Grain boundary dislocation networks as electron diffraction gratings

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Abstract
Electron diffraction patterns from thin-film gold bicrystal specimens having grain boundaries containing periodic networks of grain boundary dislocations (GBD's) have been studied. It has been demonstrated that planar GBD networks (which were examined in the electron microscope at normal incidence) give rise to arrays of extra diffraction sports centred around the main f.c.c. gold reflections. The periodic structure of the grain boundary region there fore acts very much as a difraction grating. Examples of this effect are presented for orthogonal grids of screw GBD's in twist boundaries and arrays of parallel edge GBD's in tilt boundaries. The importance of this phenomenon in the study of GBD structure is discussed. It is pointed out that, since the spacing of the GBD spots is reciprocally related to the actual GBD spacing, this effect would be particularly useful in examining fine GBD networks. Also, the possibility of forming a direct image of the GBD network using the GBD spots is emphasized.