A COMPARATIVE-STUDY OF THE ADSORPTION OF HOT-FILAMENT ACTIVATED HYDROCARBONS ON SILICON, GALLIUM-ARSENIDE AND CVD DIAMOND

Adsorption studies of hot filament activated methane and methane-hydrogen mixtures on non-diamond and diamond surfaces reveal considerable differences in both the nature of the species formed on the surface and the subsequent surface lifetimes of these forms. the case of GaAs(100), no evidence is seen either for adsorption of the species believed to be present in the activated gas mix (such as C1 and C2 hydrocarbons) in an unreacted form or for thermal decomposition of the adlayer into carbon. On Si(100), adsorption of C1 and C2 hydrocarbons is observed, but the thermal dehydrogenation of these forms to give carbon competes with the thermal desorption and polymerization giving volatile species. In contrast, the available data for crystalline and chemically vapour deposited diamond surfaces suggests that the hydrocarbons which adsorb undergo complete thermal dehydrogenation to give surface carbon. These differences are discussed and kinetic parameters are calculated for the processes observed.