Cu, Ag and Au atoms deposited on the α-Al2O3(0 0 0 1) surface: a comparative density functional study

A comparative study of the interaction between single copper, silver and gold atoms and the regular Al-terminated α-Al2O3(0 0 0 1) surface is reported. The surface was simulated by means of periodic slabs and the calculations were undertaken using the spin-polarized density functional theory within the generalized gradient approach. For metal adsorption, five different sites were considered, two on top of Al and O atoms, and three on hollow positions in which the transition metal binds three surface O atoms. Metal–surface interaction is relatively weak with adsorption energies in the range 0.7–1.1 eV, following the order Cu > Au > Ag. The preferred site for Cu and Ag are the three fold hollow oxygen sites while Au atoms prefer to bind the surface on top of the oxygen atoms. Examination of the electron density plots shows that some charge transfer toward the surface takes place according to the sequence Cu > Ag > Au. An analysis of the bond mechanism based on model cluster calculations indicates that for Cu and Ag the largest contribution to the interaction energy arise from the charge transfer from the adsorbed atom to the surface while in the case of Au, the interaction is dominated by the polarization of the transition metal.