The source of the color of brown diamonds was considered. The associated defect, which was not impurity-related, could be removed by high-pressure high-temperature treatment. Collections of vacancies were suggested to be the source of the color according to theoretical calculations and positron annihilation experiments. Therefore, simulations were carried out in order to determine whether the suggested sizes of vacancy clusters could be seen using high-resolution transmission electron microscopy. Substantial contrast was revealed in defocused images. In light of the simulations, experimental defocus series were acquired in lattice resolution for brown and colorless, natural and synthetic type IIa diamonds. A small-scale patchiness was apparent in the lattice images of brown but not of colorless diamond. Further analysis, including simulations of multiple vacancy clusters, suggested this contrast in brown diamond could be due to many irregularly distributed vacancy clusters.

HR-TEM Imaging and Image Simulation of Vacancy Clusters in Brown Diamond. R.Barnes, U.Bangert, P.Martineau: Physica Status Solidi A, 2006, 203[12], 3081-7