Spectral properties of metal-ceramic solar selective absorbing coatings with columnar structure prepared by glancing angle deposition

The spectral selectivity of metal-ceramic solar selective absorbing coatings is jointly determined by both nanoparticles and microstructure. However, achieving performance optimization through microstructural control remains a challenging task. A multilayer metal-ceramic coating with a tilted columnar structure, Cr/AlCrNbSiTiVN /AlCrNbSiTiVNO/SiO₂, was fabricated by employing glancing angle deposition for the dual-absorber layers by tuning the deposition angle. Scanning electron microscopy (SEM)-based microstructural analysis unveiled a pronounced tilted columnar morphology within the dual-absorber layers. Subsequently, phase analysis conducted via XRD and XPS corroborated that these layers are high-entropy ceramic phases featuring a face-centered cubic (FCC) structure. A significant finding was that, despite a fixed composition, the spectral selectivity improved as the columnar tilt increased, highlighting the crucial role of the tilt angle in photothermal conversion performance. With the dual-absorber layers deposited at 80°, the coating exhibited the maximum columnar tilt and optimal performance, achieving an absorptance of 0.91 and an emittance of 0.25, which is attributed to the synergistic coexistence of multiple absorption mechanisms, including intrinsic absorption, surface plasmon resonance, optical trapping, and interlayer interference. In addition, the development of inclined columns is attributed to the shadowing effect, which confines atomic deposition to the tops of growing nuclei by inhibiting condensation in their immediate shadowed regions. The research provides innovative design perspectives for optimizing the spectrally selective absorption properties of multilayer metal-ceramic coatings, thus paving new ways for enhancing photothermal conversion.