Optimization of AlxOy/Pt/AlxOy multilayer spectrally selective coatings for solar–thermal applications

Spectrally selective AlxOy/Pt/AlxOy multilayer absorber coatings were deposited onto corning 1737 glass, Si (111) and copper substrates using electron beam (e-beam) vacuum evaporator at room temperature. The employment of ellipsometric measurements and optical simulation was proposed as an effective method to optimize and deposit multilayer solar absorber coatings. The optical constants (n and k) measured using spectroscopic ellipsometry, showed that both AlxOy layers, which used in the coatings, were dielectric in nature and the Pt layer was semi-transparent. The optimized multilayer coatings exhibited high solar absorptance α ∼ 0.94 ± 0.01 and low thermal emittance ɛ ∼ 0.06 ± 0.01 at 82 °C. The Rutherford backscattering spectroscopy (RBS) data of AlxOy/Pt/AlxOy multilayer absorber indicated the AlxOy layers present in the coating were nearly stoichiometry. The scanning electron microscope analysis (SEM) result indicated that the average diameter and inter-particles distance of Pt grains were statistically about 146 ± 0.17 nm and 6–10 ± 0.2 nm respectively.

► AlxOy/Pt/AlxOy multilayer coatings were fabricated using electron beam evaporator.
► Solar absorptance ∼0.94 ± 0.01 and low thermal emittance ∼0.06 ± 0.01 was achieved.
► Ellipsometric measurements and optical simulation were used to optimize the coatings.
► Optical constants of AlxOy and Pt vary with thickness.