Ⅲ-2

Materials Sciences

BL1UⅢ -2. Materials Sciences

BL1U

Evidence for Suppression of Cation Vacancies in Ce:Gd3Al2Ga3O12
Scintillator by Mg Codoping
K. Fujimori1, M. Kitaura1, Y. Taira2, M. Fujimoto3, Y. Okano4, H. Zen5, M. Katoh3,8,
M. Hosaka6, J. Yamazaki3, K. Kamada7 and A. Ohnishi1
1
Faculty of Science, Yamagata University, Yamagata 990-8560, Japan
National Institute of Advanced Industrial Science and Technology, Tsukuba 305-8568, Japan
3
UVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
4
Center for Mesoscopic Sciences, Institute for Molecular Science, Okazaki 444-8585, Japan
5
Institute of Advanced Energy, Kyoto University, Uji 611-0011, Japan
6
Synchrotron Radiation Research Center, Nagoya University, Nagoya 464-8603, Japan
7
New Industry Creation Hatchery Center, Tohoku University, Sendai 980-8579, Japan
8
Hiroshima Synchrotron Radiation Center, Hiroshima University, Higashi-Hiroshima, 739-0046
2

Recently, it was clarified that Mg codoping is aneffective manner to suppress the trapped electron
centers responsible for phosphorescence of Ce doped
Gd3Al2Ga3O12 (Ce:GAGG) scintillator [1]. The trappedelectron centers are formed due to charge compensationof Ga/Al vacancies at the octahedral site. It is thus
expected that such Ga/Al vacancies are decreased by
Mg codoping. The Gamma-ray induced positronannihilation lifetime spectroscopy (GiPALS) is known
to be the unique experimental method that can obtain
the information on negatively charged defects such as
cation vacancy of bulk crystal [2]. This method makes
it clear whether Mg codoping is effective for the
suppression of cation vacancies in Ce:GAGG
scintillators. In the present study, GiPALS spectra of
GAGG, Ce:GAGG, and Ce,Mg:GAGG crystals were
measured using ultrashort -ray pulses available in
BL1U, UVSOR [2]. The preliminary result of the
GiPALS has been reported in Ref. [3].
Figures 1(a)-1(c) show PALS spectra of GAGG,
Ce:GAGG, and Ce,Mg:GAGG crystals, respectively.
These data were obtained at 300 K. The relative
intensities and lifetimes were analyzed using the
program LT10 [4]. The analyzed results are listed inTable 1. As shown by broken lines in Fig.1, PALS
spectra are reproduced by two exponential decayfunctions with different lifetimes. This fact suggests that
there are at least two annihilation sites for positrons.
Such two annihilation sites are of intrinsic origins in
GAGG, because the relative intensities and lifetimes arealmost the same within uncertainties between GAGG
and Ce:GAGG. The first and second components are
assigned to positron annihilation at bulk and defectstates respectively. The lifetimes of the second
component are almost the same as those for positronannihilation at the sites of Al monovacancy and Al-O
divacancy, which were obtained from the theoretical
calculation [5]. On this basis, the second component is
assigned to the positron annihilation at the defect sites
of Ga/Al monovacancy and Ga/Al-O divacancy.
It was pointed out that Mg codoping has the ability to
reduce cation vacancies. Figures 1(a)-1(c) revealed thatthe relative intensities of the second component areclearly decreased by Mg codoping. From this result, it isevident that Mg codoping is effective for the suppressionof cation vacancies in Ce:GAGG scintillator.

Fig. 1 :PALS spectra of (a) GAGG, (b) Ce:GAGG,(c) Ce,Mg:GAGG crystals, measured at 300 K underultrashort -ray pulses.
Table 1. Lifetimes i and relative intensities Ii of thefirst and second components for GAGG, Ce:GAGG,
Ce,Mg:GAGG crystals.
GAGG
Ce:GAGG
Ce,Mg:GAGG

1 (ps)
165±1
161±2
161±1

I1 (%)
92±3
92±4
99±1

2 (ns)286±17304±17812±30I2 (%)8±3
8±4
1±1[1]M. Kitaura et al., Appl. Phys. Lett. 113 (2018) 041906.
[2] Y. Taira et al., Rev. Sci. Instrum. 84 (2013) 053305.
[3] K. Fujimori et al., UVSOR Activity Report 201846 (2019) 44.
[4] D. Giebal and J. Kansy, Phys. Procedia 35 (2012)
122.
[5] A. G. Marinopoulos, Eur. Phys. J. B 92 (2019) 242.

47

Ⅲ02- 1 -Ⅲ-2

BL1B Sciences
Ⅲ -2. Materials

BL1B

Effect of Electron-Irradiation on Acceptor State of Germanium
A. Hara and T. Awano

Faculity of Engineering, Tohoku Gakuin University, Tagajo 985-8537, Japan
were eliminated at temperatures at 400 °C. This
indicates that simple structure, such as vacancies, selfinterstitials and their aggregates, are not the origin ofholes. In addition, new lines related to effective-massstates were not found.
2.0
1.8

400 ℃

In acceptor

1.6

300 ℃

1.4
Transmiitance

Ⅲ-2

Germanium (Ge) has better mobility for bothelectrons and holes than those of silicon (Si). Moreover,as the melting point of Ge is lower than that of Si byapproximately 450 °C, crystallization occurs at a lower
temperature than Si. Thus, Ge is attracting attention asa semiconductor material for plastic substrates andthree-dimensional integrated circuits. However, a large
number of holes are generated in polycrystalline Ge due
to crystal defects; hence, defect control is an important
issue.
Although it is proposed by theoretical approach that
Ge vacancies are related with source of the holes,
detailed researches have not been disclosed. As Ge hasa high dielectric constant, the energy level of theacceptor is expected to be very shallow as group-III
impurities; hence, the BL1B line of UVSOR was
selected to detect such defects.
Electron irradiation (e-irradiation) is convenientmethod to introduce vacancies and self-interstitials.
Bulk p-type [Indium (In)-doped] Ge samples with 2.0mm thickness and 12 ohm-cm resistivity were used inthis experiment. The samples were irradiated with anelectron beam at 4.5 MeV with 3 × 1015 cm-2 at room
temperature to introduce lattice defects related to Ge
vacancies, and the transmission spectra was measured
at liquid He temperature. Samples were annealed at 200,
300, and 400 °C for 30 min in a conventional furnace
system to evaluate variations of the spectra.
Figure 1 shows the optical transmission spectra of the
In-acceptor [1,2]. Sharp lines correspond to electronictransition between ground and excited states. Owing to
the complex structure of the Ge valence band, manylines exist. Figure 1 shows the spectra of as-grown andas-e-irradiated samples; in addition, samples annealed
at 200, 300, and 400 °C.
Intensity of the In-acceptor decreased after eirradiation, but increased and returned to that of asgrown sample with increasing annealing temperature at
400 °C. This indicates that e-irradiation introduced
donors that were eliminated at 400 °C. Thus, simple
structural defects, such as vacancies, self-interstitials
and their aggregates, are not the origin of holes because
the holes survive in polycrystalline Ge annealed at
500 °C.
In addition, it was clarified that the new sharp lines
related to effective-mass states did not form between 20
and 100 cm-1. The thermal stability of e-irradiation
defects and hole-related defects generated in poly-Ge
are different. Thus, more complex defects including
impurities may be related to the generation center ofholes.
In summary, optical transmission spectra of eirradiated Ge were measured at liquid He temperature.
It was found that e-irradiation generated donors that

1.2

200 ℃

1.0
0.8

As e-irradiation

0.6

As-grown

0.4
0.2
0.0

20

30

40

50
60
70
80
Wave number (cm-1)

90

100

Fig. 1. Transmittance of Ge.
[1] R. L. Jones and P. Fisher, J. Phys. Chem. Solids 26(1965) 1125.
[2] W. Kohn, in Solid State Physics, ed. F. Seitz and D.
Turnbull (Academic Press, New York, 1957) Vol. 5, p.
257.

48

Ⅲ02- 2 -BL1B

Ⅲ -2. Materials Sciences

BL1B

Change of Phase Transition Temperature of KDP Single Crystal by
Alanine Doping
Z. Mita1, A. Goto1, H. Watanabe1,2 and S. Kimura1,2

Graduate School of Frontier Biosciences, Osaka University, Suita, 565-0871, Japan
Department of Physics, Graduate School of Science, Osaka University, Toyonaka 560-0043, Japan
1

2

Second harmonic generation (SHG) is used in laser
pointers and other compact laser devices. Among many
SHG materials, potassium dihydrogen phosphate(KH2PO4, KDP) is well known and used in applications.
Recently, it has been reported that the doping of 0.5wt% alanine in KDP improves the SHG efficiency by afactor of about two [2].
However, many basic physical properties about theorigin of the increase of the SHG efficiency due to thealanine doping has never been reported so far. To clarify
the origin of the SHG efficiency change by the doping,
we have measured polarization and temperaturedependences of optical conductivity spectra of singlecrystalline samples of pristine KDP and L-alaninedoped KDP.
We have grown KDP single crystals with and without
the doping of 0.5-wt% L-alanine using the solvent
evaporation method and confirmed to be orthorhombic
structure at room temperature by taking X-ray Lauediffraction patterns. Anisotropic optical reflectivity
spectra in the terahertz (THz) region around the phasetransition temperature from 117 K to 124 K has beenmeasured by using BL1B of UVSOR-III and laboratorial
equipments. The obtained spectra were converted to
optical conductivity [σ(ω)] spectra by the KramersKronig analysis. Temperature dependence of the σ(ω)
spectrum with the electric vector perpendicular to the caxis (E ⊥ c) in the THz region is shown in Fig. 1.
As shown in Fig. 1, we found a unique peak
appearing only at the low-temperature phase (namely Ι).
By the fitting of a Gaussian function to the peak Ι after
subtracting the high-temperature–phase spectrum, thetemperature dependences of the energy, intensity, andwidth of the peak were obtained as shown in Fig. 2. The
peak energy shifts to the higher energy side and theintensity and width increases as the temperature
decreases. The peak energy shift suggests thecontraction of the lattice constant at lower temperature,so the spectra in Fig. 1 are considered to be the spectrawith the electric vector parallel to the a axis because
only the axis monotonically shrinks of the three
independent axes [1]. Figure 3 shows the temperaturedependence of the peak area of Ι. For pristine KDP, thephase transition temperature can be evaluated as 122 K,
which is the same as that reported in the previous work[1]. For 0.5-wt% doping, the transition temperatureslightly increased. To clarify the doping effectsystematically, further experiments with more doping
amounts or detailed temperature steps are needed.

Ⅲ-2
Fig. 1. Anisotropic optical conductivity [σ(ω)] spectra
at temperatures from 118 to 123 K in the THz region
perpendicular to the c-axis (E ⊥ c). A peak at 14.8 meV(namely Ι) appears below the phase transition
temperature of 122 K.

Fig. 2. Peak energy (red), intensity (blue), and width(green) of the 14.8-meV peak as a function oftemperature.

Fig. 3. Temperature dependence of the area of the
14.8-meV peak of pristine KDP (blue) and 0.5-wt% Lalanine-doped KDP (red). The area is normalized by
the intensity at 117 K.
[1] G. Busch and P. Scherrer, Naturwiss. 23 (1935) 737.
[2] K. D. Parikh et al., Cryst. Res. Technol. 45 (2010) 603.

49

Ⅲ02- 3 -BL2A Sciences
Ⅲ -2. Materials

BL2A

Mo LIII--edge XANES Study of Catalytically Active Mo Species on
H-MFI for Methane Dehydroaromatization with Hydrogen
H. Aritani1, K. Kuramochi2, R. Yamazaki2, S. Sato1, Y. Nozawa1, A. Kato1 and A. Nakahira31

Ⅲ-2

Graduate School of Engineering, Saitama Institute of Technology, Fukaya 369-0293, Japan 2Advanced Science
Research Laboratory, Saitama Institute of Technology, Fukaya 369-0293, Japan
3
Graduate School of Engineering, Osaka Prefecture University, Sakai 599-8531, Japan

Molybdenum-modified H-MFI zeolite is a typical
GTL (Gas To Liquid) catalyst for methane dehydroaromatization (Methane To Benzene: MTB). On the
Mo/H-MFI catalysts, it is a serious problem fordevelopment of MTB reaction, and thus, clarificationof the deactivation process over the catalysts is one of
the important points. Not only carbon deposition onacid sites of H-MFI but also excess carbonization ofactive Mo species causes the deactivation of MTB.
Hydrogen addition to methane reactant is effective forinhibiting the deactivation [1]. However, reductive
effect for active Mo species (well dispersed Mo2C, inmajor) cannot be avoided. In the present study, Mo L3edge XANES study is introduced to characterize theactive Mo-carbide species on H-MFI after the methane
dehydroaromatization with H2. For inhibiting excess
Mo carburization, V co- modification effect on Mo/HMFI has also been studied.
Mo(5wt%)/H-MFI and Mo-V/H-MFI catalysts wereprepared by impregnation of H-MFI (Si/Al2=30-72)
support with MoO2(acac)2−CHCl3 or MoO2(acac)2−
VO(acac)2−CHCl3 solution (Mo/V=10-40), and followedby drying overnight and calcination at 773 K. The
reaction condition for methane dehydroaromatization
was described in a previous report [2,3]. Mo LIII-edge
XANES spectra were obtained in BL2A of UVSOR-IMS
in a total-electron yield mode using InSb double-crystal
monochromator. Photon energy was calibrated by using
Mo metal-foil at Mo LIII--edge, and normalized XANES
spectra were presented by using REX-2000 (Rigaku)
software.
As shown in Fig. 1 (top), edge energy of LIII-edgestrongly relate to the valence of Mo ions. Using thereferences of Mo metal and α-Mo2C, the reduction
degree of active Mo species on H-MFI after the MTB
reaction with H2 are evaluated. For the XANES
spectra of Mo-H-MFI catalysts in Fig. 1 (middle), theactive Mo species are likely due to deeply reduced
carbide species which is more carbonized than Mo2C.
The reduction degree almost independent on H2 cofeed in the MTB reaction, and therefore, The MoCx
(x>0.5) species are formed through the deep reduction
by methane. On these catalysts, H2 co-feed (1-2 %)affect the inhibition of coke deposition. To suppress
excess reduction, V co-modification on Mo/H-MFI (inMo/V=10) has been found to be effective towards theenhancement of reactivity. In Fig. 1 (bottom), XANES
spectra of these catalysts are shown. By V comodification, the reduction degree of Mo species

slightly suppressed in MTB reaction. The study about
optimal Mo/V ratio is now in progress.

Fig. 1. Mo LIII-edge XANES of reference Mo samples[top], Mo/H-MFI catalysts reacted with CH4-H2(0-3 %)[middle], and V co-modified catalysts reacted with
CH4-H2(1 %). First derivatives of XANES are shown inupper right of each figure.
[1] H. Aritani et al., J. Environm. Sci. 21 (2009) 736.
[2] H. Aritani et al., UVSOR Activity Report 2018 46(2019) 49.
[3] H. Aritani et al., UVSOR Activity Report 2017 45(2018) 44.

50

Ⅲ02- 4 -BL2A

Ⅲ -2. Materials Sciences

BL2A

Local Environment of Mg2+ on Hydroxyapatite Surface
T. Nakamura, R. Kawanabe, H. Murata and A. Nakahira

Department of Materials Science, Osaka Prefecture University, Sakai 599-8531, Japan
Hydroxyapatite (Ca5(PO4)3OH, HAp) is a main
inorganic component of human bones and teeth. It has
both of cation- and anion-exchange abilities. In humanbodies, it is exposed to various ions of body fluids.
Indeed, biological HAp is not pure but contains
various kinds of defects and impurity ions, which
affect properties of HAp [1,2]. Therefore, it isimportant to investigate reactions of these ions withthe surface of HAp.
Mg2+ is one of the main impurities of human bones,
which plays an important role of bone-remodeling. In
the present study, we investigated local environmentsof Mg2+ reacted on the surface of HAp using X-ray
absorption near edge structure (XANES).
HAp samples were synthesized by the solutionprecipitation method [3]. Starting materials were 0.1
mol/L Ca(NO3)2 and 0.1 mol/L (NH4)2HPO4 aqueous
solutions. They were mixed and matured at 80 °C for
5 h. The pH was kept at 10 by adding 0.1 mol/L KOH
aqueous solution. In order to prevent formation of Ca2+
vacancies, the initial Ca/P was set to 2, which is larger
than stoichiometric composition of HAp, 1.67. Then,they were filtrated, washed by ion-exchanged waterand dried at 50 °C. Mg2+-doped HAp samples as areference material were also synthesized by sameprocedures with addition of 0.1 mol/L Mg(NO3)2
aqueous solution to starting materials.
Obtained HAp powders were pressed into pellets of
10 mm in diameter. Parts of them were calcined at1100 °C. The pellets were soaked in 50 mL of 0.01
mol/L Mg(NO3)2 aqueous solution for 10 min. Then,they were well washed by ion-exchanged water.
Mg-K XANES spectra were collected by the partial
fluorescent (PFY) mode using a silicon-drift detector(SDD) at BL2A in UVSOR. Fluorescence X-ray
spectra were de-convoluted using gauss functions,which was reported elsewhere [4]. X-ray beams weremonochromated using beryl double crystals. Samples
were mounted using carbon tapes on an Ti plate.
X-ray diffraction measurements indicated thatsamples consists of HAp and no secondary phases
were observed even after calcination at 1100°C. This
result indicates that our HAp samples havestoichiometric composition [1,3].
Figure 1 shows Mg-K XANES of Mg2+-adsorbed
samples. They have the same features to those of
Mg2+-doped HAp. This results indicated that Mg2+ wasincorporatied into HAp crystals. As-dried HAp gavesmooth spectra but ones calcined at 1100 °C gaverather noisy spectra. In this case, we observed only 1
cps of fluorescence X-ray of Mg even at the peak,1312 eV. Such weak fluorescence X-ray of Mg
indicated that HAp calcined at 1100 °C catched only

small amounts of Mg2+. Since the as-dried HAp
samples have higher solubility in water than ones
calcined at 1100 °C [3], there results implies that thereaction of Mg2+ with surface of HAp proceeds via a
dissolution-reprecipitation process.

Mg-K
PFY

Mg2+-adsorbed HAp(1100°C)

Intensity / arb. units

Mg2+-adsorbed HAp(as-dried)
Mg2+-doped
HAp

Mg(OH)2

MgO

1290

1300

1310 1320 1330
Photon energy / eV

1340

Fig. 1. Mg-K XANES of Mg2+-adsorbed HAp samples(red lines) and reference materials (black lines).

[1] J. C. Elliott, Structure and Chemistry of the Apatites
and Other Calcium Orthophosphates (Elsevier,
Amsterdam, 1994).
[2] E. Boanini et al., Acta Mater. 6 (2010) 1882.
[3] K. Shitara et al., J. Asian Ceram. Soc. 2 (2014) 64.
[4] H. Murata, UVSOR Activity Report 2018 46 (2019)53.

51

Ⅲ02- 5 -Ⅲ-2

BL2A Sciences
Ⅲ -2. Materials

BL2A

XAFS Analysis of Ga2O3 Loaded Al2O3 Photocatalysts for Carbon Dioxide
Reduction
T.Yoshida1, M. Akatsuka2, R. Ito2, A. Ozawa2, M. Yamamoto1 and T. Tanabe1

Advanced Research Institute for Natural Science, Osaka City University, Osaka 558-8585, Japan
2
Graduate School of Engineering, Osaka City University, Osaka 558-8585, Japan1

Ⅲ-2

Gallium oxide (Ga2O3) photocatalysts can reduce CO2
to CO with H2O, although the efficiency of CO
production is very low [1]. Generally, photocatalytic
activity depends on the local structure of the surface
active site. However, there are few works investigating
the influence of Ga2O3 local structure on the CO2
photoreduction activity. In the present study, we havefocused to geometrical or morphological effects of Ga2O3
particles supported on Al2O3 (referred as Ga2O3/Al2O3,
hereafter) for CO2 reduction under UV light irradiation.
The reasons of utilization of Al2O3 as the support are
twofold, (1) to increase surface area of Ga2O3, as
evidenced by the observation that Ga2O3/Al2O3 was used
for the removal of NOx, and (2) that Al2O3 hardly show
the photocatalytic activity for both water splitting and
CO2 reduction.
Ga2O3/Al2O3 samples were prepared by impregnationof γ-Al2O3 with aqueous solution of gallium nitratefollowed by dry and calcination in the air at 773 K for 4h, as described elsewhere [2]. The loading amounts of
Ga2O3 were 1, 5, 10 and 20 wt%. Unsupported Ga2O3 andGa2O3/SiO2 samples were also prepared in the similar
way to Ga2O3/Al2O3. The Ga2O3 sample was employed
for XRD measurement to identify the crystal phase of
Ga2O3. Surface areas of all the prepared samples were
measured by BET method. Ga L3-edge XANES were
measured with the beam line of BL2A at UVSOR,
Institute for Molecular Science in Japan, in a total
electron yield mode.
Photocatalytic CO2 reduction with H2O was carried out
over the Ga2O3/Al2O3 sample. CO production rates over5, 10 and 20 wt% Ga2O3/Al2O3 samples were higher thanthose over -Ga2O3 and Al2O3 samples, while over 1 wt%
Ga2O3/Al2O3, it was almost the same as that over Al2O3
sample.
Unsupported Ga2O3 was identified as γ-Ga2O3 by the
XRD pattern. On the other hand, very weak and broadlines due to Ga oxide phase were observed for
Ga2O3/Al2O3 samples but could not be identified clearly.
Based on the BET measurements for a bare Al2O3 andGa2O3/Al2O3 samples, we roughly estimated the surface
area of Ga oxide phase in each Ga2O3/Al2O3 sample bysubtracting the component of Al2O3 support. We regarded
that the surface areas of Ga oxide phase are almost thesame each other.
Figure 1 shows Ga L3-edge XANES spectra. Twopeaks around 1121 and 1123 eV are observed for
Ga2O3/Al2O3 samples. A peak appeared near 1123 eV iscaused by a Ga-O-Al bond [3], indicating that someinteraction between Ga2O3 and Al2O3 occurred in all thesamples. On the other hand, Ga2O3/SiO2 samples showedno prominent peaks in XANES, suggesting that Ga
species are highly dispersed on SiO2 surface.

Fig. 1. Ga L3-edge XANES spectra of all preparedsamples. The spectrum of β-Ga2O3 is also given forcomparison.

[1] H. Yoshida, L. Zhang L, M. Sato, T. Morikawa, T.
Kajino, T. Sekito, S. Matsumoto and H. Hirata, Catal.
Today, 251 (2015) 132.
[2] K. Nishi, K. Shimizu, M. Takamatsu, H. Yoshida,
A. Satsuma, T. Tanaka, S. Yoshida and T. Hattori, J.
Phys. Chem. B 102 (1998) 10190.
[3] K. Shimizu, M. Takamatsu, K. Nishi, H. Yoshida,
A. Satsuma, T. Tanaka, S. Yoshida and T. Hattori, J.
Phys. Chem. B 103 (1999) 1542.

52

Ⅲ02- 6 -BL2A

Ⅲ -2. Materials Sciences

BL2A

Local Structure Investigations of Al in Spinel Compounds Induced on Swift
Heavy Ion Irradiations
S. Yoshioka1, K. Yasuda1, S. Matsumura1, E. Kobayashi2 and K. Okudaira3

Department of Applied Quantum Physics and Nuclear Engineering Kyushu University, Fukuoka 819-0395, Japan
2
Kyushu Synchrotron Light Research Center (SAGA-LS), Tosu 841-0005, Japan
3
Graduate School of Advanced Integration Science, Chiba University, Chiba 263-8522, Japan

1

Magnesium aluminate oxide (MgAl2O4) is one of
the common spinel compounds. Since it shows avariety of interesting physical and chemical properties,
its microstructure has been extensively investigated. A
cationic disordered MgAl2O4 spinel is represented by
the formula of [Mg1−xAlx](MgxAl2−x)O4, where thesquare brackets and the parentheses denote thetetrahedral and octahedral sites, respectively. The
variable x is called the inversion parameter, whichquantifies the cation disorder. Radiation with swift
heavy ions (SHIs) interacts with materials and causes
the structural change. It is therefore applied to material
processing, modifications, etc. SHI irradiation
provides high energy deposition through electronic
stopping to the materials. SHIs in insulating solidmaterials are known to leave trails of damage along theion path with a diameter of several nanometers.
Structural change related to the cationic disorder has
been also observed in MgAl2O4 with SHI irradiation
using transmission electron microscopy observation.
In this study, we clarify local coordination of eachcation element, on which we conducted synchrotron
radiation-based X-ray analysis.
Plates of poly-crystal MgAl2O4 with the shape of
10×4×0.5 mm were used in this study. These
specimens were irradiated with 200 MeV Xe ions tofluences of 1×1013 cm-2 at the H1 beamline of thetandem ion accelerator facility in the Japan Atomic
Energy Agency (JAEA)-Tokai. At the beginning ofeach paragraph, two space characters should be
inserted as an indent. Mg K-edge and Al K-edge
XANES measurements were performed at the BL2A
beamline of UVSOR Okazaki, Japan, using the partial
fluorescence yield method (PFY). A KTiOPO4 (KTP)
double crystal monochromator defined Mg K and Al K
absorption edges in the energy region from 1290 to1340 eV and 1540 to 1610 eV, respectively. The
samples were set with their surface perpendicular to
the incident X-ray beam. Fluorescence X-rays of Mg
Kα and Al Kα were collected using an energy
dispersible silicon drift detector (SDD). All
measurements of XANES spectra were carried out invacuum of 1 × 10−5 Pa at room temperature.
Figure 1 shows the XANES spectra with the Mg Kedge (1300 eV) acquired from the MgAl2O4 samples
before and after irradiation with 200 MeV Xe ions withfluences of 1×1013 cm-2. The Mg K-edge spectrum
features of the irradiated MgAl2O4 sample wereclearly different from those of the pristine sample.

Especially, both the peak intensity ratio of A/B and C/B
decreased after the irradiation. The spectrum shapes on
Al K-edge also changed by the irradiation. Detailed
analyses on the local environment of Mg and Al in the
MgAl2O4 irradiated with SHI are in progress by
combined use of the XANES and the first principles
band structure calculations.

Mg K-edge

C

A
B

Pristine

Irradiated

1300

1310

1320

Photon energy (eV)1330

Fig. 1. Mg K-edge XANES spectra of pristine andirradiated MgAl2O4 with 200 MeV Xe ions to fluencesof 1×1013 cm−2.

[1] T. Yamamoto et al., Nucl. Instrum. Meth. B. 245(2006) 235.
[2] K. Yasuda et al., Nucl. Instrum. Meth. B. 250 (2006)
238 .

53

Ⅲ02- 7 -Ⅲ-2

BL2A Sciences
Ⅲ -2. Materials

BL2A

X-ray Absorption Analysis of Rb Ions in FAPbI3
K. Osonoe1,2, M. Tohyama1, M. Ishida1, K. Hirose1,2 and T. Yamamoto1,3,4

Faculty of Science and Engineering, Waseda University, Tokyo 169-8555, Japan
Institute of Space and Astronautical Science, JAXA, Sagamihara 252-5210, Japan
3
Institute of Condensed-Matter Science, Waseda University, Tokyo 169-8555, Japan
4
Kagami Memorial Research Institute for Materials Science and Technology, Waseda University,
Tokyo 169-0051, Japan1

2

tape is also attached on the film surface and dinode,
which could keep the electrical conductivity between
sample film and dinode.
Observed Rb-L3 XANES spectra are shown in Fig. 1
together with the reference spectrum of RbI. Significant
difference between these spectra depending upon thegrain size could be clearly seen. From the results, we
could confirm that the local environment of Rb ions issensitive to change in grain size of (CsFAMA)Pb(IBr)3.

RbI
large grain
midium grain
small grain

100

Normarized Intensity

Ⅲ-2

Organic-inorganic hybrid perovskite-type solar cells
have attracted significant interest owing to their lowcost fabrication and high performance, exhibiting a
rapid increase in power conversion efficiency after the
discovery of its application for solar-cells [1]. The
organic-inorganic hybrid perovskite is used as a lightabsorption layer in the stacking structure of the thinfilms in a perovskite solar cells (PSC). Although
methyl-ammmonium lead tri-iodide (CH3NH3PbI3;
hereafter MAPbI3) was used at early stage, MAPbI3 is
not stable at high temperature and under humid
condition. Recently, FAPbI3, FA = formamidinium:
CH(NH2)2, based materials have been investigated toget higher stability and efficiency than MAPbI3. In theseresearches, cations at FA site and anions were often
partially replaced by other ions to control the tolerance
factor, which is a well-known parameter to estimate astability of perovskite structure [2]. It was reported
among such studies that Rb-doping could enhance thelight absorption efficiency. However, the mechanism ofsuch enhancement of efficiency has not yet been
understood. Although it is important to know a local
environment of such doped ions in the host materials in
an atomic scale, such analysis is often skipped due to adifficulty of the analysis for dilute dopants. In thepresent study, we have synthesized Rb-doped(CsFAMA)Pb(IBr)3 and the local environment of doped
Rb ions in the synthesized materials have been
investigated by the X-ray absorption near-edge structure(XANES) measurements.
Thin films of Rb-doped (CsFAMA)Pb(IBr)3 wereprepared by the spin coating method on the glass
substrate. After the coatings, thermal treatment wasgiven changing the temperature. Rb concentration wasapprox. 3 at% to CsFAMA. Synthesized films werecharacterized by the conventional powder X-ray
diffraction method using Cu Kα X-rays, which showed
all the synthesized films crystallized in a singularphased perovskite structure. Sample morphology was
also observed by the scanning electron microscope(SEM), which showed the grain size changes according
to the temperature of thermal treatment. Rb L3-edge Xray absorption near edge structure (XANES) spectra ofsynthesized films were observed at BL2A in UVSOR
by the total electron yield method. Sample films on theglass substrate were put on the carbon adhesive tape,which were attached on the first dinode of the electron
multiplier. In order to avoid charge-up of the sample
films on the insulating glass substrate, carbon adhesive

50

0

1810

1820

Energy (eV)1830

Fig. 1. Observed Rb-L3 XANES spectra of RbI and(RbCsFAMA)Pb(IBr)3.

[1] A. Kojima et al., J. Am. Chem. Soc. 131 (2009) 6050.
[2] S. Burger et al., J. Mater. Chem. A 6 (2018) 21785.

54

Ⅲ02- 8 -BL2A, BL5B

Ⅲ -2. Materials Sciences

BL2A, BL5B

Luminescence Decay Curves of Inorganic Scintillators Excitedwith Soft X-ray Pulses under Single Bunch Operation ModeK. Kawai1, H. Zen2, E. Nakamura3, M. Kitaura1, K. Kamada4 and A. Ohnishi1
Faculty of Science, Yamagata University, Yamagata 990-8560, Japan
Institute of Advanced Energy, Kyoto University, Uji 611-0011, Japan
3
UVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
4
New Industry Creation Hatchery Center, Tohoku University, Sendai 980-8579, Japan1

2

The single bunch operation mode in UVSOR
synchrotron facility is one of the advantages over othersynchrotron facilities. This mode is characterized by therepetitive light pulses of sub-micro second. Users can
carry out time-resolved spectroscopy experiment ofsolids, liquids, and gases. On the other hand, thebeamlines used under the single bunch operation mode
are not so many, so we have to develop experimental
systems to explore unique time-resolved spectroscopy
with vacuum ultraviolet (VUV) light and soft X-ray(SX). Actually, there are many proposals for the usage
of VUV and SX photons in measurements ofluminescence decay curves.
In order to respond such user’s request, we tried tomeasure luminescence decay curves of typicalinorganic scintillators at the BL2A and BL5B beamlines.
The former and latter allow us to use photons in SX andVUV regions, respectively. The luminescence detection
systems with a time correlated single photon counting
were installed at the two beamlines. Here, we report theresults of luminescence spectra and luminescence decay
curves of Ce-doped Gd3Al2Ga3O12 (Ce:GAGG) andMg-codoped Ce:GAGG scintillators, measured at 300
K under excitation with SX photons of 1.05 keV.
Figure 1 shows luminescence spectra of Ce:GAGG
and Ce,Mg;GAGG scintillators. The intensities werenormalized to unity at the maximum of Ce:GAGG. A
prominent band is observed around 550 nm. This bandhas been assigned to Ce3+ 5d-4f transition [1]. The Ce3+
band is weakened by Mg codoping. Luminescencedecay curves of the 550-nm band were shown in Fig. 2.
The luminescence decay curves are composed of shortand long-lived components. The long-lived component
appears as a pile-up component. This component isenhanced under host excitation with VUV and SX
photons, compared to Ce3+ 4f-5d excitation with visible
photons [2]. Since the luminescence intensity is givenby time-integration of the decay curve, it should beclearly decreased by Mg-codoping. This situation canbe seen in Fig. 1. The lifetime of the short-lived
component also becomes shorter, and the pile-up
component is weakened. These results are in agreementwith those in Refs. 3.
Now, the BL2A and BL5B beamlines are ready to use
SX and VUV light pulses under the single bunch
operation mode. Especially, the research anddevelopment of scintillators, requiring high-energy lightpulses, may be suitable. Users who want to use VUVand SX pulses are welcome to the use of thesebeamlines.

Ⅲ-2

Fig. 1: Luminescence spectra of Ce:GAGG, andCe,Mg:GAGG scintillators, measured at 300 K under
excitation with SX photons of 1.05 keV.

Fig. 2: Luminescence decay curves of Ce:GAGG,
and Ce,Mg:GAGG scintillators, measured at 300 K
under excitation with SX photons of 1.05 keV.
[1] M. Kitaura et al., J. Appl. Phys. 113 (2014) 041906.
[2] M. Kitaura et al., Opt. Mater. 41 (2015) 45.
[3] K. Kamada et al., Opt. Mater. 41 (2015) 63.
[4] M. Kitaura et al., Appl. Phys. Express 9 (2016)072602.

55

Ⅲ02- 9 -BL3B Sciences
Ⅲ -2. Materials

BL3B

Intrinsic Luminescence from Self-trapped Excitons in(Ca1-xNax)2(Mg1-2xAl2x)Si2O7 Single Crystals upon Vacuum UV Excitation
N. Kodama, T.Takahashi, T. Inoue and Y. Takahashi

Faculty of Engineering and Resource Science, Akita University, Akita 010-8502, Japan

Ⅲ-2

Na- and Al-substituted melilite (Ca1-xSrx)2MgSi2O7
crystals are expected to exhibit incommensurate
modulations similarly to Sr-substituted (Ca1-xSrx)2
MgSi2O7 [1]. To date, little research has focused on theformation of self-trapped excitons (STEs) in terms ofthe dimensionality and modulation of the structure. We
report intrinsic luminescence from STEs. In addition,
we examine the correlation between the intensity andbandwidth of intrinsic luminescence and the twodimensionality and structure modulation in (Ca1-xNax)2(Mg1-2xAl2x)Si2O7 (x = 0.0, 0.05, 0.10, 0.25) crystals.
Absorption, luminescence, and excitation spectra of
STEs in (Ca1-xNax)2(Mg1-2xAl2x)Si2O7 (x = 0, 0.05, 0.10,0.25) single crystals were measured in the temperature
range of 5-293 K using the undulator beamline BL3B at
the UVSOR facility. Under VUV excitation at 160 and
70 nm, intrinsic luminescence from STEs was observedin these crystals.
Figures 1(a)-1(d) show the luminescence spectra for(Ca1-xNax)2(Mg1-2xAl2x)Si2O7 (x = 0.0, 0.05, 0.10, 0.25)
excited at 160 nm in the 5-293 K range. The
luminescence spectra of (Ca1-xNax)2(Mg1-2xAl2x)Si2O7
with x = 0.0, 0.05, 0.10, and 0.25 consisted of two broad
bands with peaks at 246-255 nm and 311-332 nm,
associated with STE(I) and STE(II) in the 5-293 K
range. The STE(I) and STE(II) luminescence intensities
decreased rapidly with increasing temperature. With
increasing x, the intensity of STE(I) passed through amaximum at the intermediate fraction x = 0.10. On theother hand, the intensity of STE(II) increased withincreasing x. There are two plausible explanations forthe dependence of luminescence intensities on the
Na/Al fraction, x, involving (i) a two-dimensional effector (ii) an incommensurate structural modulation effect.
The magnitude of two-dimensionality for (Ca1-xNax)2(Mg1-2xAl2x)Si2O7 increased with increasing x due to thelarger ionic radius involved in substituting Na2+. Thus,
the dependence of the STE(II) intensity on x can be
explained in terms of a two-dimensional effect. On theother hand, the dependence of the STE(I) luminescencecannot be accounted for by two-dimensionality, because
the maximum of the intensity varies with x. The otherpossible explanation is that the structural modulation
effect of an incommensurate phase increases thenumber of local sites with larger distortion potentials.
The formation of STEs and the luminescence intensity
may be strongly affected by whether or not the crystals
form a modulated structure (commensurate or
incommensurate phase) and by the modulation
amplitude. We found that the (Ca1-xNax)2(Mg1-2xAl2x)

Si2O7 crystal with x = 0.10 showed the most intense
luminescence among the four compositions examined(x = 0.0, 0.05, 0.10, and 0.25). The Na- and Al-substituted(Ca1-xSrx)2MgSi2O7 crystals with Na fractions, x,
ranging from 0.0 to 0.25 are expected to exhibit twodimensional incommensurate modulations
with a__modulation vector along [110] and [110], depending on
the composition, similarly to Sr-substituted (Ca1-xSrx)2
MgSi2O7 [1]. These structural changes with varying Na
composition suggest that the intense luminescence at x
= 0.10 is mainly due to a structural modulation effect.
The Na composition dependence of the bandwidths of
STE(I) and (II) suggests inhomogeneous broadening of
the STE luminescence due to the random distributionsof the Ca2+/Na+ and Al3+/Mg2+ sites; this distribution
creates different environments for SiO4 and AlO4
tetrahedra than STE sites followed by incommensurate
modulation.
Wavelength / nm
600 500 400300
λex=160nm(a)Wavelength / nm
600 500 400 300

20

STEⅡ

50

200

20

Wavelength / nm
600 500 400
300

(d)

STEⅡ
5K
45K
77K
100K
125K
160K
180K
200K
240K
293K

50

5K

30
40
Wavenumber/×103 cm-1

λex=160nm

STEⅠ

30
40
Wavenumber/×103 cm-1

200
STEⅠ

(b)
5K
45K
77K
100K
125K
160K
180K
200K
240K
293K

20
30
40
Wavenumber/×103 cm-1

(c)Wavelength / nm
600 500 400300
λex=160nm

STEⅠ

STEⅡ

λex=160nm

200

45K
77K
100K
125K
160K
180K
200K
240K
293K

50

200
STEⅠ

STEⅡ
5K

20
30
40
Wavenumber/×103cm-1

45K
77K
100K
125K
160K
180K
200K
240K
293K

50

Fig. 1. Dependence of intrinsic luminescence on Na
fraction, x, in (Ca1-xNax)2(Mg1-2xAl2x)Si2O7: (a) x=0.0,(b) x=0.05, (c) x=0.10, and (d) x=0.25 under excitation
at 160 nm in the temperature range 5-293 K.

[1] J.C. Jiand, M. Schosnig, A.K. Schapaer, K. Ganster,H. Ragaer and L. Toth, Phys. Chem. Minerals 26 (1998)
128.

56

Ⅲ02- 10 -BL3B, BL5B

BL3B, BL5B

Ⅲ -2. Materials Sciences

Evaluation of Fluorescence Lifetimes of Scintillatorsfor High-energy Particle Experiments

H. Ikeda, H. Oikawa, Y. Hiruma, M. Kitaura, A. Ohnishi, Y. Tajima and H.Y. Yoshida
Department of Physics, Yamagata University, Yamagata 990-8560, Japan

Recently, the operation of particle detectors at higher
counting rates is required in a high-energy physics
experiment. To satisfy this requirement, the scintillators
used in a particle detector need to have a shortfluorescence lifetime, which enables fast time response.
For this purpose, we have measured fluorescence
spectra and decay curves for plastic scintillators used in
the J-PARC E14 KOTO experiment [1], commerciallyavailable recycled resin plates, and inorganic crystals.
The fluorescence decay curves were measured by using
light pulses from visible to vacuum ultraviolet undersingle bunch operation, which ensures a time-correlated
single-photon counting method.
The top of Fig. 1 shows the decay curve of a plastic
scintillator EJ-200 for the 430 nm band under
excitation at 400 nm, and the bottom of Fig. 1 shows
for the 420 nm band under excitation at 20 nm. They
were measured at room temperature. The blue lines
indicate experimental data. Lifetimes were analyzed
by using the data analysis framework ROOT [2].
We assumed that the obtained decay curves are
fitted with the formula

bottom of Fig. 2 shows for the 430 nm band under
excitation at 20 nm. The fitting curves reproduce theexperimental data. The fluorescence lifetimes of EJ200 and Scintirex, determined from our analysis, aresummarized in Table 1.

Ⅲ-2

Fig. 1. Decay curve of EJ-200 measured at room
temperature under excitation at 400 nm (top) and 20
nm (bottom). The former and latter are obtained for the
430 and 420 nm photoluminescence band.

�𝐼𝐼�𝑡𝑡� = � 𝑃𝑃�𝑡𝑡 � �𝜃𝜃�𝑡𝑡 � − 𝑇𝑇� �𝐺𝐺�𝑡𝑡 𝑡 𝑡𝑡 � � 𝑑𝑑𝑑𝑑 � + 𝐵𝐵,

where

and

��

�

𝑡𝑡
𝑃𝑃�𝑡𝑡� = � 𝐴𝐴� exp �− �,
𝜏𝜏�
���

�

(𝑛𝑛 = 1, 2, 3 and 𝐴𝐴� = 1)

𝐺𝐺�𝑡𝑡 𝑡 𝑡𝑡 � � = � �� exp �−���Fig. 2. Decay curve of Scintirex measured at room
temperature under excitation at 265 nm (top) and 20
nm (bottom). The former and latter are obtained for the
436 and 430 nm photoluminescence band.

�𝑡𝑡 𝑡 𝑡𝑡 � − 𝜇𝜇� ��
�.
2𝜎𝜎��

(𝑚𝑚 = 1, 2)𝐼𝐼�𝑡𝑡� represents the observed decay curve, and 𝑃𝑃�𝑡𝑡�
represents the true fluorescence decay curve. If the true
decay curve is composed of multiple components, it isdescribed as the linear combination of exponential
decay functions with the parameters of lifetime 𝜏𝜏� andinitial intensity 𝐴𝐴� . 𝜃𝜃�𝑡𝑡 � − 𝑇𝑇� � is a step function todecide the time origin 𝑇𝑇� . 𝐺𝐺�𝑡𝑡 𝑡 𝑡𝑡 � � represents theresolution of the measurement system, the time
structure of the beam, and so on, and is given by a single
gaussian or a sum of two gaussians. 𝐵𝐵 is a backgroundconstant that has a role in increasing a baseline. Redlines are the fitting curves which reproduce theexperimental data.
We carried out the lifetime analysis for a plastic
scintillator Scintilex [3] in the same method. The topof Fig. 2 shows the decay curve of Scintirex for the
436 nm band under excitation at 265 nm, and theTable 1. Fluorescence lifetimes of EJ-200 and Scintirex,
determined from our data analysis.
Sample
EJ-200
Scintirex

λEX
[nm]
400

λEM
[nm]
430

20

420

265

436

20

430

τ1[ns](Ratio)1.27±0.00
2.25±0.00(82.5 %)
24.79±0.08
16.89±0.38(83.3 %)

τ2[ns](Ratio)10.56±0.22(17.5 %)
4.92±0.03(16.7 %)

[1] J. Comfort et al., Proposal for 𝐾𝐾� → 𝜋𝜋 � 𝜈𝜈𝜈𝜈̅
Experiment at J-PARC (2006).
[2] R. Brun and F. Rademakers, Nucl. Instrum. Methods
Phys. Res. A 389 (1997) 81.
[3] H. Nakamura et al., Europhys. Lett. 95 (2011) 22001.

57

Ⅲ02- 11 -BL3B Sciences
Ⅲ -2. Materials

BL3B

Thermoluminescence of Yttrium Aluminum Garnet (YAG) Crystals Grown
by Core Heating Method and Micro-pulling Down Method
Y. Kurashima1, S. Kurosawa2, R. Murakami3, A. Yamaji1, K. Kamada2,3, M. Yoshino1,
S. Tomida2, H. Sato2, Y. Yokota2, Y. Ohashi2 and A. Yoshikawa1,2,3
2

Ⅲ-2

1
Institute for Materials Research, Tohoku University, Sendai 980-8577, JapanNew Industry Creation Hatchery Center, Tohoku University, Sendai 980-8579, Japan
3
C&A Corporation, Sendaii 980-0811, Japan

Scintillators are used in medical imaging such as
Positron Emission Tomography (PET). Gamma-ray
stopping power is one of the important scintillation
properties for the PET camera and other gamma-ray
detectors. Gamma-ray stopping power is proportional
to (Zeff)a, where Zeff denotes effective atomic number
and a=4-5. Hf-based materials like Ce-doped
SrHfO3[1] are attractive scintillation materials withhigh gamma-ray stopping power due to high density
and high effective atomic number.
However, Growth of such materials by theconventional melt-growth methods with crucibles likemicro-pulling down (µ-PD) method[2] are hard
technique, because the melting points of Hf-basedmaterials are typically higher than softening andmelting point of the crucibles. The softening andmelting point of Ir, for instance, 2000 °C and 2447 °C,
respectively, while the melting temperature of SrHfO3
is 2730 °C.
Thus, we have developed a novel crystal growthmethod to search novel materials with higher melting
point than the melting point of the crucibles, and thismethod is named “Core Heating (CH) method” using
electric arc or other heat source. Since, the scintillation
properties of crystals grown by the CH method havenot been evaluated yet, and we need to confirm thefeasibility of CH method as a material search method.
To compare the growth method, we compared thescintillation properties for (Y0.99 Ce0.01)3Al5O12 (Ce:YAG),
because the melting point of Ce:YAG is 1940 °C and theconventional melt-growth is available. Ce:YAG crystals
were grown by the CH and µ-PD method.. The samples
grown by CH method (CH sample) and µ-PD method (µPD sample) were cut and polished. If the scintillation andoptical properties for CH samples are similar to those forthe µ-PD sample, the CH method is judged to be a usefultechnique as a material search method.
We found some optical and scintillation properties
such as emission wavelength, transmittance, light
output excited by gamma-ray for the CH sample were
the same level as those for µ-PD sample. Here, thedetail of the results is reported in other papers.
However, only scintillation decay time of the CH
sample was different from that of the µ-PD sample.
This result indicated that the CH sample has different
trap sites, defects from the µ-PD sample. Therefore,
we measured thermoluminescence (TL) spectra andTL glow curve to compare the trap sites. Measurementof TL spectra and TL glow curves were performed at
the beam line BL3B of UVSOR facility. The sample
was irradiated with 165-nm photons for 10 min at 7 K.
After we check no after-glow emission with a chargecoupled device (CCD, Roper Scientific, SPEC-10)
attached to a polychromator (Acton Research
Corporation, spectrapro-300i), the sample was heated
up to 300 K with a heat rate of approximately 4 K/min.
During the heating, the TL emission spectra wereobserved with the CCD.
Figure 1 shows TL glow curves of CH and µ-PD
samples. The results of TL glow curves indicated nodifferences of number of traps and their depths wereobserved clearly between the CH and µ-PD samples.
Therefore, such we found such trap sites are not thefactor to change the decays.
In this time, the TL glow curves up to 300 K was
measured, and we observed relatively shallow traps.
On the other hand, deep traps observing the glow
curves over 300 K might be related to be the decaytime deference, or other defects are also the candidates
to make the decay time slower. As future works, weevaluate and discuss such factors.

Fig. 1. TL glow curves of CH sample and µ-PD sample.
[1] S. Kurosawa, J. Pejchal, S. Wakahara, Y. Yokota
and A. Yoshikawa, Radiat. Meas. 56 (2013) 155.
[2] A. Yoshikawa, M. Nikl, G. Boulon and T. Fukuda,
Opt. Mater. (Amst). 30 (2007) 6.

58

Ⅲ02- 12 -BL3B

Ⅲ -2. Materials Sciences

BL3B

Optical Properties of a Ce2Si2O7 Single Crystal Using BL3B of the UVSOR
Facility
T. Horiai1, S. Kurosawa2, A. Yamaji1, S. Kodama1, S. Yamato1, Y. Kurashima1, M. Yoshino1,
S. Toyoda2, H. Sato2, Y. Ohashi2, K. Kamada2,3, Y. Yokota2 and A. Yoshikawa1,2,3
2

1Institute for Materials Research, Tohoku University, Sendai 980-8577, JapanNew Industry Creation Hatchery Center, Tohoku University, Sendai 980-8579, Japan
3
C&A Corporation, Sendai 980-0811 Japan

radii of Ce3+ and La3+ in the eight-coordinate sites, theionic radii are 1.143 and 1.160 Å, respectively [8].
Therefore, it was attributed to the stronger crystal fieldin Ce2Si2O7 than in La2Si2O7.
The Ce3+ 4f-5dx (x=1-5) transition peaks wereobserved in the excitation spectrum of the Ce2Si2O7 at
7 K. The excitation peaks from 4f-5d1, -5d2, -5d3, -5d4
and -5d5 were positioned around 327, 292, 273, 254
and 228 nm, respectively. In addition, the excitation
peak around 170 nm was observed, and determined tobe the host excitation band peaking.

Scintillators convert energy of ionizing radiation into
ultra-violet or visible light. When combined with suitable
photodetectors such as a photomultiplier tube (PMT),
scintillators are used in radiation detectors. Recently, Cedoped pyrosilicate type crystals, Ce:RE2Si2O7 (RE = rareearth), have been studied, and Ce-doped (Gd,La)2Si2O7(Ce:La-GPS) has been reported to have a high light yield(~42,000 photons/MeV), relatively short decay time (~63ns), good energy resolution (~5.0 %, 662 keV, FWHM)
and shows a good temperature stability of light output up
to 150 ºC [1-3].
Ce2Si2O7 nanocrystals and films were found that theemission peaks were located around 358 nm, which
well matches the wavelength sensitivity of a typical
PMT [4-6]. In addition, the internal quantum efficiencyof the Ce2Si2O7 was determined to be approximately
37 % at room temperature. Therefore, the Ce2Si2O7 isalso expected to have good scintillation properties. Thus,in this study, we tried to grow a relatively large mmscale Ce2Si2O7 single crystal, and estimated the opticalproperties.
We prepared the Ce2Si2O7 single crystal using micropulling-down method. As starting materials, we used
CeO2 and SiO2 powders the purities of which were atleast 99.99 %. After cutting and mirror polishing thesample to thickness of 1 mm, we measured thephotoluminescence spectra with a spectrometer (FLS920,
Edinburgh Instruments) consisting of a Xe lamp at room
temperature. Moreover, the emission and excitation
spectra at 7 K were measured using excitation photons at
BL3B of UVSOR, and evaluated the optical properties
independent of the lattice vibration. The sample wascooled down to 7 K with liquid helium.
Figure 1 shows the emission and excitation spectra of
the Ce2Si2O7 at room temperature and 7 K. The emission
spectrum of the Ce2Si2O7 at room temperature has asingle peak around 380 nm, while the emission
spectrum at 7 K has double peak of 5d1-2F5/2 (358 nm)
and 5d1-2F7/2 (387 nm). The emission peak around 358
nm consisted with the result measured by Choi in Ref.
4. From the results of emission and excitation spectra of
the Ce2Si2O7 at room temperature and 7 K, the emission
peak of 5d1-2F5/2 at room temperature was quenched by
the self-absorption. Comparison with the emission
spectrum of Ce-doped La2Si2O7, which has the same
space group as Ce2Si2O7 (monoclinic, P21/c) in theprevious study, the emission peak of Ce2Si2O7 is shiftedto longer wavelength [7]. Here, comparing the ionicFig. 1. Emission and excitation spectra of the Ce2Si2O7
single crystal at room temperature and 7 K.

[1] A. Suzuki, S. Kurosawa, A. Yoshikawa et al., Appl.
Phys. Express 5 (2012) 102601.
[2] A. Yoshikawa, S. Kurosawa et al., Cryst. GrowthDes. 15 (2015) 1642.
[3] S. Kurosawa, A. Yoshikawa et al., Nucl. Instruments
Methods Phys. Res. Sect. A 772 (2015) 72.
[4] W.C. Choi et al., Appl. Phys. Lett. 75 (1999) 2389.
[5] L. Li et al., Sci. Rep. 5 (2015) 1.
[6] L. Kȩpiński et al., J. Alloys Compd. 341 (2002) 203.
[7] Q. Wei et al., Materials Letters 126 (2014) 178.
[8] R.D. Shannon, Acta. Cryst. A32 (1976) 751.

59

Ⅲ02- 13 -Ⅲ-2

BL3B Sciences
Ⅲ -2. Materials

BL3B

Low-temperature Photoluminescence Properties of Rb2HfI6
S. Kodama1, S. Kurosawa2, A. Yamaji1, M. Yoshino1, S. Toyoda2, H. Sato2,
Y. Ohashi1, K. Kamada2,3, Y. Yokota2 and A. Yoshikawa1,2,3
Institute for Materials Research, Tohoku University, Sendai 980-8577, JapanNew Industry Creation Hatchery Center, Tohoku University, Sendai 980-8579, Japan
3
C&A Corporation, Sendai 980-0811 Japan12(a) 800
λex : 335 nm

700
Intensity (a.u.)

600
500
400
300

λex : 215 nm

λex : 455 nm

200
100
0

300 400 500 600 700 800 900 1000
Wavelength [nm](b) 800
700

λem: 440 nm

600
Intensity (a.u.)

Ⅲ-2

STE. For future works, the temperature dependence ofeach PLE-PL band should be studied to determine theemission mechanism.

Rb2HfI6 has been developed as a novel red-emitting
scintillator as a K2PtCl6-type compound [1]. By
substituting Rb into Cs, the scintillation emission peak of
Rb2HfI6 shifted towards longer wavelength than Cs2Hf6,
and reached ~725 nm. Rb2HfI6 has a scintillation light
output of ~40,000 photons/MeV, and such red-emission
scintillator with a high light output can be used for aremote scintillation detector coupled with an optical fiber[2]. The mechanism of shift of emission wavelength has
been still unclear, thus we evaluated the fundamental
photoluminescence properties of Rb2HfI6. We measured
the low-temperature photoluminescence excitation(PLE) and emission (PL) spectra in order to determine thefundamental luminescence properties of Rb2HfI6.
A single-crystalline Rb2HfI6 specimen was
synthesized by the vertical Bridgman growth method in
our laboratory from 99 %-pure HfI4 and 99.9 %-pure RbI
powders. We measured the PLE-PL spectra at 8 K in
BL3B. As photo-detectors for PLE measurement, photomultiplier tubes (PMTs) (Hamamatsu K.K.) of R4220
and R636-10 were used for a blue-green and red region,
respectively.
Figures 1 (a) and (b) illustrate the PL and PLE spectra
at 8 K, respectively. The excitation and emission
wavelengths were indicated as λex and λem, respectively.
Rb2HfI6 had three PLE-PL bands as follows: the blue
band (λex: 215 nm and λem: 440 nm), green band (λex:335 nm and λem: 590 nm) and red band (λex: 455 nm andλem: 725 nm). The green and red bands were reported
also in the case of Cs2HfI6 at 8 K [3], and in addition,
Rb2HfI6 was identified to have the blue band whose λexand λem were similar to the room temperature emissionof Rb2HfCl6 [4]. The green band had a highest intensity,
approximately 3 times higher than the red band, while
only red-band emission was observed in the X-ray
radioluminescence spectra at room temperature [1].
Although all emission bands had broad and single
peaked spectra, PLE spectra of three bands had several
excitation peaks, for example, ~180 nm and ~260 nm
for blue band, ~335 nm and ~400 nm for green band.
For the red band, an intense excitation peak was
confirmed at ~455 nm, additionally a small peak at ~520
nm was also observed.
The splitting of the room temperature emission at
low temperature was reported in the self-trapped
exciton (STE) luminescence of CsI [5]. We confirmedthat Rb2HfI6 had three photoluminescence bands at 8
K while the room temperature emission was the single
band. Thus, the obtained results in this study implies
that the emission origin of Rb2HfI6 was passively the

0.00045

λem : 725 nm

0.00040.00035

λem : 590 nm

500

0.00030.00025400

0.0002300

0.00015200

0.0001100

0.00005

0

100

200

300
400
500
Wavelength [nm]6000Fig. 1 (a) PL and (b) PLE spectra of Rb2HfI6 at 8 K.
The PMTs of PLE spectra measurement of the redband (λem = 725 nm) were R636-10, and others wereR4220.

[1] S. Kodama et al., IEEE Trans. Nucl. Sci. (2020) in
print.
[2] S. Kodama et al., Appl. Phys. Express 13 (2020)
047002.
[3] S. Kodama et al., UVSOR Activity Report 2018 46(2019) 62.
[4] K. Saeki et al., J. J. Appl. Phyis. 55 (2016) 110311.
[5] H. Nishimura et al., Phys. Rev. B 51 (1995) 2167.

60

Ⅲ02- 14 -BL3B

Ⅲ -2. Materials Sciences

BL3B

Temperature Dependence of PL Spectra of p-terphenyl at 6-300 K
S. Yamato1, S. Kurosawa2, A. Yamaji1, M. Yoshino1, H. Sato2,
Y. Ohashi2, K. Kamada2,3, Y. Yokota2 and A. Yoshikawa1,2,3

Institute for Materials Research (IMR), Tohoku University, Sendai 980-8577, JapanNew Industry Creation Hatchery Center (NICHe), Tohoku University, Sendai 980-8579, Japan
3
C&A Corporation, Sendai 980-0811, Japan.
1

2

Neutron detectors can be used in several fields suchas neutron diffraction for crystal structure, fusion
physics [1,2]. Here, nuclear fusion technology is
expected as next effective energy generation
technology. In fusion reactors, neutrons are emitted
from nuclear fusion reactions, and the monitoringthese particles is a important technology to control
fusion reactors and generate energy effectively.
Among several nuclei, the neutron cross section ofhydrogen nucleus is the largest in higher energy range.
1
H has relatively higher cross section for the fast neutron
than other materials. We focused on organic scintillators
which contains many 1H and have low detection
efficiency for gamma rays as background noise.
Although the neutron detectors in fusion reactors
can be exposed on higher temperature than 373 K,
conventional organic scintillators cannot be used athigh temperature. Plastic scintillators melt at around
343 K. Liquids evaporate at high temperature and are
difficult to handle. Even crystals, only low-meltingpoint materials were developed. As a first step, we
aimed to develop the organic scintillation crystals forsuch applications at over 373 K.
We grew the pure p-terphenyl crystal by the selfseeding vertical Bridgman method using an enclosed
chamber [3]. Pulling down rate for growth was ~1
mm/h. The melting point of p-terphenyl is 485 K.
We measured the photoluminescence (PL) emission
spectra of the samples under 13-300 K at the beamline
BL3B of UVSOR Synchrotron Facility. The excitationand emission spectra of p-terphenyl are shown in Fig.
1 and Fig. 2, respectively. The excitation spectra wererecorded with a cut filter for the shorter wavelengththan 370 nm. The emission spectra were recorded forthe p-terphenyl crystal excited by 280 nm photons.
In Fig. 1, absorption edge around 340 – 360 nm has
been monotonically shifted to the lower energy side as
the temperature rose, and the emission peaks of 375
and 390 nm were observed for p-terphenyl at 300 K(Fig. 2). The shapes of the spectra for p-terphenylchanged significantly between 300 K and others (200K and less than 200 K), and relatively sharp peaks
around 350 nm were observed at except 300 K. This isbecause of structural phase transition at 193.5 K by
twisting in a molecule [4,5].
As future works, we study on the relationshipbetween these results and temperature dependence ofphoto-luminesce decay time.

Ⅲ-2

Fig. 1. Excitation spectra of p-terphenyl crystal at 13300 K.

Fig. 2. Emission spectra of p-terphenyl crystal excitedby 280 nm photons at 13-300 K.
[1] H. K. Lee et al., J. Supercond. Novel Magn. 31(2018) 1677.
[2] Y. K. Kim et al., J. instrum. 7 (2012) C06013.
[3] A. Arulchakkaravarthi et al., J. Crystal Growth 234(2002) 159.
[4] Y. Yamamura et al., J. Phys. Condens. Matter 10 15(1998) 3359.
[5] Hervé Cailleau et al., Faraday Discuss. Chem. Soc.
69 (1980) 7.

61

Ⅲ02- 15 -BL3B Sciences
Ⅲ -2. Materials

BL3B

Composition Dependence of 4f-4f Emission Spectra in Pr:SrZr1-xTixO3
M. Yoshino, T. Kuyama and J. Sugiyama

Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan

Ⅲ-2

In this study, the excitation spectra and emission
spectra of Pr3+ in SrZr1-xTixO3 crystal have beenmeasured and changes in the spectra with composition
and temperature are examined.
The excitation spectra in x = 0.6 sample are shown in
Fig. 1. The rising energy in excitation spectra is close to
the band gap energy estimated from diffuse reflectancespectra. This is also the case in other composition. In
order to excite host oxides, higher energies than band gap
are selected for excitation. Fig. 2 shows the emission
spectrum in x = 0.6 sample at 350 nm excitation. The
sharp peaks around 500 nm (Greenish-blue) and 600-650
nm (Red) originate from 4f-4f transitions of Pr3+. The
intensity ratios R/(R+G) of Red emission (R) to sum of
Red and Greenish-blue emission (G) in Pr:SrZr1-xTixO3
are shown in Fig. 3. It is found that the ratios are large in
the intermediate composition. As shown in Fig. 4 and Fig.
5, changes in the intensities of emission in x = 0.6 withtemperature are different between excitation energy.
Thermally activated process is included in 280 nm
excitation.

Fig. 3. The intensity ratios R/(R+G) of Red emission(R) to sum of Red and Greenish-blue emission (G) in
Pr:SrZr1-xTixO3 (300 K).

Fig. 4. Change in the intensities of Red emission andGreenish blue emission with temperature in
Pr:SrZr0.4Ti0.6O3 (λem = 350 nm).
Fig. 1. Excitation spectra of Pr:SrZr0.4Ti0.6O3 (30 K).

Fig. 5. Change in the intensities of Red emission andGreenish blue emission with temperature in
Pr:SrZr0.4Ti0.6O3 (λem = 280 nm).

Fig. 2. Emission spectrum of Pr:SrZr0.4Ti0.6O3(λem = 350 nm, 300 K).

62

Ⅲ02- 16 -BL3B

Ⅲ -2. Materials Sciences

BL3B

Excitation Process of Ce3+ Ions in La Doped Gd2Si2O7 Crystals Caused
by VUV Photons
R. Tarukawa1, M. Kitaura1, S. Kurosawa2, T. Makino3 and A. Ohnishi1

Faculty of Science, Yamagata University, Yamagata 990-8560, JapanNew Industry Creation Hatchery Center, Tohoku University, Sendai 980-8579, Japan3
Department of Electrical and Electronics Engineering, University of Fukui, Fukui 910-8507, Japan1

2

1 (b). In the region below 7.5 eV, one can see broad
bands due to Ce3+ 4f-5d transitions. No sharp peaks arefound in Fig. 1(b). This fact suggests the Gd3+Ce3+
energy transfer does not occur in La-GPS:Ce, and iscontrast with Gd3Al2Ga3O12:Ce (GAGG:Ce) [3]. In theregion above 7.5 eV, the excitation spectra in Figs. 1(a)and 1(b) are almost the same with each other. This fact
explains as follows. Hot photoelectrons and photoholes
created by VUV photons relax into the conduction band
minimum and valence band maximum, respectively.
They are immediately captured by Ce3+ ions, and form
the excited state of Ce3+ ions. Consequently, it isreasonable that the excitation spectrum for the 393 nm
band reflects that for the 316 nm band.

Multiplication of electronic excitations (MEEs) inwide-gap oxides takes place when the energy of
excitation photon exceeds several times of the bandgap energy. The fundamental process of MEEs isbased on inelastic scattering of valence electrons with
hot photoelectrons. On the other hand, the excitation
process of luminescent ions doped in wide-gap oxides
by vacuum ultraviolet (VUV) photons is complex,
because a number of relaxation processes compete
under excitation [1]. Studies on such VUV excitation
processes of luminescent ions give us complementary
information on impact excitation of luminescent ionsby hot carriers, which is important in both sides offundamental and applied physics.
Ce-doped and La-admixed gadolinium pyrosilicate((La,Gd)2Si2O7:Ce, La-GPS:Ce) is known as aninorganic scintillator. Luminescence properties of LaGPS:Ce crystals have been investigated under
excitation with VUV photons [2]. However, theprocess of MEEs in La-GPS has not yet been cleared.
Furthermore, the excitation of Ce3+ ions by VUVphotons still remains unknown.
In the present study, we have measured emission
and excitation spectra of an undoped La-GPS and LaGPS:Ce crystals at 10 K. Experiment was performedat the BL3B beamline of UVSOR in the Institute for
Molecular Science (IMS). The emission spectrum ofan undoped La-GPS crystal exhibited an emission
band peaking at 316 nm. This band is assigned to Gd3+
4f-4f transition. The excitation spectrum for the 316
nm band is shown in Fig. 1 (a). In the region below 7.5
eV, one can see sharp peaks due to Gd3+ 4f-4ftransitions. The stepwise structures are found around
14 and 20 eV. The bad-gap energy was reported to be
6.6-6.8 eV. The former and latter are close to twice andtreble of the band-gap energy, respectively. The
fundamental process of MEEs in wide-gap oxides has
to satisfy the conservation laws of energy andmomentum. When hot photoelectrons and photoholes
are created by VUV photons, the threshold energy for
MEEs exceeds the twice of the band-gap energy [1].
Especially, it is expected that the threshold energy
reaches the treble of the band-gap energy for La-GPS
with the wide valence band. It is, therefore, likely that
the MEEs in La-GPS occurs in the region above 20 eV.
The excitation spectrum of a La-GPS:Ce crystal
showed an emission band at around 393 nm at 10 K.
This band is assigned to the Ce3+ 5d-4f transition. The
excitation spectrum for the 393 nm band is shown in Fig.

Fig. 1. (a): Excitation spectrum for the 316 nm band of
an undoped La-GPS crystal. (b): Excitation spectrum
for the 393 nm band of a La-GPS:Ce crystal. These
spectra were measured at 10 K.

[1] M. Kitaura et al., J. Lumin. 172 (2016) 243.
[2] M. Koshimizu et al., J. Rare Earths 34 (2016) 782.
[3] M. Kitaura et al., J. Appl. Phys. 115 (2014) 083517.

63

Ⅲ02- 17 -Ⅲ-2

BL3B Sciences
Ⅲ -2. Materials

BL3B

Dynamical Behaviors of the Localized Exciton in NaCl:I− Crystals
T. Kawai

Graduate School of Science, Osaka Prefecture University, Sakai 599-8531, Japan
Wavelength (nm)200180

NaCl:I 8K(a) (b) (c) (d)(e)

Luminescence
excited at 6.89 eV

8060

Absorption

40
20

NE lumi.
5.5

-1

220

Absorption Coefficient (cm )Luminescence Intensity (arb. units)

240

6.0
6.5
7.0
Photon Energy (eV)7.5

0Fig. 1. Luminescence and absorption spectra of
NaCl:I− crystals at 8 K.

103Luminescecn Intensity (normalized scale)

Ⅲ-2

When alkali chloride crystals are doped with heavier
hetero-halogen ions, the absorption bands due to theheavier hetero-halogen ions are observed in the lower
energy region than the fundamental absorption edge ofthe host crystals. The photo-excitation on the absorption
bands induces various kinds of relaxed excitons
localized to the heavier hetero-halogen ions and theluminescence bands called BG, B, UV, and NE areobserved [1-3]. Though the BG, B, UV, and NE
luminescence bands are observed in many alkali
chloride crystals doped with heavier hetero-halogen
ions, NaCl:I− crystals exhibit only the NE luminescenceband in the wide temperature range from a lowtemperature to room temperature. The NE luminescenceis attributed to the radiative transition from the relaxed
excited states of the one-center-type relaxed exciton,
which consists of a hole localized on a hetero-halogen
anion and a bound electron. We have investigated the
dynamical behaviors of the one-center-type relaxed
exciton in the NaCl:I− crystals at the BL3B line of
UVSOR.
In the NaCl:I− crystals, the absorption band due to the
localized exciton and the NE luminescence areobserved around 6.95 and 5.7 eV, respectively, as shownin Fig. 1. Figure 2 shows the temporal profiles of the NE
luminescence under various excitation energies aroundthe absorption band. Under the excitation near peakenergy of the absorption band, the NE luminescenceexhibits the almost single exponential decay profile. On
the other hand, it seems that there are two exponential
components under the excitation at the off-peak energyof the absorption band. The decay time constants of thefast and slow components are about 2.6 ns and 120 ns,
respectively. The decay time constant of 2.6 ns is almost
equal to that of the fast component of the intrinsic typeI self-trapped exciton (STE) luminescence in pure NaCl
crystals [4]. The intrinsic type I STE exhibits the broad
luminescence band around 5.2 eV and the luminescenceoverlaps with the NE luminescence band.
The exciting light with the off-peak energy penetrates
deeper into the crystal than that with the peak energy of
the absorption band. Thus, the excitation at the off-peakenergy of the absorption band would create the onecenter-type relaxed exciton inside the crystals. Then, theintrinsic type I STE may be formed from the one-centertype relaxed exciton. Further studies will probably benecessary.

10

NaCl:I-

8K
det. 5.72eV20(a) ex.6.70eV(b) ex.6.89eV(c) ex.7.08 eV(d) ex.7.29 eV(e) ex.7.51 eV
50Time (ns)100

Fig. 2. Temporal profiles of the NE Luminescence
under various excitation energies around the absorption
band at 8 K. The excitation energies are shown by thedown arrows in Fig. 1.

[1] T. Higashimura et al., J. Phys. Soc. Jpn. 53 (1984)
1878.
[2] K. Kan'no et al., J. Phys. Soc. Jpn. 55 (1986) 2443.
[3] I. Akimoto et al., Phys. Status Solidi C 6 (2009) 342.
[4] T. Matsumoto et al., J. Phys. Soc. Jpn. 61 (1992)
4229.

64

Ⅲ02- 18 -BL3B

Ⅲ -2. Materials Sciences

BL3B

VUV Spectroscopy of Magnesium Oxide Treated with Hydrogen Reduction
E. Kobayashi1, K. K. Okudaira2, M. Imamura3, K. K. Bando3, H. Kakiuchida3,
S. Yoshioka4 and O. Takahashi5
Kyushu Synchrotron Light Research Center, Tosu 841-0005, Japan
2
Chiba University, Chiba, Chiba 263-8522, Japan
3
National Institute of Advanced Industrial Science and Technology, Tsukuba 305-8565, Japan
4
Graduate School of Engineering, Kyushu University, Fukuoka 819-0395 Japan
5
Graduate School of Science, Hiroshima University, Higashi-Hiroshima 739-8526, Japan
1

Magnesium oxide (MgO) is a typical wide
electronic band gap insulator and is used in devices
such as optical, electrical and catalytic. Characteristics
such as light transmission and thermal insulation are
greatly affected by defects generated in the production
process of crystals and thin films and practicalmaterials. In compounds such as oxide, various typesof defects such as point, line and planar defects exist,
and the electronic state derived from the defect causes
electrical, optical, or magnetic functions. For thisreason, many point defects of metal oxides have beenstudied. MgO defects are generated by methods suchas X-ray irradiation [1], UV irradiation [2], neutron
scattering [3], electron beam irradiation [4,5], and heat
treatment [6,7].
This study focused on magnesium oxide heated in ahydrogen atmosphere and the correlation between theamount of defects and optical properties was investigatedusing UV absorption spectroscopy. In addition, the planeorientation dependence of the MgO crystal wasinvestigated.
The MgO (100) and MgO (111) were annealed atseveral temperatures at 473 K ~1173 K in a hydrogen
atmosphere for 4 hours. The samples were graduallycooled to room temperature, exposed to the air, thenintroduced into a vacuum apparatus, and the spectrum
was measured. UV spectra of MgO single crystal were
measured at the BL3B of UVSOR in the Institute of
Molecular Science.
Figure 1 shows UV spectra of MgO(100) andMgO(111). A distinct increase in absorption from 5.6 eV
to 7.0 eV in MgO(100) was observed for the treated underhydrogen, compared to an untreated one. This result
indicated that a new electronic state was formed in the
conduction band due to the oxygen defect produced by
the hydrogen reduction treatment, which made the band
gap narrower. On the other hand, a decrease in absorptionin MgO(111) was observed for the treated underhydrogen. This suggests that the interaction withhydrogen depends on the crystal plane. The spectrum
changes because MgO (111) is an unstable polar surface,whereas MgO (100) is electrically neutral. The exact
cause has been investigated using other techniques.

Ⅲ-2

Fig. 1. UV spectra of MgO single crystal.

[1] J. P. Molnar et al., Phys. Rev. 79 (1950) 1015.
[2] Y. Chen et al., Phys. Rev. 182 (1968) 960.
[3] H. R. Day, Phys. Rev. 91 (1953) 822.
[4] V. E. Henrich et al., Phys. Rev. B 22 (1980) 4764.
[5] P. R. Underhill et al., Solid State Commun. 43 (1982)
9.
[6] M. Wu et al., Phys. Rev. B 19 (1992) 12688.
[7] L. A. Kappers et al., Phys. Rev. B 1 (1970) 4151.

65

Ⅲ02- 19 -BL3B Sciences
Ⅲ -2. Materials

BL3B

Luminescence Characteristics of Cs2BaCl4
K. Takahashi1, M. Koshimizu1, Y. Fujimoto1, T. Yanagida2 and K. Asai1

Department of Applied Chemistry, Graduate School of Engineering, Tohoku University, Sendai 980-8579, Japan
2
Division of Materials Science, Nara Institute of Science and Technology, Ikoma 630-0192, Japan1

Ⅲ-2

Auger-free luminescence (AFL) is caused by theradiative transition of an valence electron to a core hole
state. The transition is competitive with the Auger
process, which is a much faster process, efficient AFL
cannot be observed in many compounds. In other words,
efficient AFL has been observed in limited compounds
such as alkaline- or alkaline-earth fluorides or CsClbased compounds.
AFL has been applied to fast scintillators owing to its
fast decay. A representative one is BaF2; however, CsClbased compounds have an advantage of long emission
wavelength appropriate for detection with aphotomultiplier tube. Thus far, we have developed fast
scintillators based on ternary CsCl-based compounds[1,2]. In this study, we developed fast scintillators basedon Cs2BaCl4.
Crystal samples of Cs2BaCl4 were fabricated using aself-seeding solidification method and the Bridgman
method. Powders of CsCl (99.99 %, Mitsuwa Chemical
Co. Ltd., Japan) and BaCl2 (99.9 %, Kojundo Chemical
Laboratory Co Ltd., Japan) were mixed in a
stoichiometric ratio. The mixed powders were poured
into quartz ampoules and heated at 350 °C in vacuumfor 1 day to remove adsorbed water. For the self-seeding
solidification method, the quartz ampoule was set in atubular furnace, and the furnace was heated to 950 °C
for 12 h and subsequently cooled to room temperature
over 72 h. For the Bridgman method, the ampoule wasset in a Bridgman furnace. The temperatures of theupper and lower heaters in the furnace were set at
950 °C and 750 °C, respectively, during crystal growth,and the ampoules were lowered at a rate of 1.5 mm/h.
The luminescence properties were characterized withvacuum ultraviolet (VUV) light as an excitation source.
Measurements were performed at BL7B for the steadystate spectra and at BL3B for temporal profiles at the
UVSOR Synchrotron Facility at the Institute for
Molecular Science, Japan. Synchrotron radiation being
monochromatized with a 3-m normal-incidence
monochromator was used for the excitation. The
luminescence spectra were measured at different
excitation wavelengths, and the excitation spectra wereobtained from the luminescence spectra. The
luminescence temporal profiles were observed using atime-correlated single photon counting method. The
single-bunch operation mode was used, and the period
between successive pulses was 176 ns.
Figure 1 shows the luminescence spectra with VUVexcitation at 150 nm, 180 nm, and 84 nm. For theexcitation at 150 nm and 180 nm, the bands at 430 nm
and 480 nm were observed, respectively. For theexcitation at 84 nm which corresponds to the excitation

for the outermost core level of Cs, broad band at 450 nm
was observed, but clear bands at 250–320 nm, whichcorresponds to the expected AFL wavelength, was notobserved. Considering that the band gap energy of CsCl
is 8.3 eV, that of Cs2BaCl4 is possibly located at theenergy corresponding to 150–180 nm. Therefore, thebands at 430 nm and 480 nm can be attributed to STEs
though it is required to clarify the band structure of
Cs2BaCl4.
Figure 2 shows the excitation spectrum for the
luminescence at 270 nm. A steep rise at approximately
87 nm was observed for the luminescence at 270 nm.
This excitation spectrum was quite similar to those of
CsCl-based compounds [2,3], and the result clearly
indicates that Cs2BaCl4 exhibits AFL though clear bands
were not observed in the photoluminescence spectrumwith the excitation at 84 nm.

Fig. 1. Luminescence spectra of Cs2BaCl4 for theexcitation at 84 nm, 150 nm, and 180 nm.

Fig. 2. Excitation spectra of Cs2BaCl4 for monitored
wavelength of 270 nm.
[1] N. Yahaba et al., Appl. Phys. Express 7 (2014)062602.
[2] M. Koshimizu et al., Opt. Mater. 36 (2014) 1930.
[3] A. Ohnishi et al., J. Phys. Soc. Jpn. 72 (2003) 2400.

66

Ⅲ02- 20 -BL3B

Ⅲ -2. Materials Sciences

BL3B

Evaluation of Achromatic Vacuum-ultraviolet Lens
T. Shimizu, Y. Minami, K. Kuroda, K. Shinohara, D. Umeno and N. SarukuraInstitute of Laser Engineering, Osaka University, Suita 565-0875, Japan

Vacuum ultraviolet (VUV) has numerous scientificand technological applications including spectroscopy,
environmental monitoring, surface micromachining,sterilization and so on. In the study of VUV materials,
it has been found that fluoride materials can be applied
as new VUV optics including lenses. For VUV lenses,
the material must be transparent to the light in the
VUV region, have chemical stability, have a highmelting point, and be uniform and of good quality. In
this study, an achromatic lens made of two materials
was fabricated based on a design that minimizes
chromatic aberration in the 150-300 nm range using
fluoride crystals with high VUV transmittance.
A combination of LiCaF6 and BaLiF3 was used asmaterials for the convex and concave lenses of the
VUV achromatic lens because it has the lowest
chromatic aberration in combinations of fluoride
crystals with high transmittance in the vacuum
ultraviolet region. Chromatic aberration at 150 nm and
300 nm is corrected for in this design. In addition,
since there is no lens adhesive that can transmit
vacuum ultraviolet light, there is a gap between theconvex and concave lenses, which is fixed bysandwiching them with a lens folder. The coating
agent used for the anti-reflection coating, which
suppresses reflections on the lens surface, is notapplied because it cannot penetrate VUV light andmay reduce the transmittance and degrade the vacuum
due to vaporization.
The performance of VUV achromatic lenses isevaluated in the following three areas: transmittance,
chromatic aberration, and focusing performance. In thefirst half of the year, measurements of transmittancewere carried out using BL7B. The evaluation ofchromatic aberration was carried out in the second halfof the experiment using BL3B. The chromaticaberration is evaluated by measuring the focal length ofthe light in the range of 150 to 300 nm and comparing
them. The results are shown in Fig. 1. The color of thelines indicates the difference in wavelength. Although
the complete analysis is not yet complete, there is notmuch difference in the light-focusing trend for eachwavelength.
From the experimental results, it was confirmed that
the VUV achromatic lens is practical for themeasurement system with a certain beam intensity. In
addition, it was confirmed that the design policy of theprevious study is useful for the design of achromaticlenses in the VUV region. In order to improve theperformance, it is necessary to develop AR coating
materials that suppress the reflected light and transmit
vacuum ultraviolet light, and to improve the purity anduniformity of the lens materials.

In the future, a rigorous evaluation is required, and
it is important to further increase the knowledge of
achromatic lenses in the vacuum ultraviolet region. In
addition, the development of an imaging spectrometerwith a VUV achromatic lens is expected to be carriedout in parallel for practical use.

Ⅲ-2

Fig. 1. Chromatic aberration measurement results.

[1] K. Shimamura, H. Sato, A. Bensalah, H. Machida, N.
Sarukura and T. Fukuda, J. Alloys Cmpds. 343 (2002)
204.
[2] M. V. Luong, M. J. F. Empizo, M. Cadatal- Raduban,
R. Arita, Y. Minami, T. Shimizu, N. Sarukura, H. Azechi,
M. H. Pham, H. D. Nguyen, Y. Kawazoe, K. G.
Steenbergen and P. Schwerdtferger, Opt. Mater. 65(2017) 15.
[3] R. Arita, Y. Minami, M. Cadatal-Raduban, M. H.
Pham, M. J. F. Empizo, M. V. Luong, T. Hori, M.
Takabatake, K. Fukuda, K. Mori, K. Yamanoi, T. Shimizu,
N. Sarukura, K. Fukuda, N. Kawaguchi, Y. Yokota and A.
Yoshikawa, Opt. Mater. 47 (2015) 462.
[4] T. Shimizu, M. V. Luong, M. Cadatal-Raduban, M. J.
F. Empizo, K. Yamanoi, R. Arita, Y. Minami, N. Sarukura,N. Mitsuo, H. Azechi, M. H. Pham, H. D. Nguyen, K.
Ichiyanagi, S. Nozawa, R. Fukaya, S. Adachi, K. G.
Nakamura, K. Fukuda, Y. Kawazoe, K. G. Steenbergenand P. Schwerdtfeger, Appl. Phys. Lett. 110 (2017)
141902.
[5] M. V. Luong, M. Cadatal-Raduban, M. J. F. Empizo,
R. Arita, Y. Minami, T. Shimizu, N. Sarukura, H. Azechi,
M. H. Pham, H. D. Nguyen and Y. Kawazoe, Jpn. J. Appl.
Phys. 54 (2015) 122602.
[6] K. Yamanoi, T. Murata, Y. Arikawa, T. Nakazato, M.
Cadatal-Raduban, T. Shimizu, N. Sarukura, M. Nakai, T.
Norimatsu, H. Nishimura, H. Azechi, S. Fujino, H.
Yoshida, A. Yoshikawa, N. Satoh and H. Kan, Opt. Mater.
35 (2013) 1962.

67

Ⅲ02- 21 -BL3B Sciences
Ⅲ -2. Materials

BL3B

Electronic States and Charge Dynamics of Sm1-xCexS
Y. Yokoyama1, H. Hasegawa1, J. Shibutani1, Y. Kadowaki1, Y. Okamoto1, H. S. Suzuki2,
K. Takehana3, Y. Imanaka3 and K. Takenaka1
Department of Applied Physics, Nagoya University, Nagoya 464-8603, JapanThe Institute of Solid State Physics, The University of Tokyo, Kashiwa 277-8581, Japan
3
National Institute for Materials Science (NIMS), Tsukuba 305-0003, Japan1

2

Reflectivity

1
0.8

0.20

0.6
0.4
0.2
0

0.10

0.10
Sm1-xCexS
at 295 K
-3

10

-2

10

Sm1-xYxSat 295 K

x=0
-1

10

0.20
0.28

-3

0

-2

10
10
10
Photon Energy (eV)

x=0
-1

10

10

0

Fig. 1. Reflectivity spectra of Sm1-xRxS (R=Ce (left),
Y (right) [3]) single crystallines at 295 K. Broken lines
represents the Hagen-Rubens extrapolation.

3

-1

-1

Conductivity (10  cm )Ⅲ-2[2,4]. Considering these facts together with the present
results, it is strongly suggested that the characteristic
structure in the IR region of the σ(ω) spectra reflects thevalence fluctuating states. The findings in the present
study raise a new question: why the valence transition
occurred at lower Ce composition level? To answer thisquestion precisely, it is useful that the differences in theelectronic states between Y and Ce are elucidated byother methods such as the photoelectron spectroscopy.

Samarium monosulfide (SmS), in which twoelectronic configurations ((4f)6 and (4f)5(5d)1) of Sm
are energetically competed, is known as a valencefluctuation materials. The electronic state of Sm
undergoes transition to (4f)5(5d)1 by applying pressure
and chemical doping, while the (4f)6 state is stable
under ordinary pressure and temperature condition [1].
It is promising to be applied to materials for negative
thermal expansion (NTE) and actuators by controllingthese electronic states [2], because this phenomenon isaccompanied with a large volume change up to 10 %.
To study changes in the electronic states due to thevalence transition, we recently conducted systematic
optical reflectivity measurements toward Sm1-xYxS
single crystalline samples, covering wide energy andcompositional region [3]. Consequently, it is clarified
that a characteristic structure, which showed thechanges in electronic states induced by the valencetransition, became appeared in the optical spectra at Ycomposition of 0.28 [3].
In this study, to investigate the changes in theelectronic states by the other dopant, we measured theoptical reflectivity R(ω) spectra of Sm1-xCexS single
crystalline samples in the wide (from far-IR tovacuum-UV) energy regions. Normal incident
reflectivity spectra were collected at 295 K by using a
Fourier-type interferometer (0.005–1.6 eV) and a
grating spectrometer (1–3 eV) installed with amicroscope. For the measurements from visible tovacuum-UV region (2–30 eV), we used a synchrotron
radiation at BL3B of UVSOR, Institute for Molecular
Science. Then, optical conductivity σ(ω) was deduced
from the R(ω) using the Kramers-Kronig relation.
Figure 1 shows the R(ω) spectra of Sm1-xCexS taken
at 295 K. The corresponding spectra of Sm1-xYxS [3]are shown in the right column for the comparison. As
the Ce doping proceeds to x = 0.20, reflectivity edge
moves to higher energy and the characteristic structurearound 1 eV appears, in common with the Y-dopedcase. However, it seems that the spectral changes
occur at lower Ce doping level comparing to the Ydoped case. The σ(ω) spectra (Fig. 2) show that the Ce
doping also generates a significant structure in the IR
region, which is not characterized by a simple Drude
response, at lower dopant composition than the Ydoped case.
The recent works of the NTE function of the Sm1-x
RxS (R: rare-earth elements) reported the steep changes
in the lattice parameter induced by the doping; 0.2 < x <0.3 for the Y-doping and 0.1 < x < 0.2 for the Ce-doping

6
5
4
3
0.20
2
0.10
1
x=0
0
0
0.5

Sm Ce S
1-x

Sm Y S

x

1-x x

0.28

at 295 K

at 295 K

0.20
0

1

0.10

1.5
0
0.5
Photon Energy (eV)1

1.5

Fig. 2. Optical conductivity spectra of Sm1-xRxS (R=
Ce (left), Y (right) [3]) at 295 K.

[1] A. Jayaraman et al., Phys. Rev. B 11 (1975) 2783.
[2] K. Takenaka et al., Sci. Rep. 9 (2019) 122.
[3] Y. Yokoyama et al., Phys. Rev. B 100 (2019)245143.
[4] D. Asai et al., Appl. Phys. Lett. 114 (2019) 141902.

68

Ⅲ02- 22 -BL4U

Ⅲ -2. Materials Sciences

BL4U

Analysis of Lithium Insertion/Extraction Process in One-dimensional Singlecrystalline Active Materials by Scanning Transmission X-ray Microscopy
E. Hosono1,2,3, D. Asakura1,2, H. Yuzawa4 and T. Ohigashi4,5Research Institute for Energy Conservation, National Institute of Advanced Industrial Science and Technology,
Tsukuba 305-8568, Japan
2
AIST-UTokyo Advanced Operando-Measurement Technology Open Innovation Laboratory (OPERANDO-OIL),
National Institute of Advanced Industrial Science and Technology (AIST), Kashiwa 277-8565, Japan.
3
Global Zero Emission Research Center, National Institute of Advanced Industrial Science and Technology,
Tsukuba 305-8568, Japan
4
UVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
5
School of Physical Sciences, The Graduate University for Advanced Studies, SOKENDAI, Okazaki 444-8585, Japan
1

Innovative technologies for clean energy devices
are desired for the realization of sustainable society by
preventing global warming. Development of highperformance Li-ion batteries (LIBs) for electricvehicles and large-scale power storage in renewableenergy power plants is attracting much attention.
We have studied the morphology control method ofmaterials, because the properties of materials dependon crystal direction and facet of materials [1]. In
addition, we have been studying the charge-discharge
mechanism of LIBs. Nevertheless, there are many
unsolved mechanisms in the research field of LIBs.
Soft X-ray spectroscopy is a powerful technique tounderstand the electronic structures of transition-metaloxides used for active materials of LIBs. Moreover, byusing scanning transmission X-ray microscope(STXM), we can get the electronic structural
information with special information. For the singlecrystalline active materials of LIBs, positiondependent Li insertion/extraction reaction is expected
to be observed by STXM. Especially, singlecrystalline nanowire materials have diffusion paths
with limited direction based on the crystal structure. In
the case of LiFexMn1-xPO4 single-crystalline nanowire
materials, the diffusion path is limited to one direction.
Here, we exhibit a result of ex situ STXM for
LiFexMn1-xPO4 single-crystalline nanowire. Figure 1
shows the STXM image measured with an excitationenergy of 700 eV. Nanowire image of LiFexMn1-xPO4
is obtained by STXM. The Fe L3,2-edge absorption
spectra of selected regions are shown in Fig. 2. Eachspectrum is ascribed to Fe3+ state compared withprevious X-ray absorption result [2]. Now, we are
analyzing the Fe L3,2-edge, Mn L3,2-edge, and O Kedge results for the LiFexMn1-xPO4.
In the near feature, we will establish operando
STXM measurement system.

Ⅲ-2

Fig. 1 A STXM image of the LiFexMn1-xPO4 singlecrystalline nanowire

Fig. 2. Fe L3,2-edge absorption spectra of selected
regions. The numbers correspond to the regions in Fig. 1.

[1] E. Hosono, J. Ceram. Soc. Japan 120 (2012) 47.
[2] D. Asakura, E. Hosono, M. Okubo, Y. Nanba, H. S.
Zhou, P. A. Glans and J. H. Guo, ChemPhysChem 17(2016) 4110.

69

Ⅲ02- 23 -BL4U Sciences
Ⅲ -2. Materials

BL4U

Elucidation of Mechanisms of Nucleation and Crystal Growth for Clean
Energy Materials in Aqueous Solutions by Scanning Transmission X-ray
Microscope

Ⅲ-2

Y. Miseki 1,2, E. Hosono1,3,4, D. Asakura3,4, H. Yuzawa5 and T. Ohigashi5,6Global Zero Emission Research Center, National Institute of Advanced Industrial Science and Technology,
Tsukuba 305-8568, Japan
2
Research Center for Photovoltaics, National Institute of Advanced Industrial Science and Technology, Tsukuba
305-8565, Japan
3
Research Institute for Energy Conservation, National Institute of Advanced Industrial Science and Technology,
Tsukuba, 305-8568, Japan
4
AIST-UTokyo Advanced Operando-Measurement Technology Open Innovation Laboratory (OPERANDO-OIL),
National Institute of Advanced Industrial Science and Technology (AIST), Kashiwa 277-8565, Japan.
5
UVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
6
School of Physical Sciences, The Graduate University for Advanced Studies, SOKENDAI, Okazaki 444-8585, Japan1

We have studied the clean energy devices including
lithium ion batteries [1,2] and photocatalytic devices[3] by controlling the morphology and crystal growth.
Ceramics materials such metal oxides are mainmaterials to construct many kinds of clean energy
devices. The properties of metal oxide materials are
depended in large part on crystal direction and facet ofmaterials. Thus, nanostructural control methods havebeen studied by many researchers to improve eachdevice performance.
For sophistication of nanostructural control techniques,
understanding of crystal growth is very important.
Especially, the surface and interface between materials
and solution is active site for the catalytic reaction in thecase of photocatalytic devices. Accurate design ofcrystal direction and facet and fabrication techniques
are needed to create ideal reaction places.
To establish the high-level crystal growth techniquesand morphology control methods, we considered thattheoretical understanding from electronic structure levelby using synchrotron radiation soft X-ray is necessary.
A Scanning Transmission X-ray Microscope (STXM)
exhibits electronic structure information with spatial
information (minimum spatial resolution is ca. 30 nm).
We tried the preparation of operando measurement
system for crystal growth in STXM.
Figure 1 shows the optical microscope image of Fe2+
solution sandwiched by Si chips with Si3N4 windows.
One of the major features of STXM is that it ispossible to obtain a spectrum of the solution by
sandwiching it between the Si3N4 windows.
Figure 2 shows the spectrum of Fe from othersandwich cell constructed by photocatalytic materials
and Fe solution.
In near feature, we will establish in-situ measurement
system.

100μm

Fig. 1. Optical microscope image of Fe solution

Fig. 2. Absorbance spectrum of Fe.
[1] E. Hosono, J. Ceram. Soc. Jpn. 120 (2012) 47.
[2] D. Asakura, E. Hosono, M. Okubo, Y. Nanba, H. S.
Zhou, P. A. Glans and J. H. Guo, ChemPhysChem 17(2016) 4110.
[3] Y. Miseki and K. Sayama, Chem. Commun. 54(2018) 2670.

70

Ⅲ02- 24 -BL4U

Ⅲ -2. Materials Sciences

BL4U

Characterization of Network-Domain of Sulfur Cross-linked Isoprene
RubberK. Miyaji1, Y. Sakaki1 and Y. Ikeda2

Graduate School of Science and Technology, Kyoto Institute of Technology, Kyoto 606-8585, Japan
Faculty of Molecular Chemistry and Engineering, Kyoto Institute of Technology, Kyoto 606-8585, Japan
1

2

Nowadays, rubber materials have become
indispensable to applications such as automobile andairplane tires as well as seismic isolation materials.
Many of these products are produced by cross-linking
raw rubbers, which forms a three-dimensional network
structure with good rubber elasticity. Among
conventional cross-linking reactions, sulfur crosslinking reaction, known as “vulcanization” is mostwidely used all over the world. Despite the progressachieved in this field, controlled formation of rubber
networks is generally very difficult and complicated in
the rubber industry primarily because of theheterogeneous nature of the cross-linking reactions
resulting from various factors such as the influence ofcross-linking reagents, fillers, and processing methods.
Therefore, the rational design of rubber network
structures to produce sturdier and more stable rubbermaterials is still a challenge. Consequently, a deeper
understanding of the rubber network structures isimportant for the development of rubber science andtechnology. In 2009, our group revealed the effects ofthe combination and composition of sulfur crosslinking reagents on the formation of an isoprene rubber
network by using small-angle neutron scattering(SANS) [1]. The results showed that the combinationof ZnO with other reagents was crucial for controllingthe structural network inhomogeneity in the N-(1,3benzothiazol-2-ylsulfanyl)cyclohexanamine (CBS)accelerated vulcanization system. This specificmorphology was found to be controlled by changing
the amount of cross-linking reagents. There are several
analytical methods to investigate the morphology ofrubber vulcanizates. Scanning transmission X-ray
microscopy (STXM) is one of methods which
provides chemical mapping in nanometer scales. Also,
both spatial and compositional chemical information
are provided at the same time. In this study, STXM
was used to confirm the two network-domain of
isoprene rubber vulcanizate in terms of the distributionof sulfur.
The rubber compound was prepared by conventional
mixing at room temperature on a two-roll mill with awater cooling system; isoprene rubber was mixed withzinc oxide, CBS and sulfur. Rubber vulcanizate wasprepared by conventional pressing method. This rubber
vulcanizate was extracted by tetrahydrofuran (THF) toremove the un-reacted sulfur. The vulcanized rubber
sheet after THF extraction was cut by an ultra-microtome
to prepare a smooth and flat surface with a thickness ofapproximately 100 nm for STXM measurement.

Figure 1 shows the STXM image of the vulcanizedisoprene rubber at 165.4 eV. The intensity of theabsorption indicates the concentrations of sulfur. Thus,
the green to red regions shown in Figure 1 are the
network-domains of the vulcanized isoprene rubber.
As predicted by the SANS results, the network domains
were formed by the absorption of sulfur and theaccelerator, CBS on the ZnO clusters, and followed bysulfur cross-linking on the surface of ZnO clusters [1].
Furthermore, it was also found that the region of strong
absorption and the mechanical properties of thevulcanizates increased linearly with the amount of thereagents.
This STXM image successfully confirmed the
network-domains in the vulcanized isoprene rubberfrom the view point of sulfur distribution. The amountof ZnO was clearly suggested to be a key to control the
total fraction of network domain phases in thevulcanizates.

Fig. 1. STXM image of the vulcanized isoprene rubber
at 164.5eV.

[1] Y. Ikeda et. al., Macromolecules 42 (2009) 2741.

71

Ⅲ02- 25 -Ⅲ-2

BL4U Sciences
Ⅲ -2. Materials

BL4U

Single-Atom Nickel Decorated Graphitic Carbon Nitride for Efficient
Water Splitting
Y. C. Huang1,2, Y. R. Lu1,2, C. H. Chuang1, Y. Li3, S. Shen3, W. C. Chou2, C. L. Dong1,
W. F. Pong1, T. Ohigashi4 and N. Kosugi4

1
Department of Physics, Tamkang University, Tamsui 251, Taiwan
Department of Electrophysics, National Chiao Tung University, Hsinchu 30010, Taiwan
3International Research Center for Renewable Energy, State Key Laboratory of Multiphase Flow in PowerEngineering, Xi’an Jiaotong University, Xi’an 710049, China
4
UVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan2

Ⅲ-2

incorporated g-C3N4 photocatalysis for spontaneous
overall water splitting is promising. The single-atom Ni
act as the capping agent for polymerization reaction,building novel coordinated structure with a mid-gap
state for increasing the photogenrated electrons andholes separation.

Incorporation of single atomic metals on graphite
carbon nitride (g-C3N4) has been a promising strategy
for designing advanced energy materials over the past
decade. The single atom has the ability to separate
charge in an aromatic conjugated ring by disrupting thecoordination bonds in the microstructure. However, therelative polymerization based on metal ions and its
subsequent charge separation are rarely reported. Here,single atomic nickel is used as a polymerization capping
agent, which is synthesized by a chemisorption route tocontrol the interface free energy. Scanning transmission
X-ray microscope (STXM) and near-edge X-ray
absorption fine structure (NEXAFS) were performed to
study the chemically imaged K-edge of carbon, nitrogenand oxygen.
In order to hinder the recombination of photogenerated
electrons and holes, a novel coordinated structure is
proposed to insert an in-gap intermediate state. By
adjusting the sp2 coordination, efficient charge separationand charge transfer can be achieved to enhancephotocatalytic ability. These results provide important
insights into single-atom Ni/g-C3N4 which is of great
importance for future overall water decomposition fromatomic and electronic perspectives. It is likely that the
capping agent Ni can terminate the growing of heptazine
chain and build an extra energy state in the gap of the
conduction and valence band, which is critical efficient
separation of photogenerated electrons and holes.
The optical density images and corresponding stackmapping STXM images for C K-edge and N K-edge ofbare ((a) and (b)) and Ni decorated g-C3N4 ((c) and (d))
are shown in the Fig. 1. The stack mappings display
yellow, red and green areas, corresponding to thedifferent regions that are associated with different
regions and chemical properties of the nanorods whichis revealed by the NEXAFS spectra. Notably, theincorporation of single atom Ni alters significantly theelectronic structure both at C and N sites. Shortly, theincreased intensity of NA resonance suggests thecoordination with metal Ni; the decreased intensity of
NB resonance indicates a structure breaking of bridge
nitrogen, possibly is caused by the capping agent atomic
Ni during the polymerization reaction. This results is
consistent with the fact that the atom- distribution Ni
could be coordinated with N atom in the heptazine units.
Consequently, the strategy to synthesis single-atom Ni

Fig. 1. Optical density images, stack mapped STXM
images and corresponding NEXAFS at C and K-edgeof pure g-C3N4 ((a), (b)) and single atom Ni decorated
g-C3N4 ((c), (d)).
[1] A. Wang et al., Nat. Rev. Chem. 2 (2018) 65.
[2] L. Cao et al., Nat. Catal. 2 (2019) 134.
[3] H. Yang et al., Nat. Commun. 10 (2019) 4585.

72

Ⅲ02- 26 -BL4B

Ⅲ -2. Materials Sciences

BL4B

Electronic Structure of AlFeN Films Grown on Various Substrates
S. Imada and N. Tatemizo

Faculty of Electrical Engineering and Electronics, Kyoto Institute of Technology, Kyoto 606-8585, Japan
Wurtzite AlN is a wide- and direct-band-gap
semiconductor that is a promising material for deepultraviolet (DUV) optoelectronic devices, such as
light-emitting diodes (LEDs) or laser diodes (LDs). As
the energy of deep ultraviolet light is high enough tosterilize and decompose toxic molecules, it is useful inthe fields of medicine and healthcare. At present, DUVlight sources are mercury lamps and metal halide
lamps, which require a measurable amount of power,
have a short life-span, and are large in size. To replace
the lamps with LED systems that will be energysaving, long-lasting, and small, the design anddevelopment of DUV-LEDs have been sped up aroundthe world.
In the course of the studies, however, it became
evident that AlN and related materials have difficult
issues in realizing high efficiency devices owing tosome electronic properties in the form of thin films,
which are traced back to the crystal axis orientation of
AlN, i.e. the polar-axis orientation. Therefore, nonpolar-axis oriented AlN films have generated a lot ofinterest, because they can avoid these problems.
We have succeeded in growing non-polar-axis
oriented wurtzite films by heavy-doping of Fe in AlN
films on SiO2 glass substrates [1] and found that the
Fe-doping raised large gap states in the gap of AlFeN
via Fe-d and N-p hybridization [2]. To remove the gap
states, we conducted annealing of the films andsucceeded in desorption of Fe atoms from the AlFeN
lattice, resulting in a drastic decrease of the gap states
while maintain the non-polar axis orientation [2].
To increasing the crystallinity of the annealed films,
Si is more favorable as a substrate because its linear
expansion coefficient is similar to that of AlN. Thus, wehave grown AlFeN films on Si(100) substrates andinvestigated the crystallographic orientation andelectronic structures. It was found that the AlFeN films
with Fe concentrations higher than 10 % have a-axis
orientation and similar electronic structure to that of thefilms grown on SiO2 glass substrates. As representative
data, N K-edge XANES spectra grown on Si(100) andSiO2 glass substrates with 18 % Fe are shown in Fig. 1.
The main structure between 400 eV and 409 eV and thepre-edge peak at around 397 eV of the film on a Si(100)substrate are coincident with those of the films on a SiO2
glass substrate. This result also implies that the a-axis
oriented growth by heavy Fe doping can proceeds as
self-nuclear formation. We are attempting to obtain
growth-time dependences of the crystallographic
orientation and electronic structures of as-grown AlFeN
films. The results from these efforts are expected to bereported in our future publications.

Ⅲ-2

Fig. 1. N K-edge XANES spectra of AlFeN (Fe: 18 %)films deposited on SiO2 glass and Si(100) substrates. The
electric field vectors E of the incident X-rays wereparallel to the film plane. The measurements were
performed in vacuum ~10−6 Pa at RT in the fluorescencedetection mode.

[1] N. Tatemizo , S. Imada, K. Nishio and T. Isshiki,
AIP advances 8 (2018) 115117.
[2] N. Tatemizo , S. Imada, K. Okahara, H. Nishikawa,
K. Tsuruta, T. Ina, Y. Miura, K. Nishio and T. Isshiki,
Scientific Reports 10 (2020) 1819.

73

Ⅲ02- 27 -BL4B Sciences
Ⅲ -2. Materials

BL4B

Valence State Analysis of Mn Ions in SnO2
T. Yamamoto1,2,3

Department of Materials Science, Waseda University, Tokyo 169-8555, Japan
Institute of Condensed-Matter Science, Waseda University, Tokyo 169-8555, Japan
3
Kagami Memorial Research Institute for Materials Science and Technology, Waseda University,
Tokyo 169-0051, Japan1

2

Mn2+(MnCl2)

3+

Mn (Mn2O3)

Intensity (arb. units)

Ⅲ-2

Dilute magnetic materials (DMMs) have been
extensively studied after a discovery of ferromagnetismin InAs doped with dilute amount of Mn ions [1], sincesuch materials have a potential to be applied in
spintronics. At early stage, a Currie temperature, TC,
was low in this type of DMMs. Hence a lot of attempts
have been devoted to increase TC for the application inindustrial uses. Recently, it was reported that some
DMMs show ferromagnetism beyond room
temperature, e.g., Mn-doped GaN, Co-doped TiO2 and
Mn, Fe co-doped In2O3. However, the mechanism of
appearance of ferromagnetism in DMMs have not yet
been understood. Although it is essential to know a local
environment of doped magnetic ions in host materials,
such analysis has not often been done due to a difficulty
to analyze it for dilute dopants. It was proposed that two
types of local environments of doped magnetic ionsexist in DMMs, i.e., substitution and precipitate types.
In the former, doped magnetic ions substitute at one of
the cation site in the host material, while in the later
doped magnetic ions precipitate as small particles. For
such analysis, X-ray absorption spectroscopy (XAS) is
quite powerful. We have successfully determined the
local environment of doped Mn and Fe ions in In2O3 byusing the XAS analysis [2,3].
In the current study, valence state of Mn ions in SnO2
was investigated by the Mn-L3 XAS. Samples wereprepared with conventional solid-state reaction methodchanging a concentration of doped Mn ions. Crystal
structures of the synthesized samples were examined bypowder X-ray diffraction, which suggest all the samples
were in singular phase of rutile structured SnO2. Mn-L3
XAS were recorded at BL4B in UVSOR by total
electron yield mode using electron multiplier. Sample
powders were placed on the carbon adhesive tape,which were attached on the first dinode of the electron
multiplier.
Observed Mn-L3 XAS of Mn(1 %) doped SnO2 isshown in Fig. 1 together with the representative spectraof Mn2+, Mn3+ and Mn4+ for comparison. Most intense
peak in XAS of Mn-doped SnO2 coincides with that of
Mn2+ and the second overlaps that of Mn3+. This result
suggests that the major component of Mn ions is 2+ andMn3+ exists as minor one in SnO2. In the carrier
mediated type of the models for DMMs, mixed valence
is a key to make the material ferromagnetic as suggested
in our earlier work [3]. From our current analysis, it has
been suggested that Mn-doped SnO2 has a possibility to
be a ferromagnetic DMM.

Mn4+(MnO2)

SnO2:Mn(1%)

640

645

Energy (eV)650

Fig. 1. Mn-L3 X-ray absorption spectra of MnCl2.
Mn2O3, MnO2 and Mn-doped SnO2.

[1] H. Ohno et al., Phys. Rev. Lett. 68 (1992) 2664.
[2] T. Yamamoto et al., J. Phys.:Condens. Matter 21(2009) 104211.
[3] T. Okazaki et al., Solid State Comm. 151 (2011)
1749.

74

Ⅲ02- 28 -BL4B

Ⅲ -2. Materials Sciences

BL4B

XAFS Measurements of 1-nanometer Indium-tin Oxide Particles Focusing
on O K-edge
1

T. Tsukamoto1,2, H. Iwayama3, M. Nagasaka3, A. Kuzume2 and K. Yamamoto1,2

Laboratory for Chemistry and Life Science, Institute of Innovative Research, Tokyo Institute of Technology,
Yokohama 226-8503, Japan
2
ERATO, JST, Kawaguchi 332-0012, Japan
3
Institute for Molecular Science, Okazaki 444-8585, Japan

Sub-nanoparticles (SNPs) with extremely small size
reaching 1 nm recently attract attention because theyoften exhibit unique properties not seen in bulk or
general nanoparticles (NPs). One of the interesting
behavior in this size range is the change in thechemical states of oxygen atoms in metal oxide SNPs.
They don’t have crystal structures but amorphous ones
with many defects due to their extremely small
structures. Additionally, they tend to substitute theirlack of oxygen atoms (O2– state) to low-valenthydroxyl groups (OH– state). Actually, it is reported
that tin oxide SNPs and copper oxide SNPs containmany OH– species in contrast to the bulk and NPs [1,2].
In this study, we newly investigated the effect of thehybridization of different metals in the SNPs for thechemical states of oxygen atoms. We chose indium andtin as two metal elements with different valence
electrons in the same period in the periodic table. The
oxygen species in indium-tin oxide SNPs wereobserved and analyzed by XAFS measurements
focusing on the O K-edge using BL4B beamline in
UVSOR. As a bulk of metal oxides, indium oxide(In2O3) and tin oxide (SnO2) purchased from SigmaAldrich Co. LLC. were used. As NPs, indium oxide(100 nm), tin oxide (100 nm), and indium-tin oxide (50nm, In2O3/SnO2 = 9:1) purchased from Sigma-Aldrich
Co. LLC. were used. As SNPs, indium oxide (1 nm,
In28Ox), tin oxide (1 nm, Sn28Ox), and indium-tin oxide(1nm, In12Sn16Ox) synthesized by the atomhybridization method [3] were used. All the samples
were cast on the silicon substrate and dried in vacuo in
the instrument overnight. The XAFS spectra wererecorded according to both the total electron yield andthe partial fluorescence yield. The O K-edge XAFS
spectra of samples were standardized using the oxide
layer on the surface of the reference Si substrate.
In comparison among the bulks, NPs, and SNPs
composed of a single metal element, it was suggested
that only the SNPs contain OH– species in contrast to
their bulks or NPs, judging from the XAFS spectra in
O K-edge region [4,5] (Fig. 1). Moreover, the indiumtin bimetallic oxide SNPs showed remarkably higher
peak intensity than the monometallic ones (Fig. 2).
This result indicated that the indium-tin oxide SNP has
more OH– species. On the other hand, in the case of
the indium-tin oxide NP, the peaks corresponding to
OH– species were not observed. Therefore, theincrease in the amount of OH– species in such binary
systems would be a specific phenomenon in the SNPs

with 1 nm particle size.
In conclusion, it was suggested that the
hybridization of two metal elements in metal oxide
SNPs with quantum-sized structure produces more
defect structures, leading to the unique chemical statesof metal oxides.

Ⅲ-2

Fig. 1. O K-edge XAFS spectra of bulks, NPs, and
SNPs of metal oxides on Si substrate by (A) total
electron yield and (B) partial fluorescence yield. Only
for the SNPs, signals originating OH– species at 534
and 542 eV were superimposed on those of O2– one.

Fig. 2. O K-edge XAFS spectra of indium oxide, tinoxide, and indium-tin oxide SNPs on Si substrate by (A)total electron yield and (B) partial fluorescence yield.
For the bimetallic oxide SNPs, signals originating OH–
species at 534 and 542 eV were superimposed on thoseof O2– one.
[1] A. Kuzume et al., Sci. Adv. 5 (2019) eaax6455.
[2] K. Sonobe et al., ACS Nano 14 (2020) 1804.
[3] T. Tsukamoto et al., Nat. Commun. 9 (2018) 3873.
[4]M. Yoshida et al., J. Phys. Chem. C 119 (2015) 19279.
[5]M. Nagasaka et al., Chem. Phys. Lett. 375 (2003) 419.

75

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BL3B
Ⅲ -2. Materials

BL4B, BL3B

Soft X-ray Excitation Impurity Luminescence of Aluminum Nitride
1

Ⅲ-2

Y. Maegawa1, T. Banno1, K. Fukui1 and K. Yamamoto2

Department of Electrical and Electronics Engineering, University of Fukui, Fukui 910-8507, Japan2
Far-infrared region Development Research Center, University of Fukui, Fukui 910-8507, Japan

AlN is a material having the largest band gap energy(Eg = 6.2 eV) among group III-V nitride semiconductors,
and is important as a key material of an ultraviolet (UV)region light emitting device (LED). For LED study,
impurity luminescence (IL) that is due to the existenceof the state of impurity and/or defect in the band gap
gives important information about the impurity atoms.
In the case of our bulk AlN sample, visible (VIS) - UV
region excitation photoluminescence measurements,
three kinds of IL bands (BL around 2.6 eV, BH around
2.8 eV, UV around 4.0 eV) were observed [1]. These IL
bands were only observed in the excitation region up to
Eg. Band to band excitation (> Eg) is not able tocontribute to these IL. Our results are quite similar to
those of Alder et al. and are considered that BH and UVbands may be due to carbon (C) defects [2]. Then, we
performed soft X-ray excitation IL measurements,
because the inner-shell excitation by using soft X-ray
shows C, nitrogen (N), and oxygen (O) 1s electron
contributions to those IL.
A bulk AlN sample is commercially available diskshaped one and manufactured by physical vapor
transport method. Excitation photon energy regions
were around C K-edge (270 - 298 eV), N K-edge (400
- 415 eV), O K-edge (538 - 550 eV) and 4.0 – 6.8 eV(BL3B). All measurement were carried out at 10 K.
Figure 1 shows an emission spectrum at an excitationenergy of 292 eV (black) and a result of component
decomposition. The IL spectrum due to soft X-ray
excitation consists of a main peak around 2.7 eV with
tail shape on the higher energy side and is different fromthat due to under Eg energy excitation, which has no tailfeature. However, main peak and tail shape of the IL
spectrum due to soft X-ray excitation are able todecompose into BL, BH, and VL, VH emission bands,
respectively, where VL band corresponds to theemission band observed under electron beam excitation[3]. Since the energy region of VH band matches that of
UV emission, VH band probably includes UV band.
Figure 2 shows the excitation spectrum of each bandnear each absorption edge. The characteristic spectrum
shape at C K-edge and the flat-like spectrum shape at O
K-edge clearly suggest that C impurity is corresponding
to those IL and O impurity is not. The intensity decrease
above N K-edge is caused by the decrease of penetration
depth of excitation light.

Fig. 1. Emission spectrum (exci. at 292 eV) andcomponent decomposition results

Fig. 2. Excitation spectrum of each emission bandaround (a) C-, (b) N-, (c) O-K edge, respectively.

[1] W. Kamihigoshi et al., UVSOR Activity Report2018 46 (2019) 103.
[2] D. Alden et al., Phys. Rev. Appl. 9 (2018) 054036.
[3] M. Morita et al., Jpn. J. Appl. Phys. 21 (1982) 7.

76

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Ⅲ -2. Materials Sciences

BL5U

Electronic States of Antiferromagnetic Half-heusler GdPtBi Studied by
High-resolution ARPES
D. Takane1, T. Suzuki2, S. Souma3,4, K. Nakayama1, K. Hori1, Y. Kubota1, T. Ren1,
K. Sugawara1,3,4, T. Takahashi1,3,4, J. G. Checkelsky2 and T. Sato1,3,4

1
Department of Physics, Tohoku University, Sendai 980-8578, Japan
Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
3
Center for Spintronics Research Network, Tohoku University, Sendai 980-8577, Japan
4
WPI Research Center, Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
2

Topological insulators are a novel quantum state ofmatter in which an inverted nontrivial bulk-bandstructure leads to gapless edge or surface states
protected by the time-reversal symmetry [1-3]. The
discovery of topological insulators triggered the search
for new types of topological materials, as represented
by the experimental discoveries of topologicalcrystalline insulators with gapless surface states
protected by the mirror symmetry of the crystal [4] andtopological Dirac semimetals with three-dimensionalbulk Dirac fermions protected by the rotational
symmetry of the crystal [5].
Recent theoretical studies predicted exotic topologicalphases originating from the interplay between nontrivial
band topology and long-range order, e.g. magnetism andsuperconductivity. A leading platform for exploring suchnovel topological states is the rare-earth half-Heusler
RePtBi (Re: rare-earth) which exhibits various orderedphases depending on the rare-earth [see Fig. 1(a) for
crystal structure]. Among them, antiferromagnet GdPtBi(Néel temperature TN = 9K) is attracting particularinterests because it exhibits the peculiar physicalproperties including the large anomalous Hall effect andchiral anomaly [6,7]. It is thus highly desirable toexperimentally establish the electronic band structure of
GdPtBi and clarify its topological character andrelationship with unconventional physical properties.
In this study, by using high-resolution angle-resolved
photoemission spectroscopy (ARPES), we determined
the fine electronic structure on the GdPtBi (111) surface[see Fig. 1(b) for corresponding bulk and surface
Brillouin zones]. High-resolution ARPES measurements
have been performed at BL5U. The sample was cleaved
in situ under an ultrahigh vacuum of 1.0 × 10-10 Torr.
Figure 1(c) displays the valence-band dispersion in
the paramagnetic phase measured along a momentum
cut crossing the Brillouin-zone center. We observed
highly dispersive holelike bands which cross the Fermi
level to form Fermi surfaces. The Fermi surfaces are
three-fold symmetric, in agreement with the rotational
symmetry of the crystal. Also, the observed band
dispersions are qualitatively consistent with the firstprinciples band-structure calculations, confirming theirbulk-band nature which was further corroborated by thehν-dependent ARPES measurements. Furthermore, wehave performed high-resolution ARPES measurements
to search for the topological surface sates as well as theelectronic
reconstruction
inducedbytheantiferromagnetic transition. Our results provide
important insights into the origin of exotic physicalproperties and also into the topological property of
GdPtBi.

Fig. 1. (a) and (b) Crystal structure and corresponding
bulk (bottom) and surface (top) Brillouin zones of
GdPtBi, respectively. (c) ARPES intensity plotted as afunction of binding energy and wave vector, measured
at T = 40 K.

[1] Y. Ando, J. Phys. Soc. Jpn. 82 (2013) 102001.
[2] X.-L. Qi and S.-C. Zhang, Rev. Mod. Phys. 83 (2011)1057.
[3] M. Z. Hasan and C. L. Kane, Rev. Mod. Phys. 82(2010) 3045.
[4] Y. Tanaka et al., Nature Phys. 8 (2012) 800.
[5] Z. K. Liu et al., Science 343 (2014) 864.
[6] T. Suzuki et al., Nature Phys. 12 (2016) 1119.
[7] M. Hirschberger et al., Nature Mater. 15 (2016) 1161.

77

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BL5U Sciences
Ⅲ -2. Materials

BL5U

Electronic Structure Study on WSe2 / hBN Heterostructure Using
Micro-ARPES
D. J. Oh1,2, S. Lee1,2, H. Park1,2, K. Tanaka3, S. R. Park4 and C. Kim1,2

Department of Physics and Astronomy, Seoul National University (SNU), Seoul 08826, Republic of Korea
Center for Correlated Electron Systems, Institute for Basic Science (IBS), Seoul 08826, Republic of Korea
3
Editorial Board, UVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
4
Department of physics, Incheon National University, Incheon 406-772, Korea

1
2

Ⅲ-2

Brillouin zone (BZ) (Fig. 2). Here, we did not have torotate the sample for the BZ mapping because we useda photoelectron analyser equipped with deflectors. By
following the procedure, we were able to attain ARPES
data with a relatively high success rate.

Eccentric properties ensue from moiré superlattices
formed by constituent layers in van der Waals (vdW)
heterostructures. For example, the Hofstadter butterfly
pattern stemming from the interplay between the moiré
superlattice and an applied magnetic field was measured
in monolayer (ML) graphene / h-BN heterostructures[1]. An essential step towards understanding novel
properties of these heterostructures is to have electronic
structure information. In that respect, direct electronic
structure measurement of the ML graphene / h-BN
heterostructure by using ARPES was an importantdevelopment [2]. Recently, mini bands induced bymoiré superlattice were observed in graphene / WS2
heterostructures [3]. These developments open thepossibility that a similar scheme may be applied totransition metal dichalcogenide (TMD)-based
heterostructures. Since a plethora of intriguing physicalproperties such as superconductivity, Weyl physics andcharge density waves exist in TMDs, even more
exciting phenomena may arise in vdW heterostructures
constructed from these materials.
Among variety of TMDs, group VI TMDs (MX2, M=
Mo,W, X= S, Se) have been extensively studied due totheir valley and spin degrees of freedom induced bylarge spin-orbit interaction and Berry curvature [4]. In
addition, MX2’s are stable in atmosphere, making themsuitable for surface-sensitive experiments as well as
applications in optoelectronic devices. In order to study
electronic structure of TMD-based heterostructures, thesamples are fabricated using the following procedures.
First, Pt was evaporated into an inverse-T shape on Nb
doped TiO2 or degenerately doped SiO2 / Si substrates,
such that Pt comes into contact with the metal strip andmakes a conducting channel for electrons (Fig. 1a).
Using the dry-transfer method, mechanically exfoliatedh-BN and 1ML WSe2 are sequentially transferred, sothat they make partial contact with a corner of the Pt
pattern (Figs. 1b-1d). Thus, we could effectively avoid
sample charging at low temperatures (~100 K) eventhough samples are placed on insulating substrates. In
order to efficiently find the precise position of thesample, we mapped out photoemission intensity at the
Fermi level (Figs. 1e-1f) and W 4f7/2 core (Fig. 1g) near
the Pt corner by utilizing the micro beam (~30 µm). The
so-obtained spatial map was found to be consistent with
an optical image of the sample. Then, we moved to theregion of interest (1ML WSe2 region) and obtained theelectronic structure of 1ML WSe2 / h-BN over the

Fig. 1. Optical image (a~d) and spatial map ofphotemission intensity (e~g) of the monolayer WSe2 /h-BN heterostructure. Scale bar, 100 µm.

Fig. 2. Electronic structure of monolayer WSe2 / hBN heterostructure.

[1] B. Hunt et al., Science 340 (6139) (2013) 1427.
[2] E. Wang et al., Nat. Phys. 12 (2016) 1111.
[3] S. Ulstrup et al., arXiv : 1904.06681 (2019).
[4] X. Xu et al., Nat. Phys. 10 (2014) 343.
[5] Q. Zhu et al., Sci. Adv. 5 (1) (2019) eaau6120.

78

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Ⅲ -2. Materials Sciences

BL5U

Three-dimensional Angle-resolved Photoemission Study of
Ullmannite NiSbS with the Cubic Chiral Crystal Structure
1

T. Ito1,2, T. Hosoya2, M. Nakatake3, S. Ideta4,5, K. Tanaka4,5, M. Kakihana6, D. Aoki7,
A. Nakamura7, T. Takeuchi8, H. Harima9, M. Hedo10, T. Nakama10 and Y. Ōnuki10

Nagoya University Synchrotron radiation Research center (NUSR), Nagoya University, Nagoya 464-8603, Japan
2
Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan
3
Aichi Synchrotron Research Center, Seto, 489-0965, Japan
4
UVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
5
The Graduate University for Advanced Studies, SOKENDAI, Okazaki 444-8585, Japan
6
Graduate School of Engineering and Science, University of the Ryukyus, Nishihara-cho 903-0213, Japan
7
Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan8
Low Temperature Center, Osaka University, Toyonaka 560-0043, Japan
9
Graduate School of Science, Kobe University, Kobe 657-8501, Japan
10
Faculity of Science, University of the Ryukyus, Nishihara-cho 903-0213, Japan
we are going to perform linear and circular polarization
dependent ARPES on this system in near future.

Non-centrosymmetric compounds have attracted
much attention due to their interesting phenomena
relating with inversion symmetry breaking. The
ullmannite type NiSbS with the non-centrosymmetriccubic chiral structure has recently been suggested to bea possible candidate of Weyl semimetal [1]. Indeed,
split Fermi surface topologies reflecting the cubic chiral
crystal structure and the spin-orbit interactions havebeen reported [2]. In this study, we have performed
angle-resolved photoemission spectroscopy (ARPES)
on NiSbS to directly investigate the electronic band
structure of this system.
ARPES measurements were performed at the
UVSOR-III BL5U. Data were acquired at T = 25 K withhν= 40 - 96 eV. To directly trace the ΓR high-symmetryline with using photon energy dependent ARPES at thenormal emission angle (θ = 0°), clean sample surfaces
were obtained by in situ cleaving on (111) plane.
Figures 1(a) and (b) show the kx-kz constant energy
image at the Fermi level EF (a) and 400 meV (b) onΓXRM plane of NiSbS. We have clearly found theinclined shape of the obtained images. The observed
inclined shape is consistent with the tetragonal shapeof ΓXRM plane where kz axis corresponds to the
diagonal ΓR line (Fig.1(c)). From the symmetry of theobtained images, we have estimated the inner potentialof V0 = 33 eV which is relatively larger than one of(001) cleaved surface (V0 = 24.7eV) [3].
Figure 1(c) shows the band structure along ΓR line
obtained from the normal emission ARPES spectra.
From the comparison with the band structure
calculation (solid lines), we have found slightnarrowing of the dispersive features relative to thecalculation, while the rough tendency seems to be
similar. According to the band calculation, existenceof Weyl point (WP) has been expected around kz = 5.2
Å-1, where we found no band crossing except for thebroad distribution between the non dispersive featurearound 400 meV and the dispersive featureapproaching EF. To understand the relation between
the electronic structure and the chiral crystal structure,

Fig. 1. (a,b) kx-kz constant energy image at EF (a) and
400 meV (b) on ΓXRM plane of NiSbS. (c) Band
structure along ΓR line. Solid lines are band calculation[2]. (d) Cubic Brillouin zone shown with kx and kz axis
defined for the sample surface obtained by cleaving on(111) plane.

[1] A. Furusaki, Sci. Bulletin 62 (2017) 788.
[2] M. Kakihana et al., J. Phys. Soc. Jpn. 84 (2015)084711.
[3] T. Ito et al., UVSOR Activity Report 2018 46 (2019)
96.

79

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Ⅲ -2. Materials

BL5U

Electronic Band Structure of Sn4Sb3
W. Wen1,2, C. Y. Hong1,2, G. Zhao1,2, Z. Song1,2 and R. -H. He2

Department of Physics, Fudan University, Shanghai 200433, China
School of Science, Westlake Institute for Advanced Study, Westlake University, Hangzhou 310064, China
1

2

Ⅲ-2

Nevertheless, there are some states observed in theexperiment but absent in the calculations. These states aremarked as rounded dashed curves around the K points(corners of the hexagonal Brillouin zone) in Fig. 2 where
the kx-ky energy contours at binding energy -0.3 eV
measured with different photon energies are shown.
These states exhibit linear dispersions extending
toward the Fermi level (Fig. 3). This appears to beconsistent with the presence of Weyl points in the bulk
band structure. Further analyses and comparison with
first-principles calculations based on the slab model arenecessary in order to establish this plausible connection
before one can draw a conclusion on the Weyl nature of
Sn4Sb3.

Recently, alloys consisting of heavy elements havereceived much attention because of their strong spinorbit coupling (SOC), which could give rise to a variety
of topological phases [1,2], including topologicalsemimetals (TSM), topological (crystalline) insulators
and Topological superconductors (TSC). Topologicalsuperconductors (TSC) are the superconducting
analogues of TI, and have potential applications in faulttolerant quantum computing [2-4]. The superconducting
binary compound Sn4Sb3 has been proposed to be a
candidate for TSC [5].
To study the electronic band structure of Sn4Sb3, we
performed systematic ARPES measurements on its
cleaved (001) surface, and a series of Fermi surface
intensity maps were measured with linearlyhorizontally (LH) polarized photons of photon energy(hν) from 60 eV to 140 eV and T=7.0 K. Figures 1(a)and (b) are two Fermi surface maps obtained withhν=70 eV and hν=115 eV. Figures 1 (c) and (d) show
the Fermi surface obtained with first-principles
calculations in the kx-ky plane at kz=0 and kz=π.
Through comparison, we can see the experimental
Fermi surface of hν=70 eV agrees with the calculated
one at kz=0, and that of hν=115 eV agrees with that atkz=π. A good overall agreement on the Fermi surface
between the measured photon energy dependence andthe calculated kz dependence can be obtained byassuming an inner potential V0 = 12.8 eV (and the caxis lattice constant 24.85 Å as determined from x-ray
diffraction).

Fig. 2. Observation of surface states with hν=60 eV,
80 eV, 100 eV and 115 eV. kx-ky energy contours areshown at binding energy -0.3 eV, with the surface
states eyeguided by the white dashed curves.

Fig. 3. Bulk-band structure and observation of the
Weyl point. (a) Fermi surface maps measured withhν=105 eV. (b) Band dispersion along the blue dashedline in (a).
[1] M. Z. Hasan and C. L. Kane, Rev. Mod. Phys. 82(2010) 3045.
[2] X. L. Qi and S. C. Zhang, Rev. Mod. Phys. 83 (2011)
1057.
[3] J. Alicea, Rep. Prog. Phys. 75 (2012) 076501.
[4] M. Sato and Y. Ando, Rep. Prog. Phys. 80 (2017)076501.
[5] B. Liu et al., Phys. Rev. Mater. 3 (2019) 084603.

Fig. 1. ARPES measurements of the Fermi surface
with LH polarized light with (a) hν = 70 eV and (b)hν= 115 eV. (c) and (d) show the Fermi surfaces in the
kx-ky plane at kz = 0 and kz =π respectively. Dashedcurves in different colors identify features observablein both the experiment and calculation.

80

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Ⅲ -2. Materials Sciences

BL5U

High-resolution ARPES Study of Antiferromagnetic Topological-insulator
Candidate CeBi
S. Souma1,2, K. Nakayama3, D. Takane3, Y. Kubota3, T. Kawakami3, K. Sugawara1,2,3,
M. Yoshida4, A. Ochiai3, T. Takahashi1,2,3 and T. Sato1,2,3

1
Center for Spintronics Research Network, Tohoku University, Sendai 980-8577, JapanWPI Research Center, Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan3
Department of Physics, Tohoku University, Sendai 980-8578, Japan
4
Max-Planck-Institute for Solid State Research, Heisenbergstrsse 1, 70569 Stuttgart, Germany

2

Cerium monopnictides CeXp (Xp = P, As, Sb, andBi) are a typical example of heavy-fermion systems
showing an exotic and complicated magnetic phase
diagram as a function of temperature, pressure, andmagnetic field, known as a “devil’s staircase” [1-4].
Recently, it was predicted that isostructural material
LaXp becomes a topological insulator due to the bandinversion at the X point of bulk Brillouin zone [5]. The
proposal of the non-trivial electronic bands has
renewed the interest for RXp (R = La and Ce) systems,
and has triggered intensive theoretical andexperimental investigations, resulting in the discovery
of extremely large magnetoresistance and unusual
resistivity plateau in LaSb and LaBi, as well as theobservation of Dirac-cone-like energy band in some
RXp compounds. Taking into account such topologicalaspects of RXp family, one would naturally expect that
CeBi is an excellent candidate to study the interplay
between magnetism and topological properties, since
it shows interesting magnetic phases characterized bya two-step antiferromagnetic (AF) transition at T = 25
and 14 K under zero-magnetic field [3, 4], in addition
to the expected topological nature. In a broader
perspective, it is of great importance to experimentally
clarify the role of antiferromagnetism to the
topological properties, which is currently a target ofintensive debates in theories while no concrete
experimental data have been hitherto reported.
In this study, we performed high-resolution angleresolved photoemission spectroscopy (ARPES) of
CeBi to determine the bulk and surface electronic
states and their evolution across the Néel temperatures.
For this sake, we utilized high- energy-resolution andlow-accessible-temperature capabilities of BL5U.
Single crystalline samples were cleaved in situ in an
ultrahigh vacuum of 1 × 10-10 Torr along the (100)crystal plane [see Fig. 1(a) for corresponding bulk andsurface Brillouin zones].
Figures 1(b) ___and
1(c) show the ARPES intensity_ __plots along the  M cut measured in the paramagnetic(PM) and AF states, respectively. In the PM phase, we
observed several bulk bands displaying the ___holelike_ __and electronlike dispersions centered at the  and M
points, respectively. In addition, we found the_ __surface
states with a Dirac-cone-like dispersion at the M point.
In the AF phase, the overall bulk band dispersions are

similar to those in the PM phase. However, the surface
states show a drastic change across T
N; linearly___
dispersive Dirac-like band appears at the  point. Thisfinding suggests an intricate interplay between
antiferromagnetism and topological surface states in
CeBi.

Fig. 1. (a) Bulk and surface Brillouin zones ofCeBi(111). (b) and (c) ARPES intensity plots at T = 30
K and 10 ___K,_ __respectively, measured with h = 53 eValong the  M cut.

[1] J. Rossat-Mignod et al., Phys. Rev. B 16 (1977)
440.
[2] J. Rossat-Mignod et al., J. Magn. Magn. Mater. 3134 (1983) 398.
[3] H. Bartholin et al., Le J. Phys. Colloq. 40 (1979)
C5.
[4] M. Kohgi et al., Physica B 281-282 (2000) 417.
[5] M. Zeng et al., arXiv:1504.03492 (2015).

81

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Ⅲ -2. Materials

BL5U

ARPES Studies of the Superconductors with Row-carrier-density
Y. Akimoto1, K. Kuroda1, K. Kawaguchi1, S. Sakuragi1, Y. Arai1, Y. Wan1, K. Kurokawa1,
H. Tanaka1, S. Ideta2, K. Tanaka2, D. Hirai1, Z. Hiroi1, T. Yamada3 and T. Kondo1
ISSP, The University of Tokyo, Kashiwa 277-8581, JapanUVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
3
IMRAM, Tohoku University, Sendai, 980-0812, Japan12hν (eV)

64

H

37

Ⅲ-2

NaAlSi is a three-dimensional superconducting
material with Tc ~7 K [1]. Previous first-principles
calculations indicate that the electronic structure of
NaAlSi shows semimetallic low carrier density states
because of occurring of the carrier compensation. In thecase of general superconductor with dilute carrier state,Tc~7 K is too high to explain in the standpoint of pastreports. Thus, to understand the relationship between
electronic states and the superconducting mechanism of
NaAlSi will open the new way to develop the high Tc
superconductor. In addition, recent theoretical study has
shown that the electronic structure of NaAlSi shows
Dirac nodal line, and this material is the candidate of
topological superconductor [2].
Although the superconductivity of this material has
been discovered over 10 years ago [3], the electronic
structure has not yet been determined experimentally
due to the unstable nature of the material under theatmosphere. In this beamtime, we solved this problem
by preparing the sample in a glove box, and directly
observed the electronic structure of NaAlSi using
angle-resolved photoemission spectroscopy (ARPES)
using synchrotron radiation.
As a result of the ARPES measurement, the crossing
between valence band originating from the Si-2p
orbitals and the conduction band originating from theAl-3sp orbitals is occurred, and Dirac nodal line,
which predicted by theoretical study, is observed. The
valence band has a flat shape near the Fermi level. The
result of kz dependent band dispersion measurement
indicates that the electronic structure of NaAlSi
showing pseudo two dimensionally (Fig. 1). As shownin Fig. 1, the Fermi wave number kF is observed onlyat specific kz.
We tried to evaluate the superconducting gap in thiselectronic structure from the synchrotron ARPES
measurement in BL5U having low temperature / highresolution measurement system. From the comparison
between the leading-edge-midpoint measured at 4 K(superconducting state) and that of 8 K (normal state),the leading-edge-midpoint shift, i.e., superconducting
gap is observed at 4 K. This result suggests thepossivillity of the relationship between unique twodimensional electronic structure with the dilute carrierstate and occurring of the superconductivity in thismaterial.
In future, if the superconducting mechanism andtopological states of this material are fixed, we may
establish the new standpoint in order to develop thehigh Tc topological superconductor.

L
-0.4

0

0.4

k// (Å-1)

Fig. 1. kz dispersion around Fermi level of NaAlSi.

[1] H. B. Rhee et al., Phys. Rev. B 81 (2010) 245114.
[2] L. Jin et al., J. Mater. Chem. 7 (2019) 10694.
[3] S. Kuroiwa et al., Physica C 466 (2007) 11.

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BL5U

Demonstration of Final State Effect:
Deflector Map in Double Layer Cuprate Bi2212
S. Ideta1,2, S. Ishida3 and K. Tanaka1,2

National Institutes of Natural Science, Institute for Molecular Science, Okazaki 444-8585, Japan
2
The Graduate University for Advanced Studies, SOKENDAI, Okazaki 444-8585, Japan
3
Electronics and Photonics Research Institute, National Institute of Advanced Industrial Science and Technology,
Tsukuba 305-8565, Japan1

To understand the mechanism of high-Tc
superconductivity in cuprates is one of the crucial
issues. Angle-resolved photoemission spectroscopy(ARPES) is a powerful tool to investigate theelectronic structure of solids directly, and has
contributed significantly towards an elucidating of thenature of superconductivity of cuprates [1]. However,
ARPES spectrum have a strong constraint of the final
state effect arising from especially the energy andpolarization of the incident photons [2,3]. In addition,in the conventional ARPES experiment, one needs torotate samples to obtain the information of momentum
space. Recently, deflector mode for mapping has beendeveloped and we do not need to rotate samples. We
report that the final state effect using a state of the art
ARPES system with a new electron lens withdeflectors (MB Scientific AB) in Double-layer Bibased cuprate superconductor, Bi2Sr2Ca2CuO8+δ
(Bi2212).
Bi2212 is the one of the most common samples tostudy the electronic structure using ARPES. Bi21212
has two equivalent CuO2 planes and therefore shows
the bilayer splitting reflecting bonding and antibonding bands. In this study, as a first step to elucidate
the final state effect using the deflector mode andsample rotation mode, we have investigated themomentum space mapping using the deflector modeon underdoped Bi2212 along the Cu-O and Cu-Cu
directions (s polarization).
High-quality single crystals of underdoped
Bi2Sr2Ca2CuO8+δ (UD Bi22212, Tc = 65 K) were grownby the TSFZ method. ARPES experiments were carriedout at BL5U of UVSOR-III Synchrotron. Clean sample
surfaces were obtained for the ARPES measurements
by cleaving single crystals in-situ in an ultrahighvacuum better than 8×10-9 Pa. The measurements were
performed at 20 K.
In order to estimate the distribution of the spectral
weight on momentum space, ARPES experiments
have been demonstrated by linearly polarized light andFermi surfaces (FSs) are observed as displayed in Fig.
1. Figures 1(a) and 1(b) show FSs highlighted by red
dotes corresponding to the Fermi momentum, kF, but
the experimental momentum cut is along the Cu-O andCu-Cu directions, respectively. Due to the photon
energy, we could not resolve the bilayer splitting in thepresent study (hν = 60 eV). From this result, we foundthat the deflector mode mapping shows a similar FS

reported in previous ARPES study [4-7]. In addition,
integrated spectral intensity plotted as a function of FS
angle [Figs. 1(c) and 1(d)], and these two experimental
geometries have different momentum dependence forthe spectral intensity.
As future work, we need to investigate FS mapping
using the conventional sample rotation method tocompare the spectral weight on momentum space withthe result of Fig.1. In addition, we will demonstrate
doping dependence and photon energy dependence.
These experimental studies will put additional
experimental constraint on various microscopic
theories and data analysis.

Fig. 1. Momentum-space mappings in underdoped(UD) Bi2212 at energies of -0.01 eV and 0.01 eV (hν =60 eV, T = 20 K). (a) Mapping along Cu-O direction(nodal direction). (b) Mapping along the Cu-Cu
direction (antinodal direction). (c), (d) Spectral intensity
integrated by ±2 degree around kF is plotted as afunction of Fermi surface angle.
[1] A. Damascell et al., Rev. Mod. Phys. 75 (2003) 473.
[2] A. Bansil et al, Phys. Rev. Lett 83 (1999) 5154.
[3]D. L. Feng et al., Rhys. Rev. B 65 (2002) 220501(R).
[4]T.-G. Zhong et al., Phys. Rev. B 98 (2018) 140507(R).
[5]J. D. Rameau et al., Phys. Rev. B 90 (2014) 134509.
[6]K. Tanaka et al., J. Phys. Soc. Jpn. 88 (2019) 044710.
[7] P. B. Bogdanov et al., Phys. Rev. Lett. 89 (2002)
167002.

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Ⅲ -2. Materials

BL5U

Polarization Dependence of the Photoelectron Intensity Distribution from
MoS2
2

Ⅲ-2

S. Tanaka1, K. Ueno2, S. Ideta3 and K. Tanaka3

The institute of Scientific and Industrial Research, Osaka Univ., Ibaraki 567-0047, Japan
Graduate School of Science and Engineering Saitama University, Saitama 338-8570, Japan
3
UVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan1

The photoelectron intensity in the angle-resolved
photoelectron spectroscopy (ARPES) is determined by
the Femir’s golden rule, where the matrix element
plays a crucial role. In the matrix
element,
denotes the final state which isapproximately the plane wave;
corresponds toandthe photoexcitation Hamiltonian andrespectively denote the vector potential of the photon
and the momentum of the electron. We can change
by controlling the polarization of the photon, anddetailed electronic properties of the initial state
can be investigated by the polarization-dependent
photoelectron intensity distribution.
For this purpose, we made an investigation for theband at the top of the valence band in MoS2, which ismainly constructed from the Mo-4d and S-3p orbitals.
Figures 1 show the constant energy maps at thebinding energy of 0.77 eV taken at hν=60 eV. The
polarizations of the incident photons are linearlyhorizontal (i.e., p-pol), linearly vertical (i.e., s-pol),circularly right-handed (CW), and circularly lefthanded (CCW). The band forms a circular shapearound the Γ-point. This means that the operation ofrotation for the wavefunction does not change theenergy (the eigenvalue of the Hamiltonian), and theangle around the Γ-point is a good quantity fordescribing the system. The photoelectron intensity
distributions are drastically changed with changing thepolarization. The intensity distributions as functions of
the azimuthal angle are displayed after expanding by
repeating the signals as the period of 2π in Figs. 2. The
distribution taken with the vertical polarized lightshows a complete different one from the other three.
The horizontal, CW, and CCW polarizations yield the,
distribution of nearly the same form
although the phases are shifted as changing thepolarization. The phase-shift in the photoelectron
intensity distribution with changing the photon
polarization was reported for the Dirac cone of thegraphene, where the “Berry’s phase” of the
wavefunction in the Dirac cone plays a key role [1].
Accordingly, an important information about the
wavefuntion of the valence band MoS2 will be given.
Theoretical investigation and more detailed analysis
are in progress.

Fig. 1. Polarization-dependent photoelectron intensity
map at the binding energy of 0.77 eV near the Γ-pointof MoS2.

Fig. 2. Photoelectron intensity distribution at thebinding energy of 0.8 eV as a function of the angle
around the Γ-point of MoS2. Solid lines show
, where is the phase-shift.
[1] Y. Liu et al., Phys. Rev. Lett. 107 (2011) 166803.

84

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BL5B

Study on Optical Properties of Metallic Sodium by Vacuum Ultra Violet
in UVSOR (2)1

M. Kawaguchi 1,2, J. Saito1, H. Daido3 and T. Suemoto4

Sodium Technology Development Group, Japan Atomic Energy Agency, Tsuruga 919-1279, Japan
2
Research Institute of Nuclear Engineering, University of Fukui, Tsuruga 914-0055, Japan
3
Institute for Laser Technology, Suita 565-0871, Japan4
Toyota Physical and Chemical Research Institute, Nagakute 480-1192, Japan

Metallic sodium is well-known as a typical alkali
metal, but the optical properties in vacuum ultraviolet(VUV) range are controversial [1,2]. One of the authors(H. D.) demonstrated VUV light (Wave length: 115-180nm) penetrates in several millimeters of sodium withhigh transmittance for the first time [3]. Inspired by theexperiment, the transmittance measurement of metallic
sodium using VUV has been performed at BL5B in
UVSOR [4]. In this year, we adopted calcium fluoride(CaF2, Pier Optics Co, ltd.) for windows of the sodium
sample (Diameter: 18 mφ, Thickness: 2.0 mmt) todecrease interaction between the sodium and thewindows, which were seemed to be one of significant
causes of decreasing drastically the transmittance.
Figure 1 shows intensities of 0th light, 1st light andtransparent VUV, which denote the raw light radiatedfrom UVSOR, the light passed through lithium fluoride(LiF) filter, and the transparent light passed through the
LiF filter and the CaF2 windows, respectively. Becauseof the band gaps, the LiF and the CaF2 can betransparent to more than about 100 nm and about 120
nm in wave length, respectively. Therefore, theintensities of the 1st light and the transparent VUV show
the stepwise increases in the characteristic wave lengths,
which are corresponded to those of the LiF and the CaF2.
Figure 2 shows the transmittance of the CaF2 windows,
which was obtained by dividing the intensity of thetransparent VUV by that of the 1st light. In thiscalculation, the 0th light can’t be used because it
includes the short-range wave-length light. The
measured transmittance of CaF2 windows is almost
consistent with the literature datum [5], and it concluded
that there were no problems in the transmittancemeasurement and CaF2 windows.
However, the transparency phenomenon of VUV in
the metallic sodium has never been confirmed by ourgroup. Because the reaction (deterioration) of thesodium on the surface of the windows proceeded
gradually and the products might hinder thetransparency of VUV, we need to improve the techniqueof making the sodium sample.

Intensity (a.u.)

10-8
10-9

Ⅲ-2

10-10
0th light
LiF
LiF and CaF 2

10-11
10-12
100

120

140
160
Wave length (nm)

180

200

Fig. 1. Intensities of 0th light at BL5B and of lights
through LiF and CaF2 windows (2mmt), andtransmittance of CaF2 window.
1

Transmittance (-)

0.8
0.6
0.4

CaF2

0.2
0

120

140
160
Wave length (nm)

180

200

Fig. 2. Transmittance of CF2 windows[1] J. C. Sutherland et al., Optical properties of sodiumin the vacuum ultraviolet (ORNL-TM-1776, Oak Ridge
National Laboratory, 1967).
[2] R. W. Wood, Phys. Rev. 44 (1933) 353.
[3] H. Daido et al., Optics express 21 (2013) 28182.
[4] M. Kawaguchi, J. Saito, H. Daido and T. Suemoto,UVSOR Activity Report 2018 46 (2019) 89.
[5] http://www.pier-optics.com/transparent.html

85Ⅲ02- 39 -BL6U Sciences
Ⅲ -2. Materials

BL6U

Temperature-dependent Electronic Structure of a Quasi-2D Material
-Mo4O11
T. Kobayashi1, E. Iwamoto2, K. Sakamoto2, M. Koyano3, F. Matsui4 and S. Suga5

Department of Material and Life Science, Osaka University, Suita 565-0871, Japan2
Department of Applied Physics, Osaka University, Suita 565-0871, Japan3
School of Materials Science, Japan Advanced Institute of Science and Technology, Nomi 923-1292, Japan
4
UVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
5
Institute of Scientific and Industrial Research, Osaka University, Ibaraki 567-0047, Japan1

Ⅲ-2

Angle resolved photoelectron spectroscopy (ARPES)
with extremely high resolutions in both energy andmomentum is indispensable to obtain detailed
understanding of various phenomena in condensed
matters physics, such as charge density wave (CDW),
Rashba effect, properties of topological materials, andso on. These kind of studies may be effectively
performed by momentum microscopy (MM) in the near
future.
In order to check the performance of the beam line
BL6U, where the MM is planned to be setup, we havemeasured the electronic structure of a quasi-2D material
-Mo4O11 at different temperatures. By performing
electrical resistivity measurements, -Mo4O11 has beenreported to show transitions at Tc1=109 K and Tc2=30 K
that are very likely due to CDW instabilities [1].
However, neither band gap opening nor band folding,which should be present in case of CDW transition, hasbeen observed in the former ARPES study [2]. In thepresent study, we performed ARPES measurements at
temperatures above and below the two CDW transitions
to obtain more detailed information on the property ofthis material.
Figure 1 shows the Fermi surface of -Mo4O11
measured at 8.6 K. Straight lines indicating thepresence of three 1D metallic bands in different
direction are clearly observed. The observation of
three 1D metallic bands is consistent with that reported
in Ref. [2] but not with the electrical resistivity
measurements [1] since the measurement temperaturein Fig. 1 is lower than Tc2. The Fermi wave number ofthe metallic bands are ca. 35 % of the Brillouin zone.
In Fig. 2, we show the energy distribution curves(EDC) measured at T>Tc1 (300 K), Tc1>T>Tc2 (60 K),
and Tc2>T (8.6 K). As well as the result in Fig. 1, notrace of CDW transition can be confirmed in Fig. 2.
The peak just below the Fermi level shift a bit to lower
binding energy and becomes shaper as the temperature
decreases. The energy shift and the change in the
Fermi wave vector (not shown) indicate hole-doping
during the cooling. The closer the Fermi surface is tothe half of the Brillouin zone the more likely the CDW
transition occurs. In the present case, the Fermi surface
is much smaller than the half of the Brillouin zone andthus the metallic behavior at all temperatures might be
resulting from the hole-doping induced by the residual
gas adsorption.

Since the in situ cleavage was successful to provide
single crystal domains of the order of sub-mm, andbecause very complex band structures were detectedin the present study, -Mo4O11 would be a suitablematerial for checking the performance of the MM in
the near future.

Fig. 1. Fermi surface of -Mo4O11 measured at 8.6 K.

8.6 K
60 K
300 K

Fig. 2. EDC spectra obtained by integrating the data
surrounded by the red rectangule shown in Fig. 1.

[1] H. Guyot et al., J. Phys. C 16 (1983) L1227.
[2] G.-H. Gweon et al., Phys. Rev. B 72 (2005) 035126.

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BL6U

Angle-Resolved Photoemission Spectroscopy of Topological Insulators for
Clarification of Origin of Pressure-Driven Superconductivity
1

Y. Kubozono1, R. Eguchi1, H. Goto1, T. He1, K. Kobayashi1, T. Takahashi1,
H. Ozaki2, K. Hayashi2 and F. Matsui3

Research Institute for Interdisciplinary Science, Okayama University, Okayama 700-8530, Japan
2
Nagoya Institute of Technology, Nagoya 466-8555, Japan
3
Institute for Molecular Science, Okazaki 444-8585, JapanAg atoms are included may be selectively cleaved in
the AgxBi2-xSe3 crystal.
Moreover, we measured the ARPES of Nb0.5Bi2Se3. A
clear superconducting transition at ~3 K was observed in
the magnetic susceptibility for this material. Figure 1
shows the band dispersion of Nb0.5Bi2Se3 measured at
10 K. Fermi energy is 55.5 eV in kinetic energy. A single
Dirac cone and the top of the valence band wereobserved.
Now, we are trying to measure the ARPES of new
topological insulators which was recently found toshow the pressure-driven superconductivity.

Two-dimensional angle-resolved photoelectron
spectroscopy (ARPES) is a powerful tool to study theelectronic structure of crystalline materials, in particular
the unique electronic structures of topological materials
such as topological insulators, Dirac / Weyl semimetals,
and axion insulators have been extensively investigatedduring a past decade. The initial state binding energy (E)and the wave vector (k) can be easily determined fromthe kinetic energy and the direction of the detected
ARPES data. Some of topological insulators such as
Bi2-xSbxTe3-ySey [1] and Sr or Ag doped Bi2Se3 [2,3]provided the pressure-driven superconducting phases.
To understand the correlation between the electronic
property and pressure-driven superconductivity, wemust obtain the detailed information of electronic
structures of topological insulators at ambient pressure.
Admittedly, in case of Bi2-xSbxTe3-ySey, the Fermi level
and Dirac point significantly shifted against x and y [4].
Therefore, the superconductivity of topologicalinsulators induced by pressure must be investigated byassociating exactly with their electronic structures, aswell as with the structural transitions. In addition, thesuperconducting gap function (Cooper pair symmetry)of pressure-driven superconductivity in topologicalinsulators must be clarified to show the topologically
non-trivial nature of superconductivity, which requires
the exact information of electronic structures at ambientpressure. For these purposes, the study on electronic
structure by ARPES is indispensable for topologicalinsulators. In this study, we measured the ARPES dataof Ag doped Bi2Se3 (AgxBi2-xSe3; x = 0.05), Nb doped
Bi2Se3 (NbxBi2Se3; x = 0.5), Bi2-xSbxTe3-ySey (x = 1.0, y= 2.0) and those precursor sample, Bi2Se3 using the
MBS A-1 Lens#5 analyzer installed at BL6U.
We measured the ARPES data of the non-doped
Bi2Se3 single crystal recorded at room temperature. A
clear band dispersion showing a single Dirac cone, andconduction / valence bands was recorded as previously
reported [5]. This means that the measurement system
is available for detecting the exact information ofelectronic structures of topological insulators.
We measured the ARPES of AgxBi2-xSe3 (x = 0.05)
single crystal at 10 K. At the present stage, the ARPES
of AgxBi2-xSe3 was not distinguished from that of
Bi2Se3, i.e., the Ag doping was ambiguous. The reason
is not clear, but one possibility that the cleaved surfaceof single crystal of AgxBi2-xSe3 might not include Ag
atom was suggested. In other words, the area where noFig. 1. Band dispersion of Nb0.5Bi2Se3.

[1] T. He et al. Phys. Rev. B 100 (2019) 094525.
[2] Y. Zhou et al. Phys. Rev. B 93 (2016) 144514.
[3] T. He et al. Phys. Rev. B 97 (2018) 104503.
[4] T. Arakane et al. Nature Commun. 3 (2012) 636.
[5] Y. L. Chen et al. Science 329 (2010) 659.

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BL6U Sciences
Ⅲ -2. Materials

BL6U

Photon-energy-dependence in the Photoelectron Angular Distribution
from MoS2
2

Ⅲ-2

S. Tanaka1, K. Ueno2, H. Matsuda3 and F. Matsui3

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

2H-MoS2 is one of the most typical transition metal
dicalchogenides, and its electronic property is afundamental issue for the fabrication of new functional
low-dimensional electronic devices. In this report, weshow a comparison in the momentum space between the
ARPES measurement by using photons in the wide
energy range (60-200 eV) and the DFT-calculation todemonstrate the validity of the photon-energydependent ARPES for identifying the characterizationof the valence band of the materials.
The ARPES measurements were carried out at theroom temperature, and the DFT calculation was madeemploying the QUANTUM ESPRESSO package(version 6.3), which had been installed in the computer
at Research Center for Computational Science in IMS.
Figures 1 show a part of the series of the photon-energydependence in the photoelectron angular distribution
from MoS2 at the same binding energy (1.8 eV). The
first Brillouin zones are indicated as black lines. Shapes
clearly change as a function of the photon energy; at 7393 eV and 149 eV, a hexagon consisting of small
triangles is shown; at 113 eV, a smaller hexagram isshown; and at 103 eV, both are shown. This behavior is
not consistent with the calculated kz value (not shownhere), and thus cannot be interpreted to the dispersion
along the kz axis. Instead, this can be ascribed to thecharacter of the band. Figures 2 show the calculated
projected density of states for the Mo-4d and S-3p
orbitals in the momentum space at the binding energy of-1.2 eV. The binding energy for the calculation waschosen so as to display shapes similar to theexperiments. The discrepancy of 0.6 eV may partly beto the difference in the reference (in the ARPES, it is the
Fermi level measured by using Au film, and in the DFT
calculation it is the valence band maximum). It is clearthat ARPES results at photon energies of 73-93 eV
resembles to the band provided by Mo-4d while thehexagram shape obtained by ARPES at 103-113 eVresembles to the band of S-3p. Figure 3 shows thephotoexcitation cross section of the atomic orbitals. The
photoexcitation cross section of Mo-4d is higher than S3p in the photon energy regions below ~70 eV andabove ~170 eV. Although the crossing point at ~70 eV
in Fig. 3 is significantly lower than ~100 eV which isderived from Figs. 1, a general trend shows a good
agreement, and thus the characteristics of the band iswell explained. More detailed analyses are in progress.

Fig. 1. Photoelectron angular distributions of the same
binding energy from MoS2 at various photon energies.

Fig. 2. Calculated density of states at BE=-1.2 eV which
are projected into the Mo-4d and S-3p orbitals

Fig. 3. Phototexcitation cross sections of S3s, S3p andMo4d atomic orbitals [1].

[1] J. J. Yeh et al., At. Data Nucl. Data Tables 32 (1985) 1.

88

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Ⅲ -2. Materials Sciences

BL6U

Anisotropy of Photoelectron Intensity Distribution upon Hole-Vibration
Coupling in Perfluoropentacene Monolayer on Ag(111)
Y. Hasegawa1, K. Maduwantha2, R. Koswattage2, T. Nakamura3, F. Matsui4 and S. Kera1,4
Department of Photo-Molecular Science, Institute for Molecular Science, Okazaki 444-8585, Japan2
Sabaragamuwa University of Sri Lanka, Belihuluoya 70140, Sri Lanka
3
Department of Physics, Graduate School of Science, Osaka University, Toyonaka 560-0043, Japan
4
UVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan

1

Organic semiconductor thin films have been getting
attention as next promising optical and electronic devices.
Optimizing charge transfer between weakly connectedmaterials is one of a key issue to improve theperformance. Considering the charge transfer is affectedby the coupling of the charge to specific vibrationalmodes of molecules, the impact of anisotropic
deformation of a molecule upon ionization at theinterface on the transfer efficiency should be investigated.
We have found perfluoropentacene (PFP) monolayer
on inert crystalline substrate shows hole-vibration
coupling upon angle-resolved ultraviolet photoelectron
spectroscopy (ARPES) measurement and distinct
angular distribution of highest occupied molecularorbital (HOMO) features depending on the vibronic
couplings [1]. To address the origin of the photoelectron
intensity distribution of the vibronic states, a precise
experiment of the photoelectron momentum map(PMM) was carried out to evaluate the intensity
modulation.
PFP monolayer of 2.5 Å was deposited onto a clean
Ag(111) substrate. Low energy electron diffraction(LEED) and PMM were carried out at the sample
temperature of 16 K. PMM was taken by means ofacceptance-cone-tunable spectrometer equipped with A1 analyzer (MBS) which enables mechanical deflector
scan. Detail of the setup is reported elsewhere [2].
ARPES measurement of PFP monolayer on Ag(111)shows HOMO with fine structure, a main peak of
HOMO, labeled H(00), followed by the vibrational
progression of satellite peaks toward higher binding
energy. Figures 1(a) and (b) are PMM taken from H(00)and the first satellite, H(01), respectively. The PMMs
correspond to the photoelectron intensity integrated forthe two different domains, where the moleculararrangements of A and C are shown in Fig. 1 (c). Notethe one from arrangement A is marked by dashed oval.
Figure 2 shows the line profiles of the PMMs takenfrom k1 and k2 direction marked by dashed and solid
allows in Fig. 1, respectively. In direction of k2 subtle
difference of the intensity between H(00) and H(01) isobserved whereas little difference is evaluated indirection of k1. This observation indicates that the nuclei
position is not fixed during the photoionization process
as found in gas-phase system, meaning the breaking of
sudden approximation in the thin film. Moreover the
wavefunction of the molecular orbital is modulated only
in a certain direction upon a specific hole-vibration

coupling, thus designing a distortion of the molecular
structure in real space upon ionization would be
important to control device characteristics. The
correlation between the distortion of the molecule upon
vibronic excitation and the PMM would be further
discussed beyond Franck-Condon approximation.

Fig. 1. PMM image taken at the HOMO of the (00) and(01) peaks (ΔE ~ 50 meV) of PFP/Ag(111) with hv = 50
eV. The color scaling and intensity are normalized at
maximum intensity. (c) Geometry for the measurement.

Fig. 2. Line profiles taken from H(00) and H(01)indicated by white arrows, (a) k1 and (b) k2 in Figs. 1(a)and (b), respectively. Origins of k1 and k2 in (kx,ky) are(1, -0.3) and (1.0, 0.0), respectively.

[1] S. Kera et. al., Prog. Surf. Sci. 84 (2009) 135.
[2] H. Yamane et. al., Rev. Sci. Instrum. 90 (2019)093102.

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BL7B
Ⅲ -2. Materials

BL6B, BL7B

Anisotropic Metal-Insulator Transition in RuAs
Y. Nakajima1, Z. Mita2, H. Watanabe2,1, Y. Ohtsubo2,1, T. Ito3,4, H. Kotegawa5, H. Sugawara5,
H. Tou5 and S. Kimura2,1
Department of Physics, Graduate School of Science, Osaka University, Toyonaka 560-0043, Japan
2
Graduate School of Frontier Biosciences, Osaka University, Suita 565-0871, Japan
3
Nagoya University Synchrotron Radiation Research Center, Nagoya University, Nagoya 464-8603, Japan
4
Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan
5
Department of Physics, Graduate School of Science, Kobe University, Kobe 657-8501, Japan
1

Ⅲ-2

Ruthenium mono-antimonide, RuAs, which is one ofrelated materials to iron-pnictide superconductors,
shows a metal-to-insulator (MIT) transition
accompanied with structural change [1]. The metallic
character at room temperature changes to an insulating
one detected by an electrical resistivity measurement [2]through a two-step structural phase transition at about
250 K (TMI1) and about 200 K (TMI2). The orthorhombic
crystal structure with space group Pnma at room
temperature changes to the formation of a 3×3×3
superlattice of the original unit cell of the monoclinic
structure with space group P21/c below TMI2. However,
the origin of the two-step phase transition has not beenclarified yet because the intermediate phase attemperatures between TMI1 and TMI2 has not been
identified. So, to clarify the change of the electronic
structure due to the two-step phase transition, we
measured temperature-dependent polarized opticalconductivity [σ(ω)] spectra and revealed the anisotropicchange of the electronic structure.
Optical reflectivity [R(ω)] spectra as well as σ(ω)
spectra of single-crystalline RuAs samples, with thelargest size of about 0.1×0.5×0.2 mm3, were measured
along the b and c axes in the photon energy range from15 meV to 30 eV to ensure an accurate Kramers-Kronig
analysis (KKA). Infrared (IR) and terahertz (THz)measurements at the photon energy regions of 15 meV
to 1.5 eV have been performed using conventionalreflectivity measurement setups and IR and THz
microscopes at BL6B. In the photon energy range of
1.2–30 eV, the R(ω) spectrum was measured only at 300
K at BL7B for accurate KKA.
Figure 1 shows the temperature dependence of theσ(ω) spectra at around 200 K (~TMI2), where large
spectral change is expected. In E // bH, which is the baxis above TMI2, the spectrum changes little above 200
K, but below the temperature, the intensity at ~ 0.1 eV
decreases, and that at about 0.16 eV increases,suggesting the appearance of an energy gap. At 160 K,
the energy gap structure becomes recognized spectrumat 210 K slightly changes from that at 230 K, whereclearly, as shown in Fig. 1. On the other hand, in E // cH,
the spectrum at 210 K slightly changes from that at 230
K where the intensity below (above) 0.22 eV decreases(increases). The change becomes clearer withdecreasing temperature, which indicates the energy gap
opening. These results imply that the spectral change in

E // bH starts at T ≲ 210 K, but that in E // cH graduallyoccurs between 210 and 230 K. This suggests that thetemperature of the σ(ω) spectral change as well as thechange of the electronic structure is anisotropic, i.e., thechange along the bH (cH) axis occurs at lower (higher)temperature. The anisotropic change of the electronic
structure is considered to be the origin of the two-stepphase transition [3].

Fig. 1. Temperature-dependent polarized σ(ω) spectraof RuAs in E // bH and E // cH near the first-order phasetransition temperature of ~200 K (TMI2).
[1] D. Hirai et al., Phys. Rev. B 85 (2012) 140509(R).
[2] H. Kotegawa et al., Phys. Rev. Mater. 2 (2018)055001.
[3] Y. Nakajima et al., Phys. Rev. B 100 (2019) 125151.

90

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BL6B

Infrared Reflectivity Spectrum for Au-codoped Mg2Si:Bi Crystal
T. Tanimoto1, M. Kitaura2, H. Udono3 and A. Ohnishi2

Graduate school of Science and Engineering, Yamagata University, Yamagata 990-8560, Japan
2
Faculty of Science, Yamagata University, Yamagata 990-8560, Japan3
Department of Electrical and Electronics Engineering, Ibaraki University, Hitachi 316-8511, Japan1

Mg2Si is a thermoelectric material with high figure of
merit ZT. This material is composed of nontoxicity andabundant elements, and attract much attention as a
KANKYO semiconductor [1]. The value of ZT isgenerally influenced by the carrier concertation. The
increase in carrier concertation is mainly caused by
impurity doping. The effect of such impurity doping on
thermoelectric properties of Mg2Si has been studied sofar. The Bi atom is known as an effective element forelectron doping in Mg2Si. The electronic structure of
Bi-doped Mg2Si (Mg2Si:Bi) has been studied [2].
Recently, it was reported that the carrier concentration
above 1020 cm-3 is attained by multiple impurity doping[3]. On the other hand, the effect of impurity codopingon the carrier concertation has not yet been reported for
Mg2Si:Bi.
In the present study, the effect of Au codoping on the
carrier concertation in Mg2Si:Bi was investigated. In thiswork, infrared reflective spectra were measured at 300 K
to determine the carrier concentration of an Au-codoped
Mg2Si:Bi crystal. In n-type semiconductors, infrared
reflectivity spectra exhibit the structure due to the plasmareflection, which arises from collective excitation of freeelectrons [4]. The carrier concentration can be determinedby analyzing the plasma reflection.
Au-codoped Mg2Si:Bi crystals were grown from themelt by the Bridgeman method. Infrared reflectivity
spectra were obtained using a FT-IR spectrometer at thebeamline BL6B. The infrared reflectivity spectra wereanalyzed using the software RefFit [5]. The parametersof the plasma frequency ωp , dielectric constant ε∞ , anddamping constant Γp were determined by the fit of theDrude-model to the experimental data. Using theseparameters, the carrier concentration N and relaxation
time  were also determined, and was compared to that
determined by the Hall effect experiment.
Generally, it is hard to determine the absolutereflectivity correctly, because the absolute reflectivity issensitive to roughness and contamination of the crystal
surface. The absolute reflectivity was corrected using
the refractive index and dielectric constant at 5000 cm-1
in the transparent region [4,6]. The infrared reflectivity
spectrum for an Au-codoped Mg2Si:Bi crystal, thus
obtained, is shown in Fig. 1. The reflectivity spectrum
exhibits a dip around 1100 cm-1. The reflectivity is
rapidly increased with decreasing wavenumber. Thisfeature is explained as so-called Drude-like behavior.
The reflectivity spectrum is almost agreement to theresult of the curve fit analysis. The parameters obtained
are listed in Table 1. The values of N and  determined

were also listed in Table 1. The value of N isapproximately consistent with that (=5.01019 cm-3)
determined by the Hall effect experiment. On the other
hand, the value of  is larger than those in Ref. [3]. It is
known that  becomes small with increasing N. The
value of N in our sample is one-order magnitude smaller,
compared to those in Ref. 3. It is thus reasonable toattribute the difference in  to that in N. The analysis of
the infrared reflectivity spectrum apparently gives
reasonable physical parameters dominating electric
properties of n-type Mg2Si.

Fig. 1. Infrared reflective spectrum for an Au-codoped
Mg2Si:Bi crystal. Red and blue lines indicate theexperimental data and the fit curve, respectively.
Table 1. Summary of the parameters in Drude-model,
determined from the curve fit analysis.
ωp (cm-1)

Γp (cm-1)

τ (s)N (cm-3)

1026.2310.1

1.1×10-13

1.3×1019[1]K. Kambe et al., J. Electron. Mater. 43 (2014) 2212.
[2] N. Farahi et al., Dalton Trans. 43 (2014) 14983.
[3] J. Zhao et al., J. Mater. Chem. A. 39 (2015) 19774.
[4] D. McWilliams et al., Phys. Rev. 130 (1963) 2248.
[5] A. B. Kuzmenko, Rev. Sci. Instrum. 76 (2005) 083108.
[6] D. McWilliams et al., J. Opt. Soc. Am. 53 (1963) 298.

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dxy Orbital Character of Hole Bands in NdFeAs1-xPxO0.9F0.1 Observed byAngle Resolved Photoemission Spectroscopy
Z. H. Tin1, T. Adachi1, A. Takemori1, S. Miyasaka1, S. Ideta2,3, K. Tanaka2,3 and S. Tajima1

Department of Physics, Osaka University, Osaka 560-0043, JapanUVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan3
School of Physical Sciences, The Graduate University for Advanced Studies, SOKENDAI, Okazaki 444-8585, Japan
1

2

Ⅲ-2

parameter, hpn and α. The hpn (α) decreases (increases)
with phosphorus doping. Our result is consistent withthe shift down of γ band with decreasing hpn. On theother hand, the flat xy band near Fermi level overlaps
with the top of the xz hole band, which shows thesystematic energy shift with P doping [2]. The present
results suggested that the yz/xz band splitting is inducedby the mixing of xy/xz orbital characters on the top of
the hole band.
Finally, a suspicious intensity enhancement isobserved on this flat band below Tc. This suggests thatthe flat band is related to the high-Tc SC. We needfurther investigation to clarify this mixing xy orbital
character on the flat band.

The iron-based superconductors (IBSs) has provided
us new opportunity to investigate the unconventional
superconductivity (SC). Among various systems of
IBSs, 1111 system has highest Tc. In this 1111 system,
however, it is difficult to synthesize the single crystals
with high quality, and there are a few reports for studyof angle resolved photoemission spectroscopy(ARPES). In this system, the electronic structure (Fermi
surfaces (FSs)) can be controlled by the phosphorus
doping on the arsenide site. Our previous result
indicated that there are two superconducting states in
NdFeAs1-xPxO0.9F0.1 and the critical P concentration isx~0.2 [1]. The previous result of ARPES using the ppolarization configuration shows that FS topology ischanged by P doping at the same value of x=0.2 [2].
Theoretical investigation predicted that the hole pocketwith xy orbital character is important in realizing highTc SC, but the hole bands with this orbital character havenot been observed in our previous work [2,3]. In orderto clarify the origin of FS topology change and therelationship between the xy hole band and high Tc, we
perform the ARPES measurements on the single
crystals of NdFeAs1-xPxO0. 9F0.1(x=0 and 0.2).
The ARPES was measured at 10K. (Tc=43 K and 24
K for x=0 and 0.2, respectively.) In the present work, the
Fe-Fe direction of the single crystal is parallel to theanalyzer slit of detector. The photoenergy of incident
light was 18eV for high energy resolution, and the spolarization configuration was used to detect the xy/yz
orbital character bands around the Brillouin zone center.
As shown in Fig. 1, we observed the yz band (green
dotted line) in NdFeAsO0.9F0.1. In addition, we haveobserved other hole band below -50 meV, which we
assign to γ band. This hole band should have the xy
orbital character, since there should be only one bandwith the yz character in the result of the theoretical
calculation. This γ band may play an important role infull-gapped s± wave symmetry based on spinfluctuation theory. However, this band does not crossFermi level. Interestingly, the small flat band appears atzone center around the binding energy of -18 meV. Thisflat band may also have xy character.
In x=0.2 sample, the similar band dispersion has been
observed. As shown in Fig. 2, this compound has 3 holebands around zone center, and the energy levels of γ andflat bands are slightly different from those in x=0. The γband shifts down by 10 meV with P doping, while theflat band shift upward by 6 meV. This behavior can be
explained by the sensitivity of γ band to the structuralFig. 1. ARPES results of NdFeAsO0.9F0.1 around zone
center. The ARPES intensity plot (a) and its 2nd derivativeplot (b) with respect to k, respectively.

Fig. 2. ARPES results of NdFeAs0.8P0.2O0.9F0.1 aroundzone center. The ARPES intensity plot (a) and its 2ndderivative plot (b) with respect to k, respectively.
[1] S. Miyasaka et al., J. Phys. Soc. Jpn. 82 (2013)
124706.
[2] A. Takemori et al., Phys. Rev. B 98 (2018)
100501(R).
[3] K. Kuroki et al., Phys. Rev. B 79 (2009) 224511.

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High-resolution ARPES Study of High-temperature Iron-based
Superconductor Fe(Se,Te)
K. Nakayama1, R. Tsubono1, Y. Kubota1, F. Nabeshima2, T. Ishikawa2, T. Shikama2,
A. Maeda2, T. Takahashi1,3,4 and T. Sato1,3,4

1
Department of Physics, Tohoku University, Sendai 980-8578, Japan
Department of Basic Science, the University of Tokyo, Tokyo 153-8902, Japan
3
Center for Spintronics Research Network, Tohoku University, Sendai 980-8577, Japan
4
WPI Research Center, Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
2

Since the discovery of topological insulators, thesearch for new material phases characterized bynontrivial topology of electronic wave functions is a hot
topic in condensed-matter physics. A leading example
is a topological superconductor in which gapless boundstates appear at edges and/or vortex cores. The gaplessbound states in topological superconductors consist ofMajorana quasiparticles which have the unique property
that the particle is own antiparticle, and are predicted to
be useful for various applications such as fault-tolerant
quantum computations. Therefore, the experimental
demonstration of topological superconductivity is highly
desired.
Recently, it was suggested that an iron-based
superconductor Fe(Se,Te) (a superconducting transition
temperature Tc of 14 K) hosts topological Dirac-conesurface states, and proximity-induced s-wave
superconductivity therein leads to two-dimensional
topological superconductivity with Majorana boundstates in vortex cores [1].
In this study, to explore ‘high-Tc’ topologicalsuperconductivity, we performed angle-resolved
photoemission spectroscopy (ARPES) measurements ofcompressive-strained Fe(Se,Te) thin films which show a
1.5 times higher Tc (~23 K) than bulk counterpart [2-4],
and searched for the topological surface states
responsible for topological superconductivity.
High-quality compressive-strained Fe(Se,Te) thinfilms with the thicknesses of approximately 400 layers
were grown on CaF2 substrate by pulsed laser
deposition. High-resolution ARPES measurements
were performed by using a MBS-A1 spectrometer at
BL7U with linearly-polarized energy-tunable photonsof 7-25 eV. The clean surface necessary for the ARPES
measurements was obtained by cleaving the thin film insitu in an ultrahigh vacuum better than 1 × 10-10 Torr.
Since the topological Dirac-cone surface states are
expected to emerge at the center of the Brillouin zone inFe(Se,Te), we performed band-structure mapping nearthe Γ point with high energy and momentum resolutions
by utilizing a low photon energy of 7 eV at BL7U.
Figure 1(a) displays the ARPES intensity map at the
Fermi level plotted as a function of two-dimensional
wave vector, measured in the normal state (T = 30 K).
One can find a strong intensity spot at the Γ point and a
relatively large circular-shaped intensity distribution.
Next, we determined the band dispersion along the

momentum cut crossing the Γ point [Fig. 1(b)]. One cansee a holelike band approaching the Fermi level in thevicinity of the Γ point, which produces the strong
intensity spot in Fig. 1(a). One can also find anotherholelike band forming the circular Fermi surface seen in
Fig. 1(a). In this study, we also performed photonenergy dependent ARPES measurements and tried to
distinguish the topological surface states from the threedimensionally-dispersive bulk states.

Fig. 1. (a) Fermi surface mapping plotted as a functionof two-dimensional wave vector measured oncompressive strained Fe(Se,Te) thin film (Tc = 23 K) at
T = 30 K. (b) ARPES intensity plot as a function ofbinding energy and wave vector.

[1] P. Zhang et al., Science 360 (2018) 182.
[2] F. Nabeshima et al., Appl. Phys. Lett. 103 (2013)
172602.
[3] Y. Imai et al., Proc. Natl. Acad. Sci. USA 112 (2015)
1937.
[4] Y. Imai et al., Sci. Rep. 7 (2017) 46653.

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Pd-doping Dependent Energy Level of Dirac Point in Ni1-xPdxTe2 Observedby Angle Resolved Photoemission Spectroscopy
A. Kanayama1, K. Yoshino1, Z. H. Tin1, S. Miyasaka1, S. Tajima1, S. Ideta2,3 and K. Tanaka2,3
Department of Physics, Graduate School of Science, Osaka University, Toyonaka 560-0043, Japan
2
UVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan3
School of Physical Sciences, The Graduate University for Advanced Studies, SOKENDAI, Okazaki 444-8585, Japan1

Ⅲ-2

the Dirac point exists above EF, as reported previously[3].
Next, we have focused the Pd-doping dependence ofDirac point energy level. Figures 1 and 2 show the
ARPES intensity plot along k// (parallel to -M direction)at (0, 0, 0.37c*) for x=0.05 and 0.10, respectively. Bothsamples have linear band dispersion indicating theexistence of Dirac cone. The Dirac point, where the twobands with linear k// dispersion cross, shifts down with Pd
doping, as shown in Figs. 1 and 2. This result indicatesthat in NiTe2, the energy level of Dirac pint can becontrollable by Pd doping.

The Ni, Pd, and Pt dichalcogenides MX2 (M=Ni, Pd,
Pt; X=S, Se, Te) have several crystal structures such as
the 2-dimensional (2D) CdI2-type, the pseudo-2D
PdSe2-type and the 3-dimensional pyrite-type structures.
We have studied MX2 and their solid solution systems
to explore the new physical properties. These systems
show various physical properties coupled with the
crystal structures.
Recently 2D CdI2-type MTe2 revisited from aviewpoint of Dirac fermion [1-3]. The experimental
studies on PdTe2 and PtTe2 have indicated that thesecompounds have type II Dirac fermion state [1,2]. The
results of angle resolved photoemission spectroscopy(ARPES) have revealed that the Dirac point exists at (0,0, kz) and the Dirac cone is strongly tilted along -Adirection (kz-direction) in PdTe2 and PtTe2. The ARPES
result for related material NiTe2 indicates that thiscompound also has type II Dirac cone. The Dirac point
exists just above Fermi level (EF) (~ +0.2 eV) in NiTe2,
while they in Pd and Pt systems are located around -0.6
~ -0.8 eV below EF [1-3].
We have tried to control the energy level of Diracpoint in the Pd-doped NiTe2 system Ni1-xPdxTe2. In theend members, NiTe2 and PdTe2, the Dirac point islocated above EF (~ +0.2eV) and below EF (~ -0.6 eV),
respectively. We expected that the energy level of Diracpoint can be turned near EF by slightly Pd doping in
NiTe2 and the systematic change of Dirac pint energy
level with Pd doping can be observed by ARPES
measurements.
The single crystals of Ni1-xPdxTe2 (x=0, 0.05, and 0.10)
were synthesized by a flux method in an evacuated silica
tube. The results of the energy dispersive X-ray
spectroscopy (EDX) indicated that the actual Pd
concentration was the same as the nominal one. The
ARPES spectra were measured at BL7U of UVSOR
facility in Institute for Molecular Science using incident
photons with h=10-30 eV. All the measurements werecarried out at ~10 K.
First of all, we measured the kz-dependence of band
structure by changing the incident photoenergy from 10
eV to 30 eV for x=0.05 and 0.10 samples. In all thesingle crystals, we observed the clear band crossing
around (0, 0, 0.37c*) just below EF indicating that thesematerials have Dirac point around this point. In the end
member NiTe2, the similar kz-dependence of band
structure has been observed. Below EF, however, we did
not observe the band crossing related with the Diracpoint in NiTe2. The present result has suggested that

Fig. 1. ARPES intensity plot along k// (parallel to -Mdirection) at (0, 0, 0.37c*) for x=0.05.

Fig. 2. ARPES intensity plot along k// (parallel to -Mdirection) at (0, 0, 0.37c*) for x=0.10.

[1] H.-J. Noh et al., Phys. Rev. Lett. 119 (2017) 016401.
[2] K. Zhang et al., Phys. Rev. B 96 (2017) 125102.
[3] B. Ghosh et al., Phys. Rev B 100 (2019) 195134.

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Three Dimensional Comparison between the ARPES Measurements and
DFT Calculation for MoS2
2

S. Tanaka1, K. Ueno2, S. Ideta3 and K. Tanaka3

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

2H-MoS2 is one of the most typical TMDCs, and its
electronic structure has been extensively studied byusing angle-resolved photoelectron spectroscopy(ARPES). In these studies, comparison with thetheoretical calculation was commonly made forrevealing the electronic structure. However, most of
the comparison has been made only on the highly
symmetric lines in the Brillouin zone, and the otherpoints are usually omitted. In this report, we made thecomparison of the constant energy map derived fromthe photoelectron angular distribution in the ARPES
measurement to those derived from the rst principles
calculation in the momentum space.
The experiments were carried out at the BL7U. The
sample temperature was 9K and the photon energy used
was 21 eV. The A-1 electron energy analyzer collects
the photoelectron within the window of 30o along thephoton-incident plane (dened as kx axis hereafter) , andthe volume map was obtained by changing the sample
tilt angle which is perpendicular to the photon incidence
plane (dened as ky axis hereafter).
The energy band of MoS2 was calculated within thedensity functional theory (DFT) framework, employing
the QUANTUM ESPRESSO package (version 6.3),
which had been installed in the computer at ResearchCenter for Computational Science in IMS. The eigen
energies are calculated at 64×64×16 grid points in the
Brillouin zone. Then, the band energies are broadenedby the convolution with the Gaussian-peak function
with the width of 0.05 eV at each k-point; which is ausual procedure for obtaining a density of states curve.
The dispersion along the kz line is averaged by adding
all 16 spectra at one (kx, ky) point. The nal constantenergy maps for comparing the experiments were madeby the broadening in the k-space with the Gaussianfunction with the width of 0.02 Å−1.
Figure 1 show the comparison between the constantenergy maps derived from the ARPES measurements(left-hand side) and those from the DFT calculations(right-hand side). The binding energies are scaled withrespect to the valence band maximum. The energy here
are determined so as that the calculation and experiments
show similar shape and symmetry. The relation ofenergies used in Figs. 1 are phenomenologically given by
the formula Ecalc = 0.078Eexp2 +1.43Eexp(eV). This
indicates that there are errors of the binding energies inthe DFT calculation of this work. In spite of thisconsiderable disagreement in the electron energy, theoverall shape and symmetry in the constant-constantenergy map by ARPES is well represented by thecalculation. This means that characteristics of the electronband is well reproduced by the DFT calculation,suggesting an advantage of the comparison in the k-space
to a comparison of dispersions only on the highly
symmetric lines in which the energetic agreements arenecessary to match.
The method of the comparison in the three dimensions
shown above, is instinctive and easy to understand.
However, in order to achieve scientifically new results, it
is required to take more detailed measurements
combining e.g., the photon-energy-dependence and thepolarization dependence, which are in progress.

Fig. 1. Comparison of the constant energy maps
between the ARPES measurements (left) and the DFT
calculation(right).

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Charge Density Wave State of CeTe3
Investigated by Angle-resolved Photoemission Spectroscopy
Y. Arai1, K. Kuroda1, Y. Wan1, Y. Dong1, Y. Fujisawa2, S. Ideta3, K. Tanaka3
Y. Okada2 and T. Kondo1
1
ISSP, University of Tokyo, Kashiwa 277-8581, Japan
Quantum Material Science Unit, OIST, Onna-son 904-0495, Japan
3
UVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
2

(a)

(b)

Te
Ce

Low

Hig h

ky (π/a)

0.5
0

(c)
(d)
(e)

−0.5

c
b

−1.0 −0.5a0.5
0kx (π/a)

1.0(f) ky=(c)

E−EF (eV)Intensity (a.u.)

E−EF (eV)

0
−0.5
−1.0
−1.5
(d)
0
−0.5
−1.0
−1.5
(e)
0
−0.5
−1.0
−1.5

−0.03

−1.0

0
1.0
kx (π/a units)

0

(g )

E−EF (eV)Δ ECDW (eV)−0.52(π/a) −1.5 −1.0 −0.5

E−EF (eV)Ⅲ-2

In strongly correlated electron systems, the manybody effect often significantly reconstructs theelectronic structure of matter in the vicinity of the
Fermi energy; for example, charge density wave
(CDW) opens a band gap, and Kondo effect leads toheavy quasi-particle bands. The conflict or interplay
among such multiple many-body effects is of greatinterest in condensed matter physics. CeTe3 with 4f
orbitals exhibits CDW state, thus offers an excellent
playground to study such an intriguing physics.
CeTe3 is composed of an alternate stacking of Te
planes and CeTe slabs as shown in Fig. 1 (a). Te planes
mainly contribute to the Fermi surface and host the
CDW state. The transition temperature of CDW is morethan 400 K [1] and the lattice originally of square Teplans is distorted by as much as 0.2 Å [2], indicating that
the CDW state is quite robust; this is further confirmed
by a large CDW gap as large as 400meV observed byangle-resolved photoemission spectroscopy (ARPES)[3]. The electronic state of CeTe3 is also characterized
by the Kondo effect, which is observed in the electricalresistivity increasing below 10 K with a local maximum
value at 6 K [1]. Since this temperature is associatedwith the coherence derived from the Kondo lattice, both
CDW and Kondo effects are expected to affect theelectronic structure below 6 K in CeTe3.
Although ARPES is a suitable probe to investigate theelectronic reconstruction due to CDW and Kondo effect,
the previous research observed the band structure only
down to 25 K, where only the CDW occurs. In this study,
therefore, we have conducted the ARPES measurements
down to 6 K comparable with the Kondo temperature, inorder to realize the coexistence between the CDW andKondo effect and study the relationship of these.
Figure 1(b) shows the Fermi surface mapping,where the ARPES intensities are integrated from EF to
EF-200 meV. Due to the interlayer coupling between
Te planes and Ce-Te slabs, Te plane bands are folded
along the three-dimensional Brillouin zone [3]. We
clearly observed that a CDW gap is opened along the
Fermi surface, and its size increases from ky ~ 0 Å-1 toky = ±0.4 Å-1 (Fig. 1(g)), reaching the maximum of
about 400 meV. This result at 6 K is consistent with theprevious ARPES studies at 25 K; this indicates that
CDW in the Te plane is almost independent of the
Kondo effect associated with Ce ions in the slab
probably because the interaction between the Ce-Te
slab structure and the Te planes is relatively weak.

0.4
0.3
0.2
0.1
0
−0.4 −0.3 −0.2 −0.1 0.0
ky (π/a)Fig. 1. Electronic structure in CDW state of CeTe3. (a)Crystal structure of CeTe3. Note that, unlike theconvention, the c axis is set to be perpendicular to the
Te planes. (b) Fermi surface map at 6 K measured by
ARPES. Red lines represent calculated Fermi surface
dominated by the Te plane, and red dotted lines are thatfolded about the 3D BZ [1]. (c-e) Band dispersions
measured at black dotted lines in (b). Red arrows
highlight CDW gaps. (f) Energy distribution curves
along the Fermi surface corresponding to the black
points in (b). Red points indicate the leading edge ofthe spectra. (g) k dependence of the CDW gap along(f).

[1] N. Ru et al., Phys. Rev. B. 73 (2006) 033101.
[2] H. J. Kim et al., Phys. Rev. Lett. 96 (2006) 226401.
[3] V. Brouet et al., Phys. Rev. Lett. 93 (2004) 126405.

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High-resolution ARPES Study on the Electronic Structure of
Heterointerfacial Superconductors
R. Tsubono1, K. Nakayama1, Y. Kubota1, F. Nabeshima2, T. Ishikawa2, T. Shikama2,
A. Maeda2, T. Takahashi1,3,4 and T. Sato1,3,4

1
Department of Physics, Tohoku University, Sendai 980-8578, Japan
Department of Basic Science, the University of Tokyo, Tokyo 153-8902, Japan
3
Center for Spintronics Research Network, Tohoku University, Sendai 980-8577, Japan
4
WPI Research Center, Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
2

Since the discovery of superconductivity in a
LaAlO3/SrTiO3 heterostructure consisting of band
insulators [1,2], heterointerfaces have been an interesting
research target for investigating unconventional
superconductivity due to the low dimensionality, spatial
inversion-symmetry breaking, and interfacial interactions.
A recently-discovered interfacial superconducting
system is the hybrid between a topological insulator
Bi2Te3 and a parent compound of iron-based
superconductors FeTe [see Fig. 1(a) for a schematic viewof the heterostructure] [3]. Although both Bi2Te3 andFeTe are non-superconducting, the superconducting
transition temperature Tc of Bi2Te3/FeTe heterostructure
reaches ~12 K, which is about ten times higher than thatof LaAlO3/SrTiO3. This finding triggered intensive
investigations on Bi2Te3/FeTe, and, consequently, several
peculiar properties have been reported in Bi2Te3/FeTe andrelated heterostructures. An intriguing finding is the lackof interfacial superconductivity in the selenide
counterpart, Bi2Se3/FeSe. Understanding the origin ofsuch a remarkable difference in the superconducting
property between structurally identical Bi2Te3/FeTe andBi2Se3/FeSe would provide a key to clarify the nature of
exotic interfacial superconductivity. Therefore, acomparative study on the electronic states of Bi2Te3/FeTeand Bi2Se3/FeSe is of crucial importance.
In this study, we performed high-resolution angleresolved photoemission spectroscopy (ARPES) anddetermined the electronic structure relevant to theinterfacial superconductivity of Bi2Te3/FeTe andBi2Se3/FeSe. ARPES measurements at BL7U were
performed using a MBS-A1 spectrometer with energytunable photons. The energy and angular resolutions were
set to be 5–20 meV and 0.3º, respectively. The sample
was kept at T = 30 K during the ARPES measurements.
We plot in Fig. 1 the representative ARPES results
obtained on the as-grown FeSe films. As seen from Fig.
1(b), the as-grown FeSe film has small Fermi surfaces
centered at the Γ and M points in the Brillouin zone.
These Fermi surfaces originate from holelike andelectronlike energy bands of Fe 3d orbtials [see Fig.
1(c)], indicating the semimetallic character of FeSe.
Upon interfacing Bi2Se3 layers, we observed clear
differences in the FeSe-derived energy bands. We
compared these results to those obtained in Bi2Te3/FeTe[4] and found an important insight into the origin ofinterfacial superconductivity.

Ⅲ-2

Fig. 1. (a) Schematic of Bi2Te3/FeTe heterostructure.
(b) ARPES intensity mapping at the Fermi levelplotted as a function of two-dimensional wave vector,
measured at T = 30 K at hν = 21 eV in FeSe. (c)Experimental band dispersion measured along the ΓMhigh-symmetry line.

[1] A. Ohtomo and H. Y. Hwang, Nature (London) 427(2004) 423.
[2] N. Reyren et al., Science 317 (2007) 1196.
[3] Q. L. He et al., Nat. Commun. 5 (2014) 4247.
[4] K. Owada et al., Phys. Rev. B 100 (2019) 064518.

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Doping Dependence of the Superconducting Gap in Bi2223 Observed byAngle-Resolved Photoemission Spectroscopy
S. Ideta1,2, T. Yoshida3, A. Fujimori4, S. Adachi5, N. Sasaki5, S. Yamaguchi5, T. Watanabe5
T. Noji6 and K. Tanaka1,2
National Institutes of Natural Science, Institute for Molecular Science, Okazaki 444-8585, Japan
2
The Graduate University for Advanced Studies, SOKENDAI, Okazaki 444-8585, Japan
3
Graduate School of Human and Environmental Studies, Kyoto University, Kyoto 606-8501, Japan
4
Department of Applied Physics, Waseda University, Tokyo 169-8555, Japan
5
Graduate School of Science and Technology, Hirosaki University, Hirosaki 036-8561, Japan
6
Department of Applied Physics, Tohoku University, Sendai 980-8579, Japan1

Ⅲ-2

To understand the mechanism of high-Tc
superconductivity in cuprates is one of the crucial issues.
Especially, the energy gap seen in the superconducting(SC) and normal states is believed to be an importantpiece of evidence for the non-BCS behavior of the SC
transition from the underdoped to overdoped regime in
the high-Tc cuprate superconductors. In cuprates, twodifferent representative energy gaps are present in the
SC and normal states, namely, the SC gap andpseudogap [1-3]. Doping dependence of the SC gap has
been considered as the direct evidence to reveal high-Tc
superconductivity and sheds light on its nature.
Triple-layer Bi-based cuprate superconductor,
Bi2Sr2Ca2Cu3O10+δ (Bi2223), which shows the highest
Tc (110 K) among the Bi-based cuprates, has two
inequivalent CuO2 planes with different hole carrier [46]. In this study, we have investigated the momentum
and doping dependence of the energy gap anisotropy
and found that the SC gap obtained from different
doping showed a similar magnitude. We observed two
bands corresponding to the outer (OP) and inner (IP)CuO2 planes. Hole concentration was deduced from the
IP and OP Fermi surfaces actually increases in goingfrom the underdoped to overdoped samples.
High-quality single crystals of underdoped, optimallydoped, and overdoped Bi2Sr2Ca2Cu3O10+δ (UD, Opt, andOD Bi2223, Tc = 80 K, 110 K, and 110 K, respectively)
were grown by the TSFZ method. Underdoped Bi2223
samples were successfully obtained in the two-stepannealing in order to control their doping levels [7].
ARPES experiments were carried out at BL7U of
UVSOR-III Synchrotron. Clean sample surfaces wereobtained for the ARPES measurements by cleaving
single crystals in-situ in an ultrahigh vacuum better than
6×10-9 Pa. The measurements were performed at 10 K.
In order to estimate the doping and momentum
dependence of the SC gap, as shown in Fig. 1, the SC
gap (10 K) estimated along the Fermi surface is plotted
as a function of the d-wave order parameter. For the
IP band, the extrapolated SC gap from the nodal to theantinode (a black dotted line) shows a similar
magnitude at the antinode. As for the OP band too, theSC gap at the antinode shows the same magnitude inspite of different doping. Note that we need to exclude
the result of the OP-bonding band (BB) [8]. These

results are similar to the double-layer cuprate
Bi2Sr2CaCu2O8+δ observed by ARPES [9]. Here, thepresent ARPES study raises a question about themechanism; why the SC transition temperature andhole carrier is different in Bi2223, the SC gap keeps
the same magnitude at the antinode.
As future work, we need to investigate the pseudogap
and the Fermi arc length above Tc in order to determine
the relationship between the Tc and effective SC gap in
Bi2223.

Fig. 1. Superconducting (SC) gap of Bi2223 withdifferent doping. (a) SC gap of the IP band. (b) SC gapof the OP band.
[1] D. S. Marshall et al., Phys. Rev. B 76 (1996) 4841.
[2] A. G. Loeser et al, Science 273 (1996) 325.
[3] H. Ding et al., Nature (London) 382 (1996) 51.
[4] S. Ideta et al., Phys. Rev. Lett. 104 (2010) 227001.
[5] S. Ideta et al., Phys. Rev. B 85 (2012) 104515.
[6] S. Ideta et al., Physica C 470 (2010) S14-S16.
[7] S. Adachi et al., Physics Procedia 65 (2015) 53.
[8] S. Ideta et al., UVSOR Activity Report 2016 44(2017) 90.
[9] I. M. Vishik et al., PNAS 109 (2012) 18332.

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Ⅲ -2. Materials Sciences

BL7U

Angle-resolved Photoemission Study of MAX Phase Compound Ti2SnC
1

T. Ito1,2, M. Ikemoto2, D. Pinek3, M. Nakatake4, S. Ideta5,6, K. Tanaka5,6 and T. Ouisse3

Nagoya University Synchrotron radiation Research center (NUSR), Nagoya University, Nagoya 464-8603, Japan
2
Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan
3
Grenoble Alpes, CNRS, Grenoble INP, LMGP, F-38000 Grenoble, France
4
Aichi Synchrotron Research Center, Seto, 489-0965, Japan
5
UVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
6
The Graduate University for Advanced Studies, SOKENDAI, Okazaki 444-8585, JapanMAX phase compounds, i.e., Mn+1AXn where M is atransition metal, A belongs to groups 13-16 and X is the
C or N element, have recently been attracted muchattention due to their possible application for new class of
two-dimensional systems called MXenes by removing A
atoms [1]. On the other hand, the bulk electronic structureof MAX phase has been studied mostly by calculations,mainly because of lack of well-established single
crystalline samples. In this study, we have performed
angle-resolved photoemission spectroscopy (ARPES) on
MAX phase compound Ti2SnC [2] to directly investigate
the electronic structure of this system.
ARPES measurements were performed at the
UVSOR-III BL5U. Data were acquired at T = 25 K withhν = 22.5 eV which enables us to trace around the ΓKM
plane with inner potential of V0=10.7 eV estimated fromthe photon energy dependent measurement (not shown).
It should be noted that each ARPES images wereobtained without changing the photon incident angle
relative to the sample surface by utilizing twodimensional mapping lens mode of MBS A-1 analyzer.
Figure 1 shows the obtained Fermi surface (FS)image on the ΓKM plane (a) compared with the FS
topologies calculated by DFT method (b,c). Aroundthe corner of hole-like FS (β), a broad egg-shaped FS
counter has been observed. To elucidate the detailelectronic structure around the observed egg-shaped
FS, the band structure near the Fermi level (EF) andmomentum distribution curve (MDC) at EF along thekx (#1) and ky (#2) cut across the FS are shown in Fig.
2 (a) and (b), respectively. From the comparison with
DFT calculation, the egg-shaped FS seems to be inconsistent with Dirac-cone like dispersive features ofγ - blanch. In addition, we have found the Dirac point(DP) or bottom of the upper Dirac cone locates around
250 meV from the present ARPES, while DP around
400 meV has been expected by DFT calculation. To
pursue the relation between the complicated FS andthe thermodynamic properties of Ti2SnC, further
studies are intended.

Ⅲ-2

Fig. 1. Fermi surface (FS) image on ΓKM plane of
Ti2SnC (a). (b,c) FS calculated by DFT shown asprojection along the [001] axis (b) and enlarged FS
around the KH axis (c).

Fig. 2. Band structure near EF (lower panel) and MDC
spectra at EF (upper panel) along the CUT#1 (a) andCUT#2 (b) indicated in Fig. 1(a) of Ti2SnC. Dirac-conelike dispersive features have been observed on the γ branch. Solid and dashed lines are DFT calculation
along the ΓK and AH lines, respectively.

[1] M. Basoum, MAX phases (Wiley, Weinheim 2013).
[2] J. Y. Wu, Y. C. Zhou and J. Y. Wang, Mat. Sci. Eng.
A 422 (2006) 266.

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Ⅲ -2. Materials

BL7B

Evaluation of Achromatic Vacuum-ultraviolet Lens
T. Shimizu, Y. Minami, K. Kuroda, K. Shinohara, D. Umeno and N. SarukuraInstitute of Laser Engineering, Osaka University, Suita 565-0875, Japan

Ⅲ-2

Vacuum ultraviolet (VUV) has numerous scientificand technological applications including spectroscopy,
environmental monitoring, surface micromachining,sterilization and so on. In the study of VUV materials,
it has been found that fluoride materials can be applied
as new VUV optics including lenses. For VUV lenses,
the material must be transparent to the light in the
VUV region, have chemical stability, have a highmelting point, and be uniform and of good quality. In
this study, an achromatic lens made of two materials
was fabricated based on a design that minimizes
chromatic aberration in the 150-300 nm range using
fluoride crystals with high VUV transmittance.
A combination of LiCaF6 and BaLiF3 was used asmaterials for the convex and concave lenses of the
VUV achromatic lens because it has the lowest
chromatic aberration in combinations of fluoride
crystals with high transmittance in the vacuum
ultraviolet region. Chromatic aberration at 150 nm and
300 nm is corrected for in this design. In addition,
since there is no lens adhesive that can transmit
vacuum ultraviolet light, there is a gap between theconvex and concave lenses, which is fixed bysandwiching them with a lens folder. The coating
agent used for the anti-reflection coating, which
suppresses reflections on the lens surface, is notapplied because it cannot penetrate VUV light andmay reduce the transmittance and degrade the vacuum
due to vaporization.
The performance of VUV achromatic lenses isevaluated in the following three areas: transmittance,
chromatic aberration, and focusing performance. For
the transmittance measurement, VUV achromaticlenses were irradiated with synchrotron radiation of 50
to 1000 nm wavelengths at BL7B (Fig. 1). The
transmittance can be measured by measuring the beam
intensity of the incident light and the beam intensity
after passing through the VUV achromatic lens. The
transmittance of the VUV achromatic lenses wasmeasured in the wavelength region of 100-300 nm. The
absorption edge was found to be 123 nm, which isenough to transmit the light in the range of 150-300 nm,
which was the target in the original design. We haveconcluded that the degradation of the absorption edgesof LiCaF6 and BaLiF3 was caused by the quality of thecrystals. In addition, since no AR coating was applied,
it was confirmed that the overall transmittance was low
due to the reflection of the lens surface.
The evaluation of chromatic aberration will be
carried out in the second half of the experiment using
BL3B.

In the future, a rigorous evaluation is required, and
it is important to further increase the knowledge of
achromatic lenses in the vacuum ultraviolet region. In
addition, the development of an imaging spectrometerwith a VUV achromatic lens is expected to be carriedout in parallel for practical use.

Fig. 1. Transmittance measurement results.

[1] K. Shimamura, H. Sato, A. Bensalah, H. Machida,
N. Sarukura and T. Fukuda, J. Alloys Cmpds. 343(2002) 204.
[2] M. V. Luong, M. J. F. Empizo, M. Cadatal- Raduban,
R. Arita, Y. Minami, T. Shimizu, N. Sarukura, H.
Azechi, M. H. Pham, H. D. Nguyen, Y. Kawazoe, K. G.
Steenbergen and P. Schwerdtferger, Opt. Mater. 65(2017) 15.
[3] R. Arita, Y. Minami, M. Cadatal-Raduban, M. H.
Pham, M. J. F. Empizo, M. V. Luong, T. Hori, M.
Takabatake, K. Fukuda, K. Mori, K. Yamanoi, T.
Shimizu, N. Sarukura, K. Fukuda, N. Kawaguchi, Y.
Yokota and A. Yoshikawa, Opt. Mater. 47 (2015) 462.
[4] T. Shimizu, M. V. Luong, M. Cadatal-Raduban, M.
J. F. Empizo, K. Yamanoi, R. Arita, Y. Minami, N.
Sarukura, N. Mitsuo, H. Azechi, M. H. Pham, H. D.
Nguyen, K. Ichiyanagi, S. Nozawa, R. Fukaya, S.
Adachi, K. G. Nakamura, K. Fukuda, Y. Kawazoe, K.
G. Steenbergen and P. Schwerdtfeger, Appl. Phys. Lett.
110 (2017) 141902.
[5] M. V. Luong, M. Cadatal-Raduban, M. J. F. Empizo,
R. Arita, Y. Minami, T. Shimizu, N. Sarukura, H.
Azechi, M. H. Pham, H. D. Nguyen and Y. Kawazoe,
Jpn. J. Appl. Phys. 54 (2015) 122602.
[6] K. Yamanoi, T. Murata, Y. Arikawa, T. Nakazato, M.
Cadatal-Raduban, T. Shimizu, N. Sarukura, M. Nakai,
T. Norimatsu, H. Nishimura, H. Azechi, S. Fujino, H.
Yoshida, A. Yoshikawa, N. Satoh and H. Kan, Opt.
Mater. 35 (2013) 1962.

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