Optimization of Al _xO _y/Pt/Al _xO _y multilayer spectrally selective coatings for solar-thermal applications

摘要

Spectrally selective Al _xO _y/Pt/Al _xO _y 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 Al _xO _y 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 ε ～ 0.06 ± 0.01 at 82°C. The Rutherford backscattering spectroscopy (RBS) data of Al _xO _y/Pt/Al _xO _y multilayer absorber indicated the Al _xO _y 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.