It was recalled that, although vacancies and their complexes were well-understood, interstitials were much less studied; although theoretical modelling studies had assisted in the identification of relevant structures and processes. The N interstitial had been established to have a buckled bond-centered structure, with the splitting of local modes due to isotope substitution being observed. It had a metastable structure that was more stable in the negative charge state; which helped to explain some anomalous annealing results. The various models for the self-interstitial concurred that it had a (001) split structure. However, it was difficult here to identify the experimental data with the defect. A brief review of the experimental data, together with the theoretical models, led to the conclusion that the R2 centre, as detected by means of electron paramagnetic resonance, could be derived from the split interstitial. The 5RL optical centre and the 1570/cm infra-red absorption had vibrational modes which had similar energies to those of the split interstitial. However, a high annealing temperature implied that the interstitial was trapped in these centres.

Modelling of Interstitial-Related Defects in Diamond. A.Mainwood: Diamond and Related Materials, 1999, 8[8-9], 1560-4