Quantitative analysis of nanoparticle growth through plasmonics

Plasmon excitation appears to be a powerful and flexible tool for probing in situ and in real time the growth of supported conducting metal nanoparticles. However, although models exist for analysing optical profiles, limitations arise in the realistic modelling of particle shape from the lack of knowledge of temperature effects and of broadening sources. This paper reports on the growth of silver on alumina at 190-675 K monitored by surface differential reflectivity spectroscopy in the UV-visible range. In the framework of plasmonic response analysis, particles are modelled by truncated spheres. Their polarizabilities are computed within the quasi-static approximation and used as an input to the interface susceptibilities model in order to determine the Fresnel reflection coefficient. The pivotal importance of the thermal variation of the metal dielectric constant is demonstrated. Finite-size effects are accounted for. As size distribution fluctuations contribute marginally to the lineshape compared to the aspect ratio (diameter/height) distribution, a convolution method for representing the experimental broadening is introduced. Effects of disorder on the lineshape are discussed. It is highlighted that beside the quality of the fit (not a proof by itself!), physical meaning of the parameters related to the sticking probability, growth and wetting is crucially required for validating models. The proposed modelling opens interesting perspectives for the quantitative study of growth via plasmonics, in particular in the case of noble metals.