STM IMAGING AND ELECTRONIC CONDUCTIVITY MECHANISMS IN OXIDATIVELY DOPED POLY(N-METHYLPYRROLE) THIN-FILMS

Scanning tunneling microscopy (STM) images, localized current vs bias potential curves, and localized current vs tip displacement (normal to the sample plane) curves have been obtained for thin films of oxidatively doped poly(N-methylpyrrole) on polycrystalline gold. STM images of the polymer are quite noisy but are otherwise relatively featureless. Current vs tip displacement data taken over the polymer are characterized by currents that persist long after they would have died away at a bare metal surface; we postulate that the tip is buried in the polymer film, probably even while imaging. Current vs bias potential data acquired over polymer films reveal ohmic behavior at low bias but exponentially rising currents at high bias. This behavior is described in terms of an electric-field-driven electron-hopping process where the field is probably localized around the STM tip.