Annealing of vacancies and interstitials in diamond

Optical absorption (OA) and electron spin resonance measurements have been performed on IIa, Ib, IaA and IaB type diamonds irradiated by 3 MeV electrons. OA reveals that the GR1 system in diamond is usually accompanied by an underlying broad background band, which is tentatively attributed to strained neutral vacancies (V deg. ). The photochromic changes in OA suggest that the concentration calibration constants for the V deg. , H3 and H4 defects should be halved, that the 3H and 5RL centres could be different charge states of a di-interstitial related defect and that the di-interstitial R1, 3H and 5RL centres in diamond are stable to annealing temperatures up to at least 800 deg. C. The generation and annealing of interstitials and vacancies have been studied as a function of the nitrogen concentration and aggregation state. The results suggest that single substitutional nitrogen (NS) efficiently traps carbon interstitials, but releases them upon annealing at 400 deg. C. Defects related to nitrogen aggregation in IaB diamond also trap interstitials, but do not release them upon annealing. Carbon interstitials are not trapped by NS-NS pairs. Instead, an increase in the concentration of NS-NS centres enhances the production rates of vacancies and interstitials, reduces their annealing temperatures and favours formation of the 3H over R1 di-interstitials