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In Auger electron spectroscopy (AES, or simply Auger) the surface of a sample is irradiated by a beam of energetic (focussed) electrons. These electrons interact with the atoms in the surface of the sample causing further electrons to be emitted with characteristic energies. The energy of these secondary electrons is measure in an electron energy analyser.
Both X-rays and Auger electrons are produced throughout the volume excited by the electron beam. The X-rays can escape from the sample with little attenuation. Only those Auger electrons produced by atoms in the outermost atomic layers of the sample can escape with their characteristic energy unaltered. This makes Auger a surface sensitive technique.
The surface of the sample can be eroded by a beam of inert gas ions. By monitoring the signals from elements of interest as a function of time, depth profiles for those elements are produced.
It is also possible to image the distribution of elements across the surface, usually by focussing and scanning the irradiating electron beam - hence "scanning Auger microprobe" - or SAM.
All elements with the exception of hydrogen and helium produce Auger electrons: detection sensitivity is typically between 1 and 0.1 percent of a monolayer.