Energy distribution secondary electrons

Figure Al.7.12. Secondary electron kinetic energy distribution, obtained by measuring the scadered electrons produced by bombardment of Al(lOO) with a 170 eV electron beam. The spectrum shows the elastic peak, loss features due to the excitation of plasmons, a signal due to the emission of Al LMM Auger electrons and the inelastic tail. The exact position of the cutoff at 0 eV depends on die surface work fimction.

Auger electron spectroscopy (AES) is a technique used to identify the elemental composition, and in many cases, the chemical bonding of the atoms in the surface region of solid samples. It can be combined with ion-beam sputtering to remove material from the surface and to continue to monitor the composition and chemistry of the remaining surface as this surface moves into the sample. It uses an electron beam as a probe of the sample surface and its output is the energy distribution of the secondary electrons released by the probe beam from the sample, although only the Ai er electron component of the secondaries is used in the analysis. 

Fig. 27. Product translational energy distribution of the H-atom production channel in the secondary photodissociation of ethoxy radical at 193.3 nm. The onsets of the relevant electronic states of the possible CH3CHO product are indicated in the figure. The signals from the primary photodissociation of ethanol are labelled. (FYom Xu et al.171)...

In Bohr s theory, only estimates of maximum and minimum impact parameters are necessary. Better computations are required for determining the transverse distribution of lost energy or the effect of secondary electrons. The minimum impact parameter according to classical mechanics is ze2/mv2 from angular momentum consideration in quantum mechanics, it is h /mv. In practice, the larger of these two is taken. Also, the impulse approximation used by Bohr for the maximum impact parameter is not an absolute rule energy transfer beyond bmax falls off exponentially (Orear et al., 1956 Mozumder, 1974). 

These classical formulas still do not account for the motion of the bound electrons in the atom or molecule. To be more appropriate to the interaction of an incident electron with the bound target electron, one must recognize that the velocity vector of the bound electron can be randomly oriented with respect to the incident electron providing a broadening of the energy of the secondary electron as calculated by the modified Mott cross section. If one integrates over the velocity distribution of the bound electron, the more familiar binary encounter approximation is derived that, in its simplest form, is given by Kim and Rudd [39] as... 

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