Ellipsometric characterization of thin nanocomposite films with tunable refractive index for biochemical sensors

ABSTRACTCreating optical quality thin films with a high refractive index is increasingly important for waveguide sensor applications. In this study, we present optical models to measure the layer thickness, vertical and lateral homogeneity, the refractive index and the extinction coefficients of the polymer films with nanocrystal inclusions using spectroscopic ellipsometry. The optical properties can be determined in a broad wavelength range from 190 to 1700 nm. The sensitivity of spectroscopic ellipsometry allows a detailed characterization of the nanostructure of the layer, i.e. the surface roughness down to the nm scale, the interface properties, the optical density profile within the layer, and any other optical parameters that can be modeled in a proper and consistent way. In case of larger than about 50 nm particles even the particle size can be determined from the onset of depolarization due to light scattering. Besides the refractive index, the extinction coefficient, being a critical parameter for waveguiding layers, was also determined in a broad wavelength range. Using the above information from the ellipsometric models the preparation conditions can be identified. A range of samples were investigated including doctor bladed films using TiO2 nanoparticles.