
copper and oxygen ions has been proposed in ref. [6]. However, some theoretical studies
refute the interpretation [7], and no definitive conclusion has been reached on the proposed
anapole-ordered state in CuO. The purpose of this study is to examine the anapole order andits domain state through scanning RXD and RIXS using circularly polarized x-rays.
We measured circularly polarized RXD and RIXS on a plate-shaped single crystal of
CuO with the widest face parallel to the (10-1) plane. These measurements were carried out at
BL07LSU, SPring-8. The incident x-ray energy was set near the
Cu L3 absorption edge. The incident x-ray beam was focused into
~34 μm (~5 μm) in the horizontal (vertical) direction at the
sample surface position. RXD and RIXS at qICM were measured
in the ICM phase while those at qCM were obtained in the CMphase. The scattering geometry is illustrated in Fig. 2. The
circular polarization dependence of these reflections and their
spatial distributions were examined. We also examined the effectFig. 2. Schematic drawingof electric fields on them. To apply the electric field, a pair of of scattering geometry.
gold electrodes were deposited on the crystal surface (Fig. 2).
The magnetic reflections in the two phases showed resonant enhancement at theenergies around the Cu L3 absorption edge (≈ 930 eV). In addition, they showed substantial
circular polarization dependence. The circular polarization dependence in the ICM phase is
explained by the spiral magnetic structure in the ICM phase while no confirmed mechanism

of that in the CM phase has not been provided yet. However, the electric field effect on thecircular polarization dependence gives some clues for the understanding. Figure 3 shows the
sample position dependence of the magnetic reflections in the ICM and the CM phases. For
these measurements, the x-ray beam was scanned along the Z direction on the sample surface,and a positive or negative electric field was applied during the cooling of the sample andmeasurements. Figures 3(a) and 3(b) were obtained using the magnetic reflection with qICM at
220 K (ICM phase) while Figs. 3(c) and 3(d) were taken using that with qCM at 200 K (CMphase). All the data shown in Fig. 3 were taken using incident x-rays with an energy of 929.7
eV. In all the measurements, a nearly uniform circular polarization difference over the sample
area was observed. However, the sign of the circular polarization difference is reversed by asign reversal of the electric field in both the phases. In addition, the sign of the circularpolarization difference of the CM phase is the same as that of the ICM phase. At the present
stage, we do not have a clear explanation for the origin of the circular polarization
dependence in the CM phase. Clear supporting evidence of anapole order in the CM phase
was not obtained. However, the similarity of the electric field effect observed in the ICM andthe CM phases suggests that the order parameters of these two phases are correlated.

Fig. 3. Sample position dependence of magnetic reflection intensity measured using circularly polarized x-rays.
(a,b) One dimensional scans of magnetic reflection at qICM = (0.507, 0, -0.486) in the ICM phase. (c,d) Those at
qCM = (0.5, 0, -0.5) in the CM phase. The scanning direction is along the Z direction. Measurements were carriedout using right-circularly polarized (RCP) and left-circularly polarized (LCP) x-rays with energy corresponding
to the Cu L3 edge. The data of (a,c) were obtained in a positive electric field while those of (b,d) were taken in anegative electric field.

REFERENCES[1] C. M. Varma, Phys. Rev. B 55, 14554 (1997).
[2] Jing Xia, Elizabeth Schemm, G. Deutscher, S. A. Kivelson, D. A. Bonn, W. N. Hardy, R. Liang, W. Siemons,
G. Koster, M. M. Fejer, and A. Kapitulnik, Phys. Rev. Lett. 100, 127002 (2008).
[3] L. Zhao, D. H. Torchinsky, H. Chu, V. Ivanov, R. Lifshitz, R. Flint, T. Qi, G. Cao & D. Hsieh, Nat. Phys.
12, 32 (2016).
[4] T. P. Croft, E. Blackburn, J. Kulda, Ruixing Liang, D. A. Bonn, W. N. Hardy, and S. M. Hayden, Phys. Rev.
B 96, 214504 (2017).
[5] T. Kimura, Y. Sekio, H. Nakamura, T. Siegrist, and A. P. Ramirez, Nat. Mater. 7, 291-294 (2008).
[6] V. Scagnoli, U. Staub, Y. Bodenthin, R. A. de Souza, M. GarcíaFernández, M. Garganourakis, A.
T. Boothroyd, D. Prabhakaran, and S. W. Lovesey, Science 332, 696 (2011).
[7] Y. Joly, S. P. Collins, S. Grenier, H. C. N. Tolentino, and M. De Santis, Phys. Rev. B 86,
220101(R) (2012).

ELECTRONIC STRUCTURE ANALYSIS OF OXYFLUORIDECATHODE OF ALL-SOLID-STATE FLUORIDE BATTERY USINGRESONANT INELASTIC X-RAY SCATTERING
Kentaro YAMAMOTO1, Datong ZHANG1, Hisao KIUCHI2, Jun MIYAWAKI2,
Tomoki UCHIYAMA1, Toshiki WATANABE1, Tsuyoshi TAKAMI1,
Toshiyuki MATSUNAGA1, Yoshihisa HARADA2, Yoshiharu UCHIMOTO1
1

2

Graduate School of Human and Environmental Studies, Kyoto University

Synchrotron Radiation Laboratory, The Institute for Solid State Physics, The University of Tokyo

All-solid-state fluoride-ion battery is expected to be next-generation battery due to highelectrochemical stability of F anion as charge carriers, as well as excellent theoretical energy
densities which largely exceed those of conventional lithium-ion battery. Intercalation-type
host materials, such as perovskite-, Ruddlesden−Popper-1, etc., are particularly attractive
owing to their high structural reversibility and F intercalation tolerance, compared withwidely used conversion-type metal/metal fluoride systems (M/MFx)2. It is important for
topotactic materials to have anionic vacancies surrounding cationic coordination centers as F−intercalation sites; therefore, those with low-coordination environment of cations can bepromising host materials for F (de)intercalations. In this study, we introduced Ca0.85CuO2 as
high-energy cathode material for all-solid-state fluoride-ion battery with an
infinite-layer-related modulated chain structure. Slightly distorted square planar [CuO4]
provide sufficient rooms for F− intercalation. Considering the large contributions to charge
compensation from redox of oxygen in Ca0.85CuO2, the electronic structure of O wasinvestigated by resonant inelastic X-ray scattering (RIXS) techniques.
Ca0.85CuO2 was synthesized via solid-state reactions. CaCO3 and CuO were ground,pelletized and calcined at 800 °C for 20 hours with immediate regrinding afterward. The
calcining and regrinding were repeated several times until single phase was acquired.
Electrochemical properties were studied using bulk-type cells, with La0.9Ba0.1F2.9 (LBF),
Ca0.85CuO2/LBF/ vapor grown carbon fiber (VGCF) composite, and Pb/PbF2/LBF/VGCF
composite as solid electrolyte, cathode and anode, respectively. Ex situ Cu K-edge, Cu
L2,3-edge and O K-edge XAS data were acquired in the partial fluorescence yield (PFY)mode at BL14B2 and BL27SU in SPring-8. Resonant inelastic X-ray scattering (RIXS)
measurements were performed at BL07LSU in SPring-8 using a grazing flat-field type highresolution soft X-ray emission spectrometer. The measurements were conducted undervacuum and the samples were transferred from an Ar-filled glove box without exposure to air.
The Ca0.85CuO2 cathode showed high capacity of 890 and 630 mAh g-1 in initial charging
and discharging in the cut-off range of -1.5 to 3.0 V, respectively, corresponding to approx.
4.3 and 3.1 F− intercalation/deintercalation (Figure 1). A large irreversible capacity in initialdischarging might be related to the loss of oxygen or irreversibility of oxygen redox. After
controlling the oxidation state of oxygen by cut the initial capacity to that of 3.0 F
intercalation, the initial coulombic efficiency was greatly enhanced. According to XAS results,
in initial charging process, oxygen redox is the major contributor to charge compensation. In
initial discharging, both Cu and O were reduced; the uncomplete reduction of O species was
highly possible to be the origin of low coulombic efficiency of initial cycle. In RIXS resultsof charged Ca0.85CuO2F3.0 sample, the peaks at the emission energy of 523.5 eV with anincident photon energy of 530.9 eV revealed the generation of O-O bond. This was also
supported by the vibrations at 529 to 531 eV (energy loss of -2.0 to 0 eV), as well as thecorresponding frequency of the first vibrational level (0.2 eV, approx. 1600 cm-1)3. In addition,
it is also highly possible that Cu2+ in pristine-state Ca0.85CuO2 could be further oxidized tohigher valency upon charging since the number of intercalated F anions exceeds the capabilityof oxygen redox, which requires more decisive evidence.
(a)

(b)

Fig. 1 (a) Charge-discharge profile of Ca0.85CuO2 cathode material with various cut-off conditions. (b) O
K-edge XAS (inset) and corresponding RIXS results of charged Ca0.85CuO2F3.0 sample.

REFERENCES[1] M. A. Nowroozi, K. Wissel, J. Rohrer, A. R. Munnangi, and O. Clemens, Chem. Mater. 2017, 29,
3441–3453.
[2] M. Anji Reddy and M. Fichtner, J. Mater. Chem. 2011, 21, 17059–17062.
[3] R. A. House, U. Maitra, M. A. Pérez-Osorio, J. G. Lozano, L. Jin, J. W. Somerville, L. C. Duda, A.
Nag, A. Walters, K.-J. Zhou, M. R. Roberts, and P. G. Bruce, Nature 2020, 577, 502–508.

OPERANDO AMBIENT PRESSURE PHOTOELECTRON
SPECTROSCOPY OF CHEMICAL REACTION ON THE
FUNCTIONALIZED BASAL AND EDGE SURFACES OF MoS₂
F. OZAKI, Y. CHOI, H. Li, Y. SAWAGUCHI, S. TANAKA, K. MUKAI, M. HORIO,
I. MATSUDA and J. YOSHINOBUThe Institute for Solid State Physics, The University of Tokyo

Introduction
Molybdenum disulfide (MoS₂) is a layered
substance that exists as a natural mineral (Fig. 1),
and recently it is expected to be used for various
applications such as field-effect transistors andphotoelectric devices due to its unique physicalproperties [1]. In addition, it has been used as acatalyst for a long time. For example, Co-MoS₂ hasbeen used industrially as a hydrodesulfurization
catalyst to remove sulfur from oil [2]. Thus, theMoS₂ surface is a various catalytic reaction field
involving hydrogen, and it is important tounderstand the interactions between the hydrogenmolecules and MoS₂ surface.
It is known that the exfoliated MoS₂ (0001) basal
surface is inert to the dissociation of molecular
Figure 1 Structural model of MoS2hydrogen, and the active site as a catalyst is mainly
the edge of MoS₂. Tanaka and Okuhara havereported that the edge site plays a vital role, by comparing the catalytic activity of an un-cut
MoS2 with that of a MoS₂ cut by a pair of scissors to increase the edge area [3]. So far, the edge
sites have only been studied by microscopic observation using scanning tunnelling microscopy
and theoretical first-principles calculations due to their small scale and the difficulty of
preparing a defined surface [4,5]. Therefore, it is a challenging issue to observe the chemicaland electronic states of edge sites. In particular, the mechanisms of these reactions at the edge
surfaces have not been elucidated yet. Therefore, we have conducted experimental observationof the chemical and electronic states of the edge surface using an ambient pressure
photoelectron spectroscopy (AP-XPS).
Experimental
In this study, we prepared the edge surfaces of MoS2 which were sharply cut perpendicular
to the MoS₂ basal plane by ultrashort laser pulse processing at Kobayashi Laboratory in LASOR
of The Institute for Solid States Physics (ISSP). In the case of mechanical cutting, possible
metal contaminations from a scissors and edge-sagging by scission are inevitable. Laser
processing does not cause edge-sagging and produces a fine edge surface (Figure 2). The spot
size of SPring-8 BL07LSU is about 50 × 10 μm², and thus the edge can be selectively
illuminated by synchrotron radiation. The incident photon energy was 655 eV and allmeasurements were carried out at room temperature. The MoS₂ single crystals were heated inultra-high vacuum (UHV) to remove impurities, and the clean edge surfaces were observed by

XPS
atSPring-8
BL07LSU.
AP-XPS
measurements were performed in hydrogen gas inorder to investigate the reactivity of the edge
surface with hydrogen molecules.
Results and discussion
The edge surface of MoS2 was observed by XPS
in UHV in order to investigate the changes causedby heating treatment. Figure 3 shows a series of Mo
3d XPS spectra in UHV. The Mo 3d spectrum of an“As installed” sample (Figure 3: blue) shows small Figure 2 A secondary electron microscopy
oxidized components at ~230.9 and ~234.0 eV on image of the MoS2 edge prepared by
the high binding energy side of the main Mo 3d5/2 ultrashort laser pulse processing
and 3d3/2 peaks, respectively. After annealing at 700
K for 30 min, the oxidized components decreased inintensity. After further annealing at 700-800 K for
220 min, a shoulder appeared at ~228.3 eV. Thisshoulder component may be assigned to Mo2+
indicating a less coordinated state (missing S) thanMo4+ in the bulk MoS2.
The annealed sample was then transferred andinstalled at an AP-cell to investigate the reaction
between the unsaturated Mo sites and hydrogen gas.
The shoulder peak of Mo 3d XPS that appeared after
the heat treatment decreased with the introductionof hydrogen (not shown here). This may be due tothe dissociative adsorption of hydrogen at the lesscoordinated Mo sites at the edge. The details of the
Figure 3 A series of Mo 3d XPS spectrapresent study will be reported elsewhere.
of the MoS2 edge surface in UHV.
In this study, we have succeeded in directly
measuring the electronic state of the coordinatively
unsaturated Mo sites on the edge surface which was prepared by ultrashort pulse laser
processing. AP-XPS results have shown that these sites are involved in the adsorption.
ACKNOWLEDGMENTS
We thank Dr. S. Tani (Kobayashi laboratory in LASOR, ISSP) for preparing the edge surfaceof MoS2 by ultrashort pulse laser processing. The AP-XPS measurements using synchrotron
radiation were performed at SPring-8 BL07LSU as joint research between the Synchrotron
Radiation Research Organization and The Institute for Solid State Physics, The University ofTokyo (Proposal No. 2021B7432).
REFERENCES[1] M. Chhowalla et al., Nat. Chem. 5, 263-275 (2013).
[2] Y. Okamoto, Catal. Today 132, 9 (2008).
[3] K.-I. Tanaka, T. Okuhara, J. Catal. 78, 155-164 (1982).
[4] F. Besenbacher, J.V. Lauritsen, J. Catal. 403, 4-15 (2021).
[5] M. Sun et al., J. Catal. 233, 411-421 (2005).

ELECTRONIC STATE ANALYSIS OF EARTH-ABUNDANT FE–AL–SI
THERMOELECTRIC (FAST) MATERIALS USING SCANNING
PHOTOELECTRON MICROSCOPY
Yoshiki TAKAGIWA1, Shunsuke TSUDA1, Naoka NAGAMURA1,2, Asako YOSHINARI1,3,
Shingo TAKEZAWA1,3, Kenta OISHI1,2,3, Kentaro FUKU4, Wenxiong ZHANG5
12

National Institute for Materials Science (NIMS), Tsukuba, Ibaraki, Japan.
PRESTO, Japan Science and Technology Agency, Honcho, Saitama, Japan.
3
Tokyo University of Science, Katsushika, Tokyo, Japan
4
Tohoku University, Sendai, Miyagi, Japan
5
The University of Tokyo, Kashiwa, Chiba, JapanTo develop new thermoelectric materials that are non-toxic and low-cost with sufficient
power output for autonomous power supplies to drive sensor devices, in particular, at a lowtemperature region below 400 K, we performed materials screening of ternary Fe-Al-Si systemusing first-principles band structure calculations [1,2]. We found that the ternary τ1-Fe3Al2Si3
phase forms a narrow bandgap of ~0.2 eV near the Fermi level and has shown potential as anovel thermoelectric material (FAST materials: Fe-Al-Si Thermoelectric Materials). We havedemonstrated that the Al/Si ratio fine-tuning could control its conduction type and enhance thepower factor without chemical substitutions [2]. Relatively large power factors were obtained
for both p- and n-type thermoelectric materials below 400 K, which possessed high oxidation
resistance and excellent mechanical properties [3]. Recently, we enhanced the power factor at
mid-temperatures using machine-learning-assisted synthesis and evaluation [4]. We haveestablished a mass production process for FAST materials and succeeded in the bonding
technology to build a small-sized and highly integrated thermoelectric power generation
module: the operation of temperature/humidity sensors and wireless transmission was
performed [5]. Furthermore, we have succeeded in a synthesis of composition graded samples
to find an optimized composition using a bulk combinatorial method with diffusion couple andmapping measurements [6]. Both theoretical [7,8] and experimental works [6,9] are essential
to enhancing the thermoelectric properties. The remaining issue is to investigate the electronic
structure experimentally and obtain the additional route for better thermoelectric performance.

Fig. 1 Research and development of FAST materials using experiments, theoretical calculation, machine learning,and module development.

In this experiment, based on the
FAST material of τ1-Fe3Al2Si3, (1)bulk samples of n-type and p-typesemiconducting FAST materials withhigh thermoelectric properties and (2)composition gradient samples wereprepared. The core level spectra (FeFig. 2 Photos of sample holders.
2p, Al 2p, Si 2p, C 1s, O 1s) andvalence spectra were measured in eachsample. At first, a sample wasprepared, as shown in Fig. 2(a). Since
severe surface oxidation and carrier
charging were observed, the bulk
sample was fixed with silver paste,
and gold was deposited, as shown in
Fig. 2(b). And then made it break in a
Fig. 3 (a) Si 2p core level spectra (b) valence spectrum.
vacuum.
The beamline used BL07LSU,
which has high energy resolution in the soft X-ray region, and the device used a multidimensional operando photoelectron spectroscopy named "operando 3D nano-ESCA", which
has a high spatial resolution (~ 70 nm). For the single composition bulk samples of FAST
material, the spectrum derived from the oxide is significantly reduced in the spectrum measured
by the sample holder of Fig. 1(b), as compared with the spectrum measured by the sample
holder of Fig. 1(a). It was found that a spectrum derived from a bulk sample excluding theinfluence of surface oxidation was successfully obtained, as shown in Fig. 3(a). For thecomposition graded sample, the core level spectrum derived from the dopant could not be
obtained with sufficient intensity; therefore, the sample preparation and measurement sample
were considered major issues for the next beam time.
The valence spectrum is also measured, and the valence band maximum in each sample is
specified from the rising edge, as shown in Fig. 3(b). Based on the results obtained this time,
we will acquire data to quantitatively evaluate the difference in thermoelectriccharacteristics/transport characteristics and the core level spectrum/valence spectrum of FAST
material samples at the next beam time.
REFERENCES[1] Y. Takagiwa, Y. Isoda, M. Goto, and Y. Shinohara, J. Therm. Anal. Calorim. 131, 281(2018).
[2] Y. Takagiwa, Y. Isoda, M. Goto, and Y. Shinohara, J. Phys. Chem. Solids 118, 95 (2018).
[3] Y. Takagiwa and Y. Shinohara, Scripta Mater. 172, 98 (2019).
[4] Z. Hou, Y. Takagiwa, Y. Shinohara, Y. Xu, and K. Tsuda, ACS Appl. Mater. Interfaces 11,11545 (2019).
[5] Y. Takagiwa, T. Ikeda, and H. Kojima, ACS Appl. Mater. Interfaces 12, 48804 (2020).
[6] Y. Takagiwa, Z. Hou, K. Tsuda, T. Ikeda, and H. Kojima, ACS Appl. Mater. Interfaces 13,53346 (2021).
[7] Z. Hou, Y. Takagiwa, Y. Shinohara, Y. Xu, and K. Tsuda, J. Phys.: Condens. Matter 33,
195501 (2021).
[8] N. Sato and Y. Takagiwa, crystals 11, 388 (2021).
[9] A. K. Srinithi, H. Sepehri-Amin, Y. Takagiwa, and K. Hono, J. Alloys Compds. 903, 163835(2022).

ANALYSIS OF WATER STRUCTURE OF THERMORESPONSIVEPOLYMER MODIFIED INTERFACE
Kenichi NAGASE1, Naoya KURAHASHI2, Hisao KIUCHI2, Yoshihisa HARADA2
1

Faculty of Pharmacy, Keio University
Synchrotron Radiation Laboratory, The Institute for Solid State Physics, The University of Tokyo

2

Introduction
Thermoresponsive
polymer,poly(N-isopropylacrylamide)(PNIPAAm),
exhibits
temperature-responsive hydration and dehydration across lower critical solution temperature(LCST) of 32°C [1]. Using the property, PNIPAAm have been utilized various types ofbiomedical applications, such as drug delivery systems, bioseparation materials, and cell
culture substrates [2,3]. However, the detailed investigation of the hydration property of
PNIPAAm on substrate were not investigated, although the PNIPAAm hydration/dehydration
in solution state was already clarified. In this study, we investigate the water structure in themodified PNIPAAm on substrate using high-resolution soft X-ray emission spectroscopy(XES).
Experimentsa) Sample preparation
PNIPAAm was synthesized by activator regenerated by electron transfer atom transfer
radical polymerization (ARGET-ATRP) [4]. NIPAAm was dissolved in 2-propanol and water
mixed solvent. Then, ATRP catalyst, CuCl2, tris[2-(dimethylamino)ethyl]amine, andL-ascorbic acid, were added in the solution. ARGET-ATRP of NIPAAm was performed at
25°C for 16 h. After the polymerization, the prepared PNIPAAm was purified by dialysis andfreeze drying. The prepared PNIPAAm was dissolved into methanol, and the PNIPAAm
solution was casted to Au-coated SiC membrane. The methanol in casted solution was
evaporated in a drying oven.
b) Soft X-ray emission spectroscopy (XES) measurement
Soft XES measurement of PNIPAAm cast film was performed by using ultra-highresolution soft X-ray emission spectrometer HORNET [5] installed at the SPring-8 BL07LSU.
Water vapor was supplied by steam-generation equipment, and nitrogen was used as thecarrier gas. Ultrapure water was used as the water source. Moisture was passed over the
PNIPAAm casted film and then drained from the outlet port. Relative humidity was ranged
from 0%-100%. Temperature was set at 20°C and 40°C.
Results
The water content of the PNIPAAm modified cast film was estimated at various relative
humidity (Figure 1). Water content λ (water molecule/oxygen atom) increased with increasing
the relative humidity, because the adsorbed water on PNIPAAm increased with relative
humidity. Higher water content of the PNIPAAm was observed at 20°C compared to that of
40°C, because of the temperature-dependent hydration of PNIPAAm. The XES spectra at
20°C and 40°C were observed (Figure 2). Higher peak intensity was observed at 20°C
compared to that at 40°C. The result indicates that the adsorption of water molecules tocarbonyl group of PNIPAAm is enhanced at 20°C compared to that at 40°C, which is
attributed to the temperature-dependent hydration of casted PNIPAAm on the substrate.
The XES measurement can observe the temperature-dependent adsorption of watermolecules onto the carbonyl group of the modified PNIPAAm on the substrate. The obtained
results can be utilized for the design of the PNIPAAm modified substrate.

(a)

(b)

Fig.1 Water content (water molecule/oxygen atom) in PNIPAAm cast film at various relative
humidity (a) at 20°C and (b) at 40°C.

Fig.2 XES spectra of PNIPAAm cast film at 20°C and 40°C.

REFERENCES[1] Heskins, M., Guillet, J. E., J. Macromol. Sci. A 2: 1441-1455, (1968)[2] Nagase, K., Yamato, M., Kanazawa, H., Okano, T., Biomaterials 153: 27-48, (2018)[3] Nagase, K., Advances in Colloid and Interface Science 295: 102487, (2021)[4] Nagase, K., Shimura, M., Shimane, R., Hanaya, K., Yamada, S., Akimoto, A. M., Sugai, T.,
Kanazawa, H., Biomaterials Science 9(3): 663-674, (2021)[5] Yamazoe, K., Higaki, Y., Inutsuka, Y., Miyawaki, J., Cui, Y.-T., Takahara, A., Harada, Y.,
Langmuir 33(16): 3954-3959, (2017)

RESONANT INELASTIC X-RAY SCATTERING SPECTROSCOPYOF CU-PROTEINS
Kentaro FUJII1,2, Jun MIYAWAKI2, Naoya KURAHASHI3, Hisao, KIUCHI3,
Yoshihisa HARADA3, Motoyasu ADACHI1, Akinari YOKOYA1
1

Institute for Quantum Life Science, National Institutes for Quantum Science and Technology
2

Advanced Synchrotron Radiation Centre, National Institutes for Quantum Science andTechnology

3

Synchrotron Radiation Laboratory, The Institute for Solid State Physics, The University ofTokyo

Amicyanine and Azurin are classified as Class I TICu protein amicyanine, whose axial
ligand is the sulfur atom of methionine. Both protein molecules share the asymmetricstructure of four amino acids, Met, Cys, and two His, as the ligand for the copper atom
(Fig. 1). Azurin contains an additional second axial ligand in addition to methionine in
one axial position, as seen in the difference in distance to the oxygen atom.
Crystallographic analysis has revealed that this asymmetry differs by a few percent
between azurin and amicyanine1. Their redox potentials differ by about 30 mV at pH 8.0.
In addition, both amino acid mutations have been introduced by genetic recombination
technology, and significant redox potential changes of 500 mV or more have been
observed when amino acid substitutions are introduced directly or indirectly at the copper
atom. Especially, the changes of nearly 100 mV have been reported even at positions morethan 10 Å from the copper atom. In order to reveal these phenomena, we examined theresonant inelastic soft X-ray scattering (RIXS) measurement of these solutions.
Both proteins were prepared as recombinant proteins expressed in E. coli using BL21
(DE3) and pET24a vector. The samples were purified with Ni-sepharose and ionexchange columns. The ion-exchange columns used were HiTrap Q XL columns foramicyanine and HiTrap SP XL columns for azurin. The final solutions (~ 3mM) were

FIG 1 Molecular picture of (a) amicyanin and (b) azurin. The structures around Cu-atom aresuperimposed. Cu-atom is surrounded by Met, Cys and two His.

obtained by dialyzing in 20 mM Tris-HCl buffer (pH 8.0). The measurement the protein
solutions was performed using a solution cell under ambient pressure by circulating thesample solution. To avoid oxidation of the sample, the circulated solutions were bubbled
with nitrogen gas during the measurement.
Soft X-ray emission spectra around Cu-Ledge and resonant inelastic scattering
emission spectra after Cu-L pre-edge resonance excitation (931eV excitation) were shownin Figure 2 and Figure 3, respectively. These spectra were obtained using a highresolution soft X-ray emission spectrometer HORNET2 installed at the end of theBL07LSU of SPring-8. The apparent peak structures of each spectrum were observed. Inorder to assign these peak structures, we are currently performing density functional
theory simulations using a model molecule that imitates the coordination of amino acidsaround Cu. N.J. Fowler et al., predicted reduction potentials for several Cu proteins
containing mutants using DFT calculation. In the future, we plan to perform RIXS
spectroscopy on mutants with different amino acid residues surrounding Cu or different
pH to obtain information on the correlation between the structure and electronic
properties around Cu. This information regarding copper proteins has useful for generaluse in biotechnology, such as enzyme-catalyzed fuel cells or valorization of
lignocellulosic biomass.

FIG 2 Cu L-edge XAS of (a) amicyanin and(b) azurin with 20mM Tris-HCl buffer

FIG 3 Cu L-edge RIXS spectra of (a)solutions (~3mM).

amicyanin and (b) azurin with 20mM TrisHCl buffer solutions (~3mM).

REFFERENCES[1] N.J. Fowler, C.F. Blanford, J. Warwicker, S.P. de Visser, Chem. Eur. J. 12 (2017)
15436-15445.
[2] Y. Harada et al., Rev. Sci. Instrum. 83 (2012) 013116.

STUDY ON THE HELICAL SPIN TEXTURE OF TOPOLOGICALSURFACE STATE IN SUPERCONDUCTOR 2M-WS2
Soonsang Huh1, Soohyun Cho2, Hua Bai3, Yuqiang Fang2, Fuqiang Huang2, Yuto
Fukushima1, Ayumi Harasawa1, Yunhao Lu3,, Gang Mu2 and Dawei Shen2,4 and Takeshi
Kondo1,5
1. Institute for Solid State Physics, University of Tokyo, Kashiwa 277-8581, Japan
2. Center for Excellence in Superconducting Electronics, State Key Laboratory of Functional
Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, Chinese
Academy of Sciences, Shanghai 200050, China
3. Zhejiang Province Key Laboratory of Quantum Technology and Device, Department of Physics,
Zhejiang University, Hangzhou 310027, China
4. Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of
Sciences, Beijing 100049, China
5. Trans-scale Quantum Science Institute, University of Tokyo, Tokyo 113-0033, Japan.

Layered transition metal dichalcogenides (TMDs) of MX2 (M = Mo, W; X = S, Se, Te)
have been studied intensively because of a great interest in both fundamental and appliedresearch. Among the stable phases of TMDs, Monolayer 1T′-MX2 (M = Mo, W; X = S, Se,Te) were suggested as a promising candidate to realize quantum spin Hall (QSH) effect instrictly two-dimensional systems [1-4]. QSH insulators are expected to have two conductingedge channels with quantized electric conductance 2e2/h and opposite spin polarizations,which are robustly protected by the time-reversal symmetry. It could provide a possible
alternative to quantum electronic devices with low dissipation. However, because of thelimitation of monolayer, the TSS of QSH insulators in TMDs have been not addressed by theexperimental tools.
Recently, new stable structure phase 2M-MX2 have been found with the topological surface
state (TSS) and the superconductivity with the highest transition temperature 8.8 K among
TMDs [5-10]. Because the crystal structure of bulk 2M phase is identical with monolayer
1T′-MX2, 2M-MX2 have a similar band structure and TSS that is similar dispersion with TSS
of monolayer 1T′-MX2. The observation of TSS in 2M-MX2 can provide the information of
topological feature in monolayer 1T′-MX2 as well as own great interesting feature such as apossible candidate for the QSH insulator and the Majorana bound state together with thesuperconductivity [11].
We investigated the electronic and spin structure of the TSS in 2M-WS2 utilizing
high-resolution angle- and spin- resolved photoemission spectroscopy. The low-energy
photoemission spectra taken from the laser-based ARPES with 6.994 eV photons clearly
describe the fine dispersion of the topological surface state with the higher momentum
resolution in Fig. 1(a). The hole-like band dispersion near the ky = 0 is corresponding to thelower part of the Dirac cone of topological surface state, and the crossing point is expected to
be located above the Fermi level. To show the helical spin structure of the topological surface
state, we exploit the spin-resolved ARPES. Figure 1(b) show the spin-resolved EDCs of sy
with red and blue colour code with spin up and spin down, respectively. The result indicatesthat the sign of sy is reversed between kL and kR. Moreover, we obtain that the in-planespin-polarization Py is reversed between kL and kR near the Fermi level, but anotherspin-polarization Px and Pz are negligible. It was expected that the topological surface state of
2M-WS2 show the helical spin
texture, thus allowing the opposite
spin direction between left andright momentum at the Fermi level.
In the view of the Fermi surface as
the schematic picture based on our
experimental results, the lower
Dirac cone branch of the
topological surface state in
2M-WS2 has the helical spin Figure 1(a) ARPES spectra of 2M-WS2 with the TSS obtained
texture with a clockwise rotation as from the band calculation and the possible direction of the spin
momentum based on the experimental results. The red (blue)
shown in Fig. 1(d). Given the arrow indicates the spin up (down). (b) Spin-resolved EDCs of
crystal and electronic structural the TSS at the left and right momentum cuts as marked in (a).
similarity between 2M-WS2 and The spin-resolved EDCs at kL and kR shows spin texture along
the Sy direction. (c) Representative spin-polarization magnitude
monolayer 1T′-MX2, our results for the TSS at kL and kR, whose obtained from the spin-resolved
can provide the general knowledge EDCs in (b). (d) Schematic picture of the helical spin texture
for the TSS at Fermi surface based on the spin-resolved EDC
about the edge conductance and and polarization. in (b) and (c)spin-based device as manufactured
with quantum spin Hall insulator,
monolayer 1T′-MX2.

REFERENCES[1] M. S. Lodge et al., Adv. Mater. 2021, 33, 2008029.
[2] Z. Fei et al., Nat. Phys. 2017, 13 677.
[3] X. Qian et al., Science 2014, 346, 6215.
[4] S. Wu et al., Science 2018, 359, 6371 76.
[5] Y. W. Li et al., Nat. Commu. 2021, 12, 2874.
[6] Y. Fang et al., Adv. Mater. 2019, 31, 1901942.
[7] X. Che et al., npj Quantum Mater. 2019, 4, 50.
[8] L. S. Wang et al., Rev. B 2020, 102, 024523.
[9] Y. Fang et al., J. Mater. Chem. C 2019, 7, 8551.
[10] P. Samarawickrama et al., ACS Omega 2021, 6, 4 2966.
[11] Y. Yuan et al., Nat. Phys. 2019, 15 1046.

ENHANCED RASHBA-SPLITTING OF AU(111) SURFACE STATES BY
THE MELAMINE HONEYCOMB LAYERS
Rena MOUE1, Yuta KOKUBO1, Kozo MUKAI2, Hirotaka MIZUSHIMA1, Yuto
FUKUSHIMA2, Kaishu KAWAGUCHI2, Takeshi KONDO2,3, Ayumi HARASAWA2, Jun
YOSHINOBU2, Shik SHIN2, Kaname KANAI1
1

2
3

Department of Physics, Faculty of Science and Technology,

The Institute for Solid State Physics, The University of Tokyo,

Trans-scale Quantum Science Institute, The University of Tokyo.

In quasi-two-dimensional electron systems with broken spatial inversion symmetry, such as
metal surfaces and semiconductor interfaces, Rashba-type spin-orbit interactions (Rashba
effect) are known to occur through atomic spin-orbit interactions. The Rashba effect has
been actually demonstrated in quantum wells and thin films based on III-V semiconductors,
as well as in two-dimensional electron gases in the metal surface, and is expected to play animportant role as an elemental technology in spintronics.
Many studies have shown that the Rashba coupling can be modified by the adsorption of
atoms and molecules on metal surfaces and by distortions at the semiconductor interface. In
recent years, it has become possible to intentionally control the strength of the Rashba
coupling and design systems for various applications. For example, adsorption of noble gases
or organic molecules on noble metal (111) changes the strength of the Rashba coupling1.
Organic materials such as metal-organic frameworks (MOFs) and covalent organic
frameworks have been extensively studied over the past few decades and are potentiallyattractive for a variety of applications, including gas storage and separation, catalysis,
chemical sensors, and drug delivery2. On the other hand, new porous materials calledhydrogen-bonded organic frameworks (HOFs), which are constructed from pure organic or
metal-containing organic building blocks by hydrogen bonds, have recently attracted muchattention. Although many pioneering studies have been conducted on HOFs, their progresshas lagged behind that of MOFs and others. The main reason for the lag is that the structure ofmany HOFs collapses when solvent molecules are removed from the pores formed by weakhydrogen bonds. On the other hand, the instability of HOFs is caused by weak hydrogenbonds, but on the contrary, they are rather flexible compared to strong covalent orcoordination bonds. The use of this soft hydrogen bond is also beneficial for the flexibility of
the framework of porous materials. Carbon nitride molecules such as melamine(1,3,5-Triazine-2,4,6-triamine) and melem (2,5,8-triamino-heptazine) are typicalsupramolecular species that form HOFs through highly electronegative nitrogen-mediatedhydrogen bonds. The studies in these HOFs are rather well known for cyanuric acid andmelamine complexes, which have been studied for many years, where cyanuric acid andmelamine are combined by N-H···O and N-H···N hydrogen bonds to form rosette-shaped
superstructure3. On the other hand, melamine and melem are known to readily form highlyoriented monolayers consisting of two-dimensional ordered supramolecular structures byadsorption on metal surfaces (surface HOF: SHOF), without the help of solvent molecules.
This is probably due in large part to the flexibility of hydrogen bonding. Surfaces modified bysuch supramolecular structures are becoming powerful tools in applications such as chemicalsensors and nanoelectronics, thanks to their ability to exhibit molecular recognition features.
However, melamine is one of the most basic units in the systems that create such SHOFs, buteven for the structure of the SHOFs of melamine, the determination of their structures
remains arbitrary so far, although there are a few reported studies using STM4. Furthermore,
there are no reported studies that have conducted detailed investigations of the formation
process of melamine SHOFs, their electronic structure, or their interfacial electronic structurewith metal surfaces. Therefore, even now, many problems remain in understanding the basic
physical properties of melamine SHOFs as a prototype of SHOF.

In this study, we determine the formation process and the structure of melamine SHOFs on
Au(111) by X-ray photoemission spectroscopy (XPS), low-energy electron diffraction(LEED) and their effect on the Au(111) surface electronic structure by angle-resolved
photoemission spectroscopy (ARPES) and spin-resolved and angle-resolved photoemission
spectroscopy (SARPES). The SHOF formed when melamine adsorbs on Au(111) is a simple
but most typical system, so clarifying its formation is inevitable for understanding theformation of other SHOFs. From the LEED results shown in Figure 1, melamine, uponadsorption on Au(111), immediately forms a unique hexagonal SHOF through cooperativeintermolecular hydrogen bonds. Many other organic molecules, whose main cohesive force isdispersion force, do not form such cooperative superstructures and usually involve molecular
deformation upon adsorption to a surface, but in the case of melamine SHOFs, molecular
deformation is minimized by multiple hydrogen bonds between the molecules. The SHOF
retains its two-dimensionality, like graphene adsorbed on Au(111). Theoretical calculations
also show that the SHOF induces a slight, but obvious, change in the position of nuclei in theoutermost layer of Au(111) in the surface vertical direction. This indicates that there is strong
orbital mixing between SHOF and Au(111), meaning that SHOF forms a new periodic
potential on the surface. Such a strong coupling between the SHOF and the metal surface
electron system has a significant effect on the electronic structure of the surface electron
system, leading to a reconfiguration of the surface charge density and a modulation of theelectrostatic potential in the outermost layers of the surface. As a result, it is shown tosignificantly enhance Rashba coupling in Shockley state (SS) of Au(111). The conclusions
drawn here indicate that SHOF may provide new guidelines in the manifestation of thespin-galvanic effect, the Edelstein effect, and the inverse Edelstein effect, which are attracting
attention as elemental technologies in spintronics.

Figure 1. a) Experimental and simulated LEED results for melamine/Au(111). The left half ofthe circle shows the LEED pattern observed at primary energy of Ep = 41.9 eV; the right halfof the circle shows the simulated LEED pattern. Red and blue arrows indicate diffraction
spots from two domains a and b with different pseudo-chirality, respectively. b) Schematic
drawing of the adsorption structure of domains a and b of melamine/Au(111).
REFERENCES[1] For example, F. Forster et al., Surf. Sci., 2006, 600, 3870–3874[2] For example, H. Li, M. Eddaoudi et al., Nature, 1999, 402, 276–279[3] For example, S. J. Makowski et al., Chem. Eur. J. 2012, 18, 3248–3257[4] For example, P. A. Staniec et al., J. Phys. Chem. C, 2007, 111, 886-893

ELECTRONIC STATES OF TOPOLOGICAL SEMIMETALSSTUDIED BY SPIN- AND ANGLE-RESOLVED PHOTOEMISSION
SPECTROSCOPY
Y.X. Wan1, K. Kuroda1, C. Bareille1, Y. Ishida1, A. H. Mayo2,3,
H. Takahashi 2, 3, M. S. Bahramy1,4, C. Lin1, Y. Arai1，H. Tanaka1,
Y.Y. Dong1, M. Hashimoto5, D.H. Lu5, T. Muro6, S. Ishiwata2, 3, T. Kondo1
1The Institute for Solid State Physics, The University of Tokyo
2Department of Applied Physics, The University of Tokyo
3Graduate School of Engineering Science, Osaka University
4Center of Spintronics Research Network (CSRN), Osaka University
5Department of Physics and Astronomy, The University of Manchester
6Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory
7Japan Synchrotron Radiation Research Institute (JASRI)

INTRODUCTION
By breaking the time reversal symmetry in Dirac semimetals, one would obtain
topological Weyl semimetals or nodal line semimetals [1]. However, usually only extremely
large external magnetic field can realize such topological phase transition, which is
challenging in the laboratory. A layered phosphide, EuP3, has been reported to archive
topological phase transition when external magnetic field is applied: it would be a magnetic
Weyl semimetal in perpendicular magnetic field, but nodal-line semimetal in in-planemagnetic field [2]. This material has drawn increasing attention for it can be an ideal platform
to study the topological phase transition, as well as its promising
application in engineering.
We have observed of the band structure in α-EuP3 byangle-resolved photoemission spectroscopy (ARPES) with synchrotron
lightsource. We used resonant photoemission to directly confirm the f-p
coupling. Further, with the high-resolution ARPES, we discovered an
unexpected band splitting in the valence band. This band splitting
occurs only along ky direction without any global symmetry breaking.
To compare with the results, we also measured an isostructural material
SrP3, and found similar splitting. This result suggests that the crystal
structure contributes to the band splitting. We need to confirm Fig.1 Band dispersion of EuP3,
whether this kind of band splitting is intrinsic by measure their spin showing an unconventional
splitting.
texture with SARPES.

EXPERIMENTS
During the experiment, all EuP3 and SrP3 samples were cleaved in situ with top posts, and theab plane [(001) surface] was exposed and measured. The ab plane is flat and shiny, suggestingthat the compounds is metallic. It should be noted that there is another cleavage except (001)surface but no band dispersion can be observed from that.
The experiment was carried out with the spin-resolved laser ARPES (SARPES) at ISSP, theUniversity of Tokyo. The light source is 7 eV laser from KBBF crystal.

RESULTSWe measured the in-plane spin texture of EuP3 and SrP3. Although due to the matrix
element effect, we cannot directly observe the two splitting band dispersions, we found thatthe valence bands are spin-polarized. The spin textures of both materials are Dresselhaus-like,suggesting the space reversion symmetry is broken by unknown mechanism. However, weneed further study to confirm whether the splitting is a combination of Dresselhaus andZeeman effects because we have not excluded the out-of-plane spin polarization. μSR candirectly demonstrate direct evidence of the spin fluctuation [3]. We also need theoretical study
to explain why Dresselhaus effect occurs in the centrosymmetric EuP 3 and SrP3 crystals.

Fig. 2 Spin texture of EuP3. The valence band is spin-polarized along both x and y directions, suggesting a
Dresselhaus-like band splitting.

REFERENCES[1] M. Koshino et al., Phys. Rev. B 93, 045201 (2016)[2] A. H. Mayo et al., Phys. Rev. X 12, 011033 (2022)[3] J. Z. Ma et al., Sci. Adv. 5, eaaw4718 (2019).

LASER-SARPES STUDY OF SPIN-POLARIZED ELECTRONICSTATES FOR PB(BI1-XSBX)2TE4
Koichiro YAJI1, Yuya HATTORI2, Shunsuke YOSHIZAWA1, Shunsuke TSUDA1,
Youhei YAMAJI3, Yuto FUKUSHIMA4, Kaishu KAWAGUCHI4, Takeshi KONDO4,
Yuki TOKUMOTO5, Keiichi EDAGAWA5, and Taichi TERASHIMA2
1

Research Center for Advanced Measurement and Characterization, NIMS
2

3International Center for Materials Nanoarchitectonics, NIMS

Center for Green Research on Energy and Environmental Materials, NIMS
4

Institute for Solid State Physics, The University of Tokyo

5

Institute of Industrial Science, The University of Tokyo

The formation mechanism of a topological surface state (TSS) is well established, where thebulk band inversion between the top of the valence band and the bottom of the conduction bandis required. The phase transition from a trivial insulator to a topological insulator is known as a
topological phase transition. The topological phase transition can be controlled by tuning thecomposition, the lattice constant, and the film thickness of the system [1-4]. Understanding themodification in an electronic structure induced by topological phase transitions is essential not
only for fundamental interests but also for applications.
A family of Pb-based ternary compounds, Pb(Bi1-xSbx)2Te4, has been revealed to be
topological insulators [5-8]. In the previous angle-resolved photoemission spectroscopy(ARPES) studies [7,8], the TSSs above a Dirac point (DP) have been clearly observed, where
the TSSs exist in a projected bulk band gap. On the other hand, the dispersive feature is unclear
below DP, which might be due to the existence of the bulk electronic states in the close vicinityof the TSSs. In addition, no spin-resolved ARPES (SARPES) study has been reported so far.
In the present study, we have investigated spin-polarized electronic states of Pb(Bi1xSbx)2Te4 (x = 0.70, 0.79) by SARPES using a laser (laser-SARPES). Our laser-SARPES
reveals Rashba-type occupied surface resonances near the TSSs. Besides, the TSSs
continuously connects to a branch of the Rashba-type surface resonances. Our results provide
direct evidence that the present system undergoes the
topological phase transition.
Laser-ARPES and -SARPES measurements havebeen performed at the Institute for Solid State Physics,
The University of Tokyo [9]. The samples were cleavedwith scotch tape in an ultra-high vacuum chamber
below the base pressure of 2.0 x 10-8 Pa. The
photoelectrons were excited by a quasi-continuouswave laser with a photon energy of 6.994 eV. Theenergy resolutions for laser-ARPES and -SARPES
were set to 5 and 10 meV, respectively. The sample
temperature was kept at 30 K during the measurements.
Figure 1 displays an ARPES intensity map for x =_ _0.70 taken along the GM direction. Overall dispersive
features of the TSS and the bulk conduction bands
agree with the previous studies [7,8]. The precise band
structure near the Dirac point has been demonstrated
thanks to the high-resolution laser-ARPES. The Dirac

Fig. 1 ARPES intensity map for x = 0.70
_ _along GM. A dashed curve represents the
projected bulk band edge determined by aleading edge of the corresponding
photoelectron intensity.

point (DP) is observed at the binding energy of
190 meV. The photoelectron intensity from the
TSS in the bulk band gap is prominent. The TSS
penetrates into the projected bulk bands at k =±0.05 Å-1, indicating that the surface stateschange to surface resonances. The surface
resonances disperse in the binding energy rangeof 0.2-0.5 eV. One can notice here that the
spectrum widths of the surface resonances arebroadened compared with those of the TSSs. We
also find several bands below EB ~ 0.7 eV.
Laser-SARPES measurements have been
performed for x = 0.70 and x = 0.79 samples_ _[Fig. 2(a,b)] in the GM direction with a ppolarized light. The dispersive feature for x=0.79
is quite similar to that for x = 0.70. Here, the DP
for x=0.79 is located above EF. The observed_

spin direction is inverted with respect to the G Fig. 2 SARPES images for (a) x = 0.70 and (b) x_ _point, meaning the TSSs possess a helical spin = 0.79 along GM. (c) Spin- and angle-resolved
texture. More interestingly, spin components spectra for x = 0.79.
opposite to the TSS are observed below DP,
corresponding to the spin textures of the surface resonances.
The band structures of the TSS and the surface resonances are identified from spin-resolved
energy distribution curves [Fig. 2(c)]. The surface resonances are spilt into two in the energy
direction in |k| = 0.1–0.2 Å-1. The surface resonance that appears in the lower binding energy
side possesses the same spin orientation as the TSS. Another surface resonance dispersing in
the energy range of 0.2–0.3 eV possesses the spin direction opposite to that of the counterpart.
_In addition, the spin polarizations of the surface resonances are inverted with respect to the G
point. Thus, we conclude that the surface resonances exhibit the Rashba-type spin splitting.
More importantly, the upper branch of the surface resonances is continuously connected to the
TSS. Our result provides direct evidence that the system undergoes the topological phasetransition.
REFERENCES[1] S.-Y. Xu et al., Science 332, 560 (2011).
[2] M. Brahlek et al., Phys. Rev. Lett. 109, 186403 (2012).
[3] Y. Zhang et al., Nat. Phys. 6, 584 (2010).
[4] C. Lin et al., Nat. Mater. 20, 1093 (2021).
[5] T. V. Menshchikova et al., JETP Lett. 93, 15 (2010).
[6] H. Jin et al., Phys. Rev. B 83, 041202(R) (2011).
[7] S. Souma et al., Phys. Rev. Lett. 108, 116801 (2012).
[8] K. Kuroda et al., Phys. Rev. Lett. 108, 206803 (2012).
[9] K. Yaji et al., Rev. Sci. Instrum. 87, 053111 (2016).

ELECTRONICSTRUCTURES
OF
HALF-METALLICFERROMAGNET La1-xSrxMnO3 BY HIGH-RESOLUTION SPINRESOLVED PHOTOEMISSION SPECTROSCOPY
T. Setoguchi1, N. Kataoka1, K. Kawaguchi2, Y. Fukushima2, A. Harasawa2, K. Kuroda2,
T. Kondo2, S. Shin2, T. Wakita1,3, Y. Muraoka1,3, and T. Yokoya1,31Graduate School of Natural Science and Technology, Okayama University, Okayama 700-8530, Japan

2

Institute for Solid State Physics, The University of Tokyo, Kashiwa, Chiba 277-8581, Japan

3

Research Institute for Interdisciplinary Science, Okayama University, Okayama 700-8530, Japan

Half metallic ferromagnets have a unique spin dependent electronic structure near the
Fermi level (EF), where only one of the spin states cross EF [1]. The unique electronic
structure gives rise to many body effects different from other systems. Theoretically, theelectronic states induced by many-body effects in half metals has been proposed as non
quasiparticle (NQP) states [2]. The experimental verification for NQP states has been
made recently for a half metallic ferromagnet CrO2 by using high-resolution (HR) spinresolved photoemission spectroscopy (SRPES) [3]. In the present research, we have
performed HRSRPES of another half metallic ferromagnet La1-xSrxMnO3 toexperimentally explore the characteristics and universality of NQP states. La1-xSrxMnO3
is one of the famous perovskite materials, exhibiting colossal magnet resistance aroundSr concentration x of 0.3. The previous SRPES study has provided evidence for half
metallic electronic structure of La1-xSrxMnO3 at 40 K[4]Homoepitaxial films of La1-xSrxMnO3 were grown on the atomically-flat (001) surfaceof Nb-doped SrTiO3 substrates using a laser MBE method. Laser-based SRPES
experiments were performed at the Institute for Solid State Physics, The University ofTokyo [7]. The p-polarized light with hν = 6.994 eV was used to excite the photoelectrons.
Photoelectrons were analyzed with a combination of a ScientaOmicron DA30L analyzer
and a very-low-energy-electron-diffraction (VLEED) type spin detector. The energy andangular resolutions were set to 6 meV and 0.3˚ (corresponding to ~0.005 Å) for spinintegrated ARPES and 10 meV and 1˚ (corresponding to ~0.02 Å) for SARPES,
respectively. During the measurement, the instrumental energy resolution was set to 20
meV and the base pressure was kept below 1 × 10#$ Pa. Calibration of EF for the
samples was achieved using a gold reference. The data were taken at T = 20, 50, 100 and
150 K. Clean surfaces of the samples for all measurements were obtained by in situ
annealing at 200℃ for 20 minutes. We magnetized the LSMO(001) sample along themagnetic easy axis ([110] direction) by bringing the sample close to a magnet . The
approximate magnitude of the magnetic field at the sample position was 700 Oe.
We obtained HRSRPES data at 20, 50, 100, and 150K. Compared to the minority spinstates showing negligible intensity around the near-EF region, the minority spin states
have enhanced intensity with a Fermi edge at all measured temperatures. These results
are in line with the previous SRPES studies reporting that LSMO is a half metallic
ferromagnet. However, we found that polarization is slightly smaller than 100%. We
tentatively attribute the reduced polarization to detecting the information of the substrate.
We plan to measure HRARPES with thicker films in the future experiment.
ACKNOWLEDGEMENT
This work was partially supported by JSPS KAKENHI Grand Numbers(JP20H0185313) from MEXT. We acknowledge M. Minohara and H. Kumigashira forproviding the samples.
REFERENCES[1] M.I. Katsnelson et al., Rev. Mod. Phys. 80, 315-378 (2008).
[2] V.Y. Irkhin and M.I. Katsnelson, Usp. Fiz. Nauk 164, 705 (1994).
[3] H. Fujiwara et al., Phys. Rev. Lett. 121, 257201 (2018).
[4] J.-H. Park et al., Nature 392, 794-796 (1998).
[5] K. Yaji et al., Rev. Sci. Instrum. 87, 053111 (2016).

5．Staff
Director:

HARADA Yoshihisa, Professor
MATSUDA Iwao, Professor
KIMURA Takashi, Associate Professor
KONDO Takeshi, Associate Professor
HAYASHI Tomohiro, Visiting Associate Professor
KURODA Kenta, Research Associate (~2021.8)
HORIO Masafumi, Research Associate
KIUCHI Hisao, Research Associate
TAKEO Yoko, Research Associate
HARASAWA Ayumi, Senior Technical Specialist
SHIBUYA Takashi, Technical Specialist
KUDO Hirofumi, Technical Specialist

Project Academic Specialist:
FUKUSHIMA Akiko
KOSEGAWA Yuka
ARAKI Mihoko
Secretary:
AIHARA Yumiko
YOSHIZAWA Motoko
TSUTSUMI Yumiko
IKEDA Kuniko
TERAMOTO Tomoka
Project Researcher:
OSHIMA Masaharu
OHDAIRA Takeshi
ZHANG Wenxiong
KURAHASHI Naoya
KITAKATA Emi
Al Samarai Mustafa (2021.8~)
LIU Daobin (2021.9~)
NIIBE Masahito (2021.10~)
TATSUTA Kazuo (2021.10~)
ANDO Hiroshi (2021.11~)

Graduate Student:
UGALINO Ralph John
SATO Yusuke
TSUJIKAWA Yuki
YANG Tianqi
ZHAO Yuhao (~2021.9)
KAMEDA Ayako
KUDO Yoshiki
SUMI Toshihide
WADA Tetsuya
LI HaoZHANG Xiaoni
ZHAO Haochong
FURUYA Noboru
SAKURAI Kai
SENOO Tomoaki
YIN Heming

Harima Paper 2021
No

Title

Authors

JournalVol.

No. Page

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Fumihiko Ozaki, Shunsuke Tanaka,1

Functionalization of the MoS­­­2 basal plane for activation ofmolecular hydrogen by Pd deposition

Wataru Osada, Kozo Mukai, Masafumi

AppliedHorio, Takanori Koitaya, Susumu

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Operando resonant soft X-ray emission spectroscopy of LiMn2O4 Hideharu Niwa, Hisao Kiuchi, Jun

Phys. Chem.

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24

Matsuda, Yoshihisa Harada, Eiji Hosono
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Hole Dynamics in Photoexcited Hematite Studied withHirata, Yujun Zhang, Kohei Yamagami,

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Chem. Lett.

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19

Ufuk Halisdemir, Gertjan Koster,
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雰囲気軟 X 線光電⼦分光を⽤いた触媒表⾯反応のオペランド計測⼭本達、⼩板⾕貴典、松⽥巌、吉信淳

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35

Ryosuke Matsuno, Yokajaksusri
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Electronic Structure of Carbon Dioxide in Sylgard-184 evaluatedby using X-ray Emission Spectroscopy

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51

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Shigenori Fujikawa, Yoshihisa Harada,
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8910

Editorial: Interfacial Water：A Physical Chemistry Perspective,
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Front. Chem.

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朝倉⼤輔、細野英司、原⽥慈久

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126-GHz lattice response in a quantum spin-orbital liquid probed by Huiyuan Man, Kohei Yamamoto, Yujun
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Critical In-plane Density of Polyelectrolyte Brush for the Ordered
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Kosuke Yamazoe, Yuji Higaki, Yoshihiro
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Takahara, Yoshihisa HaradaInterpretation of the x-ray emission spectra of liquid water

Osamu Takahashi, Ryosuke Yamamura,through temperature and isotope dependence

Takashi Tokushima, Yoshihisa Harada

Identification of Valence Electronic States Reflecting theHydrogen Bonding in Liquid Ethanol

Ryosuke Yamamura, Kosuke Yamazoe,
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Takahashi

J. Phys. Chem.
B

Daiki Murakami, Kosuke Yamazoe,
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Hydration Mechanism in Blood-Compatible Polymers Undergoing
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Shin-nosuke Nishimura, Naoya
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Tanaka, Yoshihisa Harada

Langmuir

J. Tang, O. Seo, D. S. R. Rocabado, T.
Hydrogen Absorption and Diffusion Behaviors in Cube-Shaped
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Koitaya, S. Yamamoto, Y. Nanba, C.

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Growth of MoS2-Nb-doped MoS2 lateral homojunctions: A

Anh Khoa Augustin Lu, Naoya Okada,monolayer p?n diode by substitutional doping

Wen-Hsin Chang, Takeshi Nakanishi,

APL Materials

Tetsuo Shimizu, Toshitaka Kubo,
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Fast and versatile polarization control of X-ray by segmented

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AAPPS

cross undulator at SPring-8

Yoshihisa Harada

Bulletin

31

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44585

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Methods Phys. 1018

1658042021

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20 Soft X-Ray Emission Studies on Hydrate-Melt Electrolytes

Watanabe, Yuki Yamada, Yi-Tao Cui,

J. Phys. Chem.

Yoshihisa Harada, Masashi Okubo,

B

Atsuo Yamada
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21

Comparative Study of H2O and O2 Adsorption on the GaN
Surface

Takeda, Masaki Kobayashi, Susumu

The Journal of

Yamamoto, Iwao Matsuda, Jun

PhysicalYoshinobu, Yoshiaki Nakano, Masakazu Chemistry C
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Hydrogen-bonded structure of water in the loop of anchoredpolyrotaxane chain controlled by anchoring density

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Frontiers in
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Scientificreports

S. Suga
A novel measurement approach for near-edge x-ray absorption
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Harada, Jin-Ming Chen, Jinghua Guo
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⽇本物理学会誌

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Phys. Rev.
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Kondo, and Iwao Matsuda
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