application of

Auger electron spectroscopy

The Auger effect is the emission of a second
electron after high energy radiation has expelled another. The first electron to depart
leaves a hole in a low-lying orbital, and an upper electron falls into it. The energy this
releases may result either in the generation of radiation, which is called X-ray fluorescence
(Fig. 25.10a) or in the ejection of another electron (Fig. 25.10b). The latter is the
secondary electron of the Auger effect. The energies of the secondary electrons are
characteristic of the material present, so the Auger effect effectively takes a fingerprint
of the sample. In practice, the Auger spectrum is normally obtained by irradiating the
sample with an electron beam of energy in the range 1–5 keV rather than electromagnetic
radiation. In scanning Auger electron microscopy (SAM), the finely focused
electron beam is scanned over the surface and a map of composition is compiled; the
resolution can reach below about 50 nm.