Abstract
Elucidation of a complex defect configuration arising from the interaction between eight first-order twin boundaries in a diamond thin film prepared by chemical vapour deposition on a silicon substrate is reported. The defect has been identified by ultrahigh-resolution electron microscopy at 0.12nm resolution. It is shown to consist of a nearly perfect fivefold twin centre closely connected to two smali portions of original ∑= 9, {122} and ∑= 27, {255} grain boundaries (GBs). Extensive image simulation has been used to deduce the detailed core structure and to propose a plausible three-dimensional atomic-scale model, which contains no dangling bonds. The observed a bond stretching and bond bending are found to be remarkably consistent with recent ab initio calculations of minimum-energy configurations for related defect structures in diamond and in silicon carbide. Moreover, the core structure of the two particular GBs, which consists of alternating columns of five- and seven-membered rings of carbon atoms, is perfectly consistent with the structures at present known to be the most stable forms of such second-order and third-order GBs in diamond and cubic diamond materials.