New interpretation of the IR reflectance spectra of SiO₂-rich films on soda-lime glass

A new interpretation of the reflectance spectra of weathered or silica-coated soda-lime glass between 1250 and 900 cm^-1 is suggested. Traditionally, the presence and intensity of each spectral band observed were attributed to the concentration of a given chemical species in the film. Contributions due to the substrate and to the film thickness were excluded. On the basis of a more rigorous model, with the help of mathematical and physical simulations, it is shown that the penetration depth is much higher than previously assumed. Accordingly, all the spectral features observed for coatings or weathered films are a function not only of the nature of the film, but also of film thickness and type of substrate.