Growth morphology with anisotropic surface kinetics

Abstract

A Monte Carlo model is used to simulate the morphological evolution of crystals growing from an incongruent vapor phase. The model combines nutrient transport, based on a modified diffusion-limited aggregation process, with anisotropic surface kinetics and surface diffusion. Through a systematic variation of the simulation parameters (temperature, bond strength and supersaturation), the whole range of growth morphologies from fully facetted to side-branched dendritic growth is recovered. The diffusion in the bulk nutrient and the anisotropy in the interface kinetics are seen to be morphilogically destabilizing and stabilizing, respectively. It is found that for a given set of simulation parameters and symmetry of the lattice, there is a critical size beyond which a crystal cannot retain its stable, macroscopically facetted growth shape. This critical size scales linearly with the mean free path in the vapor. Since both thermal and kinetic roughening reduce the kinetic anisotropy, the critical size decreases as either temperature of supersaturation is increased. Surface diffusion is seen to stabilize facetted growth on the shorter scale of the mean surface diffusion length. In simulations with a uniform drift superimposed on the random walk nutrient transport, crystal faces oriented towards the drift exhibit enhanced morphological stability in comparison to the purely diffusive situation. Rotational drifts with periodic reversal of direction are found to be morphologically stabilizing for all faces of the crystal.