Ⅲ-2

Materials SciencesⅢ -2. Materials Sciences

BL7U

Electronic Structure of Sr1-xCaxFe2(As1-xPx)2 Revealed by Angle Resolved
Photoemission Spectroscopy II
T. Adachi1, S. Ideta2, 3, K. Tanaka2, 3, T. Z. How1, S. Miyasaka1 and S. Tajima1

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

It is well known that there is a remarkablecorrelation between a crystal structure and Tc in ironbased superconductor. Thus, it is essential forunraveling the superconducting (SC) mechanism inthis system to clarify how the electronic structure (thetopology of a Fermi surface (FS) and the SC gap
structure) changes with the crystal structure. Recently
we have performed ARPES measurements on Sr1-xCax
Fe2(As1-yPy)2 (x = 0.25, y = 0.08) whose c/a (the ratioof a- and c-axes lattice constants), which is index ofstructural anisotropy, is smaller than that ofBaFe2(As1-yPy)2. We have revealed two salient featuresof this compound. First, the innermost dxy hole band is
below EF around the Γ point, while in BaFe2(As1-yPy)2,
all the hole bands are above EF in the entire kz region[1]. Second, there is a gap minimum on one of theelectron FS.
In this measurement, we have performed the
ARPES measurement on Sr1-xCax Fe2(As1-yPy)2 (x =0.25, y = 0.08) to confirm the gap minimum on one of
the electron FSs and clarify the momentum
dependences of the SC gaps around all the highsymmetry points. Figure 1 shows the SC gaps on theelectron FSs around the X point. One can see the gap
minimum around 40 degrees on the δ electron FS in
Fig. 1 (a). This feature has been confirmed bymeasurements for other 4 samples summarized in Fig.
1 (c). Therefore, we conclude that there exists the gap
minimum on the δ electron FS, indicating the existenceof a node. All results about the SC gaps are
summarized in Fig. 2. There is weak anisotropy of the
SC gap on the γ hole FS around the Z point, implying
the contribution of the spin fluctuation to the SC
mechanism [2]. On the other hand, other gaps on thehole FSs are nearly isotropic. As discussed above,
there exist the gap minima or nodes on the δ electron
FS while the SC gap on the ε electron FS is almost
isotropic. This result indicates the orbital fluctuation
plays an important role on the SC mechanism [3].
[1] T. Yoshida, I. Nishi, S. Ideta, A. Fujimori, M.
Kubota, K. Ono, S. Kasahara, T. Shibauchi, T.
Terashima, Y. Matsuda, H. Ikeda and R. Arita, Phys.
Rev. Lett. 106 (2011) 117001.
[2] K. Suzuki, H. Usui and K. Kuroki, J. Phys. Soc.
Jpn 80 (2011) 013710.
[3] T. Saito, S. Onari and H. Kontani, Phys. Rev. B 88
(2013) 045115.

Ⅲ-2

Fig. 1. (a), (b) The photoemission spectra divided byFermi-Dirac function at various Fermi surface angles
FS for electron FSs. (c) Energy gap as a function of
FS. (d) In-plane FS mapping around the X point.

Fig. 2. Color plots of the SC gap distribution on theFSs of Sr1-xCax Fe2(As1-yPy)2 (x = 0.25, y = 0.08).

Ⅲ02- 1 41

Ⅲ -2. Materials Sciences
BL1B
BL1B

Terahertz Spectroscopy of Ionic Liquids
T. Awano

Faculty of Engineering, Tohoku Gakuin University, Tagajo 985-8537, Japan-1

ABSORPTION COEFFICIENT(cm )

40
30
20

[C2mim][Tf 2N]

for 78K

300K
227K
158K

10
0

20

30
40
50
60
-1
WAVE NUMBER (cm )70

INTENSITY (arb. units)

Fig 2. Absorption increment spectra of [C2min][Tf2N] against the absorption spectrum at 78 K.
[Tf 2N]

2

1[C2min]101
102-1WAVE NUMBER (cm )Fig. 3. Autocorrelation function of velocity of ions in[C2min] [Tf2N] at 300 K.
0.6

20

(a)
10

0

C2min
Tf2N

IN T E N SIT Y (arb. units)[1] T. Awano and T. Takahashi, J. Phys. Soc. Jpn. 79(2010) Suppl. A 118.
[2] T. Yamada, Y. Tominari, A. Tanaka and M. Mizuno,
J. Phys. Chem. B 119 (2015) 15696.
[3] T. Awano and T. Takahashi, KURRI rep. 2016.

(a)
(b).
Fig. 1. Ionic structures of [C2min] (a) and [Tf2N]

INTENSITY (arb. units)

Ⅲ-2

Terahertz absorption bands had been observed insuperionic conductors of crystals and glasses[1]. Thesebands seems to be due to collective motion of conductive
ions, although the correlational dynamics of mobile ionsis not clear.
Ionic liquid (IL) is molten salt at room temperature
because of large radius of component ions. Figure 1
shows
molecular
structuresof
1-Ethyl-3methylimidazolium [C2min] cation and bis (trifluoromethyl) sulfonyl imide [Tf2N] anion. It is interesting tocompare ionic motion in ionic liquids with those insuperionic conductor for investigation of dynamics ofmobile ions. In superionic conducting glasses, only
cation is mobile.
Temperature dependence of absorption spectra of ionicliquids in spectral range between 20 to 60 cm-1 havemeasured to investigate change of dynamics of mobileions. Transmittance spectra of one and two filter papers
with the ionic liquid of the same quantity per the paper
were measured. Absorption spectra were obtained bysubtracting each other. To eliminate interference fringe
remaining in the spectra, absorption difference spectra ofeach spectrum from that at 78 K are shown in Fig. 2.
Molecular dynamics (MD) simulation was excuted using
GROMACS5.0.
There observed some structures in the absorption
spectra in terahertz region contrary to the previously
reported THz-TDS result[2]. Temperature dependence of
the absorption spectra showed similar tendency as theresults in millimeter wave region [3]. Four types of thespectral change occurred at temperature above melting
point or glass transition temperature. The intensities of
the absorption bands in the ILs which are crystal in thesolid state showed rapid decrease at their melting points.
On the other hand, those in ILs which are vitreous in thesolid state weakened and shifted gradually. Some others
showed complicated change. The other type showed noabsorption band in this spectral range.
Figure 3 shows MD simulation spectra of each ion in[C2min] [Tf2N] at 300 K. Terahertz absorption bands arecoincident with those in observed spectra in Fig. 2.
Figure 4 shows contribution of rotation of molecules(a) and temperature dependence of that of the anion (b).
A part of the observed spectral change seems to be due tothe rotation of ions.

[Tf2N]

0.4
0.2

(b).
600K
500K
400K

0
-0.2

10 20 30 40 50
WAVE NUMBER (cm -1)

10

20
30
40
50
WAVE NUMBER (cm -1)

60

Fig. 4. (a) Rotational velocity autocorrelation
function of the cation and anion at 300 K. (b)Increment spectra of anion against that at 300 K.

Ⅲ02- 2 42

Ⅲ -2. Materials Sciences
BL2A
BL2A

XAFS Measurement for Alloying Element in Tempered Nitrogen Martensite
M. Sato and S. Shimaya

Institute for Materials Reseach, Tohoku University, Sendai 980-8577, Japan
It is well known that the martensite phase obtainedby quenching is hard but brittle. Therefore the balance
between hardness and toughness is adjusted by thesubsequent tempering treatment. At that time,
cementite is precipitated in case carbon steel, and Fe4N
is precipitated in case of nitrogen steel [1, 2].
Although it is known that alloying elements partiallydissolve as solid solution in these precipitates, there isa little knowledge on the chemical state of thesesubstitution elements in the precipitates. In this study,changes in the chemical state of the substitutional
elements such as Si and Mo before and after tempering
treatment were investigated by XAFS measurement.
Fe-1mass%Si and Fe-1mass%Mo alloys were usedas starting materials. They were homogenized at 1523
K for 24h and furnace-cooled until room temperature.
The Fe-1Si alloys were prepared by nitriding andquenching (N-Q) process using NH3/H2 mixed gas at1273 K for 1 h. Then obtained Fe-1Si-0.3N alloys
were tempered at 773 K. and precipitates generated
during tempering were extracted using Iodine-alcohol
procedure. The Si K-edge XANES spectra werecorrected by fluorescence method using InSb double
crystal monochrometer and silicon drift detector(SDD) at BL2A in UVSOR, respectively. Obtained
data were analyzed using Athena software.
Figure 1 shows Si K-edge XANES spectra of Fe1Si-0.3N samples before and after tempering. The
XANES spectrum of the as-quenched sample showedsimilar spectrum to that previously reported. thespectrum shape changed at tempering above 400C,
and the peak at 1840 eV decreased and that at 1845
and 1850 eV increased. These peaks at 1845 and 1850eV are the same as the peak positions obtained from
Si3N4 and SiO2 reference samples [3]. Therefore, it isthought that Si kept a solid solution state in Fe at low
tempering temperature below 300C and it
precipitated as Si3N4 or made a solid solution in Fe4N
precipitates at the tempering temperature above 400
C. In addition, it is considered that the component of
SiO2 is the oxidation of the surface.
XANES spectra of Mo alloy slightly changed bytempering only at 500C, implying the precipitation of
Mo compounds, or it made a solid solution in Fe4N
precipitates. In the future, detailed examination should
be carried out by analysis of the EXAFS region andcalculation using FEFF code.

Ⅲ-2

Fig. 1. Si K-edge XANES spectra of Fe-1Si-0.3N
samples. (a) as-quenched sample and tempered at (b)100C (c) 200C (d) 400C and (e) 500C for 1 hour.

Fig. 2. Mo L-edge XANES spectra of Fe-1Mo-0.3N
samples. (a) as-quenched and (b) tempered at 500 C
for 1 hour.
[1] L. Cheng and E. J. Mittemeijer, Met. Trans. A 21A(1990) 13.
[2] L. Cheng, A. Bottger and E. J. Mittemeijer, Met.
Trans. A 23A (1992) 1129.
[3] M. Sato, UVSOR Activity Report 44 (2016).

Ⅲ02- 3 43

Ⅲ -2. Materials Sciences
BL2A
BL2A

Catalytically Active Mo2C Species on H-MFI Zeolites for Methane
Dehydroaromatization with Hydrogen
H. Aritani1, R. Yamazaki2, M. Tsutsumi1, H. Miyanaga1, M. Akutsu2, S. Mogi2,
K. Ogasawara2, K. Kuramochi2 and A. Nakahira3

Graduate School of Engineering, Saitama Institute of Technology, Fukaya 369-0293, Japan
Advanced Science Research Laboratory, Saitama Institute of Technology, Fukaya 369-0293, Japan
3
Graduate School of Engineering, Osaka Prefecture University, Sakai 599-8531, Japan1

2

after MTB reaction with H2. In case of the H-MFI(Si/Al2=28) support, it is definitely that metallic Mo
species are formed after the reaction with/without H2.
These catalysts shows durable reactivity, and thus,
excess reduction to form the metallic Mo species act
as the highly reactive sites. For the H-MFI (Si/Al2=40)
support, reduction of Mo species are slightly andalmost as similar as α-Mo2C. On these catalysts,
suppressing effect for deactivation was shown byaddition of H2. However, highly reduced Mo ions are
not formed on H-MFI (Si/Al2=40) support. The
relation between the reduction of Mo species and thecatalytic activity and its durability for MTB is now inprogress.

TEY (Normalized)

1.0

Before react.
React. CH4
React. CH4+H2(1%)
React. CH4+H2(2%)
React. CH4+H2(3%)
-Mo2C [Ref.]
Mo metal [Ref.]

Mo/H-MFI(Si/Al2=28)

0.5

0.0
2520

1.0
TEY (Normalized)

Ⅲ-2

MoO3-modified H-MFI (Mo/H-MFI) is a noted
typical catalyst for methane dehydroaromatization,
which is an important reaction for direct GTL (Gas To
Liquid) processes. Since detail of the MTB reaction
process is still unknown, It has been accepted that theactivity is based on strong acidity and sieving effects
onto MFI zeolite support. During the reaction, MoOx
species must be reduced and carbonized to form
carbide-like species[1]. At the same time, catalytic
deactivation is brought about by carbon contamination
on MFI. The deactivation strongly depends on thestrong acidity on H-MFI, and excess carbonization Mo
species also affect the lowering of methane conversion.
In our previous study, Mo/GaAl-MFI (using Gacontained H-MFI) catalysts employed to MTB
reaction[2]. In these cases, formation of Mo-carbide
species with durable MTB activity is different fromthose of Mo/H-MFI catalysts. Since H2 co-feed with
CH4 reactant is effective for suppression of carbon
coking on H-MFI, reduction of active Mo species canproceeds. It is concluded that formation of active Mo
carbide-like species, as well as restraint of the carbon
deposits on H-MFI supports, may become thebreakthrough for the design of high and durable MTB
catalysts[3]. In the present report, Mo LIII-edge
XANES study is applied to characterize the Mo/HMFI catalysts to evaluate the Mo species after the
MTB reaction with H2.
Catalysts were prepared by impregnation of H-MFI
support with MoO2(acac)2−CHCl3 solution (5.0wt%
as MoO3) , and followed by drying overnight andcalcination at 773 K for 3 h. H-MFI supports(SiO2/Al2O3 ratio is 27 or 40) were synthesizedhydrothermally at 413 K for a week, and followed byion-exchanging with NH4Cl and calcination at 873 K.
The catalytic activity of MTB was evaluated by meansof fixed bed flow reaction, as described in a separate
paper[1]. The reactant gas is CH4(20%)+H2 (03%)+He(base) at the flow rate of 30 mL/min, and thereactivity was evaluated at 1023 K by using the 0.25 gof each Mo/H-MFI catalyst. Mo LIII-edge XANES
spectra were obtained in BL2A of UVSOR-IMS in a
total-electron yield mode using InSb double-crystal
monochromator. Photon energy was calibrated byusing Mo metal-foil at Mo LIII-edge, and normalized
XANES spectra are presented by using REX-2000(Rigaku) software.
Figure 1 shows the XANES spectra of Mo/H-MFI

2525

2530
2535
Energy / eV

2540 react.
2545
BeforeReact. CH4
React. CH4+H2(1%)
React. CH4+H2(2%)
React. CH4+H2(3%)
-Mo2C [Ref.]
Mo metal [Ref.]

2525

2530
2535
Energy / eV

2540

Mo/H-MFI(Si/Al2=40)

0.5

0.0
2520

2545

Fig. 1. Mo LIII-edge XANES over Mo/H-MFI [Si/Al2
ratios are 28 (top) and 40 (bottom)] catalysts after the
MTB reaction with H2.
[1] H. Aritani et al., J. Environm. Sci. 21 (2009) 736.
[2] H. Aritani et al., UVSOR Activity Report, 43(2016) 49.
[3] H. Aritani et al., UVSOR Activity Report, 44(2017) 52.

Ⅲ02- 4 44

Ⅲ -2. Materials Sciences
BL2A
BL2A

Mg K-edge XANES of MgO Single Crystal
1

K. K. Okudaira1, S. Yoshioka 2 and E. Kobayashi3

Graduate School of Science and Engineering, Chiba University, Chiba 263-8522, Japan
2
Gradiate School of Engineering, Kyushu University, Fukuoka 819-0395, Japan
3
Kyushu Synchrotron Light Research Center, Tosu 841-0005, Japan

A large number of applications have lead to thestudy of magnesium oxide in recent years. In the fieldof organic electronics, magunesium oxides (MgOs)
are used as encaplation, high-k substrate, andinsulating material deposited between the organic
layer and the metal cathode for organic light emitting
diode (OLED), organic thin film transistor (OTFT),
and organic photovoltaic solar cell (OPV),
respectively[1-3]. Particularly, MgOs are used as
insulating barriers and play an essential role in state of
the organic devices. In this context the electronic
structure MgO has been widely studied. Furthermore,
MgO single crystal has attracted attentiondue to its
simple electronic structure, giving rise to a series ofvery interesting basic physics questions. In general, toobtain the information on electronic strucuture ofvalence band and conduction band, UPS and XANESor IPES are used, respectiveity [4]. The photoelectron
spectroscopy such as UPS and XANES using electron
yield method are not available due to low conductivity(high insulation) of MgO single crystal.
In this report, we investigated the electronic
structure of MgO single crystal by means of XANES
using fluorescence yield method.
Mg K-edge XANES measurements were performedat the BL2A of UVSOR Okazaki, Japan, using thepartial fluorescence yield method (PFY). A KTiOPO4(KTP) double crystal monochromator defined Mg K
absorption edges in the energy region from 1290 to1340 eV. The samples were set with their surface
perpendicular to the incident X-ray beam.
Fluorescence X-rays of Mg Kα were collected using
an energy dispersible silicon drift detector (SDD). All
measurements of XANES spectra were carried out invacuum of 1×10−5 Pa at room temperature. To interpretthe local structure from the experimental spectra, weused theoretical spectra by the full-potential linearized
augmented plane wave (APW) plus local orbitals
technique as implemented in WIEN2k code[5].
Firstly, magnesium oxide (MgO), which is typicalinsulating material for electronic devices, wasmeasured. Fine structures of Mg K-edge XANES wereobserved in MgO, as shown in Fig. 1. Theoretical
spectra of rock salt-type MgO was performed with 216
atoms supercell. The calculation of MgO successfully
reproduced the major peaks (a, b, c and d) andshoulders of the experimental spectrum with respect torelative energy and intensity. In XANES experimentswith fluorescence mode for highly concentrated
sample, the peak intensities sometime do not be
observed correctly due to thickness effect. However,the degree of distortion in MgO spectrum in this study
was improved by devising the sample-detector
arrangements. We will study the interaction between
MgO and organic molecules by this method.

Ⅲ-2

Fig. 1. Mg K-edge XANES spectra of MgO.
Experimental (red) and calculated (blue) spectrum.
[1] Y. C. Han, C. Jang, K. J. Kim, K. C. Choi, K. H.
Jung, B. –S. Bae, Org. Electron 12 (2011) 609.
[2]1 S.-S. Cheng, C.-Y. Yang, C.-W. Ou, Y.-C. Chuang,
M.-C. Wu, and C.-W. Chu, Electrochem. Solid State
Lett. 11 (2008) H118.
[3] 1 D.-H. Kim, J.-H. Kim, Y.-H. Hwang, J.-W. Shin,and J.-G. Park, J. Korean Phys. Soc. 3 (2013) 490.
[4] NEXAFS J Stöhr Springer-Verlag Berlin 1992.
[5] P. Blaha, K. Schwarz, G.K.H. Madsen, D.
Kvasnicka, and J. Luitz, WIEN2K: An Augmented
Plane Wave plus Local Orbitals Program for
Calculating Crystal Properties (Vienna: Vienna
University of Technology, 2001).

Ⅲ02- 5 45

Ⅲ -2. Materials Sciences
BL2A
BL2A

Structural Evaluation and Synthesis of Various Hydroxyapatite Dopedwith Al Ion
A. Nakahira1, M. Togo1, M. Sato2, T. Ujike1, T. Sakuma1, T. Moriya1, M. Minami1and H. Aritani3
Faculty of Engineering, Osaka Prefecture University, Sakai 599-8531, Japan
Industrial Materials Research (IMR), Tohoku University, Sendai 980-8577, Japan
3
Saitama Institute of Technology, Fukaya 369-0293, Japan
1

2

Ⅲ-2

Hydroxyapatite, Ca10(PO4)6(OH)2, similar to the
inorganic components of bone and teeth, is one of most
attractive bioceramics (calcium phosphate) for
implants and replacements in orthopedics fields. At thesame time hydroxyapatite possesses the excellent
biologically active properties and the highbiocompatibility. It is well-known that natural bones
have higher osteoconductive activities, because thesenatural bones contain generally some cations in thehydroxyapatite
structure.
However,thebiocompatibility strongly depends on the nature andamount cation. Especially, it is inexplicit on the
behaviors of aluminum ion for biocompatibility andosteoconductive activities.
The purpose in this study was to evaluate the local
structure of aluminum ion for hydroxyapatite addedwith aluminum ion synthesized by the solutionprecipitation method such as static hydrothermal
process. The effect of aluminum ion amount on the
microstructure for various hydroxyapatite added withaluminum ion was specially investigated.
All chemicals were analytical reagent-grade, andthey used without further purification. Undoped andAl-doped hydroxyapatite samples were synthesizedusing the static hydrothermal process as a solutionprecipitation method. Starting aqueous solutions were
0.1 mol/L solutions with Ca(NO3)2·4H2O,
Al(NO3)3·6H2O and (NH4)2HPO4. Precipitations werematured at 353 K for 5 hours in air atmosphere andsubsequently synthesized at 423 K for 12h to 24h by
the static hydrothermal process. Nominal Al/(Ca+Al)
ratio was set to 0, 1, 3, 5 and 10 at%. The samples
prepared through this process were characterized with
X-ray diffraction technique. The microstructures wereobserved by SEM.
Al-K XANES was measured at BL2A in UVSOR.
The pellets of samples were mounted on carbon tapes.
The incident X-ray beam was monochromatized withusing beryl double crystals. Al-K XANES signals werecollected with GaAsP photo-diodes (Hamamatsu: G1127-02).
Theoretical spectra were obtained by the firstprinciples supercell method with a core-hole effect andevaluated for a detailed analysis of Al-K XANES.
According to the XRD results, all samples wereidentified to hydroxyapatite structure without anotherphase. In especial, aluminium phosphate and calcium
phosphate were not contained for Al-dopedhydroxyapatite samples synthesized using the statichydrothermal process.
Figure 1 shows the results of Al-K XANES spectraof various Al-doped hydroxyapatite samples
synthesized using the static hydrothermal process. As
shown in Fig. 1, Al-K XANES spectra of sample
obtained by hydrothermal process were quite similar.
Furthermore, Al-doped hydroxyapatite samples withthe high contents of aluminum ion were most of thesame as ones with low content of aluminum ion. As aresult, Al-doped hydroxyapatite samples with
Al/(Ca+Al) ratio of 1, 3, 5 and 10 had the similar Al
local structure.

Fig. 1. Al-K XANES spectra of various products
synthesized by the hydrothermal process at 423 K.Aldoped hydroxyapatite samples: Al/(Ca+Al) ratio of 1,
3, 5 and 10.

Ⅲ02- 6 46

Ⅲ -2. Materials Sciences
BL2A
BL2A

Change in Charge States of Mo Ions in Sr2FeMoO6 by Incorporations of Ba
and Nb Ions
S. Obunai1 and T. Yamamoto1, 2Faculty of Science and Engineering, Waseda University, Tokyo 169-8555, Japan
Institute of Condensed-Matter Science, , Waseda University, Tokyo 169-8555, Japan
1

2

Normarized intensityof Ba and Nb ions, which support the experimental
change in the spectral shapes.
1

x=0
x=0.5
x=1
x=1.5
x=2

0.5

0

2510

Ⅲ-2

2515
Energy (eV)2520

Fig. 1. Mo-L3 XANES spectra of Sr2-xBaxFeMoO6.

Normarized intensity

The half-metallic materials have been widely
studied due to their potential applications in newtechnologies such as spintronics. Sr2FeMoO6 is thepromising candidates of half-metals, since it has highCurie temperature (420 K) and colossal
magnetoresistance (CMR) at room temperature [1]. It
was studied that the partial replacements of Sr and Mo
by Ba and Ta, respectively, change magnetic property.
There are two aspects to understand such change inmagnetic property, that is 1) change in magnetic
moments on Fe and Mo and 2) change in magnetic
ordering. In order to investigate the first one 1),
valence states of magnetic ions should be determined.
For such purpose, XANES analysis is quite powerful.
In the current study, we have investigated the change
in valence states of Mo ions in Sr2FeMoO6 byincorporations of Ba and Nb ions using the Mo-L
XANES measurements.
Sr2-xBaxFeMoO6 and Sr2FeMo1-xTaxO6, weresynthesized by the conventional solid state reaction
method changing the cation ratio, x. SrCO3, BaCO3, aFe2O3, MoO3 powders were used for the starting
materials. Crystal structures of all the synthesizedmaterials were examined by the powder X-ray
diffraction with Cu-Kα X-rays.
XANES measurements at Mo-L3 of the samples
here synthesized were carried out at BL2A in UVSOR
with a total electron yield method. All the sample
powders were put on the carbon adhesive tape, whichwere attached onto the Al plate, and the drain current
was measured instead of counting the number of
emitted electrons from the samples. The InSb doublecrystal monochromator was employed.
Observed Mo-L3 XANES spectra of Ba
incorporated Sr2FeMoO6, i.e., Sr2-xBaxFeMoO6, areshown in Fig. 1. The component in lower energy sidedecrease as increase of Ba concentration when x is 0.5
and 1.0, and at x = 1.5 that of higher energy sidedecreases. Finally, lower energy side recovers with nochange in higher energy side as that at x = 1.5. From
this analysis, we can discuss change in magnetic
moment derived from Mo ions. Same analysis havebeen also carried out for Sr2FeMo1-xTaxO6, whose
spectra are shown in Fig. 2. In both cases, i.e.,
Sr 2-x Ba x FeMoO 6 and Sr2FeMo1-xTaxO6, it was foundthat simple peak shift without spectral change does notoccur due to the Ba and Ta incorporations. The firstprinciples calculations within a density functional
theory were also carried out to investigate the change
in charge states of Mo ions due to the incorporations

1

x=0
x=0.25x=0.5
x=0.75

0.5

0

2510

2515
Energy (eV)2520

Fig. 2. Mo-L3 XANES spectra of Sr2FeMo1-xNbxO6.
[1] K. –I. Kobayashi et al., Nature 395 (1998) 677.

Ⅲ02- 7 47

Ⅲ -2. Materials Sciences
BL2A
BL2A

Study of Local Structure of Al-K Edge forNovel Modified Layered Double Hydroxide by Rehydration Process
A. Nakahira1, M. Iida1, M. Togo1, M. Sato2 and H. Aritani3

Faculty of Engineering, Osaka Prefecture University, Sakai 599-8531, Japan
Industrial Materials Research (IMR), Tohoku University, Sendai 980-8577, Japan
3
Saitama Institute of Technology, Fukaya 369-0293, Japan
1

2

Ⅲ-2

Layered double hydroxide (LDH) is one of uniqueclay minerals with a layered structure and possess theexcellent exchangeable anions ability owing tosubstitution to various cations and anions in LDH. Its
composition formula is [M(II)1-x M(III)x(OH)2]x+･[An-x/n･YH2O]. M(II), M(III) for layered doublehydroxide. Here, we focus on the structure evaluationof novel modified NiAl-LDH synthesized from MgAlLDH composed of Al3+ and Mg2+, which is calledhydrotalcite. In special, it was found that in our
experiments the rehydration treatment for MgAl-LDH
samples heat-treated at 473 K to 773 K in air
atmosphere resulted in the synthesis of novel modified
NiAl-LDH. The purpose in this study was to evaluate
the local structure of aluminum ion for novel modified
NiAl-LDH synthesized by the rehydration treatment
for MgAl-LDH in aqueous nickel acetate solution. The
effect of concentration of aqueous nickel acetate
solution on the microstructure for novel modified
NiAl-LDH through the rehydration treatment was
specially investigated.
Mixing solution was adjusted by mixing 0.2
mol/dm3 MgCl2 aqueous solution and 0.1 mol/dm3
AlCl3 aqueous solution. MgAl-LDH with M2+/M3+ =2
were synthesized by adding mixing solution into 0.05
mol/dm3 NaHCO3 at room temperature through theco-precipitation process. 1 mol/dm3 NaOH wassimultaneously added into the aqueous solution inorder to keep pH 10. After precipitation was finished,
the products for MgAl-LDH were aged at room
temperature for 2 hours. They were separated fromliquid phase with Buchner funnel and sufficiently
washed by deionized water and finally air-dried at 323
K for 24 hours. Mixed oxides (Mg-Al double oxide)
were prepared by calcination at 473 K to 773 K in air
atmosphere for 2 hours of MgAl-LDH. The
rehydration treatment for mixed oxides (Mg-Al doubleoxide) was carried out in aqueous nickel acetate
solution with 0.1 M to 0.5 M at room temperature. The
samples prepared through this process werecharacterized with X-ray diffraction technique. The
microstructures were observed by SEM. The local
structures around Al were characterized by measuring
X-ray adsorption near edge structure (XANES) at
BL01A in UV-SOR with KTP. Al-K XANES was
measured at BL2A in UVSOR. The pellets of samples
were mounted on carbon tapes. The incident X-ray
beam was monochromatized with using KTP crystals.

Al-K XANES signals were collected with GaAsP
photo-diodes (Hamamatsu: G-1127-02). Theoretical
spectra were obtained by the first-principles supercell
method with a core-hole effect and evaluated for a
detailed analysis of Al-K XANES.
XRD results indicated that MgAl-LDH samples
prepared by the co-precipitation process wereidentified to hydrotalcite structure without anotherphase. After calcination at 573 K to 773 K in air
atmosphere for 2 hours of MgAl-LDH, samples wereidentified to amorphous mixed oxides (Mg-Al doubleoxide), not hydrotalcite structure. Using theseamorphous mixed oxides, the rehydration in aqueous
nickel acetate solution was attempted to synthesize themodified NiAl-LDH. According to XRD, samples
after the rehydration in aqueous nickel acetate solution
were identified to hydrotalcite structure and modified
NiAl-LDH was successfully obtained by therehydration in aqueous nickel acetate solution. Figure
1 shows the results of Al-K XANES spectra formodified NiAl-LDH synthesized by the rehydration
process. As shown in Fig. 1, Al-K XANES spectra ofsample obtained by rehydration process were quite
similar aluminum hydroxide. As a result, NiAl-LDH
prepared by rehydration process the same structure as
the coprecipitation process.

Fig. 1. Al-K XANES spectra of various products.

Ⅲ02- 8 48

Ⅲ -2. Materials Sciences
BL2A
BL2A

Local Structure Investigations of Gd3Ga5O12
Irradiated with Swift Heavy Ions
2

S. Yoshioka1, K. K. Okudaira2 and E. Kobayashi3

Gradiate School of Engineering, Kyushu University, Fukuoka 819-0395, Japan
Graduate School of Science and Engineering, Chiba University, Chiba 263-8522, Japan
3
Kyushu Synchrotron Light Research Center, Tosu 841-0005, Japan
1

Gadolinium gallium garnet (Gd3Ga5O12 or GGG) is
considered as an important material for laser opticalapplication. Ion irradiations are currently used to tailormaterials properties. In particular, for garnet structurematerials, swift heavy ion irradiations, produce
amorphous tracks that can change the microstructure
and the magnetic or magneto-optical properties. In thepresent study, we made a combined study of NEXAFS
measurements and first principles calculations on
Gd3Ga5O12 with special interests on the local
environment of Ga and Gd after irradiated with swift
heavy ions.
Synthetic single crystals of Gd3Ga5O12 were used inthis study. The crystals were cut into sheets with a(111) plane surface and were polished to a mirror
finish. The specimens were irradiated with 200 MeV
Xe ions to fluences of 1 × 1013 cm-2 at the H1 beamlineof the tandem ion accelerator facility at the Japan
Atomic Energy Agency (JAEA) in Tokai. Ga L3-edge
XANES measurements were performed at the BL2A
beamline of UVSOR Okazaki, Japan, using the partial
fluorescence yield method (PFY). A Beryl double
crystal monochromator defined Ga L3 absorption
edges in the energy region from 1105 to 1160 eV. The
samples were set with their surface perpendicular to
the incident X-ray beam. Fluorescence X-rays of Ga
Lα were collected using an energy dispersible silicon
drift detector (SDD). All measurements of XANES
spectra were carried out in vacuum of 1 × 10−5 Pa atroom temperature. To interpret the local structure fromthe experimental spectra, we used theoretical spectraby the full-potential linearized augmented plane wave
(APW) plus local orbitals technique as implemented in
WIEN2k code[1].
Figure 1 shows calculated Ga L3-edge XANES
spectrum of monoclinic type gallium oxide (β-Ga2O3)
as standard samples together with experimental
spectra. Theoretical spectrum was performed with 120
atoms supercell. The calculation of Ga2O3 successfully
reproduced the major peaks and shoulders of theexperimental spectrum with respect to relative energy
and intensity. Detailed analyses on the local
environment of Gd3Ga5O12 irradiated with swift heavy
ions are in progress by combined use of the NEXAFS
and the first principles band structure calculations.

Ⅲ-2

Fig. 1. Ga L3-edge XANES spectra of Ga2O3.
Experimental (a) and calculated (b) spectra.
[1] P. Blaha, et al., WIEN2k, An Augmented Plane
Wave + Local Orbitals Program for Calculating
Crystal Properties (Karlheinz Schwarz, Techn.
Universität Wien, Austria, 2001).

Ⅲ02- 9 49

Ⅲ -2. Materials Sciences
BL2B
BL2B

Ultraviolet Photoelectron Spectroscopy Reveals Small Intermolecular Band
Dispersion in an Acceptor-donor Blend
Institute of Functional Nano & Soft Materials (FUNSOM), Soochow University, Suzhou 215123, P. R. China
2
Institut für Angewandte Physik, Universität Tübingen, 72076 Tübingen, Germany

7,8,15,16-tetraazaterrylene (TAT) thin films grownon highly oriented pyrolytic graphite (HOPG)
substrates were studied by means of ultraviolet
photoelectron spectroscopy (UPS). Photon energydependent UPS performed perpendicular to themolecular planes of TAT multilayer films at room
temperature clearly reveals band-like intermoleculardispersion of the TAT highest occupied molecularorbital (HOMO) energy. Based on a comparison witha tight-binding (TB) model, a relatively narrow
bandwidth of 54 meV is derived. Upon additional
deposition of 2,2':5',2'':5'',2'''-quaterthiophene (4T), a
4T/TAT donor-acceptor blend is formed. The 4T/TAT
blend likewise exhibits intermolecular dispersion of
the TAT HOMO energy, yet with a significant
decreased bandwidth.
Photon energy-dependent UPS measurements of
TAT thin films were carried out at BL2B of UVSOR
III in a UHV chamber with a base pressure of 1×10−8
mbar at normal electron emission and at room
temperature (300 K). Energy calibration of the spectra
was enabled by separately recording the particularFermi edge on metallic components of the sample
manipulator for each photon energy. TAT and 4T
molecules were deposited by in-situ sublimation fromquartz crucibles.
Figure 1 shows the photon-energy dependent UPSof a) a TAT thin film on HOPG and b) of a TAT thinfilm in a heterostructure with 4T. Figure 1 c shows the
maxima of the HOMO-derived peak of the pristine
TAT film. In a TB-model the dispersion can be
expressed as
𝐸𝐸� �𝑘𝑘� � � 𝐸𝐸�� � 2�����𝑎𝑎� 𝑘𝑘� �with the normal component of the electron
momentum�2𝑚𝑚�∗ ��� � 𝐸𝐸� � �� �.
𝑘𝑘� � 𝐸ℏ
�
In this context, 𝐸𝐸� denotes the energy of the band
centre, t the transfer integral, 𝑎𝑎� the lattice spacing
along the surface normal, hν the photon energy, V0 the
inner potential and Eb the HOMO binding energy withrespect to the vacuum energy. The data points werefitted by a least-squares fitting procedure with 𝐸𝐸𝐸�� , t
and V0 being treated as fitting parameters. In this way,t = 13.5 meV, 𝐸𝐸𝐸�� = 6.546 eV and V0 = -0.5 eV wereobtained for the TAT HOMO energy dispersion.
Regarding the 4T:TAT blend, the TB model yields t =6.065 meV, 𝐸𝐸𝐸�� = 6.423 eV and V0 = -5.6 eV.
In conclusion, intermolecular energy-band
dispersion of the TAT HOMO perpendicular to themolecular planes, is clearly identified for both the TAT

multilayer film and the 4T:TAT blend. Comparatively
narrow bandwidths well below 0.1 eV are identified,with the 4T:TAT bandwidth being significantly
decreased compared to the initial TAT multilayer film.
Therefore, suchlike donor-acceptor heterojunctions
are rendered promising candidates as integral parts oforganic-based devices. We further demonstrate that anexperimental determination of very narrow
bandwidths at room temperature is indeed feasible bymeans of UPS.
The results have been published in [1].
a)b)Intensity (a.u.)

Ⅲ-2

N. Aghdassi1, Q. Wang1, 2, R.-R. Ji1, B. Wang1, J. Fan1 and S. Duhm1

Binding energy w.r.t. Evac Binding energy w.r.t. Evac
HOMO energy w.r.t. Evac (eV)1

Momentum k⊥(Å)

Fig. 1. HOMO region of photon energy-dependent
normal emission UPS spectra of a) a TAT thin filmwith a nominal thickness of 150 Å and b) a 120 Å 4T/
150 Å TAT blend on HOPG. c) TAT HOMO energy
dispersion perpendicular to the molecular planes asderived from photon energy-dependent UPS. Black
dots denote experimental data, whereas red curves areassociated with the TB mode.
[1] N. Aghdassi, Q. Wang, R.-R. Ji, B. Wang, J. Fanand S. Duhm, Nanotechnology 29 (2018) 194002.

Ⅲ02- 10 50

Ⅲ -2. Materials Sciences
BL3B
BL3B

Characterization of Intrinsic Luminescence from Orthophosphate andBorophosphate Crystals with Multiple Nonequivalent Oxoanions upon
Vacuum UV Excitation
N. Kodama, C. Takahashi, H. Kubota and T. Takahashi

Graduate School of Engineering Science, Akita University, Akita 010-8502, JapanTo date, there has been very little work focusing on
the formation of molecular-type excitons in the local
structure of low-symmetry complex rare-earth oxides
with multiple nonequivalent oxoanions of the PO43- orBO33- group. To the best of our knowledge, for thesecomplex oxoanion crystals, a comprehensive
understanding of the correlation between intrinsic
luminescence bands and the number and symmetry of
nonequivalent oxoanion groups such as PO43- and/or
BO33- is still lacking. We focused on orthophosphateandborophosphatecrystalswithmultiple
nonequivalent PO43- and/or BO33- oxoanion groups.
The first type is Li3Sc2(PO4)3 (LSP) with threenonequivalent PO43- groups. The second type is
CaK(PO4)2 (CKP) with two nonequivalent PO43groups. The third type is Ba3(BO3)(PO4) (BBP) with
one PO43- group and one BO33- group.
We report intrinsic luminescence from self-trapped
excitons (STEs) as intra-anion excitons in thesecrystals. In addition, we discuss the correlation
between intrinsic luminescence bands from STEs andthe number of nonequivalent PO43- and/or BO33groups in LSP, CKP, and BBP.
Luminescence and excitation spectra of STEs in
LSP, CKP, and BBP polycrystals were measured at
twelve temperatures in the range of 8-293 K using theundulator BL3B at the UVSOR Synchrotron Facility.
The emission spectra were corrected for the
wavelength dependence ofthe diffraction
monochromator and CCD detector using calibrated
deuterium and halogen lamps as standard light sources.
Time-resolved spectra were measured using a pulse
with a width of 10 ns from a F2 pulsed laser operating
at 157 nm, and the decay times were determined.
All samples were found to exhibit multiple STE
luminescence bands in the UV region under VUVexcitation at 70 and 160 nm. The excitation spectral
intensity in the 70-220 nm wavelength range for theorthoborate and borophosphate crystals increased
rapidly below about 175-180 nm. Broad excitation
bands were assigned to bandgap excitations ormolecular transitions of the PO43- or BO33- group.
Figures 1(a)-1(f) show the luminescence spectra for
LSP, CKP, and BBP at 8 and 293 K, excited at 70 nm.
In order to estimate the number and peak energy of the
bands, the spectra are deconvoluted into Gaussians in
Figs. 1(a)-1(d). The luminescence spectra of LSP at
293 K and 8 K comprised, respectively, three distinct
broad bands associated with STE(I), (II), and (III)having peaks at 263-247, 351, 430-476 nm, as shownin Figs. 1(a) and 1(b). These three intrinsic bands are
assigned to STE(I), STE(II), and STE(III) in three setsof nonequivalent PO43- groups. The spectra of CKP at
8 K consisted of two broad bands with peaks at 245
and 303 nm, and 281 and 364 nm, respectively, as
shown in Figs. 1(c) and 1(d), associated with STE(I)and STE(II) in two sets of nonequivalent PO43- groups.
On the other hand, as shown in Figs. 1(e) and 1(f), BBP
exhibited one broad band at 8 and 293 K. In LSP and

CKP, the number of intrinsic luminescence bands
corresponds to the number of nonequivalent PO43groups, whereas in BBP, only one band appears,
despite the presence of a PO43- group and a BO33group. The number of bands is inconsistent with thenumber of PO43- and BO33- groups. A possible
explanation for this discrepancy is that a self-trappingof excitons takes place in either the PO43- or BO33group with different geometries. The peaks of the STE
luminescence bands in all samples (LSP, CKP, BBP)
shifted to shorter wavelengths with decreasing
temperature from 293 to 8 K.
The radiative decay curves consist of a fast and aslow component due to high-spin and low-spin STEs
associated with the two possible spin orientations forthe exciton electron-hole pair, as observed in alkali
halides [1]. For LSP, the decay times for STE(I)luminescence at 243 nm are 15 ns and 174 ns, andthose for STE(II) at 300 nm are 28 ns and 148 ns.
The fast decay components for STE(I) and STE(II)in LSP may originate from singlet STE states in two
PO43- groups with C1 symmetry. In contrast, the slow
decay components for STE(I) and STE(II) are
attributed to triplet STEs in two PO43- groups in which
triplet STE states occur.

Fig. 1. The decompositions of intrinsic luminescence
spectra excited at 160 nm in (a) and (b) LSP, (c) and(d) CKP, and in (e) and(f) BBP at 8 K and 293 K.The
calculated components of the Gaussians are
represented by yellow, orange, and gray lines.
[1] T. T. Williama, K. S. Song, J. Phys. Chem. Solds.
51 (1990) 679.

Ⅲ02- 11 51

Ⅲ-2

Ⅲ -2. Materials Sciences
BL3B
BL3B

Bandgap Energy of La and Y admixed Gd2Si2O7 Crystals Using the UVSOR
Facility
T. Horiai1, S. Kurosawa2, 3, A. Yamaji1, S. Kodama1, S. Yamato1, Y. Shoji1, 4, M. Yoshino1,
Y. Ohashi2, K. Kamada2, 4, Y. Yokota2 and A. Yoshikawa1, 2, 4
Institute for Materials Research, Tohoku University, Sendai 980-8577, JapanNew Industry Creation Hatchery Center (NICHe), Tohoku University, Sendai 980-8579, Japan3
Department of Physics, Yamagata University, Yamagata 990-8560, Japan
4
C&A Corporation, Sendai 980-8579, Japan
1

2

Table 1. Light outputs of (Gd0.59-x, Ce0.01, La0.40,
Yx)2Si2O7 at 25ºC and 175ºC
Samplex = 0.00
x = 0.05
x = 0.10
x = 0.15

Light output @ 25ºC
[photons/MeV]
42,00043,00036,00033,00020
Transmittance [%]Ⅲ-2

Scintillation crystals convert energy of ionizing
radiation such as gamma-ray and X-ray into multiple
photons of energy 2~8 eV. Scintillators are used inseveral fields, and oil-well exploration is one of theapplication fields [1-3]. Specifically, scintillators areused in gamma-ray detectors in combination with aphotodetector to discriminate geologic layers at oil
well exploration sites. Since the ground temperature in
shale layer is reached approximately 200ºC, the noiseby dark current of the photomultiplier tube (PMT) is
become larger. On the other hand, the light outputs are
dropped for conventional scintillators. To solve
degrading the signal-to-noise ratio, the development of
new scintillator which could keep high light output
even at high temperature is required.
To
satisfythisrequirement,
Ce-doped(Gd,La)2Si2O7 (Ce:La-GPS) has been investigated.
Ce:La-GPS has a light output of ~42,000 photons/MeV,
and the light output is maintained even at 150°C [4];however, for high temperature applications, further
improvement is needed. In this study, we focus on Yadmixed Ce:La-GPS and optimize Y concentration to
improve the temperature dependence. Here, inprevious studies, the thermal quenching of Y-admixed
Ce-doped Lu2SiO5 (Ce:LYSO) was suppressed whencompared to Y-free sample (Ce:LSO) [5, 6].
We prepared (Gd0.59-x Ce0.01 La0.40 Yx)2Si2O7(Ce:LaY-GPS) single crystals grown by the micropulling-down method, and UV absorption edge forthese samples were evaluated with a photo diode (IRD,
AXUV 100) at BL3B of UVSOR. The bandgap
energies were calculated from the UV absorption edge.
From the result of the temperature dependence oflight output at 25ºC and 175ºC, Y5% substituted
Ce:La-GPS was improved (Table 1). On the other hand,
the light output of Y15% substituted Ce:La-GPS wasdegraded.
Figure 1 shows the UV absorption spectra of Y0%
and 15% substituted Ce:La-GPS. From this figure, theUV absorption edge wavelength were constantregardless of Y concentration (~174 nm), and the
bandgap energies were determined appoloximately
7.14 eV. Thus, the improvement factor of temperaturedependence of light output was not the effect of the
bandgap energy.

Light output @ 175ºC[photons/MeV]
34,00040,00034,00024,000x = 0.00
x = 0.15

15
10
5
0
160

170

180
190
Wavelength [nm]200Fig. 1. UV absorption spectra of (Gd0.59-x, Ce0.01,
La0.40, Yx)2Si2O7 at 6 K.
[1] C. Rozsa, R. Dayton, P. Raby, M. Kusner and R.
Schreiner, IEEE Trans. Nucl. Sci. 37 (1996) 966.
[2] A. Baberdin, A. Dutova, A. Fedorov, M. Korzhik,
V. Ligoun, O. Missevitch, V. Kazak, A. Vinokurov andS. Zagumenov, IEEE Trans. Nucl. Sci. 55 (2008) 1170.
[3] C.L. Melcher, J.S. Schweitzer, R.A. Manente andC.A. Peterson, J. Crystal Growth 109 (1991) 37.
[4] S. Kurosawa, T. Shishido, T. Sugawara, A. Nomura,
K. Yubuta, A. Suzuki, R. Murakami, J. Pejchal, Y.
Yokota, K. Kamada and A. Yoshikawa, Nucl. Instrum.
Methods Phys. Res. A 772 (2015) 72.
[5] H. Suzuki, T.A. Tombrello, C.L. Melcher and J.S.
Schweitzer, IEEE Trans. Nucl. Sci. 40 (1993) 380.
[6] L. Pidol, A. Kahn-Harari, B. Viana, E. Virey, B.
Ferrand, P. Dorenbos, J.T.M. Haas and C.W.E. Eijk,
IEEE Trans. Nucl. Sci. 51 (2004) 1084.

Ⅲ02- 12 52

Ⅲ -2. Materials Sciences
BL3B
BL3B

Insight into the High Light Output of Ce:(Gd, La)2Si2O7 Scintillator
S. Kurosawa1, 2, A. Yamaji3, T. Horiai3, S. Kodama3, S. Yamato3, Y. Shoji3, 4, Y. Ohashi3,
Y. Yokota1, K. Kamada1, 4, A. Yoshikawa1, 3, 4 and M. Kitaura2
1

New Industry Creation Hatchery Center (NICHe), Tohoku University, Sendai 980-8579, Japan
2
Faculty of Science, Yamagata University, Yamagata 990-8560, Japan
3
Institute for Materials Research (IMR), Tohoku University, Sendai 980-8577, Japan
4
C&A Corporation, Sendai 980-8577, Japan.

Crystalline scintillators have been used in various
fields such as medical imaging, astronomy and so on.
Recently, scintillation properties of (Ce0.01, Gd0.90,
La0.09)2Si2O7 (Ce:La-GPS) have been studied. The
Ce:La-GPS crystal had the light output of around
4,000 photons/MeV and the FWHM energy resolutionof 5.0% at 662 keV [1, 2]. Moreover, the light output
was constant in the temperature range from 10 to 423
K [3]. Thus, the Ce:La-GPS crystal is applicable toradiation detection at high temperatures.
The evaluation of the bandgap energy is very much
important for the development of more functional
scintillators. From this viewpoint, we have evaluatedthe bandgap energy of La-GPS crystals at the BL3B of
UVSOR. The bandgap energy of La-GPS wasestimated to be over 7.130.03 eV. Compared withother oxide scintillators, Ce:La-GPS was found tohave wider bandgap. Generally, the light output of
scintillator is inversely proportional to the band-gap
energy. Despite such a large bandgap energy, the light
output is larger than those of other oxide scintillatorswith small bandgap energies. This result implies thatthe product of transfer efficiency and/or electron-hole
pair generation efficiency in Ce:La-GPS is higher thanthose in others. The cause may be due to small numberof traps in Ce:La-GPS. In order to clarify high light
output in Ce:La-GPS, we have investigated thermoluminescence (TL) properties under irradiation withvacuum ultraviolet (VUV) radiation.
Figure 1 and 2 show TL emission spectra and TL
glow curve for Ce:La-GPS, respectively, where the TL
intensity is the integrated value from the TL emission
spectrum at each temperature. The TL glow peak isfound at around 120 K. The TL glow curve for 1.5%
Ce-doped Gd2SiO5 (Ce:GSO) was also measured for areference. Apparently, the integrated value of the 120
K peak for Ce:La-GPS is smaller than the sum ofintegrated values of a number of peaks for Ce:GSO up
to 300 K. Since Ce:La-GPS have small number of thetraps which block the electron transportation into
luminesce center, the transfer efficiency becomes high,compared to Ce:GSO. Details of the present study will
be reported in Ref. 4.

Ⅲ-2

Fig. 1. TL-emission spectra for Ce:La-GPS at 120K
and Ce:GSO at 282K.

Fig. 2. TL glow curves of Ce:La-GPS (solid line) andCe:GSO (dotted line).
[1] A. Suzuki et al., Applied Physics Express 5 (2012)
102601.
[2] S. Kurosawa et al., Nucl. Inst. and Meth. in Phys.
Res. A774 (2014)30.
[3] S. Kurosawa et al., Nucl. Inst. and Meth. in Phys.
Res. A772 (2015)72.
[4] S. Kurosawa et al., IEEE Trans. Nucl. Sci.
Acceptted.

Ⅲ02- 13 53

Ⅲ -2. Materials Sciences
BL3B
BL3B

PL Decay Times of Trans-stilbene and 1,4-Bis(2-methylstyryl) Benzene(BisMSB)-doped Trans-stilbene at 13-300 K
Institute for Materials Research (IMR), Tohoku University, Sendai 980-8577, JapanNew Industry Creation Hatchery Center (NICHe), Tohoku University, Sendai 980-8579, Japan
3
Fuculty of science, Yamagata University, Yamagata 990-8560, Japan
4
C&A Corporation, Sendai 980-8577, Japan.
1

2

Ⅲ-2

S. Yamato1, A. Yamaji1, S. Kurosawa2, 3, M. Yoshino1,
Y. Ohashi2, K. Kamada2, 4, Y. Yokota2 and A. Yoshikawa 1, 2, 4

Neutron detectors can be used in several fields suchas homeland security and maintenance of social
infrastructure. In such applications, gaseous detectors
can be used due to high and low detection efficiency
for neutron and gamma rays as background noise,respectively. However, gaseous detectors containexpensive gas or toxic gas like 3He and BF3, andscintillators are expected to be an alternative detector.
Here, neutron energy is evaluated using Time-ofFlight (TOF) method, and the energy resolution
depends on the timing response of the scintillator.
Therefore, inorganic scintillators with long decay time
are not suitable for measurements of neutron energies.
Organic scintillators are used as neutron detectors,
and trans-stilbene crystals, for example, have decay
time of 6.4 ns [1] and good pulse shape discrimination(PSD) property, which is often operated todiscriminate neutron/gamma [2]. Organic non-singlecrystal scintillators such as liquid scintillators (LSs)and plastic scintillators (PSs) are applied to detectionof underground environment neutron and energy
spectrum measurement of fast neutrons, etc., because
these scintillators have faster scintillation decay thanorganic “crystal” scintillators. However, LSs areflammable and toxic, and PSs have low radiation
hardness. Therefore, we focused on organic crystal
scintillators which are safer and more stable than LSs
and PSs.
We grew pure trans-stilbene crystal and 1,4-Bis(2methylstyryl) benzene (BisMSB)-doped trans-stilbene
crystal, by the self-seeding vertical Bridgman method
using an enclosed chamber [3]. The doping amount of
BisMSB was 1wt%. Pulling down rate for growth was
1.44 mm/h. BisMSB was used as solutes in LSs andPSs, and BisMSB doped LSs have fast decay times of~2 ns [4].
We measured the photoluminescence (PL) emission
spectra of the samples excited by 260-nm photons at
13 and 300 K as shown in Fig. 1, with the BL3B at
UVSOR Synchrotron Facility, using a photo multipliertube (PMT) (C5594, Hamamatsu Photonics) and a
CCD camera (MODEL:TN/CCD/100PBVISAR,
Princeton Instruments). At 300 K, the emission peaks
ranged from 400 to 550 nm were appeared for theBisMSB-doped crystal. Although the spectrum wasshifted by doping BisMSB at 13 K, the peak was blueshifted compared to that at 300 K.
The PL decay times of the samples excited by 260-nm photons at 13-300 K are summarized in Table 1.
The ranges of excitation wavelength and emission
wavelength for PL decay measurements were from226 to 293 nm and from 295 to 680 nm, respectively.
The PL decay time of trans-stilbene matched the value
in previous report [5]. Despite the difference ofluminescence spectra, there was almost no differencein photoluminescence decay times between the two
crystals. Further study is necessary to reveal the reason.

Fig. 1. Emission spectra of grown crystals excited by
260 nm at 13 K and 300 K.
Table 1. Photoluminescence decay times of grown
crystals excited by 260 nm at 13-300 K
Trans-stilbene +Trans-stilbene
T [K]BisMSB(1wt%)
τ1 [ns]τ1 [ns]
13
1.9
1.8
50
1.9
1.8
100
1.7
1.7
200
1.2
1.5
250
1.1
1.5
300
1.0
1.1
[1] J. B. Birks, The Theory and Practice of
Scintillation Counting, (Pergamon, Oxford, 1964).
[2] N. Zaitseva et al., IEEE Trans. Nucl. Sci. 58 (2011)3411.
[3] A. Arulchakkaravarthi et al., J. Crystal Growth 234(2002) 159.
[4] M. M. de Souza et al., Synth. Metals 101 (1999)
631.
[5] D. J. S. Berch et al., Chem. Phys. Lett. 38 (1976)
432.

Ⅲ02- 14 54

Ⅲ -2. Materials Sciences
BL3B
BL3B

Temperature Dependence of Cs2HfI6 Transmittance Spectra
S. Kodama1, S. Kurosawa2, 3, A. Yamaji1, M. Yoshino1, Y. Ohashi1, K. Kamada2, 4,
Y. Yokota2 and A. Yoshikawa1, 2, 4
Institute for Materials Research (IMR), Tohoku University, Sendai 980-8577, JapanNew Industry Creation Hatchery Center (NICHe), Tohoku University, Sendai 980-8579, Japan
3
Faculty of Science, Yamagata University, Yamagata 990-8560, Japan
4
C&A Corporation, Sendai 980-8577, Japan
1

2

A2HfX6 (A: monovalent cation, X: halogen ion)compounds are host-emitting materials originatedfrom self-trapped exciton. Since the crystal lattice of
A2HfX6 compounds can be a well-ordered and highsymmetry cubic structure (space group: Fm-3m),
producing a transparent single crystal is easy. Actually,Cs2HfCl6 (CHC) or anion-admixed Cs2HfCl2Br4 hadbeen reported as single-crystalline scintillators so far[1-2], and CHC has a high scintillation light-output ofover 50,000 photons/MeV.
Generally, the light output of scintillator (Y) is
inversely proportional to band-gap energy of the hostmaterial (Egap); Y ∝ (Egap)-1. In order to realize thehigher light output than CHC, Cs2HfI6 (CHI) is
investigated in this study, because the Egap of CHC
and CHI were calculated as ~6.4 eV and ~3.9 eV,
respectively [3].
A single-crystalline CHI specimen was synthesizedfrom 99%-pure HfI4 and 99.999%-pure CsI using thevertical Bridgman growth method. CHI was revealed
to emit orange-red light around 650 nm, and had a highlight output of ~70,000 photons/MeV, a moderate fast
scintillation decay of ~2.5 µs. We found that CHI is a
first noble red-emitting scintillator applicable to thephoton-counting detect technique.
To develop CHI furthermore, the evaluation of
fundamental optical properties should be necessary,and we measured transmittance spectra of CHI at room
temperature and 8 K cooled by liquid Helium in acryostat chamber of UVSOR BL3B. Transmittancespectra were measured with a photo-diode (IRD,
AXUV 100). The light source was a synchrotron light.
Figures indicate the obtained transmittance spectraof CHI at room temperature and 8 K. The
transmittance gradually decreased towards shorter
wavelength from 700 nm. We observed atransmittance drop around ~480 nm at room
temperature, and the dropping wavelength was
revealed to shift to ~440 nm at 8 K due to lattice
vibration. Since CHI was revealed to absorb the blueyellow visible light around ~480 nm, CHI crystal had
the orange color. CHI should have an absorption edgearound ~320 nm based on the calculated Egap of ~3.9
eV. The transmittance drop at ~480 nm was considered
to be an absorption of the self-trapped exciton.

Ⅲ-2(a) Room temperature(b) 8 K
Fig. Transmittance spectra of CHI crystal. (a) and (b)are spectra at room temperature and 8 K, respectively.
[1] A. Burger et al., Appl. Phys. Lett. 107 no. 14(2015) 34.
[2] S. Lam, C. Guguschev, A. Burger, M. Hackett, and
S. Motakef, J. Cryst. Growth 483 (2018) 121.
[3] B. Kang and K. Biswas, J. Phys. Chem. C 120 no.
22 (2016) 12187.

Ⅲ02- 15 55

Ⅲ -2. Materials Sciences
BL3B
BL3B

Evaluation of Optical Basic Properties of Ultra-Violet Emitting Zinc
Aluminate Phosphor

The UV light is used for various applications
depending on the wavelength as well as thesterilization described above. The lights of 200-280
nm (UV-C) region as for the sterilization, 280-320 nm(UV-B) region as the treatment of the skin disease,320-400nm (UV-A) region as application of
purification of water and air, and photocatalysts.
Recently, from the viewpoint of consideration to theenvironment, the mercury free UV emission devices
have been demanded for the application of catalyst andmedical situations. In our previous work, it wasclarified that ZnAl2O4 phosphor was suitable for theUV field emission lamp because of its stability andluminescent property. It shows strong UV emission
peaked around 250 nm which suitable for sterilization.
In ZnAl2O4, the application as the sterilization lightsource is expected from the luminescence wavelengtharea, but it is not sure about the application as otherultraviolet light sources. Therefore, the possibility of
the application of the ultraviolet light source is thought
about by controlling composition of ZnAl2O4.
Zn(Al1-xGax)2O4 powders were prepared by solid
phase synthesis using ZnO (99.999%), α-Al2O3(99.99%) and Ga2O3 (99.9%) powders. The Ga ratio x
was changed from 0 ~ 1 for control the phase. The
powders were fired at 1000 ~ 1300 oC for 3 hours inair. And the powders were evaluated using X-ray
diffraction (XRD), Cathodoluminescence (CL) andPhotoluminescence (PL, PLE).
Figure 1 shows cathodoluminescent spectra ofZn(Al1-xGax)2O4 phosphors fired at 1300oC in air. The
emission peak was shifted from 250 nm to 350 nm
according to increasing of Ga ratio X. However, CLintensity of phosphors were quite different by Ga
composition. Especially, the powders at x = 0.5 and 1
showed poor luminescence. It is thought that the
distortion of crystallinity was occurred for the powderof x = 0.5. On the other hand, for the powder of x = 1,
the optimum firing condition of ZnGa2O4 was different
from ZnAl2O4.
Figure 2 shows Photoluminescent excitation spectraof Zn(Al1-xGax)2O4 phosphors fired at 1300oC in air,measured at 8K. The excitation band was shifted tolonger wavelength according to increase of Ga ratio X.
From our previous work, the PLE absorption edge of
ZnAl2O4 was equivalent to forbidden gap. It indicatesthat forbidden gap of Zn(Al1-xGax)2O4 phosphors
became narrower according to increase of Ga ratio.
The energy of absorption edge was changed linearly.
From XRD measurement also shows Zn(Al1-xGax)2O4

phosphors successfully synthesized at 1300oC firing
because of the shift of diffraction peak obeyed
Begard’s law. it seems that the replacement of Ga to
Al-site was occurred smoothly.

CL Intensity (a.u.)

Ⅲ-2

Graduate School of Integrated Science and Technology, Shizuoka University, Hamamatsu 432-8651, Japan
2
Faculty of Engineering, Shizuoka University, Hamamatsu 432-8651, Japan

3000

VA=10 kV

Zn(Al 1-xGax)2O4
1300oCx=0
x = 0.25
x = 0.50
x = 0.75
x=1

2000
1000
×10
0
200

300

400
500
Wavelength (nm)600

Fig. 1. CL spectra of Zn(Al1-xGax)2O4 alloy phosphor.

PLE Intensity (norm..)

1

H. Kominami1, K. Hada1, S. Kubota1, K. Kijima1, M. Ohkawa1, Y. Kato1,
T. Matsuura2, M. Arimura2, K. Imagawa2 and K. Warita2

1
0.8
0.6
0.4
0.2
0

moni. = PL peak
at 8K
Zn(Al 1-xGax)2O4
x=0
x = 0.25
x = 0.50
x = 0.75
x=1
200
300
Wavelength (nm)Fig. 2. PLE spectra of Zn(Al1-xGax)2O4 phosphor at
8K monitored at CL peak.

Ⅲ02- 16 56

Ⅲ -2. Materials Sciences
BL3B
BL3B

Emission Spectra of Pr-doped SrY2O4
M. Yoshino, S. Nishiki, T. Kuyama and S. Watanabe

Graduate School of Engineering, Nagoya University, Nagoya 464-8603, JapanThe trivalent lanthanide ions (e.g., Ce3+, Nd3+, Er3+)in oxide crystals have drawn attentions due to theirapplication for luminescent materials in NIR to UV
regions such as solid-state lasers, phosphors or
scintillators. The trivalent praseodymium ion, Pr3+, hasalso attracted attentions as luminescence centers. In
this work, the excitation spectra and emission spectra
for Pr3+ in SrY2O4 crystal have been measured. The Prdoped SrY2O4 samples are synthesized by solid state
reactions. The samples are annealed in N2-H2
atmosphere in order to reduce Pr4+ to Pr3+. The
concentration of Pr in the samples are 0.5, 1.0, 1.5, 2.0
and 3.0 mol%.
The excitation spectrum monitored at 520 nm
emission contains absorption around 315 nm and 273
nm and they originate the 4f-5d transitions of Pr3+ [1].
The emission spectra at 315 and 273 nm excitation in
300 K are shown in Fig. 1 and Fig. 2, respectively.
Peaks A, B, C, D, E exist in the each spectra. On theother hand, peak F appears only in 273 nm excitationand has different dependency to Pr concentrationcompared with the other peaks. The intensity of F
decrease with Pr concentration while it decreases after
the increase in A, B, C, D and E. The emission spectra
at 315 and 273 nm excitation in different temperaturesare shown in Fig. 3 and Fig. 4, respectively. It is foundthat the peak F has also different dependency totemperature compared with the other peaks. The
intensity of F is high when it measured in hightemperature while it decreases monotonously withtemperature in the other peaks. The peak F is not seenin the spectrum of 315 nm excitation in eachtemperature.

Fig. 1. Emission spectra of SrY2O4:xPr.
(λex= 315 nm, 300 K).

Ⅲ-2

Fig. 2. Emission spectra of SrY2O4:xPr.
(λex= 273 nm, 300 K).

Fig. 3. Emission spectra of SrY2O4:0.005Pr.
(λex= 315 nm).

Fig. 4. Emission spectra of SrY2O4:0.005Pr.
(λex= 273 nm).
[1] M. Yoshino, S. Nishiki and S. Watanabe, UVSOR
Activity Report 43 (2016) 95.

Ⅲ02- 17 57

Ⅲ -2. Materials Sciences
BL3B
BL3B

Energy Transfer from I− Centers to Tl+ Centersin Co-Doped NaCl: I−, Tl+ Crystals
O. Yagi and T. Kawai

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

Lumi. Int. [arb.units]

RT

NaCl:Tl
Absorption

Abs. Int. [arb. units]-

NaCl:I
Luminescence
NE

A

4.5

B

C

5.0
5.5
6.0
Photon Energy [eV]6.5

Fig. 1. Luminescence spectrum (Red) of NaCl:I− andabsorption spectrum (blue) of NaCl: Tl+ at RT.

Intensity [arb.units]

Ⅲ-2

Energy transfer mechanism in solid crystals is oneof the interesting research topics in solid state physics.
Many experimental investigations have been
performed on the crystals co-doped with two kinds ofimpurities. The resonant transfer and the emission
reabsorption are well-known as the mechanism of theenergy transfer. Both the mechanisms can occur if
there is the overlap between the donor’s luminescenceband and the acceptor’s absorption band [1].
In this study, we have investigated the NaCl crystals
co-doped with I− and Tl+ ions (NaCl:I−,Tl+) to discuss
the existence and the mechanism of the energy
transfer. NaCl crystals have the wide band-gap up to
the vacuum ultraviolet energy region and are a suitable
candidate host for doping of impurity ions. NaCl
crystals doped with iodine anion (NaCl:I−) exhibit
intense luminescence in deep ultra-violet region evenat room temperature (RT), so iodine anions in NaCl area suitable donor impurity.
Figure 1 shows the absorption spectrum of NaCl:Tl+
and the luminescence spectrum of NaCl:I− at RT.
NaCl:Tl+ produces three absorption bands labeled with
A, B, and C at 4.8, 5.3, and 6.2 eV respectively. Theseabsorption bands are attributed to the intra-ionictransitions from the ground 1S0 state to the excited 3P1,
3
P2, and 1P1, states. NaCl:I− shows the luminescenceband appearing around 5.2 eV. It is called the NE
luminescence band and comes from the one-center
type localized exciton, which is localized on thecentral site of a substituted I− impurity with smalllattice relaxation [2]. The NE luminescence band in
NaCl:I− has almost no overlap with the absorption
bands in NaCl:Tl+. This fact indicates that the resonant
energy transfer and the emission reabsorption from theI− centers to the Tl+ centers are hard to occur.
Figure 2 shows the decay profiles of the NE
luminescence in the NaCl:I−,Tl+ under the excitationon the I− absorption band (6.8 eV) at 6, 160, 200, and
240 K. The decay profiles at 6~160 K exhibit a single
exponential decay. The decay time constants at 10 and
160 K are 88 and 43 ns, respectively, which are thesame as the decay time of the NaCl:I−. On the other
hand, the decay profiles at 200~300 K exhibit two
exponential decay components. Both decay
components become faster with increasing
temperature. The behavior of the decay profiles
indicates the existence of the energy transfer from theI− centers to the Tl+ centers at more than 200 K. We are
analyzing the decay profiles with the energy transfer
model via carrier diffusion reaction.

10-

NaCl:I ,Tl+

Single-exp

6K
200 K

160 K
240 K

Synchrotron radiation

1

0.1

0.01
0

10

20

Time [ns]3040Fig. 2. Decay profiles of the NE luminescence in the
NaCl:I−,Tl+ at 6, 160, 200, and 240 K.
[1] A. Iguchi, T. Kawai and K. Mizoguchi, Phys.
Status Solidi. C 13 (2015) 85.
[2] I. Akimoto, M. Shimozato and K. Kan’no, Phys.
Status Solidi. C 6 (2009) 342.

Ⅲ02- 18 58

Ⅲ -2. Materials Sciences
BL3B
BL3B

Comparison of Luminescence Properties at Room Temperature between
NaI:Tl+ and NaI:In+ Crystals
S. Watanabe and T. Kawai

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

Photon Energy [eV]
3
2.5
2.0

4

1.8

Lumi. Int. [arb.units]

RT

+

A'

NaI:In+NaI:Tl

A'

Ⅲ-2

300

400

500
600
Wavelength [nm]700Fig. 1. Luminescence spectra of NaI:In+ (red) andNaI:Tl+ (blue) crystals excited at 200 nm at RT.
65

Photon Energy [eV]
4.5
4.0

RT

+

0.08

A

1.0

NaI:Infor 520 nm

0.0
2.0
1.0

A

240

+

C

0.04
0.00
200

2.0

Optical Density

C

RT

0.12

3.5

NaI:Tlfor 425 nm

Lumi. Int. [arb.units]

Alkali halide crystals doped with Tl+-type centers
have been extensively studied until now. The Tl+-type
centers exhibit the optical bands called A, B, and C,
which are attributed to intra-ionic transitions from the1
A1g ground state to the 1T1u, 3T2u+3Eu, and 3T1u excitedstates, receptively [1,2].
Among the alkali halides doped with the Tl+-type
centers, CsI:Tl+ and NaI:Tl+ crystals have been widelyused as a scintillator and investigated in detail.
Especially, NaI crystals doped with the Tl+ centers
have the high scintillation yield and faster time
response. On the other hand, optical studies on NaI
crystals doped with In+ centers have not been reported
to our knowledge. In this study, optical properties of
the NaI:In+ crystals have been investigated at room
temperature (RT).
NaI:In+ and NaI:Tl+ crystals were grown by the
Bridgman method from NaI beads and InI or TlI
powders, respectively. The samples used for themeasurements were cleaved in a nitrogen-filled glove
box. Optical measurements were performed at theBL3B of UVSOR.
Figure 1 shows the luminescence spectra of NaI:In+
and NaI:Tl+ under excitation at 200 nm at RT. In
NaI:Tl+, the A’ luminescence band due to the radiativetransition from the relaxed excited state of 3T1u is
confirmed at 425 nm [3]. The NaI:In+ crystal exhibitsa broad luminescence band around 520 nm, which
would assigned to the A’ luminescence of the In+
centers from the comparison with NaI:Tl+.
Figure 2 shows the absorption (broken curve) andthe excitation (solid curve) spectra for the A’
luminescence of NaI:In+ and NaI:Tl+ at RT. The
absorption band at 295 nm in NaI:Tl+ corresponds to
the A absorption band [3]. Since the absorption bandsof the In+ center in alkali halide crystals are located at
the lower energy region than those of the Tl+ centers,
the band at 275 nm in NaI:In+ would correspond to the
C band. The A’ luminescence bands in both the
crystals are efficiently excited at the respective
absorption bands. Furthermore, both excitation spectra
demonstrate that the A’ luminescence bands have
responses even in the higher energy range than about
230 nm, where correspond to the energy region above
the fundamental absorption edge of NaI host crystals.
The fact indicates that the energy absorbed by the host
crystals transfers to the energy level of the impurity
centers. The luminescence properties of NaI crystals
activated with various kind of impurity centers should
be extensively investigated.

280
320
Wavelength [nm]

0.0
360

Fig. 2. Absorption (broken) and Excitation (solid)
spectra for the A’ luminescence of NaI:In+ and NaI:Tl+
at RT.
[1] A. Ranfagni et al.: Advances in Physics 32 (1983)
823.
[2] P. W. M. Jacobs: J. Phys. Chem. Solids 52 (1991)
35.
[3] M. P. Fontana and W. J. Van Sciver: Phys. Rev.168(1968) 960.

Ⅲ02- 19 59

Ⅲ -2. Materials Sciences
BL3B, BL7B
BL3B, BL7B

Total Photoelectron Yield Spectroscopy on 3d Transition Metal Doped AlN
Films
N. Tatemizo1, S. Imada1, S. Hirata2, W. Kamihigoshi2 and K. Fukui2

Faculty of Electrical Engineering and Electronics, Kyoto Institute of Technology, Kyoto, 606-8585, Japan
2
Faculty of Electrical and Electronics Engineering, University of Fukui, Fukui, 910-8507, Japan

Ⅲ-2

Intermediate band (IB) materials proposed by Luqueet al., have gained attention for use in absorption layersof solar cells to increase their conversion efficiency [1].
Heavy 3d-transition metal (3d-TM) doped AlN films
are one of the candidates of IB materials. Exploring thepossibility of them, we have synthesized Ti [2], V [3]and Cr [4,5] doped AlN films and investigated theirband structures.
The films were deposited on SiO2 glass or Ti metal
polycrystalline substrates by RF sputtering from an AlN
target with Ti or Cr metal chips on it. Results of XRD,
TEM and 3d-TM K-edge EXAFS showed that the films
have wurtzite structures with Ti and Cr atoms occupied
the Al sites of AlN [2,5]. To investigate the potentials of
the electron occupied states (Valence band and/or a partof IB), we carried out total photoelectron yield
spectroscopy (TPYS) [6] for the films deposited on Ti
metal substrates. As show in Fig. 1. electrical contacts
with the film were made both back (thorough the Ti
substrate) and front (a Cu metal plate with hole). A
photoelectron corrector was set in front of the film witharound 1mm interspace. A negative bias was applied tothe sample against the grounded photoelectron corrector.
The number of photoelectrons was obtained bymeasuring the current needed to compensate for thephotoexcited holes at the sample with an ammeter. The
photoemission yield was measured as a function ofincident photon energy.
Figure 2 shows TPY spectra of AlN films doped with
11.0 and 8.3% Ti and 12.3 and 9.3% Cr. It is clear that
the Cr-doped films have threshold at around 5.5 eV,
while threshold of the Ti-doped films is at around 6.0
eV. These results agree well with the theoretical levelsof Cr and Ti in AlN [7]. We have obtained different
thresholds for other different 3d-TM elements, whichmeans the potential of IB can be controlled via choiceof 3d-TM elements and adjust the band structure for theeffective photoconversion. To reveal all potentials of theelectron occupied band of the films, we will extend theenergy region of the measurements to larger one.
[1] A. Luque et al., Phys. Rev. Lett. 78 (1997) 5014.
[2] N. Tatemizo et al., J. Mater. Chem. A 5 (2017)
20824.
[3]N. Tatemizo et al., J. App. Phys., 123 (2018) 161546.
[4] N. Tatemizo et al., J. of Phys.: Conden. Matter, 29(2017) 085502.
[5] N. Tatemizo et al., AIP advances, 7 (2017) 055306.
[6] M. Honda et al., J. Appl. Phys. 102 (2007) 103704.
[7] U. Gerstmann et al., Phys. Rev. B, 63 (2001) 1.

Fig. 1. Schematic of sample setting for the TPYS
measurements.
10-4

Photoelectron Yield (/photon)

1

10-5

Ti: 11.0%
Ti: 8.3%
Cr: 12.3%
Cr: 9.3%

10-6

10-7

10-8
5.0

5.5

6.0

6.5

7.0

7.5

Photon Energy (eV)Fig. 2. Total photoelectron yield spectra of 3d-TM
doped AlN films (12.3 and 9.3 % of Cr and 11.0 and
8.3 % of Ti) deposited on Ti metal substrates.

Ⅲ02- 20 60

Ⅲ -2. Materials Sciences
BL3B
BL3B

Study of Defect Induced by Hydrogen Reduction in MgO Single Crystal by
UV Absorption Spectroscopy
E. Kobayashi1, K. K. Okudaira2, S. Yoshioka3, K. K. Bando4 and O. Takahashi5

Kyushu Synchrotron Light Research Center, Tosu 841-0005, Japan
2
Chiba University, Chiba 263-8522, Japan
3
Gradiate School of Engineering, Kyushu University, Fukuoka 819-0395 Japan
4
National Institute of Advanced Industrial Science and Technology, Tsukuba 305-8565, Japan
5
Institute for Sustainable Science and Development, Hiroshima University, Higashi-Hiroshima, 739-8526, Japan
1

1173 K1073 K
873 K
673 K
nontreatment

Absorbance (arb. units)

Magnesium oxide (MgO) is a typical wide band gap
insulator and is used in a wide range of devices [1-4].
Physical characteristics such as optical or electricalperformances are greatly affected by the presence
defects. Various types of defects are found in metaloxides, which are composed of points, lines and planes.
The electronic state derived from those defects
controls electrical, optical, or magnetic functions ofdevices. Therefore, a lot of efforts have been made so
far to understand the effect of point defects on theelectronic states of metal oxides so far, but moredetailed atomic level investigation of defects is still
desired.
In this study, we focused on magnesium oxide to see
the effect of typical oxygen point defects on theelectronic states derived from oxygen. We investigatedthe correlation between the defects and the electronic
states using near-edge X-ray absorption fine structure(NEXAFS) spectroscopy and ultraviolet absorption
spectroscopy.
The MgO single crystals were annealed at several
temperatures at 673 K ~1173 K in a hydrogen
atmosphere for 4 hours. The sample was graduallycooled to room temperature, exposed to the air, thenintroduced into a vacuum apparatus, and the spectrum
was measured. UV spectra of MgO single crystal were
measured at the BL3B of UVSOR in the Institute of
Molecular Science.
The change in the band gap created by oxygen
defects was investigated with transmission spectra in
the ultraviolet region. Figure 1 shows UV spectra ofMgO(100). A distinct increase in absorption from 5.6
eV to 7.2 eV was observed for the samples treatedunder hydrogen, compared to an untreated sample. On
the other hand, in the NEXAFS measurement, a new
maximum appeared in the pre-edge area. The
appearance of pre-edge peaks suggested that defects
created new electronic states in the conduction band.
The results of both UV and NEXAFS indicated thata new electronic state was formed in the conduction
band due to the oxygen defect produced by thehydrogen reduction treatment, which made the band
gap narrower.

7.5

7.0

6.5

6.0

5.5

5.0

4.5

4.0

Photon Energy (eV)Fig. 1. UV spectra of MgO(100).
[1] D. M. Roessler and W. C. Walker, Phys. Rev. 159(1967) 733.
[2] E. A. Colbourn, Surf. Sci. Rep. 15 (1992) 281.
[3] G. H. Rosenblatt, M. W. Rowe, G. P. Williams, Jr.,
R. T. Williams and Y. Chen, Phys. Rev. B 39 (1989)
10309.
[4] M. M. Freund, F. Freund and F. Batllo, Phys.
Rev.Lett. 63 (1989) 2096.

Ⅲ02- 21 61

Ⅲ-2

Ⅲ -2. Materials Sciences
BL3B
BL3B

Luminescence Possibly Due to Localized Excitons in CH3NH3Pb (I,Cl)3
Alloyed Thin Films
T. Makino and K. Waza

Depeartment of Electrical and Electronics Engineering, University of Fukui, Fukui 910-8585, Japan

Ⅲ-2

Perovskite-halide semiconductors (CH3NH3PbI3)
have attracted intense research interest due to theirpotential applications in solar-cells. The radiative andnonradiative recombination processes between thelight harvesting and the hole transport layers are very
important to understand the light-electricity
conversion mechanism. However, the emission
mechanism which is intimately related to theabovementioned recombination in CH3NH3PbI3 is notunderstood completely.
Here, we are rather interested in the opticalproperties of its alloyed system, namely,
CH3NH3Pb(I,Cl)3. The physical origin of spontaneousemission in CH3NH3Pb(I,Cl)3 may be attributed to therecombinationoflocalized
excitons.
Nophotoluminescence (PL) studies have been reported inthis alloy, whereas the corresponding PL studies havebeen reported in unalloyed CH3NH3PbI3. An S-shaped(red–blue–redshift) temperature dependence has been
observed for the peak positions of the PL spectra evenThisstronglysuggests
in
CH3NH3PbI3.
Strongerinhomogeneities
inCH3NH3PbI3.
inhomogeneity is expected to exist in the alloy becauseof the microscopic fluctuation of the concentration.
This anomalous behavior is reminiscent to what one
observed in alloys or quantum structures in nitride
semiconductors. Essentially, no quantitative approachhas been made to interpret the temperature dependenceof the PL spectra in CH3NH3Pb(I,Cl)3.
Let us briefly review the history for the explanationof the exciton localization mechanism in nitride
semiconductors. Several simulation-based studies
have been performed. The band-tail-filling model has
been adopted to describe the recombination of thelocalized excitons. However, this model failed to
explain the low-temperature dynamics of excitons.
Low-temperature excitonic localization has beeninterpreted using numerical solutions of Schrödinger
equations. This numerical approach has not
successfully been applied to high temperature exciton
dynamics. Finally we successfully interpreted thetemperature dependence based on Monte Carlosimulation of phonon-assisted exciton hopping andrelaxation, considering effects of the earliermentioned potential fluctuations.
We are interested in the anomalous opticalbehaviors of CH3NH3Pb(I,Cl)3. Whether can it beinterpreted along the abovementioned model
applicable for nitrides?
In this work, we currently study about thetemperature dependence of the PL spectra in

CH3NH3Pb(I,Cl)3.
As a preparation of its detailed analysis, we show in
Fig. 1 the PL spectrum taken in a low temperature(10 K). It should be noted that this spectrum has notbeen yet corrected with the instrumental function.
Therefore, the final line-shape has possibility to bechanged significantly during the correction.

Fig. 1. Photoluminescence from alloyed thin film
taken at 10 K. Excitation is made with the light sourceat the UVSOR Synchrotron Facility.
[1] Md. S. Hasan, Md. S. Islam, Md. R. Islam, I. M.
Mehedi, T. Makino, J. Comput. Electron. 17 (2018)373.

Ⅲ02- 22 62

Ⅲ -2. Materials Sciences
BL3B
BL3B

Improvement of Persistent Luminescence Intensity of Ba2SiO4:Eu2+
Phosphor by Lanthanide Ion Co-doping Based on VRBE Diagram
K. Asami, K. Yasuda, J. Ueda and S. Tanabe

Graduate School of Human and Environmental Studies, Kyoto University, Kyoto 606-8501, JapanThe Eu2+ doped barium silicate phosphors are
attracting much attention in optical application for
scintillation materials [1] and persistent phosphors [2].
In this study, we focused on Ba2SiO4 host in which
Eu2+ doped persistent luminescence property has notbeen investigated. For understanding the electrontransfer processes and a suitable trap ion for long
persistent luminescence, a vacuum referred binding
energy (VRBE) diagram is useful[3]. Thus, weconstructed the diagram by the spectroscopic dataobtained from photoluminescence excitation (PLE)
spectra of both Ce3+ and Eu3+- singly doped Ba2SiO4
phosphors. Based on the VRBE diagram, we found thesuitable lanthanide ion co-dopant as a trap center for
improvement of persistent luminescence intensity.
Figure 1 shows the PLE spectrum of the Ce3+- doped
Ba2SiO4 phosphor at 15 K which was measured at
BL3B. In the PLE spectrum, the host exciton peak was
observed at around 7.05 eV and three bands derived
from Ce3+ were observed at 3.2-5.8 eV. From the hostexciton peak, the bandgap energy was estimated to be
7.61 eV.
Figure 2 shows PLE spectrum of the Eu3+- doped
Ba2SiO4 phosphor at 10 K. The strong broad band wasobserved at around 4.0-7.0 eV, which is attributed tothe charge transfer (CT) transition of Eu3+. The CTband is deconvoluted into two bands because there are
two Ba sites in Ba2SiO4 structure. From the peak oflower CT band shown as red curve in Fig. 2, the CT
energy was estimated to be 4.40 eV.
From the obtained spectroscopic data, VRBE
diagram of Ba2SiO4 host with 4f ground states ofdivalent and trivalent lanthanide ions was constructed
as shown in Fig. 3 based on the procedure developed
by Dorenbos [3].From the constructed diagram, weselected Er3+ ion as a trap center of Ba2SiO4:Eu
phosphor. This is because estimated trap depth of Er3+
in Ba2SiO4 host (0.64 eV) from the VRBE diagram issimilar to that of Dy3+ in SrAl2O4:Eu2+-Dy3+ bright
persistent phosphor (~0.60 eV)[4].
Figure 4 shows the photographs of Eu2+ doped (left)
and Eu2+-Er3+codoped (right) Ba2SiO4 phosphors
under white light (upper), UV light (middle) andwithout light (lower). By co-doping Er3+ into
Ba2SiO4:Eu phosphor, persistent luminescence wasclearly observed. Persistent luminescence duration
time on 0.32 mcd/m2 is 7 min and 3.5 h for Eu2+- andEu2+-Er3+ co-doped Ba2SiO4 phosphor, respectively.

Fig. 1. PLE spectrum of Ba2SiO4:Ce3+.

Fig. 2. PLE spectrum of Ba2SiO4:Eu3+.

Fig. 3. VRBE diagram of Ba2SiO4 host.

Fig. 4. Photographs of Eu2+ doped and Eu2+Er3+codoped Ba2SiO4 phosphors.
[1] Y. Eagleman, et al., IEEE Trans. Nucl. Sci. 59(2012) 479.
[2] Y. Jia, et al., Mater. Des. 90 (2016) 218.
[3] P. Dorenbos , J. Lumin. 135 (2013) 93.
[4] H. Takasaki, S. Tanabe and T. Hanada, J. Ceram.
Soc. Japan. 104 (1996) 322.

Ⅲ02- 23 63

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BL4U

In-situ Studied the Oxygen 2p-vacancy in the TaOx Interlayers of Resistive
Switching Materials
J. W. Chiou1, Y. F. Wang2, W. F. Pong2, J. S. Chen3, T. Ohigashi4 and N. Kosugi4

Department of Applied Physics, National University of Kaohsiung, Kaohsiung 811, Taiwan
2
Department of Physics, Tamkang University, Tamsui 251, Taiwan
3
Department of Materials Science and Engineering, National Cheng Kung University, Tainan 701, Taiwan
4
UVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
1

Ⅲ-2

Resistance random access memory (ReRAM) using
the change in resistance between crystalline andamorphous states of a chalcogenide compound has
attracted a great deal of attention for use as nextgeneration nonvolatile memories. The ReRAM
memory cell has a capacitor-like structure composedof insulating or semiconducting materials sandwiched
between two metal electrodes. Due to its simple
structure, highly scalable cross-point and multilevel
stacking memory structures have been proposed. In
the resistive switching phenomenon, A. Sawa [1]reports that a large change in resistance (>1000%)
occurs on applying pulsed voltages and the resistanceof the cell can be set to a desired values by applying
the appropriate voltage pulse.
In this work, we have in-situ studied the electronic
structure and the location of oxygen 2p-vacancy in the
TaOx interlayers and identified the type of conducting
path by scanning transmission x-ray microscopy(STXM) and x-ray absorption near-edge structure(XANES). During the STXM measurements, a various
voltage, 0, +50, -50, 0 volts, has exerted on both endsof the Ta/TaOx/Pt thin film, respectively, to specify theelectronic structure associated with the conducting
path. The amorphous TaOx thin film of thickness of~75 nm was deposited on Pt/SiO2/Si substrate byelectron beam evaporation method. Active electrodesof Ta were thermally evaporated respectively on the
TaOx thin film with an equivalent thickness of ~130
nm. As shown in Fig. 1, the STXM stack mapping
displays the cross-sectional views of the Ta/TaOx/Pt
thin film under various applied voltages. The
experiments were performed at the BL4U. The
corresponding O K-edge STXM-XANES spectra of
the Ta/TaOx/Pt thin film were recorded at TaOx
interlayers, as shown in Fig. 2. According to thedipole-transition selection rule, the features at ~530545 eV are attributed to the electron excitations from
O 1s core level to O 2p-derived states, which areapproximately proportional to the density of theunoccupied O 2p-derived states. The intensities of theO K-edge STXM-XANES spectra are significantly
lower as a voltage applied on both ends of the
Ta/TaOx/Pt thin film, which reflects the decrease in thenumber of unoccupied O 2p-derived states. In otherwords, the STXM-XANES results demonstrate thatthe population of defects at the O sites in the TaOx
interlayers and intensely support the phenomena thatthe existence of O 2p-vacancy in the TaOx interlayers

plays a main role for the mechanics of charge transfer
in resistive switching materials.

Fig. 1. The STXM stack mapping obtained inapplying (a) 0, (b) +50, (c) -50, and (d) 0 volts on bothends of the Ta/TaOx/Pt thin film, respectively.

Fig. 2. The corresponding O K-edge STXM-XANES
spectra were recorded at TaOx interlayers undervarious applying voltages.
[1] A. Sawa, Materials Today 11 (2008) 28.

Ⅲ02- 24 64

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BL4U

Nano-Scale Chemical Mapping of Vapor Processed-(PEA)2(MA)n-1PbnI3n+1
Quasi-2D Perovskite Solar Cells
H. W. Shiu1, M. S. Li2, L. C. Yu1, Y. L. Lai1, T. Ohigashi3, N. Kosugi3, P. Chen2 and Y. J. Hsu1
National Synchrotron Radiation Research Center, Hsinchu 300, Taiwan
Department of Photonics, National Cheng Kung University, Tainan 701, Taiwan
3
Institute for Molecular Science, Okazaki 444-8585, Japan1

in Fig. 2a. Figure 2b shows the reference NEXAFS
spectra of n = 1, n = 20, n = 40 and MAPbI3 (n = ∞)for comparison. When the PEAI is doped into the PbI2
film for n = 2 without MAI vapor reaction, theabsorption profile along with characteristic peaks are
similar to the 2D (PEA)2PbI4 perovskite (n = 1). After
MAI vapor treatment, the n = 2 film starts growing in
the mixture phase containing CH3NH3+ (MA+) cation
and aggregates onto TiO2 substrate. The spectrum issimilar to the measurement of MAPbI3. For lower
MAI dosage, an intermediate state is observed asshown in Fig. 2a that may explain the reaction processof MAI vapor treatment.
(a) (b)(b)(a)

Fig. 1. C K-edge optical density images of n = 2
quasi-2D perovskite (a) without and (b) with MAI
vapor treatment onto SiN/TiO2 substrate. The carbon
OD images are obtained at 293.5 eV.
(a) (b)n = 2 w/o MAI vaporn = 2 w/ low MAI vaporn = 2 w/ low MAI vapor

280

285

290

295

300

305

Photon Energy (eV)

310

n=1

Intensity (a. u.)

In the last couple years, a dimensionally tuned
quasi-2D perovskite thin film was developed which issystematically synthesized by introducing a largeorganic cation, phenylethylammonium (PEA =C8H9NH3) at a judiciously-chosen stoichiometry [1].
The quasi-2D perovskite exhibits the capability of
combination of enhanced stability of 2D perovskite
and outstanding optoelectronic properties of 3D
perovskite [2]. In this work, we systematically studied
the layer number dependent behavior of(PEA) 2 (MA) n-1 Pb n I 3n+1 Quasi-2D perovskite by Xray photoelectron spectroscopy (XPS), Near-edge Xray absorption fine structure (NEXAFS), and scanningtransmission X-ray microscopy (STXM).
In our previous studies, we have successfully
synthesized dimensional tunable quasi-2D perovskite
by mixing stoichiometric quantities of lead iodide(PbI2), MAI (Ch3NH3I) and PEAI to yield a series ofcompounds, (PEA)2(MA)n-1PbnI3n+1 with different
layer numbers of n. The MAI vapor-assisted method
can control the morphology to achieve compact andhighly stable crystalline layer. The PCEs up to 19.1%
and 18.69% were achieved for n = 40 and n =60 layers
compound, respectively. Both of them showed better
performance than the pristine 3D perovskite of
MAPbI3 (PCEs = 17.31%, n = ∞) and 2D perovskiteof (PEA)2MAPb2I7 (PCEs < 15%). Besides, comparewith the SEM results, it indicated that PEAI may play
an important role for the photovoltaic performance,
because the change of the morphology was correlatedwith the amount of large organic cation.
To further confirm the correlation between themorphology, photovoltaic properties and the effect of
MAI vapor, chemical mapping of carbon, nitrogen andtitaniumintheaggregation
of
SiN/TiO2/(PEA)2(MA)n-1PbnI3n+1 (n =1, 2, 20, 40 and∞) are studied by NEXAFS and STXM. Figure 1
shows the STXM OD images of n = 2, quasi-2D
perovskite with and without MAI vapor treatment at
293.5 eV, which is corresponding to the C-Cσ*
resonances. As shown in Fig. 1 (a), most of the areas
is covered by the plump caterpillar-like perovskite
films without MAI treatment. In contrast, theperovskite becomes slim and aggregating on to TiO2
nano-structures as observed in Fig. 1 (b). Some brightspots with intense spherical shapes in carbon mapping
is observed at low dose of the MAI treatments while itis not observed at higher dosage.
The corresponding micro NEXAFS spectra atcarbon K-edge with circular marks in Fig. 1 are shown

Intensity (a. u.)2n = 20n = 40
MAPbI3

280

285

290

295

300

305

Photon Energy (eV)310

Fig. 2. (a) C K-edge spectra of n = 2 quasi-2D
perovskite without (Fig.1a) and with low (Fig.1b)
MAI vapor dosage. (b) C K-edge reference spectra for
n =1, n = 20, n = 40 and MAPbI3 (n = ∞).
[1] I. C. Smith, E. T. Hoke, D. S.-Ibarra, M. D.
McGehee, H. I. Karunadasa, Angew. Chem. Int. Ed. 53(2014) 1.
[2] L. N. Quan, M. Yuan, R. Comin, O. Voznyy, E. M.
Beauregard, S. Hoogland, A. Buin, A. R. Kirmani, K.
Zhao, A. Amassian, D. H. Kim, E. H. Sargent, J. Am.
Chem. Soc. 138 (2016) 2649.

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BL4U

Phase Evolution of Complex Metal Hydrides during De/Rehydrogenation
J. L. White1, 2, T. Ohigashi3, K. G. Ray2, 4, Y.-S. Liu2, 5, V. Stavila1, 2, M. D. Allendorf1, 2
and J. Guo2, 5Sandia National Laboratories, Livermore, CA 94551, United States
Hydrogen Materials–Advanced Research Consortium (HyMARC), Livermore, CA 94551, United States
3
UVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
4
Lawrence Livermore National Laboratory, Livermore, CA 94550, United States5
Lawrence Berkeley National Laboratory, Berkeley, CA 94720, United States1

Ⅲ-2

Lightweight complex metal hydrides are of interestfor use as energy-dense on-board vehicular hydrogen
stores [1]. One material of particular interest,
magnesium borohydride (Mg(BH4)2), has very highhydrogen capacity, at 14.9 wt.% H, but suffers fromslow kinetics and the need for extreme conditions forboth dehydrogenation and rehydrogenation frommagnesium diboride (MgB2) [2]. In order to establish
methods to improve the kinetic properties of thissystem, a greater understanding of the nucleation andgrowth of various solid phases is essential.
Several samples of partially dehydrogenated
Mg(BH4)2 and partially hydrogenated MgB2 were
examined by Scanning Transmission X-Ray
Microscopy (STXM) at the boron K-edge using thetransfer system from a glovebox to BL4U to preventoxidation upon exposure to air. The resulting series of
X-ray absorption images were analyzed using
computed spectra for several B containing species (Fig.
1), since the experimental XAS spectra showed
substantial amounts of oxidized boron.
The STXM maps revealed some intriguing phasepropagation patterns not heretofore observed. MgB2
partially hydrogenated at 400 °C and either 200 or 700
bar H2 over the course of 72 h (Fig. 2) showed thathydrogenation to Mg(BH4)2 began at the exterior of
the particles and spread inward, with greater
conversion evident at the higher pressure, as expected.
However, the Mg(BH4)2, partially dehydrogenatedat 400 °C and H2 overpressures of 200 and 360 bar,
showed a much more counterintuitive phasetransformation (Fig. 3). It has commonly been
hypothesized that the dehydrogenated phase forms
first on the outside of hydride particles as the hydride
releases H2 from the surface [3]. Instead, our STXM
results on Mg(BH4)2 show that the hydride remains on
the exterior, whereas the interior becomesdehydrogenated first. The higher overpressure sample
decomposed less, and consequently its interior
retained more of the hydride phase. Therefore,
nucleation of the dehydrogenated material begins in
the bulk, and hydrogen atoms diffuse toward thesurface where they can combine and desorb as H2 gas.
Information regarding the phase evolution in in the
Mg-B-H system provides valuable insights into therate-limiting step of hydrogen desorption.

Normalized Intensity (a.u.)2

Mg(BH4)2
MgB12H12
MgB2
B2O3

180

185

190

195

200

205

210

Photon Energy (eV)Fig. 1. Simulated B K-edge XAS spectra of relevant
chemical species used in STXM analyses.

200nm

200nm

Fig. 2. STXM maps of MgB2 hydrogenated for 72 h
at 400 °C and (a) 200 or (b) 700 bar H2. Red indicates
Mg(BH4)2, green MgB12H12, and blue B2O3.

200nm

200nm

Fig. 3. STXM maps of Mg(BH4)2 dehydrogenated for
72 h at 400 °C and H2 overpressures of (a) 200 and (b)360 bar H2. Red indicates Mg(BH4)2, green MgB12H12,and blue B2O3.
[1] S.-i. Orimo et al., Chem. Rev. 107 (2007) 4111.
[2] K. G. Ray et al., Phys. Chem. Chem. Phys. 19(2017) 22646.
[3] B. C. Wood et al., Adv. Mater. Interfaces 4 (2017)
1600803.

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BL4U

Probing the Electronic Structure of BiVO4 Coated ZnO Nanodendrite Core
- Shell Nanocomposite Using Spatially Resolved Scanning Transmission Xray Microscopy Studies
M. M. Shirolkar1, J.-W. Chiou2, T. Ohigashi3, N. Kosugi3 and W.-F. Pong1

Department of Physics, Tamkang University, Tamsui 251, Taiwan
Department of Applied Physics, National University of Kaohsiung, Kaohsiung 811, Taiwan
3
Institute for Molecular Science, Okazaki 444-8585, Japan
1

2

Recently, it has been reported that ZnO
nanodendrites (NDs) coated with BiVO4 nanolayers
core-shell nanocomposite thin film structure forms a
multiple-level hierarchical heterostructure, which isremarkably beneficial for light absorption and charge
carrier
separationforthecompetent
photoelectrochemical (PEC) properties compared totheir individual counterparts [1]. As PEC properties
are essentially a function of band alignment andatomic – electronic structures, we studied thenanocomposite thin film using various X-ray
spectroscopic and microscopy studies. We haveprobed the origin and nature of localized electronstates in core-shell structures using valance band
spectroscopy, X-ray absorption spectroscopies andspatially resolved scanning transmission X-ray
microscopy (STXM). The valance band studies show
band alignment at the core-shell interface, whichallowsefficientchargetransfer
betweenheterostructure. While, X-ray absorption studies
essentially show that in core-shell structure tetrahedral
environment of V5+ in BiVO4 is unusually distorted
and the inter-band gap states related to another valence
state of vanadium, namely, V4+ is present. The
presence of multiple valance states of vanadium gives
favorable conditions for small polaron formation in
BiVO4, thereby degrading PEC activities. However, it
was observed that V4+ coordinates with ZnO lattice
thereby giving rise to conditions similar to vanadium
doped ZnO. These studies reveal electronic structure
over few micrometers length scale within the thin film,
which contains hundreds of nanostructures and precise
locations of the coordination within individual
nanostructure remain unrevealed. Moreover, highresolution transmission electron microscopy - electronenergy loss spectroscopy could not effectively resolve
above-mentioned coordination features.
On the other hand, STXM is powerful technique andretains the ability to efficiently resolve the observed
coordination features efficiently within single orcluster of nanocomposite structure because of its highspatial resolution features [2]. Figure 1 depicts STXM
results obtained on the core – shell nanostructure. With
STXM measurements, we able to probe core-shellcoordination and the sites in ZnO NDs contributing toV4+ doped ZnO within single nanocomposite structure.
Consequently, our STXM investigations strongly
support our other synchrotron measurements.

Ⅲ-2

Fig. 1. (a) shows transmission electron microscope
micrograph of BiVO4 coated ZnO nanodendrite coreshell nanostructure, (b) shows magnified STXM
optical image of core-shell nanodendrite highlighted
in (a), (c) – (h) shows STXM mapping of O – K edge
representing various coordination among core andshell structures: Bi – V – O (red), Zn – O (yellow), Bi– O (cyan) and Zn – V – O (green) and (i) represents
O – K edge spectra obtained on various clusters.
[1] J.-S. Yang and J.-J. Wu, Nano Energy 32 (2017)232.

Ⅲ02- 27 67

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BL4B

X-ray Irradiation Effect on the Local Structural Modification in Charge
Transfer Salts (BEDT-TTF)2X
T. Sasaki

Instutute for Materials Research, Tohoku University, Sendai 980-8577, JapanⅢ-2

It has been known that X-ray irradiation to theorganic materials causes molecular defects anddisorders. We have investigated the X-ray irradiation
effect widely in the series of molecular materials κ(BEDT-TTF)2X showing superconductivity or Mott
insulating state from the viewpoint of the relation
between the correlated electronic states and disorders[1, 2]. The experimental and theoretical investigations
suggest that the -CN parts in the anion molecules X aremainly damaged and the modification of the local
structure may occur.
In this study, we investigated the soft X-ray
absorption spectra in the nitrogen K-edge region for
the anion layers X of the charge transfer salts of(BEDT-TTF)2X with X = Cu[N(CN)2]Br, Cu2(CN)3and RbZn(SCN)4. X-ray irradiation to the crystals wasdone by using the tungsten tube with 40 kV, 20 mA atroom temperature. The dose amount was controlled by
the irradiation time. BL4B soft X-ray beamline wasused for X-ray Absorption Near Edge Structure(XANES) spectroscopy measurements in the nitrogen
K-edge region. The spectra were taken by means of thetotal electron yield method using EM at room
temperature.
Figure 1 shows the nitrogen K-edge XANES spectra
around 400 eV for (a) the non-irradiated pristine and(b) 500 hours X-ray irradiated κ-(BEDTTTF)2Cu2(CN)3. The angle θ indicates the soft X-ray
incidence angle from the a*-axis in the a*-(b+c) plane.
The structure of anion molecules and the configuration
to the incident soft X-ray beam are shown in Fig. 2. In
the spectra, several absorption peak structures
originating from the nitrogen atoms are observed. The
major sharp A and broad B peaks can be attributed tothe π* and σ* orbitals, respectively, coupled to thecarbon or cupper atoms in the anion molecule layer. The
peak intensity of A and B show characteristic
dependence of the incident beam angle θ, which should
contain the information of the local bonding structurearound the nitrogen atoms. In these results, we foundthat the incident beam angle dependence changes in the
X-ray irradiated crystals. These observations clearlyshow that X-ray irradiation causes the local
modification of the anion structure around the nitrogen.
The details are under analysis in parallel with thecomparison to the results of the other compounds with
X = Cu[N(CN)2]Br and RbZn(SCN)4.
[1] T. Sasaki, Crystals 2 (2012) 374.
[2] L. Kang, K. Akagi, K. Hayashi and T. Sasaki, Phys.
Rev. B 95 (2017) 214106.

Fig. 1. Nitrogen K-edge XANES spectra of (a) nonirradiated pristine and (b) 500 hours X-ray irradiatedκ-(BEDT-TTF)2Cu2(CN)3. The angle θ indicates theincidence angle from the a*-axis in the a*-(b+c) plane.

Fig. 2. The anion Cu2(CN)3 structure from the viewalong the long direction of BEDT-TTF molecule.

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BL4B

Preparation of TiO2 Film Photocatalysts for Effective Nitrogen Doping toProvide Visible Light Response
T. Yoshida1, S. Niimi2, M. Yamamoto2, Y. Kato3, A. Ozawa3 and S.Yagi4

Advanced Research Institute for Natural Science, Osaka City University Osaka 558-8585, Japan
2
Graduate School of Engineering, Nagoya University, Nagoya, 464-8603, Japan
3
Graduate School of Engineering, Osaka City University, Osaka 558-8585, Japan
4
Institute of Materials and Systems for Sustainability, Nagoya University, Nagoya 464-8603, Japan
Photocatalytic reactions at the surface of titanium
dioxide (TiO2) under UV light irradiation have been
attracting much attention in view of their practicalapplications to environmental cleaning such as self
cleaning of tiles, glasses, and windows. Recently,
Asahi et al. reported that the doping of nitrogen into
TiO2 contributes to band gap narrowing to provide
visible-light response.
The photocatalysis of TiO2 and nitrogen-doped TiO2
are derived from the formation of photogenerated
electrons and holes. Therefore, from a perspective of the
improvement of photocatalytic properties of TiO2, theeffective depth (TiO2 thickness) in which the electronhole pairs capable to diffuse and contributephotocatalysis at the surface should be determined.
In the present work, we employed a pulsed laser
deposition (PLD) method to fabricate the TiO2 thinfilm and tried to estimate the effective depth bycomparison of photocatalytic activities for TiO2 film
samples with various thicknesses. In addition, we tried
to dope nitrogen into the effective depth region of TiO2
by nitrogen implantation method, and investigated thechemical states of nitrogen effective for the visible
light response of a TiO2 photocatalyst by XAFS
analysis.
Thickness-controlled TiO2 film samples were
fabricated on the (001)-face of LaAlO3 or (LaAlO3)0.3(SrAl0.5Ta0.5O3)0.7 single-crystal insulator substrates bya pulsed laser deposition (PLD) with a KrF excimer
lazer at 973 K in an atmosphere with oxygen pressureof 5 Pa.
High-resolution X-ray diffraction measurements
revealed that the deposited TiO2 thin films on thesubstrates are highly (001)-oriented crystalline phaseof anatase TiO2. TEM and SIMS measurements
confirmed the formation of homogeneous TiO2 thinfilms. The thicknesses of the TiO2 thin film samples
have been estimated as 3, 10, 16, 19, 30 and 59 nm.
We also have prepared a thick anatase TiO2 film withthe thickness of 167nm as a reference bulk sample.
The prepared TiO2 film samples promoted
photocatalytic degradation of methylene blue (MB)under UV-light irradiation. Decrease of MB
concentration well obeyed the first-order kinetics, andthe reaction rate constant was calculated. The reaction
rate constant increased with increasing the TiO2
thickness up to 10 nm. Then, it decreased until the
thickness becomes ca. 30 nm, followed by staying

constant. Thus, it is notable that the 10 nm thicknessof TiO2 on the insulator substrate would be theoptimum structure.
We also doped nitrogen into the effective depth
region (ca. 10 nm) of TiO2 by 5 keV N+ implantationand the nitrogen doped TiO2 samples promoted
photocatalytic degradation of MB under visible-lightirradiation. Figure 1 shows N K-edge XANES spectraof a TiN powder, the photocatalytic active andinactive samples. The XANES profile of the active
sample was well reproduced by the theoreticalprediction using FEFF code when N occupies one of
the O sites of TiO2. On the other hand, the XANES
spectrum of the inactive sample showed a distinct
single peak around 401 eV. This peak could be
empirically attributed to formation of NO2 species.
54
I / I0

1

3

c)

2

b)

1

a)

0
390

400
410
420
X-ray energy (eV)Fig. 1. N K-edge XANES spectra of (a) TiN, (b) thephotocatalytic active sample and (c) the photocatalytic
inactive sample.
[1] A. Fujishima, X. Zhang and D. A. Tryk, Surf. Sci.
Rep. 63 (2008) 515.
[2] R. Asahi, T. Morikawa, T. Ohwaki, K. Aoki and Y.
Taga, Science 293 (2001) 269.
[3] T. Yoshida and E. Kuda, Stud. Surf. Sci. Catal., T.
Yoshida and E. Kuda, Stud. Surf. Sci. Catal. 175(2010) 267.

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BL4B

Valence State Analysis of Mn Ions in Mg2TiO4 and Mg2SnO4
T. Yamamoto1, 2 and K. Akiya1

Faculty of Science and Engineering, Waseda University, Tokyo 169-8555, Japan
Institute of Condensed-Matter Science, , Waseda University, Tokyo 169-8555, Japan1

2

emissions.

Fig. 1. Photograph of red (left) and green (right)
emissions from Mn doped Mg2TiO4 and Mg2SnO4,
respectively, by UV irradiation.

Mn2+ (MnCl2)
Intensity (arb. units)

Ⅲ-2

Phosphor materials are widely studied because of
their useful application for industrial use. Doping
technique, i.e., incorporation of new elements in thehost materials, have been widely employed tosynthesize an effective phosphors, in which rare-earth
elements have been often used as dopants. Recently,
rare-earth free phosphors has become a new target, inwhich Mn has been selected as an emission center forthe red-emitting phosphor. Although it is essential toknow the charge state of the doped Mn ions for theunderstanding of emission spectra and efficiency, mostof the research did not reveal it. In the current study,
Mn doped Mg2TiO4 and Mg2SnO4 have beensynthesized and the valence states of Mn ions in thesematerials were investigated by the Mn-L XANES
measurements.
Mn doped Mg2TiO4 and Mg2SnO4 were synthesized
by the solid state reaction method, in which high purity
powders of MgO, TiO2, SnO2 and Mn2O3 were used
for starting materials. Concentrations of doped Mn are
0, 0.005, 0.1, 0.05 and 0.1 with respect to Ti or Sn. The
crystal structures of all the synthesized powders were
examined by the conventional powder X-ray
diffraction technique, which suggested all the samples
crystallized in a single-phased spinel structure. The
photoluminescence spectra of these synthesizedmaterials were measured, in which Mn-doped
Mg2TiO4 and Mg2SnO4 showed red and green
emissions, respectively, as shown in Fig. 1. XANES
spectra at Mn L-edge were collected at BL4B in
UVSOR with the total electron yield method. Incident
beam was monochromatized by the varied-spacegrating (800 l/mm). Samples were attached on the
carbon adhesive tape, which were put on the first CuBe dinode of the electron multiplier.
Observed Mn-L3 XANES spectra of Mn-doped
Mg2TiO4 and Mg2SnO4 are shown in Fig. 2 with thoseof standard Mn compounds. It is widely accepted that
the Mn-L XANES profile is sensitive to change incharge states and fingerprint type analysis is possible.
As shown in this figure, spectral profile of Mn-doped
Mg2TiO4 and Mg2SnO4 are different, which suggest
charge states of Mn ions in these two host materials
are different. From the comparison of the profiles withthose of standard materials, that of Mn-doped
Mg2TiO4 shows similar profiles as that of MnO2,
which suggests majority of the doped Mn ion is 4+ in
Mg2TiO4. On the other hand, the profile of Mn-doped
Mg2SnO4 seems to be derived mainly from Mn2+.
These charge states of Mn ions in Mg2TiO4 and
Mg2SnO4 deduced from the XANES results can
explain their emission colors, i.e., red and green

3+

Mn(Mn2O3)

Mg2SnO4:Mn
Mg2SnO4:Mn
4+

Mn
650

655
Energy (eV)(MnO2)

660

Fig. 2. Observed Mn-L3 XANES spectra of MnCl2(Mn2+), Mn2O3 (Mn3+), Mn-doped Mg2SnO4, Mndoped Mg2TiO4 and MnO2 (Mn4+). Mn concentrationin Mg2TiO4 and Mg2SnO4 are 0.05.

Ⅲ02- 30 70

Ⅲ -2. Materials Sciences
BL4B
BL4B

Evaluation of Chemical State of Nitrogen in Nitrided Alloy by Soft X-ray
Spectroscopy
M. Sato and S. Matsumoto

Institute for Materials Reseach, Tohoku University, Sendai 980-8577, Japan
Machinery structural materials such as gears, shafts
and molds are required to have high surface hardness
and high toughness because of the severe friction
and/or abrasion at the surface.
Nitriding is a surface hardening technique widelyused industrially and flows nitrogen from the surface
and combining with strong nitride forming elements(for example, Al, Cr, V, Ti, etc.) contained in steel toprecipitate clusters and alloy nitrides at near thesurface. Compared to other surface hardening methods
such as carburizing and shot peening, the nitriding has
advantages of less strain because it does not involve
phase transformation and deformation during
treatment. Therefore, the importance of nitriding
process is increasing in recent high-precision materials.
In the nitriding treatment, a sufficient amount of
nitrogen flows in the vicinity of the surface toprecipitate the alloy nitride at the initial stage of
nitriding, whereas precipitation is delayed at the insideof the sample because it takes long time for thenitrogen diffusion. As a result, the concentration
gradient of nitrogen is formed in a sample.
In this research, we aimed to investigate whether
such gradient change of nitrogen can be captured by
XAFS method. Since this measurement is our firstbeam time at BL4B, it is also an important object toacquire how to use the devices and to obtain the correctdata.
A sample with a nitrogen concentration gradientfrom the surface to the inside was prepared by plasma
nitriding treatment at 550 C for 16 hours using the Fe0.5V-1.5Al alloy. In addition, nitrogen martensite steel
including 0.3, 0.5 and 2 mass% N prepared bynitriding and quenching (N-Q) treatment using thepure iron, and the γ’-Fe4N and the BN powder wereused as reference materials.
XAFS measurement was carried out at the BL4B,
and the N-K edge (380 ~ 450 eV) and the Fe-L edge
(700 ~ 760 eV) XANES spectra were collected by the
total electron yield method, respectively. Since the
SDD detector had been out of order, we could notmeasure by fluorescence method during beam time.
The measurement time was kept to 30 minutes for one
scan. The measurement on the low concentration
sample was performed a plurality of times, and theobtained spectrum was merged.
In the measurement of the Fe-L edge, the similar
spectrum to pure iron was obtained for all bulk

samples, and it had the same shape as the spectrum
reported in various papers. Therefore, it is consideredthat acquisition of measurement method was carriedout without problems. On the other hand, the XANES
spectrum obtained from the Fe4N powder had the same
shape as the Fe2O3, suggesting the possibility that thesurface is oxidized. Since Fe4N sample was extracted
from tempered N-Q sample, it is necessary to pay
attention to handling and storage conditions in the
future.
Figure 1 shows the N-K edge XANES spectra ofsamples. Since the SDD detector could not be used inthis beam time, low concentration samples could notmeasure. Therefore, only the spectrum of the relatively
high nitrogen concentration of BN, Fe4N and2mass%N alloy are shown. It was also confirmed thatthe obtained spectrum of BN powder was similar tothat previously reported one [1].
The nitrogen atom in the N-Q treated sample isconsidered to be in a solid solution state. However,spectrum of nearly the same shape with Fe4N was
obtained. Therefore, further investigation is necessary
in combination with simulation using FEFF code in
the next time.

Fig. 1. N-K edge XANES spectra of BN, Fe4N and NQ treated Fe specimen.
[1] L. Liu et al., Phys. Chem. Chem. Phys. 15 (2013)
6929.

Ⅲ02- 31 71

Ⅲ-2

Ⅲ -2. Materials Sciences
BL5U
BL5U

High-Resolution ARPES Study of TaSe2 Atomic-Layer Ultrathin Film
Y. Nakata1, K. Sugawara2, 3, T. Yoshizawa1, T. Nakamura1, H. Oinuma1, T. Takahashi1, 2, 3 and
T. Sato1, 3
2

Ⅲ-2

1Department of Physics, Tohoku University, Sendai 980-8578, JapanWPI Research Center, Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
3
Center for Spintronics Research Network, Tohoku University, Sendai 980-8577, Japan

Atomic-layer materials (single-layer nano-sheet in
the thinnest limit of bulk layered materials) have beena target of intensive investigations since they exhibit
novel physical phenomena related to the degree of
freedoms in electrons such as charge, orbital, spin, andvalley. Amongst layered bulk materials, transition
metal dichalconenide (TMD) NbSe2 has attracted
considerable attention more than half century becauseof the coexistence of superconductivity and charge
density wave (CDW). On the other hand, atomic- layer
NbSe2 show physical properties distinct from the bulk
counterpart,suchas
two-dimensional
superconductivity with the giant enhancement ofupper-critical magnetic field due to spin-momentum
locking at the Brillouin zone corners (K and K’) in theelectronic state arising from the strong spin-orbit
coupling and the breaking of space inversion
symmetry [1]. However, the physical properties suchas the transport properties and the electronic state insingle-layer TaSe2 (the same family as IV group with
spin-orbit interaction stronger than that of NbSe2) has
not been experimentally reported yet, desipite
theoretical studies [2].
In this study, we carried out high-resolution angleresolved photoemission spectroscopy (ARPES) on
single-layer TaSe2 grown on bilayer graphene
substrate. By utilizing energy-tunable photons fromsynchrotron radiation, we determined the overall VB
structure and Fermi surface of single-layer TaSe2.
Monolayer TaSe2 films were grown on bilayer
graphene by using MBE system constructed at Tohoku
University. Bilayer graphene was fabricated byannealing Si-terminated 6H-SiC(0001) single crystal.
Monolayer TaSe2 films were grown by evaporating Ta
on the bilayer-graphene/SiC substrate in Se
atmosphere. The as-grown film was annealed at
450 °C for 30 min. Then, we additionally deposited Se
atoms on monolayer TaSe2 films to protect the surface
from the atmosphere. Se-capped monolayer TaSe2
films was then installed to a preparation chamber at
BL5U and the Se capping-layer was removed byradiation heating.
Figure 1(b) shows the ARPES-intensity plot at
Fermi energy (EF) as a function of 2D wave vectors
measured along the ΓΚM direction at hν = 50 eV withlinear polarization. We clearly find a large hole-like
Fermi surface (FS) centered at the Γ point of both firstand second Brillouin zone, indicating the wellordered samples. Around the M point of the second

Brillouin zone, a small FS with the strong intensity
which is assigned as the π* band of bilayer graphene,
was found. On the other hand, the spin-polarized FSs
which are theoretically expected around the K point
are not clearly observed because of the matrixelement effect. Figures 1(c) and (d) show the valenceband structure along the Γ-M and the Γ-K cuts. Theenergy band with the top of 1 eV at the Γ point and themetallic band near the Fermi level can be found along
both Γ-M and the Γ-K cuts. Although the theoretical
calculation has predicted the spin-split band at the ΓK cut due to protection with the mirror symmetry atthe Γ-M cut [2], it is unclear from the present
expeirment that whether such band splitting exists or
not, likely because of the quite small domain sizes ofour films.

Fig. 1. (a) Crystal structure of monolayer TaSe2. (b)Plot of ARPES intensity at EF as a function of 2D wave
vector measured at T = 40 K along the ΓΜ cut withlinearly polarized 50 eV photons. (c) and (d) ARPES
intensity plots in the VB region measured at T = 40 K
along the ΓM and the ΓK line with linearlypolarized 50 eV photons, respectively.
[1] X. Xi et al., Nat. Phys. 12 (2016) 139.
[2] J. -A. Yan et al., Sci. Rep. 5 (2015) 16646.

Ⅲ02- 32 72

Ⅲ -2. Materials Sciences
BL5U
BL5U

Search for Nematicity in the Cuprate Superconductor YBa2Cu3Oy by AngleResolved Photoemission Spectroscopy
S. Nakata1, K. Koshiishi1, K. Hagiwara1, C. Lin1,
S. Ideta2, K. Tanaka2, T. Nishizaki3 and A. Fujimori1

Department of Physics, University of Tokyo, Tokyo 113-0033, JapanUVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan3
Department of Electrical Engineering, Kyushu Sangyo University, Fukuoka 813-8503, Japan1

2

In cuprate superconductors, to understand the originof the pseudogap region in the phase diagram remains
a most significant issue. Recently, experimental
evidence for several kinds of order (e.g. charge density
wave, spin density wave, nematic order) has beenreported in the pseudogap region [1]. Nematicity,which does not break the translational symmetry but
breaks the fourfold rotational symmetry of the lattice,
has been reported below the pseudogap temperatureand may play an important role in the pseudogap
region [2]. For instance, evidence for nematicity
appeared in YBa2Cu3Oy (YBCO) from transport [3,4],
neutron scattering [5] and magnetic susceptibility [6]measurements and in Bi2SrCaCu2O8+δ from resistivity
measurement [7].
Nematicity has been discussed also in Fe-based
superconductors [8] and studied by angle-resolved
photoemission spectroscopy (ARPES) [9], which is
the most direct way to reveal the electronic structure.
However, at the moment, there has been no report thatreveals the nematicity in cuprates by ARPES. We
performed ARPES measurements in order to study thenematicity in cuprates. Furthermore, by ARPES one
can investigate whether the nematicity is specific to
the pseudogap state or remains in the superconducting
state.
YBCO single crystal samples were grown by theflux method. It was nearly optimally doped sample andTc and T* were 92 K and 180 K, respectively. ARPES
measurements were carried out at UVSOR BL5U. We
used linearly polarized light with hν = 57.1 eV. The
total energy resolution was set at 32 meV. The samples
were cleaved in-situ under the pressure of ~ 2 × 10-8
Pa.
Figure 1 shows Fermi surface mapping at the Fermi
level taken at various temperatures. Figure 2 showsenergy distribution curves (EDCs) around k = (-π, 0)(X point) and (0, π) (Y point). As one can expect fromthe symmetry of the CuO2 plane, the difference
between EDCs around the X and Y points can be seen
throughout all temperatures. So far, it is difficult to
identify whether this anisotropy originate fromnematicity or merely from the anisotropy of the crystal
structure although the difference seems to depend on
temperature. More detailed measurements with many
temperatures especially in the pseudogap state arenecessary.

Ⅲ-2

Fig. 1. Fermi surface mapping integrated over ±10
meV of the Fermi level taken at (a) 220 K, (b) 110 K,(c) 50 K and (d) 6 K, respectively.

Fig. 2. EDCs of YBCO at various temperatures. Each
EDC has been integrated from kx = -1. 2 to -0. 75 (fromky = 0. 75 to 1. 2). The difference between thelineshape of EDCs around the X and Y points are also
shown.
[1] B. Keimer et al., Nature 518 (2015) 179.
[2] S. A. Kivelson et al., Nature 393 (1998) 550.
[3] Y. Ando et al., Phys. Rev. Lett. 88 (2002) 137005.
[4] R. Daou et al., Nature 463 (2010) 519.
[5] V. Hinkov et al., Science 319 (2008) 597.
[6] Y. Sato et al., Nat. Phys. 13 1074 EP (2017).
[7] K. Ishida et al., JPS fall meeting (2016) 14pJC-12.
[8] S. Kasahara et al., Nature 486 (2012) 382.
[9] M. Yi et al., PNAS 108 (2011) 6878.

Ⅲ02- 33 73

Ⅲ -2. Materials Sciences
BL5U, BL7U
BL5U, BL7UElectronic Structure of a Bi Atomic Chain on InAs(110) Surface
T. Nakamura1, Y. Ohtsubo2, 1, Y. Yamashita1, S. Ideta3, K. Tanaka3, K. Yaji4, A. Harasawa4,
S. Shin4, F. Komori4, R. Yukawa5, K. Horiba5, H. Kumigashira5 and S. Kimura2, 1
Department of Physics, Graduate School of Science, Osaka University, Toyonaka 560-0043, Japan
2
Graduate School of Frontier Biosciences, Osaka University, Suita 565-0871, Japan
3
Institute for Molecular Science, Okazaki 444-8585, Japan
4
Institute for Solid State Physics, The University of Tokyo, Kashiwa 277-8581, Japan
5
Photon Factory, Institute of Materials Structure Science, High Energy Accelerator Research Organization(KEK), Tsukuba 305-0801, Japan1

Ⅲ-2

Low dimensional electronic structures on a solid
surface has been studied extensively, such as Rashbatype spin split states due to the space-inversion
asymmetry [1], and non-Fermi liquid electrons in onedimensional (1D) metal [2, 3]. In this study, toinvestigate the 1D state with spin splitting due toRashba effect, we have observed the surface electronic
structures of Bi/InAs(110)-(2×1) by angle-resolved
photoelectron spectroscopy (ARPES). The Bi atoms
on an InAs(110) substrate form strongly buckled zigzag atomic chains along ሾͳതͳͲሿ [4]. This quasi-1D(Q1D) structure formed by heavy Bi atoms, which
would play an important role for Rashba effect on thissurface due to its strong spin-orbit interaction, is agood candidate for a research about Rashba-type spin
splitting in 1D surface states.
The InAs(110) surface was prepared by cleaving theside face of the InAs(001) wafer in an ultra-highvacuum chamber. Then, a Bi layer with the thicknessof ~5 monolayers was evaporated from a Knudsen cellat room temperature. After annealing at 563 K for 15
minutes, a (2×1) periodic structure was observed,
consistent with an earlier report [4]. The surface
electronic structure of Bi/InAs(110) was observed at
BL5U and 7U of UVSOR-III.
Figure 1 shows the ARPES constant energy contour
at a binding energy at 700 meV measured withpolarized photons at 85 eV. kx (ky) is defined parallel to[001] ( ሾͳതͳͲሿ ). The contour shows quasi-1D shapealong kx direction. A waving feature along ky in Fig. 1
indicates a finite inter-chain interaction.
Figure 2 displays the second derivative ARPES
intensity plot along ky at the kx point indicated by thedashed line in Fig. 1. A pair of the hole bands lies
slightly below the Fermi level, indicating almost
metallic but semiconducting electronic structure.
Photon-energy-dependent ARPES data (not shownhere) suggest that the hole bands are surface states
because of no photon energy dependence.
Assuming parabolic dispersions (dashed lines in Fig.
2) with spin splitting along kx, the size of the Rashba
spin splitting is evaluated as 5.5 eV Å-1. This value isthe largest among other 1D and Q1D Rashba systems[5, 6] and is comparable with typical giant Rashba
systems such as BiTeI and Bi/Ag surface alloys [7, 8].
The giant spin splitting in the Q1D surface state

discovered here would be a promising template for
future spintronic devices.

Fig. 1. A constant energy contour at the binding
energy of 700 meV (hν = 85 eV).

Fig. 2. Second derivative ARPES intensity plots
along ky at kx = 0.34 Å-1 (hν = 85 eV).
[1] Y. A. Bychkov and E. I. Rashba, JETP Lett. 39(1984) 78.
[2] M. Grioni et al., J. Phys.: Condens. Matter 21(2009) 023201.
[3] C. W. Nicholson et al., Phys. Rev. Lett. 118 (2017)
206401.
[4] M. G. Betti et al., Phys. Rev. B 59 (1999) 15760.
[5] J. Park et al, Phys. Rev. Lett. 110 (2013) 036801.
[6] A. Takayama et al., Phys. Rev. Lett. 114 (2015)066402.
[7] C. R. Ast et al., Phys. Rev. Lett. 98 (2007) 186807.
[8] K. Ishizaka et al., Nat. Mater. 10 (2011) 521.

Ⅲ02- 34 74

Ⅲ -2. Materials Sciences
BL5U
BL5U

ARPES Study of Transition-Metal Dichalcogenides NbSe2 and NbS2
I. Watanabe1, K. Sugawara2, 3, Y. Nakata1, K. Shigekawa1, K. Ueno4, T. Takahashi1, 2, 3 and
T. Sato1, 3

1Department of Physics, Tohoku University, Sendai 980-8578, JapanWPI Research Center, Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
3
Center for Spintronics Research Network, Tohoku University, Sendai 980-8577, Japan
4 Department of Chemistry, Graduate School of Science and Engineering, Saitama University, Saitama 3388570, Japan

2

Transition-metal dichalchogenides (TMDs) haveattracted considerable attention since they show
variety of physical properties such as magnetic
ordering, charge-density wave (CDW), Mott-insulator,and superconductivity. Amongst TMDs, 2H-NbSe2[see Fig. 1(a)] has been intensively studied since it
exhibits coexistence of CDW (TCDW~33 K) andsuperconductivity (TC ~ 7 K) [1], and there has been
an intensive discussion on whether the CDW is the
precursor of superconductivity or competes with thesuperconductivity. It is known that a cousin materialof 2H-NbSe2, 2H-NbS2, shows the superconductivity
below 5.7 K without any indication of CDW [2]. Thus,
a comparative study of NbS2 and NbSe2 would enable
us to clarify the interplay between the
superconductivity and CDW in great detail. Veryrecently, it has been suggested from the theoretical
calculation that the two-gap superconductivity can berealized in 2H-NbSe2, and it could originate fromstrong coupling of electrons with low-energy
anharmonic phonons [3]. To elucidate these important
issues, electronic states of 2H-NbSe2 and 2H-NbS2
need to be investigated by angle-resolved
photoemission spectroscopy (ARPES) with energytunable photons from synchrotron radiation.
In this study, we have performed high-resolution
ARPES on 2H-NbSe2 and 2H-NbS2. By utilizing
energy-tunable photons from synchrotron radiation,
we determined the electronic states near the Fermi
level and found that Fermi surface topology of 2HNbS2 is the same as that of 2H-NbS2, while FS volume
centered at the K point of 2H-NbS2 is slightly smaller
than that of 2H-NbS2. These results play an important
rule to understand the origin of CDW in TMDs.
Figures 1(b) and (c) show experimental Fermi
surfaces on 2H-NbSe2 and 2H-NbS2 determined by
ARPES. One can immediately recognize that the
Fermi-surface topology of 2H-NbSe2 resembles to thatof 2H-NbS2. The Fermi surface consists of the large
pockets centered at the Γ and K points, respectively,
which originate from Nb 4d orbitals. These Fermi
surfaces commonly have hole-like character asrecognized from the Fermi level (EF) crossing of thevalence band (VB) in Figs 1(d) and (e). By comparing
the Fermi-surface volume between 2H-NbS2 and 2HNbSe2, we found that a large hole pocket centered at
the K point in NbS2 is slightly larger than that in NbSe2.

It has been experimentally shown in bulk 2H-NbSe2
that there exist three “hot spots” on K/K’-centered FS
which are interconnected by three equivalent 3 × 3
CDW vectors (QCDW) [Fig. 1(b)), which enhance theelectron-phonon interaction, leading to the CDW
instability [4]. The present result indicates that K/K’centered FS in 2H-NbS2 is not well interconnected by
3 × 3 QCDW because of the suppression of CDW in 2HNbS2. Therefore, the present result suggests thatFermi-surface topology plays an important role to the
CDW instability in TMDs.

Fig. 1. (a) Crystal structure of 2H-NbSe2 and 2HNbS2. (b) and (c) APRES intensity at EF in 2H-NbSe2
and 2H-NbS2 plotted as a function of two-dimensional
wave vector measured at hν = 50 and 40 eV,
respectively. (d) and (e) Experimental band dispersion
along the Γ-M high-symmetry line in NbSe2 and NbS2,
respectively.
[1] J. A. Wilson et al., Adv. Phys. 24 (1975) 117.
[2] M. Naito et al., J. Phys. Soc. Jpn. 51 (1982) 219.
[3] C. Heil et al., Phys. Rev. Lett. 119 (2017) 087003.
[4] S. V. Borisenko et al., Phys. Rev. Lett. 102, (2009)
166402.

Ⅲ02- 35 75

Ⅲ-2

Ⅲ -2. Materials Sciences
BL5U
BL5U

Possible CDW Effects on ARPES Spectra in the Antinodal Region of Bi2212
C. Lin1, K. Koshiishi1, S. Nakata1, M. Suzuki1, S. Ideta2, K. Tanaka2,
D. Song3, Y. Yoshida3, H. Eisaki3 and A. Fujimori1

Department of Physics, University of Tokyo, Tokyo 113-0033, JapanUVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
3
National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba 305-8568, Japan
1

2

Ⅲ-2

With more and more recent observations of various
symmetry-breaking orders found in the pseudogap
state of high-Tc cuprates [1], the understanding of thisintertwisted phase becomes increasingly important.
The ubiquitous charge density wave (CDW) has been
discovered in all hole-doped cuprates and even in someelectron-doped cuprates, nevertheless whether CDW
competes with superconductivity and whether it isrelated to the pseudogap are still under hot debate.
The signature of CDW-associated band folding has
not been observed by angle-resolved photoemission
spectroscopy (ARPES) with one exception that may be
the closest—the revelation of particle-hole symmetry
breaking in the pseudogap state of single-layer Bi2201,
which refutes the preformed superconductivity natureof the pseudogap and suggests a possible association
between the pseudogap and CDW [2]. In order toinvestigate whether particle-hole symmetry is broken
in the bilayer Bi2212 due to possible charge ordering,
we have performed temperature-dependent ARPES
measurements at UVSOR BL5U.
To avoid ultra-high energy scale and complex band
structure due to super-modulation, over-doped Bi1.7
Pb0.5 Sr1.9CaCu2O8 (Tc = 87 K, OD87) single crystals
with Pb doping were used and cleaved in-situ under thepressure of ~ 2 × 10-8 Pa. The photon energy of theincident light was 57 eV with linear polarization
perpendicular to the analyzer slit and the total energy
resolution was set to 20 meV. Samples were grown by
the floating-zone method and the hole concentration
was controlled by annealing the samples in N2 or O2
flow.
Figure 1 shows the temperature evolution of theantinodal electronic states. The antibonding band wasenhanced by using current photon energy [3]. By
ploting the peak positions of the energy distribution

curves (EDCs) and summing up in Fig. 2, a clear
misalignment between the Fermi momenta (kF (±))
determined in the normal state and the band bending
momenta (kG (±)) can be observed, indicating theparticle-hole symmetry breaking for OD87 Pb-Bi2212.
Currently, we suppose a similar CDW nature of thisbroken particle-hole symmetry as in the case of Bi2201[2,4], detailed explanation is planned in the near future.

Fig. 2. Misalignment between the Fermi momenta (kF(±)) determined in the normal state and the band
bending momenta (kG (±)) indicating the particle-holesymmetry breaking in the pseudogap state of OD87
Pb-Bi2212.
[1] R. Comin and A. Damascelli, Annu. Rev. Condens.
Matter Phys. 7 (2016) 369.
[2] M. Hashimoto et al., Nat. Phys. 6 (2010) 414.
[3] A. A Kordyuk et al., Phys. Rev. Lett. 89 (2002)
077003.
[4] R. He et al., Science. 331 (2011) 1579.

Fig. 1. Temperature evolution of the antinodal dispersions of OD87 Pb-Bi2212. The antibonding band wasenhanced and the symmetrized spectra were divided by the resolution-convolved Fermi–Dirac function (FD) toeffectively remove the Fermi cutoff. Red circles indicate the peak positions of the FD-EDCs and red arrow shows
the cut position in the first Brillouin zone.

Ⅲ02- 36 76

Ⅲ -2. Materials Sciences
BL5U
BL5U

Detwinned Electronic Structure of Ba0.75K0.25Fe2As2 Observed by ARPES
S. Ideta1, 2, M. Nakajima3 and K. Tanaka1, 2

UVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki, 444-8585, JapanThe Graduate University for Advanced Studies (SOKENDAI), Okazaki, 444-8585, Japan3
Department of Physics, Graduate School of Science, Osaka University, Toyonaka 560-0043, Japan1

2

Iron-based superconductors have an interesting
phase diagram with the antiferromagnetic (AFM)
transition and the structural phase transition. Recently,
nematicity, defined as broken rotational symmetry [atrigonal(C4)-to-orthorhombic (C2) structural transition],
has shed light on the understanding of the mechanismon the iron-based superconductivity [1-4]. In holedoped BaFe2As2 (Ba122) system, Ba1-xNaxFe2As2 andBa1-xKxFe2As2 (K-Ba122) have shown the magnetic
order without C4 symmetry breaking [5, 6] and themoment’s direction would be swapped from in-planeto out-of-plane [7]. Besides, the superconductivity issuppressed between the superconductivity and the C4magnetic phase. The electronic structure at the C4
magnetic phase has been unclear yet, and it would give
us a great interest to elucidate the mechanism of thehole-doped Ba122.
Here, we demonstrated a temperature dependent
angle-resolved photoemission spectroscopy (ARPES)
experiment to elucidate the electronic structure of
detwinned K-Ba122 (x ~ 0.25) with the C4-magnetic
phase in order to prevent from two domains in theorthorhombic (C2) phase below the structural and
AFM transition temperatures (TN,S ~ 60 K).
High-quality single crystals of Ba0.75K0.25Fe2As2 (Tc~ 25 K) were grown by self-flux technique. ARPES
experiments were carried out at BL5U of UVSOR-III
Synchrotron using the linearly s polarized light of hν= 60 eV. Temperature was set at T = 6 K-230 K andclean sample surfaces were obtained for the ARPES
measurements by cleaving single crystals in-situ in an
ultrahigh vacuum better than 1×10-8 Pa.
Figures 1(a) and 1(b) show the second-derivative
ARPES intensity plots along the Z-X and Z-Y
directions, respectively, corresponding to the Z points.
In Figs. 1(a) and 1(b), the direction of the uniaxialpressure is parallel or perpendicular to the spolarization vector, respectively [4], and both band
dispersions are considered to be the electronic
structure from the strain free single domain. Here, we
confirmed that the electronic structure for both
directions (Z-X and Z-Y) was the same at 230 K. In
future work, we focus on the dyz and dxz orbitals asshown in Figs. 1(a) and 1(b) and will analyze thetemperature dependent ARPES spectra. In theelectronic structure of the Z-X and Z-Y directions, we
expect that the occupation of the dyz and dxz orbitals
might be the same due to the reentrant C4-magnetic
phase.
In summary, we have performed an ARPES study ofdetwinned K-Ba122 (x ~ 0.25) and measured theelectronic structure in the Z-X and Z-Y directions. We
found that the electronic structure in both Z-X and ZY directions shows different band dispersions,reflecting the electronic structure from the single
domain due to the uniaxial pressure. We will analyze
the detailed temperature dependence of the ARPES
spectrum of dyz and dxz in future work.

Ⅲ-2

Fig. 1. (a), (b) Second-derivative ARPES intensity
plots of detwinned Ba0. 75K0.25 Fe2As2 taken at hν = 60
eV (T = 6 K), corresponding to the Z point. The dyz anddxz bands are clearly observed differently. (c)Schematic Brillouin Zone. Blue and red arrows
indicate the direction of the momentum cut of panels(a) and (b).
[1] R. M. Fernandes et al., Nat. Phys. 10 (2014) 97.
[2] R. M. Fernandes et al., Phys. Rev. Lett. 111 (2013)
127001.
[3] T. Shimojima et al., Phys. Rev. B 90 (2014) 12111(R).
[4] Y. Ming et al., PNAS 108 (2011) 6878.
[5] L. Wang et al., Phys. Rev. B 93 (2016) 014514.
[6] A. E. Böhmer et al., Nat. Commun. 6 (2015) 7911.
[7] D. D. Khalyavin et al., Phys. Rev. B 90 (2014)
174511.

Ⅲ02- 37 77

Ⅲ -2. Materials Sciences
BL5U
BL5U

Observation of Dirac Cone in Layered NiTe2
by Angle Resolved Photoelectron Spectroscopy
M. Nishino1, S. Miyasaka1, Z. H. Tin1, T. Adachi1, S. Tajima1, S. Ideta2, 3 and K. Tanaka2, 3

Department of Physics, Graduate School of Science, Osaka University, Toyonaka 560-0043, Japan
2
UVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan3
School of Physical Sciences, The Graduate University for Advanced Studies (SOKENDAI), Okazaki 444-8585,
Japan
1

Ⅲ-2

Transition
metal
dichalcogenides
MX2(M=transition metal elements, X=S, Se and Te) has alayered structure. These systems show various
physical phenomena such as charge density wave
(CDW), superconductivity and so on. MX2 has been
attracted significant attention because of theirinteresting properties.
Recently PdTe2 and PtX2(X=Se,Te) revisited from aviewpoint of Dirac fermion [1, 2]. Several
experimental and theoretical studies has confirmed theexistence of type-II Dirac cone with Dirac point at(0,0,kz) between -A points. We have investigated theangle resolved photoemission spectroscopy (ARPES)of the related system NiTe2 to confirm the existence ofthe type-II Dirac cone and to clarify its different
features between NiTe2 and other systems.
The single crystals of NiTe2 were synthesized by aflux method in an evacuated silica tube [3]. The resultsof the energy dispersive X-ray spectroscopy (EDX)
indicated that the actual Ni/Te ratio is 1.17:2. The
ARPES spectra were measured at BL5U of UVSOR
Synchrotron Facility in Institute for Molecular Science
using incident photons with h=60-80 eV. All themeasurements were carried out at 20 K.
Figure 1 shows the APRES intensity plot along ky at
various kz (=0, 0.25 and 0.38c*). At kz =0, there is ahole band near Fermi level around the zone center(ky=0,  point), indicated by red break lines in Fig. 1(a).
As shown in Figs. 1(a)-(c), this hole bandsystematically sinks down with increasing kz. Aroundkz =0.38c*, the top of this band is located very near
Fermi level, and the band show the linear dispersion
along ky.
We also measured the band dispersion along kz (A direction), and found the band crossing point near
Fermi level around kz =0.38c*. The present result of
ARPES indicates that the Dirac point is located around(0,0,0.38c*) near Fermi level in this compound. In
addition, the Dirac cone is tilted along kz, i.e., NiTe2 isa type-II Dirac fermion system.
The band calculation in consideration of the spinorbit interaction suggests the existence of type-II Diraccone with Dirac point around (0,0,0.36c*), which isconsistent with the present ARPES results [4]. On theother hand, the energy level of the calculated Diracpoint is +0.1 eV above Fermi level, and slightly
different from the present experimental result. In thepresent work, we used the single crystals of Ni1.17Te2,

which includes excess Ni. This excess Ni introduces
the electrons into this material. As a result, the electron
doping shifts up to the Fermi level and the energy levelof Dirac point is located very near Fermi level in thepresent compound.

Fig. 1. ARPES intensity mapping along ky direction
at different kz (=0, 0.25c*, and 0. 38c*) in Ni1.17Te2.
[1] K. Zhang et al., Phys. Rev. B 96 (2017) 125102.
[2] H. -J. Noh et al., Phys. Rev. Lett. 119 (2017)016401.
[3] J. A. Wilson and A. D. Yoffe, Adv. Phys. 18 (1969)
193.
[4] H. Usui and K. Kuroki, private communication.

Ⅲ02- 38 78

Ⅲ -2. Materials Sciences
BL5U
BL5U

Polarization-dependent Angle-resolved Photoemission Study of V2AlC
T. Ito1, 2, M. Ikemoto2, D. Pinek3, M. Nakatake4, S. Ideta5, 6, K. Tanaka5, 6 and T. Ouisse3

Nagoya University Synchrotron radiation Research center (NUSR), Nagoya University, Nagoya 464-8603,
Japan
2
Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan3
Univ. Grenoble Alpes, CNRS, Grenoble INP, LMGP, F-38000 Grenoble, France
4
Aichi Synchrotron Research Center, Seto, 489-0965, Japan
5
UVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
6
The Graduate University for Advanced Studies, Okazaki 444-8585, Japan1

MAX phase compounds, i.e., Mn+1AXn where M isa transition 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]. On the other hand, the bulk
electronic structure of MAX phase has been studied
mostly by calculations, mainly because of lack of wellestablished single crystalline samples. In this study, we
have performed angle-resolved photoemission
spectroscopy (ARPES) on MAX phase compound
V2AlC [2] to directly investigate the electronic
structure of this system.
ARPES measurements were performed at the
UVSOR-III BL5U. Data were acquired at T = 30 K
with hν = 70 eV which enables us to trace around theΓKM plane with inner potential of V0=22.5 eVestimated from the photon energy dependentmeasurement (not shown). With using horizontally (P)and vertically (S) polarized photons, we have obtained
the orbital dependent ARPES image. It should be
noted that all ARPES images were obtained at thenormal emission geometry without changing thephoton incident angle relative to the sample surface byutilizing 2D mapping lens mode of MBS A-1 analyzer.
Figures 1(a) and (b) show the polarization
dependent band structure along the ΓM line obtainedby P- and S-polarized photons, respectively. We foundthat the highly dispersive electron band (e) around theΓ point dominates in Fig. 1(b). On the other hand, thespectral weight of electron band seems to be
suppressed around 300 meV in Fig.1(a) where holelike dispersive feature (h) appears below the Fermi
level (EF). From the comparison with the bandcalculation (Fig. 1(c)), the observed electron and holeband are correspond to larger electron and a hole
pocket, respectively. To investigate the band structurenear EF in detail, we have shown the comparison ofpolarization-dependent EDC and MDC spectra in
Figs.1(e) and (f), respectively. Here the measured
momentum point of each EDC spectrum is indicatedat the top of Fig.1(f). It has clearly been observed on
the S-polarized spectra that the band e shows
continuous dispersive feature similarly to thecalculation. On the other hand, the band e on the Ppolarized ones appears as intense narrow peak justbelow EF together with a sudden decrease of spectral
weight as approaching to the h band. As a result, thedispersive feature on the P-polarized seems to form thenarrow band with its bottom locates around 200meV(h'). Though the observed narrow dispersive feature on
the P-polarized electronic structure is not reproducedby the band calculation, it suggests that a orbitaldependent electron correlation effect plays a role forthe mass enhancement on V2AlC [1].

Fig. 1 Band structure along the M line of V2AlC
obtained by P-(a) and S- (b) polarized photons. (c)Band calculation of V2AlC. EDC (e) and MDC (f)spectra of V2AlC obtained by P- (red) and S- (blue)
polarized photons. In (e) and (f), solid and dashed lines
are guide for eyes.
[1] M. Barsoum, MAX phases (Wiley, Weinheim,2013).
[2] T. Ouisse et al., J. Cryst. Growth 384 (2013) 88.

Ⅲ02- 39 79

Ⅲ-2

Ⅲ -2. Materials Sciences
BL6B
BL6B

Large Size Crystal Growth of p-terphenyl Crystal
A. Yamaji1, S. Yamato1, S. Kurosawa2, 3, T. Horiai1, S. Kodama1, Y. Ohashi2, Y. Yokota2,
K. Kamada2 and A. Yoshikawa1, 2Institute for Materials Research, Tohoku University, Sendai 980-8577, JapanNew Industry Creation Hatchery Center, Tohoku University, Sendai 980-0845, Japan
3
Faculty of Science, Yamagata University, Yamagata 990-8560, Japan
1

2

Ⅲ-2

Novel neutron imaging methods using a pulsed
neutron source and neutron-resonance-absorption
spectroscopy technique have been developed. Thesemethods require position sensitive detectors forneutron with the Time-of-Flight (TOF), and one of theissues is development of fast response scintillator.
Although some halide scintillators show high lightyield and fast decay time, most halide materials havehygroscopic nature. Then, we focused on the organic
scintillator crystals, which have fast decay time in thenanosecond range and no hygroscopic nature.
The organic scintillators include hydrogen with highreaction cross-section for thermal and fast neutron.
However, conventional organic scintillator has low
melting temperatures, and scintillation properties
would degrade with overheating. Therefore, we havedeveloped organic crystals for neutron scintillatorswith high melting temperatures and fast decay times.
As a first step, we grew p-terphenyl crystals by the
self-seeding vertical Bridgeman technique (SSVBT)[1]. In this report, we tried to grow large size pterphenyl crystals for the neutron detector.
Growth of p-terphenyl crystals was performed in the
double-wall quartz ampoule by using the SSVBT, as
shown in Fig. 1. Raw material of p-terphenyl powders(98%up purity, Tokyo Chemical Industry) was loaded
into both the inner and outer ampules. The ampoule
was set in a closed chamber, and was heated by usinga resistive heater under nitrogen atmosphere. Due tothe low purity of raw material, the ampoule was moveup and down several times like zone melting for
purification, and pulling rate was 0.7 mm/h.
We succeeded in growing the p-terphenyl crystal
with a diameter of 22 mm as shown in Fig. 2. This
crystal had some pores, and the tail portion was not flat.
The surface of the tail portion (Fig. 2(a)) and the first
position at the bottom of the outer ampoule (Fig. 2(c))
looked brownish and black, respectively.
Since different phases can be generated, the phasesof these portions and the inner of the grown crystal(Fig. 2(b)) were measured by using transmission
Fourier Transform infrared spectroscopy (FT-IR). The
FT-IR transmittance spectra as shown in Fig. 3 showthat only p-terphenyl phase, and no impurity phasepeaks were observed, and these brownish and blackparts can be some impurities such as carbon.

Fig. 1. Schematic of crystal growth setup by using
SSVBT.

Fig. 2. Photographs of the grown crystal (left) and thebottom of the outer ampoule (right).

Fig. 3. FT-IR transmittance spectra of the grown pterphenyl crystal.
[1] A. Arulchackkar avarthi et al., J. Cryst. Growth234 (2002) 159.

Ⅲ02- 40 80

Ⅲ -2. Materials Sciences
BL6B
BL6B

Upper Ground State of Ultrashallow Thermal Donors in Silicon
A. Hara and T. Awano

Faculity of Engineering, Tohoku Gakuin University, Tagajo 985-8537, Japan

1.0

Sample-A
Sample-B

8K

0.9
0.8

Transmittance

0.7
0.6
0.5

8K

0.4
0.3

USTD-1
USTD-3

0.2
0.1
0.0

USTD-1 USTD-3

50

100

150
200
Wave number (cm-1)

250

300

Fig. 1. Transmittance of USTDs observed in two
different samples at 8 K.
2.6

USTD-1 USTD-3

2.4

Trans.(40 K) / Trans. (8 K)

We have found ultrashallow thermal donors(USTDs) in carbon-doped and hydrogen-doped
Czochralski silicon (CZ Si) crystals.[1, 2] To the bestof our knowledge, these are the shallowest energy
levels among those of currently reported donors in Si
crystals. In addition, the ground state (1S state) of the
USTDs was found to be split into at least two states.[3]This is direct evidence that the ground state of the
USTDs is composed of a linear combination of the
wave functions of the conduction band minimum. To
evaluate the upper ground states, we measured thetransmittances of various samples with different
USTD concentrations between 8 and 60 K.
Carbon-doped CZ Si samples were doped withhydrogen by annealing in wet oxygen at 1300°C for 60
min. The samples were then cooled to room
temperature by rapid exposure to air. For carbon
doping, the Si melt used to prepare the ingot wasdoped with carbon powder during CZ Si crystal
growth. Transmittance spectra were obtained with a
far-IR spectrometer at the BL6B using a flowing
cryostat.
Figure 1 shows the transmittance spectra of two
samples, where sample A shows features related to
USTD-1, but sample B shows weak USTD-1 features.
Both samples show spectral features of USTD-3.
Figure 2 shows Trans. (40 K)/Trans. (8 K), where
Trans. (T K) represents the transmittance at T K.
According to our previous research, the two broad dips
observed at approximately 100 and 150 cm-1 at 40 K
originate in the transition from the upper ground state
to the 2P0 and 2P+− states. The upper ground states areoccupied by thermal excitation of electrons from theground state. After comparing these data, we conclude
the following. Features c and c* are correlated with
USTD-3, but not USTD-1. Thus, feature c (c*)
corresponds to the transition from the upper groundstate of USTD-3 to the 2P+− (2P0) state. Namely, theenergy levels of the upper ground state are inverted
compared to those of the ground state. The electronictransitions are summarized in Fig. 3.
In summary, the ground-state splitting of USTDs
was evaluated. The energy levels of the upper groundstate are inverted compared to those of the ground state.

Sample-A
Sample-B

b

2.2
2.0

Ground state – 2P+-

1.8

Ground state – 2P0

1.6

USTD-1

USTD-3

a

1.4
1.2

a* b*

1.0
c*d*

0.8
0.6
0.4

c d
50

100

150
200
Wave number (cm-1)

250

300

Fig. 2. Trans. (40 K)/Trans. (8 K) for two different
samples in Fig. 1.
USTD-1

USTD-3

2P+2P0a*Upper ground state

a d*

d

b*

c

0.8 meV
2.4 meV

Ground stateb c*

4.0 meV

0.8 meVFig. 3. The energy levels of upper ground state areinverted against those of ground state.
[1] A. Hara, T. Awano, Y. Ohno and I. Yonenaga, Jpn.
J. Appl. Phys. 49 (2010) 050203.
[2] A. Hara and T. Awano, Jpn. J. Appl. Phys. 54(2015) 101302.
[3] A. Hara and T. Awano, Jpn. J. Appl. Phys. 56(2017) 068001.

Ⅲ02- 41 81

Ⅲ-2

Ⅲ -2. Materials Sciences
BL6B
BL6B

UV-induced Infrared Absorption Band in Ce:Lu3-xGdxAl2Ga3O12 Crystals
T. Yagihashi1, M. Kitaura1, K. Kamada2, S. Kurosawa1, 2,
S. Watanabe3, A. Ohnishi1 and K. Hara4

Faculty of Science, Yamagata University, Yamagata 990-8560, JapanNew Industry Creation Hatchery Center, Tohoku University, Sendai 990-8560, Japan
3
Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan
4
Reseach Institute of Electronics, Shizuoka University, Hamamatsu 432-8011, Japan
1

2

Ⅲ-2

We have investigated shallow electron traps in
Ce:Gd3Al2Ga3O12 (Ce:GAGG) crystals, which havebeen known as a scintillator with high-light out. From
infrared absorption spectroscopy under irradiation
with ultraviolet (UV) light, it was found that a broadband appears at around 12000 cm-1 [1]. This band
quenched at 60 K, the depth was estimated 80 meV.
These facts indicate that the infrared absorption band
originates in shallow electron traps. It was also
clarified that the infrared absorption band is enhancedby high-temperature annealing in a reduced
atmosphere. At first glance, it seems likely thatshallow electron traps in Ce:GAGG crystals areassociated with oxygen vacancies. However, sinceabsorption bands due to such oxygen vacancies appear
in UV region, the origin of the infrared band isdifferent from simple oxygen vacancies. The origin of
shallow electron traps in Ce:GAGG crystals still
remain unclear, and is an open subject to be solved forbetter understanding of the development of opticalmaterials such as scintillators and long-persistentphosphorescent phosphors [2, 3].
The purpose of the present study is to clarify
whether shallow electron trap centers are formed byconstituents. To do so, we have chased the change of
the UV-induced infrared absorption band at cm-1 for
Ce:Lu3-xGdxAl2Ga3O12 mixed crystals. The crystals
were grown by the micro pulling down method. The
concertation of cerium ions was set 0.5 mol% in all of
crystals. Experiment was performed at the BL6B of
UVSOR synchrotron facility in the Institute for
Molecular Science.
Figure 1 shows UV-induced absorption spectra of
Ce:Lu3-xGdxAl2Ga3O12 mixed crystals at 12 K. The
data were obtained by subtracting UV-unirradiatedspectra from UV-irradiated spectra. As Gd3+ ions are
replaced by Lu3+ ions, the infrared absorption band at
12000 cm-1 is gradually weakened. It disappears
completely for x=0 (Ce:Lu3Al2Ga3O12). From thecreation spectra for photostimulated luminescence, it
was confirmed that the bottom of the conduction bandis almost unchanged for Lu3-xGdxAl2Ga3O12 mixed
crystals. It is thus apparent that the low-energy shift ofthe conduction band is not responsible for thedisappearance of the UV-induced absorption band.
The present result demonstrates that Gd3+ ionsparticipate in the formation of shallow electron traps
centers in Ce:GAGG crystals. It is, therefore, most

likely that excited electrons are shallowly trapped by
Gd3+ ions adjacent to oxygen vacancies. The Gd3+ ions
may locate at the octahedral cation sites (B site). This
type of the cation is named as antisite defect [4],because Gd3+ ions normally occupy the dodecahedral
sites (A site). The theoretical calculation for theformation energy of such antisite defects revealed thatthey are more stable at the octahedral site rather than
the tetrahedral site (C site) [5]. On this basis, Gd2+ ionsat B sites adjacent to oxygen vacancies are mostplausible candidate for the origin of shallow electron
traps in Ce:GAGG crystals.

Fig. 1. UV-induced
absorption
spectrafor
Ce:Lu 3-x Gd x Al 2 Ga 3 O 12 mixed crystals at 12 K. The
data were obtained by subtracting UV-unirradiatedspectra from UV-irradiated spectra.
[1] M. Kitaura et al., APEX 9 (2016) 072602.
[2] K. Kamada et al., J. Cryst. Growth 352 (2012) 88.
[3] K. Asami et al., Opt. Mater. 62 (2016) 171.
[4] M. Nikl et al., Appl. Phys. Lett. 88 (2006) 141916.

Ⅲ02- 42 82

Ⅲ -2. Materials Sciences
BL6B
BL6B

Far-Infrared Reflective Spectrum of Lattice Vibration Modesin Lead-Free Alkali Niobate Piezoelectric Materials
H. Nishiyama, D. Ando, D. Xie, R. Hasegawa, S. Maeda, T. Fuchigami and K. Kakimoto
Graduate School of Engineering, Nagoya Institute of Technology, Nagoya 466-8555, Japanreferring to the TO modes detected in crystal.
: θ = 30o: θ = 45o: θ = 60o
: θ = 75o

: θ = 90o

Reflectivity [a.u.]: θ = 0o: θ = 15o

Ⅲ-2
200

300 400 500 600
2Wave number [cm ]Fig. 1. Angle of polarized light dependence of FIR
reflectivity for KNbO3 crystal. θ = 0o means polarized
light of incident FIR is parallel to the stripe domain
structure.
Measured points
Fitting spectrum

Reflectivity [a.u.]

100

(a)
TO1

''

Piezoelectric materials are widely used in theindustry to convert electrical energy to mechanicalenergy. The piezoelectric property deteriorates byapplying repeated electric field. This phenomenon iscalled as fatigue and serious problem for long use.
Elucidation of the fatigue phenomenon is necessary to
produce piezoelectric materials with high fatigue
resistance. There are two origins of piezoelectriceffect: lattice expansion and domain structure change.
Some researchers attributed the fatigue phenomenon
to pinning of the domain structure, however, there
have been no investigation about the change of
intrinsic effect. In previous reports, we have tried toinvestigate domain structure from the permittivity
change in the line mapping measurement and avibration mode of Nb - O oxygen octahedra for (Na,K)NbO3 piezoceramics before and after fatigue
processing using far-infrared (FIR) reflective analysis[1, 2]. However, we had not reached identification of
the vibration mode in detail because ceramics have a
lot of grains and randomly-oriented polarization
structure. Therefore, vibration modes of KNbO3 single
crystal which has crystal system same as (Na, K)NbO3
piezoceramics were investigated by FIR reflective
analysis to clarify intrinsic effect in ceramics.
KNbO3 single crystal was prepared by self flux
method. It was confirmed that stripe domain structureappeared on the mirror polished surface. FIR
measurement was conducted by a FT-IR spectrometer
in BL6B from 100 to 660 cm-1. BL1B was also used toobtain an information of optic mode TO1 at low wave
number area, 15 – 110 cm-1. Synchrotron light wasused for polarized FIR light source in both BL1B and
BL6B. The spectrum was fitted to obtain complex
permittivity according to Drude-Lorentz equation and
Fresnel equation. Fitting details are shown in theprevious report [2].
Figure 1 shows angle of polarized light dependenceof FIR reflectivity for KNbO3 crystal. Reflectivity
spectra changed every 15o periodically. This result
showed the KNbO3 crystal had a periodical structureon the surface. Figure 2 (a) shows FIR reflectivity for
KNbO3 crystal. Large FIR attenuations were appeared
at 22.1, 190.0, 427.9 cm-1. Figure 2 (b) shows
imaginary part of permittivity ε’’ calculated from thefitting spectrum shown in Fig.2 (a). Three transverse
optic modes, TO1, TO2 and TO3, were appeared
corresponding to the FIR attenuations. These results
indicated that it is possible to investigate vibration
modes of piezoelectric materials by combining of FIR
reflectivity measurements of BL1B and BL6B.
Vibration mode of ceramics should be clarified by

Calculated data

(b)

TO2
TO3

100 200 300 400 500 600-1Wave number [cm ]Fig. 2. FIR reflective analysis for KNbO3 crystal in awide range of wave number from 15 to 660 cm-1.
Angle of polarized light θ was zero in thismeasurement. (a) Measurement points of FIR
reflectivity and fitting spectrum (b) Imaginary part ofpermittivity ε’’ calculated from the fitting spectrum.
[1]J. Hlinka et al., Phys. Rev. Lett. 101 (2008) 167402.
[2] H. Nishiyama, N. Matsubara, K. Yoshida, D. Ando,
T. Fuchigami and K. Kakimoto, UVSOR Activity
Report 2016 44 (2017) 84.

Ⅲ02- 43 83

Ⅲ -2. Materials Sciences
BL6B, BL7B
BL6B, BL7B

Anisotropic Metal-to-Insulator Transition of RuAs
Probed by Polarized Infrared Micro-Spectroscopy
Y. Nakajima1, Z. Mita2, J. Hibi2, S. Kamei2, H. Watanabe2, 1, H. Kotegawa3, H. Sugawara3,
H. Tou3, T. Ito4 and S. Kimura2, 1
Department of Physics, Osaka University, Toyonaka 560-0043, Japan
Graduate School of Frontier Biosciences, Osaka University, Suita 565-0871, Japan3
Department of Physics, Kobe University, Kobe 657-8501, Japan
4
Synchrotron Radiation Research Center, Nagoya University, Nagoya 464-8603, Japan
1

2

Ⅲ-2

Ruthenium mono-pnictides, RuX (X = P, As, Sb),with orthorhombic crystal structure (space groupPnma) attract attention because of the relationship toiron-arsenide (Fe-As) superconductors. Thesematerials also have various physical properties such as
metal-to-insulator transition (MIT) in RuAs [1],charge density wave in RuP [2] and superconducting
transition in Rh-doped RuP, RuAs, and non-doped
RuSb [1]. These properties are believed to be related
to the superconducting property of Fe-As’s, but theorigin has not been clarified yet.
Recently, thanks to the successful synthesis ofsingle-crystalline RuAs, its physical properties havenow been investigated [3]. There are two structuraltransition at TMI1 = 255 K and TMI2 = 195 K, which aresecond-order and first-order transitions, respectively.
The electrical resistivity slightly (rapidly) increases
below TMI1 (TMI2) suggesting that a partial (full) energy
gap opens. However, there is no information of the gap
opening TMI1 and TMI2 because of the limited sample
size of 0.8×0.3 mm2 at most.
To investigate the origin of MIT and the anisotropic
energy gap of RuAs, we performed a polarized opticalreflection spectroscopy on single-crystalline RuAs
along b and c axes using IR and THz microscopes in
the photon energy ranges of 0.05 – 1 eV and 20 – 60
meV, respectively, at BL6B combined with VUVreflectivity spectra at BL7B. To obtain more
information, we have also performed an angleintegrated photoelectron spectroscopy (PES) at AichiSR.
Figure 1 shows temperature-dependent PES spectraof RuAs along the c axis. The spectrum does notchange so much with changing temperature. Thissuggests that the overall electronic structure does notchange by MIT. The PES spectra are consistent withthe calculated density of states without any electron
correlations [3]. It suggests that the intensity of theelectron correlation in RuAs is weak.
Figure 2 shows polarized optical conductivity[σ(ω)] spectra of RuAs in the IR region along two
independent axes derived from the Kramers-Kronig
analysis of the polarized reflectivity spectra. The
strong temperature dependence is visible below thephoton energy of 0.5 eV in E // c and 0.4 eV in E // b,
but weak temperature dependence appears above thesephoton energies. The result is consistent with the PES
result shown in Fig. 1, where the overall spectrum has

almost no temperature dependence. Along the c axis
(E // c), the σ(ω) intensity below 0.5 eV gradually
decreases below the temperature of 230 K (< TMI1) andsuddenly drops below 190 K (~ TMI2). This spectralchange seems to be consistent with the structuraltransition. In contrast, along the b axis, the σ(ω)
intensity below 0.4 eV gradually decreases withdecreasing temperature.
The different behavior along the different axes is
considered to be important for the origin of MIT of
RuAs.

Fig. 1. Temperature-dependent angle-integrated
photoelectron spectra of RuAs along the c axis.

Fig. 2. Temperature-dependent optical conductivity[σ(ω)] spectra of RuAs along the b and c axes.
[1] D. Hirai et al., Phys. Rev. B 85 (2012) 140509(R).
[2] R. Y. Chen et al., Phys. Rev. B 91 (2015) 125101.
[3] H. Kotegawa et al., submitted.

Ⅲ02- 44 84

Ⅲ -2. Materials Sciences
BL6B
BL6B

Infrared Microspectroscopy Using UVSOR BL6B
A. Irizawa1, S. Suga1, T. Nagashima2, A. Higashiya2, M. Hashida3 and S. Sakabe3

The Institute for Scientific and Industrial Research, Osaka University, Ibaraki 567-0047, Japan
2
Faculty of Science and Engineering, Setsunan University, Neyagawa 572-8508, Japan
3
Advanced Research Center for Beam Science, Institute for Chemical Research, Kyoto University, Uji 611-0011,
Japan
1

Optical study is one of the most powerful techniques
for investigating electronic states of solids. Great dealof information about electronic state, band structure,
crystal structure, and dielectric response can beobtained by using spectroscopic techniques. From its
handling for experiments, the optical study isextremely compatible with microscopy and undermultiple conditions such as low temperature, highmagnetic field, and high pressure. In the case of solids,
it is well known that the temperature is one of thedecisive factors for the electronic states. In case ofstrongly correlated systems, the considerable types ofphase transition are induced by the change of thetemperature. Particularly, the multiferroic compounds
can be controlled of its physical properties mutually by
the external fields such as magnetic, electronic, andelastic ones. The other particular condition, thepressure will directly affect the electron-electroninteractions through the change of lattice constants.
There we need microscopic technique for probing thesmall space in DAC. IN other cases, 2D scanningmicrospectroscopy ca detects the change of electronic
and/or chemical states in particular regions such aschanged and damaged by beam irradiations. The
BL6B in UVSOR is adjusted for the investigations at
low temperature and microscopy in the low-energy
infrared region. There equips two type interferometersof both Michelson and Martin-Puplett types for FIR
region and microscopy for MIR region.
In this report, we have performed the opticaltransmittance measurements in MIR region for several
compounds having damages by THz-FEL irradiation.
THz-FEL at The Institute of Science and Industrial
Research (ISIR) in Osaka University is a FEL lightsource in the terahertz band or the far-infrared region(frequency: 2.5 - 7.5 THz, wavelength: 40 - 120 μm,
wavenumber: 83 - 250 cm-1) which is the boundary
region of electromagnetic wave between radio waves
and lights. The electric field of this intense
monochromatic laser reaches several MV/cm which isenough to make ablations and/or discharge phenomena
for materials. Recently, our group can be found a
strange mark constructed on a surface ofsemiconductors, Si [1]. This stripe mark has been
known as LIPSS (laser induced periodic surface
structure) for the damage by NIR fs-laser irradiation,
but in THz-FIR region, this is the first observation inquite different wavelength. LIPSS has been known for
its fine structures having smaller period compared forthe wavelength. In case of THz-FIR LIPSS, the period

is about 10 times smaller than that of NIR fs-laser
LIPSS. Therefore, the models of LIPSS formationconsidered for NIR laser can not be explicable for THz
LIPSS.
Experiments are performed by using MIR
microscope installed in BL6B. 2D mapping was
performed for THz-FEL irradiated sample of Si. The
size of aperture is 100*100 μm and 10*10 areas aremeasured. Both thermal light source and SR lightsource were used for the measurement. The spectra ofirradiated and non-irradiated areas are compared rightnow. We will discuss the difference of spectra and theeffects of THz-FEL irradiation constructing LIPSS on
Si in the article under construction.

Fig. 1. MIR spectroscopic 2D mapping of THz-FEL
irradiated Si.
[1] A. Irizawa, S. Suga, T. Nagashima, A. Higashiya,
M. Hashida and S. Sakabe, Appl. Phys. Lett. 111(2017) 251602.

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BL7U

ARPES Study of Van Der Waals Ferromagnet Cr2Ge2Te6
M. Suzuki1, B. Gao2, A. Solomon2, K. Koshiishi1, S. Nakata1, K. Hagiwara1, C. Lin1,
S. Ideta3, K. Tanaka3, M. Kobayashi4, S-W. Cheong2 and A. Fujimori1
Department of Physics, The University of Tokyo, Tokyo 113-0033, Japan
Rutgers Center for Emergent Materials, Rutgers University, Piscataway, New Jersey 08854, USA
3
Editorial Board, UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
4
Center for Spintronics Research Network, The University of Tokyo, Tokyo 113-0033, Japan
1

2

Ⅲ-2

In recent years, van der Waals (vdW) ferromagnets,
which have attractive physical properties, have been
intensively studied in order to investigate the origin of
their ferromagnetism with 2D crystalline [1]. A
representative vdW ferromagnetic insulator Cr2Ge2Te6(CGT) exhibits ferromagnetism below ~ 61 K [2]. It
has also been reported that the magnetic behavior of
CGT atomic layer is well described as ideal 2D
Heisenberg model [3].
We have conducted angle-resolved photoemission
spectroscopy (ARPES) measurement of CGT withusing two linearly polarization in order to clarify its
electronic states directly. As shown in Fig. 1, hole-likeband along the Γ point below Fermi level wasobserved, confirming its insulating property. We havealso performed DFT calculations. The spectra nearby
Fermi level obtained by the experiments andcalculated partial density of states (PDOS) of Cr 3delectrons are shown in Fig. 2. We found that the
spectrum for p-polarization has a large peak aroundbinding energy of 2eV different from the case of spolarization showing a peak at lower binding energy.
Comparison between the experiments and thecalculations suggests that the peak for p-polarization
comes mainly from Cr 3dx2-y2 and 3dxy orbitals, and thespectrum for s-polarization reflects Cr 3dz2 PDOS.
For the future prospect, we would like to perform
ARPES measurements for other vdW compounds such
as Cr2Si2Te6 in order to investigate the effect by thedifference in composition.

Fig. 1 ARPES spectra for different polarization.

Fig. 2 The exprimental spectra near EF for different
polarization and Cr 3d PDOS by DFT calculation.
[1] N. Smith, Nature 546 (2017) 216.
[2] X. Zhang et al., Jpn. J. Appl. Phys. 55 (2016)
033001.
[3] C. Gong et al., Nature 546 (2017) 265.

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BL7U

ARPES Study of Topological Line-Node Semimetal CaAgAs
D. Takane1, K. Nakayama1, S. Souma2, 3, T. Wada4, Y. Okamoto4, 5, K. Takenaka4,
Y. Yamakawa5, 6, A. Yamakage5, 6, T. Takahashi1, 2, 3 and T. Sato1, 2

Department of Physics, Tohoku University, Sendai 980-8578, JapanWPI Research Center, Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
3
Center for Spintronics Research Network, Tohoku University, Sendai 980-8577, Japan
4
Department of Applied Physics, Nagoya University, Nagoya 464-8603, Japan
5
Institute for Advanced Research, Nagoya University, Nagoya 464-8601, Japan
6
Department of Physics, Nagoya University, Nagoya 464-8602, Japan
1

2

Topological semimetals are recently attracting aconsiderable attention. In contrast to conventional
semimetals with a finite band overlap between valenceband (VB) and conduction band (CB), topologicalsemimetals show the touching of the VB and CB at thediscrete points (called Dirac/Weyl semimetals) oralong a one-dimensional curve (line-node semimetals;
LNSMs) in the bulk Brillouin zone. Such Dirac/Weylcone states are known to provide a platform to realize
exotic physical properties. The existence of threedimensional Dirac semimetals was first confirmed in
Cd3As2 and Na3Bi, where the VB and CB touch witheach other at the point (Dirac point) protected byrotational symmetry of the crystal. Recent studies on
noncentrosymmetric transition-metal monopnictides(TaAs family) have clarified pairs of bulk Weyl-conebands and Fermi-arc surface states, supporting their
Weyl-semimetallic nature. While Dirac/Weylsemimetals with point nodes have been intensively
studied experimentally, the experimental studies of
LNSMs with line nodes are relatively scarce despite
many theoretical predictions.
Recently, it was theoretically proposed that
noncentrosymmetric ternary pnictides CaAgX [X = P,
As] are the candidate of LNSM and topologicalinsulator [1]. These materials crystallize in the
ZrNiAs-type structure [see Figs. 1(a) and 1(b)]. Firstprinciples band-structure calculations have shown that,
under negligible spin-orbit coupling, CaAgX displays
a fairly simple band structure near the Fermi level (EF)with a ring-like line node (nodal ring) surrounding theΓ point of bulk hexagonal Brillouin zone (BZ). In thisstudy, we performed an angle-resolved photoemission
spectroscopy (ARPES) study on CaAgAs. By utilizing
low-energy bulk sensitive ARPES at BL-7U, we
determined the VB structure near EF and revealed the
LNSM nature of CaAgAs [2].
___Samples were cleaved in situ along the (11 2 0)
crystal plane. This indicates that the cleaved plane is
the ky-kz plane in the hexagonal bulk BZ. Figures 1(c)and 1(d) show the momentum distribution curves atvarious binding energies (EB’s) and the corresponding
second-derivative intensity plot, respectively,
measured at T = 40 K along a cut crossing the Γ point.
One can recognize linearly-dispersive hole-like bands
approaching EF [see orange dashed lines in Fig. 1(d)].

The observed band dispersions are well reproduced by
the band calculations and assigned as the lower branchof the Dirac-like energy bands. Through the detailed
band mapping over three-dimensional BZ, we
observed ring-shaped Fermi surface on the (0001)
mirror plane. These observations strongly suggest that
CaAgAs is characterized by the bulk Dirac-like bandand ring-torus Fermi surface associated with the line
node on the mirror plane, in line with the bandcalculations.

Fig. 1. (a) and (b) Two different views of crystal
structure of CaAgAs. (c) Momentum distribution
curves at various EB’s measured along a cut near the Γpoint at T = 40 K with linearly-polarized 16 eV
photons. (d) Second-derivative intensity of (c) plotted
as a function of EB and wave vector. Orange dashedlines are a guide for the eyes to trace the linear band
dispersions.
[1] A. Yamakage et al., J. Phys. Soc. Jpn. 85 (2016)
013708.
[2] D. Takane et al., npj Quantum Materials 3 (2017) 1.

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BL7U

Mott Insulating State in Eu2Ir2O7 Revealed by ARPES
M. Nakayama1, T. Kondo1, Z. Tian1, J. J. Ishikawa1, M. Halim1, C. Bareille1, K. Kuroda1,
T. Tomita1, S. Ideta2, K. Tanaka2, M. Matsunami3, S. Kimura4, L. Balents5,
S. Nakatsuji1 and S. Shin1
ISSP, University of Tokyo, Kashiwa, Chiba 277-8581, JapanUVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan3
Toyota Technological Institute, Nagoya 468-8511, Japan
4
Graduate School of Frontier Biosciences, Osaka University, Suita, Osaka 565-0871, Japan
5
Kavli Institute for Theoretical Physics, Santa Barbara, California 93106, USA
1

2

Ⅲ-2

The 5d iridium oxides (iridates), having comparable
scales for their kinetic energy, Coulomb interaction,and spin-orbit coupling, provide an excellent platform
for studying new types of strongly correlated
phenomena. Amongst them, the pyrochlore iridates(Ln2Ir2O7, where Ln is a lanthanide), endowed withfrustrated geometry and cubic symmetry, have aparticularly fascinating phase diagram. Pr2Ir2O7, withthe largest Ln ion, is a metallic spin liquid and exhibits
an anomalous Hall effect. For Ln ions with a smaller
ionic radius, an antiferromagnetically orderedinsulating phase appears at low temperature.
Theoretically, topological band structures have been
ascribed to the Ln2Ir2O7 series. The metallic phase ispredicted to exhibit quadratically, dispersing
conduction and valence bands touching at the Γ pointclose to the Fermi level (EF). We have indeed
identified this structure by angle-resolved
photoemission spectroscopy (ARPES) in Pr2Ir2O7 [1].
Theory predicts that such a quadratic Fermi node state
may be converted into various topological states suchas a topological insulator or a Weyl semimetal byappropriate symmetry breaking.
Antiferromagnetism in these materials is of theIsing type, consisting of an “all-in–all-out” (AIAO)
configuration of Ir moments on alternating tetrahedra.
This can be considered an “octupolar” spin orderwhich breaks time-reversal but preserves cubic
symmetry, and does not enlarge the unit cell. Early
density functional studies predicted the magnetic state
to be a Weyl semimetal, and general arguments imply
that, if a quasiparticle picture applies at low energy inthe antiferromagnetic phase, and the magnetic
ordering is weak, it must exhibit Weyl points andcannot have a true gap. Nevertheless, optical andtransport measurements indicate a gapped insulating
ground state for Nd2Ir2O7, despite its low
antiferromagnetic–metal-insulator (MI) transition
temperature TMI ≈ 30 K and proximity to metallic
Pr2Ir2O7. We have investigated the evolution of theelectronic structure through the MI transition in
Nd2Ir2O7 by ARPES, and found a dramatic Slater toMott crossover with reducing temperature [2].
We further investigated the electronic properties ofEu2Ir2O7, an insulator with all-in all-out
antiferromagnetic ordering. While the band dispersion
deep below the Fermi level (~-1eV) is similar to thatof the metallic Pr2Ir2O7, the spectral weight at the
Fermi level is completely diminished in Eu2Ir2O7(Fig.1). The gapped state lacking long-lived
quasiparticles indicate that this material is a Mott
insulator. We find a significant reduction of Mott gap
with a little amount of carrier doping due to offstoichiometry, and an anomalous filling of spectral
weight at EF across Neel temperature in the doped
samples. These features imply that Eu2Ir2O7 is situatednear the border between the Mott- and Slaterinsulating phases, suggesting a tunability by carrier
doping to realize correlated topological states
theoretically predicted.

Fig. 1. (a) The Brillouin zone of Eu2Ir2O7. (b) The
ARPES dispersion map, measured along kx crossing Γ.
(c) EDCs of (b). The red points indicate peak positions.
(d) Comparison of EDCs at the Γ point for threecompounds.
[1] T. Kondo et al., Nature communications 6 (2015)
10042.
[2] M. Nakayama et al., Phys. Rev. Lett. 117 (2016)056403.

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Superconducting Gap and Pseudogap in the Surface States of PrFeAsO1-yObserved by Angle-resolved Photoemission Spectroscopy
K. Hagiwara1, M. Horio1, K. Koshiishi1, S. Nakata1, C. Lin1, M. Suzuki1, M. Ishikado2, 3, 4,
S. Ishida3, H. Eisaki3, S. Shamoto4, S. Ideta5, K. Tanaka5, T. Yoshida6 and A. Fujimori1
Department of Physics, The University of Tokyo, Tokyo 113-0033, Japan
Comprehensive Research Organization for Science and Society, Tokai 319-1106, Japan
3
National Institute of Advanced Industrial Science and Technology, Tsukuba 305-8568, Japan
4
Japan Atomic Energy Agency, Tokai, 319-1184, Japan
5
UVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
6
Graduate School of Human and Environmental Studies, Kyoto University, Kyoto 606-8501, Japan1

2

In the 1111-type iron pnictides, superconductivity isrealized by electron doping through substituting F for
O or Co for Fe, or introducing oxygen deficiencies [1].
According to previous angle- resolved photoemission
spectroscopy (ARPES) studies [2, 3], however, the1111 compounds exhibit heavily hole-doped electronic
structures for cleaved surfaces, which has been
attributed to charge transfer due to the polar surfaces.
In some ARPES studies, it has been reported that theheavily hole-doped surfaces are superconducting, but
the nature of the superconductivity nor relationshipbetween the surface electronic structure and thesuperconductivity has not been known yet. Therefore,
more detailed knowledge about the superconducting
gap at the surface is required.
In this work, we have performed ARPES studies on
the 1111 compounds and have measured thetemperature dependence of the energy gap in thesurface states in order to study possiblesuperconductivity at the surface of the 1111 system.
High-quality single crystals of the electron-doped
superconductor PrFeAsO1-y (Tc = 16 K) weresynthesized by the high pressure technique as
described in Ref. [4]. ARPES measurements were
performed at BL7U of UVSOR using linearlypolarized light with the photon energy of 22.5 eV. A
MBS A1 electron analyzer was used. The total energy
resolution of ~ 10 meV. The crystals were cleaved insitu at T = 12 K. The measurements were carried out
in an ultrahigh vacuum of ~ 10-10 Torr.
Figure 1 shows a Fermi surface (FS) mapping for
the PrFeAsO1-y at T =12 K using s-polarization. One
can clearly observe a large circular hole pocket and asmall hole pocket around zone center, referred to as“Outer” and “Inner”, respectively. This result is
consistent with previous reports [2, 3]. Figure 2 shows
the analysis of the energy gap on the “Outer” hole
pocket, which originates from the surface. Panel (a)shows symmetrized energy distribution curves (EDCs)
after the background subtracted at the Fermi wave
vector (kF) of the “Outer” hole pocket. The background
spectra are defined by an orange line in Fig. 1. One canfind an energy gap opening and a coherence peak at
low temperatures. In order to quantify the energy gap,

we have estimated gap size from the position where
deviation from the normal-state EDCs starts indicatedby triangles as shown in panel (a). We also estimatedthe gap area surrounded by the symmetrized EDC andthe normal-state EDC. As shown in panel (c), theenergy gap remains open above Tc, which may indicate
a pseudogap opening. In the case of low temperature,
one can observe coherence peaks, which may indicate
a superconducting gap caused by proximity effect.

Fig. 1. E-k plot. Inset shows schematic FS.

Fig. 2. Analysis of the energy gap at the “Outer” kF.
(a) Temperature dependence of the symmetrized EDCs.
(b) Temperature dependence of the gap magnitude.
[1] Y. Kamihara, et al., J. Am. Chem. Soc. 130 (2008)3296.
[2] I. Nishi et al., Phys. Rev. B 84 (2011) 014504.
[3] A.Charnukha et al., Sci. Rep. 5 (2015) 10392.
[4] M. Ishikado et al., Physica C 469 (2009) 901.

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Temperature Dependent Angle-resolved Photoemission Study of(TMTCF)2AsF6
1

Ⅲ-2

T. Ito1, 2, S. Ideta3, 4, K. Tanaka3, 4, S. Kimura5, 6 and T. Nakamura7

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
UVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
4
The Graduate University for Advanced Studies, Okazaki 444-8585, Japan
5
Graduate School of Frontier Biosciences, Osaka University, Suita 565-0871, Japan
6
Department of Physics, Osaka University, Toyonaka 560-0043, Japan
7
Institute for Molecular Science, Okazaki 444-8585, JapanThe Bechgaard salts (TMTCF)2X (C = S, Se; X =PF6, AsF6, etc.) belong to a family of quasi-onedimensional (Q1D) organic conductors. Thesematerials allow for a variety of ground states from
antiferro-magnetism, a Peierl’s-like spin density wave,
to a superconducting state by tuning the chemicalpressure with the combination of TMTSF/TMTTF andanion X [1]. Among these compounds, (TMTTF)2X
system is especially important to elucidate the relation
between the electronic structure and the origin of
anomalous properties, because of its relatively hightransition temperature from metallic to Mott localized(loc), charge ordered (CO), and antiferro-magnetic(AF) states [2]. In this study, we have performed
temperature dependent angle-resolved photoemission
spectroscopy(ARPES)onsingle-crystalline(TMTCF)2AsF6 to clarify the relation between theelectric structure and the thermodynamic properties,
especially the intrinsic temperature dependence
originating in the phase transitions.
ARPES measurement were performed at UVSORIII BL7U by utilizing the bulk-sensitive low photon
energy (hν = 8 eV) as well as the micro focus beam
(15×100 μm2).
Figures 1 (a-d) and (e-h) show the temperaturedependence of the band structure near the Fermi level(EF) of (TMTSF)2AsF6 and (TMTTF)2AsF6,
respectively. It is evident that the clear dispersive
feature of TMTCF molecular orbital has been
observed at T = 30 K (Figs. 1(a) and (e)) for both case.
With increasing temperature, the dispersive TMTSF
band on metallic (TMTSF)2AsF6 remain existing until
T = 260 K (Fig. 1(d)). On the other hand, TMTTF
features on (TMTTF)2AsF6 show anomalous
temperature dependence. At CO state (T = 30 K), theelectronic structure of (TMTTF)2AsF6 is dominatedwith the dispersive feature folded around kx = 0.30 Å-1.
With increasing temperature at the loc. state, the top ofdispersive feature gradually shifts to higher binding
energy side while the spectral weight of nondispersive broad feature around 1 - 1.5 eV increases asshown in Fig. 1 (j). Then the electronic structure at themetallic state is dominated with the localized featureon (TMTTF)2AsF6 in contrast to the dispersive featureon (TMTSF)2AsF6. We expect that the observed

characteristic itinerant to localized transition of the
TMTTF states play a dominant role in the CO-loc.metal phase transition on (TMTTF)2AsF6.

Fig. 1. Temperature dependent ARPES images and
EDC spectra at kx=0.20 Å-1 and 0.30 Å-1 of(TMTSF)2AsF6 (a-d and i) and (TMTTF)2AsF6 (e-hand j), respectively. Phase diagram of (TMTCF)2X [2]is also indicated.
[1] T. Ishiguro et al., Organic Superconductors(Springer-Verlag, Berlin, 1998).
[2] E. Rose et al., J. Phys.: Condens. Mat. 25 (2013)
014006.

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Low-Energy Heavy-Fermion Bands in YbCdCu4 Observed by AngleResolved Photoemission Spectroscopy
H. Shiono1, S. Ishihara1, K. Mimura1, H. Sato2, E. F. Schwier2, K. Shimada2, M. Taniguchi2,
S. Ideta3, K. Tanaka3, T. Zhuang4, K. T. Matsumoto4, K. Hiraoka4 and H. Anzai1
Graduate School of Engineering, Osaka Prefecture University, Sakai 599-8531, Japan
Hiroshima Synchrotron Radiation Center, Hiroshima University, Higashi-Hiroshima 739-0046, Japan
3
UVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
4
Graduate School of Science and Engineering, Ehime University, Matsuyama 790-8577, Japan1

2

the magnetic susceptibility measurements [2]. Thisconsistency implies that the heavy-fermion state in
YbCdCu4 stems from the hybridization between the
Furtherobserved 4f7/2 and conduction bands.
experiments in wide momentum ranges are needed tounderstand the evolutions of the heavy-fermion bandsof YbCdCu4.
(a)(b)
YbCdCu4

EF

4f7/2

-0.5

Intensity (arb.units)

Energy, ω (eV)

0

High

-1.0
Low

(c)

Г

-0.4
0
Momentum, k (Å-1)
15 K
50 K
100 K
180 K

-0.3

4f5/2

K

0.2 eV

(d)
60

4f7/2

-0.2
-0.1
0
Energy, ω (eV)Peak Energy (meV)-1.5

Intensity (arb.units)

In rare-earth compounds, the hybridization effectbetween conduction and localized-4f electrons (c-fhybridization) leads to the formation of heavy
electrons, and it is characterized by a renormalizedband structure near the Fermi level (EF). According to
the single-impurity Anderson model, the Yb2+ 4f7/2
peak of Yb compounds appears at the energy scales of
the Kondo temperature TK, which is a measure of thehybridization strength [1]. Hence, the electronic band
structure near EF provides important clues to heavy
fermion state.
The Laves-phase structure YbCdCu4 is known as aheavy fermion compound with the electronic specificheat coefficient γ ~ 175 mJ/K2mol [2] and as a goodreference for studies the first-order valence transitionof YbInCu4 [3]. To understand the heavy-fermion
state in YbCdCu4, it is essential to unveil the nature of
the Yb 4f and conduction-band states.
Angle-resolved photoemission spectroscopy (ARPES)
is a direct probe to measure the electronic excitation asfunctions of energy and momentum. Here, we reporton a study of the hybridization effect in YbCdCu4
based on ARPES data of the electronic band structurenear EF. The experiments were performed at BL7U of
UVSOR and BL-1 of Hiroshima Synchrotron
Radiation Center (HSRC).
Figure 1(a) shows ARPES spectra of YbCdCu4
� direction of the surface Brillouintaken along the Γ�-Kzone. Two flat bands at |ω| ~ 0.02 and 1.3 eV are
assigned to the spin-orbit split Yb2+ 4f7/2 and 4f5/2 states,
respectively. A dispersive band was observed over anenergy range of 0.1 < |ω| < 1.2 eV. This conduction
band intersects with the 4f7/2 state and reaches EF, asseen from the peaks of momentum distribution curves
in Fig. 1(b). Thus, Fermi surface of YbCdCu4 at leastconsists of one hole band around the Γ� point.
For quantification of the hybridization strength, wehave measured the temperature dependence of theYb2+ 4f7/2 state. A significant shift and an intensity
enhancement in the 4f7/2 peak are observed, as shownby angle-integrated photoemission spectra in Fig. 1(c).
We plotted the peak positions as a function oftemperature in Fig. 1(d), which reveals a continuous
decrease in the energy with decreasing temperature.
The peak energies extrapolated to zero temperature isestimated to be ~ 26 meV and corresponds to TK ~ 300
K, which is roughly consistent with TK reported from

-0.4
0Momentum, k (Å-1)
Data from
UVSOR
HiSOR

40

20

0
0

100
200
Temperature (K)Fig. 1. (a) ARPES spectra of YbCdCu4 taken along� direction at 15 K. The data were obtained atthe Γ�-K
BL-1 of HSRC. (b) Momentum distribution curves
near EF. (c) Angle-integrated spectra at various
temperatures. (d) Energy shift of the Yb2+ 4f7/2 peak inpanel (c), together with the data from UVSOR.
[1] R. I. R. Blyth et al., Phys. Rev. B 48 (1993) 9497.
[2] J. L. Sarrao et al., Phys. Rev. B 59 (1999) 6857.
[3] I. Felner et al., Phys. Rev. B 35 (1987) 6935.

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High-Resolution ARPES Study of FeSe Superconductor
G. Phan1, K. Nakayama1, H. Oinuma1, T. Nakamura1, D. Takane1, Y. Nakata1,
T. Urata2, Y. Tanabe1, K. Tanigaki1, 3, F. Nabeshima4, M. Kawai4, Y. Imai1,
A. Maeda4, T. Takahashi1, 3, 5 and T. Sato1, 5

1Department of Physics, Tohoku University, Sendai 980-8578, Japan
Department of Crystalline Material Science, Nagoya University, Nagoya 464-8603, Japan3
WPI Research Center, Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
4
Deptment of Basic Science, The University of Tokyo, Tokyo 153-8902, Japan
5
Center for Spintronics Research Network, Tohoku University, Sendai 980-8577, Japan2

Ⅲ-2

Iron chalcogenides FeSe1-xTex, the structurally
simplest iron-based superconductors, are the target ofintensive research because of rich physical properties
such as superconductivity, antiferromagnetism,structural transition, and electronic nematicity. It wasalso reported that the physical properties of FeSe1-xTex
show gigantic pressure effects. For instance, thesuperconducting transition temperature (Tc) of FeSe is
dramatically enhanced from 8 K to 36 K by theapplication of high pressure. Elucidating the origin ofsuch pressure effects would provide a key tounderstandingthemechanismofhigh-Tc
superconductivity.
Recent advances in fabricating epitaxial thin filmsof FeSe1-xTex have opened a door to controlling thelattice parameters by tuning the lattice mismatch with
substrate. This strain engineering has capability for
manipulating various physical properties. For
FeSe 1-x Te x , compressive strain enhances the Tc up to
12 K in FeSe [1] and further to 23 K in FeSe0.8Te0.2 [2].
In addition, strain-induced drastic changes in the
structural, magnetic, and nematic properties have been
discovered [3]. These discoveries have provided agreat opportunity for investigating the interplay
between the physical properties and the lattice
parameters at ambient pressure. In this study, we have
performed
high-resolution
angle-resolved
photoemission spectroscopy (ARPES) on compressive
strained FeSe1-xTex thin films on CaF2 substrate at BL7U and compared their electronic structure with that ofstrain-free FeSe. We have revealed the evolution ofelectronic structure with epitaxial strain.
High-quality FeSe thin films were grown on CaF2
substrate by pulsed laser deposition. The film
thicknesses are approximately 300 monolayers. In Fig.
1, we show representative electronic structure
measured in the normal state of bulk FeSe. One canrecognize hole-like and electron-like band dispersions
at the Brillouine-zone center (Γ point) and corner (Mpoint), respectively, indicative of semimetallic natureof FeSe. When compressive strain is applied on CaF2
substrate, hole-like and electron-like bands shift
upward and downward, respectively. This observation
indicates a strain-induced change in the semimetallic
band overlap [4]. We have also determined theelectronic structure of Te-substituted films on CaF2

and found a marked change in the electronic structurecompared with that in pristine FeSe. Our observations
provide important insights into the interplay between
Tc enhancement and lattice parameters.

Fig. 1. (a) and (b) ARPES intensity plot around theBrillouin-zone center and corner, respectively, on
FeSe at T = 280 K, obtained after dividing by the
Fermi- Dirac function convoluted with the
instrumental resolution. The data have been obtainedwith linearly- polarized 21-eV photons.
[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] G. Phan et al., Phys. Rev. B 95 (2017) 224507.

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Electronic Structures of Methylanmmoniumlead Trihalides Single Crystals
S. Yamanaka1, K. Tonami1, S. Ideta2, K. Tanaka2, K. Yamada3, H. Yoshida4 and Y. Nakayama1
1

Department of Pure and Applied Chemistry, Tokyo University of Scienece, Noda, 278-8510, Japan
2
UVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
3
College of Industrial Technology, Nihon University, Narashino 275-8575, Japan
4
Graduate School of Engineering, Chiba University, Chiba 263-8522, Japan

CH3NH3PbX3 (X = Br, I) thin films are used as lightabsorption and charge separation materials of
perovskite solar cells [1]. However, many structuraldefects (such as crystal grain boundaries) and
impurities remain in polycrystalline thin films, which
may cause problems in evaluating the precise
electronic structure of the substances. In this study, we
aimed to clarify the intrinsic electronic structures of
CH3NH3PbX3 by using single crystal samples.
CH3NH3PbBr3 was produced from CH3NH3Br and
PbBr2 in N, N-dimethylformamide; CH3NH3PbI3 wassynthesized from CH3NH3I and PbI2 in γbutyrolactone. In either case, single crystal samples(typically as Figs. 1(a) and 1(b)) were prepared byinverse temperature crystallization methods [2, 3]. For
the sake of obtaining the clean surface of the
CH3NH3PbX3 single crystals, cleavage of the crystal
surface in vacuum was examined by breaking aceramic post bounded on top of each sample.
Ultraviolet photoelectron spectroscopy (UPS)
measurements on the CH3NH3PbX3 single crystals
were conducted at BL7U of UVSOR. The excitationenergy was set at 40 eV. In order to avoid charging of
the sample during the measurements, the samples were
irradiated with a laser beam (512 nm) at the same time.
Figure 2 (a) shows UPS spectra of a CH3NH3PbBr3
single crystal before and after cleavage. It was
confirmed that the peak intensity derived from Pb5d(binding energy (BE) around -20 eV) was enhanced
and valence band structures (BE of -2 to -15 eV) were
defined as a result of cleavage. This suggests that theclean surface is successfully obtained by cleavage invacuum. Nevertheless, a new peak derived frommetallic Pb (Pb0) appeared at BE ~ -18 eV. This isplausibly due to damages in the CH3NH3PbBr3 sample
caused by irradiation with ultraviolet light during themeasurements.
Figure 2 (b) shows UPS spectra of a CH3NH3PbI3
single crystal before and after cleavage. Similarly to
the CH3NH3PbBr3 case, enhanced intensities of the
Pb5d peaks suggest successful cleaning of the
CH3NH3PbI3 surface by cleavage in vacuum.
Furthermore, in the case of CH3NH3PbI3, it was
confirmed that the peaks of Pb5d shifted by +0.20 eV,
which suggests change in band bending. On the other
hand, shift in the secondary electron cutoff measured
with a separate equipment (“off-line ARPES” device)indicated that the vacuum level moves by 0.7 eV on
the high energy side after cleavage in vacuum. These
results suggest that impurities on CH3NH3PbI3 single
crystals induce a negative vacuum level shift of -0.5

eV and downward band bending of -0.2 eV. Thisimplies the formation of a surface electric double layer
due to the electrons being donated from the surface
impurities to the CH3NH3PbI3 side. In addition, it was
revealed that the Pb0 peak intensity was minor incomparison to the CH3NH3PbBr3 case, suggesting that
CH3NH3PbI3 is more robust to the ultraviolet light.
This work was conducted as Joint-Studies-Programs[27-545 and 27-835] of IMS.

(a)

(b)

Fig. 1. Photographs of the (a) CH3NH3PbBr3 and (b)CH3NH3PbI3 single crystal samples.

Fig. 2. UPS spectra of the (a) CH3NH3PbBr3 and (b)CH3NH3PbI3 single crystal samples before and aftercleavage in vacuum.
[1] A. Kojima et al., J. Am. Chem. Soc. 131 (2009)
6050.
[2] F. Zhang et al., J. Mater. Chem. C. 5 (2017) 8431.
[3] H. Wei et al., Nat. Mater. 16 (2017) 826.

Ⅲ02- 53 93

Ⅲ-2

Ⅲ -2. Materials Sciences
BL7U
BL7U

Superconducting Gap of Iron-Based Superconductor Ba0.75K0.25Fe2As2
S. Ideta1, 2, M. Nakajima3, N. Murai4, R. Kajimoto4 and K. Tanaka1, 2

UVSOR, Synchrotron Facility, Institute for Molecular Science, Okazaki, 444-8585, JapanThe Graduate University for Advanced Studies (SOKENDAI), Okazaki, 444-8585, Japan3
Department of Physics, Graduate School of Science, Osaka University, Toyonaka, 560-0043, Japan
4
Materials and Life Science Division, J-PARC Center, Japan Atomic Energy Agency, Tokai 319-1195, Japan
1

2

Ⅲ-2

Iron-based superconductors have a complex phase
diagram with the antiferromagnetic (AFM) transition
and the structural phase transition. Recently, nematicity,
defined as broken rotational symmetry [a trigonal (C4)to-orthorhombic (C2) structural transition], has shedlight on the understanding of the mechanism on theiron-based superconductivity [1-4]. In hole-doped
BaFe2As2 (Ba122) system, thermal expansion, specificheat, and neutron diffraction measurements of Ba1xNaxFe2As2 and Ba1-xKxFe2As2 (K-Ba122) have shown
the magnetic order without C4 symmetry breaking [5, 6].
Besides, the superconductivity is suppressed between
the superconducting (SC) and the C4-magnetic phase.
The mechanism of the suppressed superconductivity
has been unclear yet, and it would give us a greatinterest to elucidate the hole-doped Ba122
superconductor.
Here, we have investigated the electronic structureof Ba0.75K0.25Fe2As2 focusing on the superconducting
gaps using high energy resolution angle-resolved
photoemission spectroscopy (ARPES). We found thatthe hole Fermi surfaces (FSs) showed the FS
dependent SC gap, and the suppressed SC gap would
be responsible for the low Tc in K-Ba122 with x ~ 0.25.
High-quality single crystals of Ba0.75K0.25Fe2As2 (Tc~ 25 K) were grown by self-flux technique. ARPES
experiments were carried out at BL7U of UVSOR-III
Synchrotron using the linearly polarized light of hν =18 eV-32 eV photons. Temperature was set at T = 12
K and 35 K and clean sample surfaces were obtained
for the ARPES measurements by cleaving single
crystals in-situ in an ultrahigh vacuum better than
6×10-9 Pa.
Figures 1(a1) and 1(a2) show the ARPES intensity
plot as a function of energy and momentum taken at hν= 21 eV and 32 eV, corresponding to the Γ and Z points,
respectively. We observe at least two hole bands for Γ
and Ζ points, indicating that the degenerated innerbands (dyz, dxz) and outer (dxy/dz2) bands. Taking into
account the electronic structure of K-Ba122 (x ~ 0.25)
in the kz direction [7], we observed the SC gap at the Γand Ζ points on the hole FSs. In Figs. 1(c1)-1(d2),energy distribution curve (EDC) at Fermi momentum(kF) for inner (α) and outer (γ) hole bands are shown.
EDCs are divided by the Fermi-Dirac function and thepeak position corresponds to the SC gap shown by agray circle. Here, we found that the energy gap is
suppressed on the outer hole FS (γ) only for K-Ba122(x ~ 0.25) compared with the nearly optimally doped
K-Ba122 (x = 0.3).

The present study reveals that the SC gap on holeFSs shows finite nodeless gaps but is strongly
suppressed in K-Ba122 (x ~ 0.25), and therefore, we
propose that the suppressed outer hole FS reflects the
suppressed Tc in this material.

Fig. 1. (a1), (a2) Energy-momentum plots of the holeFSs at the Γ and Ζ points (T = 12 K) (b) Temperaturedependence of ARPES spectrum. (c1)-(d2) EDCs of
the α and γ bands at the kF position divided by FermiDirac (FD) distribution function for K-Ba122 (x ~ 0.25
and 0.3).
[1] R. M. Fernandes et al., Nat. Phys. 10 (2014) 97.
[2] R. M. Fernandes et al., Phys. Rev. Lett. 111 (2013)
127001.
[3] T. Shimojima et al., Phys. Rev. B 90 (2014) 12111.
[4] Y. Ming et al., PNAS 108 (2011) 6878-6883.
[5] L. Wang et al., Phys. Rev. B 93 (2016) 014514.
[6] A. E. Böhmer et al., Nat. Commun. 6 (2015) 7911.
[7] S. Ideta et al., UVSOR Activity Report 44 (2016) 76.

Ⅲ02- 54 94

Ⅲ -2. Materials Sciences
BL7U
BL7U

Temperature Dependence of Mott Gap in Ca2RuO4 Investigated by ARPES
D. Shibata1, M. Kawamoto1, K. Yamawaki1, D. Ootsuki1, C. Sow2, Y. Maeno2, F. Nakamura3
and T. Yoshida1
1Graduate School of Human and Environmental Studies, Kyoto University, Kyoto 606-8501, Japan2
Department of Physics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan
3
Kurume Institute of Technology, Fukuoka 830-0052, Japan

A t2g-electron system Ca2-xSrxRuO4 with a layered
perovskite structure shows a rich phase diagram [1].
Sr2RuO4 is a leading candidate of a spin triplet
superconductor. On the other hand, Ca2RuO4 is an
antiferromagnetic insulator below T = 110 K and aparamagnetic insulator between T = 110 K and 357 K.
Ca2RuO4 undergoes a metal to insulator (MI)transition at TMI = 357 K accompanied by a ﬁst-order
structural phase transition. The RuO4 octahedra shrink
along the c-axis and dxy orbital becomes dominant in
the insulating phase [2]. The insulator to metaltransition can be achieved not only by raisingtemperature, but also by chemical substitution,
applying pressure and electric field. In this work, we
studied temperature dependence of the Mott gap in
Ca2RuO4 using angle-resolved photoemission
spectroscopy (ARPES).
Figure 1 shows ARPES spectra of Ca2RuO4 takenwith hν = 23 eV. In order to determine the orbital
character of the band structure near EF, we measured
the incident light polarization dependence of thespectra. The intensity at ~ -1.8 eV is enhanced with ppolarized light, indicating dyz/zx orbital character. On
the other hand, the intensity at ~ -0.8 eV is enhancedin the s-polarized spectrum, indicating dxy orbital
character. The parabolic band structure from -0.8 eV
to -2.5 eV can be assigned to dxy orbital. These results
are consistent with the previous ARPES study [3]. The
DMFT calculation also indicates that the intensity at ~-0.8 eV and at ~ -1.8 eV correspond to dxy and dyz/zx
orbital, respectively [3, 4].
Figure 2 (a) shows the angle-integrated photoemission
spectra of Ca2RuO4 along Γ-S line. The gap size
decreases with increasing temperature. To clarify thetemperature evolution of the gap, we estimated the gap
size by using linear extrapolation from the slope ofspectra. The gap size is consistent with that estimatedfrom the optical conductivity [5]. The suppression of
the gap size may be caused by the elongation of c-axis.
These results imply that the dxy orbital plays a crucialrole in the insulator to metal transition.
[1] S. Nakatsuji and Y. Maeno, Phys. Rev. Lett. 84(2000) 2666.
[2] M. Braden et al., Phys. Rev. B 58 (1998) 847.
[3] D. Sutter et al., Nat. Comm. 8 (2017) 15176.
[4] G. Zhang et al., Phys. Rev. B 95 (2017) 075145.
[5] J. H. Jung et al., Phys. Rev. Lett. 91 (2003) 056403.

Ⅲ-2

Fig. 1. ARPES spectra along -S line taken at T = 170
K using (a) s- and (b) p-polarized light.
size decreases with increasing temperature.

Fig. 2. Temperature dependence of gap structure. (a)Angle-integrated spectra along Γ-S line. (b) Gap size
estimated from the spectra in panel (a).

Ⅲ02- 55 95

Ⅲ -2. Materials Sciences
BL7B
BL7B

Analysis of Luminescence and Scintillation Processes of Organic–inorganic
Perovskite-type Compounds Using VUV Excitation Light
N. Kawano1, M. Koshimizu2, G. Okada3, Y. Fujimoto2, N. Kawaguchi3,
T. Yanagida3 and K. Asai1

Graduate School of Engineering Science, Akita University, Akita 010-8502, Japan
2
Graduate School of Engineering, Tohoku University, Sendai 980-8579, Japan
3
Graduate School of Materials Science, Nara Institute of Science and Technology, Ikoma 630-0192, Japan1

Ⅲ-2

To develop a scintillator with excellent time
resolution, we focused on the phenomena exhibited byconfined excitons in nanoscale semiconductors.
Among the compounds with a low-dimensional
system, scintillation materials based on luminescencefrom organic–inorganic layered perovskite-type
compounds are of particular interest. These hybridmaterials have self-organized multiple quantum wellstructures. An inorganic quantum well exhibits
luminescence of confined excitons, and its organic
layer acts as a barrier of confinement structures. In thecompounds, excitons confined in the inorganic layer
have large binding energies and oscillator strengths
due to the quantum confinement and the image charge
effects.
We have demonstrated that the organic–inorganic
layered perovskite-type compounds exhibit efficient
scintillation due to exciton emission from theinorganic layer. Among them, (C6H5C2H4NH3)2PbBr4
exhibits fast scintillation decay (~10 ns) and efficientluminescence that exceeds 10,000 photons per MeV
under synchrotron X-ray (67.4 keV) [1, 2] and gammaray irradiation [3]. We reported that the excellent
scintillation properties of (C6H5C2H4NH3)2PbBr4
originate from the fast radiative rate of the excitons,
which is caused by the lattice distortion in the inorganic
layers verified with single- crystal structural analysis [4].
In addition to the effect on the crystal structure, theorganic moieties in the organic layers would influence
the scintillation properties via possible energy transferfrom the organic layers to the inorganic layers. We havereported that the energy transfer slower than the time
resolution of the measurement systems (100 ps) andhave a negligible contribution to the scintillation
properties of the compounds [5]. However, thecomponent of energy transfer faster than the time
resolution (100 ps) could have an influence on the
scintillation properties of organic–inorganic layered
perovskite-type compounds.
In this study, a crystal of (C6H5C2H4NH3)2PbBr4
was fabricated by the poor-solvent diffusion method.
Luminescence spectra and decay curves were
measured under VUV irradiation at the UVSOR
Synchrotron Facility (BL7B; Okazaki, Japan) toanalyze the possible contribution of the energy transfer.
Table 1 summarizes the decay time constants andrelative
intensities(inparentheses)ofphotoluminescence decay at 410 nm with different

excitation wavelengths. The rise time behavior
observed in the luminescence decay curve showed nodifference among the excitation wavelengths of 60–300
nm. The decay can primarily be attributed to radiativetransition of the Wannier excitons in the inorganic layers.
In addition, no excitation peak of benzene such as anintense peak at 180nm (1A1g→1E1u) in the vacuum
ultraviolet region was observed in the excitation spectra
measured while monitoring the exciton emissions fromthe inorganic layer. These results indicate that the effectof energy transfer from the organic layer to the
inorganic layer has negligible contribution to theluminescence properties of organic–inorganic layered
perovskite-type compounds.
Table 1. Decay time constants and relative intensities(in parentheses) of photoluminescence decay at 410
nm with different excitation wavelengths.
Excitation
First
SecondWavelength (nm)component component
(ns)
(ns)
60
1.4 (95%)
14 (5%)
150
1.3 (94%)
21 (6%)
180
1.7 (92%)
19 (8%)
250
2.0 (91%)
15 (9%)
300
3.0 (91%)
18 (9%)[1] S. Kishimoto, K. Shibuya, F. Nishikido, M.
Koshimizu, R. Haruki and Y. Yoda, Appl. Phys. Lett.,
93 (2008) 261901.
[2]N. Kawano, M. Koshimizu, A. Horiai, F. Nishikido,
R. Haruki, S. Kishimoto, K. Shibuya, Y. Fujimoto, T.
Yanagida and K. Asai, Jpn. J. Appl. Phys., 55 (2016)
110309.
[3]N. Kawano, M. Koshimizu, G. Okada, Y. Fujimoto,N. Kawaguchi, T. Yanagida and K. Asai, Sci. Rep. 7(2017) 14754.
[4] N. Kawano, M. Koshimizu, Y. Sun, N. Yahaba, Y.
Fujimoto, T. Yanagida and K. Asai, J. Phys. Chem. C,
118 (2014) 9101.
[5] N. Kawano, M. Koshimizu, Y. Sun, N. Yahaba, Y.
Fujimoto, T. Yanagida and K. Asai, Jpn. J. Appl. Phys.,
53 (2014) 02BC20.

Ⅲ02- 56 96

Ⅲ -2. Materials Sciences
BL7B
BL7B

Anomalous Thermoelectric Response and Charge Dynamics of Pyrochlore(Eu1-xCax)2Ir2O7
J. Fujioka1, 2, R. Kaneko1 , M. Masuko1, K. Ueda1 and Y. Tokura1, 3

Department of Applied Physics and Quantum-Phase Electronics Center (QPEC), University of Tokyo, Tokyo
113-8656, Japan
2
PRESTO, Japan Science and Technology Agency, Kawaguchi 332-0012, Japan
3
RIKEN Center for Emergent Matter Science (CEMS), Wako 351-0198, Japan1

The interplay between the relativistic spin-orbit
interaction and electron correlation provides a fruitful
field to research unconventional quantum phenomena
such as the topological semimetal and Kitaev spin
liquids. The pyrochlore-type iridates R2Ir2O7(R=rare earth elements) is one of candidate materials
to study the Mott physics or magnetism of correlated
Weyl electron. Wan et al. , proposed the possible
emergence of antiferromagnetic Weyl semimetallic
phase on the verge of Mott transition [1]. The giant
negative magnetoresistivity and metallic edge state
emerging at the antiferromagnetic domain walls of
Nd2Ir2O7 have been argued in terms of the magnetic
field-induced topological transition and topologicaledge state of Weyl electrons [2, 3]. Moreover, even in
the paramagnetic phase, possible non-Fermi liquidbehavior due to the zero-gap semiconducting band or
flat-band with long-lived spin moment have been
proposed [4]. In this study, we have investigated thecharge transport and charge dynamics of hole-doped
Eu2Ir2O7 to explore the novel non-Fermi liquidbehavior.
Figure 1(a) shows the temperature dependence ofresistivity for Eu2Ir2O7 and its Ca-doped analogs (Eu1Eu2Ir2O7 (x=0) exhibits insulating
xCax)2Ir2O7.
behavior below 300 K and the resistivity shows a kinkupon the antiferromagnetic magnetic ordering at 123
K. In the hole doped systems, the resistivity shows asimilar behavior and the kink is discernible for x=0.01,
0.02 and 0.03. On the other hand, for x=0.05 and 0.1,
the kink is no longer discernible and paramagnetic
metallic behavior subsists down to 2 K.
Figure 1(b) shows the Seebeck coefficient ofmetallic systems. With decreasing temperature, theSeebeck coefficient is enhanced and reaches 30 μV/K
around 50 K for x=0.1. Similar behavior is also
observed for x=0.05 and 0.2. Such a non-monotonic
temperature dependence and relatively large value are
not common among conventional correlated metals.
To explore the electronic structure in theparamagnetic metallic state, we show the opticalconductivity spectra of (Eu1-xCax)2Ir2O7 in Fig. 2. The
charge gap with a magnitude of 0.1 eV is discernible
for x=0. On the other hand, the gap is closed and a
Drude response shows up for x=0.05 and 0.2. It should
be noted that an absorption peak with narrow width isobserved around 0.05 eV besides the broad continuum
above 0.1 eV. Such an absorption band suggests the

emergence of flat-band with enhanced density of state(DOS). Since the Seebeck coefficient is sensitive to
the DOS, the appearance of flat-band with high-DOS
may be related to the anomalous enhancement ofSeebeck coefficient.
(a)

(b)

Fig. 1 Temperature dependence of (a) resistivity and(b) Seebeck coefficient.

Fig. 2 Optical conductivity spectra at 10 K.
[1] X. Wan et al., Phys. Rev. B 83 (2011) 205101.
[2]K. Ueda, et al., Phys. Rev. Lett. 115 (2015) 056402.
[3] E. Y. Ma, et al., Science 350 (2015) 538.
[4] H. Shinaoka et al., Phys. Rev. Lett. 115 (2015)
156401.

Ⅲ02- 57 97

Ⅲ-2

Ⅲ -2. Materials Sciences
BL7B
BL7B

Study of Optical Absorption of Parasitic Transition Metal ions (Fe3+, Cr3+)
at Low Temperature in Nonlinear Crystal YAl3(BO3)4 (YAB) in the 100 –600 nm Range
E. Lafitte-Houssat1, 2, А. Kausas1, L. Zheng1, H. Ishizuki1, G. Aka2 and T. Taira1

Laser Research Centre, Institute for Molecular Science, Okazaki 444-8585, JapanPSL Research University, Institute de Recherche de Chimie Paris IRCP, Chimie ParisTech, Paris 75005, France
1

2

Ⅲ-2

YAB crystals are very promising NLO material for
UV applications, one of them being the fourthharmonic generation of Nd3+ based lasers at 266 nm .
The UV cut-off wavelength is measured to be 170 nm ,but Fe3+ and Cr3+ impurities in the crystals generally
cause parasitic UV absorption. The conversion process
of YAB crystals is then jeopardized in the deep UV.
Low temperature transmittance spectra as function ofpolarization should allow us to clearly identify
transition ions responsible for parasitic opticalabsorption in the UV range of interest. As absorption
band intensities increase at low temperature, thecharacterization of the peaks should be eased. During
our experiment at BL7B, we have studied theinfluence of temperature on optical transmission for
YAB samples within 30 K-300 K temperature range.
Three samples were studied at 300 K to identify thetransitions related to transition ions Fe3+ and Cr3+, (Fig.
1(a)) in the range of 150 nm to 600 nm . For thisscanning, YAB#1 had its Y axis perpendicular to thelight polarization, while YAB#2 had its Y axis parallelto the light polarization. The axis for YAB#3 could not
be determined. Two absorption bands can be identified
around 240 nm and 280 nm . They may be attributed
to charge transfer processes from oxygen to iron O2p5Fe3d6: (e2t24, 240 nm ) and (e3t23, 280 nm ). For YAB#1,
there is another absorption around 425 nm , that
corresponds to a d-d transition of Cr3+ (4A2g4T2g),
that usually occurs at 425 nm in Cr doped YAB
crystals. However, the absence of that transition for thetwo other samples is not usual. It can be explained bydifferent purities of the starting materials, or by the
crucible used for YAB#1 crystal growth (one-monthexperiment). For the sample YAB#1, we can also
notice that the cut-off wavelength is higher than for
YAB#2 and YAB#3. This is most likely caused by thehigher thickness of the sample. For the three samples,the cut-off wavelength is higher than 170 nm , whichis caused by the optical absorption of the transition
ions. Also, there is no absorption at 532 nm for all
three samples, which confirms that YAB crystals arewell suited for SHG from 532 nm to 266 nm .
At low temperature, as thermal motion is reduced, weshould be able to better visualize transition ion
absorptions. The results we obtained were not totally inaccordance with that assumption. For all three samples,
we could see that there were few overall differences
when the temperature varies, even from 30 K to 300 K
range.
The influence of the orientation of the crystal ismuch more visible and interesting. The results areshown in Fig.1(b) for the sample YAB#2, but they
were the same for the other samples. For all thesamples, the orientation has an effect in the range 225350 nm . The absorption at 280 nm is weaker when
the Y axis is parallel to light polarization. However, forthe transition at 240 nm , it is more visible when the Yaxis is parallel. As the absorption at 266 nm must be
limited, the orientation of the crystal must be
controlled to have the best performance in frequency
conversion. For all the samples, the absorption around
266 nm is weaker when the Y axis is parallel to thepolarization of the incoming light. It means that thisorientation is to be preferred for FHG experimentswith YAB crystals.
We have studied three YAB samples under UVpolarized light and their transmission spectra. The
parasitic absorption of transition ions Fe3+ and Cr3+
was confirmed. Charge transfer processes O2p5-Fe3d6
were identified around 240 nm and 280 nm , and d-dtransitions of Cr3+ may be visible in one of the YAB
samples. The influence of temperature and theorientation of the crystals was also investigated. The
orientation of the crystals influences greatly thetransmission profiles, especially for the charge transfer
transitions. The scanning under low temperature did
not deliver a better characterization but still confirmed
the assumptions about parasitic absorptions.

Fig. 2. Optical transmission spectra for YAB#1,
YAB#2 and YAB#3 crystals (a) and comparison of
crystal orientation for YAB#2 (b).
[1] Y. Wang and R.K. Li, Opt. Materials 32 (2010)1313.

Ⅲ02- 58 98

Ⅲ -2. Materials Sciences
BL7B
BL7B

Auger-Free Luminescence in K2ZnCl4 Crystals
A. Ohnishi and M. Kitaura

Faculty of Science, Yamagata University, Yamagata 990-8560, JapanThe blue line in Fig. 1 shows the excitation spectrum
for the 4.4 eV band. The excitation spectra for the 5.9
and 2.8 eV bands were practically the same as that for
the 4.4 eV band. These bands are excited in the energy
region above 14.4 eV. The photon energy of 14.4 eV isalmost agreement with the energy sum of Eg and EVC.
Since this satisfies the condition for the occurrence of
AFL, the three bands mentioned above are assigned to
the AFL bands due to the radiative recombination of avalence electron and an outermost core hole.
Luminescence decay measurements were also
performed using a time-correlated single-photon
counting technique under the single bunch operation.
It was proved that, at 10 K, the AFL bands arecomposed of a fast decay component with the lifetimeof about 8 ns.

K2ZnCl4 10 K
Emission Intensity (arb. units)

The Auger-free luminescence (AFL) is a peculiar
type of intrinsic luminescence in ionic crystals inwhich the valence excitation through a nonradiative
Auger process is forbidden. The AFL is characterized
by a high quantum yield and a short lifetime of theorder of ns. Therefore, it is very useful as the fast
scintillator for high-energy physics, positron emission
tomography and so on.
In previous works [1-4], we have studied opticalproperties of Cs2ZnCl4 and Rb2ZnCl4 molecular ionic
crystals with the use of synchrotron radiation as a lightsource. We have observed AFL in these crystals.
K2ZnCl4 is one of molecular ionic crystals and has thesame crystal structure as Cs2ZnCl4 and Rb2ZnCl4 [5].
In this crystal, the outermost core level is supposed to
be built up by Zn 3d states, because the K 3p stateshould be deeper-lying inner shells than the Zn 3d state
in comparison with the binding energies of electrons
between them. Therefore, it is expected that AFL due
to interatomic p-d transitions between the Zn 3d outermost core level and the Cl 3p valence band is observedin K2ZnCl4. In the present study, we have investigatedthe luminescence of K2ZnCl4 crystals under theoutermost core excitation, in order to find theexistence of AFL.
K2ZnCl4 crystals were prepared by evaporating a
stoichiometric mixture of solutions of KCl and ZnCl2.
The reflection, emission and excitation spectra were
measured at the BL7B of UVSOR.
As indicated by a red line in Fig. 1, sharp peaks at
7.3 and 7.9 eV were observed in the reflection
spectrum measured for the cleaved surface of
K2ZnCl4. The 7.3 and 7.9 eV peaks are assigned to then = 1 and 2 exciton peaks due to the transition from the
Cl 3p valence band to the conduction band,
respectively. From the positions of the two peaks, theband gap energy (Eg) is estimated to be about 8.0 eVby assuming that the exciton energy levels arehydrogen-like.
From the result of X-ray photoelectron
spectroscopy (XPS), it was clear that the outer-mostcore level in K2ZnCl4 is composed of the Zn 3d states.
We estimated the energy difference (EVC) between the
top of the valence band and that of the outer-most core
band by referring to the XPS spectrum. The value of
EVC was 6.5 eV. Since this value is smaller than that ofEg, the appearance of AFL due to the interatomic Cl 3p→ Zn 3d transitions is expected for K2ZnCl4, when acore hole is created in the Zn 3d outer-most band byphoto-excitation.
When K2ZnCl4 was excited at 10 K with 21.4 eV
photons above the value of Eg + EVC, threeluminescence bands appeared at 5.9, 4.4 and 2.8 eV.

5

10

15

20

25

30

Photon Energy (eV)Fig. 1. Excitation spectrum (blue line) at 10 K for the
4.4 eV band in K2ZnCl4. For reference, reflection
spectrum is also shown by a red line.
[1] A. Ohnishi, T. Otomo, M. Kitaura and M. Sasaki,
J. Phys. Soc. Jpn. 72 (2003) 2400.
[2] A. Ohnishi, M. Saito, M. Kitaura, M. Itoh and M.
Sasaki, J. Lumin. 132 (2012) 2639.
[3] A. Ohnishi, M. Kitaura, M. Itoh and M. Sasaki, J.
Phys. Soc. Jpn. 81 (2012) 114704.
[4] M. Kitaura and A. Ohnishi, Kogaku 45 (2016) 175(in Japanese).
[5] J. A. Mcginnery, Inorg. Chem. 13 (1974) 1057.

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Ⅲ-2

Ⅲ -2. Materials Sciences
BL7B
BL7B

Optical Property of Compound Fluoride Materials CaxSr1-xF2
at Low Temperature
K. Suzuki, R. Yamazaki, J. Otani and S. Ono

Nagoya Institute of Technology, Nagoya 466-8555, Japan

Ⅲ-2

Vacuum ultraviolet (VUV) light source is used invarious applications such as surface treatment, opticalcleaning of semi-conductor substrates and sterilization.
Accordingly, the detector for monitoring the lightsource is also required. Currently, many researchersdeveloped VUV detectors based on oxide, nitride anddiamond. However, the detectors require the filters for
cutting off deep-UV when being used for monitoringof the light source. On the other hand, our group isproceeding to development of the VUV detectors
using fluorides [1-3]. Some fluorides have extremely
wider band gap than oxides and nitrides so that theytransmit deep-UV region. Until now, we achieved
filterless VUV detectors by applying such fluorides.
And spectral response of the detectors varies
according to band gap of the material. Therefore, we
may realize the detectors possessing arbitrary response
region by controlling band gap of the material. Here,
we report on controlling band gap of compound
fluoride materials CaxSr1-xF2 and the temperaturedependence of the band gap of these materials.
CaxSr1-xF2 crystals were grown by Bridgman
method and they were controlled composition ratio as
Ca0.85Sr0.15F2 and Ca0.5Sr0.5F2. Absorption coefficient
was calculated by measuring transmission spectrum of
VUV region as shown in Fig.1. Herewith, band gapsof CaF2, Ca0.85Sr0.15F2, Ca0.5Sr0.5F2 and SrF2 were
calculated as 10.24, 9.98, 9.83 and 9.73 eV at R.T.,
respectively. Therefore, the band gap of CaxSr1-xF2 isexpanded by increasing composition ratio of CaF2 inthe crystals.
Additionally, the band gap at low temperature (50 300K) was obtained by cooling the samples with liquid
helium. Solid lines in Fig.2 were calculated from
Bose-Einstein type equation as given below

spectral response of filterless VUV photoconductive
detector using CaxSr1-xF2 crystals.

Fig. 1. Temperature characteristic of band gap.

Fig. 2. Temperature characteristic of band gap.

where E(0) is band gap energy at 0 K, 𝑎𝑎 is strength of
exciton-phonon interaction, and  is averagetemperature of phonons. As a result of that, the bandgaps of CaF2, Ca0.85Sr0.15F2, Ca0.5Sr0.5F2 and SrF2 at 0 K
were estimated as 10.69, 10.46, 10.23 and 10.13 eV,
respectively.
In summary, we found capable of controlling theband gap of CaxSr1-xF2 and evaluated the band gap of
CaxSr1-xF2 at low temperature. The band gap was
expanded by increasing composition ratio of CaF2 inthe crystals. Such result shows that we can control the[1] M. Ieda, T. Ishimaru, S. Ono, N. Kawaguchi, K.
Fukuda, T. Suyama, Y. Yokota, T. Yanagida and A.
Yoshikawa, Jpn. J. Appl. Phys. 51 (2012) 062202.
[2] T. Ishimaru, M. Ieda, S. Ono, Y. Yokota, T. Yanagida
and A. Yoshikawa, Thin Solid Films 534 (2013) 12.
[3] M. Yanagihara, H. Ishikawa, S. Ono and H. Ohtake,
Testing and Measurement: Techniques and Applications(2015) 151.

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