Imaging breakthrough could mean sharper analysis of semiconductors and quantum materials
NewsMay 28, 2021
ITHACA, N.Y. Researchers at Cornell University have improved their own high-powered microscope that now enables users to see atoms at record resolution, resulting in an ultraclose image with picometer (one-trillionth of a meter) precision.
The backstory: In 2018, Cornell researchers built a high-powered detector that -- together with an algorithm-driven process called ptychography, set a world record by tripling the resolution of a state-of-the-art electron microscope; the weakness of that approach, however, was that it worked only with ultrathin samples a few atoms thick, with anything thicker causing the electrons to scatter and become unvisualizable. Ptychography, according to the Cornell team, works by scanning overlapping scattering patterns from a material sample and watching out for changes in the overlapping region.
Now a team -- once again led by David Muller, Cornell University's Samuel B. Eckert Professor of Engineering -- has built on that work by a factor of two with an electron microscope pixel array detector (EMPAD) that uses increasingly sophisticated 3D reconstruction algorithms. Using the new algorithms, the EMPAD's resolution is so fine that the only blurring that remains is the thermal jiggling of the atoms themselves.
Set out in a paper in the latest issue of Science, "Electron Ptychography Achieves Atomic-Resolution Limits Set by Lattice Vibrations,” (with lead author listed as postdoctoral researcher Zhen Chen), the team asserts that this latest form of electron ptychography will enable scientists to find individual atoms in all three dimensions, atoms that would likely be hidden using other imaging methods.
Researchers will also be able to find impurity atoms in unusual configurations and view them and their vibrations singly, an aspect that they say may be particularly helpful in imaging semiconductors, catalysts, and quantum materials – including those used in quantum computing – as well as for analyzing atoms at the boundaries where materials are joined together.
“This doesn’t just set a new record,” stated Muller. “It’s reached a regime which is effectively going to be an ultimate limit for resolution. We basically can now figure out where the atoms are in a very easy way. This opens up a whole lot of new measurement possibilities of things we’ve wanted to do for a very long time. It also solves a long-standing problem -- undoing the multiple scattering of the beam in the sample, which Hans Bethe laid out in 1928 -- that has blocked us from doing this in the past.
“With these new algorithms," Muller continued, "we’re now able to correct for all the blurring of our microscope to the point that the largest blurring factor we have left is the fact that the atoms themselves are wobbling, because that’s what happens to atoms at finite temperature. When we talk about temperature, what we’re actually measuring is the average speed of how much the atoms are jiggling.”
