Metal films grown on nonwetting substrates evolve from an early stage of isolated compact islands to a later stage of elongated islands and percolation. Results are presented of a scanning electron microscopy study of Pb on SiO2 showing that the critical island radius Rc at which this crossover occurs is strongly dependent on temperature and weakly dependent on deposition rate. The experimental results are semiquantitatively described by a kinetic freezing model, in which the rate of island coalescence due to surface diffusion competes with the rate of island growth due to deposition.

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We describe an efficient Monte Carlo simulation of profile decay via surface diffusion on a (1+1)D square-lattice system with suppressed roughening. Our algorithm takes advantage of analytical results for a one-dimensional random walker and is valid in the low-temperature limit of noninteracting activated walkers. We find that an initially sinusoidal profile decays nonexponentially with a characteristic decay time which increases with the initial amplitude. At a fixed ratio of initial amplitude to wavelength, the decay time~increases with wavelength A, as~-A, "+ '. In this model, profile decay arises from irreversible decay of the peak and valley terraces rather than from step-step interactions.How does a corrugated surface on a crystalline solid relax toward equilibrium?The dominant relaxation mechanism is often surface diffusion. Above the roughening temperature T"a continuum picture is appropriate and the surface-mass current is driven by gradients in the surface curvature. ' The continuum model predicts that corrugations of wavelength A, decay exponentially with a time constant~-A, , a prediction that has been verified by profile decay experiments on metal surfaces ' at T) T". At T (T", corrugated metal surfaces are observed to form facets, but the scaling of the decay time with wavelength has not been established.Monte Carlo simulations * of profile evolution via surface diffusion at T & T, have produced a rich array of decay characteristics, but neither clear evidence of faceting nor a simple scaling of the decay time has been observed.These simulations have employed various simplifying assumptions in order to reduce an otherwise intolerable computation time. Analytical efforts to describe smoothing dynamics via surface diffusion at T & T" include thermodynamic models, which treat the crystal as a continuum, ' and microscopic models, which include the effects

We give a theoretical argument which indicates that the combined effect of substrate inhomogeneity and grain boundaries can be very important in determining the growth morphology of thin metal films on non-wetting substrates. An elongated metal island on a smooth non-wetting substrate, with a single grain boundary at its center, is shown to be in a state of unstable equilibrium. Any substrate inhomogeneity is then able to pin the island in a metastable state. An estimate of the depinning temperature is also given.

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