Pulsed sputter deposited HfOx/M/HfO2 (M- Hf,Al)multilayer absorbers for solar selective applications

摘要

Spectrally selective HfOx/M/HfO2 (M-Hf, Al) multilayer absorber coatings were deposited on copper substrates using a pulsed direct current unbalanced magnetron sputtering system. The compositions and thicknesses of the individual component layers were optimized to achieve high solar absorptance ( = 0.916-0.925) and low thermal emittance ( = 0.05-0.07). The X-ray diffraction data showed that the HfOx/Hf/HfO2 coating consists of tetragonal and monoclinic phases of HfO2. The bonding structure of the HfO2 layers was confirmed using X-ray photoelectron spectroscopy. In order to study the thermal stability of the HfOx/M/HfO2 (M-Hf, Al) coatings, they were subjected to heat treatment in air at different temperatures and durations. The HfOx/Hf/HfO2 coating deposited on Cu substrates exhibited high solar selectivity (/) of 0.912/0.06 even after heat-treatment in air up to 400 °C for 2 h. Whereas, HfOx/Al/HfO2 coating was thermally stable in air up to 350 °C for 2 h. The structural stability of the absorber coatings heat-treated in air (up to 400 °C) was confirmed by micro-Raman spectroscopy measurements.