Thin films of adsorbates on solid surfaces often exhibit irreversible clustering and island growth phenomena where the mean island size grows larger with a temporal power law dependence, accompanied by a scaling island size distribution function. This coarsening process is typically described within a thermodynamic framework using the Ostwald ripening formalism. However, there are strong indications that the Ostwald formulation is incomplete since it omits critical atomic level phenomena such as island mobility, spatial correlation between kinetic processes, and surface roughening of the islands. We have simulated thin film coarsening on an FCC(100) surface using a large Monte Carlo lattice gas model. Scaling exponents and island distribution functions were extracted from the simulations. From the Monte Carlo, we have computed rate constants for island evaporation–recondensation and island coalescence. Using a high-dimensional set of rate equations, a quasichemical mean field approach is formulated as a high dimensional set of second-order kinetics equations. The power law scaling behavior of the coarsening is reproduced by both the Monte Carlo simulations and the mean field theory. The relative importance of Ostwald theory versus island coalescence is evaluated.

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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.

The diffusion and evaporation kinetics of two-dimensional islands and vacancy islands on surfaces are studied over a wide range of island sizes. These kinetic processes are central in surface phenomena such as thin film coarsening, island aggregation, and coalescence on surfaces. Several studies have utilized scaling theories to infer the atomic level mechanisms responsible for the kinetics of island diffusion and evaporation. Using a dynamic Monte Carlo model, we study a model system where two-dimensional islands diffuse via an evaporation-condensation mechanism on a face-centered-cubic (100) surface. We examine the diffusion (evaporation) kinetics for isolated islands as a function of the island’s size in the range of 100 to 100 000 atoms. The diffusion coefficient and the island evaporation rate exhibit a power law scaling of the island size. We find crossover behavior in the scaling exponents between the regime of intermediate sized islands (between 100 and 1000 atoms) and large islands (greater than 1000 atoms). At high coverages, we also examine these quantities for vacancy islands. We find that intermediate island sizes exhibit unusual scaling behavior.