Effect of elastic constants on the critical thickness of an epilayer

Elastic constants of an epilayer usually differ from that of its substrate. The effect of this difference on the critical thickness of an epilayer is investigated via isotropic elasticity. The results indicate that the self-energy of a mismatch dislocation is controlled by the soft phase between the epilayer and the substrate. while the interaction energy depends only on the elastic constants of the thin film. It is easier for a dislocation to be formed if the substrate is softer than the film, and consequently the critical thickness is smaller. On the other hand, a soft epilayer can be very thick without any mismatch dislocation