Solar selective absorbing coatings TiN/TiSiN/SiN prepared on stainless steel substrates

TiN/TiSiN/SiN solar selective absorbing coatings (SSACs) with and without a copper underlayer were deposited on stainless steel (SS) substrates via dc reactive magnetron sputtering. In this SSAC, SS/Cu or SS, TiN, TiSiN and SiN act as the metal reflector layer, high metal volume fraction layer, low metal volume fraction layer and anti-reflection layer, respectively. An absorptance (α) of 0.95 and a total hemispherical emittance (ε (70 °C)) of 0.04 were achieved in coatings with Cu underlayer. On the other hand, the SS/TiN/TiSiN/SiN SSAC showed a similar absorptance (∼0.95) but a poorer emittance and solar selectivity. X-ray diffraction analysis showed that the Cu layer is polycrystalline, while TiN, TiSiN and SiN are amorphous. The chemical-bonding states of each layer of the TiN/TiSiN/SiN SSAC were analyzed by using X-ray photoelectron spectroscopy. The solar selective absorbing performance of the Cu/TiN/TiSiN/SiN SSAC did not show significant changes after they were heat-treated in vacuum up to 700 °C. Raman spectra and atomic force microscopy images were collected to illustrate the structural and morphological stabilities of this SSAC upon heating in vacuum. Lastly, heat treatments in air for 150 and 300 h based on the PC nomenclature were carried out to demonstrate long term thermal stability of SS/TiN/TiSiN/SiN.