ANALYSIS OF ELECTRONIC STATES IN WATER MOLECULESCONFINED IN BIOCOMPATIBLE POLYMER BRUSH DERIVATIVESUSING SOFT X-RAY EMISSION SPECTROSCOPY
Keishi Akada1, Shin-nosuke Nishimura2, Kosuke Yamazoe1 , Daiki Murakami2,3,
Jun Miyawaki1, Masaru Tanaka2,3, Yoshihisa Harada1
1
2

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

Institute of Materials Chemistry and Engineering, Kyushu University,
3 Graduate School of Engineering, Kyushu University,

A characteristic water (Intermediate water) appearing at the liquid-polymer interface isconsidered as an origin of anti-fouling property of biocompatible materials such as poly(methoxyethyl acrylate) (PMEA) [1]. Control of intermediate water is possibly essential for thedevelopment of excellent biocompatible materials, but a mechanism of the biocompatibility is
not fully understood. The intermediate water is considered to have a specific water structure[2], and an evaluation technique focusing on water is effective for understanding the physicalproperties. In this study, for investigating the structure of intermediate water, we conductedmeasurements using synchrotron soft X-ray emission spectroscopy (XES) which has anadvantage in the measurement of hydrogen bond in water. An effect of polymer shape on
biocompatibility was investigated by comparing the state of water on PMEA brushes, where
the one polymer end is free in water, and in cyclic PMEA (cPMEA) brush, where both of ends
are fixed on substrate (Fig. 1). The difference of absorbed water may contribute to theimprovement of biocompatibility, and will serve as a guideline for a development of
biocompatible material.
As shown in Fig. 2, PMEA andcPMEA brushes were fixed onto an
Au-coated150
nm-thick
SiC
membrane for vacuum isolation in asolution cell. A humidifier (HUM-1,
Rigaku Corp.) was used to flow a
steam-nitrogen gas mixture over the
SiC/Si substrate, enabling precise
control of the humidity environment.
This system enable us to detect
Fig. 1 Schematics and molecular structure of PMEA andchanges of the electronic state of an
cyclic PMEA brushes
absorbed water, from the first layer ofwater attached on the material surface
to the multilayered state similar tobulk water. The O 1s XES
measurement was performed using theSPring-8
BL07LSUultra-highresolution soft X-ray emission
spectrometer HORNET[3]Fig. 3 shows a comparison of XES
spectra of the PMEA and cPMEA
brushes. The shapes of these peaks
were almost the same up to 90%RH.
This result indicates that there is no Fig. 2 Schematics of liquid cell for soft X-ray emission
difference in the hydrogen-bonded spectroscopynetworkofwater
adsorbed on both samples
at low humidity, and thisresultisreasonablebecause both polymers
are composed of the same
monomer.
However,above
95%RH,adifference
appeared
between these samples. In
PMEA, the amount of theadsorbed water rapidly
increased at 98%RH, and Fig. 3 Comparison of XES spectra from cPMEA (colored) and PMEA
peak
shape
was (black). The left panel is an enlarged plot of the right panel.
drastically changed to theshape of bulk water. On the other hand, the spectrum of cPMEA gradually increased, and thebulk shape was not obtained even at RH98%. This indicates that cPMEA can contain large
amount of water in its looped structure. Finally, the shape similar to the bulk was obtained at
RH 99%, but the 1b1" peak derived from the distorted hydrogen bond was still smaller thanthe bulk shape.
The detected water at low humidity was considered to be water molecules adsorbed on thefunctional groups of methoxyethyl acrylate (MEA), which is commonly exist in bothpolymers, because the spectral profiles were very similar between the two samples. On theother hand, water molecules adsorbed at high humidity (>95%RH) reflect the difference
between the two samples, that was the absence/presence of the loop structure of the polymer.
To discuss the properties of water adsorbed on cPMEA at each humidity, difference spectra
between the neighboring humidities were extracted as shown in Fig. 4. Unexpectedly small
increase in humidity caused a large change in the difference spectra, implying the presence ofvarious stages of the water uptake in cPMEA. The difference spectrum to 96%RH has
dominant 1b1" component while that to 98%RH has
dominant 1b1' component, which would suggest thepresence of water with highly distorted and orderedhydrogenbonddependingonthehumidity-controlled configuration of the trappedsite in the looped PMEA chain.
In conclusion, O 1s XES spectra of water inbetween the PMEA and cPMEA brushes showedsignificant difference at high (>95%RH) humidity:
the cPMEA brush contained larger amount of water
than the PMEA brush, possibly due to water uptake
in the looped chain. The observed change in thewater structure unique to the looped chain may
open a novel approach to control biocompatibility Fig. 4 Difference XES spectra from cPMEA
by designing materials surface to optimize theamount and hydrogen bonded structure of water.
REFERENCES
1.
2.
3.

Tanaka, M. & Mochizuki, A. J. Biomater. Sci. Polym. Ed. 21, 1849–1863 (2010).
Morita, S., Tanaka, M. & Ozaki, Y. Langmuir 23, 3750–3761 (2007).
Harada, Y. et al. Rev. Sci. Instrum. 83, 013116 (2012).

RESONANT SOFT X-RAY EMISSION SPECTROSCOPY OF A
HIGH-VOLTAGE CATHODE MATERIAL
Daisuke Asakura1,2, Eiji Hosono2,3, Akihiro Ohira1, Takaaki Sakai3, Kosuke Yamazoe4,
Naoya Kurahashi4, Ralph J. Ugalino4, 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

All-solid-state Li-ion battery (LIB) is attracting much interest due to the safe operation of
the solid-state electrolytes, while further enhancement of the energy density and power
density is expected as with conventional LIBs which use organic-solvent electrolyte.
LiNi0.5Mn1.5O4 (LNMO) is one of the 5-V-class high-voltage cathode materials which
contribute to enhance the power density and energy density of all-solid-state LIBs. LNMO
has a high redox potential near 5 V vs. Li/Li+ which is relatively higher than those of typicalcathode materials such as LiCoO2 (~3.9 V vs. Li/Li+), LiMn2O4 (~4.0 V vs. Li/Li+) and
LiFePO4 (~3.5 V vs. Li/Li+). The electrochemical, chemical and physical properties of
LNMO have been intensively investigated using general organic-solvent electrolyte. In
parallel, studies for the application of LNMO to all-solid-state LIBs have been reported.1
Previous studies including X-ray spectroscopic techniques have pointed out that the highvoltage of LNMO is realized through a redox reaction of Ni2+⇔Ni4+.2 On the other hand, theproperty of the high oxidation state of Ni4+ for the charged LNMO is still under debate. Nanba
et al. clarified a strong charge-transfer effect (O 2p→Ni 3d orbital) for the Ni4+ state of
Ni-oxide cathode materials using Ni L-edge X-ray absorption spectroscopy (XAS) withmultiplet calculation.3 Here, we demonstrate Ni L-edge XAS and resonant X-ray emission
spectroscopy (RXES) for LNMO to further understand the Ni 3d electronic structure.
A powdered LNMO sample was pasted with acetylene black and PTFE. The pasted LNMO
electrode was assembled as coin-type cell with Li-metal counter electrode, an organic
electrolyte solution and a separator. We prepared two cells to make charged-state samples
with different modes; one is constant-current (CC) and the other is constant-voltage (CV)modes. The charged cells were disassembled in an Ar-filled glovebox. The LNMO samples
were transferred from the glovebox to a transfer vessel without exposure to air. Ex situ Ni
L-edge XAS and RXES measurements for the pristine and the two charged samples werecarried out by HORNET spectrometer at BL07LSU, SPring-8. For XAS, bulk-sensitive
partial-fluorescence-yield detection mode was employed. The energy resolution for the RXES
measurement was set to 440 meV at 855 eV.
Figure 1 shows the Ni L3,2-edge XAS spectra. The pristine sample showed Ni2+ multiplet
structure.3 For the charged sample with the CC mode, the XAS line shape can be roughly
explained by the Ni3+ state while small amount of Ni2+ component should coexist.3 For the
charged sample with the CV mode, the Ni L3 and Ni L2 XAS main peaks further shifted tohigher energy, indicating further oxidized state.
The RXES results with an excitation energy of 854.2 eV (the dotted line in Fig. 1) are
shown in Fig. 2. The RXES line shape for the charged sample with the CC mode is mostly
different from that for the pristine sample, suggesting oxidation reaction to Ni3+, while some

peaks from 1.6 to 3.4 eV remain unchanged. For the charged sample with the CV mode, theline shape is considerably different from that for the pristine sample.
The XAS and RXES results indicate that the charged sample with the CV mode was further
oxidized. For more interpretations the XAS and RXES spectra will be analyzed with multiplet
calculations. Also, we will try operando XAS/RXES measurement using an all-solid-statetype cell in the near future.

Fig. 1. Ni L3,2-edge XAS for the LNMO samples.

Fig. 2. Ni L3-edge XES for the LNMO samples (excitation energy: 854.2 eV).
REFERENCES[1] For example, H. Kawasoko et al., ACS Appl. Mater. Interfaces 13, 5861 (2021).
[2] For example, C. A. Kim et al., Electrochim. Acta 184, 134 (2015) and S. Mukerjee et al.,Electrochim. Acta 49, 3373 (2004).
[3] Y. Nanba et al., Chem. Mater. 28, 1058 (2016).

ELECTRONIC STATE OF BULK SINGLE CRYSTAL Co2FeSi
HEUSLER ALLOY PROBED BY RESONANT INELASTIC SOFT
X-RAY SCATTERING (SX-RIXS) IN MAGNETIC FIELD
Rie Y. Umetsu1, Hidenori Fujiwara2, Jun Miyawaki3, Kohei Nishimoto2, Rika Kasahara2,
Yuto Arinaga2, 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), Hyogo, 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
Institute of Scientific & Industrial Research, Osaka University, Osaka, Japan
2

Introduction
Some of Mn- and Co-based Heusler alloys have been predicted to be half-metallic ferro- or
ferri-magnets with the spin polarization of ∼100 % around the Fermi level (EF) fromtheoretical calculations [1,2]. If the electrons are completely polarized around EF, it is very
efficient as a magnetic electrode in various spin dependent devices in the field of spintronics.
In the aspect of the fundamental investigations for half-metallic materials, it has been
considered how to show the real evidence of the band gap character in their electronic state.
Attempts have been made worldwide to observe the detailed electronic structure of Heusler
alloys by photoelectron spectroscopy. The photoelectron orbit is greatly affected by themagnetic field, although a magnetic field must be applied in order to make a sample into asingle domain state. In our previous work, we have studied the detailed electronic structure of
single crystals of Mn2VAl and Co2MnSi alloys by soft x-ray resonant inelastic x-ray
scattering (SX-RIXS) measurements in magnetic field [3,4]. The RIXS is a bulk sensitive
photon-in and photon-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 in element- and symmetry-specific ways. In this study, we performed the
RIXS experiments for single crystal of bulk Co2FeSi Heusler alloy, which has been
controversial being as the half-metallic ferromagnet, because the given spin polarization isdifferent depending on the theoretical calculation method [5].
Experiments
Sample preparation
A single crystal of bulk Co2FeSi was prepared by Bridgman method after preparing amaster alloy by induction melting in Ar gas atmosphere, and annealed at 1423 K. The sample
composition identified by scanning electron microscope-energy dispersive x-ray spectrometryis Co: 49.3, Fe: 25.4, Si: 25.3 at.%. Crystal orientation was checked by the Laue method andthe specimens were cut out 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 spontaneous magnetization at 5 K was 157.6 emu/g (= 5.7 μB/f.u.),
being comparable to the literature [6].
a)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 specimen was fractured ina chamber. The RIXS spectra for Fe 2p core excitation were measured with use of the rightand left helicity circularly polarized light at room temperature. A permanent magnet with thefield of 0.25 T was installed in the chamber and arranged as the x-ray incidence direction andthe magnetic field direction become parallel.
b)Results
Figure (a) indicates averaged RIXS spectra obtained in parallel (μ+) and antiparallel (μ−)
configurations between the photon helicity and the magnetic field at incoming photon energy,
for Fe-2p3/2 edge. Strong scatterings without any energy loss are the elastic component, andthe other scatterings in the larger energy loss region are the so-called fluorescence component.
Clear fluorescence component is observed and their circular polarization dependence (MCD =μ+ − μ−) is also confirmed as shown in the Fig. (b). Between the elastic component and strong
fluorescence component, a weak structure is observed at the incoming photon energy regions
from 706 to 708 eV. Figs. (c) and (d) indicate simulated MCD spectra calculated based on thegeneralized gradient approximation (GGA) and local density approximation with considering
the electron-electron correlation (LDA+U), respectively. The weak structure is well
reproduced by the calculated spectra by GGA, suggesting the existence of the density of statesof Fe-3d around EF, that is, the spin polarization of the Co2FeSi alloy would not be perfect.
REFERENCES[1] J.J. Kübler, A.R. Williams, C.B. Sommers, Phys. Rev. B 28 (1983) 1745-1755.
[2] S. Ishida, S. Akazawa, Y. Kubo, J. Ishida, J. Phys. F 12 (1982) 1111-1122.
[3] R.Y. Umetsu, H. Fujiwara, et al., Phys. Rev. B 99 (2019) 134414.
[4] H. Fujiwara, R.Y. Umetsu et al., Preprint, DOI: 10.21203/rs.3.rs-637357/v1.
[5] S. Wurmehl, G.H. Fecher, H.C. Kandpal, V. Ksenofontov, C. Felser, H.J. Lin, J. Morais,
Phys. Rev. B 72 (2005) 184434.
[6] P.J. Brown, R. Kainuma, T. Kanomata, K.-U. Neumann, A. Okubo, R.Y. Umetsu, K.R.A.
Ziebeck, J. Phys.: Condens. Matter 25 (2013) 206002.

Figs. Averaged RIXS spectra recorded for parallel (μ+) and antiparallel (μ−) configurations of thephoton helicity at Fe-2p3/2 (a), and the MCD (=μ+ − μ−) spectra (b). (c) and (d) are calculated
MCD spectra obtained by GGA and LDA + U, respectively.

NONPOLARIZING OXYGEN-REDOX CAPACITY WITHOUT O-O
DIMERIZATION IN Na2Mn3O7
Akihisa Tsuchimoto, Masashi Okubo

Department of Chemical System Engineering, School of Engineering, The University of Tokyo

There is an increasing demand for developing electrochemical energy storage with larger
energy density, which can achieve electric vehicles with longer cruising range or large-scale
applications for power grids. Lithium-ion battery is presently the most widely used energy
storage device in commercial applications because of its high energy density, but its energy
density has reached a plateau owing mainly to the small capacity of cathodes.
The capacity of conventional transition-metal layered oxides cathode materials like LiMO2(M: transition metals) is solely based on transition-metal redox, leading to a limited capacity.
The recent discovery of Li1+xM1-xO2 Li-rich transition-metal layered oxides with anionic redox
chemistry are promising alternatives to traditional cathodes materials. In LiMO2 conventional
cathode materials, all oxygen 2p orbitals have σ-type bonds with transition metals and theirenergy level is lower than M eg orbitals, hence oxygen 2p orbitals have no contribution to redox
capacity. On the other hand, Li1+xM1-xO2 cathode materials have localized oxygen 2p orbitals
along the Li-O-Li axis without σ-type bonds, which enables additional oxygen redox capacityand nearly doubled energy density.
However, most oxygen redox cathode materials suffer from large voltage hysteresis between
charge and discharge, which means energy loss, and the mechanism for this energy loss havenot been fully understood yet. Although kinetic hysteresis arising from the structural instability
such as cation migration and surface densification considered to be a part of cause of energy
loss, a large voltage hysteresis is still observed in sodium counterpart NaxMyO2 where cation
migration are suppressed by the larger difference of ionic size. As high energy efficiency isrequisite to commercial applications, the voltage hysteresis of oxygen redox cathodes needs tobe improved.
Although it is generally accepted that oxygen 2p states without M-O σ-type bonds are
localized and then contribute to redox
capacity, the chemical state of oxidized
oxygen is still under debate. The large
voltage hysteresis indicates that it
includes thermal hysteresis from thetransformation of oxygen atoms.
Oxidized oxide ions O−• are considered
to form stable peroxide-like O22− dimers
upon charge, and these O22− dimers may
be initially reduced to O24− and thendecomposed to O2− upon subsequent
discharge1.
We have recently found a “nonpolarizing” oxygen-redox capacity of
Na Mn O that possesses inherent Mn
vacancies in a layered structure2. Unlike
most oxygen redox cathode materials, Figure 1. Schematic illustration of charge/discharge curves andoxygen redox in Na2Mn3O7 is expected dQ/dV plots (Q: specific capacity, V: reaction voltage)
to be based on the reversible redox for a conventional oxygen redox with large polarization2−2−
couple of O2−/O−•. However, although (O2−/O2−• ), and b ideal oxygen redox with small polarization(O /O ). The red sphere denotes oxygen atom.
preliminary theoretical calculations
2

3

7

suggested that the nonbonding 2p orbitals of oxide ions neighboring the Mn vacancies
contribute to the oxygen-redox capacity, the origin for the non-polarizing oxygen-redox
capacity of Na2Mn3O7 is yet to be fully understood. In this work, using resonant inelastic X-ray
scattering (RIXS) spectroscopy for O K-edge and magnetic susceptibility measurements, we
attempt to probe the electronic structural change and the chemical state of the oxidized oxygen
species.
Na2Mn3O7 was synthesized from a solid-state reaction following a reported procedure2.
Galvanostatic charge/discharge measurements are performed using coin-type Na half cells withsynthesized Na2Mn3O7 as the cathode active material. Na2-xMn3O7 delivers a reversible
capacity of approximately 70 mAh/g at C/20 rate between 3.0 and 4.7 V vs. Na/Na+, which isconsistent with a previous report2. Figure 2a shows the dQ/dV plot for Na2-xMn3O7 during thesecond charge/discharge cycle. As the valence state of Mn in Na2-xMn3O7 is 4+ which is
maximum of Mn in octahedral sites, this redox capacity is attributed to oxygen redox.
Importantly, the voltage hysteresis in the charge/discharge of Na2-xMn3O7 (0.03-0.04 V) is
significantly smaller than that of other oxygen redox cathodes(~ 1.00 V), indicating reversible
redox couple of O2−/O−•.
O K-edge X-ray absorption spectroscopy (XAS)
and RIXS data are collected in BL07LSU in
SPring-8 to probe the electronic structural changeof oxygen. In the O K-edge XAS spectra on thesecond cycle (Figure 2b inset), a new emerged
absorption peak at 531.5 eV is observed, whichcorrespond to the excitation of O 1s to O 2p hole.
To probe the electronic structure of occupied statein addition to unoccupied state probed by XAS,RIXS spectra were measured using 531.5 eV
incident X-ray. The emergence of a new emission
peak at 523.0 eV is observed and this behavior istypical for other oxygen redox materials. This new
inelastic scattering can be explained by both cases,
O−• formation and peroxide-like O22− formation,
therefore, further experimental evidence is needed
to identify the chemical states of oxygen.
Considering the spin state of oxidized oxygen,oxygen species should be distinguished bymagnetic susceptibility measurements. While thespin state for O−• is S=1, the spin state for O22− is
S=0. The change in Curie constants before/after
the second cycle is deduced from χ-1 vs. T plot Figure 2. a dQ/dV plot (Q: specific capacity, V:(χ: magnetic susceptibility ) based on the Curie- reaction voltage) of Na2-xMn3O7 at C/20 during thecycle between 3.0–4.7 V
Weiss law, and the experimental values (5.77 cm3 second charge/discharge
vs. Na/Na+. Inset shows the crystal structure of−1
3−
K mol ⇄ 4.22 cm K mol ) are more plausible Na2Mn3O7. b O K-edge resonant inelastic X-ray
when assuming O−• as an oxidized species (5.63 scattering (RIXS) spectra for Na2-xMn3O7 before
cm3 K mol−1 ⇄ 4.75 cm3 K mol−) than O22− (5.63 the second charge (3.0 V, black line), after the
cm3 K mol−1 ⇄ 5.63 cm3 K mol−)3. Overall, the second charge (4.7 V, red line), and after the second(3.0 V, blue line) with excitation energy
existence of stable O−• was identified in dischargeof 531.5 eV. Inset shows corresponding O K-edge
Na2Mn3O7.
X-ray absorption spectra (XAS).
REFERENCES
1. Sathiya, M. et al., Nat. Mater. 12, 827–835 (2013). 2. Mortemard de Boisse, B. et al., Adv. Energy
Mater. 8, 1800409 (2018). 3. Tsuchimoto, A. et al., Nat Commun 12, 631 (2021).

Operando analysis of electronic structure of catalytic active sites inredox flow batteries
Akihiro Ohiraa,b, Eiji Hosonoa,b,c, Daisuke Asakuraa,b,c, Takaaki Sakaia,b, Kosuke Yamazoee,
Naoya Kurahashie, Yoshihisa Haradac,d,eacNational Institute of Advanced Industrial Science and Technology (AIST), Research Institutefor Energy Conservation, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japanb
National Institute of Advanced Industrial Science and Technology (AIST), Global Zero
Emission Research Center, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan
AIST-UTokyo Advanced Operando-Measurement Technology Open Innovation Laboratory,
5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8565, Japand
Institute for Solid State Physics (ISSP), The University of Tokyo,
5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8581, Japane
Synchrotron Radiation Research Organization, The University of Tokyo, 7-3-1
Hongo, Bunkyo-ku, Tokyo, 113-8656, JapanWe are exploring materials to improve the performance for redox flow batteries (RFBs), oneof the energy storage technologies that will facilitate the mass adoption of renewableenergies.1,2 RFBs mainly consist of an electrolyte containing the active materials responsible
for redox reactions, an electrolyte membrane that divides the positive and negative electrodes,
and electrodes that carry out the redox reactions of the active materials. RFB typicallyinvolves a redox reaction between vanadium's V4+ ⇆ V5+ (cathode) and V3+ ⇆ V2+ (anode) atboth electrodes, and the electromotive force is obtained from the difference in their respective
reaction potentials, resulting in a battery capacity that depends on the vanadium
concentration.3
High performance in RFBs mean improvement of energy density and power density, and torealize the improvement of energy density and power density, it is important to understand theredox reaction at the interface between the active material and the electrode. Specifically, it isnecessary to clarify the solvation and de-solvation behavior of the active material due to theredox reaction in solution, and the active sites that contact and react with the active material at
the electrode interface. In particular, it is important to analyze the electronic state of theelectrode material, because the electronic state is different between the catalytic state alongwith the electrochemical reaction and the non-reacted powder state. Considering theelectronic state of an electrochemical catalyst in an oxidation reaction, theoccupied/unoccupied orbitals examined in absorption and emission spectroscopy are very
different because the Fermi level is shifted by about 1 V in the oxidation state of +1 V
electrochemically (vs. SHE) from the unreacted state. Therefore, it is necessary to analyze theelectronic state during operation as a device in order to better understand the electrodereaction and discuss the correlation between the high-performance material and the electronic
state. Therefore, in this project, we will attempt to analyze the above solvation andde-solvation behaviors and the reaction active sites on the electrode surface by detailed
electronic analysis using techniques such as soft x-ray absorption spectroscopy (XAS) andsoft x-ray emission spectroscopy (XES). In this study, XAS and XES measurements of
vanadium solid and solution with different valence were carried out as a preliminary
investigation of the change in electronic state of the active material, which is an importantfactor in the analysis of catalytic reactions.
Solutions of V5+, V4+, V3+, and V2+ were prepared by charging and discharging 3M H2SO4
dissolved with 1M VOSO4 (V4+) at a current density of 70 mA/cm2 and discharge voltage of
1.6V to 1.0V using a small RFB cell. The UV spectra confirmed that the respective

electrolytes were prepared.
About 10 μl of these vanadium solutions were dropped onto a 5 mm2 Si3N4 substrate, and thesolid samples of V5+, V4+, V3+, and V2+ were prepared by heating and vacuum drying. In
addition, oxygen K-edge absorption and emission measurements were carried out by XAS and
XES experiments using an operando cell with SiC window/Ti/Au electrodes developed by
AIST and the University of Tokyo using BL07LSU.
The powder sample on Si3N4 substrate was mounted on a sample holder to perform XAS and
XES measurements (Fig 1). For the solution samples, 3M H2SO4 was used as a reference. In
the XAS measurement at the oxygen K-edge, different spectra were obtained depending on
the valence of the solution: V5+, V4+, V3+, and V2+. In the XES spectra with excitation energyof 550 eV, 1b', an indicator of hydrogen bond formation, and 1b", an indicator of hydrogenbond breaking, were also different. The trend of change was different between the cathodeside (V4+ and V5+) and the anode side (V2+ and V3+).
300

VOSO4
250

V4＋

V 2＋

Intensity

200

150

100

V5＋

V3＋
50

0
516

518

520

522
524
526
Emission energy (eV)

528

530

Figure 1. Vanadium solid samples and oxygen K-edge XES spectrum of VOSO4 powder.

REFERENCES[1] B. Zakeri. S. Syri, Renewable and Sustainable Energy Reviews, 42, 569 (2015).
[2] F. Shi, Reactor and Process Design in Sustainable Energy Technology, Elsevier
Amsterdam (2016).
[3] M. S. Kazacos, M. Rychcik, R. G. Robin, A. G. Fane, J. Electrochem. Soc., 133, 1057
(1986).

SOFT X-RAY CORE-LEVEL SPECTROSCOPY ON SURFACES INMIXED CONDUCTIVE OXIDES DURING OXYGEN PERMEATION
Isao Kagomiyaa, Tomohiro Hirano a, Yutaro Yagia, Susumu Yamamotob, Iwao MatsudacaLife Science and Applied Chemistry, Nagoya Institute of Technology,
Institute of Multidisciplinary Research for Advanced Materials, Tohoku UniversitycSynchrotron Radiation Laboratory, The Institute for Solid State Physics, The University of Tokyob

Oxygen permeability of mixed ionic-electronic conductive oxide (MIEC) is an importantcompound for developing applications, such as cathodes employed in solid oxide fuel cells(SOFCs) and oxygen separation membranes used for supplying oxygen from the air. For theapplications, we need higher oxygen permeability at lower temperatures than 800 °C. To
improve oxygen permeability, promoting surface exchange reaction during the oxygen
permeation is a significant strategy. However, the detailed factor dominating surface
exchange reaction is still unclear. This study tried to make clear the factor by investigating
soft X-ray core-level spectroscopy (XPS) on the MIEC surface during permeating oxygen.
This study focuses on La0.65Ca0.35FeO3- (LCF) perovskite as a MIEC, which shows higher
oxygen permeability, compared to the La0.6Sr0.4Co0.2Fe0.8O3- of a typical MIEC [2, 3]. The
LCF films were prepared on the one side of dense yttria-stabilized zirconia (YSZ) pellets byusing a spin-coating technique. After spin-coating, the LCF film on the YSZ pellet was fired
at 600 °C for 5 min. The thickness of the prepared LCF film was approximately 1.2 m. The
Pt paste including the 10wt% carbon was printed on the opposite side of the YSZ pellet andthen fired at 1200 °C.
XPS spectra of the prepared LCF film on YSZ
were collected at the soft x-ray beamline
BL07LSU at SPring-8. Energy of the incident
beam was set at 700 eV. The sample was heatedfrom ambient temperature up to approximately
600 °C. The current was applied in the range of-0.5 to 0.5 mA to let the LCF film permeate
oxygen at 600 °C as illustrated in Fig. 1. The
binding energy was calibrated by using Au 4f.
Each intensity and position of peak top in XPS
spectra with applying current was normalized bythose with no applying current.
Figure 2 shows XPS spectra of O1s core level at
600 °C under different applying current
conditions of 0.42, 0 and -0.34 mA. The O1s XPS
spectra is composed of three components,
corresponding to lattice oxygen (~529 eV),surface-lattice termination layer (~530 eV) andsurface secondary phases of hydroxides orcarbonated oxides (~531 eV). Figure 2 shows that

Fig. 1: Setup for XPS measurement
during oxygen permeation

Fig. 2: XPS spectra of O1s core level at
600 °C under different applying current
condition

amount of the oxygen on surface-lattice termination layer decreases with applying negative
current. When the negative current is applied, the surface oxygen is incorporated into LCF
film. We consider that oxygen on the termination layer disappears during incorporating
oxygen. Based on the consideration, the oxygen on the termination layer corresponds todesorbing or adsorbing oxygen during permeating oxygen. The component of ~530 eV in Fig.
2 depended on no applied positive current, suggesting that amount of surface oxygen relating
to desorption kept constant during the oxygen permeation. The other components (latticeoxygen and surface secondary phases) depended on no applying current.
This study concludes that oxygen on surface-lattice termination layer take an important roleof the surface exchange reaction during the oxygen permeation.

REFERENCES[1] E.J. Crumlin, E. Mutoro, Z. Liu, M.E. Grass, M.D. Biegalski, Y-L. Lee, D. Morgan, H.M. Christen,
H. Bluhm, Y. Shao-Horn, Energy Environ. Sci., 5, 6081 (2012)[2] I. Kagomiya, T. Murayama, K. Tsunekawa, K. Kakimoto, Y. Ogura, J. Eur. Ceram. Soc., 39, 1082
(2019).
[3] I. Kagomiya, T. Takahashi, K. Kakimoto, Chem. Mat., 31, 10135 (2019).

AMBIENT PRESSURE X-RAY PHOTOELECTRON SPECTROSCOPY
ON SURFACES IN MIXED CONDUCTIVE OXIDES AT ELEVATEDTEMPERATURES
Isao Kagomiyaa, Tomohiro Hiranoa, Takayuki Katoa, Susumu Yamamotob, Iwao MatsudacaLife Science and Applied Chemistry, Nagoya Institute of Technology
Institute of Multidisciplinary Research for Advanced Materials, Tohoku UniversitycSynchrotron Radiation Laboratory, The Institute for Solid State Physics, The University of Tokyob

Mixed ionic-electronic conductive oxides (MIEC) show oxygen permeability, which
properties are applicable to cathodes employed in solid oxide fuel cells (SOFCs) and oxygen
separation membranes used for supplying oxygen from the ambient air. The higher oxygen
permeability of mixed conductive oxides reduces activation polarization resistances when
they are used as cathodes in SOFCs and allows the generation of pure oxygen gas at higher
rates. Thus we need MIEC with higher oxygen permeability. Particularly, the application
requires high oxygen permeability at lower temperatures than 1073 K for decreasing theoperation temperatures. The slower surface exchange reaction at lower temperatures is a main
reason for limiting oxygen permeability at lower temperatures.
The previous our study found that oxygens on the surface take an important role of thesurface exchange reaction. The state of the surface would strongly depend on thecircumambient atmosphere, particularly oxygen partial pressure (PO2) near the MIEC sample
surface. With the point of view, this study investigated near-ambient pressure X-ray
photoelectron spectroscopy (XPS) of the MIEC surface under different PO2 conditions.
The precursor ceramic powders of a mixed conductive La0.65Ca0.35FeO3- (LCF) [1, 2] wereprepared by a citrate-based liquid mixing technique [3]. The prepared ceramic powders were
calcined at 1173 K for 5 h. The calcined powders were molded into a pellet and then pressedwith 300 MPa pressure by using a cold isostatic pressing machine (CIP). Finally, the pressedpellets were sintered at 1573 K for 10 h under ambient air. The XPS spectra of the prepared
LCF ceramic samples were collected by using the ambient pressure XPS instrument installed
at BL07LSU at SPring-8. Energy of the incident beam was set at 700 eV. To investigate theinfluence of temperature on the XPS spectra, the LCF sample was heated from ambient
temperature up to 660 K. The binding energy was calibrated by using Au film located on the
LCF sample surface.
Figure 1 shows XPS spectra of O1s core level at 660 K under the different PO2 conditions of
1 and 0.1 mbar. The component corresponding to surface secondary phases of hydroxides orcarbonated oxides (~531 eV) increased with increases in PO2. The other components
corresponding to lattice oxygen (~529 eV) and surface-lattice termination layer (~530 eV)
showed no remarkable changes. The result suggests that the increase in PO2 adsorbs morehydroxides or carbonated oxides on the LCF film surface. The secondary phases on thesurface would prevent permeating oxygens. More detailed PO2 dependence of surface state
during the oxygen permeation is needed to make clear effects of PO2 on the surface exchange
reaction.

Fig. 1: XPS spectra of O1s core level at 600 °C under different PO2 condition. OL: lattice oxygen;
Os(1): surface-lattice termination layer; Os(2): surface secondary phases.

REFERENCES[1] I. Kagomiya, T. Murayama, K. Tsunekawa, K. Kakimoto, Y. Ogura, J. Eur. Ceram. Soc., 39, 1082
(2019).
[2] I. Kagomiya, T. Takahashi, K. Kakimoto, Chem. Mat., 31, 10135 (2019).
[3] M.P. Pechini, U.S. Patent #3330697 (1967).

ANALYSIS OF INTERACTIONS BETWEEN POLYAMIDE AND
WATER MOLECULES IN REVERSE OSMOSIS MEMBRANES BY XAS,
XES AND RIXS
Jumpei Yahiro1, Koichi Ozaki1, Masaru Nakada1, Masahiro Kunisu1, Harutoki Shimura2,
Shinya Mitsui2, Naoya Kurahashi3, Kosuke Yamazoe3, and Yoshihisa Harada3
1
Toray Research Center, Inc.,
2
Toray Industries, Inc.
3
The Institute for Solid State Physics, The University of Tokyo
Introduction
The demand for seawater desalination has been increasing in the background of the water
shortage with the global economic development and the environmental pollution. In particular,
reverse osmosis (RO) desalination has been especially focused on from the viewpoint ofenergy saving [1]. A typical RO membrane consists of three layers: a separation functional
layer, a supporting layer, and a substrate. The separation functional layer has sub-nanometerscale pore structure inside it. This pore structure selectively separates water molecules andother substance, e.g., ions and organic compounds. In our previous study, the pore structure in
the RO membrane contained at least two kinds of water molecules: the water which confinedby hydrogen bonding with polyamide chains (bound water), and the water which existed at a
distance from polyamide chains (free water) [2]. Additionally, it is suggested that the strengthof the amide-amide hydrogen bonds in polyamide interacts the growth of water channels
which are composed with free water [3]. The water channels make rapid diffusion of watermolecules. Therefore, the control of both bound and free water in the water channel structure
is important to improve both the permeability and the selectivity in the RO membrane.
Furthermore, the method to analyze the state of the bound and the free water is necessary. In
this study, we examine the electronic states of the water in water channel structure using
X-ray absorption spectroscopy (XAS), X-ray emission spectroscopy (XES) and resonant
inelastic X-ray scattering (RIXS).
Experimental
The RO membranes were prepared as below procedures. The dried RO membrane wasprepared to dehydration under a vacuum condition at room temperature for 12 h. The watercontent RO membranes at different concentrations were prepared in a condition of 90%
relative humidity. O K-edge XAS, XES and RIXS measurements were performed at theBL07LSU HORNET station in SPring-8. The dried RO membrane was measured in a highvacuum condition by mounted on a Cu sample plate. The water content RO membranes were
measured using a liquid flow cell which could place RO membranes under flowing liquid orgas [4]. The low water content RO membrane was measured by fastened in a liquid flow cellin a condition of 90% relative humidity. The high water content RO membrane was measured
by fastened in the liquid flow cell under flowing dried nitrogen gas after flooded.
Results and Discussion
Figure 1 shows the O K-edge XES spectra of pure water, the water content RO membranes,
and the dried RO membrane at the excitation energy of 550 eV (non-resonant). The XES
spectra were normalized by integral intensity in the region 510 eV and 540 eV. In the XES
spectrum of pure water, the characteristic peaks (1b1', 1b1'', 3a1) were observed. The O K-edge
XES spectra of the water content RO membranes contain X-ray emission signals fromoxygens both of water molecules and polyamide chains. Subtracting the spectrum of the dried
RO membrane from that of the water content RO membrane, we could extract the spectrum of
the water molecules in the pore. Figure 2 shows the extracted spectra of water contribution in
RO membranes. The 1b1' peak intensity was lower than 1b1'' peak in the low water content
RO membrane clearly. Furthermore, the 3a1 peak intensity increased with decreasing watercontent. The XES spectrum of gas phase water has the dominant 1b1'' and 3a1 peaks [5],which features are similar to the low water content RO membranes. Therefore, it is indicatedthat the water molecules exist in isolation in the pore. Figure 3 shows the O K-edge RIXS
spectra of the low water content RO membrane and dried RO membrane at the excitationenergy of 531.3 eV. The RIXS spectra were normalized by integral intensity in the region 510
eV and 530 eV. In the XAS spectra, the absorption peak of the carbonyl bond oxygen
appeared at 531.3 eV (data not shown). Therefore, the RIXS spectra at the excitation energyof 531.3 eV are attributed to the electronic states around the carbonyl bond oxygen inpolyamide. The peak intensity around 523.5 eV in the low water content RO membrane washigher than that in dried RO membrane. The peak dominantly appeared in the low watercontent RO membrane, indicating to attribute to the change of electronic states by interaction
between the carbonyl bond oxygens and water molecules. In conclusion, we observed theelectronic states of water molecules in the pore and the interactions between water moleculesand polyamide chains. As a next step, we aim to observe the water contents dependence of thewater molecules behavior in the pore and to assign the peaks in RIXS spectra at the excitationenergy of 531.3 eV related the interactions of polyamide chains.

Figure 1. O K-edge XES spectra of pure water, watercontent RO membranes and dried RO membrane at
the excitation energy of 550 eV.

Figure 2. O K-edge XES spectra of water content
RO membranes subtracted the spectrum of the dried
RO membrane from the raw spectrum.

References[1] S.S. Shenvi, et al., Desalination 368, 10 (2015).
[2] T. Kawakami, et al., Polym. J., 50, 327 (2018).
[3] D. Surblys, et al., J. Membr. Sci., 596, 117705(2020).
[4] K. Yamazoe et al., Langmuir 33 3954 (2017).
[5] T. Tokushima et al., Chem. Phys. Lett. 460 387(2008).

Figure 3. O K-edge RIXS spectra of watercontent RO membrane and dried RO membraneat the excitation energy of 531.3 eV.

STUDY ON HYDROGEN BOND STRUCTURE OF WATER
MOLECULES IN POLYMER ELECTROLYTE
Naoya Kurahashi1, Kosuke Yamazoe2, Ugalino Ralph John3, Jun Miyawaki4, Keishi Akada1
and Yoshihisa Harada1
1

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

Japan Synchrotron Radiation Research Institute3

Graduate School of Frontier Sciences, The University of Tokyo

4

National Institutes for Quantum and Radiological Science and Technology

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. Polymer electrolyte fuel cells(PEFCs) are being installed in automobiles because they are small and can generate electricity
at low temperatures. However, further spread and expansion are required.
In PEFCs, when hydrogen gas is supplied to the anode, hydrogen ions (protons = H+) are
generated on the electrodes. The generated protons pass through the polymer electrolyte
membrane (PEM) and move to the cathode, where the protons react with oxygen gas togenerate energy and water molecules. Therefore, the PEM must have high gas barrier
properties, water resistance, and mechanical strength, while allowing only protons topermeate with high efficiency. Most of the polymers used in PEMs have a structure in whicha strong acid group such as a sulfo group is introduced at the end of a hydrophobic skeleton.
When these macromolecules aggregate, they take an inverted micelle structure and form
nanometer-order channel structures.1 When the PEM is humidified, water is taken into thechannel and protons are released from the superacid group, which is thought to be a
conduction path for protons.2 Therefore, it is necessary to evaluate the network structure ofwater molecules in the PEM in order to understand the proton permeability. However,experimental research was lacking because it was difficult to directly observe the watermolecules incorporated inside the membrane. One of the authors have previously attempted toevaluate the mobility of water molecules incorporated into the Nafion membrane using
nuclear magnetic resonance spectroscopy. As a result, it was clarified that the mobility ofwater molecules changes significantly
across a temperature of around 15 oC. The
authors predicted that the change in themobility was induced by the change in thesize of the proton channel, but could notreach a conclusion only by the NMR
measurement. Therefore, in this work, we
explored more detail of the hydrogen bond
network of water through the electronic
states of water molecules in the proton
channel
by
soft
X-ray
emission
spectroscopy. The sample was prepared bycasting a commercially available Nafionsuspension onto a SiC plate and volatilizing Fig. 1 Soft X-ray emission spectrum of bulk water
the solvent. By controlling both the and water molecules in Nafion at 80% relative
humiditytemperature and humidity using an atmosphere control cell, the temperature dependence ofthe electronic state was measured.
We evaluated the irradiation damage to Nafion because it was reported that soft X-rays
would damage fluorinated materials.3 In the emission spectroscope, the sample is moved atregular intervals to prevent damage to the SiC window and the sample, so that the same placeis not continuously irradiated with synchrotron X-rays. From our systematic test by changing
the X-ray irradiation time per point, it was concluded that damage to Nafion can be avoided if
the X-ray irradiation time is 5 seconds per point or less. Within the damage-free scan, soft
X-ray emission spectra of Nafion in two conditions, circulating nitrogen gas in a dry and
80 % relative humidity conditions were measured, and the difference spectra between the twowere obtained for different temperatures, which extract the emission signal derived fromwater molecules incorporated into the Nafion membrane.
The soft X-ray emission spectra measured with photon energy of 550 eV and energy
resolution of 150 meV are shown in Fig. 1. The XES profile of the water incorporated into the
Nafion suggests that the water molecules form clusters with highly distorted or brokenhydrogen bonds. To analyse the temperature dependence of the XES profile, each spectrum
was fitted with four gaussians, and the intensity ratios of the 1b1' and 1b1" derived peaks (Fig.
2 red circle) as well as the separation energy of the 1b1' and 1b1" peaks (Fig. 2 blue square)
were evaluated. In bulk water, the 1b1"/ 1b1' intensity ratio increases with temperature because
the hydrogen bonds in water are distorted by thermal fluctuations. The energy separation of
the 1b1' and 1b1" peaks also increases with temperature because the 1b1" peak shifts to higher
energy with temperature to accommodate entropy gain while the 1b1' peak stays constantsince the tetrahedrally coordinated water is stabilized only by enthalpy gain and just decrease
the population with temperature.4 Intriguingly, the results observed for Nafion water are
different from the trends expected forbulk water in terms of both theintensity ratio (1b1"/ 1b1') and thepeak separation energy; both have aminimum at around 18 oC, albeit thevalues are still larger than those ofbulk water at 27 oC. The uniquetemperature-dependent behaviour of
this water should be related to thetemperaturedependent
local
configuration figured by Nafion. In
the near future, the determinants ofthe structure of water in Nafion will
be clarified by comparison with Fig. 2 Area intensity ratio of the 1b1' and 1b1" peaks (circle,
simulations, which is expected to lead left axis) and the peak energy difference (square, right axis)
to the fine control of proton of water in Nafion evaluated from peak separation of the
XES spectra. The black circle and square are the results ofconductivity.
bulk water.

REFERENCES[1] M. Rikukawa, J. Synth. Org. Chem. Jpn. 66, 488 (2008).
[2] M. Yoshida-Hirahara et al., RSC Adv. 10, 12810 (2020).
[3] L. G. de A. Melo et al., Microsc. Microanal. 21, 2443 (2015).
[4] P. Gallo et al., Chem. Rev. 116, 7463 (2016).

METHANE CONVERSION REACTION ON PT AND PD MODELCATALYSTS STUDIED BY OPERANDO AMBIENT-PRESSURE XPS
Takanori Koitaya
Department of Materials Molecular Science, Institute for Molecular Science

INTRODUCTION
Activation of methane on metal surfaces has been widely studied. For example, symmetryof methane adsorbed on Pt surfaces is reduced to C3v [1], and electronic interaction between
methane molecules and Pt substrate is detected by X-ray absorption spectroscopy (XAS) [2].
Recently, we have investigated the interaction of methane with the Pd(110) surface by meansof X-ray photoelectron spectroscopy (XPS), XAS and first-principle calculations, andrevealed that one of the C-H bonds in adsorbed methane is softened through the electronicinteraction with the Pd surface [3]. The previous studies indicate that transition metals aregood catalysts for methane activation, but they are conducted under ultra-high vacuum (UHV),
which is a quite different condition compared with real catalytic reaction conditions.
In this study, the methane oxidation reaction on Pt surfaces was studied by ambient-pressure(AP-XPS). AP-XPS is a powerful tool for Operando observation of catalytic reaction. The
surface chemical states are detected by measurements of chemical shift of substrate andadsorbate core-levels. In addition, reaction products desorbed from a catalytic surface are also
monitored by photoionization of gas-phase molecules.
EXPERIMENTAL
The experiments were performed using the AP-XPS apparatus equipped at BL07LSU [4].
The AP-XPS measurements were carried out using a differentially pumped electron analyzer(SPECS, PHOIBOS 150 NAP) with an ambient-pressure gas cell. The gas cell was equippedin an UHV analysis chamber (base pressure = 3 × 10-10 mbar), which makes it possible toperform the AP-XPS measurements under well-defined conditions. XPS measurements can be
performed in near-ambient pressure up to 20 mbar by using a small aperture ( 0.3 mm).
The Pt surfaces were cleaned by cycles of Ar+ sputtering and annealing at 1000 K in a
preparation chamber (base pressure = 3 × 10-10 mbar). All the XPS spectra were obtained witha photon energy of 715 eV.
RESULTS AND DISCUSSION
The methane oxidation reaction was investigated at a sample temperature of 650 K. The
reaction products are monitored C 1s, O1s XPS and quadrupole mass spectrometer (QMS)
equipped in a differentially pumped lens chamber. The main products under this reaction
condition are CO2, CO and water. Fig. 1 shows QMS signals of produced CO2 on Pt(111) as afunction of oxygen flow rate. At lower flow rate less than 0.4 cm3/min, the amount of CO2
increased linearly, indicating that collision frequency of oxygen molecules onto the Pt surface
is a key factor determining reaction rate for the methane oxidation. In contrast, the higher
oxygen flow rates lead to a steep decrease in the reactivity.

Fig. 1. The amount of produced CO2 as a function of oxygen flow rate (sample temperature = 650 K, methane
flow rate = 7.0 cm3/min)

The flow-rate dependent reactivity was further investigated by AP-XPS. Fig. 2 shows Pt 4f
core-levels spectra of Pt(111) at oxygen flow rates of (i) 0.2 cm3/min (reactive condition), and1.5 cm3/min (inert condition). The spectrum of the reactive Pt surface shows a peak at 70.5
eV, which is assigned to bare Pt atoms at the surface. This results clearly shows that thePt(111) surface is clean even in the near-ambient condition. On the other hand, the baresurface Pt peak was completely disappeared and a new peak was appeared at higher binding
energy in the case of the inert reaction condition. The new peak is attributed to be Pt atoms
binding with surface oxygen atoms. Therefore, the active site for the methane oxidation is abare metallic surface, and surface oxygen significantly suppress the methane activation.

Fig. 2. AP-XPS spectra of the Pt(111) surface in the reaction condition (i) and (ii) indicated in Fig. 1.

REFERENCES[1] J. Yoshinobu, H. Ogasawara, and M. Kawai, Phys. Rev. Lett. 75, 2176 (1995).
[2] H. Öström, H. Ogasawara, L. Å. Näslund, K. Andersson, L. G. M. Pettersson, and A. Nilsson, J.
Chem. Phys. 127, 144702 (2007).
[3] T. Koitaya, A. Ishikawa, S. Yoshimoto, and J. Yoshinobu, J. Phys. Chem. C 125, 1368 (2021).
[4] T. Koitaya et al., Top. Catal. 59, 526 (2016).

DIRECT OBSERVATION OF METHANE OXIDATIVE COUPLING
REACTION ON PALLADIUM BASED ALLOYS BYAMBIENT-PRESSURE XPS
Takanori Koitaya
Department of Materials Molecular Science, Institute for Molecular Science

INTRODUCTION
It is indispensable to develop a highly functional catalyst for efficient use of methane as achemical feedstock. Alloying is one of the promising methods for controlling catalytic
activity of transition-metal catalysts. Palladium is a good catalyst for oxidation of methane. A
previous our study has shown that the active site for the methane oxidation is a PdO film thatis formed on the surface in the presence of the feed gases. Therefore, in-situ observation of
surface chemical states is important for understanding the reaction mechanism.
In this study, methane conversion reaction on the Pd-Au alloy foil was investigated bymeans of the operando AP-XPS to reveal the effect of the alloying.

EXPERIMENTAL
The experiments were performed using the AP-XPS apparatus equipped at BL07LSU [1].
The AP-XPS measurements were carried out using a differentially pumped electron analyzer(SPECS, PHOIBOS 150 NAP) with an ambient-pressure gas cell. The gas cell was equippedin an UHV analysis chamber (base pressure = 3 × 10-10 mbar), which makes it possible toperform the AP-XPS measurements under well-defined conditions. The AP-XPS
measurements can be performed in near-ambient pressure up to 100 mbar by using a small
aperture ( 0.05 mm).
The Pd-Au alloy samples (Au: 18 at%) were cleaned by cycles of Ar+ sputtering andannealing at 723 K in a preparation chamber (base pressure = 3 × 10-10 mbar). All the XPS
spectra were obtained with a photon energy of 1096 eV.

RESULTS AND DISCUSSION
The methane oxidation reaction was investigated using a quadrupole mass spectrometer(QMS). Fig. 1 shows sample temperature and QMS spectra of produced CO2, CO and water.
In this experiment, 16 mbar O2 and 17 mbar methane was introduced into the gas-cell, andthen the sample was heated at a rate of 0.05 K/s. When the sample was heated to 615 K ((i) in
Fig. 1), the amount of the products was very small, indicating that the sample surface wasinert. The Pd 3d spectrum in Fig. 2(a) shows two peaks: bulk Pd and surface oxide.

Fig. 1. Sample temperature and QMS signal of reaction products as a function of reaction time.

During heating to 800 K, the QMS signals of the reaction products increased in intensity as
a function of the sample temperature. The sample was then cooled to 615 K again (ii). It
should be noted that the reactivity on this surface is significantly higher compared to thecondition (i). The Pd 3d AP-XPS spectra show oxidation of Pd to PdO. In addition, theintensity of Au 4f spectra is decreased. These spectral changes indicate that the Pd atoms in
the alloy sample are segregated on the surface, and active PdO sites are formed. Surface
adsorbate and reaction products are monitored C 1s (Fig. 2c). The surface coverage ofreaction intermediates is very small, and only the peaks of the gas-phase molecules (methane
and CO2) were observed. This result suggests that reaction and desorption of reaction
intermediates and products are fast, and that rate controlling step in the methane oxidation is adissociative adsorption of methane.

Fig. 2. (a) Pd 3d, (b) Au 4f, and (c) C 1s AP-XPS spectra measured in the reaction conditions (i) and (ii)indicated in Fig. 1.

REFERENCES[1] T. Koitaya et al., Top. Catal. 59, 526 (2016).

Broad Spectral Feature due to p-d Hybridization in p-Type Ferromagnetic
Semiconductor (In,Mn)As
Masaki Kobayashi1,2, Kohsei Araki1, Takahito Takeda1, Le Duc Anh1, Atsushi Fujimori3,4,
Jun Miyawaki5,6, Yoshihisa Harada5, Shinobu Ohya1,2, and Masaaki Tanaka1,2
1

Department of Electrical Engineering and Information Systems, The University of Tokyo
2
Center for Spintronics Research Network, The University of Tokyo
3
Department of Physics, The University of Tokyo
4
Department of Applied Physics, Waseda University
5
Synchrotron Radiation Laboratory, The Institute for Solid State Physics, The University of Tokyo
6
Institute for Advanced Synchrotron Light Source, National Institutes for Quantum and Radiological
Science and Technology

Intensity (arb. units)

Ferromagnetic semiconductors (FMSs) are alloy semiconductors doped with a sizable amountof magnetic impurities (typically a few percent or more). The ferromagnetism in FMS isconsidered to be induced by charge carriers, thus called carrier-induced ferromagnetism. Since
this property enables us to control the magnetic properties by carriers through electrical andoptical means, FMSs have attracted much attention in the research field of spintronics [1,2].
From the fundamental science point of view, the origin of the carrier-induced ferromagnetismin FMS is still under debate. (In,Mn)As is a conventional p-type III-V-based FMS showing
carrier-induced ferromagnetism [3,4]. Previously, it has been found that post-growth annealingon (In,Mn)As thin films leads to the increase of hole-carrier concentration and raises the Curie
temperature (TC) [5,6]. Thus, (In,Mn)As provides an ideal platform to elucidate the carrierconcentration dependence of the physical properties of (In,Mn)As. The knowledge of theelectronic structure of FMS is indispensable for understanding the mechanism offerromagnetism [7-10]. In this study, we have performed X-ray absorption spectroscopy (XAS)
and resonant inelastic X-ray scattering (RIXS) measurements on (In,Mn)As thin films withvarying hole-carrier concentrations to reveal the origin of the ferromagnetism in (In,Mn)As.
(In0.93,Mn0.07)As thin films were grown on conductive n+-InAs(100) substrates by themolecular beam epitaxy (MBE) method. The sample structure was In0.93Mn0.07As (50 nm)/InAs(50 nm)/n+-InAs(100) substrate from top to bottom. The samples were covered by anamorphous As layer to protect the surface from oxidization. Post-growth annealing at 250 oC
was performed on the as-grown samples for 10 min or 30 min to increase the hole-carrier
concentration. The Curie temperature (TC) increases with increasing the annealing time, while
the as-grown (In,Mn)As film show paramagnetism due to its low carrier concentration. The TC
values of the samples annealed for 10 min and 30 min were 35 K and 55 K, respectively, as
determined by the Arrott plot of the magnetic circular dichroism intensity. The holeconcentrations estimated from TC were
(In,Mn)As
below 3 × 10!" , ~4 × 10!" , and#$-3
Mn L2,3 XAS~3 × 10 cm for the as-grown, 10PFY
min annealed, and 30-min annealed
samples, respectively. The RIXS and
30-minAnnealed
XAS experiments were conductedusing the high-resolution soft X-ray
10-minemission spectrometer HORNET [12]Annealed
at beamline BL07LSU of SPring-8 [13].
The total energy resolution for the
As-grown
RIXS measurements was ~170 meV at
630
635
640
645
650
655
660
PhotonEnergy(eV)
the Mn L3 edge. The RIXS spectra were
measured with linear horizontal FIG. 1: Fe L2,3 XAS spectra of (In0.93,Mn0.07)As thin films.
The signals were collected in the TFY mode. The arrowpolarization at room temperature. The denotes the excitation energy for RIXS measurements.

Intensity (arb. unit)

XAS signals were collected in the total-fluorescence yield (TFY) mode. Here, the probing
depths of RIXS and TFY-XAS are expected to be several hundreds nm due to the long
penetration depth of X-rays.
Figure 1 shows the Fe L2,3 XAS spectra of the (In0.93,Mn0.07)As thin films. All the threesamples show a similar spectral feature having a single peak at the L3 edge and double peaks at
the L2 edge. Note here that there are finite changes in the spectra, i.e., a shoulder structure andsmall peaks appear with annealing. Interstitial Mn defects acting as double-donors in (In,Mn)Asare supposed to be thermally diffused out to the surface by the post-growth annealing, thusincreasing the hole concentration. The small spectral changes may come from the modificationof the electronic structure of the Mn ion with increasing the hole concentration as well as fromthe out-diffused Mn atoms that were oxidized on the surface.
Figure 2 shows the Mn L3 RIXS spectra ofthe (In,Mn)As thin films measured at 639.7(In,Mn)As
Mn L3 RIXS
eV. The spectra are normalized to the areashν = 639.7 eV
and plotted as a function of energy loss. In
30-min Annealed
10-min Annealed
general, a RIXS spectrum is sensitive to the
As-grown
local electronic structure of the Mn 3d
orbitals [14]. Although the energy resolution
is high enough to resolve each d-d excitation
peak [12], the RIXS spectra of the doped Mn
8
7
6
5
4
3
2
1
0
-1
ions show a broad spectral feature
Energy Loss (eV)irrespective of the hole concentration. Since
FIG. 2: Mn L3 RIXS spectra of (In0.93,Mn0.07)As thin
the d-d excitation energy of localized 3d films. The excitation photon energy is 639.7 eV.
orbitals like MnO are discrete, RIXS spectraof such localized 3d orbital show a spectral feature with multiple peaks [12]. Thus, the broaden
spectral line shape observed in (In,Mn)As suggests the d-d excitation involving a localizedbound hole state due to strong hybridization between the Mn 3d orbitals and ligand As 4p bands.
For a further analysis, comparison of the RIXS spectra with configuration-interaction clustermodel calculation is desirable [8]. This analysis will enable us to estimate the electronic
structure parameters. The calculations will reveal the difference in the electronic structure
between (In,Mn)As and (Ga,Mn)As [8].
In conclusion, we have performed XAS and RIXS measurements at the Mn L edge of(In,Mn)As thin films with varying the hole concentration. The RIXS spectra show a broad
spectral feature irrespective of the hole concentration, indicating that the Mn 3d orbitals wellhybridizes with the ligand band in (In,Mn)As as well as (Ga,Mn)As.
REFERENCES[1] T. Dietl, Nature Mater. 9, 965 (2010).
[2] M. Tanaka, Jpn. J. Appl. Phys. 60, 010101 (2021).
[3] H. Munekata et al., Phys. Rev. Lett. 63, 1849 (1989).
[4] H. Ohno et al., Nature 408, 944 (2000).
[5] Y. Hashimoto et al., J. Cryst. Growth 237-239, 1334 (2002).
[6] Y. Iye et al., Mater. Sci. Eng. B 63, 88 (1999).
[7] M. Kobayashi et al., Phys. Rev. B 89, 205204 (2014).
[8] M. Kobayashi et al., Phys. Rev. Lett. 112, 107203 (2014).
[9] S. Sakamoto et al., Phys. Rev. B 95, 075203 (2017).
[10] T. Takeda et al., Phys. Rev. B 101, 155142 (2020).
[11] M. Kobayashi et al., Phys. Rev. B 103, 115111 (2021).
[12] Y. Harada et al., Rev. Sci. Instrum. 83, 013116 (2012).
[13] Y. Senba et al., Nucl. Instrum. Methods Phys. Res., Sect. A 649, 58 (2011).
[14] L. J. P. Ament et al., Rev. Mod. Phys. 83, 705 (2011).

LI INSERTION MECHANISM OF OCTAHEDRAL LI4TI5O12 SINGLECRYSTALLINE PARTICLE BY MAPPING MEASUREMENT OF
3DNANOESCA
Wenxiong Zhanga, Eiji Hosonob,c,d, Daisuke Asakurac,d, Naoka Nagamurae,
Masaharu Oshimaf, Yoshihisa Haradaa,d,faInstitute for Solid State Physics (ISSP), The University of Tokyo,
5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8581, Japanb
National Institute of Advanced Industrial Science and Technology (AIST), Global Zero Emission
Research Center, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japanc
National Institute of Advanced Industrial Science and Technology (AIST), Research Institute forEnergy Conservation, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japand
AIST-UTokyo Advanced Operando-Measurement Technology Open Innovation Laboratory, 5-1-5
Kashiwanoha, Kashiwa, Chiba 277-8565, Japane
National Institute for Materials Science, Research Center for Advanced Measurement andCharacterization, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japanf
Synchrotron Radiation Research Organization, The University of Tokyo, 7-3-1
Hongo, Bunkyo-ku, Tokyo, 113-8656, Japan

Li4Ti5O12 (LTO) has drawn considerable attention as lithium-ion battery anode materials
owing to its cycling stability and high-rate performance, as well as its improved safety overgraphite. It features that: relatively safe operational potential (1.55V vs. Li+/Li), zero volume
change during the discharge/charge process and excellent Li ions insertion/extraction
reversibility, which makes it one of the most promising anode materials. Recently,
microspectroscopic photoelectron images of the LTO electrode with a spatial resolution of
100 to 200 nm have been obtained by using 3DnanoESCA. The change in the valence of Ti
due to Li insertion was observed on LTO active material during the charge/discharge
process.1 However, the Li insertion mechanism is not yet clear for LTO octahedron single
crystalline particle, which is essential for material optimization. To elucidate the mechanism,
the ex-situ LTO samples with octahedral morphology after the discharge treatment have been
prepared (Figure 1a). By the mapping of the particles via 3DnanoESCA at BL07LSU ofSPring-8,2 it is anticipated to see the Li-rich and Li-poor phases from the mapping image oftriangular facet of LTO octahedron particle (Figure 1a).
During the 3DnanoESCA measurement, after focusing on the LTO particle (adjustment of
the place of the holder, Fresnel zone plate and order-sorting pinhole aperture), a rough imageof a wide area would be scanned. Subsequently, the resolution would be improved to about
100 nm to obtain a local image of the octahedral particle by further adjusting the focus. Then,the mapping process would appropriately be employed to elucidate the Li distribution on the
LTO particle surface.
As shown in Figure 1c, O 1s mapping image of the LTO particles obtained by
3DnanoESCA measurement shows the resolution comparable to the optical image (Figure 1b).
SEM images obtained after the measurement showed clear octahedral LTO particle withtriangular facet (Figure 1d). Correspondingly, the triangular facet from the mapping image
showed relatively inferior resolution (Figure 1c). Taken into consideration of low
conductivity of LTO, the charging-up happened during the mapping process of the LTO
particle when smaller scanning step was used for mapping (100 nm/spot). Therefore, thelarger scanning step (200 nm/spot) was conducted with sacrificing the resolution of the
mapping image. As a result, it was not possible to observe the movement of the domain wallof the two phases depending on the amount of Li insertion. In the near future, increasing theconductivity by coating the carbon on the LTO surface will be conducted to directly observe
the domain wall movement with better resolution.

Figure 1 (a) CV (cycling voltammetry) and LSV (linear sweep voltammetry) characteristic of
LTO battery cell to 1 V and SEM image of LTO particles. (b) Optical image of LTO particles.
(c) O 1s intensity mappings by 3D nanoESCA of LTO. (d) SEM images of LTO after
measurement.

ACKNOWLEDGEMENT
This work is partially conducted on the basis of the International joint research program forinnovative energy technology by Ministry of Economy, Trade and Industry, Japan.
REFERENCES[1] K. Akada, T. Sudayama, D. Asakura, H. Kitaura, N. Nagamura, K. Horiba, M. Oshima, E. Hosono,
Y. Harada, Operando measurement of single crystalline Li4Ti5O12 with octahedral-likemorphology by microscopic X-ray photoelectron spectroscopy, J. Electron Spectrosc. Relat.
Phenom., 233, 64 (2019).
[2] K. Horiba, Y. Nakamura, N. Nagamura, S. Toyoda, H. Kumigashira, M. Oshima, K. Amemiya, Y.
Senba, H. Ohashi, Scanning photoelectron microscope for nanoscale three-dimensional
spatial-resolved electron spectroscopy for chemical analysis, Rev. Sci. Instrum. 82, 113701 (2011).

AMBIENT-PRESSURE X-RAY PHOTOELECTRON SPECTROSCOPYSTUDIES OF CO2 HYDROGENATION ON PD-BASED ALLOY
Jiayi Tang
Departnment of Engineering, University of Hyogo

Introduction
CO2 hydrogenation to methanol and formic acid has received many attentions because it
can efficiently reduce the greenhouse-gas emission as well as synthesize chemicals. In orderto further improve the activity, selectivity and stability of catalyst, the origins of catalytic
properties, transition metal Pd is an excellent candidate to activate hydrogen molecules,
leading to a catalyst surface with highly reduced state, which can facilitate the hydrogenation
process. Alloy sites have been considered as the active sites in the CO2 hydrogenation, such as
Pd-based bimetallic catalyst [1]. The study of bimetallic surfaces has gained considerable
interest because it is difficult to know the correlations between electronic and chemical
properties of the intermixed bimetallic surfaces and the catalytic reaction. In recent, Pd-based
alloys were reported as highly reactive catalysts for CO2 hydrogenation reactions, where
ethanol (2CO2 + 6H2 → C2H5OH + 3H2O) and methanol (CO2 + 3H2 → CH3OH + H2O) were
produced on the PdCu bimetallic catalysts under different catalytic conditions [2-4]. The
formation of formic acid was observed on PdAg alloy nanoparticles through the reaction of
CO2 and H2 (CO2 + H2 → HCOOH) [5]. In order to clarify the kinetics of CO2 hydrogenation,
the reaction paths were studied on the PdCu(111) single crystal surface using DFT
calculations [3]. Since the influences of the surface compositions, structure properties, andgas conditions on the catalytic behavior were required to be studied to improve the efficiency,
selectivity and stability of the catalysts, the precise understanding of this reaction is still
incomplete with regard to the reaction mechanism under ambient pressure and temperature.
Experimental
In the present study, the CO2 hydrogenation process over PdCu(fcc), PdCu(B2) and PdAg
alloys were studied by in-situ ambient-pressure X-ray photoelectron spectroscopy (AP-XPS)
to clarify the relationship between the surface electronic properties and the catalytic
mechanism. All the high-resolution AP-XPS measurements were performed using thesynchrotron radiation at BL07LSU, SPring-8, Japan [6,7]. We carried out the temperature andgas pressure dependent measurements to clearly observe the surface catalytic reactions. The
temperature dependence was conducted under H2 pressure PH2 at 0.4 mbar and CO2 pressure
PCO2 at 1.6 mbar at 300 K, 310 K and 320 K. During the gas pressure dependentmeasurements, the PH2:PCO2 were performed at 0.4:0.8, 0.4:1.6 and 0.4:2.4, at temperature of
300 K. The time evolutions of C 1s spectra and Pd 3d, Cu 2p, Ag 3d core-level spectra weretaken during the CO2 hydrogenation.
Results and Discussion
C 1s spectra measured before and during the gas exposure at PH2 of 0.4 mbar and PCO2 of
1.6 mbar at 300 K on PdCu(fcc) and PdCu(B2) are shown in Fig.1. C 1s spectrum measured
at 8 min after gas exposure (blue solid) obviously shows that three components located at thebinding energies of 284.4 eV, 286.1 eV, 287.5 eV are initially formed on the surface, which
are assigned to the C0, CO species, and intermediate species formate (HCOO), respectively.
We found that the amount of the formate gradually increased with the exposure time on both
PdCu(fcc) and PdCu(B2). It is newly found that the formate is formed under the relatively
low gas pressure at 300 K on the PdCu alloy, which indicates a relatively high reactivity and a
low energy barrier for the formate formation compared to the monometallic catalyst surface.
Figure 2 shows the time evolutions of C 1s components during the CO2 hydrogenation at 300

K on PdCu(fcc) and PdCu(B2). We found that the formation of formate on PdCu(fcc) is more
active than PdCu(B2), which indicates the surface structure may influence the activity of H2
dissociation and HCOO formation. Moreover, we observed that the formate was also formedon the PdAg surface and the reaction was strongly influenced by the gas pressure and thetemperature. The detailed reaction mechanism and the relationship between the surface
electric properties and the reactivity will be further discussed.
REFERENCES[1] X. Jiang et al., Appl. Catal. B 170 (2015) 173.
[2] X. Jang et al. Catalysis Communications 118 (2019) 10-14.
[3] X. Nie et al. ACS Catal. 2018, 8, 4873-4892.
[4] S. Bai et al. J. Am. Chem. Soc. 2017, 139, 20.
[5] K. Mori et al. J. Am. Chem. Soc. 2018, 140, 8902.
[6] S. Yamamoto, et al., J. Synchrotron Rad. 21 (2014) 352.
[7] T. Koitaya, S. Yamamoto, et al., Topics in Catalysis 59 (2016) 526.

Fig.1 C 1s spectra measured before and during CO2 hydrogenation on PdCu(fcc) and PdCu(B2) surfaces
under H2 gas pressure of 0.4 mbar and CO2 gas pressure of 1.6 mbar at 300 K.

Fig.2 Time evolutions of the components obtained from C 1s spectra on PdCu(fcc) and PdCu(B2) surfaces
under 0.4 mbar H2 and 1.6 mbar CO2 at 300 K.

INVESTIGATION OF LPSO-STRUCTURE FORMATIONMECHANISM BY SMALL ANGLE INELASTIC X-RAY SCATTERING
1

Kakeru Ninomiya, 3Yoshihisa Harada, 1,2Maiko Nishibori

1Interdisciplinary Graduate School of Engineering Sciences, Kyushu University
International Center for Synchrotron Radiation Innovation Smart, Tohoku University
3
Synchrotron Radiation Laboratory, The Institute for Solid State Physics, The University of Tokyo
2

INTRODUCTION
Magnesium based ternary alloys which containing a long-period stacking ordered structure(LPSO) has attracted attention because of their excellent mechanical properties and flame
retardance[1]. The LPSO phase has a lamellar-like structure consisting of stacked hcp Mg
layers with transition metal (TM) and rare-earth (RE) elements rich stacking fault layers[2].
Recent studies have reported that solute-rich layers regularly arrange TM6RE8 L12-typeclusters[3]. The details of the LPSO structure have been investigated by electron microscopy,
but the mechanism of LPSO phase formation is still controversial.
Various types of LPSO structures are reported, which are expressed as 12R-, 10H-, 18R-,
14H- and 24R-types. There are assumed to be constructed of stacking structural blocks with
4-,5-,6-,7- and 8-close packed atomic layers, respectively[4]. However, the mechanism for theappearance of these polytypes and the introduction of periodic stacking faults are notunderstood. Recently, the appearance of solute nanoclusters before the L12 cluster in
Mg85Zn6Y9 alloy was investigated by in-situ small-angle X-ray scattering (SAXS)
measurement with aging[5]. This suggests that the chemical interaction between solute atoms
is essentially important for forming the L12 clusters. However, the interaction between TM
and RE, in other words, the driving force for cluster formation has not been clarified.
In this study, for the purpose of the formation mechanism of L12 cluster, we investigated
the relationship between the electronic state of solute atoms and the cluster arrangement byobserving the electronic state change of LPSO-Mg alloys with different LPSO structures by
X-ray emission spectroscopy (XES).
EXPERIMENTAL METHOD
Mg79Ni9Y12(at.%) and Mg82Ni7Y11 alloys by high-frequency induction melting of Mg, Ni,
and Y pure metals have been prepared. These alloys were kept at 1023 K and cast in an argon
atmosphere, and then annealed at 793 K for
100 h.
Small-angle X-ray scattering (SAXS)
measurements were conducted to examine
the nanoscopic heterogeneous structure (Fig.
1). In Mg82Ni7Y11, a sharp peak and a diffuse
peak have appeared at 4.8 nm-1 (12.9 Å) and
6.1 nm-1(10.3 Å) respectively. These peaks
are regarded as a 10H-type LPSO structure.
On the other hand, sharp peaks are confirmed
at 4.8 nm-1 and 5.9 nm-1 in Mg79Ni9Y12.
These peaks are considered as the scattercorresponding to the interplane distance of
10H and 12R-type LPSO structures.
Therefore, Mg82Ni7Y11 consists of the single
10H-type LPSO structure, and Mg79Ni9Y12 Fig. 1 SAXS profiles of Mg79Ni9Y12 (red line) andcontains the 10H- and 12R-type LPSO Mg82Ni7Y11 (blue line) alloys (λ = 0.92 Å, camera
length = 1129.57 mm)
structure.

X-ray absorption/emission spectroscopy(XAS/XES) measurement was performed
at BL07LSU in SPring-8. Ni L2,3 XAS
spectra were obtained by the fluorescence
yield method (Fig. 2). We confirmed thatthe strongest peak of Ni L3 absorption
edge was located at 854 eV and Ni L2
absorption edge was at 870 eV. Therefore,
we used the incident X-ray energy from
854 to 866 eV in 2 eV steps for XES
measurement. The total energy resolution
for XES was set to E/ΔE = 3000 at the Ni
Fig. 2 Ni L3 XAS spectra of Mg79Ni9Y12 and Mg82Ni7Y11
L3 edge. The diffraction angle was set to alloys.
90° and the polarization of incident X-ray
energy was vertical.
RESULTS AND DISCUSSION
XES measurement was performed toconsider the electronic state changes due
to LPSO polytype structures (Fig. 3). XES
spectra were the same spectral shapes
when the incident X-ray energy was set to854 eV. On the other hand, the XES
spectrum was sharper in Mg79Ni9Y12 thanin Mg82Ni7Y11 measured at 866 eV. This
result suggests that the electronic statewith a deeper energy level changes
depending on the LPSO polytype
structure, although the electronic statenear the Fermi level does not change.
From these results, it was suggested thatthe electronic state of Ni changes
depending on the LPSO structure, that is,
the interlayer distance of L12 cluster.
However, the relationship between thecluster ordering and the electronic state ofsolute atoms has not yet been clarified,and it is necessary to consider structural
information
andelectronic
state Fig. 3 Ni L3 XES spectra of Mg79Ni9Y12 and Mg82Ni7Y11
alloys.
information at the same time.
Mg-Ni-Y alloy was provided by Prof. M. Yamazaki, Kumamoto University. This work was
supported by MEXT/JSPS KAKENHI, Grant-in-Aid for Scientific Research on Innovative
Areas, MFS Materials, Grant Numbers JP19H05130.
REFERENCES[1] Y. Kawamura, K. Hayashi, A. Inoue, Mater. Trans., 42 (2001) 1172.
[2] M. Yamasaki, M. Sasaki, M. Nishijima, K. Hiraga, Y. Kawamura, Acta Mater., 55 (2007) 6798.
[3] D. Egusa, E. Abe, Acta Mater., 60 (2012) 166.
[4] E. Abe, A. Ono, T. Itoi, M. Yamasaki, Y. Kawamura, Philos. Mag. Lett., 91 (2011) 690.
[5] H. Okuda, M. Yamasaki, Y. Kawamura, M. Tabuchi, H. Kimizuka, Sci. Rep. 5 (2015)) 14186.

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MAPPING ANALYSIS OF ACTIVE MATERIALS FOR LITHIUM ION
BATTERIES BY 3D NANOESCA
Eiji Hosonoa,b,c, Wenxiong Zhangd, Daisuke Asakurab,c, Naoka Nagamurae,
Masaharu Oshimaf, Yoshihisa Haradac,d, faNational Institute of Advanced Industrial Science and Technology (AIST), Global Zero
Emission Research Center, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japanb
National Institute of Advanced Industrial Science and Technology (AIST), Research Institutefor Energy Conservation, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japanc
AIST-UTokyo Advanced Operando-Measurement Technology Open Innovation Laboratory,
5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8565, Japand
Institute for Solid State Physics (ISSP), The University of Tokyo,
5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8581, Japane
National Institute for Materials Science, Research Center for Advanced Measurement andCharacterization, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japanf
Synchrotron Radiation Research Organization, The University of Tokyo, 7-3-1
Hongo, Bunkyo-ku, Tokyo, 113-8656, Japan

In order to improve the performance of active electrode materials and to develop innovativeelectrode materials for lithium-ion batteries (LIBs), we have been investigating the electronic
structure change due to redox reaction in various electrode materials during charge-discharge
process using soft X-ray absorption spectroscopy (XAS) and soft X-ray emission
spectroscopy (XES). The electronic state change by redox reaction is one of the determinantsof the energy density, i.e. charge/discharge capacity and operating voltage of the electrodematerials. Thus, detailed analysis for understanding of the electronic state undercharge-discharge operation is important. In the past few years, position-sensitive electronic
structure analysis on the electrode materials has been strongly desired in order to obtainstrategies for improving the performance such as surface modification to improvecharge-discharge cycle characteristics, controlling the thermophysical stability of active
electrode materials, and controlling the crystal axis for the Li diffusion direction.
Soft X-ray microspectroscopy is considered to be one of the suitable methods for spatial
analysis of the electrode materials for LIBs because local electronic structures can beanalyzed in detail. Soft X-ray microspectroscopy includes photoelectron emission microscopy(PEEM) using electron lenses, scanning transmission soft X-ray microscopy (STXM) using aFresnel zone plate, and scanning photoelectron spectroscopy (3DnanoESCA)1. The highest
spatial resolution of these techniques is better than 100 nm, which is sufficient to investigate
the distribution of electronic and chemical states in electrode materials.
We have developed a microspectroscopic system using synchrotron radiation soft X-rays toobtain soft X-ray photoemission spectroscopy of electrode active materials during operationof all-solid-state LIBs with a spatial resolution of 100-200 nm (“Operando measurement of
single crystalline Li4Ti5O12 with octahedral-like morphology by microscopic X-ray
photoelectron spectroscopy”, J. Electron Spectrosc. Relat. Phenom., 233, 64 (2019)2,“Microscopic photoelectron analysis for single crystalline LiCoO2 particles during thecharge-discharge in an all solid-state lithium ion battery”, Sci. Rep. 9, 12452 (2019))3.
In this study, we focus on the analysis of each facet in single crystalline active materials for
LIBs. Figure 1 shows a SEM image of LiCoO2 particles and O 1s intensity map on one of theparticles. The O 1s XPS map successfully corresponds to the SEM image; the same shape andthe same facets are observed. The next step is to analyze the XPS data of each facet of thesingle crystalline particle. In the near future, we will develop the operando measurementsystem and conduct the XPS mapping measurement.

Figure 1. (left) SEM image and (right) O 1s intensity map by 3D nanoESCA of LiCoO2.
ACKNOWLEDGEMENT
This work is partially conducted on the basis of the International joint research program forinnovative energy technology by Ministry of Economy, Trade and Industry, Japan.
REFERENCES[1] K. Horiba, Y. Nakamura, N. Nagamura, S. Toyoda, H. Kumigashira, M. Oshima, K.
Amemiya, Y. Senba, H. Ohashi, Scanning photoelectron microscope for nanoscale
three-dimensional spatial-resolved electron spectroscopy for chemical analysis. Rev. Sci.
Instrum. 82, 113701 (2011).
[2] K. Akada, T. Sudayama, D. Asakura, H. Kitaura, N. Nagamura, K. Horiba, M. Oshima, E.
Hosono, Y. Harada, “Operando measurement of single crystalline Li4Ti5O12 withoctahedral-like morphology by microscopic X-ray photoelectron spectroscopy”, J. Electron
Spectrosc. Relat. Phenom., 233, 64 (2019).
[3] K. Akada, T. Sudayama, D. Asakura, H. Kitaura, N. Nagamura, K. Horiba, M. Oshima, E.
Hosono, Y. Harada, “Microscopic photoelectron analysis of single crystalline LiCoO2
particles during the charge-discharge in an all solid-state lithium ion battery”, Scientific
Reports, 9, 12452 (2019).

Structure-Selective Electronic Structure Analysis
by 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.
The fact that elementary excitations can be measured by RIXS can be explained by
the energy conservation law, hvin = hvout + Eh − Ee and the momentum conservation law, qin =qout + kh − ke + G for the inelastic scattering. Here, hvin (qin) and hvout (qout) are the energies(momenta) of incident and scattered X-rays, Eh (kh) and Ee (ke) are the energies (momenta) ofholes in the valence band and electrons in the conduction band generated in the final state,
and G is the reciprocal lattice vector of the crystal. In the case of the so-called X-ray
diffraction, the elastic scattering is considered, and thus Eh = Ee, kh = ke, and qin = qout + G,
which is the well-known Bragg's law.
When inelastic scattering and diffraction occur simultaneously, both qin =qout_inelastic + kh − ke + G and qin = qout_elastic + G must be satisfied, leading qout_inelastic + kh − ke= qout_elastic (Fig. 1), and the intensity of the inelastic scattering is expected to be enhanced in adiffractive manner. In the case of nanoparticles, the energy-momentum dispersion ofelementary excitations is small and flat, and the momentum conservation law can be satisfied
with any combination of kh and ke. The diffraction from
nanoparticles in the soft X-ray region will also show a profile thatreflects structural information similar to that of small-angle X-ray
scattering (SAXS) in hard X-ray region (although peaks appear in
the wide-angle region due to the longer wavelength of soft X-rays).
Thus, the diffraction from nanoparticles is expected to enhance theinelastic scattering intensity from nanoparticles of a specific size.
This enhancement of the inelastic scattering intensity is an inelastic
version of diffraction, and can be called resonant inelastic X-ray
diffraction (RIXD). RIXD could be a completely new technique toreveal the electronic state of specific sizes and structures by Fig. 1 Schematic of theconservation
choosing specific q, which corresponds selecting the structure by momentum
law in RIXD.
diffraction, and measuring the enhanced intensity of RIXS.
In order to demonstrate the feasibility of RIXD, we have developed the experimental
setup of SAXS and RIXD measurement for nanoparticle. As a result, we have succeeded in
obtaining SAXS profiles in the soft X-ray region for FePt and Fe3O4 nanoparticles for the firsttime, and have also succeeded in observing the enhancement of inelastic scattering intensity
by RIXD in FePt nanoparticles. Figure 2 shows the measured SAXS intensities of FePt andFe3O4 nanoparticles. The incident X-ray energy of 708.1 eV was used in both cases,corresponding to the peak top of the L3 edge, which are assigned to metallic Fe in FePt andmainly to the Fe2+ peak in Fe3O4. The obtained profiles are in good agreement with thesimulation for the nanoparticles of the particle sizes evaluated by transmission electron
microscopy, confirming that the profiles are SAXS from nanoparticles.

Fig. 2 Experimental (red) and simulated (blue) SAXS profiles of FePt (left) and Fe3O4 (right) nanoparticles.

Figure 3 shows the results of RIXD for FePt nanoparticles. In response to thediffraction peak (purple), the intensity of the inelastic scattering, especially in the area of a3,
is clearly enhanced (green): RIXD, the diffraction-assisted inelastic scattering, was observed.
The absence of the enhancement in the scattering channel closer to the elastic line (the area of
a1 or a2) proves that the a3 enhancement does not pick up the enhancement of the elastic tail.
On the other hand, in the case of the Fe3O4 nanoparticles, although SAXS was clearlyobserved, RIXD could not be observed. This may be due to the difference in the coherence of
the intermediate state of RIXS [1]. Since the intermediate state for insulating Fe3O4 is more
localized than that for metallic FePt, the diffraction assisted mechanism required for RIXD
probably did not work. Although there is still much to be considered, such as the effect of thelocalized or itinerant intermediate state, the clear intensity enhancement by RIXD was
observed in FePt, and we believe that we have succeeded in demonstrating RIXD.
(b)Intensity [arb. units](a)Area_a1
Area_a2
Area_a3
Area_a123
Elastic = SAXS

0
25

30
35
Theta [degree]

40

Fig. 3 (a) RIXS spectra of FePt nanoparticle measured at 708.1 eV and 2θ=66°. (b) Experimental
results of RIXD for FePt nanoparticles. The integration areas are indicated in (a).

REFERENCES[1] Y. Ma, Phys. Rev. B 49, 5799 (1994).

OBSERVATION OF DEHYDRATION PROCESS OF
THERMOSENSITIVE POLYMERS BY SOFT X-RAY ABSORPTIONAND EMISSION SPECTROSCOPY
Kosuke Yamazoe,a Ralph John Ugalino,b Jun Miyawaki, a,b,c Yoshihisa Harada,a,b,caInstitute for Solid State Physics, The University of Tokyo, Kashiwa, Chiba 277-8581, Japanb

Department of Advanced Materials Science, Graduate School of Frontier Sciences,

The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8561, Japan.
cSynchrotron Radiation Research Organization, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku,
Tokyo 113-8656, Japan

Poly(N-isopropylacrylamide) (PNIPAM) is important for applications in soft functional
materials with stimuli-responsive properties. PNIPAM is soluble in cold water but precipitates
above the lower critical solution temperature (LCST). LCST is observed at around 32℃ [1].
Phase separation beyond LCST is accompanied by a coil-globule transition of the polymer inwater, and in many cases the polymer forms aggregates. Water plays an important role in the
coil-globule transition of polymers, but it is unclear how dehydration relates to thecoil-globule transition and the subsequent formation of mesoscopic polymer-rich aggregates.
Studies of PNIPAM have reported on the relationship between cooperative dehydration
processes and phase separation [1], estimates of the number of water molecules dehydrated
during the coil-globule transition [2], and investigation on the order of which changes first in
the phase transition process of PNIPAM, the structural change of water or the structuralchange of polymer. [3]. Furthermore, the observed structural transformation of water isrelated to the ripening of aggregates composed of long-chain polymers [3].
Here, we aimed to use soft X-ray absorption spectroscopy (XAS) and soft X-ray emission
spectroscopy (XES) to reveal how PNIPAMs dehydrate in the process of collapse to form
mesoscopic
polymer-richaggregates. The concentrationof the PNIPAM solution usedin the experiment is 2.5 wt%.
The temperature of theaqueous solution samples wascontrolled using a variabletemperature liquid cell. This isa system using a chiller, where
the working fluid is supplied
to the liquid cell body. Figure
1 shows the chemical formulaof PNIPAM and the schematic
illustration of phase transitionand dehydration of PNIPAM inwater. PNIPAM solution istransparentatlower
temperatures than LCST but
becomes cloudy at higher Figure 1. Chemical formula of PNIPAM and schematic diagram
temperatures than LCST.
of the phase transition and dehydration of the polymer in water.
Figure 2(a) shows the PNIPAM solution is transparent at low temperatures thantemperature dependence of the LCST but becomes cloudy at high temperatures.

the oxygen K-edge XAS spectra of PNIPAM aqueous solution. the peak near 532 eV is theabsorption of oxygen at the C=O double bond. For comparison, the XAS spectrum of bulk
water measured at room temperature is also plotted. The concentration of the PNIPAM
solution used in the experiment is 2.5 wt%. Figure 2(a) shows the temperature dependence ofthe soft X-ray absorption spectrum of the oxygen K-edge of the PNIPAM aqueous solution.
the peak near 532 eV is the absorption of oxygen at the C=O double bond. For comparison,
the XAS spectrum of bulk water measured at room temperature is also plotted. As thetemperature increases, a peak at 531.5 eV appears, which is in a different position from thepeak at 532.4 eV. To assign the C=O double bond, resonant soft X-ray emission spectroscopy
was performed. Figure 2(b) shows the temperature dependence of the resonant soft X-ray
emission spectra when the
excitation X-ray energy is set
to 531.5 eV. On the other
hand, in the resonant soft
X-ray emission spectrum
measured at an excitationenergy of 532.4 eV, anotherpeak was observed inaddition to the above two
peaks (Fig. 2(c)). This newpeak may be related tohydrogen bonding between
watermolecules
and
PNIPAM, suggesting theexistence of at least twowater-PNIPAM
hydrogen-bonded states attemperatures above 32°C
LCST. The excitation energy
dependence near 532eV at
36°C was also investigated.
This result supports that there
are mainly two types ofhydrogen-bonded states ofwater and PNIPAM. This
result indicates that theprocess of dehydration was
directlyobserved
with
Figure 2. (a) Temperature dependence of XAS spectra ofincreasing temperature. It is
PNIPAM aqueous solution. (b) Temperature dependence of the
expected that theoreticalresonant XES spectra at hv=531.5eV. (c) Temperature
calculations will reveal thedependence of the resonant XES spectra at hv=532.4eV. (d)detailed hydrogen-bonding
The excitation energy dependence of XES near 532eV at 36°C.
states in the future.

REFERENCES[1] M. Philipp et al. J. Phys. Chem. B 118 4253 (2014).
[2] Y. Ono and T. Shikata. J. Am. Chem. Soc. 128 10030 (2006).
[3] K. Mochizuki and D. Ben-Amotz. J. Phys. Chem. Lett. 8 1360 (2017).

Upgrade of ambient pressure X-ray photoelectron spectroscopy system
at SPring-8 BL07LSU
Susumu Yamamoto1,2, Takanori Koitaya3,4, Iwao Matsuda5, and Jun Yoshinobu5
1

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

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

3
4

Department of Materials Molecular Science, Institute for Molecular Science

Precursory Research for Embryonic Science and Technology (PRESTO), Japan Science andTechnology Agency (JST)5The Institute for Solid State Physics, The University of Tokyo

Introduction
Operando spectroscopy is an experimental technique that directly observes materials anddevices under actual operation conditions to find a correlation between structure and function
in materials. This experimental approach is especially important in energy conversion materials
such as catalysts, photocatalysts, fuel cells, and lithium-ion batteries, because the surface
structure and composition of these materials is often changed under reaction conditions.
Operando X-ray spectroscopy has been limited to the hard X-ray region, but Operando
spectroscopy in the soft X-ray region has rapidly developed in recent years with use of highbrilliance synchrotron radiation light source and the development of new instruments. We havedeveloped ambient pressure X-ray photoelectron spectroscopy (AP-XPS) system [1] at thehigh-brilliance soft X-ray beamline BL07LSU of SPring-8, and have been promoting researchon operando observation of catalytic reactions [2-9] over the last seven years. The limitationsof the AP-XPS system were revealed by the past experiments: (i) low maximum gas pressure,and ii) low temporal resolution. As for i) low maximum gas pressure, the maximum gas pressurein the AP-XPS measurements is limited to about 20 mbar for bulk samples. The low maximum
gas pressure leads to low reactivity and selectivity in catalytic reactions and small amount ofwater on the surface of polymers and semiconductor photoelectrodes. Regarding ii) low
temporal resolution, the temporal resolution of the present AP-XPS system is limited tosec~min.
Therefore, in our long-term project, we set two goals to upgrade the AP-XPS system at SPring8 BL07LSU: (i) the increase of the maximum gas pressure, and (ii) the development ofpicosecond time-resolved AP-XPS system. In this report, we describe our recent efforts toachieve (i) the increase of the maximum gas pressure.

Results and discussion
The XPS signal attenuation in a gas phase is proportional to exp 𝑧𝜎𝑝 , where z is the
distance between the sample and the entrance nozzle of an electron spectrometer, scatteringcross section of photoelectrons, p gas pressure. In order to mitigate the XPS signal attenuation,
one effective approach is to keep z small. When the distance z is small, however, the local gas
pressure on the sample surface is decreased due to the differential pumping through the entrance
nozzle. To avoid the decrease of local gas pressure, the opening of the entrance nozzle needs tobe decreased.
In the present AP-XPS system, the diameter of the nozzle opening was 300 m, and the
distance z was set at ~300 m. We developed a new nozzle with the opening diameter of 50 m(Figure 1). The nozzle body was manufactured by an electroforming technique at Institute for
Molecular Science. The opening hole was made by a focused ion beam. The distance z was set
at ~100 m. Using the new 50 m nozzle, we have succeeded in measuring Au4f XPS spectrain the presence of 100 mbar N2 gas. Therefore, the maximum gas pressure of the AP-XPS
system was improved from 20 mbar to 100 mbar. Now we start to measure various systems
which require high gas pressures; H2 absorption process in Pd alloys and CO2 hydrogenation
reactions on catalyst surfaces.

Figure 1. New entrance nozzle of an electron spectrometer for AP-XPS system at SPring-8
BL07LSU. (a) Overview picture of the nozzle (50 m opening at the apex of nozzle), (b) asample approaches to the nozzle and the distance between the sample and the nozzle was about
100 m.
REFERENCES
[1]
[2]
[3]
[4]
[5]
[6]
[7]
[8]
[9]

S. Yamamoto et al., J. Phys.: Condens. Matter 20, 184025 (2008).
T. Koitaya, S. Yamamoto et al., Topics in Catalysis 59, 526-531 (2016).
S. Yamamoto et al., Phys. Chem. Chem. Phys. 20, 19532-19538 (2018).
J. Tang, S. Yamamoto et al., Appl. Surf. Sci. 463, 1161-1167 (2019).
J. Tang, S. Yamamoto et al., Appl. Surf. Sci. 480, 419-426 (2019).
T. Koitaya, S. Yamamoto et al., ACS Catalysis 9, 4539-4550 (2019).
T. Koitaya, S. Yamamoto et al., e-J. Surf. Sci. Nanotechnol. 17, 169-178 (2019).
M. Sato, S. Yamamoto et al., J. Phys. Chem. C 124, 12466-12475 (2020).
Y. Imazeki et al., J. Phys. Chem. C 125, 9011-9019 (2021).