The contrast of dynamical images of small lattice defects in the electron microscope

Starting with the differential equations for the Bloch wave amplitudes a simple formula for the dynamical bright field and dark field intensities in a distorted crystal is derived. It completely describes the dependence of the contrast on foil thickness and on depth of the lattice defect. A quadratic approximation can be deduced. The following results are discussed in detail: the contrast of small lattice defects in thin foils and in foils of medium thickness, the dependence of the contrast on the magnitude of the anomalous absorption, the determination of the habit plane of a small dislocation loop, and the dependence of the inner structure of the black-white contrast of small dislocation loops on the magnitude of g· b.