First principles simulations of Cu and Au deposition on a-Al2O3 (0 0 0 1) surface

A theoretical study of the interaction between single gold atoms and the regular Al-terminated a-Al2O3 (0 0 0 1) surface is reported. The surface is simulated by means of periodic slabs and the calculations have been undertaken within the density functional theory using a generalized gradient approach (GGA). For the metal adsorption five different sites have been considered, two on top of Al and O atoms, and three on hollow positions in which the transition metal binds three surface O atoms. Adsorption energy is found to be in the range between 0.39 and 0.81 eV, the preferred site being on top of surface oxygen atoms in contrast with the results obtained for Cu adsorption, where the preferred site was a hollow position with an Al atom underlying in the subsurface plane. Although for both Cu and Au a noticeable contribution to the adsorption energy from the surface relaxation is observed, the analysis of density of states plots and electron density differences suggest a change in the metal-surface bonding mechanism.