Control over emissivity of zero-static-power thermal emitters based on phase-changing material GST

Controlling the emissivity of a thermal emitter has attracted growing interest, with a view toward a new generation of thermal emission devices. To date, all demonstrations have involved using sustained external electric or thermal consumption to maintain a desired emissivity. In the present study, we demonstrated control over the emissivity of a thermal emitter consisting of a film of phase-changing material Ge2Sb2Te5 (GST) on top of a metal film. This thermal emitter achieves broad wavelength-selective spectral emissivity in the mid-infrared. The peak emissivity approaches the ideal blackbody maximum, and a maximum extinction ratio of >10 dB is attainable by switching the GST between the crystalline and amorphous phases. By controlling the intermediate phases, the emissivity can be continuously tuned. This switchable, tunable, wavelength-selective and thermally stable thermal emitter will pave the way toward the ultimate control of thermal emissivity in the field of fundamental science as well as for energy harvesting and thermal control applications, including thermophotovoltaics, light sources, infrared imaging and radiative coolers. The use of phase-change materials can provide tunable control over the emissivity of a thermal emitter. This discovery, made by Kaikai Du and co-workers at Zhejiang University in China, could be useful for applications in thermophotovoltaics, infrared imaging and radiative cooling. The team coated gold substrates with thin layers of the phase-change material Ge2Sb2Te5 (GST). They found that the emissivity of these samples changed with the thickness of the GST layer and the sample temperature. Specifically, the wavelength of the emissivity peak shifted from around 9 to 13 micrometres as the thickness of the GST layer increased from 360 to 540 nanometres. Furthermore, gradually changing the temperature of the GST layer to switch it between its amorphous and crystalline states provided continuous control over the emissivity.