BL1B

Electronic Structure and Correlation Effects in K0.49RhO2
R. Okazaki1, Y. Nishina1, Y. Yasui1, S. Shibasaki2 and I. Terasaki1
1

Department of Physics, Nagoya University, Nagoya 464-8602, Japan
Department of Applied Physics, Waseda University, Tokyo 169-8555, Japan2

The layered cobalt oxide NaxCoO2 is a fascinating
material because of its highly unusual transport
properties, i.e., a large Seebeck coefficient with low
electrical resistivity [1], as well as a rich electronic
phase diagram. With increasing Na content x, thesystem varies from a Pauli-paramagnetic metal to a
Curie-Weiss metal through a charge-ordered insulator
around x = 0.5. Furthermore, hydration induces asuperconductivity near x = 0.3.
To elucidate the origin of such intriguing
phenomena in this material, the knowledge of thedetailed electronic structure is crucially important.
The optical conductivity spectra in NaxCoO2 captured
wide electronic structure [2,3], which can be assigned
to the local density approximation (LDA) band
structure. However, the LDA + Hubbard U
calculations, which well explain the results of theangle-resolved photoemission spectroscopy studies
on NaxCoO2, seriously worsen the consistency
between the LDA and the optical conductivity spectra[4], puzzling a precise role of electron correlations forthe electronic structure in this compound.
Here we investigate an optical property ofisostructural 4d-electron Rh oxide K0.49RhO2 [5]. We
used the beamline BL1B in UVSOR facility tomeasure the reflectivity spectra of K0.49RhO2 single
crystals in an energy region of 2 – 30 eV, whichenables us to evaluate the optical conductivity
through the Kramers-Kronig analysis. In Fig. 1 (a),we show the optical conductivity spectrum below 8 eV.
The peak locations are well defined near 0.9, 3.1, and
5.5 eV as labeled by Ȗƍ, ȕƍ, and Įƍ, respectively. For
comparison, we depict the room-temperature opticalconductivity spectra of NaxCoO2 in Fig. 1 (b), whichwere taken from previous reports [2,3]. In NaxCoO2,
three conductivity peaks labeled by Ȗ, ȕ, and Į areclearly recognized at 0.5, 1.6, and 3 eV, respectively.
Within the LDA scheme, the Ȗ peak corresponds to thetransition between t2g bands and the ȕ peak to t2g-eg
transition. The Į peak is responsible for the
charge-transfer transition from occupied O 2p tounoccupied eg states, as schematically illustrated inFig. 1 (c). The peak positions in K0.49RhO2 are clearlyshifted to higher energies relative to the spectra of
NaxCoO2. It is also found that the peak widths arebroader than those of NaxCoO2. These differences arenaively captured by broader 4d orbitals in K0.49RhO2
as schematically shown in Fig. 1(d). A large
crystal-field splitting pushes the Į and ȕ peaks in
NaxCoO2 to higher energy Įƍ and ȕƍ peaks in
K0.49RhO2, respectively. The bandwidth of t2g
complex is expanded by broad orbitals of Rh 4delectrons, leading to a higher-energy shift of the Ȗ

peak as well. We also find that the effective mass of
K0.49RhO2 is nearly half that of NaxCoO2 from acomparison of the spectrum weights. The electronic
structure and correlation effects in K0.49RhO2 are welldescribed by the difference between Co 3d and Rh 4d
orbitals.

Fig. 1. Optical conductivity ı1(Ȧ) of (a) K0.49RhO2
and (b) NaxCoO2. The data for NaxCoO2 was takenfrom previous reports [2,3]. The peak locations in
K0.49RhO2 (NaxCoO2) spectra are labeled by Įƍ (Į), ȕƍ(ȕ), and Ȗƍ (Ȗ), which correspond to the O 2p-eg, t2g-eg,
and t2g-t2g transitions, respectively, as illustrated inschematic energy diagrams (c,d).
[1] I. Terasaki, Y. Sasago and K. Uchinokura, Phys.
Rev. B 56 (1997) R12685.
[2] N. L. Wang et al., Phys. Rev. Lett. 93 (2004)
237007.
[3] J. Hwang, J. Yang, T. Timusk and F. C. Chou,
Phys. Rev. B 72 (2005) 024549.
[4] M. D. Johannes, I. I. Mazin and D. J. Singh, Phys.
Rev. B 71 (2005) 205103.
[5] R. Okazaki et al., Phys. Rev. B 84 (2011) 075110.

77

BL2A

Characterization of Phosphorus Doped Titanium Oxide
T. Kurisaki, M. Iwase, Y. Nagino, S. Yokoyama and H. Wakita
Department of Chemistry, Faculty of Science, Fukuoka University, Nanakuma, Jonan-ku, Fukuoka 814-0180,
Japan
to analyze this change from comparison of P K-edge
XANES and calculated spectra by DV-XĮ molecularorbital calculations.

Normalized Intensity/ a.u.

Doping TiO2 with nonmetal such as nitrogen [1],carbon [2] and sulfur has received a lot of attention inrecent years since it can extend the photoresponse of
TiO2 from ultra violet to the visible region, which isadvantageous for using the sunlight as the energy
source. As for Phosphorus-doped TiO2 withvisible-light photocatalytic activity, two kinds of
P-TiO2 [3,4] prepared using phosphate as precursor of
P has been reported. However, some reports showedthat P-TiO2 prepared using phosphate cannot absorb
visible-light. Thus, we attempted to prepare P-TiO2
using phosphide as a new method. P-TiO2 wassynthesized through the hydrolysis of titanium
tetraisopropoxide in suspension containing TiP
compound [5], which was prepared by the treatmentof titanium tetrachloride with cyclohexylphosphine.
The synthesized P-TiO2 nanoparticles exhibit avisible-light photocatalytic activity. However, theelectronic structure of phosphorus in the P-TiO2
nanoparticles is not well known.
For various light element compounds, we havestudied the electronic structure by X-ray absorption
spectroscopy [6]. These results suggested that there isa correlation between XANES spectra and the local
structures.
In this work, we performed the XANES spectra
measurement about various phosphorus doped
titanium oxides and reference samples such astitanium phosphide (TiP). The obtained experimental
XANES spectra are analyzed using the calculated
theoretical spectra from DV-XĮ calculations. The
XANES spectra were measured at BL2A of the
UVSOR in the Institute of Molecular Science,
Okazaki [7]. The ring energy of the UVSOR storage
ring was 750MeV and the stored current was 300 mA.
P K-edge XANES spectra were recorded in the regionsof 2125-2270eV by use of two InSb crystals. The
absorption was monitored by the total electron yieldusing a photomultiplier. The samples were spread into
the carbon tape on the first photodynode made of
CuBe of the photomultiplier.
Figure 1 shows the observed P K-edge XANES
spectra for the TiP and the phosphorus doped titaniumoxide. The P K-edge XANES spectra of TiP and
P-TiO2 show different peak profiles at second peaks.
The peaks that appear at approximately 2176 and2185 eV on observed XANES spectrum of TiP arelabeled A and B. The peak positions of A and B are
estimated to the P-3 and P5+. On the other hand, theobserved XANES spectrum of P-TiO2 showed only
one peak at 2186 eV. The result suggests that
phosphorus in the synthesized P-TiO2 nanoparticle
surface exists as phosphoric acid. We are going to try

A

B

TiP
P-TiO22160 2170 2180 2190 2200 2210 2220
Energy / eV
Fig. 1. Observed P K-edge XANES spectra of TiP
and P-TiO2.
[1] R. Asahi et al., Science 293 (2001) 269.
[2] Y. Nosaka et al., Sci. Tech. Adv. Mater. 6 (2005)
143.
[3] L. Lin and W. Lin, Chem. Lett. 34 (2005) 284.
[4] Q. Shi et al., J. Mol. B: Enzym. 43 (2006) 44.
[5] T. S. Lewkebandara et al., Chem. Mater. 7 (1995)
1053.
[6] T. Kurisaki et al., Anal. Sci. 24 (2008) 1385.
[7] S. Murata et al., Rev. Sci. Instrum. 63 (1992)
1309.

78

BL2A

Mg-K Edge XAFS Measurement of Mg Doped Hydroxyapatite by
Fluorescence Mode
M. Sato1, Y. Nishio2, T. Nagayasu2 and A. Nakahira1, 2
1

2

Kansai Center for Industrial Materials Research, Tohoku University, Osaka 599-8531, Japan
Department of Material Science and Engineering, Osaka Prefecture University, Osaka 599-8531, Japan

Hydroxyapatite (Ca10(PO4)6(OH)2, HAp) has been
well understood as an alternate materials of our hardtissue because of their excellent osteoconductivity
and biocompatibility. Furthermore, because HAp also
has good protein adsorption ability and ion exchange
ability, many studies for bioactivity and dissolution
behavior of Mg, Mn, Fe, Si, Zn doped HAp havebeen performed. Since we could not obtain effective
data of Mg doped HAp by total electron yield modeso far, we tried fluorescence mode and investigated a
local structure of around Mg atom of Mg doped HAp.
In this study, Mg doped HAp were prepared by
microwave
assistedhydrothermal
process,
respectively, and local structure of around P atom wasinvestigated by XAFS measurement.
0.1 mol/l Ca(NO3)2, (NH4)2HPO4 and Mg(NO3)solutions were used as starting materials. These
solutions were mixed up each other becoming theratio of Ca to P of 1.67 and the ratio of Mg from 1 to
15 mol% for Ca solution, respectively. Mixed
solutions were set into autoclave and hydrothermallytreated at 423 K for 60 min. with irradiation of
microwave (2.45 GHz). After that, they were filteredand dried at 323 K for overnight. Mg-K edge XANES
spectra of Mg doped HAp powders were measured byfluorescence method at room temperature using beryl
double-crystal monochrometer at BL2A station of
UVSOR and obtained spectra were compared to thatobtained by a total electron yield mode.
Figure 1 shows a comparison of Mg-K edge
XANES spectra of Mg doped HAp collected by total
electron yield mode and fluorescence mode.
Intensity of obtained spectra by total electron yieldmode was too weak to analyze. Consequently,
obtained spectrum is strongly affected by noise whichis caused by a top-up. On the other hand, clear spectra
can be obtained in the case of fluorescence mode.
From analysis using fluorescence mode and P-K
edge XANES data, it is indicated that the Mg was
replaced with the Ca (II) site. In addition, it is thoughtthat the solid solubility limit of Mg ion into a HAp
structure is approximately 15 mol%.

79

Fig. 1. Comparison of Mg-K edge XANES spectra of
Mg doped HAp collected by total electron yield modeand fluorescence mode.

BL2A

Investigation of Local Structure of Si-K and Al-K Edge in Zeolites
Prepared from Waste Materials
M. Sato1, Y. Takamatsu2, K. Kumadani2 and A. Nakahira1, 2
1

Kansai Center for Industrial Materials Research, Tohoku University, Osaka 599-8531, Japan
Department of Material Science and Engineering, Osaka Prefecture University, Osaka 599-8531, Japan2

The depletion of natural resources is one of the ourserious problems. Therefore, the development of thenovel recycling technology has been performedenergetically. Blast furnace slag (BF slag) is one of
the waste materials that the development of theeffective recycling technology and establishment ofrecycle system become the urgent assignment. The
BF slag has been produced approximately 25 million
tons per year and recycled as Portland cement, basecoarse materials, fine aggregate for concrete andground improvement materials, etc. However,recycling rate of BF slag is insufficient by comparing
to the amount of generation. In this study, A, P and Y
type zeolite were prepared using BF slag as a starting
material to reduce an emission of waste materials, andlocal structure of BF slag and its products were
investigated.
Water cooled BF slag was ground to become their
particle size less than 70 Pm. Ground slag powder
was undergone an acid treatment to remove a Cacomponent. And then, Ca removed slag powder washydrothermally treated in 0.23 mol/l NaOH solution
at 368 K for 48 h. In this study, the ratio of Si to Al
was changed in the range from 0.5 to 2.4. Si-K and
Al-K edge XANES spectra of samples were measured
by a total electron yield mode at room temperatureusing KTP double-crystal monochromator at BL2A
station of UVSOR.
Figure 1 shows Si-K edge XANES spectra of watercooled BF slag, acid treated BF slag and A typezeolite prepared using acid treated BF slag. The local
structure around Si atom of BF slag is relatively
amorphous and changed by acid treatment.
Furthermore, the local structure of A type zeolite
prepared using slag as a starting material differedfrom commercial A type zeolite and that synthesizedusing reagents.
Figure 2 shows Al-K edge XANES spectra of A
and P type zeolites prepared using acid treated BF
slag. Obtained spectra of A type zeolite preparedusing BF slag was different from the result of Si-K
edge spectra, and similar spectra to that ofcommercial A type zeolite was obtained. This result
indicates that the local structure of around Al atom ofsample is almost same.

Fig. 1. Si-K edge XANES spectra of water cooled
BF-slag and its products.

Fig. 2. Al-K edge XANES spectra of water cooled
BF-slag and its products.

80

BL2A

Investigation of Local Structure of P-K Edge in Fe, Mg and Mn Doped
Hydroxyapatite
M. Sato1, Y. Kawabe2, S. Misu2, S. Hayashi2 and A. Nakahira1, 2
1

2

Kansai Center for Industrial Materials Research, Tohoku University, Osaka 599-8531, Japan
Department of Material Science and Engineering, Osaka Prefecture University, Osaka 599-8531, Japan

Hydroxyapatite (Ca10(PO4)6(OH)2, HAp) has been
well understood as a alternate materials of our hardtissue because of their excellent osteoconductivity
and biocompatibility. Furthermore, because HAp also
has good protein adsorption ability and ion exchange
ability, many studies for bioactivity and dissolution
behavior of Mg, Mn, Fe, Si, Zn doped HAp havebeen performed.
In this study, Fe, Mg and Mn doped HAp wereprepared by conventional wet process, hydrothermal
process and microwave assisted hydrothermal process,respectively, and local structure around P atom wasinvestigated by XAFS measurement.
0.1 mol/l Ca(NO3)2, (NH4)2HPO4 and FeCl3,
Mg(NO3) and MnCl2 solutions were used as starting
materials. These solutions were mixed up each otherbecoming the ratio of Ca to P of 1.67 and the ratio of
Fe from 0.1 to 1 mol%, Mg from 1 to 15 mol% and
Mn from 1 to 5 mol% for Ca solution, respectively. In
the case of wet process, mixed solution was aged for
1 h at room temperature. For the hydrothermal andmicrowave assisted hydrothermal process, mixed
solutions were set into autoclave and samples wereprepared at 423 K for each preparation time. After
that, they were filtered and dried at 323 K for
overnight. P-K edge XANES spectra of obtained
HAp powders were measured in a total electron yieldmode at room temperature using InSb double-crystal
monochrometer at BL2A station of UVSOR.
From XRD measurement, obtained all samples had
a HAp structure. Figure 1 shows P-K edge XANES
spectra of Fe, Mg and Mn doped HAp powders. In
the case of Mn and Fe doping, obtained P-K edge
XANES spectra of Fe and Mn doped HAp samples
were similar to that of commercial HAp, and achange of the spectral pattern was not clearlyobserved within any ratio of Fe and Mn. This result
indicates that the local structure of around P atom of
Fe doped HAp samples is almost same withcommercial HAp. From this result, it is estimated thatthe doped Fe and Mn substitutes to Ca site. On theother hand, minimal peak shift and broadening ofspectrum was observed for the 15 mol% Mg doped
HAp. This result may be caused by the decrement ofcrystallinity and generation of Mg3(PO4)2 phase.

Fig. 1. P-K edge XANES spectra of Fe, Mn and Mg
doped HAp (black line) and references (red line).

81

BL3B

Energy Transfer Caused by Emission Reabsorption in CsI:Agí Crystals
T. Kawai1, S. Nagata1 and T. Hirai2
1

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

2

Energy transfer mechanism from host crystals to
impurity ions has been widely studied from theviewpoint of applications of scintillators and/or
phosphors [1]. In CsI crystals doped with Tl+ or Na+
ions, the hopping motion of self-trapped excitons or
Vk centers plays an important role in the energy
transfer. In this study, we have investigatedluminescence properties of CsI:Agí crystals in orderto reveal the energy transfer mechanism from the hostCsI crystals to the impurity Agí ions.
Figure 1 shows the absorption and luminescence
spectra of the Agí centers doped in the CsI crystals at
10 K. The C absorption band due to the Agí centers isobserved at 3.76 eV. Excitation by the photon energy
corresponding to the C absorption band on theCsI:Agí crystals induces luminescence bands peaking
at 2.53 and 3.45 eV. These luminescence bands are
attributed to the radiative transitions from the relaxed
excited states of 3T1u and 1T1u in the Agí centers andare called the A’ and C’ luminescence bands,
respectively [2].
Under excitation at 6.42 eV which is higher thanthe band-gap energy of CsI crystals, the broad
luminescence bands peaking at 3.6 eV are observed inaddition to the A’ luminescence band. The 3.6 eVluminescence bands are attributed to the off-center
self-trapped excitons (STEs) in CsI host crystals.
Though the STE luminescence band usually has astandard Gaussian shape, the off-center STE
luminescence band of the CsI:Agí crystals has asmall shoulder at 3.45 eV and a slight dent around3.70 eV. The small shoulder at 3.45 eV comes fromthe C luminescence band of the Agí centers. The dent
at 3.70 eV in the off-center STE luminescence band is
attributed to the reabsorption by the C absorption
band, because the C absorption band located around3.7 eV is covered with the off-center STE
luminescence band. This fact implies that the Agícenters reabsorb the off-center STE luminescence.
Figure 2 shows the excitation spectra for the A’ andoff-center STE luminescence band up to the vacuum
ultraviolet energy region. The excitation spectra for
the A’ luminescence bands exhibit a remarkable
response at 3.78 eV which corresponds to the Cabsorption band. In general, luminescence bands dueto the Tl+-type centers doped in alkali halide crystals
are not efficiently excited in the energy region above
the band gap of the host crystal, because
photo-excited carriers are immediately self-trapped
owing to the strong electron-phonon interaction.
However, the luminescence bands due to the Agícenters doped in CsI crystals are efficiently excitedeven in the energy range above the band gap of CsI

500

450

Wavelength (nm)
400
350

2

STE

-

CsI:Agex. 6.42 eV
CsI:Ag ex. 3.82 eV
non-doped CsI

10 K

C
1

A'

C'

2.5

3.0
3.5
Pnoton Energy (eV)0Absorption Intensity (O. D. )Luminescence Intensity (arb. units)

host crystals. The excitation spectrum for the A’
luminescence band exhibits the similar structure tothat for the off-center STE luminescence band in thisenergy range above the band gap. These results
indicate that the efficient energy transfer from the CsI
host crystals to the Agí centers occurs through thereabsorption of the off-center STE luminescence by
the C absorption band.

4.0

Luminescence Intensity (arb. units)

Fig. 1. Luminescence and absorption spectra of
CsI:Agí and non-doped CsI crystals.

350 300

250

Wavelength (nm)
200

150
10 K

non-doped CsI
for 3.59 eV
CsI:Ag for 2.52 eV

4.0

5.0

6.0
7.0
8.0
Photon Energy (eV)

9.0

10.0

Fig. 2. Excitation spectra for the A’ luminescenceband of CsI:Agí and the off-center STE luminescenceband of non-doped CsI crystals.
[1] M. J. Weber, J. Lumi. 100 (2002) 35.
[2] S. Shimanuki, M. Watanabe and T. Kawai, Phys.
Stat. Sol. (b) 208 (1998) 105.

82

BL3B

Relaxed Exciton Luminescence of CsCl Heavily Doped with CsI
N. Ohno and A. Ohno
Graduate School of Engineering, Osaka Electro-Communication University, Neyagawa, Osaka 572-8530, Japan
Extensive studies have been made on luminescencearising from localized relaxed excitons in alkali
chlorides containing iodine impurities. Stimulation in
iodine absorption bands of dilute I–-doped alkali
chlorides produces characteristic luminescence bands
under excitation with UV light or with X-rays at low
temperatures. These luminescence bands have been
well explained in terms of localized relaxed excitons
at ICl– molecule (I– monomer) and a complex of two
iodine ions (I– dimer) [1,2]. However, optical andluminescence properties of heavily iodine-doped
alkali chloride crystals have not been examinedsufficiently for applying to high efficient scintillationmaterials. The authors have reported luminescence
properties of KCl heavily doped with KI so far [3].
The present report describes the results of CsClheavily doped with CsI.
The crystals of CsCl:I were grown by the
Bridgeman method from reagent grade CsCl addedwith an appropriate amount of CsI (up to 5 mol %).
The optical measurements were made at 6 K.
The luminescence spectra excited with photons
near the exciton absorption region of CsCl were
almost the same as those of the previous studies [3]:two luminescence bands peaking at 3.95 eV (monomer emission) and 5.12 eV (dimer emission) are foundat 6 K. Photoexcitation spectra detected at 5.11 eV forvarious CsI mol % of CsCl:I crystals are shown in Fig.
1. The each spectrum has been normalized at unity at
the maximum. The excitation peaks at 6.50 and 6.65
eV of 0.01 mol % crystal move toward the lower
energy side with increasing CsI concentration. The
low energy shift of the excitation bands suggests that
there coexist dimers, trimers and lager sizes of I – ions(CsI cluster) in heavily-doped CsCl:I crystal as canbeen seen in the case of heavily-doped KCl:I [4].
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 photoluminescence spectra excited
at various photon energies. The results for 1 mol %crystal are shown in Fig. 2. It is clearly confirmed thatthe peak energy of the luminescence band moves
towards the low energy side when excited with lower
photon energy. These luminescence bands aresupposed to be the composite bands due to radiativeannihilation of the relaxed exciton at dimers, trimers
and clusters of I – ions [4].
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 thanthose of monomers and dimers. However, theluminescence intensities of such large-sized centers

Normalized Intensity

are found to be comparable with that of the dimer
emission. This fact suggests that the excitons trappedin CsI clusters in heavily doped CsCl:I crystals would
give the high luminescence efficiency. The similar
mechanism has been reported in and heavily-doped
KCl:I [4] and CsI:Na systems [5], where the observed
luminescence enhancement originates from excitonsin small-sized KI or NaI particles in host crystals.

CsCl:I 6K

1

5.11 eV
0.01mol%
1mol%
3mol%

0.5

0

7
8
Photon Energy [eV]Fig. 1. Photoexcitation spectra of CsCl:I crystals
detected at 5.11 eV for various CsI mol % at 6 K.

Intensity [a. u.]

6

6

CsCl:I 6K
1mol%
6.44 eV
6.28 eV3

6.20 eV
6.12 eV6.05 eV

0

4.5

5.0
5.5
Photon Energy [eV]Fig. 2. Photoluminescence spectra of CsCl:I (1 mol %)excited at various photon energies at 6 K.
[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] A. Ohno and N. Ohno, Phys. Status Solidi C 8(2011) 112.
[5] M. Nakayama, N. Ando, T. Miyoshi, J. Hirai
and H. Nishimura, Jpn. J. Appl. Phys. 41 (2002)
L263.

83

BL3B

Origin of Luminescence Bands in NaBi(WO4)2 Crystals
M. Kitaura1, M. Fujita2, A. Ohnishi1, M. Sasaki1 and Sangeeta31

Department of Physics, Facility of Science, Yamagata University, Yamagata 990-8560, Japan
2
Japan Coast Guard Academy, Kure 737-8512, Japan
3
Bhabha Atomic Research Center, Munbai 400 085, India

NaBi(WO4)2 belongs to the family of double
tungstates expressed by the chemical formula
NaT(WO4)2, in which T is occupied by trivalentcations. This material attracts interest for practical use
as Cerenkov radiator to detect ultra high-energy
radiation and charged particles. Despite of such animportant material in high-energy physics experiment,
optical properties of NaBi(WO4)2 have not beenmuch investigated, as compared to other metaltungstates. In the present study, reflectivity andphotoluminescence spectra of NaBi(WO4)2 have beenmeasured using synchrotron radiation.
The crystals of NaBi(WO4)2 were provided from
Bhabha Atomic Research Centre, Mumbai, India.
They were grown from melt by the Czochralski
method. The samples used in our experiment wereattached at the cold finger of a LHe flow-type
cryostate, and cooled down at 10 K. The reflectivity
spectra were measured using a calibrated silicon
diode in the measurement chamber. The photoluminescence spectra were measured for various
excitation wavelength by the combination of a grating
monochromator and a CCD detector.
Figure 1 shows the contour plot of excitationemission spectra of NaBi(WO4)2 (lower part),
together with reflectivity spectrum (upper part).
These data were measured at 10 K. A prominent peakis observed at 312 nm in the reflectivity spectrum. An
emission band appears at 538 nm under excitation
with photons around 340 nm. As the excitation
wavelength is decreased from 340 nm to 320 nm, the538 nm band is weakened, and another band appears
at 484 nm. This band is predominantly observed
under excitation in shorter excitation wavelength.
These results are almost agreement with the results by
Tyagi et al. [1].
Two emission bands are observed at 484 and 538
nm in NaBi(WO4)2 excited by photons in thefundamental absorption region. The 484 and 538 nm
bands are similar to the blue (443 nm) and green (551nm) bands in PbWO4, respectively. Itoh et al. [2] have
explained the origin of these bands as follows: Theblue band is ascribed to radiative decay of excitons
self-trapped on regular WO4 tetrahedra, while thegreen band is likely assigned to excitons localized on
WO6 octahedra of inclusions. NaBi(WO4)2
crystallizes in the scheelite structure in which W ionslocate inside tetrahedrons of four O ions. It is thus
more likely that the 2.65 eV band is linked to regular
WO4 tetrahedra. The 2.34 eV band may be due to
WO6 octahedra, because there is the possibility that
sodium tungstates composed of WO6 octahedra, e.g.,

84

NaWO3 and Na2W2O7, are included as low
temperature phases. Decay kinetics of the 2.65 and2.34 eV bands is now in investigation with Nd3+:YAG
laser system, in order to clarify excited state
dynamics of the self-trapped excitons of complex
molecular ion type.

Fig. 1. Reflectivity spectra (upper part) and contour
plot of excitation-emission spectra (lower part) of
NaBi(WO4)2 measured at 10K.
[1] M. Tyagi et al., J. Lumi. 132 (2012) 41.
[2] M. Itoh et al., Phys. Rev. B 62 (2000) 12825.

BL4B

Valence State Analysis of Co Ions in Pr1-xCaxCoO3-į
T. Yoshioka1 and T. Yamamoto1, 2
1Faculty of Science and Engineering, Waseda University, Tokyo169-8555, Japan
Institute of Condensed-Matter Science, Waseda University, Tokyo 169-8555, Japan

2

Rare-earth cobaltates, R1-xAxCoO3-į (R = rare-earth,A = alkaline-earth), have been extensively studied forlast fifty years because of their characteristic thermal,
electrical, and magnetic properties [1-3]. For athorough understanding of such properties, it isnecessary to investigate the charge compensation
mechanism due to the doping of the alkaline-earth
ions in RCoO3. However, the mechanisms of charge
compensation have not yet been thoroughly
understood for these rare-earth cobaltates withalkaline-earth ions. In this study, the valence state
analysis of Co ions in Pr1-xCaxCoO3-G (x=0, 0.5 arecarried out by the Co-L3 X-ray absorption near-edge
structure (XANES) measurements at different
temperature.
All Pr1-xCaxCoO3-G samples were synthesized by
the conventional solid-state reaction method. Co-L3
XANES spectra were recorded at BL4B in UVSOR
using the total-electron-yield (TEY) method. All thesample powders were mounted on carbon adhesive
tape. Synchrotron radiation from the storage ring was
monochromatized by a varied-line-spacing planegrating (800 lines/mm). The energy resolution of theincident beams (E/'E) was set to 3000 by tuning theslit width at the upper and lower reaches of the grating.
To see a temperature dependence of the Co-L3
XANES spectra, all the spectra were collected atroom temperature and 105 K.
Prior to the XANES analysis, all the samples werecharacterized by the X-ray diffraction (XRD). No
extra peaks were found in the observed XRD patterns
except for those of the perovskite structured
Pr1-xCaxCoO3-G. Then the samples were determined tobe crystallized in a single-phased orthorhombic
perovskite structure (Pbnm).
Observed Co-L3 XANES spectra of PrCoO3 andPr0.5Ca0.5CoO3-G are compared in Fig. 1. In order toinvestigate the difference in the spectral profiles
among these two, the observed spectra were
deconvoluted into three components by using
Gaussian functions (dashed lines in Fig. 1). It is foundthat relative intensity of peak A to B increases andpeak C to B decrease with doping Ca2+ ions both atroom temperature and 105K. In order to see thechange in spectral profiles of Co-L3 XANES
quantitatively, the relative intensities of peaks A and
C to B, i.e., IA/IB and IC/IB, respectively, are plotted in
Figs. 2(a) and (b), respectively.
As shown in Fig. 2, the relative intensities of peak
A and C to B increase and decrease, respectively, withincreasing of doped Ca2+ ions both at room
temperature and 105K. Furthermore, if we compare

the spectra at 105K to the spectra of room
temperature, the relative intensity IA/IB and IC/IB issmaller and larger, respectively. These experimental
results suggest that the distributions of Co 3d band of
Pr1-xCaxCoO3-G are different between at room
temperature and 105K.
(a)(b)
PrCoO3100 㧬105K

B

Normalized Intensity

Normalized Intensity

PrCoO3100 㧬RTC

50
A
0

Pr0.5Ca0.5CoO3-Ǭ
100 㧬RT
B
50

C

A

0
772

B
C

50
A
0

Pr0.5Ca0.5CoO3-Ǭ
100 㧬105K B
50

776
780
Energy (eV)

C

A

0
772

776

780

Energy (eV)Fig. 1. Observed Co-L3 XANES spectra of PrCoO3
and Pr0.5Ca0.5CoO3-G (a) at room temperature and (b) at
105K. Dashed lines denote spectra deconvoluted into
three components of the Gaussian function.
(b)

Relative intensity, IC/IB

Relative intensity, IA/IB

(a)
0.3
0.2
0.1
0

0

0.25

0.5

Ca concentration, x

0.5

㧬RT
㧬105K

0.4
0

0.25

0.5

Ca concentration, x

Fig. 2. Relative intensities of (a) Peak A to B, IA/IB,and (b) Peak C to B, IC/IB in Co-L3 XANES spectra ofPr1-xCaxCoO3-G (x=0, 0.5 as a function of theconcentration of Ca2+ ions.

[1] G. Ch. Kostogloudis et al., Solid State Ionics 106(1998) 207.
[2] H. Masuda et al., J. Phys. Soc. Jpn. 72 (2003)
873.
[3] S. Tsubouchi et al., Phys. Rev. B 69 (2004)
144406.
[4] J. Zhou et al., J. Phys.: Condens. Matter 20 (2008)
055222.

85

BL5U

Angle-Resolved Photoemission Spectroscopy of a Mixed Valence System
Sm1-xYxSK. Imura1, T. Hajiri1, 2, M. Kaneko2, Y. Nishi3, H. S. Suzuki4, N. K. Sato3, T. Ito2,
M. Matsunami1, 5 and S. Kimura1, 5
1

UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan
3
Graduate School of Science, Nagoya University, Nagoya 464-8602, Japan
4
Nuclear Scattering Group, National Institute for Materials Science, Tsukuba 305-0047, Japan
5
School of Physical Sciences, The Graduate University for Advanced Studies, Okazaki 444-8585, Japan
2

In the golden phase of x = 0.33 shown in Fig.1 (e),on the other hand, the top of the Sm2+ 4f state shifts to
the Fermi level. This result is consistent with themetallic property in the golden phase. The
observation suggests that the insulator-to-metaltransition occurs owing to the touch of the Sm2+ 4f
state to the Fermi level.

Samarium monosulfide (SmS) is a prototypicalcompound that exhibits an insulator-to-metaltransition by applying external pressure. This phasetransition is accompanied by a color change fromblack to golden-yellow, namely B-G transition. Theenergy gap of about Eg ~ 0.1 eV evaluated by anelectrical resistivity measurement at ambient pressure
decreases forward a critical pressure of the B-Gtransition. Although angle resolved photoemission
spectroscopy (ARPES) is one of powerful techniques
to study electronic structure as well as a mechanismof this transition, unfortunately, pressure study is
impossible.
On the other hand, it has been reported that the
B-G transition is induced by site substitution [1].
Then we focused onto the Sm1-xYxS system andperformed ARPES measurement in order to reveal themechanism of the B-G transition.
Single crystals of Sm1-xYxS (x = 0, 0.17, 0.33) weregrown by the Bridgman technique using ahigh-frequency induction furnace installed at NIMS
[Figs.1 (a) and 1 (b)]. ARPES measurement on thesecrystals was performed at the VUV-ARPES beamline
BL5U of UVSOR. The obtained inner potential V0values 13.4 eV for x = 0, 13.7 eV for x = 0.17 and15.2 eV for x = 0.33, by analyzing hQ-dependence (27- 84 eV) of energy distribution curve ofhighly-dispersive S 3p bands.
Figure 1 (c) shows the x-dependence of lattice
constant. As increasing x up to 0.17, lattice constantdecreases monotonically. At x = 0.17, the lattice
constant suddenly shrinks by the B-G transition. This
discontinuous volume change suggests a valence
Sm3+ + e-), because
transition of Sm ions (Sm2+3+
the ionic radius of Sm is smaller than that of Sm2+.
The ARPES image of pure-SmS near the * point(hQ = 61 eV) at 10 K is shown in Fig. 1 (d). The
dispersive feature of the S 3p bands at the binding
energy of about 3.2-6.5 eV is consistent with previous
ARPES study and LDA band structure calculation [2,3]. Flat bands in the binding energy below 2.5 eVoriginates from the multiplet structure of the Sm2+ 4f
final state. The top of the flat Sm2+ 4f state is far fromthe Fermi level. This is consistent with theactivation-type T-dependence of electrical resistivity
U(T) [4] and the absence of the Drude response of
the optical conductivity V(Z) [5].

Fig. 1 Single crystals of (a) pure-SmS (black phase)and (b) Sm0.67Y0.33S (golden phase). (c) Yttrium
substitution dependence of lattice constant. Dottedlines are guide to the eye. ARPES images near the *point on the X-*-X line of (d) x = 0 (hQ = 61 eV) and(e) x = 0.33 (hQ = 66 eV) at 10 K.
[1] T. Penny and F. Holtzberg, Phys. Rev. Lett. 34(1975) 322.
[2] T. Ito et al., Phys. Rev. B 65 (2002) 155202.
[3] V. N. Antonov, B. N. Harmon and A. N. Yaresko,
Phys. Rev. B 66 (2002) 165208.
[4] K. Matsubayashi et al., J. Phys. Soc. Jpn. 76(2007) 064601.
[5] T. Mizuno et al., J. Phys. Soc. Jpn. 77 (2008)
113704.

86

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Valence-Band Electronic Structure of Fe2-xMxVAl (M = Co, Ir)
T. Nomoto1, K. Soda2, H. Kondo1, S. Harada2, M. Kato2, H. Miyazaki3 and Y. Nishino3
1Department of Physical Science and Engineering, Nagoya University, Nagoya 464-8603, Japan
2
Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan
3
Graduate School of Engineering, Nagoya Institute of Technology, Nagoya 466-8555, Japan

Heusler-type alloy Fe2VAl is a half metal, the Fermi
level EF of which is located within a pseudo gap. Dueto this electronic structure, small change in its
composition or substitution of the fourth element may
remarkably enhance its thermoelectric properties [1].
For Fe2-xMxVAl (M = Co, Rh, Ir), their thermoelectric
power negatively increases on the M substitution. In
spite of Co belonging to the same group as Rh and Ir,
however, the dependence of its thermoelectric power
S on substituting amount x is different from those of
the Rh and Ir substitutions [1]. In this report, we havestudied electronic structures of Fe2-xMxVAl by meansof photoelectron spectroscopy and first principle
calculation to clarify the origin of the difference in S.
Photoelectron spectroscopy was carried out in theangle-integrated mode for polycrystalline samples ofFe1.96M0.04VAl. Electronic structures were calculatedwith the Wien2k code [2] and a 2x2x2 super-cell of
Fe63MV32Al32. In the calculation, the lattice constant
was set at an experimental one of Fe2VAl withoutlattice relaxation and magnetic ordering.
Figure 1 shows typical valence-band photoelectron
spectra of Fe1.96M0.04VAl recorded at the excitation
photon energy hQ of 44 eV, which is sufficiently
lower than the Fe 3p-3d threshold, and so-called
off-resonance (anti-resonance) spectra at hQ = 52 eV,
where the Fe 3d photoemission is suppressed due tothe Fe 3p-3d resonance. Thus the off-resonancespectra show the partial density of states (DOS) for
other than the Fe 3d states, while the difference
spectra between those recorded at hQ = 44 and 52 eV
represent the Fe 3d partial DOS. The spectra for Co
substitution resemble quite well ones for the Ir
substitution but show a small hump around thebinding energy EB of 0.4 eV.
Calculated total and partial DOS of Fe63MV32Al32
are presented near EF in Fig. 2. Compared to Fe2VAl,
the overall shape of total DOS is little changed but isshifted towards the high binding energy side as awhole on the Co and Ir substitutions. This explains
the observed negative S, since S may be proportional
to the energy gradient of DOS at EF. For both Ir andCo substitutions, the Ir 5d and Co 3d states form acommon band; the Ir 5d states dominate the higher
binding energy side of the main Fe-V 3d band, while
the Co 3d states are well hybridized with the whole 3dband. Most noticeable spectral difference between Co
and Ir substitutions is the appearance of a peak justabove EF, derived from the Co 3d impurity-like states.
These differences are ascribed to the difference in thespatial extent and energy position of the Co 3d and Ir

5d states, and hence their hybridization withsurrounding elements. The calculated DOS suggeststhat the thermoelectric power for Fe63CoV32Al32 (-110
PVK-1 at 300 K) may be larger in magnitude than thatfor Fe63IrV32Al32 (-70 PVK-1), which is, however,inconsistent with the experimental results [1]. The
peak in the present spin-independent calculation
would split in the ferromagnetic phase, which might
reduce S for Fe2-xCoxVAl. Such in-pseudogap states
are not clear in the present experimental spectra, since
the spectra are suffered from modification by surface.
[1] Y. Nishino, Mater. Sci. Eng. 18 (2011) 142001.
[2] P. Blaha et al., Comput. Phys. Comun. 59 (1990)
399.

120

-1

DENSITY OF STATES / eV CELL

-1

Fig. 1. Valence-band spectra of Fe1.96M0.04VAl.

0

Fe63MV32Al32
M = Co
total
Fe
V
Al
Co

4

M = Ir
total
Fe
V
Al
Ir

0
1

0.5
0
BINDING ENERGY / eV

-0.5

Fig. 2. Calculated density of states of Fe63MV32Al32.

87

BL5U

Fabrication of Single-Crystalline EuO Thin Films with SrO Buffer Layer
H. Momiyama1, H. Miyazaki2, T. Hajiri3, 4, M. Matsunami4, 5, T. Ito3 and S. Kimura4, 5
1

Department of Frontier Materials, Nagoya Institute of Technology, Nagoya 466-8555, Japan
Center for Fostering Young and Innovative Researchers, Nagoya Institute of Technology, Nagoya 466-8555,
Japan
3
Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan
4
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
5
School of Physical Sciences, The Graduate University for Advanced Studies (SOKENDAI), Okazaki 444-8585,
Japan
2

Europium monoxide (EuO), a ferromagnetic
semiconductor, with Curie temperature (Tc) of 69 K, isattracting attention due to its anomalous
magneto-optical and transport properties [1, 2]. In thecase of electron doping, Tc increases to as high as 200
K. Therefore EuO is one of candidate compounds fornext-generation spintronics applications such as
spinfilter [3, 4]. To growth high quality ultrathin films,
it is important to satisfy small lattice mismatch
between EuO and substrate or buffer layer. Then we
adopt SrO as buffer layer in between EuO thin film
and SrTiO3 substrate, as shown in Fig. 1. SrO forms arock-salt type crystal structure with a lattice constantof 0.5144 nm, which is the same crystal structure andsimilar lattice constant as EuO (The lattice mismatch
between SrO and EuO is 0.3 %). Due to the quite smalllattice mismatch, EuO ultrathin films with a few
atomic layers are expected to be epitaxially grown on
the SrO buffer layer. To check the existence of the
impurity, such as Eu2O3 Eu-metal and Eu valence
number of the surface of the thin films, we performed
photoemission spectroscopy (PES) measurements ofthe fabricated thin films.
Single-crystalline EuO ultrathin films and SrO
buffer layer with thickness of about 2 and 5 nm,
respectively, were grown using a molecular beam
epitaxy (MBE) method onto 0.05 wt% Nb-doped
SrTiO3 (001) single-crystalline substrates. The PES
measurements were performed at the beamline BL5U
of UVSOR-II combined with the MBE system. The
EuO ultrathin films were prepared in the growthchamber and were transferred to a 3D-ARPES
chamber under UHV condition.
Figure 2 shows the PES spectra of EuO 2 nm / SrO 5
nm / SrTiO3 [Fig. 2 (a)] and EuO 5 nm / SrTiO3 [Fig.
2(b)] measured at hQ 38 eV at 10 K. In the case of
EuO 2 nm / SrO 5 nm/ SrTiO3 in Fig. 2 (a), only Eu2+
4f and O2- 2p exist, in spite that the Eu3+ 4f andmetallic states originating from Eu2O3 and Eu metal,
respectively, are observed in EuO 2 nm / SrTiO3 in Fig.
2(b) [5]. These results suggest that the SrO buffer layer
protects the oxygen diffusion from SrTiO3 substrate to
the EuO thin film. Due to the quite small latticemismatch at the interface and protect the oxygen
diffusion, we successfully fabricated single crystalline
EuO ultrathin films with a few atomic layers. The
technique is useful for next generation spintoronics

devices such as a spin filter.

Fig. 1. Atomic structure of EuO (001) thin film with
SrO buffer layer onto SrTiO3 substrate. Lattice
constant of SrTiO3, SrO and EuO and lattice mismatch
between SrTiO3–SrO and SrO–EuO are shown in the
figure.

Fig. 2. Photoemission spectra of EuO 2 nm / SrO 5
nm / SrTiO3 (a), EuO 5 nm / SrTiO3 (b) at thetemperature of 10 K with the photon energy of 38 eV,
respectively.
[1] N. Tsuda et al., Electronic Conduction in Oxides
(Springers College) (1976).
[2] A. Mauger et al., J. Phys. (paris) 39 (1978) 1125.
[3] A. Schmehl et al., Nature Mater. 6 (2007) 882.
[4] M. Müller et al., J. Appl. Phys. 105 (2009)
07C917.
[5] H. Lee et al., J. Appl. Phys. 102 (2009) 053903.

88

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Angle-Resolved Photoemission Study on YbPtSb
Y. Shimura1, R. Niwa1, T. Ito1, 2, T. Hajiri1, S. Kimura3, 4, M. Matsunami3, 4 and H. S. Suzuki5
1

Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan
Nagoya University Synchrotron Radiation Research Center, Nagoya University, Nagoya 464-8603, Japan
3
Editorial Board, 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
5
National Institute for Materials Science, Tsukuba 305-0047, Japan2

A topological insulator, whose physical properties
at the bulk of the system are characterized as
insulating or semimetal, while those at the surface asan anomalous metal, attracts much attention as a new
spintronics device. It becomes central issue toinvestigate the anomalous metallic surface states,
which appears as the linear dispersions intersecting
each other between the bulk energy gap (‘so called
Dirac-corn’). So far, angle-resolved photoemission
spectroscopy (ARPES) plays a dominant role toestablish the 3D topological insulating nature and toprobe the topology of their surface states especially inthe binary Bi-based series of compounds [1].
Recently, half-Heusler ternary compounds XYZ(XY: transition or rare-earth metal, Z: pnictogen)have been expected to be a new platforms for
topological quantum phenomena as spintronic
utilizationwithtunablemultifunctionalities(superconductivity, magnetism, heavy-fermion etc.),
since the ground state changes from topologicallytrivial (semiconducting) to topologically nontrivial(semimetallic) as the characteristic energy difference
between the *6 and *8 energy levels changes fromnegative to positive by changing combination of X, Y,
and Z atoms [2, 3].
Among half-Heusler ternary compounds, YbPtSb
with mostly localized Yb3+ ions [4] might becategorized as a border between the nontrivial and thetrivial case as a reference compound LuPtSb.
Furthermore, the exceptionally large specific heatcoefficient J = 8 J/mol K2 as well as a very tinyordered moment below Tc = 0.4 K has been observed
on YbPtSb suggest its additional functionalities due
to strong electron correlation effects [5].
In the present study, we have performed ARPES
measurements on YbPtSb to clarify the existence of a
topologically nontrivial state as well as its relation
with extremely heavy carriers.
Figure 1 (a) shows the band structure along theīKX symmetry line of YbPtSb obtained by plotting
the intensity of ARPES spectra with hQ = 30 eV
photons. Fig. 1(b) shows the result of LDA bandcalculation of LuPtSb, referred as the localized Yb3+
ground state, with spin-orbit coupling using theWIEN2k code for comparison. We found that thevalence electronic structure around the G point can bequalitatively reproduced by the band calculation
though the bandwidth in the experiment seems to be

narrower by twice than the calculation, possibly due
to electron correlation effect. On the other hand, we
found qualitative discrepancies near the Fermi level.
For example, while the calculation on LuPtSb expects
only one zero-gap semiconducting nature, two typesof Fermi surfaces (FSs), suggesting the semimetallic
nature, have been observed by ARPES. One is lightFSs at the * point and the other is a heavy FS at the X
point. Though the origin of the observed differences
is not clear yet, one possibility is a sizablehybridization effect of the Yb 4f states with
conduction electrons. To elucidate the character ofthe observed FSs as well as the symmetry of theenergy dispersions, further studies using polarization
dependent ARPES and systematic studies on LuPtSb
are intended.

Fig. 1. (a) ARPES image along the īKX symmetryline. White lines are guide for eyes. (b) Band
structure calculation of LuPtSb.
[1] For example, M. Z. Hasan and C. L. Kane, Rev.
Mod. Phys. 82 (2010) 3045.
[2] S. Chadov et al., Nature Mat. 9 (2010) 541.
[3] H. Lin et al., Nature Mat. 9 (2010) 546.
[4] T. Koyama et al., J. Phys. Soc. Jpn. 80 (2011)
SA097.
[5] Y. Nakanishi et al., Phys. Status Solidi B 247(2010) 754.

89

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Temperature Dependent Photoemission Spectra of CaCu3Ti4O12
H. J. Im1, T. Sakurada1, M. Tsunekawa2, K. Kawata1, T. Watanabe1, H. Miyazaki3 andS. Kimura4, 5
1

Department of Advanced Physics, Hirosaki University, Hirosaki 036-8561, Japan
2
Faculty of Education, Shiga University, Shiga 522-8522, Japan3
Department of Environmental and Materials Engineering, Nagoya Institute of Technology, 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
A-site ordered perovskite CaCu3Ti4O12 (CCTO)
has been attracted much attention due to an extremely
high dielectric constant (H) and its intriguing
properties [1]. Particularly, the temperaturedependence of physical properties has been of interest.
For example, the absence of any structural phasetransition around the temperature of 100 K, where thehigh H dramatically drops, is quite a different pointwith the typical perovskites, the so-called
ferroelectrics, where the crystal structural phasetransition usually causes the large change of H. In
addition, the electrical resistivity measurements haveshowed the variable range hopping conductivity inthe insulator phase below about 150 K. To clarify themechanism of such unusual physical properties, wehave carried out the temperature dependent
photoemission (PES) experiments on a single crystal
CCTO.
PES measurements have performed at BL5U. The
used photon energy is 90 eV. The sample surface inthe (100) plane was prepared by cleaving in situ intheultra-highvacuum.
The
measurement
temperatures are from 150 to 300 K. A wide
acceptable angle-integrated mode (r16q) was used toaccumulate the data. The Fermi level was referred tothat of gold thin film electrically connected with thesample. In PES experiments of an insulator sample,
one should take care of the possibility of charging inthe sample during measurement. Therefore, we haveinvestigated the intrinsic properties of CCTO bycomparing with spectra obtained by controlling thephoton flux with the slit size of the beamline.
Figure 1 (a) shows PES spectra in valence band
regime at hv = 90 eV and T = 300 K with various slit
sizes. The mainly Cu 3d peak is observed around 4
eV with intense intensity. The broad peak of mainly O
2p states is observed around 5 - 8 eV. Small broad
shoulder of mainly Cu 3d – O 2p hybridized states isobserved around 2 eV as in our previous results [2]. It
is found that the whole shapes of spectra are almost
the same in the various slit sizes. However, the small
shift of Cu 3d peak is observed in the slit sizes larger
than 70u70 Pm2. We recognize that the typicalbehavior of the charging is the decease of theintensity of 2 eV peak with increasing the photon flux
as shown in the inset of Fig. 1 (a). This can be a goodstandard point in analyzing the PES spectra.
Figure 1 (b) is the plot of temperature dependent

PES spectra in the valence band regime at hv = 90 eVwith the slit size of 30u30 Pm2 where the sample is
not charged up safely as in the above photon flux
dependent PES experiments. We find that the whole
spectra shapes are almost the same over wholetemperature. There is a small shift of Cu 3d peakaround 4 eV to the higher binding energy withdecreasing the temperature. And the PES spectra
reveal that the intensity of Cu 3d – O 2p hybridized
states around 2 eV increases with decreasing thetemperature, particularly below T = 200 K. This iscompletely the opposite behavior to the typical caseof the charging, indicating the intrinsic property of
CCTO. It should be also noted that this temperature isroughly consistent with the temperature where thetype of the transport property is changed as
mentioned above. The physical meaning and therelation with the high H are not clear yet and should
be studied further.

Fig. 1. (a) Photon-flux dependent and temperaturedependent photoemission spectra of CaCu3Ti4O12 in
the valence band regime, obtained with the photon
energy of 90 eV.
[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.

90

BL6B

Electric Field Effect on Superionic Conductor
T. Awano
Department of Electronic Engineering, Tohoku Gakuin University, Tagajo 985-8537, Japan
Ionic conductivity of superionic conductors is aslarge as those in liquids. Movement of ions insuperionic conductors is not in phase bout random as
in liquids. However, existence of correlative
movement of conduction ions by Coulomb repulsive
interaction has been expected for a long time.
Recently calculation simulation has been showing
attractive interaction between conduction ions byelectronic effect. Low energy spectral characteristics
indicate such collective motion of conductingions[1,2]. If coherent excitation of ionic movement
occurs by coherent external electric field, ionic
conductivity seems to increase drastically. In thisstudy, I have investigated far-infrared and millimeterwave spectra of superionic conducting crystal RbAg4I5
in external electric field.
Fig. 1 shows reflectivity deviation at far-infrared
region of RbAg4I5 applied electric field. Reflectivity
around 74 and 91 cm-1 were increased by applying
1kHz sinusoidal wave of amplitude of 3.0 Vpp. This
spectral change disappeared after removing theapplied electric field. These peaks seem to be due todeformed breathing modes of Ag-I tetrahedron. Suchenhancement of breathing mode seems to be due toincrease of the number of silver and iodine tetrahedronpairs. Contrary to this result, in my previous
experiment of silver atom doping, absorption bands at
45 and 70 cm-1 decreased [3].
Fig. 2 shows change of reflectivity ratio at
submillimeter region of RbAg4I5 applied electric field.
The ratio means reflectivity divided by that before
applying the electric field. Red line shows that inapplying 1kHz sinusoidal wave of amplitude of 3.0
Vpp. Intensity of “attempt mode” around 19 cm-1
increased. This spectral change disappeared after
removing the applied electric field. The attempt mode
is a motion of silver ion trying to escape surrounding
tetrahedron. Such enhancement of attempt mode
seems to be due to increase of the collective
movement of silver ions. Contrary to this result, in myprevious experiment of silver or iodine doping, thedielectric constants decreased by silver addition andincreased by iodine addition in the spectral region
below 20cm-1[3].
In Raman scattering spectra of the doped RbAg4I5,
drastic spectral changes were reported previously[4,5].
The scattering intensity in terahertz region (under
50cm-1) increased by silver addition and decreased byiodine addition. Moreover fine structures at low
temperature disappeared in the case of iodine addition.
Reflectivity results of this study described above were
contrary to those of the Raman spectroscopic study.
A part of the spectral change by applying electricfield seems to be interpreted as change of local densityof silver ion or iodine ion. (The latter means silver ion
vacancy.)
0.02

RbAg 4I5

3V
0V

Ǎ㧾

0.01

0

40

50

60 70 80 90 100
WAVE NUMBER (cm -1)

Fig. 1. Reflectivity change of RbAg4I5 by applying
electric field. Red line shows that in applying AC1kHz,
3V. Blue line shows that after reducing the voltage tozero. The dotted line shows Gaussian curves at 74 and91 cm-1. Small peaks are due to remaining interference
fringes.

R/R0

1.05

RbAg 4I5

3V
0V

1

0.95
10

20

30

40

WAVE NUMBER (cm -1)

Fig. 2. Change of reflectivity ratio of RbAg4I5 by
applying electric field. Red line shows that in applying
AC1kHz, 3V. Blue line shows that after reducing thevoltage to zero. R0 means the reflectivity before
applying the electric field. The dotted line shows
Gaussian curve at 19cm-1. Small peaks are due toremaining interference fringes.
[1] T. Awano, Infrared Phys. and Tech. 51 (2008) 458.
[2] T. Awano and T. Takahashi, J. Phys. Soc. Jpn. 79
Suppl. A (2010) 118.
[3] T. Awano, UVSOR Activity Report 36 (2009)100.
[4] S. Bredikhin, T. Hattori and M. Ishigame, Solid
State Ionics 67 (1994) 311.
[5] S. Bredikhin, N. Kovaleva, T. Hattori and M.
Ishigame, Solid State Ionics 74 (1994) 149.

91

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Temperature Dependences of Electronic Structure and Chemical Potentialof FeSb2
T. Takeuchi1, 2, 3, 4 and T. Shimada4
1

EcoTopia Science Institute, Nagoya University, Nagoya 464-8603, Japan
Department of Crystalline Materials Science, Nagoya University, Nagoya 464-8603, Japan
3
PRESTO, Japan Science and Technology Agency, Saitama 332- 0012, Japan
4
Department of Applied Physics, Nagoya University, 464-8603, Japan2

contribution of chemical potential on Seebeckcoefficient, ( P (T )  H F ) / ( e T ) [2], together with themeasured Seebck coefficient in Fig. 2 (b). The
temperature dependence of ( P (T )  H F ) / ( e T ) shows
extremely good consistency with the measured value.
This fact unambiguously indicates that the large
magnitude of Seebeck coefficient is brought about by
the electronic structure effect rather than thephonon-drag effect.

FeSb2 is known to possess an extremely large
magnitude of Seebeck coefficient reaching -40 mV/K,
which is 200 times larger than that of practical
thermoelectric materials [1]. The mechanism leading
to this huge Seebeck coefficient has not been wellunderstood yet. Therefore, in this study, byemoplyinghigh-resolutionangle
resolvedphotoemission
spectroscopy(ARPES),
we
investigated the characteristics of electronic structurenear the chemical potential because it is the main
factor to determine the electron transport properties
including Seebeck coefficient.
Single grained FeSb2 samples were grown in the
Sb-flux, and we succeeded in obtaining FeSb2 single
crystals of ~1x1x1 mm3 in dimension. The sample
possesses a large evolution of Seebeck coefficient ataround 10~30 K as it was reported previously, though
the magnitude of Seebeck coefficient is slightly
smaller than the reported value.
ARPES measurements were conducted at BL7U of
UVSOR using photon energy of 22 eV. This photon
energy was selected so as the measurable momentum
area to cover the whole first Brillouin zone. The
orientation of samples were determined by taking
Laue pictures, and the clean surface was prepared bycleaving samples in the ultra high vacuum chamber of
APRES apparatus just before the measurement.
Figure 1 shows temperature dependence of EDC
spectrum measured at * point. The peak intensity andspectrum weight increases with decreasing
temperature, and it becomes evident especially at low
temperatures where the large magnitude of Seebeckcoefficient is observable. Since the peak was locatedat the energy 200 meV below the chemical potential,
it is naturally understood that the evolution of thepeak in measured EDC cannot contribute theincreasing magnitude of Seebeck coefficient. The
observed evolution of peak suggests the presence ofthe similar increase of peak intensity near thechemical potential in the conduction band to cause
the large increase in the magnitude of Seebeckcoefficient with negative sign. In such a case, thechemical potential must possess drastic variation withtemperature in the same manner as the significant
variation of Seebeck coefficient. Thus, in the next
step, we focused on the chemical potential shift.
The temperature dependence of chemical potential
P (T )  H F estimated from the peak energy in EDC
was plotted in Fig.2 (a). We also plotted the

(a)
-0.21

-0.22
0

Seebck coefficient, S(T) / PV K

-1Peak energuy, Hpeak P / eV

Fig. 1. (a) ARPES intensity I(k, H ) of FeSb2
measured at 13 K near the * point. The energy
distribution curves I(*, H ) measured at various
temperatures are shown in (b). Evolution of the Peakintensity is observable with decreasing temperatureespecially below 30 K, where the magnitude ofSeebeck coefficient increases.

50

100

150

Temperature, T / K
(b)

0
-200
-400
-600
0

50
100
Temperature, T / K

150

Fig. 2. Temperature dependence of (a) peak energy,(b) Seebeck coefficient and ( P (T )  H F ) / ( e T ) . The
peak energy at 0 K is assumed to be 0.219 meV. The
characteristic temperature dependence of Seebeckcoefficient was clearly reproduced by that calculated
from the chemical potential shift.
[1] A. Bentien, et al., EPL 80 (2007) 17008.
[2] T. Takeuchi et al., Mat. Trans. 51 (2010) 421.

92

BL7U

Observation of Anomalous Peaks in the Photoelectron Spectra of Highly
Oriented Pyrolytic Graphite: Folding of the Band due to the Surface
Charge Density Wave Transition
S. Tanaka1, M. Matsunami2,3 and S. Kimura2,3
1

The Insititue of Scientific and Industrial Research, Osaka University, Mihogaoka, Ibaraki 567-0047, Japan
2
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
2
School of Physical Sciences, The Graduate University for Advanced Studies, Okazaki 444-8585, Japan㪧㪿㫆㫋㫆㪼㫃㪼㪺㫋㫉㫆㫅㩷㪠㫅㫋㪼㫅㫊㫀㫋㫐 㩷㪙㫀㫅㪻㫀㫅㪾㩷㪜㫅㪼㫉㪾㫐㩷㩷㩷㩷㩷㩷㩷㩷㩿㪘㫉㪹㪅㩷㪬㫅㫀㫋㫊㪀㩷㩷㩷㩷㩷㩿㪼㪭㪀Graphite has been regarded as a “textbook” system
for solid state physics for many years because of its
unique characteristics. In this study, theangle-resolved photoelectron spectroscopy (ARPES)
with low-photon energy (7-16eV) is used for theinvestigation of HOPG (Highly Oriented Pyrolytic
Graphite) at a low temperature. We observed for the
first time peaks in the low binding energy region(from the Fermi level to 0.7 eV) of the surface normal
photoelectron spectra at 11K, which disappear above~30K. Based on the dispersion along both the paralleland normal to the surface, the peaks are ascribed tothe emission from the K(H)-point that is backfolded
into the *-point as a result of the two-dimensional
superperiodicity. The surface charge density wave
(CDW) transition is proposed for the driving
mechanism of the superperiodicity based on thetemperature-dependence of the photoelectron
intensity[1].
The ARPES experiments were carried out at theBL7U SAMRAI of the UVSOR-II. Figure (a) showsa series of normal-emission photoelectron spectra of
HOPG at 11K using the photon energies from 7.3 to16eV (0.3eV-step). A distinct peak just below theFermi level and a smaller peak at the binding energy(EB) ~0.7eV are visible when the photon energy isnear 11.5eV with a relatively high intensity. In thenormal emission, only the electron states along the*-A line of the Brillouin zone (BZ) can be observed.
Therefore, the peaks at EB~0eV and 0.7eV in the
ARPES spectra [Fig. (a)] are paradoxical since theS-band of the graphite crosses EF near the K-point,and no corresponding bands near EF have beenreported at the center of the BZ.
In order to obtain the information about the two
anomalous peaks, we measured the band dispersion
by using ARPES at 11K. In Fig. (b), the dispersionsof these peaks as a function of k// (inverse vector
parallel to the surface) are displayed. The color map
shows photoelectron intensity taken at hQ=13eV. The
dispersions of the two peaks closely resemble thoseof the S-bands around the K-point in the graphite.
According to the photon-energy dependence of thesurface normal photoelectron emission, it is also
shown that the dispersion of these peaks along the kz(surface normal) direction is similar to that along theK-H line. Therefore, these peaks cannot be assigned
to the defect, edge, or surface states, but are㪇㩿㪹㪀㩷 㪿Q㪔㪈㪊㪼㪭㪈㩿㪺㪀㩷'㩿㪫㪀㪉
㪠㫅㫋㪼㫅㫊㫀㫋㫐

㪈
㪇

㪄㪇㪅㪉

㪈㪅㪌

㪇㪅㪇㪄㪈

㫂㪆㪆㩿㪘 㪀㪇㪅㪉㪫㪚㪔㪉㪐㪢㪇㪫㪆㪫㪚㪈㩿㪸㪀㩷㪥㫆㫉㫄㪸㫃㩷㪜㫄㫀㫊㫊㫀㫆㫅
㪈㪈㪢

㪈㪍㪼㪭
㪈㪅㪇
㪇㪅㪌
㪇㪅㪇
㪙㫀㫅㪻㫀㫅㪾㩷㪜㫅㪼㫉㪾㫐㩷㩿㪼㪭㪀㪎㪅㪊㪼㪭㪧㪿㫆㫋㫆㫅
㪜㫅㪼㫉㪾㫐㩷

unambiguously ascribed to the electron emission
from the S-band at the K(H)-point of the graphite.
Then, we can conclude that the K-point of HOPG at
11K is backfolded into the *-point as a result of theformation of the p 3 u 3 R 30 $ or larger
superperiodicity. The detection of the photoelectron
emission from the K-point at the surface normal canbe provided by the diffraction (scattering) by thereciprocal lattice vector of the 2D superlattice.
We measured the sample-temperature dependenceof the photoelectron spectra in order to reveal thecondition for the superperiodicity formation. In Fig.
(c), the photoelectron intensity at EB=0.016eV (solid
circles) in the surface normal PES at hQ=11.5eV isplotted as a function of the reduced temperature(divided by the critical temperature TC=29K). Thistemperature-dependence is very similar to that of the
X-ray reflection intensity of some materials
corresponding to the superlattice formation as a resultof the charge density wave (CDW) transition, which
is well described with the square of theorder-parameter ' predicted by the BCS-law (solidline). Consequently, it is strongly suggested that theformation of the superlattice in HOPG is caused by
the CDW transition. This observation demonstrates
the advantage of the photoelectron spectroscopy withthe tunable photons of the low energy.
[1] S. Tanaka, M. Matsunami and S. Kimura, Phys.
Rev. B 84 (2011) 121411 (R) .

93

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Three-Dimensional Fermi Surface of YbAl2 Studied by Angle-Resolved
Photoemission Spectroscopy
M. Matsunami1, 2, T. Hajiri1, H. Miyazaki1, M. Kosaka3 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
Graduate School ofScience and Engineering, Saitama University, Saitama 338-8570, Japan2

The topology of the Fermi surface (FS) in theheavy-fermion systems directly reflects the degree ofthe hybridization between conduction band and 4f
state (c-f hybridization) as a key concept for
describing the heavy-fermion nature. Angle-resolved
photoemission spectroscopy (ARPES) is a powerfultool to probe the c-f hybridized electronic structures.
However, most of ARPES measurements have been
performed on the basis of the surface Brillouin zone
or by using the 4d-4f resonant process, in which the kz
dependence of the electronic structure and FS are
ignored. Since the heavy-fermion systems generally
have three-dimensional electronic structure and FS,
ARPES measurements should be done along the bulk
Brillouin zone.
YbAl2, which crystallizes in the cubic Laves
MgCu2 structure, is a prototypical valence fluctuation
system. The Yb mean valence has been estimated tobe ~ +2.2 by the hard x-ray photoemission
spectroscopy [1]. It strongly suggests that a strong c-f
hybridization effect can be realized in YbAl2. Hence
YbAl2 is well-suited system for studying the c-f
hybridized electronic structures and the FS,
particularly in comparison with the band structure
calculations.
In this work, we have performed a three
dimensional mapping of the FS for YbAl2 by meansof ARPES. The ARPES experiment was carried out at
the undulator beamline BL7U "SAMRAI" inUVSOR-II [2]. The crystal orientation wasdetermined by Laue x-ray diffraction. The single
crystals of YbAl2, which were grown by the Lithium
flux method, were cleaved in situ along the (111)plane. The LDA band structure calculations were
performed using the WIEN2k code.
Figure 1 (a) shows the bulk Brillouin zone of
YbAl2. Comparing the photon-energy dependence(16-29 eV) of ARPES data leading to the FS in the
kx-kz plane with the LDA calculations as shown in Fig.
1 (b), the inner potential in this system was estimatedto be 13.7 eV. Thus, the photon energy of hQ = 20 eV
are chosen so as to obtain the FS in the kx-ky planeasshown in Fig. 1 (c). Two FSs around * point in boththe kx-kz and the kx-ky planes are well described by the
LDA calculations. The results suggest the small
renormalization effect in YbAl2, which can beprovided by the strong c-f hybridization, consistent
with the extremely high Kondo temperature (above
2000 K).

kz

(a)

W

L
*

K

X

kx

ky

(b)

hQ = 29 eV-1kz (Å )

3.5
3.0
2.5
2.0
-1.0

0.0

0.5

(c)

-1

ky (Å )

0.5

-0.5

20 eV
16 eV
1.0

0.0
hQ = 20 eV

-0.5
-1.0

-0.5

0.0
0.5
-1
kx (Å )

1.0

Fig. 1. (a) Brillouin zone of YbAl2, in which the kz
corresponds to the (111) direction of the fcc Brillouinzone. (b) and (c) Fermi-surface (FS) mapping of
YbAl2 in the kx-kz plane and the kx-ky plane,
respectively. The green dots and lines indicate the FSs
obtained by the LDA bandstructure calculations.
[1]M. Matsunamiet al., J. Phys. Soc. Jpn. 81 (2012)
073702.
[2] S. Kimura et al., Rev. Sci. Instrum. 81 (2010)053104.

94

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The Orbital Characters of Low-Energy Electronic Structure in theIron-Chalcogenide Superconductor KxFe2-ySe2
F. Chen1, Q. Q. Ge1, M. Xu1, Y. Zhang1, X. P. Shen1, 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, Okazaki 444-8585, Japan£, and ¤, two electron-like band, å and ¦, andtwo rather flat bands, ¹ and ¹’, around Z in Fig.
1.

The newly discovered KxFe2-ySe2 superconductor
exhibits many distinct properties from otheriron-based superconductor [1], such as its parent
compound and electronic structure [2, 3]. Since theelectronic structures of iron-based superconductors
are dominated by multiple 3d orbitals [4, 5], tounderstand the unique properties of KxFe2-ySe2, one
needs to understand its orbital characters.
The intrinsic phase separation in KxFe2-ySe2
superconductor
leads
torelatively
lower
concentration of superconducting phase compared toother iron-based superconductors, however, thestrong photon intensity and variable polarizations ofbeamline BL7U at the ultraviolet synchrotron orbitalradiation facility (UVSOR) enable us to successfully
resolve the orbital characters of low-energy electronic
structure.

Fig. 2. (a) The summary of the orbital characters of
low-energy electronic structure in KxFe2-ySe2
superconductor along Z-A direction. (b) The
illustration of the orbital characters on the Fermi
surface sheets around *, M, Z, and A. The almost
overlapping G and G’ Fermi surface sheets around M
and A are separated for a better illustration.
Exploitingthepolarization-dependent
angle-resolved photoemission spectroscopy (ARPES),
we have determined the orbital characters of thelow-energy electronic structure of KxFe2-ySe2
superconductor (Fig. 2) by considering the spatial
symmetries of Fe 3d orbitals and their matrix element
effects mentioned in refs.4 and 5. We found that thesmall electron pocket near the Z point is mostly
dominated by the dz2 orbitals, while the large Fermi
cylinders around the zone corner are dominated by
the dxz, dyz, and dxy orbitals. Moreover, we find that
the Fermi cylinders are actually composed of two
highly degenerate ones, indicating negligibleinteractions between them.
To a large extent, the KxFe2-ySe2 superconductor
shares similar orbital characters with other iron-based
superconductors [4, 5], but with its own
characteristics. The determined orbital characterswould help to construct realistic model for
KxFe2-ySe2.

Fig. 1. The polarization-dependent APRES dataaround Z taken with 30 eV photon. (a) The
photoemission spectra and their corresponding second
derivatives with respect to energy taken in the s and pgeometries, respectively, along Z-A direction. (b) is
the same as panel a, but taken along Z-R direction.
Figure 1 shows the photoemission spectra around
the Z point. In Fig. 1(a), the upper panels are thephotoemission spectra taken along =-A (#1) directionin the s and p geometries, respectively, and the lower
panels are the corresponding second derivatives withrespect to energy. Fig. 1(b) is similar to Fig. 1(a),except that the data were taken along Z-R (#2)
direction. We could resolve three hole-like bands, ¢,[1] J. G. Guo et al., Phys. Rev. B 82 (2010) 180520.
[2] Y. Zhang et al., Nature Mater. 10 (2011) 273.
[3] F. Chen et al., Phys. Rev. X 1 (2011) 021020.
[4] Y. Zhang et al., Phys. Rev. B 83 (2011) 054510.
[5] Y. Zhang et al., Phys. Rev. B 85 (2012) 085121.

95

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Angle-Resolved Photoemission Study on Non-Superconducting Li1+xFeAs
T. Hajiri1,2, T. Ito1,3, R. Niwa1 , S. Hirate1, M. Matsunami2,4, B. H. Min5, Y. S. Kwon5 andS. 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
LiFeAs is an intriguing iron pnictide superconductor because it shows superconductivity (TC = 18 K)
without any structural and SDW/AFM transitions [1].
In pristine LiFeAs, we have demonstrated that theelectronic structure can be fundamentally explainedby a LDA band structure calculation. We have also
pointed out the importance of the interband scattering
between hole and electron Fermi surfaces in terms of
the appearance of superconductivity [2]. In this system, the excess or deficiency of Li-ions from thestoichiometry has been reported to suppress the superconductivity [3] and enlarges spin fluctuation [4].
However, the reason of the suppression of the superconductivity owing to the off-stoichiometry has notbeen clarified yet.
To elucidate the effect of the Li excess or deficiency to the electronic structure, we performed apolarization-dependent
three-dimensional
angle-resolved
photoemission
spectroscopy(3D-ARPES) of a Li-excess LiFeAs (Li1+xFeAs)
without superconducting transition at BL7U,UVSOR-II.
Figure 1 shows a normal emission (k = 0 Å-1) ARPES image of Li1+xFeAs measured at T = 12 K along
the Z-A direction. The blue line indicates the trace ofthe peak positions of the momentum distribution
curves (MDCs) and the green dashed lines indicate
the dispersion curves derived from an LDA band calculation. The obtained band dispersion is strongly
renormalized below 100 meV. The renormalized bareband is assumed as the green solid line in Fig. 1. The
obtained band dispersion has kink structure that isaway from the assumed bare band at about 20 meV
and 100 meV.
In order to argue about the kink structure qualitatively, we performed the self-energy analysis. Figure
2 shows the real part of the self-energy Re6(Z),which is obtained by the subtraction of the assumed
bare band dispersion from the MDC dispersion. The
Re6(Z) spectrum clearly has two peaks; one is located at about 20 meV and the other at about 100
meV. The former is consistent with phonon energy
position as shown by the dashed lines reported by
Raman spectroscopy [5] and theory [6]. However, thelater peak cannot be explained by the phonon origin.
A recent inelastic neutron scattering (INS) study indicated that the spin excitation peak appears at around

100 meV as shown by a blue line [7], which is consistent with the observed higher-energy kink. Thissuggests that the higher-energy kink originates frommagnetic excitations.

Fig. 1. ARPES image of Li1+xFeAs measured at T =12 K along the Z-A direction.

Fig. 2. The real part of the self-energy Re6(Z) indicated by a red solid line. Vertical dashed lines indicate the phonon energy position [5, 6] and blue line
indicates the energy dependence of the local susceptibility of Li0.94FeAs obtained by INS [7].
[1] X. C. Wang et al., Solid State Commun. 148(2008) 538.
[2] T. Hajiri et al., Phys. Rev. B 85 (2012) 094509.
[3] M. Wang et al., Phys. Rev. B 83 (2011)
220515(R).
[4] L. Ma et al., Phys. Rev. B 82 (2010) 180501(R).
[5] Y. J. Um et al., arXiv:1109.5797.
[6] R. A. Jishi et al., Adv. Condens. Matter Phys.
2010 (2010) 804343.
[7] M. Wang et al., Phys. Rev. B 83 (2011)
220515(R).

96

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Angle-Resolved Photoemission Study on Quasi-One-Dimensional Organic
Conductor (TMTSF)2AsF6
S. Hirate1, T. Hajiri1, T. Ito1, 3, S. Kimura2, 4 and T. Nakamura4, 5
1

Graduated 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
Institute for Molecular Science, Okazaki 444-8585, JapanThe Bechgaard salts (TMTSF)2X (TMTSF:
tetramethyl-tetraselenofulvalene, X=AsF6, PF6, ClO4,
etc.)
are
the
well-known
modelsofquasi-one-dimensional systems. Owing to the stacksof planar TMTSF molecules in columns,
quasi-one-dimensional conductivity appears. At low
temperatures, this quasi-one-dimensionality results inanintriguing ground
state
such
as
a
spin-density-wave (SDW) state, or a superconducting
state, depending on anion X and pressure [1]. For(TMTSF)2AsF6, the SDW transition occurs at 12 K atambient pressure.
In this study, we have performed angle-resolved
photoemission
spectroscopy(ARPES)onsingle-crystalline (TMTSF)2AsF6 to clarify theelectric state and its relation to the anomalous
properties. By utilizing the bulk-sensitive microfocus
low-energy photons (hQ = 8 eV, 15100 μm2) at theBL7U, we have succeeded in directly observing the
intrinsic electronic structure of (TMTSF)2AsF6 .
Figure 1 shows the ARPES image near EF alongthe īX high-symmetry line measured at T = 30 K. At
the * point, the hole-like dispersive feature, which
can be assigned to the TMTSF band [2], was clearlyobserved. In order to clarify the relation between theobserved dispersive feature and the anomalous
property, we analyzed the electronic structure near EF
around the Fermi/Luttinger surface in detail.
Figure 2 shows the second derivative of the
ARPES image (Fig. 1) with enlarged scales. The
weak dispersions (b) and (c) other than the mainfeature (a) appear at the low-binding energies. The
origin of anomalous multiple dispersive features are
not clear yet. Two separated excitations of spin andcharge in one-dimensional electron systems has been
expected by so called spin-charge separation model,
which has recently been demonstrated on SrCuO2 by
the ARPES experiments [3]. Furthermore, anadditional low-energy excitation due to theelectron-photon coupling has been predicted by the
recent theory [4]. To elucidate the present observationof the anomalous multiple dispersive features on(TMTSF)2AsF6, further studies are intended.

024311.
[3] B. J. Kim et al., Nat. Phys. 2 (2006) 397.
[4] F. F. Assaad, Phys. Rev. B 78 (2008) 155124.

Fig. 1. ARPES image of (TMTSF)2AsF6 along the īX
high-symmetry line measured at T = 30 K. Dashedlines are guide for eyes to trace a main dispersive
feature.

Fig. 2. Second derivative of ARPES image (Fig. 1) of(TMTSF)2AsF6 enlarged near EF around the
Fermi/Lutinger surface. Dashed lines (a), (b) and (c)are guide for eyes to trace the observed dispersive
features.

[1] T. Ishiguro et al., Organic Supercondutors(Springer-Verlag, Berlin, 1998).
[2] S. Ishibashi, Sci. Techonol. Adv. Mater. 10 (2009)

97

BL7B

Optical Characterization and Computational Chemical Evaluation ofElectronic Localized States in Polyolefin
T. Arai1, M. Hosobuchi1, N. Fuse2, K. Takeda1 and Y. Ohki1
1-1

Absorption Coefficient (cm )

1

6.5

0.8

6
0.6
5.5
0.4
5
0.2

4.5
4

2

2.5

3

3.5

4

4.5

0

5

Detected Photon Energy (eV)

1

6.5

0.8

6
0.6
5.5
0.4
5
0.2

4.5
4

PL Intensity (a.u.)(a) PE
7

2

2.5

3

3.5

4

4.5

0

5

Detected Photon Energy (eV)(b) PP
Fig. 2. Two-dimensional intensity distributions ofvarious PL peaks observed for PE (a) and PP (b) at
10 K.
x
z
y
CB

CB

D3 ppSC : py1500

C : pyD2 ppSPE (30 Pm)
PP (46 Pm)
PMP (50 Pm)

1000

VB

Fig. 3.
(b).

500

3

4
5
6
Photon Energy (eV)D1 ppS*VB

D1

O : py(a) C25H52

0
2

PL Intensity (a.u.)7

E (eV)

Optical absorption spectra and photoluminescence
spectra were obtained for eight kinds of polyolefin
sheet samples using photons in a range from visible
to vacuum ultraviolet. Almost all samples were found
to exhibit an absorption peak at around 6.5 eV and aluminescence band at around 4.3 eV as shown in Figs.
1 and 2. The luminescence was found to be inducedby the absorption. Furthermore, it was found thatsuccessive absorption of ultraviolet photons weakens
the luminescence intensity [1, 2]. It is assumed fromthese results that D, E-unsaturated carbonyls are
luminous and that the carbonyls are decomposed
through the Norrish type II reaction by absorbing
ultraviolet photons [3, 4]. In Norrish type II reaction,
DE-unsaturated carbonyls change to EJ-unsaturated
carbonyls, which are then separated into pure carbon
double bonds and pure carbonyls by main chain
scissions.
Quantum chemical calculations were carried out
using polyethylene models with and without anunsaturated carbonyl to verify the above-mentioned
assumption. From the calculation results, the modelwith an unsaturated carbonyl was found to have
localized electronic states in the forbidden band as
shown in Fig. 3. One of the differential energies
between the states is close to the photon energy, bywhich the luminescence is induced. The bond lengthof a double bond, which is next to the carbonyl, wasfound to be longer at the excited singlet state than at
the ground state. These results obtained by thequantum chemical calculations support the above-
mentioned assumption of the luminescence center andits decomposition.

Excitation Photon Energy (eV)

Waseda University, 3-4-1 Ohkubo, Shinjuku-ku, Tokyo 169-8555, Japan
Central Research Institute of Electric Power Industry, 2-6-1 Nagasaka, Yokosuka-shi, Kanagawa 240-0196,
Japan

Excitation Photon Energy (eV)27(b) C25H48O

The energy levels of C25H52 (a) and C25H48O[1] T. Ito et al., IEEJ Trans. FM 121 (2001) 865 (inJapanese).
[2] T. Ito, N. Fuse and Y. Ohki, IEEJ Trans. FM 124(2004) 624.
[3] N. S. Allen, J. Homer and J. F. McKellar, J. Appl.
Polym. Sci. 21 (1977) 2261.
[4] N. S. Allen and J. F. McKellar, J. Appl. Polym. Sci.
22 (1978) 3277.

8

Fig. 1.
Absorption spectra measured by
vacuum ultraviolet spectroscopy observed for
PE, PP and PMP. The numerals in parentheses
are the thicknesses of the samples.

98

BL7B

Optical Investigation on K2NiF4-Type Cobalt-Oxides in Vacuum
Ultra-Violet Region
J. Fujioka1, K. Ueda1, M. Uchida1, J. S. Lee2 and Y. Tokura1
1

2

Department of Applied Physics, University of Tokyo, Tokyo 113-8656, Japan
Department of Photonics and Applied Physics, Gwangju Institute of Science and Technology (GIST), Gwangju
500-712, Korea

Spin state of the Co ions, particularly Co3+, incobalt-oxides has long been a controversial issue.
Depending on the relative magnitude of the crystal
field splitting against the Hund’s rule coupling, thespin state for Co3+ with six 3d electrons can be low
spin (LS, S=0), high spin (HS, S=2), or evenintermediate spin (IS, S=1). Although this additional
degree of freedom complicates the problem inunderstanding magnetic and relevant properties, it canalso provide a chance to invoke novel functionality,
such as the large thermoelectric power or spin state
dependent charge transport.
Forthehalf-doped
layeredperovskite
La1.5Ca0.5CoO4, a checkerboard-type charge order of
Co2+ and Co3+ is realized with a high transition
temperature TCO~850 K, and the magnetic orderoccurs at comparably low temperature (T) around 30
K. Concerning the local spin state, Co2+ is usuallyconsidered to be in the HS state. As for Co3+,
Hollmannetal.
recently
proposedthetemperature-induced
spin-statetransitionbyexamining high-temperature magnetic susceptibility[1], although the high-temperature spin state is notdetermined between IS and HS.
In this article, we report the spin-state issue in thelayered perovskite cobaltate based on the optical
spectroscopy. From the temperature dependency ofinfrared-active optical phonons, we observed clear
signatures of the temperature-induced spin-statetransition particularly to IS around 400 K.
We measured reflectivity spectra for single crystalsof La1.5Ca0.5CoO4 between 12 meV and 5 eV using
Fourier-transform spectrometer and grating-type
spectrometer in temperature range between 300 K and
850 K. We obtained the reflectivity between 5 and 30
eV at room temperature by using synchrotron
radiation at BL7B in UVSOR. We determined
complexopticalconstants
throughthe
Kramers-Kronigtransformation
withproperextrapolations of reflectivity in the low and highenergy regions.
Figure 1 (a) shows the reflectivity spectra up to 30
eV. Sharp peaks below 0.1 eV are assigned to infrared
active optical phonons. A peak structure in energy
range from 0.1-4 eV is assigned to charge transfer
type transition between O-2p band and Co-3d band,or Co-3d interband transition. In the following, we
focus the temperature dependence of the phonon
spectra. Figure (b) shows optical conductivity spectrain the energy range between 20-50 meV. At 300 K,

three peaks are visible around 33, 37 and 44 meV.
These peaks are assigned to the Co-O bond bending
mode. With increasing temperature, the peaks
gradually broadens, as expected by structuralanharmonicity. It should be noted that there are
additional modes developing as temperature increases
above 400 K around 30 meV (indicated by red
triangles). This indicates that there is an additional
structural distortion going on with an increase of
temperature, and such a distortion should beunderstood differently from the structural distortion
related to the charge order. Considering that the mode
itself, supposing the tetragonal symmetry, is an apicaloxygen bending mode, it would be reasonable toassume that the corresponding structural distortion isrelated to the apical oxygen, and the most plausible
candidate should be Jahn-Teller distortion. It is ofimportance to note that among possible spin states of
Co3+, it is only the IS state that involves the
Jahn-Teller distortion. This leads us to suggest thatwhile the LS state of Co3+ would be dominant at the
low temperature, the IS becomes populated as T
increases across 400 K, which is substantially lower
than the charge ordering transition temperature (850
K) .
0.8

(a) La Ca CoO EZ || ab
1.5
0.5
4
300K
400K
500K
600K
700K
800K
850K

0.6
0.4
0.2
0 -2
10

-1

-1

Optical conductivity (: cm )Reflectivity

1

10-1
100
101
Photon energy (eV)
(b)

200

100

0
0.02

0.03
0.04
0.05
Photon energy (eV)Fig. 1. (a) Reflectivity and (b) optical conductivity
spectra for La1.5Ca0.5CoO4 at various temperatures.
[1] N. Hollmann et al., Phys. Rev. B 83 (2011).
174435.

99

BL7B

Decay Behaviors of Auger-Free Luminescence in Cs2ZnCl4
A. Ohnishi1, M. Saito1, 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, Japan2

The crystal of Cs2ZnCl4 is composed of anionic
ZnCl4 tetrahedra separated from each other andinterstitial Cs cations between them [1]. In theprevious work [2], we have investigated opticalproperties of Cs2ZnCl4 crystals with the use ofsynchrotron radiation as a light source, and observed
Auger-Free luminescence (AFL) resulting from aradiative transition between the Cl 3p valence bandand the Cs 5p outermost core band. In the present
study, we have studied decay behaviors of AFL using
a time-correlated single-photon counting method
under the single bunch operation.
Cs2ZnCl4 crystals were prepared by evaporating a
stoichiometric mixture of solutions of CsCl and ZnCl2.
Experiments were performed at the BL7B beamlineof UVSOR. Luminescence from samples wasdispersed by a grating monochromator and detectedby a microchannel-plate photomultiplier.
When Cs2ZnCl4 is excited at 10 K at 21.4 eV, three
AFL bands peaking at 3.2 4.1 and 4.8 eV are
observed. In Fig. 1, decay curves of AFL measured at
3.2, 4.1 and 4.8 eV are shown in semi-logarithmic
scale, where decay curves are vertically displaced forcomparison. The photo-excitation was made at 21.4
eV at 10 K. Three decay curves are parallel with eachother. That is, the decay profile is fundamentally thesame for each band. This result suggests that the life
time is governed by that of the holes created on theoutermost core band. We can see a somewhat fastcomponent in the earlier stage of the decay curves. If
we estimate the lifetime from a least-square fit to thesingle exponential decay by neglecting thecomponent, the decay time is about 2.0 ns. The redstraight line drawn on the experimental data of the 3.2
eV AFL shows a single exponential curve withlifetime of 2.0 ns. Figure 2 shows decay behaviors of
the 4.1 eV band at 10 and 300 K. The decay time at
300 K is estimated to be 1.6 ns. The decay time is alittle shorter than that at 10 K. This temperaturedependence was the same for the AFL at 3.2 and 4.8
eV.
The life time of AFL is much longer compared to thelattice relaxation time. Thus, it is probable that the corehole induces some lattice distortion within the life timeand interacts with the lattice vibrations. In fact, theAFL spectrum observed was red-shifted than theenergy range expected within the rigid band model.
Furthermore, the linewidths of AFL bands were foundto be gradually broadened as increasing the sample
temperature, though the overall structures of AFL
spectrum were not very sensitive to the sample
temperature between 10 and 300 K. These details will
be reported somewhere.

100

Fig. 1. Decay behaviors of AFL detected at 3.2, 4.1,
and 4.8 eV in Cs2ZnCl4.

Fig. 2. Decay behaviors of AFL detected at 4.1 eV at
10 and 300 K in Cs2ZnCl4.
[1] J. A. Mcginnery, Inorg. Chem. 13 (1974) 1057.
[2] A. Ohnishi, T. Otomo, M. Kitaura and M. Sasaki,
J. Phys. Soc. Jpn. 72 (2003) 2400.

BL7B

Electronic Status of Rare-Earth Ion in Glass Host by Characterizing
Photoluminescence of Rare-Earth Doped APLF Glass Scintillator
M. Tsuboi1, M. Kouno1, K. Takeda1, T. Nakazato1, T. Shimizu1, M. Cadatal-Raduban1,
K. Yamanoi1, K. Sakai1, R. Nishi1, Y. Minami1, Y. Arikawa1, N. Sarukura1, T. Norimatsu1,
M. Nakai1, H. Azeti1, T. Murata2, S. Fujino3, H. Yoshida4, T. Suyama5, K. Fukuda5,
A. Yoshikawa6, N. Sato7, H. Kan7 and K. Kamada8
1

Inst. Laser Engineering, Osaka Univ. ,2Kumamoto Univ. ,3Kyushu Univ. ,4Ceramic Research Center of Nagasaki,
5
Tokuyama Corp. ,6Inst. Materials Research, Tohoku Univ. ,7Hamamatsu Photonics K.K. ,8Furukawa Co., Ltd.

㪉㪉㪏㫅㫄㩷㪘㪧㪣㪝㪂㪧㫉㩷㪇㪅㪌㫄㫆㫃㩼㩷㪘㪧㪣㪝㪂㪧㫉㩷㪈㫄㫆㫃㩼㩷㪘㪧㪣㪝㪂㪧㫉㩷㪉㫄㫆㫃㩼㩷㪘㪧㪣㪝㪂㪧㫉㩷㪊㫄㫆㫃㩼㩷㪧㫉㪑㪣㫀㪚㪘㪝㪠㫅㫋㪼㫅㫊㫀㫋㫐㩷㩿㪸㫉㪹㪅㩷㫌㫅㫀㫋㫊㪀

㪉㪍㪇㫅㫄

㪇

㪌㪇

㪈㪇㪇

㪈㪌㪇

㪉㪇㪇

㪉㪌㪇

㪊㪇㪇

㪊㪌㪇

㪋㪇㪇

㪋㪌㪇

㪌㪇㪇

㪌㪌㪇

㪍㪇㪇

㪍㪌㪇

㪎㪇㪇

㪎㪌㪇

㪮㪸㫍㪼㫃㪼㫅㪾㫋㪿㩷㩿㫅㫄㪀

Fig. 1. PL spectra of APLF+Pr and Pr:LiCAF.

㪈㪍㪉㫅㫄㩷㪉㪋㪇㫅㫄㩷㩿㪋㪽㪌㪻㸢㪋㪽㪉㪀㩷㪋㪏㪇㫅㫄㩷㩿㪋㪽㪉㸢㪋㪽㪉㪀㪈㪐㪏㫅㫄㪠㫅㫋㪼㫅㫊㫀㫋㫐㩷㩿㪸㫉㪹㪅㫌㫅㫀㫋㫊㪀The realization of nuclear fusion is highly expectedto satisfy the energy demand in the future. Fusion
plasma diagnostics at higher plasma areal density
than 3 g/cm2 is one of the biggest breakthrough innuclear fusion research. Scattered-neutron diagnostics
20Al(PO3)3-80LiF[1]
utilizing
Pr3+-doped(APLF+Pr) glass scintillator is expected to achieve
plasma areal density measurement in fusion core.
APLF+Pr, which have high sensitivity for scatteredneutrons and fast response time about 5.4 ns, is the
key factor of the measure.
In this work, we report the luminescence properties
of APLF+Pr at different Pr3+ concentrations(0.5mol%㨪3mol%).
We have measured Photoluminescence (PL) spectra
and Photoluminescence Excitation (PLE) spectra of
APLF+Pr at 30K, 50K, 150K, 200K, 250K, and 300K.
The experiment was conducted at BL7B utilizing G2
grating. PL spectra are measured with excitation
wavelength at 80nm, 120nm, 150nm, 180nm, and200nm. The APLF+Pr samples, having Pr+ density at
0.5mol%, 1mol%, 2mol%, and 3mol%, and cut into
10 mm  10 mm  10 mm, were prepared. PL
and PLE spectra of Pr3+-doped LiCaAlF6 (Pr:LiCAF)
was measured as well for comparison.
The PL spectra of APLF+Pr and Pr:LiCAF excitedby 180 nm radiation are shown in Fig. 1. The green
colored lines are corresponding to spectra of APLF+Pr
with Pr3+ density at 0.5mol%, 1mol%, 2mol% and3mol% and red line to that of Pr:LiCAF. The UV
luminescence around 250 nm are observed for eachsamples.
The PLE spectra of APLF+Pr monitoring 240 nm,
400 nm, and 480 nm are illustrated in Fig. 2. The 240
nm emission is attributed to 4f5dψ4f2 transition. In
the other hand, the 400 nm emission occurs from both
4f5d and 1S0.
These consequences indicate that 5d state of Pr3+ in
APLF glass host vary in wide range as shown in Fig.
3.

㩷㪋㪇㪇㫅㫄㩷㩿㪋㪽㪌㪻㪃㪈㪪㪇㸢㪋㪽㪉㪀

㪈㪍㪍㫅㫄

㪌㪇

㪈㪇㪇

㪈㪏㪇㫅㫄
㪈㪐㪋㫅㫄

㪈㪌㪇

㪉㪇㪇

㪉㪌㪇

㪊㪇㪇

㪊㪌㪇

㪮㪸㫍㪼㫃㪼㫅㪾㫋㪿㩷㩿㫅㫄㪀

Fig. 2. PLE spectra of APLF+Pr.

[1] M. Moran et al., Rev. Sci. Instrum. 75 (2004)
3592.

Fig. 3. Energy status of Pr3+ in APLF glass host.

101

BL7B

Vacuum UV Reflectance Spectrum of Diamond
H. Okamura
Graduate School of Science, Kobe University, Kobe 657-8501, Japan
Diamond is one of the most familiar and classicalmaterials of all, with its well known crystal structure
and the covalent bonding. Accordingly, its band
structure has been studied extensively since the earlystage of the band calculation technique. To examine
the energy dependent band structure of a material, it
is very useful to compare the dielectric function
H Z derived from the calculated band structure withthat derived from the measured optical spectra. The
Kramers- Kronig analysis is often used to derive H Zfrom a reflectance spectrum R(Z) measured over awide photon energy range.
In spite of the familiarity of this material in thecondensed matter and materials physics, experimental
studies of its optical properties above the fundamental
absorption edge have been only reported by a small
number of papers [1-5]. Namely, several papers on
the UV and vacuum UV (VUV) reflectancemeasurements of diamond appeared in the 1960’s, butsince then, no further measurements seem to havebeen reported [6], in spite of the persisting interest
from the theoretical point of view [6-8].
In view of the above situation, we have measured
the reflectance of diamond in the VUV using thesynchrotron radiation source at BL7B of UVSOR.
The diamond sample used was a diamond anvil used
for high pressure optical experiments in ourlaboratory at Kobe University. The anvil was of type
IIa with low density of impurities, and had a table
diameter of 3.1 mm, a culet diameter of 0.4 mm, anda height of 1.7 mm. The light beam was incident on
the table side of the diamond. Below the fundamental
absorption edge, there may have been reflection fromthe back (culet) surface, but this should not occur
above the absorption edge.
Figure 1 shows the measured reflectance spectrum
R(Z) of diamond at room temperature. It has a highreflectance band at 12-22 eV and peaks at 7 and 12.5
eV, which had been observed previously [1-5]. The
weak structure at 5.5 eV is due to the fundamental
absorption edge of diamond. This structure is only
weak since the fundamental absorption edge is due toan indirect band gap. The peak at 7 eV is due to thesmallest direct band gap, which was studied in detailincluding its temperature dependence [4]. However,the shoulder at 10 eV and the dip at 23 eV were notclearly observed in the previous works [1-5]. In theold measurements made in the 1960’s, discrete lines
from discharge lamps were used as the light source,
and then the measured reflectance at the discrete
photon energies were interpolated. This resulted inpoor spectral resolution, and these structures had
probably been overlooked. We plan further

measurements in the future, including the temperaturedependences, to make available more complete
optical spectra of this important material forcomparison with the results of band calculations.

Reflectance

0.8
Diamond (type IIa)
300 K

0.6
0.4
0.2
0

5

10
15
20
25
Photon Energy (eV)30

Fig. 1. Reflectance spectrum a type IIa diamond anvil
at room temperature.
[1] H. R. Philipp and E. A. Taft, Phys. Rev. 127(1962) 159.
[2] W. C. Walker and J. Osantowski, Phys. Rev. 134(1964) A153.
[3] H. R. Philipp and E. A. Taft, Phys. Rev. 136(1964) A1445.
[4] R. A. Roberts, D. M. Roessler and W. C. Walker,
Phys. Rev. Lett. 17 (1966) 302.
[5] R. A. Roberts and W. C. Walker, Phys. Rev. 161(1967) 730.
[6] V. V. Sobolev, A. P. Timonov and V. Val. Sobolev,
Optics and Spectroscopy 88 (2000) 255.
[7] A. D. Papadopoulos and E. Anastassakis, Phys.
Rev. B 43 (1991) 5090.
[8] S. Logothetidis, J. Petalas, H. M. Polatoglou andD. Fuchs, Phys. Rev. B 46 (1992) 4483.

102

BL7B

Photoluminescence - Photoluminescence Excitation Spectra of a-Plane AlN
R. Ikematsu, H. Iwai, K. Ozaki and K. Fukui
Fac. Engi., Univ. Fukui, Fukui 910-8507, JapanThe uppermost of the valence band (VB) at the *point of the AlN is split into three bands, LH, HH,
and CH bands. These splits are due to the crystal-field
splitting and the spin-orbit splitting. However, boththe crystal-field splitting energy ('cr) and thespin-orbit splitting energy ('so) of the AlN are
different from those of the GaN [1]. Then, theuppermost VB ordering at the * point of the AlN and
GaN are CH-HH-LH (top-to-bottom order) andHH-LH-CH, respectively. The important point is thatthe transition from CH band, and HH and LH bands
to the conduction band (CB) are allowed for E // cand E A c, respectively, where E represents theelectric field vector of the excitation light and c the
crystal axis. It means that it is not easy to measure theminimum bandgap of AlN, because the AlN samples
are usually thin films and the c axis are perpendicular
to the surfaces (c-plane AlN). On the other hand, thec-axis is parallel to the sample surface in the case of
a-plane AlN (See Fig. 1). Then, we can measure theoptical anisotropy of AlN by the in-plane rotating. In
this report, we present the photoluminescence (PL) PL excitation (PLE) spectra of the a-plane AlN single
crystalline film.

regions) in E A c configuration. The white region at
the lower photon energy side and the white slant line
at the higher photon energy show the impurity PL andRayleigh scattering of the excitation light,
respectively. In the E // c configuration, the PL - PLE
spectrum shows at least three slant line like trajectory
parallel to that of the Rayleigh scattering. The energy
differences among these lines are always 1, 2 or 3 u
110 meV. Here the photon energy difference, 110
meV, is in good agreement with the LO photon
energy of the AlN. Then, we consider that these lines
are attributed to the resonance Raman lines.
㩷

㩷

㪍㪅㪋

㩷

㪍㪅㪊

㪊㪇㪇㪅㪇
High
㪉㪎㪇㪅㪇
㪉㪋㪇㪅㪇
㪉㪈㪇㪅㪇
㪈㪏㪇㪅㪇
㪈㪌㪇㪅㪇
㪈㪉㪇㪅㪇
㪐㪇㪅㪇㪇
㪍㪇㪅㪇㪇
㪊㪇㪅㪇㪇
㪇㪅㪇㪇㪇

㪍㪅㪌
㪍㪅㪋
㪍㪅㪊

㩷

Excitation Energy (eV)

㪍㪅㪌

Low

㪍㪅㪉
㪍㪅㪈
5.0

5.2

5.4

5.6

5.8

6.0

6.2

6.4

6.6

㩷Photon Energy (eV)Fig. 2. The photoluminescence – photoluminescence
excitation (PL – PLE) spectra at 20 K of a-plane AlN
thin film with E A c (above) and E // c (below)
configurations.

Fig. 1. c-plane (left) and a-plane (right) of thewurtzite AlN
The AlN single crystalline film was grown on ther-plane sapphire substrate by the MOVPE method [2].
All measurements have been performed at BL7B. The
PL from the sample at about 20 K is measured by theconventional 0.3 m monochromator with the Liq. N2
cooled CCD.
Figure 2 shows the PL-PLE spectrum of thea-plane AlN at 20 K with E A c (above) and E // c(below) configurations. The horizontal and thevertical axes represent the photon energy of the PL
and the excitation energy, respectively. The verticalstraight-line like trajectory at 6.05 eV in eachconfiguration represents the well-known PL peak due
to the free and bound excitons of the AlN, and arestrongly excited at 6.3 – 6.35 eV (red and white103[1] T. Onuma, S. F. Chichibu, T. Sota, K. Asai, S.
Sumiya, T. Shibata and M. Tanaka, Appl. Phys. Lett.
81 (2002) 652.
[2] N. Okada, N. Kato, S.Sato, T. Sumii, N. Fujimot,
M. Imura, K. Balakrishnan, M. Iwaya, S. Kamiyama,
H. Amano, I. Akasaki, T. Noro and A. Bandoh, J.
Cryst. Growth 300 (2007) 141.

BL7B

Refractive Index of Heavily Boron Doped Diamond with Impurity Band
T. Inushima1, Y. Ota1 and K. Fukui2
1

Department of Electronics, Tokai University, 4-1-1 Kitakaname, Hiratsuka 259-1292, Japan
Department of Electrical and Electronics Eng., University of Fukui, Bunkyo, Fukui 910-8507, Japan104

4u1018cm-3, it has k-space dependence and changes
the refractive index in the visible region.
3
5000 ppm Boron doped diamond2

Reflectivity (arb. units)

Refractive index

1

0.20

0.15

0.10

500

600

700 800

900 1000 1100

Wavelength (nm)

0

1.0

1.2

1.4

1.6

1.8

Photon energy (eV)Fig. 1. Refractive index of 5000 ppm boron doped
diamond. Inset shows the sinusoidal oscillation of thereflection spectrum caused by interference of thetransmitted light.

6

C2
C63B
C53B

4

Refractive index (Re)

Since the discovery of superconductivity inboron-doped diamond, its impurity band structure has
been a key issue for the understanding of thesuperconductivity. Recently we reported that when
the boron concentration exceeds NB=4u1018cm-3, an
impurity band forms at the first excited levels (2p) of
the impurity boron at 0.06 eV above the valence band
maximum. At higher NB, the wave functions of the 2P
states begin to overlap and the impurity band spreads
in the k-space. Simultaneously, Fermi level rises tothe impurity band and a variable range hopping isrealized [1]. When the impurity band has k-spacedependence, the refractive index should change,
especially in the visible region. However, precise
refractive index measurement was not been reported.
Hence we measure the refractive index of boron
doped diamond with impurity band using BL7B andcompare it with that obtained by the density
functional first principle calculation.
Figure 1 shows the refractive index of 5000 ppm
boron doped diamond measured at 300 K by a
combination of G3 grating (1.2~7.7 eV) and aphoto-diode detector of BL7B. The value of 5,000
ppm corresponds to NB=1u1019cm-3. The reflection
spectrum shown in the inset shows weak sinusoidal
interference fringes caused by the interference of thetransmitting light of the homo-epitaxial diamond film.
Using the film thickness of 1.6 Pm, the refractive
index is obtained from the oscillatory order of theinterference so as to fit the optimum refractive index
of 2.4 at 1.8 eV, where the oscillation disappears. The
observed refractive index is much smaller than that of
the bulk diamond (n~2.4), and shows a continuous
decrease as the photon energy decreases and becomesless than 1 around 1.2 eV.
Figure 2 shows the refractive index of boron doped
diamond obtained by ab initio calculation. The used
program is Advance/PHASE and the cutoff
wavefunction energy is 25 Hartree. The calculation
model is the diamond C63B super cell, where theBravais unit cell of diamond is expanded to 2u2u2
and one carbon atom is replaced by a boron, whichcorresponds to NB=2.7ucm-3. For comparison,refractive indices of single unit cell diamond and
C53B super cell are also plotted. The calculated
refractive index is in good agreement with thatobtained in Fig. 1, which indicates that the impurity
band forming in the boron doped diamond with
NB=1u1019cm-3 is similar to that with a boron
concentration two orders of magnitude larger.
In conclusion, when the impurity band isestablished in boron doped diamond when NB>

Refractive index (Re)2

6

oscillator stregth
per electron

4

0.994
0.819
0.8533

2
0
0

10

20
30
Photon energy (eV)

40

2
0
0

1

2

3

4

5

Photon energy (eV)Fig. 2. Refractive indices of diamond, C63B and C58B
super cells obtained by ab initio calculations.
[1] T. Inushima, R. F. Mamin and H. Shiomi, Phys.
Rev. B 79 (2009) 045210.

BL8B

Photoelectron Spectroscopy of Sc3N@C78*
S. Hino1, M. Zenki1, T. Zaima1, Y. Aoki1, S. Okita1, T. Ohta1, H. Yagi1, T. Miyazaki1,
R. Sumii2, 3, H. Okimoto4, Y. Ito4 and H. Shinohara4
1

Graduate School of Science and Engineering, Ehime University, Matsuyama 790-8577, Japan
2
UVSOR, Institute for Molecular Science, Okazaki 444-8585, Japan
3
Research Center for Materials Science, Nagoya University, Nagoya 464-8602, Japan
4
Graduate School of Science, Nagoya University, 464-860, Japan

Extensive ultraviolet photoelectron spectroscopic
studies ofsingle metal
atom entrapped
metallofullerenes, M@C82, established an empiricalrule that the cage structure principally governs theelectronic structure of these metallofullerenes and adifference in the amounts of transferred electrons tothe cage is another factor to modify it. A similar
relationship was found in the UPS of endohedral
fullerenes encapsulating multiple atoms, such as
Sc2C2@C82 [1], Y2C2@C82 [2] and M3N@C80 (M =Sc, Tm and Dy) [3]. However, the UPS of La2@C78
and Ti2C2@C78 were significantly different [4], eventhough their cage symmetry was the same D3h.
Isolation of another C78 cage endohedral fullerene,
Sc3N@C78, has also been reported. Since its
absorption spectrum is significantly different fromthose of La2@C78 and Ti2C2@C78, it is highlyplausible that their electronic structure might bemutually different. We measured the ultraviolet
photoelectron spectra of Sc3N@C78 and comparedthem with the UPS of La2@C78 and Ti2C2@C78.
Density functional theory (DFT) calculation was also
performed to elucidate the plausible geometry of
Sc3N@C78.
The valence band UPS of Sc3N@C78 obtained withhQ = 20 – 60 eV photon energy. The spectral onset
was 0.75 eV below the Fermi level. There are 8
explicit structures labeled A to H in the UPS of
Sc3N@C78. Approximate peak positions of thestructures are indicated with dotted lines.
The UPS of La2@C78, Ti2C2@C78 and Sc3N@C78
obtained with hQ = 40 eV photon energy are shown in
Fig. 1. These three endohedral fullerenes have thesame cage symmetry of D3h (78:5). For the electronic
structures located in the 5 - 11 eV binding energy
region, there is a fairly good correspondence among
these three UPS, although there are slight deviationsin the corresponding structure peak positions(indicated by dotted lines) and slight difference intheir relative intensity. Since the structures in thisregion are due to V-electrons, the present findings
suggest that the V-electronic structures of these threeendohedral fullerenes do not differ significantly. On
the other hand, there is a significantly large differencein the upper valence band UPS (between the Fermi
level and BE = 5 eV), which is against the empirical
rule. X-ray photoelectron spectra of these endohedral
fullerenes and the DFT calculation revealed that there
was a critical difference in these fullerenes in theamounts of transferred charge from the entrapped
species to the cage.
DFT geometry optimization of Sc3N@C78 gave
three possible structures and one of them reproduced
the UPS very well (Fig. 2). Therefore, we concluded
that Sc3N@C78 took the geometry shown in the inset
of Fig. 2.

Fig. 1. UPS of La2@C78, Ti2C2@C78 and Sc3N@C78.

Fig. 2. DFT calculated simulation spectra and the
UPS of Sc3N@C78 and its estimated structure.
*This work was publiushed in J. Chem. Phys. C 116(2012) 165.
[1] T. Pichler et al,. PRB 62, (2000) 13196.
[2] S. Hino et al., PRB 72 (2005) 195424.
[3] H. Shiozawa et al., PRB 72 (2005) 195409.
[4] S. Hino et al., PRB 75 (2007) 125418.

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BL8B

Ultraviolet Photoelectron Spectra of Er2@C82 (I), Er2@C82 (III),
Er2C2@C82 (I) and Er2C2@C82 (III)T. Miyazaki1, R. Sumii2, 3, H. Umemoto4, H. Okimoto4, Y. Ito4, T. Sugai4, H. Shinohara4,
T. Zaima1, H. Yagi1 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
series of structures ȕ, Ȗ, į appear between 6.7 and 8.6
eV with a slight intensity variation and a difference intheir intervals. These peak positions of structure ȕ andį do not shift so much, but peak top position of
structure Ȗ moves in slightly wider range. Thesefindings indicate that the skeletal C–C ı-bonds inendohedral fullerenes are similar in these endohedral
fullerenes and they are not seriously affected byentrapped species. As for the upper valence band UPSof these endohedral fullerenes, the situation is quite
different. The electronic structure is principallydependent on the cage structure, and entrapped
species do not bring serious change to the electronic
structure of endohedral fullerenes. That means theempirical rule that the electronic structure ofmono-metal entrapped endohedral fullerenes isprincipally governed by the cage structure seems to
be held in multiple atoms encapsulated fullerenes.
The difference spectrum between the UPS of Er2@C82(III) and Er2C2@C82 (III) has the same C3v structure
reveals two excess electrons on the cage of Er2@C82.
Photoelectron counts

Fullerenes cages often encapsulate metal atoms andmetal-carbide clusters, and entrapped metal atoms
donate electrons to the cage so that the electronic
structure of the fullerene cage is altered by theencapsulation. Recently, erbium atoms and erbium
carbide encapsulated C82 fullerenes, Er@C82 (I),
Er2@C82 (I), Er2@C82 (III), Er2C2@C82 (I) andEr2C2@C82 (III), have been isolated. The NMR study
revealed their cage symmetry as follows, C2v (82:9) for
Er@C82 (I), Cs (82:6) for Er2@C82 (I) and Er2C2@C82(I), C3v (82:8) for Er2@C82 (III) and Er2C2@82 (III). It
is worthwhile to examine what kind of change
entrapped multiple Er atoms bring to the electronic
structure of the C82 cage. In this report, ultraviolet
photoelectron spectra (UPS) of Er2@C82 (I), Er2@C82(III), Er2C2@C82 (I) and Er2C2@C82 (III) are presented
and compared with the valence band electronic
structure of their endohedral C82 fullerenes.
Er2@C82 (I), Er2@C82 (III), Er2C2@C82 (I) andEr2C2@C82 (III) were synthesized and isolated fromthe soot containing them. Specimens for photoelectron
spectra measurement were prepared by vacuum
deposition onto a gold deposited molybdenum disk
from a quartz crucible under 5×10-7 Pa. The
temperature of the crucible during vacuum depositionof endohedral fullerenes was 650°C ~ 700°C. The
UPS was measured at the beamline BL8B of
Ultraviolet Synchrotron Orbital Radiation Facility of
Institute for Molecular Science. The base pressure of
the UPS measurement chamber was 4×10-8 Pa and thepressure during the measurement was about 6×10-8 Pa.
The measured UPS were referenced against the Fermi
level (EF) of gold and were plotted as a function ofbinding energy relative to EF. All UPS werenormalized by the peak height of a structure appearedat around 5.5 eV. The energy resolution of the UPS
was 110meV, which was estimated from the width of
the Fermi edge of gold.
The UPS of these endohedral fullerenes taken by
40eV photon energy are collected in Figure 1 forcomparison. The spectral onset energy of theseendohedral fullerenes is around 0.8 䎃 ~  0.9 eV,
which is larger than that of Er@C82 (I) of 0.4 eV [1].
As for the deeper binding energy region (structureslabeled by Į – İ), the electronic structure of theseendohedral fullerenes seems to be almost analogous
although there are minute differences among them: A
large structure ‘Į’ appears at around 5.4 ~ 5.6 eV, a

G J

UPS

hQ = 40 eVE
DH

S-bond region
F

ED
CB

A

Er2C2@C82(III)

E

D

CB
A

Er2C2@C82(I)F

E DC B

E

D

C

A

Eonset10

Er2@C82(III)B

V-bond region

12

A

Er2@C82(I)86420 = EF
Binding Energy / eV

Fig. 1. UPS of Er atoms encapsulated fullerenes were
measured by incident photon energy of 40 eV.
[1] T. Miyazaki et al., Chem. Phys. 378 (2010) 11.

106