Sputter-deposited Pt-Al 2O 3 selective absorber coatings

Abstract

In this paper we describe an investigation of several configurations of selective absorber coatings which incorporate sputter deposited Pt-Al 2O 3 cermet layers. The potential application is for medium and high temperature collectors. The coatings were prepared by codeposition using Al 2O 3 and platinum cylindrical-post magnetron sputtering sources. Three coating configurations were investigated:(1) a Pt-Al 2O 3 cermet, with a linearly graded platinum content and an Al 2O 3 antireflection layer, which was deposited onto platinum-coated glass; (2) a Pt-Al 2O 3 cermet, with a uniform platinum content and an Al 2O 3 antireflection layer, which was deposited onto platinum-, chromium- and molybdenum-coated glass; (3) an Al 2O 3/M/Al 2O 3 (AMA) type of coating, with an M layer consisting of a uniform Pt-Al 2O 3 cermet, which was deposited onto platinum-, chromium- and molybdenum-coated glass. Hemispherical absorptances α H greater than 0.9 were obtained for all three configurations. Hemispherical emittances of less than 0.1 at 20 °C were obtained for the graded and AMA configurations. The uniform cermets possessed higher emittances (approximately 0.13). Coatings deposited at 500 °C onto platinum-coated glass appear to be stable (less than 1% loss in α H) at 600 °C in air. Coatings deposited at lower temperatures (about 150 °C), or onto chromium or molybdenum substrates, were less stable but show promise for many applications in the range 300–500 °C.