Towards a Uniform Model for Lattice Defect Image Simulations

For more than seven decades, diffraction contrast in the TEM has been used for the study of both linear and planar lattice defects, such as dislocations, stacking faults, anti-phase boundaries, and so on. In recent years, several alternative approaches for defect imaging have become available: using a standard annular dark field detector, the STEM diffraction contrast image (DCI) mode produces medium angle annular dark field (MAADF) images which display strong defect contrast, even for relatively thick foils [1], while suppressing contrast due to foil bending and such. Both systematic row and zone axis orientations can be used in the STEM-DCI technique, in contrast with conventional TEM bright field/dark field imaging, where the zone axis orientation is mostly avoided. The arsenal of scanning electron microscopy (SEM) modalities has been extended with the electron channeling contrast imaging (ECCI) approach, which allows for the imaging of low density surface penetrating lattice defects over large sample areas. It is to be noted that in all of these techniques, the diffraction contrast is caused by the same dynamical scattering mechanisms; the only differences are the instrument accelerating voltage, the illumination mode (parallel or conical, stationary or scanning), and the shape and position of the detector (CCD, annular detector). The common underlying physics principles suggest that a single computational approach to defect image simulations might be possible, covering all the above mentioned observations modes.