(327h) Tuning Optical Parameters of Nanocrystal-Based Optical Metamaterials By Doping at Atomic and Mesoscopic Lengthscales

Assembling plasmonic nanocrystals (NCs) in regular superlattices can produce effective optical properties not found in homogeneous materials. These properties are broadly tunable based on the characteristics of the individual NC components and on coupling between NCs in the assembled array. Here, we demonstrate unprecedented control of the optical response across infrared wavelengths by doping at two lengthscales. At the atomic scale, the concentration of tin dopants is varied in indium tin oxide (ITO) nanocrystals to adjust their localized surface plasmon resonance (LSPR) frequency. Then, ITO NCs with low LSPR frequency are “doped” into a monolayer superlattice of NCs with a high LSPR frequency; LSPR coupling within the heterogeneous superlattice results in unusual optical functionality. For example, the introduction of undoped indium oxide NCs to an assembly of 3 Sn% ITO NCs reduced the long-wavelength refractive index by weakening the coupling between the 3 Sn% ITO NCs. On the other hand, the introduction of 1 Sn% ITO NCs modifies the dielectric function near the resonance wavelength due to coupling between the LSPR modes of the two off-resonant plasmonic NCs. As a result, the optical response of the metamaterial exhibits a spectrally broadened epsilon near zero (ENZ) region. This multiscale doping strategy offers a new, highly tunable approach to control the interaction with infrared light for enhanced absorption, tunability reflectivity or transmission, adaptive optics, and more.