Advanced scan generator unlocks new possibilities in 4DSTEM at UCLA user facility

More analytical methods for materials research now available at CNSI technology center

A convergent electron probe is rastered across a 2 dimensional (2D) region containing the region of interest. All the while, a camera mounted below the sample collects 2D diffraction patterns at each point in the raster scan. The 4 dimensional (4D) dataset can select regions is real space and what diffraction patterns they contain, or what features in reciprocal space give contrast in real space. (Image courtesy: EICN at CNSI / UCLA)

The addition of a new advanced scan detector at the Electron Imaging Center for Nanomachines (EICN) expands the palette of analytical techniques available to investigators developing or characterizing new types of materials.

The Direct Electron DE-FreeScan makes possible 4D scanning transmission electron microscopy (STEM), in which diffraction patterns are simultaneously captured for every position in a specimen. At the EICN, a technology center of the California NanoSystems Institute at UCLA, the DE-FreeScan unlocks this possibility in concert with the FEI Titan 80-300and DE-64 electron counting camera.

“4DSTEM can detect crystals too small to analyze with other methods,” said Matthew Mecklenburg, managing director of the EICN. “Crystals that are just a few nanometers in size can be seen and analyzed from the scattered pattern captured on the camera. This enables the study of defects, interfaces and crystal domains in finer detail than before. FreeScan adds the 2D mapping to the 2D diffraction that makes 4DSTEM possible.”

Access to these instruments — along with training and expert consultation — is available to researchers from UCLA and other academic institutions, as well as private companies.

The advantages of FreeScan derive from the capacity to alter scan patterns in ways that open up a variety of subsampling strategies for evaluation. Scientists and engineers can reconstruct differential phase contrast and center of mass images, characterize internal electric fields, identify crystal phase and orientation as a function of position, and generate strain maps.

Using nonstandard scan patterns, researchers can also limit exposure of samples susceptible to damage or efficiently focus in on the specific features they are studying. In addition, up to four simultaneous external analog signals can be connected to the FreeScan to enable simultaneous recording of high-angle annular dark-field and 4DSTEM signals.

“4DSTEM parallelizes the contrast in dark-field and bright-field imaging into one single acquisition,” Mecklenburg said. “The FreeScan unit gives us this access to 4DSTEM with our counting camera. This is a powerful way to access spatial frequencies over a wide range of imaging modes.”

Those interested in general information, project consultation and proof-of-concept, or training and assistance with the FEI Titan, DE-64 and FreeScan can contact the EICN helpdesk at