Figure 4

XPS characterisation illustrating the Nb 3d, Al 2p core levels for Al₂O₃ capped Nb (a) unannealed, annealed at (b) 300 °C and (c) 600 °C and (d) the Nb 3d and Mg 2 s core levels for MgO capped Nb. The carbonate peak observed at roughly 90 eV can be explained simply by atmospheric contaminants. All Nb films are 30 nm thick. The binding energies for all elements and compounds seen within this figure are corroborated by those ascertained in previous works ^{50,51,52,53,54,55,56,57,58}.