There are two methods of electronic relaxation for an atom excited by the removal of an inner (non-valence) electron. The first is through the emission of an X-ray photon (the detection of which gives rise to techniques such as EDX). The other method is through the emission of an electron, using energy liberated by the transition of another electron to a lower energy state - the Auger process.
The process was discovered in the 1920's by both Lise Meitner and subsequently Pierre Auger, after whom the process was named (whether due to political or gender issues).
The Auger process - initiated by an incident electronThe Auger process is initiated by the removal of an electron from an inner energy level of an atom. This can be achieved by either a high energy electron probe, or an X-ray photon (hence Auger features are also present on XPS spectra). An electron from a less tightly bound shell then fills the vacancy, with the energy liberated used to eject a third electron into the vacuum. The energy of the ejected electron is therefore dependent on the energy levels of the atom from which it was emitted, giving the technique elemental sensitvity.
The Auger process is the dominant method of relaxation for lighter elements, with the process accounting for ~90% of all transitions for elements Z<20.
