Oxidation of Nb as studied by the uv-photoemission technique

The initial stages in the oxidation of Nb have been studied by the uv-photoemission technique for photon energies below 12 eV. Changes of structure in the electron distribution curves for different oxygen exposures and temperatures are correlated with formation of different types of Nb oxides. Electronic structure changes due to formation of at least three different oxides or mixtures of oxide have been observed. NbO2 and the NbO oxides seem to form first as a thin protective layer. The pentoxide, Nb2O5, is obtained after heavy oxidation. Practical implications of the formation of NbO in the interface between Nb2O5 and Nb metal are discussed.