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It was proposed by August and Wernisch [1] that backscattering coefficient (η) of electrons can be given by,

            ------------- [4564a]

where

This analytical expression was derived with good fit to experimental data, especially with regard to low electron energies. Figure 4564a shows the comparison of backscattering coefficient between experimentally fitted Equation and Monte Carlo (MC) simulation for C, Si, and Cu. Good agreement is obtained to within 10% of the analytical expression. η can be further classified to coefficients of elastic backscattering electrons  and coefficients of inelastic backscattering electrons.

Figure 4564a. Comparison of backscattering coefficient between experimentally fitted Equation
and Monte Carlo (MC) simulation for C, Si, and Cu [2].

When the angle of incidence of the electron beam to a sample is increased, the backscattered electron yield increases.

[1] H. J. August and J. Wernisch, Phys. Status Solidi 114, 629 (1 989).
[2] C. L. Lee and C. K. Ong, Bethe Ionization Cross-sections: a Quantitative Survey on Calculating the Backscattering Factor in AES, Surface and Interface Analysis, 19, 227-231 (1992).