Semi-empirical and ab initio studies of low-temperature adsorption of oxygen and CO at [110] face of SnO2

Using a first principles electronic structure calculation method based on the density functional theory (DFT), and also using a semi-empirical (PM3) method, surfaces of the [110] face of SnO₂ with and without CO and oxygen adsorbates have been studied. For semi-empirical and DFT calculations, cluster models and the slab models were constructed, respectively. It was found that oxygen adatoms on a perfect stoichiometric [110] surface do not form without precursor for O₂ dissociation. The chemisorbed atomic oxygens are metastable, but may stabilize in the form of carbon-related complexes in CO environment, which is enhanced by the energy barrier for CO₂ formation. It is energetically favorable for CO to form structures like oxalate and bidentate carbonate. It is proposed that, in a low-temperature range, chemisorption processes may contribute to the sensitivity of SnO₂ film.