Structural and optical properties of DC sputtered AlxOy/Cr/AlxOy multilayer selective absorber coatings

AlxOy/Cr/AlxOy multilayered selective absorber was theoretically optimized using the individual layers' optical constants acquired through fitting the transmittance and reflectance measurements into SCOUT software. The optimized multilayer was deposited onto polished aluminium substrates by DC magnetron sputtering at room temperature. The structural analysis of the multilayer stack revealed low crystalline diffraction peaks of Cr at 2 theta approximate to 43.3 degrees ascribed to (110) diffraction plane of BCC Cr metal. However, due to the amorphous nature of the deposited films, no AlxOy phase was detected by XRD. SEM and AFM analysis revealed the uniformly and densely distributed small grains with a considerably average surface roughness of similar to 5.6 nm. The deposited AlxOy/Cr/AlxOy multilayered stack was found to have an optical absorptance of 0.91 and thermal emittance of 0.12 at a temperature of 373 K, which is potential and suitable for selective solar absorbers applications.