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.