Abstract
The dislocation image has a line or dotted feature, which depends essentially upon the reflecting condition. This dependency has been clarified by the dark field image method and also by the method of small variation of the incident angle of electron beam, as follows:-
Line images of dislocations: 1) Generally the contrast of dislocation image near an extinction contour is mainly due to the reflection of the same index as that of the contour. 2) The dislocation image usually appears as a single line, sometimes as a double image, when it is due to one reflection. 3) On the contrary, sometimes the image looks like a single line even when it is due to multiple reflections. 4) The image having black contrast is generally accompanied by white side-lines, and when the latter predominates, the image is observed as a white dislocation image. 5) Near the intersection of dislocations of two families, there are found some variations in the image features, which may be not only due to the interaction between strain fields of the intersecting dislocations, but also due to the systematic interaction of the reflections.
Dotted images of dislocations: 1) Each dot in the dotted images is frequently composed of the white and the black regions lying side by side and distributed alternately along the dislocation line. 2) The zig-zag image is considered as a special feature of the dotted image, which is occasionally produced by two reflections. 3) Complex features of the dotted images, for instance, the image interposed between two black lines, are due to multiple reflections.
Finally, it is shown that the foil is bent by the dislocation for relief of the dislocation stress, and that some of the image features may be affected by this phenomenon because of variation of the reflecting condition.
