Photoelectron spectroscopy and diffraction of surface nanoscale NbO/Nb(110) structures

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 NbO _x /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 NbO _x 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 NbO _x -like linear clusters on Nb(110). A model of the NbO _x /Nb(110) surface takes into account a distortion of the structure of NbO _x clusters: a periodic vertical shift of metal atoms in Nb-chains and changes in Nb-O bond angles. Original Russian Text Copyright ? 2009 by M. V. Kuznetsov, A. S. Razinkin, and E. V. Shalaeva __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 50, No. 3, pp. 536–543, May–June, 2009.