Relaxation model of coherent island formation in heteroepitaxial thin films

A model for coherent island formation in heteroepitaxial thin films is pres ented by focusing on the interplay between surface and strain relaxation en ergies. The resulting free energy is mapped onto the Landau free energy, an d yields the local surface slope as the order parameter for island formatio n. Isotropic islands are found to exhibit second-order transitions. We argu e that our model is appropriate for describing the nucleation and stability of island formation. The spinodal curve indicates that there exists an uns table regime where spinodal-like islands emerge as low-slope islands, even in a highly mismatched heteroepitaxial system. (C) 2000 American Institute of Physics. [S0021- 8979(00)00521-1].