Electron Beam Precession Enhances Serial Crystallography in 3D Electron Diffraction

What is it about?

This research investigates the application of electron beam precession in (scanning) transmission electron microscopy for serial crystallography experiments, specifically focusing on 3D electron diffraction. The methodology involves collecting electron diffraction patterns from numerous randomly oriented BaSO₄ crystals, both with and without the use of precession angles selected to exceed the Bragg angle, across different microscopes and imaging setups. Data acquisition protocols included automated or manual selection of crystalline targets, the collection of diffraction patterns for each, and subsequent processing using adapted serial crystallography pipelines. The study demonstrates that precession electron diffraction (PED) reduces dynamical scattering effects within individual patterns, allowing for fewer patterns to achieve reliable crystal structure determination and refinement. Key findings show that merging data from fewer crystals with precession achieves similar or improved data quality compared to larger datasets without precession, as evidenced by significantly improved Rᵢₙₜ and Rᵣᵢₘ values and reduced residual electrostatic potentials. Dynamical refinement of the structures is shown to be more accurate, with better agreement to reference models and lower noise levels, when precession is used. The results suggest that PED in serial electron crystallography enables efficient, accurate structure determination with reduced experimental requirements, broadening accessibility to laboratories lacking advanced automation or specialized instrumentation.

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Why is it important?

This research thoroughly investigates the application of electron beam precession in (scanning) transmission electron microscopes for serial crystallography, aiming to enhance crystal structure determination and refinement using 3D electron diffraction methods. The study addresses the need for improved methodologies in structural analysis of nanocrystals, especially where access to advanced X-ray facilities is limited, and highlights the advantages of electron-based approaches for broader laboratory adoption. Key Takeaways: 1. The research demonstrates that integrating electron beam precession in serial electron diffraction experiments significantly reduces dynamical effects in individual diffraction patterns, enabling the extraction of pseudo-kinematical reflection intensities with fewer measured crystals. 2. Findings reveal that precession facilitates more accurate and reliable crystal structure refinements, allowing for anisotropic refinement of atomic displacement parameters and lowering residuals and noise in difference Fourier maps compared to non-precessed data. 3. The study shows that utilizing precession minimizes the number of required diffraction patterns for successful structure determination, streamlining data acquisition and making advanced structure analysis feasible in laboratories without specialized automation or tomography setups.