Graphitization at diamond dislocation cores

We examine possible mechanisms for graphitization at dislocation cores in d iamond, both as an explanation for brown coloration in natural brown diamon d and as a model for annealing in amorphous carbon materials. We find a met astable structure for the 90 degrees partial dislocation core where bonds a re broken in both single- and double-period structures leading to a row of paired sp(2) c atoms. We examine the effect of hydrogen and other impuritie s on this core structure both through direct interaction and potential char ging effects. We also investigate a mechanism for progressive aromatization through the migration and aggregation of 30 degrees partial dislocations.