Precision Synthesis: Designing Hot Spots over Hot Spots via Selective Gold Deposition on Silver Octahedra Edges

A major challenge in plasmonic hot spot fabrication is to efficiently increase the hot spot volumes on single metal nanoparticles to generate stronger signals in plasmon‐enhanced applications. Here, the synthesis of designer nanoparticles, where plasmonic‐active Au nanodots are selectively deposited onto the edge/tip hot spot regions of Ag nanoparticles, is demonstrated using a two‐step seed‐mediated precision synthesis approach. Such a “hot spots over hot spots” strategy leads to an efficient enhancement of the plasmonic hot spot volumes on single Ag nanoparticles. Through cathodoluminescence hyperspectral imaging of these selective edge gold‐deposited Ag octahedron (SEGSO), the increase in the areas and emission intensities of hot spots on Ag octahedra are directly visualized after Au deposition. Single‐particle surface‐enhanced Raman scattering (SERS) measurements demonstrate 10‐fold and 3‐fold larger SERS enhancement factors of the SEGSO as compared to pure Ag octahedra and non‐selective gold‐deposited Ag octahedra (NSEGSO), respectively. The experimental results corroborate well with theoretical simulations, where the local electromagnetic field enhancement of our SEGSO particles is 15‐fold and 1.3‐fold stronger than pure Ag octahedra and facet‐deposited particles, respectively. The growth mechanisms of such designer nanoparticles are also discussed together with a demonstration of the versatility of this synthetic protocol. A “precision synthesis” approach is demonstrated to selectively deposit Au nanodots on tips/edges of Ag octahedra, adding hot spots exclusively along the edges (hot spot regions). The enhanced local electromagnetic fields are directly visualized using hyperspectral cathodoluminescence spectroscopy. Single‐particle surface‐enhanced Raman scattering demonstrates 10‐fold signal enhancement on these precisely designed nanoparticles over pure Ag nanoparticles.