Videos of gold nanoparticles snapping together show how some crystals grow

Mesmerizing videos offer a new look at the ways crystals form.

The real-time clips, described March 30 in Nature Nanotechnology, show closeup views of microscopic gold particles tumbling, sliding and flitting about before clicking into place in crystalline structures.

Before embarking on the study, physicist Erik Luijten of Northwestern University in Evanston, Ill., had expected to simply confirm century-old perceptions about how crystals form. But, he says, “there was still so much to discover about crystallization.”  

Atoms that make up familiar crystals such as salt, sugar and quartz are hard to image in action. So the team turned to gold nanoparticles, each about 60 billionths of a meter across, or roughly one-thousandth the diameter of a typical human hair. The researchers used transmission electron microscopy to track the particles as they snapped into position after floating in a salty fluid.

Among the surprises in the videos, Luijten says, is the way crystallization depended on the gold nanoparticles skittering across crystal surfaces, as well as how the particles rapidly made their way to the growing crystals from the surrounding fluid. The videos allowed the researchers to find ways to control both of those processes.

By adjusting the chemistry of the fluid, the researchers tuned the rate at which the nanoparticles were deposited from the surrounding solution to build up the crystals. Choosing among shapes including cubes, cubes with indented faces and spheres changed how the particles moved along the crystals. By changing both fluid chemistry and particle shape, the researchers controlled whether the nanoparticle crystals grew smooth planes or rough surfaces.

The nanoparticles are hundreds of times the size of atoms. But the researchers think that atoms grow into crystals in much the same way, making the nanoparticles handy stand-ins. The study could aid in the design of bendable electronics, high-efficiency solar cells and other materials with properties that rely on crystal structures (SN: 6/1/18; SN: 7/26/17).