| 摘要 |
Electron optical aberrations of an energy filtering system of an energy filtering transmission electron microscope (EFTEM) are automatically corrected under computer control to set up the EFTEM for use. Optics of the electron microscope preceding an energy filter are used to scan the beam at the entrance to the filter in a pattern corresponding to a defined geometry. The beam can either be finely focused to yield a spot at each position visited during the pattern scan, or the beam can be spread out and imprinted with a well-defined intensity distribution, such as normally occurs due to passage of the beam through a specimen, so that its relative scanned displacements can be assessed using cross-correlation techniques. In the case of the finely focused beam, electron images of the scanned pattern directly yield a spot pattern image. Deviation of the recorded spot pattern image from the defined scan geometry reflect the imaging aberrations introduced by the energy filter. In the case of the spread out beam, post-filter electron images of the scanned beam are cross-correlated with an image of the beam taken without scanning yielding cross-correlation peak images that give the effective displacement of each scanned beam position due to the aberrations/distortions of the filter. Summing the cross-correlation peak images again yields a spot pattern image that is equivalent to that obtained in the focused beam case. Deviations of the recorded spot pattern image from the defined scan geometry are analyzed to assess and subsequently correct aberrations introduced by the energy filter.
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