Determination of the optical constants of gold nanoparticles from thin-film spectra

We determine the optical properties of nanocomposites comprising gold nanoparticles embedded in a titania matrix using spectroscopic ellipsometry. We then apply the spectral representation formalism due to Bergman, to extract the dielectric function of the individual gold nanoparticles (NPs). We show that analytical forms of the spectral representation function can be generated, which enable local clustering and the width of the surface plasmon resonance to be accounted for. The model also explains anomalously high, near-infrared absorption by small metal particles, reported by Tanner. The procedure provides a method to determine the optical constants of a wide range of metallic and semiconducting nanoparticles from ellipsometric data