Dependence of EELS Signal on TEM Specimen Thickness
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Mkhoyan et al.  presented SSDs (single scattering distributions) obtained from experimental EELS data from silicon (Si) specimens with four different thicknesses as shown in Figure 2401a. The band gap or electronic states in the gap presented in the figure were inaccurate due to the low energy-resolution. In their measurements, the energy resolution was 0.7 eV, and the channel size 0.22 eV so that it was impossible to quantify features located below 2 eV.
Figure 2401a. SSDs obtained from experimental EELS data from Si specimens with four different thicknesses. Adapted from 
Note that the surface plasmon-loss (Is) has dependence on TEM-specimen thickness only when the specimen is extremely thin (e.g. <10 nm in general). On the other hand, for very thin TEM specimens, e.g. ≤30 nm for Si (≤0.25 λP), several surface-induced effects contribute to plasmon signal:
In general, the requirements of TEM specimen thickness for EELS and EFTEM measurements are:
Figure 2401b shows that the background increases dramatically with increase of the thickness of TEM specimen, while the signal of Pt M4,5 edge decreases significantly. The highest signal in the range of these TEM specimen thicknesses for Pt occurs at 20 nm.
Figure 2401b. EELS of Pt M4,5 edge.
 K.A. Mkhoyan, T. Babinec, S.E. Maccagnano, E.J. Kirkland, and J. Silcox, Separation of bulk and surface-losses in low-loss EELS