Optimal experiment design for element specific atom counting using multiple annular dark field scanning transmission...

Area of Science:

• Materials Science
• Physics
• Chemistry

Background:

• Accurate elemental identification in atomic columns is crucial for nanomaterial characterization.
• Scanning Transmission Electron Microscopy (STEM) with Annular Dark-Field (ADF) detectors is a powerful tool for atomic resolution imaging.
• Distinguishing between different atom types within the same atomic column presents a significant analytical challenge.

Purpose of the Study:

• To investigate the benefits of using multiple 2D ADF detector regimes in STEM for improved atom counting of different chemical species.
• To quantify the probability of error in determining the number of atoms of various types within atomic columns.
• To establish optimal experimental designs for atom counting by minimizing error probabilities.

Main Methods:

• Application of statistical detection theory to formulate atom-counting as a hypothesis test.
• Quantification of error probability considering electron counting noise and scattering cross-sections.
• Simulation of core-shell nanoparticles (Au@Ag, Au@Pt) to evaluate detector regime combinations.
• Comparison with pixelated 4D STEM detector performance.

Main Results:

• The combination of a narrow low-angle ADF detector with a wider annular detector regime is found to be optimal for distinguishing two atom types.
• The effectiveness of this optimal configuration increases with a larger difference in atomic numbers (Z) between elements.
• Subdividing detector regimes into three areas further improves accuracy for heterogeneous nanostructures with three or more atom types.
• The proposed method shows potential for reducing incident electron dose compared to pixelated 4D STEM detectors.

Conclusions:

• Optimizing ADF detector configurations significantly enhances the accuracy of multi-element atom counting in STEM.
• Statistical detection theory provides a robust framework for designing optimal imaging strategies in electron microscopy.
• These findings offer a pathway to more precise characterization of complex nanomaterials and heterogeneous nanostructures.