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Abstract
Abstract
Measurement of lattice fringe spacings to determine the expansion vector at {100}〈f00〉 platelet defects in type la diamonds is critically examined. Computer-simulated lattice images were measured and the apparent expansion parameter f′ was found to vary from 0·2 to 0·50 for one structural model of the platelets (f = 0·33); f′ was found to be strongly dependent on crystal thickness, specimen orientation and objective-lens defocus. Despite this it was possible to define electron-optical conditions for which f′=f, when reliable f values should be obtainable. Analyses of one- and two-dimensional lattice images were all consistent with f = 0·33 ± 0·05, after correction for electron-optical effects where necessary. The technique proved far less accurate than an alternative moire fringe measurement, which gave 0·350 ≤ f ≤ 0·362.