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 depos ited at room temperature lead to a dramatic roughening of the steps in volving a substantial restructuring of the copper template. It is argu ed that this restructuring is caused by the cobalt-induced misfit stra in. 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 eve ntually above about 5 to 8 monolayers one has step flow growth with sm ooth steps. In agreement with earlier observations we find that pinhol es 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 sha ped 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.