RESEARCH ACTIVITIESElectronic Property of Functional Organic
Materials
Department of Photo-Molecular Science
Division of Photo-Molecular Science III

MemberAssistant Professor
FUKUTANI, Keisuke

Education
1996 B.E. Chiba University
1998 M.E. Chiba University
2001 Ph.D. Chiba University
Professional Employment
1998 JSPS Research Fellow
2001 Research Associate, Chiba University
2003 Research Associate, Institute for Molecular Science
2003 Postdoctoral Fellow, Wuerzburg University
2004 Assistant Professor, Chiba University
2007 Associate Professor, Chiba University
2009 Visiting Associate Professor, Institute for Molecular Science2013 Adjunct Lecturer, The Open University of Japan
2013 Visiting Associate Professor, Soochow University
2014 Professor, Institute for Molecular ScienceProfessor, The Graduate University for Advanced Studies
Visiting Professor, Chiba University
2019 Visiting Professor, Kyoto University, Hiroshima University
2020 Visiting Professor, Tohoku University

KERA, Satoshi
Professor[kera@ims.ac.jp]

Keywords

Graduate Student
NISHINO, Fumi
PALASSERY ITHIKKAL, Jaseela
YAMAUCHI, Saki*SEMA, Ryota*
Secretary
KAMIYA, Miho

Photoelectron Spectroscopy, Molecular Assemble, Electronic State

Functional organic materials (FOM) have recently attracted
considerable attention both for fundamental research anddevice applications because of peculiar properties not found ininorganics and small molecules. However, the mechanisms
and the origin of various device characteristics are still underdebate. Scientific discussions have been redundant because oflong-standing beliefs that the electronic structure of FOM
would be conserved as in an isolated molecule even for solid
phases due to the weak van der Waals interaction. To reveal
characteristics of FOM, it is essential to investigate precisely
the electronic structure at various interfaces, including organic–organic and organic–inorganic (metal/semiconductor) contacts.
Recently we realized that the weak electronic interaction
manifests itself as small intensity modulations of fine struc­tures in photoelectron spectra, depending on the adsorption
and aggregation conditions on the surface. Thanks to recent
instrumentation improvements, we can assess hidden finefeatures in the electronic states, e.g. electron–phonon cou­pling, quasi-particle states, very small densities of gap states,
narrow band dispersion, and dynamic electronic polarization.
To elucidate what really impacts on the electronic states of theFOM in their assembly as well as at the interface upon weakinteraction, an evaluation of the wave-function spread of theelectronic states is very important because the interface states
are described as a delocalized molecular orbital state depend­ing on the strength of weak electronic coupling (hybridiza­tion). Observing modifications of electron wave functions
upon weak electronic coupling as well as strong electron–
phonon coupling is a central issue on our agenda.

Figure 1. Overview of our agenda. A rich assortment of surface andinterface structures of FOM to provide complicated spectral featuresof ultraviolet photoelectron spectroscopy.

Selected Publications• Y. Nakayama, S. Kera and N. Ueno, J. Mater. Chem. C 8, 9090–9132 (2020). [review]• S. Kera, T. Hosokai and S. Duhm, J. Phys. Soc. Jpn. 87, 061008 (7pages) (2018). [review]26• J.-P. Yang, F. Bussolotti, S. Kera and N. Ueno, J. Phys. D: Appl.
Phys. 50, 423002 (45 pages) (2017). [review]• S. Kera and N. Ueno, J. Electron Spectrosc. Relat. Phenom. 204,2–11 (2015). [review]

Annual Review 2023

1. Surface Characterization of Covalent
Organic Frameworks1)
Covalent organic frameworks (COFs), as a large class of
porous organic materials, have attracted intense research in thepast few decades due to the great potential for applications.
Substituting carbon with silicon in organic molecules andmaterials has been an attractive way to modify their electronic
structure and properties. Silicon-doped graphene-based mate­rials are known to exhibit exotic properties, yet conjugatedorganic materials with atomically precise Si substitution haveremained difficult to prepare. We present the on-surface syn­thesis of one- and two-dimensional covalent organic frame­works whose backbones contain 1,4-disilabenzene (C4Si2)
linkers. Silicon atoms were first deposited on a Au(111)
surface, forming a AuSix film on annealing. The subsequentdeposition and annealing of a bromo-substituted polyaromatichydrocarbon precursor on this surface led to the formation of
the C4Si2-bridged networks, which were characterized by a
combination of high-resolution scanning tunnelling micros­
copy and X-ray photoelectron spectroscopy taken at BL2B ofUVSOR supported by density functional theory (DFT) calcu­
lations. Each Si in a hexagonal C4Si2 ring was found to becovalently linked to one terminal Br atom. For the linear
structure obtained with the pyrene-based precursor, the C4Si2
rings were converted into C4Si pentagonal siloles by further
annealing.

important issue in the field of organic electronics to under­
stand the efficiency of charge injection and fundamental
conduction mechanisms. The spectroscopic data of organic
cations seem slightly insufficient, comparing to that of organic
anions using strong molecular acceptor and alkali metal
doping. Halogens are fundamental elements and have been
widely used as hole dopants for organic electronics since thevery early stages of research. Perylene doped with bromine
exhibit a dramatic increase in conductivity. In this study, weobserved the geometric and electronic structures of a mono­
layer of perylene molecules on the surfaces of Au(110) andAu(111). The effect of bromine doping was studied using C-K
NEXAFS, angle-resolved photoemission spectroscopy (ARPES),and X-ray photoelectron spectroscopy (XPS). C-K NEXAFS
can be used to observe vacant states, particularly a hole state,
which is essential for p-type organic semiconductors. More­over, the inclined molecular orientation is analyzed by mea­suring the polarization dependence. ARPES and 2D momen­
tum map using a photoelectron momentum microscope atBL6U of UVSOR is a powerful technique for discussing thechanges in the molecular orbital character upon the doping.

Figure 3. (a) HOMO distribution of a perylene molecule. (b) Simu­
lated photoemission momentum maps of HOMO. (c) Experimentalmomentum map at binding energy of 1.5 eV. The figure is after ref 2).

3. Other Activities in UVSOR
We have conducted beamline R&D and user supports incollaboration with other universities. Experiments using photo­
electron momentum microscope are developing at BL6U.2,3)
The perspectives required for future light-source facility havebeen discussed with communities.4)

References
Figure 2. Top: Scheme of on-surface reaction for the aryl–Si coupling
reaction on Au(111). Bottom: High-resolution constant height dI/dV
map of the COF taken with a CO tip and the top and side views ofDFT simulation. The figure is after ref 1).

2. Photoemission Tomography of Br-DopedPerylene Monolayer2)

1) K. Sun, O. J. Silveira, Y. Ma, Y. Hasegawa, M. Matsumoto, S. Kera,O. Krejčí, A. S. Foster and S. Kawai, Nat. Chem. 15, 136–143(2023).
2) O. Endo, F. Matsui, S. Kera, W.-J. Chun, M. Nakamura, K. Amemiya
and H. Ozaki, J. Phys. Chem. C 126, 15971–15979 (2022).
3) Y. Hasegawa, F. Matsui and S. Kera, e-J. Surf. Sci. Nanotechnol.
20, 174–179 (2022).
4) H. Ota et al., J. Phys: Conf. Ser. 2380, 012003 (5 pages) (2022).

Energy level alignment at the organic–metal interface is an* carrying out graduate research on Cooperative Education Program of IMS with Nagoya University27