Observations of hierarchical grain-boundary dislocation structures in [001] symmetric tilt boundaries in gold

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Abstract
Molecular statics calculations using pairwise interatomic potentials by Sutton, Vitek and Wang have predicted the existence of a hierarchy of localized edge-type grain-boundary dislocations (GBDs) in [001] symmetric tilt boundaries in f.c.c. noble metals. Furthermore, the geometry of these GBDs can be well described by the structural unit/GBD model of Sutton and Vitek as extended by Balluffi and Bristowe. In the present work, a search was made for the presence of such a hierarchy in [001] symmetric tilt boundaries in gold by means of transmission electron microscopy. Numerous arrays of various localized GBDs were detected under various conditions of observation in specimens of differing thickness under a variety of imaging conditions. When the present results are combined with results from other investigations, it is concluded that the first four members of the hierarchy have been detected. One GBD array belonging to an appreciably higher-order hierarchical member has been found, and it seems likely that higher-order members (which became increasingly difficult to detect) also exist. The results provide support for both the calculations and the structural unit/GBD model.