Au and Pd atoms adsorbed on pure and Ti-doped SiO_2/Mo(112) films

摘要

The interaction of Pd and Au atoms with a silica surface and SiO_2/Mo(112) ultrathin films has been studied with periodic density-functional theory-generalized gradient approximation calculations.On both unsupported and supported silica,Pd and Au are weakly bound.No charge transfer occurs to the empty Pd and Au orbitals.Differently from Au,Pd can easily penetrate with virtually no barrier into the hexagonal rings of the supported silica film and binds strongly at the SiO_2-Mo interface.The same process for Au implies overcoming a barrier of 0.9 eV.Completely different is the behavior of Ti-doped silica films.Au forms a direct covalent bond with substitutional Ti at the expense of the Ti...O-Mo interface bond which breaks.The global process is exothermic by 1 eV and nonactivated,showing that Ti doping results in solid anchoring points for the adsorbed Au atoms and for nucleation and growth of small gold particles.The effect of Ti doping is less pronounced for Pd but still visible with substantial enhancement of the Pd adsorption strength.