Effect of co-adsorbed dopants on initial diamond growth steps: H abstraction from an adsorbed CH3

The effect induced by a neighbouring co-adsorbed dopant on H abstraction from an adsorbed CH₃ species on diamond has been investigated by using an ultra-soft pseudo-potential density functional theory (DFT) method under periodic boundary conditions. Both the (100) and (111) diamond surface orientations were considered with various types of dopants in two different hydrogenated forms; AH_x (A = N, B, S, or P; X = 0 or 1 for S; X = 1 or 2 for N, B and P, and X = 2 or 3 for C). The H abstraction by gaseous radical H was found to be energetically favoured by the presence of the dopants in all of their different hydrogenated forms. For NH₂, SH, or PH₂, this effect is induced by a destabilisation of the diamond surface by sterical repulsions between the adsorbed growth species CH₃ and the co-adsorbed dopant. For BH₂ and the dopants in their radical form, the abstraction reaction is favoured due to the formation of a new covalent bond between the dopant and the co-adsorbed CH₂ (product of the abstraction reaction), which strongly stabilises the surface after the abstraction process.