3D Optical Metamaterials from Colloidal Nanocrystal Assemblies

Colloidal nanocrystals (NCs) have inorganic cores and are commonly synthesized with organic shells. Chemical exchange of the long ligands used in NC synthesis with more compact ligand chemistries reduces the interparticle distance (<i>d</i>) and increases interparticle coupling [1, 2]. Similarly, thermal annealing can decompose ligands, reduced <i>d</i>, and drive NC fusion. We pattern 2D structures using one large-area imprint lithography step. Then, we exploit the different chemical and physical properties of NC assemblies from bulk thin films, to construct NC/bulk bilayer heterostructures that fold into three-dimensional structures upon ligand exchange and/or mild thermal annealing [3-5]. Using this simple fabrication route, we demonstrate 3D chiral metamaterials with configurable bandwidth and reconfigurable optical responses in the infrared.<br/>A. T. Fafarman, S.-H. Hong, H. Caglayan, X. Ye, B T. Diroll, T. Paik, N. Engheta, C. B. Murray, C. R. Kagan, “Chemically Tailored Dielectric-to-Metal Transition in the Design of Metamaterials from Nanoimprinted Colloidal Nanocrystals,” Nano Lett 13, 350-357 (2012).<br/>W. Chen, J. Guo, Q. Zhao, P. Gopalan, A. T. Fafarman, Au. Keller, M. Zhang, Y. Wu, C. B. Murray, C. R. Kagan, “Designing Strong Optical Absorbers via Continuous Tuning of Interparticle Interaction in Colloidal Gold Nanocrystal Assemblies,” ACS Nano, 13, 7493-7501 (2019).<br/>M. Zhang, J. Guo, Y. Yu, Y. Wu, H. Yun, D. Jishkariani, W. Chen, N. J. Greybush, C. Kubel, A. Stein, C. B. Murray, C. R. Kagan, “3D Nanofabrication via Chemo-Mechanical Transformation of Nanocrystal/Bulk Heterostructures,” Adv. Mater. 30, 1800233 (2018).<br/>J. Guo, J.-Y. Kim, M. Zhang, H. Wang, A. Stein, C. B. Murray, N. A. Kotov, C. R. Kagan, “Chemo- and Thermomechanically Configurable 3D Optical Metamaterials Constructed from Colloidal Nanocrystal Assemblies,” ACS Nano 13, 1427-1435 (2019).<br/>J. Guo, J.-Y. Kim, S. Yang, J. Xu, Y. C. Choi, A. Stein, C. B. Murray, N. A. Kotov, C. R. Kagan, “Broadband Circular Polarizers via Coupling in 3D plasmonic Meta-Atom Arrays,” ACS Photonics, 8, 1286-1292 (2021).