Mo/AlMoONH/AlMoONL/AlxOy solar selective absorption coatings (SSACs) were deposited on stainless steel substrates via magnetron sputtering, a typical vacuum coating technology. The optimized four-layer structure comprises an infrared-reflective Mo layer, dual gradient absorption layers (AlMoONH with high metal volume fraction and AlMoONL with low metal volume fraction), and an AlxOy antireflection layer. The spectral reflectance of the coatings was measured by a UV-Vis-NIR spectrophotometer (0.3–2.5 μm) and a Fourier transform infrared spectrophotometer (2.5–25 μm). Additionally, scanning electron microscopy, x-ray diffraction, and x-ray photoelectron spectroscopy were conducted on the high-temperature treated coatings to analyze their phase composition and micromorphology after high-temperature treatment, as well as to investigate the coating thermal stability mechanism. The as-deposited coatings exhibited excellent solar absorptance and emissivity, with slight changes in optical properties and intact structure without failure after heat treatment at 400–600 °C for 12–36 h. This study focuses on the stability and degradation mechanisms of oxynitride-based multilayer selective absorbers in air, provides insights into the design of oxidation-resistant SSACs for medium-to-high-temperature solar thermal applications, and enriches the application of magnetron sputtering in the preparation of high-performance vacuum coatings.
Zhou et al. (Tue,) studied this question.