Fourier amplitude replacement for reliable probe initialization in 4D-STEM datasets of crystalline materials

Multislice electron ptychography (MSEP) holds great promise for low-dose, depth-resolved structural characterization of materials, yet its reconstruction efficiency strongly depends on reliable probe initialization. This initialization relies on displacement analysis of single-pixel bright-field scanning transmission electron microscopy (BF-STEM) images. For crystalline specimens, however, the overlap between the bright-field disk and diffraction disks introduces additional contrast that weakens image similarity, thereby compromising the reliability of displacement measurements. Here, we propose a Fourier amplitude replacement (FAR) preprocessing strategy, in which the Fourier amplitude distribution of each single-pixel BF-STEM image is replaced with that of the axial BF-STEM image, thereby enhancing image similarity while preserving displacement-related Fourier phase information. Simulations and experiments demonstrate that FAR-assisted displacement analysis provides reliable probe initialization, leading to substantially higher quality MSEP reconstruction. This strategy offers a practical preprocessing approach for robust and efficient MSEP reconstruction of crystalline materials.