Efficient phase contrast imaging in STEM using a pixelated detector. Part II: optimisation of imaging conditions

Area of Science:

• Materials Science
• Physics
• Electron Microscopy

Background:

• Scanning transmission electron microscopy (STEM) is crucial for atomic resolution imaging.
• Phase contrast imaging in STEM traditionally uses methods like ABF and DPC.
• Ptychography offers a novel approach to phase contrast imaging in STEM.

Purpose of the Study:

• To quantitatively analyze the performance of ptychographic phase reconstruction with pixelated detectors in STEM.
• To compare ptychography with existing STEM phase contrast techniques.
• To optimize imaging parameters for weak phase objects and beam-sensitive specimens.

Main Methods:

• Theoretical analysis and simulations of ptychographic phase reconstruction.
• Comparison with annular bright field (ABF) and differential phase contrast (DPC) imaging modes.
• Evaluation of detector pixel array size and convergence angle effects.

Main Results:

• Ptychography with pixelated detectors demonstrates higher contrast transfer efficiency than ABF and DPC.
• The method offers superior performance at low electron doses.
• Applying ptychography to DPC segmented detectors improves contrast transfer and reduces noise.
• A 16x16 pixel array is sufficient for high signal-to-noise ratio (SNR) imaging of weak phase objects.
• Adjustable convergence angles enhance contrast transfer based on specimen spatial frequencies.

Conclusions:

• Ptychographic phase reconstruction with pixelated detectors is a highly efficient and robust method for STEM imaging.
• This technique surpasses conventional STEM phase contrast methods in contrast transfer and low-dose capabilities.
• Optimizing detector configuration and imaging parameters further enhances image quality for advanced materials analysis.