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High-strength magnetically switchable plasmonic nanorods

Fabrication of hybrid nanorods. Low- (lower left) and high- (lower right) resolution SEM images, of hybrid nanorod arrays before release. Upper right, SEM image of released hybrid nanorods. Red arrows highlight nanorods sitting on the substrate on their sides.

Next-generation 'smart' nanoparticle systems should be precisely engineered in size, shape and composition to introduce multiple functionalities, unattainable from a single material. Bottom-up chemical methods are prized for the synthesis of crystalline nanoparticles, i.e., nanocrystals with size-and shape-dependent physical properties, but they are less successful in achieving multifunctionality. Top-down lithographic methods can produce multifunctional nanoparticles with precise size and shape control, yet this approach becomes increasingly difficult at sizes of order 10 nm.

Here, a team of five MRSEC faculty (Kikkawa, Engheta, Gianola, Murray, Kagan) fabricated multifunctional, smart nanoparticle systems by combining top-down fabrication and bottom-up self-assembly methods (see Figures). Nanorods were templated from a mixture of superparamagnetic Zn0.2Fe2.8O4 and plasmonic Au nanocrystals. The super-paramagnetism of the Zn0.2Fe2.8O4 prevented the nanorods from experiencing magnetic-dipole-induced aggregation, while their magnetic anisotropy made them responsive to an external field.

The resulting combined superparamagnetic and plasmonic functions enable switching of the infrared transmission of a hybrid nanorod suspension with an external magnetic field.

M. Zhang, D.J. Magagnosc, I. Liberal, Y. Yu, H. Yun, H. Yang, Y. Wu, J. Guo, W. Chen, Y.J. Shin, A. Stein, J.M. Kikkawa, N. Engheta, D.S. Gianola, C.B. Murray, C.R. Kagan, Nature Nanotechnology 12, 2017