Exchange processes in interlayer diffusion - kinks, corners and the growthmode

Interlayer diffusion, i.e. mass transport between different terraces, is kn own to be an essential process for obtaining layer-by-layer growth, avoidin g formation of three-dimensional (3D) islands when growing thin films. We p resent experimental results for the growth of cobalt on Pt(111), which demo nstrate the importance of kinks and corners for interlayer diffusion. We sh ow that Co grows two-dimensionally as long as strain caused by the Pt-Co in terface keeps the step edges rough, with a high kink density, and then tran sforms to 3D growth with straight steps. The results for growth with adsorb ed carbon monoxide show that CO acts as a surfactant, causing two-dimension al growth unless heterogeneous nucleation occurs. Again, this process is re lated to roughening of the steps, being a new mechanism for the action of a surfactant. A scanning tunneling microscopy study at the atomic scale conf irms the fact that step descent happens only at kinks and (concave) corners , and in conjunction with simulations allows us to identify some of the rel evant atomic-exchange processes. We finally argue that the dependence of th e growth mode on the step morphology, together with straightening of the st eps by step-step interaction, can lead to an instability of the growth mode .