Observation of dynamic extinction from high-order Laue zones by convergent beam electron diffraction

Abstract

The rules for the observation of the dynamical extinction of some kinematically forbidden reflections in convergent beam electron diffraction (CBED), due to the presence of complicated interaction among glide planes or/and screw axes in the crystalline samples, are examined. This interaction is manifested by the characteristics of the sum of the indices h+ k+ l, which will show up when the high-order Laue zones (HOLZ) are involved in CBED work. Then the complication of interpreting possible dynamic extinction arises. A procedure is therefore devised to decompose a multi-scattering process into basic kinematical scattering steps which can then be rigorously analyzed on the basis of the well-documented knowledge of X-ray crystallography, without relying on the sometimes deceptive intuitive argument. The usefulness of the decomposition table is demonstrated with two examples.