PHOTOCURRENT SPECTROSCOPIC STUDY OF THE INITIATION AND GROWTH OF POLY(3-METHYLTHIOPHENE) FILMS ON ELECTRODE SURFACES WITH DIFFERENT ADSORPTION PROPERTIES

Photocurrent spectroscopy, where the photocurrent response of the electrode is measured as a function of the illumination wavelength, has proven a powerful technique for the characterization of ultrathin conductive polymer films on semiconductor and metal electrodes. In electropolymerization, the initiation of the growth of poly(3-methylthiophene) film is dependent on the nature of the electrode surface. On clean, native indiumtin oxide (ITO) electrodes the polymerization commences with the deposition of long oligomeric chains on the surface. When the surface-reagent interactions are enhanced, favoring adsorption, e.g., on platinum or silylated ITO electrodes, short chains are deposited on the surface, and the initial step may be a direct reaction with surface-bound species. This is especially true with ITO electrodes covalently modified with thiophene-containing groups. The addition of small amounts of oligomeric species in the polymerization medium results in the electrochemical modification of the electrode surface, and further deposition can take place on the organic surface so formed. The electropolymerized films do not have a controlled structure at the molecular level and consist of a mixture of species with different conjugation lengths, which hampers their utilization in molecular electronics and other sophisticated applications. The surface reactions leading to a more ordered film could be favored under carefully controlled conditions.