Investigation of laser-induced inter-welding between Au and Ag nanoparticles and the plasmonic properties of welded dimers
Noble metallic nanoparticles with unique plasmonic properties are useful in a variety of applications including bio-imaging, sensing, cancer therapy, etc. The properties of metallic nanoparticles can be tuned in multiple ways, among which laser welding is a highly efficient method. In this study, laser-induced inter-welding of Ag–Au nanoparticle (NP) dimers was investigated using in situ transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDX). For the first time, the welding process was directly visualized. The structural and compositional evolution of Ag–Au dimers was studied in detail, and several typical nanostructures formed during the welding process, including two types of core–shell structures, were discovered. Based on these observations, we proposed a complete mechanism explaining how welding proceeds under the influence of a laser. Finite difference time domain (FDTD) simulations demonstrated that the plasmonic properties of welded Ag–Au dimers were different from those of pure Au–Au or Ag–Ag dimers and can be tuned by forming shells, alloying or changing the size ratio of Ag and Au NPs.