Auger electron emission

Figure 8.21 The competitive processes of X-ray fluorescence (XRF) and Auger electron emission...

Fig. 14. Schematic of the Auger electron emission process induced by creation of a K level electron hole.

An alternative mechanism of excess energy release when electron relaxation occurs is through x-ray fluorescence. In fact, x-ray fluorescence favorably competes with Auger electron emission for atoms with large atomic numbers. Figure 16 shows a plot of the relative yields of these two processes as a function of atomic number for atoms with initial K level holes. The cross-over point between the two processes generally occurs at an atomic number of 30. Thus, aes has much greater sensitivity to low Z elements than x-ray fluorescence. 

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 incoming electron beam interacts with the sample to produce a number of signals that are subsequently detectable and useful for analysis. They are X-ray emission, which can be detected either by Energy Dispersive Spectroscopy, EDS, or by Wavelength Dispersive Spectroscopy, WDS visible or UV emission, which is known as Cathodoluminescence, CL and Auger Electron Emission, which is the basis of Auger Electron Spectroscopy discussed in Chapter 5. Finally, the incoming... 

Fig. 16. Processes involved in Auger electron emission during X-ray photoelectron spectroscopy.

When an excited state is converted by ejection of an atomic electron, a high positive charge can be produced through subsequent Auger electron emission. Within the period of molecular vibration this charge is spread throughout the molecule to all atoms, and a Coulomb explosion results. This primary phenomenon occurs, of course, not only as a result of [ decay, but must be taken into account in all cases of nuclear reaction when deexcitation by inner electron conversion occurs... 

Jonsson, A.C. Jonsson, B.A. Strand, Se. Grafstrom, G. Spanne, P. Cell survival after Auger electron emission from stable intracellular indium exposed to monochromatic S5mchrotron radiation. Acta Oncol. 1996, 35 (7), 947-952. 

Auger Electron-emission Yields from Metal Surfaces67... 

Ideally, we would like to study the structure and composition of supported, dispersed catalyst particles in the same configuration used in the chemical technology. However, the determination of the atomic surface structure of the catalyst particle that is situated inside the pores of the high-surface-area support by LEED, for example, is not possible. This technique requires the presence of ordered domains 200 A or larger to obtain the sharp diffraction features necessary to define the surface structure. Even Auger electron emission, which is the property of individual atoms and can even be obtained from liquid surfaces, can only be employed for studies of supported catalyst surfaces with difficulty. Identification of the active sites does require the determination of the structure and composition of the catalyst surface, however. To avoid the difficulties of carrying out these experiments on supported... 

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

Fig. 1. Comparison of the four different physical processes which can be observed during the interaction of X-ray photons with matter 2 1. The two phenomena scetched below, namely photoelectron emission and Auger electron emission, can be detected and measured in a photoelectron spectrometer by determining the kinetic energy of the ejected free electrons...

The discussion above has considered only what happens to the electron that is removed from an inner shell. An atom with an inner-shell electron removed is unstable, and an electron from a higher orbital will soon fill the inner-shell void. Therefore, the energy difference between these two orbitals must be emitted by the atom (called a secondary process). This can occur by two competing processes (a) emission of a fluorescent photon or by (b) Auger electron emission (Stohr, 1992 pll6). If the atom in question is at a surface, the energy of the Auger electron can... 

For a correct treatment of Auger electron emission as a resonance in the double ionization continuum, one has to start with the transition rate P ... 

As a special application of the two-step model the non-coincident observation of photon-induced Auger electron emission will be considered further. In this case one has to integrate the transition rate P of equ. (8.66a) over dKa, because the photoelectron is not observed, i.e.,... 

Finally, the conditions necessary for deriving the given two-step formula for Auger electron emission will be summarized. Equ. (8.66) describes the coincident observation of the Auger electron with its preceding photoelectron for ... 

Couplings for Auger electron emission In this case one has to consider the decay of the intermediate photoionized state (J,) to the final ionic state J( by emission of the Auger electron (j2) taking care also of the Coulomb matrix elements (operator Op2) ... 

From the general form of non-coincident observation of angle-dependent Auger electron emission, equ. (8.117b),... 

---