Nano-breakthrough: Solving the case of the herringbone crystal
Hexagon-shaped nanoplates arranged themselves into different crystal patterns, depending on the length of the sides of the hexagons. Long hexagons fit together in a grid like a stretched honeycomb, but researchers were surprised that hexagons whose sides were all the same lengths ended up in a herringbone pattern. University of Michigan engineering researchers helped figure out why, and the work could lead to a new tool to control how nanoparticles arrange themselves. (Image credit: Xingchen Ye, University of Pennsylvania)
Leading nanoscientists created beautiful, tiled patterns with flat nanocrystals, but they were left with a mystery: Why did some sets of crystals arrange themselves in an alternating, herringbone style? To find out, they turned to experts in computer simulation at the University of Michigan and the Massachusetts Institute of Technology. The result gives nanotechnology researchers a new tool for controlling how objects one-millionth the size of a grain of sand arrange themselves into useful materials—and a means to discover the rest of the tool chest. "The excitement in this is not in the herringbone pattern, it's about the coupling of experiment and modeling, and how that approach lets us take on a very hard problem," said Christopher Murray, the Richard Perry University Professor and professor of chemistry at the University of Pennsylvania. Ultimately, researchers want to modify patches on nanoparticles in different ways to coax them into more complex patterns. The goal is a method that will allow people to imagine what they would like to do and then design a material with the right properties for the job. "By engineering interactions at the nanoscale, we can begin to assemble target structures of great complexity and functionality on the macroscale," said U-M's Sharon Glotzer, the Stuart W. Churchill Collegiate Professor of Chemical Engineering. Glotzer introduced the concept of nanoparticle "patchiness" in 2004. Her group uses computer simulations to understand and design the patches. Recently, Murray's team made patterns with flat nanocrystals made of heavy metals, known to chemists as lanthanides, and fluorine atoms. Lanthanides have valuable properties for solar energy and medical imaging, such as the ability to convert between high- and low-energy light.