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- and n-doped poly-3-methylthiophene (P3MT) deposited onto highly oriented pyrolytic graphite (HOPG) were characterized on a microscopic scale by using Kelvin probe force microscopy (KFM) and in situ atomic force microscopy (ECAFM) techniques. Two different types of surface structures were found on different sites of the polymer surface, one of them representing relatively amorphous polymer globules, and the other highly crystalline polymer grains. For the two structures, in both the p- and n-doping processes, the doping-level distribution was again found to be directly related to the polymer surface morphology, as was the case for p-doped polybithiophene (PBT) [O.A. Semenikhin, L. Jiang, T. Iyoda, K. Hashimoto, A. Fujishima, J. Phys. Chem. 100 (1996) 18603; O.A. Semenikhin, L. Jiang, T. Iyoda, K. Hashimoto, A. Fujishima, Electrochim. Acta 42 (1997) 3321]. At the same time, the relatively amorphous structure featured a higher degree of microheterogeneity: the observed polymer granules featured both oxidized and reduced regions. The crystalline grains of the second structure were more uniformly doped. However, in the cathodic doping, some of these grains remained undoped or even p-doped.