Separation and identification of phases with through-focus dark-field electron microscopy

Abstract

The use of out-of-focus dark-field images combined with stereoviewing to obtain more information than is available from a single dark-field image and its corresponding diffraction pattern, has been demonstrated recently. In this technique, called through-focus dark-field electron microscopy, an artificial stereo-image effect can be produced by utilizing the image shifts in out-of-focus dark-field images. The technique basically involves obtaining two beam-tilted dark-field images, selecting several spots with the objective aperture, such that one image is slightly over-focus and the other slightly under-focus. Examination of the two images through a conventional stereoviewer produces elevation differences between regions contributing to the several spots chosen with the objective aperture. These elevation differences are unrelated to object positions in the thin foil, and no specimen tilting is required. Applications of this technique to rapid separation and identification of phases in complex alloy systems are discussed.