Direct determination of lattice distortions by digital processing of HRTEM images of crystals

A detailed theoretical analysis of the possibility of obtaining the information on lattice distortions from high-resolution images of crystal structures is presented. The analysis is based on the calculation of the image intensity of a deformed crystal by means of the many-beam dynamical theory and employing a reconstruction procedure similar to that in off-axis holography. It is shown that if the crystal structure is nearly centrosymmetric or has axial symmetry, reliable results can in general be obtained, independent of the wave aberration and the thickness of the crystal. For non-centrosymmetric crystals, reliable results can only be expected if the crystal stucture has mirror symmetry or if the crystal thickness does not significantly change within the image area of interest.