Mechanisms of long-range edge retraction of metal bilayer films

Abstract

The agglomeration of thin films on substrates is driven by minimization of the free surface and film/substrate interface energies and has been studied extensively for single component metal films. Only a few studies have investigated the agglomeration of kinetically constrained metal bilayer films, for which unusual long-range edge retraction was recently reported. This study has explored the agglomeration of kinetically constrained thin films of Au and Ni that were subsequently deposited on SiO2/Si substrates and annealed under high vacuum conditions at 545, 675, and 730 °C. Long-range edge retraction of the metal bilayer films revealed seven regions across the receding edge that are microstructurally distinct. The absolute and relative widths of the regions depend on the deposition sequence of the two metal films and annealing temperature. Arrhenius analysis of growth rates for different regions was used to identify energy barriers for mass transport mechanisms. The presence of native nickel oxide was found to have a significant effect on the kinetics of long-range edge retraction. The experimental results suggest that the formation of multiple regions across the receding edge is part of the kinetic evolution of long-range edge retraction of metal bilayer films.