An annealing study of the R1 EPR centre (the nearest-neighbour di-< 100 >-split self-interstitial) in diamond

Results are reported of both isochronal and isothermal annealing studies of the R1 EPR centre (known to be a pair of parallel nearest-neighbouring [10 0]-split self-interstitials) produced by 2 MeV electron irradiation of synt hetic type IIa diamonds of very low defect concentration before irradiation . The annealing out of R1 is not associated with any overall change in the concentration of isolated vacancies or interstitials. The isothermal decay corresponds to a first-order process with a rate constant conforming to an Arrhenius relationship with activation energy 0.6(1) eV and an unusually lo w attempt frequency. That the activation energy is much lower than the migr ation energy of isolated interstitials (1.68(15) eV) is taken to indicate t hat it corresponds to a combination of the energy required to excite Ri int o an S = 0 state and that required to translate one of the split interstiti als over the potential barrier into the next lattice site. This process may be linked to an associated rise in the concentration of the 3H (2.462 eV) optical defect; but the precise relationship between the diamagnetic site f ormed by the decay of R1 and the 3H optical centre is not revealed by this study.