Laser-Induced Tuning and Spatial Control of the Emissivity of Phase-Changing Ge₂Sb₂Te₅ Emitter for Thermal Camouflage

The tuning of a material's emissivity in the atmospheric window range of 8–13 µm is crucial for infrared (IR) adaptive applications such as thermal camouflage, IR stealth, and radiative cooling. A resonator structure comprising a phase-changing Ge₂Sb₂Te₅ (GST) film on a metal mirror is promising as a tunable thermal emitter because its long-wavelength IR emissivity can be varied by adjusting the degree of crystallization of the GST film through annealing. However, the space-selective tuning of the emissivity required for practical use remains a significant challenge. Herein, a hybrid method combining laser irradiation and heat treatment is presented for space-selective and continuous tuning of the emissivity of a GST-based resonator. The current study shows that a laser-induced crystalline layer formed in the near-surface region of a 400 nm thick amorphous GST film can act as heterogeneous nuclei for crystallization when the film is subsequently annealed, thereby increasing the crystallization rate of the GST film. This results in a large difference in emissivity between the irradiated and nonirradiated areas, and the emissivity difference can be tuned by changing the annealing temperature. Thermal camouflage is experimentally demonstrated by making high-and low-temperature regions with low and high emissivity, respectively.