Preparation of polythiophene thin films by UV laser-assisted deposition of 2,5-dichlorothiophene with a 248 nm excimer laser beam

Polythiophene thin films are prepared by UV laser-assisted deposition (UV-LAD) of 2,5-dichlorothiophene (2,5-DCT) with a 248 nm (KrF) beam at several fluence values. Surface morphologies of the films depended strongly on laser fluence and deposition rate of the reactant. In the optimized conditions, mesh-like structures consisting of numerous fibers were observed. Electric conductivity of the film prepared by UV-LAD at 10 mJ cm(-2) pulse(-1) increased from less than 10(-7) S cm(-1) up to 10(-3) S cm(-1) on iodine doping. FT-IR, X-ray photoelectron spectroscopy (XPS) and ultra violet-visible (UV-vis) spectroscopy measurements show that, although sulfur atoms are eliminated to some extent, polymerization occurs basically at 2 and 5 positions of 2,5-DCT by effective elimination of halogen atoms to form polythiophene with various pi-conjugation lengths. The film contained both soluble and insoluble components in tetrahydrofuran (THF) and acetonitrile (AN) solvents. Components with pi-conjugation length corresponding to those of an oligothiophene with 3 +/- 1 thiophene units are dominant for soluble components. Optical band gap is estimated to be 2.93 eV for insoluble components in the film. (C) 1998 Elsevier Science S.A. All rights reserved.