Correction of Objective Astigmatism with
Minimum Background Contrast Technique
- Practical Electron Microscopy and Database -
- An Online Book -  

This book (Practical Electron Microscopy and Database) is a reference for TEM and SEM students, operators, engineers, technicians, managers, and researchers.


In order to obtain the best spatial resolution in EMs, astigmatism correction needs to be done. In some cases, the correction of objective astigmatism is done at hole edges of specimen in TEM mode and on rough surface in SEM mode. However, in the cases without holes or rough surfaces, it is best to correct the astigmatism using fine background image structures. In this method, the objective lens is fist focused for minimum background contrast. Any residual contrast then comes from the variations in defocus of the objective lens from astigmatism that produces phase contrast. Therefore, the objective astigmator is carefully adjusted for minimum, but sharp background contrast, resulting in uniform objective focal length. Note that this technique is especially useful for most crystalline specimens by using the fine background structures of the images induced by thin oxide layers on the specimen surfaces.




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