Solar selective absorbers based on two-dimensional W surface gratings with submicron periods for high-temperature photothermal conversion

Spectral properties and thermal stability of two-dimensional (2D) W surface gratings with submicron periodicity are investigated to develop solar selective absorbers for high-temperature applications. Numerical calculations based on the rigorous coupled-wave analysis technique have been performed for simulating the spectral properties of W gratings. The results indicate that the gratings with microcavities have a good spectral selectivity suited for high-temperature applications, while the gratings with micropyramids realize a high solar absorptance over 0.92. 2D surface gratings with submicron holes have been fabricated on W substrates by the fast atom beam etching with highly ordered porous alumina masks. They have shown good spectral selectivity and sufficient thermal stability at 1170 K under a vacuum atmosphere. The observed absorption band is considered to originate from the standing wave resonance between the electromagnetic fields and the standing wave mode generated inside the holes.