Auger spectroscopy

When a material surface is bombarded with electrons with an energy sufficient to ionize one of the inner shells of an atom, for example, K, a primary vacancy arises, which is instantly (in 10 ⁻¹⁶ –10 ⁻¹⁴ s) filled by an electron transferred from another shell of the atom, for example M. As a result, a secondary vacancy arises. If E _K and E _M are the energies needed to transfer an electron from K and M levels to infinity, then the energy released during this transition is equal to E _K - E _M. This energy difference can be distributed across different channels. On the one hand, in the form of the released quantum of characteristic x-ray radiation, hv = E _K - _EM (radiation transition), and on the other hand, it is transferred to the electron of the outer shell of the atom, for example N (non-radiative transition or Auger transition). Energy | E _K - E _M | - E _N can be positive (or equal to zero). In this case, the electron is emitted into a vacuum and registered as an Auger electron. The probability of its exit depends on the sequence number Z of the atoms of the material under study. Since the probability of a radiative transition with increasing Z increases (in proportion to Z ⁴ ), the probability of the appearance of an Auger transition decreases. So, for light elements, it is about 95%, and for elements with Z> 70 it does not exceed 10%. The depth of exit of Auger electrons d ₀ in the range of energies that are of interest for electron Auger spectroscopy is 5 - 10 monatomic layers. Therefore, we can say that the information obtained by this method relates to the surface region of the sample under study.

The emitted electrons of an element that arise as a result of the Auger process are always characterized by certain values ​​of energy. Hence, if we analyze the energies of the electrons emitted by the substance under the action of a beam of primary electrons, select from the general energy spectrum those electrons that have arisen as a result of the Auger process and determine their energies, we can conclude that there is one or another element on the surface.

The intensity of the emission of Auger electrons is significantly influenced by various factors, such as the dependence of the cross section of ionization of the internal levels of atoms on the energy of primary electrons, the backscattered electron flux, the probability of the transition of an atom to an unexcited state with the appearance of a photon, and other processes.

Since the value of the energy of primary electrons E is an important factor in the formation of primary vacancies in atoms, its change should significantly affect the magnitude of the current of Auger electrons.

The geometry of the process has a significant effect on the Auger electron current, namely, the angle of incidence of electrons on the sample and the angle of registration of Auger electrons. We are talking about the angle between the direction of the primary electron beam and the normal to the surface under study and the angle between the normal and the direction of the Auger electrons entering the detector.

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