Initial adsorption of Co on Cu(001): A first-principles investigation

We present total-energy calculations for the initial adsorption of Co on Cu(001). By studying different adsorption geometries we find that the substitutional adsorption is strongly favored compared to the on-surface adsorption at a fourfold hollow site. The electronic and structural effects actuating this tendency are analyzed. We investigated the coverage dependence of the adsorption energy and find that it is particularly favorable for low coverages (theta<0.25 ML) while at higher coverages we predict the formation of compact islands. In addition the paper also explores the influence of magnetism. We find that magnetic Co adatoms induce a weak spin polarization in the substrate with an oscillatory character: nearest Cu adatoms couple parallel while next-nearest adatoms couple antiparallel. However, we find that spin polarization has little influence on the energetic trends. Due to the tendency of deposited Co to adsorb substitutionally, it follows that under initial growth conditions two different mobile adatom sorts will be on the surface, on-surface Co (not yet incorporated substitutionally) as well as Cu created by the already substitutionally incorporated Co. The role of the substitutional Co atoms as pinning centers for subsequent island nucleation is investigated quantitatively.