Three-dimensional optical transfer functions in the aberration-corrected scanning transmission electron microscope

Area of Science:

• Electron Microscopy
• Optics and Vision

Background:

• Hardware aberration correctors in scanning transmission electron microscopes (STEM) can correct for positive spherical aberration in round electron lenses.
• These correctors utilize nonround optics (e.g., hexapoles, octupoles), introducing nonround aberrations as potential performance limitations.

Purpose of the Study:

• To investigate the impact of various potential limiting aberrations on STEM imaging performance.
• To analyze the behavior of optical transfer functions (OTFs) in response to changes in defocus.

Main Methods:

• Analysis of optical transfer functions (OTFs) to assess imaging performance.
• Examination of the three-dimensional OTFs to evaluate system performance for specific applications.

Main Results:

• Nonround aberrations can become the limiting factor in imaging performance after spherical aberration correction.
• The response of the OTF to defocus variations was analyzed, highlighting its critical role in image acquisition.
• Three-dimensional OTFs provide a comprehensive assessment of system capabilities.

Conclusions:

• Understanding the influence of nonround aberrations and defocus is crucial for optimizing STEM imaging.
• The methodology allows for the assessment of STEM systems for advanced applications like focal-series experiments and optical sectioning.