Wetting layer thickness and early evolution of epitaxially strained thin films

We propose a physical model which explains the existence of finite thicknes s wetting layers in epitaxially strained films. The finite wetting layer is shown to be stable due to the variation of the nonlinear elastic free ener gy with film thickness. We show that anisotropic surface tension gives rise to a metastable enlarged wetting layer. The perturbation amplitude needed to destabilize this wetting layer decreases with increasing lattice mismatc h. We observe the development of faceted islands in unstable films.