Nanophotonic resonators offer the ability to design nanoscale optical elements and engineered materials with unconventional properties. Dielectric-based resonators intrinsically support a complete multipolar resonant response with low absorption, while metallic resonators provide extreme light confinement and enhanced photon–electron interactions. Here, we construct resonators out of a prototypical metal–insulator transition material, vanadium dioxide (VO2), and demonstrate switching between dielectric and plasmonic resonances.
In this project I first characterized the temperature-dependent infrared optical constants of VO2 single crystals and thin-films (grown by Stephen Wilson’s group and Ivan Schuller’s group respectively). Out of the thin-films, I then developed a nanofabrication process (using electron-beam-lithography and an Ar/Cl2 reactive-ion-etch) to fabricate VO2 wire arrays and disk arrays. I found that the wire resonators support dielectric resonances at low temperatures, a damped scattering response at intermediate temperatures, and plasmonic resonances at high temperatures. In the disk resonators, however, upon heating, there was a pronounced enhancement of scattering at intermediate temperatures and a substantial narrowing of the phase transition, which was not present upon the cooling portion of the hysteresis loop.
These findings lead to an improved understanding of VO2-based resonators, which we’re now exploring in the design of reconfigurable diffractive devices.