Plasma within templates: Molding flexible nanocrystal solids into multifunctional architectures

Recently, there has been a great deal of progress in the synthesis of colloidal nanocrystals with tailored physical and chemical properties through control of size and shape, chemical composition, and surface functionalization (Alivisatos, A. P. Science 1996, 271 (5251), 933-937; Burda, C.; Chen, X. B.; Narayanan, R.; El-Sayed, M. A. Chem. Rev. 2005, 105 (4), 1025-1102). Nanocrystals are thus ideal building blocks for hierarchical self-assembly of topologically complex, multifunctional architectures with properties tuneable at each level of the hierarchy. Here, we present a method, which combines template-assisted self-assembly of nanocrystals with plasma polymerization (Cademartiri, L.; von Freymann, G.; Arsenault, A. C.; Bertolotti, J.; Wiersma, D. S.; Kitaev, V.; Ozin, G. A. Small 2005, 1 (12), 1184-1187) to realize hierarchical architectures that both retain the properties of the nanocrystals and offer multifunctionality. As examples, we describe CoFe2O4-PbS mixed nanocrystal nanorods, which photoluminesce, and align and move in unison with an applied magnetic field and PbS nanocrystal inverse opals, which emit and Bragg diffract near-infrared light. Such hierarchical nanocrystal architectures can be envisioned to spawn new nanotechnologies that integrate multiple functionalities into a single construct.