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The elements with larger atomic number (Z) has stronger elastic and thermal diffuse scattering and thus, a solid composed of element with larger Z can have larger mean free path value λ, i.e. weaker inelastic scattering. In the measurements of electron diffractions in TEM, the contribution of inelastically scattered electrons increases with decreasing atomic number and increasing foil thickness.
The fraction F of electron scattering (including both elastic and inelastic scatterings) at angles smaller than a scattering angle β can be given by, [1]
 [3504]
where,
θ_{0}  (≈λZ^{1/3}/(2πa_{0})) The soft cutoff to the Lorentzian angular distribution,
θ_{E} ≈ 0.5E_{m}/E_{0} (nonrelativistically)
Figure 3504 shows the experimental values of λ_{el} [2] and λ_{in}(Z) [3] 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 3504. The mean free path of elastic scattering λ_{el} of 200 keV electrons (solid squares) [2] and that of inelastic values λ_{in} (open circles) (Adapted from [3]).
[1] F. Lenz, Z. Naturforsh 9A (1954) 185.
[2] 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.
[3] Iakoubovskii K, Mitsuishi K, Nakayama Y and Furuya K (2008) Phys. Rev. B 77, 104102.
