# Quantifying the Full Damage Profile of Focused Ion Beams via 4D‐STEM Precession Electron Diffraction and PSNR Metrics

## TL;DR

This paper introduces a new method using 4D-STEM and PSNR metrics to accurately measure the full damage profile of focused ion beams, even at very low doses.

## Contribution

The study introduces a novel approach to quantify FIB damage using 4D-STEM and PSNR, capturing low-dose tails previously overlooked.

## Key findings

- 4D-STEM provides ultra-sensitive defect quantification at low ion densities (<0.1 ions nm−2).
- PSNR analysis is more robust against scanning artifacts than conventional dark-field imaging.
- The method enables comprehensive mapping of ion-induced damage for application-specific FIB optimization.

## 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 nm−2. 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 Ga+ 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.

Four‐dimensional scanning transmission electron microscopy (4D‐STEM) is used to acquire multiple convergent beam electron diffraction (CBED) patterns around focused ion beam (FIB) dwelled spots. Peak signal‐to‐noise ratio (PSNR) analysis, following calibration with well‐known implantation dose squares, enables full quantification of the FIB profile, including its low‐dose tails.