Dislocations and elastic anisotropy in heteroepitaxial metallic thin films

The influence of elastic anisotropy on the critical thickness for the plastic relaxation of epitaxial layers is examined with the help of a coupled discrete-continuum simulation. The latter incorporates a rigorous treatment of the boundary conditions and of mismatch stresses, as well as the elastic properties of a single threading dislocation. Numerical experiments conducted on model Cu/Cu, Cu/Au and Cu/Ni systems with a (001) interface show that, through several distinct effects, elastic anisotropy induces a significant increase in the critical thickness with respect to the values predicted by Matthews et al. The isotropic model of a comparison of the anisotropic critical thicknesses for (001) and (111) interfaces shows that Cu-(111) films on Ni substrates are about 50% 'harder' than (001) films. This feature is discussed in relation to the strength of thin metallic films.

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