Wavelength-tunable mid-infrared thermal emitters with a non-volatile phase changing material.

The ability to continuously tune the emission wavelength of mid-infrared thermal emitters while maintaining high peak emissivity remains a challenge. By incorporating the nonvolatile phase changing material Ge2Sb2Te5 (GST), two different kinds of wavelength-tunable mid-infrared thermal emitters based on simple layered structures (GST-Al bilayer and Cr-GST-Au trilayer) are demonstrated. Aiming at high peak emissivity at a tunable wavelength, an Al film and an ultrathin (∼5 nm) top Cr film are adopted for these two structures, respectively. The gradual phase transition of GST provides a tunable peak wavelength between 7 µm and 13 µm while high peak emissivity (>0.75 and >0.63 for the GST-Al and Cr-GST-Au emitters, respectively) is maintained. This study shows the capability of controlling the thermal emission wavelength, the application of which may be extended to gas sensors, infrared imaging, solar thermophotovoltaics, and radiative coolers.

Multi-color modulation of solid-state display based on thermally induced color changes of indium tin oxide and phase changing materials.

A multi-color solid-state display structure has been fabricated and characterized, which is based on phase-change material Ge2Sb2Te5 (GST) and conducting transparent material indium tin oxide (ITO). The significant influence of ITO is investigated by experiments as well as simulations. We found that the ITO layer in fact plays a significant or even a dominate role in the color change of GST-based multi-layer solid state display structure. Multi-color modulation can be achieved by changing the phase state of both ITO and GST. Based on those results, better color presentation can be realized by improving the design of this new solid-state display.

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.