Kelvin probe force microscopic study of anodically and cathodically doped poly-3-methylthiophene

The doping-level distribution and surface morphology of thin films of p- an d n-doped poly-3-methylthiophene (P3MT) deposited onto highly oriented pyro lytic graphite (HOPG) were characterized on a microscopic scale by using Ke lvin probe force microscopy (KFM) and in situ atomic force microscopy (ECAF M) techniques. Two different types of surface structures were found on diff erent sites of the polymer surface, one of them representing relatively amo rphous polymer globules, and the other highly crystalline polymer grains. F or the two structures, in both the p- and n-doping processes, the doping-le vel distribution was again found to be directly related to the polymer surf ace morphology, as was the case for p-doped polybithiophene (PBT) [O.A. Sem enikhin, L. Jiang, T. Iyoda, K. Hashimoto, A. Fujishima, J. Phys. Chem. 100 (1996) 18603; O.A. Semenikhin, L. Jiang, T. Iyoda, K. Hashimoto, A. Fujish ima, Electrochim. Acta 42 (1997) 3321]. At the same time, the relatively am orphous structure featured a higher degree of microheterogeneity: the obser ved polymer granules featured both oxidized and reduced regions. The crysta lline grains of the second structure were more uniformly doped. However, in the cathodic doping, some of these grains remained undoped or even p-doped . (C) 2000 Published by Elsevier Science S.A. All rights reserved.