Early interdiffusion stages in epitaxially grown reaction couples were investigated by means of high-resolution and Z-contrast electron microscopy. Interdiffusion in the lattice-matched Ag/Au system obeyed Fick’s laws from the outset, but a complex 2-stage reaction was observed in lattice-mismatched Cu/Au samples. Fast diffusion at the beginning of heat treatment produced a planar zone of lattice defects along the interface, which released most of the induced stress. This first reaction stage ceased upon attaining a diffusion length of about 15nm. Further interdiffusion took place via a recrystallization mechanism which involved the heterogeneous nucleation of new grains and diffusion-induced grain boundary migration. During this second stage, discontinuous composition profiles revealed the occurrence of stress release at high-angle grain boundaries. The recrystallization mechanism also dominated the formation of ordered intermetallics at lower reaction temperatures.

Interdiffusion and Reaction of Metals - the Influence and Relaxation of Mismatch-Induced Stress. F.Hartung, G.Schmitz: Physical Review B, 2001, 64[24], 245418 (13pp)