THE GROWTH OF COBALT FILMS ON VICINAL COPPER SURFACES

We have studied the morphology of thin cobalt films on Cu(1117) using scanning tunneling microscopy. Submonolayer quantities of cobalt deposited at room temperature lead to a dramatic roughening of the steps involving a substantial restructuring of the copper template. It is argued that this restructuring is caused by the cobalt-induced misfit strain. Films of 2-3 monolayer thickness display a rather rugged structure with many steps oriented perpendicular to the original step direction. With further deposition of cobalt, the steps become smoother and eventually above about 5 to 8 monolayers one has step flow growth with smooth steps. In agreement with earlier observations we find that pinholes remain in the film during growth. Their density decreases with the film thickness and disappears above five monolayers. Upon annealing to 380 K, the pinholes in the thin layers grow to large, rectangular shaped pits with a mean size of about 10 nm. Eventually copper begins to migrate onto the cobalt film. The growth of the pits is attributed to the release of misfit strain in the cobalt layer. The relation between the film morphology and the magnetic anisotropy is discussed.