Practical Electron Microscopy and Database

The background due to zero and other energy loss may vary across the specimen due to local changes in composition and thickness. Due to composition variation in materials, this will cause background variation in EELS and EFTEM, that is, it causes the changes in the background signal of the spectrum or image that arise from differences in the elemental composition of a material.

In EELS, the background signal is the part of the spectrum that precedes the ionization edge of an element, and it is typically modeled as a power-law decay. However, this background is not uniform across different regions of a material, especially when the composition varies. Variations in the local composition affect the scattering cross-section and the inelastic scattering processes, leading to changes in the background intensity. For instance, regions with heavier elements might show a different background slope compared to regions with lighter elements due to the difference in the inelastic scattering cross-section.

 Similarly, in EFTEM, where images are formed by filtering specific energy ranges of electrons, the background intensity can vary with composition. This variation can affect the contrast and interpretation of chemical maps, particularly when distinguishing between areas with subtle compositional differences. The background variation needs to be carefully considered and often subtracted or accounted for to accurately quantify elemental distributions and avoid misinterpretation of the material's composition.

Addressing background variation due to composition involves techniques like careful background fitting in EELS or using advanced filtering and normalization methods in EFTEM. These approaches help in isolating the true signal from the compositional features of the material, ensuring accurate analysis and imaging results.