ABSTRACT
This chapter focuses on correctors of geometric aberrations for transmission electron microscopes (TEM), that is, on correctors of aberrations that depend on the angle or the position of an electron ray but not on the electron energy. Correctors constructed up to the early nineties are best called proof-of-principle or first-generation correctors. Working correctors have also been developed for instruments other than TEMs, scanning TEMs, and scanning electron microscopes. The chapter reviews the main challenges of day-to-day corrector operation. Quantifying the performance of a particular corrector system requires that the electron trajectories through the system be worked out in detail. Correction of geometric aberrations amounts to identifying and incorporating optical elements able to adjust the different terms in the expansions of the aberration function. The aberration function is changed by all the optical elements of the system, which typically include accelerators, round lenses, and multipoles.
