First principles calculations of the energetics of Co/Cu(111) multilayers

A first principles study of various relevant energetics for Co films deposited on Cu(111) is presented. The tendency of Cu diffusion to the surface is explained in terms of a lower surface energy of Cu than that of Co. In the low Co coverage regime, the growth of the fcc stacking is found to be predominantly determined by the following considerations: (1) the diffusing Cu atoms prefer fcc sites when they are present on the Cu(111) substrate; (2) both a Cu overlayer (i.e., in the case of Cu atoms locally forming a capped overlayer) and a Co overlayer on Cu(111) prefer fcc stacking. On the other hand, Co adatoms on fcc-Co(111) substrate strongly prefer hcp sites, suggesting that the layer stacking sequence becomes pure hcp as the diffusion of Cu atoms to the surface diminishes. Energetically, Co and Cu atoms are found not to mix with each other on the surface. Since Cu has an fcc preference, a coexistence of fcc- and hcp-type domains is expected in the intermediate Co coverage regime.