EELS of Niobium and Stoichiometric Niobium-Oxide Phases-Part I: Plasmon and Near-Edges Fine Structure

A comprehensive electron energy-loss spectroscopy Study of niobium (Nb) and stable Nb-oxide phases (NbO, NbO(2), Nb(2)O(5)) was carried out. In this work (Part 1), the plasmons and energy-loss near-edge structures (ELNES) of all relevant Nb edges (Nb-N(2,3), Nb-M(4,5), Nb-M(2,3), Nb-M(1), and Nb-L(2,3)) up to energy losses of about 2600 eV and the O-K edge are analyzed with respect to achieving characteristic fingerprints of Nb in different formal oxidation states (0 for metallic Nb, +2 for NbO, +4 for NbO(2), and +5 for Nb(2)O(5)). Chemical shifts of the Nb-N(2,3), Nb-M(4,5), Nb-M(2,3), and Nb-L(2,3) edges are extracted from the spectra that amount to about 4 eV as the oxidation state increases from 0 for Nb to +5 for Nb(2)O(5). Four different microscopes, including a 200 keV ZEISS Libra with monochromator, were used. The corresponding wide range of experimental parameters with respect to the primary electron energy, convergence, and collection semiangles as well as energy resolution allows an assessment of the influence of the experimental setup on the ELNES of the different edges. Finally, the intensity of the Nb-L(2,3) white-line edges is correlated with niobium 4d-state occupancy in the different reference materials.