| AVS 56th International Symposium & Exhibition | |
| Surface Science | Wednesday Sessions |
| Session SS1-WeA |
| Session: | Water/Surface Interactions & Environmental Chemistry II |
| Presenter: | A.E. Becerra-Toledo, Northwestern University |
| Authors: | A.E. Becerra-Toledo, Northwestern University D.M. Kienzle, Northwestern University L.D. Marks, Northwestern University |
| Correspondent: | Click to Email |
Strontium titanate, SrTiO3, has been largely studied as the quintessential model system for perovskite oxides. In the field of surface science, the presence of multiple cation valence states has allowed for insights into the stabilization mechanisms in mixed-metal oxides. Multiple SrTiO3 surface structures have been conclusively described at the atomic scale, which lets us go beyond bulk-like caricature descriptions of oxide surfaces. In turn, this allows for a more realistic study of the interaction of oxide surfaces with foreign species such as water, whose ubiquity makes such analysis inescapable.
Density functional theory (DFT) calculations were performed to study the surface energetics of several observed and theoretical SrTiO3(001) surface reconstructions, both dry and with chemisorbed water. A repeated slab configuration was used to model all surface structures, which include not only bulk-like truncations, but also the 2x1, c(4x2), (√13x√13)R33.7º reconstructions, as well as the theoretically predicted low-energy (√2x√2)R45º structure. The use of an augmented plane wave plus local orbital (APW+lo) basis, coupled to the full-electron potential implementation, accurately reflects the character of single-particle wavefunctions. The TPSSh hybrid meta-GGA exchange-correlation functional [Tao et al., PRL 91,146401 (2003)] was employed, which allows for an improved treatment of strongly correlated systems. Both the molecular and dissociative water adsorption modalities were taken into account.
Our analysis suggests that water mediation is responsible for the fact that the thermodynamically favorable (√2x√2)R45º structure [Warschkow et al., Surf.Sci. 573, 446 (2004)] has never been detected while other reconstructions of identical stoichiometry and significantly higher surface energy, such as the 2x1, have been readily observed. In the latter, the adsorption of water is much more favorable, which insinuates that the formation of the (√2x√2)R45º reconstruction is kinetically limited if there is any exposure to water vapor. Several experimental results back up this observation.