The spectrally selective properties of Ag 2S films on silver

Abstract

Silver was reacted in sulfur vapor to form Ag 2S films of varying thickness. Absorptance and emittance measurements were made to discern the spectral selectivity. A sharp transition of reflectance versus wavelength occured in Ag 2S films at about 1.2–1.4 μm. The plasma wavelenght calculated from the band-gap energy was 1.2 μ which supported Christie's model of spectral selectivity. The ratio of absorptance to emittance increased with increasing film thickness, but differences were observed for different sulfidation treatments. The Ag 2S films were tested for stability at 200 and 500°C in air and were found to be unstable at these temperatures. Absorptance decreased with increasing exposure time due to dissociation of the Ag 2S and/or to the formation of Ag 2SO 4 nodules on the surface. it appears that the use of Ag 2S films would be limited to temperatures below about 150°C.