Factors limiting quantitative phase retrieval in atomic-resolution differential phase contrast scanning transmission...

Area of Science:

• Materials Science
• Electron Microscopy
• Imaging Physics

Background:

• Quantitative differential phase contrast (DPC) imaging in atomic-resolution scanning transmission electron microscopy (STEM) faces limitations.
• Factors affecting DPC imaging include aberrations, detector issues, and scan distortions.
• Accurate phase reconstruction is vital for material characterization.

Purpose of the Study:

• To identify critical parameters for reliable quantitative phase interpretation in STEM DPC imaging.
• To compare experimental results with simulations for materials like graphene.
• To determine the impact of various factors on phase reconstruction accuracy.

Main Methods:

• Experimental imaging of monolayer and few-layer graphene using atomic-resolution STEM.
• Quantitative differential phase contrast (DPC) imaging with segmented detectors.
• Comparison of experimental data with detailed image simulations.

Main Results:

• Coherent and incoherent lens aberrations were identified as the most significant factors affecting phase reconstruction.
• Beam deflections coupled to beam scanning (imperfect tilt-shift purity) introduced substantial artifacts.
• Noise and non-periodic boundary conditions had less impact in this specific case study.

Conclusions:

• Precise characterization of lens aberrations is paramount for quantitative DPC imaging in STEM.
• Understanding and mitigating scan-related artifacts are essential for reliable phase interpretation.
• This study provides guidelines for optimizing DPC imaging of 2D materials.