Colloidal plasmonic nanocrystals (NCs) are known for their size- and shape-dependent localized surface plasmon resonances. Here we show these plasmonic NCs can be used as building blocks of mesoscale materials.1 Chemical exchange of the long ligands used in NC synthesis with more compact ligand chemistries brings neighboring NCs into proximity and increases interparticle coupling. This ligand-controlled coupling allows us to tailor a dielectric-to-metal phase transition seen by a 1010 range in DC conductivity and a dielectric permittivity ranging from everywhere positive to everywhere negative across the whole range of optical frequencies. We realize a "diluted metal" with optical properties not found in the bulk metal analog, presenting a new axis in plasmonic materials design and the realization of optical properties akin to next-generation metamaterials. We harness the solution-processability and physical properties of colloidal plasmonic NCs to print NC superstructures for large-area, active metamaterials. We demonstrate quarter-wave plates with extreme bandwidths and high polarization conversion efficiencies in the near- to-mid infrared.2 By fabricating colloidal NC superstructures on the surface of hydrogels, we fabricate optically-responsive sensors suitable for large-area monitoring of soil moisture. Finally, by combining superparamagnetic Zn0.2Fe2.8O4 NCs and plasmonic Au NCs, we fabricate multifunctional, smart superparticles, that in suspensions, switch their polarization-dependent transmission in the infrared in response to an external magnetic field.3
(1) Fafarman, A. T.; Hong, S.-H.; Caglayan, H.; Ye, X.; Diroll, B. T.; Paik, T.; Engheta, N.; Murray, C. B.; Kagan, C. R. Nano Lett. 2013, 13 (2), 350–357.
(2) Chen, W.; Tymchenko, M.; Gopalan, P.; Ye, X.; Wu, Y.; Zhang, M.; Murray, C. B.; Alu, A.; Kagan, C. R. Nano Lett. 2015, 15 (8), 5254–5260.
(3) Zhang, M.; Magagnosc, D. J.; Liberal, I.; Yu, Y.; Yun, H.; Yang, H.; Wu, Y.; Guo, J.; Chen, W.; Shin, Y. J.; Stein, A.; Kikkawa, J. M.; Engheta, N.; Gianola, D. S.; Murray, C. B.; Kagan, C. R. Nat. Nanotechnol. 2016, 12 (3), 228–232.