STRUCTURE OF CO FILMS GROWN ON CU(111) STUDIED BY PHOTOELECTRON DIFFRACTION

The structure of epitaxial cobalt on Cu(111) single-crystal surfaces was studied by angle-resolved x-ray-photoelectron diffraction and low-energy electron diffraction. We find that initial growth of Co is in the metastable fcc phase. The first cobalt monolayer occupies the substrate fcc continuation sites and grows as a flat layer coherent to the substrate lattice. The fcc stacking sequence continues for two-layer-thick cobalt films. As the film thickness increases beyond two layers, hcp stacking faults occur as domains in mixed fcc-hcp layers. The transition from the metastable fcc stacking sequence to the bulk hcp(0001) structure is not abrupt, but occurs gradually as the film thickness increases.