Nitric oxide adsorption on Nb(1 1 0) surface

We have studied nitric oxide (NO) adsorption and dissociation on the Nb(1 1 0) surface by means of density-functional theory and total-energy calculations. The top adsorption sites on the Nb(1 1 0) surface are found to be energetically the most favorable at the p(1 × 1) surface periodicity, which is in line with experiments investigated by high-resolution electron energy-loss spectroscopy (HREELS). On the Nb(1 1 0) surface, NO prefers to adsorb in top sites uprightly. With decreasing the coverage NO gradually tilts in hollow sites. At lower coverage (∼0.25 ML), the tilted hollow site has been determined to be the preferred adsorption site from total-energy comparison. We have found that NO is easy to dissociate on the Nb(1 1 0) surface. Four typical dissociation pathways with oxygen atoms of NO dissociated to bridge and top sites are discussed. The further analysis based on electronic states reveal that at 0.25 ML the essential interaction between a NO monomer and metal substrate is the hybridization of NO 5σ, 2π*-orbital and the d-bands of surface niobium atoms for p(2 × 2) surface.