Exploring 4D-STEM in SEM with an event-driven direct electron detector: Low-dose, high-speed, and sparse data

The four-dimensional scanning electron microscopy (4D-STEM) using a direct electron detector has been widely adopted in transmission electron microscopy (TEM), enabling virtual detector imaging, electron ptychography, strain, electric field, and orientation mapping from sub-angstrom to microscale. However, this technology has rarely been implemented into scanning electron microscopy (SEM). In this study, we integrated an event-driven direct electron detector into a focus ion beam scanning electron microscopy (FIB-SEM) system, offering a time resolution of 1.56 ns without readout noise and fast data processing in sparse data workflow. This advancement enables high-speed 4D-STEM applications in SEM, as demonstrated through three key experiments. Multi-frame 4D-STEM analysis of FePt alloy nanoparticles revealed enhanced diffraction contrast and enabled nanoscale crystal orientation mapping. Strain mapping was successfully conducted on an AlCrFeMnTi high-entropy alloy, showcasing the technique's versatility. Furthermore, we demonstrated ultrafast acquisition (50 ns/pixel) of high-quality diffraction patterns for γ-phase CsPbI₃ halide perovskites at ultralow electron doses (4.62 × 10⁻³ e⁻/Ų) for mapping grain boundaries. These findings underscore the significant advancements in SEM capabilities through the application of 4D-STEM, paving the way for further explorations in materials science.