Electrochemically induced shifts in the plasmon resonance bands of nanoscopic gold particles adsorbed on transparent electrodes

We have examined the plasmon resonance spectra of nanoscopic gold panicles of average radii 9 nm, 14 nm, and 21 nm, adsorbed on transparent semiconductor electrodes in contact with three aqueous electrolytes (0.075 M KPF6, KCl, and KBr). In all electrolytes, the plasmon resonance bands are red-shifted and decreased in intensity as the applied potential is made more positive. The potential-induced spectral effects are greatest for the 9 nm radius particles in contact with KCl and KBr solutions. Simulations using a Rayleigh limit coated-sphere scattering theory suggest that the spectral red-shifting and intensity damping cannot be explained on the basis of free electron depletion and consequent reduction in the metal plasma frequency, omega(p). For gold particles in contact with PF6- anions, the subtle potential-induced spectral effects are likely due to reduction in the electron mean free lifetime, tau. The more pronounced effects for particles in contact with Cl- and Br- may arise from more severe reductions in tau, and/or the formation of a metal-adsorbate complex which is highly absorbing in the spectral region of the plasmon resonance band. (C) 1999 The Electrochemical Society. S0013-4651(97)06-118-1. All rights reserved.