Potassium-promoted oxidation of β-SiC

An investigation of potassium-promoted oxidation of β-SiC has been performed by means of x-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, and the work-function change measured from the shift of the slow secondary-electron cutoff in the ultraviolet photoemission, for different potassium coverages and substrate temperatures. It is shown that there exist saturations for both K- and Si-bonded oxygen after sufficient oxygen doses at room temperature no matter what the coverage of the alkali metal, while there exists a saturation only for the K-bonded oxygen even after a much higher exposure at the elevated temperature of 500 K than that required for the saturation at RT; the oxygen bonded to the catalyst is in the state of ${\mathrm{O}}_2^{2\mathrm{-}}$ at room temperature, and it converts to ${\mathrm{O}}^{2\mathrm{-}}$ ion at 500 K; the existence of silicon suboxides ${\mathrm{SiO}}_x$ $\mathrm{}(x<\mathrm{}2\mathrm{})\mathrm{}$ is proved for substrate temperatures lower than 500 K, and they convert to ${\mathrm{SiO}}_2$ at 700 K in an oxygen diffusion-controlled way.