POTASSIUM-PROMOTED OXIDATION OF BETA-SIC

An investigation of potassium-promoted oxidation of beta-SiC has been performed by means of x-ray photoelectron spectroscopy, ultraviolet ph otoelectron spectroscopy, and the work-function change measured from t he shift of the slow secondary-electron cutoff in the ultraviolet phot oemission, for different potassium coverages and substrate temperature s. It is shown that there exist saturations for both K-and Si-bonded o xygen after sufficient oxygen doses at room temperature no matter what the coverage of the alkali metal, while there exists a saturation onl y for the K-bonded oxygen even after a much higher exposure at the ele vated temperature of 500 K than that required for the saturation at RT ; the oxygen bonded to the catalyst is in the state of O-2(2-) at room temperature, and it converts to O2- ion at 500 K; the existence of si licon suboxides SiOx (x<2) is proved for substrate temperatures lower than 500 K, and they convert to SiO2 at 700 K in an oxygen diffusion-c ontrolled way.