Plasmon Resonance Shifts of Au-Coated Au₂S Nanoshells: Insight into Multicomponent Nanoparticle Growth

In this Letter we present a coherent description of the optical properties of a unique type of nanoparticle, metal-coated dielectric nanoparticles. These structures occur naturally in the form of Au-coated Au₂S nanoparticles. During the course of nanoparticle growth, the plasmon-related absorption peak undergoes very large shifts in wavelength, from ∼650 to ∼900nm. We show that this plasmon peak shift is purely classical in origin and is determined solely by the relative thickness of the Au shell and the Au₂S core diameter. This understanding of the optical properties of these nanoparticles is used to elucidate the nanoparticle growth kinetics.