Towards sub-angstrom electron beams

The prospects for reaching sub-Angstrom electron probes through aberration correction in the scanning transmission electron microscope (STEM) are eval uated. The design, results and practical experience gained from a working 1 00 keV STEM C-s corrector ape presented and discussed. The design of a seco nd-generation quadrupole-octupole C-s corrector that pays particular attent ion to the influence of instabilities is outlined. Probe shapes calculated for the new corrector indicate that it will be able to produce a probe smal ler than 1 Angstrom at 100 keV. (C) 1999 Elsevier Science B.V. All rights r eserved.