An electron microscope that uses a beam of electrons—accelerated to high energy and focused on the sample—to scan the sample surface, ejecting secondary electrons that form the picture of the sample.

A Transmission Electron Microscope (TEM) passes the electron beam through a very thin slice of a specimen. A Scanning Electron Microscope (SEM) looks at the exterior of a specimen. A Scanning Transmission Electron Microscope (STEM) can produce a magnification of 90 million times.