On the kinematical theory of diffraction contrast of electron transmission microscope images of perfect and partial screw dislocations

Hirschet al. (1960) have developed a kinematical theory for the diffraction contrast of the electron microscope image of a perfect screw dislocation parallel to the surface of the crystal foil. The present author (Gevers 1962 a, b) has extended their theory for a perfect dislocation of mixed type with slip plane parallel to the surface. In this paper the theory is applied to a partial screw dislocation parallel to the surface. Numerical calculations have been performed for n = ± ⅓, ± ⅔, ± 4/3, ± 5/3, ± 7/3, ± 8/3, where n = g • b (g: diffraction vector, b: Burgers vector). It is found that for n = ⅓ the line contrast is unimportant, probably negligible, that for n = ⅔ an observable line image superposed on the stackingfault contrast should be present, and that for larger values of n the line contrast becomes much more important than the stacking-fault contrast.