Drift correction methods for multi-pass 4D-STEM.

Area of Science:

• Electron microscopy
• Materials science
• Imaging techniques

Background:

• Phase contrast imaging in scanning transmission electron microscopy ((S)TEM) offers near atomic resolution for beam-sensitive materials.
• Low electron fluence in (S)TEM imaging results in poor contrast and low signal-to-noise ratio (SNR).
• Multi-pass data acquisition improves SNR but is complicated by sample drift, especially at high magnifications.

Purpose of the Study:

• To develop and evaluate effective drift correction methods for multi-pass 4D-STEM data acquisition in low-fluence electron ptychography.
• To address the challenge of sample drift in high-resolution imaging of delicate samples.
• To improve the quality of phase contrast reconstructions in ptychographic imaging.

Main Methods:

• Developed two novel approaches for calculating drift vectors between acquisition passes: one using reconstructed ptychographic phase in real space, and another using diffraction patterns.
• Utilized a defocused probe during 4D-STEM data acquisition.
• Applied drift correction to multi-pass data to mitigate sample movement artifacts.

Main Results:

• Demonstrated the effectiveness of both developed methods in calculating and correcting drift vectors.
• Showed significant improvement in the contrast of ptychographic phase reconstructions obtained from low SNR data.
• Validated the approach for low-fluence electron ptychography using a defocused probe.

Conclusions:

• The reported drift correction methods are effective for multi-pass 4D-STEM data acquisition in low-fluence electron ptychography.
• These methods successfully improve image contrast and SNR, enabling better structural analysis of beam-sensitive materials.
• The findings open new possibilities for high-resolution imaging of biological and other weakly scattering samples using ptychography.