Thermal effect on K-promoted oxidation of β-SiC

Thermal effect on potassium-promoted oxidation of β-SiC has been investigated by means of X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS) and the work function measurement from the shift of the slow secondary electron cut-off in the ultraviolet photoemission for different potassium coverage and substrate temperature. It is found that the substrate temperature influences the adsorption kinetics of oxygen on the alkali metal atoms and Si in the substrate; an elevated substrate temperature can promote the oxygen transferring from the catalyst to Si and penetrating into the substrate; the K-bonded oxygen is in the state of O22− at room temperature, and in the state of O2− at 500 K; a SiO2 layer only forms from silicon suboxide after the sample was annealed at 700 K. The experimental result shows that a proper selection of temperature is even more important to the promoted oxidation than the amount of the promoter does in the present case.