Abstract

Some problems which arise in the characterization of surfaces and coatings by internal reflection spectroscopy are described. The ir spectra of bare CaF2 trapezoids and of ThF4- and ZnSe-coated trapezoids exhibit absorption bands in the same spectral region as those of H2O and hydrocarbon impurities. In accord with previous investigations, it is observed that the absorptance due to water is much greater in the ThF4 films than in the ZnSe films or on the CaF2 surfaces. These results suggest that the water is distributed throughout the ThF4 films, whereas for ZnSe it resides primarily on the surface. In addition, a number of interesting observations on the desorption and adsorption of water and hydrocarbons to these materials are made. The experimentally observed absorptances are analyzed on the basis of the reflectance for a three-layer system. The analysis enables reasonably quantitative values for the absorption coefficient to be determined for these thin-film coatings.

© 1978 Optical Society of America

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