Two major problems that limit the resolution and interpretation of electron microscopy images are lens aberrations and multiple scattering. Cornell University’s Professor David Muller and colleagues from the United States, Switzerland and Germany overcame these issues with a computational imaging technique called ptychography. Using sophisticated 3D reconstruction algorithms and an electron microscope pixel array detector (EMPAD), they achieved ultimate resolution better than the thermal vibration of atoms in a praseodymium orthoscandate (PrScO3) crystal and showed that it is theoretically possible to identify single atoms.
Ptychography works by scanning overlapping scattering patterns from a material sample and looking for changes in the overlapping region.
“We’re chasing speckle patterns that look a lot like those laser-pointer patterns that cats are equally fascinated by,” Professor Muller said.
“By seeing how the pattern changes, we are able to compute the shape of the object that caused the pattern.”
The EMPAD detector is slightly defocused, blurring the beam, in order to capture the widest range of data possible.
These data are then reconstructed via complex algorithms, resulting in an image with picometer (one-trillionth of a meter) precision.
“With these new algorithms, 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,” Professor Muller said.
“When we talk about temperature, what we’re actually measuring is the average speed of how much the atoms are jiggling.”
The physicists could possibly top their record again by using a material that consists of heavier atoms, which wobble less, or by cooling down the sample.
But even at zero temperature, atoms still have quantum fluctuations, so the improvement would not be very large.
This latest form of electron ptychography will enable the researchers to locate individual atoms in 3D when they might be otherwise hidden using other imaging methods.
They will also be able to find impurity atoms in unusual configurations and image them and their vibrations, one at a time.
“We want to apply this to everything we do,” Professor Muller said.
“Until now, we’ve all been wearing really bad glasses. And now we actually have a really good pair.”
“Why wouldn’t you want to take off the old glasses, put on the new ones, and use them all the time?”
The team’s paper was published in the journal Science.
Zhen Chen et al. 2021. Electron ptychography achieves atomic-resolution limits set by lattice vibrations. Science 372 (6544): 826-831; doi: 10.1126/science.abg2533
Source link: https://www.sci.news/physics/ultraprecise-images-atoms-09738.html