Diffuse interface electron scattering in epitaxial Co/Cu bilayers

Abstract

We have examined the origin of diffuse electron scattering at Co/Cu interfaces using in situ resistance measurements and scanning tunneling microscopy (STM) on a model system consisting of epitaxial (111)-oriented Co on Cu and Cu on Co. We grew epitaxial Co/Cu bilayers on 40 Å Cu(111)/Si(111) substrates, and monitored the resistance and surface morphology during the initial stages of growth for both Co on Cu and Cu on Co. For the case of Co on Cu, the resistance initially increases by 10% at submonolayer coverage, and then drops after 1–1.5 ML coverage. In situ STM topographs taken at similar stages of growth reveal that 20–30 Å Co islands initially nucleate above Cu step edges at submonolayer coverage and then grow inward to cover the Cu terraces. These islands introduce new steps at the surface, dramatically reduce the lateral correlation length of the surface profile, and consequently increase its contribution to the surface scattering resistance. We find that the nucleation and percolation of these islands is strongly correlated with the resistance behavior. In contrast, for Cu deposited on Co, we observe no island nucleation, and no corresponding resistance increase.