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 S or Se 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.