Auxetic Thermoresponsive Nanoplasmonic Optical Switch.

Development and use of metamaterials have been gaining prominence in large part due to the possibility of creating platforms with "disruptive" and unique optical properties. However, to date, the majority of such systems produced using micro or nanotechnology are static and can only perform certain target functions. Next-generation multifunctional smart optical metamaterials are expected to have tunable elements with the possibility of controlling the optical properties in real time via variation in parameters such as pressure, mechanical stress, and voltage or through nonlinear optical effects. Here, we address this challenge by developing a thermally controlled optical switch, based on the self-assembly of poly( N-isopropylacrylamide)-functionalized gold nanoparticles on a planar macroscale gold substrate. We show that such meta-surfaces can be tuned to exhibit substantial changes in the optical properties in terms of both wavelength and intensity, through the temperature-controlled variation of the interparticle distance within the nanoparticle monolayer as well as its separation from the substrate. This change is based on temperature-induced auxetic expansion and contraction of the functional ligands. Such a system has potential for numerous applications, ranging from thermal sensors to regulated light harnessing.