The structure of a stoichiometric TiO2 nanophase on Pt(111)

The structure of a rectangular TiO2 nanophase grown epitaxially on a Pt(111) substrate has been investigated by a combined experimental-theoretical approach. It is found that such nanophase is stoichiometric, incommensurate to the substrate and has the structure of a lepidocrocite layer. The film is weakly bound to the metal surface via the O atoms of the oxide layer and consequently it does not have a fully wetting behavior. Two almost iso-energetic structures have been found based on first principles DFT calculations, one characterized by a short and one by a long interface distance, this latter being energetically slightly preferred. However, when the strain due to lattice mismatch is accommodated on the Pt(111) substrate instead of the TiO2 film, only the long interface structure is found. The analysis of measured and computed valence band spectra and STM images supports the long interface, weakly interacting model.