Scientists from UCLA have discovered a new way to look at nucleation. By using 4D atomic resolution (which is three dimensions of space and time), the team was able to record how atoms rearrange. Their new discovery, which can be found in the journal Nature, offers a different perspective from predictions made on the original theory of nucleation that can be found in textbooks.
Nanoparticles in an iron-platinum alloy changes state three different times. Observations were recorded using a state-of-the-art microscope with a unique technique. (Image Credit: UCLA, Alexander Tokarev)
Research conducted by the team and collaborators from Lawrence Berkeley National Laboratory, University of Colorado at Boulder, University of Buffalo and the University of Nevada, Reno, uses a powerful imaging technique called “atomic electron tomography.” It uses a state-of-the-art electron microscope, which takes live image samples through electrons. The sample gets rotated and produces three-dimensional images of atoms located in a material.
The team used this technique to study an iron-platinum alloy taking the formation of tiny nanoparticles to take a closer look at the effects of nucleation. This was completed by heating the nanoparticles up to 520 degrees Celsius (968 degrees Fahrenheit) and developed images of them after 9, 16 and 26 minutes, respectively. At 526 degrees Celsius, the alloy went through a transitional phase between two different solid states. During the transitions from a naked eye, the alloy looks like it didn’t go through any changes, but under the microscope, the team was able to determine differences in the atomic arrangements. After the alloy was heated up, the team could see how the structure altered. It went from a scattered chemical state to an organized, more layered state made of iron and platinum atoms. The transitional phases can be compared to a Rubik’s cube, when starting out, all the colored squares are disorganized and misaligned, which is similar to the scattered state. However, when the Rubik’s cube is solved, the colors are more organized and aligned, very similar to the layered state.
Jihan Zhou and Yongsoo Yang’s team were also able to trace the 33 nuclei, some of which were similar to the size of 13 atoms, down to one nanoparticle. They found that nuclei have irregular shapes, which is opposite of what the theory suggests, that nuclei are perfectly round and have a sharp boundary. In their observations, the team also found that nuclei have a core of atoms that altered to the organized phase, but each arrangement became disorganized when it was close to the nucleus’ surface.
Classical nucleation theory also suggests that a nucleus will continue its growth pattern when it reaches a certain point, but there seems to be a more complex process than that. Nuclei in the study actually shrunk in size, while some divided, merged and others completely dissolved.
These studies prove that nucleation theory is inaccurate when compared to what actually takes place at the atomic level of nuclei. This can also progress and improve research in physics, chemistry, materials science, environmental science and neuroscience.
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