Effects of surface stress relaxation on the electron microscope images of dislocations normal to thin metal foils

Abstract

The two-beam dynamical theory of Howie and Whelan is used to calculate the electron microscope image contrast from dislocations normal to a thin crystal and parallel to the direction of the incident electron beam. Bending of the lattice planes due to surface relaxation and change in lattice parameter are taken into account. Strong contrast in the form of black-white spots is predicted for dislocations with a screw component, while contrast from pure edge dislocations is expected to be very weak. Observations on platinum and copper are in good agreement with the predictions for dislocations with a screw component. It is possible from these contrast effects to determine the sense of the screw component of the dislocation.