Experts have developed powerful new technology that can be used in electron microscopes to allow them to view electrons individually.
The world's most advanced electron microscopes have allowed scientists to look at individual atoms. However, even at the highest resolutions, the resulting images have not been very clear.
Researchers at Cornell University have devised a new method that allowed them to achieve record-breaking electron microscopy resolutions. When retrofitted into electron microscopes, the technology lets them see a vast range of intensities, from single electrons to beams containing millions of them.
Aberration Correctors No Longer Needed
Electron microscopes use high-energy electron wavelengths that are smaller than visible light. However, the lenses of electron microscopes are riddled with aberrations that can distort the images.
To remedy this, scientists use special aberration correctors, which can be likened to vision-correcting eyeglasses for people with eyesight problems. These correctors can only do so much, though.
As the aberrations increase, experts also have to increase the number of correctors they use. It is like putting on eyeglasses on top of eyeglasses on top eyeglasses. It can get too bulky to use.
A team of Cornell physicists, led by David Muller, co-director of the Kavli Institute at Cornell for Nanoscale Science, has developed a new way to achieve high-resolution electron microscope images without the need for such correctors.
Achieving Sub-Angstrom Resolutions
In a new study published in the journal Nature, the physicists have achieved a new world record for electron microscope resolutions. Called Electron Microscope Pixel Array Detector, the technology uses a one-atom-thick layer of molybdenum disulfide to achieve a resolution of 0.39 angstrom.
One angstrom is equivalent to 0.1 nanometers. In general, atomic bonds measure 1 to 2 angstroms in length. Any resolution below 1 angstrom should allow experts to see individual atoms.
In electron microscopes, the resolution depends mostly on the aperture of the lens. On a basic camera, the aperture is defined by the f-stop. A lower f-stop yields better resolutions. For instance, a good camera typically has its lowest f-stop at less than 2.
Electron microscopes, on the other hand, typically have an f-stop of 100. With a good array of correctors, this number can be reduced to 40, which is a significant improvement but still not that great.
What EMPAD Can Do
Previous attempts to improve resolution included increasing the aperture and the high-energy electron beam, which illuminates the object being observed by the microscope. The most recent record involved using a super-high-energy beam at 300 kiloelectronvolts or keV to reach a resolution below 1 angstrom.
EMPAD uses a lower energy beam of 80 keV to keep it from damaging the molybdenum disulfide. It also uses a technique called ptychography, which takes full-position and momentum distributions of the sample before creating an image from the dataset.
The result is a resolution so good that the researchers were able to see that one sulfur atom was missing in a 2D material, an "astounding" feat, according to co-author Sol Grunner.
"The analogy I like to use is, a car is coming at you at night," says Grunner. "And you're looking at the lights coming at you, and you're able to read the license plate between them without being blinded."