Plasmonic Metal Oxide Nanocrystals as Building Blocks for Infrared Metasurfaces

Metamaterials operating at infrared (IR) frequencies have garnered significant attention due to the opportunities for resonant interactions with vibrational modes of molecules and materials and manipulation of thermal emission. These metamaterials usually consist of periodic arrangements of subwavelength scale metallic or dielectric elements, patterned either top-down by nanolithographic methods or bottom-up by nanocrystal (NC) assembly. However, conventional metals are inherently constrained by their fixed electron concentrations, which limits the degrees of freedom in the design of the meta-atom unit cells to achieve the desired optical response. In this context, doped metal oxide NCs, with the prototypical case being tin-doped indium oxide (ITO) NCs, are exceptional candidates for self-assembled IR metamaterials, owing to their relatively low and synthetically tunable electron concentrations that govern the frequencies of their IR plasmon resonances. Focusing on ITO NCs as building blocks, this Account describes recent progress in the synthetic tuning of NC optical properties, NC superlattice monolayer preparation methods for fabricating IR resonant metamaterials, and the emerging understanding of the optical response, facilitated by recently developed simulation methods.