Vanadium dioxide as a natural disordered metamaterial: perfect thermal emission and large broadband negative differential thermal emittance

TL;DR

This study demonstrates that thin VO2 films on sapphire exhibit perfect thermal emission and broadband negative differential emittance due to their disordered metamaterial structure during the insulator-metal transition, enabling advanced thermal management applications.

Contribution

It reveals the anomalous thermal emittance behavior of VO2 films during the IMT, showing perfect blackbody-like emission and negative differential emittance, which was not previously demonstrated in natural disordered metamaterials.

Findings

VO2 films exhibit near-perfect thermal emissivity over a narrow wavelength range.

Large broadband negative differential thermal emittance observed over >10°C.

Potential applications in infrared camouflage and thermal regulation.

Abstract

We experimentally demonstrate that a thin (~150 nm) film of vanadium dioxide (VO2) deposited on sapphire has an anomalous thermal emittance profile when heated, which arises due to the optical interaction between the film and the substrate when the VO2 is at an intermediate state of its insulator-metal transition (IMT). Within the IMT region, the VO2 film comprises nanoscale islands of metal- and dielectric-phase, and can thus be viewed as a natural, disordered metamaterial. This structure displays "perfect" blackbody-like thermal emissivity over a narrow wavelength range (~40 cm-1), surpassing the emissivity of our black soot reference. We observed large broadband negative differential thermal emittance over a >10 {\deg}C range: upon heating, the VO2/sapphire structure emitted less thermal radiation and appeared colder on an infrared camera. We anticipate that emissivity engineering with thin film geometries comprising VO2 will find applications in infrared camouflage, thermal regulation, infrared tagging and labeling.