Auger Electrons

1. Ionization: A hole in an inner shell (here: K shell) is generated by an incident high-energy electron that loses the corresponding energy E transferred to the ejected electron.*
2. Auger-electron emission: The hole in the K shell is filled by an electron from an outer shell (here: L₂). The superfluous energy is transferred to another electron which is subsequently ejected (here: from the L₃ level) as Auger electron.

Since Auger electrons have an energy in the range of some 100 eV to a few KeV, they are strongly absorbed by the specimen. Consequently, only Auger electron from the surface can be measured, making Auger spectroscopy a surface method.

* Energy losses of the incident electrons are measured by EELS.