Determining the Relative Contributions of Electron Confinement and Chemical Interface Damping in Small Functionalized Spherical Gold Nanoparticles with Non-Lorentzian Line Shapes

Abstract

Understanding the factors that control the localized surface plasmon (LSPR) damping mechanisms in plasmonic nanoparticles is an essential aspect of plasmonics. Classical electromagnetism, together with solid-state physics theories, states that the experimental LSPR bandwidth accounts for the different independent mechanisms involved: bulk or natural plasmon losses, surface scattering arising from electron confinement (EC), radiative damping arising from the emission of radiation of a given LSPR mode, and chemical interface damping (CID). In functionalized spherical Au plasmonic nanoparticles with dimensions smaller than the mean free path, determining the relative contributions of electron confinement as well as chemical interface damping from the experimental LSPR bandwidth is a difficult task. This occurs because interband transitions give rise to non-Lorentzian line shapes so that the full width at half-maximum contains both mechanisms (CID and EC) connected in a nontrivial way. In the present work, we propose a method for determining the relative contributions of EC and CID by Mie theory simulations of the experimental spectra using an appropriate modification of the bulk dielectric function of Au. The proposed method is applied for AuNP functionalization with thiophenol and p-chlorothiophenol. The results show that the magnitude of CID is linearly dependent on the fraction of volume occupied by the organic compound in the shell of the functionalized Au nanoparticle and that the contribution of CID can be several times greater than EC.