IN-SITU STM INVESTIGATION OF AG(111) ELECTROCHEMICAL ROUGHENING IN PERCHLORATE SOLUTIONS

The surface structures generated by oxidation-reduction cycles (ORCs) on a well characterized silver (111) single crystal face have been examined by in situ STM. The ORCs, carried out in aqueous KClO4, produce surface structures which span from atomic-scale clusters to large-scale features with linear dimensions of some hundreds of nanometers. While the surface structures produced by the ORC are stable at the most negative potentials, application of increasingly positive potentials causes a rearrangement of the surface with progressive predominance of the large-scale features over the small-scale ones, quite probably by a mechanism involving silver dissolution and redeposition of silver ions. This increase in dimensions is accompanied by a decrease in the SERS activity of the metal surface. The atomic-scale clusters, which are clearly visible by in situ STM at far negative potentials, are responsible for a substantial increase in Raman enhancement. Bumps with dimensions of the order of tens of nanometers, which are responsible for the excitation of local modes, are shown by in situ STM to persist at -0.5 V/SCE. However, a further positive shift in potential causes a decrease both in their number and in the SERS activity.