Adsorbate-Induced Quenching of Hot Electrons in Gold Core−Shell Nanoparticles

We have investigated the effect of molecular adsorbates on the ultrafast electron dynamics in nanoshell particles. These nanoparticles consist of a thin gold shell surrounding a gold sulfide core. Pump−probe transmission measurements at 1.5 eV on unmodified nanoshells in aqueous solution yield an electron relaxation lifetime of ∼2.7 ps. The lifetime decreased with the adsorption of p-aminobenzoic acid (∼1.7 ps) or aniline (∼1.9 ps) on the nanoshells. With adsorbed p-mercaptobenzoic acid or n-propylamine, electron thermalization occurred in ∼2.4 or ∼2.8 ps, respectively. Surface-enhanced Raman signals were detected from the aromatic molecules, confirming their adsorption on the nanoshells. Density functional theory calculations indicate that the molecules providing the strongest modification of the dynamics possess the largest induced dipole moments near a metal surface. This suggests that the adsorbate-induced perturbation of the nanoshell electron dynamics is primarily electronic in nature.