E.S.R. in diamond electron-irradiated at low temperature

Abstract

The effect of an electron irradiation near helium temperature on the E.S.R. spectrum of type IIa diamond has been measured. The unirradiated stones showed a small isotropic line with a g value within 0·2% of the free-spin value. It is known as the ‘a’ line. Marked changes in the intensity of the ‘a’ line occurred during exposure to light and ionizing radiation and during annealing. They can be attributed to charge redistribution. Careful control of the experimental conditions was therefore necessary to establish the intrinsic effect of the low-temperature irradiation.

The size of the ‘a’ line remained unchanged during the irradiation at 17 K for doses up to 10¹⁷ electrons/cm². On annealing the diamond to 80 K the line was enhanced. It decreased to its pre-irradiation value on annealing to 300 K. Structure was observed at about 60 gauss either side of the ‘a’ line. In one case it was seen during the irradiation at 17 K and appeared to grow linearly with dose. In another case it was only observed after it had been enhanced by an anneal to 80 K. This side structure annealed out on heating the diamond to 140 K. It is thought that both the increase in intensity of the ‘a’ line and the side structure arise from defect centres involving the interstitial. The fact that they anneal out is taken as evidence that the interstitial in diamond is mobile below room temperature.