This article shows how the scanning transmission electron microscope provides a Z-contrast image (where Z is atomic number) that is often directly interpretable and can show higher resolution than a phase-contrast image. It represents an incoherent mode of imaging, similar to that described by Lord Rayleigh for the optical microscope over a century ago. Today, resolution has reached a half Ångstrom, and spectroscopic analysis of individual atomic columns, even of individual atoms in two-dimensional materials, has become possible.
