MICROSCOPY Vol.45▶No.2 2010

■Lectures

Electron Optics for Aberration Correction in Electron Microscopy

**Abstract:** Electron optical systems for aberration correction in electron microscopy are outlined starting from Scherzer theorem established in 1936. There are two types of third-order spherical aberration correction-lens systems that used multipoles. One is the so-called hexapole corrector developed by Rose, Haider et al., and the other is the quadrupole−octupole corrector. Self-aligned quadrupole correction-lens is introduced to simplify the construction of the quadrupole−octupole corrector. Axial chromatic aberration can be also corrected by combination of electrostatic and magnetic quadrupoles, or electrostatic multipole system satisfying optimum relation between the axial potential and the quadrupole strengths.

**Key words:** aberration correction, quadrupole, hexapole, octupole, duodecapole