Exploiting Dynamical Scattering to Characterise Functional Materials

Fast electrons interact strongly with the electrostatic potential of matter and are scattered “dynamically”. Put colloquially, this means that electrons scatter multiply within and between different scattering paths as they are transmitted within the specimen. Dynamical scattering can deliver a wealth of specimen information, such as the phase of a crystal structure factor, that is absent from experiments that are limited to single scattering.<br/>Despite the complexity of dynamical scattering, under relevant conditions some properties of the specimen, such as electrostatic potential and symmetry, can be revealed in the distribution of scattered intensity as stable features, independent of experimental parameters, such as thickness or accelerating voltage. This is a consequence of mathematical structures, such as eigenvalue confluences, that are stable and embedded within the mathematics of dynamical scattering.<br/><br/>In this talk, we will explore how to exploit these features in the intensity distribution to measure different types of specimen information efficiently from various electron-optical configurations, including convergent beam electron diffraction (CBED) and four-dimensional scanning transmission electron microscopy (4D-STEM). We consider how to do this in different detection planes, providing access to coordinate, momentum and energy space and discuss the pros and cons in terms of information content, speed, and electron dose. We illustrate these approaches with applications to the measurement of structure, electronic structure and structural dynamics of functional materials, including photoactive and ferroic perovskites and plasmonic and semiconducting nanoparticle systems.<br/><br/>Acknowledgements: This work was supported by Australian Research Council (ARC) grants DP200103070, DP220103800, FL220100202. The authors acknowledge the use of the instruments and scientific and technical assistance at the Monash Centre for Electron Microscopy and used a Titan3 80-300 FEG-TEM (ARC LE0454166) and the Spectra Phi FEG-TEM (ARC LE170100118).