Growth of a Copper-Gold Alloy Phase by Bulk Copper Electrodeposition on Gold Investigated by In Situ STM

Simultaneous in situ scanning tunneling microscopy measurements and recordings of voltammograms were used to study in real time the initial cycles of potentiostatic copper electrodeposition and subsequent dissolution on a clean gold polycrystalline electrode. The cycles were carried out by sweeping the potential in the double-layer charging region from 500 to —100 mV and back to 500 mV at a sweep rate of 1 mV/s in an acidified copper sulfate electrolyte (0.01M H₂S04J 0.01M CuSO_4l and Millipore water). After completion of the first cycle the gold surface had recrystallized and nuclei of an alloy phase were formed. After completion of subsequent cycles the distribution of crystallite dimensions and the shape of the crystallites changed and the growth was compared with features of concomitant voltammograms. Relations between charge densities and potentials were deduced from data of the voltammograms. A shift in peak potential for the anodic current transient from E = 20 mV to E = —2 mV was observed after completion of four subsequent cycles of copper electrodeposition/dissolution. The shift is suggested to be equal to the change in potential of the working electrode owing to the formation of the alloy phase.