THE AGGREGATION OF NITROGEN AND THE FORMATION OF A-CENTERS IN DIAMONDS

Topographic infra-red spectroscopy has been used to investigate the in homogeneity of the aggregation of nitrogen in {111} growth sectors of synthetic diamonds. The aggregation rate constant was established to b e different even within the same {111} growth sector. In particular, c hanges in the growth temperature, most likely changing the impurity co ntent, 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 const ant, and vice versa. These results indicate that the presence of Co im purities in the {111} growth sector influences the aggregation rate. I t 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 se ctors is measured as 5.5 +/- 0.7 eV. It is also found that increasing the applied pressure during the annealing process reduces the aggregat ion rate constant, such that there is a significant difference between annealing at ambient pressure and annealing at 10 GPa. (C) 1997 Elsev ier Science S.A.