High-resolution STEM imaging with a quadrant detector--conditions for differential phase contrast microscopy in the...

Area of Science:

• Materials Science
• Physics
• Electron Microscopy

Background:

• Differential phase contrast (DPC) is a key technique in scanning transmission electron microscopy (STEM) for mapping magnetic and electric fields.
• Various detector geometries exist for DPC, with recent focus on ring quadrant detectors for high-resolution imaging.

Purpose of the Study:

• To evaluate and compare the contrast transfer characteristics of different quadrant detector geometries for DPC in STEM.
• To determine the impact of detector geometry on the achievable resolution in aberration-corrected STEM.

Main Methods:

• Analytical calculation of phase gradient transfer functions for different quadrant detector geometries (two ring quadrant detectors and a conventional quadrant detector).
• Modeling was performed for an ideal microscope and a weak phase object assumption.

Main Results:

• The phase gradient transfer functions reveal that ring quadrant detectors, particularly those with small inner angles, limit resolution.
• A barely illuminated ring quadrant detector setup for magnetic field imaging in STEM reduces resolution to approximately 2.5 angstroms.
• Conventional quadrant detectors offer significantly improved resolution compared to ring quadrant detectors.

Conclusions:

• The choice of detector geometry critically impacts the resolution achievable with DPC in STEM.
• Conventional quadrant detectors are superior to ring quadrant detectors for high-resolution DPC imaging, enabling resolutions better than 2.5 angstroms in aberration-corrected STEM.