Oxidation of clean and H-terminated SiC surfaces

The oxygen uptake on H-terminated and on differently reconstructed, clean 3C-SiC(001) and 6H-SiC0001 surfaces was investigated by X-ray photoelectron spectroscopy (XPS). The samples were cleaned in ultrahigh vacuum (UHV) by heating them in the presence of a Si flux at different temperatures. H-terminated surfaces were prepared by exposure to hydrogen atoms in the UHV-system. Atomic hydrogen was produced by thermal dissociation of H2-molecules at a tungsten filament heated to 2200 K. Clean and H-terminated surfaces were exposed to research grade oxygen in the range of 1013–1028 O2-molecules cm−2. During exposures any excitations of the surface or the gas were avoided. The uptake of oxygen on clean surfaces proceeds in two subsequent steps. We attribute the first one to dissociative chemisorption which saturates at about one monolayer. The second process follows an inverse-logarithmic growth law and we describe it by field-assisted oxidation, i.e. the Mott-Cabrera mechanism. On H-terminated surfaces, the initial sticking coefficient is reduced by a factor of approximately 1010.