Gap-free Information Transfer in 4D-STEM via Fusion of Complementary Scattering Channels

TL;DR

This paper introduces Fused Full-field STEM (FF-STEM), a novel 4D-STEM technique that combines ptychography and dark-field imaging to achieve gap-free, high-contrast, quantitative phase images efficiently.

Contribution

The paper presents FF-STEM, a new 4D-STEM modality that fuses ptychographic and dark-field data to overcome contrast gaps without increasing experimental complexity.

Findings

Achieves contrast transfer gap-free imaging with high fidelity.

Enables dose-efficient, near-real-time reconstruction.

Preserves depth-sectioning and upsampling capabilities.

Abstract

Linear phase-contrast scanning transmission electron microscopy (STEM) techniques compatible with high-throughput 4D-STEM acquisition are widely used to enhance phase contrast in weakly scattering and beam-sensitive materials. In these modalities, contrast transfer is often suppressed at low spatial frequencies, resulting in a characteristic contrast gap that limits quantitative imaging. Approaches that retain low-frequency phase contrast exist but typically require substantially increased experimental complexity, restricting routine use. Dark-field STEM imaging captures this missing low-frequency information through electrons scattered outside the bright-field disk, but discards a large fraction of the scattered signal and is therefore dose-inefficient. Fused Full-field STEM (FF-STEM) is introduced as a 4D-STEM imaging modality that overcomes this limitation by combining ptychographic phase reconstruction with tilt-corrected dark-field imaging within a single acquisition. Bright-field data are used to estimate probe aberrations and reconstruct a high-resolution phase image, while dark-field data provide complementary low-frequency contrast. The two channels are optimally fused in Fourier space using minimum-variance weighting based on the spectral signal-to-noise ratio, yielding transfer-gap-free images with high contrast and quantitative fidelity. FF-STEM preserves the upsampling and depth-sectioning capabilities of ptychography, adds robust low-frequency contrast characteristic of dark-field imaging, and enables dose-efficient, near-real-time reconstruction.