On the Nature of the Long‐Range Dislocation Contrast in Electron Transmission Micrographs

The background contrast of dislocations is investigated theoretically using modified Bloch waves. As a result it is found that interband scattering can be neglected outside the dark line (width ≦ one extinction distance) of the dislocation image. The contrast outside the dark line is quantitatively explained by “phase contrast” [4]. i.e. exclusively by the movement of the excitation points of the modified Bloch waves on the dispersion branches. It is shown that the asymmetry often observed in the background intensities adjacent to the black line is an intrinsic contrast phenomenon rather than a consequence of stress relaxation at the foil surface.