ADSORPTION OF HALOGEN-CONTAINING METHANE ON DIAMOND

The adsorption of methane and different halogen-containing methanes to hydrogen-and halogen-terminated diamond (111) surfaces, respectively, has been investigated by using a cluster approach and two different q uantum mechanical methods. The halogens used were F, Cl and Br. The th eoretical methods used in these calculations were the ab-initio molecu lar-orbital method and the local-density-approximation (LDA) method. O nly minor differences in calculated adsorption energies were observed by using the different quantum mechanical methods. The calculated adso rption energy of CF3 to a H-terminated diamond (111) surface was found to be numerically the largest one in comparison with the other adsorp tion processes studied in the present investigation, and in particular much larger than the corresponding adsorption energy of CH3. The calc ulated adsorption energies of CClH2 and CBrH2, respectively, to a H-te rminated surface, were found to be numerically the largest adsorption energies in their respective halogen-containing group of methanes. The latter were also numerically very similar to the corresponding adsorp tion energy of CH3. These calculated adsorption energies support a dia mond growth process in systems incorporating both hydrogen and halogen s in the growth vapour, to be at least as fast as a corresponding grow th process based only on CH3 species as the dominant growth species. ( C) 1998 Elsevier Science S.A.