Effect of substitutional N on the diamond CVD growth process: A theoretical approach

For both (111) and (100) diamond surface orientations, one C atom within the first or second surface carbon layer has substitutionally been replaced by an N atom. The effects of this impurity on CH3 adsorption and H abstraction from a newly adsorbed CH3 have been carefully investigated by using ultra-soft pseudo-potential density functional theory (DFT) under periodic boundary conditions. The effects of N at various positions within the two atomic layers were especially studied. It was generally found that nitrogen in the first atomic layer will never affect the initial growth reactions. An exception exist for the dopant in one of the three studied positions within the (100) surface, where a β-scission rearrangement is observed. When N is positioned within the second carbon layer for both surface orientations with all surface carbons H-terminated (i.e. no surface radicals), nitrogen is moving off-site and one of the N–C bonds is thereby broken. On the other hand, when a radical is present on the surface (formed by the abstraction of one surface H), N move back on-site and one electron is transferred from N to the surface C radical with a resulting electron lone pair formation. When CH2 is bonded to the surface as a result of gaseous H abstraction from the adsorbed CH3 species and with N directly bonded to the surface carbon onto which CH3 is initially adsorbed, a β-scission rearrangement is also observed.