Electrochemistry of conductive polymers. 32. Nanoscopic examination of conductivities of polyaniline films

The conductivities of electrochemically prepared polyaniline (PAn) films have been determined using an atomic force microscopic tip with a conducting probe after the films were doped/dedoped at various potentials. The results indicate that the PAn films are rather inhomogeneous, even though the film is doped or dedoped until no further anodic or cathodic currents flow. This inhomogeneity was shown to be present even in the PAn nanostructures. The conductivities of the film ranged as widely as by three orders of magnitude on the same surface of 2 x 2 mum(2) depending on the location, at which the measurements were made. The range of highest conductivities was obtained when the film was doped at +0.30 V vs Ag\AgCl (in saturated KCl) while the one dedoped at -0.30 V and the one oxidized at +0.80 V were practically insulating. It was also discovered that the film prepared in the perchloric acid medium displayed very poor electrical characteristics compared to those prepared in the nitric acid medium. It is concluded from this study that the electrical properties are determined by the morphology of the film, which in turn is determined by the preparation conditions.