Abstract

The electroformation of a Cu 2S phase, obtained by sulfidization of a thin film of copper placed by the spin-coating technique onto the gold surface of a gold/quartz crystal that is part of an electrochemical quartz crystal microbalance (EQCM), was studied by cyclic voltammetry (CV) and electrochemical quartz crystal microgravimetry. The electrolytic medium employed was a bisulfide-containing aqueous buffered solution (pH 9.2). CV parameters showed that the formation of the Cu 2S phase occurred by means of an irreversible diffusion-controlled mechanism, where a first uncomplicated electron transfer was the rate-determining step. The EQCM data showed that the initially formed phase was Cu 2S, which was later oxidized to nonstoichiometric compounds (Cu( 2-x)S) and CuS. Furthermore ?Q/?m data analysis established that the electron reaction valence (n) was close to 2 for all electrochemical processes where Cu/S compounds were involved. The nucleation and growth mechanism (NGM) of the Cu 2S phase corresponded to a bidimensional instantaneous mechanism containing two contributions, one controlled by diffusion and the other controlled by charge transfer. Atomic force microscopy (AFM) revealed that the Cu 2S phase electroformed on the gold/crystal quartz electrode was deposited as hemispherical particles (sized between 40 and 130 nm) on the terraces and in the cavities present in the gold film.