物理系colloquium：Observation of Carrier Motion and Induced polarization in Organic Thin Films by Optical Second Harmonic Generation

报告题目： Observation of Carrier Motion and Induced polarization in Organic Thin Films by Optical Second Harmonic Generation 报告人： Mitsumasa Iwamoto Department of Physics Electronics, Tokyo Institute of Technology 报告时间： 2013-8-29 16:00 报告地点：理科楼郑裕彤大讲堂摘要： Optical second harmonic generation (SHG) measurement has been widely used to characterize the structure of organic thin films, including Langmuir films on the water surface, where non-linear optical susceptibilities of organic films which originates from arrangement of molecules and non-linear molecular susceptibility are well probed [1]. However once we focus on the electric fields coming out from electrons and dipoles, which are governed by the Gauss law, we can extend the SHG measurement to probe carrier motion and induced polarization in organic thin films, including in domains of monolayer [2,3]. Here by using a novel optical second harmonic generation technique, we visualize carrier motions in organic devices [4,5], i.e., organic field transistors, organic electroluminescence, etc., as well as polarized domain structure in Langmuir films [6].
Probing and modeling of carrier motions in organic materials is a fundamental research subject in science and electronics. According to the Maxwell’s electromagnetic field theory, injected carriers polarize organic materials. Thus by probing nonlinear dielectric polarization induced in active layer of organic devices by moving electrons, we can visualize and model carrier motion in organic devices. The method used here is a novel optical method based on electric field induced optical second harmonic generation (EFISHG) measurement [2-4]. In this presentation, basic concept for probing dynamical carrier motions by using EFISHG is discussed. Then using ambipolar organic field transistors, we show how carrier motion is visualized by the EFISHG measurement, and also show how carrier path is modeled based on the visualized carrier motion.
Also we here introduce the advanced conventional optical secodharmonic generation measurement cupled with the Brewster Angle Microscope(BAM), which is capable of visualizing polarization structure of Langmuir-monolayers [6]. We then demonstrate that the domian shapes of mixed lipid layers which are visualized by SHG and BAM are the same, but we can see textures originated from induced dipoles, differennt from domain patters.
References
1 Y. R. Shen, The Principles of Nonlinear Optics. , New York, Wiley 2002.
2 M. Iwamoto, T. Manaka, T. Yamamoto, and E. Lim, Thin Solid Films 517, 1312 ( 2008).
3 M. Iwamoto, T. Manaka, M. Weis, and D. Taguchi, J. Vac. Sci. Technol. B 28 C5F12 (2010).
4 T. Manaka, E. Lim, R. Tamura and M. Iwamoto, Nature Photon. 1, 581 (2007).
5 Y.Mashiko, D.Taguchi, M.Weis, T.Manaka and M.Iwamoto, Appl. Phys. Lett. 101, 243302 (2012)
6 Y.Matsuoka, D.Taguchi, T.Manaka and M.Iwamoto, Thin Solid Films, in press.