Air-based sputtering deposition of TiNxOy films for solar selective absorber coatings applications

Abstract Titanium oxynitride (TiNxOy) thin films with tunable electrical and optical properties were produced by sputtering using air as a reactive gas at a high base pressure of 1.3 × 10−2 Pa. Pure N2 and O2 with a fixed ratio of 79/21 was also used as a reference reactive gas (denoted as S-air) at a low base pressure of 6.7 × 10−4 Pa to investigate the influence of trace components in air on the characteristics of the films. By merely changing either the air/Ar or the S-air/Ar flow ratio within suitable processing windows, crystal phases, microstructures, electrical resistivities, and optical properties could be tailored. In practice, the TiNxOy thin films produced by such air-based sputtering could turn from conductive, semiconductive, to dielectric and would correspondingly change from opaque, translucent, to transparent. For solar selective absorber (SSA) coatings evaluations, bilayer and gradient TiNxOy-based SSA structures were tested, respectively. The gradient TiNxOy SSA coatings exhibited the best performance with solar absorptance of 86.3% and thermal emittance of 11.3%. This facile air-based sputtering technique with such a gradient coating design has great potential for solar selective absorber coatings applications.