PHOTOELECTRON SPECTROSCOPY AND DIFFRACTION OF SURFACE NANOSCALE NbO/Nb(110) STRUCTURES
M. V. Kuznetsov, A. S. Razinkin, E. V. Shalaeva
Keywords: XPS, XPD, STM, surface, niobium, niobium oxide, surface structures
Pages: 536-543
Abstract
X-ray photoelectron spectroscopy and diffraction (XPS and XPD) are applied to analyze oxygen-induced surface structures on the Nb(110) face formed due to oxygen segregation from the crystal bulk on thermal annealing to 2000 K in vacuum and/or oxygen adsorption in situ at temperatures above 1100 K. The Nb3d, O1s electronic states and valence band spectra of the NbOx/Nb(110) surface are studied by XPS, and the results are compared with data for NbO, NbO2, and Nb2O5 oxides. It is shown that niobium atoms entering the composition of surface oxide structures on Nb(110), from the standpoint of the nearest environment and chemical bond, are similar to metal states in NbO. The NbOx layer thickness is estimated to be 0.5 nm. Two chemically inequivalent oxygen states are distinguished on Nb(110), which are, presumably, atomic chemisorbed oxygen on the parts of the clean surface of the Nb monolayer with hexagonal packing and oxygen in the composition of NbOx-like linear clusters on Nb(110). A model of the NbOx/Nb(110) surface takes into account a distortion of the structure of NbOx clusters: a periodic vertical shift of metal atoms in Nb-chains and changes in Nb-O bond angles.
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