Trace analyses from LACBED patterns

Abstract

Trace analysis is of major interest in transmission electron microscopy since the identification of the ( h k l ) indices of lattice planes or the [ uvw] indices of lattice directions is required for the complete analysis of crystal defects (stacking faults, dislocations, etc). It is usually carried out from observations of micrographs and corresponding selected area electron diffraction patterns. The main difficulty comes from the rotation occurring between the image and the diffraction pattern. Therefore, the method requires a careful calibration of this rotation. The LACBED patterns have a unique property: they display information connected both with the direct and the reprocal lattices. The shadow image of the illuminated area of the specimen (direct lattice) is superimposed with the LACBED pattern composed of Bragg lines (reciprocal lattice). Since this shadow image is not rotated (or rotated by 180°C) with respect to the diffraction pattern, LACBED patterns can be conveniently used to identify planes and directions. Several experimental methods are described. Most of them require observation of Bragg lines which are parallel or perpendicular to the trace of the analysed plane or direction.