Interim Berkeley Lab Director Paul Alivisatos and Ulrich Dahmen, director of Berkeley Lab’s National Center for Electron Microscopy (NCEM), led a team of experts in nanocrystal growth and electron microscopy 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.
A new technique known as “liquid cell in situ transmission electron microscopy,” in which the powerful resolution capabilities of a transmission electron microscope (TEM) are brought to bear on a liquid cell that allows liquids to be observed inside a vacuum, enables the visualization of single nanoparticles in solution. The Berkeley researchers deployed this technique on NCEM’s JEOL 3010 In-Situ microscope. Utilizing an electron beam operating at 300 kilovolts of energy, the JEOL 3010 provides outstanding specimen penetration and spatial resolution of about 8 angstroms through the thick liquid cell sample.
Zheng H, Smith RK, Jun YW, Kisielowski C, Dahmen U, Alivisatos AP (2009): Observation of Single Colloidal Platinum Nanocrystal Growth Trajectories. Science Jun 5;324(5932):1309-12.