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TEHRAN, Jun 29 -Scientists have for the first time captured atomic nucleation in 4D, the movement of atoms across space and time.
TEHRAN, Young Journalists Club (YJC) -Nucleation is the coalescence of atoms and molecules that happens as matter changes states -- during freezing, melting or evaporation. Using a new high-tech imaging technique, scientists were able observe the movement of atoms during nucleation in four dimensions.
"This is truly a groundbreaking experiment -- we not only locate and identify individual atoms with high precision, but also monitor their motion in 4D for the first time," Jianwei "John" Miao, professor of physics and astronomy at UCLA, said in a news release.
Using a powerful electron microscope at Berkeley Lab's Molecular Foundry, researchers deployed an imaging technique called "atomic electron tomography." As a molecular sample spins, the microscope captures 3D images of the atoms inside the sample.
For their experiments, scientists used the novel imaging technology to observe iron-platinum alloy nanoparticles as they were heated to 968 degrees Fahrenheit, a temperature that triggers a transition between two different solid phases. Researchers snapped 3D images after 9 minutes, 16 minutes and 26 minutes.
Before heating, the alloy's internal structure is more haphazard. Images of the atomic movements showed the material's atomic structure takes on a more rigid pattern, with alternating layers of iron and platinum atoms, after being heated.
Scientists were able to track the movements of the same 33 nuclei, some containing as few as 13 atoms, at 9 minutes, 16 minutes and 26 minutes.
Until now, scientists assumed nuclei were relatively round and boasted a sharp boundary, but the new imaging breakthrough showed nuclei formed irregular shapes. Images showed each nuclei was formed by a collection of atoms that had adopted the structure of the new phase. However, the atoms closer to the center of the nuclei were more disorganized than the atoms farther away.
During the phase transition, scientists observed nuclei shrinking, dividing, merging and even disappearing. Previous theories of nucleation posited that nuclei, once formed, can only get bigger and bigger.
"Nucleation is basically an unsolved problem in many fields," said Peter Ercius, a staff scientist at the Molecular Foundry. "Once you can image something, you can start to think about how to control it."
The new findings -- published this week in the journal Nature -- may force scientists to rethink the atomic models describing a variety of chemical and physical phenomena.
source:upi
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