Spectral properties and thermal stability of CrN/CrON/Al2O3 spectrally selective coating

Multilayered CrN(H)/CrN(L)/CrON/Al2O3 spectrally selective coatings, designed with a gradually decreasing refractive index from the base layer to the top layer, were deposited on stainless steel substrates by reactive DC magnetron sputtering. The thicknesses of the CrN(H), CrN(L), CrON, and Al2O3 layers were optimized to achieve the best spectral properties. The thermal stability test was carried out at 300-500 °C in air. An absorptance of 0.93 and a thermal emittance of 0.14 were obtained when the CrN(H)/CrN(L)/CrON/Al2O3 multilayer coating comprised 60 nm-thick CrN(H), 50 nm-thick CrN(L), 40 nm-thick CrON, and 40 nm-thick Al2O3 layers. The CrN(H)/CrN(L)/CrON/Al2O3 was thermally stable up to 400 °C in air. Oxidation of the CrN(L) layer and phase transformation of the CrON layer destroyed the multilayered structure and degraded the spectral properties when the CrN(H)/CrN(L)/CrON/Al2O3 was heated at 500 °C in air.