The observation of edge dislocation loops by high resolution lattice imaging
IntroductionThe characterization of small defects by diffraction contrast methods in the electron microscope becomes uncertain when the image widths approach the dimensions of the defect. In the case of small defect aggretates, it becomes difficult not only to distinguish between interstitial and vacancy character but also between volume and planar defects.These small defect aggregates, or rather the disturbances that they produce, can also be investigated by lattice imaging where the interference of two or more beams, whose phases have been disturbed by the defect, produces an image. The images obtained in this way, although not a one-to-one mapping of the atomic arrangement, do bear an unique relationship to it; however, this uniqueness is lost in an electron micrograph since the phase relationships are not recorded. The image interpretation therefore relies upon the effect that the phase relationships have on the image intensity being sufficient to distinguish between likely candidates for the atomic distribution, since the image intensities from this type of microscopy are not in general straightforward to predict.