UNITED STATES. Ithaca: A group of research scientists at Cornell University, Ithaca, have pictured the jiggling atoms through their state-of-art technique called ptychography. Their research paper, “Electron Ptychography Achieves Atomic-Resolution Limits Set by Lattice Vibrations,” was published in May in Science magazine. The paper’s lead author is postdoctoral researcher Zhen Chen.
David Muller at Cornell University in Ithaca, New York, and his colleagues captured this image using a praseodymium orthoscandate (PrScO3) crystal. They used a technique called ptychography, in which they shone x-rays on the crystal and then used the angles of scattered electrons to work out the shape of the atoms that scattered them. Ptychography can be used with visible light, X-rays, extreme ultraviolet (EUV), or electrons. Unlike conventional lens imaging, ptychography is unaffected by lens-induced aberrations or diffraction effects caused by the limited numerical aperture.
This image is double the resolution of a zoomed-in image of atoms made in 2018 by Muller and his team, which was itself triple the resolution of others taken at the time with different techniques.
In 2018, Cornell researchers built a high-powered detector that, in combination with an algorithm-driven process called ptychography, set a world record by tripling the resolution of a state-of-the-art electron microscope. As successful as it was, that approach had a weakness. It only worked with ultrathin samples that were a few atoms thick. Anything thicker would cause the electrons to scatter in ways that could not be disentangled.
Now a team, again led by David Muller, the Samuel B. Eckert Professor of Engineering, has bettered its own record by a factor of two with an electron microscope pixel array detector (EMPAD) that incorporates even more sophisticated 3D reconstruction algorithms.
“The key breakthrough we had this year was we figured out a way to unscramble this multiple scattering, and this is an 80-year-old problem,” says Muller. “For 80 years we haven’t had a general solution and now with some very clever algorithms developed by our colleagues [who work with x-rays] and then modified for electron scattering, we were able to untangle this multiple scattering,” Muller said.
This allowed the team to look at thicker samples and achieve a better resolution. The blurring in the current image comes from the movement of the atoms themselves.
“We can do a little bit better by cooling the sample down because when you cool the sample, the atoms don’t jiggle as much,” says Muller.