Synthesis and Real Structure Group

Selected Area Diffraction (SAD)

Selected Area Diffraction (SAD)

Selected area diffraction mode is similar to XRD (X-Ray Diffraction) but with a higher resolution so it is possible to observe nano structures. In SAD mode the atoms of the sample act like a diffraction grating. The complex scenario of transformations, orientational changes of crystals such can be studied in detail by the means of advanced scattering analyses.

The diffraction pattern (DP) contains electrons from the whole area of the specimen when the beam is illuminated.  Such a pattern is not very useful because the specimen will often be buckled. Furthermore, the direct beam is often so intense that it will damage the viewing screen or saturate the CCD camera. So we perform a basic TEM operation with both selects a specific area of the specimen to contribute to the DP and reduces the intensity of the direct beam in the DP on the screen. By this approach the beam can be made smaller and we can insert an aperture above the specimen which will only permit electrons that pass trough it to hit the specimen.

 

 

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