Atomic structure of [011] and [001] near-coincident tilt boundaries in germanium and silicon

High resolution electron microscopy (HREM) has been used to investigate the structure of [001] and [011] pure tilt grain boundaries, both near-coincident and coincident, in crystals of Ge and Si. The resolution limit for the detection of the rigid body translation using HREM has been established, and compared with the α-fringe technique. Several structural units for primary and secondary relaxations have been found; it is shown that the core extension of a secondary relaxation covers one primary period. Likewise, a detailed comparison between simulated and experimental images for a σ = 9 grain boundary is presented. Some atomic sites in the period of the grain boundary appear to be preferentially attacked by impurities.