Thin (100nm) films of Ag, followed by Cu, were deposited consecutively onto inert substrates by means of magnetron sputter deposition. Constant anodic current densities were then applied, at room temperature, in order to dissolve the outer Cu film to various depths. It was found that the 50Cu/50Ag interface, as detected in Auger electron spectroscopic concentration/depth profiles, initially moved into the Cu; towards the outer dissolving surface. This indicated an enhanced diffusion of Cu into the Ag. After longer times at all anodic current densities, the interface reversed and moved back towards the underlying Ag-rich layer. This indicated that the diffusion of Ag into Cu eventually predominated. The reversal time was inversely proportional to the anodic current density. The results were explained in terms of the anodic formation of sub-surface vacancies which migrated as di-vacancies to the Cu/Ag interface and there affected interface movement via the well-known Kirkendall mechanism. The calculated diffusivities (up to 10-12cm2/s at maximum anodic current densities of 900μA/cm2) were markedly above the values which were normally observed at room temperature.

D.A.Jones, A.F.Jankowski, G.A.Davidson: Metallurgical and Materials Transactions A, 1997, 28[3], 843-50