Time-dependent morphology changes in thin silver films on mica: A scaling analysis of atomic force microscopy results

Abstract

The postdeposition evolution of the morphology of a thin Ag film on a mica substrate was studied using a combination of experimental and theoretical techniques. Atomic force microscopy (AFM) was used to follow the surface morphology as a function of time at temperatures in the range 30–56 °C. The AFM images were numerically processed to obtain the distribution function of island sizes, defined as island height (h), as a function of time, f(h,t). The Ag films were observed to coarsen, i.e., small Ag islands disappeared while larger Ag islands increased in size. The island height distribution function was of a scaling form, f(h,t)∼f[h/h̄(t)], where h̄(t), the mean island height, increased monotonically as a power law h̄(t)∼tβh up until a crossover time t×. The experimental results for this low temperature annealing process are most consistent with a mechanism whereby the film coarsens through an island–island coalescence process. From the temperature dependence of the annealing kinetics, it was found that the coarsening process is thermally activated and has an activation energy of 13±2 kcal/mol. It was observed that the coarsening process terminates past the crossover time yielding a stable asymptotic distribution of islands which was independent of temperature (in the range 30–100 °C). Thus, it is suggested that a Ag film can be stabilized at room temperature by subjecting the film to a low temperature annealing process.