Spherical Aberration Rings in Ronchigram
- Practical Electron Microscopy and Database -
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Figure 2747 (a) shows the coherent electron Ronchigram formed from an amorphous material. The interference pattern of the Ronchigram at the smooth center flashes randomly due to the small movements of the incident electron probe and specimen. Figure 2747 (b) shows a schematic illustration of the Ronchigram indicating the location of the rings caused by spherical aberration (Cs) and the shadow image inside the rings. The aperture size should be small enough in order to exclude these rings. However if a too small aperture is used the available high frequencies will not be included and the probe becomes diffraction limited. In practice, the probe-forming aperture marked by the red dotted circle in Figure 2747 (a) is just inside the consequence of the Cs  rings.

(a) The coherent electron Ronchigram formed from an amorphous material, and (b) Rings caused by spherical aberration and shadow image inside the rings

Figure 2747 (a) The coherent electron Ronchigram formed from an amorphous material, and (b) The rings caused by spherical aberration and the shadow image inside the rings. [1]

[1] M. Weyland and D. A. Muller, Tuning the convergence angle for optimum STEM performance, FEI nanoSolutions, (2006) 24.

 

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