Ⅲ-4
Surface,
Interface andThin Films

Ⅲ -4. Surface, Interface and Thin Films
BL3U
BL3U

In-situ O K-edge XAFS Measurements of MnOx Oxygen Evolution
Catalysts Containing Alkali Metal Cations
M. Yoshida1, 2, F. Yamamoto1, M. Nagasaka3, H. Yuzawa3, N. Kosugi3 and H. Kondoh1
Department of Chemistry, Keio University, Yokohama 223-8522, Japan
Cooperative Research Fellow, Institute for Catalysis, Hokkaido University, Sapporo 001-0021, Japan
3
Institute for Molecular Science, Okazaki 444-8585, Japan
1

2

121

changed from 0.0 to 1.0 V, the O K-edge XAFS spectra
did not change so much, meaning that the electronic
states of oxygen species in the δ-MnO2 structure were
almost the same between lower and higher electrodepotentials. On the other hand, a peak of higher energy
around 531.8 eV was slightly disordered for Cs:MnOx
compared with Na:MnOx and K:MnOx, indicating thatthe larger amount of hydroxide or hydroxyl group may
be generated for Cs:MnOx, in response to the presenceof Mn3+ species.
In conclusion, we measured in-situ O K-edge XAFS
for M:MnOx catalysts and revealed that the chemical
state of M:MnOx was δ-MnO2 under OER condition.
The presence of Mn3+ species in the Cs:MnOx is likely
to be the key of OER activity.

Normalized Intensity / a. u.

Electrochemical hydrogen production from waterusing renewable energy attracts attention to construct asustainable society. For this purpose, electrocatalysts forhydrogen and oxygen evolution reactions (HER and
OER, respectively) are used to decompose water(2H2O→2H2+O2). However, the efficiency of OER is
insufficient compared with that of HER. Thus, thedevelopment of efficient OER catalysts has beenrequired to improve the activity for overall water
splitting. In this situation, the layered manganese oxide
containing K+ cation (K:MnOx) was reported to function
as an efficient catalyst for OER over a wide pH range[1]. Meanwhile, we found that the OER activity of thelayered Mn oxide is enhanced when Cs+ cation iscontained in the catalysts (Cs:MnOx). Therefore, in thisstudy, we investigated the reaction mechanism of
M:MnOx (M = Na, K, Cs) catalysts by in-situ O K-edge
X-ray absorption fine structure (XAFS) measurements
under potential control conditions and discussed theeffect of cations in the catalysts.
Electrochemical O K-edge XAFS measurementswith transmission mode using soft X-rays were
performed at BL3U in the UVSOR Synchrotron,
according to the previous works [2]. A home-madeelectrochemical cell was used with Au/Cr/SiC thin film
substrates as working electrodes, a Pt counter electrode,and a Ag/AgCl reference electrode. The Na:MnOx,
K:MnOx, and Cs:MnOx catalysts were electrodepositedon the Au/Cr/SiC working electrode at 0.6 V inmethylphosphonate electrolyte containing MnCl2 andXOH (X = Na, K, and Cs, respectively).
Prior to the O K-edge XAFS, in-situ Mn K-edge
XAFS measurements were tested for the Na:MnOx,
K:MnOx, and Cs:MnOx. The results exhibited that the
manganese species in the catalysts were present as
Mn3+ with δ-MnO2 structure at lower electrodepotential and as Mn4+ with δ-MnO2 structure at higher
electrode potential. In addition, the estimation ofmanganese valence suggested that the fraction of Mn3+
species in the Cs:MnOx under OER condition was
higher than those in the Na:MnOx and K:MnOx.
Next, the in-situ O K-edge XAFS spectra for
Na:MnOx, K:MnOx, and Cs:MnOx were taken underelectrode potential control in a phosphate buffered
electrolyte, as shown in Figure 1. An absorption peak
was observed around 529 eV at 0.0 and 1.0 V for all
catalysts. From the comparison with reference samples,
it was found that the absorption peak was attributed tothe δ-MnO2, consistent with the results of Mn K-edge
XAFS. However, even if the electrode potential was

Na:MnOx
K:MnOxCs:MnOx
MnO2
δ-MnO2
MnOOH
Mn2O3
Mn3O4
MnO

526

528
530
532
Photon Energy / eV

Fig. 1. In-situ O K-edge XAFS spectra of Na:MnOx,
K:MnOx, Cs:MnOx electrocatalysts at 1.0 V (solidline) and 0.0 V (dotted line) in phosphate buffered
electrolyte.
[1] (a) D. G. Nocera et al., J. Am. Chem. Soc. 136(2014) 6002. (b) J. Am. Chem. Soc. 137 (2015) 14887.
[2] (a) M. Nagasaka et al., J. Phys. Chem. C 117(2013) 16343. (b) M. Yoshida et al., J. Phys. Chem. C
119 (2015) 19279.

Ⅲ- 4

Ⅲ -4. Surface, Interface and Thin Films
BL2A
BL2A

Studies on Interface of Thin Film by Near-edge X-ray Absorption Fine
Structure
E. Kobayashi1, K. K. Bando2, O. Takahashi3, K. K. Okudaira4 and T. Okajima1

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

2

X-ray

metal meshVsample(Al/SiO2/Si)
metal plate

Fig. 1. experimental setup.

PFY● : before discharge● : V=10 V● : after discharge

TEY● : before discharge● : after discharge

Intensity (arb. units)
Intensity (arb. units)

Ⅲ- 4Resistive random access memory (ReRAM) is
expected as a new next generation memories. The
memory operates by applying a voltage to a structurein which an oxide film is sandwiched between
electrodes. However, the mechanism of action anddegradation mechanism have not been clarified yet. It
is important to investigate the metal/oxide interface toelucidate them. Near-edge X-ray absorption finestructure (NEXAFS) is effective as one of methods toinvestigate the change in chemical state and depth
profiling of the film. In this paper, we investigated theinterface of Al/SiO2/Si(111) by NEXAFS.
The silicon oxide thin films (~3ML) prepared on
Si(111) using molecular beam epitaxy (MBE). Si
K-edge NEXAFS spectra of thin film were measured
at the beamline 2A of the UVSOR. The experimental
setup for NEXAFS measurement is shown in Fig. 1.
The soft x-ray was passed through a metal mesh andwas irradiated to the sample. In the total electron
yield (TEY), the drain current of the sample wasmeasured. The fluorescence from sample was
detected by silicon drift detectors. Potential of thesample was applied between the metal mesh andmetal plate. All experiments were performed at room
temperature.
Figure 2 shows the Si K-edge NEXAFS spectra of
Al/SiO2/Si(111) obtained from partial fluorescence
yield (PFY) and TEY mode.
The spectra of TEY mode show a strong peak ataround 1847 eV. The spectral features are similar tothat of bulk SiO2. Although the overall structure of
the spectrum has hardly changed before and after
discharging, the peak intensity of spectrum after
discharging became weak. This indicates thatinteraction occurs at the interface between Al and
SiO2 by voltage application.
The peak of the spectrum in the PFY mode wasobserved on the lower energy side than in the TEY
mode. The spectrum peak of bulk Si is observed atabout 1840 eV. Therefore the origin of the observed
peak is near the SiO2/Si interface. The intensitychanged when a potential was applied. This indicatesthat the silicon oxide changed due to voltage
application.

1840 1845 1850 1855 1860 1865
Photon Energy (eV)Fig. 2. Si K-edge NEXAFS spectra of Al/SiO2/Si(111)
obtained from PFY and TEY mode.

122
Ⅲ-4-2

Ⅲ -4. Surface, Interface and Thin Films
BL2A
BL2A

Studies on Chemical State of Oxide Film under Applied Voltage by
Near-edge X-ray Absorption Fine Structure
K. K. Okudaira1, O. Takahashi2, K. K. Bando3 and E. Kobayashi4

Chiba University, Chiba 263-8522, Japan
Institute for Sustainable Science and Development, Hiroshima University, Higashi-Hiroshima 739-8526, Japan
3
National Institute of Advanced Industrial Science and Technology, Tsukuba 305-8565, Japan
4
Kyushu Synchrotron Light Research Center, Tosu 841-0005, Japan1

2

voltage becomes higher. Furthermore, after discharge
the intensity of the main peak does not turn back tothat at V = 0 V This indicates that the application ofvoltage affect the structure of the Al-OH moiety inthe film.

Intensity (arb, units)

High-k aluminum oxide (Al2O3) is considered apotential alternative gate dielectric material on Si
substrates for application to not only conventional
inorganic transistor but also organic filed-effecttransistors (OTFT). In particular, OTFT have been thefocus of considerable research activity during the past
10 years [1]. The performance of OTFT depends
critically on the use of high-performance dielectrics
that form active interfaces with low defect densities.
In principle, for a given thickness of dielectric, ahigh-k dielectric is preferable to a low-k dielectric for
an FET application that requires the FET to exhibit ahigh drive current at low drive voltage. Various
solution-processible high-k dielectrics for low-voltage
OFET have been used such as anodized aluminumoxide (dielectric constant = 8–10) [2]. The charge
injection efficiency depends on energy levelalignment of the interface between the dielectrics
surface and the organic semiconductor layer. The
surface Al2O3 is strongly influenced by the degree of
surface hydroxylation [3].
In this paper, we investigated the chemical state ofan Al2O3 under applied voltage by NEXAFS.
An alumina film was made on a polished stainlesssteel plate by dip-coating with a diluted alumina sol(Kawaken Fine Chemicals, F1000). The coated plate
was dried at 333 K, 6 hours and calcined at 473 K, 3
hours in an oven.
Al K-edge NEXAFS spectra of aluminum oxidethin film were measured at the beamline 2A of the
UVSOR. The soft x-ray was passed through a metal
mesh and was irradiated to the sample. The
fluorescence from sample was detected by silicon
drift detectors. Potential of the sample was applied
between the metal mesh and metal plate. All
experiments were performed at room temperature.
Figure 1 shows the Al K-edge NEXAFS spectra ofaluminum oxide obtained from PFY mode at various
applied voltage. The spectra were measured while
applying a voltage. This sample caused breakdown at~ 0.8 V. After breakdown, the potential to the sample
could not be applied. The spectra show a strong peakat around ~1568 eV, attributed to Al bonded to OH
group in the Al2O3 film. Although the overall
structure of the spectrum has hardly changed, theintensity of the main peak decreases as applied

V=0V
V=0.2 V
V=0.4 V
V=0.8 ～ 0.6 V
after discharge

1555 1560 1565 1570 1575 1580 1585
Photon Energy(eV)Fig. 1. Al K-edge NEXAFS spectra of aluminumoxide thin film obtained from PFY mode at various
applied voltage.
[1] H. Sirringhaus, Adv. Mater. 17 (2005) 2411.
[2] L. A. Majewski, M. Grell, S. D. Ogier and J. Veres,
Org. Electron. 4 (2003) 27.
[3] P. J. Eng, T. P. Trainor, G. E. Brown Jr., G. A.
Waychunas, M. Newville, S. R. Sutton and M. L. Rivers,
Science 288 (2000) 1029.

123
Ⅲ-4-3

Ⅲ- 4

Ⅲ -4. Surface, Interface and Thin Films
BL2B
BL2B

Modification of the Overlapping of the Frontier Orbitals
Y. Yamada1, Y. Hasegawa1, T. Maeda1, T. Hosokai2 and K. R. Koswattage3

1
Institute of Applied Physics, University of Tsukuba, Tsukuba 305-8573, Japan
National Institute of Advanced Industrial Science and Technology, Tsukuba 305-8568, Japan
3
Institute for Molecular Science, Department of Photo-Molecular Science, Okazaki 444-8585, Japan
2

The ARPES spectrum along the molecular rows isshown in Fig. 2 (b). The molecular orbitals are broad
because of the presence of five bands. Althoughenhanced π-stacking in the molecular row is expected,
we found almost no apparent dispersion in the upper
frontier orbitals such as HOMO and HOMO-1. On
the other hand, weak dispersing feature is seen in thelower-lying orbitals which is not seen in the ARPES
spectrum taken perpendicular to the row. The detailed
calculation is ongoing in order to determine theorbitals responsible to the observed dispersion.

(a)

(b)

0
1
2
3
4
5
6

0 10 20 30 40 50 60 0 10 20 30 40 50 60

Angle (deg)Fig. 1. (a) STM image of several layer of DNTT/Ag(110). (b) ARUPS along and perpendicular to themolecular axis.
Γ-K direction

Γ-M

Binding energy (eV)

0
-1
-2
-3
-4

11nm

-5
2.0

1.5

2.0

1.5

1.0

Wave number (

0.5
! "

0

)

Fig. 2. (a) STM image of monolayer of sumanene/cu(111). (b) ARUPS along and perpendicular to themolecular row.
[1] Y. Hasegawa et al., J. Phys. Chem. C, 120 (2016)
21536.
[2] S.Berkebile, et al., Phys. Rev. B 77 (2008) 115312.
[3] G. Koller, et al., Science 317 (2007) 351.
[4] Y. Yamada, (in preperation).

124
Ⅲ-4-4

Binding energy (eV)Ⅲ- 4Organic
semiconductors
withenhancedintermolecular interaction have attracted attentions
since they may exhibit an enhanced intermolecular
overlapping of the frontier orbitals and thus the
band-like transport. By tailoring unique ordering ofthese molecules on the well defined substrate, we areable to modify the intermolecular overlapping of thefrontier orbitals, resulting in significant alteration of
the electronic states from that of the bulk. In thisstudy, we focused on simple examples of thesemolecules such as DNTT and sumanene.
In order to realize the control of molecular packing
and electronic structure of these molecules in arealistic environment, all the experiments were doneat room temperature. ARPES measurements are donein BL2B of UVSOR with the incident light of 28 eV.
[1. DNTT on Ag(110)]We have shown that, there exist two types ofordering of the monolayer of DNTT, i.e, the dense
phase and the loose phase, and that the dense packing
induces a considerable splitting of HOMO due tooverlapping [1]. Recently, we found that the
one-dimensional structure of the "loose" DNTT
monolayer can be formed on the anisotropic Ag(110)substrate (Fig. 1 (a)). The monolayer consists ofapparent molecular rows; the long axis of moleculesin the row is parallel to the direction of the rows.
In the ARPES spectra obtained along the direction of
the molecular rows, i.e, parallel to the molecular axis
(Fig. 1 (b)), the intra-molecule dispersion-like feature
was observed, similarly to the case of well-orderedpentacene [2] or 6P [3]. The intramolecule dispersion
apparently exhibits a backfolding due to the periodicityof half-length of the molecule, possibly reflecting thecharacteristic molecular shape. On the other hand, inthe perpendicular to the row, i.e, perpendicular to themolecular axis, each orbitals show almost negligible
band dispersion, suggesting that the intermolecule
overlapping is small because of the loose packing inthis structure, in contrast to our previous observation in
the dense monolayer of DNTT [1]. Therefore, we notethat the band dispersion in this type of system does notnecessarily reflect the band dispersion of the bulk
system.
[2. Sumanene/Cu(111)]
Sumanene on Au(111) and Ag(111) are found to takea flat-lying geometry with the bowl-up and bowl-down
molecules [4]. On the other hand, Sumanene monolayer
on Cu(111) exhibit one-dimensional stacking of slightlytilted sumanene molecules (Fig. 2 (a)). The monolayer
consists of the five different rows of sumanene.

Ⅲ -4. Surface, Interface and Thin Films
BL2B
BL2B

ARUPS of Pentacene on a-TES Film Prepared on SiO2
1

Y. Urabe1, Y.Aoki2 and K. K. Okudaira1

Association of Graduate Schools of Science and Technology, Chiba University,Chiba 263-8522, Japan
2
Faculty of Engineeringy, Chiba University, Chiba 263-8522, Japan

An organic thin-film transistor (OTFT) has been
actively studied in recent years. To achieve highmobility it is important to improve the charge injection
efficiency at the interface between the substrate and theorganic semiconductor layer and charge transfer
probability. Self-assembled monolayers (SAMs) has
been introduced on metal electrode and insulator layer
in order to arrange the molecular orientation of organic
semiconductor film and energy level alignment of theinterface [1].
For the case of a bottom-contact type OTFT, it isnecessary to introduce two kinds of SAM chemicallybonded to not only metal electrode but also insulator
layer. A triazine-based molecular adhesion agent (aTES : 6-triethoxysilyl propylamino-1,3,5- triazine-2,4dithiol(TES)) was used for preparing thin film like
self-assembly monolayers on Cu surface as well as SiO2
insulator layer
In this work we used a-TES modified SiO2 substrateand examined the molecular orientation of pentacene
thin films thermally deposited on the surface by angleresolved ultraviolet photoelectron spectroscopy(ARUPS) measurements. To obtain the quantitative
analysis on the molecular orientation; we compare
observed take-off angle dependence of π band andcalculated ones by the independent-atomic-center (IAC)/
MO approximation [2].
ARUPS measurements were performed at the beamline BL2B of the UVSOR. The take-off angle (θ)
dependencies of photoelectron spectra were measured
with the photon energy (hν) of 28 eV. We use a-TES
modified SiO2 and SiO2 as substrate. SiO2 substrate
was subjected to ultrasonic cleaning for 10 minutes in
acetone, isopropanol, and then ozone cleaning for 30
minutes. a-TES modified SiO2 substrate was obtainedby dipped in 0.1% solution at 20°C for 30 minutes.
Pentacene was deposited on 1.4 nm on both substrates.
We observed take-off angle (θ) dependence of
HOMO peak in UPS of pentacene deposited on
a-TES/SiO2 and SiO2 (thickness of 1.4 nm ).
The HOMO peaks of pentacene on a-TES/SiO2 andon SiO2 appear at binding energy of about 1 eV and
2eV, respectively. The HOMO peaks of pentacene
both on a-TES/SiO2 and on SiO2 show intense peaks
at higher take-off angle (θ = 60°), and at lower θ these
intensities become small. For a-TES/SiO2, HOMO
intensity at θ = 20° is smaller than that at θ = 0°. On
the other hand, for SiO2 substrate, HOMO intensity atθ = 20° is almost same as that at θ = 0°. Due to thedifference of θ dependence of HOMO peak on
a-TES/SiO2 and on SiO2, it is found that the molecularorientation of pentacene on a-TES/SiO2 is different

from that on SiO2. The difference of surface energy of
a-TES and SiO2 indicates that the surface modification
by a-TES affects the molecular orientation of organic
semiconductor layer, which would have an effect on
the characteristics of OTFT such as mobility.

θ=

θ=

Ⅲ- 4

Fig. 1. ARUPS of pentacene(1.4nm)/SiO2 (a) andpentacen(1.4nm)/a-TES/SiO2 (b).
[1] F. Wang et al., Nanoscale Res. Lett. 6 (2011) 483.
J. –P. Hong et al., Appl. Phys. Lett. 92 (2008) 143311.
[2] N. Ueno et al., J. Chem. Phys. 99 (1993) 7169.

125
Ⅲ-4-5

Ⅲ -4. Surface, Interface and Thin Films
BL2B
BL2B

Electronic States of Self-assembled Peptide Films on the Graphite Surface
Y. Nakayama1, T. Narimatsu2 and Y. Hayamizu2, 3Faculty of Science and Technology, Tokyo University of Science, Noda 278-8510, Japan
Department of Materials Science and Engineering, Tokyo Institute of Technology, Tokyo 152-8550, Japan
3
PRESTO, Japan Science and Technology Agency (JST), Kawaguchi 332-0012, Japan
1

2

Ⅲ- 4

One promising route for bioelectronics and biosensing
is functionalization of electrodes by proteins such as
enzymes and antibodies. Therefore, attachment of theprotein molecules onto the electrode surfaces is a crucial
problem. Thiol groups of the cysteine residues can beutilized as “anchors” for binding the protein molecule
covalently onto the noble metal electrodes, whose
interface properties our group has already reported so far[1]. Besides these conventional electrode materials,
graphene is attracting growing interests due to its
biocompatibility. On the graphene or graphite, benzene
rings of some amino residues (such as tyrosine)
preferentially adsorb on the surface through the π-πinteraction.
Recently, peptides, fragments of proteins, of certain
sequences are discovered to build regular networked
structures spontaneously on the graphite surface [2].
Some of these peptide molecules dope the graphene
electric devices to switch the transport properties [3],yet the electronic origins of such functionalities arestill unsolved. In the present study, we examined theinterface electronic structures between a functional
peptide GrBP5-WT [2] and the graphite surface.
Self-assembled peptide film samples were preparedby procedures described elsewhere [2, 3]. Ultraviolet
photoelectron spectroscopy (UPS) measurements
were conducted at BL2B of UVSOR.
Figure 1 (a) shows UPS spectra of submonolayer
and multilayer films of the peptide. The profile of thelatter is fairly consistent to simulated density-of-states(DOS) curve based on quantum-chemical calculation
results for the whole GrBP5-WT molecule, while thatof the former rather resembles the DOS of theleft-half fragment of this peptide molecule. Taking
into consideration that the anchoring groups ongraphite are tyrosine (Y) residues in the right-half of
this peptide, this changing tendency of the UPS
profiles implies disordering in the molecularorientation from the first adsorbed layer to themultilayers. The UPS spectra of the highest-occupied
molecular orbital (HOMO) and secondary-electron
cutoff (SECO) regions are shown in Figs. 1 (b) and (c),respectively. From the low-energy onset position of
the HOMO and work function value derived from the
SECO spectra, the ionization energy of this peptide isdetermined to be 7.6 eV. A rise in the work function
by formation of the GrBP5-WT film indicateselectron transfer from graphite to the overlayer, whichrationalizes the reported functionality of this peptide
as an acceptor for the graphene devices [3].

Fig. 1. (a-c) UPS spectra of self-assembled peptide
GrBP5-WT (upper inset) films on graphite substrates.
Simulated DOS distributions and molecular orbital(MO) energies are also displayed in (a).
[1] K. R. Koswattage et al., e-J. Surf. Sci. Nanotechnol.
13 (2015) 373; idem, UVSOR Activity Reports 40(2013) 90.
[2] C. R. So et al., ACS Nano 6 (2012) 1648.
[3] Y. Hayamizu et al., Sci. Rep. 6 (2016) 33778.

126
Ⅲ-4-6

Ⅲ -4. Surface, Interface and Thin Films
BL2B
BL2B

Electronic Structures of Organic-Metal Interface Measuring by UPS:
bis(l,2,5-thiadiazolo)-p-quinobis(l,3-dithiole) andTris-(8-hydroxyquinoline)aluminum Alq3
1

N. Ohashi1, S. Kobayashi1, M. Hikasa2, Y. Nakayama2 and Y. Watanabe1

Department of Electrical and Electronic Engineering, Faculty of Engineering, Tokyo University of Science, Chino
391-0292, Japan2
Department of Pure and Applied Chemistry, Faculty of Science and Technology, Tokyo University of Science,
Noda 278-8510, Japan

In this report, we were investigated two types of metalorganic interface. First one is bis (l, 2, 5-thiadiazolo)p-quinobis (l, 3-dithiole) (BTQBT)-aluminum interface.
BTQBT was known as high performance organic
semiconductor which shows maximum mobility of 4
cm2/Vs. [1] A vertical type transistors with BTQBT
shows current density of 1 A/cm2 and on/off current ratioof over 105. [2] These reports prove a superiority of
BTQBT, however, device operation mechanism of thevertical-type transistor is still unclear. So we investigate
BTQBT and aluminum interface by ultraviolet
photoelectron spectroscopy (UPS) at the first of theresearch.
The UPS measurement was performed at BL2B ofUVSOR. Photon energy was 38 eV. We have preparedSi substrate covered with gold film. Aluminum and
BTQBT were fabricated on the substrates by vacuum
deposition. All experiments were carried out in vacuo.
Figure 1 shows UPS spectra of BTQBT on aluminumelectrode. BTQBT thickness dependence with UPS
spectra was examined for the purpose of estimating theenergy level diagram of BTQBT-aluminum interface.
The UPS results of SECO position indicates that thevacuum level varies with thickness of BTQBT. The
vacuum level shift of the bulk region correspond to the
HOMO edge of BTQBT shown in Fig. 1 (b). It is
attributed band bending of BTQBT. We summarizedvacuum level shift of BTQBT film in Fig. 2. The
Vacuum level is abruptly changed at the very interfaceof BTQBT and aluminum. The vacuum level is stable
near the interface, then varies with thickness at the bulk
region. The charge injection barrier of BTQBTaluminum interface was estimated 0.78 eV.
Next then, we briefly explained second topic, Alq3PEI-ITO interface. (Alq3 and PEI stand for Tris(8-hydroxyquinoline)aluminum and poly ethylene imine,
respectively.) Recently, it was reported that ITO
covered with ultrathin PEI performed excellent electron
injection layer. [3] We investigated electronic structureof Alq3-PEI-ITO interface by UPS. Figure 3 shows
UPS spectra of Alq3. Energy level of the Alq3
spectrum was shifted to low kinetic energy side, andthere was no interface state. It suggest that vacuum
level shift (0.5 eV) by PEI partly diminished electron
injection barrier (1.5 eV). The electron injection
mechanism of PEI is still under investigation.

Fig. 1. Photo emission spectra of BTQBT on Al
interface. (a) the secondary electron cut-off (SECO)
position (b) the Fermi edge position. Black solidlines indicates HOMO edge of BTQBT.

Fig. 2. SECO vs film thickness of BTQBT.

Fig. 3. UPS spectra of Alq3 on ITO interface, with andwithout PEI ultrathin layer.
[1] S. Hasegawa, et al., J. Chem. Phys. 100 (1994) 6969.
[2] H. Fukagawa, Y. Watanabe, et al., AIP Advance 6(2016) 045010.
[3] H. Fukagawa et al., APEX 7 (2014) 082104.

127
Ⅲ-4-7

Ⅲ- 4

Ⅲ -4. Surface, Interface and Thin Films
BL3B
BL3B

Oxygen Vacancy in Solution-processed IGZO Thin-Film Transistors and
Its Effect on Transistor Characteristics
Y. Ochiai1, T. Morimoto1, N. Fukuda3 and Y. Ohki1,2

Waseda University, Tokyo 169-8555, Japan
Research Institute for Materials Science and Technology, Waseda University, Tokyo 169-8555, Japan
3
Flexible Electronics Research Center (FLEC), National Institute of Advanced Industrial Science andTechnology (AIST), Tsukuba 305-8565, Japan1

ID [A]

10-3
10-4
10-5
10-6
10-7
10-8
10-9
10-10
10-11
10-12
10-13
0

10-4
10-5
10-6
10-7
10-8
10-9
10-10
10-11
10-12
10-13
-40

0

40

VG [V]

80

20
40
60
Ga Content [mol%]

80

Fig. 1. ID as a function of Ga content measured at VG= 80 V for IGZO films sintered at 300 (○) and 800 °C(∆). (Inset) Transfer characteristics measured at VD = 40
V for IGZO films with Ga contents of 0 (─) and 80%(---) sintered at 300°C.
1000

O1s Intensity

O1s Intensity

1500

1000

500

0
526 528 530 532 534 536

Binding Energy[eV]

500

0
0

20
40
60
Ga Content [mol%]

80

Fig. 2. Intensities of O1s XPS component due to oxygen
adjacent to oxygen vacancy (VO) in IGZO films
sintered at 300 (○) and 800 °C (∆), as a function of Ga
content. (Inset) O1s spectrum of IGZO film with Ga
content of 0% sintered at 300°C (─) and its components
due to oxygen bonding with metal (---), VO (∙∙∙), andhydroxide (-•-).
200

15200

PL Intensity

PL Intensity

Ⅲ- 4Using a solution process, by which films can beproduced at low cost, we have successfully made IGZO
thin-film transistors (TFTs) with a mobility of 5.1
cm2/Vs, which is higher than that of amorphous Si
TFTs [1]. In this paper, the transfer characteristics ofthese TFTs are studied, focusing on the effects ofoxygen vacancy, Ga content, and sintering temperature.
Six precursor solutions of IGZO were prepared bydissolving each nitrate of In, Ga, or Zn with a molar
ratio of 1:x:1 (x: 0 to 8) in 2-methoxyethanol. The
solution was spin-coated on a 300-nm thick thermally
oxidized SiO2 on a p-type silicon substrate and sinteredat 300 or 800 °C for 1 hour in air. Then, Al was
vacuum-evaporated on the film to form a drainelectrode and a source electrode, by which we obtained
a TFT with a gate length of 50 μm and a width of 500
μm. Next, its transfer characteristics were measured byraising the gate voltage applied to the substrate from-40 to +80 V, while the source electrode was earthedand the drain electrode was biased to +40 V dc.
The inset in Fig. 1 shows the drain current as afunction of gate voltage, while Fig. 1 shows the relation
between the on-current (ID at VG = 80 V) obtained fromthe transfer characteristics and the Ga content. For thefilms sintered at 300°C, the on-current decreases
monotonically with the increase in Ga content, whereas
it becomes maximum at the Ga content of 40% in thefilms sintered at 800°C.
The inset in Fig. 2 shows an XPS spectrum of O1selectrons observed in an IGZO film with a Ga content
of 0% sintered at 300°C and its three components at
530 eV due to oxygen bonding with metal, at 531 eV
due to oxygen adjacent to oxygen vacancies (VO), andat 532 eV due to hydroxide [2]. As shown in Fig. 2, theintensity of VO peak increases with the increase in Ga
content in the films sintered at 300°C, whereas it
becomes minimum at Ga contents of 20 and 40 % in
the films sintered at 800°C.
The inset in Fig. 3 shows PL spectra observed in
IGZO films with Ga contents of 0 and 80 % sintered at
300°C, while Fig. 3 shows the intensities of the PL at
2.5 eV as a function of Ga content. The 2.5-eV PL has asimilar Ga-content dependence to the O1s intensity due
to oxygen vacancy shown in Fig. 2. A similar PL
appearing in ZnO at 2.36 eV has been attributed tooxygen vacancy [3]. Thus, the present 2.5-eV PL
should be due to oxygen vacancy. This indicates that PL
can detect the presence of oxygen vacancies in IGZO
films.
It has also become clear that the on-current becomesmaximum when the density of oxygen vacancies isminimized, namely, at Ga content of 0% for the films
sintered at 300°C or at 40% for the films sintered at
800°C. These results indicate that oxygen vacancies act
as electron scattering centers.

ID [A]

2

100

0
0

15100
15000
14900
1.5 2

3

4 4.5

Photon energy [eV]

20
40
60
Ga Content [mol%]

80

Fig. 3. PL intensities due to oxygen vacancy in IGZO
films sintered at 300 (○) and 800 °C (∆). (Inset) PL
spectra of IGZO films with Ga contents of 0 (─) and
80% (---), sintered at 300°C.
[1] S. Ogura et al., Flex. Print. Electron. 1 (2016) 045001.
[2] K. K. Banger et al., Nature Mat. 10 (2011) 45.
[3] K. Vanheusden et al., J. Appl. Phys. 79 (1996) 7983.

128
Ⅲ-4-8

Ⅲ -4. Surface, Interface and Thin Films
BL4U
BL4U

STXM Analysis of Adsorbent for Effective Recovery of Radioactive Elements
Y. Sano1, S. Watanabe1, Y. Miyazaki1, S. Kibe1, H. Matsuura2, T. Uchiyama2 and Y. Katai2
Japan Atomic Energy Agency (JAEA), Tokai 319-1194, Japan
2
Tokyo City University, Tokyo 158-8557, Japan1

radioactive elements. It will be important to select theappropriate pore size in SiO2 support and coating
condition (thickness and CDP) of SDB.
1.6

SiO2-P-HDEHP (after Zr adsorption)
SiO2-P-HDEHP

1.4
1.2
Optical density

Spent nuclear fuels generated from nuclear power
plants contain U and Pu which can be reused, andseveral long-lived radioactive elements. It will be quite
important for effective utilization of energy andenvironmental loading reduction to process the spent
fuel adequately. JAEA has been developing theselective recovery process of radioactive elements,
which uses adsorbents of SiO2 supports coated withstyrene-divinylbenzene (SDB) copolymer (SiO2-P) andextractants on its surface. Scanning transmission X-ray
microscopy (STXM) is one of useful techniques toobtain the information about such an adsorbent surface.
Our previous study using STXM analysis showed that
the SDB polymer and extractants were distributed
within several hundred nanometers from the poresurface in SiO2 supports, and their distributions werespread by the increase of crosslinking degree ofpolymer (CDP) [1]. In this study, the change ofadsorbent surface, such as thickness of polymer anduniformity of extractants, after adsorbing metal ions
was investigated by STXM analysis.
The adsorbents in which Di-(2-ethylhexyl) phosphoricacid (HDEHP) was impregnated as an extractant weresynthesized by the flowsheet reported by Wei et al. [2].
The average diameter and pore size of the SiO2
supports were 50 μm and 600 nm, respectively. Some
adsorbents were mixed with Zr/HNO3 solution andfiltered for preparing the adsorbents adsorbing Zr.
These adsorbents were sliced to 300 nm in thickness
by focused ion beam (FIB), and were supplied to
STXM analysis.
The O-NEXAFS spectra observed on the adsorbents
before and after adsorbing Zr were shown in Fig. 1.
The intensity of pre-edge peak at 532 eV increased
after Eu adsorption at any position in the adsorbent.
Figure 2 shows the colorized composition maps on the
cross section of sliced adsorbents before and after
adsorbing Zr, which were calculated by fitting
C-NEXAFS spectra with those of SDB polymer and
HDEHP. The SDB polymer and HDEHP were
distributed within several hundred nanometers from thepore surface, and their distributions, especially SDB
polymer, were spread uniformly in the adsorbent
adsorbing Zr.
The increase of pre-edge peak at 532 eV in
O-NEXAFS spectra after Zr adsorption indicates theadsorption of some kinds of molecules contained in
Zr/HNO3 solution, such as H2O. The adsorption of Zr
and these molecules will bring the swelling of SDB
polymer in the pore of SiO2 support, which wasobserved in Fig. 2. The excessive swelling of SDB
polymer is undesirable for the recovery process of

1

0.8

pre-edge

0.6
0.4
0.2

520

530

540
550
Photm enegy [eV]

560

570

Fig. 1. Change of O-NEXAFS spectra (O-K edge).

SiO2
Pore

500nm
(a) before Zr adsorption

500nm(b) after Zr adsorption

Fig. 2. Colorized composition maps (black; SiO2,
white; pore, red; SDB, blue; HDEHP (purple; mixtureof red and blue) ).
[1] Y. Sano, S. Watanabe and S. Kibe, UVSOR
Activity Report 43 (2016) 120.
[2] Y. Wei, M. Kumagai and Y. Takashima, Nucl.
Technol. 132 (2000) 413.

129
Ⅲ-4-9

Ⅲ- 4

Ⅲ -4. Surface, Interface and Thin Films
BL4B
BL4B

Nanoscale Magnetic Coupling at the Interface of Mn/Fe Thin Film
Heterostructures
T. Miyamachi1, S. Nakashima1, Y. Takahashi1, T. Hattori1, Y. Takagi2, 3, M. Uozumi2, 3,
T. Yokoyama2, 3 and F. Komori1

Institute for Solid State Physics, University of Tokyo, Kashiwa 277-8581, Japan
Department of Materials Molecular Science, Institute for Molecular Science, Okazaki 444-8585, Japan3
Department of Structural Molecular Science, The Graduate University for Advanced Studies (SOKENDAI),
Okazaki 444-8585, Japan
1

2

Ⅲ- 4

Electronic and magnetic properties of a multilayer
system strongly rely on its interfacial conditions. In thecase of a magnetic heterostructure composed ofantiferromagnetic (AFM) and ferromagnetic (FM) thinfilms, the strength of the magnetic coupling at the
AFM/FM interface, e.g., the exchange energy, isconsiderably lower for experimental values compared totheoretical ones with the ideal interface. This difference
is mainly attributed to the interface roughness caused byintermixing or alloying between AFM and FM layers.
Thus, detailed information on the AFM/FM interface
structure is essential to understand its intrinsic magnetic
coupling. In this study, we performed a complementary
study for structural, electronic and magnetic propertiesof the AFM/FM Mn/Fe thin film heterostructures incombination with scanning tunneling microscopy (STM)
and x-ray absorption spectroscopy/x-ray magnetic circulardichroism (XAS/XMCD) [1].
7 monolayer (ML) Fe thin films on Cu(001) in the fcc
phase were chosen as a FM layer. AFM Mn layers witha thickness ranging from 0 to 5 ML were subsequently
grown at room temperature in ultrahigh vacuum. The
electronic and magnetic properties of fcc Fe thin films
are sensitive to the structural variation on the surface [2],which is advantageous to investigate the impact of theinterface roughness on the magnetic coupling of the
AFM/FM thin film heterostructure. The growth andstructural properties of the heterostructures werechecked by STM before XAS/XMCD measurements.
The XAS/XMCD measurements were performed at
BL4B in UVSOR at B = 0, ± 5 T and T = 80 K. The
spectra were recorded in the total electron yield modein the normal (NI :θ = 0°) and the grazing (GI: θ =55°) and incidences. Note that θ is the angle between
the sample normal and the incident x-ray. The XMCD
is defined as μ+ – μ–, where μ+ and μ– denote XAS at
the Fe L2,3 adsorption edge with the photon helicity
parallel and antiparallel to the sample magnetization.
Figure 1 (a) displays XAS and remanent (± 5 → 0 T)
XMCD spectra of bare 7 ML Fe/Cu(001). As previously
reported by surface magneto-optic Kerr effectmeasurements [3], the XMCD signal arising fromferromagnetically-coupled top two Fe layers is slightly

larger in NI than GI geometry, indicating the magnetic
easy axis towards out-of-plane direction.
In contrast, we find that adding Mn layers induces thespin reorientation transition (SRT) to Fe layers. Figure 1(b) displays XAS and remanent (± 5 → 0 T) XMCD
spectra of 5 ML Mn/ 7ML Fe/Cu(001). The absence of
the XMCD signal in GI geometry is observed, while the
XMCD signal in NI geometry is nearly unchanged. The
result demonstrates the SRT from out-of-plane toin-plane directions. In addition, the enhanced magnetic
anisotropy is expected from the larger difference in the
XMCD signal between NI and GI geometries. An
Mn-thickness dependence of the XMCD signal
combined with atomically-resolved STM observations
on the surfaces with thin Mn thickness ranges (0-3 ML)
reveal that the SRT is driven by the alloy formation in
the vicinity of the Mn/Fe interface.

Fig. 1. Fe L2,3 edge XAS and remanent XMCD spectraof (a) bare 7 ML Fe/Cu(001) and 5ML Mn/7ML
Fe/Cu(001) at NI and GI geometries. Solid and dashedlines for XAS spectra represent μ+ and μ–, respectively.
[1] S. Nakashima et al., submitted.
[2] T. Miyamachi et al., Phys. Rev. B 94 (2016) 045439.
[3] J. Thomassen et al., Phys. Rev. Lett. 69 (1992) 3831.

130
Ⅲ-4-10

Ⅲ -4. Surface, Interface and Thin Films
BL4B
BL4B

XMCD Measurements on a Ferromagnet/Topological Insulator
Heterostructure
R. Nakanishi1, R. Akiyama1, Y. Okuyama2, Y. Takagi3, T. Yokoyama3, S. Hasegawa1
and T. Hirahara2

Department of Physics, University of Tokyo, Tokyo 113-0033, Japan
Department of Physics, Tokyo Institute of Technology, Tokyo 152-8551, Japan3
Department of Materials Molecular Science, Institute for Molecular Science, Okazaki 444-8585, Japan
1

2

Topological insulators (TI) are extensively studied
recently due to its peculiar properties [1]. The Diraccone surface states of TI are protected by time-reversal
symmetry (TRS) and backscattering among thesesurface states is prohibited. But when TRS is broken
by application of a magnetic field or incorporating
magnetic materials, a gap opening in the Dirac cone is
expected and an intriguing phase called the quantum
anomalous Hall state can be realized [2]. This phase is
expected to show even more exotic phenomena such as
the topological magnetoelectic effect. To realize suchstate, two types of sample fabrication techniques havebeen employed up to now: (1) magnetic doping while
growing the single crystal or thin film of TI [3], and (2)magnetic impurity deposition on the surface of TI [4].
While method (1) was successful and showed evidenceof the TRS violation, no one has succeeded using
method (2), which should be a more direct way to
examine the interaction between the topologicalsurface states and magnetism.
Previously, we have found that when we make aheterostructure of Bi2Se3 (TI) and a magnetic insulator
MnBi2Se4, it is possible to observed a massive Diraccone with a gap of ~ 80 meV. This is a novel method toincorporate magnetism into topological insulators. The
calculated band structure reproduced the experimental
observation nicely, and the gap opening was
reasonably explained as due to the time-reversal
symmetry breaking of the Dirac cone due to theferromagnetic MnBi2Se4. In the present work, we have
performed XMCD measurements at BL4B toexperimentally prove that the MnBi2Se4/Bi2Se3 isferromagnetic. Figure 1 shows the X-ray absorption(XAS) spectra and the corresponding XMCD spectra at
5T. One can find clear XMCD peaks at the Mn L3 andL2 edges. The measurements were also performed atremanence, and the result is shown in Fig. 2. Althoughvery weak, one can find a dip structure at the L3 edge
and this shows that the heterostructure is ferromagnetic,
consistent with the prediction of the ab initio
calculations.

Fig. 1. XAS and XMCD spectra at 5T.

Fig. 2. XAS and XMCD spectra at remanence.
[1] M. Hasan and C. Kane, Rev. Mod. Phys. 82 (2010)3045.
[2] X.-L. Qi and S.-C. Zhang, Rev. Mod. Phys. 83(2011) 1057.
[3] For example, C. Z. Chang et al., Science 340 (2013)
167.
[4] For example, M. Ye et al., Phys. Rev. B 85 (2012)205317.

131
Ⅲ-4-11

Ⅲ- 4

Ⅲ -4. Surface, Interface and Thin Films
BL4B
BL4B

XMCD Study of Ferro Orbital Ordered System: FeV2O4
J. Okabayashi1* and S. Miyasaka2

Research Center for Spectrochemistry, University of Tokyo, Tokyo 113-0033, Japan2
Department of Physics, Osaka University, Toyonaka 560-0043, Japan
orbital magnetic moments remain in the V3+ states,
which is consistent with the ferro orbital ordering. Using
the integrals over XAS spectra and assuming that the V
3d electron number to be 2, we deduced the orbital
magnetic moments (ml) to be less than 0.1 μB/(V atoms)
from the orbital sum rule. This value is small but finite.
This result indicates that unquenched orbital magnetic
moments contribute to the formation of the complex
wave functions in V sites that the dyz+idzx type wave
functions consist of the ground states. Although the Fe
L-edge XAS includes the oxidized states, the finite
orbital moments also remain in the Fe sites through the
Jahn-Teller distortion.
The t2g states in V 3d states are split into two levels by
the tetragonal distortion and the lowest xy states areoccupied by one of the electrons. The other electron
occupies the yz or zx states. The existence of the small
but finite orbital magnetic moments in the V sites can be
explained by the (i) complex orbital ordering as
discussed in the case of FeV2O4, (ii) domain formation,and (iii) mixing of the real and complex orbital
orderings due to the trigonal distortion around the Vsites [2].
We acknowledge to Prof. T. Yokoyama, Dr. Y. Takagi,
and Dr. K. Uemura for the technical supports at BL4B.
10

4

XAS intensity

Ⅲ- 4

The orbital degree of freedom has attracted interestin the condensed-matter physics because of adding of
new functional functionalities. Couplings between
orbital and spin degrees of freedom in transition metal(TM) oxides exhibit a wide variety of interesting
physical phenomena studied in strongly correlated
electron systems. The orbital degeneracy of t2g or eg
orbitals, split by the crystal field in TM oxides, gives
rise to the orbital ordering phenomena inperovskite-type Fe or V oxides accompanied by
Jahn-Teller distortion. Spinel-type FeV2O4 is acandidate to study orbital ordering since orbital
magnetic moments of Fe2+ (d 6) are strongly affected by
the Jahn-Teller distortion in the Fe sites, which brings
the ferro orbital ordering in V sites through thespin-orbit interaction. An unresolved issue related toorbital ordering of spinel-type vanadium oxides is therelationship between the orbital magnetic moments invanadium sites and orbital ordering [1]. In case of
FeV2O4, the V orbital states consist of complex wave
functions of degenerated yz and zx states, which expect
the ferro-orbital ordering with the large orbital
moments of almost 1 μB. On the other hand, in the caseof MnV2O4, real wave functions in the V sites which
are described as dyz and dzx are ordered alternatively,
resulting in an antiferro orbital ordering with
quenching orbital moments. Therefore, theinvestigation of orbital moments in V sites enables todiscuss the types of orbital ordering. X-ray absorption
spectroscopy (XAS) and X-ray magnetic circulardichroism (XMCD) with the sum-rule analysis enables
to estimate the orbital moments. In this study, weinvestigated the element specific electronic andmagnetic properties of FeV2O4 using XAS and XMCD,
and examined the relationship between orbital
magnetic moments and orbital ordering.
Single crystals were grown by the floating-zone
method. The magnetic and orbital ordering temperaturesof FeV2O4 were estimated to be 110 K and 70 K,
respectively, accompanying the lattice distortions fromtetragonal to orthorhombic structures with decreasing
temperature. The XAS and XMCD measurements were
performed at BL4B, UVSOR, Institute of Molecular
Science. Total photoelectron yield mode by directly
detecting the sample current was adopted. A magnetic
field of ±5 T was applied along the direction of theincident polarized soft x-ray.
Figure 1 shows XAS, XMCD spectra of Fe and V
L2,3-edge regions taken at 5 K, which is sufficiently
lower than the orbital ordered transition temperature.
The resulting residuals from the XMCD integrals forboth L2 and L3 edges suggest that the finite values of

8

3

Fe L-edge

62
4
1

V L-edge

0

2
0

0.20

XMCD intensity

1

0.15
0.0

0.10
0.05

-0.5

0.00
-0.05

-1.0

-0.10
510

515

520

Photon Energy (eV)

525

700

710

720

Photon Energy (eV)Fig. 1. V and Fe L-edge XAS and XMCD spectra in
FeV2O4.
[1] Y. Nii et al., Phys. Rev. B 86 (2012) 125142.
[2] J. Okabayashi et al., J. Phys. Soc. Jpn. 84 (2015)
104703.
*e-mail: jun@chem.s.u-tokyo.ac.jp132
Ⅲ-4-12730

Ⅲ -4. Surface, Interface and Thin Films
BL4B
BL4B

Oxygen Adsorption on Single and Double Fe Ultrathin Films
T. Nakagawa1, T. Nomitsu1, M. T. Kibria1, S. Mizuno1, Y. Takagi2 and T. Yokoyama2
1

Department of Molecular and Material Sciences, Kyushu University, Kasuga 816-0955, Japan
2
Institute for Molecular Science, Okazaki 444-8585, Japan

Iron oxides have been widely studied both due tofundamental research interests and its application for
catalysis and solid devices. However, the magnetismof its thinnest unit, a single layer Fe oxide, and the Fethin films with oxygen adsorption have not been wellstudied [1]. The magnetic order at the surface ofoxide has not been well understood yet [2, 3].
Experiments were done in the x-ray magnetic
circular dichroism (XMCD) endstation with the basepressures of 2×10-8 Pa for sample preparation andbetter than 1×10-8 Pa for XMCD measurement. Single
and double Fe layers were grown on W(110). Oxygen
was dosed via a variable leak valve at 2×10-7 Pa withthe sample kept at the room temperature, and the Fe
films exposed up to 150 L(1 L = 1.3×10-4 Pa s) ofoxygen were examined by XMCD. XMCD spectra
were taken with a circularly polarized light (circularly
polarization ~ 0.6) at H = ±5 T at a sample temperatureof 8 K.
Figure 1 shows x-ray absorption spectra (XAS) and
XMCD spectra for single and double Fe layers withincreasing the oxygen exposure. At 150 L, XAS forthe single layer (SL) and double layer (DL) show
splitting at the L2 edges, which indicates a transition
from metallic to oxide states. XMCD signals both for
the SL and DL are almost zero. On the contrary, atleast up to 5 L, the L2 edges does not show splitting,which indicates that the Fe films are in metallic
states.
On the SL, at 0.2 L, corresponding to ~1/4 monolayer
oxygen adsorption, the magnetic moment that is a sumof spin and orbital magnetic moments drasticallydecreases to 0.4 μB, which is much smaller than that of
the clean SL, 2.1 μB. After 5 L, the magnetic moment isrestored to 1.1 μB. At 150 L exposure of oxygen, the
XMCD single is almost zero.
On the DL, at 0.2 L, XMCD does not change muchas compared with that for the clean DL. The magnetic
moment at 0.2 L is 2.0 μB. With increasing the oxygen
exposure, the magnetic moment slowly decreases andit is 1.6 μB at 5 L.
With increasing the oxygen adsorption, the SL
rapidly loses its ferromagnetic order, resulting in
reduced magnetic moments. On the other hand, theDL maintains its magnetic moment until it is oxidized,
although the magnetic moment for the DL
monotonically and slowly decreases with increasing
the oxygen adsorption. This different is attributed toferromagnetic coupling. On the SD, the oxygen
adsorption strongly weakens its ferromagnetic order.
However, on the DL, the second layer Fe in theproximity of the W substrate, which is not directly

affected by oxygen adsorption, ferromagneticallycouples with the topmost Fe layer.

Ⅲ- 4Fig. 1. XAS and XMCD spectra for single (1.0 ML)
and double (1.7 ML) Fe layers with increasing oxygen
exposure (0 ~ 150 L). (a) XAS spectra taken at ±5 T
for the single iron layer (SL). (b) XMCD spectra forSL. (c) the same as (a), but for the double layer (DL).
(d) the same as (b), but for DL.
[1] K. Feindl et al., Surf. Sci. 617 (2013) 183.
[2] K. Mori et al., Phys. Rev. B 72 (2005) 014418.
[3] E. Vescovo, Phys. Rev. B74 (2006) 026406.

133
Ⅲ-4-13

Ⅲ -4. Surface, Interface and Thin Films
BL4B
BL4B

XMCD Study of Fe Nanoparticles Synthesized on h-BN Nanomesh
S. Sakai1, 2, T. Watanabe1, 2, Y. Yamada2, S. Entani1, A. Koide3, Y. Takagi3 and T. Yokoyama3

Quantum Beam Science Research Directorate / QST Future laboratory, National Institutes for Quantum andRadiological Science and Technology QST, Tokai 319-1106, Japan
2
Japan Institute of Applied Physics, University of Tsukuba, Tsukuba 305-8577, Japan3
Department of Materials Molecular Science, Division of Electronic Structure, Institute for Molecular Science,
Okazaki 444-8585, Japan
Tailoring magnetic properties of nanomagnets ishysteresis at 6.8 K and 140 K and the change of thethe central research issue in developing magnetic andcurve shape by the incidence direction in Figs. 2 (b)spintronic memory devices. Recent studies haveand 2 (c). The magnetic anisotropy field is roughly
demonstrated
graphene-induced
perpendicularestimated to be 0.6 T from the intercept of the normal
magnetic anisotropy in a ultra-thin cobalt film on
and grazing incidence curve, which is reasonably
graphene [1, 2] and at the interface region of
attributed to the shape anisotropy of the planer Fegraphene/Ni(111) [3]. It was also shown that in Co
nanoparticles (Fig. 1).
atoms on graphene/metal substrate the magnetizationeasy axis of the Co atoms changes by the choice ofthe metal substrate [4]. In addition, single layer
graphene and hexagonal boron nitride on Rh(111) andRu(0001) (so-called graphene and h-BN nanomesh)were shown to be useful as a template for fabricating
100nm
regularly-arranged nanoparticles of magnetic metals[4-6] relevant to the nanoscale periodicity of the
Moiré pattern. The above results in the previous
Fig. 1. (left) AFM image and (right) the height crossstudies make the magnetic metal/atomic layer
section profile of 1.4 nm Fe/h-BN/Pt(111)material structures promising for the magnetic andspintronic memory device applications.
In this study, we investigated the magnetic property
of Fe nanoparticles synthesized on h-BN nanomesh(h-BN/ Ru(0001)) with X-ray magnetic dichroism(XMCD) spectroscopy. Total electron yield X-ray
absorption (XAS) and XMCD measurements were
performed at BL-4B of UVSOR III using an
ultra-high-vacuum XMCD apparatus with a basepressure of 10-8 Pa. The sample was prepared in-situ
by depositing Fe on the surface of h-BN/Ru(0001) at
ambient temperature. The Fe L2,3 edge XAS andXMCD were measured at low temperatures (6.8 K
and 140 K) under the magnetic field up to 5 T.
Figure 1 shows the atomic force microscopy(AFM) image of the Fe/h-BN/Ru(0001) sample after
the deposition of Fe with a nominal thickness of 1.4
nm. The AFM image and the height cross section
profile indicate planar Fe nanoparticles with a mean
diameter of ~10 nm and the thickness less than 2 nm.
Figure 2 shows (a) the Fe L2,3 edge XAS spectra of
the same sample at 6.8 K measured under the grazing
Fig. 2. (a) Fe L2,3 edge XAS spectra of 1.4 nm
incidence (30º) and by applying the magnetic fields
Fe/h-BN/Pr(111) at 6.8 K under the grazing incidenceof ±5 T (the red and blue lines represent the spectra
and the hysteresis at 6.8 K and 140 K of the Fe L3
under the conditions of the circular x-ray vector
intensity
under the (b) normal and (c) grazing incidence
parallel and antiparallel to the magnetic field) and themagnetic hysteresis loops at 6.8 K and 140 K under[1] C. Vo-Van et al., New J. Phys. 12 (2010) 103040.
the (b) normal and (c) grazing incidence as a function[2] J. Coraux et al., J. Phys. Chem. Lett. 3 (2012) 2059.
of the magnetic field, which were measured for the L3[3] Y. Matsumoto et al., J. Mater. Chem. C 1 (2013) 5533.
edge absorption intensity. A clear XMCD signal from
[4] F. Donati et al., Phys. Rev. Lett. 113 (2014) 177201.
the Fe nanoparticles was detected as shown in Fig. 2 (a).
[5] R. Zhang et al., Phys. Rev. B 78 (2008) 165430.
The Fe nanoparticles are found to be ferromagnetic[6] I. Bihuega et al., Surf. Sci. 602 (2008) L95.
and have an in-plane easy axis of magnetization as[7] B. Wang et al., J. Phys. Chem. Lett. 2 (2011) 2341.
can be judged from the good coincidence between the
1

Ⅲ- 4

134
Ⅲ-4-14

Ⅲ -4. Surface, Interface and Thin Films
BL5U
BL5U

Growth and Electronic Structure of Ultrathin Te Films Grown on Bi2Te3
Y. Okuyama1, Y. Sugiyama1, S. Ideta2, K. Tanaka2 and T. Hirahara1
Department of Physics, Tokyo Institute of Technology, Tokyo 152-8551, Japan
2
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan

1

Chirality is a geometric property of materials and ismostly discussed in chemistry or biology. A chiralmolecule/ion is non-superposable on its mirror image(enantiomers) and individual enantiomers are often
called as either “right-” or “left-handed”. Some solid
crystals also have chirality such as elements tellurium(Te) and selenium (Se). They are trigonal structuresthat can be regarded as a hexagonal array of helicalchains at ambient pressure. They lack inversion
symmetry and possess chirality depending on therotation direction of the screw axis. Due to thispeculiar crystal structure, Te shows intriguing
properties such as the circular photon drag effect or
the current-induced spin polarization.
It is also well known that the physical properties ofTe and Se can be tuned by controlling the lattice
constant, which can be achieved by applying pressure.
They will eventually undergo a structural transition to
the monoclinic or the triclinic phases at very highpressure in the order of ~10 GPa. The electronic
structure can also be changed from a semiconductor(the band gap is 0.33eV and 2.0 eV for Te and Se,
respectively) to a metal by applying pressure. Recently,
based on ab initio calculations, it was predicted that Teundergoes a trivial insulator to a strong topologicalinsulator (metal) transition under shear (hydrostatic or
uniaxial) strain in the trigonal phase [1]. Furthermore,
it was predicted that the lack of inversion symmetry
and spin–orbit interaction leads to the existence ofDirac points or Weyl nodes in the band structure of Te
or Se [2]. Such states possess an unconventional spin
texture and furthermore, if one can fine-tune the lattice
constant by carefully controlling the applied pressure,Te and Se are expected to show the Weyl semimetal
phase [3].
In the present work, we have attempted to mimic
the lattice constant change by growing a thin Te film
on a substrate and utilizing the epitaxy to apply strain.
We have adopted Bi2Te3 as our substrate since it has
been reported as a promising material for Te thin film
growth [4]. Figure 1 shows the low-energy diffraction(LEED) pattern of the grown films, and we havefound that a six domain Te(10-10) film can be grown
on Bi2Te3 [5]. We have performed angle-resolved
photoemission (ARPES) measurements at BL-5U as
shown in Fig. 2. The measurement was performed at
30 K. A Dirac-cone like linear dispersion near the
Fermi level was found at the H point of the Brillouinzone. Further work is needed elucidate the entire
picture of the band structure.

Fig. 1. LEED pattern of the six domain Te(10-10)
film grown on Bi2Te3.

Ⅲ- 4

Fig. 2. Band dispersion of the Te(10-10) film near
the Fermi level.
[1] L.A. Agapito, N. Kioussis, W.A. Goddard and N.P.
Ong, Phys. Rev. Lett. 110 (2013) 176401.
[2] M. Hirayama, R. Okugawa, S. Ishibashi, S. Murakami
and T. Miyake, JPS Conf. Proc. 5 (2015) 011024.
[3] M. Hirayama, R. Okugawa, S. Ishibashi, S. Murakami
and T. Miyake, Phys. Rev. Lett. 114 (2015) 206401.
[4] K. Hoefer, C. Becker, S. Wirth and L.H. Tjengb,
AIP Adv. 5 (2015) 097139.
[5] Y. Okuyama, Y. Sugiyama, S.-I. Ideta, K. Tanaka and
T. Hirahara, Appl. Surf. Sci. 398 (2017) 125.

135
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Ⅲ -4. Surface, Interface and Thin Films
BL5U
BL5U

Towards Direct Observation of Spatial Modulation on Molecular Orbitals
by the Organic–metal Interaction
T. Ueba1, 2, K. Yonezawa1, C. Numata3, R. Shiraishi2, S. Ideta1, 2, K. Tanaka1, 2 and S. Kera1, 2, 3
Department of Photomolecular Science, Institute for Molecular Science, Okazaki 444-8585, Japan
School of Physical Sciences, The Graduate University for Advanced Studies (SOKENDAI), Okazaki 444-8585, Japan3
Department of Nanomaterial Science, Graduate School of Advanced Integration Science, Chiba University,
Chiba 263-8522, Japan
1

2

Ⅲ- 4

Understanding the weak interaction at the organicmetal interface, including intermolecular interaction
and molecule-metal interaction, is of great importancebecause even such weak interaction can cause therearrangement of molecular orbitals both in energy andspace, which determines the electronic properties atinterfaces. Photoelectron angular distribution (PAD)
measured by angle-resolved ultraviolet photoelectron
spectroscopy (ARUPS) contains information of thespatial distribution and the phase of molecular orbitals(MOs) [1, 2]. Therefore, a careful comparison between
experimental and theoretical PADs will enable us todirectly discuss a modulation on electronic structuresdue to the weak interaction. In this work, we performed
ARUPS for the perfluoropentacene (PFP, shown in theinset of Figure 1) monolayer film grown on the Ag(111)substrate as a model system, in order to examine how
the ARUPS with a photoelectron deflector analyzer inthe beam line BL5U shows PAD of MOs.
A PFP monolayer film on Ag(111) was preparedby multilayer deposition on the clean Ag(111)substrate and the following annealing at 400 K, andwas kept at 45 ± 5 K during measurements to obtainan ordered structure [3].
Figure 1 (b) shows the kx-ky maps converted fromARUPS two-dimensional images measured at hν =60 eV with p-polarization, at the respective kinetic
energies, as schematically shown in Fig. 1 (a). The
momentum kx is set to be parallel to the Γ-K direction.
The energy region I includes merely the sp-band of
the Ag substrate. In the regions II/III, on the other
hand, not only the sharp sp-band but also some
additional vague structures can be seen. These
structures can be attributed to the corresponding MO
orbitals, by comparing to the simulated kx-ky maps
from the PAD simulation [2], as shown Fig. 1 (c).
Unfortunately, even at the lowest photon flux
condition (diode current, the pinhole and the exit slit
widths were ~350 pA, 4 mm and 100 µm, respectively,
at the multi-bunch operation), a radiation damage tothe present sample was found, which prevented us toobserve clear kx-ky maps. For a detailed ARUPS
measurement for organic thin films, the photon flux
density needs to be further reduced by the use of a
defocusing condition or of the single-bunch operation.

Fig. 1. (a) Angle-resolved UPS image and its angleintegrated spectrum of PFP monolayer on Ag(111). (b)Experimental kx-ky maps taken at regions I-III. (c) The
corresponding PAD simulation of HOMO/HOMO-1.
The three-fold pattern reflects the (111) symmetry. The
molecular structure of PFP is also shown in the inset.
[1] P. Puschnig et al., Science 326 (2009) 702.
[2] S. Nagamatsu et al., e-J. Surf. Sci. Nanotechnol. 3(2005) 461.
[3] M. Marks et al., J, Phys. Chem. C 116 (2012) 1904.

136
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Ⅲ -4. Surface, Interface and Thin Films
BL5U, BL7U
BL5U, BL7U

Two-dimensional Electronic States on InSb(110) Localized in Subsurface
Atomic Layers and its Temperature Dependent Energy Shift
Y. Ohtsubo1, 2, H. Watanabe1, 2,Y. Yamashita2, K. Hagiwara2, S. Ideta3, K. Tanaka3and S. Kimura1, 2

Graduate School of Frontier Biosciences, Osaka University, Suita 565-0871 Japan
Department of Physics, Graduate School of Science, Osaka University, Toyonaka 565-0043, Japan
3
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan1

2

On the surface of crystals, two-dimensional (2D)electronic states, so called surface states are formedby two mechanisms as limiting cases [1]. In a
localized-bond picture, surface states can be induced
by an alternation of the localized chemical bonds dueto the reconstruction of the surface atomic structure atthe very surface layer. The surface states by suchmechanism are usually assumed to have wave
functions localized in a few topmost layers. On theother hands, in a perturbed-bulk-band picture, surface
states are derived from bulk Bloch states, which are
perturbed by the truncation of the periodic potential at
the surface and consequently localized at near-surface
region. While surface states in general have bothcharacters with varying relative importance, it issometimes intuitive to consider these two limiting
pictures. Recently, there is a renewed interest in thesurface states originating from bulk bands, which
include the spin-orbital polarized surface states on
topological insulators [2] and 2D metallic states ontransition-metal oxides [3].
The (110) surface of III-V semiconductors is known
to exhibit the well-ordered cleaved surface without any
surface reconstruction nor dangling-bond formation [4].
In this project, we observed the surface electronic
structure of the InSb(110) cleaved surface. As shown in
Fig. 1, two parabolic bands dispersing downwards
from the center of surface Brillouin zone was clearlyobserved by angle-resolved photoelectron spectroscopy(ARPES). Although these band dispersions are quite
similar to its bulk-band counterparts, heavy hole andlight hole bands, they showed no dispersion along thesurface normal checked by changing the incident
photon-energy for ARPES. It suggests that theseparabolic states have 2D character and derived fromthe perturbation of the bulk bands by the truncation of
the three-dimensional periodicity at the surface. These
dispersion of 2D states are similar to the subsurface
electronic states on the Ge(111) surfaces covered withvarious adsorbates [5], suggesting their common origin
from subsurface layers of substrates.
Moreover, the 2D states on InSb(110) changed its
binding energies depending on the sample
temperature. From 13 to 300 K (room temperature),
the maximum of the 2D bands moved downwards aslarge as ~160 meV. Usually, such temperaturedependence of semiconductor states are understood
due to surface photo-voltage (SPV) effect and surface

band bending. However, we have detected a tiny SPV
effect by changing the incident photon flux with its
sign the opposite to the temperature-driven shift ofthe 2D bands. Such unusual energy shift can bequalitatively explained by the chemical potential shift
due to the low density of states of the conduction
bands of InSb [6]. Detailed analysis to understand thetemperature-driven energy shifts and further research
to use this energy shift to tune energies of the othersurface states are in progress.

Ⅲ- 4Fig. 1. Surface band dispersion of the InSb(110) cleaved
surface observed by ARPES at 13 K (h = 20 eV).
[1] H. Ibarh, Physics of Surfaces and Interfaces(Springer-Verlag, Berlin, Heidelberg, 2006).
[2] M. Z. Hasan and C. L. Kane, Rev. Mod. Phys. 82(2010) 3045.
[3] A. F. Santander-Syro et al., Nature 469 (2011) 189.
and K. Yoshimatsu et al., Science 333 (2011) 319.
[4] L. Pfeiffer et al., Appl. Phys. Lett. 56 (1990) 1697.
[5] Y. Ohtsubo et al., Phys. Rev. B 88 (2013) 245310.
[6] L. Walczak et al., Surf. Sci. 608 (2013) 22.

137
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Ⅲ -4. Surface, Interface and Thin Films
BL5U, BL7U
BL5U, BL7U

Surface Electronic Structure of Kondo Insulator SmB6(111)
Y. Ohtsubo1, 2, K. Hagiwara2, C. Wang2, S. Ideta3, K. Tanaka3, F. Iga4 and S. Kimura1, 2
2

Ⅲ- 4

1
Graduate School of Frontier Biosciences, Osaka University, Suita 565-0871 Japan
Department of Physics, Graduate School of Science, Osaka University, Toyonaka 565-0043, Japan
3
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
4
Department of Physics, Ibaraki University, Mito 310-0056, Japan

Topological Kondo insulator (TKI) is a new groupof topological materials. On the surface of TKI, robust
topological surface state (TSS) disperses across a tinyenergy gap owing to the strong correlation between
itinerant and localized electrons (Kondo effect) [1].
Therefore, TKI phase is realized thanks to thesynergetic effect between strong electron correlationand spin-orbit interaction (SOI), which results in the
non-trivial parity eigenvalues across the Kondo gap.
Since such synergetic effect can cause new exotic
physical phenomena, such as superconductivity
without inversion symmetry [2], the surface electronic
structure of TKI is gathering much attention in thesedays.
So far, most of the experimental and theoreticalstudies about TKI have been performed on the (001)cleaved surface of SmB6 and the surface state exhibits
metallic dispersion and spin-polarization, which are
the major characteristics of TSS [3-5]. Recently, we
found a new TKI, YbB12 [6]. On the (001) cleansurface of YbB12, angle-resolved photoelectron
spectroscopy (ARPES) showed a metallic surface
state dispersing across the bulk Kondo gap and its
orbital angular momentum (OAM) polarization that isoften connected to spin polarization via SOI. For thisstudy, we have established a method to obtain theclean surface of a group of Kondo insulators such as
SmB6 and YbB12 in situ without cleaving [7]. The
clean surface preparation without cleaving also pave
the way to observe the surface electronic states and its
topology not only in cleavage planes but in generalsurfaces of the crystal. It is important to discuss the
topological nature of the crystal from its surface
states, because the topological order of the bulk
crystal should govern the general character of thesurface states without regarding detailed atomic
structure and mirror indices of the surface plane.
In this project, we studied the electronic structureof the SmB6(111) clean surface by ARPES. The cleansurface of SmB6(111) cannot be obtained by cleaving
but was obtained in-situ by heating the single crystal
up to 1600 K in an ultra-high vacuum chamber. The
quality of the clean surface was evaluated by the
sharp and low-background electron diffraction
patterns as well as sharp photoelectron spectra itself.
Figure 1 shows the ARPES result indicating thehighly dispersive itinerant states which exhibits clear
hybridization with nearly localized 4f states lying justbelow the Fermi level. The hybridized state disperses

across the Kondo gap and clearly indicates themetallic dispersion across the Fermi level at the sametime. It strongly suggests its topological origin since
the similar surface states are expected to appear on
different surfaces of the same TKI crystal. Further
analysis to understand the topological origin andwhole picture of the topological electronic states of
SmB6 is in progress.

Fig. 1. Surface band dispersion of the SmB6(111)clean surface observed by ARPES at 13 K (hν = 26eV). Dashed lines are guides to the eye. The ARPES
intensities are symmetrized with respect to k = 0 Å-1.
[1] M. Dzero et al., Phys. Rev. Lett. 104 (2010) 106408.
[2] E. Bauer et al., Phys. Rev. Lett. 92 (2004) 027003.
[3] N. Xu et al., Phys. Rev. B 88 (2013) 121102(R).
[4] M. Neupane et al., Nature Commun. 4 (2013) 2991.
[5] J. Jiang et al., Nature Commun. 4 (2013) 3010.
[6] K. Hagiwara, Y. Ohtsubo et al., Nature Commun. 7(2016) 12690.
[7] K. Hagiwara, Y. Ohtsubo et al., Proc. SCES 2016.

138
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BL5U
BL5U

Electronic Structure of a (1×1) VO Film on Ag(100): Soft X-ray
Photoelectron Spectroscopy Study
Y. Sugizaki1, H. Motoyama1 and K. Edamoto1, 2

Department of Chemistry, Rikkyo University, Tokyo 171-8501, Japan
Research Center for Smart Molecules, Rikkyo University, Tokyo 171-8501, Japan
1

2

The mechanism of metal-insulator transitions(MITs) in vanadium oxides has been a matter ofongoing controversy for decades. The discussion has
been focused on whether the transition is triggered byan electron-lattice interaction (Peierls-type model) orby an electron-electron interaction (Mott-type model),and a vast amount of studies have been performed on
the electronic structures of vanadium oxides (mostly
VO2 and V2O3). However, very limited information isavailable on the electronic structure of vanadiummonoxide (VO) at present, and it is not clear whether
MIT also occurs in VO or not. This is primarily
because it is hard to synthesize a VO single-crystal in
an atmospheric condition, which makes it difficult tomake an experimental study on the electronic
structure of VO. Recently we found that a VO(100)single-crystal film can be formed on Ag(100) byreactive deposition of V atoms [1], which would
enable the detailed spectroscopic studies on theelectronic structure of this substance. In this study, we
performed a high-resolution PES study for theVO(100) film on Ag(100).
Experiments were performed at BL-5U of the
UVSOR Facility, Institute for Molecular Science. The
spectra presented below were measured at the photon
energy of 54 eV. In this study, the estimation of the
Fermi edge is primarily important, and it wasestimated by fitting the spectrum of a gold film
attached to the sample holder in the Fermi edge
region using Gaussian convoluted Fermi distributionfunction. The VO(100) film was prepared by electron
beam deposition of V atoms in O2 at 3.0×10-7 Pa andsubsequent annealing at 450°C for 30 min.
Figure 1. shows the valence band PES spectrum of
the VO film on Ag(100) measured at room temperature(red line) and that at 4.86 K (blue line). The band
observed at 0 - 4 eV is ascribed to a V 3d band, andthe band at 4 – 10 eV is ascribed to a V 3d – O 2p
hybrid band (valence band) overlapping with a 4d
band of the underlying Ag substrate. We measured
magnified spectra in the vicinity of the Fermi level(EF) at both temperatures, and confirmed that there isa clear cut-off in both spectra. The positions of the
cut-off were carefully determined by fitting thespectra using Gaussian convoluted Fermi distributionfunctions, and it was confirmed that the cut-off
positions were identical to that observed in the
spectrum of the gold film. These results imply that
VO in the ground state should have a metallic

electronic structure. It has been controversial whether
the ground state of VO is a metal or an insulator; forexample, Yamazaki et al. made a theoretical study
using the energy band calculations utilizing GW
approximation and predicted that VO has a metallic
nature [2], while Mackrodt et al. proposed that VO in
the ground state is a Mott-Hubbard type insulator
using a hybrid DFT calculations [3]. We think that thelong-standing controversy is settled by the result of
the present PES study. In addition, it is found that VO
has a metallic nature in the temperature range of 4,86
K – room temperature. This result suggests that MIT
does not occur in VO unlikely to the case of othervanadium oxides.

Ⅲ- 4Fig. 1. The PES spectrum of the VO(100) film on
Ag(100) measured at room temperature (red line) andthat at 4.86 K (blue line) (hν = 54 eV).
[1] T. Nakamura et al., Jpn. J. Appl. Phys. 55 (2016)075501.
[2] A. Yamasaki and T. Fujiwara, Phys. Rev. B. 66(2002) 245108.
[3] W. C. Markrodt et al., Phys. Rev. B. 69 (2004)
115119.

139
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BL5B
BL5B

Vacuum Ultra-Violet Absorption Spectra of Amorphous Chalcogenide
Semiconductor Thin Films
K. Hayashi

Department of Electrical, Electronic and Computer Engineering, Gifu University, Gifu 501-1193, JapanⅢ- 4

Amorphous chalcogenide semiconductor materials,
such as a-As2S3, a-As2Se3 and a-Se etc., show a varietyof photo-induced phenomena. Therefore, thesematerials are expected as materials for optoelectronic
devices. A lot of work have been done on thephoto-induced phenomena of these amorphoussemiconductor materials and various mechanisms havebeen proposed for these photo-induced phenomena[1-3]. However, the details of the mechanisms are still
unknown. For device applications, it is necessary to
sufficiently understand the fundamental properties ofthese materials. These phenomena were studied byexciting outer core electrons with the irradiation oflight with the energy corresponding to the optical
bandgap or sub-bandgap. The interest has been
attracted for the change of the optical properties in theenergy region of the visible light. We are interesting forthe changes of the optical properties in the higher
energy region. To our knowledge, little attention has
been given to photo-induced changes at the vacuum
ultra-violet (VUV) absorption spectrum. In this report,
we measure the VUV absorption spectra on
as-deposited evaporated amorphous AsxSe1-x (for x=0.3,
0.4 and 0.5) thin films.
Samples used for the measurement of the VUVabsorption spectra were amorphous AsxSe1-x (for x=0.3,
0.4 and 0.5) thin films prepared onto aluminum thinfilms by conventional evaporation technique. Using
different bulk glass of the composition as a source
material, different amorphous film of the compositions
was prepared. Typical thickness of the amorphous film
and the aluminum film were around 200 nm and 100
nm, respectively. The aluminum film of the thicknessof 200 nm was also used in order to eliminate thehigher order light from the monochromator in the VUVregion. The measurements were carried out at room
temperature at the BL5B beam line of the UVSOR
facility of the Institute for Molecular Science. And thespectrum was measured by using the silicon
photodiode as a detector. Two pinholes of 1.5 mm in adiameter were inserted between the monochromatorand sample to remove stray light. The intensity of the
VUV light was monitored by measuring the total
photoelectron yeild of a gold mesh. The positions of
the core levels for the samples were calibrated byreferencing to the 2p core level absorption peak of thealuminum film.
Figure 1 shows the VUV absorption spectra ofas-deposited amorphous AsxSe1-x (for x=0.3, 0.4 and0.5) thin films in the energy region from 40 to 60 eV.
Two main absorption peaks were observed in thisenergy region. One absorption peak around 44 eVcorresponds to the 3d core level of arsenic atom.
Another absorption peak around 56 eV corresponds tothe 3d core level of selenium atom. The broad
structures observed in the absorption spectra consistof two or more components. The origin of eachcomponent is not clear now. I would like to clarify theorigin of each component in the future. As shown infigure, the ratio of the two main absorption peaks
changes depending on composition of the film. The
spectrum shape also changes depending on
composition of the film. We think that those changes
are related to the local structures of the amorphous
network. We will observe the composition dependenceof the change in the spectrum before and after
irradiation of light in future. And we are going toinvestigate the relations between those changes.

Fig. 1. VUV absorption spectra of as-deposited
amorphous AsxSe1-x (for x=0.3, 0.4 and 0.5) thinfilms in the energy region from 40 to 60 eV.
[1] K. Tanaka, Rev. Solid State Sci. 4 (1990) 641.
[2] K. Shimakawa, A. Kolobov and S. R. Elliott, Adv.
Phys. 44 (1995) 475.
[3] K. Tanaka, Encyclopedia of Nanoscience andNanotechnology 7 (2004) 629.

140
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Ⅲ -4. Surface, Interface and Thin Films
BL6U
BL6U

Electronic Structures of Two-dimensional Alloys of Silicon and Germanium
1

A. Fleurence1, C. Huet1, S. Wallace1, F. Wiggers3, H. Yamane2, N. Kosugi2
and Y. Yamada-Takamura1

School of Materials Science, Japan Advanced Institute of Science and Technology, Nomi 923-1292, Japan
2
Institute for Molecular Science, Okazaki 444-8585, Japan
3
MESA+ Institute for Nanotechnology, University of Twente, 7500 AE Enschede, The Netherlands

Silicene and germanene are honeycomb lattices
made of Si and Ge atoms, respectively, with buckled
structures due to the mixed sp2/sp3 hybridization in
their chemical bondings [1]. The electronic structures
calculated for free-standing silicene and germanene
both exhibit Dirac cone regardless of the buckling [1].
Although silicon-germanium alloys with diamondstructure are known as isomorphous system, up tonow, there is no experimental study for their
two-dimensional (2D) counterparts.
Silicene and germanene exist only in epitaxial forms.
Among them, epitaxial silicene on ZrB2 thin films
grown on Si(111) has the particularity to form in aspontaneous and self-terminating way by segregationof Si atoms from the silicon substrate [2]. Epitaxial
silicene forms a ZrB2(0001)-(2×2) reconstruction andis semiconducting as a 350 meV-wide gap is opened in
the Dirac cones.
We had demonstrated by means of low energy
electron diffraction (LEED) and scanning tunnelingmicroscopy at our home laboratory that the depositionof germanium on silicene can give rise to silicenegermanene heterostructures, 2D silicene-Ge alloy inthe form of Ge incorporation into the silicene lattice,and vertical silicene-germanene heterostack structures,
depending on the preparation conditions [3]. The
experiments carried out at UVSOR were aimed atgetting insights into (i) how Ge atoms are integrated in
the silicene lattice and heterostacks, and (ii) what theirelectronic band structures are.
Water-cooled mini K-cell, which we use for theexperiments in our home-based setup, was installed in
the preparation chamber of BL6U for evaporating Ge.
Epitaxial silicene samples were prepared on-site byannealing ZrB2/Si(111) samples at 800oC underultrahigh vacuum [2]. Ge deposition was realizedwith a substrate temperature of 350°C.
For low Ge coverages giving rise to silicene-Gealloy, no significant change in the Si2p core-level
spectrum are observed and the structure remains
ZrB2(0001)-(2×2)-reconstructed. The Ge core-level(Fig1.(a)) shows a single component which indicatesthat the Ge atoms are incorporated in a unique site in
the silicene lattice. Angle-resolved photoemission
spectroscopy (ARPES) spectra (Fig. 1 (b)) indicatethat the band structure is essentially the same as thatof pristine silicene. In contrast, for coverage beyond
0.2 ML Ge, a complex LEED pattern and a different
core-level spectrum (Fig. 1 (c)) suggests a more

drastic transformation of the silicene structure related
to the growth of a Si-Ge heterostack.
This work was supported by the Joint Studies
Program (No. 203, 2016-2017) of the Institute for
Molecular Science.

Ⅲ- 4

Fig. 1. (a): Ge 3d core-level (hν = 80 eV) andZrB2(0001)-(2×2) LEED pattern (EB = 40 eV) after
deposition of 0.06 ML Ge. (b): ARPES spectra after
deposition of 0.04 ML Ge (hν = 43 eV). (c): Ge 3dcore-level (hν = 80 eV) and LEED pattern (EB = 40 eV)
after deposition of 0.41 ML Ge. All the measurements
were carried out at room temperature.
[1] K. Takeda and K. Shiraishi, Phys. Rev. B 50 (1994)
14916.
[2] A. Fleurence et al., Phys. Rev. Lett. 108 (2012)
245501.
[3] Y. Awatani, A. Fleurence and Y. Yamada-Takamura,
Bulletin of the American Physical Society, 2016 March
Meeting, T1.307.

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Ⅲ -4. Surface, Interface and Thin Films
BL6U
BL6U

Bilayer Silicon on ZrB2(0001)
A. Fleurence1, F. Wiggers2, S. Wallace1, C. Huet1, H. Yamane2, N. Kosugi2
and Y. Yamada-Takamura1

School of Materials Science, Japan Advanced Institute of Science and Technology, Nomi 923-1292, Japan
2
MESA+ Institute for Nanotechnology, University of Twente, 7500 AE Enschede, The Netherlands
3
Institute for Molecular Science, Okazaki 444-8585, Japan

1

Ⅲ- 4

The experimental observation of silicene provides anevidence that silicon can crystallize in a graphitic form
with chemical and physical properties different fromthose of bulk silicon in which Si atoms are sp3
hybridized. Even though the graphene-like character ofsilicene was verified by the observation of π-electronic
states [1], the hybridization of the Si atoms in silicene
is not pure sp2 as for C atoms in graphene, but adopts
an intermediate sp2/sp3 hybridization reflected by the
buckling of the honeycomb structure of free-standing
silicene [2]. The resulting flexibility of silicene
structure makes it less robust than graphene against its
environment. Therefore, the possibility of stacking
silicene layers in a manner similar to other layeredmaterials such as graphite or chalcogenides isquestionable.
It was recently claimed that multilayer silicene canbe grown. In our group, we demonstrated that a bilayer
silicon can be fabricated on ZrB2(0001) thin films
grown on Si(111) substrates by depositing silicon on
the epitaxial silicene sheet that forms spontaneously on
the ZrB2(0001) surface [3]. The resulting bilayer
silicon sheet has structural and electronic properties
distinct from both silicene and bulk silicon: The bilayer
silicon is metallic as the density of states at Fermi levelis non zero [3] as shown by tunneling spectroscopy andpreliminary characterizations of the band structure byangle-resolved photoemission spectroscopy (ARPES).
Low-energy electron diffraction (LEED) pattern showsthat the bilayer has a lattice parameter slightly larger
than that of silicene. As a consequence, the (√3×√3)
unit cell of the bilayer does not commensurate with the(2×2) unit cell of ZrB2(0001) as that of silicene does.
The purpose of this study was to get acomprehensive picture of the band structure of the Si
bilayer by measuring high resolution ARPES spectra
along both the Γ-K and Γ-M directions of the Brillouinzone of ZrB2(0001).
Epitaxial silicene samples were prepared on-site byannealing ZrB2/Si(111) samples at 800oC underultrahigh vacuum [1]. Silicon was evaporated byheating a piece of silicon in front of the sample held at
a temperature of 320°C. The formation of the bilayer isverified by the observation of features specific to thebilayer silicon in LEED pattern [3]. ARPES spectra
were then recorded with a photon energy of hν=43 eV
at a temperature of 20 K.
The parabolic band centered on the M point (which
also corresponds to the K point of epitaxial silicene) isreminiscent of the π band observed for epitaxial
silicene on ZrB2(0001).

However, it is shifted upward by 200 meV. In
addition, the band structure features several new
bands crossing linearly at the Fermi level. The mostintense band of these new bands intersect the Fermi
level at a position slightly inward with respect to the
M point of the Brillouin zone of ZrB2(0001). This
shift is consistent with a silicon structure with alattice parameter slightly larger than that of epitaxial
silicene as previously deduced from LEED patterns[3]. The mismatch between the ZrB2(0001) unit celland that of the bilayer silicon causes a back-folding of
the linear bands which are replicated near the Γ andM points of the Brillouin zone.
These results may suggest that the silicon layers
have slightly different lattice parameters that results inthe decoupling of the topmost layer. This hypothesis
will be investigated further by ab-initio calculations
using the conclusions drawn from the experimental
data as inputs.
This work was supported by the Joint Studies
Program (No. 203, 2016-2017) of the Institute for
Molecular Science.

Fig. 1. ARPES spectra of the bilayer silicon along theΓ-M direction of the Brillouin zone of the ZrB2(0001)
recorded with hν = 43 eV at 20K.
[1] A. Fleurence et al., Phys. Rev. Lett. 108 (2012)
245501.
[2] S. Cahangirov et al., Phys. Rev. Lett. 102 (2009)
236804.
[3] T. G. Gill et al., 2D Mater. 4 (2017) 021015.

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BL6U
BL6U

Hydrogenation of Epitaxial Silicene on ZrB2(0001)
A. Fleurence1, T. Yonezawa1, S. Wallace1, S. Horibe1, T. Kato1, H. Yamane2, N. Kosugi2
and Y. Yamada-Takamura1
Japan Advanced Institute of Science and Technology, Nomi 923-1292, Japan
2
Institute for Molecular Science, Okazaki 444-8585, Japan

1

Silicene is a 2D Dirac material made of a Si
honeycomb lattice [1]. However, in contrast to its
analogue, graphene, for which the sp2 hybridizationof the orbitals makes the structure perfectly planar,
the structure of silicene is buckled due to sp2/sp3
hybridization [1]. For this reason, it was predicted bytheoretical calculations that the hydrogenation ofsilicene would have an even stronger effect on the
structure of silicene than on that of graphene with the
opening of a gap as wide as 1.2 eV [2].
ZrB2 thin films grown on Si(111) has the particularity
to promote the spontaneous formation of silicene bysegregation of Si atoms from the substrate [3]. Thisepitaxial form of silicene has a structure in which all
atoms but one are laying at the same height and one isprotruding. The band structure is also affected as the
Dirac cones are turned into parabolic bands [3].
Previous experiments confirmed that thehydrogenation of epitaxial silicene sheets on Ag(111)[4] and ZrB2(0001) causes structural change of thesilicene structures. In the latter case, this is reflectedby a different electron energy dependence of thelow-energy electron diffraction (LEED) pattern. The
surface is ZrB2(0001)-(2×2)-reconstructed as pristinesilicene does, but for an electron energy (EB) of 30 eV,
the inner fractional spots are not visible anymore.
The purpose of the experiments carried out at BL6U
was to get insights into the nature of the change
induced by hydrogenation in the structure and the band
structure of epitaxial silicene, which has not beenreported yet. Si2p core-level spectra were recorded at
different photon energies including a surface-sensitive
photon energy of hν = 130 eV. For Angle-resolved
photoemission spectroscopy (ARPES), a photon energyof hν = 43 eV were used.
Epitaxial silicene samples were prepared on-site byannealing ZrB2/Si(111) samples at 800oC underultrahigh vacuum [3]. Silicene was hydrogenated atroom temperature by means of a hot W filament used
to crack H2 molecules fed in the chamber through aleak valve. The complete hydrogenation of silicene
was verified by the vanishing of the ZrB2(0001)-(2×2)
fractional spots in LEED pattern recorded with EB = 30
eV. Fig. 1. (a) compares the Si2p core-level spectra
recorded before and after hydrogenation of epitaxial
silicene. It shows that hydrogenation causes a 0.2 eVshift of the Si2p core-level towards higher binding
energies. The spectrum features two components
broader than those of silicene. More surprisingly, the
ARPES spectra shown in Figs. 1. (d) and (e) recorded
around the K point of silicene show that all thesilicene-related bands (visible between the Fermi level
and EB=1.5 eV) have faded upon hydrogenation
whereas those of the ZrB2 remained.
These results although insightful, suggest that further
characterizations by scanning tunnel microscopy are
required to determine whether the silicon structure
remains two-dimensional upon hydrogenation.
This work was supported by the Joint Studies
Program (No. 203, 2016-2017) of the Institute for
Molecular Science.

Ⅲ- 4

Fig. 1. (a) Si2p core-level spectra before (black) andafter (red) hydrogenation. (b) and (c): LEED patterns
corresponding respectively to the spectra. (d) and (e):ARPES spectra before and after hydrogenation
around the K point of silicene. All the measurements
were carried out at a temperature of 20K.
[1] K. Takeda and K. Shiraishi, Phys. Rev. B 50
(1994) 14916.
[2] M. Houssa et al., Appl. Phys. Lett. 97 (2010)
112106.
[3] A. Fleurence et al., Phys. Rev. Lett. 108 (2012)
245501.
[4] J. Qiu et al., Phys. Rev. Lett. 114 (2015) 126101.

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Electronic Structure of GaSe Thin Films Grown on Ge(111) Wafers
T. Yonezawa1, A. Fleurence1, H. Yamane2, S. Wallace1, S. Horibe1, T. Kato1,
N. Kosugi2 and Y. Yamada-Takamura1
1

Ⅲ- 4

Japan Advanced Institute of Science and Technology, Nomi 923-1292, Japan
2
Institute for Molecular Science, Okazaki 444-8585, Japan

Gallium selenide (GaSe) belongs to a class ofmaterial called “metal chalcogenides” which is
attracting a lot of interests as a two-dimensional
semiconducting material, since a single layer ofmolybdenum disulfide (MoS2) was made into atransistor [1]. Like graphite, layers of chalcogenides
stack via weak van der Waals interaction, and theselayers can be exfoliated easily using adhesive tapes,
which is advantageous to prepare atomically-flat andclean surfaces. We are particularly interested in GaSe
as a lattice-matching and less-interacting substrate for“silicene” which is a Si-version graphene [2], so thatthe combination will realize epitaxial silicene with theproperties of those of free-standing one.
GaSe thin films used in this study were grown on
Ge substrates by molecular beam epitaxy (MBE)
method. Ge(111) wafers (undoped) were cleaned
ultrasonically with acetone, ethanol, and deionizedwater. The substrates were then fixed to amolybdenum block with indium, and introduced into
the MBE system via a load-lock. Surface oxides were
removed by heating the substrates at 600oC underultrahigh vacuum (UHV). Oxide-free surface kept at
growth temperature of 525oC was first exposed to Se
vapor for 30 seconds, and then GaSe growth wasstarted by exposing the surface simultaneously to Ga
vapor and Se vapor with a flux ratio of Ga/Se = 7/100
for 20 minutes. GaSe growth was monitored in situ
by reflection high energy electron diffraction, and an
epitaxial relationship of GaSe(0001)//Ge(111) andGaSe[11-20]//Ge[1-10] was determined.
For the GaSe thin film surface prepared bycleavage using adhesive tape at UVSOR prior to theintroduction to the preparation chamber of BL6U via
load-lock, we found traces of carbon in photoelectron
spectroscopy results, which are not shown here.
Seeing this result, the following measurements werecarried out without this preparation process.
Angle-resolved
photoemission
spectroscopy(ARPES) was carried out on an as-grown GaSe thinfilm surface using a photon energy of 50 eV at room
temperature. GaSe thin film sample was degassed at
300oC under UHV before the measurement. The results
are plotted along the Γ-K direction of GaSe(0001),
which is shown in Fig. 1. Clear double parabolic bands
similar to what has been observed for cleaved GaSe
single crystal [3] can be identified, but at larger binding
energy indicating possible doping. The lack of feature
at K point makes this surface an ideal substrate forfree-standing-like silicene.

Raising annealing temperature to 500oC resulted ina change in the low energy electron diffraction(LEED) pattern. As shown in Fig. 2, additional spots
appeared around original GaSe(0001)-(1x1) spots
which corresponds well with Moiré constructed by
GaSe(0001) and Ge(111). This change was associatedwith loss of oxygen from the surface and change in
Ga- and Ge-related states observed by core-level
photoelectron spectroscopy, indicating possible
change at the film-substrate interface.
This work was supported by the Joint Studies
Program (No. 203, 2016-2017) of the Institute for
Molecular Science.

Fig. 1. ARPES spectra of GaSe thin film surface
measured along Γ-K direction of GaSe(0001).

Fig. 2. LEED pattern of GaSe/Ge(111) sample surface
showing spots corresponding to Moiré.
[1] B. Radisavijevic et al., Nat. Nanotechnol. 6 (2011)147.
[2] A. Fleurence et al., Phys. Rev. Lett. 108 (2012)
245501.
[3] L. Plucinki et al., Phys. Rev. B 68 (2003) 125304.

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Epitaxial Silicene on h-BN Terminated ZrB2 Thin Films
F. B. Wiggers1, A. Fleurence2, K. Aoyagi2, T. Yonezawa2, H. Yamane3, Y. Yamada-Takamura2,
N. Kosugi3, A. Y. Kovalgin1 and M. P. de Jong1
MESA+ Institute for Nanotechnology, University of Twente, 7500 AE Enschede, The Netherlands
Japan Advanced Institute of Science and Technology, School of Materials Science, Nomi 923-1292, Japan3
Department of Photo-Molecular Science, Institute for Molecular Science, Okazaki 444-8585, Japan
1

2

Silicene is the silicon analogue of graphene, i.e. a
two-dimensional (2D) silicon allotrope featuring an
atomically buckled honeycomb-lattice. Theory predicts
Dirac electrons and an electrically tunable spin-orbit
bandgap of a few meV, leading to the topologicalquantum spin Hall phase [1]. However, theseproperties of free-standing silicene remain hypothetical,
because so far only epitaxial silicene has beensynthesized on metallic substrates such as Ag(111) [2],ZrB2(0001) [3], Ir(111) [4], and ZrC(0001) [5],introducing non-negligible hybridization of electronic
states and denying direct electrical characterization
without complex processing.
The synthesis of silicene on insulating, weaklyinteracting substrates is therefore highly desired.
Motivated by this, we studied the growth andproperties of 2D silicon layers grown on theh-BN(0001)-terminated surface of a ZrB2(0001) thinfilm on a Si(111) substrate. The h-BN terminatedsubstrates were prepared ex-situ using plasma
nitridation and annealing of epitaxial ZrB2 films.
Surface cleaning was performed at BL6U prior tosilicene growth using annealing at about 800 °C toremove oxides. Silicon was deposited in steps byheating a Si strip by direct current. The resulting
highly ordered 2D silicon layer on the h-BN
terminated ZrB2 surface was studied by LEED,ARPES, and core level PES.
It was found that the electronic structure of theso-obtained Si layer is very similar to that of epitaxial
silicene on ZrB2, which has been characterized
previously [3]. Figure 1 shows the valence band
structure as determined by ARPES measurements
recorded with a photon energy of 50.5 eV. Besides
ZrB2 derived bands, characteristic Si-related bands
can be identified centered around the K-point of the
Si lattice, the most prominent of which is indicated by
the dotted line. This particular electronic structure isvirtually identical to that of silicene on ZrB2, strongly

suggesting that intercalation underneath the h-BN
layer takes place. This conclusion is further supportedby the Si 2p spectra (not shown). Interestingly, theh-BN layer has a negligible effect on the electronic
structure of the silicene that it covers. This is
promising for non-destructive capping of silicene,
which is required for any analysis or application ofsilicene outside ultra-high vacuum.

Ⅲ- 4Fig. 1. ARPES spectra measured along the Γ-K
direction of the 2D Si layer.
[1] M. Ezawa, New J. Phys. 14 (2012) 33003.
[2] P. Vogt, P. De Padova, C. Quaresima, J. Avila, E.
Frantzeskakis, M. C. Asensio, A. Resta, B. Ealet and
G. Le Lay, Phys. Rev. Lett. 108 (2012) 155501.
[3] A. Fleurence, R. Friedlein, T. Ozaki, H. Kawai, Y.
Wang and Y. Yamada-Takamura, Phys. Rev. Lett. 108(2012) 245501.
[4] L. Meng, Y. Wang, L. Zhang, S. Du, R. Wu, L. Li,
Y. Zhang, G. Li, H. Zhou, W. A. Hofer and H.-J. Gao,
Nano Lett. 13 (2013) 685.
[5] T. Aizawa, S. Suehara and S. Otani, J. Phys. Chem.
C 118 (2014) 23049.

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Electronic Structure of Iron Phthalocyanine (I): Temperature-Dependent
Interface-Specific Electronic State in Monolayer on Au(111)2

Ⅲ- 4

H. Yamane1, 2, A. Carlier1, 3 and N. Kosugi1, 2Institute for Molecular Science, Okazaki 444-8585, JapanThe Graduate University for Advanced Studies (SOKENDAI), Okazaki 444-8585, Japan3
Department of Physics, University of Namur, Namur B-5000, Belgium
1

Iron phthalocyanine (FePc) is well known as one ofimportant organic semiconductors with uniqueelectronic and magnetic properties. Among them, it
was found that FePc molecule on Au(111) exhibits
unique Kondo effects depending strongly on theadsorption configuration, e.g., ontop site at 2.6±1.4 K
and bridge site at 110~150 K [1]. In the present work,in order to investigate the change in the electronic
structure introduced by the Kondo effect, we haveapplied angle-resolved photoemission spectroscopy(ARPES) to the FePc monolayer on Au(111).
The experiment was performed at the in-vacuum
undulator beamline BL6U. The clean Au(111) surface
was obtained by the repeated cycles of the Ar+
sputtering and the subsequent annealing at 700 K, asconfirmed by the low-energy electron diffraction(LEED) and the Shockley state in ARPES. The
ordered monolayer was obtained by flashing the FePc
thin multilayer on Au(111) at 470 K.
Figure 1 shows the photoemission angle (θ)
dependence of the ARPES spectra measured for the
FePc monolayer on highly oriented pyrolytic graphite(HOPG) and on Au(111) at 20 K using hv = 45 eV. At
the FePc/HOPG interface, the C 2p- and Fe 3dderived peaks appear at the binding energy of 1.2 eV
and 1.5 eV, respectively. The large backgroundobserved at θ = 30° originates from the π band of
HOPG. The Fe 3d intensity is getting stronger thanthe C 2p intensity when hv > 60 eV (not shown) as
observed for the gas phase [2]. On the other hand, at
the FePc/Au(111) interface, the C 2p peak at 0.7 eV
exhibits the clear θ dependence with the intensity
maximum at θ = 32° (k ≈ 1.7 Å−1), while no clear Fe
3d-derived peaks appear below the C 2p-derived peak,as observed at the CoPc/Au(111) interface [3],indicating the modification of the Fe 3d orbital with
the Au(111) surface. It is worthy of note here that aquite weak peak is appeared below the Fermi level(EF) but is not observed at the clean Au(111) surface.
Figure 2 (a) shows the temperature dependence of
ARPES at k ≈ 1.7 Å−1 for the FePc/Au(111) interface.
With decreasing the temperature, the Fermi edge is
getting sharpened and the interface-specific peak at
0.12 eV is getting visible. The difference ARPES
spectrum between 30 K and 240 K shown in Fig. 2 (b)indicates the presence of the temperature-dependentinterface states at 0 eV and 0.12 eV, which disappear
at ca. 160 K. The increase in the density of states at
EF is the indication of the Kondo resonance, asreported in Ref. [1], which may also introduce theformation of the interface state observed at 0.12 eV.

Fig. 1. Photoemission angle (θ) dependence of
ARPES (hv = 45 eV) measured for the interfaces of
FePc/HOPG and FePc/Au(111) at 20 K.

Fig. 2. (a) Temperature dependence of ARPES at k ≈1.7 Å−1 measured for the FePc/Au(111) interface. (b)Difference spectrum between 30 K and 240 K, which
is obtained after the substrate-background subtraction
and the smoothing.
[1] E. Minamitani et al., Phys. Rev. Lett. 109 (2012)
086602.
[2] B. Brena et al., J. Chem. Phys. 134 (2011) 074312.
[3] H. Yamane and N. Kosugi, J. Phys. Chem. C 120(2016) 24307.

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Electronic Structure of Iron Phthalocyanine (II): Intermolecular ElectronicBand Dispersion in Crystalline Multilayer
2

H. Yamane1, 2, A. Carlier1, 3 and N. Kosugi1, 2Institute for Molecular Science, Okazaki 444-8585, JapanThe Graduate University for Advanced Studies (SOKENDAI), Okazaki 444-8585, Japan3
Department of Physics, University of Namur, Namur B-5000, Belgium
1

The intermolecular electronic band dispersion,
originating from the periodicity of the molecular
stacking structure, is essential to investigate thecharge transport mechanism related to organic
electronics. Recently, we have succeeded in precise
observation of the quite weak intermolecular band
dispersion for crystalline films of phthalocyanines[MPc, M = metal or H2 (metal free)], such as MnPc,
CoPc, ZnPc, F16ZnPc and H2Pc, by angle-resolved
photoemission spectroscopy (ARPES) [1]. In thiswork, we have investigated the intermolecular band
dispersion of the FePc crystalline film, which isdifficult to observe precisely with respect to the other
MPc films since the C 2p and Fe 3d energies are close
to each other.
The experiment was performed at the in-vacuum
undulator beamline BL6U. The cleanliness of theAu(111) surface was confirmed by the low-energy
electron diffraction (LEED) and the Shockley state in
ARPES, as obtained from the repeated cycles of theAr+ sputtering and the subsequent annealing at 700 K.
The FePc multilayer is obtained by the vacuum
deposition of purified FePc molecules onto theAu(111) as kept at 350 K.
Figure 1 shows the incident angle (α) dependenceof N K-edge X-ray absorption spectra for the 300-Åthick FePc films on Au(111). The sharp 1s → π*transition peaks appear at hν = 398-405 eV. Thesepeaks are strongest at grazing incidence (α = 70°) andare getting weaker with decreasing α, except for peak
X at 399 eV due to the hybridization with Fe 3d
orbital. Other broad 1s → σ* transition features (hν >405 eV) show the opposite polarization dependence.
Furthermore, the FePc multilayer shows the clear
LEED pattern as shown in the inset of Fig. 2. These
evidences indicate that the FePc molecules on
Au(111) form the flat- lying (β ≈ 0°) crystalline film.
Figure 2 shows the photon energy (hν) dependenceof the normal-emission ARPES spectra for the FePc
crystalline film. Since the FePc crystalline film on
Au(111) shows a Stranski-Krastanov growth mode,
there are remanent substrate signals such as the Fermi
edge, which we used for the fine hν calibration. The
topmost peak exhibits two components derived fromthe C 2p and Fe 3d orbitals as labeled in Fig. 2. The
relative peak intensity between C 2p and Fe 3d isdependent on hv, which is slightly different from thecase in the gas-phase FePc [2]. This difference can be
ascribed to the weak intermolecular orbital overlap
between C 2p and Fe 3d.

The C 2p peak shows a dispersive behavior with hv,
while the Fe 3d-derived peak does not show such abehavior. This indicates the presence of the relatively
strong intermolecular π-π interaction with the transfer
integral of 25-30 meV and the localization of the Fe
3d-derived electronic state. The detailed lineshapeanalysis of the ARPES peak for the energy-versuswavevector relation is now in progress.

Fig. 1. Incident angle (α) dependence of N K-edge
X-ray absorption spectra and the intensity plot ofpeak A for the FePc crystalline film at 20 K.

Fig. 2. hv-dependent ARPES spectra at the normal
emission and the LEED image (E = 60 eV) for the
FePc crystalline film at 20 K.
[1] H. Yamane and N. Kosugi, Phys. Rev. Lett. 111(2013) 086602.
[2] B. Brena et al., J. Chem. Phys. 134 (2011) 074312.

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Large Intermolecular π-Band Dispersion in Crystalline Films of
Hexa-Peri-Hexabenzocoronene on Graphite(0001)
2

Ⅲ- 4

H. Yamane1, 2 and N. Kosugi1, 2Institute for Molecular Science, Okazaki 444-8585, JapanThe Graduate University for Advanced Studies (SOKENDAI), Okazaki 444-8585, Japan
1

Polycyclic aromatic hydrocarbons, e.g., hexa-perihexabenzocoronene (HBC) used in the present work,
have attracted attention as a fragment of graphene. It
has been reported that the HBC films on a highlyoriented pyrolytic graphite (HOPG) exhibit a new
substrate-induced polymorph, where all molecules
adopt a recumbent orientation with planar π-stacking[1]. In the present work, we have investigated thepresence of the intermolecular π-band dispersion in
the HBC multilayer grown on a single crystalline
graphite(0001) surface by means of angle-resolved
photoemission spectroscopy (ARPES).
The experiment was performed at the in-vacuum
undulator beamline BL6U. The single crystalline
graphite(0001) surface was obtained by heating thenitrogen-doped 6H-SiC(0001) wafer based on the
stepwise surface treatment [2]. The crystallinity of thegraphite(0001) surface was confirmed by the lowenergy electron diffraction (LEED).
The LEED image of the 250-Å-thick HBC
crystalline multilayer on graphite(0001), displayed in
the inset of Fig. 1, shows a sharp diffraction pattern,
together with the incident-energy-dependent multiple
scattering spots. We found that the diffraction patternof the HBC multilayer agrees well with that of the
HBC monolayer (not shown), and that the multiple
scattering spots are not observable in the HBC monolayer, indicating the highly-ordered layer-by-layer
growth of the HBC molecules on graphite(0001).
Figure 1 shows the photon energy (hv) dependenceof the normal-emission ARPES spectra measured for
the HBC multilayer on graphite(0001) at 20 K and
300 K. At 20K, the topmost valence band shows alarge dispersion as 220 meV with hv. This dispersion
is observable even at 300 K, indicating the presenceof the stable and strong intermolecular π-stacking.
Figure 2 shows the energy-vs.-wavevector (E-k)
map of the HBC multilayer on graphite(0001) at 20 K,
which is obtained from the second-derivative curvesof the normal-emission ARPES spectra in Fig. 1. The
dispersion periodicity gives the intermoleculardistance a = 3.369 Å, which is slightly larger thanthat of the graphite (a = 3.335 Å). The tight-binding
fitting to the topmost band dispersion gives theintermolecular transfer integral t = 55 meV. Similar
evidence is observable for the case of the HOPG
substrate (not shown).
The present observation clearly indicates that the
band-like hole transport can be realized in the newpolymorphs of HBC on graphite.

Fig. 1. Photon energy dependence of the normalemission ARPES spectra for the HBC multilayer ongraphite(0001) at 20 K and 300 K. The LEED image
measured at E = 40 eV is show in the inset.

Fig. 2. E-k map of the HBC multilayer on graphite(0001) at 20 K, obtained from the second derivativesof the normal-emission ARPES data. For the kconversion, we used the inner potential V0 as −3.0 eV.
[1] P. Beyer et al., ACS Appl. Mater. Interfaces 6(2014) 21484.
[2] I. Forbeaux, J.-M. Themlin and J.-M. Debever,Phys. Rev. B 58 (1998) 16396.

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Origin of the Interface State at the Tetraphenyldibenzoperiflanthene
Monolayer on Ag(111)
R. Shiraishi1, 2, K. Yonezawa2, T. Yamaguchi1, 2, T. Ueba1, 2, H. Yamane1, 2,
N. Kosugi1, 2 and S. Kera1, 2

The Graduate University for Advanced Studies (SOKENDAI), Okazaki 444-8585, Japan
Department of Photomolecular Science, Institute of Molecular Science, Okazaki 444-8585, Japan
1

2

Strong modification of the electronic property in
π-conjugated molecules adsorbed on a metal substrate
has been reported, for example, 2D band dispersion,
Kondo effect, and so on. These phenomena are
induced by the hybridization of the electronic wave
function between the molecule and the metal surface.
Thus, the formation mechanism of the interface state
has attracted attention for a long time.
Tetraphenyldibenzoperiflanthene (DBP, Fig. 1 (a))
is an interesting molecule for investigating the
hybridized state between molecule and metal surface,because the molecule is lying-flat on the substrate andits large π-conjugated plane is expected to be far apartfrom the surface due to its phenyl rings. We reported
DBP forms a well-ordered monolayer (ML) film on
Ag(111) [1]. Here the interfacial electronic state of
DBP(ML)/Ag(111) is investigated by angle-resolved
ultraviolet photoelectron spectroscopy (ARUPS).
As shown in Fig. 1 (b), while UPS spectra of the gas
phase and the ML film on HOPG show similar featuresdue to weak interaction, the ML on Ag(111) shows theshift and broadening of these features. Moreover, nosignificant feature around the Fermi level and an
additional feature at 1.4 eV are detected for DBP/Ag(111). The secondary cut-off of the DBP ML becomes
lower by 0.8–1.0 eV than that of a clean Ag(111). The
negative shift is more significant than that due toelectron push-back effect of Xe/Ag (~0.5 eV) [2]. In
general, hybridized states in many organic/metal
systems appear as the filled LUMO. However, thisassumption is hardly applicable to the case of DBP/Ag(111), because the electron transfer from the substrate to
the LUMO would contribute positive surface potential
shift. Therefore we concluded that these interface states(I1-I4) are caused by a hybridization between DBP andAg(111) , hence the HOMO region is largely affected
to give bonding and antibonding features of I1 and I2.
The features I3 and I4 are described to HOMO-1(-2) and
HOMO-3(-4) derived states, respectively.
This conclusion is further confirmed by thecomparison of photoelectron angular distribution(PAD) between experiment and simulation [3]. In Fig.
1 (c) left, the azimuthal dependence of the I1 and I2
region is shown. Fig. 1 (d) shows the calculated PAD
for HOMO and LUMO of a free molecule by multiple
scattering theory. In Fig. 1 (c) right, the experimental
intensities of I1 and I2 are compared to the theoreticalsimulations of HOMO and LUMO taken from Fig. 1 (d).
The experimental pattern of I1 (blue circle) wellagrees with the simulation of the HOMO (black line),

rather than that of the LUMO (red line). A deviationof experimental data from the simulation mightreflect a spatial modulation of the HOMO due to thehybridization with the substrate band which is nottaken into account for the present calculation.

Ⅲ- 4

Fig. 1. (a) Chemical structure of DBP. (b) UPS of
gaseous DBP (bottom), ML on graphite (middle), andML on Ag(111) (top). (c) azimuthal ARUPS (left) anda comparison between experimental and theoretical
pattern of HOMO and LUMO. All the intensity werenormalized at φ = 0˚ for comparison. (d) PAD
simulation of HOMO/LUMO for an isolated DBP.
Two differently oriented molecules in a unit cell [1]and the (111) surface symmetry were considered.
[1] T. Kirchhuebel et al., Langmuir 32 (2016) 1981.
[2] K. Wandelt et al., Surf. Interf. Anal. 12 (1988) 15.
[3] S. Nagamatsu et al., e-J. Surf. Sci. Nano. 3 (2005)
461.

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On the Long-wavelength Approximation in the Photoelectric Effect
Y. Ishida1, S. Ideta2, K. Tanaka2 and S. Shin1

1
ISSP, University of Tokyo, Chiba 444-8585, JapanUVSOR, Institute for Molecular Science, Okazaki 444-8585, Japan

2

Ⅲ- 4

A long-wavelength approximation is often assumed
a priori when the interaction between light and matteris concerned. The assumption, however, may bestrongly invalidated in the surface region at theatomic scale particularly when the photon energy is
low [1]. Here, we test the validity of the assumption
in the photoelectric effect.
When the long-wavelength approximation is valid,
the electrons subjected to the photon field A cannot
sense the direction of the light propagation. The
validity can thus be tested by investigating whether or
not the angular distribution of photoelectrons depends
on the direction of the incident light. Figure 1 (a) shows
the setup for the test. The incident light is s-polarized,
and the angular distribution of the photoelectrons areinvestigate by the analyzer [2]. In this configuration, it
is only the direction of the light that breaks the mirror
symmetry of the setup with respect to the plane
spanned by the s-polarization vector and surface
normal of the sample. The photoelectron distribution
thus becomes asymmetric (symmetric) with respect tothe geometrical mirror plane when the photoelectriceffect is susceptible (unsusceptible) to the propagation
vector. Note, we adopt the scalar gauge.
In the setup, the following two conditions are also
imposed on the sample side: (1) The sample should notbreak the mirror symmetry of the geometry; (2) Near thesurface Γ point, the sample has to have surface localizedstates, because they can strongly overlap to the photon
field in the surface region that is under investigation. To
this end, we chose highly-oriented Bi microcrystals
grown on a highly-oriented pyro-graphite for the sample[3]. The Bi microcrystals are randomly oriented in planewith their 111 face oriented normal to surface, so that theeffect of the crystal symmetry is averaged out in theazimuth. In other words, the sample has a highsymmetry of C. In addition, Bi(111) harbors Rashbasplit surface states around the surface Γ point.
Figure 1 (a) shows the angular distribution ofphotoelectrons I(EB, α) emitted from the highly-oriented
Bi(111) microcrystalline thin film with the incidence of
17 eV light. Here, EB and α are the binding energy andthe emission angle, respectively. Clear dispersions areobserved: The structures in [~0.1, 0 eV] are mainly due
to the Rashba-split surface states. In order to investigate
whether the distribution is symmetric about α = 0, weshow in Figure 2 (b) Δsym (EB, α)  I(EB, α) - I(EB, -α).
We observe some asymmetric distributions from thephotoelectrons emitted from the Rashba bands, as wellas those from the states occurring below 0.3 eV. Thus,
the photoelectron distribution senses the direction of theincident light.
Based on the jellium model, the breakdown occurs
only for p-polarized component of A [1]. The present
results indicating that the approximation is broken evenin the s-polarized case thus calls for a description
beyond. We note that the three-slab model often usedin the field of surface nonlinear optics can qualitatively
explicate the phenomena.

Fig. 1. Experimental geometry for testing the longwavelength approximation in the photoelectric effect.
When the long-wavelength approximation is valid, amirror-symmetric photoelectron distribution is expected(a); if not valid, or when the direction of the incident
light matters, the angular distribution becomesasymmetric (b).

Fig. 2. Angular distribution of photoelectrons fromhighly-oriented Bi(111) thin film (a) and theasymmetry in the distribution (b).
[1] H. J. Levinson, E. W. Plummer and P. J. Feibelman,
Phys. Rev. Lett. 43 (1970) 952.
[2] S. Kimura et al., Rev. Sci. Instrum. 81 (2010)053104.
[3] Y. Ishida et al., Rev. Sci. Instrum. 87 (2016) 123902.

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Ⅲ -4. Surface, Interface and Thin Films
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Interfacial Interaction between Coronene Thin Film and Graphite
T. Yamaguchi1, 2, T. Ueba1, 2, M. Meissner2, K. Yonezawa2, R. Shiraishi1, 2, S. Ideta1, 2,
K. Tanaka1, 2 and S. Kera1, 2
1

The Graduate University for Advanced Studies (SOKENDAI), Okazaki 444-8585, Japan
2
Institute for molecular science, Okazaki 444-8585, Japan

Interactions between organic thin films and solid
surfaces strongly affect the electronic structure at theinterface which contributes to the performance oforganic-based devices. Tanaka et al. observed a replicaof a π-band of the highly oriented pyrolytic graphite(HOPG) surface appearing at the Γ-point below a criticaltemperature of 29 K [1]. The intensity of the replicaband is enhanced at a low-energy photon (hv ≈ 11.5 eV),
indicating that the transition occurs resonantly via
unoccupied states at 11.5 eV above the Fermi level. The
authors suggested that the origin of the band is asuperstructure due to surface defects, a charge density
wave transition, or the adsorption of residual gas
molecules [1, 2]. We observed similar replica bands for acoronene thin film on HOPG which, however, differ inthe critical temperature and the resonance energy.
A clean surface of HOPG was obtained by cleaving in
air and subsequent annealing in UHV. Coronene waspurified twice by sublimation. The sample preparation
was performed in a custom UHV chamber designed fororganic molecules, with a base pressure of 2 × 10-7 Pa. A
coronene layer with a nominal thickness of 2.5 Å was
deposited at room temperature (RT) at a rate of 1 Å/min.
Figures 1 (a) and 1 (b) depict temperature dependencesof E(k) intensity maps at RT and 50 K. Fig. 1 (c) showsenergy distribution curves (EDCs) derived from the E(k)images. In Fig. 1 (b), the replica bands appear not onlyat the Γ-point as in the case of the pristine HOPG but

also at 0.63 Å-1, 1.11 Å-1, and 1.26 Å-1 (not shown).
Upon cooling, the shape of the highest occupied
molecular orbital (HOMO) is markedly changed,
namely the intensity decreases and the energy is higher
by 60 meV as shown in Fig. 1 (c). The hv dependence of
the intensity at the Γ-point around the Fermi level isshown in Fig. 1 (d). An intensity maximum is observed
at 12.8 eV, which is clearly different from the case ofpristine HOPG, indicating a strong modification of theunoccupied state due to weak hybridization at theinterface.
We observed similar multi-replica bands below 180 K.
The critical temperature of 180 K is much higher thanthat of the pristine HOPG. The coronene molecules forma superstructure on HOPG at RT [3], however, there isno clear features of the replica band at RT, which may besmeared out by nuclear motions and/or weak
wavefunction overlap. The occupied and unoccupied
states are strongly modified by the weak interaction at
the physisorbed interface nontrivial way and the impact
may possibly enhanced at low temperature due to larger
wavefunction overlap. A gap-opening and a change in
effective hole mass should occur due to the interaction.
They may be observed by more precise experiments.
[1] S. Tanaka et al., Phys. Rev. B 84 (2011) 121411.
[2] S. Tanaka et al., private communications.
[3] K. Walzer et al., Sur. Sci. 415 (1998) 37.

Fig. 1. E(k) intensity maps of coronene/HOPG at (a) RT and (b) 50 K taken at 13.0 eV. (c) Momentumintegrated EDCs at RT (red) and 50 K (blue). (d) Intensity plot in red area in (b) as a fucnction of hv. The
intensity of each energy is nomalized by photon flux. The red curve is a fitted curve using two Lorentzian functions.

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