A Lapping Technique: To Improve the Image Quality of Electron Microscope Lenses

Abstract

One factor inherent in most electron microscopes is the magnetic asymmetry (astigmatism) in the objective lens. This is often due to imperfect machining, localized defects (impurities) in the iron, or grain anisotropies. The lapping technique described herein effectively reduces the effect of imperfect machining (misalignment of components). Critical faces and the bores through the pole piece are lapped with a series of powders (alumina) which increase in fineness until the final process is that of polishing. A set of jigs and laps (brass and hard wood) are described; their specifications and use so as to properly alter the critical pole piece surfaces are also described. Electron micrographs illustrating the value of this lapping procedure in the improvement in objective lens symmetry are included.