Very high atomic oxygen coverages on Ru(001)

Abstract

Very high oxygen coverages−up to θO ≊ 40 (forty)−were obtained by dissociative adsorption of NO2 on Ru(001) at elevated temperatures. O2 desorption data show three desorption peaks at ≊1100, ≊1000, and ≊900 K, and suggest strong oxygen–oxygen repulsions in the overlayer. An Arrhenius plot of the leading edge desorption rates of the 900 K peak yields EA = 53 kcal/mol, implying zero-order desorption kinetics. O2 is the only desorption product for θO< 3; additional RuO+x (x=0–3) species were detected at higher coverages. However, neither the O 1s and Ru 3d core levels, nor the valence band spectra showed any evidence for chemical changes, i.e., an oxide formation. The process of an underlayer formation as a distinct stage in the oxidation of the Ru metal will be discussed in terms of a model for subsurface penetration of O on transition metals.