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The Emergence of Aberration Correctors for Electron Lenses

In 1936, Otto Scherzer published his famous theoretical paper on the correction of aberrations in round magnetic electron lenses. For fundamental reasons, the aberration coefficients are positive and to introduce negative corrections, the electron optical elements have to produce either charges or poles on the optic axis, or contain a mirror or be a multipole system. In 1997, three papers appeared with actual demonstrations of the correction of aberrations in imaging lenses, probe forming lenses and electron mirrors. It took almost two thirds of a century for this seemingly straightforward development to occur and for the promise of wavelength limited electron imaging to emerge as a practical proposition.