Chemically induced step edge diffusion barriers: Dendritic growth in 2D alloys

To investigate the effects of multiple film components on the morphology of thin films, the growth of Co and Ag on Ru(0001) has been studied by scanning tunneling microscopy. Two types of growth have been identified. In the first, the Co from the vapor phase is directly incorporated into existing Ag islands. In the second, islands composed of a Co-Ag mixture are formed by etching of the existing pure Ag islands. These two mechanisms, which occur simultaneously, lead to dramatically different morphologies. In the second case, dendritic growth of the alloy is found despite the fact that neither of the component metals alone exhibit this behavior. We attribute the dendritic growth to chemically induced step edge diffusion barriers which must generally exist in multicomponent film growth.