Two growth modes of nanostructures near Cu(111) step edges in CoCu and PtCu surface alloys

The formation of CoCu and PtCu alloys on the stepped Cu(111) substrate was simulated. Dendritic and finger-like protrusions grow near the edges of the steps. The shape and the internal structure of the protrusions depend on the type of the step edge, temperature and concentrations of impurity atoms. The internal structure and the shape of the protrusions are significantly different in PtCu and CoCu alloys. Pt atoms tend to be surrounded by Cu atoms and Co atoms tend to combine into Co backbones. The dendritic protrusions usually grow at 200 K and the finger-like protrusions usually grow at 300 K. The shape of the protrusions also depends on the type of the step edge and the concentration of impurity atoms. The main differences of PtCu and CoCu protrusions can be explained by the values of the diffusion barriers of the key processes.