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Three-dimensional binary superlattices of magnetic nanocrystals and semiconductor quantum dots


Recent advances in strategies for synthesizing nanoparticles—such as semiconductor quantum dots1, magnets and noble-metal clusters2—have enabled the precise control of composition, size, shape3, crystal structure4, and surface chemistry. The distinct properties of the resulting nanometre-scale building blocks can be harnessed in assemblies with new collective properties2,5,6, which can be further engineered by controlling interparticle spacing and by material processing. Our study is motivated by the emerging concept of metamaterials7—materials with properties arising from the controlled interaction of the different nanocrystals in an assembly. Previous multi-component nanocrystal assemblies have usually resulted in amorphous or short-range-ordered materials8,9 because of non-directional forces or insufficient mobility during assembly10,11,12,13,14. Here we report the self-assembly of PbSe semiconductor quantum dots and Fe2O3 magnetic nanocrystals into precisely ordered three-dimensional superlattices. The use of specific size ratios directs the assembly of the magnetic and semiconducting nanoparticles into AB13 or AB2 superlattices with potentially tunable optical and magnetic properties. This synthesis concept could ultimately enable the fine-tuning of material responses to magnetic, electrical, optical and mechanical stimuli6.

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Figure 1: TEM micrographs and sketches of AB13 superlattices (isostructural with intermetallic phase NaZn13, SG 226) of 11-nm γ-Fe2O3 and 6-nm PbSe NCs.
Figure 2: TEM micrographs and sketches of AB2 superlattices (isostructural with intermetallic phase AlB2, SG 191) of 11-nm γ-Fe2O3 and 6-nm PbSe NCs.

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This work was supported primarily by the MRSEC Program of the National Science Foundation. Further support was granted by the DARPA Metamaterials initiative and by DARPA through the Army Research Office.

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Correspondence to S. O'Brien.

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Redl, F., Cho, KS., Murray, C. et al. Three-dimensional binary superlattices of magnetic nanocrystals and semiconductor quantum dots. Nature 423, 968–971 (2003).

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