Materials Science

Flat Pack

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Science  08 Apr 2011:
Vol. 332, Issue 6026, pp. 150
DOI: 10.1126/science.332.6026.150-b
CREDIT: DONG ET AL., NANO LETT. 11, 10.1021/NL200468P (2011)

Superlattices combining colloidal particles or nanocrystals with two distinct sizes can exhibit unusual magnetic and electronic properties. It has proven easier to make three-dimensional rather than two-dimensional structures of this sort, particularly for samples that extend over large areas. Dong et al. used a liquid-air fabrication method with a low concentration of nanocrystals in the feedstock to form single and binary superlattices that extend over cm2 areas. The nanocrystals were deposited from hexane onto the surface of diethylene glycol and allowed to dry. Cocrystallization of Fe3O4 with Au, Fe3O4 with FePt, and NaYF4:Yb/Er with Fe3O4 nanocrystals showcased the generality of the method. The superlattice structure could be controlled by changing the ratio of the diameter of the particles, with both AB- and AB2-type lattices obtained. In hexagonally packed AB2 lattices, the smaller particles occupied the interstices of three larger neighboring particles. Shifting to A2B3 bilayer structures (above), the authors found that the smaller particles sat on only half of the larger particles, and this anisotropy drove the formation of a beltlike morphology rather than a membrane. The method was extended to ternary ABC2 structures using a mixture of three types of particles, although in this case the structure was more prone to defects.

Nano Lett. 11, 10.1021/nl200468p (2011).

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