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In TEM analysis, the mean free path of elastic scattering of an electron represents how thin the specimen needs to avoid or minimize plural scattering.
The inelastic scattering of electrons occurs at smaller angles than that for elastic scattering. Figure 2863a shows an example of angularresolved electron scattering profiles in logarithmic scale. The reference spectrum (vacuum) in blue is dominated by unscattered electrons in the range −4 to 4 mrad. Due to the scattering of the incident electrons with a rhenium (Re) TEM specimen, the modified spectrum in red was formed.
Figure 2863a. An example of angularresolved electron scattering profiles of electrons in vacuum and Re film in logarithmic scale. The reference spectrum (vacuum) is dominated by unscattered electrons in the range −4 to 4 mrad.
[1]
The mean free path of elastic scattering (λ_{el}) is given by, [1]
λ_{el} = −t/ln(I_{Sample}/I_{Vacuum})  [2863]
For instance, I_{Sample} is equal to I_{Re} in Figure 2863a.
Figure 2863b shows the experimental values of λ_{el} [1] and λ_{in}(Z) [2] as oscillatory functions of Z for Z > 20. Comparison of λ_{el} and λ_{in} values suggests that the elastic component should dominate scattering of incident highenergy electrons for most inorganic solids and of incident electrons penetrating thin TEM specimens.
Figure 2863b. The mean free path of elastic scattering λ_{el} of 200 keV electrons (solid squares) [1] and that of inelastic values λ_{in} (open circles) (Adapted from [2]).
[1] Konstantin Iakoubovskii and Kazutaka Mitsuishi, Elastic scattering of 200 keV electrons in elemental solids: experimental observation of atomicnumberdependent oscillatory behavior, J. Phys.: Condens. Matter 21 (2009) 155402.
[2] Iakoubovskii K, Mitsuishi K, Nakayama Y and Furuya K (2008) Phys. Rev. B 77, 104102.
