Thickness measurement of thin polymer films by total internal reflection Raman and attenuated total reflection infrared spectroscopy

For the first time total internal reflection (TIR) Raman spectroscopy was utilized for thickness measurements of thin isotropic polystyrene films on polypropylene substrate. In the presented method, the band intensity ratios of polystyrene to polypropylene were defined from the spectra, and the film thicknesses in a range from 50 nm to 350 nm were calculated mathematically from these ratios. The quantitativeness of the method was validated by applying the same principle to attenuated total reflection infrared (ATR-IR) spectroscopy and comparing the results to values obtained by ellipsometry and a spin-coating model. The results showed that the novel and non-invasive TIR Raman method reveals the film thickness quantitatively, and the method is applicable for thin films on soft substrates with similar refractive indices.