Towards sub-إ electron beams

The prospects for reaching sub-Å electron probes through aberration correction in the scanning transmission electron microscope (STEM) are evaluated. The design, results and practical experience gained from a working 100 keV STEM CS corrector are presented and discussed. The design of a second-generation quadrupole–octupole CS corrector that pays particular attention to the influence of instabilities is outlined. Probe shapes calculated for the new corrector indicate that it will be able to produce a probe smaller than 1 Å at 100 keV.