Forbidden Reflection Intensity in Electron Diffraction and Its Influence on the Crystal Structure Image

Publisher Website
Google Scholar
Abstract
The forbidden reflection intensity from crystals containing the two-fold screw axis depends strongly on the incident beam direction, and this influences the contrast of crystal structure image. Taking cementite (Fe3C, orthorhombic, Pbnm) as an example, intensity calculation and image simulation have been made. It is shown that the forbidden reflection intensity increases with the tilt angle of the incident beam direction from the zone axis and becomes comparable with the normal reflection intensity. The forbidden reflection introduces a contrast modification with lattice period to the structure image in the direction of the two-fold screw axis. These results are in accordance with observations.