Scientists record first real-time direct observations of nanocrystal growth in solution

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Washington, August 10 (ANI): In a new research, scientists at Berkeley Lab in the US have recorded first real-time direct observations of the growth of single nanocrystals in solution.

Interim Berkeley Lab Director Paul Alivisatos and Ulrich Dahmen, director of Berkeley Lab's National Center for Electron Microscopy (NCEM), led the research team, who combined their skills to observe the dynamic growth of colloidal platinum nanocrystals in solution with subnanometer resolution.

Their results showed that while some crystals in solution grow steadily in size via classical nucleation and aggregation - meaning molecules collide and join together - others grow in fits and spurts, driven by "coalescence events," in which small crystals randomly collide and fuse together into larger crystals.

Despite their distinctly different growth trajectories, these two processes ultimately yield a nearly monodisperse distribution of nanocrystals, meaning the crystals are all approximately the same size and shape.

"Coalescence events have been previously observed in flask synthesis of colloidal nanocrystals and has been considered detrimental for achieving monodisperse colloidal nanocrystals," said Haimei Zheng, a chemist in Alivisatos' research group.

"In our study, we found that coalescence events are frequently involved in the early stage of nanocrystal growth and yet monodisperse nanocrystals are still formed," he added.

According to Alivisatos, "This direct observation of nanocrystal growth trajectories revealed a set of pathways more complex than those previously envisioned and enables us to re-think the nanocrystal growth mechanism with an eye towards more controlled synthesis."

"Video-rate acquisition allowed us to track nanocrystal growth trajectories from frame-to-frame," said Haimei Zheng, a chemist in Alivisatos' research group.

"This allowed us to observe that each nanocrystal can either grow steadily through the addition of monomers from solution or by merging with another nanocrystal in random coalescence events," he added.

Zheng said that it has been assumed that coalescence events would result in some crystals being much larger than others, a bad thing in that the physical properties of nanocrystals are so dependent upon size and shape that for many applications it is critical that monodispersed nanocrystals be produced during synthesis.

Consequently, strategies such as the use of surfactants to coat nanocrystal surfaces have been adopted to avoid coalescence events.

"Our observations provide invaluable direct information on how nanocrystals grow and indicate how we might directly control nanocrystal synthesis for tailored properties," said Zheng.

"Also, our in situ liquid cell TEM (transmission electron microscope) technique can be applied to other areas of research such as soft matter imaging and nanoparticle catalysis, and offers great potential for addressing many fundamental issues in materials science, chemistry and other fields of science," he added. (ANI)

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