Synchrotron radiation studies of the formation of niobium carbide layers on niobium

The formation of a NbC overlayer on Nb has been observed with the use of valence-band photoemission, near-edge absorption at the C K edge, and photon- and electron-stimulated Auger decay. The sample was produced by depositing an amorphous C layer on a Nb substrate either by dc glow discharge in a hydrocarbon ambient or by sputtering from a graphite target. Annealing this film first produced a previously reported graphitic phase and finally the carbide. Features in the spectra agreed well with bulk NbC density-of-states features. The results are also related to those obtained in electron-stimulated Auger measurements of carbidic and graphitic layers on catalytic surfaces, and show some agreement with calculations by Feibelman for such surface layers. Comparison of the photoemission measurements with Auger results for variously prepared samples showed a greater sensitivity of the former to details of the electronic structure.