Growth and morphology of polythiophene on thiophene-capped monolayers: 1. Single component monolayers

Thin polythiophene films were grown at a variety of oxidizing potentials by electrochemical polymerization on indium. tin-oxide surfaces that were modified with a thiophene-capped, self-assembled monolayer (SAM) composed of 11-(3-thienyl)-undecyltrichlorosilane (3TUTS). The evolution of those growing films was tracked via cyclic voltammetry and infrared spectroscopy, and the surface morphology was probed with atomic force microscopy. To allow comparison, similar data were obtained for polythiophene films grown on bare indium. tin-oxide (ITO) (no SAM). Our results show that 3TUTS layers can nucleate growth of polythiophene films at potentials below the oxidation potential of monomeric thiophene in solution, and the cyclic voltammetry signature is characteristic of a surface-confined, redox-reversible species; however, at these low potentials no polythiophene growth on the bare ITO electrodes is seen. At higher potentials where polythiophene growth is observed on both types of surfaces, an additional amount of charge corresponding to the amount of thiophene groups along the SAM is transferred across the SAM-modified electrodes. Although spectroscopic data reveal no differences in the films grown on bare and 3TUTS-modified ITO, atomic force microscopy results show that the latter class of films are more homogeneous, have lower roughness, and are denser than the corresponding film grown on bare ITO. We attribute this difference in the morphology of the films to the high nucleation density arising from the pendent thiophene rings of the monolayer.