LACBED characterization of dislocation loops

The characterization of the amplitude and sign of the Burgers vector of perfect or partial dislocations from large-angle convergent-beam electron diffraction (LACBED) patterns is now a routine technique following the original idea proposed by Cherns and Preston [Proceedings of ICEM-11, Kyoto, Japan, pp. 721-722 (1986)]. The technique has already been applied to large dislocation loops present in semiconductors but in many specimens submitted to irradiation, implantation or thermal treatments, the size of the dislocation loops that are encountered are too small to be identified from normal LACBED experimental conditions. The aim of this paper is to propose solutions to enable the analysis of small dislocation loops, with diameter less than 100 nm. Examples of perfect and partial dislocation loops present in austenitic steels, Al-Cu-Mg alloys and in doped silicon are given, in which the vacancy or the interstitial type of the loops is inferred. The minimum loop size that can be studied with the present technique is about 30 nm. The present technique is similar in its capabilities to the range of methods based on the 'inside-outside' contrast observed on weak-beam images but is has some main operational advantages: the experiments are easy to perform and to interpret and no specific crystal orientation is required.