Intermixing and growth kinetics of the first Co monolayers on Cu(001)

We report on the interfacial intermixing of ultrathin Co films on a Cu(001) single crystal, two materials that are immiscible in the bulk. With increasing deposition rate we find a crossover from layer-by-layer to bilayer growth due to a hindered diffusion from the first layer to the substrate. Above two monolayers, growth proceeds in a layer-by-layer fashion. These effects are explained in terms of surface free energies.