Kyoji Tsutsui

High Carrier Mobility of 3.8 cm2 V-1 s-1 in Polydiacetylene Thin Films Polymerized by Electron Beam Irradiation

The highest carrier mobility of polydiacetylene (PDA) thin films in field-effect transistors has been limited to less than 0.8 cm2 V-1 s-1, although the main chain conduction should show higher carrier mobility potentially. We revealed that the cause of the low carrier mobility is due to the presence of local upheaval regions generated by the volume change through the polymerization process of diacetylene monomers. In order to suppress the occurrence of the upheaval regions, we found that electron beam (EB) irradiation is effective, resulted in the highest carrier mobility of µmax = 3.8 cm2 V-1 s-1.

Fabrication of One-Dimensionally Oriented Fluorene–Thiophene Copolymer Thin Films and Anisotropic Transistor Characteristics

One-dimensionally oriented poly(9,9-dioctylfluorene-co-bithiophene) (F8T2) thin films with the thickness of approximately 50 nm were deposited by friction-transfer technique. Films were investigated using polarized optical spectroscopy. The dichroic ratio of absorption was estimated to be approximately eight. By means of transmission electron microscope (TEM), we revealed that the main-chains of F8T2 were aligned along the friction direction. Atomic force microscope (AFM) images of as-prepared films showed a roughened surface, whereas the film after subsequent thermal treatment showed remarkably smooth surface. Field-effect transistors utilizing the friction-transferred F8T2 films exhibited a field-effect mobility of 1.88×10-4 cm2 V-1 s-1 along the friction direction, which is about six times higher than that perpendicular to the friction direction.

A Small-Angle X-ray Study on Polymer Films Containing Crystalline Particles of Fatty Acid

Small-angle and wide angle X-ray scattering studies were carried out on polymer thin films containing microcrystalline behenic acid. Measurements were made on samples in various optical states prepared by appropriate heat treatment. The results were consistent with the picture which presupposes the existence of voids around the crystallites when the composite film is in the opaque state. It was found that, upon cooling, molten behenic acid crystallizes in B or E polymorph, but not in C polymorph. It was concluded that the crystallization temperature for the C form is very low for small particles (0.2–2 µm) so that the molten BA, upon cooling, becomes unstable due to the formation of the crystalline state of the B form at a temperature above the crystallization temperature of the C-form.