Silver Nanoparticles and Nanorings for Surface-Enhanced Raman Scattering

Silver (Ag) nanoparticles (NPs) and Ag nanorings (NRs) have been fabricated. Due to the inherent features of Ag NPs and Ag NRs, strong electromagnetic (EM) near-field distributions were expected, and hence surface-enhanced Raman scattering (SERS) activity was demonstrated. Size and interparticle gaps distribution of Ag NPs were estimated to be 48.14 ± 10.14 nm and 14.11 ± 5.24 nm respectively along with estimated coverage density of ~ 4 × 10¹⁰ cm⁻². On the other hand, Ag NRs were found to consist of Ag clusters and of various shapes and sizes, instead of a perfect ring structure. High-resolution FESEM revealed that the individual constituent clusters were different from each other, particularly in terms of size and shape in addition to the cases how such clusters were connected to form the edge of the NR. However, the coverage density of Ag NRs was estimated to be ~ 5.6 × 10⁶ cm⁻². Based on the scenarios, it was speculated that the local EM near-field distribution would excel and thus led to enhanced SERS signals. SERS enhancement of R6G was estimated as high as 2.18 × 10⁴ and 2.78 × 10⁴ at 610 cm⁻¹ (C − C ring bending mode in phenyl rings) for Ag NPs and Ag NRs respectively. FDTD analysis was carried out to elucidate the EM near-field distributions. Graphical abstract: Ag NPs and Ag NRs from an ultrathin layer of Ag on ZnO/Glass (middle pane) confirming high EF of R6G adsorbed on Ag NRs (right pane) and Ag NPs (left pane) supported by corresponding EM near-field distributions. [Figure not available: see fulltext.]