Modeling intraframe dynamics in STEM imaging and their impact on three-dimensional nanoparticle reconstruction: when...

The unique properties of nanoparticles arise from their specific structures and sizes. In particular, the dynamics of atoms on the surface of a nanoparticle are of great interest as they may influence properties such as optical response, electronic structure, magnetic behavior, and catalytic activity. Annular dark field scanning transmission electron microscopy (ADF-STEM) combined with atom counting enables the 3D reconstruction of nanoparticles at the atomic scale from a single projection. This approach implicitly assumes that the nanoparticle remains static during the acquisition of a single image. While surface dynamics have been investigated through time series of images, the intraframe dynamics that occur during the acquisition of a single image have been ignored so far. Since single pixel dwell times are typically of the order of microseconds, significant atomic dynamics may occur during the acquisition of an entire image. In this study, we use a controlled simulation framework to investigate the effect of intraframe dynamics on the quantitative interpretation of ADF-STEM images by explicitly modeling atomic motion during image acquisition and analyzing its impact on atom counting and the 3D reconstruction. Our results provide a physics-based interpretation of single frame ADF-STEM images of simulated dynamic nanoparticles and show that 3D reconstructions closely approximate the nanoparticle's median occupancy structure, suppressing low occupancy positions corresponding to mobile surface features.