A contrast-optimized hollow cone dark field imaging method for nanocrystalline in glass-ceramic materials

Hollow-cone dark-field (HCDF) imaging provides valuable structural information about polycrystalline and nanocrystalline materials. However, conventional HCDF imaging suffers from low contrast, particularly in samples containing amorphous phases in glass-ceramics. In this study, we propose an improved HCDF imaging method that replaces the continuous beam-tilting approach with a series of discrete dark-field (DF) images acquired by stepwise rotation of the electron beam. Each DF image corresponds to a specific position along the targeted diffraction ring. To enhance contrast, we introduce a selective averaging strategy that includes only the crystalline regions, segmented through a customized thresholding and morphological filtering process. This approach significantly improves the visualization of crystalline domains compared to conventional HCDF images. The method was validated using polycrystalline Au, LaSi₂/TaSi₂/Si composite nanomaterials, and in-situ annealed Li₃PS₄ sulfide electrolytes. The results demonstrate enhanced contrast and clarity, particularly under conditions of low crystallinity, making the method especially effective for structural studies of glass-ceramics and other materials with low crystallinity.