SURFACE ALLOY FORMATION BY INTERDIFFUSION ACROSS A LINEAR INTERFACE

Interdiffusion profiles across a linear interface separating two metal s that are miscible as monolayers [Co and Cu on a Ru(0001) surface] ha ve been measured as a function of time. The interface remains sharp ev en after substantial intermixing, in dramatic contrast to bulk interdi ffusion experiments between miscible metals. The unusual concentration profiles are explained by a combination of adatom surface diffusion a nd exchange of adatoms with atoms in the monolayer films. A simple Mon te Carlo simulation of the adatom exchange mechanism quantitatively ag rees with observations.