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Why Diffraction-Contrast of Defects is a Sad Song and How to Make it Better

Published online by Cambridge University Press:  02 July 2020

J. A. Eades
J. A. Eades*
Affiliation:
Department of Materials Science and Engineering, Lehigh University, PA18015-3195
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Extract

Modern TEM's are not suited for the taking of diffraction-contrast images of defects. Figures in books and papers taken more than a quarter century ago show defects (dislocations, small precipitates and so on) against a uniform background, reflecting constant diffraction conditions across the field of view. Such pictures can not be taken today. Even if the sample is quite flat, TEM images are crossed by “bend contours” which arise, not from the bending of the sample, but from the changing orientation of the beam. In modern TEM's, the objective lens is an immersion lens. The sample sits deep within the magnetic field of the lens and, thus, the electrons are travelling in a helical pattern as they strike the sample. Even with a so-called parallel beam, at different places across the image, the electrons strike the sample at different angles (see figure 1).

Type
The Theory and Practice of Scanning Transmission Electron Microscopy
Information
Microscopy and Microanalysis , Volume 6 , Issue S2: Proceedings: Microscopy & Microanalysis 2000, Microscopy Society of America 58th Annual Meeting, Microbeam Analysis Society 34th Annual Meeting, Microscopical Society of Canada/Societe de Microscopie de Canada 27th Annual Meeting, Philadelphia, Pennsylvania August 13-17, 2000 , August 2000 , pp. 134 - 135
Copyright
Copyright © Microscopy Society of America

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References

Christenson, K. K. and Eades, J. A., Skew Thoughts on Parallelism Ultramicroscopy 26 (1988) 113–132CrossRefGoogle Scholar
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Eades, J.A., Zone-Axis Patterns formed by a new Double-Rocking Technique Ultramicroscopy (1980), 5, 71–74.Google Scholar