Characterization of thin films and their structures in surface plasmon resonance measurements

An approach to quantitative evaluation of surface plasmon resonance (SPR) measurements is given. In order to determine thicknesses and refractive indices, measured SPR curves were fitted numerically with a theoretical model based on the Fresnel equations. The model also takes into account additional roughness layers, representing real properties of the interfaces, which significantly improves the fitting accuracy. The intermediate layers have physical thicknesses and effective complex refractive indices, responsible for light losses at the interfaces. This model has been verified by direct measurement of surface roughness with the help of an atomic force microscope (AFM). It has turned out that the fitting procedure can reveal microstructures of a substrate and deposited layer, and when combined with the AFM for roughness measurement, this model can find simultaneously both the thickness and the refractive index of the metal film.