The importance of molecular nitrogen within the chemical vapour deposition (CVD) growth process of diamond has been frequently reported since 1994, when Locher et al. observed it for the first time.1 It is well known that a few ppm of nitrogen will promote the (100) surface orientation, and the increase of growth rate. Theoretical and experimental studies have been focused on this subject, but the effect is still not fully understood.2
The aim with the present study has been to study carefully the effect induced by the presence of substituting nitrogen in the diamond bulk on the CH3 adsorption and on the H abstraction reactions for both (111) and
(100) surface orientations. The main goal is to get a deeper knowledge in the possibility for nitrogen to largely affect the diamond CVD growth process. The investigation is based on an ultrasoft pseudopotential density functional theory (DFT) method, using generalized gradient approximation (GGA) under periodic boundary conditions.
To perform this study, a carbon atom is replaced by N in the first or in the second carbon layer, on both the (100) and (111) diamond surface orientations. Moreover, for each layers, the nitrogen is positioned in two different places: next to the reaction site or with carbon atoms separating N and the reactive surface carbon.
As result, the calculations show clearly that when N is positioned in the second carbon layer the CH3 adsorption is disfavoured, and the H abstraction, by using gaseous H, species is favoured. On the other hand, when nitrogen is present in the first carbon layer, it appears that the H abstraction is slightly favoured on the (100) surface orientation but not on the (111) surface and the presence of N does not affect significantly the CH3 adsorption energy.