arXiv:2511.00320v1 Announce Type: new
Abstract: Focused ion beams (FIBs) are widely used in nanofabrication for applications such as circuit repair, ultra-thin lamella preparation, strain engineering, and quantum device prototyping. Although the lateral spread of the ion beam is often 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 typically characterise 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 $