X-ray photoemission spectroscopy studies of conducting polymer-substrate interfaces: Interfacial electrochemical diffusion

Interfaces between conducting polymer polypyrrole (PP) and transparent conductive materials such as indium tin oxide (ITO) and SnO₂ were investigated by x-ray photoemission spectroscopy (XPS). XPS lines of In 3d_5/2,3/2 and Sn 3d_5/2,3/2 were observed in the XPS spectra of electrochemically reduced PP film sides of PP/ITO and PP/SnO₂, respectively. The results indicate that electrochemical diffusion of substrate materials into conducting polymer films takes place by applying negative voltage to the substrate. The energy positions of the 3d lines of the diffused In and Sn which are close to those of the metal oxides support the proposition that the diffused species are metal oxide ions. In the electrochemically diffused PP/ITO and PP/SnO₂ interfaces, XPS spectra of substrate sides exhibit In 3d and Sn 3d lines associated with satellite peaks, which indicates magnetic splitting of 3d levels or electron transfer typed shake-up. This indicates that electrochemical diffusion affects the substrate electronically.