Electronic structure of stoichiometric and reduced Ta2O5 surfaces determined by resonant photoemission -: art. no. 075420

The electronic properties of stoichiometric and reduced Ta2O5 thin films have been studied with resonant photoemission using synchrotron radiation. It was found that Ar+ bombardment induces electronic states in the band gap region and an attenuation of the overall valence band. These changes are associated with the formation of oxygen vacancies during the reduction of the surface by Ar+ bombardment. For both stoichiometric and Ar+-bombarded Ta2O5 films, resonant photoemission from the valence band was observed when the photon energy was in the neighborhood of the Ta 5p-->5d, 5p-->6sp, and 4f-->5d transition energies. The constant initial-state curves show multiple resonance maxima that are explained in terms of the Ta 5p-->5d, 5p-->6sp, and 4f-->5d photoabsorption mechanisms, the spin-orbit splitting of the Ta 5p and Ta 4f core levels, and the splitting of the Ta 5d final states by crystal-field interactions. Contrarily to 3d and 4d transition metals no differences have been found in the resonance behavior of the valence-band features lying in the similar to4-10-eV range. This is attributed to the more extended nature of Ta 5d and 6sp orbitals with respect to 3d and 4d cationic orbitals.