Reuniting crystallography with real space: Ab initio structure elucidation with 4D-STEM

Area of Science:

• Crystallography
• Materials Science
• Electron Microscopy

Background:

• Traditional single-crystal structure elucidation relies solely on diffraction-space data.
• Experimental access to real-space information has been limited in crystallography.
• Agglomerated nanostructures pose challenges for conventional microcrystal electron diffraction.

Purpose of the Study:

• To integrate real-space information into the crystallographic workflow using 4D scanning transmission electron microscopy (4D STEM).
• To overcome limitations of conventional methods for structure determination of challenging nanoscale materials.
• To enable direct methods for solving scanning nanobeam electron diffraction structures.

Main Methods:

• Exploiting the dual-space imaging capabilities of 4D STEM.
• Utilizing virtual apertures created by segmenting high-angle annular dark-field (HAADF) images.
• Separating coherent Bragg signals from closely spaced nanocrystals.
• Selectively extracting integrated intensities from specific subregions of specimens.

Main Results:

• Pixel-by-pixel separation of Bragg signal from nanocrystal clusters.
• Selective intensity extraction for tuning multiple scattering artifacts.
• Successful structure solution of the metal-organic framework UiO-66 from intractable specimens.
• Demonstration of subangstrom resolution structures determined by direct methods using scanning nanobeam electron diffraction.

Conclusions:

• The developed 4D STEM strategy effectively integrates real-space and diffraction-space data for structure elucidation.
• This method allows for the selection of optimal nanoscale regions for high-quality diffraction data acquisition.
• It provides a powerful new approach for solving crystal structures of nanomaterials, including those with complex morphologies.