To explain the nitrogen low rate in CVD CNx layers, and their amorphisation, a release of gaseous species containing N was proposed. Previous modelling studies based on local density functional theory use pyrite type CN2 as starting model to assess the release of molecular nitrogen. This model is completed here to investigate another mechanism of release of cyanogen as another gaseous species. The theoretical pyrite-like C2N wherein C and N atoms form dumbbells in octahedral sites of a carbon face-centred sub-lattice is proposed as likely to model it. It demonstrates a good compressibility (B0 = 272 GPa) and a mechanical instability, which supports both release of atoms and the amorphisation of layers. However, the variation of interatomic distances under strain leads to propose the formation of a radical species radical dotC6-point triple bond; length half of m-dashN. This is enforced by the consideration of the chemical bonding and its evolution in the model with the ECOV and ELF functions. The release of nitrogen in molecular cyanogen is consequently substituted by a mechanism which implies a radical dotC6-point triple bond; length half of m-dashN radical species, which is likely to recombinate at the CVD layers surfaces.
A model study for the breaking of cyanogen out of CNx within DFT