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 compon ents of the stray magnetic field deflect the primary beam, but a stray field of the same value acting along the optical axis does not influe nce the primary beam significantly. We designed a shielding for our lo w-voltage scanning electron microscope which suppresses the influence of the transversal stray magnetic field by two orders but does not inf luence the field of the focusing lens. Therefore, unlike the full shie lding of a small diameter, the segmental shielding proposed does not i mpair resolution.