Monolayer and multilayer film characterisation using surface plasmon resonance

Abstract The surface plasmon resonance measurement technique has been enhanced by improved accuracy of measurement and speed of analysis. By this means, separate determination of thickness and refractive index information is possible even for monolayer films. A computer-controlled, angle-scan reflectometer for internal reflectance measurement by prism coupling has been calibrated by a novel method to eliminate systematic errors and reduce noise below 0.04%. The instrument has been used for characterisation, of thin dielectric films deposited using the Langmuir-Blodgett method. The Levenberg-Marquardt optimisation algorithm has been applied using a simple model for rapid assessment of film parameters. An analysis of multilayer films of behenic acid has exhibited excellent consistency of measurement down to a single molecular monolayer. A refractive index of 1.55 ± 0.01 and a layer thickness of 2.65 nm are found and layer quality is assessed from scattering losses. A molecular tilt angle of 26° is deduced from comparison with a molecular model, and is in agreement with infrared spectroscopic data. A monolayer film of an organo-ruthenium complex molecule has been analysed to assess film thickness and quality.