Surface-defect-mediated channel for oxygen incorporation into Ru(0001)

The capacity of intentionally created defects to act as possible channels for oxygen incorporation into the subsurface region has been studied by means of thermal desorption spectroscopy and ultraviolet photoelectron spectroscopy (21.2 eV). Thermal-energy atom scattering has been applied to determine the overall surface roughness as achieved by exposing the surface to a flux of low-energy Ar+ ions. Within a wide range of experimental conditions the low-temperature (T less than or equal to 600 K) and high-pressure (p approximate to 1 bar) oxidation regime applied here does not lead to a significant formation of bulk oxides. Instead two competing channels for oxygen incorporation into the subsurface region have been identified. The first path proceeds via the penetration of the oxygen monolayer adsorbed on top of the defect-free surface areas. The second path is defect-mediated and exhibits a maximum capacity of about 10 oxygen atoms per defect. This reaction channel is thermally activated with an apparent activation energy of 0.15 eV, which is nearly 3 times lower than the activation energy corresponding to the growth of oxide domains.