Ⅲ-2

Materials Sciences

BL6UⅢ -2. Materials Sciences

BL6U

Angle-resolved Photoelectron Spectroscopic Study of TiSe2 using a Newly
Developed Software for the Momentum Microscope Apparatus
S. Tanaka1, K. Ueno2 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.
12which is well-known free software for a scientificvisualization. We only prepare the input file for“Paraview” by transforming the ARPES data into the“vtk” format, which is standard as the 3D format. The
usage of this sort of well-established software andformat gives us advantages in many aspects including
cutting the development time, and a convenience foran additional transformation, etc. Figures 1(b)-(d) areintensity maps in the 2D-cut indicated by the blacklines in Fig. 1(a). These maps can be easily provided,
thanks to our new program together with the“PyQtGraph” library, at any lines in the volume. The
two momentum distribution curves and an energy
distribution curve are also automatically created (notshown here).
We are progressing the investigation of the TiSe2 byusing the momentum microscope with the help of the
new software.

1T-TiSe2 is one of the transition metal dicalchogenides(TMDC). Among TMDCs, TiSe2 is quite interesting
because it exhibits a unique charge-density-wave
transition at Tc of ~200K into the (2x2x2) 3Dsuperstructure despite the quasi-2D character of the
TMDC. Currently, for the investigation of TiSe2, weare developing a new software for the analysis andpresentation of the data obtained with a new momentum
microscope apparatus. In this report, we demonstratesome of ARPES results of the TiSe2 at the room
temperature taken using the new software.
The software is written with the Python languagewith the help of some open-source libraries andadditional software; e.g., “PyQtgraph”, “Mayavi”,“OpenCV”, “vtk”, “Paraview”. The software can be
operated in multiple OS’s; such as Windows-10, MacOS, and Linux. Fig.1 (a) shows the stereogram pictureof the ARPES volume map of TiSe2 taken at hν=80eV.
In fact, the stereogram is created by using “Paraview”(a)kx - ky(c)

kx- KEkx(A-1)(d)ky - KEElectron Energy (eV)Electron Energy (eV)ky(A-1)(b)kx(A-1)ky(A-1)

Fig. 1. ARPES volume maps of TiSe2 at room temperature. The photon energy used is 80 eV. (a) :stereogram of the whole volume map, (b)-(d): intensity maps in 2D-cut along the black lines shown in (a).

51

Ⅲ-2

BL1U,Sciences
BL7B
Ⅲ -2. Materials

BL1U, BL7B

Crystallinity Evaluation of Gd3Al2Ga3O12:Ce Crystals Grown by Cz and-PD Methods Using Gamma-ray-induced Positron Annihilation Lifetime
Spectroscopy and High-Resolution UV Absorption Spectroscopy
M. Kitaura1, Y. Taira2,3, K. Kamada4, S. Watanabe5 and A. Ohnishi1

Faculty of Science, Yamagata University, Yamagata 990-4560, JapanUVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
3
The Graduate University for Advanced Studies, SOKENDAI, Okazaki 444-8585, Japan
4
New Industry Hatchery Center, Tohoku University, Sendai 980-8579, Japan
5
Institute of Innovative Research, Tokyo Institute of Technology, Tokyo 152-8550, Japan
1

2

Ⅲ-2

be used as a simple probe to see the change inenvironment around the Gd atoms. The 8S7/2  6P3/2
peak consisted of two subpeaks resulting from the
Stark effect [6]. The peak positions and FWHM were
evaluated by curve-fit analysis assuming the sum of
two Lorentz functions. The results are listed in Table
II. No differences are found between the Cz and -PD
crystals. Detailed structural studies based on a single
crystal X-ray diffraction (XRD) measurement will be
performed to obtain more sophisticated information on
the structure of the GAGG:Ce crystals.

The Czochralski (Cz) method is well-known to be aconventional technique to grow crystals from hightemperature melt [1]. The Cz method enables us toobtain large size crystals of high quality. Because thegrowth rate is not so high, it generally takes time togrow crystals. The micro-pulling down (-PD) method
is a melt-growth technique similarity to the Cz method[2]. There are a number of advantages for the -PD
method: (i) The growth rate is relatively high, (ii) the
effective doping of impurities is possible, and (iii) the
crystal shape is controllable. The -PD method issuitable for the screening test in the development offunctional crystalline materials. In comparison
between the Cz and -PD methods, it has generally
been believed that the crystallinity of Cz grown
crystals are better than that of -PD grown crystals.
However, to our knowledge, no comparison on
crystallinity between the Cz and -PD methods has not
yet been carried out. In the present study, we haveinvestigated the existence of vacancy type defects andthe local structures of Gd atoms in Cz and -PD grown
Gd3Al2Ga3O12:Ce (GAGG:Ce) crystals by gamma-rayinduced positron annihilation lifetime spectroscopy(GiPALS), and UV and absorption spectroscopy,
respectively. GiPALS experiment was performed at theBL1U. High resolution UV absorption spectroscopy
were conducted at the BL7B, respectively.
The results of GiPALS analysis are shown in Table
I. The data for the Cz crystal were reported [3]. The
lifetimes for the -PD crystal are longer than those for
the Cz crystal. The bulk lifetime was calculated to be
167 ps for GAGG [4]. This value was the same as thebulk lifetime for the Cz crystal, but did not agree withthat (=200 ps) for the -PD crystal. It is likely that the
-PD crystal includes cation vacancies of highconcentration, compared to the Cz crystal. The defectlifetime for the -PD crystal is longer than that for theCz crystal, indicating that vacancy clusters are formedin the -PD crystal.
A number of peaks are observed in UV absorption
spectra for GAGG:Ce crystals [5]. These peaks wereassigned to the 8S7/2 6P7/2, 6P5/2 and 6P3/2 transitions inthe (4f)7 configuration of a Gd3+ ion. Because the peak
position and full-width-half-maximum (FWHM) are
sensitive for the local structure of Gd atoms, they canTable I: Lifetimes and relative intensities determined
by GiPALS analysis for the Cz and -PD crystals.
Lifetime (ps)Relative intensity (%)
161

1.5
92.4  3.7
Cz [3]
304  19
7.6  3.7
198  1.1
98.45  0.21
-PD625  36
1.55  0.21
Table II: Peak positions and FWHM of the Gd3+ 8S7/2
 6P3/2 absorption peak for the Cz and -PD crystals.
Peak position (nm)
FWHM (nm)301.430.20
Cz
301.650.21
301.420.19
-PD301.640.18[1] J. Czochralski, Zeitschrift für Physikalische Chemie
92 (1918) 219.
[2] T. Fukuda, V. I. Chani, Shaped crystals: micropulling-down technique and growth (Springer, Berlin,
New York, 2007).
[3] K. Fujimori et al. Appl. Phys. Express 13 (2020)
085505.
[4] M. Kitaura et al., J. JSSRR. 34 (2021) 37 (inJapanese).
[5] M. Kitaura et al., J. Appl. Phys. 115 (2014) 083517.
[6] M. Kitaura et al., J. Alloys Compd. 867 (2021)
159055.

52

Ⅲ02- 2 -BL1U

Ⅲ -2. Materials Sciences

BL1U

Vacancy-Type Defect in Mg2Sn Crystals Studied by Gamma-Ray-Induced
Positron Annihilation Lifetime Spectroscopy
M. Kitaura1, Y. Taira2,3, S. Watanabe4, W. Saito5, K. Hayashi5 and A. Ohnishi1
Faculty of Science, Yamagata University, Yamagata 990-4560, JapanUVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
3
The Graduate University for Advanced Studies, SOKENDAI, Okazaki 444-8585, Japan
4
Institute of Innovative Research, Tokyo Institute of Technology, Tokyo 152-8550, Japan
5
Graduate School of Engineering, Tohoku University, Sendai 980-8579, Japan1

2

average size of VMg defects was also estimated 11 nm.
Figure 1 revealed that only a bulk component appears
in the GiPALS spectrum. This result does not meanthat VMg defects are not included in the Mg2Sn crystal
investigated here, because GiPALS is silent for the
existence of vacancies with the radii larger than a few
nm [5]. The missing of defect components in the
GiPALS spectrum is consistent with the result of SCXRD analysis.

Thermoelectric (TE) materials attract much attention
because they can directly convert waste heat into
electricity. Exploration of TE materials is significant tosecure energy resources in future.
Intermetallic
compounds are one of the promising candidates that canbe applied to TE materials. Magnesium stannate(Mg2Sn) has been studied for the TE application. The
control of point defects such as vacancies andinterstitials is crucial for this purpose, because they
influence the carrier concentration and thermal
conductivity included in the expression of thedimensionless figure of merit. Recently, an analysis ofpoint defects was performed to reveal the relationshipbetween point defects and TE properties [1]. Primarypoint defects in Mg2Sn were Mg vacancies at the 8c site
(VMg) and Mg interstitials at the 4b site (Mgi), which
generated valence holes and conduction electrons,
respectively, by ionization of acceptors and donors.
Saito et al. succeeded in observing the existence of VMg
defects by a transmission electron microscope (TEM),
and confirmed by an inductively coupled plasma mass
spectroscopy. Furthermore, they demonstrated that the
TE properties of Mg2Sn are optimized by adjusting thefraction of VMg. It is therefore meaningful to evaluate
the fraction of VMg quantitatively. In the present study,
we have measured gamma-ray-induced positronannihilation lifetime spectroscopy (GiPALS) spectra of
Mg2Sn crystals grown under various conditions.
Experiment was performed at the beamline 1U in
UVSOR synchrotron facility. Details of GiPALS
experiment were described in Ref. [2].
Figure 1 shows the GiPALS spectrum of the Mg2Sn
crystal grown from high-temperature melt under an Ar
atmosphere of 0.6 atm. The data was obtained at room
temperature. The GiPALS spectrum is of an exponential
decay component with the lifetime of 255 ps. We
performed a first-principles calculation using the
ABINIT [3,4], to determine the positron annihilation
lifetime at the bulk state (bulk lifetime) which means the
crystal lattice without vacancy-type defects. The bulk
lifetime was calculated 257 ps. This value is in good
agreement with the lifetime determined from an curve
fit analysis of the GiPALS spectrum. It is likely to assign
this component to the positron annihilation at the bulk
state.
In Ref. [1], the fraction of VMg was estimated 5.6 %by single crystal x-ray diffraction (SC-XRD). The

Fig. 1. GiPALS spectrum of a Mg2Sn crystal,measured at room temperature.

[1] W. Saito et al., Sci. Rep. 10 (2020) 2020.
[2] K. Fujimori et al., Appl. Phys. Express 13 (2020)
085505.
[3] X. Gonze et al., Computer Phys. Comm. 248(2020) 107042.
[4] J. Wiktor et al., Phys. Rev. B 92 (2015) 125113.
[5] R. Krause-Rehberg and H. S. Leipner, Positron
Annihilation in Semiconductors: Defect Studies Chap. 3(Springer, Berlin, 2010),.

53

Ⅲ02- 3 -Ⅲ-2

BL1U Sciences
Ⅲ -2. Materials

BL1U

In-situ Observation of Oxygen Vacancy in CeO2
Using Gamma-ray Induced Positron Annihilation Spectroscopy

reported that molecular oxygen adsorbed on theoxygen vacancy clusters of CeO2 surface desorbed ataround 150 °C and lattice oxygen atoms of CeO2
surfaces desorbed at around 450 °C [4]. Taking into
this consideration, the result obtained in this study, i.e.,
the larger I2 at 300 °C, is considered to be due to thedesorption of oxygen molecules adsorbed on theoxygen vacancy clusters on the CeO2 surface. In thenext fiscal year, we will investigate the temperature
and atmosphere dependence about the behavior of theoxygen vacancies of CeO2 surface in detail.

Counts (arb. unit)

Ⅲ-2

CeO2 has been extensively studied as a heterogeneous
catalyst for automotive exhaust gas purification, CO
oxidation, and VOC oxidation reactions. Such catalytic
activity of CeO2 is due to the redox property of
Ce4+/Ce3+ and the associated formation of oxygen
vacancies. Recently, it is reported that the existence ofoxygen vacancies, especially oxygen vacancy clustersof CeO2 surface is a key role for the oxidation reactions
with molecular oxygen as an oxidant. The gaseous
oxygen can be adsorbed and activated on the oxygen
vacancy clusters of CeO2 surface, resulting in theformation of active oxygen species and high catalytic
activity [1].
On the other hand, positron annihilation spectroscopy(PAS) is a well-known method to detect lattice defects
with high sensitivity. Among positron annihilation
spectroscopy, gamma-ray induced positron annihilation
spectroscopy (Gi-PAS) is an ultimate method to havethe following features. 1) Since positrons could be
generate inside a sample and observe their annihilation
process, making it possible to perform measurements
under harsh conditions such as high temperatures and/or
high pressures. 2) In addition, the positron lifetime
spectrum does not include the source component, whichallows for detailed discussion of a positron lifetime [2].
In this study, we performed in-situ observation ofoxygen vacancies in CeO2 at a high temperature using
Gi-PAS.
We have set up a gamma-ray spectroscopy system atthe laser-Compton scattering (LCS) beamline of BL1U
at UVSOR-III [3], and measured the lifetime of theannihilation gamma-rays at room temperature and
300 °C using BaF2 scintillation detector. We used thesoftware Lifetime9 (LT9) to analyze the spectra.
Figure 1 shows the positron annihilation lifetime
spectra of CeO2 measured at room temperature and
300 °C. The positron annihilation lifetime and relative
intensity analyzed using LT9 are also listed in Table 1.
The lifetime of the positron annihilation is able to giveinformation about the size, type and relative
concentration of defects/vacancies. The positronannihilation lifetime spectra of CeO2 at room
temperature and 300 °C yielded two distinct lifetime
components, τ1 and τ2 with relative intensities I1 (I1 =100 - I2) and I2. At both temperatures, the lifetimes (τ1and τ2) were almost the same, however the relative
intensities (I1 and I2) were different: I2 for 300 °C waslarger than that for room temperature. Wang et al.

10

4

10

3

10

2

10

1

10

0

@R.T
Counts (arb. unit)

2

S. Dohshi1, H. Toyokawa2, K. Maeda1, Y. Taira3 and T. Hirade4

Osaka Research Institute of Industrial Science and Technology, Izumi 594-1157, 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
Japan Atomic Energy Agency, Tokai-mura 319-1195, Japan
1

0

1

2

3

Time (ns)

4

5

10

4

10

3

10

2

10

1

10

0

@300 ºC

0

1

2

3

Time (ns)45Fig. 1. Positron annihilation lifetime spectra of CeO2
measured at room temperature and 300 °C
Table 1 Positron annihilation lifetime and relative
intensity of CeO2.
Temp.
R.T.
300 ºCτ1 (ps)206.5 ± 1.7
204.0 ± 3.3

τ2 (ps)489.0 ± 14490.0 ± 8.8

I2 (%)
17.1± 3.0
25.5± 1.0

[1] X. Liu et al., J. Am. Chem. Soc. 131 (2009) 3140.
[2] H. Toyokawa et al., Proc. AccApp'07 (2007) 331.
[3] Y. Taira et al., Rev. Sci. Instr. 84 (2013) 053305.
[4] L. Wang et al., Catal. Sci. Technol. 6 (2016) 4840.

54

Ⅲ02- 4 -BL1B

Ⅲ -2. Materials Sciences

BL1B

Existence of Shallow Donor in Mg2Si Crystals Revealed by Terahertz
Absorption Spectroscopy
M. Kitaura1, M. Fujimoto2,3, H. Udono4, S. Watanabe5 and A. Ohnishi1

Faculty of Science, Yamagata University, Yamagata 990-4560, JapanUVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
3
The Graduate University for Advanced Studies, SOKENDAI, Okazaki 444-8585, Japan
4
Deparment of Electrical and Electronics System Engineering, Ibaraki University, Mito 310-8512, Japan
5
Institute of Innovative Research, Tokyo Institute of Technology, Tokyo 152-8550, Japan
1

2

Magnesium silicide (Mg2Si) is known to be asemiconductor which has the fundamental absorption of
an indirect transition type. The fundamental absorption
edge locates at around 0.6 eV. Because Mg2Si can
responds to the infrared (IR) light with photon energies
above 0.61 eV, this material is expected to be a plausible
candidate for the application of an IR photodetector.
Mg2Si shows n-type conductivity without incorporating
impurities. This is because an interstitial Mg atom at the4b site works as an intrinsic donor [1]. Electricalproperties of Mg2Si crystals have been reported so far[2]. The existence of shallow donors with the activationenergy of 8-9 meV was suggested in Mg2Si crystals withthe carrier density of 1015 cm–3 order. Although the
Mg2Si crystals were grown from high purity Mg and Si
sources, they contained various impurities. Thus, it still
remains unclear whether such shallow donors areassociated with interstitial Mg atoms. Terahertz
absorption spectroscopy is an experimental technique toexplore the existence of shallow donors in solids.
Practically, the existence of shallow donors in Si crystals
has been found so far [3]. In the present study, we havecarried out terahertz absorption spectroscopy for
undoped Mg2Si crystals to find the existence of shallow
donors.
Mg2Si crystals were grown from high-temperature
melt in Ar atmosphere by a vertical Bridgeman furnace.
Experiment was performed at the beamline BL1B. The
carrier concentration of the sample used in this work
was determined to be 4.31015 cm–3 by a Hall-effectmeasurement. The terahertz absorption spectra of an
undoped Mg2Si crystal is shown in Fig. 1. The data
were obtained at 5 K. Two prominent peaks appear at
58 and 66 cm–1. These peaks were weakened underirradiation with 800 nm photons from a Ti:Sa laser.
Furthermore, the two peaks were weakened withincreasing temperature, and disappeared around 20 K.
The temperature dependence of the two peaks wasanalyzed by assuming a simple model that a donor
creates a conduction electron. The activation energy
for the donor originating in the two peaks was 7-8 meV,in good agreement with that determined from thetemperature dependence of the carrier concentration[2]. It is therefore reasonable to assign the origin of thetwo peaks to shallow donors in Mg2Si. The weakeningof the two peaks by photoirradiation result is explained
as photoionization of shallow donors. Now, we areinvestigating experimentally and theoretically whether
such shallow donors are formed by interstitial Mg
atoms.

Ⅲ-2

Fig. 1 Terahertz absorption spectra of an undoped
Mg2Si crystal, measured at 5 K under non-irradiation(blue) and irradiation (red) with 800 nm photons froma Ti:Sa laser.

[1] A. Kato et al., J. Phys.: Condens. Matter 21 (2009)
205801.
[2] H. Udono et al., Jpn. J. Appl. Phys. 54 (2015)
07JB06.
[3]A. Hara et al., Jpn. J. Appl. Phys. 49 (2010) 050203.

55

Ⅲ02- 5 -BL1B Sciences
Ⅲ -2. Materials

BL1B

Electron-Irradiation Effects on Germanium
A. Hara and T. Awano

Faculity of Engineering, Tohoku Gakuin University, Tagajo 985-8537, Japanthat are eliminated at temperatures of 400 °C. The
difference in thermal stability between the e-irradiation
defects and acceptors in poly-Ge thin films clearly
indicates that the origins of these two types of defects
are different.
3.5
400℃

Intensity

3.0

G

D

C

2.5

300℃

2.0

200℃

1.5

100℃

1.0

As-e-rad.

0.5

As

0.0

40

50

60

70

80

Wave number (cm-1)

90

100

Fig. 1. Transmission spectra of e-irradiated p-type Ge

Normalized intensity

Ⅲ-2

Polycrystalline germanium (poly-Ge) is attractive asa material for three-dimensional integrated circuits
owing to its high mobilities for both electrons andholes and its lower melting temperature than Si at
approximately 450 °C. However, a large number ofholes are generated in poly-Ge film because of crystal
defects; hence, identification of the origin of theacceptors in poly-Ge is an important consideration.
As Ge has a high dielectric constant, the energy
levels of the acceptors are expected to be shallow inGe, similar to other group-III impurities; hence, theBL1B line of UVSOR is suitable for detecting defects
attributable to the acceptors. In our previous research,
we used electron irradiation (e-irradiation) to introduce
vacancies and self-interstitials in bulk p-type [Indium(In)-doped] Ge samples of 2.0 mm thickness and 12Ω∙cm resistivity; we observed that e-irradiation
introduces donors that are eliminated at temperaturesof 400 °C [1]. However, the main peaks (lines C and D[2. 3]) of the In acceptor were saturated owing to thehigh In concentration. Thus, we used the satellite peakreferred to as line G to obtain the above results [1].
In the present work, we used low-In-content bulk Ge
samples (33 Ω∙cm) and high e-irradiation of 4.5 MeV
and 6×1015 cm-2. Following this, the samples wereannealed at 100, 200, 300, and 400 °C for 30 min in aconventional furnace system to evaluate the changes tothe spectra. The optical transmission spectra were
measured at liquid He temperature using BL1B.
Figure 1 shows the spectra of as-grown and as-eirradiated samples, along with samples annealed at 100,
200, 300, and 400 °C. The intensities of the lines
corresponding to the In acceptor (lines C and D)
decreased after e-irradiation, but began recovering tothose of the as-grown sample when the annealing
temperature increased to 400 °C. Figure 2 shows thevariations in the peak intensities of lines C and G,
which were normalized by those of as-grown Ge.
Variation in the intensity of line G was obtained fromthe experimental results of Ref. [1], which indicatesthat e-irradiation introduces donor defects but
eliminates at 400 °C.
In general, it is believed that e-irradiation introduces
simple structural defects, such as vacancies, selfinterstitials, and their aggregates. However, acceptors
are generated in poly-Ge thin films crystallized at
500 °C. The difference in thermal stability between thee-irradiation-induced defects and acceptors in poly-Ge
indicates that the acceptors in poly-Ge films are notsimple defects, such as those introduced by eirradiation.
In summary, the optical transmission spectra of eirradiated Ge were measured at liquid He temperatures,and it was observed that e-irradiation generates donors

1.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0

Line CLine G-100As-e-rad.
0
100 200 300 400 As-grown
500 600
Annealing temperature (℃)

Fig. 2. Annealing dependencies of lines C and G. The
plot of line G was obtained from Ref. [1].

[1] A. Hara and T. Awano, UVSOR activity report 201947 (2020) 48.
[2] R. L. Jones and P. Fisher, J. Phys. Chem. Solids 26(1965) 1125.
[3] W. Kohn, in Solid State Physics, ed. F. Seitz and D.
Turnbull (Academic Press, New York, 1957) Vol. 5, p.
257.

56

Ⅲ02- 6 -BL2A

Ⅲ -2. Materials Sciences

BL2A

Formation of Catalytically Active MoCx Species during Methane
Dehydroaromatization over Mo-V Co-Modified H-MFI Zeolites
K. Kuramochi1, R. Yamazaki1, Y. Nozawa2, Y. Sonobe3 and H. Aritani2,3Advanced Science Research Laboratory, Saitama Institute of Technology, Fukaya 369-0293, Japan
2
Graduate School of Engineering, Saitama Institute of Technology, Fukaya 369-0293, Japan
3
Faculty of Engineering, Saitama Institute of Technology, Fukaya 369-0293, Japan

1

A Molybdenum-modified H-MFI zeolite (Mo/ HMFI) catalyst is a typical GTL (Gas To Liquid) catalyst
for methane dehydroaromatization. The reaction socalled MTB (Methane To Benzene) one is valuable fordirect conversion from natural gases to usefulpetroleum compounds. Over the Mo/H-MFI catalysts,
definite deactivation due to coke deposition has been aserious problem for enhancement of MTB reactivity,
and thus, clarification of the deactivation process overthe catalysts is one of the important points. A cause of
the deactivation is based on coke deposition on strongacid sites over H-MFI and structural deactivation on
carbonized Mo species. Thus, clarification of active
Mo sites with high and durable activity for methane
dehydrogenation is one of the most important subjects.
In the present study, Mo LIII-edge XANES is applied
to characterize the active Mo-carbide species on
Mo/H-MFI and Mo-V co-modified H-MFI.
Mo(5wt%)/H-MFI and Mo-V/H-MFI (Mo/V=10)
catalysts were prepared by impregnation of H-MFI,and followed by drying overnight and calcination at
773 K. The methane dehydroaromatization reactivity
was evaluated at 1023 K as described in a previous
report.[1, 2] Mo LIII-edge XANES spectra were obtainedin BL2A of UVSOR-IMS in a total-electron yieldmode using InSb double-crystal monochromator. REX2000 (Rigaku) software were used for normalization ofeach XANES spectra.
For L-edge XANES spectra over Mo/H-MFI catalysts(on time course of the MTB reaction) as shown in Fig.
1, the active Mo species in both Mo/H-MFI and Mo/V/H-MFI are due to more deeply carbonized species
than α-Mo2C. It suggests the formation of MoCx (x >0.5) as an important species for high MTB reactiity. By
Mo-V co-modification on H-MFI, the carbonization toform active MoCx species became faster. It indicatesthe formation of easily reduced Mo sites to form
deeply carbonized species. For 185 minutes on the
MTB reaction (during the deactivation), excesscarbonization was inhibited by V co-modification as
exhibited in the edge energy shown in Table 1. The
result is likely to relate to a suppression effect ofdeactivation.

1.0

30 min.
55 min.
185 min.
-Mo2C (ref.)Mo Metal (ref.)Mo/H-MFI

TEY (Norm.)(Si/Al2=28)

Ⅲ-2

0.5

0.0
2515

2520

2525 2530
Energy / eV

1.0

2540

30 min.
60 min.
185 min.
-Mo2C (ref.)Mo Metal (ref.)Mo-V/H-MFI[Mo/V=10]TEY (Norm.)

2535

0.5

0.0
2515

2520

2525 2530
Energy / eV

2535

2540

Fig. 1. Mo LIII-edge XANES spectra of Mo/H-MFI(Si/Al2=28) and Mo-V/H-MFI (Mo/V=10) catalysts
after methane dehydroaromatization at 1023 K for 30– 185 min. The references, α-Mo2C and Mo metal, arealso shown in each figure.
Table 1. Edge energy values obtained by 1stderivatives of LIII-edge XANES shown in Fig. 1.
Mo/H-MFI(28)Time onEdge Energy
Stream / min.
/ eV[1] H. Aritani et al., UVSOR Activity Report 2018 46(2019) 49.
[2] H. Aritani et al., UVSOR Activity Report 2017 45(2018) 44.

57

30

2521.36

Mo-V/H-MFI (Mo/V=10)

Time onEdge Energy
Stream / min.
/ eV
302520.9655

2520.8655

2520.861852520.48185

2520.60

 -Mo2C
Mo Metal

2520.962520.22

-Mo2CMo Metal

2520.962520.22

Ⅲ02- 7 -BL2A Sciences
Ⅲ -2. Materials

BL2A

Local Environment of Heat Treated Ag-Doped PHI-Type Zeolite
H. Murata, Y. Minami and A. Nakahira

Department of Materials Science, Osaka Prefecture University, Sakai 599–8531, Japan.
were still maintained in the partially collapsed zeolites.
It has been reported that some Ag-doped zeolite
phosphors are affected by humidity. [5] Our results leadto new phosphors stable in air since partially collapsed
zeolite lost continuous pores.

Ag-PHI
700°C

Intensity / arb. units

Ⅲ-2

Zeolites are crystalline aluminosilicates which havenano-sized cavities in their crystal structures. Zeolite
frameworks were classified into over 250 types by theinternational zeolite associations. [1] They havecation-exchange abilities due to their unique crystal
structures. Ag-doped zeolites have attracted many
researchers as rare-earth free phosphors. [2] They wereprepared by ion-exchange in Ag+ aqueous solution andsubsequent heat-treatments. In these processes, Ag
nano-clusters were formed in zeolitic cavities andbehave as luminescent center. In addition, some Agdoped zeolites are not stable at high temperature andbecome amorphous phases. [3]In the present study, we investigated local environmentsof heat-treated Ag-doped PHI-type zeolite (Ag-PHI)
using X-ray absorption near edge structure (XANES).
Ag-PHI samples were synthesized by ion-exchange
and subsequent heat treatments. PHI-type zeolite wasprepared by a hydrothermal method. The starting
material was soaked in 0.1 mol/L of Ag(NO3)2 aqueous
solution for 1 h under dark condition. The samples
were washed by ion-exchanged water and dried at
50 °C in air. Then, they were heated at 450 °C and
700 °C for 4 h.
XANES spectra were collected by the partial
fluorescent yield method using a silicon drift detector at
BL2A in UVSOR. Fluorescence X-ray spectra were deconvoluted using gauss functions, which was reported
elsewhere. [4] X-ray beam was monochromated by KTP
double crystals for Al-K and InSb ones for Si-K and AgL3.
X-ray diffraction (XRD) patterns of the Ag-PHI
heated at 450 °C have same features to the starting
material. On the other hand, the samples heated at
700 °C gave amorphous pattern. No Ag compound
were observed. It is noted that Ag nano-particles were
not observed by scanning electron microscope either.
Al-K and Si-K XANES were measured in order toinvestigate the structure of the amorphous samples.
The samples heated at 700 °C have the similar features
to those of PHI-type zeolite and Ag-PHI heated at
450 °C. The features were different from those of
typical glasses. These results indicated that samples
heated at 700 °C were not a mere glass, but partiallycollapsed zeolite.
Figure 1 shows Ag-L3 XANES of the Ag-PHI
samples. The samples heated at 450 °C and 700 °C havesame features. Their spectra were different from thoseof typical Ag compounds while the absorption edge ofthe samples agrees that of Ag foil. These results
indicated that Ag in the samples were metallic, but it has
different local environment from bulk Ag metal. They

450°C

Ag foil

Ag2O
AgO
3340

3360
3380
Photon energy / eV

3400

Fig. 1. Ag-L3 XANES of Ag-doped PHI samples andreferences.

[1] C. Baerlocher and L.B. McCusker,
Database of Zeolite Structures,
http://www.iza-structure.org/databases/[2] D. Grandjean et al., Science 361 (2018) 686.
[3] H. Aono et al., J. Ceram. Soc. Jpn. 124 (2016) 82.
[4] H. Murata, UVSOR Activity Report 2018 46 (2019)53.
[5] E. Coutino-Gonzalez et al., J. Vis. Exp. 117 (2016)
e54674.

58

Ⅲ02- 8 -BL2A

Ⅲ -2. Materials Sciences

BL2A

Local Structure Investigations of Mg1-xNixAl2O4 by NEXAFS
1

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, Tosu 841-0005, Japan
3
Graduate school of Advanced Integration Science, Chiba University, Chiba 263-8522, Japan

Spinel oxides with the general formula AB2O4 can beformed with various kinds of divalent A and trivalent B
cations. Owing to their unique mechanical, electronic,
and magnetic properties, the spinel oxides have gained
considerable attention not only from the fundamental
research fields but also from the industrial application
point of view. Some spinel compounds accommodate alarge degree of cationic disorder. The cationic disordering
naturally affects the structural properties of the spinels.
For example, magnesium aluminate (MgAl2O4) andnickel aluminate (NiAl2O4) spinels are generally known
as normal and inverse spinel structures, respectively.
However, their inversion degrees for synthetic specimens
were also reported to be fluctuating between 0 and 1,
respectively, due to the cationic disordering. Recently,
the structure of Mg1-xNixAl2O4 was reported using
neutron total scattering to understand the cationicdisordering process [1]. X-ray absorption spectroscopy(XAS) is a powerful structure characterization methodthat uses an X-ray probe to reveal local atomic
coordination and electronic structures. In this study, we
focus on the local structures in MgAl2O4–NiAl2O4 solid
solutions, particularly cationic-disordered structures.
The polycrystalline samples of Mg1-xNixAl2O4 (x =0.0, 0.05, 0.2, 0.5, 0.8, 1.0) were synthesized by a solidstate reaction. They were sintered in air at 1300 ºC for
10 h followed by furnace. Mg and Al K-edge XANES
measurements were performed on BL2A beamline at
UVSOR Synchrotron Facility, Okazaki, Japan, using thepartial fluorescence yield method. A KTiOPO4 doublecrystal monochromator gives Mg and Al K-absorption
edges in the energy regions 1290 – 1340 eV and 1540 –
1610 eV, respectively. The measurements of Mg and Al
K-edge XANES spectra were carried out in vacuum at apressure and temperature of 1×104 Pa and 20 ºC,
respectively. Fluorescence X-rays of Mg Kα and Al Kα
were collected utilizing an energy-dispersible silicon
drift detector.
The Al K-edge XANES spectra for Mg1-xNixAl2O4 areshown in Fig. 1 with the composition values x = 0, 0.05,
0.2, 0.5, 0.8, and 1.0. The intensity of each spectrum was
normalized to a value of 1 at the photon energy of 1588
eV after the removal of the background intensity. The
spectral shapes of the Al K-edge XANES clearly changed
depending on the Ni content x in Mg1-xNixAl2O4. It is seenthat the identical peak appeared at the absorption edge as
indicated by an arrow in Fig. 1, and its intensity increased
with the increasing x. Alternatively, in the higher energy
region, the large peak at 1579 eV broadened with theincreasing x or Ni content. Such spectral changes suggestthat the Al at tetrahedral sites increased with increasing
Ni concentrations instead of Al at octahedral sites.

Ⅲ-2

Fig. 1. Al K-edge XANES spectra of Mg1-xNixAl2O4.

[1] E. O’Quinn et al., J. Am. Chem. Soc. 139 (2017)
10395.

59

Ⅲ02- 9 -BL2A Sciences
Ⅲ -2. Materials

BL2A

X-ray Absorption Fine Structure Measurements of Sulphur Chain
Encapsuled in Carbon Nanotubes
2

Chalcogen atoms are bonded with two-fold covalentbonds, and form rings or chains. They bind each otherwith inter-ring or inter-chain interactions. The
chalcogen atoms form isolated chains within narrow
space, such as, carbon nanotube, morodenite, and so on[1-3]. In this study, we are studying structure of sulfur
chain in the CNT (S@CNT) with X-ray absorption finestructure (XAFS) measurements.
The XAFS measurements of crystalline S (c-S) andS@CNT were done at BL2A in UVSOR with total
electron yield and SDD detectors. Intensity of incident
X-ray were observed with Au or Cu meshes. Figure 1
shows spectrum of S@CNT with Au mesh. A sharp
white line of S K-edge and XAFS oscillations wereobserved. Unfortunately, steps were observed around
2.5 and 2.9 keV. The steps may be brought about bymonitoring of the intensity of the incident X-ray with
Au mesh.
Figure 2 shows extended X-ray absorption finestructure (EXAFS) oscillations reduced from thespectrum of Fig. 1 with miXAFS code [4]. EXAFS
oscillation is obtained. It contains steps around 8.5 and11.5 A-1, which correspond with the steps of Fig. 1.
Figure 3 shows Fourier transform of EXAFS
oscillation to account for backscattering form factor,
phase shift calculated with FEFF code. There is a main
peak around 2.0 A, which is close to the covalent bondlength of c-S. The position of the peak coincident withthe covalent bond length of c-S. However, it isnecessary to verify whether the peak position iscoincidental because the correct EXAFS function is
obtained, or whether they coincide by chance.
The EXAFS spectra were obtained, but the qualities
were not sufficient for the EXAFS analysis to obtainthe structural parameters, such as, interatomic
distances, coordination numbers, and so on. To obtainthe structure parameters of S@CNT much
improvements may be required, such as, monitoring of
the intensity of the incident X-ray, increment of theintensity above 3.0 keV.

6×10145×1014I/I0

4×10143×10142×1014
1014
0

2

2.5

E(keV)

3

3.5

Fig. 1. Spectrum of S K-edge for S@CNT.

Fig. 2. EXAFS oscillation of S@CNT.

0.4
0.3

|FT(r)|

Ⅲ-2

H. Ikemoto1 and T. Miyanaga2

Department of Physics, University of Toyama, Toyama 930-8555, Japan
Department of Mathematics and Physics, Hirosaki University, Hirosaki 036-8561, Japan.
1

0.2
0.1
0

0

2

4

6

8

10

r(A)

Fig. 3. Fourier transform of EXAFS oscillation of
S@CNT.
[1] T. Fujimori et al., ACS Nano 7 (2013) 5607.
[2] M. Inui et al., J. Phys. Soc. Jpn. 57 (1988) 553.
[3] H. Ikemoto et al., J. Phys. Chem. C 124 (2020)
26043.
[4] H. Ikemoto, J. Synchrotron Rad. 25 (2018) 61.

60

Ⅲ02- 10 -BL3U

Ⅲ -2. Materials Sciences

BL3U

First Trial of Precise Analysis of Super-structures of Chiral Smectic Liquid
Crystals by Resonant Soft X-ray Scattering (RSoXS) at UVSOR
Y. Takanishi1, F. Araoka2 and H. Iwayama3,4Faculty of Science, Kyoto University, Kyoto 606-8502, JapanRIKEN Center for Emergent Matter Science, Wako 351-0198, Japan
3
UVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
4
School of Physical Sciences, The Graduate University for Advanced Studies, SOKENDAI, Okazaki 444-8585, Japan
1

2

Smectic liquid crystals have one-dimensional
positional order, so-called layer structures. In particular,chiral tilted chiral smectic phases have attracted muchattention because molecular clinicity in neighboringlayers influence the macroscopic polarity; ferroelectricand antiferroelectric order appears in synclinic andanticlinic structures, respectively. Furthermore, thesuccessive phase transition between synclinic SmC*
and anticlinic SmCA* is one of the most interesting
subjects, in which the appearance of some subphases
due to the competition between SmC* and SmCA* hasbeen experimentally determined and the existence offurther subphases has been theoretically predicted basedon the long-range interlayer interaction and thefrustration of clinicity (synclinic or anticlinic).
Conventional X-ray diffraction is a powerful tool forstudying the layer structure, but difficult to distinguishthe difference of the clinicity because the electron
density along the layer normal of left and right tilting
molecules are the same.
This subject was resolved by resonant X-ray
scattering. In this technique, by using X-ray whoseenergy is coincident with a certain atom absorption edge,
the structure factor becomes a tensor instead of thescalar in conventional X-ray diffraction. As a result,scattering intensity is sensitive for the system symmetry,
and also molecular orientation. In this technique, thestructure analysis of tilted chiral phase has dramatically
evolved. So far, however, sample compounds have topossess an atom with the same absorption energy as theused X-ray, and such atoms as sulphur, selenium,
chlorine and bromine. Recently, carbon K edge resonant
scattering has been applied to study, and successful inobtaining the precise structures of polymer blends,
block copolymer, and liquid crystals. Hence this time
we tried to perform this technique, and to investigate theprecise structures of chiral liqud crystals.
The experiment was performed at BL3U of UVSOR(Okazaki). For the measurement, a new vacuum chamber
was created, as shown in Fig. 1. Liquid crystals wasfilled in the isotropic phase between two pieces of 100
nm-thick Si3N4 membranes (NTT-AT). The scattering
was detected by CCD (ANDOR DO940P-BN). Incident
X-ray beam was tuned between 270~300 eV. Typicalabsorption spectrum was shown in inset of Fig.1; in thiscompound, carbon K-edge energy is 286 eV.
Figure 2 shows the first obtained results of RSoXS.
When the incident energy E0 is 285 eV(a), clear scatteringpeaks are observed at wider angle, while these peaks
disappear at E0=270 eV. Center position of two peaks
just corresponds to twice of the fundamental layer
spacing of this chiral smectic SmCA* phase, which
proves the anticlinic bilayer structure. Furthermore, two
resonant peaks comes from the macroscopic helicalstructure of SmCA*, and splitting width corresponds to
ca. 250 nm, which is coincident with the obtained helicalpitch from the optical measurement.

Fig. 1. Photo of experimental setup & absorption
spectrum of chiral liquid crystals.

Fig. 2. Schematic image of experimental geometry(a),and obtained 2D scattering image at E0=285 eV(onresonance) (b) and E0=270 eV(off resonance)(c).

61

Ⅲ02- 11 -Ⅲ-2

BL3B Sciences
Ⅲ -2. Materials

BL3B

Intrinsic Luminescence from Self-trapped Excitons in BaMBe2(BO3)2F2(M=Mg,Ca) Crystals with Two-dimensional Single Layers upon VUVExcitation
N. Kodama and T. Takahashi

Faculty of Engineering and Resource Science, Akita University, Akita 010-8502, Japan
BMBF under excitation at 160 nm as seen in Fig. 2. The
same is true for luminescence under excitation at 50 nm.
There are two plausible explanations for the dependenceof luminescence intensity on the Ca2+-substitution for
Mg2+, involving (i) a two-dimensional effect or (ii) an
incommensurate structural modulation effect. The
magnitude of two-dimensionality is defined as the ratio of
the interlayer distance to the intralayer distance. Here, themagnitude of two-dimensionality can be expressed by thec/a axis ratio. The magnitude of two-dimensionality for
BCBF with c/a ratio of 3.42 is higher than that for BMBF
with the c/a ratio of 3.34, with the increase being due tothe larger ionic radius of Ca2+ than of Mg2+. Taking into
account the above result, the dependence of the STE
intensity on Ca2+substitution can be explained in terms ofa two-dimensional effect. The other possible explanationis that the structural modulation effect increases thenumber of local sites with larger distortion potentials.
These structural changes would result in broadening of
the luminescence. This possibility is unlikely because
there is no significant difference in the STE bandwidth
between the BCBF and BMBF crystals.
600 500

0.07

400

200

300

0.04
0.03
0.02
0.01

1.5

2.5

3.5

4.5

13K
45K
77K
100K
125K
160K
200K
240K
293K

Wevenumber / ×104 cm-1

Intensity / a.u.

Intensity / a.u.

400

200

300

(b)
0.1

0.05

0

600 500

0.12

(a)

0.06

13K

0.08

45K
0.06

77K

0.04

100K
125K
160K

0.02

200K

0

1.5

2.5

3.5

4.5

240K
293K

Wevenumber / ×104 cm-1

Fig. 1. Temperature dependence of luminescence
spectra of (a) BaCaBe2(BO3)2F2 and (b) BaMgBe2(BO3)2F2
excited at 50 nm in the range of 13-293 K.
2.5
Intensity / a.u.

Ⅲ-2

Mixed anion compounds have gained increasing
attention recently from the point of view of theirincreased degree of freedom regarding parameters suchas electric charge, electronegativity, polarizability, andorbital energy, arising from the coordinated anions. The
formation energy and luminescence properties of
excitons are considered to depend on the degree of twodimensionality or two-dimensional modulation. To date,very little research has focused on the formation of selftrapped excitons (STEs) in terms of the dimensionality
and modulation of the structure. Fluorine-beryllium
borates BaMBe2(BO3)2F2 (M = Mg, Ca) have a layered
structure which consists of flexible two-dimensional[Be3B3O6F3] ∞ single layers. [1] We examined thecorrelation between the intrinsic luminescence intensity
and the degree of two-dimensionality in BaCaBe2(BO3)2F2(BCBF) and BaMgBe2(BO3)2F2 (BMBF) crystals. We
discuss the structural correlation of the intrinsic
luminescence intensity from STEs.
Under VUV excitation at 50 and 160 nm, intrinsic
luminescence from STEs was observed in thesecrystals. The excitation spectral intensity for BCBF
and BMBF increased rapidly below about 180-200 nm.
These observations support the conclusion that theluminescence band originates from STE formed byband-gap excitations, or to molecular transitions in the
BO33- group.
Figures 1(a) and 1(b) show the luminescence spectra
for BCBF and BMBF excited at 160 nm in the rangeof 13-293 K. One luminescence band with a peak at
305-340 nm associated with STE appears for BCBF,
and the corresponding peak appears at 310-320 nm for
BMBF. In BCBF, the STE intensity decreases
gradually from 13 K to 193 K. The BMBF crystal
exhibited an STE intensity that increased gradually as
the temperature increased to 125 K, above which theintensity decreased. These decreases in the intensity of
STE luminescence likely resulted from a thermal
quenching process. The peaks of the STE emission
band in the two samples shifted to slightly shorter
wavelengths with increasing temperature from 13 to
293 K.
Figure 2 shows the luminescence spectra for BCBF
and BMBF excited at 160 nm at 13 K. The dependenceof the intensity and bandwidth of the intrinsic
luminescence on the substitutional effects of Ca2+ for
Mg2+ was examined for these crystals. As an example, Fig.
2 shows the luminescence spectra for BCBF and BMBF
excited at 160 nm in the range of 13 K. We found theintensity of the STE for BCBF to be greater than that for

λex=160nm

2

T=13K

1.5

ー BCBF
ー BMBF

1
0.5
0

200

400
Wevelength / nm

600

Fig. 2. The luminescence spectra for BaCaBe2(BO3)2F2
and BaMgBe2(BO3)2F2 excited at 160 nm at 13 K.
[1] S.Guo, X.Jiang, M.Xia, L.Liu, Z.Fang, Q.Huang,
R. Wu, X. Wang, Z. Lin, C. Chen, Inor. Chem.Phys. 56(2017) 11451.

62

Ⅲ02- 12 -BL3B

Ⅲ -2. Materials Sciences

BL3B

Intrinsic Nature of Luminescence Bands for undoped and Sn doped
-Ga2O3 Crystals
R. Tarukawa1, M. Kitaura1, K. Miki2, A. Ohnishi1, K. Sasaki3 and A. Kuramata3
Faculty of Science, Yamagata University, Yamagata 990-8560, Japan
Graduate School of Engineering, University of Hyogo, Himeji 671-2280, Japan
3
Novel Crystal Technology Inc., Sayama 350-1328, Japan1

2

and 400 nm bands increased in proportion to the squareof the laser power. It is therefore concluded that the
340 and 400 nm bands are intrinsic origins in -Ga2O3.
Further experiments are needed to identify the originsof the 340 and 400 nm bands.

-Ga2O3 is a wide-gap semiconductor with the bandgap of 4.8 eV. Tetravalent cations doping causes the ntype conductivity in -Ga2O3. The electric properties arechanged by high-temperature annealing under various
atmospheres. The high-temperature annealing under
nitrogen atmosphere (nitrogen annealing) remarkably
lowers the electrical resistance of -Ga2O3, resulting inhigh electrical conductivity. The oxygen annealing
keeps the electric insulation with high electricalresistance. Because high-temperature annealing varies
lattice defects, it is likely that the change in electricalresistance of -Ga2O3 is caused by the interaction oftetravalent cations with lattice defects. Such latticedefects influence luminescence properties of -Ga2O3.
So far, there are many studies on luminescence propertiesof -Ga2O3. Luminescence spectra exhibited a prominent
band at around 400 nm. Bient et al. were assigned the
400 nm band to an intrinsic nature due to radiativeannihilation of relaxed excitons or radiative
recombination between donor-acceptor pairs [1]. Usuiet al. assigned the 400 nm band to an extrinsic origin
associated with Sn 5s-5p transitions [2]. Thus, the natureof the 400 nm band still remains unclear.
In the present study, luminescence properties of
undoped and Sn-doped -Ga2O3 crystals were
investigated at the BL3B beamline [3]. Here, an
undoped crystal, and Sn-doped crystals annealed underoxygen and nitrogen atmosphere were named as #1, #2,
and #3 samples, respectively. Figure 1 shows absorption
spectra of #1-#3 samples, measured at 15 K. The
absorption spectra exhibit a stepwise structure at around260 nm, which corresponds to the indirect absorption
edge of -Ga2O3 crystals. Luminescence spectra of #1#3 samples were measured at 15 K under excitation
above the indirect absorption edge. The results areshown in Fig. 2. The photon energy was 200 nm. A
prominent band appears at around 400 nm. A weak bandis also observed at around 340 nm. These bands wereeffectively excited in the region above the indirectabsorption edge. This feature indicates that the 340 and
400 nm bands are of intrinsic feature in -Ga2O3 crystals.
Other bands are seen in the long wavelength side of the
400 nm band. Because they were excited at the longer
wavelength side than the indirect edge, they are
attributed to extrinsic origins.
Luminescence spectra of #1-#3 samples were
measured under two-photon excitation (TPE) with
THG pulses from a Nd:YAG laser system. The TPE
luminescence spectra of #1 and #2 samples exhibitedthe 340 and 400 nm bands. The intensities of the 340

Ⅲ-2

Fig. 1. Absorption spectra of #1-#3 samples, measured
at 15 K.

Fig. 2. Luminescence spectra of #1-#3 samples,
measured at 15 K under excitation with 200 nm photons.
The intensities for #2 and #3 samples were multipliedby 10.

[1] L. Binet et al., J. Phys. Chem Solid 59 (1998) 1241.
[2] Y. Usui et al., J. Phys. Chem Solid 117 (2018) 36.
[3] K. Fukui et al., J. Synchrotron Rad. 21 (2014) 452.

63

Ⅲ02- 13 -BL3B Sciences
Ⅲ -2. Materials

BL3B

Temperature Dependence of Ce-doped CaHfO3 Crystals Synthesized by theCore Heating Method2High-melting-point oxides are frontier and attractive
materials for scintillators with higher gamma-ray
stopping power. Although the Skull-melting process iscommercial use to grow such materials, growth time
was too long to feedback the growth conditions or
parameters in the research and development phase. Thus,
we developed a novel crystal growth method, Core
Heating (CH) method. In previous research, we reported
the CH method is available for the material quick search[1, 2].
In this report, we focused on Ce-doped CaHfO3(Ce:CHO) as a first step of crystal growth of highmelting point materials by the CH method. Ce:CHO
has a melting point of 2440 °C, and higher gamma-ray
stopping power than conventional scintillators such as
Ce:(Lu,Y)2SiO5 because of the highly effective atomic
number (65).
We succeeded in growing transparent (>50%)
Ce:CHO samples by the CH method for the first time.
The use of transparent samples is expected to determine
the scintillation light output with more accuracy whencompared to non-transparent samples such as ceramics.
Optical and radio photoluminescence spectra of
Ce:CHO crystals were similar to the low transparency
Ce:CHO samples or powders. However, the light
outputs of our crystals were smaller than previous
studies with that of 4,000-5,000 photons/MeV [3,4] atroom temperature (RT).
One of the possible reasons for the low light output isthe thermal quenching of Ce3+ 5d-4f emission in
Ce:CHO at RT, so that we measured the temperaturedependence (TD) of photoluminescence (PL) spectra of
Ce:CHO at the UVSOR-III facility. TD of PL emission
for the main emission band located at ~ 400 nm wasmeasured with a CCD SPEC-10 (Roper Scientific) at
the beamline BL3B operating in a multi-bunch mode.
Additionally, the TD of PL decay times were alsomeasured under the single-bunch mode.
Figure 1 shows the TD of emission intensity for
Ce:CHO excited with 193 and 330-nm photons. Eachemission intensity was calculated by integrating theemission spectra. The TD results showed different
behavior clearly between two excitation energy; Theemission intensity for Ce:CHO excited at 193 nm
continuously increased from 150 to 300K, and decreased
above 300K.
Figure 2 shows TD of PL decay times of Ce:CHO
excited with 193 and 330-nm photons; The decay
times of Ce:CHO excited 193 nm rapidly increased at
200 and 250K, while at over 300K, the times were

Intensity (arbitary unit)

almost the same value as that at low temperature.
Meanwhile, decay times excited at 330 nm were stablefrom 10 to 250K, and gently decreased above 250K.
These results of TDs suggested (i) thermal quenchingof Ce3+ 5d-4f emission is not the main reason for the low
scintillation light yield at RT, (ii) the sample had
additional trap level(s) related to defect(s) corresponding
to 200-300K at TD of emission intensity and decay time.
Moreover, One of the possible causes for the low output
of Ce:CHO is due to such trap(s).

3

20x10

16

: ex193nm: ex330nm

12
8
4
100
200
300
Temperature [K]400Fig. 1. TD of emission intensity of Ce-doped CaHfO3
excited at 193 and 330 nm.
100

Decay time [ns]Ⅲ-2

Y. Kurashima1, S. Kurosawa1,2 and A. Yamaji1,2

Institute for Materials Research, Tohoku University, Sendai 980-8577, JapanNew Industry Creation Hatchery Center, Tohoku University, Sendai 980-8579, Japan
1

80:ex193nm:ex330nm

60
40
20
0
100

200
300
Temperature [K]400Fig. 2. TD of PL decay times of Ce-doped CaHfO3
excited at 193 and 330 nm.

[1] Y. Kurashima et al., Cryst. Growth Des. 21 (2021)
572.
[2] Y. Kurashima et al., UVSOR Activity Report 201947 (2020) 58.
[3] S. Kurosawa et al., Radiat. Meas. 56 (2013) 155.
[4] H. Chiba et al., Radiat. Meas. 90 (2016) 287.

64

Ⅲ02- 14 -BL3B

Ⅲ -2. Materials Sciences

BL3B

Temperature Dependence of Photoluminescence Properties of Cs2HfCl3Br3
S. Kodama1, S. Kurosawa2, A. Yamaji2, M. Yoshino1, T. Hanada1, S. Toyoda2, H. Sato2,
Y. Ohashi2, K. Kamada2,3, Y. Yokota1 and A. Yoshikawa1,2,3
Institute for Materials Research, Tohoku University, Sendai 980-8577, JapanNew Industry Creation Hatchery Center, Tohoku University, Senda 980-8579, Japan
3
C&A Corporation, Sendai 980-0811 Japan1

2

Intrinsic-luminescence halide scintillators with thechemical formula of A2BX6 (A: alkali metal, B:
tetravalent ion, X: halogen ion) have been reported to
exhibit the excellent scintillation performances such as
Cs2HfCl6 with the blue emission around ~400 nm [1]and Cs2HfBr6 with the emission peak at ~450 nm [2].
We developed Cs2HfI6 as the novel red-emitting
scintillator with the emission peak around ~700 nm [3].
Above studies imply the emission peak shifts towards
the longer wavelength depending on the host X ion (Cl< Br < I).
The emission mechanism of A2BX6 halides is still
unclear. To reveal the luminescence phenomena in
A2BX6 halides, the relationship of the host ions,structures and luminescence properties should beunderstood. As a first step, the halogen-mixture
compound Cs2HfCl3Br3 was studied in this study.
Cs2HfCl3Br3 crystal was grown by the vertical
Bridgman method. The crystal structure was analyzed
by the single-crystal X-ray diffraction to be cubic(space group: 𝐹𝐹𝐹𝐹3� 𝑚𝑚 ) which is the same as that ofCs2HfCl6 and Cs2HfBr6 [4]. The photoluminescence
properties were evaluated in BL3B. The temperaturedependences were measured at 10, 50, 100, 150, 200,
250, 300 and 350 K.
Figure 1 shows the photoluminescence excitationand emission spectra of Cs2HfCl3Br3. The excitationand emission spectra were illustrated as the dashed andsolid lines, respectively. At 300K, Cs2HfCl3Br3 had
two photoluminescence bands. One band with the blue
emission peak at ~435 nm was excited by ~270 nm.
The other band had the broad green emission at ~515
nm excited by 315 nm. These two photoluminescencebands stably existed at the whole temperature range.
The emission intensities of such blue- and greenemission bands gradually increased as cooled downfrom 350K to 10K. The emission peak wavelengths ofboth bands shifted towards the longer wavelengths
from 350K to 10K.
The photoluminescence emission wavelength ofCs2HfCl6, Cs2HfCl3Br3, Cs2HfBr6 were summarized inTable 1. Cs2HfCl3Br3 rather had the quite similar
emission wavelength to Cs2HfBr6 than the medium
wavelength between Cs2HfCl6 and Cs2HfBr6. Therefore,
the emission wavelength of A2BX6 halides might bedetermined by the host halogen ion X. For further study,
more crystals with the different Cr/Br ratios, Br-I
mixture and Cl-I mixture compounds are synthesized,
and the photoluminescence properties should be
evaluated.

Ⅲ-2

Fig. 1. Temperature dependence of photo-luminescence
excitation and emission spectra of Cs2HfCl3Br3.
Table 1. Photoluminescence emission peaks
Compounds
Emission wavelength at 300K
Cs2HfCl6
375nm, 440 nm [5]Cs2HfCl3Br3
435 nm, 515 nm
435nm, 525 nm [2]Cs2HfBr6[1] A. Burger et al., Appl. Phys. Lett. 107 (2015) 34.
[2] K. Saeki et al., Jpn. J. Appl. Phys. 57 (2018) 030310.
[3] S. Kodama et al., Radiat. Meas. 124 (2019) 54.
[4] S. Kodama et al., Opt. Mater. 106 (2020) 109942.
[5] K. Saeki et al., Appl. Phys. Express. 9 (2016) 042602.

65

Ⅲ02- 15 -BL3B Sciences
Ⅲ -2. Materials

BL3B

Emission Spectra of Pr-doped Y3Ga5-xZnxO12-δM. Yoshino 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 Y3Ga5O12 crystal have been measured
and changes in the spectra with doping of Zinc andhydration are examined. The samples are synthesized bysolid state reactions followed by annealing in N2-H2
atmosphere in order to reduce Pr4+ to Pr3+. The oxygen
vacancies are created in Zn-doped Y3Ga5O12 andprotons are incorporated by hydration of the vacancies.
The concentration of Pr is 0.5 mol% and that of Zn are
3, 10 and 15 mol%. The Zn-doped samples are hydrated
at 523 K in humidified N2. The emission spectra andexcitation spectra are measured at 30 K.
The emission spectra of Y3Ga5-xZnxO12-δ:Pr at 275
nm excitation are shown in Fig. 1. The sharp peaks
around 500-700 nm originate from 4f-4f transitions of
Pr3+. The emissions of 5d-4f transitions are notobserved in Zn-doped samples as in the case of
Y3Ga5O12:Pr. The emission intensities of Pr3+ increase
with 3 mol% Zn doping, but they do not increase
monotonically and decrease above 10 mol%. Figure 2
shows the excitation spectra of Pr3+ in Y3Ga5-xZnxO12-δ
at 485 nm. The host absorption band (-220 nm) and 4f5d absorption band (230-300 nm) are observed in eachsample. The absorption spectrum of Y3Ga5-xZnxO12-δ
shows that the band gap becomes smaller with theaddition of Zn. The decrease in the emission intensityof Pr3+ with Zn addition shown in Fig. 1 may relate to
the change in the energy difference between band gap
and the 4f-5d transition. Since the addition of Zn
promotes the formation of oxygen vacancies, there
should also be a contribution of the defect level in theband gap in the emission decrease. The excitation
spectrum of Y3Ga5-xZnxO12-δ:Pr (x = 0.75) at 485 nm
and 617 nm are shown in Fig. 3 and Fig. 4. The
emission changes before and after hydration are foundto be different for host and 4f-5d excitation. These
characteristic changes can be attributed to the defectlevels of oxygen vacancy and hydrogen, respectively.

Fig. 2. Excitation spectra of Y3Ga5-xZnxO12-δ:Pr. at 30 K
(λem = 485 nm).

Fig. 3. Change in the excitation spectra with hydrationin Y3Ga4.25Zn0.75O12-δ:Pr (λem = 485 nm).

Fig. 4. Change in the excitation spectra with hydrationin Y3Ga4.25Zn0.75O12-δ:Pr (λem = 617 nm).

Fig. 1. Emission spectra of Y3Ga5-xZnxO12-δ:Pr at 30 K
(λex = 275 nm).

66

Ⅲ02- 16 -BL3B

Ⅲ -2. Materials Sciences

BL3B

Optical Conductivity Spectra of a Locally Noncentrosymmetric Material
LaRh2As2
S. Kimura1,2,3, A. Goto1, J. Sichelschmidt4 and S. Khim4

Graduate School of Frontier Biosciences, Osaka University, Suita 565-0871, Japan
Department of Physics, Graduate School of Science, Osaka University, Suita 565-0871, Japan
3
Institute for Molecular Science, Okazaki 444-8585, Japan
4
Max Planck Institute for Chemical Physics of Solids, 01187 Dresden, Germany
1

2

Recently, noncentrosymmetric crystal structure andinversion symmetry breaking at crystal surfaces haveattracted attention for physical properties combinedwith spin-orbit interaction (SOI). By using the SOI and
the electric field gradient generated by the spatial
symmetry breaking, spin-polarized current originatingfrom spin-polarized bands is generated and is regarded
to be useful for spintronics applications.
The breaking of the spatial inversion symmetry also
generates a Cooper pair with a helical spin structure,
which produces a superconducting state with a highcritical field. Actually, the heavy-fermion superconductor
CePt3Si (Tc ~ 0.75 K) has an extremely high upper
critical field Hc2 as high as 5 T has been observed [1].
Recently, CeRh2As2 was discovered as a new heavy
fermion superconductor (Tc = 0.26 K) with the local
inversion symmetry breaking while overall crystal
structure remains centrosymmetric [2]. RM2X2 (R = rareearth, M = transition metals, X = Si, Ge) compounds
usually have a tetragonal ThCr2Si2-type crystal structurewith inversion symmetry (I4/mmm), CeRh2As2,
however, crystalizes in the CaBe2Ge2-type structure,
which lacks local inversion symmetry as the Ce and oneof Rh and As sites (P4/nmm) as shown in Fig. 1. This
results in a local electric field at the Ce site. Therefore,
the Ce band undergoes Rashba splitting. It is necessary
to investigate how this Rashba splitting affects theelectronic structure. In this study, we measured theoptical conductivity [σ(ω)] spectra of LaRh2As2, areference material without 4f electrons, and comparedthem with the LDA band calculations to investigate theelectronic structure without spatial inversion symmetry.
In the experiment, the vacuum-ultraviolet reflectivity
spectrum measured at BL3B was connected to theinfrared THz spectrum measured in the laboratory, andthe σ(ω) spectrum was obtained by using the KramersKronig analysis.
Figure 2 shows the experimental σ(ω) spectrum
below 1.2 eV and the calculated spectrum for interband
transitions with and without SOI. In comparing the
calculated spectrum with SOI with that without SOI,
almost no change is observed. Since the Rashba
parameter is as large as 0.1eV Å (not shown here), theRashba splitting is not effective so much to the band
structure. While, the comparison of the calculated σ(ω)
spectra of P4/nmm structure to that of I4/mmm structure,
the increase of the σ(ω) intensity below 0.8 eV suggeststhat the bands of the P4/nmm structure are clustered near
the EF. It can be seen that the calculated σ(ω) spectrumof P4/nmm explains the experimental results well. In
particular, the experimental 0.4-eV peak can be
explained by the calculation. This peak is hardly
observed in I4/mmm structure, which suggests a uniqueelectronic structure in the P4/nmm structure.

Ⅲ-2

Fig. 1. Crystal structure of RRh2As2 (R = La, Ce).

Fig. 2. Optical conductivity [σ(ω)] spectrum of
LaRh2As2 (Experiment, dotted line). The interband
transition part of the σ(ω) spectra subtracted by theDrude fitting curve is the thick line. Calculated σ(ω)
spectra with and without spin-orbit interaction are shownby red and blue lines, respectively. The calculated
spectrum with the I4/mmm crystal structure is alsoplotted as a dashed line.

[1] E. Bauer et al., Phys. Rev. Lett. 92 (2004) 027003.
[2] S. Khim et al., arXiv: 2101 (2021) 09522.

67

Ⅲ02- 17 -BL3B Sciences
Ⅲ -2. Materials

BL3B

Optical Investigation on Fluoro-olefins in Vacuum-Ultraviolet for
New Refrigerant Gas Development
K. Yamanoi1,2, Y. Sakata1, H. Iwayama3, Y. Hasumoto1,2, T. Takakuwa1,2, O. Yamamoto1, 2
and M. Noumi1, 2
1Osaka university, Suita 565-0871, JapanDAIKIN Industries Ltd, Settsu 566-8585, Japan
3
UVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan2

Ⅲ-2

Chlorofluorocarbon (CFC), hydrochlorofluorocarbon (HCFC), and hydrofluorocarbon (HFC) havebeen used as a refrigerant. These gases have highglobal warming potential (GWP) over 100. Recently,
the hydrofluoroolefin (HFO) gases are expected as
new low environmental load refrigerant due to its low
GWPs since olefin gas is unstable and easily
decompose by ultraviolet light in nature. In order to put
HFO into practical use as a refrigerant, it is necessary
to clarify the physical characteristics of HFO such as
UV absorption and decomposition process. In thisstudy, we measured the vacuum ultraviolet (VUV)
light induced decomposition of HFO.
The decomposition spectra measurements werecarried out in BL3B in UVSOR facility. C2H2F2 gas
was flowed into vacuum chamber through the capillary
tube. The pressure in vacuum chamber was kept lessthan 3x10-4 Pa. The VUV light from 12 to 30 eV was
irradiated on sample gas and the ionized molecularfragments were detected TOF-mass spectrometershown in Fig. 1.
Figure 2 shows the decomposition spectra of C2H2F2.
We could clearly observe the ionization energies ofeach fragments. The ionization threshold of C2HF2,C2H2F, C2HF, CH2F, and C2F2 were 12.8 eV, 14.2 eV,
14.4 eV, 14.8 eV, and 17 eV, respectively. From ourprevious results, the C2H2F2 has the absorption from
135 nm (9.2 eV) to190 nm (6.5 eV) as shown in Fig. 3.
The absorption at 145 nm is attributed to the stretching
and twisting of carbon double band and the 190 nm is
the transition from π to π* in C=C bonds, respectively[1]. However the ionization threshold is quite higher
than these absorption.
In conclusion, we could observe the optical properties
and ionization energy of decomposition process of
C2H2F2 in VUV region. The results let us know the UVor VUV-induced decomposition dynamics of fluoroolefins as refrigerant in next-generation.

nozzleelectron detector

Beam

ion detector

Fig. 1. Schematic image of the experimental setup in
BL3B.

Fig. 2. Decomposition spectra of C2H2F2

Fig. 3. Absorption spectrum of C2H2F2.
[1] G. Belange et al., J. Chem. Phy 55 (1971) 2055.

68

Ⅲ02- 18 -BL3B

Ⅲ -2. Materials Sciences

BL3B

Absorption Bands of Tl+ Centers in KCaCl3 and CsCaCl3 Crystals
T. Kawai and K. Kubota

Graduate School of Science, Osaka Prefecture University, Sakai 599-8531, JapanTl+ centers in alkali halide crystals exhibit the
optical bands called A, B, and C, which are attributed
to intra-ionic transitions from the 1A1g ground state to
the 1T1u, 3T2u +3Eu, and 3T1u excited states, receptively[1-3]. Though the optical properties of the Tl+ centersin alkali halide crystals have been studied for a longtime, there have been few reports on the Tl+ centers in
ternary halide compounds, which recently have an
attracted attention as host crystals of new scintillator
materials [4,5]. In this study, we focused on Tl+ centersin ternary halide crystals of KCaCl3 and CsCaCl3.
KCaCl3:Tl+ and CsCaCl3:Tl+ crystals were grown by
the Bridgman method from the starting material
powders. The optical measurements were performed at
low temperatures at the BL3B line of UVSOR.
Figure 1 shows the absorption spectra of (a)KCaCl3:Tl+ and (b) CsCaCl3:Tl+ crystals at 10K. The
several absorption bands are observed in the transparent
energy region below the respective fundamental
absorption edge. These absorption bands exhibit nosimple Gaussian shape.
Owing to the dynamical Jahn-Teller effect, the A andC bands of the Tl+ centers in alkali halide crystals often
exhibit the double or triple structures, respectively [1-3].
We resolved the absorption bands observed in
KCaCl3:Tl+ and CsCaCl3:Tl+ into two or three Gaussian
shapes. As shown by thin curves in Fig.1, the absorption
bands located around 5.4 eV for KCaCl3:Tl+, and 5.6 eV
for CsCaCl3:Tl+ can be resolved into two Gaussian
shapes. The intense absorption bands around 6.8 eV for
KCaCl3:Tl+, and 7.1 eV for CsCaCl3:Tl+ can be resolved
into three Gaussian shapes. Thus, the absorption bands
at 5.4 eV for KCaCl3:Tl+, and 5.6 eV for CsCaCl3:Tl+
are assigned to the A band of the Tl+ centers, and theabsorption bands at 6.8 eV for for KCaCl3:Tl+, and 7.1
eV for CsCaCl3:Tl+ are assigned to the C band of the Tl+
centers. Furthermore, a small absorption band isobserved at 6.4 eV in KCaCl3:Tl+ and the shoulder
structure is observed at 6.6 eV in CsCaCl3:Tl+. The
absorption band and the shoulder structure are assigned
to the B band of the Tl+ centers.
On the basis of a theoretical treatment for the Tl+
centers [1-3], the relative positions of the absorption
bands and their relative intensity ratios are determinedby the Coulomb energy F, the exchange energy G
between the s- and p-electron, the spin-orbit interactionenergy ξ of the p-electron and the King-Van Vleck factor
λ, which account for the differences between the radial
wave functions of the p-electron in the triplet and singlet
states. These parameters F, G, ξ and λ can be evaluatedfrom the energy positions of the center of the A, B andC absorption bands and the dipole strength ratio R of the
C to A bands. These parameters characterizing the Tl+
centers were estimated by analyzing our experimental

data, as shown in Table I. In the same Table, similar data
for the Tl+ centers doped in alkali chloride crystals arealso presented. From a comparison of these values, it isfound that our assignment of the absorption bands
observed in the KCaCl3:Tl+ and CsCaCl3:Tl+ crystals is
reasonable.

Optical Density (arb. units)

240

5.0

220

Wavelength (nm)200(a) KCaCl3:Tl
10 K

180

C

+

Ⅲ-2

A
B
(b) CsCaCl3:Tl+
10 K

C

A
B
5.5

6.0
6.5
Photon Energy (eV)

7.0

7.5

Fig. 1. Absorption spectra of (a) KCaCl3:Tl+ and (b)CsCaCl3:Tl+ crystals at 10K. The thin curves represent
Gaussian components decomposing the absorption
bands.
Table 1. Parameters characterizing the Tl+ centers.
Except for λ, all parameters are in eV.
F
G
ζ
λ
Ref.
Crystals
KCaCl3:Tl+ 5.9 0.25 0.72 1.2
CsCaCl3:Tl+ 6.1 0.31 0.83 0.89
NaCl:Tl+
5.7 0.26 0.66 1.1[1]
KCl:Tl+5.7 0.28 0.7
0.99 [1][1] A. Fukuda, Sci. Light (Tokyo) 13 (1964) 64.
[2] A. Ranfagni, et al., Advance in Physics 32 (1983)
823.
[3] P.W.M.Jacobs, J. Phys. Chem. Solids 52 (1991) 35.
[4] M. Tyagi, et al., J. Appl. Phys. 113 (2013) 203504.
[5] N.V. Rebrova, et al., J. Lumin. 182 (2017) 172.

69

Ⅲ02- 19 -BL3B Sciences
Ⅲ -2. Materials

BL3B

Influence of Crystal Structures of CsCaI3:Tl+ and Cs4CaI6:Tl+
on Absorption Bands
S. Ito and T. Kawai

Graduate School of science, Osaka Prefecture University, Sakai 599-8531, Japan

Ⅲ-2

Thallium impurity centers in alkali halides, which arebinary compounds, have been extensively investigated[1]. However, thallium impurity centers in ternarycompounds, which have attracted attention as scintillator
materials, have been less reported. In this study, weinvestigated absorption bands of CsCaI3:Tl+ andCs4CaI6:Tl+.
The single crystals of CsCaI3:Tl+ and Cs4CaI6:Tl+
were prepared by a cell method [2]. The quartz-cellswith the narrow gap are made of a pair of two quartz
plates. The melt of the staring materials was percolated
into the gap of the quartz-cells through capillary action
and thin crystals were grown in the gap by natural
cooling.
Figure 1 shows the absorption spectra of CsCaI3: Tl+and non-doped CsCaI3 crystals. In the non-doped
CsCaI3 crystal, no absorption bands are observed in theenergy region below the fundamental absorption edgeof 5.7 eV. On the other hand, the three absorption
bands are observed in CsCaI3:Tl+.
Figure 2 shows the absorption spectrum of Cs4CaI6:Tl+
crystals. The five absorption bands are observed in
Cs4CaI6:Tl+. That is to say, the appearance of theabsorption bands of Cs4CaI6:Tl+ is complicated thanthose of CsCaI3:Tl+.
In both crystals, the Tl+ ions replaced the Cs+ ionsbecause of the equal valance of both ions. Thus, thenearest neighbor ion of the Tl+ ion is iodide ions. In
CsCaI3:Tl+, the Tl+ ion is surrounded with a distorted
square antiprism geometry by eight iodide ions [3]. In
Cs4CaI6:Tl+, on the other hand, there are two types of
Tl+-occupied sites: one with a distorted square antiprism
geometry and another with a trigonal prism geometry. In
the site with the trigonal prism geometry, the Tl+ ion issurrounded by six iodide ions [4]. The Tl+ ions occupied
two types of sites exhibit the diverse absorption bands.
Thus, the appearance of the absorption bands of
Cs4CaI6:Tl+ becomes complex as against those of
CsCaI3:Tl+.
In the case of the Tl+ centers in alkali halides, theabsorption bands often exhibit the double or triple
structures due to the Jahn-Teller effect. The double or
triple structures due to the Jahn-Teller effect become
conspicuous with increasing temperature. The bandshape of the absorption bands in Cs4CaI6:Tl+ may beseen as the double structures. However, the bandshape of the absorption bands in Cs4CaI6:Tl+ did not
become conspicuous with increasing temperature.
Thus, the complicated absorption bands in Cs4CaI6:Tl+
do not come from the Jahn-Teller effect.

Fig. 1. Absorption Spectrum of CsCaI3:Tl+ at 10K.
Insert shows an absorption spectrum of non-doped
CsCaI3 at 25K.

Fig. 2. Absorption Spectrum of Cs4CaI6:Tl+ at 10K[1] A. Ranfagni, et al., Advances in Physics, 32 (1983)
823[2] S. Hashimoto and M. Itoh, Jpn. J. Appl. Phys. 27(1988) 726.
[3] M. Tyagi, et al., J. Appl. Phys. 113 (2013) 203504.
[4] L. Stand, et al., J. Cryst. Growth, 486 (2018) 162.

70

Ⅲ02- 20 -BL3B

Ⅲ -2. Materials Sciences

BL3B

Photoluminescence and Scintillation of CsCl-based Ternary Crystals
1

M. Koshimizu1, K. Takahashi1, 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, Japan

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,CsCl-based compounds have an advantage of longemission wavelength appropriate for detection with aphotomultiplier tube. Thus far, we have developed fast
scintillators based on ternary CsCl-based compounds[1-2]. In this report, we present some results on thephotoluminescence properties with VUV excitationand scintillation properties of several CsCl-based
ternary compounds.
Crystal samples of the ternary CsCl-based
compounds were fabricated using a self-seeding
solidification method and the Bridgman method. Raw
materials were mixed in a stoichiometric ratio. The
mixed powders were poured into quartz ampoules andheated at 350 °C in vacuum for 1 day to remove
adsorbed water. For the self-seeding solidification
method, the quartz ampoule was set in a tubular
furnace, and the furnace was heated to 950 °C for 12 hand subsequently cooled to room temperature over 72
h. For the Bridgman method, the ampoule was set in a
Bridgman furnace. The temperatures of the upper andlower heaters in the furnace were set at 950 °C and
750 °C, respectively, during crystal growth, and theampoules were lowered at a rate of 1.5 mm/h.
The luminescence properties were characterizedwith vacuum ultraviolet (VUV) light as an excitation
source. Measurements were performed at BL3B for
temporal profiles at the UVSOR facility at the Institutefor Molecular Science, Japan, using a time-correlated
single photon counting.
Photoluminescence temporal profiles of the CsClbased ternary compounds are presented in Fig. 1. The
excitation wavelength was 84 nm, whose photon energy
corresponds to the excitation from the outermost corelevel to the bottom of the conduction band. The
emission wavelengths correspond to the emission peak
whose excitation spectra have a step at around 84 nm,
which strongly suggests that the emission is owing to
the AFL. The decay behavior shown in Fig. 1 was fittedwith an exponential decay function. The decay time
constants were 0.8 – 1.2 ns, which are typical for the AFL.
Scintillation temporal profiles of the CsCl-based ternarycompounds are presented in Fig. 2. The decay behavior
is similar to those of the photoluminescence, whichindicates that the scintillation of these compounds ismainly of AFL.

Ⅲ-2

Fig. 1. Photoluminescence temporal profiles of CsClbased ternary compounds.

Fig. 2 Scintillation temporal profiles of CsCl-based
ternary compounds.

[1] K. Takahashi et al., Jpn. J. Appl. Phys. 59 (2020)
032003.
[2] K. Takahashi et al., Jpn. J. Appl. Phys. 59 (2020)
072002.

71

Ⅲ02- 21 -BL4U Sciences
Ⅲ -2. Materials

BL4U

Microscopic Evidence of Complex Cobalt Oxides Electrodeposited on
Graphene Window
C. H. Chuang1, J.-J. Velasco Velez2, Yi-Ying Chin3, W. F. Pong1, T. Ohigashi4 and N. Kosugi4
Department of Physics, Tamkang University, Tamsui 251, Taiwan
2Max Planck Institute for Chemical Energy Conversion, M𝑢𝑢� lheim 45470, Germany
3
Department of Physics, National Chung Cheng University, Chiayi 62102, Taiwan
4
UVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan1

Ⅲ-2

2p–Co 4s state are located at the broad peak at PE of
538.9 eV [6].
In Fig. 1(e), the multiple features of the Co XA spectraat the L3- and L2-edges were divided into two regions(774–781 eV and 789–795 eV), which are involved by
the oxidation state, crystal field splitting, and low/highspin states of Co 3d [6]. Our theoretical simulation
indicated three components (Metal Co0, Oct. symmetricalCo2+, and Oct. symmetrical Co3+ species) existed inregion 1, 2, and 3, depending on the linear combinationof three reference spectra through the lowest deviation
between the experimental and fit data. The curve-fitting
statistics reflects the increasing metal Co0 and Oct. Co2+
state by the elimination of Oct. Co3+ state for the mixing
state of Co NPs in region of 1, 2, and 3.
Through STXM, the multiple carbonyl-like states (C–OH, HO–C=O, and O–C(O)–O/C=O) and multiple Co
states (Co0, Co2+, and Co3+) were found on the surface.
Our chemical mapping evidence signified the bonding
tendency of graphene and de-oxidation stages of Co-NPs,
which accounts for the synergistic reason of Co-basedenergy materials.

The X-ray-in (electron-in) and electron-out techniques[1,2] using the surface-sensitive analysis are quite
important for the electrochemical interface. Graphene as
an early example of two-dimensional materials has been
received a lot of attentions i.e. a promising use of window
membrane, because of the remarkable points (such as
vacuum-liquid environment separation, thinnest
thickness, and X-ray/electron transparency). Studies foran essential role of graphene-based working electrode arestill missing in the wide-range applications due to thedifficulties in solid-liquid phase and nanoscale-resolved
approaching. The electrocatalytic project is one ofinterests of energy materials; thus, the critical factor anddiverse function are devoted for the heterogeneous
system owing to the interface correlation.
In the work, we have investigated various oxidation
states of electrodeposited Co and underlying graphene
window by using scanning transmission X-ray
microscopy (STXM) at BL4U. The electronic structure
and bonding configuration of electrodeposited Co layer
were studied to solve the answer of the catalytic synergyof oxygen evolution reaction. The electrochemical
reduction and deposition of the aqueous Co2+ ions wereformed on the graphene electrode through the cathodic
electron reduction in the CoSO4 solution. Diverse lattice
structures of cobalt nanoparticles (Co-NPs) grown on thegraphene electrode were characterized throughtransmission electron microscopy (TEM) measurement,
shown in Fig. 1(a)~(c). High-magnified TEM images
highlights the local region (green squares) of Co-NPs forthe ordered particle size ranging from 5 to 10 nm for the
initial stage and the amorphous structure for the later andthick stage. The inset images of Fig. 1(d)~(f) were taken
at the pre-edge energy to observe the background images,
which consistent with the same area of TEM image. The
X-ray absorption (XA) spectra at C K-edge in Fig. 1(d)show absorption peaks at photon energies (PEs) of 284.9,
286.6, 288.4, 290.2, and 292.5 eV, which are known for
π*(C=C), π*(C–OH), π*(C=O in HO–C=O) or defect,
π*(O–C(O)–O or C=O at the edge), and σ*(C=C) bonds[3,4]. The spectral evidences between region 1, 2, and 3
reflect the oxidation evolution of graphene with afunction of Co NPs thickness. The XA spectra at O Kedge in Fig. 1(e) indicate three π* resonances (530.8,
532.4, and 534.0 eV) and two σ* resonances (536.8 and538.9 eV), corresponding to the oxidation states of thegraphene electrode and the electrodeposited Co-NPs [4,5].
The hybridized O 2p-Co 3d states [6] are located at two
peaks at PEs of 532.4 and 534.0 eV, and the hybridized O

Fig. 1 (a)–(c) High-resolution TEM images ofelectrodeposited Co–graphene membranes. (d)–(f)Selected areas of the XA spectra of the C K-edge, O Kedge, and Co L-edge and the corresponding averaged
areas (insets) of the element maps.
[1] D. Waldmann et al., ACS Nano 7 (2013) 4441.
[2] M. Krueger et al., ACS Nano 5 (2011) 10047.
[3] Y. Wang et al., Sci. Rep. 5 (2015) 15439.
[4] L. R. De Jesus et al., J. Phys. Chem. Lett. 4 (2013) 3144.
[5] J. G. Zhou et al., J. Mater. Chem. 21 (2011) 14622.
[6] J. Wang et al., Energy Environ. Sci. 6 (2013) 926.

72

Ⅲ02- 22 -BL5U

Ⅲ -2. Materials Sciences

BL5U

High-resolution ARPES Study of Topological Dirac-semimetal Candidates
D. Takane1, Y. Kubota1, K. Nakayama1,2, S. Souma3,4, K. Sugawara1,2,3,4, T. Takahashi1,3,4,
K. Segawa5 and T. Sato1,3,4

Department of Physics, Tohoku University, Sendai 980-8578, Japan
Precursory Research for Embryonic Science and Technology (PRESTO), Japan Science and Technology Agency(JST), Tokyo 102-0076, 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
5
Department of Physics, Kyoto Sangyo University, Kyoto 603-8555 Japan1

2

The search for novel fermions, which has long been
an important research target in elementary-particle
physics, is recently becoming an exciting challenge incondensed-matter physics, as highlighted by thediscovery of two-dimensional (2D) Dirac fermions ingraphene and helical Dirac fermions at the surface of
three-dimensional (3D) topological insulators. The
recent discovery of 3D topological Dirac semimetals(TDSs) that host massless Dirac fermions further
enriches the category of exotic fermions. TDSs show
exotic quantum phenomena such as high carrier
mobility and giant linear magnetoresistance governedby the linearly dispersive Dirac-cone energy band.
Also, TDS can be switched to other novel topologicalphases, e.g., by breaking the time-reversal/crystalline
symmetry or by chemical substitution. Therefore, TDS
provides a fertile playground for realizing a variety of
topological phases. However, despite many theoreticalpredictions for TDS candidates, TDSs that have been
experimentally verified are still rare. In addition, wellknown TDSs, Na3Bi and Cd3As2 [1-3], are not well
suited for the physical-property measurements anddevice applications because Na3Bi is extremely activein the air and there exists a critical controversy
between experiments and theories in Cd3As2 on the
Dirac-cone states. Thus, it is highly desirable toexplore new TDS materials that overcome suchdifficulties.
It was recently predicted that BaMg2Bi2 is a TDS [4].
In BaMg2Bi2, Ba atoms can be easily replaced withother elements, so this system seems suitable formanipulating topological and physical properties. In
this study, we performed high-resolution angle-resolved
photoemission spectroscopy (ARPES) of BaMg2Bi2.
By utilizing energy tunable photons, we mapped out
the band structure over the entire 3D Brillouin zone
[Fig. 1(a)] to search for the Dirac-cone band dispersions.
High-quality single crystals of BaMg2Bi2 weresynthesized by the self-flux method. ARPES
measurements were performed with micro-focused
VUV synchrotron light at BL5U. Samples were cleaved
in situ along the (0001) plane of the hexagonal crystal inan ultrahigh vacuum.
Figure 1(b) shows the 2D ARPES intensity plot at
EF measured at kz ~ 0, where the presence of Diraccone bands is predicted by the band calculations. One

can find a circular Fermi surface centered at the Γ point.
This Fermi surface originates from the EF crossing ofa holelike band that shows linear dispersions, as seenfrom Fig. 1(c). We doped electrons to the crystal
surface by alkaline-metal deposition and searched fora predicted point touching between the valence andconduction bands due to the Dirac-cone bandformation. The present study lays the foundation forunderstanding the topological property of BaMg2Bi2.

Fig. 1. (a) 3D bulk Brilloiun zone of BaMg2Bi2. (b)ARPES intensity at EF plotted as a function of 2D wave
vector. (c) ARPES-intensity plot measured along a
momentum cut crossing the Γ point.

[1] Z. K. Liu et al., Science 343 (2014) 864.
[2] M. Neupane et al., Nat. Commun. 5 (2014) 3786.
[3] Z. K. Liu et al., Nat. Mater. 13 (2014) 677.
[4] Z. Zhang et al., J. Phys. Chem. Lett. 9 (2018) 6224.

73

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BL5U Sciences
Ⅲ -2. Materials

BL5U, BL7U

Determination of Contribution of Atomic Orbital to the Valence Band in SnS

Ⅲ-2

I. Suzuki1, S. Kawanishi1, L. Zexin1, T. Omata1 and S. Tanaka2

Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai 980-8577, Japan2
The institute of Scientific and Industrial Research, Osaka Univ., Ibaraki 567-0047, Japan
101
100

10-1
10-2
10-3
10-4
0

Sn 5p

S 3p

S 3s
Sn 5s
60 eV

Photoionization
cross-section / 106 barn

SnS is a compound semiconductor with a band gapof ~1.2 eV, which is expected as an novel absorbermaterial for the thin-film solar cells due to being
composed of abundant and safe elements. Therefore,
SnS solar cells have been actively studied for decades,
whereas there has been limited experimental studies on
the electronic structures of SnS. Since the electronic
structure at the band edge is largely responsible for the
optical and electrical properties of the material, it isimportant to understand them by experimental approach
as well as by the theoretical analysis considering its
application to the optoelectronic devices. In this study,
we have experimentally determined the contribution of
atomic orbital to the valence band using difference ofeach atomic orbital in the photoionization cross section(Fig. 1).
The electronic structure of the valence band of SnS
was observed by high-resolution angle-resolved
photoemission spectroscopy (ARPES) at BL5U and
BL7U. Single crystalline Br-doped SnS grown by flux
method [1] were subjected to the measurement after
being cleaved in the measurement chamber prior to themeasurement. First-principles calculations of theelectronic structure of SnS were performed using the
Quantum Espresso package.
Figure 2 shows the band dispersion in the Γ-Z
direction measured with excitation energies of 60 eV(BL7U) and 21 eV (BL5U). It is indicated that thevalence band maximum (VBM) is located at a k-point
slight offset from the Z-point to Γ-point as reported in
the previous first-principles calculations [2]. The
relative intensity of each band differs depending on the
excitation energies. For a simple comparison, Fig. 3(a)shows the energy distribution curve, which integrated
over the whole wavenumber space, where the intensity
was normalized at –4 eV. The valence band iscomposed of three major bands (Band I, II and III),
which is well reproduced in the partial density of states(PDOS) obtained by first-principles calculation (Fig.
3(b)). In the measurement with excitation energy of 21eV, the intensities of band I and III were obviously
lower than those of 60 eV. Since the photoionization
cross section is small only for Sn 5s at 21 eV comparedto other atomic orbitals (Fig. 1), it is suggested that Sn
5s orbital strongly contributes to the band I and II. Thisis well consistent with the calculated PDOS. In
conclusion, it is experimentally clearly shown that the
VBM is mainly composed of Sn 5s orbitals.

21 eV

1

20
40
60
80
Photon energy / eV

100

Fig. 1. Photoionization cross-section of each atomic
orbital in SnS [3].

Fig. 2. E-k plot of SnS measured with an excitationenergy of (a) 21 eV and (b) 60 eV. The while arrows in
the figures indicate the location of the VBM.
(a)

(b)
I

II

III

Fig. 3. (a) EDC and (b) PDOS plots of the SnS.
[1] S. Kawanishi et al., Cryst. Growth Des. 20 (2020) 5931.
[2] J. Vidal et al., Appl. Phys. Lett. 100 (2012) 032104.
[3] J. J. Yeh et al., At. Data Nucl. Data Tables 32 (1985) 1.

74

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Ⅲ -2. Materials Sciences

BL5U

Band Dispersion Unique to the Cobalt Intercalation in theNoncentrosymmetric Antiferromagnet CoNb3S6
H. Tanaka1, S. Okazaki2, K. Kuroda1, S. Ideta3, K. Tanaka3, T. Sasagawa2 and T. Kondo1
Institute for Solid State Physics, The University of Tokyo, Kashiwa 277-8581, Japan
Materials and Structure Laboratory, Tokyo Institute of Technology, Yokohama 226-8503, Japan
3
UVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
1

2

CoNb3S6 is a transition metal dichalcogenide NbS2
with cobalt intercalation. Neutron scattering experiments
have revealed that intercalated Co atoms emerge
collinear antiferromagnetic structure along in-plane
direction [1]. Furthermore, weak ferromagnetism
along out-of-plane direction and anomalous Hall effecthave been observed recently [2]. However, theanomalous Hall response is giant even though theferromagnetic moments are weak, and the mechanismof this giant anomalous Hall effect has been undiscovered.
We studied the electronic structure of CoNb3S6 bycomparing with that of NbS2 without the intercalation.
Single crystals of CoNb3S6 and NbS2 were synthesizedby chemical vapor transport method. Angle-resolved
photoemission spectroscopy (ARPES) measurements
using the vacuum ultraviolet (VUV) light were
performed at BL5U of UVSOR. We used the 120 eV
photons, and the energy resolution was 45 meV. The
measurement temperature was kept at 20 K, lower thanTN ~ 28 K. All samples were cleaved in situ along the(001) direction at an ultrahigh vacuum of 4.0 x 10-9 Pa.
Figure 1(a) shows Fermi surfaces of NbS2 andCoNb3S6. NbS2 has pockets around the Γ and K points.
These pockets are hole pockets, as revealed in Fig. 1(b)left panel. These dispersions were also observed in theband dispersion of CoNb3S6, as highlighted by pinkdashed rectangles in Fig. 1(b). In CoNb3S6, thesedispersions were shifted down, because of the electron
doping from Co cations. This band shift is also
observed as a smaller hole pocket around the Γ pointin CoNb3S6 [Fig. 2]. Furthermore, an additional band
dispersion appeared near the Fermi level [blue dashedrectangles in Fig. 1(b) right panel]. This dispersion
seems to come from Co atoms, because such a band
dispersion does not exist in NbS2, even if the band shift
is considered. The additional band dispersion ofintercalated atoms crossing the Fermi level is notreported in the ARPES study of CrNb3S6 [3], which
has the same crystal structure as CoNb3S6. Therefore,
we conclude that this electronic structure is unique tothe cobalt intercalation, and possibly responsible forthe particularly large anomalous Hall effect of
CoNb3S6.

Ⅲ-2

Fig. 1. VUV-ARPES measurements of NbS2 andCoNb3S6. (a) Fermi surfaces of NbS2 and CoNb3S6.
Solid and dashed hexagons represent the Brillouinzones of NbS2 and CoNb3S6, respectively. (b) Banddispersion along the ky direction [black arrows in (a)].

Fig. 2 Momentum distribution curves (MDCs) of NbS2
(pink) and CoNb3S6 (light blue) along the ky direction at
the Fermi level. Spectrum peaks corresponding to thehole pocket around the Γ point are label by A and A’.

[1] S. S. P. Parkin, et al., J. Phys. C: Solid State Phys.
16 (1983) 2765.
[2] N. J. Ghimire et al., Nat. Commun. 9 (2018) 3280.
[3] N. Sirica et al., Phys. Rev. B 94 (2016) 075141.

75

Ⅲ02- 25 -BL5U Sciences
Ⅲ -2. Materials

BL5U

Orbital-resolved 3d Band Structure of Fe Layers
1

J. Okabayashi1, K. Tanaka2 and S. Mitani3

Research Center for Spectrochemistry, The University of Tokyo, Tokyo 113-0033, JapanUVSOR Synchrotron Facility, Institute of Molecular Science, Okazaki 444-8585, Japan
3
National Institute for Materials Science, Tsukuba 305-0047, Japan2

Ⅲ-2

polarization enhances the yz and zx orbitals, respectively.
Figures 1(a) and 1(b) show the energy-momentum Ek curves in ARPES using p- and s-polarized beams,
respectively, with different momentum points along ΓΔ-H symmetric line. At the Γpoint, specific feature is
obtained such as parabolic band from the energy of 0.2
eV. The states near the Fermi level (EF) appear in the Δline, which is enhanced in p-polarization and 3z2-r2
orbital contributes to the crossing of the EF. In Fig. 1(b),the dispersion feature is different. Specific features of
the changes of dispersion curvatures are explained by
the DFT calculation results as the spin majority- andminority-band mixing. These will be resolved by spinresolved ARPES. Therefore, the E-kx-ky threedimensional detection of band dispersions for Fe bulk isachieved, which brings the future developments forhigh-quality crystal growth and spin detector for spinresolved ARPES system.
This work was partly supported by KAKENHI
Kiban(S) and Toyota-Riken projects.

Iron-based materials have been widely investigated
for the practical uses and fundamental science. For the
spintronics device applications, Fe-based alloys facing
on other materials have a high potential for producing
functional properties such as perpendicular magnetic
anisotropy derived from the symmetry broken spinorbit effects at the film interfaces. On the other hand,clean Fe surface is required for the development of thespin- and angle-solved photoemission spectroscopy(ARPES) system as a target material of spin detector
using very-low energy electron diffraction. In order todevelop the researches and applications, a fundamental
knowledge about the fundamental Fe 3d orbital-resolved
band structures is necessary.
Density-functional-theory (DFT) calculation in the
bcc Fe bulk exhibits the band dispersions along the ΓΔ-H symmetric line in Fe [001] direction [1,2]. The
dispersion in the Δ1 band is well known as a fully spinpolarized band which corresponds to the coherent
tunneling phenomena in tunneling magnetoresistancedevices. However, there are few reports detecting theband dispersions directly with orbital resolutions in
ARPES. In these motivations, we aim to access thelinear polarization dependence in ARPES to detect theorbital-resolved 3d states in Fe which is comparablewith the band-structure calculation in the momentum
space.
Sample was prepared on MgO (001) substrate using
Fe electron-beam evaporation. The MgO substrate wascleaned by annealing at 800 °C. Then, after cooling toroom temperature, Fe was deposited in the growth rateof 0.015 nm/min to 100-nm thickness. Post-annealing
at 800 °C was performed to obtain clear LEED pattern.
After the sample was introduced from the air condition,
the sample surface was cleaned by Ar-ion sputtering to
remove the oxide contamination and by annealing at
800 °C.
ARPES was performed at BL5U, UVSOR, where
photoemission chamber is connected to the sample
preparation chamber. The measurement conditions wereset at 15 meV energy resolution and 10 K. Linear
polarized beams of s- and p-polarization were used todetect the orbital symmetry. We employ the photon
energy of 60 eV to enhance the Fe 3d photo-ionization
cross section, where the Γ-H line is scanned by the
angular mode of ±15°.
For the Fe 3d states, s- and p-polarized beams(vertical and horizontal) probe the wave functions in
odd (xy, yz) and even symmetry (zx, x2-y2, z2) along themirror plane, respectively [3]. Considering the effect of
matrix element in photoemission process, s- and p-

Fig. 1. Polarization dependent APRES images of 100nm thick Fe film taken at 60 eV for (a) p-polarizationand (b) s-polarization. Each image consists of energy
and in-plane momentum. Another in-plane axis isshown in other panel along Γ-H line in the bcc Brillouinzone.
[1] J. Schafer et al., Phys. Rev. B 72 (2005) 155115.
[2] M.Dabrowski et al., Phys. Rev. Lett. 113 (2014)
067203.
[3] Y. Zhang et al., Phys. Rev. B 83 (2011) 054510.

76

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Ⅲ -2. Materials Sciences

BL5U

Angle-resolved Photoemission Study of i-MAX Phase Compound(Mo2/3Ho1/3)2AlC2
1

T. Ito1,2, K. Furuta2, D. Pinek3, M. Nakatake4, S. Ideta5, K. Tanaka5 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, JapanMAX phase compounds, i.e., Mn+1AXn where M is atransition metal, A belongs to groups 13-16 and X is the
C or N element, have recently been attracted muchattention due to their possible application for new classof two-dimensional systems called MXenes byremoving A atoms [1]. Among MAX phases, RE-iMAX phase (RE = rare earth), with the general formula(M2/3RE1/3)2AC, was recently synthesized system where
the emergence of magnetic phase transition has beenreported [2]. In this study, we have performed angleresolved photoemission spectroscopy (ARPES) on REi-MAX phase compound (Mo2/3Ho1/3)2AlC (TN = 7.8 K)
to directly investigate the electronic structure of thissystem, especially the role of 4f electrons on its physicalproperties.
ARPES measurements were performed at the
UVSOR-III BL5U. Data were acquired at T = 20 K
with hν = 96 eV and 83 eV. It should be noted that themeasured axis is defined on the (001)-projectedsurface hexagonal Brillouin zone (BZ) (Fig. 1(c)).

Ⅲ-2

Fig. 1. (a,b) Wide valence band ARPES image along―――――ΓΚΜ line (a) and AIPES spectrum (b) of (Mo2/3
Ho1/3)2AlC acquired with hv = 96 eV. Blue and green
vertical bars indicate Ho3+ final state multiplets of bulk
and surface states, respectively [3]. (c) The monoclinic
C2/c BZ of (Mo2/3Ho1/3)2AlC in the extended zone
scheme. Red lines are ΓF and ΓXY lines. Orange shaded
area is projected surface hexagonal BZ.

―――――

Figure 1(a) show the ARPES image along the ΓΚΜline of (Mo2/3Ho1/3)2AlC at the wide valence band region.
PES spectrum obtained by integrating the ARPES
intensity over the whole kx region is shown in Fig. 1(b).
It has been found that the electronic structure of(Mo2/3Ho1/3)2AlC is characterized by the non- dispersive
bands at the high binding energy of 4-13 eV and thehighly-dispersive bands near the Fermi level (EF),respectively. Since the relative energy positions andintensities of the former are similar with the calculated
Ho3+ final state multiplets when taking account of thebulk and surface components, the former can be
attributed to the localized Ho 4f states.
Figures 2(a) and (b) show the band structure near EF―――

Fig. 2. (a,b) ARPES image of the dispersive features
along ΓM (a) and ΓΚM line (b) of (Mo2/3Ho1/3)2 AlC
acquired with hv = 83 eV. The white lines in Fig. 2(a)and (b) are DFT+U calculations (U = 3 eV) along theΓFZ and ΓXY lines on the bulk BZ, respectively.

―――――along the ΓΜ and ΓΚΜ lines, respectively. Clear
dispersive features matching with the BZ symmetry
have been observed clearly. From the comparison withDFT+U calculation (U = 3 eV) along the ΓFZ and ΓXYlines, we have found that the observed dispersive
features were mostly well reproduced by thecalculation. To pursue into the characteristic propertiesof this system, further studies across the magnetic
phase transition are intended.

[1] M. Barsoum, MAX phases (Wiley, Weinheim 2013).
[2] Q. Tao, et al., Chem. Mater. 31 (2019) 2476.
[3] J.K. Kang et al., J. Phys. F:Met. Phys. 11 (1981) 121.

77

Ⅲ02- 27 -BL5U Sciences
Ⅲ -2. Materials

BL5U

Change of Fermi Surface Topology in NdFeAs1-xPxO0.9F0.1 Observed byAngle-Resolved Photoemission Spectroscopy
S. Miyasaka1, N. Katayama1, K. Yoshino1, Z. H. Tin1, 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

Since the discovery of iron-based superconductors(IBSs), many experimental and theoretical studies havebeen performed, but the superconducting mechanism of
this system has not yet been clarified. The IBSs are
multiband systems with several two-dimensional Fermi
surfaces (FSs). In this work, we have studied the change
of FS topology by P-doping in NdFeAs1-xPxO0.9F0.1 byangle-resolved photoemission spectroscopy (ARPES).
The present system NdFeAs1-xPxO0.9F0.1 is one offamous IBSs, where P doping induces the change of
local crystal structure around Fe site concomitantly withthe gradual decrease of critical temperature Tc from 55
K (x=0) to 4 K (x=1.0) [1,2].
In the present work, we synthesized the single
crystals of NdFeAs1-xPxO0.9F0.1 with various P
concentration xs using high pressure technique. The
ARPES measurements have been performed in BL5U
at Institute of Molecular Science. We have measured
ARPES spectra using P- and S-polarization geometries
of incident beam to clarify the orbital characters of FSs
and electronic bands.
Figure 1 shows the in-plane FS mapping for x=0, 0.2,
0.4, and 0.6. We observed several FSs around Brillouinzone (BZ) center (kx=ky=0) and zone corner (kx=ky=π).
In this work, we focused the FSs around BZ center. All
samples have a large hole FS around BZ center, which
is observed in P-polarization and has 3z2-r2 character.
In addition, the middle hole FS with xz/yz character isobserved in S-polarization in all P concentrations.
Only in x=0.4 and 0.6, the additional FS with small
size appears.
We have carefully measured polarization dependenceof hole bands at BZ center. Figure 2 shows theschematic band dispersions and their orbital charactersaround BZ center for each P concentration samples.
Below Fermi level, we have observed the xy band, andthis band has shifted down with increasing P content.
On the other hand, the most inner xz/yz band shifts up
with increasing x, and this band makes FS above x=0.4.
This band shows anomalous feature that the orbital
character is xy at band top and xz/yz in other parts. In
addition, the present results of polarization dependenceshow the P-doping-induced change of orbital characterin the inner and middle hole bands from xz/yz to(xz+yz)/(xz-yz), as shown in Fig. 2.

Fig. 1. In plane ARPES intensity mapping for (a, b)x=0, (c, d) x=0.2, (e, f) x=0.4, and (g, h) x=0.6 in
NdFeAs1-xPxO0.9F0.1.

Fig. 2. Schematic band dispersions for x=0-0.6 in
NdFeAs1-xPxO0.9F0.1.
[1] A. Takemori et al., Phys. Rev. B 98 (2018) 100501.
[2] S. Miyasaka et al., J. Phys. Soc. Jpn. 82 (2013)
124706.

78

Ⅲ02- 28 -BL5U

Ⅲ -2. Materials Sciences

BL5U

Doping and Temperature Dependence of the Nodal Spectral Weight in Bi2212
S. Ideta1,2, S. Ishida3 and K. Tanaka1,2

UVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
School of Physical Sciences, The Graduate University for Advanced Studies, SOKENDAI, Okazaki 444-8585, Japan
3
National Institute of Advanced Industrial Science and Technology, Tsukuba 305-8568, Japan
1

2

Which momentum space on Fermi surfaces (FSs)contributes to superconductivity is one of the important
issues to elucidate the mechanism of high-Tc
superconductivity. According to the Fermi arc picture[1], carrier concentration is proportional to the Fermi arc
length and the effective SC gap scales with Tc [1,2].
These results suggest that the superconductivity near thenodal direction plays an important role ofsuperconductivity in cuprates. On the other hand, there
is a report that spectral weights (SWs) which are
distributed over the FSs, observed by angle-resolved
photoemission spectroscopy (ARPES) would contributeto high-Tc superconductivity in cuprates [3]. Therefore,
it has been unclear which parameters contribute tosuperconductivity dominantly so far.
In the present report, we studied that to what extent thenodal region on FSs contributes to superconductivity inthe cuprate superconductors. We have performed an
ARPES experiment to investigate doping andtemperature dependence of SW in the nodal direction.
High-quality single crystals of underdoped (UD),
optimally doped (OPT), and overdoped (OD)
Bi2Sr2CaCu2O8+δ, Bi2212 (Tc = 70, 92, and 75 K) weregrown by the TSFZ method. ARPES experiments werecaried out at BL5U of UVSOR-III Synchrotron. Clean
sample surfaces were obtained for the ARPES

measurements by cleaving single crystals in-situ in an
ultrahigh vacuum better than 5×10-9 Pa, and total energy
resolution was set at 15 meV. The measurements were
performed at 20 K – 110 K.
Figures 1(a)-1(c) show AREPS spectra ofsymmetrized energy-distribution curves (EDCs) in the
nodal direction taken at T = 20 K, 90 K, and 110 K for
OD75, OPT92, and UD70 samples. EDCs are subtracted
as shown in Figs. 1(d)-1(f) to see the change of SW in
the SC and normal states. The difference is shown by
blue shaded area in Figs. 1(d)-1(f) and the area is plottedin Fig. 1(g). In contrast with the speculation that thenodal momentum region is related with Tc, the nodal
SW is almost independent of hole concentration and Tc.
The present result suggests that we need to study the
momentum dependence of SW on entire FSs in futurework.

[1] M. Oda et al., Phys. Soc Jpn. 69 (2000) 983.
[2] S. Ideta et al., Phys. Rev. B 85 (2012) 104515.
[3] T. Kondo et al., Nature 457 (2009) 296.
[4] M. R. Norman et al., Phys. Rev. B 57 (1998) R11093.
[5] D.A. Shirley, Phys. Rev. 55 (1972) 4709.

Fig. 1. Doping and temperature dependence of double-layer cuprate Bi2212. (a)-(c) Temperature dependence ofsymmetrized EDCs in the SC and normal states. The data is fitted by phenomenological function [4] including
Shirley-type background [5]. (d), (e), and (f) are symmetrized EDCs obtained from subtraction of EDC in the SC
and normal states shown in (a), (b), and (c), respectively. Shaded area shown in panels (d)-(f) is plotted in panel(g) with the Tc dome of Bi2212 as a function of hole concentration.

79

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BL6B Sciences
Ⅲ -2. Materials

BL6B

Infrared Reflectivity Spectra for Undoped and n-type Mg2Si Crystals
1

Ⅲ-2

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, Japan
3
Ibaraki University, College of Engineering, Hitachi 316-8511, Japan

Mg2Si belongs to the cubic system with the spacegroup Fm-3m, and it has anti-fluorite structure [1].
This material is called environmentally-friendly
semiconductor, because it is composed of nontoxic andearth-abundant elements. Mg2Si attracts much attentions
as optoelectronic and thermoelectric substance. The
band-gap energy is reported 0.61 eV [2], and thus
Mg2Si can respond to the illumination of mid-infrared(MIR) light [3]. This feature opens the way to apply toa MIR detector. Actually, pn-junction Mg2Si diodes
were fabricated, and they showed a clear response forphotons with the energies above 0.6 eV [3]. Despite anindustrially important material, free carrier behaviors
in Mg2Si have been little studied so far. Plasma
oscillation is regarded as a fingerprint for the creationof free carriers in semiconductors. The information onsuch plasma oscillation can be obtained from themeasurement of reflectivity in the infrared region. In
the present study, we have measured reflectivity
spectra of undoped and n-type Mg2Si crystals at
various temperatures. Because low grade reagentswere used as starting materials, carriers were naturally
introduced, resulting in n-type Mg2Si crystals. The
carrier concentrations of undoped and n-type Mg2Si
crystals were 1.8×1015 and 2.2×1018 cm-3. The surfacesof crystals were mechanically polished.
Figure 1 shows reflectivity spectra of an undoped nMg2Si crystal. Red and blue lines indicate reflectivity
spectra at 20 and 300 K, respectively. A prominent
peak due to Reststrahlen band is observed around 300
cm-1, in good agreement with the previous paper [4].
The spectral shape was approximated by a Lorentz
oscillator model. No Drude peak due to the plasma
oscillation of free carriers is found in the wavenumber
region below the Reststrahlen band. The reflectivity
spectrum at 20 K is slightly changed with increasing
temperature.
Figure 2 shows reflective spectra of an n-type Mg2Si
crystal. Red and blue lines indicate reflectivity spectra
at 20 and 300 K, respectively. The Reststralen band
deforms compared to that for the undoped crystal.
Furthermore, a spectral change in the low-wavenumber
region of the Reststrahlen band is conspicuous. Becauseof high-carrier concentration in the n-type Mg2Si crystal,
the Drude peak due to plasma oscillation of free carriersappears in the low-wavenumber region of the
Reststrahlen band. The reflectivity spectrum at 20 K isslightly changed with increased temperature. This result
implies that the carrier concentration is independent of
temperature.

Fig. 1. Reflective spectra of an undoped Mg2Si crystal.
Red and blue lines indicate reflectivity spectra at 20 and
300 K, respectively.

Fig. 2. Reflective spectra of an n-type Mg2Si crystal.
Red and blue lines indicate reflectivity spectra at 20
and 300 K, respectively.

[1] N. V. Morozova et al., J. Appl. Phys. 115 (2014)
213705.
[2] K. Sekino et al., Physics Procedia, 11 (2011) 171.
[3] H. Udono et al., Jpn. J. Appl. Phys. 54 (2015) 07JB06.
[4] D. McWilliams et al., Phys. Rev. 130 (1963) 2248.

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Ⅲ -2. Materials Sciences

BL6B

Optical Evidence of Current-Induced Local-to-Nonlocal Transition of SmS
H. Watanabe1,2, S. Tatsukawa2, K. Imura3, H. S. Suzuki4, N. K. Sato3 and S. Kimura1,2,5
Graduate School of Frontier Biosciences, Osaka University, Suita 565-0871, Japan
Department of Physics, Graduate School of Science, Osaka University, Toyonaka 560-0043, Japan3
Department of Physics, Graduate School of Science, Nagoya University, Nagoya 464-8602, Japan
4
Institute for Solid State Physics, The University of Tokyo, Kashiwa 277-8581, Japan
5
Institute for Molecular Science, Okazaki 444-8585, Japan
1

2

60 K and 150 K, which suggests the current-induced
local-to-nonlocal transition of SmS.

Samarium monosulfide SmS is a black-colored
semiconductor with an energy gap of about 0.1 eV atambient pressure. Applying pressure above 0.7 GPa,the electronic properties changes to a golden-colored
metallic one with the change of Sm valence, namely
Black-to-Golden phase Transition (BGT) [1,2]. The
origin of the BGT is now still under debate. However,one possibility of the transition between Bose-Einsteincondensation (BEC) and BCS state of excitons is
discussed [3], but no definitive evidence has beenobtained.
Recently, Ando et al. reported that the nonlinear
relation between the voltage (V) and electric current (I)with increasing current at lower temperatures than 100
K, which suggests the electrical resistivity changes
discontinuously [4]. To investigate the origin of thenonlinear V/I curve and the relation to the BGT, we
measured the current and temperature dependence ofthe reflectivity spectrum in the THz region using theTHz microscope at BL6B to detect the current-induced
electronic structural change.
The single crystalline SmS with the typical sample
size of 1×1×1 mm3 was mounted in a liquid-heliumcooled cryostat and connected to the current source.
Figure 1 shows the I-dependence of the reflectivity
spectrum at temperatures (T) of 60 K and 150 K. At T
= 60 K and I = 0.0 A, only a large peak originatingfrom a TO-phonon was observed at 200 cm-1, whichsuggests carriers do not exist. With increasing electric
current, the reflectivity intensity at the lowest
wavenumber increases suggesting the Drude weight
and the carrier density increase. At T = 150 K, theDrude weight is visible even at I = 0.0 A. To evaluate
the effective carrier density N* (= N0m0/m*, where N0
is the carrier density, and m0 and m* the rest mass andthe effective mass of an electron), we fitted thereflection spectra [R(ω)] by the Drude-Lorenz function
shown below.
����� (�)𝑅𝑅�𝜔𝜔� = � ������ (�)𝜀𝜀̃(𝜔𝜔) = 𝜀𝜀∞ −Ⅲ-2

Fig. 1. Current dependence of THz reflectivity spectra
at 60 K and 150 K. The dashed black lines result fromthe Drude-Lorenz function fitting.

�

� ,

� �

��� �

�� �����

+

� ��
���
�
��� ��� ������

,Fig. 2. The current dependence of the square of plasma
frequency of carriers.

where c is the fitting constants of reflectivity, ε∞ thebackground of dielectric constant, ωpf (ωpb) and Γf(Γb) the plasma frequency and damping constant of
free carriers (phonons). Figure 2 shows the current[1] A. Jayaraman et al., PRL 25 (1970) 1430.
[2] T. Mizuno et al., JPSJ 77 (2008) 113704.
[3] B. I. Halperin and T. M. Rice, RMP 40 (1968) 755.
[4] H. Ando et al., JPS Conf. Proc. 30 (2020) 011132.

��dependence of the 𝜔𝜔� , which is proportional to N*.
��𝜔𝜔� as well as N* increase with applied current both at

81

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Ⅲ -2. Materials

BL6B

Development of an Infrared Spectro-microtomography Using a Mid-IR
Supercontinuum Laser: Preliminary Report
H. Yabuta1, Y. Ikemoto2, F. Teshima3 and K. Tanaka3

Department of Earth and Planetary Systems Science, Hiroshima University, Higashi-Hiroshima 739-8526, Japan
2
Japan Synchrotron Radiation Research Institute (JASRI), Sayo 679-5198, Japan
3
UVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan1

Ⅲ-2

This study aims to develop a three-dimensional
infrared spectro-microtomography using a mid-infrared
supercontinuum laser, for investigating the threedimensional spatial distributions of micron-sized organic
materials and hydrous minerals of extraterrestrial
samples and for understanding the chemical history in
the early Solar System.
The first step for establishing the element techniquesof three-dimensional infrared spectro-microtomography
was to introduce a laser optical system in a FTIR
Linear Array Imaging Microscope (JASCO) at an IR
BL6B, UVSOR. For this purpose, we purchased a midinfrared supercontinuum laser (fiber laser) (NOVAE,
Coverage, 782 mW, 1.9-3.9 μm) (Fig. 1) in September,
2019 (Hiroshima University). As the infrared laser isinvisible and it is not easy to check its optical path, a
red semiconductor laser (5 mW) was firstly used as anexternal light to check the shape and size of the laser.
Introduction of the red laser in the spectroscopy wasconfirmed by detection of a sharp absorption peak at
14850 cm-1 in an FTIR spectrum (Fig. 2). Introductionof the red laser in the center of the field of view of theinfrared microscopy was confirmed as well by
optimization of spectral intensity and adjusting the laser
position. However, an absorption peak was notdetected at 14850 cm-1 sedue to the detection upper
limit (7800 cm-1) of the MCT detector. After these test
experiments using a red laser, a fiber laser was
introduced in the infrared microscopy (its intensity was
reduced to 3 mW). The infrared spectrum of the fiber
was detected, but, a spectrum at the longer wavelength(< 3500 cm-1) was not detected, probably due toabsorption by a quartz window and/or CaF beam
splitter.
In order to solve the problem, a quartz window and
CaF beam splitter were replaced with a BaF2 window
and KBr beam splitter, respectively. As a result, thefiber laser-derived absorption was detected in therange of 8000-2000 cm-1 by the infrared microscope(Fig. 3). The laser spectral intensity was also improved.
Under the laser condition, an FTIR spectrum of CaCO3
powder was preliminarily obtained.
In future, we will set up a rotation stage and try toacquire the 3D FTIR spectra of several extraterrestrial
samples by using a newly-upgraded fiber laser.

Fig. 1. Photo of the mid-infrared supercontinuum laser(Fiber laser) (NOVAE, Coverage, 782 mW, 1.9 - 3.9μm) introduced in a BL6B, UVSOR.

Fig. 2. Optical system using a red semiconductor
laser (upper left), introduction of the red laser in the
spectroscopy (upper right) and microscopy (bottom
right), and FTIR spectrum of the red laser at 14850 cm1(bottom left).

Fig. 3. FTIR spectrum of the mid-infrared
supercontinuum laser acquired by the infrared
microscopy.
Acknowledgement: This work was supported by
JSPS KAKENHI Grant Number JP 19H01954

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Ⅲ -2. Materials Sciences

BL6B

Far-infrared Absorption Measurements on Single Crystal Pentacene
Y. Nakayama and J. Miyamoto

Department of Pure and Applied Chemistry, Faculty of Science and Technology, Tokyo University of Science,
Noda 278-8510, Japan
Coupling of lattice- as well as molecular-vibrations
with the electronic states is a crucial factor for
dominating the charge carrier transport in crystalline
organic semiconductors. In fact, it has been clearly
demonstrated that both intra- and inter-molecularvibrations deforms the valence bands of single crystal
rubrene, a representative p-type organic semiconductormaterial exhibiting the charge carrier mobility over 10
cm2V-1s-1 [1]. In order to understand the natures of suchelectron-phonon (vibration) coupling, experimental
measurements not only for the electronic (band)
structures but also for the inter- and intra-molecularvibational modes has been demanded.
Pentacene is another representative p-type organic
semiconductor material of considerable charge carrier
mobility. In its single crystal phase, energy-momentum
dispersion relationships have been demonstrated byangle-resolved photoelectron spectroscopy [2]. Theinter-molecular vibrational modes and their couplingstrength with the electronic states have been predicted
theoretically [3]. Experimentally, Raman spectroscopy
measurements were conducted on the single crystal
pentacene to characterize the symmetric lattice andlow-frequency molecular vibrational modes [4]. In thepresent work, we attempted far-infrared absorption
measurements on the single crystal pentacene forcomplementation of its vibrational characteristics.
Far-infrared absorption spectra were obtained at
BL6B by using a Michelson-type interferometer (Bruker
Vertex70v) and a bolometer (Infrared Laboratories). A
pentacene single crystal (PnSC) sample was fixed on a
CVD diamond plate (thickness 0.4 mm) and was attached
to a home-made sample holder for adjustment of the inplane azimuthal angle (Fig. 1(a)). The crystallographic
orientation of the PnSC sample was settled using thepolarized optical microscopy (Fig. 1(b)). The spectra
were collected in a transmission geometry. All themeasurements were conducted at room temperature.
Figure 2(a) shows far-infrared absorbance spectra of
the PnSC and blank diamond samples. Although thesignal intensity was small, spectral contribution of
PnSC could be extracted by dividing the absorbance of
the PnSC/diamond sample by that of blank sample, as
shown in Fig. 2(b). A peak in 450 - 500 cm-1 can be
assigned to low-frequency intra-molecular vibration
modes (Fig. 2(c)). On the other hand, whereas thesignal in the inter-molecular phonon range was faint,
intensity in 100 - 200 cm-1 may be attributed to au
lattice vibration modes predicted theoretically [3].

Fig. 1. (a) Photograph of the sample holder used inthis work. (b) Polarized micrographs of the sample.

Fig. 2. (a) Far-infrared absorbance of the PnSC/
diamond and (blank) diamond plate samples. (b)APnSC/Adiamond spectrum where the background oscillation
was reduced by Fourier filtering. Dipole moment for
intra-molecular vibrations (calculated with Gaussian09,
b3lyp, 6-31g*) and wave number distributions for intermolecular vibrations in the symmetry ag and au [3] arealso shown. (c) Calculated intra-molecular vibration for
492 cm-1 and 477 cm-1.
[1] F. Bussolotti et al., Nat. Commun. 8 (2017) 173.
[2] Y. Nakayama et al., J. Phys. Chem. Lett. 8 (2017)1259; ibid, J. Mater. Res. 33 (2018) 3362.
[3] A. Girlando et al., J. Chem. Phys. 135 (2011) 084701.
[4] R. Valle et al., J. Phys. Chem. B 108 (2004) 1822.

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Ⅲ -2. Materials

BL7U

Energy Shift of Dirac Point in Ni1-xPdxTe2 Observed by Angle-Resolved
Photoemission Spectroscopy
S. Miyasaka1, K. Yoshino1, N. Katayama1, 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

Transition metal dichalcogenides with layered
structures show a variety of physical phenomena suchas the charge density wave, superconductivity and soon. Recent experimental studies on Pd and Pt
dichalcogenides with CdI2–type structure have indicatedthat these systems have new exotic electronic state,type II Dirac fermion state [1-3]. The results of angle
resolved photoemission spectroscopy (ARPES) haverevealed that the Dirac point exists at (0,0,kz) and the
Dirac cone is strongly tilted along -A direction (kzdirection) in the Pd and Pt dichalcogenides. In thesecompounds, the Dirac point is located below Fermi
level. For example, one of the target materials in thepresent work, PdTe2, the energy level of Dirac point isabout -0.6 eV below Fermi level. On the other hand,
the theoretical study has demonstrated that another end
member NiTe2 has Dirac point just above Fermi level(about +0.02 eV).
In the present work, we have tried to control theenergy level of Dirac point in NiTe2-PdTe2 solid solution
system. In this system Ni1-xPdxTe2, we expected that the
Dirac point energy shifts from +0.02 eV to -0.6 eV withincreasing Pd doping level. We have performed themeasurements of ARPES in Ni1-xPdxTe2 to observe theelectronic structure and Dirac cone directly. The single
crystals of Ni1-xPdxTe2 were grown by Te flux method.
The ARPES experimental was carried out at BL7U in
UVSOR Facility, Institute for Molecular Science.
The band calculation in consideration of spin-orbit
interaction has indicated that as well as Pd and Pt
systems, NiTe2 is the type II Dirac fermion system with
the Dirac point at (0,0,kz). The results of ARPES alsosuggested the existence of Dirac point at (0,0,kz). We
measured the band dispersion along k// (k//kz) at
different kz. At kz=0, there are several hole-like bands
around  points. With increasing kz, the energy levelof the hole band around  point shifts down, and the
top of this band is located just above Fermi level at
kz~0.37c*. (Fig. 1(a)) At this kz, the band dispersion
shows a linear k//-dependence around Brillouin zone
center. This result has suggested that Dirac point exists
very near Fermi level at (0,0,~0.37c*) in NiTe2. The
observed band dispersion is roughly consistent withthe band calculation, as shown in Fig. 1(a).
By Pd doping, the electronic band around Brillouinzone center shifts down at the same kz (~0.37c*). As
presented in Fig. 1(b), the crossing point of the linear
band dispersion, i.e. Dirac point has been observed justbelow Fermi level at Pd-doping level x=0.04. With

increasing Pd-doping level x, the energy of Dirac point
shifts down to deeper binding energy region, as shownin Figs. 1(c) an (d). The present results indicate that the
Dirac point energy level can be continuously controlled
by Pd substitution of Ni site in NiTe2.

Fig. 1. ARPES intensity plot along k// (parallel to -Mdirection) at (0, 0, 0.37c*) for (a) x=0, (b) x=0.04, (c)x=0.20, and (d) x=0.50 in Ni1-xPdxTe2. In panel (a), thecalculated band dispersion is also shown by red solidlines. Red arrows indicate the position of Dirac point inpanels (b), (c) and (d).

[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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Ⅲ -2. Materials Sciences

BL7U

Reconstruction of the Electronic Structure in FeSe1-xTex/CaF2
K. Nakayama1,2, R. Tsubono1, F. Nabeshima3, N. Shikama3, T. Ishikawa3, Y. Sakishita3,
A. Maeda3, T. Takahashi1,4,5 and T. Sato1,4,5

Department of Physics, Tohoku University, Sendai 980-8578, Japan
Precursory Research for Embryonic Science and Technology, Japan Science and Technology Agency,
Tokyo 102-0076, Japan3
Department of Basic Science, the University of Tokyo, Tokyo 153-8902, Japan
4
Center for Spintronics Research Network, Tohoku University, Sendai 980-8577, Japan5
WPI Research Center, Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan1

2

Iron selenide FeSe, a superconductor with the criticaltemperature Tc of ~8 K, is recently attracting great
attention because of the structural simplicity and various
exotic properties such as anisotropic superconductivity
and electronic nematicity without long-range magnetic
order. These properties are sensitive to chemical
substitution, high-pressure application, and/or carrier
doping. Therefore, one can investigate the interplay
between nematicity and superconductivity while
controlling some physical parameters. In this respect,
isovalent-substituted FeSe1-xTex films grown on CaF2
substrate (FeSe1-xTex/CaF2) offer an excellent platform
because nematicity is realized in FeSe/CaF2 (x = 0) as inbulk FeSe and the highest Tc of 23 K among non-carrierdoped FeSe-based compounds has been reported at thecritical Te concentration xc of ~0.2 at ambient pressure[1-3]. Also, FeSe1-xTex/CaF2 is a candidate to realize‘high-Tc’ topological superconductivity hosting Majorana
fermions because possible topological superconductivity
has been proposed for the bulk counterpart.
In this study, we performed systematic angle-resolved
photoemission spectroscopy (ARPES) measurements of
FeSe1-xTex/CaF2 with a series of different x values, anddetermined the evolution of the electronic structure
across xc = 0.2 [4].
High-quality compressive-strained FeSe1-xTex 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 photons of
7-25 eV.
Figure 1 shows a comparison of the electronic
structure between x = 0 and 0.4. At x = 0, The near-EF
band structure around the Γ point consists of two highly
dispersive bands and a relatively flat band [red curves inFig. 1(b)], which are ascribed to the Fe 3dxz/dyz orbitals
and the Fe 3dxy orbital, respectively. Around the M point,
there are two holelike bands [Fig. 1(c)], which are
attributed to the dxz/dyz-derived bands originating fromthe lifting of orbital degeneracy by nematicity. Due tothe nematicity, the Fermi surface shape around the M
point is elongated along kx [Fig. 1(a)]. On the other hand,
the Fermi surface around the M point is more rounded
for x = 0.4 [Fig. 1(d)]. This result signifies the absenceof nematicity for x = 0.4 [Fig. 1(f)]. In addition, aremarkable x dependence beyond the effect of nematicity
manifests itself in the band dispersion around the Γ point[Fig. 1(e)]. Namely, the top of the dxy band shifts upward
and nearly touches EF at x = 0.4, resulting in an increaseof the density of states. The appearance of the dxy orbital
character around the Γ point also modifies an interband(intraorbital) scattering between the hole and electron
pockets, which has been proposed as a key to controllingthe superconducting and nematic properties. Our
systematic measurements revealed that these changes inthe electronic structure occur in the close vicinity of xc,
where the Tc shows a large jump. The present results
provide important insights into the interplay among
high-Tc superconductivity, nematicity, and orbital
degrees of freedom.

Fig. 1. (a)-(c) Fermi surface and the band dispersions
around the Γ and M points for FeSe/CaF2. (d)-(f) Sameas (a)-(c) but for FeSe0.6Te0.4/CaF2.

[1] F. Nabeshima et al., Appl. Phys. Lett. 103 (2013)
172602.
[2] Y. Imai et al., Proc. Natl. Acad. Sci. USA 112 (2015)
1937.
[3] Y. Imai et al., Sci. Rep. 7 (2017) 46653.
[4] K. Nakayama et al., Phys. Rev. Research 3 (2021)
L012007.

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Ⅲ -2. Materials

BL7U

Temperature Dependence of Nodal Spectral Weight in High-Tc Cuprate
Superconductor Bi2212
S. Ideta 1,2*, S. Ishida3 and K.Tanaka1,2

UVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
School of Physical Sciences, The Graduate University for Advanced Studies, SOKENDAI, Okazaki 444-8585, Japan
3
National Institute of Advanced Industrial Science and Technology, Tsukuba 305-8568, Japan
1

2

Ⅲ-2

Angle-resolved photoemission spectroscopy (ARPES)
is a powerful toot to investigate the electronic structure in
the normal and superconducting states ofsuperconductors [1-3]. The essential origin of
superconductivity is coupled electrons so-called“Cooper pairs”, and these coupled electrons condenses
into the ground state. The volume of the condensed
electrons, namely, the superfluid density, is strongly
related to the spectral weight (SW) obtained by ARPES.
Temperature dependence of SW might give informationof an important role of superconductivity in strongly
electron correlated system [4].
According to the 2-dimentional t-J models [4], SW
abruptly changes upon a transition from the projected
Fermi-liquid (pFL) state with electron correlation to theresonating valence bond (RVB) state. In the present
study, we have performed an ARPES experiment toinvestigate temperature dependence of SW in the nodal
direction in order to understand the electron correlationof the double-layer Bi2Sr2CaCu2O8+δ, (Bi2212) asreported in the previous ARPES study [5,6].
High-quality single crystals of optimally doped
Bi2212 (Tc = 92 K) were grown by the TSFZ method.
ARPES experiments were caried 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 7×10-9 Pa, and total energy resolution was set at
6-8 meV. The measurements were performed at 20 K –108 K.
Figure 1 shows the ARPES result of temperaturedependence of the nodal SW in Bi2212 taken at hν = 8
eV. In order to estimate the change of SW, we havemeasured the temperature dependence from well below(20 K) to above Tc (108 K) as shown in Fig. 1(a).
Energy-distribution curve (EDC) at the nodal point on
the Fermi surface (FS) are extracted and symmetrized toremove the contribution from Fermi-Dirac function. As
shown in Fig. 1(b), difference of the intensity for EDC,
I, at certain temperature is estimated from subtraction byusing the EDC at 108 K, I108K. We estimated SW
obtained from Fig. 1(b) and the result is plotted as afunction of temperature in Fig. 1(c). One can see that SW
abruptly changes at the superconducting phase transition
shown by a dotted line. Therefore, the temperaturedependence of the nodal SW is related with thesuperfluid density and is consistent with the previous
ARPES study of triple-layer cuprate Bi2Sr2Ca2Cu3O10+δ
[5]. This result suggests that the suppression of SW

would be universal behavior in the strongly electron
correlated system. In addition, the present result is
consistent with the RVB picture based on the 2dimensional t-J model. We will study the temperaturedependence of SW on the entire FS as future work.

Fig. 1. Temperature dependence of optimally doped
Bi2212 in the nodal direction. (a) Raw symmetrized
ARPES spectra well below and above Tc. (b)Subtracted symmetrized EDC. As an example of thespectral weight (SW), shaded area (red) at 100 K isshown. (c) SW is plotted as a function of temperature.
Several experiments are demonstrated in Bi2212 toconfirm the data accuracy. BB shown in the schematic
FS is the bonding band in Bi2212[1] Z.-X. Shen et al., Phys. Rev. Lett. 70 (1993) 1553.
[2] A. Lanzara et al., Nature 412 (2001) 510.
[3] M. R. Norman et al., Phys. Rev. B 63 (2001) 148508(R).
[4] C-P. Chou, T. K. Lee and C-M. Hou, Journal of
Physics and Chemistry of Solids 69 (2008) 2993.
[5] S. Kudo et al., Phys. Rev. B 92 (2015) 195123.
[6] S. Kudo, Master Thesis, Tokyo University (2008).
*Present address: Hiroshima Synchrotron Radiation
Center, Hiroshima University 739-0046

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Ⅲ -2. Materials Sciences

BL7U

Angle-resolved Photoemission Study of Solid Electrolytes LixLa(1-x)/3NbO3Bulk Single Crystal
T. Ito1,2, R. Yamamoto2, M. Nakatake3, S. Ideta4, K. Tanaka4, Y. Fujiwara5 and Y. Iriyama2
1

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
Faculty of Engineering, Shinshu University, Nagano 380-8553, Japan

In recent years, as the use of secondary Li-ion
batteries has expanded, the development of all-solid
batteries using solid electrolytes has progressed torealize greater safety, wider thermal stability range,easier material handling. To understand their electronic
properties and transport characteristics, the electronic
structure is essentially important. However, there arefew examples of experimental observations on solid
electrolytes. In this study, we performed direct
observation of the electronic structure of LixLa(1x)/3NbO3 (LLNO; x = 0.07 - 0.08) bulk single crystals[1,2] by using angle-resolved photoemission
spectroscopy (ARPES) in order to clarify theelectronic structure of solid electrolytes, especially theelectronic band structure.
ARPES measurements were performed at the
UVSOR-III BL7U. Data were acquired with hν = 18
eV at room temperature. To minimize photoirradiation
damage, photon flux was sufficiently reduced during
all measurements. Single crystals were cleaved in situ
along (001) plane, where partially occupied (A1) andunoccupied cation layers (A2) appear alternately(Fig.1(b)).
Figure 1(a) shows the ARPES spectra along ionconducting [100] axis of LLNO. At k = 0 Å-1 (Γ), twopeaks around 5 (α) and 6 eV (β) appear dominantly
relative to 9 eV feature (δ). On the other hand, theformer becomes smaller than the latter at k = –0.4 Å-1(X), following the additional feature around 7 eV (γ).
Furthermore, it has been found that the feature γ shows
clear dispersion from 6 eV splitting from the peak β
along the ΓX line.
To show the observed features clearly, we show theband structure obtained by mapping the ARPES
intensity in Fig. 2. It has been found that the electronic
structure around the valence band maximum of LLNO
seems to be characterized by the band gap of 2~3 eV
formed by the edge of almost non-dispersive α band.
In addition, highly dispersive feature γ appears among
the non-dispersive β and δ bands. We expect that thepresent result is the first experimental observation of theband structure of solid electrolytes for Li-ion battery.

Ⅲ-2

Fig. 1. (a) ARPES spectra along the ΓX line of
LixLa(1-x)/3NbO3. Solid lines are guides for eyes. (b)Average crystal structure of LixLa(1-x)/3NbO3. The
alternating partially occupied and unoccupied cation
layers parallel to the c axis are labeled as A1 and A2
layer, respectively [2].

Fig. 2. Valence band structure along the ΓX line of
LixLa(1-x)/3NbO3. Solid and dashed lines are guides foreyes.
[1] Y. Fujiwara, K. Hoshikawa and K. Kohama, J.
Cryst. Growth 433 (2016) 48.
[2] Y. Fujiwara, T. Taishi, K. Hoshikawa, K. Kohama
and H. Iba, Jpn. J. Appl. Phys. 55 (2016) 090306.

87

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BL7B

Evaluation of Optical Properties of Glass Materials in the VUV Region
T. Shimizu1, M. J. F. Empizo1, K. Shinohara1, D. Umeno1, N. Sarukura1 and T. Murata2
Institute of Laser Engineering, Osaka University, Suita 565-0875 Japan
Faculty of Advanced Science and Technology, Kumamoto University, Kumamoto 860-8555, Japan
1

2

Ⅲ-2

Recently, neutron detection is required in inertial
confinement fusion research and infrastructure
inspection. The ratio of primary neutron and scatteredneutron corresponds to the density and radiusparameter of fusion plasma. Additionally, neutron
detection is considered as one of the nondestructive
methods for inspecting the form of infrastructure.
Scintillator materials which are able to detect anddiscriminate neutrons should then be developed to beable to satisfy the technological demand.
Previously, we have developed co-dope
20Al(PO3)3-80LiF (APLF) glass with Pr and Ce for
improvement of decay times and conversion efficiencies
and investigated the optical properties of Pr/Ce-doped
APLF glasses with different concentrations. As a result,both radiative and non-radiative energy transfers from
Pr3+ to Ce3+ are observed. These results present
exciting prospects for APLF80 as a response time
improved scintillator.
In this study, Nd3+-doped APLF glasses were
investigated as potential vacuum ultraviolet (VUV)
scintillator materials. Nd3+ is used as dopant in lasermaterials and optical property of that are largely
analyzed from the UV to the near-infrared regions(200–1500 nm), but rarely in in the VUV region (170–
190 nm). Although absorption and emission properties
in the VUV region are always difficult to measure dueto the spectral limit of many devices.
We performed absorption and emission
spectroscopic analysis to investigate the opticalproperties of the Nd3+-doped APLF glass at the BL7B
solid-state spectroscopy beamline of UVSOR [1-3].
Figure 1 shows the VUV absorption spectra of theundoped APLF glass at RT and the 1.0 mol% Nd3+doped APLF glass at different sample temperatures.
The undoped glass has a room-temperature absorption
edge in the VUV region around 162.2 nm (61650 cm−1).
In contrast, the Nd3+-doped glass exhibits anabsorption edge at 300 K (RT) around 191.8 nm whichcorresponds to the interconfigurational transition fromthe 4I9/2 ground state of the 4f3 configuration to the
4f25d excited state configuration of Nd3+ ions. The
absorption edge shifts with temperature and is locatedat 189.7 nm (52710 cm−1), 190.1 nm (52600 cm−1),
190.4 nm (52520 cm−1), and 191.8 nm (52140 cm−1) at
20 K, 100 K, 200 K, and 300 K, respectively.
These absorption edges are determined bygenerating the first derivative of the absorbance withrespect to wavelength and then identifying the positionof the absolute minima, i.e., the wavelength where thedecrease in the absorbance is the highest. The shiftingof the absorption edge with sample temperature
indicates the temperature broadening of theinterconfigurational 4f25d transition which is
associated with the population of the Stark
components (Z1, Z2, etc.) of the 4I9/2 ground state of
the Nd3+ ions’ 4f3 configuration and which is often
observed in Nd3+-doped crystals and glasses.
Additionally, the low-temperature absorption spectrasuggest that the lowest energy level of the 4f25d
excited state configuration of Nd3+ ions in APLF glass
is estimated to be at a position higher than 52710 cm−1
(6.54 eV).
We have successfully investigated the absorption
and emission properties of Nd3+-doped APLF glasses
at different sample temperatures and with different
doping concentrations mainly for potential neutron
scintillator applications. Further development of theseglasses as VUV scintillator materials is thenanticipated in the future.

Fig. 1. VUV absorption spectra of (a,b) undoped
APLF glass at RT and (c,d) 1.0 mol% Nd3+-doped
APLF glass at 20 K, 100 K, 200 K and 300 K (RT)[3].

[1] T. Shimizu et al., UVSOR Activity Report 2018 46(2019) 107.
[2] Y. Minami et al., J. Noncryst. Solids 521 (2019)
119495.
[3] Y M. J. F. Empizo et al., J. Alloys Compd. 856(2021) 158096.

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