Intensity and Band Shape of Infrared Reflection Absorption Spectra of Organic Thin Films on Silica Substrate

The intensity and band shape of Fourier transform infrared reflection absorption (RA) spectroscopy have been studied for the analysis of an organic thin film formed on a SiO2 substrate. The optimum experimental condition to obtain the RA spectra with the best S/N ratio was theoretically determined for perpendicular polarization at an incidence angle of 76° on the basis of Fresnel equations using a model of a three-phase system consisting of air, a thin film and an inorganic substrate. The RA spectrum calculated from the dispersions of complex refractive indexes of a thin film and a SiO2 substrate was in good agreement with the experimental spectrum. The peak intensity of the thin film was linear up to about a film thickness of 100nm under these conditions. The calculation suggested both band distortion and a peak shift in the RA spectra.