Critical film properties for epitaxy

The conditions for overlayer coherency were investigated, by means of molecular dynamic simulations, for two-dimensional triangular Lennard-Jones solids. Up to a certain critical misfit, i.e. difference in the film-substrate lattice parameters, the film remains coherent and in a state of homogeneous strain parallel to the interface, in agreement with continuum calculations based on energy criteria. However, contrary to the predictions of such theories, the critical misfit quickly saturates as a function of film thickness. Further, the generation of misfit dislocations was favored by reducing the film-substrate bonding parameter but inhibited by an increase in this parameter. These factors indicate that in our overlayer-substrate system the occurrence of misfit dislocations is better described by a critical local force rather than a critical energy criterion.