Amazing microscope sees atoms at record resolution

This image shows an electronic ptychographic reconstruction of a crystal of praseodymium orthoscandate (PrScO3), zoomed 100 million times. Credit: Cornell University

In 2018, Cornell researchers built a high-power detector that, combined with an algorithm-based process called ptychography, defines a world record by tripling the resolution of a state-of-the-art electron microscope.

As successful as it was, this approach had a weakness. It only worked with ultra-thin samples a few atoms thick. Anything thicker would cause the electrons to scatter in a way that cannot be untangled.

Today, a team, again led by David Muller, professor of engineering Samuel B. Eckert, broke their own record by a factor of two with an electron microscopic pixel array detector (EMPAD) that incorporates algorithms even more sophisticated 3D reconstruction techniques.

The resolution is so fine that the only blur that remains is the thermal tremor of the atoms themselves.

The group’s article, “Electronic ptychography reaches limits of atomic resolution set by lattice vibrations,” published May 20 in Science. The main author of the article is postdoctoral researcher Zhen Chen.

“It doesn’t just set a new record,” Muller said. “He’s hit a diet that’s actually going to be an ultimate limit for resolution. We can now determine where the atoms are in a very simple way. This opens up a bunch of new possibilities for measuring things that we’ve wanted to do for a very long time. It also solves a long-standing problem – canceling the multiple scattering of the beam in the sample, which Hans Bethe introduced in 1928 – which has prevented us from doing so in the past.

Ptychography works by scanning for overlapping diffusion patterns from a sample of material and looking for changes in the region of overlap.

“We’re looking for speckle patterns that look a lot like those laser pointer patterns that also fascinate cats,” Muller said. “By seeing how the pattern changes, we are able to calculate the shape of the object that caused the pattern.”

The detector is slightly defocused, jam the beam, in order to capture the widest range of data possible. This data is then reconstructed using complex algorithms, which gives an ultra-precise image with picometer precision (one trillionth of a meter).

“With these new algorithms, we are now able to correct all the blurring in our microscope to the point that the biggest blurring factor we have left is the atoms themselves wobbling, because that’s what happens to the atoms. atoms at finite temperature. ”Muller said. “When we talk about temperature, what we’re actually measuring is the average speed at which atoms are shaking.”

The researchers could perhaps beat their record again by using a material made up of heavier atoms, which oscillate less, or by cooling the sample. But even at zero temperature, atoms still have quantum fluctuations, so the improvement would not be very great.

This latest form of electron ptychography will allow scientists to locate individual atoms in three dimensions when they might otherwise be hidden using other imaging methods. Researchers will also be able to find dirt atoms in unusual configurations and image them with their vibrations, one at a time. This could be particularly useful in imaging semiconductors, catalysts, and quantum materials – including those used in quantum computing – as well as for the analysis of atoms at the frontiers where materials are assembled.

The imaging method could also be applied to thick biological cells or tissues, or even synapse connections in the brain – what Muller calls “on-demand connectomics”.

Although 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 that to everything we do,” said Muller, who co-leads the Kavli Institute at Cornell for Nanoscale Science and co-chairs the Microsystems Science and Engineering working group at the nanoscale (NEXT Nano), which is part of Cornell’s radical collaborative initiative. . “Until now, we all wore really bad glasses. And now we actually have a really good pair. Why wouldn’t you want to take the old glasses off, put on the new ones, and use them all the time? “

Reference: “Electronic ptychography reaches the limits of atomic resolution set by network vibrations” by Zhen hen, Yi Jiang, Yu-Tsun Shao, Megan E. Holtz, Michal Odstrcil, Manuel Guizar-Sicairos, Isabelle Hanke, Steffen Ganschow, Darrell G. Schlom and David A. Mull, May 21, 2021, Science.
DOI: 10.1126 / science.abg2533

Co-authors include Darrell Schlom, Herbert Fisk Johnson professor of industrial chemistry; Yi Jiang, Ph.D. ’18 and now Data Scientist at the Argonne National Laboratory; postdoctoral fellows Yu-Tsun Shao and Megan Holtz, Ph.D. “17; and researchers from the Paul Scherrer Institute and the Leibniz Institute for Crystal Growth.

The research was supported by the National Science Foundation through the Cornell Platform for Accelerated Completion, Analysis and Discovery of Interface Materials (PARADIM). The researchers also used the Cornell Center for Materials Research, which is supported by the NSF Materials Research Science and Engineering Center program.

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