BL2A

Characterization of Calcium in Hydroxyapatite by an XAFS Method
T. Kurisaki1, Y. Nagino1, S. Yokoyama1 and H. Wakita1,2㪈Department of Chemistry, Faculty of Science, Fukuoka University, Nanakuma,
Jonan-ku, Fukuoka 814-0180, Japan
2
Advanced Materials Institute, Fukuoka University, Nanakuma, Jonan-ku, Fukuoka 814-0180, Japan
Hydroxyapatite is a kind of calcium phosphate.
This compound can be found in tooth and born in thehuman body. In addition, it is commonly used as afiller to replace amputated born or as a coating topromote bone ingrowth into prosthetic implants.
However, the local structure and electronic structureof calcium in a tooth and hydroxyapatite (HAP) are
not determined. For various light element compounds,
we have studied the electronic structure by X-ray
absorption spectroscopy [1]. These results suggested
that there is a correlation between XANES spectra
and the local structures.
In this work, we performed the XANES spectra
measurement about tooth, decayed tooth andhydroxyapatite. The obtained experimental XANES
spectra are analyzed using the calculated theoretical
spectra from DV-XĮ calculations. The X-ray
absorption spectra were measured at BL2A of the
UVSOR in the Institute of Molecular Science,
Okazaki [2]. The ring energy of the UVSOR storage
ring was 750MeV. Ca K-edge absorption spectra wererecorded in the regions of 4000-4200eV by use of two
InSb crystals. The absorption was monitored by the
total electron yield using a photomultiplier.

Fig. 2. Ca K-edge XANES spectra of the HAP, toothand decayed tooth.
The samples were spread onto the carbon tape on
the first photodynode made of CuBe of thephotomultiplier.
Figure 1 shows the observed Ca K-edge XANES
spectra for the calcium phosphate compounds. This
result suggested that the measured Ca K-edge
XANES spectra shows different peak profiles
depending on the electronic structure and local
structure of the these compounds.
Figure 2 shows the observed Ca K-edge XANES
spectra for the HAP, tooth and decayed tooth. The Ca
K-edge XANES spectra of HAP and tooth show thesame peak profiles. On the other hand, the Ca K-edge
XANES spectra of decayed tooth show a little
difference of the peak profiles at 4037eV incomparison with the Ca K-edge XANES spectra of
HAP and tooth. These results indicated that theelectronic structure and local structure around thecalcium in decayed tooth is different from those of
HAP and tooth.
[1] T. Kurisaki S. Matsuo, I. Toth and H. Wakita, Anal.
Sci. 24 (2008) 1385.
[2] S. Murata, T. Matsukawa, S. Naoè, T. Horigome,
O. Matsuodo and M. Watatabe, Rev. Sci. Instrum. 63(1992) 1309.

Fig. 1. Ca K-edge XANES spectra of the calcium
phosphate compounds.

93

BL2A

Defects in Metal Oxide Studied by X-ray Absorption Fine Structure
Spectroscopy
E. Kobayashi1, K. K. Bando2 and T. Okajima1,3
1

Kyushu Synchrotron Light Research Center, 8-7 Yayoigaoka, Tosu, Saga 841-0005, Japan
National Institute of Advanced Industrial Science and Technology, 1-1-1, Higashi, Tsukuba, Ibaraki 305-8565,
Japan
3
Research Center for Synchrotron light applications, Kyushu University, 6-1 Kasugakoen, Kasuga, Fukuoka
816-8580, Japan

After the hydrogen reduction, the strongest peaks
become broad peak. In addition, the intensity of thepeaks decreases with increasing temperature. These
results indicate that the oxygen vacancies were
induced by hydrogen reduction and the amorphous
phase increased with annealing.

Metal oxide is an important material from afundamental physical point of view and is widely usedin the field of catalytic, optical and electricalapplications. It is recognized that the defects in metaloxide is important for applications because it cansignificantly affect the material characteristics. To
understanding of the character of the defects is ofimportance for the development of new materials.
MgO plays a prototype of metal oxides and is also awide-gap insulator [1]. The important defects in MgO
are oxygen vacancies. We have investigated the MgO
surface defects induced by ion bombardment in metaloxide. In this study, the annealing behavior ofhydrogen defects of MgO bulk was studied by Mg
K-edge NEXAFS spectroscopy using fluorescence
yield (FY) method.
X-ray absorption fine structure spectra in the soft
X-ray region can be obtained by detecting either theelectrons or the fluorescence. For insulating materials,
the total electron yield (TEY) method cannot be used
due to the charge up. The FY can be measured formetal oxide, but the intensity is very low in the soft
x-ray region, this is sensitive to the bulk material
whereas the TEY is surface-sensitive.
The samples were MgO pellets after annealing at
673 K ~ 1073 K for 2 hours in hydrogen atmosphereand MgO reference powder. NEXAFS spectra were
measured at the beamline 2A of the UVSOR in theInstitute of Molecular Science. The NEXAFS spectra
were obtained by measuring the fluorescence fromthe sample. The incident angle of the synchrotron
radiation was 0q from the surface normal. The FY
was normalized to the incident photon flux, recorded
as a photocurrent at a photon-flux monitor consistingof a gold-evaporated mesh.
Figure 1 shows the NEXAFS spectra for the Mg
K-edge region of MgO pellets after annealing at 673
K ~ 1073 K for 2 hours in hydrogen atmosphere andMgO reference powder. Three strong peaks areobserved at around 1309.1 eV, 1314.7 eV and 1316.9
eV, respectively. The spectrum exhibits an overallsimilarity with those previously obtained byexperiments [2]. The edge of the spectrum is shiftedby annealing under a hydrogen atmosphere. This
indicates that the hydrogen reduction of MgO was
carried out. The oxygen of MgO is reduced by thehydrogen, the edge is shifted to the low energy.

㩷5reference
673 K
773 K
873 K
973 K
1073 K

Intensity (arb. units)

4

3

㩷

2

2

1

0
1305

1310

1315

Photon Energy (eV)1320

Fig. 1. NEXAFS spectra for the Mg K-edge region of
MgO pellets after annealing at 673 K ~ 1073 K for 2
hours in hydrogen atmosphere and MgO reference
powder.
[1] D. M. Roessler and W. C. Walker, Phys. Rev. 159(1967) 733.
[2] P. Luches, S. D’Addato, and S. Valeri, E. Groppo,
C. Prestipino and C. Lamberti, F. Boscherini, Phys.
Rev. B 69 (2004) 045412.

94

BL2A

Ultraviolet Emission of AlGdN by Inner-Core Excitation
K. Fujita, R. Ikematsu and K. Fukui
Department of Electrical and Electronics Engineering, University of Fukui, Fukui 910-8507, Japan
spectrum of Al0.87Gd0.13N, respectively. These spectraof Al0.98Gd0.02N were not observed. Both TY and PLE
spectra near Gd MIV-edge are in good agreements with
TY spectrum of Gd3+ ion which is well explained by
the 3d104f 7 ĺ 3d94f 8 transition
array [4].
㩷
Al0.98Gd0.02N

PL Intensity (arb.units)

III-V nitride compound semiconductors doped withrare earth (RE) elements are attractive systems
because of the possibility of magnetic ordering
coupled with a semiconducting natures andluminescence properties, so-called spintronics.
However, even in light emitter the III-V nitride wideband-gap host materials with REs have potential fordevelopment. In the case of ultraviolet (UV) region
where is used as sterilization lamp and excitation lamp
for phosphors in the visible region, Gd3+ is known as
the light emitting material having ~ 3.9 eV emission(UVE) by 6P7/2ĺ8S7/2 4f intra-transition of Gd3+. Since
the UVE is higher than the band-gap energy of the
GaN (3.4 eV), the realistic host materials are AlGaN or
AlN. In our previous work [1], we studied
photoluminescence (PL) and PL excitation (PLE)
spectra of AlN doped with Gd3+ in the band-to-band
excitation region. A sharp line of the UVE was clearlyobserved, and its PLE spectra revealed that thisemission process is host excitation. It means that there
is a process which transfers energy from theband-to-band excitation of AlN to 4f intra-transition of
Gd3+ ion, and also means that UVE does not observed
if the excitation light photon energy is less than that of
AlN bandgap. Then, we have performed the ultraviolet(UV) emission of AlGdN thin films by Al 1s and Gd
3d core excitations to investigate the emission processof AlGdN.
AlGdN thin films were grown in a MBE systemwith a RF-plasma assisted radical cell on the Si-face of(0001)-oriented 6H-SiC substrates. The thickness ofthe sample is about 120 nm. Concentration of Gd3+
ions are 2 % (Al0.98Gd0.02N) and 13 % (Al0.87Gd0.13N).
The details of the crystal growth have been reported
elsewhere [2]. All visible (VIS) – UV region
photoluminescence (PL) measurements were carriedout at ~ 20 K with a conventional 30 cm VIS – UV
monochromator and CCD image detector. PL
excitation (PLE) and total yield (TY) spectra were
measured around both Al K-edge (~ 1.5 keV) and Gd
MIV-edge (~ 1.2 keV). TY measurements were carriedout at RT.
Figure 1 shows the PL spectrum of Al0.98Gd0.02N.
The excitation energy is 1569 eV. A sharp line of the
UVE is observed. Figures 2(a) and 2(b) show the TY
and the PLE spectrum of Al0.98Gd0.02N, respectively.
The intensity of the PLE spectrum is integrated
intensity of the UVE shown in fig. 1. Both TY and
PLE spectra around Al K-edge in fig. 2 are in good
agreements with TY spectrum of AlN [3]. Since TY
spectrum in this energy region is similar to theabsorption spectrum, these results are consistent with
our previous works as mentioned above.
Figures 3(a) and 3(b) represent the TY and the PLE

Ex. 1569eV
20K

3.4

3.6

3.8

4.0

4.2

4.4

Photon Energy (eV)Fig. 1. PL spectrum of Al0.98Gd0.02N
1.0

Intensity (arb.units)

0.8

Al0.98Gd0.02N(b) PLE

22K

0.6
0.4
0.2

㩷

0.0
1.0
0.8

(a) TY

RT

0.6
0.4
0.2
0.0
1550

1560

1570

1580

1590

1600

Photon Energy (eV)Fig. 2. TY (a) and PLE (b) spectra of Al0.98Gd0.02N
around Al K edge.
1.0
0.8

Al0.87Gd0.13N(b) PLE

Intensity (arb.units)

0.6

17K

0.4
0.2
0.0
1.0
0.8

(a) TY

RT

0.6
0.4
0.2
0.0
1205

1210

1215

1220

1225

1230

Photon Energy (eV)Fig. 3. TY (a) and PLE (b) spectra of Al0.87Gd0.13N
around Gd MIV edge.
[1] K. Fukui et al., Phys. Stat. Sol. (c) 7 (2010) 1878.
[2] N. Teraguchi et al., J. Cryst. Growth 230 (2001)
392.
[3] K. Fukui et al., Phys. Stat. Sol. (b) 228 (2001)
461.
[4] C. Bonnelle et al., J. Phys. B 10 (1977) 795.

95

BL3B

Optical Spectra of NaCl:Agï Crystals up to the VUV Energy Region
T. Kawai1, T. Hirai2 and K. Bando3
1

Graduate School of Science, Osaka Prefecture University, Sakai 599-8531, Japan
Faculty of Science and Engineering, Ritsumeikan University, Kusatsu 525-8577, Japan
3
Faculty of Science, Shizuoka University, Shizuoka 422-8529 , Japan2

Agí ions belong to the family of the so-called
Tl -type ions and exhibit the optical bands called A,
B, and C [1, 2]. In alkali halide crystals doped with
the Tl+-type ions, the absorption bands labeled D areoften observed in the energy region between the C
band and the fundamental absorption edge of the host
crystals [3]. However, the existence of the D bands
has not been reported for the Agí centers in alkali
halides. In this study, optical spectra of NaCl:Agícrystals have been investigated in the energy region
between the C absorption band and the fundamental
absorption edge.
NaCl:Ag+ crystals were grown by the Bridgman
method from the NaCl powders containing the AgCl
concentration of 0.01 mol%, which corresponds to theAg+ ion concentration of about 2.31018 number/cm3
in the crystal. The conversion from the Ag+ to Agíions in the crystals was achieved by an electrolytic
coloration technique. The optical measurements were
performed at the BL-3B of UVSOR.
Figure 1 shows the absorption spectra of NaCl:Ag+
and NaCl:Agí crystals. In NaCl:Ag+, an absorption
band peaking at 6.9 eV and the steep rise from 7.2 eV
can be seen. The absorption band at 6.9 eV isattributed to the partially-allowed transition of 4d10
ψ 4d95s in the Ag+ ion. The steep rise from 7.2 eVcorresponds to the lower tail of the absorption banddue to an electronically allowed transition in the Ag+ion [4].
In NaCl:Agí, the absorption band at 6.9 eV
disappears and the steep rise from 7.2 eV shifts to thehigher energy side. The C absorption band due to the
Agí centers is obviously observed at 4.6 eV [2]. The
fact implies that the Ag+ ions are efficiently
transformed to the Agí ions by the electrolytic
coloration. In addition to the C absorption band, theintense and small absorption bands are observed at
6.51 and 7.10 eV, respectively.
Figure 2 shows the excitation spectra for the A’ andC’ luminescence bands due to the Agí centers, which
are shown in the insert of Fig. 2. The C’ luminescenceband is efficiently excited at around 6.9 eVcorresponding to the C absorption band. The A’
luminescence band is excited at the higher energy
region in the C absorption band. It should be notedthat the excitation spectrum for the A’ luminescencehas the peaks at 7.10 and 7.60 eV. The peak energy of
7.10 eV is equal to that of the small absorption bandof NaCl:Agí, as shown in Fig. 1. Thus, the small
absorption band at 7.1 eV will be related to the Agícenters and might be assigned to the D band. On theother hand, both the A’ and C’ luminescence bands are
not excited at around 6.5 eV, where the intense
absorption band is located. This fact indicates that the
6.5 eV absorption band in NaCl:Agí has no
relationship with the Agí centers. The 6.5 eVabsorption band might be associated with the Ag0
atoms which were not converted to the Agí ionsthrough the electrolytic coloration.

60-1

Absorption Coefficient (cm )+Wavelength (nm)
250
200

300

NaCl:Ag+(0.01 mol%)

6K
40

NaCl:Ag-

20

0
4.0

4.5

5.0
5.5
6.0
6.5
Photon Energy (eV)

7.0

7.5

Fig. 1. Absorption spectra of NaCl:Ag+ (red)
NaCl:Agí (blue) crystals.

Lumi. Int. (arb. units)

300

and

Wavelength (nm)200

250
for C'

Exc. 4.62 eV

NaCl:Ag6K

C'

A'

2.5

3.0

3.5

4.0

4.5

for A'
4.5

5.0

5.5 6.0 6.5 7.0
Photon Energy (eV)

7.5

8.0

Fig. 2. Excitation spectra for the A’ (red) and C’ (bule)luminescence bands. Insert is the lumi- nescence
spectrum under excitation at 4.62 eV[1] W. Kleemann, Z. Physik 234 (1970) 362.
[2] S. Shimanuki, J. Phys. Soc. Jpn. 35 (1973) 1680.
[3] A. Ranfagni et al., Advances in Physics 32 (1983)
823.
[4] R. Onaka et al., Jpn. J. Appl. Phys. 4 (1965)
Suppl.1, 631.

96

BL3B

Experimental Evidence for Migration and Trapping of Excited Electrons in
Ce:Gd3(Al,Ga)5O12 Single Crystals
A. Satoh1, M. Kitaura1, K. Kamada2, A. Ohnishi1 and M. Sasaki1
1Dept. of Physics, Faculty of Science, Yamagata University, 1-4-12 Kojirakawa, Yamagata 990-8560, Japan
2
Materials laboratory of Furukawa Co. Ltd, 1-25-13 Kannondai, Tsukuba 305-0856, Japan

Rare-earth doped A3B5O12 (A=Y, Lu, Gd; B=Sc,
Al, Ga) garnet crystals attract much attention as amaterial group of inorganic scintillators useful for xand Ȗ-ray detection. Scintillation properties of thisgroup have been remarkably improved by the
combination of band-gap engineering and rare-earth
5d level positioning strategies [1, 2]. By such great
efforts, a novel Ce3+ doped Gd3(Al,Ga)5O12(Ce:GAGG) scintillator crystal has been recently
developed [3]. Further improvement of crystal quality
is necessary in order to meet the demand for theapplication into various scientific and industrial fields.
For this purpose, it is expected that spectroscopy
experiment bring valuable information. In the present
study, we have measured absorption spectra andexcitation spectra of the 2.34 eV emission band due
to 5d - 4f transitions of Ce3+ ions at various
temperatures, in order to clarify migration andtrapping processes of photo-carriers in GAGG
crystals. Crystals of Ce:GAGG and GAGG weregrown in Ar + O2 (2%) atmosphere from melt by the
Czochralski method. Experiment was performed at
the BL3B beam line of UVSOR. The absorption andexcitation spectra measured were corrected with acalibrated silicon photodiode sensor for the
distribution of an excitation light.
Figure 1 shows absorption spectra of a Ce:GAGG
single crystals observed at 6 K and 300 K. The
concentration of Ce3+ ions in the Ce:GAGG crystal
was determined to 0.08 mol%. The absorption spectra
exhibit broad bands at 2.82 eV and 3.62 eV, andnarrow lines around 4 - 5 eV. The broad bands appear
by the incorporation of Ce3+ ions, and they are thus
assigned to the 4f - 5d transitions of Ce3+ ions. The
narrow lines were observed in absorption spectra of
GAGG single crystals. We connect these lines to the
4f - 4f transitions of Gd3+ ions. The absorption
coefficient is abruptly increased in the photon energy
range from 5.75 to 6 eV. This is due to thefundamental absorption edge of the host GAGG
crystal, the photon energy of which is determined tobe 5.96 eV at 6 K and 5.69 eV at 300 K.
Excitation spectra for the 2.34 eV emission bandof Ce:GAGG (0.08 mol%) are shown in Fig. 2. The
intensity of the 2.34 eV emission band does notalmost depend on temperature under excitation in thelowest energy Ce3+ 4f - 5d absorption band at 2.81 eV.
In contrast, the intensity is varied with increasing
temperature, when the crystal is excited in the energy
region higher than 2.81 eV absorption peak. This
result is explained as follows. At low temperature,

excited electrons are partially trapped at defect levels.
With increasing temperature, trapped electrons are
released from the defect levels via a thermal
activation process, and they migrate to electron-lostCe4+ sites. The excited states of Ce3+ ions are moreincreased, compared to those at low temperature, andthe 2.34 eV emission band is thus enhanced. The
origin of defects responsible for such an enhancement
is now in investigation.

Fig. 1. Absorption spectra of a Ce:GAGG (0.08mol%) single crystal observed at 6 K (red line) and300 K (black line).

Fig. 2. Excitation spectra for the 2.34 eV emission
band of a Ce:GAGG (0.08 mol%) single crystal,observed at 6 K (red line) and 300 K (black line).
[1] K. Kamada et al., Cryst. Growth & Des. 11(2011) 4484.
[2] M. Fasoli et al., Phys. Rev. B 84 (2011) 081102(R).
[3] K. Kamada et al., J. Cryst. Growth 352 (2012) 88.

97

BL3B

Combined Excitation-Emission Spectroscopy of Boron-Doped DiamondFilms
T. Toyoda1, K. Fukui1 and T. Inushima2
Department of Electrical and Electronics Engineering, University of Fukui, Fukui 910-8507, Japan2
Department of Electronics, Tokai University 4-1-1 Kitakaname, Hiratsuka 259-1292, Japanobserved. The origin of this band is not clear at present,
but it is clear that this emission is caused by the band toband excitation and there is no overlap of theexcitation energy between this new band and the H3band. These behaviors are consistent with the previous
work [2, 4].

Boron-doped diamond (BDD) is one of the p-typewide band-gap (5.5eV) semiconductors. Recently, thesuperconductivity has been discovered in heavily
BDD [1]. In this study, we have measured the CEES
(Combined Excitation Emission Spectroscopy) aroundthe band-gap (excitation energy 4.5 ~ 7.0eV) in orderto clarify the electron state of BDD whose boron
concentrations is in the metal-semiconductortransition region.
The BDD films used in this study are grown on
Ib-synthesized diamond substrates by the MPCVD(Microwave Plasma Chemical Vapor Deposition)
method and their boron concentration are 1000, 2000,
5000 and 10000 ppm [2]. All CEES measurements
including the diamond substrate (0 ppm) have been
performed at BL3B.
Figure 1(A) and 1(B) show the CEES spectra at 9 Kof the 1000 ppm and 10000 ppm BDDs, respectively.
The horizontal axis represents the emission energy,
and the vertical the excitation energy. A strong
emission region around 2.4 eV (white color region in
Fig. 1(A)) consists of two emission bands. One isshown at lower excitation energy side which has clear
higher energy cut of the emission spectrum shape at
2.5 eV. This characteristic emission band is known as
the band due to the H3 center (H3 band) which isnitrogen defect related center in diamond. In fact, theH3 band is clearly observed in diamond substrate (0ppm) sample. The difference of the H3 band in
between 0 ppm and 1000 ppm is the existence ornonexistence of the higher excitation energy limit,
because there is no limit in the case of 0 ppm sample
but about 6.0 eV in the case of 1000 ppm. The otheremission band has a broad Gaussian like line shapeand is observed at higher excitation energy side. The
lower excitation energy limit is about 5.5 eV where isalmost same energy as the indirect band-gap energy ofthe diamond. This emission band is often observed in
the BDD and is considered donor-acceptor pair (DAP)
emission (G band), where the acceptor is boron [3].
These results suggest that (i) the higher excitationenergy side emission band is the G band of the BDD,(ii) the lower side band is H3 band of the diamondsubstrate, (iii) 1000 ppm BDD has the direct band-gapof ~ 6.0 eV.
In the case of the 10000 ppm BDD (fig. 1(B)), thestrong regions clearly separate two regions. One isshown in the emission energy around 2.4 eV (whitecolor region in fig. 1(B)). This band is H3 band of the
diamond substrate as mentioned above. A new bandaround 2.8 eV (red color circle in fig. 1(B)) is㩷㪎㪅㪇㪋㪅㪇㪇㪇㪜㪄㪈㪈㪍㪅㪌㪊㪅㪉㪇㪇㪜㪄㪈㪈㪍㪅㪇㪉㪅㪋㪇㪇㪜㪄㪈㪈㩷㪜㫏㪺㫀㫋㪸㫋㫀㫆㫅㩷㪜㫅㪼㫉㪾㫐㩷㩿㪼㪭㪀㩿㪘㪀㩷㪈㪇㪇㪇㫇㫇㫄㪈㪅㪍㪇㪇㪜㪄㪈㪈㪌㪅㪌㪏㪅㪇㪇㪇㪜㪄㪈㪉

㪌㪅㪇

㪇㪅㪇㪇㪇

㪋㪅㪌
㪉㪅㪇

㪉㪅㪌

㪊㪅㪇

㪊㪅㪌

㪋㪅㪇

㪋㪅㪌

㪌㪅㪇

㪌㪅㪌

㪜㫄㫀㫊㫊㫀㫆㫅㩷㪜㫅㪼㫉㪾㫐㩷㩿㪼㪭㪀㩷㪎㪅㪇㪈㪅㪈㪌㪇㪜㪄㪈㪈㩿㪙㪀㩷㪈㪇㪇㪇㪇㫇㫇㫄㪜㫏㪺㫀㫋㪸㫋㫀㫆㫅㩷㪜㫅㪼㫉㪾㫐㩷㩿㪼㪭㪀㪍㪅㪌㪐㪅㪉㪇㪇㪜㪄㪈㪉㪍㪅㪇㪍㪅㪐㪇㪇㪜㪄㪈㪉㩷

1㪋㪅㪍㪇㪇㪜㪄㪈㪉㪌㪅㪌㪉㪅㪊㪇㪇㪜㪄㪈㪉

㪌㪅㪇
㪇㪅㪇㪇㪇

㪋㪅㪌
㪉㪅㪇

㪉㪅㪌

㪊㪅㪇

㪊㪅㪌

㪋㪅㪇

㪋㪅㪌

㪌㪅㪇

㪌㪅㪌

㪜㫄㫀㫊㫊㫀㫆㫅㩷㪜㫅㪼㫉㪾㫐㩷㩿㪼㪭㪀

Fig. 1. CEES of BDD (A) 1000 ppm and (B) 10000
ppm at 9 K.
[1] E. A. Ekimov, V. A. Sidorov, E. D. Bauer, N. N.
Mel'nik, N. J. Curro, J. D. Thompson and S. M.
Stishov, Nature 428 (2004) 542.
[2] A. Ogasawara, T. Inushima, T. Shiraishi, S. Ohya,
S. Karasawa and H. Shiomi, Diamond Relat. Mater. 6(1997) 835.
[3] E. Gaillou, Jeffrey E. Post, D. Rost and J. E.
Butler, Am. Mineral. 97 (2012) 1.
[4] T. Inushima, Y. Ota, K. Fukui, UVSOR Activity
Report 38 (2010) 101.

98

BL4B

Valence State Analysis of Mn Ions in In2O3:(Mn, TM) (TM = Cr, Fe, Co)
S. Nishida1, T. Yoshioka1 and T. Yamamoto1, 2
12Faculty of Science and Engineering ,Waseda University, Tokyo 169-8555, Japan
Institute of Condensed-Matter Science, Waseda University, Tokyo 169-8555, Japanobserved Mn–L3 XANES spectra of In2O3:(Mn,Cr)
and In2O3:(Mn,Fe) can be determined to be a mixtureof the spectra of Mn2+ and Mn3+, on the other hand,that of In2O3:(Mn,Co) can be determined to be Mn3+.
Mn ions are trivalent in paramagnetic
In2O3:(Mn,Co), which support our previous reportthat the coexistence of Mn2+ and Mn3+ is mandatoryforroom-temperature
ferromagnetismin
In2O3:(Mn,Fe) [6], while coexistence of Mn2+ andMn3+ is also found in paramagnetic In2O3:(Mn,Cr). It
should be noted here that the ratios between Mn2+ andMn3+ are different in In2O3:(Mn,Cr) andIn2O3:(Mn,Fe), which suggests that the ratio between
Mn2+ and Mn3+ is also quite important for theappearance of room-temperature ferromagnetism.

The dilute magnetic materials (DMMs) have been
extensively studied through experiments andtheoretical calculations [1, 2], which haveferromagnetic properties with dilute magnetic
elements, because of the possibility of their futureapplications in spintronics. Although the Curie
temperature of most DMMs were quite low, it wasrecently reported that some DMMs show
room-temperature ferromagnetism [3, 4]. Amongthem, a sintered polycrystalline specimen of Mn- andFe-codoped In2O3 (In2O3:(Mn,Fe)) shows theproperty [4]. For a deeper understanding of themechanism of ferromagnetism in In2O3:(Mn,Fe),
substitution mechanism of magnetic elements wasinvestigated, in which Mn and Fe ions are substituted
at the In sites in In2O3 [5]. In addition, it was foundthat the coexistence of Mn2+ and Mn3+ is mandatoryforroom-temperature
ferromagnetismin
In2O3:(Mn,Fe) [6]. In the present study, the valence
state analysis of doped Mn ions have been carried out
using Mn–L3 X-ray Absorption Near-Edge Structure(XANES) measurements in order to investigate thedifferenceinelectronic
structure
betweenferromagnetic In2O3:(Mn,Fe) and paramagnetic
In2O3:(Mn,Cr) and In2O3:(Mn,Co).
All polycrystalline specimens, In2O3:(Mn,TM)((In0.94Mn0.03TM0.03)2O3, TM=Cr, Fe, Co), weresynthesized by the conventional solid-state reaction
method. Mn-L3 XANES spectra were collected at
BL4B in UVSOR by the total electron yield (TEY)method. All the sample powders were mounted on thefirst Be-Cu dinode using the carbon adhesive tape.
The incident beam was monochromatized by thevaried-line-spacing plane grating (800 lines/mm). Theenergy resolution of the incident beams, E/ǻE was set
to 3000 by tuning the slit height settled at the upperand lower reaches of the grating.
Prior to the XANES analysis, all the samples werecharacterized by the X-ray diffraction (XRD). No
extra peaks were found in these XRD patterns except
for the peaks originating from the bixbyite-structured
In2O3. Then all the samples were determined to be
crystallized in a single-phased cubic bixbyitestructured (Ia3). The observed Mn-L3 XANES spectraof In2O3:(Mn,TM) are shown in Fig. 1, together withthe reference spectra of Mn2+ (MnO) and Mn3+
(Mn2O3). The profiles of the Mn–L3 XANES spectraof Mn2+ (MnO) and Mn3+ (Mn2O3) are clearly
different and can be easily distinguished from thecharacteristic peak energies of their peaks. By
comparing to these standard spectra of Mn oxides, the2+

Mn

Intensity (arb. units)

MnO

In2O3: (Mn,Cr)
In2O3: (Mn,Fe)
In2O3: (Mn,Co)
Mn3+
Mn2O3
638 640 642 644 646
Energy (eV)Fig. 1. Observed Mn-L3 XANES spectra of
In2O3:(Mn,TM) (TM=Cr, Fe, Co). Top and bottom
spectra are those of MnO [7] and Mn2O3,
respectively.
[1] H. Ohno et al., Phys. Rev. Lett. 68 (1992) 2664.
[2] T. Dietl et al., Science 287 (2000) 1019.
[3] P. Sharma et al., Nat. Mater. 2 (2003) 673.
[4] G. Peleckis et al., Appl. Phys. Lett. 88 (2006)
132507.
[5] T. Yamamoto et al., J. Phys. : Condens. Matter 21(2009) 104211.
[6] T. Okazaki et al., Solid State Comm. 151 (2011)
1749.
[7] B. Gilbert et al., J. Phys. Chem. A 107 (2003)
2839.

99

BL5U

Angle-Resolved Photoemission Study of CaCu3Ti4O12
H. J. Im1, M. Tsunekawa2, T. Sakurada1, M. Iwataki1, K. Kawata1, T. Watanabe1,
K. Takegahara1, H. Miyazaki3, M. Matsunami4, 5, T. Hajiri4, 6 and S. Kimura4, 5
1

Department of Advanced Physics, Hirosaki University, Hirosaki 036-8224, Japan
2
Faculty of Education, Shiga University, Shiga 522-8522, Japan3
Department of Environmental and Materials Engineering, Nagoya Institute of Technology, Nagoya 466-8555,
Japan
4
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan.
5
School of Physical Sciences, The Graduate University for Advanced Studies, Okazaki 444-8585, Japan.
6
Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan

A-site ordered perovskite CaCu3Ti4O12 has been
attracted much attention due to the extremely highdielectric constant and Mott-type insulator,
respectively [1]. However, there have beendifficulties to realize applications and understand theunderlying physics, e.g. strong correlation effects,
due to the absence of experimental band structures.
Therefore, we have been studied the electronic
structure by the photoemission spectroscopy [2, 3]. In
this report, we present the band dispersions obtainedtheangle-resolved
photoemission(ARPES)
measurements and discuss the strong correlation
effects by comparing with the band calculations
within the local-density approximation (LDA).
ARPES experiments were performed at thebeamline BL5U. The used photon energy and thetotal energy resolution are 90 eV and 165 meV,
respectively. Measurement temperature is about 300
K. The clean surface was prepared in the (100) planeby cleaving in situ in a vacuum better than 210-8
Pa.
Figure 1 (a) and (b) are the image of the ARPES
spectra obtained by the second derivatives of theenergy distribution curves and the band dispersions
obtained from the LDA calculations, respectively. In
Fig. 1 (a), the calculated band dispersions aresuperimposed on the ARPES image, shifting to thehigher binding energy by 1.7 eV. Before comparing
the ARPES results and the LDA calculations, it
should be noted that there are 51 bands in the valenceband region as shown in Fig. 1 (b). Unfortunately, the
ARPES experiments cannot resolve these bands dueto the limitation of energy- and momentum-resolution.
Therefore, the band dispersions observed in ARPES
experiments should be interpreted as a bundle ofbands with the similar tendency.
In the region of 0 - 2.5 eV, we find the flat bandwith weak intensity. Even though the exact size ofband dispersion cannot be estimated in the ARPES
measurements due to the band broadening, we findthat the band width is very narrow compared with the
LDA calculations. This indicates that the bands are
more localized than the expectation of the LDA
calculations. These bands are assigned to three bands
from 64 to 66 which cross the Fermi level and100

disperse by about 1 eV in the LDA calculations. In
the region of 2.5 - 5 eV, there are bands around 3 eVand bands around 3.8 eV, which are well consistent
with the LDA calculations. The former and the latterbands are assigned to bands from 60 to 63 and from55 to 59, respectively. Particularly, the bands around
3.8 are not dispersive and show the localized
character.
In the region of 5 - 8 eV, ARPES data show thehighly dispersive bands, which consist of many bands
from 16 to 50 in the LDA calculations.
As discussed above, we attribute the differences
between ARPES results and the LDA calculations tothe strong correlation effects.

Fig. 1. (a) ARPES image of CaCu3Ti4O12 obtained at
hȞ = 90 eV and T = 300 K and the band dispersions
obtained from the LDA calculations.
[1] M. A. Subramanian et al., J. Solid State Chem.
151 (2000) 323.
[2] H. J. Im et al., UVSOR Activity Report 38 (2011)87.
[3] H. J. Im et al., UVSOR Activity Report 39 (2012)
90.

BL5U

Photoemission Study of Pyrite-type Ni1-xCuxS2
K. Soda1,2,3, K. Usui2, S. Osawa3, H. Kondo1, M. Kato1,2,3, J. Iwasaki4, K. Niwa2,3,4,
K. Kusaba2,3,4 and M. Hasegawa2,3,4
1

Department of Quantum Engineering, Graduate School of Engineering, Nagoya University,
Nagoya 464-8603, Japan2
Department of Physical Science and Engineering, School of Engineering, Nagoya University,
Nagoya 464-8603, Japan3
Department of Materials, Physics and Energy Engineering, Graduate School of Engineering,
Nagoya University, Nagoya 464-8603, Japan
4
Department of Crystalline Materials Science, Graduate School of Engineering, Nagoya University,
Nagoya 464-8603, Japan
Pyrite-type transition-metal dichalcogenides MX2(M = Fe, Co, Ni, Cu, Zn; X = S, Se) show rich varietyof electronic and magnetic properties due to theelectron correlation and hybridization effects. NiS2 isclassified as a charge-transfer-type insulator andNiS2-xSex reveals a metal-insulator transition [1, 2].
CuS2 is a p-band metal, exhibiting superconductivity[3]. It is interesting to clarify the effects of solid
solution between metallic CuS2 and insulating NiS2
on the electronic structure and related properties.
Here, we will report the first preliminary results.
Photoelectron measurements were performed at 10
K at BL5U in angle-integrated mode. Polycrystalline
specimens of NixCu1-xS2 were synthesized under ahigh pressure of 6.5 GPa at a temperature of ~920 K.
Their clean surfaces for the measurement wereprepared by scraping them with a diamond file. Totalenergy resolution was estimated as ~0.07 eV at theexcitation photon energy of 40 eV. The origin of thebinding energy EB was set to the Fermi energy EF
determined by measuring the Fermi edge of anevaporated Au film electrically connected to thespecimen.
In Fig. 1, typical valence-band photoelectron
spectra of NixCu1-xS2 are compared with their X-ray
ones obtained at SPring-8 (dots) and calculated
results: configuration-interaction cluster model (bars)[4] and band structure (curves) [1, 5] calculations.
Each spectrum is normalized with the intensity
integrated up to EB = 16 eV and the excitation photon
energy is indicated in the figure. Calculated
semiconductor-like electronic structure of NiS2 ispresented so as to locate the valence-band maximum
at EF. For CuS2, the observed valence-band spectrum
agrees well with the calculated band structure [5],while the present NiS2 spectra are in less agreement
but consistent with both the calculated results [1, 4].
The intensity at EF for CuS2 is 50 % of the edge jump,
indicating its metallic nature, while that for NiS2 is~20 %, suggesting that NiS2 has a semimetallic orsemiconducting (insulating) feature, as reported [2, 3].
Bands at 2.0 and 2.6 eV in NiS2 and CuS2 are
ascribed to the Ni and Cu 3d states, respectively. In
Ni0.5Cu0.5S2, peaks are recognized at EB = 1.7 and 2.6
eV, and the intensity at EF is ~40 % of the edge jump,

101

which is in the middle of NiS2 and CuS2. Thus thevalence band of Ni0.5Ni0.5S2 seems superposition of
those of NiS2 and CuS2, although the Ni 3d peak in
Ni0.5Ni0.5S2 is 0.3 eV lower in EB than in NiS2, whichsuggests the hybridization between Ni and Cu states.
Further study is intended on the x-dependence ofthe spectral shape as well as the electric and magnetic
properties. In comparison to the reported results [1-4],
some modifications are also found in the high binding
energy region. Further examination will be tried indifferent experimental conditions including sample
preparation.

Fig. 1. Valence-band spectra of Ni1-xCuxS2.
[1] J. Kunes et al., Phys. Rev. B 81 (2010) 035122.
[2] K. Mamiya et al., Phys. Rev. B 58 (1998) 9611.
[3] H. Ueda et al., Phys. Rev. B 65 (2002) 155104.
[4] A. Fujimori et al., Phys. Rev. B 54 (1996) 16329.
[5] D. W. Bullett, J. Phys. C 15 (1982) 6163.

BL5U

Angle-Resolved Photoemission Study on Sm1-xYxS
M. Kaneko1, 2, M. Saito3, T. Ito1, 5, K. Imura4, T. Hajiri1, 2, M. Matsunami2, 6, S. Kimura2, 6,
H. S. Suzuki7 and N. K. Sato4
1

Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan
2
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan3
School of Physical Sciences, Nagoya University, Nagoya 464-8603, Japan
4
Graduate School of Physical Sciences, Nagoya University, Nagoya 464-8603, Japan
5
Nagoya University Synchrotron Radiation Research Center, Nagoya University, Nagoya 464-8603, Japan
6
School of Physical Sciences, The Graduate University for Advanced Studies (SOKENDAI), Okazaki 444-8585,
Japan
7
National Institute for Materials Science, Tsukuba 305-0047, Japan(a)

To investigate the electronic structure, we show the
ARPES image of Sm0.83Y0.17S near EF around the X
point at the Brillouin zone boundary [Fig. 1(e)]. We
clearly found EF crossing of highly dispersive bandaround the X point, where the Sm 5d states locate justabove EF on black SmS [2]. Around the bottom of thedispersive band, the Sm 4f state pushed up to around
0.5 eV show sizable dispersion. The observed Sm 4f
dispersion strongly suggests the existence of the Sm
4f-5d hybridization, which causes the insulator tometal transition with Sm-Y substitution.
In conclusion, as the Sm2+ 4f multiplet structure
shifts to EF from x = 0 to 0.17, the electron pocket
appears due to the Sm 4f-5d hybridization bandformation, which is the possible origin of
insulator-metal transition. On the other hand, the S 3p
bands pushed down to high binding energy side from x= 0.17 to 0.33 since the Sm 5d – S 3p hybridization
becomes stronger in the metallic phase.

Samarium monosulfide (SmS) is a prototypicalvalence fluctuating compound inducing insulator(Black phase) – metal (Golden phase) transition by
applying external pressure. To directly observe thepressure-induced change of the electronic structure,
we have performed angle-resolved photoemission
spectroscopy (ARPES) on Sm1-xYxS where theanalogous insulator – metal transition is achieved as afunction of chemical pressure (Sm-Y substitution).
Single crystals of Sm1-xYxS (x = 0, 0.17, 0.33) weregrown by the Bridgman technique using ahigh-frequency induction furnace installed at NIMS.
ARPES measurement on these crystals was
performed at the VUV-ARPES beamline BL5U of
UVSOR-III. The inner potentials V0 have been 0.17,
and 0.33, respectively, by analyzing hQ - dependence(27 - 84 eV) of energy distribution curve ofhighly-dispersive S 3p bands.
Figure 1 (a), (b) and (c) show the ARPES image ofSm1-xYxS (x = 0, 0.17 and 0.33) near the X point.
From the comparison with the reported ARPES on
black SmS [1], the highly dispersive features at 3 – 6
eV are ascribed to S 3p band, while nondispersive
structures, respectively. By Sm-Y substitution, thelatter structure gradually shifts to EF, while theformer to higher binding energies from x = 0.17 to0.33 (see Fig.1 (d)).
(b)(c)[1] T. Ito, A. Chainani, H. Kumigashira, T. Takahashi
and N. K. Sato, Phys. Rev. B 65 (2002) 155202.
[2] V. N. Antonov et al., Condensed Matter Physics,
7 (2004) 38.

(d)

(e)

Fig. 1. The ARPES image of (a) x = 0, (b) 0.17 and (c) 0.33 near the X point.
(d) The elemental substitution dependence of the ARPES spectrum at X point (x = 0, 0.17 and 0.33)(e) The thorough ARPES image of x = 0.17. Open circles indicate the peak positions of the bands estimated by thesecond derivative of EDC data.

102

BL6B

Annealing Behavior of Ultrashallow Thermal Donors Formed in Carbonand Hydrogen-Doped Czochralski Silicon Crystals
A. Hara and T. Awano
Electronic Engineering, Tohoku Gakuin University, Tagajo 985-8537, Japan

In the past, we have reported on ultrashallow
thermal donors (USTDs) in carbon- andhydrogen-doped Czochralski silicon (CZ Si) crystals
after annealing at 480°C [1]. USTDs arehydrogen-like donors with slightly different energy
levels, some of which show negative central-cellcorrection, and to the best of our knowledge, are theshallowest energy levels as compared to many typesof previously reported donors in Si crystals [2]. In
this study, we evaluated the relationship between theintensity of USTDs and annealing time to investigate
their formation mechanism.
Carbon-doped CZ Si samples were doped withhydrogen by annealing them in wet oxygen at 1300°C
for 60 min. The samples were then cooled to room
temperature by rapidly exposing them to air. For
carbon doping, the Si melt used for preparing theingot was doped with carbon powder during CZ Si
crystal growth. The formation of USTDs at 480°C in
wet oxygen was investigated using the far-IR
spectrometer of the BL6B beamline at Liq. He
temperature obtained using a flowing cryostat.
Figure 1 shows the annealing behavior of USTDs
and shallow thermal donors (STDs). It has beenreported that STDs are hydrogen-like donors and are
generated in hydrogen-doped CZ Si crystals at around
450°C [3]. STDs are generated rapidly within the first
10 h and then decrease with the annealing time.
However, USTDs are generated slowly and increase
with increasing annealing time.
Figure 2 shows that the intensity of STDs after
annealing at 480°C for 40 h is equal to that after 10 hof annealing in hydrogen-doped but without carbon
CZ Si crystals. Moreover, USTDs are not generated.
Figures 1 and 2 show that carbon impurities act as
atomic elements essential for the generation of
USTDs and reduction of STDs. Carbon impurities
occupy substitution sites; therefore, its diffusion
coefficient (D) is very small given by D =1.9exp(-3.2eV/kBT) cm2/s [4]. However, the value of
D for interstitial carbons is significantly greater than
this value. Thus one tentative explanation for the
results shown in Figure 1 and 2. They are that some
STDs, which are generated in the initial stage at
480°C owing to their rapid generation rate, aretransformed to USTDs during long-term annealing by
combining with interstitial carbons. Interstitial carbon
is thought to be generated in CZ Si by the formationof SiO2 precipitates.

2.2

USTDs
2p0

2p䋫䋭

3p䋫䋭

2.0

40 h
1.8

30 h
1.6

Transmittance (arb. unit)

1.4

20 h

1.2

10 h
1.0

0.8

6h

0.6

3h

0.4

STDs 2p0

0.2
100

120

140

160

180

200

2p䋫䋭

220

240

3p䋫䋭

260

280

300

Wave number (cm-1)

Fig. 1. Variations in USTDs and STDs after annealing
at 480°C in carbon- and hydrogen-doped CZ Si
crystals.
1.2

Transmittance(arb. unit)
㩷

1.1
1.0

40 h

0.9
0.8
0.7
0.6

10 h

0.5
0.4
0.3
0.2
0.1
100

120

140

160

180

200

220

240

Wave number (cm-1)

260

280

300

Fig. 2. Spectra for STDs after annealing at 480°C for
10 and 40 h in hydrogen-doped but without carbon
CZ Si crystals.
[1] A. Hara, T. Awano, Y. Ohno and I. Yonenaga,
Jpn. J. Appl. Phys. 49 (2010) 050203.
[2] A. Hara, Jpn. J. Appl. Phys. 34 (1995) 3418.
[3] R. C. Newman, J. H. Tucker, N. G. Semaltianos, E.
C. Lightowlers, T. Gregorkiewicz, I. S. Zevenbergen
and C. A. J. Ammerlaan, Phys. Rev. B 54 (1996)
R6803.
[4] F. Shimura, Semiconductor Silicon Crystal
Technology (Acadenic Press, 1988)

103

BL6B

Study of Electronic States of Solids Probed by a Microspectroscopy Using
the Synchrotron Radiation
A. Irizawa1, S. Kobayashi2, K. Yoshimura2 and S. Kimura3, 4
1

The Institute of Science and Industrial Research, Osaka University, Ibaraki 567-0047, Japan
Division of Chemistry, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan3
School of Physical Sciences, The Graduate University for Advanced Studies (SOKENDAI),
Okazaki 444-8585, Japan
4
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan2

The optical study using infrared light sources is oneof the most powerful techniques for the investigationof electronic states on solids. There can be obtained
the direct information about the change of electronic
band structure, the symmetry of crystal structure, andthe dielectric property. In the respect of experimental
affinity, the optical study is extremely compatible withthe multiple conditions such as low temperature, highmagnetic field, and high pressure. In the case ofstrongly correlated electron systems, it is well known
that the temperature is one of the decisive factors forthe electronic state. The considerable types of phasetransition are induced by the change of thetemperature. Particularly, the multiferroic compounds
can be controlled of its physical properties mutuallyby 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.
The beamline 6B in UVSOR is adjusted for theinvestigations at low temperature and high pressure in
the extremely low-energy region of FIR-THz (farinfrared-terahertz). There equips two
typeinterferometers of both Michelson and Martin-Pupletttype. In this report, we tried the optical reflectivity
measurements in the longest wavelength region by amicro spectrometer for the single crystals of newly
synthesized compound CrSe2 showing a discontinuous
resistive change and a pressure-dependent
magnetization.
The experiments are performed using a micro
spectrometer having 1D array detector and a liquid-He
flow type cryostat for controlling the temperature from300 K down to 20 K. The reflectivity was obtained
from the ratio of optical reflections between thesample and Au as a standard with mirrored surfaces.
They were installed on the sample holder and were
measured through a polypropylene window of thecryostat.
The reflectivities are obtained in the energy range
between 200 and 700 cm-1 as shown in Fig. 1. This
compound shows two discontinuous temperaturechanges at 195 K and at 175 K with hysteresis loop inelectrical resistivity [1] and magnetization [1, 2], butfrom the results of optical reflectivity experiments
there is no significant change in the energy range of

FIR. At this moment it comes out that the lower energy
experiments using larger samples are demanded as a
future study for this compound.

20 K
100
300

Reflectivity

0.5

0.0
100

200

300

400

500

600

700

wavenumber (cm-1)

Fig. 1. Temperature change of reflectivity of CrSe2.
[1] S. Kobayashi et al., 18pGB-12 (2012) JPS
meeting in Yokohama.
[2] C.F. van Bruggen et al., Physica B+C 99 (1980)
166.

104

BL7U

Increase of Quasiparticle Lifetime in FeSb2 Kondo-Semiconductor
T. Takeuchi1,2,3, T. Shimada3, M. Matsunami4 and S. Kimura4
1

EcoTopia Science Institute, Nagoya University, Nagoya 464-8603, Japan
PRESTO, Japanese Science and Technology Agency, Tokyo 102-0075, Japan3
Department of Applied Physics Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan
4
UVSOR, Institute for Molecular Science, Okazaki 444-8585, Japan2

over the range of 0.001 < J < 0.01 mJ mol-1K-2. These
small Jdefinitely indicate the very small but finite
value of electronic density of states at HF.
We also realized that the shape of ARPES spectra
drastically changes with varying temperature. The
sharp peak persisting at temperatures below 20 K
starts to be broadened above 30 K. The drastic
increase of the energy-width of spectral function
indicates that the quasiparticle lifetime is fairly
reduced. Notably, this temperature dependence wasobserved over the whole momentum-range where thepresent ARPES measurement was performed.

-0.2

-0.4

R
-1
Momentum, k / Å

0.5
0
-0.5
-1.0
*

Z T R UX * Y SR

-0.05
0Energy, HP / eV

0.05

0.10

At the same temperature range, the magnitude ofSeebeck coefficient and electrical resistivity
decreases with increasing temperature, while themagnitude of magnetic susceptibility increases. All
the experimental facts unambiguously indicate thatthe electronic structure change in association withdestruction of Kondo-lattice occurs with increasing
temperature in this particular temperature range. If weassume the formation of Kondo-peak a few meVabove the chemical potential at the temperature range
below 30 K, the large magnitude of Seebeckcoefficient with negative sign is reasonably accounted
for with it. The behavior of electrical resistivity above
30 K is understood as that in the disordered Kondo
materials where the lifetime of quasiparticle is limited
to be short by the strong spin scatterings. The
constant value of electrical resistivity below 30 K isregarded as that observed for Kondo lattice under theunitary limit in good consistency with the rather long
lifetime of quasiparticles. The increase of magnetic
susceptibility with increasing temperature above 30 K
is also accounted for with the destruction of Kondo
lattice leading to the development of local magnetic
moment.
[1] T. Bentien at al., EPL 80 (2006) 17008.

-0.2

-1

-0.10

Fig. 2. Energy distribution curves observed at a
momentum near the Fermi surface. With decreasing
temperature, the peak intensity drastically increased
at the temperature range below 60 K where the large
magnitude of Seebeck coefficient was observed.

0-0.4
Momentum, k / ÅEnergy, H HF / eV

-0.15

(b)
Energy, H P / eV

Energy,H P / eV

(a)
0

25K
30K
40K
50K
60K
80K
100K

Intensity / arb.units

FeSb2 has attracted interest because it possesses ahuge magnitude of Seebeck coefficient |S| exceeding
40 mV/K at low temperature below 40 K [1]. The
origin of this huge |S| has not been revealed yet.
Seebeck coefficient is generally determined by theelectronic structure near the chemical potential of
conduction electrons. Thus it is of great importance toinvestigate its electronic structure in detail. Since theunusual increase of |S| is observed at low
temperatures below 50 K, one has to use experimentsthat are capable of investigating the detailed
electronic structure with a high-energy resolution.
In this study, therefore, we prepared high-quality
single grained FeSb2 samples and measured theirelectronic structure in detail by means ofhigh-resolution angle resolved photoemission
spectroscopy
measurements(ARPES)
withsynchrotron radiation as the photon source at BL7U
of UVSOR. We also measured Seebeck coefficient,
low temperature specific heat, and magnetization overa wide temperature range from 2 K to 100 K.
The single grained FeSb2 samples were grown in
antimony flux under the vacuum atmosphere. The
electrical resistivity shows a very large but finite
value at low temperature. This result indicates a finite
number of electronic states persisting at the Fermi
energy (HF). We also confirmed that the electronic
specific heat coefficient of samples was distributed*

Fig. 1. (a) Electron pocket observed in the second
momentum derivative of ARPES intensity
wI(k*Z , H ) / wk*Z measured aling *-Z line. (b) Second
energy derivative of ARPES intensity wI(k*R , H ) / wH
obtained at a momentum line near R. The band
dispersion calculated by FLAPW-GGA is shown inthe bottom.

105

BL7U

Investigation of the Electron-phonon Scattering in the Graphite by Using
the Angle-Resolved Photoelectron Spectroscopy:
Direct Observation of the Indirect Transition
S. Tanaka1, M. Matsunami2,3 and S. Kimura2,3
1

The institute of Scientific and Industrial Research, Osaka University, Ibaraki 567-0047, Osaka, Japan
3
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan3
School of Physical Sciences, The Graduate University for Advanced Studies (SOKENDAI), Okazaki 444-8585,
Japan
The electron-phonon scattering is one of the key
issues in the solid state physics and has been
extensively studied for long years. Angle-resolved
photoelectron spectroscopy (ARPES) is a very
powerful tool to investigate the electronic propertiesof the condensed matter, since it allows us to measure
the band of the electron resolving both in energy andmomentum. Then, it has been used to understand theelectron-phonon scattering in solids by many
researchers. With the ARPES spectrum, however, theelectron-phonon interaction was investigated only
through the self-energy of the quasiparticle-spectral
function in an integrated manner over their branches
and momentum. In this study, our aim is observing
directly the process of electron-phonon scatteringwith resolving the energy and momentum. If theenergy and momentum of the electron before thescattering are known, the measurements for those of
the scattered electron allow us to determine theenergy and momentum of the phonons that scattered
the electron thanks to the law of the conservation.
For this purpose, we took the Graphite as a target
material. HOPG (highly oriented pyrolytic graphite)sample was cleaved in-situ and investigated with the
ARPES at BL7U of the UVSOR-III. The sample
temperature was kept at 50K, that is higher than thecritical temperature for the CDW transition [1].
Figure 1(a) shows the surface-normal photoelectron
spectra taken at photon energies from 6 to 16eV. The
spectra vary drastically depending on the photon
energy, and Fig. 1(b) shows the typical spectra indetail. The step-like edges are clearly observed not at
the Fermi level, where an edge is observed for the Au
film, but at 68meV and 155meV with respect to the
Fermi level. Differentials of the spectra are shown in
Fig. 1(c) for a convenience to eye, and the peaks areclearly observed at the edge positions. The electronic
band crosses the Fermi level at K(H)-point in the
Brillouin zone of Graphite and highest occupied bandat the *(A)-point is located at ~4eV below the Fermi
level. Therefore, the electron emission observed inFig. 1(a) is due to the electron scattering from theK(H)-point to the *(A)-point. When theelectron-phonon interaction occurs, the electron loses(emission) or gains (absorption) its energy as much as
the phonon energy. Since temperature is low (50K),
the phonon-absorption probability is negligible in thiscase. Thus, the peak positions should indicate theFig. 1. ARPES Spectra for Graphite (HOPG) and theirdifferentials with respect to the binding energy of theelectrons.
energies of the phonons that scattered the electron.
Moreover, considering the conservation rule for the
momentum, the angle-resolved measurement of thephotoelectron enables us investigate the dispersionsof the phonons around the K(H)-point. The
angle-resolved differential spectra are shown in Figs.
1(d) and (e) taken at hQ=11.1eV and 6.0eV,
respectively. They clearly show the dispersions of thephonons.
68meV and 155meV phonons are attributed to the
ZA and/or ZO, and LO and/or LA modes, respectively.
The strong photon-energy-dependence observed inFig. 1(a) indicates that the final state of thephotoexcitation determines the phonon branch thatcan scatter the electron during the photoexcitation
process. It should be ascribed to the dipole selection
rules both for the optical transition and theelectron-phonon scattering, those of which can bepredicted by using the group theory. The detail willsoon be published elsewhere.

[1] S. Tanaka, M. Matsunami and S. Kimura, Phys.
Rev. B 84 (2011) 121411(R).

106

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Change in the Electronic Structure of the Single Crystalline Graphite as a
Result of the CDW Transition
S. Tanaka1, M. Matsumoto2, M. Matsunami3,4 and S. Kimura3,4
1

The institute of Scientific and Industrial Research, Osaka University, Ibaraki 567-0047, Osaka, Japan
Institute of Industrial Science, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505, Japan.
3
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
4
School of Physical Sciences, The Graduate University for Advanced Studies (SOKENDAI), Okazaki 444-8585,
Japan
2

Charge-density-wave (CDW) transition is one of
the topics that have been extensively studied in solidstate physics. This phenomenon is a rearrangementof the atomic structure of low-dimensional solids
due to the electron-photon interaction. When thetemperature is below critical temperature for the
CDW transition, the superstructure is formed
accompanying the opening of the gap near the Fermi
level in the electronic structure. Recently, we
found the experimental evidence that thep 3 u 3 R30$ superstructure is formed at lower
temperature than 30K on the HOPG (Highly Oriented
Pyrolytic
Graphite)withAngle-resolved
photoelectron spectroscopy (ARPES), and interpreted
it as the CDW transition according to thetemperature-dependent measurement [1]. When the
superstructure is formed, the folding of the Brillouinzone occurs, and the dispersion (originally) at theK-point can be observed at the *-point with the
ARPES. However, a change in the electronic states asa result of the CDW transition was not observed in
the previous work. This is somewhat paradoxical. In
this paper, therefore, we examine a change in theelectronic structure due to the CDW transition on the
single-crystal of Graphite.
The experiments were carried out at BL-7U. The
single-crystalline Graphite samples exhibited sharp(1x1) LEED (Low Energy Electron Diffraction)
pattern. A clean surface was made by cleaving using
the Scotch tape in the ultrahigh vacuum at low
temperature. The superstructure formed at low
temperature below 30K was confirmed using the
11.5eV-photons in the same manner as the previous
study [1]. The photon energy used below was 39eV.
The left panel of Fig.1 shows the comparison of the
ARPES spectra near the K-point along the *-K-M’
direction when the sample temperature is changed
from 15K to 50K, those are respectively below andabove the critical temperature of the CDW transition.
No significant differences are observed in the mainfeatures, which show the dispersion of the S-band of
the Graphite as previously reported. However, there isa striking change for a dispersive band indicated bycircles in the left panel of Fig.1. For showing moredetail, we display the EDC curves at several k// values
in the right panel of Fig. 1. At top curves, where the S

Photoelectron Intensity (Arb. Units)

50K
15K

-0.15

k//=0

x2

k//=-0.057

x3 k//=-0.062
x6 k//=-0.085
x8 k//=-0.094
-0.10

-0.05

0.00

Binding Energy (eV)Fig. 1. ARPES Spectra near the K-point of thesingle-crystalline Graphite at 15K and 50K.
band at the K-point is only observed, there is nochange except the thermal broadening at 50K.
Meanwhile, the spectrum at higher k// show changes
with changing temperature. The energy positions of
the green (15K) and blue (50K) circles correspond to
those of the circles in the left panel of Fig. 1. Thisband shifts in energy to by about 0.01eV when thetemperature is changed. At 50K, this band crosses the
Fermi level at k//~0.1A-1 while the gap seems open at
15K where the CDW is formed.
According to the report by Zhou et al. [2], thisband is ascribed to the edge state of the zig-zag stepon the Graphite surface. Sugawara et al. also reported
a similar band [3]. Therefore, we can conclude that
the CDW transition is strongly related to the edge
state. The band folding at low temperature may beascribed to the surface Umklapp process that is due tothe CDW transition at domains near to the step edge
on the Graphite surface. This is consistent with thetheoretical calculation by Hamada et al. [4].
[1] S. Tanaka M. Matsunami and S. Kimura, Phys.
Rev. B 84 (2011) 121411(R) .
[2] S.Y. Zhou, G.-H. Gweon and A. Lanzara, Ann. ofPhy. 321 (2006) 1730–1746.
[3] K. Sugawara, T. Sato, S. Souma, T. Takahashi and
H. Suematsu, Phys. Rev. B. 73 (2006) 045124.
[4] I. Hamada and Y. Morikawa, Phys. Rev. B 85
(2012) 237401.

107

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Angle-Resolved Photoemission Study on FeSb2
S. Imada1, K. Terashima1, H. Eto1, K. Sano1, K. Tsukamura1 and H. Nakamura2
1

Faculty of Sci. and Eng., Ritsumeikan Univ., Shiga 525-8577 Japan
2
Grad. School of Eng., Kyoto Univ., Kyoto 606-8501, JapanFeSb2 shows a metal-insulator crossover; it ismetallic around room temperature, while it isinsulating at low temperatures with an upturn of theresistivity curve at ~50 K.
A number ofexperimental reports have indicated the existence ofthe energy gap at low temperatures [1-3], while themechanism for the formation of the energy gap has
not been settled yet. So far, mainly two scenarios
have been proposed, one is that FeSb2 is a Kondo
insulator [2], and the other is that FeSb2 is anarrow-gap semiconductor [1, 3]. FeSb2 has an
orthorhombic structure with a = 5.82 Å, b = 6.51 Åand c = 3.17 Å at 100 K [2].
In our previous study on FeSb2 at UVSOR [4], wehave measured temperature dependence of the densityof states (DOS) near EF. As we reduce thetemperature, the DOS suppression is observed, but
finite intensity in the vicinity of EF remains even at 15
K where the resistivity shows insulating behavior. We
also find a free-electron like band crossing EF at 15 K,
indicative of the surface state. Thus it is importantto separate the surface contribution fromphotoemission spectra to discuss bulk property and its
mechanism.
We have also performed angle-resolved
photoemission (ARPES) on FeSb2 to reveal themechanism of the crossover by directly observing thetemperature dependence of the energy gap. We haveobserved dispersive bands but interpretation was left
ambiguous due to the small amount of data.
In this study, we have preformed normal emission
measurement with larger photon energy region thanthe previous measurement and succeeded inobserving a clear dispersion.
A single crystal of FeSb2 has been synthesized by
Sb-flux method. High-resolution ARPES study has
been performed at BL-7U in the UVSOR facility.
Energy resolution was set at ~13 meV. We haveobtained a clean surface of the sample by fracturing
in an ultrahigh-vacuum of ~1x10-8 Pa.
Figure 1 (a) shows the normal emission spectrafrom the (100) surface of FeSb2 at 100 K using
photon energy (hQ) from 12 to 40 eV, where each hQ
corresponds to different k points along *-X axis. As
in Fig. 1(a), we have observed a number of dispersive
bands of FeSb2, such as Fe 3d3z2-r2 band [5] located atbinding energy (EB) of ~0.3 eV, Fe 3dx2-y2 band [5] at
EB ~ 1 eV, and so on. By comparing the dispersion
with the calculated bands [6], we estimate that in the
spectrum taken at hQ~35 eV, the bottom of thevalence band at the *point is observed at around EB108~ 6 eV. Reflection of a band around EB ~ 2.5 eV at
X point is found at around hQ ~ 23 eV. Between
these points, a clear dispersion is found. Further
ARPES study, clarifying (i) the bulk Fermi surfaces
near the Zone edge and corner [5], (ii) the location of
the surface bands, (iii) the temperature dependence ofbulk bands, is necessary to elucidate the origin of themetal-insulator crossover in FeSb2

Fig. 1. (a) ARPES spectra derived by normal
emission method using hQ = 12-40 eV at BL-7U.
(b) Plot of second derivative of (a). White area
corresponds to bands.
[1] Z. Schlesinger et al., Phys. Rev. Lett. 71 (1993)
11.
[2] C. Petrovic et al., Phys. Rev. B 72 (2005) 045103.
[3] T. Koyama et al., Phys. Rev. B 76 (2007) 073203.
[4] S. Imada et al., UVSOR Activity Report 37(2010) 106.
[5] A. V. Lukoyanov et al., Euro. Phys. J. 53 (2006)
205.
[6] J. M. Tomczak et al., Phys. Rev. B 82 (2010)
085104.

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Three-Dimensional Electronic Structure of Over-Doped BaFe1.8Co0.2As2
T. Hajiri1,2, T. Ito1,3, M. Matsunami2,4, B. H. Min5, Y. S. Kwon5 and S. Kimura2,4
1

Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan
2
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
3
Nagoya University Synchrotron radiation Research Center, Nagoya University, Nagoya, 464-8603, Japan
4
School of Physical Sciences, The Graduate University for Advanced Studies (SOKENDAI), Okazaki 444-8585,
Japan
5
Department of Emerging Materials Science, DGIST, Daegu 711-873, Republic of Korea
In iron pnictides, it is one of the most interest issues that where the nodes appear in three-dimensional(3D) electronic structures. In BaFe2As2-xPx system,
there are different two reports. One is that there are
the nodes on the hole Fermi surface (FS) of dz2 orbital
character around Z point [1], and the other is that on
the electron FS at the longer edge of the ellipsoid-shaped FS cross-section [2]. The former can be
explained by spin fluctuation mediated superconductivity theory [3], while the latter by taking into account for not only spin fluctuations but also orbital
fluctuations. On the other hand, the fundamental
physical properties of BaFe2-xCoxAs2 system suggest
the existence of orbital fluctuations in the wide doping range [4], despite spin fluctuation cannot. Therefore, it is important to determine 3D superconducting
gap symmetry.
To elucidate this, we performed a 3D angle-resolved
photoemission
spectroscopyofover-doped BaFe1.8Co0.2As2 (Tc ~ 22.5 K) at BL7U,UVSOR-III.
Figure 1(a) shows a 3D hole FSs measured in the*MAZ plane at T = 12 K. The red open circles indicate the hole FSs determined by the peak positions of
the momentum distribution curves. One and two holeFSs are clearly visible at * and Z point, respectively[Fig. 1(b, c)].
Figure 2(a) shows the symmetrized energy distribution curve (EDC) at * point. The symmetrized
EDC spectrum at T = 35 K (> Tc) shows thepseudogap [5] at around 8 meV. On the other hand, at
T = 12 K, the additional shoulder structure appears ataround 6 meV. Interestingly, when we divide thesymmetrized EDC at T = 12 K by one at T = 35 K, wefound that only the low-energy shoulder remains.
This suggests that the low-energy shoulder can be
identified as superconducting gap, while thehigh-energy one as ‘pseudogap’. Figure 2(b, c) shows
the symmetrized EDC spectra and summarized gap
size at several photon energies at 12 K. We can recognize the superconducting gap between 5~7 meV at
each photon energy and almost isotropic superconducting gaps. These results imply that there is no
horizontal line nodes, at least, on the outer hole FS in
this system.

Fig. 1. (a) Out-of-plane FSs in the *MAZ plane at T
= 12 K. (b, c) EDC along gray-lines marked by 20 (b)and 30 eV (c) in panel (a), respectively.

Fig. 2. (a, b) Temperature (a) and photon energy (b)dependent symmetrized EDC. (c) Size of the superconducting gaps estimated from panel (b).
[1] Y. Zhang et al., Nature Phys. 8 (2012) 371.
[2] T. Yoshida et al., arXiv:1301. (2013) 4818.
[3] K. Suzuki et al., J. Phys. Soc. Jpn. 80, 013710(2011).
[4] H. Kontani et al., Solid State Commun. 152(2012) 718.
[5] S. Kasahara et al., Nature 486 (2012) 382.

109

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Angle-Resolved Photoemission Study on Quasi-One-Dimensional Organic
Conductor (TMTSF)2X (X = SbF6, AsF6, PF6)
M. Mitamura1, S. Hirate2, T. Hajiri2, T. Ito2, 4, S. Kimura3, 5 and T. Nakamura3, 5
1School of Engineering, Nagoya University, Nagoya 464-8603, Japan
Graduated School of Engineering, Nagoya University, Nagoya 464-8603, Japan
3
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
4
Nagoya University Synchrotron Radiation Research Center, Nagoya University, Nagoya 464-8603, Japan
5
School of Physical Sciences, The Graduate University for Advanced Studies (SOKENDAI), Okazaki 444-8585,
Japan
2

The Bechgaard salts (TMTSF)2X (TMTSF:
tetramethyl-tetraselenafulvalene, X = SbF6, AsF6, PF6,
etc.)
are
the
well-known
modelsofquasi-one-dimensional (Q1D) organic conductor. At
low temperatures, this quasi-one-dimensionality
results in an intriguing ground state such as a
spin-density-wave (SDW) state, a superconducting
state, etc., depending on anion X (or pressure) [1].
In this study, we have performed angle-resolved
photoemission
spectroscopy(ARPES)onsingle-crystalline (TMTSF)2X (X = SbF6, AsF6, PF6)
to clarify the intrinsic electronic structure and its
relation to the anomalous properties by utilizing thebulk-sensitive microfocus low-energy photons (hQ =8 eV, 15×150 m2).
Figure 1 shows the second derivative of the
ARPES image near the Fermi level (EF) along the īX
high-symmetry line measured at T = 30 K of
(TMTSF)2X (X = SbF6(a), AsF6(b), PF6 (c)),
respectively. Three clear band dispersions (h, s and p)
successfully observed on each compounds. From thecomparison with the first principle calculation on
analogous (TMTSF)2ClO4, the hole-like dispersion of
main feature (p) around the * point can be assigned
as the TMTSF band [2]. Though the theory expects
only one TMTSF band, the observed multi dispersive
features could be attributed to, so called, spin-charge
separation. Actually, the separation of h and pdispersions on (TMTSF)2X, respectively, shows goodcorrespondence with holon and spinon bands on
inorganic Q1D conductor SrCuO2 [3].
In the one-dimensional Hubbard model, it is known
that, the width of holon and spinon band corresponds
to transfer integral along TMTSF chain ta (red) andspin-exchange interaction constant J (blue),respectively. Table 1 shows the comparison of the J
and ta estimated by the present ARPES with those by
the thermodynamic experiments [4-6]. From thecomparison, we found qualitative agreement of J andta between the experiments. Furthermore, gradualincrease of ta / J from X = SbF6 to PF6 has been
revealed, while ta shows discontinuity. The results
suggests that the balance of bandwidth between holonand spinon should .reflect the nature of TMTSF S
electrons (localized or itinerant) and scale with thephysical properties as well.

Fig. 1. Second derivative of ARPES image near EF of(TMTSF)2X (X = SbF6(a), AsF6(b), PF6 (c)).
Table 1. J and ta of (TMTSF)2X (X = SbF6, AsF6, PF6)
estimated by thermodynamic [4-6] and present
ARPES experiments.

X=
SbF6
AsF6
PF6

Thermodynamic
J
ta
(meV)
(meV)
ʊ
ʊ
120[4]
250[5]
230[6]
120[4]-250[5]

J
(meV)
139
135

ARPES
ta
(meV)
212
276

83

200

ta / J
1.53
2.04
2.41

[1] T. Ishiguro et al., Organic Supercondutors(Springer-Verlag, Berlin, 1998).
[2] S. Ishibashi, Sci. Techonol. Adv. Mater. 10 (2009)024311.
[3] B. J. Kim et al., Nat. Phys. 2 (2006) 397.
[4] M. Dumm et al., Phys. Rev. B 62 (2000) 6512.
[5] C. S. Jacobsen et al., Phys. Rev. B 28 (1983)
7019.
[6] L. Ducasse et al., J. Phys. C 19 (1986) 3805.

110

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Hybridized Band Dispersion of YbAl2
M. Matsunami1, 2, T. Hajiri1, H. Miyazaki3, M. Kosaka4 and S. Kimura1, 2
1

UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
School of Physical Sciences, The Graduate University for Advanced Studies (SOKENDAI), Okazaki 444-8585,
Japan
3
Center for Fostering Young and Innovative Researchers, Nagoya Institute of Technology, Nagoya 466-8555,
Japan
4
Graduate School of Science and Engineering, Saitama University, Saitama 338-8570, Japan

2

111

kz

W

L

kx

*

K

X
U
M’
ky

Fig. 1. Brillouin zone of YbAl2, in which kz
corresponds to the (111) direction of the fcc Brillouinzone. In the kx-ky plane, the midpoint of the zone edge(K) is referred to as M' point, which is also equivalent
to the midpoint between L and U points.

Intensity (arb. units)*-K direction*-M’ direction
(a)

(c)
*

*

0.6
0.4
0.2
0.0
Binding Energy (eV)Binding Energy (eV)The most important concept in the heavy fermion
systems is a hybridization effect between conduction(c) and f electrons. The c-f hybridization-derived
electronic structure can be directly probed by theangle-resolved photoemission spectroscopy (ARPES).
In this work, we focus on YbAl2, which is known as
one of the prototypical valence fluctuation systems,with the Yb mean valence of +2.2 [1]. Thus, YbAl2 is
a suitable system to investigate the c-f hybridized
band structure in relation with the extremely strong
valence fluctuations.
The ARPES experiment was carried out at theundulator beamline BL7U [2]. The single crystals of
YbAl2, which were grown by the Lithium flux
method, were cleaved in situ along the (111) plane.
The Brillouin zone of YbAl2 is shown in the Fig. 1.
The total energy resolution and the measurement
temperature were set to 20 meV and 12 K,
respectively. The LDA band structure calculations
were performed using the WIEN2k code.
Figures 2 (a)-(d) show the series of ARPES spectra
and the ARPES intensity plot near the Fermi level
along the *-K and *-M' directions, measured at hQ =20 eV [2]. The band dispersions obtained by the LDA
calculation are also plotted in Figs. 2 (b) and (d).
Their overall feature is well described in terms of the
LDA calculation. In particular, the observed Yb 4f7/2
band around the binding energy of 0.17 eV shows
good agreement of energy with the calculation
without any shift. This finding strongly suggests an
extremely small renormalization in YbAl2. In thelower-binding energy region compared with the 4f7/2
band, the anti-bonding bands of the c-f hybridization
are clearly observed, responsible for the valencefluctuations in YbAl2. For the *-K direction, theposition of the innermost band matches very wellwith that of LDA calculation. On the other hand, theexperimental outer band has a slightly weakerdispersion. This band might not be separated from themore outer band, which does not cross the Fermi
level as shown in the LDA calculation. For the *-M’
direction, the experimental inner and outer bands arehighly mixed, unlike those of the LDA calculation.
The “mixed” band is located on the inside of thecalculated ones and has almost same Fermi vector as
the inner band in the *-K direction. This finding
suggests that the inner Fermi surface is more circularthan that of the LDA calculation [2].

0.0

*

(b)

0.0
-1
kx (Å )

0.5

0.6
0.4
0.2
0.0
Binding Energy (eV)

*

(d)

0.2

0.4

0.6
-0.5

-0.5

0.0
-1
ky (Å )

0.5

Fig. 2. (a) and (c) Series of ARPES spectra along the*-K and *-M' directions, respectively. (b) and (d)ARPES intensity plots of (a) and (c), respectively.
The band dispersions obtained by MDC fitting (opencircle) and LDA calculation are overlapped.
[1] M. Matsunami et al., J. Phys. Soc. Jpn. 81 (2012)
073702.
[2] M. Matsunami et al., Phys. Rev. B 87 (2013)
165141.

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Unique Fermi-Surface Topology Originated from Pt Atoms: An ARPES
Study of the Electronic Structure of Ca10(Pt4As8)(Fe2гxPtxAs2)5
X. P. Shen1, S. D. Chen1, Q. Q. Ge1, Z. R. Ye 1, H. C. Xu 1, F. Chen1, M. Xia1,
B. P. Xie1, M. Matsunami2, S. Kimura2 and D. L. Feng1
1

State Key Laboratory of Surface Physics, Department of Physics, and Advanced Materials Laboratory,
Fudan University, Shanghai 200433, People’s Republic of China
2
UVSOR Facility, Institute for Molecular Science and
The Graduate University for Advanced Studies, Okazaki 444-8585, Japan

Recently, superconductivity up to 38 K was
discovered in the novel iron-based superconductor
Ca10(Pt4As8)(Fe2íxPtxAs2)5 [1]. In these compounds
the metallic Pt4As8 layer was introduced as a newintermediary layer, which distinguished them fromother usual iron pnictides.
To study whether the Pt4As8 layer contributedensity of states (DOS) at the Fermi energy (EF) andestimate the strength of interlayer coupling between
Pt4As8 and FeAs layers, we have conducted
angle-resolved photoemission spectroscopy (ARPES)
studies on Ca10(Pt4As8)(Fe2íxPtxAs2)5 at beamline
BL7U at UVSOR. The variable photon energies andpolarizations enable us to successfully resolve thelow-energy electronic structure and corresponding
orbital characters in the 3-dimensional momentum
space.

center and two electron pockets (G, K) around thezone corner, which show good correspondence to theelectronic structures of other prototype pnictides andcould be attributed to the Fe-3dxz, -3dyz, and -3dxy
orbitals, respectively [3].

Fig. 2. The Fermi surface as a function of kz in the pgeometry.
Further kz dependence of the N electron pocket isshown in Fig. 2. The intensity distribution of theNband shows a periodic variation in Fig. 2(a) if wetake the inner potential to be 13 eV. By tracing the
MDC’s at EF at each kz [Fig. 2(b)], we could conclude
that the N electron pocket shows weak dispersion
along the kz direction.
In general, our data demonstrate that the Pt atoms
indeed provide DOS at EF and the N electron pocket
may participate in superconductivity in this novel
material. However, the interlayer coupling between
Pt4As8 and FeAs layers is considerably weakaccording to the rather two-dimensional electronic
structure and absence of obvious hybridization
between NandD bands. Our results might open up
new avenues for the exploration of high-Tc
superconductor by tuning the interlayer coupling
between FeAs layer and additional metallic-likeintermediary layers.
[1] N. Ni et al., Proc. Natl. Acad. Sci. USA 108, E
1019 (2011).
[2] H. Nakamura et al., Physica C 484 (2013) 39.
[3] Y. Zhang et al., Phys. Rev. B 83 (2011) 054510.

Fig. 1. The polarization-dependent ARPES dataaround *taken with 26 eV photons.
Figure 1 reveals the polarization dependent
photoemission intensity maps and corresponding
photoemission intensity plots along *-M. As shownin Fig. 1(a) and (b), the 2D blue BZ is from FeAs
layer and the red dash one is from Pt4As8 layer. The
most remarkable feature here is that there are four
small electron pockets (N) arranged around the zone
centers of the Pt4As8 BZs, as enclosed by the dashlines in Fig. 1(a), which is very likely from Pt atoms
as proposed in the recent first-principles
calculation[3]. Besides, we resolved two hole-likebands (D, E), one hole pocket (J) around the zone

112

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Circular Dichroism ARPES Studies on Dresselhaus Effect in Non-Magnetic
Semiconductors
W. Jung1, S. Cho1, Y. Kim1, B. Kim1, Y. Koh1, M. Matsunami2, S. Kimura2 and C. Kim1
1

Institute of Physics and Applied Physics, Yonsei University, Seoul, Korea
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan

2

GaAs and InSb have been studied by many
researchers and received attention. One of the issues
in studying these semiconductors is the band splittingat the ī-point. GaAs and InSb have a zinc blende
structure and such materials have three hole bands
that belong to the bulk band at the ī-point. It is
known that band splitting is due to the inversion
symmetry breaking in the bulk. We studied thisphenomena in light of the Dresselhaus effect.
Semiconductors with zinc blende and Wurtzite
structures with a bulk inversion asymmetry such as
ZnTe, ZnSe, CdS, CdSe, GaAs and InSb have beentheoretically studied within a tight-binding model [1].
The effective one-body Hamiltonian with Dresselhaus
effect is:

Figure 1 shows ARPES data from GaAs. It is
confirmed that GaAs has two hole bands at theī-point.

‫ ܪ‬ൌ ‫ܪ‬଴ ൅ ‫ܪ‬஽‫ܪ‬஽ ൌ ɀሾɐ௫ ݇௫ ൫݇௬ ଶ െ ݇௭ ଶ ൯ ൅ ܿ‫ݏ݊݋݅ݐܽݐݑ݉ݎ݁݌݈ܿ݅ܿݕ‬ሿ
Here, HD is the Hamiltonian for the Dresselhaus effect,ı Pauli matrix, and Ȗ the material dependent
spin-orbit coupling constant. GaAs and InSb have astrong spin-orbit coupling and consequently show the
Dresselhaus effect [2].
Topological insulators have strong spin-orbit
coupling and have been studied in our group.
According to our recent results, the orbital angularmomentum (OAM) plays an important role in theformation of a Rashba-type surface band splitting [3].
We expect that OAM also greatly affects theelectronic structure of semiconductors such as GaAs
and InSb and that one should be able to obtain key
evidences for the role of OAM in the
Dresselhaus-type bulk band splitting. It was also
recently reported that OAM can be measured by
Circular Dichroism ARPES (CDARPES) [4, 5].
Therefore, we tried to study the OAM effect on the
Dresselhaus effect by using circular and linear
dichroism ARPES.
GaAs and InSb single crystals were purchased as
wafer. ARPES measurement was performed at thebeam line 7U of UVSOR-III. Crystals were cleaved
in-situ at room temperature and the chamber pressure
was better than 5×10í11 Torr. ARPES spectra wereacquired with a hemispherical photoelectron analyzer(MBS A-1). We used linearly polarized as well as left
and right circularly polarized (LCP and RCP) photonsof 921 eV photons to avoid signal from the surface
states.

113

Fig. 1. ARPES image from GaAs (110) bulk statemeasured with linearly polarized 21 eV photon. The
image is taken along the ky = 0 line.
To obtain the evidence for the Dresselhaus effect in
ARPES, we performed CDARPES experiments on
the GaAs and InSb with circularly polarized 9 eV
photons, because the Dresselhaus effect gives a 3T
symmetry in the CDARPES (ILCPIRCP)/ (ILCP+IRCP).
However, we could not reach the * point with
low-energy photons owing to the limitation of thebeamline. It is expected that three-dimensional bulk
band structure of GaAs and InSb gives us new
information. Therefore, we will perform thethree-dimensional ARPES to obtain the complete
bulk electronic structure.

[1] W. T. Wang et al., Appl. Phys. Lett. 91 (2007)
082110.
[2] J. W. Luo et al., Phys. Rev. Lett. 102 (2009)056405.
[3] S. R. Park et al., Phys. Rev. Lett. 107 (2011)
156803.
[4] B. Y. Kim et al., Phys. Rev. B 85 (2012) 195402.
[5] J. H. Park et al., Phys. Rev. B 85 (2012) 195401.

BL7U

Temperature-Dependent Dispersive In-Gap State of The Kondo
Semiconductor SmB6
H. Miyazaki1, 2, T. Hajiri2, 3, M. Matsunami2, 4, T. Ito3, S. Kunii5 and S. Kimura2, 4
1

Nagoya Institute of Technology, Nagoya 466-8555, JapanUVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
3
Nagoya University, Nagoya 464-8603, Japan
4
The Graduate University for Advanced Studies (SOKENDAI), Okazaki 444-8585, Japan
5
Tohoku University, Sendai 980-8578, Japan
2

Samarium hexaboride (SmB 6) is one of typical
Kondo semiconductors/insulators with a valencefluctuation between Sm2+ (4f6) and Sm3+ (4f5) ions [1].
The electrical resistivity decreases on cooling, like ametal, above the temperature of 100 K, and thenreveals a semiconductor-like character with activationenergy of 15 meV, but the resistivity saturates below
20 K [2]. Though the origin of the constant resistivity
at low temperatures has not been resolved for a longtime, recently this behavior has been suggested tooriginate from metallic behavior at the edge state on
the surface [topological Kondo insulator (TKI)] [3].
To clarify the origin of the anomalous electricalresistivity behavior of SmB6, we performed
three-dimensional angle resolved photoemission
spectroscopy (3D-ARPES) to determine theelectronic band structure directly.
A SmB6 (001) single crystal was cleaned by Ar+ ion
sputtering and 1400 °C annealing cycles in theultrahigh vacuum chamber with a base pressure of ~ 2
u 10-8 Pa. Clean surface of SmB6 with the 2 u 1 and 1
u 1 (001) patterns was confirmed by a low energy
electron diffraction method and no contamination,such as carbon, was observed by an Auger electron
spectroscopy. The 3D-ARPES measurements were
performed at the beamline 7U of UVSOR-III. The
total energy and momentum resolutions for the
ARPES measurement were set to 13 meV and 0.006
Å-1 at the * point (hQ = 26 eV) and 12 meV and 0.003
Å-1 at the X point (hQ = 10.6 eV), respectively.
Figure 1 shows the temperature-dependent ARPES
spectra divided by the Fermi-Dirac distribution curvealong the X̅M line. At T = 40 K, the k-dependence ofthe peak at EB = 15 meV, marked by open circles, isalmost flat. The band becomes slightly dispersive attemperature below 20 K, i.e., the c-f hybridization
gap opens near the X point. At T = 10 K, anotherband dispersion, with an electron pocket at k ~ 0.25
Å-1, appears at EB ~ 5 meV, as shown by vertical lines.
The dispersive in-gap state behavior suggests that thein-gap state is not a local state, such as an impurity
state, but has the periodicity of the SmB6 unit cell.
The ARPES data seem to be consistetnt with theelectrical resistivity; i.e., the formation of thehybridization gap is visible above 20 K, while thein-gap state becomes dominant below 10 K. The band
dispersion of the in-gap state is consistent withtheoretical calculation [4, 5], i.e., the dispersive

114

in-gap state suggests the existence of an edge state.
To determine the origin of the in-gap state, further
studies are intended.

Fig. 1. Temperature dependence of ARPES spectra
divided by the Fermi-Dirac distribution curve along
the X – M line. The hybridization band dispersions
are shown by open circles, and the observed
dispersion in-gap state is shown by vertical lines.
Insets show the second derivative curves of the
ARPES spectra at k(100) = 0.25 Å -1.
[1] R. L. Cohen et al., J. Appl. Phys. 41 (1970) 898.
[2] T. Tanaka et al., J. Appl. Phys. 51 (1980) 3877.
[3] M. Dzero et al., Phys. Rev. Lett. 104 (2010)
106408.
[4] M. Dzero et al., Phys. Rev. B 86 (2012) 075105.
[5] F. Lu et al., arXiv: 1211.5863.

BL7U

High-Resolution ARPES study of Sn1-xInxTe: Implication to TopologicalSuperconductivity
T. Sato1, Y. Tanaka1, K. Nakayama1, S. Souma2, T. Takahashi1,2, S. Sasaki3, Z. Ren3,
A. A. Taskin3, K. Segawa3 and Y. Ando3
12

Department of Physics, Tohoku University, Sendai 980-8578, JapanWPI Research Center, Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
3
Institute of Scientific and Industrial Research, Osaka University, Ibaraki, Osaka 567-0047, Japan

Topological insulators (TIs) are a novel quantum
state of matter where the bulk band gap induced by astrong spin-orbit coupling leads to the appearance of
unusual gapless edge/surface states protected bytime-reversal symmetry [1, 2]. The discovery of TIs
triggered the search for their superconducting (SC)analogues, topological superconductors (TSCs). TSCs
are accompanied by gapless Andreev bound states
inside the SC gap which are often comprised ofMajorana fermions. Very recently, point-contact
spectroscopy revealed that indium-doped tin telluride(Sn1-xInxTe, called In-SnTe here) is possibly a new
type of TSC [3]. This result is particularly intriguingin view of the fact that SnTe was recently elucidated
to be materializing a new type of topological state
called topological crystalline insulator (TCI) [4, 5]
associated with topologically-protected surface statesthat emerge due to a combination of band inversion
and mirror symmetry [4, 5]. It is thus of great
importance to experimentally clarify the electronic
states of In-SnTe relevant to the possible occurrenceof topological superconductivity.
In this study, we have performed high-resolution
angle-resolved photoemission spectroscopy (ARPES)
of In-SnTe. By utilizing the low energy and variable
photon energy (hQ) characteristics of the beamline
BL7U, we have succeeded in directly observing
topological surface state [6].
To clarify the effect of indium substitution on theelectronic states of SnTe, we paid particular attention
to the momentum space around theCX point of thesurface Brillouin zone [Fig. 1(a)], because thetopological surface states appear in this momentum
region in SnTe [5]. Figures 1(b) and (c) represent a
direct comparison of near-EF ARPES intensity
between pristine and In-doped SnTe measured along ak cut crossing theC/ point. In SnTe, we observed ahighly dispersive holelike band which is attributed toan admixture of the bulk and surface states withdominant contribution from the surface state near EF,
as confirmed by the hQ independence. While theoverall dispersive feature is significantly broader in
In-SnTe, it is still possible to extract an intrinsic band
dispersion for In-SnTe by taking second derivatives[see Fig. 1(d)]. The result of such an analysis clearlyshows a linearly dispersive holelike band approachingEF, which is similar to what is found in pristine SnTe.
This result demonstrates that the topological surface
state is likely to be present in In-SnTe. Thisconclusion is further supported by the observation of
the “M”-shaped band dispersion along the C*CX cut[Fig. 1(e)], which can be regarded as a fingerprint of
the Dirac-cone surface state of a TCI [5] where thecalculated bulk-band structure never shows any
M-shaped dispersion near EF.
The present experiments elucidate that the bulk
band inversion, which makes SnTe a TCI, is kept
unchanged in In-SnTe. This band inversion and ourobservation of the topological surface state in In-SnTeassure that this material provides a fertile ground forthe study of TSC [6].

Fig. 1. (a) Bulk fcc Brillouin zone and corresponding
tetragonal (001) surface Brillouin zone. (b) and (c)Comparison of near-EF intensity measured with hQ =21 eV plotted as a function of ky and binding energy
across theC/ point. (d) Second derivative of the datain (c). (e) Comparison of the band dispersion derived
from the second derivatives of the MDCs along the
C*CX cut between pristine SnTe (left) and In-doped
SnTe (right).
[1] M. Z. Hasan and C. L. Kane, Rev. Mod. Phys. 82(2008) 3045.
[2] X.-L. Qi and S.-C. Zhang, Rev. Mod. Phys. 83(2011) 1057.
[3] S. Sasaki et al., Phys. Rev. Lett. 109 (2012)
217004.
[4] L. Fu, Phys. Rev. Lett. 106 (2011) 106802.
[5] Y. Tanaka et al., Nature Phys. 8 (2012) 800.
[6] T. Sato et al., arXiv:1212.5886.

115

BL7U

Temperature Dependence of Auger-Free Luminescence in Cs2ZnCl4
A. Ohnishi1, M. Kitaura1, M. Sasaki1 and M. Itoh2
1

Depeartment of Physics, Yamagata University, Yamagata 990-8560, Japan
Department of Electrical and Electronic Engineering, Shinshu University,
Nagano 380-8553, Japan

2

In the present study, temperature dependence ofAuger-free luminescence (AFL) in Cs2ZnCl4 has
been investigated in the temperature range T =15300
K. Experiments were performed at the BL-7B beamline of UVSOR. This report is one of results publishedin ref. 1.
Temperature dependence of emission spectra ofCs2ZnCl4 were measured under photo-excitation at
21.4 eV. Typical results at several different
temperatures are shown in a relative scale in Fig. 1.
Three bands peaking at 3.3, 4.2 and 4.8 eV at 15 K are
the AFL in Cs2ZnCl4, which come from radiativetransitions between the Cl 3p valence band and the Cs
5p outermost-core band. On increasing thetemperature, spectral widths of the 3.3 and 4.8 eVbands become broaden appreciably, while that of the
4.2 eV band is almost unchanged. This situation isclearly recognized in Fig. 2, where the full width at
half maximum (FWHM) of the three bands is plotted
as a function of temperature.
The existence of two AFL bands peaking at 4.2 and4.8 eV is discussed. As shown in Fig. 2, when T is
increased from 15 K, the spectral width of the 4.8 eVband indicates a remarkable broadening, while that of
the 4.2 eV band is almost unchanged. Meanwhile, theirdecay times were identical to each other. It is, therefore,
supposed that the difference in thermal broadening is
attributed to the difference in the final state of theAuger-free transition, not the difference in the initialstate. In this connection, it is worth noting that the 4.2
and 4.8 eV bands in Cs2ZnCl4 are very similar innature to the AFL in CsCl [2], in which two bands at
4.5 and 5.2 eV are also ascribed to radiative transitions
between the Cl 3p valence band and the Cs 5p
outermost-core band. For CsCl, Fukaya et al. [3]. havetheoretically studied the temperature dependence of
AFL spectra by an extended deformable cluster model,
which is based on a supposition that a core holeself-traps weakly by inducing lattice deformation
around itself. Their theoretical study gives asatisfactory agreement with the experimental
observation. By referring to their arguments, weconsider on the existence of two AFL bands at 4.2 and4.8 eV as follows. The high-energy band at 4.8 eV
comes from the Auger-free transition of a self-trappedcore hole to a localized state in the valence band due toan attractive potential of lattice deformation created in
the initial state. The final state of the low-energy bandat 4.2 eV, on the other hand, is an extended state in thevalence band without lattice deformation. It is also
supposed that the lattice relaxation of core holes may

116

play an important role for the 3.3 eV band, because
this band becomes broadened significantly withincreasing the temperature.

Fig. 1. Emission spectra measured at T = 15, 70, 130,210 and 300 K under photo-excitation at 21.4 eV.

Fig. 2. Temperature dependence of the FWHMs of the
3.3, 4.2 and 4.8 eV bands.
[1] A. Ohnishi, M. Kitaura, M. Itoh and M.Sasaki, J.
Phys. Soc. Jpn. 81 (2012) 114704.
[2] M. Itoh, M. Kamada and N. Ohno, J. Phys. Soc.
Jpn. 66 (1997) 2502.
[3] M. Fukaya, Y. Kayanuma and M. Itoh, J. Phys.
Soc. Jpn. 71 (2002) 2557.

BL7B

Luminescence of CsCl Heavily Doped with CsI
N. Ohno and K. Sakae
Graduate School of Engineering, Osaka Electro-Communication University, Neyagawa, Osaka 572-8530, Japan

Stimulation in iodine absorption bands of dilute
I–-doped alkali chlorides produces characteristic
luminescence bands under excitation with UV light orwith X-rays at low temperatures. These luminescencebands have been well explained in terms of localized
relaxed excitons at ICl– molecule (I– monomer) and acomplex of two iodine ions (I– dimer) [1, 2]. However,
optical and luminescence properties of heavily iodinedoped alkali chloride crystals have not been examinedsufficiently for applying to high efficient scintillationmaterials. The present report describes the results of
CsCl heavily doped with CsI.
The crystals of CsCl:I were grown by the Bridgeman method from reagent grade CsCl added with anappropriate amount of CsI (up to 3 mol%). The photoluminescence and photoexcitation spectra were
measured at BL7B station. The photoluminescence
spectra excited with photons near the exciton
absorption region of CsCl were almost the same as
those of the previous studies [3, 4]: two luminescencebands peaking at 3.92 eV (monomer) and 5.12 eV(dimer) at 15 K. Figure 1 shows the photoexcitation
spectra for the monomer (blue) and the dimer
emission (red) for 3 mol% CsCl:I. The excitation
spectrum for the monomer is quite similar with thatfor the dilute case [3]. However, the spectrum for the
dimer band is found to show a quite different
behavior with heavily doped crystals [4]. This clear
low energy tail of the excitation band for the dimer
emission suggests that there coexist dimers, trimers
and lager sizes of I – ions (CsI cluster) in heavilydoped CsCl:I crystal as can been found in heavilydoped KCl:I [5].
The luminescence energies of the trimers andclusters of I– ions in heavily doped CsCl:I crystals are
expected to be different from that of I– dimers. We
have examined the dimer emission spectra excited atvarious photon energies. The results are shown in Fig.
2. It is clearly confirmed that the peak energy of the
dimer band moves towards the low energy side when
excited with photons of lower energy. Therefore, theluminescence bands are supposed to be the composite
bands due to radiative annihilation of the relaxed
exciton at dimers, trimers and clusters of I – ions [5].
In CsCl crystals containing CsI above 1 mol %,there exists a small amount of dimer centers ascompared with monomers, and moreover the amountof trimers and clusters of CsI is extremely smaller
than those of monomers and dimers. The present
results suggest that the excitons trapped in CsIclusters in heavily doped CsCl:I crystals would givethe high luminescence efficiency.

Intensity [arb.units]

10

CsCl:I 15K
3 mol%

6.0

emi 5.12 eV
emi 3.92 eV

6.5
7.0
Photon Energy [eV]Fig. 1. Photoexcitation spectra of CsCl:I (3 mol%)crystal for the monomer (blue) and dimer (red) bands.
7.0

CsCl:I 15K
3 mol%

6.9

6.8

Intensity [arb.units]

6.6

6.5

Excitation Energy [ev]

6.7

6.4

6.3

6.2

6.1
4.6

4.8

5.0

5.2

5.4

Photon Energy [eV]Fig. 2. Luminescence spectra of CsCl:I (3 mol%)crystal excited with photons of various energies
ranging from 6.08 to 6.90 eV.
[1] N. Nagasawa, J. Phys. Soc. Jpn. 27 (1969) 1535.
[2] K. Kan’no, K. Tanaka and T. Hayashi, Rev. Solid
State Sciences 4 (1990) 383, and references therein.
[3] M. Yoshida and N. Ohno, Proc. Int. Conf. on
Excitonic Processes in Condensed Matter (1996) 231.
[4] N. Ohno and A. Ohno, UVSOR Activity Report 38(2012) 83.
[5] A. Ohno and N. Ohno, Phys. Status Solidi C 8(2011) 112.

117

BL7B

Electronic Structure of the ZnO Treated by Microwave
K. Yoshida1, T. Sonobe2, H. Zen1, K. Hachiya2, K. Okumura1, K. Mishima1, M. Inukai1,
H. Negm1, M. Omer1, Y.-W. Choi1, R. Kinjo1, T. Kii1, K. Masuda1 and H. Ohgaki1
1

2

Institute of Advanced Energy, Kyoto University, Gokasyo, Uji, Kyoto 611-0011, Japan
Graduate School of Energy Science, Kyoto University, Yoshida-honmachi, Sakyo-ku, Kyoto 606-8501 Japanthat a new energy band was created at lower energy
than the conduction band by MW irradiation, and theexcitation and relaxation process of electron waschanged by the effect of the new energy band. As theconclusion, we found that the MW irradiation madesignificant change of the electronic structure of ZnO.

Microwave (MW) heating is considered as anadvanced method for a material processing, since it
has several unique advantages such as rapid andselective heating over conventional methods. To date,
several approaches have been investigated. For
example, K.M Parida and S. Parija achieved theenhancement of a photocatalitic activity of ZnO by
irradiating the ZnO with MW [1]. In addition, theactivity as a catalyst of MgO in chemical reaction was
also improved by irradiating the MgO catalyst with
MW [2]. In this way, MW heating is considered as aone of useful techniques for improving properties ofthe functional materials. However, the change of thephysical property, especially electronic structure, by
MW irradiation has not been clarified well. The
clarification of the effect of MW irradiation onelectronic structure is important for design ofmaterials such as photocatalyst, solar cells or material
processing. Therefore, we investigated the electronic
structure of the material treated by MW.
The photoluminescence was measured for the
analysis of the electronic structure. BL7B was used as
the light source and photon energy was changed from2.92 eV (425 nm) to 3.54 eV (350 nm). A CCD array
cooled by liquid nitrogen was used as the detector.
The exposure time was 10 s. The measurement
temperature was room temperature. Two types of
ZnO were prepared. One was sintered at 873 K for 2
hours and not irradiated with MW. The other was
sintered at 873 K for 2 hours and irradiated with MWof 500 W for 10 minutes. The treatment method of
MW irradiation is shown in the reference [3].
Figure 1 is the photoluminescence spectra of ZnO
with the MW irradiation. The sharp peaks from 1.5
eV to 1.8 eV and from 2.5 eV to 3.7 eV are thesecond order diffraction light of light source andfundamental excitation light, respectively. A broadband whose peak energy is 2.4 eV was observed.
In addition, the black and red dots in Fig. 2 show
the PLE (photoluminescence excitation) spectra for
the intensity of photoluminescence at 2.4 eV from
ZnO with and without MW irradiation. In Fig. 2, thepeak intensity of ZnO without MW irradiation is seen
constant in any excitation energy. In contrast, in thecase of the ZnO with MW irradiation, the intensity ofthe broad band peaks showed strong dependency on
the excitation photon energy. The maximum intensity
was observed at excitation energy of 3.21 eV. The
black arrow in Fig. 2 shows the band gap energy(3.27 eV) of ZnO. From these results, it is considered

Fig. 1. Photoluminescence spectra of ZnO with MW
irradiation.

Fig. 2. PLE spectra of the intensities at 2.4 eV from
ZnO with and without MW irradiation.
[1] K. M. Parida, et al., Solar Energy 80 (2006) 1048.
[2] H. Mirzaei, et al., Chin. J. Catal. 33 (2012) 1502.
[3] T. Sonobe, et al., Jpn. J. Appl. Phys. 49 (2010)
080219.

118

BL8B

Ultraviolet Photoelectron Spectra of Lu Encapsulated Fullerenes (I)T. Miyazaki1, R. Sumii 2,3, H. Umemoto4, H. Okimoto4, T. Sugai4, H.Shinohara4 and S. Hino1
1

Graduate School of Science and Engineering, Ehime University, Matsuyama, 790-8577, Japan
2
Institutes for Molecular Science, Okazaki, 444-858, Japan
3
Research Center for Materials Science, Nagoya University, Chikusa-ku, Nagoya, 464-8602, Japan
4
Graduate School of Science, Nagoya University, Chikusa-ku, Nagoya, 464-8602, Japan

119

The UPS of Lu2C2@C82 and Y2C2@C82 are almost
identical but that of Lu2@C82 shows slight differencesfrom them. These differences might be attributed tothe difference in the amounts of transferred electrons.
Probably, the amounts of transferred electrons in
Lu2@C82 and Lu2C2@C82 are so different that theirelectronic structure is modified differently. Lu4f7/2
and 4f5/2 levels may be helpful to estimate them. The
oxidation state of entrapped Lu atom might be +3.
Since Lu4f7/2 and Lu4f5/2 binding energies of Lu@C82
and Lu2@C82 are almost the same, the electronic
configuration might be (Lu3+)2@C826-. Possibly theoriginal oxidation state of Lu atoms in Lu2C2@C82 is+3, but entrapped C2 might receive two electrons
from them and hybridization or back donation takes
place among Lu atoms and C atoms resulting Lu-3+į
state.
㩷

Photoelectron counts

Fullerene cages encapsulate single as well as
multiple metal atoms, metal nitrides and metal-
carbides. Encapsulated metal atom(s) donate electrons
to the cage, and affect the electronic structure of thefullerene cage [1, 2]. The amounts of the transferred
electrons depend on the entrapped species and thefullerene cages. Recently, Lutetium atom(s) andlutetium-carbide encapsulated C82 fullerenes, Lu@C82(I), Lu2@C82 (II), Lu2@C82 (III), Lu2C2@C82 (II) andLu2C2@C82 (III) have been isolated. The NMR study
revealed their cage symmetry, C2v (82:9) for Lu@C82(I), Lu2@C82 (II) and Lu2C2@C82 (II), C3v (82:8) for
Lu2@C82 (III) and Lu2C2@82 (III). In the current work,
the UPS of Lu@C82 (I), Lu2@C82 (II), Lu2@C82 (III),
Lu2C2@C82 (II) and Lu2C2@C82 (III) will be presented
and validity of the empirical rule is examined.
Ultraviolet photoelectron spectra were measured at
BL8B2 of Ultraviolet Synchrotron Orbital Radiation
Facility of Institute for Molecular Science. The
measured UPS were referenced against the Fermi
level (EF) of gold deposited on the sample disk before
the measurements.
The valence band UPS of Lu@C82 (I), Lu2@C82 (II)and Lu2C2@C82 (II) obtained with hv = 20㧙55 eV.
Their onset energy (Eonset) are 0.25 eV (Lu@C82 (I))
and 0.64 eV (Lu2@C82 (II) and Lu2C2@C82 (II)), which
are much smaller than that of empty C82 (1.2eV).
These are the results of electron transfer from theentrapped species to the cage. These fullerenes aresemi-conductive. There are several structures labeledĮ – į and A – E in the UPS of Lu@C82 (I), Lu2@C82(II) and Lu2C2@C82 (II). The UPS of Tb@C82,
Er@C82 and Y2C2@C82 all of them have the same C2v
symmetry are also shown in Fig. 4. Remarkabledifference among these UPS is observed in the 9㧙11eV region. While there is only one structure labeled İ
is observed in the UPS of Tb, Er, Y2C2 entrappedfullerenes, two structures labeled X and Y are
observed in the UPS of Lu entrapped fullerenes. The
ionization energies of Lu 4f7/2 and 4f5/2 levels of Lu
metal are 7.5 eV and 8.9 eV, respectively. Binding
energies of X and Y are ranging from 9.3㧙9.8 eV
and 10.8㧙11.2 eV, respectively, and they are muchhigher than those of Lu metal atoms by 2.0㧙2.5 eV.
Further, energy separation between structures X and
Y is 1.4㧙1.5 eV, which coincides with that of Lu4f7/2
and Lu4f5/2. Thus, structures X and Y might be due toentrapped Lu atom(s). This could be the firstobservation of the photoelectrons of entrapped
species in the ultraviolet photoelectron spectroscopy.

X

Y

G J

E

hQ= 40eV

D

E
DC

B
A

E

DC

Lu2C2@C82(II)B
A

Lu2@C82(II)

D

C

B

E

A

DC B

G

J

Lu@C82(I)

A

E
D

H

D

Y2C2@C82-C2v

CB

D CB A
Er@C82-C2v

A
Tb@C82-C2v

12

10

8

6

4

2

0

Binding Energy / eV

Fig. 1. UPS of endohedral fullerenes at hȣ= 40eV.
[1] T. Miyazaki et al., Chemical Physics 378 (2010)11.
[2] T. Miyazaki et al., Chemical Physics 397 (2012)87.