Thickness and Bending Effects
We see diffraction contrast in an image for two reasons: either the thickness of the specimen varies or the diffraction conditions change across the specimen: the t effect and the s effect! The thickness effect: when the thickness of the specimen is not uniform, the coupling (interference) of the direct and diffracted beams occurs over different distances, thus producing a thickness effect. Don’t confuse diffraction contrast due to thickness changes with mass-thickness contrast discussed in the previous chapter. The effects are very different. The diffraction contrast changes with small changes in tilt, but the mass-thickness contrast doesn’t.
KeywordsDiffract Beam Wedge Angle Thickness Effect Bloch Wave Bragg Condition
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Some Specific Reading
- Rackham, GM and Eades, JA 1977 Specimen Contamination in the Electron Microscope When Small Probes are Used Optik 47(2) 226–232. Example of using CBED for real-space crystallographic analysis.Google Scholar