Scanning electron microscopy.

SEM uses electrons instead of light.

An electron gun sends a narrow beam of electrons across a sample in a grid pattern inside a vacuum chamber. The samples must be dry and are often polished or given a thin conductive coating so charge does not build up, which would significantly affect image resolution and quality. When the beam hits the surface, it knocks loose signals, such as electrons from the sample's atoms, that detectors can measure.

Specialized detectors capture these signals and turn them into pixels on a screen, creating detailed surface images. SEMs can also create element maps of the sample. Because their wavelengths are so small, electrons can reveal details roughly 1–10 nanometers across. This makes SEM useful for studying grains, cracks, coatings, and tiny particles, although it mainly reveals surface information rather than the entire inside of a sample.