Method for evaluation of the emissivity spectrum of a localized vibrational absorption band

Even when a material is in thermal equilibrium with its surroundings, the thermal radiation that it emits can be made evident by detecting a difference between its radiation power and that of some reference material, such as a black chopper wheel. Such a way of revealing thermal radiation from a material provides us with a possibility of characterizing radiant properties of that material without requiring any special radiant standard. In this work I develop a semiquantitative analysis of such a difference signal, which provides us with a simple relationship between the emissivity of a material and measurable quantities. Using this result, I propose a method for determining the spectral dependence of emissivity of a material. The validity and usefulness of the method are confirmed by applying it to the Si–H stretching band in two amorphous films of undoped hydrogenated amorphous silicon and of its alloy with nitrogen.