MAGNETIC SHIELDING OF STRAY MAGNETIC-FIELDS IN THE SCANNING ELECTRON-MICROSCOPE

A stray magnetic field troubles all designers of electron microscopes. The influence of this field is most critical when an ultrahigh-vacuum low-voltage scanning microscope is to be designed. Transversal components of the stray magnetic field deflect the primary beam, but a stray field of the same value acting along the optical axis does not influence the primary beam significantly. We designed a shielding for our low-voltage scanning electron microscope which suppresses the influence of the transversal stray magnetic field by two orders but does not influence the field of the focusing lens. Therefore, unlike the full shielding of a small diameter, the segmental shielding proposed does not impair resolution.