Scientists at Berkeley Lab have developed a new method to determine atomic structures from nanocrystals previously considered unusable for crystallography. This breakthrough addresses limitations in conventional X-ray crystallography, which requires large, pristine single crystals, and even MicroED, which can struggle with clustered nanocrystals.
This breakthrough addresses limitations in conventional X-ray crystallography, which requires large, pristine single crystals, and even MicroED, which can struggle with clustered nanocrystals.
A New Approach: 4D-STEM with Virtual Apertures
The new approach combines 4D-STEM (four-dimensional scanning transmission electron microscopy) with computational "virtual apertures." Key aspects of the method include:
- 4D-STEM: Uses a focused electron beam to raster-scan a sample, recording an independent diffraction pattern at hundreds of thousands of probe positions.
- Virtual Apertures: These computational tools allow researchers to selectively analyze data from specific regions of a nanoscale sample, isolating individual nanocrystals within clusters or pinpointing optimal subregions within a single nanocrystal.
- Advanced Hardware: The system utilizes a custom-built 4D Camera operating at 87,000 frames per second, generating a high data bitrate. This data is processed in real time by the Perlmutter supercomputer at NERSC.
Overcoming Conventional Hurdles
This method overcomes the limitations of traditional MicroED, where broad electron beams and physical apertures can lead to blurred diffraction patterns from clustered crystals. The virtual apertures provide granular precision, enabling the mining of data from previously problematic materials.
Demonstration and Future Applications
The team demonstrated the technique using UiO-66, a metal-organic framework (MOF). The method allowed for the determination of single-crystal structures from 4D-STEM data by direct methods at subangstrom resolution, without requiring the growth of larger crystals.
This precision could be transformative in fields such as drug delivery and gas capture, where understanding the atomic structure of porous MOFs is crucial. The researchers aim to further develop 4D-STEM to solve single-crystal structures at even smaller length scales, targeting unit cells historically inaccessible to crystallography.