Methods for modifying the structure of Ag–Cu nanoparticles

Abstract

Due to the phenomenon of localized surface plasmon resonance, one of the main possible applications of Ag–Cu nanoparticles (NPs) is in nanooptics, for example, the fabrication of Surface-enhanced Raman spectroscopy substrates. Particularly interesting is the ability to finely tune the plasmonic properties of Ag–Cu NPs by varying the target chemical composition. However, this effect is still significantly influenced by shape, size, and internal structure, which allows for control of the plasmonic effect when using Ag–Cu NPs with different structures. The processes of crystallization and annealing of Ag–Cu nanoparticles were studied using simulation methods, depending on the level of copper doping and the rate of thermal energy dissipation, with the aim of determining the resulting internal structure. It was found that most Ag–Cu NPs, regardless of the target chemical composition, exhibited an amorphous structure after cooling, with a wide distribution of Cu atoms in the central area of the NPs and a partial expulsion of Ag atoms primarily to their surface. This finding contradicts the theoretical data regarding the structure of Ag–Cu NPs, which were based on identifying structures with the minimal possible potential energy, indicating the capture of metastable structural modifications. Further thermal annealing revealed that, at low levels of copper doping in relatively large Ag–Cu NPs, the formation of fivefold symmetry was possible, and the conditions for the emergence of this effect were documented. Based on computer analysis, possible ways to control the structure of Ag–Cu nanoparticles were identified.