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

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 degrees 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)similar to f[h/(h) over bar(t)], where (h) over bar(t), the mean island height, increased monotonically as a power law (h) over bar(t)similar to t(beta h) up until a crossover time t(x). 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 degrees 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. (C) 1996 American Institute of Physics.