Imaging of the structure of ultra-thin cobalt silicide films by inelastically backscattered electrons

We have investigated the initial growth of cobalt silicide films in the Co/Si(1 1 1) system by incoherent medium-energy electron diffraction providing real-space imaging of the subsurface atomic structure. It is shown that deposition of the first few (1-3) monolayers of Co results in formation of cobalt silicide islands with composition and structure depending on the temperature. While, the clusters of B-type CoSi2 grow at elevated temperatures (T > 300 degreesC), the room temperature deposits consist of silicide grains of A- and B-type orientation. Further increase of the Co coverage results in both an enrichment of the probed layer with the metal and its disordering. Annealing of such samples at T > 250 degreesC gives rise to solid-phase reaction of Co and Si leading to gradual formation of the epitaxial disilicide layer and disappearance of A-type domains.