Surface Characterization of NbO Islands Formed on Nb(100) by X-Ray Photoelectron Diffraction

An ordered thin film of niobium oxide (NbO) was formed on the Nb(100) surface by heating the niobium single crystal at 1023 K for 2 min under an oxygen atmosphere. The surface composition was analyzed by X-ray photoelectron spectroscopy (XPS), and the surface structure was characterized by low energy electron diffraction (LEED) and X-ray photoelectron diffraction (XPD) generated by synchrotron radiation. Annealing at 1223 K in ultra-high vacuum yielded a reconstructed (3 x 1) LEED pattern. XPS measurements indicated that the surface comprised of metallic and oxidized niobium species. The comparison between experimental and theoretical XPD results indicated that 60% of the Nb(100) surface was covered by two-layered nanoislands of NbO, and 40% had bare patches.