MORPHOLOGY OF INITIAL GROWTH-STAGES AND TUNNELING SPECTROSCOPY OF ELECTROPOLYMERIZED POLYANILINE THIN-FILMS

The morphology of polyaniline electrochemically deposited onto a thermally evaporated gold electrode substrate has been investigated in the nucleation stages using scanning tunneling microscopy. The films are grown in the galvanostatic mode at 70-mu-A/cm2 current density for 25, 50 and 100 s durations and the topography is measured in air. The results show that for films deposited for 25 s, the coverage of nuclei on the electrode is sparse, but the nuclei of various shapes tend to connect in partial coalescence. For the 50 s deposition, the population of nuclei increases significantly resulting in high surface coverage, but nuclei still retain their original features. After 100 s deposition, a homogeneous film is obtained. The electronic properties of the fully protonated emeraldine salt form of polyaniline are also studied by tunneling spectroscopy. An 1100 angstrom thick film is prepared electrochemically and the I/V curves are measured at many different positions on the film. The preliminary results show that the pi-pi* gap is 4 eV which agrees with the results of optical absorption spectroscopy. The tunneling conductance at the Fermi level is finite and changes spatially, suggesting that the observed results are consistent with metallic behavior of a single polaron lattice model.