Structural modifications of Co ultrathin films grown on Au(111) vicinal surfaces

We report on structural modifications in cobalt thin films (5-90 Co monolayers thick) grown on nominally flat and vicinal Au(111) surfaces using grazing incidence x-ray diffraction. While on the (111) surface Co films are hexagonal close-packed, face-centered-cubic (fcc) structure appears on vicinal surfaces. A high step density favors this structure in the Co films independently of the step crystallographic structure of the Au substrate. These fcc structures are found twisted or untwisted, relatively to the substrate, depending on the miscut direction. This stacking is always found to display Co{111} step edges at the Co/Au interface. Besides, the influence of an Au capping layer was also investigated, showing that the Co atomic out-of-plane relaxations are modified by this overlayer.