Electrons penetration

Yes, by varying the range of electron penetration (between about 10 nm and several im), which depends on the electron-beam energy (1-40 keV). 

Nonradiative surface recombination is a loss mechanism of great importance for some materials (e.g., GaAs). This effect, however, can be minimized by increasing the electron-beam energy in order to produce a greater electron penetration range. 

In summary, CL can provide contactless and nondestructive analysis of a wide range of electronic properties of a variety of luminescent materials. Spatial resolution of less than 1 pm in the CL-SEM mode and detection limits of impurity concentrations down to 10 at/cm can be attained. CL depth profiling can be performed by varying the range of electron penetration that depends on the electron-beam energy the excitation depth can be varied from about 10 nm to several pm for electron-beam energies ranging between about 1 keV and 40 keV. 

The differences between x-ray and electron excitation must obviously stem from differences in the interaction of x-rays (1.11) and of electrons (1.4) with matter. Electrons are retarded rather quickly when they strike a sample, and they lose much of their energy in classical collision processes (4.1). Because electrons transfer their energy so rapidly, the critical thickness (Equation 6-8) for electron excitation is very much less than we saw it to be for x-ray excitation a.calculation based on experiments on a variety of materials53 gives 1CT3 cm (105 A) as a good value for the depth to which 50-kv electrons penetrate aluminum, and bears out the previous statement. Because the energy of every electron decreases as it penetrates, the x-ray excited by any electron will be of... 

Electron penetration, of aluminum, 176 of x-ray target, 8, 9 Electron-positron pair production, 290 Element determinations,. bibliography, 328-331... 

Fs is the stopping power factor. Electron penetration is a function not only of the incident electron energy (which is constant for a given analysis) but also on the stopping power of the sample, which depends somewhat on atomic number. Reed (1993) derives equations for the generated characteristic X-ray intensity, leading to expressions for Fs. 

If the critical separation is determined for a large number of relative geometries of the electron and molecule it is possible to obtain a three-dimensional picture of the probability of ionization as a function of the orientation of the molecule. Effectively, the idea of an ionization cross section, the area the target molecule presents to the electron, is extended to a three-dimensional object defined by the critical distances, with ionization occurring when the electron penetrates the surface enclosing this volume. The volume enclosed by the electron impact ionization surface may be used to obtain an estimate for the cross section (volume averaged cross section) ... 

We have described in this section and in Sect. 2.4.2 the electron penetration problem when either straggling or scattering was ignored. There is as yet no... 

In the (semi-)classical models of ETR (Marcus the Russian school), redox orbitals of reactants overlap at a close separation, followed by swift electron transfer. The activated complex, considered in equilibrium with the reactants, consists of these overlapping orbitals. In the tunneling model, the electron penetrates... 

The yield of free ions in the radiolysis of dienes is very similar to those found for monoalkenes (G = 4.0-4.2)72. Freeman and coworkers73 measured the yield of the free ions (Gg) and the secondary electron penetration (i>Gp) in radiolysis of unsaturated hydrocarbons. Some of the data are given in Table 1. It can be seen that the yield of the free ions is considerably smaller for the dienes studied. Also, the secondary electron penetration is smaller for the dienes, all of them having a similar value (3.9-4.4 nm). 

TABLE 1. Yield of free ions (Gfi) and the secondary electron penetration (hop) for radiolysis of unsaturated hydrocarbons... 

Numerical values for the effective position of the image charge at the pzc (cr = 0) are given in Table 17.1. Figure 17.4 shows a plot of 1 /Cm, calculated from Eq. (17.18), versus experimental values for the inverse Helmholtz capacity of a few sp metals in contact with an aqueous solution. Since the electrons penetrate only a short distance into the solution, we expect the interaction between the metal electrons and the solvent to be comparatively weak. If this is true, we expect from Eq. (17.5) ... 

Clearly, UV and EB radiation have a great deal in common, as shown above. However, there are also differences. Besides the nature of interacting with matter, where high-energy electrons penetrate, and photons cause only surface effects, there are issues concerning the capital investment and chemistry involved. 

In general, upon exposure to UV radiant energy, a photoinitiator can generate free radicals or ions, as pointed out earlier. These are generated at a rapid rate, and their depth profile corresponds to the inverse photon penetration profile. Similar to electron penetration, the final cure profile often deviates from the initial radical or ion distribution, since they can live much longer than the exposure time. The mechanisms of the processes for the generation of reactive species are discussed in detail in Davidson. ... 

Electron penetration range in g/nP as the function of electron energy. (Courtesy of Energy Sciences, Inc.)... 

---