Infrared chameleon-like behavior from VO2(M) thin films prepared by transformation of metastable VO2(B) for adaptive camouflage in both thermal atmospheric windows

Abstract

Adaptive materials active in the thermal infrared (IR) region have recently attracted intense research interest as they are suitable for adaptive IR camouflage applications, although significant challenges remain. Under external thermal stimuli, vanadium dioxide (VO2) thin films exhibit a reversible metal-insulator transition (MIT) from an IR transparent state to a reflecting state with heating. An alternative route is proposed for depositing thermochromic VO2(M) thin films on quartz substrates via the transformation of metastable VO2(B). A silicone elastomer sheet with high absorption in the IR region and high thermal conductivity was adhered to the back of a VO2/quartz structure to improve its thermochromic properties in the mid-wavelength (MWIR; 3–5 µm) and long-wavelength (LWIR; 8–14 µm) thermal atmospheric windows. The emissivity of the VO2(M)/quartz/silicone structure could change by 0.21 and 0.49 across MIT in the MWIR and LWIR ranges, respectively. This VO2/quartz/silicone structure showed IR chameleon-like behavior in the MWIR and LWIR atmospheric windows, respectively. When heated above the MIT temperature, the structure autonomously lowers its IR radiation intensity to appear to be at the same or even lower temperature on IR cameras. When the real temperature (Tr) of the object is 95 °C, the apparent temperature (Ta) on the MWIR camera is 51.9 °C close to the Ta of 51.8 °C at Tr = 65 °C; in the LWIR band, Ta is merely 43.8 °C when Tr is 90 °C, close to the Ta of 42.1 °C at Tr = 50 °C and even cooler than the Ta of 49.3 °C at Tr = 60 °C. These exciting results provide new opportunities for adaptive IR camouflage of military objects with dynamical temperature change and IR exposure for cheating IR cameras.