A paper sample that was coated with two thin films was analyzed using ATR – IR and IRRAS with polarized light. The pure coating materials were also measured using ATR – IR.
It was shown that the outer most coating could be detected with ATR – IR due to the formation of a Berreman peak, which is an optical thin film phenomenon. The inner coating could not be detected due to the limited penetration depth of the ATR –IR method. Using IRRAS there is no limit in the penetration depth of the infra red light and both coatings yield Berreman peaks. The optical peaks can be used to determine
the thickness of the thin films and the chemical peaks can be used to check the
chemistry of the films. For a detailed interpretation a simulation of the FTIR spectra is needed, which is possible if the optical properties of the substrate and the coatings are either known or can be measured.