3D atomic imaging reveals a new pathway to crystal formation
The most common scientific approach for thinking about how condensation, freezing and other phase transitions begin is based in classical nucleation theory, which was developed about a century ago. Thousands of experiments have supported a key equation describing how initial ordered seeds, called nuclei, form within disordered matter.
A groundbreaking study led by UCLA researchers challenges long-standing theories of crystal formation. Utilizing nanoparticles with varying degrees of atomic order, the team devised a method to capture crystal nuclei at different stages of development. When examined through a 3D imaging technique called atomic electron tomography, the crystals displayed a gradient structure, unlike the sharp boundary predicted by classical nucleation theory.
Corresponding author Jianwei John Miao, a professor of physics and astronomy at UCLA, explained that the crystals possess a core of highest crystallinity gradually transitioning to increasing disorder at the boundary. The researchers introduced a new model, the gradient nucleation pathways model, which generalizes classical nucleation theory and accounts for the observed gradient structure at the atomic level.
This finding suggests that classical theory is merely a special case, and the energy barrier for nucleation involves a more nuanced, multi-step process. The study extends beyond fundamental scientific understanding, as crystal nucleation is observed in diverse systems, from cloud droplets to industrial manufacturing. The researchers' insights could influence the design of materials with unique properties, impacting industries such as electronics, pharmaceuticals, and more.
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