Solution-Processed Phase-Change VO_2 Metamaterials from Colloidal Vanadium Oxide (VO_x) Nanocrystals

摘要

We demonstrate thermally switchable VO_2 metamaterials fabricated using solution-processable colloidal nanocrystals (NCs). Vanadium oxide (VO_x) NCs are synthesized through a nonhydrolytic reaction and deposited from stable colloidal dispersions to form NC thin films. Rapid thermal annealing transforms the VO_x NC thin films into monoclinic, nanocrystalline VO_2 thin films that show a sharp, reversible metal--insulator phase transition. Introduction of precise concentrations of tungsten dopings into the colloidal VO_x NCs enables the still sharp phase transition of the VO_2 thin films to be tuned to lower temperatures as the doping level increases. We fabricate "smart", differentially doped, multilayered VO_2 films to program the phase and therefore the metal--insulator behavior of constituent vertically structured layers with temperature. With increasing temperature, we tailored the optical response of multilayered films in the near-IR and IR regions from that of a strong light absorber, in a metal--insulator structure, to that of a Drude-like reflector, characteristic of a pure metallic structure. We demonstrate that nanocrystalbased nanoimprinting can be employed to pattern multilayered subwavelength nanostructures, such as three-dimensional VO_2 nanopillar arrays, that exhibit plasmonic dipolar responses tunable with a temperature change.