Interaction of Cu overlayers with W(001) studied by low-energy alkali ion scattering

Abstract

Low-energy alkali ion scattering, Auger electron spectroscopy, and low-energy electron diffraction have been used to study the structure of ultrathin Cu overlayers on W(100). Incident polar and azimuthal angular scans of the Cu and W single-scattering intensity have been obtained as a function of Cu coverage and annealing temperature, and are used to evaluate various models for the surface structure. Dosing submonolayer amounts of Cu near room temperature results in two-dimensional islands of Cu bonded in fourfold hollows and some dispersed Cu atoms. Annealing at 1000 K causes irreversible displacement of first-layer W atoms and Cu incorporation, as indicated by a pronounced shift in the Li+/W low-angle shadowing edge, and the changes in the shape of the Li+/Cu edge. This result is interesting in view of the immiscibility of Cu and W. Analysis of contour plots of the Li+/Cu single scattering support a growth of up to two pseudomorphic layers of Cu on W(001); although there is Cu and W mixing at the interface.