The inner-shell intensity normally rises rapidly at the ionization threshold. If the TEM sample for EELS is very thin, plural scattering can be negligible impact on the shape of the ionization edges. Both the valence electron peaks and the ionization edges represent a fine structure that reflects the crystallographic or energy band structure of the specimen.
However, most TEM specimens are so thick that plural scattering is usually significant. The plural scattering is generally unwanted since it distorts the shape of the energy-loss spectrum. A thin specimen can avoid multiple scattering which obscures the core-loss edges. That is, the sample should be so thin that the plasmon peak is smaller than one-tenth of the zero loss.