In 2018, Cornell scientists came up with a high-powered detector that set a world record by tripling the resolution of a state-of-the-art electron microscope. Despite being successful, the technique approach had a weakness: It only worked with ultrathin samples that were a few atoms thick.
Now a team, again led by David Muller, the Samuel B. Eckert Professor of Engineering, has bested its record by a factor of two with an electron microscope pixel array detector (EMPAD) that incorporates even more sophisticated 3D reconstruction algorithms.
The resolution is so fine-tuned, the only blurring that remains is the thermal jiggling of the atoms themselves.
Muller said, “This doesn’t just set a new record. It’s reached a regime that 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.”
“We’re chasing speckle patterns that look a lot like those laser-pointer patterns that cats are equally fascinated by. By seeing how the pattern changes, we can compute the shape of the object that caused the pattern.”
The detector is marginally defocused, blurring the beam to capture the largest scope of data conceivable. This data is then reconstructed using complex algorithms, coming about in an ultraprecise image with picometer (one-trillionth of a meter) precision.
Using these new algorithms, scientists were able to correct all the blurring of our microscope to the point that the largest blurring factor they have left is that the atoms themselves are wobbling because that’s what happens to atoms at finite temperature.
Muller said, “When we talk about temperature, what we’re measuring is the average speed of how much the atoms are jiggling.”
This latest electron ptychography could help scientists locate individual atoms in all three dimensions when they might be otherwise hidden using other imaging methods. Scientists could also detect impure atoms in unusual configurations and image them and their vibrations, one at a time.
This is extremely useful in imaging semiconductors, catalysts, and quantum materials and analyzing atoms at the boundaries where materials are joined together.
Muller said, “While the method is time-consuming and computationally demanding, it could be made more efficient with more powerful computers in conjunction with machine learning and faster detectors.”
“We want to apply this to everything we do. Until now, we’ve all been wearing really bad glasses. And now we have a perfect pair. Why wouldn’t you want to take off the old glasses, put on the new ones, and use them all the time?”
- Electron ptychography achieves atomic-resolution limits set by lattice vibrations. Science, 21 May 2021: DOI: 10.1126/science.abg2533