New Magnetron Sputtered Stainless Steel Nitride Cermet Solar Absorbing Coatings

This paper presents a new method for sputtering solar selective absorber coatings. Radio frequency magnetron reactive sputtering created stainless steel/stainless steel nitride (SS/SS-N) cermet (ceramic-metal composite) thin films under varied nitrogen gas flow ratios. In this present study, a stainless steel material is used for one-target sputtering to manufacture a solar selective absorber film having good solar absorptance of 0.91 and low thermal emittance of 0.06. This sputtering process shows considerable and stable usefulness due to the anti-oxidation and single target. Optical constants n and k have been determined by spectroscopic ellipsometry for cermet composite in a reactive gas flow from 0 percent to 50 percent. Based on the nitrogen content of the film, we used a different oscillator to analyze the film. When the nitrogen gas flow reaches 10 percent, the sputtered film has a significant transformation from metal to cermet properties. When the nitrogen gas flow goes above 17.5 percent, then the film transforms to a dielectric film which can be an anti-reflection layer. A solar absorptance of 0.92 was accepted as the theoretical prediction of optimal selective solar-absorbing three-layer processes which shows that the experimental results agree well with the theoretical prediction.