The profiles of the back-scattered electron intensity within electron channelling contrast images were calculated by using a 2-beam dynamic diffraction model and a simple treatment of multiple scattering. The full displacement field was used for a dislocation, in an isotropic elastic medium, which was parallel to a free surface with which it interacted. The effects of the surface stress relaxation were found to be relatively small when the dislocation was close to the free surface. However, when the dislocations were situated deeper within the specimen, the surface interaction was sufficient to cause the calculated contrast to be of the opposite sense to that which was to be expected if the free surface was ignored. It was concluded that such free-surface effects were essential for the correct interpretation of electron channelling contrast images.

A.J.Wilkinson, P.B.Hirsch: Philosophical Magazine A, 1995, 72[1], 81-103