title: Precision synthesis: designing hot spots over hot spots via selective gold deposition on silver octahedra edges.
abstract: 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.
authors.affiliation: Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore, 637371.
authors.forename: Yejing
authors.initials: Y
authors.lastname: Liu
authors.forename: Srikanth
authors.initials: S
authors.lastname: Pedireddy
authors.forename: Yih Hong
authors.initials: YH
authors.lastname: Lee
authors.forename: Ravi S
authors.initials: RS
authors.lastname: Hegde
authors.forename: Weng Weei
authors.initials: WW
authors.lastname: Tjiu
authors.forename: Yan
authors.initials: Y
authors.lastname: Cui
authors.forename: Xing Yi
authors.initials: XY
authors.lastname: Ling
keywords: cathodoluminescence spectral images; hot spots; nanocrystals; plasmonics; surface-enhanced raman scattering