In situ characterization of halide adsorption and Ag-halide growth on Ag(111) electrodes using atomic force microscopy

The structure and growth of halide adlayers and bulk Ag-halide deposits on Ag(111) has been studied by in situ atomic force microscopy as a function of electrode potential. For solutions containing F^- and Cl^-, only the underlying Ag(111) structure is observed at all potentials. However, for Br^- and I^--containing solutions ordered overlayers are present on the surface. In the Br^- case, a (3 × 3) structure is observed at positive potentials while this overlayer is removed from the surface following cathodic potential excursions. In the I^- case, a (√3 × √3) R30° structure is present on the surface throughout the entire potential range. Dissolution of the Ag(111) surface occurs at positive potentials in solutions containing F^- and Cl^- ions. However, the extent of dissolution response was less in chloride than in fluoride. In Br^--containing solutions, features not over 5 nm high grow on the surface upon initially cycling the potential positive. These features are removed from the surface upon returning the potential to more negative values leaving a much rougher surface. Subsequent positive potential scans give rise to a general smoothing of the surface and the protrusions seen on the initial sweep are not present. We attribute these two different processes to AgBr growth on the Ag(111) surface. The initial formation of AgBr on the surface considerably alters the Ag surface, producing nm-scale roughness which strongly affects subsequent AgBr growth. Anodic growth also occurs on Ag(111) in I^--containing solutions. The surface develops protrusions and becomes rougher after the initial cycle to positive potentials. When the potential is swept back negative, the rough surface features remain. Subsequent anodic potential sweeps results in a series of islands or protrusions appearing over the entire surface. The small islands are removed from the surface at negative potentials leaving a slightly rougher surface. When Ag(111) is immersed in I^--containing solution, growth occurs initially at positive potentials. Upon subsequent positive potential sweeps, island growth and surface roughening occurs.