Electron spin resonance in electron irradiated diamond annealed to high temperatures

The E.S.R. spectrum of an electron irradiated, type IIa diamond has been studied after it had been annealed at various temperatures up to 1400°C. Six sets of lines were identified following anneals in the temperature range 700°C–1000°C. They all arose from centres with ⟨110⟩ symmetry and a spin of 1. The centres are thought to be formed by the trapping of mobile vacancies at impurities to give chains of vacancies of various lengths in the ⟨110⟩ dircctions of the {110} planes. Two further spectra were observed after the 1100°C anneal. At least one of the centres has a spin of 3/2 and it seems likely that they were formed by some of the existing vacancy chains trapping an additional electron. Following the anneal at 1400°C, apart from an isotropic line with a g-value within 0.2% of the free-spin value, the only structure arose from centres with ⟨111⟩ symmetry. At this temperature the vacancies may break away from the impurity traps and condense in rings on the {111} planes.