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Electron energy loss spectroscopy
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<p>Electron energy loss spectroscopy (EELS) is a form of <a href="/facts/Electron_microscopy/XtaBktwF">electron microscopy</a> in which a material is exposed to a <a href="/facts/Charged_particle_beam/aES4kaGn">beam</a> of <a href="/facts/Electron/L0KBo5cW">electrons</a> with a known, narrow range of <a href="/facts/Kinetic_energy/aJRxUd4p">kinetic energies</a>. Some of the electrons will undergo <a href="/facts/Inelastic_scattering/nEBTw75h">inelastic scattering</a>, which means that they lose energy and have their paths slightly and randomly deflected. The amount of energy loss can be measured via an <a href="/facts/Electron_spectrometer/VhGsARoh">electron spectrometer</a> and interpreted in terms of what caused the energy loss. Inelastic interactions include <a href="/facts/Phonon/tflWW6vw">phonon</a> excitations, inter- and intra-<a href="/facts/Electronic_band_structure/W5o7oE2R">band</a> transitions, <a href="/facts/Plasmon/kuCMxx5f">plasmon</a> excitations, inner shell <a href="/facts/Ionization/W13Ceavd">ionizations</a>, and <a href="/facts/Cherenkov_radiation/lSPJAC3U">Cherenkov radiation</a>. The inner-shell ionizations are particularly useful for detecting the elemental components of a material. For example, one might find that a larger-than-expected number of electrons comes through the material with 285 <a href="/facts/Electronvolt/YMT1fqX9">eV</a> less energy than they had when they entered the material. This is approximately the amount of energy needed to remove an <a href="/facts/Electron_shell/QxI30eh9">inner-shell</a> electron from a <a href="/facts/Carbon/ukrgQexo">carbon</a> atom, which can be taken as evidence that there is a significant amount of carbon present in the sample. With some care, and looking at a wide range of energy losses, one can determine the types of atoms, and the numbers of atoms of each type, being struck by the beam. The scattering angle (that is, the amount that the electron's path is deflected) can also be measured, giving information about the <a href="/facts/Dispersion_relation/oo7RM5eg">dispersion relation</a> of whatever material excitation caused the inelastic scattering. </p>