Lattice mismatch effect in atomic migration along steps during heteroepitaxial metal growth

Lattice mismatch plays a determining role in surface atomic diffusion in epitaxy. One effect is the increasing anisotropy of diffusion along close-packed steps of adsorbed islands on (1 1 1) surfaces with increasing strain in the layer as shown by previous works on homoepitaxy and heteroepitaxy where the adlayer is under compressive strain. In most of these investigations the barrier of diffusion along steps with triangular microfacets (B steps) is greater than the barrier of diffusion along steps with square microfacets (A steps). Through atomistic simulations of a system under tensile strain, Co/Pt(1 1 1), we evidence reversal behaviour with a much smaller barrier obtained for diffusion at B step. Such effect results from a particular diffusion path along B step having a low cost in energy and being specific to tensile strain systems.