Diffraction from periodic arrays of dislocations

Abstract

The structure factor of a square grid of screw dislocations was computed using the displacement field of van der Merwe for a low-angle twist boundary. The calculations predict, for dislocations spaced d _D apart, that the electron diffraction pattern from the dislocation array viewed at normal incidence consists of square arrays of reflections spaced I/d _D apart, centred around f.c.c. reflections, in the same orientation as the square dislocation grid. No extra reflections were predicted around the reciprocal space origin. The calculated pattern showed excellent agreement with the observed electron diffraction pattern from a low-angle twist boundary in gold. The use of these reflections to study periodic arrays of closely spaced dislocations was discussed and it was estimated that d _D's as small as 4|b|, corresponding to a misorientation of 14°, would be detectable.