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BL8B2

Electronic Structure at Highly Ordered Organic/Metal Interfaces
H. Yamane*, K. Kanai, K. Seki
Department of Chemistry, Nagoya University, Nagoya 464-8602, JapanThe electronic structure at the interface formed
between an organic semiconductor film and a metalelectrode plays a crucial role in the performance ofelectronic devices using organic semiconductors suchas electroluminescent displays, field-effect transistors,
and photovoltaic cells. In particular, the energetics ofthe molecular energy levels near the Fermi level (EF)of metals, i.e., the energy level alignment at organic/
metal interfaces, are of fundamental importance indiscussing various charge phenomena related toorganic devices such as the barrier heights for the
charge injection and separation at the interface [1].
In the field of organic/metal interfaces, one of theimportant issues is the elucidation and control of theinterface state, which may dominate the energy levelalignment at organic/metal interfaces. However, it isgenerally not easy to discuss the interfacial electronic
structure precisely since the energetics at organic/
metal interfaces is easily modified by the presence of
the interface-specific electrical and geometricalphenomena. To fully clarify the possibly complicatedelectrical and geometrical phenomena at the interface,a more pertinent experimental approach to this issue
would be to use a well-characterized system, e.g.,
epitaxially grown organic thin film on atomically flatand clean metal single crystal surfaces, in quantitativeelectron spectroscopic measurements.
From the above point of view, by using angleresolved UV photoemission spectroscopy (ARUPS),
we have studied the electronic structure of wellordered thin films of metal-phthalocyanines (M-Pc),perylene-tetracarboxylic dianhydride (PTCDA), andpentacene (Pn) prepared on metal single crystal
surfaces. Among these, it was reported that Pn
molecules on Cu(110) in the monolayer regime forma highly ordered film structure with planar adsorption
geometry,
where the molecular long axis is parallel to_the [110] substrate direction [2].
Figure 1(a) and (b) shows the observed energy
versus momentum [E(k||)] relation for the flat-lying
Pn_ monolayer film on Cu(110) along (a) I = 0° (the[1 1 0] substrate direction) and (b) I = 28°. The
abscissa is the parallel momentum component (k||),and ordinate is the binding energy (Eb) relative to the
EF of the substrate. In order to map out the E(k||)
relation, we took the second derivative of the raw
ARUPS spectra [–d2I(Eb)/dEb2] at hȞ = 20 eV aftersmoothing for specifying the energies of the spectralfeatures. Open and filled circles indicate the peak
position of the Pn-derived peaks A–C in the raw
ARUPS spectra measured at hȞ = 20 and 30 eV,
respectively. The selected raw ARUPS spectra of the133

valence levels and the secondary-electron cutoff are
shown in Fig. 1(c) and (d), respectively. We foundthat (i) the change in the work function (i.e., vacuum
level shift ǻ) upon the adsorption of the flat-lying Pnmonolayer film is ǻ = –0.9 eV [Fig. 1(d)] due to theformation of the interfacial dipole layer [1], and that(ii) peaks A–C are the interface-specific states. The
latter finding (ii) was concluded since the energy
positions and the orbital symmetries of peaks A–C
cannot be explained by the UPS spectrum of thegas-phase Pn [3] and its orbital symmetries [4]. These
interface states A–C may originate from themolecular energy levels split due to the hybridization
with the wave function of the substrate, which canmodify the energies and the orbital symmetries, as in
the case of the Pn/Cu(119) interface reported by
Ferretti et al [5]. According to their theoretical
calculation in Ref 5 based on the density-functional
theory, the density-of-states just below EF and peak A
in Fig. 1 can be ascribed to the resultant split levels of
the former lowest unoccupied molecular orbital(LUMO) level, and peaks B and C in Fig. 1 can be
ascribed to the resultant split levels of the former
highest occupied molecular orbital (HOMO) level.

Fig. 1. (a,b) E(k||) relation for the highly ordered
flat-lying Pn monolayer film on Cu(110) at I = (a) 0°
and (b) 28°. The abscissa is the parallel component of
the momentum (k||), and ordinate is the binding
energy (Eb) relative to the Fermi level (EF) of thesubstrate. Open and filled circles indicate the positionof the Pn-derived peaks measured at hȞ = 20 and 30
eV, respectively. (c,d) Selected ARUPS spectra of thePn monolayer film and the bare substrate for theregions of (c) valence levels and (d) secondaryelectron cutoff.

Highlight
It is interesting to note that, as seen in Fig. 1(a) and(b), the interface states A–C show dispersive behavior.
At I = 0° [Fig. 1(a)], the E(k||) curve of peak A
measured at hȞ = 20 eV corresponds well with thatmeasured at hȞ = 30 eV, and the E(k||) curve of peak C
has turning points at the same k|| as that for peak A. At
I = 28° [Fig. 1(b)], the turning points for peak B
appears at the same k|| as that for peak A, and thephase of the E(k||) curve for peak B is opposite to thatfor
_ peak A.
_ Furthermore, the experimentally observed
ī point (īexp) exists around k|| = 15.7±0.9 nm–1 at I =0°, which is the center of the fifth Brillouin zone.
From the E(k||) curves of peaks A and C, we _canestimate the lattice constant (Ȝ) along the [1 1 0]
substrate direction using the relation Ȝ = 2ʌ/K, where
K is the size of the Brillouin zone, under theassumption of a tight-binding model. The deduced
value of Ȝ is 1.6 nm, which agrees well with thelattice constant_ of the flat-lying Pn monolayer film
along the [11 0] substrate direction [2]. Thus, theobserved dispersive behavior can be ascribed to theintermolecular band dispersion in the flat-lying Pnmonolayer film on Cu(110) with a large bandwidth of
0.25 eV for the uppermost valence band A, which
seems to form a free-electron-like parabolic
dispersion. Thus, the effective mass of the hole (mh*)
can be calculated from1

1 d 2 E (k )

m h*

!2

dk 2

.

Using this equation, we estimated mh* to be 0.24m0 at
300 K within the tight-binding approximation. In thecase of usual ʌ-conjugated flat-lying organicmonolayers, the intermolecular interaction is mainly
dominated by the weak intermolecular ı-ı interaction,
which gives small bandwidth of less than 0.05 eV.
The observed band dispersion with rather small mh*may originate from the intermolecular interaction via
the substrate due to the hybridization between themolecular orbitals and the free-electron-like Cu bands.
On the other hand, Temirov et al. reported the inplaneintermolecular band dispersion for the unoccupied
state in a PTCDA monolayer on Ag(111) with aneffective mass of electron me* of 0.47m0 by using thehigh-resolution scanning tunneling microscopy andspectroscopy [6]. The observed dispersion in Ref 6 isfar larger than expected for the PTCDA monolayer
alone [7], and they suggest that the dispersion might
be related to the surface state since the effective mass
is similar to that of the Ag(111) surface. However, inthe case of pentacene/Cu(110),
there is no known_
surface state along the [110] substrate direction on theCu(110) surface within the observed energy window.
It must therefore be concluded that the mechanisms
of interfacial dispersion of ʌ-conjugated molecules
are not yet fully understood. For further consideration
about this issue, a joint experimental and theoretical
study is now in progress.

134

Fig. 2. Energy level diagrams for the Pn/Cu(110)system and the gas phase Pn. The LUMO energy for
the Pn multilayer was estimated from Ref 8. The
ionization energy for gas phase Pn (Ig) is 6.6 eV [3],and the intermolecular polarization energy for holes
can be estimated to be 1.7 eV. If the intermolecularpolarization energy for electrons is equal to that forholes, the electron affinity for gas phase Pn (Ag) canbe estimated to be 1.4 eV.
In summary, the energy level diagram for the
Pn/Cu(110) system is presented in Fig. 2. From the
UPS spectra in Fig. 1, the work function of the cleanCu(110) surface is 4.6 eV and its change (ǻ) by thePn adsorption is –0.9 eV. For the flat-lying monolayer
film, we clearly observed the electronic structure
characteristic of the interface with the following
findings: (i) formation of the interface states withpossible modification of the orbital symmetry and theenergy position, and (ii) two-dimensional intermolecular band dispersion of these interface stateswith mh* for the upper branch being 0.24 m0 at 300 K.
These interface states can be deduced to originate
from the hybridization of the molecular orbitals suchas the HOMO and the LUMO levels with the wave
function of the substrate, which may also lead to theobserved band dispersion by the intermolecularinteraction through the substrate. Further studies on
the correlation between the electronic and the film
structures would lead to a breakthrough for theunderstanding of charge phenomena in organic solids.
*
Present address: Institute for Molecular ScienceE-mail: yamane@ims.ac.jp[1] H. Ishii et al., Adv. Mater 11 (1999) 605.
[2] S. Lukas et al., Phys. Rev. Lett. 88 (2001) 028301;
S. Söhnchen et al., J. Chem. Phys. 121 (2004) 525.
[3] V. Coropceanu et al., Phys. Rev. Lett. 89 (2002)
275503.
[4] H. Yamane et al., Phys. Rev. B, 76 (2007) 165436;
Phys. Stat. Sol. (b), 245 (2008) 793.
[5] A. Ferretti et al., Phys. Rev. Lett., 99 (2007) 046802.
[6] R. Temirov et al., Nature, 444 (2006) 350.
[7] H. Yamane et al., Phys. Rev. B, 68 (2003) 033102.
[8] F. Amy et al., Org. Electron. 6 (2005) 85.

BL4A

Synchrotron Radiation Stimulated Etching of Polydimethylsiloxane with
XeF2
T.Y. Chiang1, T. Makimura2, C. S. Wang3, T. Urisu1,4Institute for Molecular Science, Okazaki 444-8585 Japan
2
Tsukuba University, 1-1-1Tennoudai Tsukuba, Ibaraki 305-8573 Japan
3
Shanghai Jiao Tong University, 1954 Hua Shan Rd. Shanghai 200030 P. R. China
4
The Groduate University for Advanced Studies, Okazaki 444-8585 Japan1

The synchrotron radiation (SR) stimulated etchingof silicon elastomer polydimethylsiloxane (PDMS)
has been demonstrated with XeF2 as the etching gas.
An etching system with a differential pump andparaboloid mirror was constructed to perform theetching. The PDMS was found to be effectively
etched under the SR irradiation with flowing XeF2,
and the etching process was area-selective andanisotropic. An etching rate of about 45ȝm 㨯
150mA-1㨯min-1 was obtained at a XeF2 atmosphere of
0.5 Torr in etching chamber.

˘̇˶˻˸˷ʳ˷˸̃̇˻ʳˮ̈̀˰

˃

ˀ˅˃˃

ˀˇ˃˃

ˀˉ˃˃
˃

˅˃˃

ˇ˃˃
ˉ˃˃
˗˼̆̇˴́˶˸ʳˮ̈̀˰

ˋ˃˃

˄˃˃˃

Fig. 4. Depth profile of the etched pattern shown in
Fig. 3.

Fig. 1. Schematic view of the beam line 4 A. DPi:differential pumpimg chamber. TMP: turbo molecular
pump, IP: ion pump, EC: etching chamber. FM:
focusing mirror.

Fig. 2. Beam trace in focusing mirror chamber andetching chamber. S: specimen, A: aperture EC: etching
chamber FM: focusing mirror.

Fig. 3. Top view of the etched pattern on PDMS by
SR etching using XeF2 gas.

135

BL4B

Characterization of Self-Assembled Co Nanorods Grown on
Cu(001)-(2u3)N Studied by XMCD

X. D. Ma1, 2, T. Nakagawa1, 3, Y. Takagi1, 3, M. Przybylski2, J. Kirschner2, T. Yokoyama1,3
1
Department of Structural Molecular Science, The Graduate University for Advanced Studies(Sokendai), Myodaiji-cho, Okazaki, Aichi 444-8585, Japan
2
Max-Planck-Institut f¨ur Mikrostrukturphysik, Weinberg 2, 06120 Halle, Germany
3Institute for Molecular Science, Myodaiji-cho, Okazaki, Aichi 444-8585, Japanbecause the small spin magnetic moment in Co may
originate from the strong covalent bonds with N in
the present nanorods.

Introduction
Recently, York and Leibsle [1] discovered
self-assembled growth of well extended Co nanorods
on Cu(110)-(2×3)N. The Co nanorods are wellisolated from each other up to as much as ~2.0
monolayer (ML) Co coverage with six times intervals
along the [001] direction. We have here investigated
XMCD of 0.8 ML Co/Cu(110)-(2×3)N substrates.

Experimental
A Cu(110) single crystal was dosed with N by mild
N2+ bombardment and subsequent annealing at ~473
K to yield (2×3)N surfaces. Co was deposited onthese surfaces at ambient temperature using acommercial evaporator. The angle-dependent Co
L-edge XMCD measurements were performed with a
total electron yield mode using a UHV-compatible
superconducting magnet (7 T) XMCD system with aliq. He cryostat (the sample temperature of 4.9 K).

Fig. 1. Magnetization curves at T=4.9 K recordedwith the intensity at the LIII peak energy. The simulated magnetization curves using a simple magnetic
anisotropy model are also shown.

Results and Discussion
Figure 1 depicts the magnetization curves recordedwith the electron yield at the LIII peak top energy. The
magnetizations are found to be almost saturated at
H=±5 T for all the axes ([001] is the easy axis). The
curves were simulated using a simple second-ordermagnetic anisotropy model to deduce the macroscopic magnetic anisotropy constants. The two magnetic anisotropy constants KP and KA respectively
caused by the planar (film origin) and axial (rod origin) anisotropies and the size of the spin block N
were assumed. The parameters were determined as
KP=1.2×10í4 (eV/atom), KA=2.0×10í5 (eV/atom),and N=15 (atom). The planar magnetic anisotropy KP
that makes the surface normal the hardest axis isfound to be much larger than that of the rod axial
anisotropy KA.
The angle dependence of the XMCD spectra shownin Fig. 2 was analyzed. The results are mxorb=0.23 ȝB,
myorb=0.19 ȝB, mzorb=0.16 ȝB, mxT=0.005 ȝB, myT=0.011 ȝB, mzT=0.006 ȝB, and mspin=1.01 ȝB, where mT
is the magnetic dipole moment. The orbital magnetic
moment decreases in the sequence of x ([001]), y([1-10]), and z ([110]), which is consistent with theabove magnetic anisotropy constants. This consequently implies that the magnetic anisotropy originates from the difference in the spin-orbit interaction.
Note that the spin magnetic moment obtained issignificantly smaller than that of the bulk hcp Co,

Fig. 2. Co L-edge XMCD spectra of 0.8 ML Co on
Cu(110)-(2×3)N at T=4.9 K and H=±5.0 T for șin=0q(blue) and (șin,ĳin)=(55q,90q) (green) and H=±3.0 T
for (șin,ĳin)=(55q,0q) (red).
[1] S. M. York, F. M. Leibsle, Phys. Rev. B 64
(2001) 033411.

136

BL4B

Enhancements of Spin and Orbital Magnetic Moments of Submonolayer Co
on Cu(001) Studied by XMCD
1

T. Nakagawa1, Y. Takagi1, T. Yokoyama1
Institute for Molecular Science, Okazaki 444-8585, Japanvalue of 0.15 ȝB. Theoretical estimations for the spinand orbital magnetic moment of monolayer
Co/Cu(001) were reported as mspin=1.85 ȝB andmorb=0.261 ȝB [2], which are consistent with thepresent results. Enhancements of the magnetic
moments compared with the corresponding bulk
values were thus clearly elucidated: ~12% for the
spin magnetic moment and ~96 and ~53% for theorbital magnetic moments along the surface paralleland normal directions, respectively.

Introduction
Enhancements of the magnetic moments of ultrathin films have extensively been investigated boththeoretically and experimentally because of theirimportance in fundamental physics as well as technological applications to magnetic recording media. In
the present work, we have investigated the enhancements of spin and orbital magnetic moments for submonolayer Co/Cu(001) by means of XMCD using a
UHV-compatible XMCD system with a 7 T superconducting magnet and a liquid He cryostat [1].

Experimental
A submonolayer Co film was deposited on a clean
Cu(001) surface from a commercial evaporator. The
thickness of the film investigated was estimated to be
0.4 ML from the Co L-edge absorption intensity. Co
LIII,II-edge circularly polarized X-ray absorption
spectra were recorded at the X-ray incidence polar
angles șin of 60q (grazing incidence) and 0q (normal
incidence). The spectra were taken at 6.0 K byswitching the magnetic field.
Fig. 1. Magnetization curve of 0.4 ML Co/Cu(001)
at 6.0 K along the [001] direction, recorded as anormalized Co LIII XMCD intensity. The red points
are the experimental data, and the blue dashed line is
the fitted result.

Results and Discussion
Figure 1 shows the magnetization curve of 0.4 ML
Co at 6.0 K along the surface normal [001] direction,
which is the magnetically hardest axis. The data werescaled using the area of the Co LIII peak. The XMCD
intensity is found to increase linearly up to H=±2.5 T,
while the values at H=±5.0 T are apparently weaker
than the ones expected from the extrapolated linear
line. By fitting the experimentally obtained data
points with a second-order magnetic anisotropy
model, the lowest magnetic field for saturation isestimated to be ~3.4 T. The magnetic fields of ±5 T
are thus confirmed to saturate the magnetization evenalong the magnetically hardest [001] axis.
Figure 2 depicts the Co LIII,II-edge XMCD spectrafor șM=90q and 0q, where șM denotes the polar angleof magnetization. Although the two XMCD spectra
are not very different from each other, small
dissimilarities can clearly be seen around the
LIII,II-edge peaks, indicating small anisotropic featuresin the present submonolayer film.
Using the sum rules and the formulas of XMCD
angle dependence, the magnetic dipole terms wereobtained to be mT//=0.010±0.05 ȝB and mTA=í0.020±0.05 ȝB. Consequently, the spin magnetic moment
was given as 1.79±0.10 ȝB, which is larger than thatof bulk hcp Co (1.55 ȝB), and the orbital magnetic
moments of morb//=0.29±0.05 ȝB and morbA=0.23±0.05
ȝB are much more significantly greater than the bulk

Fig. 2. Co LIII,II-edge XMCD spectra of 0.4 ML Co
on Cu(001) at 6.0 K for the magnetization parallel(șM=90q) and perpendicular (șM=0q) to the surface.
[1] T. Nakagawa, Y. Takagi, Y. Matsumoto, T.
Yokoyama, this volume & also Jpn. J. Appl. Phys., inpress.
[2] O. Hjortstam, J. Trygg, J. M. Wills, B. Johansson,
O. Eriksson, Phys. Rev. B 53 (1996) 9204.

137

BL4B

Variation of Magnetic Anisotropy upon Adsorption of NO on Co/Cu(001)Studied by XMCD
1

T. Nakagawa1, Y. Takagi1, T. Yokoyama1
Institute for Molecular Science, Okazaki 444-8585, Japan
clean Co, the analysis yields morb//=0.299±0.02 PB andmorbA=0.228±0.02 PB, while the NO-adsorbed Co
gives morb//=0.106±0.01 PB and morbA=0.111±0.01 PB.
These results clarifies that the strong in-plane magnetic anisotropy in clean Co is derived from muchlarger in-plane spin-orbit interaction than theperpendicular one and that NO adsorption leads to theloss of anisotropy in the spin-orbit interaction. The
weak in-plane magnetic anisotropy for NO adsorbed
Co may originate from the demagnetization energy(shape anisotropy).

Introduction
Adsorption of atoms and molecules on magnetic
thin films is an attractive surface scientific subject
since it .is known to change drastically magnetic
anisotropy and to induce sometimes spin reorientationtransitions. In the present work, we have investigatedNO adsorption on submonolayer Co/Cu(001) bymeans of XMCD using a UHV-compatible XMCD
system with a 7 T super- conducting magnet and aliquid He cryostat [1].

Experimental
A 0.8 monolayer (ML) Co film was deposited on aclean Cu(001) surface from a commercial evaporator
at room temperature and was subsequently dosed with
NO at ~100 K. Co LIII,II-edge circularly polarized
X-ray absorption spectra were recorded at T=5.0 K
and H=5.0 T with the X-ray incidence polar angles șinof 55q (grazing incidence) and 0q (normal incidence).

Results and Discussion
Figure 1 depicts the magnetization curves of 0.8
ML Co on Cu(001), recorded as Co LIII XMCD intensity at the peak top energy. Unfortunately, the curvealong the hard axis of șin=0q is not saturated. Usingthe șin=0q data, the second-order magnetic anisotropy
constants including demagnetization energies are
obtained as K2=370 (PeV/atom) for clean Co and30 (PeV/atom) for NO adsorbed Co. This indicatessignificant suppression of the in-plane magnetic
anisotropy upon NO adsorption.
Figure 2 depicts the Co LIII,II-edge XMCD spectrafor șin=55q and 0q. NO adsorption induces the shift ofthe peak energies and the suppression of the XMCD
intensity. Using the sum rules, the spin and orbital
magnetic moments are derived. Although themagnetization for clean Co (șin=0q) is not saturated,
the ratio morb/mspin was assumed to be invariant toyield the orbital magnetic moment. In the case of NO
adsorption, both the magnetizations were assumed tobe saturated and this allows us to evaluate magnetic
dipole terms appropriately and hence the intrinsic
spin magnetic moments.
The d-hole number is found to increase significantly from dh=2.56±0.13 (clean) to 2.92±0.15(NO-ads.), implying the oxidation of Co upon NO
adsorption. The spin magnetic moment noticeably
decreases from mspin=1.780±0.18 PB (clean) to 0.89
±0.05 PB (NO-ads.). This indicates strong interaction
between an unpaired electron of NO and exchangesplit Co 3d levels. The anisotropic orbital magnetic
moments show the most prominent difference. For

Fig. 1. Magnetization curves of 0.8 ML Co on
Cu(001) at T=5.0 K before and after NO adsorption.
Fig. 2. Angle dependent Co LIII,II-edge XMCD spec-

tra of 0.8 ML Co on Cu(001) at T=5.0 K before andafter NO adsorption.
[1] T. Nakagawa, Y. Takagi, Y. Matsumoto, T.
Yokoyama, this volume & also Jpn. J. Appl. Phys., inpress.

138

BL8B2

1

Photoelectron Angular Distribution of Mn-Phthalocyanine
Monolayer on Ag(111)

T. Aoki1, S. Hosoumi1, C. Karino1, R. Sumii2, S. Nagamatsu1, N. Ueno1, S. Kera1
Graduate School of Advanced Integration Science, Chiba University, Chiba 263-8522 Japan
2
Graduate School of Science, Nagoya University, Nagoya 464-8602 Japan

Origins of the energy position and the shape of
HOMO bands are keys to understand interface
properties of organic films. The electronic structure of
the adsorbed monolayer on a metal substrate is
generally modified much by a strong electronic
coupling. In this study changes in the electronic
structure due to different spin configuration and/orchange in the ligand field upon adsorption were
investigated for Mn-phthalocyanene (MnPc) on
Ag(111).
Angle-resolved UPS (ARUPS) usingsynchrotron radiation is a powerful tool to study thegeometrical structure of the ultrathin films of organic
molecules as well as the electronic structure. In theprevious work we have succeeded to analyze theemission (T) and azimuthal (I) angle dependences of
ARUPS of thin films of large organic molecules using
single scattering approximations [1].
In this report, we show the observed T andIdependences of 2p- and 3d-orbital derived bands in
ARUPS spectra for well-ordered MnPc monolayer(ML) on the Ag(111) substrate.

the 3d-derived MO has changed. The electronic
structure, especially 3d-derived MOs, of MnPc may
be rearranged due to different spin configuration
and/or change in the ligand field upon absorption.
Now we are trying to obtain the angular dependencesby using the multiple-scattering theory combined with
MO calculation [3] under various spin configulations
and MOs.

Fig. 1. HeI UPS of 1-ML-MnPc on Ag(111) andHOPG. Both dashed curves are UPS from a clean
substrate.

Experimental

T and I dependences of ARUPS spectra wererecorded at photon incidence angle D=45o, hQ=28 eV,
and T=295 K. The purified MnPc molecules were
carefully evaporated onto a clean Ag(111) substrate.
We confirmed 6-hold molecular domains (2 domains
in each crystal axis) from LEED results.

Results and Discussion
Figure 1 shows a typical HeI UPS spectrum of
annealed-MnPc (ML)/Ag(111) at T =0o. The results
obtained for MnPc (ML) /HOPG are also shown [2].
For MnPc/Ag(111), feature A appearing at 0.35 eV,
which is located at lower energy position than
MnPc/HOPG, can be ascribed to HOMO band of
MnPc. Feature B, HOMO-1, which is located atsimilar energy position as for MnPc/HOPG, might beassigned to a single S MO as observed in othervarious Pcs. The shift of A and small satellites (s)might come from interface states formed upon orbital
hybridization.
Figure 2 shows the observed T (a) and I (b)dependences of the band A (HOMO) and band B(HOMO-1) intensities, respectively. The T patternfrom B is rather similar to that of MnPc/HOPG,
indicating the HOMO-1 is assigned to 2p-derived
orbital (a1u) as seen in other Pc/HOPG systems. We
found that the deformation of the MO uponadsorption is surely occurring but not significant. The
T pattern for A (HOMO), however, is completely
different from that of MnPc/HOPG, indicating that

Fig. 2. (a) Observed T patterns of band A (right) andB (left) obtained at D=45o, I=0o. (b) Observed I
patterns of band A and B for MnPc/Ag(111) obtainedat D=45o, T=60o.
[1] N. Ueno et al, J. Chem. Phys. 107 (1997) 2079.
[2] S. Kera et al, UVSOR Activity Report 2006
(2007) 113.
[3] S. Nagamatsu et al, e-J. Surf. Sci. Nanotech, 3(2005) 461.

139

BL8B2

Interaction between Entrapped Atoms and C78 Fullerene Cage

S. Hino 1, M. Kato2, D. Yoshimura3, 4, H. Moribe5, H. Umemoto5, Y. Ito5, T. Sugai5,
H. Shinohara5, M. Otani6, Y. Yoshimoto6, S. Okada7
1
Graduate School of Materials Sci. & Biotech., Ehime Univ., Matsuyama 790-8577 Japan
2
Graduate School of Sci. & Technology, Chiba Univ., Chiba 263-8522, Japan
3
UVSOR, Institute for Molecular Science, Okazaki 444-8585, Japan
4
Research Center of Material Science, Nagoya Univ., Nagoya 464-8602, Japan
5
Graduate School of Science, Nagoya Univ., 464-8602, Japan
6
Institute for Solid State Physics, Univ. of Tokyo, Kashiwa 277-8581, Japan
7
Center for Computational Sciences, Univ. of Tsukuba, 305-8571 Tsukuba Japan
Ultraviolet photoelectron spectra (UPS) of
metallofullerene, La2@C78 that has D3h cagesymmetry were measured using a synchrotron
radiation light source [1]. The UPS are shown in Fig.
1. Its spectral onset energy was 0.70 eV below theFermi level, indicating the semiconductive nature ofthis metallofullerene. The UPS consisted of numerous
crests and troughs. Further, a change in intensity upontuning the excitation energy was observed; however,
the intensity of the change was not as large as thoseobserved for other fullerenes. Previously measured
UPS of Ti2C2@C78 are also shown in Fig. 1 [2]. When
the UPS of Ti2C2@C78 were reported, it was thoughtthat it was the mixture of two Ti2@C80 isomers, and it
has been questioned that it is not the mixture but
actually Ti2C2@C78. Further it has been proposed thatthe cage symmetry of Ti2C2@C78 is D3h.
There are two so-called Isolated Pentagon Rulesatisfying D3h cage structure in C78 fullerene family.
The UPS of La2@C78 differ considerably from thoseof Ti2C2@C78, so that, at first, it was thought thatthese two metallofullerenes have different D3h cage.
In order to examine this assumption, DFT
calculation has been carried out in both cages with
La2 or Ti2C2 entrapped cages. Calculated DOS isshown in Fig. 1. Comparison revealed that both
metallofullerenes have the same cage symmetry
classified as D3h (78:5) according to Fowler andManolopoulos [3]. In most UPS of fullerenes, the
UPS of the fullerenes having the same cage areanalogous. Present results are rather extraordinary.
Thus distribution of wave functions (DWF) inmetallofullerenes is examined. Figure 2 shows thewave function distribution of HOMO and HOMO-1
orbitals of these two metallofullerenes.
DWF of the HOMO of both fullerenes is almost
the same, but that of the HOMO-1 differs
considerably: while HOMO-1 of La2@C78 distributeson the fullerene cage, that of Ti2C2@C78 penetrates
into the cage and tries to make hybridized bond with
Ti atoms. Titanium has a tendency to form carbide.
Possibly there might strong interaction between Ti
atoms and cage constructing carbon atoms, and this is
the reason why the same cage symmetry having
La2@C78 and Ti2C2@C78 give completely different
UPS.

10

8

B in d in g E n e rg y (e V )
6
4
2

0

(T iC ) 2 @ C 78
L a 2 @ C 78
T i(5 )T i(4 )

L a (5 )L a (4 )86

4
2
E n e rg y (e V )0-2Fig. 1. UPS of La2@C78 and Ti2C2@C78. Calculated
DOS assuming La2 or Ti2C2 species entrapped D3h C78
is also shown.

Fig. 2. Distribution of HOMO and HOMO-1 wave
functions. Green circles indicate Ti, Yellow circles La,
and grey circles C. Large grey circle indicate
entrapped carbon atom.
[1] S. Hino et al., Phys. Rev. B 75 (2007) 125418.
[2] K. Iwasaki et al., Chem. Phys. Lett. 397 (2004)
169.
[3] P. W. Fowler, D. E. Manolopoulos, “An Atlas of
Fullerenes”, Oxford University Press, Oxford, 1995.

140

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Energy Level Alignment at PTCDA / Metal Interfaces

E. Kawabe1, H. Yamane1, R. Sumii2,3, K. Koizumi1, K. Kanai2, Y. Ouchi1, K. Seki1
1
Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku,
Nagoya 464-8602 Japan
2
Research Center for Materials Science, Nagoya University,
3
Present address: Photon Factory, Institute of Materials Structure Science, High Energy
Acceleration Research Organization, Oho 1-1, Tsukuba, 305-0801 Japan
Recently extensive research has been carried out
for applying organic materials to electronic devices. It
is important to understand how the energy levels alignat organic/metal (O/M) interfaces for improving
their performance. However, the detailed mechanismof the energy level alignment at O/M interface is still
unclear. Vázquez et al. proposed the induced densityof interface states (IDIS) model [1] to theoreticallyexplain the vacuum level (VL) shift at O / M interface[2, 3]. They made several assumptions to simplify thecalculation, i.e. (1) the energy levels of the highest
occupied molecular orbital (HOMO) and the lowest
unoccupied molecular orbital (LUMO) are broadened
to form continuous levels, which is called the IDIS by
the interaction with the metal state, (2) only thes-state is taken into account as the metal state.
Although this model well explains the observed ' atorganic / Au interfaces, it has been still unclear
whether this model can be generally applied tovarious metal substrates. Thus we investigated theenergy level alignment at the interfaces between
perylene-3, 4, 9, 10-tetracarboxylic dianhydride(PTCDA, Fig. 1) and metals (Au, Ag and Cu) by
ultraviolet photoelectron spectroscopy (UPS).
The plot of the observed ' as a function of themetal work function ()M) is shown in Fig. 1. In the
IDIS model, it is expected that ' and )M show alinear relation. However, we cannot see such relation.
The UPS spectra of monomolecular layer (1 ML)
PTCDA film on Au(111), Ag(111) and Cu(111) are
shown in Fig. 2. The interface states are observed for
Ag and Cu interfaces, and they are not the broadened
states but the split states. These results indicate that

the IDIS model cannot be applied to these interfaces,
and that the interaction with the metal d-band statescannot be neglected.
Then we estimate the interface interaction bytaking into account the metal d-band states. We
expect that [5] the magnitude of the attractive
interaction depends on the inverse of the energy
separation between the LUMO of PTCDA and thecentroid of the metal d-band (Hd-LUMO), and that themagnitude of the repulsive interaction depends on the
coupling matrix element (V) between the adsorbate
state and the metal d-band state. The value of Hd-LUMO
for the PTCDA / Cu interface is the smallest. The
value of V for the PTCDA / Au interface is the largest,
since V increases with the principal quantum number.
From these results, it is found that the interaction for
the Au interface is very weak (physisorption), andthose for the Ag and Cu interfaces are strong(chemisorption). These results indicate that theobserved VL shift for the Au interface is due to therearrangement of the surface electron cloud at the Au
surface by the push-back effect, and those for the Ag
and Cu interfaces are due to the formation of theinterface states resulting in the charge redistribution
ate the interfaces.

Fig. 2. UPS spectra of 1 ML PTCDA / metalinterfaces.
[1] H. Vazquez et al., Europhys. Lett. 65 (2004) 802.
[2] S. Narioka et al., Appl. Phys. Lett. 67 (1995)
1899.
[3] H. Ishii et al., Adv. Mater. 11 (1999) 605.
[4] Y. Zou et al., Surf. Sci. 600 (2006) 1240.
[5] A. Ruban et al., J. Mol. Catal. A: Chem. 115(1997) 421.

Fig. 1. Plot of ' as a function of )M. Inset:
Molecular structure of PTCDA.

141

BL8B2

Valence Electronic Structure of Metal Phthalocyanine
Monolayers on Graphite

S. Kera1, T. Aoki1, S. Hosoumi1, N. Mitsuo1, K. Nebashi1, T. Kataoka1, R. Sumii2,
S. Nagamatsu1, N. Ueno1
1
Graduate School of Advanced Integration Science, Chiba University, Chiba 263-8522 Japan
2
Graduate School of Science, Nagoya University, Nagoya 464-8602 Japan
Angle-resolved
ultraviolet
photoelectron
spectroscopy (ARUPS) has been known as a powerful
technique to obtain crucial information on electronic
band structure for various kinds of materials.
Moreover, for organic thin films, information on themolecular orbital (MO) character, bonding nature, canbe also discussed in accordance with a quantitative
analysis of the ARUPS intensity using photoelectron
scattering theory when the geometrical structure of
the thin films are considered.
Phthalocyanines(Pcs) are a versatile class of
S-conjugated organic semiconductors applicable asdevice materials. Among these the transition metal
Pcs are interesting materials in controlling the device
performance via 3d-electron derived MOs. However,information on the electronic structure of theseorganometallic complexes is still limited. Here, weshow the electronic structure of the monolayer ofvarious transition metal (Mn-, Fe-, Co-, Ni-) Pcs ongraphite systematically.
The observed electron emission angle (T)dependences of 2p- and 3d-orbital derived MO bands
in ARUPS spectra for well-ordered Pc monolayers
were compared.

are well reproduced by the MST/MO calculation of afree molecule for MO (S: a1u), while for 3d-derived
bands (A), the observed Tpatterns are not fitted by
the calculation from MO (3d: a1g). Note that theTpattern of MO (3d: a1g) depends on the strength ofthe metal-ligand bonding, that is, on the hybridization
between 3d and 2p orbitals.
The results indicate that the 3d-derived band islocated at various energy positions due to change inthe 3d-electron occupation, while 2p-derived (S) band
appears at the similar energy. Further analysis on theintensity of feature A is necessary.

Experimental
ARUPS spectra were measured at photon incidence
angle D=45o, hQ=28 or 30 eV, and a sample
temperature T=295 K. T dependence of ARUPS
spectra was analyzed using the multiple-scattering
theory combined with molecular orbital (MST/MO)
calculation [1]. The purified Pc molecules were
carefully evaporated onto the graphite (HOPG: grade
ZYA). We have found that the molecules are oriented
nearly flat to the substrate surface [2].

Fig. 1. T dependences of ARUPS of1-ML-Pcs (MnPc,
FePc, CoPc and NiPc) on HOPG. MOs calculated for
CoPc are also shown.

Results and Discussion

Figure 1 shows T dependence of ARUPS ofannealed-Pc monolayers (MnPc, FePc, CoPc andNiPc) on HOPG. The intensity is normalized to theincidence photon flux. DFT-MO calculation suggeststhat (i) features A are ascribed to 3d-derived band of
Pcs and (ii) features B are assigned to 2p-derived
band (a single S MO). Note that the MO calculation
to discuss the electronic structure still may havedifficulties for organometallic complexes.
Figure 2 shows the comparison between observedand calculated T dependences of the band A and B
intensities for MnPc, CoPc and NiPc (FePc is still
under analysis). The Tpatterns are completely
different between 3d- (A) and 2p-derived (%) bands.
In the fitting for S bands (B), the observed Tpatterns

Fig. 2. Comparison between the observed andcalculated T patterns of the band A (left) and B(right).
[1] S. Nagamatsu et al, e-J. Surf. Sci. Nano 3 (2005)
461.
[2] T. Kataoka et al, Chem. Phys. Lett. 451 (2008)
43.

142

BL8B2

Angle-Resolved UPS of Thin Films of o-Quinonate Complex
on Graphite

N. Mitsuo1, T. Aoki1, Y. Suzuki1, S. Nagamatsu1, R. Sumii2, S. Noro3, T. Hosokai1,
K. K. Okudaira1, N. Ueno1, S. Kera1
1
Graduate School of Advanced Integration Science, Chiba University, Chiba 263-8522 Japan
2
Graduate School of Science, Nagoya University, Nagoya 464-8602 Japan
3
Research Institute for Electronic Science, Hokkaido University, Sapporo 060-0812, Japan
Bis-(o-diiminobenzosemiquinonate)
nickel(II)complex {Ni(DIBSQ)} is known to have a narrow
band-gap of 0.8 eV. Recently, high-performance
ambipolar operation in organic field effect transistorof Ni(DIBSQ) was reported [1].
We have investigated the electronic structure andmolecular orientation of Ni(DIBSQ) in a thin film byusing angle-resolved ultraviolet photoelectron
spectroscopy (ARUPS). ARUPS has been known as a
powerful technique to obtain crucial information onelectronic band structure for various kinds ofmaterials. Moreover, for organic thin films,
information on the geometrical structure of the thinfilms can be also discussed in accordance with aquantitative analysis of the ARUPS intensity using
photoelectron scattering theory.
In this report, we show the observed
electron-emission-angle (T) dependence of HOMO
bands in ARUPS spectra for the standing Ni(DIBSQ)
layer deposited on a graphite substrate.

performed the MST/MO calculation for a unit modelof 5 molecules to describe the intermolecular
scattering effects. We also found that the observed T
pattern depends on the photoelectron kinetic energy
and the sample quality (molecular packing and/or
crystallinity). These indicate that the impacts of theinterference of scattered photoelectron waves are
crucial. We are trying to compute the angulardependence by taking into account the intermolecularlayer effects.

Experimental
ARUPS spectra were measured at photon incidence
angle D=45o, hQ=40 eV, and T=295 K. The purified
molecules were carefully evaporated onto thegraphite (HOPG) substrate. T dependence wasanalyzed using the multiple-scattering theory
combined with molecular orbital (MST/MO)
calculation [2].

Results and Discussion

Figure 1(a) shows the T dependence of ARUPS of
Ni(DIBSQ) (3.5nm) on the HOPG. The intensity isnormalized to the incidence photon flux. A top featureappeared around 1.4 eV is ascribed to HOMO band ofNi(DIBSQ). One can see an energy shift of the
HOMO about 280 meV depending on the T (see theguide lines). We found that the molecules are oriented
nearly standing to the substrate surface from
NEXAFS results (as shown in the right panel in
Fig.1). Accordingly we expect that the DOS structurein the HOMO feature of UPS, which comes from the
HOMO band dispersion, could be observed even for
polycrystalline Ni(DIBSQ) films as in pentacene [3].
ARUPS study for the standing film on the single
crystal would be fascinating.
Figure 1(b) shows the comparison between
observed and calculated T dependences of the HOMO
intensity. The observed intensity gives the maximum
at around 0o. There are large differences between
observed and calculated MST/MO patterns. Here we

Fig. 1. a) Tdependence of ARUPS of Ni(DIBSQ) on
HOPG, b) Observed and calculated T patterns of the
HOMO. Chemical structure, schematic view of thefilm structure, and a unit model for the calculation are
also shown.
[1] S. Noro et al, J. Am. Chem. Soc. 127 (2005) 1001.
[2] S. Nagamatsu et al, e-J. Surf. Sci. Nanotech, 3(2005) 461.
[3] H. Fukagawa et al, Phys. Rev. B 73 (2006)
245310.

143

BL8B2

T. Miyazaki1, R. Sumii2,3, T. Kamei1, H. Tanaka1, S. Hino1
Graduate School of Science and Engineering, Ehime University, Matsuyama 790-8577,
Japan
2
Research Center for Materials Science, Nagoya University, Nagoya 464-8602, Japan
3
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, JapanE

Intensity

Hexagonal lithium nickel oxide (LiNiO2) is active
for the oxidation coupling of the methane (OCM)with a selective function of oxidation catalyst. We
have studied the crystal structure and the surface
oxygen species for understanding the selective
oxidation mechanism and synthesized hexagonal
Li-Ni
mixed
metal
oxides(LiNi1-xMxO2;
M=transition metal). The OCM activity of
LiNi1-xTixO2 (0.05x0.2), which was replaced Ti
with a part of Ni of LiNiO2, increased by the metal
substitution. In this study, the UPS spectra of
LiNi0.95Ti0.05O2 and LiNi0.995Ti0.005O2 were measured
with the dependence of the incident photon energy. In
addition, the change of the UPS spectra of LiNiO2
thin film was reported by the difference ofpre-treating of the sample.
LiNi0.95Ti0.05O2 and LiNi0.995Ti0.005O2 weresynthesized by solid state reaction. LiNiO2 thin film
was synthesized by Li ion diffusion on Ni plate. The
UPS spectra were measured at BL8B2 of UVSOR in
Institute for Molecular Science. The argon ion
sputtering and IR heating of samples were done inorder to imitate rough surface and remove thecontamination.
Figure 1 was shown the UPS spectra of LiNiO2
thin film at hȤ= 40eV. The valence band spectra
consist of five structures at Eb15eV below the Fermi
level. The top valence region was almost derived
from the Ni3d and O2p states. After the heat
treatment the intensity of Ni3d states decreased, but
the features of two O2p peaks were cleared. It wasanalogized that two kinds of oxygen species existed
and functioned for the selective oxidation. Figure 2
was shown the UPS spectra of LiNi0.95Ti0.05O2 and
LiNi0.995Ti0.005O2 of the incident photon energy at
20-60eV. The valence band spectra of LiNi0.95Ti0.05O2
and LiNi0.995Ti0.005O2 also consist of five structures inthis region. The UPS spectral features of
LiNi0.995Ti0.005O2 were analogous to those ofhexagonal LiNiO2. In the case of LiNiO2 and
LiNi0.995Ti0.005O2, the UPS spectra caused theintensity change which depended on the incident
photon energy, but only small spectral change of
LiNi0.95Ti0.05O2 was observed at 20-60eV. It was
speculated that the valence band feeling might bechanged by replacing Ti4+ in Ni3+.

D

C
B

A

a
b
c
d
15

10
5
Binding Energy / eV0Fig. 1. The UPS spectra of thin film LiNiO2 samples,a) Ar ion sputtering, b) Heating with O2 at 450Υ, c)
450Υ under 10̺6 Pa, d) 600Υ under 10̺6 Pa.
Intensity

1

Electronic Structure of LiNi1-xMxO2 Mixed Oxides (III)

LiNi0.995Ti0.005O2

LiNi0.95Ti0.05O2

60eV

55eV

55eV

50eV
45eV
40eV

60eV

50eV
45eV

35eV

40eV
35eV

30eV

30eV
25eV

25eV

21.22eV21.22eV

20eV

10

5

0

Binding energy/eV

-5

20eV
10

5

0

Binding energy/eV-5Fig. 2. The UPS spectra of LiNi0.995Ti0.005O2 and
LiNi0.95Ti0.05O2 with the dependence of the incident
photon energy at 20-60eV.

144

BL8B2

Electronic Structures of Rubrene and Its Photooxidation ProductY. Nakayama1, S. Machida2, T. Minari3, K. Tsukagoshi3, H. Ishii1,4
1Center for Frontier Science, Chiba University, Chiba 263-8522 Japan
2
Faculty of Engineering, Chiba University, Chiba 263-8522 Japan
3
Nanoscience Development and Support Team, RIKEN, Saitama 351-0198 Japan
4
Graduate School of Advanced Integration Science, Chiba University, Chiba 263-8522 Japan
Two factors should be taken into account on
considering the PES spectra of rubrene SC: the one issurface oxidation, and the other is sample charging.
Note that probing depth of PYS is much greater than
PES because PYS detects photoelectrons of
extremely slow (typically less than 1 eV). Removal of
the oxidation product by vacuum heating [4] and/or
vacuum cleavage of the crystal will possibly enable
us to observe the PES spectra of “pristine crystal”
covered with the oxide. Trials to avoid the sample
charging problem such as visible lightirradiation are
now underway.

Introduction

Photoemission intensity / arb. units

Rubrene (5,6,11,12-tetraphenyltetracene) is one of
the most promising candidates for a p-type organic
field effect transistor owing to a high hole mobility inits single-crystalline (SC) phase [1]. Since rubrene
easily reacts with oxygen to form its endo-peroxide(RubO2) under visible light illumination (Fig.2 inset),
it is believed that the surface of rubrene SC is covered
with “native” oxide layers and the oxidized productalso contributes to the conduction mechanism as adopant [1,2]. Toward understanding on the transport
nature and further improvement of the device
performance, information about the electronic
structure of not only the pristine rubrene but also its
photooxidation product is indispensable.
In the present study, we conducted photoelectron
spectroscopy (PES) and photoelectron yield
spectroscopy (PYS) measurements for a thin film of
rubrene before and after the photooxidation reaction.

Experiment
An amorphous film of rubrene was made on
indium-tin-oxide (ITO) by in-situ vacuum
sublimation. RubO2 was produced by exposing therubrene film to ambient air under illumination ofroom light for 3 days. PES measurements wereconducted at BL8B2. All the PES spectra presented
below were taken at normal emission angle (hQ = 40eV). The Fermi-level position was determined from agold foil. The work function of each sample wasestimated from the secondary electron cut-off taken at
the sample bias of –5 V. PYS measurements were
performed by a home-built system [3].

hQ = 40 eVoo
D = 45 , T = 0

(a)

(b)
12

10

8
6
4
2
Binding energy Eb / eV0Fig. 1. PES spectra of (a) the pristine rubrene filmand (b) the RubO2 film.

145

Photoemission intensity / a.u.

Figure 1 shows PES spectra of the pristine rubrene
film and the photooxidized film. The peakcorresponding to the highest occupied state of rubrene,
which is assigned to the tetracene backborn,disappears after photooxidation. It is in good
agreement with the previous report for a RubO2 film
oxidized in pure oxygen [4]. As shown in Fig. 2, theionization potential (Is) estimated from the PES
matches that from PYS results in cases of the pristine
film and RubO2. No clear sign of the oxidationinduced midgap state [2] was identified.
We also conducted PES measurement of a rubrene
SC. For SC, however, features at the binding energy(Eb) below 6 eV are absence, and apparent Is’s arecompletely different between PES and PYS results.

pristine rubrenerubrene peroxide
4567
Ionization potential Is / eV8

Differentiation photoelectron yield / a.u.

Results and discussion

PES (left axis)
PYS (right axis)

Fig. 2. Magnified PES spectra near the HOMO region(lines, left axis) and differentiation intensity of PYS
spectra (dots, right axis). [Inset] Molecular structures
before and after the photooxidation.
[1] V. Podzorov, et al., Appl. Phys. Lett. 85 (2004)
6039.
[2] O. Mitrofanov, et al., Phys. Rev. Lett. 97 (2006)
166601.
[3] H. Ishii, et al., Hyomen-kagaku 28 (2007) 264.
[4] Y. Harada, et al., Chem. Phys. Lett. 62 (1979)
283.

BL8B2

ARUPS of Diabenzo-Crown Ether Thin Film on HOPG

K. K.Okudaira1, T. Hosokai2, Y. Suzuki1, S. Kera1, N. Ueno1
Association of Graduate Schools of Science and Technology, Chiba Univererity,1-33
Yayoi-cho Inage-ku, Chiba 263-8522, Japan
2
Graduate School of Science and Technology, Chiba Univererity,1-33 Yayoi-cho Inage-ku,
Chiba 263-8522, Japan
1

Introduction
Crown ethers, which consist of flexible oligo-ethers,
have remarkable properties of recognizing andbinding specific metal atoms, and thus have potential
for use in molecular mechanics. [1] In particular,
dibenzo-18-crown-6(2,3,11,12–dibenzo-1,4,7,10,13,1
6- hexaoxacyclo- octadeca- 2,11-diene) (DB18C6),
forms a self-organized two-dimensional structure of aAu(111) substrate in HClO4 solution. [2] The
DB18C6 has a non-planar and flexible molecular
structure, shown in Fig.1.
In this study, we report the results of angle resolved
ultraviolet photoelectron spectra (ARUPS) of
DB18C6 thin films on HOPG to determine themolecular orientation of DB18C6 thin films
quantitatively.

Intensity (arb. units)

(B)

O
O

O

60°
48°
36°
24°
(C)

12°
0°

3
2
1
Binding Energy (eV)Fig. 2. Take-off angle dependence of ofDB18C6(three arrows indicate the peak position of A, B,
and C).

OO

T = 72°

4

Experimental

(A)

O

hQ

Fig. 1. Molecular structure of DB18C6.
ARUPS measurements were performed at thebeam line BL8B2 of the UVSOR storage ring at theInstitute for Molecular Science. The take-off angle(T) dependencies of photoelectron spectra were
measured at grazing incidence (incident angle ofphoton (D) = 70O with the photon energy of 20 eV.
The thin films were prepared in the preparationchamber by vacuum evaporation onto HOPG surfaces
which were cleaved under an ultrahigh vacuum. The
deposition rate was smaller than 0.1nm /min..

E
70° T

e-

Peak A
Peak B
Peak C

T=0°
30°

60°

Results and Discussion

The T dependencies of ARUPS spectra of about
2nm thick film at the binding energy region of 0-5 eV
are shown in Fig. 2, where three bands A, B, and C
appear. From the comparison of the results ofmolecular orbital calculation, band A and B are
ascribed to the S-orbitals of benzene rings, and bandC are n(O) localized at an ether ring.[3] The
intensity of the band A, B and C depends on T, while
the energy positions of these bands do not.
The band A, B, and C intensities show
characteristic T dependencies (Fig.3), which reflect
the molecular orientation of DB18C6 thin films on
HOPG. To determine the molecular orientation
quantitatively, it needs to compare the observed T
dependencies with the calculated ones.

Intensity (Normalized)

90°

Fig. 3. Take-off angle (q) dependencies ofphotoelectron intensities of peak A (‫)ە‬, B(‫)ە‬, andC(‫)ە‬.
[1] C. J. Pedersen, J. Am, Chem. Soc. 89 (1976)2495.
[2] A. Ohira, M. Sakata, C. Hirayama, M. Kuntake,Org. Biomol. Chem. 1 (2003) 251.
[3] T. Hosoaki, H. Horie, T. Aoki, S. Nagamatsu, S.
Kera, K. K. Okudaira, N. Ueno, J. Phys. Chem. C, tobe published.

146

BL8B2

R. Sumii1,2, K. Kanai2, K. Seki3
Institute of Materials Structure Science, High Energy Accelerator Research Organization,
Tsukuba, Ibaraki 305-0801, Japan
2
Research Center for Materials Science, Nagoya University, Nagoya 464-8602, Japan3
Department of Chemistry, Nagoya University, Nagoya 464-8602, Japan
set.

Introduction
Some halogen containing molecules, such asp-iodo- benzonitrile (p-IBN) (Fig. 1(a)), are known toshow strong intermolecular interaction. p-IBN
molecule has a simple structure with I and CN at the
opposite sides of a benzene ring. In the crystal, thep-IBN molecules form straight chains with CN-I
distance nearly 7% shorter than the sum of the vander Waals radii [1]. Thus we can expect thatinteresting phenomena such as intermolecular chargetransfer and anisotropic electrical conductivity may
occur in crystals with such CN-I interaction. However,there have been little studies of the electronic
structure and electrical properties. The main reason
may be sublimation by high vapor pressure in
vacuum condition required in such studies and thedissociation of the I-C bond at the contact with clean
metal surface.
To solve these problems, in this work we chose a
new compound 4-cyano-4’-iodobiphenyl (CIB) andstudied the electronic structure of the vacuum
deposited thin film by ultraviolet photoemission
spectroscopy (UPS). In CIB molecule, the benzene
ring of p-IBN is substituted with biphenyl (Fig. 1(b)).
Like p-IBN, the distance between the CN-I is about
5 % shorter than the sum of van der Waals radii andthe crystal structure contains straight chains [2].
Moreover, the molecular weight is heavier thanp-IBN, hindering the sublimation in vacuum. For
suppressing possible dissociation by the contact
with metal substrate, we used GeS (001) which is aninactive substrate.
IBN(a) p-IBN

I

C C
C
CC N
C C

I

C C
C C
C
C C
CC N
C C
C C

IBPN

(b) CIB

Results and Discussion
The observed spectra of CIB on GeS (001) and thesimulated spectra based on the MO calculations areshown in Fig. 2. In the experimental results, the
HOMO at around 3 eV shifts to low binding energy
as the film thickness increases,. This shift is well
reproduced by MO calculations for molecular chainswith increasing length from monomer to tetramer,
simulating the formation of crystal structure. For thedimmer, calculations were also performed for various
CN-I bond lengths.
HOMO

Exp.

multilayer

Intensity (a.u.)1

Electronic Structure of Molecular Crystal with CN-I Interaction

5

4

3

HOMO

5

2

1

monolayer

Calc.

4
3
2
Binding Energy / eV1tetramertrimer
Å
3.19A
4AÅ
dimer
Å
5A
monomerFig. 2. Experimentally observed UPS spectra and thesimulated spectra by the MO calculations for CIB.
Such good correspondence between the observed
spectra and the results of MO calculations indicatethat the HOMO shift is due to the intermolecularinteraction through the CN-I contact. As the detailed
mechanism, the HOMO with large component at theiodine is pushed up by the negative charge at the CN
part in the neighboring molecule (Fig. 3).

Fig. 1. Molecular structures of IBN and CIB.
Fig. 3. Unstabilization of the HOMO by the negative
charge at the CN group of the neighboring molecule .

Experimental and Theoretical
The CIB film was deposited on a clean GeS (001)surface obtained by cleaving in the vacuum chamber.
UPS measurements were performed at BL-8B2 of the
UVSOR facility. Molecular orbital (MO) calculations
were performed by density functional theory with
Gaussian98 package using a B3LYP / 3-21G** basis[1] E. O. Schlemper, Acta. Cryst. 18 (1965) 419.
[2] D.Britton, Acta. Cryst. C47 (1991) 2127.

147

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Photoelectron Spectroscopy Study of Photochromic Diarylethene Film

S. Tanaka1, M. Toba2, T. Nakashima2, T. Kawai2, K. Yoshino3
Center of Integrated Research in Science, Shimane University, Matsue 690-8504, Japan
2
Graduate School of Materials Science, Nara Institute of Science and Technology, NAIST,
Ikoma, Nara 630-0192, Japan
3
Shimane Institute for Industrial Technology, Matsue, Shimane 690-0816 Japan
1

Fig. 1. Molecular structures of open-ring isomer of
DAE (left) and closed-ring isomer of DAE (right).
The arrows indicate the reversible electrocyclic
reaction upon alternate irradiation with UV andvisible light.

as-deposited DAE film was considered amorphous.
Figure 2 shows the photoelectron spectra of DAE after
UV light irradiation (red) and under laser lightirradiation (black). The UV lamp was used to induce acoloration of the DAE film. The majority state of theDAE molecule after UV light irradiation was able toassume close-DAE. In the red-line spectrum, a peakthat appeared at around 1.5 eV was considered as thephotoelectron from HOMO of close-DAE. The
black-line in Fig. 2 is a photoelectron spectrum of the
DAE under laser light irradiation, where the majority
state was considered as open-DAE. It is obvious thatthe signal intensity around 1.5 eV was decreased
compared with the red-line. The spectrum shapearound 2 - 4 eV also showed a clear difference. The
signal intensity at around 3 eV in the black-line
spectrum was larger than that in the red-line spectrum.
The appearance and the disappearance of the HOMO
peak at 1.5 eV showed good relationship with UV andlaser light irradiation, respectively. These variationsin the spectra are attributed directly to thephotoresponsive change in the electronic structure ofDAE.

after UV irradiation
with Laser irradiation

Intensity / arb. unit

Photochromic molecules have attracted muchattention as a promising material for photonic devices.
Photochromism is defined as the reversible
transformation between two isomers having different
absorption spectra by photoirradiation.1) In addition,
the geometry and electronic structures in two isomersof the photochromic molecules are also different. The
differences in the geometry and the electronic
structure relate to the difference in the molecularproperties, such as refractive index, fluorescence
efficiency, conductivity and magnetism reference.
These photoresponsive variations of the molecularproperties can be useful for the application to various
optoelectronic devices. Among the various
photochromic
materials,
diarylethenes
withheterocyclic aryl groups are of particular interest for
applications to optoelectronic devices because of theirhigh fatigue resistance and good thermal stability [1].
1,2-Bis(5-(2,4-diphenylphenyl)-2,4-dimethyl-3-thienyl) perfluorocyclopentene (DAE) is a dithienylethene
derivative having bulky substituents [2]. DAE shows
blue coloration upon UV light irradiation, and theblue color disappears upon visible (Ȝ > 450 nm)
light irradiation. It is known that DAE undergoes ring
cyclization and cycloreversion reactions uponalternate irradiation with UV and visible light (Fig. 1).
Hereafter, open-DAE and close-DAE refer to the
open- and the closed-ring form isomers, respectively.

hQ = 40 eV

6

5

4

3

2

1

0

-1

Binding Energy / eV

In this study, the electronic structure of the DAE
thin film is revealed using photoelectron spectroscopy.
The photoelectron spectra of open- and close-DAE
showed clear differences in the density of statesaround the highest occupied molecular orbital(HOMO). The energy levels of each of the DAE
molecules were calculated by the density functional
theory (DFT) and it showed good correlation with thephotoelectron spectra [3].
The vacuum-deposited DAE film was investigatedby photoelectron spectroscopy. The structure of the148

Fig. 2. Photoelectron spectra of DAE.
[1] M. Irie, Chem. Rev. 100 (2000) 1685.
[2] M.-S. Kim, T. Sakata, T. Kawai, M. Irie, Jpn. J.
Appl Phys. 42 (2003) 3676.
[3] S. Tanaka, M. Toba, T. Nakashima, T. Kawai, K.
Yoshino, Jpn. J. Appl. Phys. 47 (2008) 1215.

BL8B2

Intermolecular Energy Band Dispersion in Highly Ordered Pentacene
Multilayer Films on Cu(110)
H. Yamane1, E. Kawabe1, R. Sumii2, K. Kanai2, Y. Ouchi1, K. Seki1
Department of Chemistry, Nagoya University, Nagoya 464-8602, Japan
2
Research Center for Materials Science, Nagoya University, Nagoya 464-8602, Japan
1

Introduction
The energy band dispersion, E(k), is a fundamental
basis for understanding charge transport mechanismsof solids. In the field of organic solids, there are two
types of band dispersion; the intra- and intermolecular band dispersions. In particular, the issue ofintermolecular band dispersion is attracting growing
attention due to the needs of the interpretation of thecharge transport mechanism in (opto)electronic
devices using organic semiconductors such as field
effect transistors. It is reported that molecules ofpentacene (Pn), a high hole mobility material,
deposited on Cu(110) in the multilayer regime (morethan 10 nm) form a highly ordered structure with an
upright-standing orientation, which is virtually
identical to the herringbone orientation for Pn films
on quartz or polyester substrates [1]. In this work, inorder to understand the hole transport mechanism in
Pn films, we studied the electronic structure of thehighly ordered upright-standing Pn multilayer film on
Cu(110) by using angle-resolved UV photoemission
spectroscopy (ARUPS).

Fig. 1. (a,b) Photoelectron takeoff angle (T)dependence of the ARUPS spectra for the highlyordered upright-standing Pn multilayer film on
Cu(110) measured at I = (a) 0° and (b) 90°. The
abscissa is the binding energy (Eb) relative to the
Fermi level (EF) of the substrate, and ordinate is theintensity of the photoelectron, normalized by theincident photon flux. (c,d) E(k__) relation for the highlyordered upright-standing Pn multilayer film on
Cu(110) at I = (c) 0° and (d) 90°. The abscissa is theparallel component of the momentum (k__), andordinate is the Eb relative to the EF of the substrate.

Experiment
The highly ordered Pn multilayer film was
prepared on the clean Cu(110) surfaces in accordancewith the sample preparation described in Ref 1.
The photoelectron takeoff angle (ș) dependence of
ARUPS spectra was measured at the photon energy
of 20 eV, the photon incidence angle of 60° from thesurface normal, and the temperature of 300 K.

From the observed E(k__) relation, one can see thatthe phase of the dispersion for band H1 is opposite tothat for band H2, and that the size of the dispersion ofbands H1 and H2 are about 150 and 240 meV,
respectively, for both azimuths within the present
total energy resolution of 100 meV at 300 K. Since
the uppermost band H1 seems to form a free-electronlike parabolic dispersion,_ we_ estimated the _effective_
mass mh* to be 3.02m0 (īXPn) and 1.86m0 (īYPn) at
300 K. This result demonstrates the presence of theanisotropy of the hole mobility in Pn crystals also at
higher temperatures as suggested by Wijs et al. [3].

Results and Discussion

Figures 1(a) and (b) shows the T dependence of the
ARUPS spectra for the 11-nm-thick Pn multilayer
film _with_ _(a)_ the upright-standing orientation alongthe ī X Pn direction (I = 0°), and (b) the ī Y Pn
direction (I = 90°). At T = 0°, the topmost peakconsists of two prominent components with an energy
separation of 0.5 eV (labelled H1 and H2 in Fig. 1,
respectively). This lineshape shows continuouschange with T. At I = 0°(90°), H1 shifts to the high Eb
side until T reaches 18°(12°), and turns to the low Eb
side until T reaches 34°(26°). Such a dispersive
behaviour can also be seen in H2. As shown in Fig. 1(c) and (d), the observed shifts can be explained as
the reflection of the two-dimensional intermolecularband dispersion using the unit cell of the uprightstanding Pn multilayer film on Cu(110) [2], which
was obtained from the previous structural studies [1].

[1] S. Söhnchen et al., J. Chem. Phys., 121 (2004) 525.
[2] H. Yamane et al., Phys. Stat. Sol. (b), 245 (2008)
793.
[3] G. A. de Wijs et al., Synth. Met., 139 (2003) 109.

149

BL8B2

Organic/Metal Interface State: Broadening and Splitting Behaviors of
Molecular Energy Levels
H. Yamane1, E. Kawabe1, R. Sumii2, K. Kanai2, Y. Ouchi1, K. Seki1
1
Department of Chemistry, Nagoya University, Nagoya 464-8602, Japan
2
Research Center for Materials Science, Nagoya University, Nagoya 464-8602, Japan
Introduction

Results and Discussion

The electronic structure at organic(O)/metal(M)interfaces plays a crucial role in the performance oforganic electronic devices. In particular, the energiesof the highest-occupied and lowest-unoccupied
molecular orbital (HOMO and LUMO) levels relative
to the Fermi level (EF) of metals are of fundamental
importance in discussing the barrier heights for the
charge injection and separation at O/M interfaces.
This is still an issue of open question since theinterfacial electronic structure is usually modified byvarious interface-specific phenomena. For deeper
understanding of the O/M interface energetics, one of
the keys is the elucidation and control of the interface
state near EF, which may dominate the energy levelalignment at the interface.
In this work, we studied the electronic structure ofvarious pentacene (Pn) monolayers grown on Au(111),
Cu(111), Cu(100), and Cu(110) surfaces using angleresolved UV photoemission spectroscopy (ARUPS).
We observed the evidences of the formation of theinterface state, which depends on the type of themetal and its surface structure.

Figure 1 shows the ARUPS spectra for the various
Pn/metal interfaces as functions of (a) the takeoffangle or (b) the azimuthal angle. For the disordered
Pn/Au(111) interface (a1), the Pn-induced peak
appears at Eb of 0.96 eV with the linewidth of 0.5 eV,
which is slightly broader than that for the Pn/graphite
interface of 0.3 eV (not shown), which can be
ascribed to the molecular level broadening due to
weak O-M interaction [Fig. 1(c1)]. On the other hand,
the Pn-induced electronic structure on Cu(111) (a2) israther different from that on Au(111): the Pn-induced
peaks on Cu(111) appear at Ebs of 0.72 and 1.34 eV.
These peaks can be ascribed to the molecular levels
split due to the hybridization of the molecular orbitals
with the substrate wavefunction [Fig. 1(c2)] [1,2],
which can modify the energies and orbital symmetries.
Such a behavior is observed also for the Pn/Cu(100)(b1) and the Pn/Cu(110) (b2) interfaces. Furthermore,at the single-domain Pn/Cu(110) interface, theresultant split levels show dispersive behavior [2].
This originates from (i) highly ordered film structureand (ii) the intermolecular interaction via the metal
substrate due to the hybridization at the interface.
These factors (c1) and (c2) may be dominated by
the different O-M bonding distance at the interface,
and we consider that the Pn-Cu bonding distance is
probably shorter than the Pn-Au bonding distance.

Experiment
All Pn monolayers were prepared on the clean
metal surfaces at the temperature of about 500 K,
which realizes the formation of flat-lying Pn monolayers. The ARUPS measurements were performed at
the surface temperature of 300 K at the photon energy
of 20 eV and the photon incidence angle of 60°.
(a2) Pn/Cu(111)
D = 60°, I = 0°
ǻ = -1.02 eV

Au(111)Cu(111)

Intensity / arb. units(a1) Pn/Au(111)
D = 60°, I = 0°
ǻ = -0.85 eV(b1) Pn/Cu(100)D = 60°, T = 58°
ǻ = -0.91 eV

T=

T=

0°
0°
10°
20°
30°
35°
38°
40°

0°
0°
10°
20°
30°
35°
38°
40°

50°

50°
gas

gas

2

1

0

58°

[1] A. Ferretti et al., Phys. Rev. Lett., 99 (2007) 46802.
[2] H. Yamane et al., Phys. Rev. B, 76 (2007) 165436.

I=

2

1

0

(c1)

I=

90°

90°

75°

75°

60°

60°

45°

45°

30°

30°

15°
gas

58°

(b2) Pn/Cu(110)
D = 60°, T = 58°
ǻ = -0.90 eV

15°

0°

1

0

LUMO

EF
HOMO

(c2)

Molecularenergy level spli

LUMO

EF
HOMO

gas

2

Energy level
broadening

0°

2

1

0

Binding Energy Eb (vs. EF) / eV

Fig. 1. ARUPS spectra as a function of (a) takeoff angle (T) and (b) azimuthal angle (I) measured for (a1) the
disordered Pn/Au(111) interface, (a2) the disordered Pn/Cu(111) interface, (b1) the multi-domain Pn/Cu(100)interface, and (b2) the single-domain Pn/Cu(110) interface. (c) Possible origins of the interface state: (c1) energy
level broadening due to the weak M-O interaction, (c2) energy level splitting due to the hybridization of themolecular orbital with the substrate wavefunction. The vacuum level shift upon adsorption (') is also shown.

150

BL8B2Modification of Shockley-Type Surface State and Formation of Charge
Transfer State at ZnPc/Cu(111) Interface
H. Yamane1, K. Kanai2, Y. Ouchi1, K. Seki1
Department of Chemistry, Nagoya University, Nagoya 464-8602, Japan
2
Research Center for Materials Science, Nagoya University, Nagoya 464-8602, Japan
1

Introduction
The electronic structure at interfaces formed by anorganic semiconductor film with a metal electrode isof fundamental importance in discussing the Schottky
barrier heights such as the highest-occupied andlowest-unoccupied molecular orbital (HOMO and
LUMO) levels at organic-devices interfaces. However,
the energetics of organic devices has not yet been
understood systematically. To clarify the possiblycomplicated electrical and structural phenomena atorganic/metal interfaces, a more pertinent approach tothis issue would be to use a well-characterized system
in quantitative electron spectroscopic measurements.
In this work, we studied the electronic structure ofthin films of zinc-phthalocyanine (ZnPc), one of thearchetypal organic semiconductor, grown on Cu(111)
using angle-resolved UV photoemission spectroscopy(ARUPS). We observed the distinctive electronic
structure induced by the charge transfer (CT).

Experiment
The ARUPS measurements were performed at thesurface temperature of 300 K at the photon energy of
20 eV and the photon incidence angle of 60°.
We obtained a saturated ZnPc monolayer byheating the 5-nm ZnPc film at 700 K; the ARUPS
spectra for the heated film shows nearly the samecharacteristic to that for the 0.3-nm film.

For the 1-ML ZnPc spectra at the surface offnormal (ș  38°), one can see two-prominent peaks
labelled B and C in Fig. 1. With increasing the film
thickness, peak B shifts gradually to higher binding
energy side probably due to the change in (i) the final
state screening and (ii) the molecular orientation [3],and the intensity of peak C decreases rapidly. Judging
from the thickness dependence of the ARUPS spectra,
peak B is ascribed to the (original) HOMO-derived
level, and peak C may be ascribed to the CT state.
The formation of the CT state at the ZnPc/Cu(111)interface is unexpected just by considering theionization energy and the electron affinity of the
ZnPc solid and the work function of the Cu(111)substrate of Is = 5.2 eV, As = 3.3 eV, and ĭm = 4.9 eV,
respectively, which were obtained from our UPS andinverse photoemission spectroscopy experiments (seeFig. 1). For the origin of the CT state, one has toconsider (i) the molecular energy level broadening
due to organic-metal interaction and (ii) the change in
the intermolecular polarization energy due to thepresence of the CT-induced dipole. Since the bonding
distance at the interface would be a key for further
consideration on the interfacial electronic structure of
ZnPc/Cu(111), we will perform the X-ray standing
wave experiment for the ZnPc/Cu(111) system at
ESRF (Grenoble, FRA).

Results and Discussion
Figure 1 shows the film thickness dependence of
the ARUPS spectra for the ZnPc/Cu(111) system. In
the energy window A, just below the Fermi level (EF)at around the surface normal (ș = 0°), the Shockleytype surface state of Cu(111) survived even upon
formation of the ZnPc monolayer. From the takeoffangle dependence of the ARUPS spectra, we foundthat the characteristics of the surviving surface state
are modified from_ that of the original one in the peak
position at the ī point (0.39 ĺ 0.18 eV), Fermi
wavelength kF (2.07 ĺ 2.23 nm–1), and the effective
mass m* (0.42m0 ĺ 1.08m0). The adsobate-induced
modification of the surface state has been reported forthe adsorption of rare gases [1] and a large energygap (~ 9 eV) molecule of n-alkane (n-C44H90) [2]. The
observed modification of the surface state upon the
ZnPc adsorption, which is slightly different from theprevious observations [1,2], may be dominated by the
combination of (1) the push back (Pauli repulsion) of
the surface electrons and (2) the CT between themolecule and the substrate.

Fig. 1. Film thickness dependence of the ARUPS
spectra for the ZnPc/Cu(111) system (left) and theenergy level diagrams of the Cu(111) substrate, theZnPc solid, and the ZnPc/Cu(111) system (right).
[1] F. Reinnert, J. Phys.: Cond. Matter, 15 (2003) S693.
[2] K. Kanai et al., Phys. Rev. B, submitted.
[3] H. Yamane et al., J. Appl. Phys., 99 (2006) 93705.

151

FEL

Asymmetric Synthesis and Decomposition of Amino Acids by UsingUVSOR-FEL

K. Kobayashi1, T. Ogawa1, S. Shima1, T. Kaneko1, H. Mita2, J. Takahashi3,
M. Hosaka4, M. Kato5
1
Graduate School of Engineering, Yokohama National University, Yokohama 240-8501, Japan
2
Faculty of Engineering, Fukuoka Institute of Technology, Fukuoka 811-0295, Japan
2
NTT Microsystem Integration Laboratory, Atsugi243-0198, Japan
3
Graduate School of Engineering, Nagoya University, Nagoya 464-8601, Japan
4
Masahiro Kato, Institute for Molecular Science, Okazake 444-8585, Japan
Introduction
The Origin of homochirality of biological molecules
such as amino acids has remained one of the mostimportant problems in the field of origins of life andastrobiology. Cronin and Pizzarello reported thatsome amino acids extracted from carbonaceouschondrites showed significant enantiomeric excessesof L-isomers [1]. Isovaline, a non-proteinous aminoacid without a-hydrogen atom, was included in such
category of amino acids (Fig. 1).
One of thepossible scenario for the generation of enantiomeric
excesses of amino acids are asymmetric formation or
decomposition of amino acids by circular polarized
light in space. Bailey found circular polarized lightof IR range in space [2]. Takano et al. reported thatenantiomeric excess of alanine was formed after
irradiation of amino acid precursors with UV-CPL [3].
Here we examine decomposition of isovaline byirradiation with UV-CPL from UVSOR-free electron
laser (FEL). We alsostudiedpossible
introduction of chirality
to amino acids in thin
films
by
UV-CPL
irradiation.
Fig. 1. Isovaline

Experimental
Aqueous solution of isovaline in a quartz cell was
irradiated with UV-CPL (Fig. 2): After either R- or
L-UV-CPL (wavelength:216-230 nm) was
irradiated, amino acids and amines in resulting
products were analyzed by cation-exchange HPLC
(Shimadzu LC-10A), and carboxylic acids were
determined by capillary electrophoresis (Photal
CAPI-3300).
D/L ratio of amino acids wasmeasured by reversed-phase HPLC after AQC
derivatization (Tosoh DP-8020).
Isovaline aqueous solution was also irradiated withhigh-energy heavy ions (290 MeV/u carbon ions from
HIMAC, NIRS, Japan) or X-rays (6 keV, 27B line of
Photon Factory, KEK, Japan).
Thin film of phenylalanine was made by vacuum
deposition on an MgF2 substrate. The film wasirradiated with D- or L-CPL. CD spectra were
measured after irradiation.

㱗=230, 217, 216 nm

Fig. 2. UV-CPL irradiation of isovaline solution
A gaseous mixture of carbon monoxide, ammonia
and water was also irradiated with UV-CPL toexamine possible formation of amino acid precursors.
The resulting product was acid-hydrolyzed, andamino acids were determined by HPLC (Shimadzu
LC-10A).

Results and Discussion
When isovaline solution was irradiated with UV-CPL,
isovaline was decomposed: Alanine was found as
predominant amino acid products, and 2-butylamine
and isovaleric acid were also detected. The release of
methyl group, carboxylic group, or amino group fromisovaline was specific to UV irradiation, since X-raysor heavy ions irradiation of isovaline solution did notgive them as major products. Enantiomeric excessesof isovaline or alanine were not detected in the present
experiments. As pH of the solution might beimportant for asymmetric decomposition, we plan toirradiate isovaline solution in acidic/basic conditions.
When phenylalanine thin films were irradiated L- or
R-CPL, the resulting films showed apparent CD
spectra at 200 nm and 220 nm. They seem tocorrespond to S-S* and n-S* transitions, individually.
It was proved that CPL irradiation introduced chirality
to thin film of aromatic amino acids.
Amino acids were formed by UV-CPL irradiation of
the gas mixture: Glycine was predominant, followedby alanine. G-value of glycine was 0.0012, which
was smaller than that by proton irradiation or that with
UV light from D2 lamp.
[1] J. R. Cronin, S. Pizzarello, Science 275 (1997)
951.
[2] J. A. Bailey et al., Science 281 (1998) 672.
[3] Y. Takano et al., Earth Planet. Sci. Lett. 254(2007) 106.

152