Preparation and optical properties of silver chalcogenide coated gold nanorods

A homogeneous layer of silver sulfide or selenide was coated onto gold nanorods in aqueous solution by exposing Au/ Ag core/ shell nanorods to S2- or Se2- in an oxidizing environment. The formation of the silver chalcogenide layers was confirmed by transmission electron microscopy ( TEM) and selective area electron diffraction ( SAED). The longitudinal plasmon resonance of the gold nanorods shifted to the red and was attenuated. The experimental spectra agree well with a simulation based on confocal ellipsoids in the quasi- static limit. The synthetic procedure was also employed to coat silver sulfide or selenide onto gold bipyramids. A red- shift of the longitudinal plasmon resonance was also seen, although the coating was not as homogeneous. These novel composite materials may present interesting nonlinear optical properties.