High emissive contrast of adaptive, thin-film, tungsten-doped VO2 composites

There is a significant interest in developing advanced materials technologies that will reduce the consumption of fossil fuel resources. One efficient way of reducing energy consumption for heating and cooling applications is the development of a passive and adaptive thermal management system that radiates heat at high temperatures while providing insulation under cooler conditions. Vanadium dioxide (VO2) is a candidate material for this type of adaptive behavior since it transitions from a low temperature reflective state to a high temperature emissive state at 68 degrees C when deposited upon a dielectric-coated ground plane. Additionally, by doping VO2 with high valence tungsten (W6+), the transition temperature can be reduced to values that are close to room temperature (22 degrees C). In this Letter, W6+-doped VO2 multilayer composites are designed to utilize thin film interference in order to maximize the infrared (IR) emission contrast between the hot and cold states of VO2 while also reducing the transition temperature. Through careful engineering of the thickness and doping of the VO2 layer within the multilayer film, a 50% emissive contrast was maintained across the 8-13 mu m spectral region, while the transition temperature was reduced from 68 degrees C in the undoped film to 29 degrees C in the 1.7 at.% W6+.