Upgrade of ambient pressure X-ray photoelectron spectroscopy system
at SPring-8 BL07LSU
Susumu Yamamoto1,2, Takanori Koitaya3, Iwao Matsuda4, and Jun Yoshinobu4
1

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

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

3

Department of Chemistry, Graduate school of Science, Kyoto University
4

The Institute for Solid State Physics, The University of Tokyo

Introduction
Operando spectroscopy allows direct observation of materials and devices under actual
operation conditions to find a correlation between structure and function in materials. As
Operando spectroscopy in the soft X-ray region, we developed ambient pressure X-ray
photoelectron spectroscopy (AP-XPS) system at the high-brilliance soft X-ray beamline
BL07LSU of SPring-8 [1, 2]. We have been promoting research on operando observation of
catalytic reactions. The limitations of the AP-XPS system were revealed by our pastexperiments: 1) low maximum gas pressure, and 2) low temporal resolution. As for 1) low
maximum gas pressure, the maximum gas pressure in the AP-XPS measurements was limited
to about 20 mbar for bulk samples. The low maximum gas pressure leads to low reactivity andselectivity in catalytic reactions. Regarding 2) low temporal resolution, the temporal resolutionof the present AP-XPS system was limited to sec~min.
Therefore, in our long-term project, we set two goals to upgrade the AP-XPS system at SPring8 BL07LSU: 1) Increase the maximum gas pressure, and 2) development of picosecond timeresolved AP-XPS system.
Results and discussion1) Increase the maximum gas pressure in AP-XPSThe 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 past AP-XPS system, the diameter of the nozzle opening was 300 m, and the distancez was set at ~300 m. We developed a new nozzle with the opening diameter of 50 m. 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 Au 4f XPS spectra in thepresence of 100 mbar N2 gas. Therefore, the maximum gas pressure of the AP-XPS system was
improved from 20 mbar to 100 mbar. After the improvement of the maximum gas pressure, the
AP-XPS system was used to study various systems such as H2 absorption process in Pd alloys,
partial oxidation of CH4, and CO2 hydrogenation reactions on catalyst surfaces.
2) Development of picosecond time-resolved AP-XPS system
We have developed the picosecond time-resolved AP-XPS system that combined AP-XPS
with femtosecond optical laser. To match the repetition rate of soft X-ray with that of opticallaser, the soft X-ray chopper was installed at the beamline. The photodiode mounted on an XYZ
stage was newly introduced to an analysis chamber to determine time zero in a pump-probe
delay time. On a p-type Si(100) substrate covered with natural oxide (SiO2/p-Si(100)), temporalvariation of Si 2p XPS peak energy due to surface photovoltage effect was observed both inultrahigh vacuum and in CO2 gas atmosphere. Furthermore, we succeeded in observing thephotoexcitation dynamics on -Fe2O3(0001) surface in a water vapor gas atmosphere.
REFERENCES[1]
S. Yamamoto et al., Synchrotron Radiat. News 35, 19-25 (2022).
[2]
S. Yamamoto et al., Journal of the Japanese Society for Synchrotron Radiation
Research 35, 182-190 (2022). (in Japanese)

DEVELOPMENT OF SOFT X-RAY MICROSCOPY SYSTEM AND
ITS APPLICATION TO MEASUREMENT OF MAMMALIAN CELLS
Yoko TAKEO,1,2 Kai SAKURAI,3 Noboru FURUYA,3 Kyota YOSHINAGA,3
Takenori SHIMAMURA,4 Satoru EGAWA,4 Hisao KIUCHI,1 Hidekazu MIMURA,4
Haruhiko OHASHI,2 Yoshihisa HARADA,1 Mari SHIMURA,5,6 and Takashi KIMURA1
1

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

Japan Synchrotron Radiation Research Institute3

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

4

Department of Precision Engineering, School of Engineering, The University of Tokyo
5

RIKEN, SPring-8 Center

6

Research Institute, National Center for Global Health and Medicine

X-ray microscopy has a wide range of applications in science due to its high spatial
resolution and variety of analytical techniques. Ptychography provides a particularly highspatial resolution by reconstructing the sample image using phase recovery calculations[1, 2].
The combination of ptychography and spectroscopy in the soft X-ray region is promising forinvestigating samples with light-element-rich heterogeneous structures. For example, in the
combination of soft X-ray ptychography with X-ray absorption spectroscopy, mapping thechemical state of magnetic nanoparticles in bacteria[3] and the visualization of the cathodedegradation mechanism of the lithium-ion batteries[4] have been demonstrated.
Ptychography, a lensless imaging technique, has rapidly developed over the past decade. By
reconstructing sample images from multiple coherent diffraction patterns using iterative phaseretrieval algorithms, it is possible to obtain high spatial resolution images that are not affectedby the performance of X-ray optics, such as fabrication accuracy. In addition, the phaseretrieval of coherent diffraction patterns allows the acquisition of both conventional
absorption images and phase images, which is a significant advantage when measuring
samples with high X-ray transmittance, such as biological cells.
Combining ptychography-based imaging with X-ray fluorescence analysis allows forinvestigating the correlation between microstructure and element distribution. In the soft
X-ray region, ptychography and X-ray fluorescence microscopy systems have been developed
using zone plates as illumination optics. Previous results have demonstrated their usefulness,such as the visualization of the chemical state of lithium-ion battery materials and the internal
microstructures of magneto bacteria and mammalian cells. Although zone-plate-based opticalsystems offer the advantages of simplicity and small focus size, they also suffer fromproblems such as chromatic aberration and short working distances. Illumination optics using
total reflection X-ray mirrors have excellent features, such as long working distances, suitablefor developing instruments combined with detectors for X-ray photography and X-ray
fluorescence analysis. In addition, total reflection mirrors are achromatic, so changing the
X-ray wavelength does not affect the focusing properties and are thus well-suited forwavelength scans without the need to readjust the optical system.
In this study, we developed a new soft X-ray microscopic imaging system that combines
soft X-ray ptychography and an X-ray fluorescence microscope, using an optical illumination
system based on a total reflection Wolter mirror[7]. Figure 1 shows the Shematic illustrationof the system called CARROT (Coherent Achromatic Rotational Reflective Optics for
pTychography.).We measured mammalian cells as samples and visualized the internal
structure with soft X-rays by the absorption and phase shift. We successfully captured
sub-micrometer-scale subtle changes in cellular structure due to drug administration by taking
advantage of the high-resolution images provided by ptychography (Figure 2). Furthermore,we demonstrated that it is possible to map the elemental distribution inside the cells using
X-ray fluorescence by seamlessly changing the irradiation wavelength from the ptychographymeasurement. We find a correlation between the internal structure and the elemental
distribution inside the cells.

Figure 1 Schematic illustration of the CARROT system. (a) The overall structure inside thevacuum chamber. (b) Ptychography measurement mode. (c) X-ray fluorescence imaging
mode.

Figure 2 Soft X-ray ptychography measurement of HepG2 cells (DMSO treated).
Reconstructed absorption (a) and phase shift (b) images. The magnified images shown in
the right panels corresponding to the dotted colored rectangles shown in (a).
REFERENCES[1] A. M. Maiden, J. M. Rodenburg, Ultramicroscopy, 109 (10), 1256 (2009).
[2] P. Thibault, et al., Science, 321, 379 (2008).
[3] X. Zhu, et al. Proc. Natl. Acad. Sci. , 113 (51) E8219 (2016).
[4] T. Sun, et al., ACS Nano, 15, 1475 (2021).
[5] Y. Takeo, et al., Appl. Phys. Lett. 117, 151104 (2020)[6] T. Kimura, et al., Opt. Express, 30(15), 26220 (2022).
[7] Y. Takeo, et al., J. Electron Spectrosc. Relat. Phenom., accepted.

CHANGES OF INTRACELLULAR STRUCTURES BY SOFT X-RAY
MICROSCOPY SYSTEM OF CT-PTYCHOGRAPHYMari Shimura,1,2 Yoko Takeo,3,4 Kai Sakurai,5Haruhiko OHASHI,4,1 Hidekazu Mimura,6 and Takashi Kimura,3
1

RIKEN, SPring-8 Center
National Center for Global Health and Medicine
3
The Institute for Solid State Physics, The University of Tokyo,
4
Japan Synchrotron Radiation Research Institute5
Department of Applied Physics, School of Engineering, The University of Tokyo
6
Department of Precision Engineering, School of Engineering, The University of Tokyo2

We had been applied biological samples such as culture cells and medical samples usingsynchrotron hard x-ray by establishing a scanning x-ray fluorescence microscopy (SXFM)
since more than 15 years ago and figured out much evidence that synchrotron x-ray has apotential ability that we have never seen with visible light and electron microscopies [1, 2].
Imaging proteins has been well developed and established in biological and medical fields byvisible light microscopies with a labelling technology such as fluorescence; however,synchrotron x-ray microscopy reminds us of a different point of view that proteins are just apart of the cellular contents. In these days, we could obtain an opportunity to apply soft x-ray
microscopy system of ptychography with x-ray absorption spectroscopy established at
BL07LSU to biological samples [3].
In this study, we prepared a common SiN basement which is available for both SXFM at
BL29XU and CARROT at BL07LSU [3]. So that we could observe the same biologicalsamples with hard and soft x-ray fluorescence and ptychography with X-ray absorption
spectroscopy in near future. We prepared HepG2 cells, a cell line derived from humanhepatoma, treated with or without a newly developed antiretroviral drug, GRL-142 [4].
GRL-142 is a HIV protease inhibitor, which often showed a severe side effect ofhyperlipidaemia. Therefore, we expected lipid droplets in cells treated with a high dose of
GRL-142. Cells were chemically fixed with 2% paraformaldehyde in PBS and air-dried. In
fact, we found increased size and number of lipid droplet-like structures in cytoplasm of thecells with GRL-142, comparing to untreated control cells, which we could hardly see thedroplets by visible light microscopies without staining. Notably, we found increase the gap
between nucleus and cytoplasm, and higher contrast at nucleus of the cells treated with
GRL-142, which we have never seen with visible light microscopies. Higher contrast at
nucleus suggested the possibility of increased the width of nucleus and/or the contents due toa stress response with a drug. It is known that cells change the width and hardness dependingon the cell cycle, and chromosomes become compact against irradiation to protect them. On
the other hand, we have no idea about an increased gap between nucleus and cytoplasm,
although this gap may be also related to stress response by the drug. It is quite essential tofigure out the molecular mechanisms of these cellular changes in near future. These changes
we observed by ptychography were submitted to the article [5].
REFERENCES[1] A. Fukunaka, et al., Scientific Report. 2023; doi: 10.1038/s41598-023-30498-y. [2] S. Matsuyama, et al.,JAAS 35, 1279, 2020: doi.org/10.1039/D0JA00128G. [3] T. Kimura, et al., Opt. Express, Optics Express 30,
2022: doi: 10.1364/OE.462190. [4] H. Bulut, et al,. Scientific Report 10, 10664, 2020. [5] Y. Takeo, et al.,JESRP, under revision.

ORBITAL CONVERSION IN COFE/CU/OXIDE
Junyeon KIM
Center for Emergent Matter Science, RIKENIntroduction
Orbital angular moment (OAM) transport opens an emerging mechanism for the spin
manipulation. Particularly, a recent experimental report presents the OAM-induced spin
manipulation in CoFe/Cu/Al2O3 stacks is much more efficient than that by conventional
mechanisms [1]. In the CoFe/Cu/Al2O3 stacks, nonzero OAM is polarized at the Cu/Al2O3
interface (Fig. 1(a)), and exerts torque when OAM is transferred to the CoFe layer. This talkis called orbital torque (Fig. 1(b)). Nowadays, the orbital torque greatly draws interest for the
spin accumulation since there is no clear restrictions on materials for the nonzero OAM
generation. It is apparently contrast to the spin angular momentum generation which is mainly
shown in material systems consisted of heavy elements.
A recent theoretical study reports that the orbital hybridization between the p-orbital ofoxygen atom and the d-orbital atom serves the formation of a chiral orbital texture by orbital
Rashba effect (Fig. 1(a)) [2]. Indeed, we recently observed very large orbital torque even if
we replace Al2O3 to other oxides such as MgO, SiO2 and TiO2 [3]. Particularly, orbital torqueis maximum when the Oxide is SiO2, and minium when the Oxide is Al2O3. For further
understand on the nonzero OAM generation at the Cu/Oxide interface, we require detailed
material characterization. Also observation of a modulation of the energy spectrum by ageneration of nonzero OAM is also desired.

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

Experimental method
For the observation of the Cu/Oxide interface, L-edge X-ray absorption spectroscopy (XAS)and X-ray magnetic circular dichroism (XMCD) was utilized. Nominally, the 3d orbital stateof Cu is known to be fully occupied. However Grioni et al. claimed that there is stillunoccupied 3d orbital state for Cu due to a hybridization between s state and d states [4]. And
the number of unoccupied 3d orbital state can be promoted by formations of compounds suchas CuOx. Thus we could expect the L2, 3 edge X-ray absorption.
As a first, we attempt to obtain the energy spectrum nearby the Cu/Oxide interface. Next,
we also attempt to obtain a clue of the nonzero OAM generation by turning on/off the charge
current.
The observation was performed in superconducting magnet magneto-optical observation
system in the free board. The CoFe/Cu/Oxide stacks are electronically connected by the silver
paste. And the observation was carried out by high speed switching of the circularly polarizedlight and total electron yield (TEY) technique. To optimize the sample condition, 2, 5, 7, 10
nm of Al2O3 was tested considering with the detection length of the TEY technique (~10 nm).
Experimental results and discussion
Figure 2 displays the XAS spectra for the Al2O3, SiO2, and TiO2 samples. The XAS
spectrum for the Al2O3 sample confirms the presence of only metallic Cu at the Cu/Al2O3
interface (Fig. 2(a)). On the other hand, we observe the formation of Cu oxide (CuO or Cu 2O)
at the Cu/Oxide interface in the XAS spectrum for the SiO2 (Fig. 2(b)), and TiO2 sample (Fig.
2(c)). We speculate that the released oxygen atoms could form Cu oxides among the larger
pool of released oxygen atoms. Considering the orbital torque is large in order of SiO2, TiO2,
and Al2O3 capped sample, the XAS spectra support the interatomic interaction between Cu
and oxygen atoms promotes the OAM polarization at the Cu/Oxide interface.

Fig. 2 (a), (b), (c) XAS spectrum for the Al2O3 sample (a), SiO2 (b), and TiO2 (c) samples. Guide lines for(b) and (c) represents the position of peak for CuO (left) and Cu 2O (right).

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

OPERANDO X-RAY CIRCULAR DICHROISM MEASUREMENT FOR
DETECTION OF ORBITAL EDELSTEIN EFFECT
Masafumi Horio1, Tomoaki Senoo1, Junyeon Kim1, Yoshichika Otani1, Iwao Matsuda1
1

The Institute for Solid State Physics, The University of Tokyo

In order to meet the demands of the information society in recent years, increasing theperformance of computing devices has become an important issue. Spintronics is astate-of-the-art technology that exploits the spin of electrons, and advances have been made inthis field through research that enables high-performance manipulation of magnetism. Amongthese, research on spin-orbit torque (SOT) [1-3] has attracted much attention due to its
scientific interest and technological applications. This technique utilizes spin transportphenomena, such as the spin Hall effect (SHE) and the Edelstein effect (EE), to inject spin
into magnetic materials. These phenomena occur in systems with strong spin-orbit interaction
and require heavy elements, which are rare and typically expensive. However, recent studies
have reported torque generation in systems without heavy elements [4,5]. It was claimed thatthe experimental results can be explained by a recently proposed interfacial transportphenomenon called the orbital Edelstein effect [OEE, Fig. 1(a)]. This discovery opened theway to new techniques and increased interest in the study of spin transport phenomena atinterfaces. However, no direct experimental evidence of OEE has been obtained. This isbecause experimental information about electronic states at interfaces has not yet been
provided.
In the present study, we focused on the interface between Cu and SiO2 where accumulationof orbital angular momentum (OAM) due to the OEE is expected [5]. We performed x-ray
circular dichroism (XCD) measurements at SPring-8 BL07LSU under electric current. In
order to detect accumulation of OAM, electric current was applied perpendicularly to theincident x-rays. The measurements were conducted at room temperature in the partial electron
yield mode. Detailed sample structure and experimental condition are illustrated in Figs. 1(b)and 1(c), respectively.
Figure 2(a) shows Cu L-edge spectra under various current values. While there appear
significant changes in the spectral line shape, the influence of electric current cannot be
separated from gradual temporal changes confirmed by performing measurements repeatedly
in the same condition [Fig. 2(b)]. The “contamination” from this temporal change by x-ray
irradiation is inevitable if one makes a full energy scan across the Cu L-edge, which takes ~30
minutes. In order to extract genuine effects of current application, we fixed the photon energy
at 934.5 eV and monitored absorption intensity for a short time (~several minutes) while
repeatedly turning on and off electric current. Figures 2(c) and 2(d) show the results of suchmeasurements performed with left and right circular polarization (LCP and RCP). In bothmeasurements, decrease of absorption intensity was observed due to the generation ofFig. 1: Experimental setups. (a) Schematic illustration of OEE. (b) Sample structure. (c)Geometry of XCD measurements.

magnetic field that traps electrons and moves them back to the sample. Comparing themagnitude of the intensity decrease between the measurements conducted with right and left
circular polarization, we found larger decrease for RCP. According to the sum rule of x-ray
magnetic circular dichroism, this is consistent with expectation from OEE shown in Fig. 1(a)Utilization of fast polarization switching that has been developed at SPring-8 BL07LSU [6]may pave the way for further clarifying the effect of electric current and eventually proving
the occurrence of OEE.

Fig. 2: XCD results on the Cu/SiO2 sample. (a) Cu L-edge spectra measured under electric
current as indicated. (b) Cu L-edge spectra measured repeatedly. (c),(d) Absorption
intensity as a function of time measured at the photon energy of 934.5 eV with LCP and
RCP. Sharp decrease is observed upon application of electric current. (e) Magnitude ofintensity decrease for LCP and RCP.

REFERENCES[1] I. M. Miron et al., Nature 476, 189 (2011).
[2] L. Liu et al., Science 336, 555 (2012).
[3] A. Manchon et al., Rev. Mod. Phys. 91, 035004 (2019).
[4] H. An et al., Nat. Commun. 7, 13069 (2016).
[5] J. Kim et al., Phys. Rev. B 103, L020407 (2021).
[6] J. Miyawaki et al., AAPPS Bulletin 31, 1-24 (2021).

XPS ANALYSES OF THE NOVEL SURFACE PHASES, GROWN BY
BORON DEPOSITION ON A COPPER CRYSTAL SURFACE
Yuki Tsujikawa, Xiaoni Zhang, Masafumi Horio, Tetsuya Wada, Masashige Miyamoto,Toshihide Sumi, Fumio Komori, Iwao Matsuda
Institute for Solid State Physics, The University of Tokyo

Takahiro Kondo
Department of Materials Science and Tsukuba Research Center for Energy Materials Science, Facultyof Pure and Applied Sciences and R&D Center for Zero CO2 Emission with Functional Materials,
University of Tsukuba

In a history of surface science, a numerous number of the ordered phases were observed atvarious crystal surfaces, depending on adsorbate elements, coverages, or growth conditions.
Recently, there have been growing interests in chemistry and physics of boron polymorphs or
metal borides on surfaces due to unique multi-center bonding between boron atoms [1]. On thewell-known Cu(111) substrate, the 2D ordered phase, √73×√39, is prepared by boron
deposition [2]. Structure analysis by the diffraction method unveiled that a 2D Cu-B compound,Cu boride is formed at the surface [3]. On the other hand, by the boron deposition on Cu(110),
we discovered a 1D anisotropic ordered phase, 3×1, as a pattern of electron diffraction [4].
These novel B/Cu surface phases are intriguing playgrounds to explore the electronic or
chemical states of these elements at the interface. In the present research, we conducted
experiments of high-resolution X-ray photoelectron spectroscopy to confirm the electronic
structure of these B/Cu .
The XPS measurement wasmade at the soft X-ray beamline
BL07LSU of the synchrotron
radiation facility SPring-8 withthe electron analyzer (Phoibos150 NAP, Specs Co.). All thedata were obtained at room
temperature. A sample wasprepared on the surface ofcommercial crystals of Cu(110)and Cu(111). The surface
phases was prepared by boron
deposition on a clean surface ofCu(110) or Cu(111). The
orderedstructures
wereexamined by observations of Figure 1 XPS spectra of the ordered surface phases of
B/Cu(110) and B/Cu(111), taken at photon energy of h𝜈𝜈 =low energy electron diffraction
1050 eV. Peaks of the B and Cu core-levels are indicated(LEED), while the chemicalwith black and white arrows, respectively. Signals of Auger
states were investigated by electron spectroscopy (AES) are shown for Cu by gray bars.
XPS. As shown in Fig.1, only
signals of B and Cu were observed, confirming no detectable impurity.
Figure 2 shows XPS spectra of the Cu 2p3/2 and B 1s core level of the √73 ×√39B/Cu(111) surface. The sample has two Cu components of the surface layer (L) and in the bulk(Bu), while a clean Cu(111) surface is composed of a single component besides the negligible
defect remanent. The (L) component can be identify as the surface Cu atom in Cu boride. In
contrast, the B 1s spectrum of the √73×√39-B/Cu(111) surface has a single component. The
binding energy of 187.8 eV, determined from curve fitting, indicates that the boron atoms arenegatively charged [3]. It is likely thatelectrons were transferred to the boron
atoms from the surrounding copper.
The surface phase of the 3×1B/Cu(110) was discovered by us at theSPring-8 beamline, BL07LSU, by LEED[4]. The XPS spectrum of the Cu 2𝑝𝑝3∕2
core-level, as measured in situ, is curvefitted with two components, as shown in
Fig.3. In addition to the peak (Bu),ascribed to the clean Cu(110) surface, a
new component, labelled (L), can be Fig.2 XPS spectra of the √73×√39-B surface
found. Since the Cu atom in the bulk phase on Cu(111): (a) Cu 2𝑝𝑝3∕/2 and (b) B 1𝑠𝑠 corecrystal (Bu) has neutral charge, the peak level. Photon energies were (a) h𝜈𝜈 = 1050 eV andposition of the L component at the higher (b) h𝜈𝜈 = 285 eV. For a reference, a spectrum of
the clean Cu(111) surface is shown. The peakbinding energy indicates that the Cu
components are obtained by the curve-fits andatoms in the 2D phase are positively labeled with different symbols.
charged. On the other hand, the B 1𝑠𝑠
core-level spectrum can be curve-fitted
by two components, labelled I and II. The
major component (I) is naturally
assigned to the 3 × 1-B/Cu(110) surface,
while the minor component (II) can be
ascribed to either a part of the surface
phase or the other contributions, such as
surface impurities. By a comparison with
Fig.2, binding energy of the component(I) at 187.4 eV indicates that the boron
atoms in the 3 × 1-B phase are also Fig.3 XPS spectra of the 3×1-B surface phase on
negatively charged. The similarity with Cu(110): (a) Cu 2𝑝𝑝3∕/2 and (b) B 1𝑠𝑠 core-level.
√73×√39-B/Cu(111) result suggest that Photon energies were (a) h𝜈𝜈 = 1050 eV and (b) h𝜈𝜈
the 3 × 1-B/Cu(110) phase are also a 2D = 285 eV. For a reference, a spectrum of the cleanCu(110) surface is shown. The peak components
Cu-B compound.
are obtained by the curve-fits and labeled with
In conclusion, we found that the different symbols.
boron atoms were negatively charged in
the surface phases of √73×√39B/Cu(111) and 3×1-B/Cu(110). The unique electronic property has also been known in theprevious research of 2D boron or borophene [1]. The layer itself is unstable in the free-standing
form but stable on a 2D metal substrate after electron doping. These microscopic findings
indicate that low-dimensional boron structures on surfaces likely have the universal
electrophilic property.
REFERENCES[1] I. Matsuda, K. Wu ed., 2D Boron: Boraphene,Borophene, Boronene (Springer, 2021).
[2] R. Wu, I. K. Drozdov, S. Eltinge, P. Zahl, S. Ismall-Belgl, I. Božović, and A. Gozar, Nat. Nanotech. 14, 44(2019).
[3] Y. Tsujikawa, M. Horio, X. Zhang, T. Senoo, T. Nakashima, Y. Ando, T. Ozaki, I. Mochizuki, K. Wada, T.
Hyodo, T. Iimori, F. Komori, T. Kondo, I. Matsuda, Phys. Rev. B 106, 205406 (2022).
[4] Y. Tsujikawa, X. Zhang, M. Horio, T. Wada, M. Miyamoto, T. Sumi, F. Komori, T. Kondo, I. Matsuda, Surf.
Sci. 732, 122282 (2023).

ELECTRONIC STRUCTURE OF WATER CONFINED IN AQUEOUS
MICROPHASE TWO-PHASE SYSTEMS
Yuji Higaki, Takumi Masuda
Faculty of Science and Technology, Oita University

Introduction
A large number of studies for the irregular structure and dynamics of water confined in
nanometer scale molecular assembly including reverse micelles, and recently, metal-organic
frameworks, carbon nanotubes, and polymer brushes.[1,2] Water molecules involved inhydration of ions experience constraints which prevent the formation of the preferred
tetrahedral configurations characteristic of bulk water to cause hydrogen-bonding distortion.
The hydrogen-bonding state of water has been studied by spectroscopic methods such as
infrared spectroscopy, sum frequency generation spectroscopy, and solid-state NMR
measurements. Soft X-ray absorption (XAS) and soft X-ray emission (XES) spectroscopies
have recently attracted attention for their ability to show the detailed hydrogen bonding
configurations from the electronic structures of the oxygen responsible for the hydrogenbonds.[3]We developed a new class aqueous phase separation system of double hydrophilic block
copolymers.[4] Double hydrophilic block copolymers comprising two kinds of zwitterionicpolymers, poly(carboxybetaine methacrylate) (PCB2) and poly(sulfobetaine methacrylate)(PSB4), exhibits microphase separation in the highly concentrated aqueous solution to produce
a highly ordered periodic lattice structure with nanometre scale compartments, and themorphology transforms in response to the polymer concentration (Figure 1). This morphology
transition is manifested by selective water partitioning to the PCB2 phase owing to the poor
water capacity of PSB4 phase. The double hydrophilic microphase-separated structure
involving hydration water could be a good prototype for investigating the structure anddynamics of water confined in the fields with crowded charged polymers.
In this study, hydrogen bonding configurations of waters confined in the microphaseseparated zwitterionic mesophases were
investigated by meas of XAS and XES
spectroscopies. Systematic experiments
were conducted by adjusting the polymer
concentration in the microphase-separated
structure to address the impact of
microphase separation at the electronic
structure level and to elucidate detailed
Figure 1. Chemical structure of the PCB2112-b-PSB4106
information on the hydrogen bonding form
block copolymer and the schematic of morphologies.
and its role in microphase separation.
Experiment
PCB2112 (Mn = 24400, Mw/Mn = 1.12), PSB4102 (Mn = 30200, Mw/Mn = 1.10), and the diblock
copolymer PCB2112-b-PSB4106 (Mn = 54000, Mw/Mn = 1.19, , volume fraction of PCB2 = 0.41)
were synthesized by reversible addition fragmentation chain transfer polymerization. The
molecular mass and molecular mass distribution were well-controlled. The PCB2112-b-PSB4106
diblock copolymer aqueous solution produces microphase separated structure with lamellar
morphology, where the long period was 46.2 nm and the PCB2 lamellar thickness was 28.0 nm,
at polymer concentration (f) = 40wt%, while the morphology transforms to columnar
morphology with hexagonally packed cylindrical domains, where the cylinder radius is 13.2
nm and the cylinder center distance is 52 nm at f = 20wt%.
XES and XAS measurements were conducted at the BL07LSU HORNET station at Spring-8
employing home-made liquid cell (Figure 2). The aqueous solution of PCB2-b-PSB4 diblockcopolymers were put onto the SiC membrane separating
vacuum chamber, and the cell was sealed with a screw
cap. Milli-Q water (Millipore Inc., Billerica, MA) with aresistance of >18 MΩ cm was used as the water source.
The excitation energy was 550 eV, which is well above
the ionization threshold. Each XES spectrum was
normalized with the integration of the intensity between
515 and 530 eV to compare the spectrum shape.
Figure 2. Schematic representation of
Results and Discussion
the experimental setup for the XES
The hydrogen-bonding structure configurations ofspectroscopy of water confined in thewater confined in microphases were investigated by O 1s
microphase separated PCB2112-bXES spectroscopy. XES spectra of the PCB2112-bPSB4106 aqueous solutions.
PSB4106 aqueous solutions exhibited two peaks at
525.8 eV and 526.7 eV, which have been assigned tothe oxygen of water with distorted and tetrahedralhydrogen bonding configurations, respectively(Figure 3(a)).[4] In comparison with the XES
spectrum of bulk water, the 1b1” peak intensity was
pronounced with respect to 1b1’ peak, indicating thesignificant hydrogen-bonding distortion in the water
confined in the zwitterionic polymer mesophase.
Meanwhile, the XES spectrum shape was independentof the f. This result suggests that the hydrogenbonding distortion remains identical with decreasing
the zwitterionic PCB2112-b-PSB4106 concentrations.
Since the PSB4 phase has water capacity limit atapproximately 50wt%, the PCB2 phase contains Figure 3. XES spectrum of (a) PCB2 -b112
relatively more water and its polymer concentration PSB4106 aqueous solutions with f = 40wt%
can be estimated to 32.2, 20.2, and 11.6wt% when the (black), 30wt% (red), and 20wt% (blue),
block copolymer concentrations are 40, 30, 20wt%, and (b) PCB2112 aqueous solutions with f
respectively. Thus, the hydrogen-bonding state of = 40wt% (yellow) and 10wt% (purple),water in the mesoscopic phase-separated structures of and a PSB4102 aqueous solution with f =(blue). The additional panels show
lamellar structure with 50wt% PSB4 and 32.2wt% 40wt%
magnified data at 1b1’ and 1b1’’ peaks.
PCB2 phases, and the columnar structure with 50wt%
PSB4 cylindrical domains and 11.6wt% PCB2 matrix were identically distorted.
We then verified the hydrogen bonding configuration of water in PCB2 and PSB4 solutions(Figure 3(b)). The 40wt% PCB2 and 40wt% PSB4 aqueous solutions showed the XES spectra
comparable to PCB2112-b-PSB4106 solutions. On the other hand, the 10wt% PCB2 solutions
showed a slight increase in the intensity of 1b’ peak relative to the 1b”, while the spectrum is
identical to that of bulk water. Thus, the water molecules in the PCB2 phase of the microphaseseparated 20wt% PCB2112-b-PSB4106 solution are perturbed relative to those in PCB2 solutions,probably because of the obstruction of hydrogen bonding network due to the phase boundary.

REFERENCES[1] M. A. Wells, Biochemistry 1974, 13, 4937–4942.
[2] K. Yamazoe, Y. Higaki, Y. Inutsuka, J. Miyawaki, A. Takahara, Y. Harada, Langmuir 2022, 38,
3076.
[3] T. Tokushima, Y. Harada, O. Takahashi, Y. Senba, H. Ohashi, L. G. M. Pettersson, A. Nilsson, S.
Shin, Chem. Phys. Lett. 2008, 460, 387.
[4] Y. Higaki, M. Takahashi, T. Masuda, Macromol. Chem. Phys. 2022, 224, 2200416.

SOFT X-RAY EMISSION SPECTROSCOPIC ANALYSIS OF 1D
WATER CHANNEL WITHIN A NONCOVALENT POROUS CRYSTAL
1

Shinnosuke HORIUCHI,1,2 Shota OGURA,1 Yuka IKEMOTO,3 Hisao KIUCHI,4 Kazuo
TATSUTA,4 Yusuke TOMIYORI,4 Yoshihisa HARADA4
Division of Chemistry and Materials Science, Graduate School of Engineering, Nagasaki University
2

Department of Basic Science, Graduate School of Arts and Sciences, The University of Tokyo
3

4

Spectroscopy Division, Japan Synchrotron Radiation Research InstituteSynchrotron Radiation Laboratory, The Institute for Solid State Physics, The University of Tokyo

Water molecules on material interfaces play crucial roles in abundant natural phenomena andmaterial sciences [1,2]. Although the importance of interfacial water has been recognized, it isstill challenging to elucidate a three-dimensional alignment of water clusters and the hydrogenbonding network on a non-flat material surface in an atomic resolution. Recently, X-ray
diffraction studies using crystalline porous materials can visualize not only the absoluteconfiguration of small molecules but clustering motifs of the guests on the pore surface [3–5].
In addition, X-ray emission spectroscopy (XES) is one of the useful techniques to probe
electronic transitions between core and valence orbitals of oxygen atoms, which can provide
useful information reflected from the hydrogen-bonding states of water molecules, because thetime scale of the excitation process and the O1s core-hole lifetime in femtoseconds are much
shorter than that related to rearrangements of the hydrogen-bonding network [6]. Thus, thecombination of these techniques will provide a clear relationship between a structure and its
character of a water cluster formed on the pore surface of the crystalline material.
We have recently synthesized a supramolecular crystal composed of coordination complex
salts and macrocyclic organic hosts (Figure 1). The supramolecular crystal contained onedimensional (1D) water channels in the crystal lattice, where the molecular alignments of thewater molecules can be determined by the single crystal X-ray diffraction analysis. In particular,
the large water cluster and its
temperature-dependent
dynamic
character were observed in the Xray analysis. This result suggeststhat this supramolecular crystal
containing 1D water channels is asuitable material for elucidating theinhomogeneous nature of interfacial
water molecules. Thus, forunveiling the electronic structure of
the water molecules in the 1D pore,
we performed the soft X-ray Figure 1. Crystal structures of the supramolecular crystal viewed
emission spectroscopic analysis of from a) the top and b) the side of the 1D water channels. Red
the 1D water channels within the spheres represent oxygen atoms of the water molecules in the pore.
supramolecular crystal.
The supramolecular crystal contains hydroxy (–OH) groups in the framework. Thus, thedehydration process of the crystal was investigated by the O1s XES measurement to eliminate
the effect of the framework. The XES measurement was performed using the SPring-8
BL07LSU ultra-high resolution soft X-ray emission spectrometer HORNET. During themeasurement, a steam-nitrogen gas mixture flowed over the sample, enabling precise controlof humidity around the sample and the dehydration rate. The intensities of the XES spectra
during the dehydration process were summarized in Figure 2a. The intensity of the spectra

gradually decreased and was mostly constant after 400 min. This result indicates that thedehydration process was completed at 400 min and the spectra after 400 min are derived fromthe hydroxy groups in the framework. Thus, the XES spectra of the water molecules in the 1D
pore of the supramolecular crystal were obtained from the difference spectra using the averaged
spectra recorded from 600 to 745 min as a background spectrum. As a result, the difference
spectrum showed characteristic features of water molecules, which involved four peaks
assigned to 1b1”, 1b1’, 3a1, and 1b2, respectively (Figure 2b). In general, the XES spectrum ofbulk liquid water consists of the four peaks corresponding to oxygen 2p orbitals of water, which
are obtained by the emitted X-ray associated with the electronic transition from the valence
state to the core level. These spectral features can be associated with two distinct structural
motifs in liquid water, where the 1b1’ peak at 525.8 eV and the 1b1” peak at 526.7 eV correspondto fourfold icelike hydrogen-bonds and less than fourfold highly distorted hydrogen-bonds,
respectively (Figure 2c). The relative intensities of the two 1b1 peaks are dependent on themeasurement conditions, which will provide spectroscopic aspects for the hydrogen bonding ofwater molecules in the 1D pore. Intriguingly, the intensity of 1b1” at 526.7 eV was higher thanthat of 1b1’ at 525.8 eV. This result strongly suggests that the structure of water molecules in
the 1D pore is mainly less than fourfold highly distorted hydrogen-bonds even at ambientconditions, rather than fourfold icelike hydrogen-bonds. Variable-temperature X-ray diffraction
studies revealed that the water molecules in the 1D pore showed temperature-sensitive anddynamic characteristics. Thus, these XES results clearly explained the flexible character of thehydrogen-bonding network of the water molecules in the supramolecular crystal.

Figure 2. a) Emission intensities of the XES spectra. b) The O1s X-ray emission spectra of bulk liquid water (blueline) and H2O molecules in the 1D pore (black line). c) Molecular structures of fourfold icelike hydrogen-bonds(upper) and less than fourfold highly distorted hydrogen-bonds (bottom) of water molecules.

In summary, O1s XES spectra of water molecules in the supramolecular crystal were obtainedby following the dehydration process of the crystal. The XES spectra indicated that the crystal
contained weakly hydrogen-bonded waters in the 1D channel, which is well-reflected with the
dynamic character of water molecules observed in the X-ray crystallographic study. This
combination study provides a clear relationship between the hydrogen-bonded structure andtemperature-sensitive and dynamic characteristics of the interfacial water molecules.
REFERENCES[1] Björneholm, O. et al. Chem. Rev. 116, 7698 (2016).
[2] Brini, E. et al. Chem. Rev. 117, 12385 (2017).
[3] Inokuma, Y. et al. Nature 495, 461 (2013).
[4] R. Kubota, Nat. Chem 6, 913 (2014).
[5] Hanikel, N. et al. Science 374, 454 (2021).
[6] Fransson, T. et al. Chem. Rev. 116, 7551 (2016).

Electronic states analysis of oxygen evolution reaction catalyst for alkaline
water electrolysis by Operando soft X-ray absorption/emission
spectroscopy
Kazuo Tatsutaa*, Jun Kikumab, Shinya Matsunob, Shin Kawashimab, Hisao Kiuchia, andYoshihisa Haradaaa
The Institute for Solid State Physics, the University of Tokyo, bAsahi Kasei Corporation*Current affiliation: Asahi Kasei Corporation
In improving the efficiency of hydrogen generation by water electrolysis, there are two
important factors: one is to reduce the voltage above the theoretical electrolysis voltage thatmust be applied for the electrolytic reaction (overvoltage), and the other is to suppress theincrease in overvoltage due to catalyst degradation. Various electrocatalysts have beendeveloped to solve these problems. Perovskite-type oxides acting as anode catalysts have awide range of elemental choices, among them, LaNiO3 is particularly promising in thenext-generation alkaline water electrolysis system because of its high electrical conductivity
and stable oxygen evolution reaction (OER) in the alkaline electrolyte. Our previous studies
have confirmed that the addition of a small amount of transition metal elements to LaNiO3
can suppress catalyst degradation for a long time, however little difference was found by hard
X-ray absorption spectroscopy (XAS) of Ni, and the correlation between durability during
operation and the chemical stability of Ni could not be found. On the other hand, the use ofsoft X-ray emission spectroscopy (XES), which can directly observe the strength of orbital
hybridization and charge transfer energy expected to clarify the correlation between durability
and the chemical state of Ni. Therefore, in this study, we worked on the development of atechnique to perform Ni-L edge XES measurements of LaNiO3 under alkaline waterelectrolysis operando conditions, with the aim of providing feedback for further anodematerial optimization.
The cell for Operando measurement was based on the liquid cell developed by Tokushima etal.[1], and was modified to enable water electrolysis in a three-electrode system by inserting
contact probes for the reference electrode (RE), counter electrode (CE), and working
electrode (WE). A screw-in Ag/AgCl RE was screwed directly into the cell. A 0.5 mm
diameter Pt wire was used as CE, inserted into the electrolyte channel in the cell, and theinsertion opening was sealed with epoxy resin. The membrane with 150 nm thick Si3N4
window with LaNiO3 and Au/Ti layers was used as WE. The cell was fabricated with acrylic
resin using a 3D printer. A 20% KOH solution was used as the electrolyte, and the flow rate
was 10 ml/min during Operand measurement.
All measurements described below were performed on the beamline BL07LSU at SPring-8.
Before Operando measurement, ex-situ Ni-L edge XAS and XES measurements were carriedout on LaNiO3 surface. The samples for Operando measurement were previously energized at
0.55 V, which is the OER potential, for 6 hours to confirm that the OER activity was enhanced.
Before XES measurements, XAS measurements were performed. For Operando Ni-L edge
XAS measurements, applied potentials were 0.35 V (before OER), 0.57 V (during OER), andthe open circuit potential, and performed at several different points on the Si3N4 window toprevent damage to the window by X-rays. For Operando Ni-L edge XES measurements, theexcitation energies were set to 853.2 eV. To prevent damage to the Si3N4 window caused by
X-ray irradiation, the irradiation positions were changed every 2 min, and the data wereobtained by integrating the spectra from all measurement positions. The applied potentials
were 0.35 V and 0.57 V.
The obtained XAS spectra were normalized to the peak intensity at 853 eV for the operando
measurement results, and the spectra obtained at multiple measurement positions werearranged by measurement potential and are shown in Figure 1 together with the ex-situ
measurement results. The peak at 850.6 eV is an absorption peak of La-M4. The spectral
shape obtained by ex-situ measurement was similar to that of LaNiO3 deposited by laser
deposition[2]. On the other hand, most of the spectral shapes obtained by the operando
measurement were significantly different from those by the ex-situ measurement, and theshapes differed depending on the measurement positions. The spectral shapes obtained fromthe operando measurements, characterized by a peak on the high energy side (~855eV) of
Ni-L3 that is significantly lower than the peak on the low energy side (~853eV), suggest thatthe catalyst layer exists as a compound with predominantly Ni2+ components[3]. This result
suggests that the catalyst layer has already changed to a chemical state different from that of
LaNiO3 during pre-energization. The large variations in spectral shape from position toposition did not allow us to determine the spectral change with potential.
The obtained XES spectra are shown in Figure 2 together with the results of ex-situ
measurement, normalized by the intensity of the main peak, where the abscissa axis isrepresented as energy transfer. The Operando measurements were integrated for about 5 hours,
but because the noise was very high in all cases, no characteristic structures other than themain peak around 1 eV could be identified, and the structural differences between the spectra
were also unclear, making it impossible to clarify changes due to electric potential.
In order to elucidate the cause of the variation of XAS spectra by measurement positions andthe large noise in XES spectra, cross-sectional SEM and TEM observations of the catalyst
layer on the Si3N4 window of the samples used for operando measurements were performed
and thickness variation of about 5 nm to 300 nm was observed. It is suggested that thevariation in thickness correlates with the variation in the chemical state of the catalyst layer
and is the cause of the variation in the shape of the XAS spectra. In addition, there are manythin regions, which may have resulted in insufficient intensity and increased noise in XES
spectra, in which the emission intensity was integrated by scanning over the window. These
results clearly indicate that improving the thickness uniformity of LaNiO3 on the Si3N4
window is a future challenge.

Fig.1 ex-situ and Operando Ni-L edge XAS spectra
Fig.2 ex-situ and Operando Ni-L3 edge
XES spectra obtained at excitation energyof 853.2 eV

REFERENCES[1] T. Tokushima, Y. Harada, Y. Horikawa, O. Takahashi, Y. Senba, H. Ohashi, L. G. M.
Pettersson, A. Nilsson, S. Shin, J. Electron Spectrosc. Relat. Phenom., 177 (2010) 192.
[2] M. Hepting, D. Li, C. J. Jia, H. Lu, E. Paris, et al., Nat. Mater., 19 (2020) 381.
[3] C. Tian, D. Nordlund, H. L. Xian, Y. Xu, Y. Liu, D. Sokaras, F. Lin, and M. M. Doeff, J.
Electrochem. Soc., 3 (2018) A696

ELECTRONIC STRUCTURE ANALYSIS OF OXYFLUORIDECATHODE OF ALL-SOLID-STATE FLUORIDE BATTERY USINGRESONANT INELASTIC X-RAY SCATTERING
Kentaro YAMAMOTO1,2, Datong ZHANG1, Hisao KIUCHI3, Yoshihisa HARADA3,
Yoshiharu UCHIMOTO1
1

2
3

Graduate School of Human and Environmental Studies, Kyoto University

Faculty of Engineering, Nara Women's University, Kitauoyanishimachi, Nara, 630-8263

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

All-solid-state fluoride-ion rechargeable batteries are expected to be high-power, high-energy
density rechargeable batteries because they can use multi-electron transfer reactions withmonovalent fluoride-ions as carriers. Until now, development of cathode materials has focusedon simple metal/metal fluoride (M/MFx) systems1,2. However, the absence of a diffusion pathfor F- during the fluorination and defluorination reactions and the large volume change
associated with the fluorination and defluorination reactions of the most densely packed metal
cathodes (such as Cu) have made it difficult to achieve the following rate characteristics. In thisstudy, we focused on Cu3N as a new cathode material to solve this problem, because Cu3N
cathode has many anion vacancy sites in its structure and is expected to show better ratecharacteristics than metal cathodes. The reaction mechanism was further elucidated by electron
spectroscopy.
Cu3N was synthesized by mixing Cu2O and CO(NH2)2 in the ratio of 1:2 mol, annealing at
190°C for 6 h, and washing and drying3. A bulk-type electrochemical cell was constructed with
Cu3N/La0.9Ba0.1F2.9/Vapor grown carbon fiber (VGCF) as a composite positive electrode,La0.9Ba0.1F2.9 as an electrolyte and Pb/PbF2/La0.9Ba0.1F2.9/VGCF as a composite negativeelectrode. Charge-discharge measurements were performed in the cutoff voltage range of -1.5
to 2.9 V at 140°C. Cu K, L-edge XAS and N K-edge XAS, RIXS measurements were performedon the samples after charge and discharge.
The charge-discharge curve measurements of the Cu3N cathode are shown in Figure 1. The
Cu3N cathode exhibits reversible charge-discharge behavior within the Cu+/Cu2+ redox range,
while showing a potential flat area at about 0.65 V (vs. Pb/PbF2) (Figure 1 a). Charge anddischarge capacities of 290 mAh g-1 and 236 mAh g-1 were obtained during initial charge anddischarge, respectively. The Cu3N cathode maintained a charge and discharge capacity of 100
mAh g-1 even when the current density was increased to 200 mA g-1, showing higher rate andcycle properties than the Cu cathode. Furthermore, the Cu3N cathode showed an extremely highcapacity of 780 mAh g-1 on initial charge and 550 mAh g-1 on discharge, exceeding thetheoretical capacity (393 mAh g-1) of the Cu+/Cu2+ redox (Figure 1b).
Cu L-edge, N K-edge XAS and RIXS measurements were performed on Cu3N during thecharging process to clarify the origin of this capacitance that cannot be explained by the
Cu+/Cu2+ redox. In the Cu L-edge XAS spectra, a peak was observed at about 930.5 eV; toward
F=3, this peak shifted to the lower energy side with charging, and the peak position of thesample charged up to F=3 was consistent with that of CuF2. Subsequently, when the samples
were charged from F=3 to F=6, no change in peak position was observed. These results indicatethat oxidation of Cu+ to Cu2+ occurred from F=0(pristine) to F=3, but that Cu was not oxidized
from F=3 to F=6. In the N K-edge XAS spectra (Figure 2a), no noticeable change in spectral
shape with charging was observed from F=0(pristine) to F=2. On the other hand, from F=2 to
F=6, the peak shape around 401 eV changed and the peak intensity increased dramatically. This
dramatically changed peak shape is very similar to that of nitrogen gas4. In the N K-edge RIXS
spectrum at 400.8 eV, vibrations similar to those of N2 gas in the previous study5, and the value

of the width of the Cu3N frequency is consistent with the N2 gas value (2360 cm-1, 0.292 eV),suggesting the presence of N2 molecules within Cu3N. These results indicate that nitrogen redox
occurs in the Cu3N cathode during charging, leading to the high capacity.
(a)x in Cu3NFx(b)Fig. 1. Electrochemical measurements of Cu3N cathode material at 140 °C. Charge/discharge
profiles under capacity limitation of (a) F=3 and (b) F = 6 at 8 mA g-1.

Normalized Absorption (a.u.)

(a)

(b)
Cu3N pristine
Chg. F=1
Chg. F=2
Chg. F=3396

398

Chg. F=4
Chg. F=5
Chg. F=6

400

402

404

Photon energy / eV

Fig. 2. (a) N K-edge XANES spectra of Cu3N cathode obtained upon charging and (b) N Kedge RIXS spectrum of Cu3N cathode after full charging.
REFERENCES[1] M. Anji Reddy and M. Fichtner, J. Mater. Chem. 2011, 21, 17059–17062.
[2] D. Zhang, K. Yamamoto, A. Ochi, Y. Wang, T. Yoshinari, K. Nakanishi, H. Nakano, H. Miki, S.
Nakanishi, H. Iba, T. Uchiyama, T. Watanabe, Y. Orikasa, K. Amezawa, Y. Uchimoto, J. Mater.
Chem. A, 2021, 9, 406–412.
[3] M. D. Reichert, M. A. White, M. J. Thompson, G. J. Miller, and J. Vela, Inorg. Chem. 2015, 54,
6356–6362.
[4] H. J. Song, H. J. Shin, Y. Chung, J. C. Lee, M. K. Lee, J. Appl. Phys. 2005, 97, 113711-7.
[5] L. Kjellsson, V. Ekholm, M. Agåker, C. Såthe, A. Pietzsch, H. O. Karlsson, N. Jaouen, A. Nicolaou,
M. Guarise, C. Hague, J. Lüning, S. G. Chiuzbăian, and J.-E. Rubensson, Phys. Rev. A, 2021, 103,022812-7.

STUDY OF SOFT X-RAY EMISSION ANGULAR ANISOTROPYOF GAS PHASE
Naoya Kurahashi1, Jun Miyawaki2, Kosuke Yamazoe3, Hisao Kiuchi1, Wenxiong Zhang1,
Ugalino Ralph1 and Yoshihisa Harada1
1

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

National Institutes for Quantum Science and Technology
3

Japan Synchrotron Radiation Research InstituteSoft X-ray emission spectroscopy is a powerful technique to observe the electronic state ofoccupied orbitals, which emits excess energy as light when valence electrons relaxation to
inner-holes generated by the excitation light of soft X-rays. The measurement under ambientpressure and measurement of wet samples are possible using the X-ray transmission window.
In contrast, photoelectron spectroscopy is another method for directly observing occupied
electron orbitals, and it is possible that photoelectron spectroscopy and emission spectroscopy
provide complementary information, as exemplified by the results of bulk water measurements.
While soft X-ray emission spectroscopy can measure samples in a variety of environments, it
tends to have a broad natural width of the spectrum, due to the short lifetime of inner-holes.
Because of this, it may not be possible to completely separate the electron orbitals, and a method
for assigning electron orbitals other than emission energies is required.
Since photoelectron spectroscopy for atoms and molecular has long been used to study photoexcitation dynamics, there has been a need for a method to understand the electronic excitation
states. To solve this problem, a photoelectron velocity mapping method1 has been developedthat enables simultaneous observation of the kinetic energy and emission angle ofphotoelectrons. In the process of photoelectron emission, the orbital angular momentum ofelectrons changes by ±1 according to the law of conservation of angular momentum. For
example, electrons from the s-orbital are emitted in the form of p-orbitals, while those in the porbital are emitted as a superposition of s- and d-orbitals. As a result, by measuring the kinetic
energy and emission angle distributions ofphotoelectrons, information on the energy levels
and angular momenta of the original orbitals canbe obtained, which enables precise assignment ofelectron orbitals.
We have planned a soft X-ray emission angularanisotropy observation experiment on a gasphase sample, because we thought that theelectron orbital information could be obtained
from the soft X-ray emission angular distribution
in the same way as the photoelectron emission
angular distribution has information on the orbital
angular momentum (Fig. 1). By using a gas-phasesample, the angular emission anisotropy is
considered to depend only on the angle between
the molecular axis and the electric field plane oflight (polarization) and the symmetry between theFig. 1 Schematic of soft X-ray emission angular core-excited intermediate and final states of theanisotropy measurement. The incident light and molecule, making it easy to compare withemission points were fixed and the spectrometer was theoretical calculations. In angle-resolved
rotated in the horizontal plane.
spectroscopy, it is necessary to consider thelifetime of the intermediate state because the angle information is lost due to molecular rotation.
However, in soft X-ray emission spectroscopy, the lifetime of the intermediate state is very
short (few femto-seconds), and the positional relationship between the molecule and the lightis considered to be conserved. Due to the trade-off between energy resolution and detection
efficiency in emission spectroscopy, and the low efficiency of X-ray fluorescence for lightelements, soft X-ray emission spectroscopy for gaseous samples has been considered difficult.
To solve this problem, we have developed a high-density gaseous sample introduction method.
This method enables us to introduce a high-density gas-phase sample into a very small area
while maintaining a high vacuum in the measurement chamber.
Using the newly developed sample introduction method, we performed soft X-ray emission
angle anisotropy observation of oxygen gas and succeeded in the first soft X-ray emission angle
anisotropy measurement of gaseous molecules. The pressure in the vacuum chamber remainedat around 10-4 Pa even though
100 kPa oxygen gas wasintroduced, and no influenceon the light source or otherdevices was observed.
The soft X-ray emission
angularanisotropy
atexcitation energy of 530.8 eV,
which is the π* excitation3Πu) was re(3Σg- →measured. In the case ofhorizontal polarization, theFig. 2 Soft X-ray emission angle anisotropy measurements of oxygen excited anisotropy parameters were at 541.3eV. The angle in the figure indicates the angle between the electric
0.62±0.04 for 3Σg- emission
field plane of the excitation light and the monochromator.
and +0.23±0.15 for 3Πgemission. These values were close to the respective anisotropy parameters of -0.57 and +0.36
obtained from geometric calculations. From this result, it is concluded that the emission processof 3Πu excitation in oxygen gas is a dipole transition, which occurs sufficiently faster than themolecular rotation. Since the lifetime of 3Πu is expected to be highly dependent on the excitationenergy, we would like to challenge the excitation energy dependence of 3Πu angular anisotropy
in the next beam time. On the other hand, no clear angular anisotropy was observed at 541.3
eV (Fig. 2), which is the Rydberg excitation, and it is possible that the molecular rotation
cancels out the angular anisotropy because the excited state lifetime tends to be long due to thehydrogen atom-like electron configuration in the Rydberg excitation. However, no clear
conclusion has been reached on the emission lifetime in this region due to a lack of examples
of studies, so we would like to compare our results with theoretical calculations.
No angular anisotropy was observed in any of the peaks when the polarization was set tovertical. This indicates that the measurement system maintains cylindrical symmetry inlongitudinal polarization. This means that the sample emission occurred at the center of rotationof the spectrometer and that the gas-phase sample measurement setup was successful.
With this study, we have successfully performed windowless experiments of soft X-ray
emission spectroscopy of oxygen gas and measured the angular anisotropy of the soft X-ray
emission. In the future, we would like to try soft X-ray emission angle anisotropy experimentsof vaporized water, which is important for comparison with bulk water.
REFERENCES[1] T. Suzuki, Annu. Rev. Phys. Chem., 57, 555 (2006).
[2] J.-E. Rubensson et al., J. Electron Spectros. Relat. Phenomena, 185, 294 (2012).

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

National Institute for Materials Science (NIMS), Tsukuba, Ibaraki, Japan.
PRESTO, Japan Science and Technology Agency, Honcho, Saitama, Japan.
3
Tokyo University of Science, Katsushika, Tokyo, Japan
4
Tohoku University, Sendai, Miyagi, Japan
5
The University of Tokyo, Kashiwa, Chiba, JapanOne of the unsolved global-scale issues is developing technology that effectively uses energy
represented by unused waste heat. It is known that exhaust heat below 200°C occupies ~70%of the total. From this perspective, thermoelectric materials that can directly convert heat toelectrical energy can be considered clean energy materials. Unfortunately, except for space andremote areas, our society has not yet implemented power generation using thermoelectricmaterials.
To develop environmentally friendly thermoelectric materials that are non-toxic and lowcost with sufficient power output to drive sensor devices, in particular, at a low-temperature
region below 400 K, we developed FAST materials (Fe-Al-Si Thermoelectric Materials)
composed of τ1-Fe3Al2Si3 phase forms a narrow bandgap of ~0.2 eV near the Fermi level [1].
We demonstrated that the Al/Si ratio fine-tuning could control its conduction type and enhance
the power factor without chemical substitutions [2]. Relatively large power factors wereobtained for p- and n-type thermoelectric materials below 400 K, which possessed highoxidation resistance and excellent mechanical properties [3]. Recently, we improved the power
factor at mid-temperatures using machine-learning-assisted synthesis and evaluation by tuning
the compositions [4,5]. Furthermore, we succeeded in the bonding technology to build a smallsized and highly integrated thermoelectric power generation module: the operation oftemperature/humidity sensors and wireless transmission was performed [6] (Fig. 1). To better
understand the intrinsic thermoelectric characteristics of FAST materials, the electronic
structure, including the magnitude of the bandgap and formation of impurity states, needs to beexperimentally investigated.

Fig. 1 Materials development, modularization technology, and power generation demonstration tests using
experiment, mapping measurement, computational science, and machine learning.

In this work, we investigated the electronic
structures of polycrystalline p- and n-type
FAST
materials
byphotoemission
spectroscopy to obtain deeper insight into
controlling the p-n characteristics to enhance
the thermoelectric properties of FAST
materials [7]. The core-level spectra of the pand n-FAST materials for Al 2p, Al 2s, Si 2p,
and Fe 3p are shown in Fig. 2, respectively.
The solid curves are the raw spectra. For
clarity, the spectra of the p-FAST material
were by 0.15 eV toward the higher bindingenergy side.
The photoemission spectra of the valencebands of the p- and n-FAST materials areshown in Fig. 3. Considering thephotoemission cross section, these spectra
Fig. 2 Photoemission spectra of the (a) Al 2p, (b) Al
strongly reflect Fe 3d orbitals. The dashed blue 2s, (c) Si 2p, and (d) Fe 3p core levels. The blue (red)curve in Fig. 3 corresponds to the spectrum of curves are the spectra of p-FAST (n-FAST) material.
the p-FAST material shifted by 0.15 eV toward The solid curves are the raw spectra, and the dashedhigher binding energy. From Fig. 3, the energy curves are the spectra shifted by 0.15 eV toward
positions of the highest intensities are almost higher binding energy.
the same. This indicates a rigid band shift
owing to carrier doping by changing the Al/Si
ratio.
We found that the photoemission spectra of
the p- and n-FAST materials were consistent
with the covalent bonding nature andsemiconducting behavior. Because the corelevel shifts were independent of the elements
and orbitals, the observed chemical-potentialchange should be the dominant factor of thecore-level shift of ~0.15 eV, close to the band
gap of ~0.18 eV obtained from transport Fig. 3 Valence-band spectra of the p- and n-FAST
materials. The blue and red solid curves are themeasurements.
spectra of the p- and n-FAST materials. The dashedblue curve is the spectrum of the p-FAST material
shifted by 0.15 eV toward higher binding energy.

REFERENCES[1] Y. Takagiwa, Y. Isoda, M. Goto, and Y. Shinohara, J. Therm. Anal. Calorim. 131, 281(2018).
[2] Y. Takagiwa, Y. Isoda, M. Goto, and Y. Shinohara, J. Phys. Chem. Solids 118, 95 (2018).
[3] Y. Takagiwa and Y. Shinohara, Scripta Mater. 172, 98 (2019).
[4] Z. Hou, Y. Takagiwa, Y. Shinohara, Y. Xu, and K. Tsuda, ACS Appl. Mater. Interfaces 11,11545 (2019).
[5] Y. Takagiwa, Z. Hou, K. Tsuda, T. Ikeda, and H. Kojima, ACS Appl. Mater. Interfaces 13,53346 (2021).
[6] Y. Takagiwa, T. Ikeda, and H. Kojima, ACS Appl. Mater. Interfaces 12, 48804 (2020).
[7] S. Tsuda, A. Yoshinari, S. Takezawa, K. Ohishi, N. Nagamura, W. Zhang, Y. Iwasaki, and
Y. Takagiwa, Mater. Res. Express 10, 055506 (2023).

ANALYSIS OF ELECTRONIC CONFIGURATION FOR A WATER
MOLECULE ENCAPSULATED INSIDE A FULLERENE
Yoshifumi Hashikawa,1 Hisao Kiuchi,2 Yoshihisa Harada2
1

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

2

Introduction. Water clusters found in hydrophobic subnanospaces such as graphitic
interlayers and cavity of carbon nanotubes have been revealed to exhibit distinct properties
essentially different from those in a bulk environment. For such water, theinduction/expression of their functions and properties is heavily dependent on their physicaland electronic structures offered by intermolecular hydrogen-bondings whilst authentic
physical nature of water, i.e., a single water molecule without any hydrogen-bonding, has still
remained unrevealed. To tackle this issue, in 2011, we have synthesized H2O@C60 where asingle water molecule was isolated within a fullerene C60 cavity.1 The X-ray absorption
spectroscopy (XAS) and X-ray emission spectroscopy (XES) at O K-edge are powerfulapproaches to clarify the nature of water. In addition, resonant inelastic X-ray scattering(RIXS) measurement by an emission spectrometer with a high energy resolution could
provide a potential energy surface of the molecule of target, thus revealing an effect of theenvironment surrounding the water molecule. Hence, these measurements are expected to be a
crucial clue to probe the interaction between the water molecule and the carbon wall. Herein,
we report our preliminary results on the physical nature of a single water molecule inside C60.
Experimental methods. First, a
powdery sample of H2O@C60 was
moulded in a shape of a φ7 pellet by
applying a hydraulic press. The
measurements of O K-edge XAS,
XES, and RIXS were performed atroomtemperature(SPring-8
BL07LSU). The XAS spectra weretaken with a partial fluorescence
yield mode using SDD (silicon drift
detector). The XES and RIXS
spectrawererecordedwithscanning the pellet sample for
reducing a local sample damage by
the irradiation with a small beam
spot size of 7 μm × 50 μm.
Results and discussion. Figure 1
shows O 1s XAS and XES spectraof H2O@C60 as well as those forwater reported previously.2 In the
XAS spectra, the energy shifts ofmolecular orbitals were observedwith vanishing a Rydberg band
(Figure 1b). This likely arises fromahybridizationofwidelydistributed molecular orbitals of
H2O with those of C60. Upon seeing Figure 1. (a) Molecular orbital diagram of water
the XES spectra, the emission band and (b) XAS and XES spectra of H2O@C60 andcorresponding to a transition from previous reports.

3a1 where the electron cloud is aligned in an axis of an electric dipole moment was found tobe significantly broadened (Figure 1b). This is suggestive of the polarization shielded by theC60 cage. To get further insights into this phenomena, the theoretical calculations are currently
ongoing.
Figure 2 illustrates
RIXS spectra at the 4a1
and 2b2 resonances of
H2O@C60 as well asgaseous water3 reported
previously, both of whichshowed multiple modesof vibration. Comparedwith gaseous water, thelarger deviation of thepeaks were confirmed for
H2O@C60at
higherenergy loss area. This isdemonstrative of theflattening of a potential
energy surface at higher
energy levels. This isconsidered to be causedbytheattractive
spectra of H2O@C60 (solid curve) andinteraction
present Figure 2. RIXS
3
betweenthesingle gaseous H2O (dashed curve).
molecule of H2O with the C60 wall, which might promote a water dissociation within the C60
cavity.
Conclusion. We examined the electronic properties of H2O@C60 by XAS, XES, and RIXS
measurements at SPring-8 BL07LSU. The XAS spectra showed a band shifts as well as avanished Rydberg band, implying the presence of an orbital–orbital interaction between H2O
and C60. This interaction was revealed to be attractive by RIXS measurements suggesting theflattening of a potential energy surface at higher energy levels. The additional measurements
and theoretical studies are in progress for further understanding the nature of a single
molecule of H2O.

REFERENCES[1] (a) Kurotobi, K.; Murata, Y. Science 2011, 333,613–616. (b) Hashikawa, Y.; Kizaki, K. Hirose, T.;
Murata, Y. RSC Adv. 2020, 10, 40406–40410.
[2] (a) Weinhardt, L.; Benkert, A.; Meyer, F.; Blum, M.; Wilks, R. G.; Yang, W.; Bär, M.; Reinert, F.;
Heske, C. J. Chem. Phys. 2012, 136, 144311. (b) Tokushima, T.; Harada, Y.; Takahashi, O.; Senba,
Y.; Ohashi, H.; Pettersson, L. G. M.; Nilsson, A.; Shin, S. Chem. Phys. Lett. 2008, 460, 387–400.
(c) Myneni, S.; Luo, Y.; Näslund, L. Å.; Cavalleri, M.; Ojamäe, L.; Ogasawara, H.;
Pelmenschikov, A.; Wernet, P.; Väterlein, P.; Heske, C.; Hussain, Z.; Pettersson, L. G. M.; Nilsson,
A. J. Phys. Condens. Matter 2002, 14, L213–L219.
[3] Cruz, V. V. d.; Ertan, E.; Couto, R. C.; Eckert, S.; Fondell, M.; Dantz, M.; Kennedy, B.; Schmitt,T.; Pietzsch, A.; Guimarães, F. F.; Ågren, H.; Gel'mukhanov, F.; Odelius, M.; Föhlisch, A.;
Kimberg, V. Phys. Chem. Chem. Phys. 2017, 19, 19573–19589.

Electrolyte Dependence of the Mn 3d Electronic Structure of LiMn2O4
Cathode Studied by Soft X-ray Emission Spectroscopy
Daisuke Asakura1,2, Yusuke Nanba1, Eiji Hosono2,3, Hideharu Niwa4, Hisao Kiuchi4, Jun
Miyawaki4, and Yoshihisa Harada2,4
1

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

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

Global Zero Emission Research Center, AIST

4

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

Li-ion battery (LIB) is one of the key energy-storage devices for CO2 reduction andrealization of sustainable society. To further enhance the performances of LIBs forapplications to electric vehicles and large-scale stationary energy storage systems, increasing
the charge-discharge capacity of the cathode is highly desired. Electronic-structure analysis
using X-ray spectroscopy has been playing an important role on the clarification of the redox
mechanism of cathode materials for LIBs, which will lead to increase of the charge-discharge
capacity. By clarifying the redox mechanism of typical cathode materials, it is expected toobtain strategies to design novel cathode materials.
We have been studying the electronic structure of several cathode materials using soft X-ray
absorption (XAS) and emission spectroscopy (XES). For example, the Mn L-edge XAS andXES studies for LiMn2O4, which is a prototypical cathode material, revealed the redox
reaction of Mn3+ ⇔ Mn4+ at the Mn3+ site in the initial state. The Mn4+ state has very strong
charge-transfer (CT) effect between the O 2p and Mn 3d orbitals, resulting in the importantrole of O 2p orbital on the redox reaction.1,2 These studies have been investigated for the
charge-discharge reaction with a conventional organic electrolyte solution, 1-mol·dm-3
LiClO4/ethylene carbonate (EC)-diethyl carbonate (DEC).
On the other hand, it is well known that LiMn2O4 could exhibit charge-discharge reaction
with aqueous electrolyte solutions.3 The usage of aqueous electrolyte solutions isadvantageous in terms of safety (non-flammable) and manufacturing cost, while the working
voltage is reduced to around 1.0 V (in contrast to ~4.0 V for organic electrolyte solutions)because of the narrow voltage window of H2O. To investigate the redox reaction of Mn3+ ⇔Mn4+ in the case of aqueous electrolyte solution, we performed Mn L-edge XES studies for
LiMn2O4 with 1-mol·dm-3 LiNO3/H2O.4
Powdered LiMn2O4 sample was fabricated by a sol-gel method.2,4 The operando XES
measurements with the aqueous electrolyte solution were carried out by HORNET
spectrometer at BL07LSU, SPring-8. The setup of operando cell and details of theelectrochemical measurements for operando XES are described in Ref. 4. To analyze the XES
spectra, we conducted configuration-interaction full-multiplet (CTM) calculations.2,4
Figure 1 shows a comparison of the Mn L3-edge XES spectra between the cases of theaqueous and organic electrolyte solutions. The line shape for the initial state is identicalbecause the powder samples were fabricated with the same method. As described in Ref. 2,
the initial state has been attributed to a mixed state of Mn3+ and Mn4+. In contrast, the line
shape after the first charge-discharge cycle is considerably different between the cases ofaqueous (spectrum A) and organic (spectrum B) electrolyte solutions, indicating that theredox reaction is dependent on electrolyte. For the organic electrolyte solution, spectrum B issimilar to the spectrum of the initial state, while the sample after the charge-discharge hasbeen measured under an ex situ condition.2 This result indicates that the redox reaction withthe organic electrolyte solution is relatively reversible for the first cycle. For the aqueous
electrolyte solution, the redox reaction for the first cycle is irreversible. However, CTM
calculations revealed that spectrum A also consist of Mn3+ and Mn4+.4 The difference fromspectrum B is mainly originated from the charge-transfer energy  (from O 2p to Mn 3d
orbitals) for each Mn3+ and Mn4+.4
The operando XES results after the second cycle with the aqueous electrolyte solution (notshown here) were similar to those after the first cycle,4 indicating that the second cycle isreversible. The change from the spectrum of the initial state to spectrum A suggests formationof surface-electrolyte interface (SEI) layer characteristic of the aqueous electrolyte solution,
while SEI layer is also formed for the cases of organic electrolyte solutions. Thus, after that
the SEI layer is once formed on the first cycle, the reversibility of the redox reaction with theaqueous electrolyte solution should be enhanced.
As above, difference of electrolytes causes different redox reaction. The SEI layer formedby the charge-discharge should strongly affect the electronic structure of cathode materials.
We will try to the Mn L-edge operando XES of LiMn2O4 with solid-state electrolyte as
all-solid-state battery.5 The LiMn2O4/solid-state electrolyte interface is expected to becompletely different from the LiMn2O4/liquid electrolyte interfaces. Thus, the redox reaction
with solid-state electrolytes should be verified in the future.

Fig. 1. Mn L3-edge XES spectra for LiMn2O4 with the cases of aqueous and organic
electrolyte solutions. The initial state corresponds to the powder sample before
charge-discharge for both electrolytes. Spectra A and B after the first cycle were measured
under operando and ex situ conditions, respectively.2,4 The excitation energy was 643.0 eV.
REFERENCES[1] D. Asakura et al., Electrochem. Commun. 50, 93 (2015).
[2] D. Asakura et al., Phys. Chem. Chem. Phys. 21, 18363 (2019).
[3] For example, W. Pei et al., J. Power Sources 63, 275 (1996) and V. A. Nikitina et al., Langmuir 33,
9378 (2017).
[4] D. Asakura et al., Phys. Chem. Chem. Phys. 24, 19177 (2022).
[5] For example, H. Kitaura et al., J. Electrochem. Soc. 157, A407 (2010).

SOFT X-RAY STRUCTURAL ANALYSIS OF CONSTRAINED WATER
MOLECULES ON NICKEL-COMPLEX ANION SALT AGGREGATESTomoko Fujino
The Institute for Solid State Physics, The University of Tokyo

Introduction
Open-shell π/d-conjugated complexes have electron-rich structures and diverse electronic
functionalities, including optical and magnetic properties. By combining the central metal andligand, the electronic structure of these complexes can be precisely adjusted. When thesecomplexes are assembled with effective intermolecular interactions such as π–π interactions,they form band structures that exhibit different electronic functionalities from those in theisolated form, including electrical and magnetic conductivities. We focused on assembling
electronically charged open-shell complexes, which offer benefits such as hydrophilicity thatenhance their fabrication applicability in environmentally friendly electronic devices. Thesecharged complexes also provide structural diversification in assembled structures andfunctions depending on the variations of counter ions. However, these complexes are still rareeven despite several decades of research because electrostatic repulsion between charged
molecules severely hampers their assembly, except for charge-transfer complexes insegregated stacks between donors and acceptors. Only a few examples, such as [M(dmit)2]2–(dmit = 2-thioxo-1,3-dithiol-4,5-dithiolate, M = Ni, Pd, Pt, etc) anion salts, have succeeded in
exhibiting a tightly π-stacked form, resulting in properties such as unique magnetic
characteristics, near-IR absorption, and superconductivity under high pressures.
We previously developed neutral metal dithiolene complexes with electron-donating
substituents on their side chains [1,2]. These complexes displayed conductive properties whenassembled in single crystals [1] or thin films [2] demonstrating the unique conductive
properties, but not in isolated salt forms. We hypothesized that combining the hydrophilic
precursors of the neutral complexes with hydrophobic counter cations that possess long-chain
alkyl chains could form amphiphilic open-shell d/π conjugated complex anion salts. Such anamphiphilic structure may form macroscopic assemblies in aqua, exhibiting strong π–πinteractions between complex anions. This mobile soft aggregate could demonstrate dynamic
macro-sized structural changes responsive to the external environment. Therefore, we
synthesized an amphiphilic salt of the d/π-conjugated complex anion with a hydrophobic
counter cation possessing double dodecyl chains, which formed a macro-sized assembly
where the complex anions showed considerable π–π stackings at room temperature,demonstratingrich
conductive
properties.
The
macrostructures
exhibited
temperature-dependent dynamical structural changes at approximately 65 °C, but the detailed
mechanism in the properties remains unclear due to the lack of atomic-level structural
information.
In this study, we investigated the origin of these unique electronic functionalities by Ni
XAS at BL07LSU, which was developed by Prof. Harada's group. By using Ni XAS, weanalyzed the electronic characteristics and temperature dependency of an aqueous solution of
the complex anion salts flowing in the system. Our analysis showed that at lower
temperatures than the transition temperature, the suspended solution displayed a spectrumwith two peaks at the Ni L3 absorption edge, unlike the isolated forms of complex anions,where only a higher-energy peak was observed. We suspect the lower-energy peak may be a
result of possible intermolecular Ni–Ni interactions. When the temperature was raised abovethe transition temperature of the dynamical change, the lower-energy peak disappeared, but itreappeared when the solution was cooled again. It appears that the interactions between Ni
elements disappeared when the assembled form was released. This is likely consistent withthe observation of high-temperature small- and wide-angle X-ray scattering that showed
macro-sized assembly was released, resulting in the loss of the formed band structures basedon the intermolecular π–π stacking. The intramolecular structural details were further
addressed with the wide-ranged XAS measurements covering the energy ranges for Ni L3 andL2 absorption edges. At 80 °C, charge-transfer satellite peaks appeared on L3 and L2
absorption edges, but not at low temperatures. This indicates that intramolecular chargetransfer occurred from the ligand to the central metal when the assembly was released into theisolated form at high temperatures. These findings confirmed that the release of themacro-sized assembly caused changes in the loss of intermolecular Ni–Ni interactions,altering the intramolecular electronic structure.
This work was supported by Prof. Yoshihisa Harada, Dr. Hisao Kiuchi, and Dr. Naoya
Kurahashi (ISSP, The Univ. of Tokyo) for their support on XAS measurements and fruitful
discussions. We appreciate their kind and professional suggestions. We also thank Assoc.
Prof. Mafumi Hishida (ISSP, The Univ. of Tokyo) for small- and wide-angle X-ray scattering
measurements. We appreciate Prof. Hatsumi Mori and Mr. Masatoshi Ito (ISSP, The Univ. ofTokyo) for the synthesis support and considerable discussions. This work was partially
supported by JSPS Grants-in-Aid for Scientific Research (JP20H05206, JP21K05018,
JP22H04523), JST PRESTO (JPMJPR22Q8), a research grant from Naito Foundation, theKao Foundation for Arts and Science.
REFERENCES[1] Yokomori, S.; Dekura, S.*; Fujino, T.; Kawamura, M.; Ozaki, T.; Mori, H.* J. Mater. Chem. C
2020, 8 (42), 14939-14947.
[2] Ito, M.; Fujino, T.*; Zhang, L.; Yokomori, S.; Higashino, T.; Makiura, R.; Takeno, K. J. Ozaki, T.;
Mori, H.* J. Am. Chem. Soc., 2023, 145 (4), 2127–2134.

AMBIENT PRESSURE X-RAY PHOTOELECTRON SPECTROSCOPYSTUDY OF THE ELECTRONIC STATES OF THE MoS₂ BASAL PLANE
DURING ANNEALING IN HYDROGEN
Fumihiko Ozaki, YoungHyun Choi, Wataru Osada, Yoshiko Sakaguchi, Shunsuke Tanaka,
Kozo Mukai, Masafumi Horio, Iwao Matsuda and Jun Yoshinobu
The Institute for Solid State Physics, The University of Tokyo

Introduction
Molybdenum disulfide (MoS2) has attracted attention in various applications such as gas
sensors, field-effect transistors, and optoelectronic devices due to its unique optical properties
and high carrier mobility. A formation of sulfur vacancies on the MoS2 surface plays animportant role in device performance because the electronic state is affected by sulfur
vacancies [1]. In addition to these applications, MoS2 has also been used as a catalyst for avariety of other applications, including hydrogenated desulfurization (HDS) catalysts. The
sulfur vacancies serve as adsorption sites for molecules such as organosulfur compounds [2].
Many studies have been conducted to characterize the properties of sulfur vacancies. In
particular, the electronic properties of MoS2 surfaces with sulfur vacancies have been
investigated by X-ray photoelectron spectroscopy (XPS) [3]. The XPS spectra of thecore-levels show the chemical components associated with the sulfur vacancies. Quantitative
explanations for this chemical shift are lacking, and the electronic state of sulfur vacancies is
not fully understood yet.
Annealing in hydrogen is one of the methods of sulfur vacancy formation; adsorbedhydrogen atoms are reacted with and sulfur and desorbed as H2S above 600 K, leading to theformation of sulfur vacancies [4]. In this study, ambient pressure (AP-) XPS measurements of
the MoS2 basal plane were performed to clarify the electronic state during annealing inhydrogen, and it is found that at the HDS reaction temperature of 600 K, a low-binding
energy component appears in both the Mo 3d and S 2p spectra. Furthermore, the intensity
ratio of the Mo 3d and S 2p spectra (S 2p/Mo 3d) decreases dramatically at 600K. This
indicates the formation of sulfur vacancies on the MoS2 basal plane.
Experimental
A natural MoS2 single crystal was used as a sample (ALLIANCE Biosystems; about 50
mm2, 0.5 mm thick). After mounting the sample on a metal plate, surface layers were peeled
off in air using Scotch tape. Within 10 minutes after peeling, the sample was transferred to aload lock chamber and annealed in an ultra-high vacuum chamber at about 550 K for 30
minutes. AP-XPS measurements were performed in a chamber equipped with a hemisphericalelectron energy analyzer at SPring-8 BL07LSU. High-purity H2 gas was introduced into thegas cell and the sample was slowly heated in H2 from 302 K to 750 K for a total of 2.5 hours.
All XPS spectra were obtained using a photon energy of 680 eV. The binding energies of themeasured XPS spectra were calibrated using the Fermi level of a gold foil attached to thesample holder.
Results and discussion
Initially, 1.5 mbar of hydrogen gas was introduced into the gas cell, and then a sample
temperature was increased from 302 K to 750 K. Figure 1 show the AP-XPS spectra of Mo 3d,
S 2p, and valence band as a function of sample temperature, respectively. The intensity ratioof the S 2p core level to the Mo 3d core level is also shown in Figure 2. The peak energies ofthe Mo 3d core-level, the S 2p core-level, and the valence band uniformly shift to a lower
binding energy of about 0.2 eV up to 600 K. Judging from this uniform energy shift, it can beattributed to band bending in the MoS2 crystal [5]. Furthermore, the S 2p/Mo 3d intensity
ratio is almost constant up to 600 K, indicating that the HDS reaction does not occur.

Figure 1. (a) Mo 3d, (b) S 2p, (c) Valence-band AP-XPS spectra of the MoS2 basal plane as a function of thesample temperature in H2 gas of ~1.5 mbar. The sample temperature increased from 302 K up to 750 K.

After 600 K heating, the peaks shift to lower binding energy
and their widths become significantly broadened. This
indicates the appearance of a new component in the Mo 3dand S 2p spectra. Furthermore, the S 2p/Mo 3d intensity ratio
decreases markedly above 600 K, indicating that the HDS
reaction takes place as indicated by the previous studies [6].
Hence, the new component observed in the Mo 3d and S 2p
spectra may be related to the formation of sulfur vacancies.
To clarify the spectral changes with new components, acomparison of the XPS spectra at 538 K and 619 K shows a Figure 2. Plot of the S 2p/Mo
decrease in intensity around 229.38 eV (162.21 eV) and an 3d intensity ratio.
increase around 229.13 eV (161.88 eV) for Mo 3d (S 2p).
Such a lower binding energy shift implies an increase in electron density at the Mo and S
atoms. The electrons left on the MoS2 surface by the desorption of sulfur as H2S would be
redistributed to the surrounding atoms. This interpretation has been supported by our recent
first-principles calculations including the estimation of absolute binding energies based on theseveral defect models as well as AP-XPS data [7].
Acknowledgments
The AP-XPS measurements using synchrotron radiation were performed at SPring-8
BL07LSU as joint research between the Synchrotron Radiation Research Organization and
The Institute for Solid State Physics, The University of Tokyo (Proposal No. 2022A7449,
2021B7432).
REFERENCES[1] M. D. Siao et al., Nat. Commun. 9, 1442 (2018).
[2] R. V. Mom et al., Nat. Commun. 10, 2546 (2019).
[3] S. W. Han et al., Phys. Chem. Chem. Phys. 21, 15302 (2019).
[4] X. S. Li et al., J. Catal. 137, 385 (1992).
[5] F. Ozaki et al., Appl. Surf. Sci. 593, 15 (2022).
[6] A. Bruix et al., ACS Nano 9, 9322 (2015).
[7] F. Ozaki et al., submitted (2023).

BAND BENDING AT (001) AND (101) INTERFACES OF ANATASEPARTICLE REVEALED BY MICROSCOPIC X-RAY
PHOTOELECTRON SPECTROSCOPY
Wenxiong Zhang1, Mustafa Al Samarai1, Hisao Kiuchi1, Daobin Liu1, Haochong Zhao1,
Fangyi Yao2, Qi Feng2, Yoshihisa Harada1
1
2

The Institute for Solid State Physics, The University of Tokyo

Department of Advanced Materials Science, Kagawa University

Titanium dioxide (TiO2) has been used in many technological areas, including
photocatalysis, solar cells, gas sensors, etc. Among different polymorphs (brookite, anatase,and rutile), anatase TiO2 is considered a superior photocatalysis due to its higher electron
mobility and longer carrier lifetime. It was reported that the (001) and (101) facets co-exposed
anatase particles showed highly improved photocatalytic properties.[1] Theoretical calculationand experimental results on the (001) and (101) facets-exposed thin films have demonstrated
that a surface heterojunction would be formed between two facets due to their difference in
the Fermi levels.[2,3] As a result, photogenerated electrons and holes could accumulate on theinterface of the (101) and (001) facets, therefore exhibiting different photocatalytic properties
on these facets. For a deeper understanding of the charge separation mechanism of anatase
TiO2, a microscopic X-ray photoelectron spectroscopy (XPS) with spatial resolution better
than 100 nm is employed to elucidate the facet-dependent electronic structure of micron-sizedanatase TiO2 particle.
Figure 1a shows the Ti 2p photoelectron intensity mapping image of the anatase TiO2
particle. The particle exhibits a truncated octahedral bipyramid morphology, which isconsisted of eight {101} facets on the sides and two {001} facets on the top and bottom. The
geometrical relationships between the photoelectron analyzer and the incident beam spot on
the sample caused the intensity difference in the mapping image.[4] Figures 1b and 1c show
the pinpoint O 1s and Ti 2p XPS spectra shown in the enlarged area of the orange square (Fig.
1a) respectively. The consecutive 4 spots (~100 nm2 each) cover the (101) and (001) facets of
the anatase particle, as well as the interface between them. It is noted that the O 1s and Ti 2p
XPS spectra of anatase TiO2 continuously shift to the low binding energy from the (101) facet
to the (001) facet. Figure 1d shows that the valence band maximum exhibits the sametendency as O 1s and Ti 2p XPS spectra, suggesting a smaller binding energy of the valenceband maximum for the (001) facet. As a result, the interface areas for both (101) and (001)
facets were calculated to be ~50 and ~80 nm respectively according to the dotted fitting
spectra results (Fig. 1d). It can be concluded that a band bending (space charge layer of 130nm) between (001) and (101) facets could be formed due to the difference of the valence band
maximum between the (101) and (001) facets, hence, the photogenerated electrons and holes
could accumulate on the interface, thereby exhibiting enhanced photocatalytic activities. For
the strategy of morphology control to improve the photocatalysis performance of TiO2,
microspectroscopy using synchrotron soft X-ray is an important technique.

Figure 1. (a) Ti 2p photoelectron intensity mapping image of anatase TiO2 particle and its
enlarged area of the orange square. Pinpoint (b) O 1s, (c) Ti 2p, and (d) valence band XPS
spectra of TiO2 particle from consecutive 4 spots shown in Fig. 1a. CBM: conduction band
minimum. VBM: valence band maximum. Eg: band gap energy. Norm.: normalization. *CBM
is only speculation according to Eg = 3.2 eV. k1 = 0.5 (0.5 x 100 nm = 50 nm, interface at area
Ⅱ). k2 = 0.8 (0.8 x 100 nm = 80 nm, interface at area Ⅲ).

REFERENCES[1] H. G. Yang et al., Nature, 453 (2008) 638-642[2] J. Yu et al., J. Am. Chem. Soc., 136 (2014) 8839-8842[3] S. Kashiwaya et al., Adv. Energy Mater., 8 (2018) 1802195[4] W. Zhang et al., CrystEngComm., 25 (2023) 183-188

Influence of surface charge induced by ultrafine wateron trans-epidermal water retention of stratum corneum lipids
explored by O K-edge spectroscopy
Mustafa al Samarai1, Wenxiong Zhang1, Hisao Kiuchi1, Shinsuke Inoue2, Yuki Tabata2,
Hiroto Kato2, and Yoshihisa Harada1
1

Synchrotron Radiation Laboratory, The Institute for Solid State Physics, The University ofTokyo
2Innovation center, Aisin Corporation.

In recent years, nanosized water clusters called ultrafine water (UFW), which have several
nanometers or less diameter, have attracted attention for their wide range of functions suchas humidification, moisture retention, deodorization, air cleaning and sterilization, and static
electricity removal. However, little is known about the mechanism of their functions. For
example, in moisturizing, penetration into the subcutaneous tissue is considered because the
UFW is smaller than the intercellular space on the skin surface. However, this alone cannot
account for the long-lasting moisturizing effect [1]. Therefore, it is necessary to clarify thephysicochemical properties of UFW to understand those macroscopic functions. In this study,
a mixed-lipid bilayer model (artificial skin) of stratum corneum film (consisting of ceramide,cholesterol, and palmitic acid in a 1:1:1 molar ratio and approx.12.5 nm thick) was preparedon Au-coated 150 nm thick SiC membrane. We investigated the electronic structure ofabsorbed UFW vs. water by regular humidification at 60% relative humidity (RH) on theartificial skin using O K-edge XAS and XES to obtain detailed information on the hydrogenbonded configuration of water on those surfaces, and to discuss the relationship between thechemical state and the function of UFW. XAS/XES will represent unoccupied/occupied
valence electronic structures of water, which is quite sensitive to various hydrogen-bonded
configurations in water [2].

Figure 1: Photo image of the artificial skin prepared on a 150 nm thick SiC membrane(purple area); it was a key to make an uniform layer on the Au-coated membrane at 12.5 nm
thickness where interference fringes were completely invisible.
The summary of the XAS/XES data for humidification by either UFW or 60%RH is shownin Fig. 2. Based on the combination of the obtained data, an obvious extraordinary increaseof hydration in the artificial skin by flowing UFW was confirmed compared to regularhumidification at 60%RH.
For both identical samples
the O K-edge XAS and
XES for the dry state were
measured (black curves inFig. 2) followed by thehumification either by
UFW vs. 60%RH. Finally,
the samples were redried
to investigate the nature of
the trapped water withinor on the artificial skinsamples.
The surface to volume
ratio in the smaller UFW
water clusters (~ 1nm) isfour orders of magnitude
higher than the water mist Figure 2. O K-edge (a) XAS and (b) XES for Dry artificial skin (black) under(~ 10m in diameter) humidification by UFW vs regular humidification at 60%RH. Retention offound in the regular hydration is reflected in the Redry data.
humidified gas flows.
Therefore we expected different water absorption behavior and amount for the UFW
humidification. For both the humidification pathways there are dominantly two water species,
the gas phase water (at ~534 eV and ~526.9 eV in Figs. 2a and 2b) and trapped water (at~538 eV and ~525.8 eV in Figs. 2a and 2b). Hereby, first the gas phase water is dominant
especially in the 60%RH case, followed by the gradual isotropic equilibrium shift towards
precipitation of additional water from the vapor to the already present water domains on thesurface of artificial skin and trapped within the lipid bilayer. Interestingly we see a higher
water /humidification absorption for the UFW-treated sample. Furthermore, following theredrying process a considerably higher amount of water was retained for the UFW treatedsample relative to the regularly humidified (60%RH) sample.
This experimental evidence suggests that initial humidification with UFW produces water
adsorption sites on the hydrophobic skin surface. In the future, by accumulating data undermore specific conditions, we can identify the coordination of various water layers and the
involved chemical bonds, which will help design the function of novel UFW.
REFERENCES[1] N. Nishimura et al., Skin Res. Technol. 25, 294 (2019).
[2] T. Tokushima et al., Chem. Phys. Lett. 460, 387 (2008).

2p3d Resonant Inelastic X-ray scattering Probing Ligand Field Perturbations in Fe-modified Co spinels
Minmin Chen,1 Marcos Sepulcre,1 Dimitrios Manganas,2 Steven Angel,3 Eko Budiyanto,2 Derek Rice,1 Harun Tüysüz,2 Hartmut
Wiggers,3 Naoya Kurahashi,4 Yoshihisa Harada,4,5 Olaf Rüdiger,1 Serena DeBeer1
1

Max Planck Institute for Chemical Energy Conversion, 45470 Mülheim an der Ruhr, Germany

2 Max-Planck-Institut für Kohlenforschung, 45470 Mülheim an der Ruhr, Germany
3 University of Duisburg-Essen, 47057 Duisburg, Germany
4 Institute for Solid State Physics, The University of Tokyo, Kashiwa, Chiba 277-8581, Japan
5 Synchrotron Radiation Research Organization, The University of Tokyo, Sayo, Sayo-gun, Hyogo 679-5148, Japan

Spinels are an essential class of minerals which
serve as fundamental structural models for advanced
functional materials. Fe loading into spinels cansignificantly alter the physical-chemical properties ofthe parent spinel.[1] BET, XRD, APT, HRTEM, SAED,EELS, Raman spectroscopy and Mössbauer
spectroscopy have been widely used to explore therole of Fe role in modulating morphology, crystal
structure, oxidation state, and geometric structure.
Recently, 2p3d RIXS has been used as a site-selective
technique to probe the mixed-valence pure Co spinel.[2]Here we used 2p3d RIXS to directly probe thegeometric and electronic environment surrounding a
Co center in Fe-loaded Co-based spinels. CoFe2O4(containing only Co2+(Oh)), CoAl2O4 (containing only
Co2+(Td)), and ZnCo2O4 (containing only Co3+(Oh))
were chosen as references to study the spectral
signatures of the different sites. Ligand-field multiplet
calculations were used to reproduce the L-edge XAS
and 2p3d RIXS of the references.[3] The calculated
Tanabe-Sugano diagrams allow for the ligand field
modulations of the low-lying excited states to bevisualized. These electronic structure changes can thenbe correlated with the differences in Fe-induced
electrocatalytic performance.
Figure 1 shows both L-edge XAS and 2p3d RIXS
can distinguish Co2+ with different site symmetries (Tdvs. Oh), but 2p3d RIXS exhibits higher resolution and
it is more sensitive to modulations in the ligand field
splitting. Co2+ is excited primarily at lower incident
energies (<780eV) than the Co3+ ions. Visuallyassigning characteristic inelastic features is achallenge. Herein, we utilize ligand-field-theory
calculations within the ORCA code in order toreproduce experimental spectra of the references(Figure 2). In addition, the contributions fromdifferent multiplets can be deconvoluted based on thecalculated spectra.

Fig. 1 Experimental cobalt (a) L3-edge XAS and (c)2p3d RIXS of CoFe2O4, CoAl2O4, ZnCo2O4 andCo3O4 at different incident energy (c) Schematic L3edge XAS of free ion with d7 in Oh and Td symmetry.
The combination of experimental and calculated
spectra, shows that the transition at 0.5 eV energy
transfer (at 779 eV incident energy) corresponds
primarily to the Co2+(Td) site. Figure 3 shows that theelectronic structure of the Co2+(Td) is sensitive to theamount of Fe loading. The sample with the lowest Fe
loading, Co2.95Fe0.05O4, exhibits an increase in theenergy transfer, compared to the pristine Co sample,
while Co2FeO4 with higher Fe incorporation shows ashift towards lower ET. This observation suggests ahigher crystal field splitting for the sample with lessFe-loading, which interestingly correlates with a lower
potential for the oxidation of the Co2+(Td) site
observed in cyclic voltammetry measurements. The
opposite effect is observed for the Co2FeO4, indicatingthat this feature can be used to provide an electronic
explanation for Fe-induced changes observed inelectrocatalytic measurements, where the samples
with the lowest Fe-loading showed enhanced
electrocatalytic water oxidation performance.

Fig.2 Experimental and ligand-field multiplet calculated L3-edge XAS and 2p3d RIXS, as well as calculated TanabeSugano diagrams of (a, d, g) CoAl2O4, (b, e, h.) CoFe2O4, and (c, f, i) ZnCo2O4.

Fig. 3 (a) 2p3d RIXS show ligand field splitting of Co2+(Td) affected by Fe loading. (b) Schematic diagram ofrelationship between 10Dq and oxidation potential. (c) Comparison of OER performance and the corresponding
enlarged pre-catalytic redox couple of Co3O4 Co2.95Fe0.05O4 and Co2FeO4.
References[1] X. Deng, H. Tüysüz, et al, Chem. Mater., 2017, 29, 40−52.
[2] R. P. Wang, F. de Groot, J. Phys. Chem. C 2022, 126, 8752−8759.
[3] F. Neese, WIREs Computational Molecular Science 2011, 2, 73-78.