Particle-optical apparatus comprising a fixed diaphragm for the monochromator filter

摘要

An electron microscope comprises an energy-selective filter (10) which is arranged ahead of the high-voltage field in the electron gun (2). Because the filter carries high-voltage potential and is arranged within the gun space (14) which is filled with SF.sub.6 gas, problems arise regarding electrical and mechanical passages to the filter. Notably the centering of the filter is problematic. In order to enable suitable aperture adjustment of the filter nevertheless (for current limitation and for avoiding optical aberrations introduced into the beam by the filter), there is provided an entrance diaphragm (30) which is rigidly connected to the filter parts, notably to a pole face or to a field- defining closing piece (48a) of the filter.