Atomic force microscopy and Kelvin probe force microscopy evidence of local structural inhomogeneity and nonuniform dopant distribution in conducting polybithiophene

Direct evidence of local structural inhomogeneity and nonuniform doping-level distribution in conducting polymer film has been obtained using Kelvin probe force microscopy (KFM) and atomic force microscopy (AFM). The KFM data suggests that the polymer consists of grains that constantly differ in work function and thus in the dopant concentration from the grain peripheral regions. For the as-grown polymer, most of the doping charge is located at the grain tops, whereas the electrochemically doped polymer features relatively higher doped grain periphery and less doped grain tons. The AFM study reveals two different kinds of the polymer molecular structure dependent on whether the image was taken at the top of a grain or the grain periphery. This result confirms the inherent inhomogeneity of conducting polymers demonstrated with KFM.