Vanadium Dioxide as a Natural Disordered Metamaterial: Perfect Thermal Emission and Large Broadband Negative Differential Thermal Emittance

Mikhail A Kats,Patrice Genevet,Shuyan Zhang,Shriram Ramanathan,Changhyun Ko,Federico Capasso,Romain Blanchard

doi:10.1103/physrevx.3.041004

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.

Highlights

We experimentally demonstrate that a thin film of vanadium dioxide (VO2) deposited on sapphire has an anomalous thermal emittance profile when heated, which arises because of the optical interaction between the film and the substrate when the VO2 is at an intermediate state of its insulator-metal transition (IMT)
Thermal radiation, which states that the emissivity of an object "ðKÞ is equal to its frequency-dependent absorptivity aðKÞ [1]
We show that a geometry comprising a thin film of VO2 on a sapphire substrate can exhibit ‘‘perfect’’ blackbodylike emissivity over a narrow range of frequencies when the VO2 is in its transitional state and operates as a natural, tunable metamaterial, i.e., an effective medium with widely tunable infrared optical properties

Summary

Introduction

We experimentally demonstrate that a thin (approximately 150-nm) film of vanadium dioxide (VO2) deposited on sapphire has an anomalous thermal emittance profile when heated, which arises because of the optical interaction between the film and the substrate when the VO2 is at an intermediate state of its insulator-metal transition (IMT). We show that a geometry comprising a thin film of VO2 on a sapphire substrate can exhibit ‘‘perfect’’ blackbodylike emissivity (approximately 1) over a narrow range of frequencies when the VO2 is in its transitional state and operates as a natural, tunable metamaterial, i.e., an effective medium with widely tunable infrared optical properties.

Results

Conclusion