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 similar to 650 to similar to 900 nm. 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.