Thermal-Radiation Properties of Thin Metallic Films on Dielectrics

The spectral radiation properties of thin metallic films are obtained through the numerical solution of the governing integrodifferential equation for the anomalous skin effect with size effects included. The theory predicts that at low temperatures there will be a film thickness for which the emittance is a minimum. This minimum, which is lower than the emittance for a bulk specimen, is apparently due to interference effects arising from the finite film thickness. It is also found that for certain cases transmission through a film is not negligible compared with the emission from the film. The analysis is extended to include metal-coated dielectric films, and the theoretical results are compared with existing experimental data.