Electronic structure of titania-based nanotubes investigated by EELS spectroscopy

We present an electron-energy-loss spectroscopy study of the O-K and Ti L_2,3 edges for anatase-, rutile-, and titania-based nanotubes. The titania-based tubes are composed of tetravalent titanium ions in an octahedral symmetry with the oxygen ligands, however the electronic structure does not correspond to that of either of the titania precursors. Crystal-field splitting is comparable with anatase but the 3d occupation number is closer to that of rutile. In addition, Ti L_2,3 spectroscopic signatures indicate that the octahedron connectivity of the tubes is different to that of the reference titania. We also report the first measurement at the scale of an individual nanometrical object of the charge-transfer satellites for the transition metal 2p edges. This may open new opportunities for the estimation of d-orbital occupation numbers for transition-metal or rare-earth elements occurring in local grains, phase-segregated regions, nanomaterials, or in the vicinity of interfaces.