Controlled Alloying of Au@Ag Core–Shell Nanorods Induced by Femtosecond Laser Irradiation

Bimetallic nanoparticles display unique physical and chemical properties, including improved chemical stability, enhanced optical properties, or higher catalytic activity. Here, a synthetic methodology is described to obtain bimetallic heterostructures and alloyed plasmonic nanocrystals through the irradiation of colloidal Au@Ag core–shell nanorods (Au@Ag NRs) with femtosecond laser pulses. Depending on the energy deposited on the Au@Ag NRs, different morphologies and degrees of alloying are obtained, such as hot-dog-like and rice-like (partially alloyed) NRs, as well as fully alloyed nanospheres. By using advanced electron microscopy techniques and energy-dispersive X-ray spectroscopy (EDX) tomography, both the morphology and the elemental distribution of the irradiated nanoparticles can be disclosed, and correlated to detailed investigations of their optical properties using electromagnetic simulations. The wide variety of bimetallic species provided by the proposed approach is a clear indication of the potential of combining synthetic colloidal methods with fs-pulsed laser irradiation for the fabrication of unique multielemental nanoparticles. The resulting control over size and composition raises promising prospects for catalytic, plasmonic, and magnetic applications of multimetallic nanocrystals.