High resolution imaging properties of the STEM.

Area of Science:

• Materials Science
• Physics
• Electron Microscopy

Background:

• Scanning Transmission Electron Microscopy (STEM) is a powerful tool for atomic-scale imaging.
• Image resolution in STEM is fundamentally limited by the interaction between the electron probe and the atom.
• Understanding the effect of finite atomic size is crucial for advancing STEM resolution.

Purpose of the Study:

• To investigate the impact of finite atomic size on STEM resolution.
• To develop a method for calculating single-atom images in STEM.
• To analyze the influence of scattering properties and probe distribution on image quality.

Main Methods:

• Developed a technique to calculate single-atom images by expanding the scattering amplitude.
• Analyzed dark field contrast using elastically scattered electrons.
• Evaluated scattering amplitude coefficients for carbon and thorium using relativistic Hartree-Fock-Slater wavefunctions.
• Simulated imaging conditions for a 100 keV microscope with and without spherical aberration correction.

Main Results:

• The study quantifies how finite atom size affects STEM image resolution.
• The developed method allows for the expansion of atomic images into spatial frequency components.
• Calculations show differences in scattering coefficients for carbon and thorium.
• Spherical aberration correction significantly increases the usable objective aperture (from 12 mrad to 30 mrad).

Conclusions:

• Finite atomic size is a critical factor influencing STEM resolution.
• The developed scattering amplitude expansion technique provides a framework for accurate atomic imaging.
• Aberration correction in STEM microscopes enhances resolution by allowing larger apertures.