In the Nature Materials paper Yang and his co-authors describe a polyol synthesis technique that was used to generate silver nanocrystals in various shapes, including cubes, truncated cubes, cuboctahedra, truncated octahedra and octahedra over a range of sizes from 100 to 300 nanometers. These uniform polyhedral nanocrystals were then placed in solution where they assembled themselves into dense supercrystals some 25 square millimeters in size through gravitational sedimentation. While the assembly process could be carried out in bulk solution, having the assembly take place in the reservoirs of microarray channels provided Yang and his collaborators with precise control of the superlattice dimensions.
"In a typical experiment, a dilute solution of nanoparticles was loaded into a reservoir that was then tilted, causing the particles to gradually sediment and assemble at the bottom of the reservoir," Yang says. "More concentrated solutions or higher angles of tilt caused the assemblies to form more quickly."
The assemblies generated by this sedimentation procedure exhibited both translational and rotational order over exceptional length scales. In the cases of cubes, truncated octahedra and octahedra, the structures of the dense supercrystals corresponded precisely to their densest lattice packings. Although sedimentation-driven assembly is not new, Yang says this is the first time the technique has been used to make large-scale assemblies of highly uniform polyhedral particles.
"The key factor in our experiments is particle shape, a feature we have found easier to control," Yang says. "When compared with cr
|Contact: Lynn Yarris|
DOE/Lawrence Berkeley National Laboratory