Poly(3-methlthiophene) films were prepared under "silent" and "sono-electrochemical" potentiostatic (SEP) conditions. A three-electrode one-compartment sono-cell was used with a working platinum disc electrode. The sono-electrochemically formed polymer films were deposited with different working electrode-to-horn distances. The composition, electrochemical, spectroscopic, and morphological characteristics of the resulting polymer films were determined. Elemental analysis, FTIR-spectra, and X-ray photoelectron spectroscopy (XPS) data proved that the polymer films prepared under SEP conditions have predominant alpha-alpha'-couplings between the 3MT units, and the aromatic ring integrity is maintained in the film. Scanning electron microscopy showed that those films are more compact and less porous compared to the films prepared under silent conditions. The use of sono-irradiation during electropolymerization enhanced the diffusion of the monomer units towards the electrode surface and resulted in relatively less doped polymers with less conductivity. Electrochemical impedance spectroscopy (EIS) data for films prepared under silent and SEP conditions were collected in a monomer-free solution. The results show that the impedance of SEP films is relatively higher than those prepared under silent conditions, and a combination of charge transfer kinetics with diffusion-controlled conduction mechanism within the films. The diffusion was found to be a function of the porosity of the film. Conductivity measurements are in good agreement with EIS, elemental analysis, and XPS data. (c) 2006 Wiley Periodicals, Inc.