Abstract

Absolute extinction measurements on individual silver nanoparticles under illumination show a steady evolution of their localized surface plasmon resonance. Their progressive transformation during light exposure and the influence of various parameters such as the nature of stabilizers, the local environment (oxygen rate), the spectral range of the incident light, and the shape of the nanoparticle (spheres or nanocubes) have been carefully investigated in correlation with transmission electron microscopy imaging. A combination of optics and electron microscopy gives evidence that photoaging mainly consists of the progressive formation of an oxide shell around a metallic silver core during light illumination. Moreover, in the case of nanocubes, the metallic core not only decreases in volume but also changes morphologically since edges and corners are rounded off during the photo-oxidation process. The generalized Mie theory and finite element method, used to calculate the optical extinction cross-section of core/shell Ag@AgxO nanoparticles, well account for the observed time evolutions of the absolute extinction spectra of the silver nanospheres and nanocubes. Furthermore, the calculated electromagnetic field at the nanocube surface, enhanced on edges and corners, can explain the higher efficiency of the photo-oxidation on edges and corners and the rounding increase under illumination.

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