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Koichiro Saiki / Professor / Division of Transdisciplinary Sciences
Department of Complexity Science and Engineering / / Molecular electronics and surface nanoscience
http://yukimuki.k.u-tokyo.ac.jp/jpf/saiki-cJ.html

Career Summary
1976: Graduated, Bachelor of Engineering (University of Tokyo)
1981: Doctor of Engineering (University of Tokyo)
1981-89: Research Associate (University of Tokyo)
1989-91: Lecturer (University of Tokyo)
1991-99: Associate Professor (University of Tokyo)
1993-94: Visiting scientist (Forschungszentrum, Karlsruhe, Germany)
1999-present: Professor (University of Tokyo)

Educational Activities
Graduate school:Atomistic processes of thin film growth
Research Activities
- Exploration of novel properties at exotic heterointerfaces -
All changes occurring in nature may fairly be said to start at the interface; the surface is also the interface between materials and a vacuum. Many semiconductor devices, a basis for the current IT era, use physical and chemical phenomena at the interface. For the last decade, applying organic substances to electronic and optical devices as an active component has been examined and organic electroluminescence displays have begun to flourish as real devices. The urgent problem is the development of organic transistors, by which flexible and green devices could be achieved. However, many other problems should be solved; one of which is related to control of the interface between organic semiconductors and inorganic metal electrodes or gate insulators. Our research focuses on controlling the arrangement of organic molecules and clarifying atomic and electronic properties at the interface. The current topics are as follows.

A. Fundamental research of organic field effect transistors (OFET)
(1) Organic film - substrate interface: Pentacene is the most promising organic semiconductor because of its rather high carrier mobility in the thin film phase. The stability of pentacene thin film is important for application to real devices. We have found instability inherent to the second pentacene layer for the first time by using a self-made special facility. The instability can be improved by modifying the substrate surface. (Ref.1)
(2) Organic film - electrode interface: Carriers are injected from the metal electrode to organic semiconductors during OFET operation. The arrangement of electronic levels between semiconductors and metals strongly affects the efficiency of carrier injection. We studied the relationship between electrical conduction and energy levels of organic semiconductors by using specially designed apparatus. The formation of interface dipole regulates the electronic arrangement, which could explain the ambipolar nature of OFET. (Ref.2)

B. Exotic electronic properties of graphene edges
Edges of graphene (one atomic sheet of graphite) are predicted theoretically to show intriguing properties such as high density of states at the Fermi level and magnetic ordering. Recently, our group succeeded in controlling the size of graphene domains, which are formed on Pt (111) substrate by annealing after exposure to a benzene atmosphere. Precise STM measurements showed a predominance of zigzag edges at the nanographenes on Pt (111). Voltage dependent STM images clearly revealed the existence of spatially and energetically localized electronic states at the zigzag edge. The magnetic ordering expected for the edge states is now under investigation.

Literature
1) G. Yoshikawa, J. T. Sadowski, A. Al-Mahboob, Y.Fujikawa, T. Sakurai, Y. Tsuruma, S. Ikeda, and K. Saiki: Spontaneous aggregation of pentacene molecules and its influence on field effect mobility: Appl. Phys. Lett. 90, 251906 (2007)
2) T. Kaji, S. Entani, S. Ikeda, and K. Saiki: Origin of carrier types in intrinsic organic semiconductors, Adv. Mater. 20 , 2084 (2008)
3) S. Entani, S. Ikeda, M. Kiguchi, K. Saiki, G. Yoshikawa, I. Nakai, H. Kondoh, and T. Ohta: Growth of nanographite on Pt (111) and its edge state, Appl. Phys. Lett. 88, 153126 (2006)

Other Activities
Physical Society of Japan (JPS)
Japan Society of Applied Physics (JSAP)
Chemical Society of Japan (CSJ)
Materials Research Society (MRS)
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Future Plan
Please visit our web site
Messages to Students
Molecular electronics and surface nanoscience is a highly multidisciplinary field, emerging from fields such as physics, chemistry, electronic engineering, and materials science. It is quite compatible with the concept of our graduate school. Young people who are interested in this field are welcome to join our group, where their talent is expected to flourish.
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