INTERACTION OF HYDROGEN WITH CHEMICAL-VAPOR-DEPOSITION DIAMOND SURFACES - A THERMAL-DESORPTION STUDY

The interaction of hydrogen with a chemical vapor deposition (CVD) dep osited polycrystalline film on Si(100), cleaned by heating to 1500 K, has been examined. No adsorption is observed unless prior activation w ith a hot filament is carried out. However atomic H thereby created is found to adsorb with a high sticking probability, subsequently desorb ing in the temperature range 1100-1225 K. Etching of the diamond surfa ce, producing gaseous methane and ethane is also seen. The reactivity patterns are rather similar to-those observed on C(100) and C(111) sur faces, suggesting these are suitable model substrates for the study of reaction mechanisms associated with CVD diamond growth. However, a ma jor difference is also seen in that a mixture of hydrogen, silane, and disilane, with other minority species, is seen to evolve from the sur face of the CVD diamond film at 1275 K when exposed to the reacting ga s and is not detected from single-crystal diamond surfaces. The result s indicate that this arises from the selective etching of Si present a t grain boundaries in the deposited films.