A complex defect configuration, which arose from interactions between 8 first-order twin boundaries, was reported for diamond thin films prepared by chemical vapour deposition onto a Si substrate. The defect was identified by means of ultra high-resolution electron microscopy at 0.12nm resolution. It was shown to consist of a nearly perfect fivefold twin center, closely connected to 2 small portions of original Σ = 9 {122} and Σ = 27 {255} grain boundary. Extensive image simulation was used to deduce the detailed core structure and to propose a plausible 3-dimensional atomic-scale model which contained no dangling bonds. The observed σ bond stretching and bond-bending were found to be highly consistent with ab initio calculations of the minimum-energy configurations for related defect structures in diamond and in SiC. Moreover, the core structure of the 2 particular grain boundaries, which consisted of alternating columns of 5- and 7-membered rings of C atoms, was entirely consistent with structures which were known to be the most stable forms of such second-order and third-order grain boundaries in diamond and cubic diamond materials.

Atomic Structure of a Complex Defect Configuration in Synthetic Diamond - a Fivefold Twin Centre Connected to Two High-Order Grain Boundaries. D.Dorignac, S.Delclos, F.Phillipp: Philosophical Magazine B, 2001, 81[11], 1879-91