First-Principles Study on the Initial Oxidization of a Nb(100) Surface

The initial oxidization of a Nb(100) surface is investigated using a first-principles method based on the density functional theory. Our theoretical results indicate that the symmetry of the Nb(100) surface is changed with the adsorption of O atoms. The p(2 X 2)-O-0.50 and p(2 X 2)-O-1.00 are stable for the on-surface adsorption at the O coverages of 0.50 and 1.00 monolayer (ML), respectively. The (4 X 1)-O and (3 X 1)-O are stable for the multilayer adsorption at the O coverages of 1.75 and 2.00 ML, respectively, which, according to the work function and local atomic structure, are the NbO(100) precursors formed on the Nb(100) surface. In addition, the thermodynamic analysis reveals that the NbO oxide is stable in a vacuum [e.g., log(P-O2/P-O) = -18] at high temperature (e.g., T > 1200 K), in agreement with the formation of NbO precursors on a Nb(100) surface.