Credit: © 2009 NPG

Quasicrystalline patterns exhibit long-range order but no translational symmetry, unlike crystalline lattices. As well as individual atoms, intermetallic and organic compounds have been arranged in quasicrystalline materials with interesting properties. Now, a team of researchers led by Dmitri Talapin and Elena Shevchenko at the University of Chicago and the Argonne National Laboratory in the US has observed the self-assembly of colloidal inorganic nanoparticles into such an ordered, yet aperiodic, superlattice1.

Talapin, Shevchenko and co-workers prepared a solution of iron oxide and gold nanocrystals, capped with surfactants to prevent their aggregation. Upon slow evaporation of the solvent, the nanoparticles usually self-assemble into crystalline binary superstructures. Under particular concentration conditions, however, transmission electron microscopy and diffraction studies revealed that large ordered aperiodic domains were also formed. This phase can be described as an Archimedean tiling of triangles and squares in which the vertices are isolated Fe2O3 nanoparticles. Each triangle and square comprises an isolated gold nanoparticle or Au6 cluster, respectively.

The same packing motif was also observed with two other binary nanoparticle systems. Combined with the sharp interfaces observed between different domains, this suggests that the aperiodic pattern formed is thermodynamically stable. Such phases may therefore be more common than previously thought, and could be used to provide insights into the structure and properties of quasicrystals.