Tuning Plasmonic Properties by Alloying Copper into Gold Nanorods

We create rod-shaped single crystalline gold−copper (Au x Cu (1- x ) ) nanoparticles and verify the presence of copper in the particles with various direct and indirect optical and electron microscopy techniques. The particles grow from small, preformed gold seeds in a growth solution containing both copper and gold ions in the presence of a surfactant and a mild reducing agent. The presence of copper in the growth solution has a pronounced effect on the spectral characteristic of the resulting nanocrystals and reduces the total volume of the resulting particles. In contrast to spherical copper particles, our rod-shaped nanocrystals show a strong plasmon resonance and the copper content varies the plasmon resonance frequency and the plasmonic line-width. Optical single particle plasmon-line-width observations suggest reduced plasmon damping at specific copper contents corresponding to stoichiometric particle compositions.