Gold Nanoparticle Chains: Synthesis, Characterization, and Modeling Using Spectroscopic Ellipsometry

In this paper, we explore the ability of ellipsometry to characterize colloidal suspensions composed of gold nanoparticle (NP) chains. The complex effective index of these suspensions is deduced from ellipsometric measurement by using a wavelength-by-wavelength inversion without any dispersion law. We show that the effective refractive index of these colloids is defined by the nature of the solvent, whereas their effective extinction coefficient is mainly sensitive to the plasmonic properties of NP chains. The influence of the NP radius distribution and arrangement on the effective extinction coefficient of NP chain are investigated through simulations based on the coupled point dipole method (CDM). We clearly show that this coefficient is mainly sensitive to the interparticle distance and the number of NPs in the longest segment of chains. We demonstrate that the distribution of the number of NPs in the longest segment of chains and their volume fractions can be directly deduced from the ellipsometry by using the CDM.