Field Astigmatism in TEMs/STEMs
- Practical Electron Microscopy and Database -
- An Online Book -

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

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In general, the requirements of aberration minimization depend on the field of view:

i) Large field of view

The off-axial coma must be eliminated in order to provide a large field of view. The optical arrangement that satisfies these requirements is called aplanatic condition. In this case, the imaging characteristics do not vary for small angular beam tilts or with the position of the scatters, in the specimen, in the vicinity of the optic axis. However, the field astigmatism and the image curvature can diminish the resolution in the region far from the optic axis.

ii) Small field of view

In the case of high-resolution TEM (HRTEM) under typical imaging conditions, the magnification is so large that the transferred object field is so small and thus, image curvature and field astigmatism do not appreciably affect the image quality.

Note that the field astigmatism is complex in the presence of an axial magnetic field.

 

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