Thickness and defocus dependence of inter-atomic electric fields measured by scanning diffraction

Area of Science:

• Materials Science
• Condensed Matter Physics
• Electron Microscopy

Background:

• Scanning diffraction in STEM analyzes electron probe interactions with sample structures.
• Diffraction intensity reveals Coulomb interactions, enabling electric field calculations.
• Previous studies suggested limitations for thick samples due to scattering and probe effects.

Purpose of the Study:

• To systematically investigate the impact of sample thickness and probe defocus on scanning diffraction measurements.
• To determine the robustness and accuracy of electric field measurements using scanning diffraction under various conditions.
• To extend the applicability of scanning diffraction for electric field mapping in thicker materials.

Main Methods:

• Utilized scanning transmission electron microscopy (STEM) with a sub-angstrom electron probe.
• Acquired and analyzed diffraction patterns to measure momentum transfer.
• Conducted experiments varying sample thickness (up to 15 nm) and probe defocus.

Main Results:

• Demonstrated quantitative measurement of strong electric fields near atoms for samples up to 5 nm thick.
• Showed qualitative accuracy for weak inter-atomic electric fields in samples up to 15 nm thick.
• Found the technique to be more robust than predicted, especially under specific imaging conditions.

Conclusions:

• Scanning diffraction is a viable technique for quantitative electric field mapping in materials up to 15 nm thick.
• Specific imaging conditions enhance the robustness of electric field measurements, overcoming previous theoretical limitations.
• This method provides valuable insights into local electric fields, crucial for understanding material properties.