W/SS thin film as high temperature infrared reflector for solar thermal applications: Intrinsic properties and impact of residual oxygen

We investigated the impact of residual oxygen on thermal emittance of tungsten on stainless steel (W/SS) in conjunction with its intrinsic absorbing properties. The optimal emittance value is limited to ∼0.13 for the least oxygen contaminated tungsten thin films and ∼0.2 thermal emittance with small residual oxygen. In addition, the synthesized tungsten structures also exhibit significant solar absorption ∼0.76 and 0.78 for the least oxygen contaminated and small oxygen contaminated tungsten thin films. The relatively large value of thermal emittance is attributed to the intrinsic interband transition in infrared region. The observed relatively large absorption for both structures in 0.2-0.9 μm wavelength range is attributed the residual oxygen, which resulted in the formation of WOx, causing the cermet structure. The results suggest that the best emittance ∼0.13 can be achieved provided oxygen contamination can be avoided while synthesizing the tungsten thin films for infrared reflector applications in spectrally selective coating structures. This is also attributed partially to the intrinsic interband absorption in tungsten metal.