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 elec trode is measured as a function of the illumination wavelength, has pr oven a powerful technique for the characterization of ultrathin conduc tive polymer films on semiconductor and metal electrodes. In electropo lymerization, the initiation of the growth of poly(3-methylthiophene) film is dependent on the nature of the electrode surface. On clean, na tive indiumtin oxide (ITO) electrodes the polymerization commences wit h the deposition of long oligomeric chains on the surface. When the su rface-reagent interactions are enhanced, favoring adsorption, e.g., on platinum or silylated ITO electrodes, short chains are deposited on t he 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 amou nts of oligomeric species in the polymerization medium results in the electrochemical modification of the electrode surface, and further dep osition can take place on the organic surface so formed. The electropo lymerized films do not have a controlled structure at the molecular le vel and consist of a mixture of species with different conjugation len gths, which hampers their utilization in molecular electronics and oth er sophisticated applications. The surface reactions leading to a more ordered film could be favored under carefully controlled conditions.