Continuously tunable multifunctional infrared smart thermal emitter based on phase-change material Ge2Sb2Te5

As energy issues gain prominence, the technology of regulating thermal radiation through phase change materials has garnered significant attention. However, fabrication challenges and monofunctionality plague the current technologies. So, we suggest a three-layer thin-film metasurface structure made of the phase-change material Ge₂Sb₂Te₅(GST) and the metals Ge and Ag. This structure can change the emissivity in both directions at the atmospheric window and has excellent "thermal switching" properties for both releasing and keeping heat. We experimentally demonstrate that the structure can realize the radiative cooling and infrared thermal camouflage functions in the amorphous and crystalline states. In the amorphous phase, the device has an average emissivity of 0.081 in the mid-infrared band (3–5 µm) and 0.083 in the long-wave infrared band (8–13 µm). In the crystalline phase, it has an average emissivity of 0.632 in the mid-infrared band (3–5 µm) and 0.739 in the long-wave infrared band (8–13 µm). The effective medium theory shows that controlling the crystallization fraction can lead to continuous thermal variation that can encrypt information. The structure is a lithography-free thin film structure that exhibits robustness under incident light of different polarization angles and has large-scale and low-cost popularization value. This study provides an innovative approach for thin film structures to modulate thermal radiation for multifunctional applications, which are expected to be applied in the military, building energy efficiency, aerospace, and other fields.