Nature of point defects on SiO2/Mo(112) thin films and their interaction with Au atoms

We have studied by means of periodic DFT calculations the structure and properties of point defects at the surface of ultrathin silica films epitaxially grown on Mo(112) and their interaction with adsorbed Au atoms. For comparison, the same defects have been generated on an unsupported silica film with the same structure. Four defects have been considered: nonbridging oxygen (NBO, Si-O-center dot), Si dangling bond (E' center, Si-center dot), oxygen vacancy (V-O, Si-Si ), and peroxo group ( Si-O-O-Si ), but only the NBO and the V-O centers are likely to form on the SiO2/Mo(112) films under normal experimental conditions. The Si-O-center dot center captures one electron from Mo forming a silanolate group, Si-O-, sign of a direct interaction with the metal substrate. Apart from the peroxo group, which is unreactive, the other defects bind strongly the Au atom forming stable surface complexes, but their behavior may differ from that of the same centers generated on an unsupported silica film. This is true in particular for the two most likely defects considered, the nonbridging oxygen, Si-O-center dot, and the oxygen vacancy, Si-Si .