Grain clusters and the geometrical origin of stress in CVD polycrystalline diamond

It is demonstrated that the individual grains of polycrystalline, chemical vapour-deposited (CVD) diamond are arranged in clusters composed of several tens of individual grains and related by twinning. Transmission electron microscopy (TEM) analysis showed that for 〈1 1 0〉-oriented growth these clusters become very large but the size of the individual twins within them are relatively small. Geometrical effects within a grain cluster can lead to large internal stresses. Scanning electron microscopy (SEM) methods are described to distinguish grain clusters from the individual grains within them.