Atomic exchange processes and bimodal initial growth of Co/Cu(001)

The initial growth of Co on Cu(001) is atomically identified by scanning tu nneling microscopy using CO titration and density-functional theory total-e nergy calculations. Both reveal that at low coverage Co adatoms occupy subs titutional sites in the Cu substrate surface that act as pinning centers fo r subsequent island nucleation. The interaction with diffusing adatoms is f ound to be attractive and stronger for nearest-neighbor Co compared to Cu. The atomic substitution process actuates a bimodal growth mode as experimen tally found in the island size distributions. This gives rise to a high den sity of small Co islands and large Go-decorated Cu islands. [S0163-1829(99) 08943-2].