AlMoN based spectrally selective coating with improved thermal stability for high temperature solar thermal applications

A novel AlMoN(H)/AlMoN(L) coating with improved thermal stability was developed for high temperature solar thermal applications. The aluminum and molybdenum target power densities and nitrogen flow rates were varied in order to attain the different chemical composition of AlMoN layers, which resulted in different optical properties. The coating deposited at a nitrogen flow rate of 1 sccm (AlMoN(H)) acts as an absorber, whereas coating deposited at a nitrogen flow rate of 4 sccm (AlMoN(L)) acts as an antireflection coating. By combining these two layers (i.e., AlMoN(H)/AlMoN(L)) an absorptance of 0.93 and an emittance of 0.13 were achieved. In order to decrease the emittance, approximately 1 μm thick tungsten coating was deposited on SS substrates. The tungsten coating acts as an infrared reflector due to which the emittance decreased drastically from 0.13 to 0.06, without affecting the absorptance. The optimized AlMoN(H)/AlMoN(L) coating deposited on SS substrates was thermally stable in air at 300 and 450 °C for 200 and 2 h, respectively. These coatings also exhibited high thermal stability in vacuum (600 °C for 435 h).