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July 2012

Revealing nanorod formation with liquid-cell TEM

Sequential TEM images show Pt3Fe nanorods forming by first making a kinked chain which then straightens out. On right, High-resolution STEM images reveal changes in crystal orientation as the chains relax.

Materials Science Division researcher Haimei Zheng, the Molecular Foundry's Stephen Whitelam, and colleagues have imaged iron-platinum nanoparticle forming from solution, helping resolve a decades-long debate about growth dynamics. By understanding how nanoparticles grow, researchers can better tailor their properties for cheap, efficient energy-related technologies.

Researchers have long assumed that nanoparticles grow in solution as molecules gradually attach to a nanoparticle nucleus, but recently they identified a second mechanism in which small nanoparticles join together like building blocks to form larger nanoparticles.

To understand this mechanism, which has been debated for decades, Zheng and coworkers took real-time transmission electron microscopy images of rod-shaped platinum-iron nanoparticles growing in solution. Their images reveal that small nanoparticle "blocks" first join into a crooked chain and then straighten out to form single-crystal rods.

The team worked with Whitelam to calculate the preferred attachment sites for a nanoparticle chain and confirmed their model for growth mechanism. With this knowledge, researchers can have greater control over nanoparticle properties and geometries, moving toward rational nanoparticle design.

"Real-Time Imaging of Pt3Fe Nanorod Growth in Solution," Hong-Gang Liao, Likun Cui, Stephen Whitelam, Haimei Zheng, Science, 336, 1011 (2012).
This work was performed using the facility at National Center for Electron Microscopy, Lawrence Berkeley National Laboratory (LBNL). This project was supported by the Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, of the U.S. Department of Energy (DOE) under Contract #DE-AC02-05CH11231. H.Z. thanks the U.S. DOE Office of Science Early Career Research Program for support and gratefully acknowledges partial support from LDRD LBNL.