ABSTRACT Focused ion beams (FIBs) are used in applications such as circuit repair, ultra‐thin lamella preparation, strain engineering, and quantum device prototyping. Although the lateral spread of the probe is overlooked, it becomes critical in precision tasks such as impurity placement in host substrates, where accurate knowledge of the ion‐matter interaction profile is essential. Existing techniques characterize only the beam core, where most ions land, thus underestimating the full extent of the point spread function (PSF). In this work, we use four‐dimensional scanning transmission electron microscopy (4D‐STEM) to resolve the ion beam tail at defect densities equivalent to 0.1 ions . Convergent beam electron diffraction (CBED) patterns were collected in calibration regions with known ion fluence and compared to patterns acquired around static dwell spots exposed to a 30 keV beam for 1–10 s. Cross‐correlation using peak signal‐to‐noise ratio (PSNR) revealed that 4D‐STEM datasets are ultra‐sensitive for defect quantification and more robust against scanning artifacts than conventional dark‐field imaging. By extending beyond conventional core‐focused resolution metrics, this approach enables comprehensive mapping of ion‐induced damage—notably at ultra‐low doses—providing a more accurate picture of FIB performance for application‐specific optimization.
Masteghin et al. (2026) studied this question.