The ejection of an electron from an atom as a result of the de-excitation of an excited electron within the atom. An electron is first ejected from an atom by a photon, electron impact, ion impact, or some other process, thus creating a vacancy. In the subsequent rearrangement of the electronic structure of the atom, an electron from a higher energy level falls into the vacancy. This process is associated with excess energy, which is released by the ejection of a second electron (rather than by emission of a photon). This second electron is called the Auger electron. Auger spectroscopy is a form of electron spectroscopy using this effect to study the energy levels of ions. It is also a form of analysis and can be used to identify the presence of elements in surface layers of solids. The effect was discovered by the French physicist Pierre Auger (1899–1994) in 1925.