A method that significantly improves the charge-transfer barrier properties of self-assembled n-alkanethiol films on polycrystalline copper is presented in this paper. Chemically-formed films were further modified electrochemically by repetitive potentiodynamic cycling in ethanolic solutions containing small quantities of n-alkanethiols. The polarization modulation infrared reflection absorption spectra (PM-IRRAS) of the electrochemically-modified thiol films showed an increase in their surface packing density and structure order in comparison to those which were chemically formed. The electrochemical impedance spectra (EIS) revealed that the ability of these films to maintain barrier properties upon exposure to corrosive environments depends directly on their chemical and structural properties, which also influenced the wettability of the surface. Electrochemically-modified thiol films offer superior charge-transfer barrier properties over chemically-formed films.