High-resolution electron microscopy was used to study the defect structure of 3-9-3 junctions in film samples. A short segment of 9 (221) boundary, with a length of about 2nm, was found to be bounded by 3 (111) twins. One of the 3 (111) twins was found to be expanded by 0.06nm, normal to the boundary plane. A junction dislocation which was related to a different rigid-body translation in 3 grains was observed in the triple junction. The coincidence-site lattice model was used to explain the observed structure of 3-9-3 junctions, and helped to rationalize the relative rigid-body translations between neighboring grains. However, unlike a 9 boundary in a Si crystal, the short segment of 9 boundary in chemical vapor deposited diamond film could not be explained in terms of a geometrical model that was based upon a constructed coincidence-site lattice dichromatic pattern. It was suggested that the equilibrium structure of the short 9 boundary was affected by the adjacent 3 twins and by trapped H atoms in the chemical vapor deposited material.

L.Chang, F.R.Chen: Materials Science Forum, 1995, 189-190, 121-8