Electronic interaction at the TiO2–Al2O3 interface as observed by X-ray absorption spectroscopy

The electronic structure of the TiO2–Al2O3 interface has been studied using X-ray absorption spectroscopy. Special attention has been paid to the early stages of growth, i.e. the sub-monolayer regime (θ<1). The Ti 2p spectra for coverages below 1 ML show significant changes with respect to those for large coverages and bulk TiO2 indicating the presence of interfacial states. The spectra have been compared with atomic multiplet calculations reported in the literature. From this comparison it is concluded that strong electronic interactions occur at the interface, as deduced from the significant lowering of the crystal field of the Ti atoms at the interface (1.0 eV) as compared with bulk TiO2 (1.8 eV). It is suggested that the important covalent character of the bonding of the Al2O3 substrate is the responsible of this crystal field lowering.