Adsorption Structures and Energies of Cu_<i>n</i> Clusters on the Fe(110) and Fe₃C(001) Surfaces

Spin-polarized density functional theory computations have been carried out to investigate the adsorption configurations of Cu_<i>n</i> (<i>n</i> = 1–7, 13) on the most stable Fe(110) and Fe₃C­(001) surfaces. On both surfaces the adsorbed Cu_<i>n</i> clusters favor aggregation over dispersion, and monolayer adsorption configurations are more favored thermodynamically than the two-layer adsorbed structures because of the stronger Fe–Cu interaction over the Cu–Cu bonding. On the basis of the computed adsorption energies the Fe(110) surface has stronger Cu affinity than the Fe₃C­(001) surface, in agreement with the experimental results. The Fe(110) surface also has stronger Cu_<i>n</i> aggregation energies and more pronounced charge transfer from surface to adsorbed Cu_<i>n</i> clusters than the Fe₃C­(001) surface. Different Cu_<i>n</i> growth modes have been discussed accordingly