Rossitza Pentcheva and Matthias Scheffler

In the context of a currently developed "magneto-electronics" Co on Cu(001) represents a model system for understanding the interplay between structural and magnetic properties. The initial stage of heteroepitaxial growth of Co on Cu(001) is studied with density-functional theory (DFT). The adsorption energies and magnetic properties of Co adatoms at on-surface and substitutional sites are analyzed. Due to the substitutional adsorption which is favorable for low coverages, an unexpected situation arises: There are not only Co but also Cu adatoms that diffuse on the surface. The substitutionally adsorbed Co atoms act as nucleation centers and are responsible for the bimodal growth observed in STM-experiments which is characterized by a high density of small Co-islands and large, Co-decorated Cu islands. The diffusion barriers of Co and Cu adatoms on the flat and stepped Cu(001) surface are calculated and the influence of magnetism on the diffusion barrier is investigated. Moreover, the rates of the microscopic processes obtained with DFT are used as input parameters in a kinetic Monte-Carlo (kMC) simulation of the initial growth of Co on Cu(001). Island sizes, shape and densities are compared to the homoepitaxial case of growth of Cu on Cu(001) and to experimental results¹. Deviations from standard nucleation theory are discussed.