Free radical reactions at the Ru(0Â 0Â 0Â 1) surface: Atomic oxygen and dissociated NH3

X-ray photoelectron spectroscopy was used to study the effect of atomic oxygen on Ru(0 0 0 1), and the effect of dissociated ammonia on RuO2/Ru(0 0 0 1), in UHV conditions at ambient temperature. The Ru(0 0 0 1) surface was exposed, at ambient temperature, to a mixed flux of atomic and molecular oxygen generated by dissociation of O2 in a thermal catalytic cracker, with ∼45% dissociation efficiency. The detailed study of the XPS spectra shows the formation of a disordered multilayer oxide (RuO2). No formation of higher oxides of Ru was observed. The formation of RuO2 proceeded without saturation for total oxygen exposures of up to 105 Langmuir, at which point an average oxide thickness of 68 Å was observed. RuO2 formed by the reaction with atomic oxygen was exposed to a flux of NHx (x = 1, 2) + H generated by the cracker. The reduction of RuO2 to Ru metal was observed by XPS. An exposure of 3.6 × 102 L of NHx + H, resulted in the observation of adsorbed H2O and OH, but no evidence of lattice oxide. The chemisorbed species were removed by additional NHx + H exposure. No nitrogen adsorption was observed.