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

Abstract

Methods of X-ray photoelectron spectroscopy and diffraction were used to investigate the oxygen-induced surface structures on the Nb(110) face which were formed as a result of oxygen segregation from the volume of the crystal upon thermal annealing at 2000 K in a vacuum and/or oxygen adsorption in situ at temperatures higher than 1100 K. The niobium atoms on the crystal surface form quasi-ordered structures in the form of monatomic Nb chains surrounded by oxygen atoms and from the viewpoint of the nearest surroundings and chemical bonding they are close to the states of the metal in NbO x . The thickness of such NbO x -like structure is estimated as 0.5 nm at the degree of coverage of the surface of 50%. Two chemically nonequivalent states of oxygen at Nb(110) have been distinguished, supposedly, (1) atomic chemisorbed oxygen on the surface of Nb metal and (2) oxygen in the composition of NbO x -like clusters on the Nb(110) plane. The NbO x /Nb(110) model of the surface allows for the distortion of the structure of NbO x clusters, i.e., periodic atomic displacements of metal atoms in Nb chains by height and changes in the Nb-O bond angles.