DYNAMICAL ELECTRON-DIFFRACTION IN SUBSTITUTIONALLY DISORDERED COLUMN STRUCTURES

For column structures, such as fee-based alloys viewed along the cube direction, the concept of electron channelling through the atom column s is more and more used to interpret the corresponding HREM images. In the case of(partially) disordered columns, the projected potential ap proach which is used in the channelling description must be questioned since the arrangement of the atoms along the beam direction might aff ect the exit wave of the electrons. In this paper, we critically inspe ct this top-bottom effect using multi-slice calculations. A modified c hannelling theory is introduced which turns out to be very appropriate for the interpretation of these results. For substitutionally disorde red column structures, it is also discussed how to link the chemical c omposition of the material to statistical data of the HREM image. This results in a convenient tool to discern images taken at different thi cknesses and focus values.