In situ atomic force microscopy of the electrochemical dissolution of a copper grain

Abstract

Dynamic evolution of the submicrometer surface morphology of a copper grain undergoing electrodissolution in the "electroetching regime" has been monitored by in situ atomic force microscopy. Images obtained for a nominal current density of 400 μA cm-2 indicate rapid etching into the surface to reveal well-defined crystallographic faces. The thermodynamically most stable {111} facets develop first, forming the initial primary dissolution faces; but as dissolution progresses, they are replaced by stably dissolving {211}and{221} facets. Hence, surface morphology can either be thermodynamically or kinetically controlled. Local current density is distributed inhomogeneously at the submicrometer level, being 1 order of magnitude larger than the global average at some locations. Identical crystallographic facets do not etch at the same rate and the dissolving facets typically evolve in a complex temporal-spatial manner. This behavior may be related to nonlinear pattern formation. Images obtained for a lower current density of 20 μA cm-2 provide unequivocal evidence of a surface recrystallization phenomenon concurrent with the anodic dissolution process. The surface reordering extends up to the submicrometer length scale and leads to development of smooth facets.