Interference method for the determination of the complex refractive index of thin polymer layers

The optical properties of thin-film layers are described by the complex index-of-refraction (N) and are commonly measured using spectroscopic ellipsometry. Once determined, they can be used to predict the optical reflection and transmission from films of any thickness. Fitting of the spectroscopic ellipsometry data for thin-film polymers and polymer-blends is difficult because numerous numerical assumptions are necessary and optical birefringence must be accounted for. Ellipsometric fitting techniques fail for thin films with strong absorption and high surface roughness. The authors present a simple method to measure N, perpendicular to the sample plane, of optically homogeneous films using a UV/Vis spectrometer and partial transmission substrates.