A Thermal Radiation Modulation Platform by Emissivity Engineering with Graded Metal-Insulator Transition.

Thermal radiation from a black body increases with the fourth power of absolute temperature (T ), an effect known as the Stefan-Boltzmann law. Typical materials radiate heat at a portion of this limit, where the portion, called integrated emissivity (ε ), is insensitive to temperature (|dε /dT| ≈ 10 °C ). The resultant radiance bound by the T law limits the ability to regulate radiative heat. Here, an unusual material platform is shown in which ε can be engineered to decrease in an arbitrary manner near room temperature (|dε /dT| ≈ 8 × 10 °C ), enabling unprecedented manipulation of infrared radiation. As an example, ε is programmed to vary with temperature as the inverse of T , precisely counteracting the T dependence; hence, thermal radiance from the surface becomes temperature-independent, allowing the fabrication of flexible and power-free infrared camouflage with unique advantage in performance stability. The structure is based on thin films of tungsten-doped vanadium dioxide where the tungsten fraction is judiciously graded across a thickness less than the skin depth of electromagnetic screening.