IN-SITU SEQUENTIAL STM IMAGING OF STRUCTURAL-CHANGES RESULTING FROM THE ELECTRODISSOLUTION OF SILVER CRYSTAL-SURFACES IN AQUEOUS PERCHLORIC-ACID - THE ROUGHENING KINETICS

Structural changes of silver terrace domains in aqueous perchloric aci d solution at constant anodic current density (j) and room temperature were followed by in situ scanning tunneling microscopy sequential ima ging. For j < 15 mu A cm(-2) silver electrodissolution proceeds at ste p edges without roughening. Conversely for j > 15 mu A cm(-2) the silv er surface becomes progressively rougher to attain, after a certain cr itical time,a steady roughness. In this case, the dynamic scaling theo ry applied to STM images indicates that the dissolving silver surface can be described as a self-affine fractal surface with a static roughe ning exponent alpha=0.90+/-0.06, and a dynamic roughening exponent bet a=0.36+/-0.08. The value of alpha is consistent with the relevant role played by surface diffusion in the silver electrodissolution mechanis m, whereas the value of beta is slightly higher than those derived fro m growth models incorporating surface diffusion. The difference in the value of beta would reflect the influence of either the electric fiel d or energetic barriers at step edges on the rate of roughness develop ment.