Defocus contrast on electron microscope images of small dislocation loops. I. Computations on the basis of dynamical theory

Abstract

The regularities for the occurrence of the black‐white contrast on defocus electron microscope images of small dislocation loops in a “thick foil” are investigated using image simulation within the two‐beam dynamical theory in the column approximation. It is shown that at defocusing of the objective lens, the black‐white contrast is observed for loops located between visibility layers L1, L2,…, while it is absent in the case of precise focusing. The black‐white contrast regularities revealed permit to define the type of a loop (vacancy or interstitial).