Stability of strained thin films with interface misfit dislocations: A multiscale computational study

The stability of thin single-crystal, internal-defect-free Fe films on Mo(110) and W(110) substrates is investigated through calculations of energetics including contributions from the misfit strain, interfacial misfit dislocations, film surface and interface. The misfit dislocation model is developed through the Peierls-Nabarro framework, employing ab initio calculations of the corrugation potential at the film/substrate interface as an input to the model. The surface and interfacial energies for pseudomorphic films are calculated as a function of film thickness from 1 to 10 layers, employing first-principles spin-polarized density-functional theory calculations in the generalized gradient approximation. First-principles calculations are also employed to obtain the Fe surface stress used in the Peierls-Nabarro model to account for the strain dependence of the surface energy. It is found that the competition between the misfit strain, misfit dislocations, film surface and interfacial energies gives rise to a driving force for solid-state dewetting of a single-crystal, internal-defect-free film, i.e., an instability of a flat film that leads to formation of thicker and thinner regions. The details of the energetics are presented to demonstrate the robustness of the mechanism. Our findings indicate that misfit dislocations and their configurations play a significant role in a morphological evolution of metallic thin films.