EELS Background versus Edge Onset
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Table 3418. Comparison between background and edge onset in EEL spectra.

Edge onset
Ionization edges

From plural-scattering events associated with outer-shell interactions, single-scattering contributions from the tails of preceding (lower) ionization edges and valence electron excitations

Provide elemental information Provide sample thickness information

In the cases that very thick TEM samples are used in EELS or EFTEM measurements, the increase of plural scattering effects induces two main problems:
         i) The background models, e.g. the form of power law, are not convenient to represent the actual background;
         ii) The low energy edge onsets are embedded in the background, meaning some edge becomes invisible.

Furthermore, plural inelastic scattering by plasmon excitation is a special concern when measuring the low energy loss (e.g. Li K-edge) because it is close to the low-energy plasmon region. For instance, double plasmon scattering distorts the pre-edge background and can mask the Li K-edge.