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

摘要

We experimentally demonstrate that a thin (~150 nm) film of vanadium dioxide(VO2) deposited on sapphire has an anomalous thermal emittance profile whenheated, which arises due to the optical interaction between the film and thesubstrate when the VO2 is at an intermediate state of its insulator-metaltransition (IMT). Within the IMT region, the VO2 film comprises nanoscaleislands of metal- and dielectric-phase, and can thus be viewed as a natural,disordered metamaterial. This structure displays "perfect" blackbody-likethermal emissivity over a narrow wavelength range (~40 cm-1), surpassing theemissivity of our black soot reference. We observed large broadband negativedifferential thermal emittance over a >10 {\deg}C range: upon heating, theVO2/sapphire structure emitted less thermal radiation and appeared colder on aninfrared camera. We anticipate that emissivity engineering with thin filmgeometries comprising VO2 will find applications in infrared camouflage,thermal regulation, infrared tagging and labeling.