On the accuracy of atomic-resolution electrostatic measurements in 2D materials

The use of differential phase contrast (DPC) in scanning transmission electron microscopy (STEM) has shown much promise for directly investigating the functional properties of a material system, leveraging the natural coupling between the electron probe and atomic-scale electric fields to map the electrostatic configuration within a sample. However, the high sensitivity of these measurements makes them particularly vulnerable to variations in both sample properties and the configuration of the instrument, stressing the need for robust methodologies to ensure more accurate analyses. In this work, the influence of key instrumental parameters - probe convergence angle, defocus and two-fold astigmatism - on atomic-resolution segmented-detector DPC-STEM measurements is evaluated through extensive image simulations. Results show a limit of interpretability at a defocus magnitude of 4 nm for a 21 mrad probe, where the electrostatic field magnitude can be underestimated by about 16 % in overfocus and just above 10 % in underfocus compared to the aberration-free image. Equivalent results for a 30 mrad probe demonstrate underestimated values around 30 % at overfocus and 20 % for underfocus, at a lower interpretability limit of 3 nm of defocus magnitude. Two-fold astigmatism introduces orientation-dependent variations that surpass 40 % when the magnitude of the aberration is below 3 nm, but a reduction in sensitivity to the aberration is observed when oriented along detector-segment edges. Overall, the analysis confirms the sensitivity and usefulness of the scattergram-based methodology and underscores the importance of optimized instrumental alignment for accurate CoM-based STEM imaging.