The aggregation of nitrogen and the formation of A centres in diamonds

Topographic infra-red spectroscopy has been used to investigate the inhomogeneity of the aggregation of nitrogen in {111} growth sectors of synthetic diamonds. The aggregation rate constant was established to be different even within the same {111} growth sector. In particular, changes in the growth temperature, most likely changing the impurity content, are shown to result in changes in the aggregation rate constant; namely an increase in the growth temperature, in diamonds grown with a Co catalyst, is found to reduce the nitrogen aggregation rate constant, and vice versa. These results indicate that the presence of Co impurities in the {111} growth sector influences the aggregation rate. It is found that the aggregation process follows second order kinetics as first established by Chrenko et al. [Nature, London, 270 (1977) 141]. The activation energy of the aggregation process in {111} growth sectors is measured as 5.5 +/- 0.7 eV. It is also found that increasing the applied pressure during the annealing process reduces the aggregation rate constant, such that there is a significant difference between annealing at ambient pressure and annealing at 10 GPa. (C) 1997 Elsevier Science S.A.