Quantitative analysis of nanoparticle growth through plasmonics

Abstract

Plasmon excitation appears to be a powerful and flexible tool for probing in situ and in realtime the growth of supported conducting metal nanoparticles. However, although modelsexist for analysing optical profiles, limitations arise in the realistic modelling of particleshape from the lack of knowledge of temperature effects and of broadening sources. Thispaper reports on the growth of silver on alumina at 190–675 K monitored by surfacedifferential reflectivity spectroscopy in the UV–visible range. In the framework of plasmonicresponse analysis, particles are modelled by truncated spheres. Their polarizabilitiesare computed within the quasi-static approximation and used as an input tothe interface susceptibilities model in order to determine the Fresnel reflectioncoefficient. The pivotal importance of the thermal variation of the metal dielectricconstant is demonstrated. Finite-size effects are accounted for. As size distributionfluctuations contribute marginally to the lineshape compared to the aspect ratio(diameter/height) distribution, a convolution method for representing the experimental broadening isintroduced. Effects of disorder on the lineshape are discussed. It is highlighted that besidethe quality of the fit (not a proof by itself!), physical meaning of the parametersrelated to the sticking probability, growth and wetting is crucially required forvalidating models. The proposed modelling opens interesting perspectives for thequantitative study of growth via plasmonics, in particular in the case of noblemetals.