Electron energy loss spectroscopy
Electron energy loss spectroscopy (EELS) is a form of electron microscopy in which a material is exposed to a beam of electrons with a known, narrow range of kinetic energies. Some of the electrons will undergo inelastic scattering, which means that they lose energy and have their paths slightly and randomly deflected.
Source: Wikipedia — Electron energy loss spectroscopy (CC BY-SA 4.0)