Sei Tsunoda

Preparation and Characterization of 3,4,9,10-Perylenetetracarboxylic dianhydride (PTCDA) Films Deposited by Organic Molecular Beam Deposition Method.

The optical and structural properties for 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) films deposited on Au-coated substrates at the various growth temperatures by the organic molecular beam deposition (OMBD) method have been studied. The planar PTCDA molecules were oriented almost parallel to the substrate surface in the films deposited at the growth temperature of -160° C. Orientational disorder of the molecular planes occurred especially in the films grown at higher substrate temperatures. These films had basically large anisotropy of refractive indices which were evaluated by the prism attenuated total-reflection (ATR) method. The anisotropy of indices decreased for the film grown at the substrate temperature of 100° C. The optical anisotropy has been understood in terms of the molecular orientation.

Device characteristics and its operation mechanism of a FET-type waveguide modulator using α-sexithienyl

An optical waveguide modulator having a field-effect transistor-type electrode using a thiophene oligomer, α-sexithienyl (6T), has been fabricated and has functioned as an electro-absorption modulator with the modulation ratio of 20%. The optical modulation is directly related with the FET device operation, and has shown a maximum at 830 nm for propagating light wavelength. Therefore, the mechanism of the optical modulation has been clarified to be the increasing absorption due to polarons induced by negative bias. The linear relationship between the modulation ratios and the FET source currents has led to the conclusion that the polaron conversion efficiency η was introduced as the new parameter to understand the device operation, which has become clear. From the analysis, the nearly intrinsic value of carrier mobility of 6T was extrapolated, and the limit of the improving the carrier mobility was also shown. The possibility of enlarging the modulation ratio and its frequency dependence is also discussed.

Large electro-optical modulation of a field-effect transistor-type waveguide modulator using α-sexithienyl

An optical waveguide modulator having a field-effect transistor-type electrode using a thiophene oligomer, α-sexithienyl, has been fabricated and has functioned as an electro-absorption modulator with the modulation ratio of 20%. The device also functions as a field-effect transistor (FET). The optical modulation is directly related with the FET device operation, and has shown a maximum at 830 nm for propagating light wavelength. Therefore, the mechanism of the optical modulation has been clarified to be the increasing absorption due to polarons induced or injected by negative bias.

Organic molecular beam deposition combined with laser-induced chemical reactions

In order to fabricate functional organic thin films, we investigated organic molecular beam deposition combined with laser-induced chemical reactions. Bis(ethynylstyryl) benzene (BESB) films of trans,trans-isomer were deposited by this new method. The cis,cis-BESB was sublimed and cis-to-trans photoisomerization was induced upon KrF excimer laser irradiation ((lambda) equals 248 nm). The growth of the well- oriented crystalline films was achieved upon the laser irradiation during the deposition at the substrate temperature of 60 degree(s)C. At this substrate temperature only trans,trans-BESB was deposited on the substrate surface, which indicated that unreacted cis,cis-isomer was re- evaporated from the substrates. It can be explained that the crystal growth favorably proceeded due to the enhancement of the surface migration of the trans,trans-isomer and no hindrance of the cis,cis-isomer. We also fabricated thin films of a reaction product by inducing an intermolecular reaction of BESB with biphenyl-dithiol upon the laser irradiation during the deposition. It is thus found that the new process made it possible to produce the functional organic thin films, which were difficult to be evaporated by the conventional vacuum process. We discussed the chemical reactions and the deposition behavior in our process.

BIS(ETHYNYLSTYRYL)BENZENE FILMS GROWN BY MOLECULAR BEAM DEPOSITION IN A PHOTON FIELD

Abstract In order to control both molecular and film structures simultaneously during film growth, we investigated organic molecular beam deposition in a photon field using KrF excimer laser ( λ = 248 nm). The preparation of bis(ethynylstyryl)benzene (BESB) films was carried out by this new method. The BESB films of trans-trans isomer were prepared by the sublimation of the cis-cis isomer and the following cis-to-trans photo-isomerization upon the laser irradiation. The laser-irradiation after or during deposition at the substrate temperature of 25°C yielded amorphous films. In contrast, the growth of the well-oriented crystalline films of the trans-trans isomer was achieved upon the laser-irradiation during deposition at the substrate temperature of 60°C. It can be explained that this crystal growth proceeded by the deposition of only the movable trans-trans isomer on the substrate surface. Thus it was found that organic molecular beam deposition combined with a photo-chemical reaction is effective for the control of molecular and film structures.