Structural evolution of Au[001]/Ni molecular-beam epitaxy multilayers with Ni thickness: Comparison with Ag/Ni and Au/Co systems

Abstract

Strain relaxation in metallic multilayers with a large misfit (15%) has been investigated by high-resolution electron microscopy. For this purpose, model systems, namely Au[001]/Ni multilayers and Ni thin films on Au[001], have been grown by molecular-beam epitaxy. The strain relaxation involves two regimes depending on the thickness of the Ni layer: pseudomorphic growth for thin layers (less than five monolayers of Ni) which is possible because of interdiffusion at the interfaces, and a structure and orientation change for thicker layers. These two modes of relaxation will be emphasized and discussed in terms of energy and symmetry considerations. Two complementary systems (Ag/Ni and Au/Co) have been studied for comparison. It will be shown that, despite the same geometrical features, the early stages of the growth are different in these three systems and that the consideration of only lattice misfit is not sufficient to predict the growth.