JOGS ON EXTENDED DEFECTS IN FCC MATERIALS.

In order to study the fine detail of extended defects in fcc materials, for example dissociated dislocations, extended threefold nodes, double ribbons or locks, it is necessary to use the weak-beam technique of electron microscopy. Using this technique Shockley partial dislocations can be imaged as line similar 1. 5nm wide which appear relatively bright against a dark background. The image peaks are displaced from the dislocation core by a distance determined partly by the character of the dislocation and partly by the nature of other dislocations present. (Other influences include foil thickness, defect position etc. ) In the case of defects which are widely extended on a single left brace 111 right brace plane it is usually reasonable to image the image peaks as defining the core position.