Simplified weak-beam dark-field STEM method for bend-contour-free dislocation loop observation using a commercial STEM system

To advance the quantitative analysis of irradiation-induced defects, we successfully applied a simplified weak-beam dark-field scanning transmission electron microscopy (WBDF-STEM) technique using a standard spherical-aberration-corrected STEM setup, requiring no specialized hardware modifications. By systematically optimizing the illumination geometry with a 10 μm condenser aperture and the imaging geometry with camera lengths of 100 cm and 40 cm, we effectively suppressed macro-scale bend contours and micro-scale surface oxide moiré artifacts. This optimization relies on the combined effect of the probe convergence semi-angle and the acceptance semi-angle to integrate and average out localized intensity fluctuations, while objective-aperture selection at the 2g position reduces oxide-derived moiré contrast. These improvements provide a more uniform background, enabling the reliable identification of the Burgers vectors of nanometer-scale dislocation loops (b = a < 100> and b = a/2<111>) through direct correlation of contrast behaviors across distinct g vectors. Consequently, this methodology provides a practical and readily implementable approach for diffraction-contrast-based analysis of radiation-induced microstructures using a commercial AC-STEM instrument.