Especially for thick TEM specimens, an incident electron that has undergone inner-shell scattering can also cause outer-shell excitation with very high probability. This mixed inelastic scatterings is the sum of both inner-shell and outer-shell scatterings, resulting in a mixed energy loss and a peak broadening (plasmon behavior) above the ionization threshold.
With a thick sample, the background is affected by plural scattering, but also the core
edges are affected. For instance, an electron that lost energy to a core electron might lose
energy to a plasmon as well. This changes the shape of the edge and moves intensity from the edge
onset to a higher energy loss.
The chromatic aberration remains or is even increased after using multipoles to correct spherical aberration. This energy spread degrades the spatial resolution in EMs’ imaging and also induces peaks broadening in an energy-loss spectrum, resulting in reduction of the amount of observable fine structure.