Auger electron spectroscopy

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The Auger electron spectroscopy [ oʒe -] (AES, by Pierre Auger ) is a spectroscopic method for the highly sensitive and non-destructive examination of the chemical composition of a material surface. It is based on the Auger effect , through which an atom that has been suitably excited emits an electron with a certain kinetic energy that varies depending on the chemical element. In Auger electron spectroscopy, the energy spectrum of the electrons is recorded which is released when a surface is bombarded with an electron, X-ray or UV beam with energies of up to a few kiloelectron volts. The radiation creates the hole states necessary for the Auger effect. The Auger electrons of a certain transition are noticeable through a peak in the spectrum, the energy of which clearly indicates the atomic number of the emitting atom.

Due to the short range of electrons in the relevant energy range (approx. 50 eV to 3 keV), Auger electron spectroscopy is  a very surface-specific method. The recorded material layer typically only comprises the top ten atomic layers. The method can therefore be used very efficiently for the locally high-resolution (0.01 µm to 100 µm) detection of contaminants. The detection limit of Auger electron spectroscopy is approx. 0.01-0.1  at% . The AES peak can only be evaluated from this value . If, on the other hand, the pure material is really to be recorded and not unintentionally applied impurities that have arisen during sample preparation, then these must be removed, for example, by sputtering with argon .

An Auger electron spectroscope can also be used to generate images of the type of a scanning electron microscope (SEM). A secondary electron detector is required for this, which converts the secondary electrons into an SEM image. In this way, a resolution comparable to that of a "normal" SEM can be achieved. In addition to this function, the AES detector can also be used to create images. In this way, images can be recorded that contain material information. This procedure is called scanning auger microscopy (SAM).

In photoelectron spectroscopy, Auger electrons emerge from the surface irradiated with ultraviolet or X-rays, in addition to photoelectrons. This causes additional "Auger peaks" in the energy spectra. These differ from the “photopeaks” in that their energy does not vary with the energy of the incident photons.

See also

literature

  • Martin Henzler, Wolfgang Göpel: Surface physics of the solid , Teubner Verlag; 2nd edition 1994
  • D. Briggs, MP Sheah: Practical Surface Analysis by Auger and X-Ray Photoelectron Spectroscopy , Wiley 1983

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