1:30 PM - *EQ08.03.01
Designing Optical Metamaterials from Colloidal Nanocrystal Assemblies
University of Pennsylvania1
Colloidal plasmonic nanocrystals (NCs) are known for their size- and shape-dependent localized surface plasmon resonances and their solution-based printing and imprinting in device fabrication. We use NCs as building blocks of assemblies and exploit their chemical and physical (electrical, optical, mechanical, thermal) tailorability to design and fabricate optical metamaterials. Chemical exchange of the long ligands used in NC synthesis with more compact ligand chemistries brings neighboring NCs into proximity, increasing interparticle coupling and allowing us to tune through 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 . This ligand-controlled coupling is useful in the design of materials that are strong, ultrathin film optical absorbers  or strong optical scatterers . Compact ligand exchange and thermal annealing of NC films also drives a large volume shrinkage in NC thin films, allowing a 10X tailorability in their Young’s modulus [4-6]. By juxtaposing plasmonic NCs and bulk materials, we exploit their different chemical and mechanical properties to create misfit strain that drives the folding of NC/bulk bilayer heterostructures and the transformation of lithographically-defined two-dimensional structures into three-dimensional structures. We use the three-dimensional structures to demonstrate the scalable fabrication of large-area metamaterials with chiroptical responses of ~40% transmission difference between left-hand and right-hand circularly polarized light and that are suitable broadband circular polarizers [5,6].
(1) Fafarman, A. T.; Hong, S.-H.; Caglayan, H.; Ye, X.; Diroll, B. T.; Paik, T.; Engheta, N.; Murray, C. B.; Kagan, C. R. Chemically Tailored Dielectric-to-Metal Transition for the Design of Metamaterials from Nanoimprinted Colloidal Nanocrystals. Nano Lett. 2013, 13 (2), 350–357. https://doi.org/10.1021/nl303161d.
(2) Chen, W.; Guo, J.; Zhao, Q.; Gopalan, P.; Fafarman, A. T.; Keller, A.; Zhang, M.; Wu, Y.; Murray, C. B.; Kagan, C. R. Designing Strong Optical Absorbers via Continuous Tuning of Interparticle Interaction in Colloidal Gold Nanocrystal Assemblies. ACS Nano 2019, 13 (7), 7493–7501. https://doi.org/10.1021/acsnano.9b02818.
(3) Chen, W.; Tymchenko, M.; Gopalan, P.; Ye, X.; Wu, Y.; Zhang, M.; Murray, C. B. C. B.; Alu, A.; Kagan, C. R. C. R. Large-Area Nanoimprinted Colloidal Au Nanocrystal-Based Nanoantennas for Ultrathin Polarizing Plasmonic Metasurfaces. Nano Lett. 2015, 15 (8), 5254–5260. https://doi.org/10.1021/acs.nanolett.5b02647.
(4) Zhang, M.; Guo, J.; Yu, Y.; Wu, Y.; Yun, H.; Jishkariani, D.; Chen, W.; Greybush, N. J.; Kübel, C.; Stein, A.; Murray, C. B.; Kagan, C. R.; Kubel, C.; Stein, A.; Murray, C. B.; Kagan, C. R. 3D Nanofabrication via Chemo-Mechanical Transformation of Nanocrystal/Bulk Heterostructures. Adv. Mat. 2018, 30 (22), 1800233. https://doi.org/10.1002/adma.201800233.
(5) Guo, J.; Kim, J.-Y.; Zhang, M.; Wang, H.; Stein, A.; Murray, C. B.; Kotov, N. A.; Kagan, C. R. Chemo- and Thermomechanically Configurable 3D Optical Metamaterials Constructed from Colloidal Nanocrystal Assemblies. ACS Nano 2020, 14 (2), 1427–1435. https://doi.org/10.1021/acsnano.9b08452.
(6) Guo, J.; Kim, J.-Y.; Yang, S.; Xu, J.; Choi, Y. C.; Stein, A.; Murray, C. B.; Kotov, N. A.; Kagan, C. R. Broadband Circular Polarizers via Coupling in 3D Plasmonic Meta-Atom Arrays. ACS Photonics 2021, 8 (5), 1286–1292. https://doi.org/10.1021/acsphotonics.1c00310.