XPS study of NbN and (NbTi)N superconducting coatings

The chemical composition of the various compounds present in the surface region of NbN and (NbTi)N coatings is studied by X-ray photoelectron spectroscopy. The high in-depth resolution of this technique enables one to investigate the spacial distribution of various phases within the surface layer, by varying the take-off angle of photoelectrons. Nb2O5 oxide covers the surface of the NbN coating, while an intermediate oxynitride compound is localized between Nb2O5 and NbN bulk. TiO2 bonds are present in the outer part of the surface layer of (NbTi)N coatings. The unique intermediate oxynitride phase which is present on NbN is split into two different oxynitride energies on (NbTi)N. In both coatings, oxynitride bonds are not found throughout the bulk, although it contains 0.7% oxygen atoms as impurity.