Aberration-corrected transmission electron microscopy

Aberration-corrected transmission electron microscopy (AC-TEM) is the general term for using electron microscopes where electro optical components are introduced to reduce the aberrations that would otherwise reduce the resolution of images. Historically electron microscopes had quite severe aberrations, and until about the start of the 21st century the resolution was quite limited, at best able to image the atomic structure of materials so long as the atoms were far enough apart.

Source: Wikipedia — Aberration-corrected transmission electron microscopy (CC BY-SA 4.0)