Raman spectroscopic evidence of thickness dependence of the doping level of electrochemically deposited polypyrrole film

In this paper, we present resonance Raman spectroscopic studies on as-grown thin polypyrrole (PPy) films electrochemically deposited on flat platinum electrode surfaces by direct oxidation of pyrrole in acetonitrile. It was found that the overall features of the Raman spectra depend strongly on film thickness, mainly due to that the doping level of PPy increases during film growth process. Electrochemical and X-ray photoelectron spectroscopic (XPS) examinations have confirmed this discovery. The doping level of PPy film with a given thickness also depends on the property of supporting electrolyte.