Visible Light and Infrared Ray Absorbance of Fine Protrusions Formed by Sputter Etching of Steels and Copper Alloys

Argon ion sputter etching was applied to steels and copper alloys at a radio frequency power of 150 or 250 W for 0.9 to 10.8 ks. Coneor ridgeshaped protrusions with many secondary fine protrusions were formed on the surface. The sizes of the protrusions were typically comparable to the wavelength range of visible light, i.e. 400 nm to 700 nm, and that of nearinfrared ray, i.e. 700 nm to 2.5 mm. Their absorbance of visible light and nearinfrared ray was more than 90, and the absorbance decreased with increasing wave length. These characteristics of the protrusions along with the high heatresistance of stainless steels and the high heatconductivity of copper alloys are suitable for the solar selective materials. The exposure of the protrusions formed on the copper alloys to oxygen gas or air just after the sputter etching increased the absorbance of visible light as well as infrared ray with an appearance of the spectrum of Cu2O near the wavelength of 16 mm. [doi:10.2320/jinstmet.J2014012]