Initial stages of Ge growth on Si(100): ad-atoms, ad-dimers, and ad-trimers

We study, using ab initio calculations, small structures that are present at the early stages of growth of Ge on the Si(1 0 0) surface. Ad-atoms, ad-dimers, and ad-trimers are investigated. We consider different configurations of the adsorbed structures, and present results for their relaxed geometries and relative energies.