Structural analysis of oxygen segregated Nb(110) surface by photoelectron diffraction

The atomic structure of the Nb(110) surface with oxygen segregated from bulk by annealing at 1500 K in UHV has been analyzed by electron and photoelectron diffraction techniques. The observed LEED patterns indicate the modulation of topmost Nb layer in [1 (1) over bar0] direction. Relation of unit cells of substrate and overlayer was determined. The surface component in the Nb 3d photoelectron spectra has a chemical shift of 1.6 eV corresponding to that of NbO. The thickness of Nb oxide overlayer is estimated to be about one or two atomic layers. The Nb 3d spectra collected at 4945 different directions are fitted with bulk and surface components. Photoelectron diffraction patterns from Nb atoms within overlayer as well as bulk are successfully extracted. Topmost oxygen atoms are found to be located at about 1.2 angstrom above the Nb plane.