Twin plane decoration of silver nanorods with palladium by galvanic exchange at a controlled rate.

Here we describe the galvanic exchange of surface-grown Ag nanorods (NRs) and nanowires (NWs) with PdCl(4)(2-) as a function of the PdCl(4)(2-) concentration. The morphology of the resulting AgPd alloy nanostructures depends on the galvanic exchange rate, which increases with increasing PdCl(4)(2-) concentration over a specific concentration range. When the concentration of PdCl(4)(2-) exceeds 7.5 × 10(-5) M (or ratio of moles of PdCl(4)(2-) in solution to moles of Ag on the surface > 542), rapid galvanic exchange results in Pd deposition over the entire Ag nanostructure in the early stages of exchange. When the concentration of PdCl(4)(2-) is in the range of 1.0 × 10(-5) to 5.0 × 10(-5) M (moles of PdCl(4)(2-) in solution to moles of Ag on the surface = 13-54), Pd deposition occurs preferentially at high energy twin plane defects in the form of well-spaced nanoparticles during the early stages of exchange. In later stages, the Pd deposits grow and coalescence into a rough shell, and etching of the Ag leads to a presumably hollow nanostructure. Composition analysis by linear sweep voltammetry as a function of time shows that the galvanic exchange rate is much slower than the diffusion-limited rate and, when correlated with UV-vis spectroscopy, shows that less than 10% Pd in the nanostructure completely dampens the Ag-localized surface plasmon band.