COMBINED SPECTROSCOPIC ELLIPSOMETRY AND VOLTAMMETRY OF TETRADECYLMETHYL VIOLOGEN FILMS ON GOLD

Dynamic measurements of changes in composition and conformation during adsorption of tetradecylmethyl viologen (C14MV) on a gold electrode w ere made using spectroscopic ellipsometry. Film thickness measurements indicated that a monolayer is initially formed in which the viologen species is in the upright extended position and that conversion to a t ilted conformation occurs during equilibration to the final monolayer film. Subsequent reduction of the film as electrode potential was scan ned from -0.2 to -0.9 V resulted in linear growth to a multilayer film in-which dications (C14MV2+) were reduced to radical (C14MV.+) and ne utral (C14MV0) species. A gradual increase of the film charge-to-thick ness ratio and of the film index of refraction during reduction indica ted densification of the deposit. The pattern in the variation of film extinction coefficient with electrode potential indicated that radica l dimers were the dominant species in the potential range correspondin g to the first reduction step. During the reverse potential scan, the radical film detached due to faster reoxidation of the layers adjacent to the electrode surface.