High-resolution transmission electron microscopy image simulation of screw dislocation core structures in body centered cubic metals

High-resolution transmission electron microscopy (HRTEM) images are simulated for the core structures of 1/2[111] screw dislocations in body centered cubic (bcc) metals to examine the possibility of determining the core structure experimentally by HRTEM. Two types of cores are studied: a polarized core and an isotropic one. For the model crystals containing the screw dislocations with the two types of cores, HRTEM images are calculated by a multi-slice method with the incident beam parallel to the [1 1-bar 0] direction that is perpendicular to the direction of the dislocation line. A qualitative difference between the images of the two types of cores is detected; for the isotropic core the image always possesses the two-fold symmetry, irrespective of the defocus value, while for the polarized core it does not. This fact suggests that HRTEM experiments with the incident beam parallel to the [1 1-bar 0] direction can distinguish between the two types of core