Total internal reflection ellipsometry (TIRE) technique was used to investigate the role of surface roughness in the hybrid system composed of octadecanethiole layer on Au thin film. The samples with Au films of different microstructure were explored. The experimental results were interpreted in the model, which took into account the surface roughness of Au film in the hybrid system. It was shown that optical parameters of octadecanethiole were in correspondence for samples of different microstructure in the case of adequate models used for interpretation of TIRE data. (c) 2009 Elsevier B.V. All rights reserved.