In recent decades, physicists have successfully probed matter at increasingly small scales until it reaches the atomic scale. These techniques are essential to understanding the internal structure – and thus the dynamics – of materials, but also the structure of biological tissues. A team of researchers broke a new record in accuracy thanks to the ptychographic algorithm, providing an unprecedented window into the behavior of atoms.
In 2018, Cornell researchers built a high-powered detector that, along with an algorithm-based process called ptychography, set a world record by tripling the resolution of an advanced electron microscope by three times. As successful as it was, this approach had a weakness. I only worked with very thin samples a few atoms thick. Anything thicker caused the electrons to be scattered in an inseparable way.
Recently, a team, led by engineering professor David Muller, broke their record for a multiplier using a Pixel Array Detection Electron Microscope (EMPAD), which includes more sophisticated 3D reconstruction algorithms. The resolution is so good that the only flux remaining is the thermal agitation of the atoms themselves.
« It doesn’t just set a new record. He’s been on a diet that will actually be a final limit to the decision. Now we can locate atoms in a very simple way. This opens up a whole host of new possibilities for measuring the matter around us. It also solves a long-standing problem: the de-dispersion of multiple beams in the sample, which Hans Beth created in 1928, and which has prevented us from doing so in the past. Mueller explains.
Record resolution thanks to textural printing
Ptychography works by scanning for overlapping diffusion patterns from a sample of material and looking for changes in the overlap region. ” We are looking for spotted patterns that closely resemble the “laser pointer” that also fascinates cats. By seeing how the pattern changes, we can calculate the shape of the object that caused the pattern. Muller says.
The detector is slightly defocused, which distorts the beam, in order to capture the largest possible range of data. This data is then reconstructed using complex algorithms, resulting in an ultra-high-resolution image with a pixel resolution.
« Using these new algorithms, we are now able to correct all of the noise in our microscope to the point that the biggest disturbance we have left is the atoms themselves oscillating, because that’s what happens to atoms. At a limited temperature Mueller explains. ” When we talk about temperature, what we’re actually measuring is the average speed of vibration of the atoms. ».
Perhaps the researchers could break their record again by using a material made of heavier atoms, which oscillated less, or by cooling the sample. But even at zero temperature, the atoms could still exhibit quantum fluctuations, so the improvement wouldn’t be much.
A technology with multiple applications
This newer form of electron modulation will allow scientists to locate individual atoms in three dimensions when they can be hidden otherwise using other imaging methods. Researchers will also be able to find dirt atoms in unusual configurations and photograph them with their vibrations, one after the other. This may be particularly useful for imaging semiconductors, catalysts, and quantum materials – including those used in quantum computing – as well as for analyzing atoms in interfaces where materials coalesce.
The imaging method can also be applied to cells or thick biological tissues, or even synaptic connections in the brain – what Mueller calls “connections on demand.” Although this method is time consuming and computationally demanding, it can be made more efficient by using more powerful computers in addition to machine learning and faster detection devices.
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