Design of Ag–Si₃N₄ Nanocermet Coatings for Photothermal Conversion Applications

For efficient photothermal conversion in solar selective coatings, high absorptance (α) in the visible region (VIS) and low thermal emittance (ε) in the infrared (IR) region at high operating temperature are the most desirable requirements. For this, nanocermet coatings are suitable candidate materials owing to their high photothermal conversion efficiency. Here we report the preparation of Ag–Si₃N₄ nanocermet spectrally selective coatings using magnetron sputtering technique from the sputtering of Ag and Si₃N₄ targets. The field emission scanning electron microscopy of the coatings confirmed the presence of Ag nanoparticles with an average diameter of 15–25 nm dispersed uniformly in the Si₃N₄ matrix. High absorptance (α = 0.933) in the VIS region and low emittance (ε = 0.15 on Cu substrate) in the IR region have been achieved for the optimized nanocermet coatings. The absorptance spectra of the coatings exhibited a strong resonance peak due to the surface plasmon resonance of the Ag nanoparticles, which shifted to higher wavelength with an increase in the size of Ag nanoparticles. Thermal stability tests of these coatings revealed their stability up to 300 °C in vacuum for 2 hrs.