Millivolt Modulation of Plasmonic Metasurface Optical Response via Ionic Conductance

A plasmonic metasurface with an electrically tunable optical response that operates at strikingly low modulation voltages is experimentally demonstrated. The fabricated metasurface shows up to 30% relative change in reflectance in the visible spectral range upon application of 5 mV and 78% absolute change in reflectance upon application of 100 mV of bias. The designed metasurface consists of nanostructured silver and indium tin oxide (ITO) electrodes which are separated by 5 nm thick alumina. The millivolt‐scale optical modulation is attributed to a new modulation mechanism, in which transport of silver ions through alumina dielectric leads to bias‐induced nucleation and growth of silver nanoparticles in the ITO counter‐electrode, altering the optical extinction response. This transport mechanism, which occurs at applied electric fields of 1 mV nm^?1, provides a new approach to use of ionic transport for electrical control over light–matter interactions.