Closer Look at Nanoparticle Growth Through a Graphene Window
Many important phenomena occur in liquids but to study them at the nanometer scale with electron microscopes, scientists must encapsulate liquid samples in tiny cells with windows of silicon nitride or quartz. These windows interfere with electron transmittance, limiting image resolution to a few nanometers – too large to see individual atoms.
Alivisatos and his team instead created a new kind of liquid cell: a graphene pocket just a few hundred nanometers across, fabricated by growing two layers of graphene on a flat surface and letting a drop of liquid wick between the layers. Using a transmission electron microscope at the National Center for Electron Microscopy, the team imaged platinum nanoparticles growing from solution in a graphene cell with sub-nanometer resolution and discovered a host of unexpected phenomena. This technique opens the door to understanding solution-phase phenomena at the atomic level.
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.