X-Ray Fluorescence and Auger-Electron Emission

Figure 14.22 Relationship between atomic number and the probabilities of X-ray fluorescence and Auger electron emission. (Reprinted with permission from Hercules, copyright 1970 American Chemical Society.)...

Fig. 4.1. X-ray photoemission from a H core level and subsequent relaxation processes leading to X-ray fluorescence and Auger electron emissions.

The interaction of an electron with an atom gives rise to two types of X-rays characteristic emission lines and bremsstrahlung. The atom emits element-characteristic X-rays when the incident electron ejects a bound electron from an atomic orbital. The core-ionized atom is highly unstable and has two possibilities for decay X-ray fluorescence and Auger decay. The first is the basis for electron microprobe analysis, and the second is the basis of Auger electron spectroscopy, discussed in Chapter 3. 

X-ray emission and Auger electron ejection are competitive processes, especially in low-Z elements. As the Z value of the material becomes higher, X-ray emission becomes the more likely process. This is reflected in tabulations of fluorescence yield, which is the ratio of X-ray transition to Auger electron plus X-ray transitions this value increases with Z from 0.01 at fluorine to 0.97 at and above polonium (Firestone 1996). 

Inductively Coupled Plasma. Mass Spectrometry Archaeological Applications. Microscopy Techniques Scanning Electron Microscopy. Surface Analysis X-Ray Photoelectron Spectroscopy Particle-Induced X-Ray Emission Auger Electron Spectroscopy. X-Ray Absorption and Diffraction X-Ray Diffraction - Powder. X-Ray Fluorescence and Emission X-Ray Fluorescence Theory. 

The photoionization process described in the section A Method of Elemental Analysis leaves an ion in an excited state, which may relax in two ways illustrated by Fig. 13a for oxygen (a) electron transition to fiU the position left unoccupied at the lower level, the energy conservation being insured by the emission of a photon this is responsible for X-ray fluorescence, and will not be discussed here and (b) Auger electron emission, which is described using the symbols of energy levels (K, L, M, etc.) used in X-ray spectroscopy. 

Fig. 16. Relative probabiUties of Auger electron emission and x-ray fluorescence for initial iClevel electron hole as a function of atomic number (19).

The ionized atom that remains after the removal of the core hole electron is in a highly excited state and will rapidly relax back to a lower energy state by one of two routes, namely X-ray fluorescence (Section 5.1.2) or by transferring the energy to an electron in another orbit, which, if it has sufficient energy, will be ejected into the vacuum as Auger emission. An example of the latter process is illustrated in Figure 5.29. 

GD-OES (glow discharge optical emission spectrometry) are applied. AES (auger electron spectroscopy), AFM (atomic force microscopy) and TRXF (transmission reflection X-ray fluorescence analysis) have been successfully used, especially in the semiconductor industry and in materials research. 

Let us turn our attention to the dominant recombination or deexcitation processes that follow the excitation of electrons from the inner shell or from the valence shell (Fig. 13). The first mode of deexcitation is the Auger process, which leads to further electron emission. The second mode of deexcitation may result in the emission of electromagnetic radiation and is commonly called X-ray fluorescence. In the Auger transition, the electron vacancy in an inner shell is filled by an electron from an outer band. The energy released by this transition is transferred to another electron in any... 

Fig. 13, Energy level diagram representation of the excitations by (a) Auger electron emission and (b) X-ray fluorescence.

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