Optical characterization of multi-layer thin films using the surface plasmon resonance method: A six-phase model based on the Kretschmann formalism

A large variety of biological and chemical sensors are based on the surface plasmon resonance (SPR) technique. The procedure for data analysis in this method (which typically involves determination of optical constants and thicknesses of multi-layered thin films) can be considerably simplified by treating the working equations of the SPR device in a phenomenological framework originally introduced by Kretschmann. Although used quite widely, the Kretschmann formalism in its present form has been limited to relatively simple thin film systems - only involving three or four material-phases. In the present work, this formalism is extended to more complex systems that are often encountered in studies of layered nanostructures. The assumptions and implications of the Kretschmann formalism are discussed in detail using a six-phase model of Fresnel reflectivity. The experimental considerations of typical SPR-based sensors are included in this model. The effects of optical absorption within the sample films are also treated. The utility of the six-phase model is demonstrated with calculated results for two recently reported experimental systems. (C) 2001 Published by Elsevier Science B.V.