THERMAL EFFECT ON K-PROMOTED OXIDATION OF BETA-SIC

Thermal effect on potassium-promoted oxidation of beta-SiC has been in vestigated by means of X-ray photoelectron spectroscopy (XPS), ultravi olet photoelectron spectroscopy (UPS) and the work function measuremen t from the shift of the slow secondary electron cut-off in the ultravi olet photoemission for different potassium coverage and substrate temp erature. It is found that the substrate temperature influences the ads orption kinetics of oxygen on the alkali metal atoms and Si in the sub strate; an elevated substrate temperature can promote the oxygen trans ferring from the catalyst to Si and penetrating into he substrate; the K-bonded oxygen is in the state of O-2(2-) at room temperature, and i n the state of O2- at 500 K; a SiO2 layer only forms from silicon subo xide after the sample was annealed at 700 K, The experimental result s hows that a proper selection of temperature is even more important to the promoted oxidation than the amount of the promoter does in the pre sent case. (C) 1998 Elsevier Science B.V. All rights reserved.