Optical properties of platinum-coated gold nanorods

The optical properties of Au/Pt nanorods with different morphologies are analyzed in detail through comparison of experimental UV-vis-NIR spectra and calculations based on the boundary element method (BEM). The studied morphologies refer to two different Pt deposition modes on Au nanorods, which have been experimentally realized through the presence or absence of Ag+ ions in solution. While in the absence of Ag+, complete overcoating was obtained, the presence of these ions induced preferential growth on the tips, as recently reported by us.(1) The changes in the optical spectra are different for both Pt deposition modes, and this is fully accounted for using appropriate geometrical models in the BEM calculations. The presence of Pt tips is shown to lead to red-shifts of the longitudinal plasmon band because of geometrical effects, though accompanied by damping due to increased absorption.