Transmission electron microscopy (TEM) is a high-resolution imaging technique in which a beam of electrons passes through a thin sample to produce an image. The electron beam is impacted by the sample’s thickness/density, composition, and in some cases, crystallinity. The electrons that are transmitted through the specimen subsequently provide contrast in the resulting image.

TEM is capable of unparalleled resolution due to the small wavelength of the transmitted electrons. Unlike scanning electron microscopy (SEM), which gathers the net intensity of secondary electrons in each point of the scan, TEM resolution is only limited by the wavelength of the individual electron and the quality of the electron optics. This means that transmission electron microscopes can routinely collect sub-nanometer scale (if not atomic-resolution) images.