Some forms of spectroscopy involve actions other than measuring a property of light. In the case of this form of spectroscopy, the energies of emitted electrons are measured.
Auger (pronounced "oh-ZHAY") spectroscopy can be considered a form of X-ray photoelectron spectroscopy (XPS) (3), at least in one of its guises. For about 30 years after its formal discovery, it actually was thought of as a nuisance in the performance of XPS. However, since the 1950s, technology has advanced to be able to take advantage of the effect as a separate spectroscopic technique (4).How It Works
where E 1, E 2, and E 3 are the original energies of the first core electron, the second electron that moves down, and the third electron that gets ejected, respectively. There is supposed to be a correction for the third energy, because it is actually an energy of the ion, not the atom, but these are usually ignored. Because three electrons are involved, Auger spectroscopy is not used to detect hydrogen or helium but can be utilized for any heavier element. Because the energy levels of the elements typically are well-known, Auger spectroscopy can be used to determine the elemental analysis of a sample, either by analysis of the X-rays emitted or the electrons emitted. Because a free electron will not travel a large distance in a solid, Auger spectroscopy is largely a surface technique, allowing users to probe the chemical composition of a surface.
As the atomic number of the elements being analyzed increases, so do the number of possible transitions, suggesting that Auger spectra get hopelessly complicated for larger elements. However, experience shows that most elements show only a few strong signals in their Auger spectra, dominated by transitions between the 1s, 2s, 2p, and occasionally the n = 3 shells.