A bright-field method for determining the nature of stacking faults in FCC materials which is applicable to thin crystals

Abstract

Two well established methods for determining whether a stacking fault is intrinsic or extrinsic have been given in the literature. Both methods involve the use of asymmetrical dark field images of stacking faults obtained under strong beam diffraction conditions. The asymmetry in these images is due to the effects of anomalous absorption and, therefore, this asymmetry can only be observed in thicker regions of a specimen. As a result these methods are more difficult to apply to crystals which have low absorption coefficients such as silicon. The authors of this paper have shown that an asymmetry found in bright field images can be used to determine the nature of a fault. This asymmetry does not depend on the effects of absorption and, therefore, can be used to determine the nature of a fault under conditions which make the conventional techniques difficult or impossible to use. The asymmetry in bright field images referred to above is associated with the inclination of the entrance surface of the specimen and/or the stacking fault plane to the incident electron beam. In the calculation of contrast obtained in the stacking fault image, this implies that symmetrical Laue diffraction conditions cannot be assumed and the column approximation cannot be made. An illustration of the asymmetry referred to above can be seen by comparing Figs. la and b.