Oxidation of carbon on (100)W and (100)Mo

Abstract

The interaction of carbon and oxygen on the (100) planes of W and Mo has been examined by Auger electron spectroscopy and flash desorption mass spectrometry. When surfaces containing up to one monolayer of carbon are exposed to oxygen at ∼ 10−8 torr at substrate temperatures of 1000 to 1300 °K, rapid removal of carbon is observed. This is described well by assuming that every adsorbed oxygen atom desorbs as a CO molecule as long as the temperature is high enough for evaporation of CO. Binding states of CO on clean and carbon covered surfaces and the diffusion of carbon to the surfaces are also examined. It is shown that the desorption properties of adsorbed oxygen and carbon are essentially identical to those of adsorbed carbon monoxide, and it is suggested that CO in the tightly bound states on these metals may be dissociatively adsorbed. Desorption as CO will occur if both bulk solution and desorption of one of the species are slow at temperatures up to the desorption temperature. This is found to be true on W but less so on Mo.