Effect of substrate on radiative properties of thin films.

An expression for the directional transmittance of an absorbing thin film on anabsorbing substrate was developed by using the classical electromagnetic theory. This expression when combined with the wellstudied reflectance can yield absorptance values that are of utmost interest in heat transfer studies. The behavior of the normal and hemispherical reflectance, absorptance, and transmittance is exhibited for some selected values of film and substrate optical constants and is presented graphically as a function of film optical thickness. The results indicate that the imaginary part of the complex index of refraction for both film and substrate should be accounted for when calculating radiative transfer and properties of such films.