On a new phase transition in the Cu/Au(111)/H2SO4 system

A new pair of current spikes has been found in the cyclic voltammogram of Au(111) in an acidic copper sulphate solution, indicative of a phase transition in the Cu adlayer. The spike potential is well inside the bulk deposition region and hence, the new feature can be observed only at low Cu++ concentration, when bulk deposition is slow. The charge under the spike correlates linearly with extent of the (root 3 x root 3-)R30 degrees structure, up to 40 mu C cm(-2) for the fully developed superstructure. The spike potential shifts with the sulphate concentration and hence, this feature is assigned to the desorption of sulphate from the well-known honey comb structure of the Cu upd layer.