Electrochemical Control of Tunable Infrared Nanocrystal Metasurfaces.

Dynamic control of photonic materials at mid-infrared wavelengths is essential for applications spanning thermal management, active imaging, and optical signal processing, yet achieving strong modulation within small material volumes remains a central challenge. Conventional approaches rely on lithographically patterned metasurfaces with limited scalability, or on ultrathin materials with weak light-matter interaction. Here, we show that cavity-coupled assemblies of sub-10 nm plasmonic tin-doped indium oxide nanocrystals function as dynamic metasurfaces with electrochemically switchable linear and nonlinear optical responses. By integrating colloidal nanocrystals into a photonic architecture, we colocate permittivity modulation and electromagnetic field confinement within the same nanoscale volume, achieving 77% absolute reflection modulation. Synthetic control of tin doping provides spectral selectivity across 2.5-4 μm, while solution processing yields centimeter-scale device uniformity. Beyond linear modulation, voltage-controlled near-field enhancement enables electrically switchable ultrafast nonlinear response with 100% relative reflection modulation (from an absolute 3 to 6%) and 0.25 ps recovery time, enabling dual-time scale optical control.