Relaxation model of coherent island formation in heteroepitaxial thin films

A model for coherent island formation in heteroepitaxial thin films is presented by focusing on the interplay between surface and strain relaxation energies. The resulting free energy is mapped onto the Landau free energy, and yields the local surface slope as the order parameter for island formation. Isotropic islands are found to exhibit second-order transitions. We argue that our model is appropriate for describing the nucleation and stability of island formation. The spinodal curve indicates that there exists an unstable regime where spinodal-like islands emerge as low-slope islands, even in a highly mismatched heteroepitaxial system.