Accurate and Robust Calibration of the Uniform Affine Transformation Between Scan-Camera Coordinates for...

Area of Science:

• Materials Science
• Physics
• Electron Microscopy

Background:

• Accurate geometrical calibration is essential for quantitative imaging and ptychographic reconstructions in four-dimensional scanning transmission electron microscopy (4D-STEM).
• Existing methods may require prior knowledge of specimen structure or struggle with distortions and defects.

Purpose of the Study:

• To develop a robust and accurate method for geometrical calibration between scan and camera coordinates in 4D-STEM.
• To improve the reliability of quantitative imaging and ptychographic reconstructions.

Main Methods:

• A hybrid method combining a J-matrix method and a Fourier method for calibrating affine transformations.
• Utilizes raw atomic-resolved, in-focus 4D-STEM data without requiring a priori knowledge of crystal structure.
• Demonstrates improved convergence and reduced residual errors in iterative error correction when used for initial calibration.

Main Results:

• The hybrid method successfully calibrates scan-camera coordinates, correcting uniform affine transformations.
• Demonstrates robustness against scan distortions, residual probe aberrations, specimen defects, and thickness variations.
• Leads to more reliable recovery of both the specimen and the electron probe in ptychographic reconstructions.

Conclusions:

• The proposed hybrid method provides accurate and robust geometrical calibration for 4D-STEM.
• Enhances the quality and reliability of ptychographic reconstructions and quantitative analysis.
• A user-friendly tool is provided to correct scan-camera coordinate affine transformations in 4D-STEM experiments.