Subsurface formation of oxygen on a Ru(0001) surface

The formation of subsurface oxygen on a clean and sputtered Ru(0001) surface is studied using thermal desorption spectroscopy (TDS) and low energy electron diffraction (LEED). The oxygen was incorporated by exposing the surface to a partial oxygen pressure in the range of 10(-8)-10(-9) Torr. By monitoring the signal of recombinatively desorbed molecular oxygen as a function of sample temperature, we found that oxygen molecules penetrated into the subsurface region after saturating the adsorbed layer characterized by the p(2 x 2) LEED pattern indicative of 0.25 monolayers (1 ML = 1.58 x 10(15) cm(-2)). In contrast, the defects generated by Ar+ sputtering on the Ru surface appear at thermally more stable sites in high-temperature O-2 thermal desorption states.