A journey that began over a century ago with the invention of the first electron microscope has progressed once again.
A group of physicists has gotten even closer to the ultimate limit of how many objects can be amplified, according to experts. The world record for the greatest resolution attained using a microscope was previously held by this group. Their most recent study, which was published in Science, reduces that record even further.
David Muller, a physicist at Cornell University and one of the paper’s authors, says: “This is the highest-resolution imaging in human history.”
With the kinds of microscopes you would have used in school, you won’t get anywhere to this level of resolution. Those microscopes perceive light, much as the ones employed by Robert Hooke over 300 years ago to see into a secret world of cells. That implies they can’t see anything smaller than the wavelength of the light they’re looking at. It’s a hard limit thousand times too high to consider seeing atoms.
In the early twentieth century, scientists had previously encountered this stumbling problem. If you want to get smaller—for example, to study viruses and build a polio vaccine—you’ll need to employ a medium with a shorter wavelength than light.
You may look into electrons, which are small charged particles that circle an atom’s nucleus. In the 1930s, scientists like Ernst Ruska began developing the first electron microscopes, which use electron beams to probe small objects in great detail.
Electrons have 100,000 times shorter wavelengths than light. They may theoretically be used to see inside atoms, which are the fundamental building blocks of all regular stuff. But there’s a problem, and it’s not the fault of the electrons. Muller claims that the lens quality of electron lenses is “terrible.”
As many astronomers know, no imaging technology is ideal. Electromagnetic lenses in electron microscopes, on the other hand, are notoriously fuzzy. According to Muller, gazing through a conventional electron microscope is like looking at the light through a beer bottle.
Attaching “aberration correctors,” which are like prescribing a pair of glasses for your electron microscope, is one approach to get around this. However, if you want to gaze at atoms, you’ll need a symphony of aberration correctors. Imagine a hundred pairs of spectacles that are continually moving.
Computers have made this possible by the 1990s and 2000s, boosting microscope resolution to new heights. Aberration correctors ruled the resolution throne for a while. However, by the 2010s, the technology had run out of steam.
To keep pushing the limits of microscope resolution, Cornell scientists went a less-traveled path: they eliminated lenses. Instead, they fired electrons at a target and observed how they dispersed.
The bombarding electrons will be thrown off course by the object’s atoms as they travel, bending them into a pattern on the object’s far side. You may take an entire album of patterns by flashing electrons at an item from numerous angles. You may stitch such patterns together using today’s technology to create a tiny representation of the original thing.
It’s known as ptychography (Tai-KAW-graf-ee). X-ray scientists now utilize their kind of ptychography, but it proved a dead end for electron-watchers. According to Yi Jiang, a physicist at Argonne National Laboratory and a co-author of the article, scientists have been talking about electron ptychography in principle for half a century, but it has just become viable in the last half-decade.
For one thing, scientists previously lacked detectors capable of pinpointing where enough electrons fell. For instance, even a single atom may hurl electrons in all kinds of crazy ways. Even with contemporary technology, this is difficult to account for. As a result, when it comes to resolution, aberration correctors had an order of magnitude advantage over ptychography.
The Cornell group, on the other hand, thought ptychography had potential. They had created cutting-edge electron detectors by the mid-2010s. They used X-ray physicists’ algorithms to do this. They also made the situation easier by reducing the size of their electron beam and filing their item to the least feasible thickness.
And it worked in 2018. The Cornell team outperformed aberration correctors to reach the best microscope resolution ever, resulting in a Guinness World Record.
It wasn’t a failsafe procedure, of course. Muller explains, “All we could do was work with these materials that were only one or two atoms thick.”
The group, though, questioned whether they could make it any smaller. They possessed the necessary equipment, but they required their computers to account for the annoying scattering of electrons. They had to push their way through a physics issue that had remained unsolved for 80 years.
It took the Cornell team three years of working with algorithms—three years that Muller said felt useless at times. However, owing to Cornell postdoc Zhen Chen’s efforts, they were able to find a solution that worked.
What’s the result? They’ve doubled their previous world record.
“This is a seminal paper,” says Matthew Joseph Cherukara, a computational scientist at Argonne National Laboratory who wasn’t involved in the research. “It’s a proof of improved algorithms and computation’s strength in breaking and surpassing physical restrictions of microscopes.”
Is it possible for scientists to go much further?
The answer is, to put it bluntly, unclear.
Look at the photos from the Cornell group, and you’ll see that the atoms are a little hazy. That isn’t a result of the detector’s aberration or air interference. It’s the atoms themselves trembling as they vibrate under heat. To keep the atoms in place, you could cool them down, but probing them with electrons only heats them again.
As far as scientists know, they won’t be able to overcome the blur until they develop a new method of looking at atoms.
“We’re almost to the end of the road,” Muller adds.