Ab initio modelling of silver adhesion on the corundum (0001) surface

The Ag/α-Al2O3(0001) interface was simulated using ab initio slab calculations. We have studied silver adhesion on both Al- and O-terminated corundum substrates. The latter case may be considered as silver adhesion on a defective Al-terminated corundum surface with external aluminium vacancies. The dependence of the adhesion energy on the interfacial distance has been analyzed for the two favorable Ag adsorption positions and for two metal coverages (a 1/3 monolayer of the Ag(111) crystallographic plane and a full Ag(111) monolayer, 1 ML). The two different terminations (Al- and O-) give rise to qualitatively different results. In the former case, the small adhesion energies per Ag atom are accompanied by a minor interfacial charge transfer, indicating physisorption, which may be explained by a weak atomic polarization. In contrast, for O-terminated corundum, substantial adhesion energies per Ag atom combined with a noticeable charge transfer towards the substrate up to formation of Ag+ ions give a clear indication for a strong interfacial ion bonding. We compare these results with the data obtained earlier for the perfect and defective Ag/MgO(001) interfaces and found some qualitative similarities in metal adhesion nature on both alumina and magnesia substrates.