XPS characterization of nanosized overoxidized polypyrrole films on graphite electrodes

Abstract

X-Ray photoelectron spectroscopy (XPS) analysis was used to verify the structure of nanosized overoxidized polypyrrole (OPPy) films that were grown on glassy carbon. The films were electrochemically grown to ca. 1.2–1.6 nm thickness from acetonitrile with tetrabutylammonium perchlorate (TBAP) and from water with adenosine triphosphate (ATP) as dopant. The films have been previously characterized by electrochemical methods, but this represents the first study of the ultrathin films by XPS. XPS analysis verifies that the key structural features of nanosized OPPy films are the same as those of much thicker films previously studied by XPS on metal substrates, where differential charging effects are much less severe. Some differences between the microstructures of OPPy and OPPy/ATP films are highlighted by the results. In addition, XPS results confirm a two-domain model of the polymer films that has been proposed from previous studies of PPy and OPPy. The results show that XPS can be used to characterize nanosized films on graphite, after correction for differential charging. Graphite represents a substrate of choice for the fabrication of permselective ultrathin membranes for biosensors from materials such as OPPy.