Towards quantitative, atomic-resolution reconstruction of the electrostatic potential via differential phase contrast...

Area of Science:

• Materials Science
• Physics
• Electron Microscopy

Background:

• Differential phase contrast (DPC) imaging in scanning transmission electron microscopy (STEM) can quantitatively relate to projected specimen potential gradients.
• Accurate potential reconstruction relies on treating the specimen as a phase object and obtaining full 2D diffraction patterns at each probe position.
• These conditions are difficult to meet in atomic resolution imaging due to probe spreading, dynamical electron scattering, and the non-routine nature of full diffraction data acquisition.

Purpose of the Study:

• To investigate the validity domain of the phase object approximation in atomic resolution DPC imaging.
• To explore the feasibility of using established segmented detector geometries for reconstructing a quantitative approximation of the projected specimen potential.
• To assess the limitations and potential of alternative DPC imaging approaches when full diffraction data is unavailable.

Main Methods:

• Analysis of the phase object approximation's limitations in the context of atomic resolution DPC imaging, considering probe spreading and dynamical scattering.
• Exploration of data acquisition and reconstruction strategies using segmented detector geometries in STEM.
• Quantitative assessment of the approximation accuracy for projected specimen potential reconstruction.

Main Results:

• The phase object approximation in DPC imaging is fundamentally limited by probe spreading and dynamical electron scattering at atomic resolutions.
• Proof-of-principle experimental data sets for full 2D diffraction patterns exist but are not yet routinely obtainable.
• Segmented detector geometries can provide a quantitatively good approximation to the projected specimen potential, offering a viable alternative.

Conclusions:

• Achieving direct and quantitative relation between DPC images and projected specimen potential gradients requires overcoming significant challenges in atomic resolution STEM.
• While full 2D diffraction pattern acquisition remains a challenge, segmented detector geometries offer a practical approach for approximating specimen potential.
• This study highlights the trade-offs and potential solutions for quantitative potential mapping in advanced electron microscopy techniques.