Structural analysis of NbC(111)-O and NbC(111)-D surfaces

The structures of oxygen-adsorbed and deuterium-adsorbed NbC(111) surfaces have been studied by impact-collision ion-scattering spectroscopy (ICISS), reflection high-energy electron diffraction (RHEED) and by computer simulation. At room temperature, both oxygen and deuterium are dissociatively adsorbed on the clean surface without long-range order, and an adsorbate atom goes into the threefold hollow site. The saturation coverage is more than 0.9 ML (monolayer) in both cases. The height of an adsorbate from the first layer is 1.10 Angstrom for oxygen and 1.00 Angstrom for deuterium, which corresponds to 2.13 Angstrom for the O-Nb distance and 2.08 Angstrom for the D-Nb distance. The O-Nb distance a little larger than the sum of the covalent radii (2.00 Angstrom) and the D-Nb distance is much larger than the sum of the covalent radii (1.64 Angstrom). Judging from the bond length and electronegativity, O and D atoms are supposed to have some negative charge.