Pt/Co(0001) superstructures in the submonolayer range:: A tight-binding quenched-molecular-dynamics study

We determine here the most stable structures of a Pt deposit onto a Co(0001) substrate, in the submonolayer range, by means of tight-binding quenched-molecular-dynamics simulations. Our essential result is that Pt/Co growth is essentially governed by the strain imposed by the substrate and by the tendency of the adatoms to avoid on-top positions. More precisely, whereas in the first stages of Pt deposition the strong adsorbate-substrate interaction leads to the formation of a high density of strained islands, these islands are able to relax before completion of the first monolayer (0.8 ML), thanks to the incorporation of Co atoms removed from the substrate. This phenomenon can be viewed as a first step towards the formation of a size-mismatch-induced surface alloy, in full agreement with photoemission spectroscopy experiments. [S0163-1829(99)07527-X].