Theory of dynamical scattering in near-edge electron energy loss spectroscopy

Abstract

Beyond chemical information, the fine structure of an absorption edge gives bonding and electronic information. We provide a synthesis of fine structure and dynamical scattering theory, allowing the exploration of the effects of dynamical scattering on the measured fine structure. We discuss the effects of experimental geometry in the context of site-specific near-edge spectroscopy of ${\text{NiAl}}_{2}{\text{O}}_{4}$ and find that large detectors serve to localize the inelastic signal and may be preferable to the small off-axis detectors currently used. We then explore the possibility of measuring changes in fine structure within a unit cell using scanning transmission electron microscopy. We demonstrate that, in principle, it is possible to measure a subtle change in the fine structure of the $\text{O}\text{ }K$ edge in ${\text{SrTiO}}_{3}$ as the probe is scanned across the unit cell. We explore the best experimental conditions to achieve this and find that large probe-forming and detector apertures help to localize the signal to the atomic sites.