Photoemission study of the electronic structure of stoichiometric and substoichiometric TiN and ZrN

Abstract

The electronic structure of stoichiometric and substoichiometric titanium nitride (TiN) and zirconium nitride (ZrN) have been studied with ultraviolet and x-ray photoelectron spectroscopy. The valence-band spectrum of stoichiometric TiN is compared with calculations of the density of states. Peak positions and widths agree quite well, whereas photon-energy-dependent intensity variations do not seem to follow the trends expected from the atomic photoionization cross sections. The more tightly bound metal core lines are shifted to higher binding energies by about 1.4 eV in the compounds compared to those in the pure metals. In contrast to earlier investigations of similar compounds, no difference in the binding energies of the metal core lines could be detected as a function of stoichiometry. Discrepancies were found between the experimental results and a coherent-potential-approximation calculation of the effects of substoichiometry in TiN. Neither the strong increase of states at the Fermi level nor the predicted shift of the valence-band peak could be detected. An extra peak around 2-eV binding energy was found in the substoichiometric TiN and ZrN samples and assigned to an occupied defect state. For $\mathrm{Ti}{\mathrm{N}}_{1\ensuremath{-}x}$ the peak intensity is comparable to that of the peak at the Fermi level, whereas for $\mathrm{Zr}{\mathrm{N}}_{1\ensuremath{-}x}$ this peak is broader and less pronounced.