Investigation of the interplay of nickel dissolution and copper segregation in Ni/Cu(111) system

The effect of segregation on the dissolution of a thin Ni layer (3-14 equivalent-monolayers (eq-ML)) into a semi-infinite Cu substrate has been investigated at different temperatures (600-730 K) by Auger electron spectroscopy. Computer simulations have also been carried out to understand the details of the dissolution and a sophisticated method is proposed to analyse the experimental kinetics. The simulations indicated a step-wise character of dissolution and an interesting interference between segregation and dissolution. Because of the strong concentration dependence (there is a fast diffusion in Cu and there is practically no diffusion into Ni), the interface remains sharp and shifts proportionally with time until it does not reach the next-to-the-last Ni layer. Then the dissolution continues by the saturation of Cu in the topmost layer, according to the segregation isotherm. After the complete coverage of the surface by Cu, the final homogenisation takes place by the total dissolution of the next-to-the-last layer. According to these results, it was possible to separate the dissolution from the segregation and to determine the average speed of the interface shift, which is proportional to the intrinsic diffusion coefficient. (C) 2001 Elsevier Science B.V. All rights reserved.