Fraction of Backscattered Electrons Depending on Sample Thickness
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As an examlpe of interaction between incident electrons and matters, Figure 1182a shows the fractions of the transmitted (ηT) and backscattered (ηB) electrons from some Al films with an incident electron beam at accelerating energies of 15 keV and 20 keV, respectively. Those fractions are thickness-dependent. The data was obtained with Monte Carlo calculations. [1] It is reasonable that the fraction of transmitted electrons at higher voltages (20 keV) is much larger than that at lower voltages (15 keV).

 Figure 1182a. Fractions of the transmitted and backscattered electrons from some Al (aluminium) films with an incident electron beam at accelerating energies of 15 keV and 20 keV, respectively. The dash curves present the fractions of backscattered electrons, while the solid curves present those of the transmitted electrons. The red curves are obtained at an accelerating voltage of 20 keV, while the green ones are from 15 keV. Adapted from [1]

Figure 1182b shows the fraction of backscattered electrons at different accelerating voltages of incident electron beam obtained by Monte Carlo modeling from some materials.

 Figure 1182b. Fraction of backscattered electrons at different accelerating voltages.

Figure 1182c shows the fractions of saturated backscattered electrons in aluminium (Al), titanium (Ti) and silver (Ag) as a function of accelerating voltages at normal incidence. These profiles indicate that their fractions are highly material-dependent and decrease with the increase of the accelerating voltage.

 Figure 1182c. Fractions of saturated backscattered electrons in aluminium (Al), titanium (Ti) and silver (Ag) as a function of accelerating voltages at normal incidence. [2-6]

[1] R Shimizu, Y. Kataoka, T. Ikuta, T. Koshikawa and H. Hashimoto, A Monte Carlo approach to the direct simulation of electron
penetration in solids, J. Phys. D: Appl. Phys., Vol. 9, 1976.
[2] Hunger H-J and Kuchler L 1979 Measurements of the ̈electron backscattering coefficient for quantitative EPMA in the energy range of 4 to 40 keV Phys. Status Solidi a 56 K45–8.
[3] Ito R, Andreo P and Tabata T 1992 Reflection ratios of electrons and photons from solids Bull. Univ. Osaka Pref. A 41, 69–76.
[4] Neubert G and Rogaschewski S 1980 Backscattering coefficient measurements of 15 to 60 keV electrons for solids at various angles of incidence Phys. Status Solidi a 59, 35–41.
[5] Yadav R K and Shanker R 2006 Backscattering of 8–28 keV electrons from a thick Al, Ti, Ag and Pt targets J. Electron Spectrosc. 151, 71–7.
[6] Alexander Klassen, Andreas Bauereiß and Carolin Korner, Modelling of electron beam absorption in complex geometries, J. Phys. D: Appl. Phys. 47, 065307, 11, (2014).

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