Phase transformation kinetics and self-patterning in misfitting thin films

We outline a computational approach for the study of phase transformations in misfitting thin films and then investigate the kinetics of a transformation to assess the role of heterogeneous nucleation sites, formed in the vicinity of misfit dislocations, in the self-patterning of these systems. Both computer simulation and analytical methods are employed to analyze spatio-temporal correlations in the transforming phase as embodied, in particular, in the transformed volume fraction. To accomplish this, we first obtain an expression for the driving force for nucleation in terms of the strain energy stored in the film under site saturation conditions. This driving force forms the basis for simulations of nucleation and growth in films in which simulation parameters, such as film thickness and temperature, are systematically varied. We find that, in a fully coherent film, there is a retardation of the transformation at certain times that is associated with the constrained film geometry and that, in the presence of misfit dislocations, a range of kinetic behavior can be correlated with the relative magnitude of the driving forces and temperature. The implications of our results for pattern formation in these systems are then discussed. (C) 2003 Published by Elsevier Ltd on behalf of Acta Materialia Inc.