Dressing Plasmons in Nanoparticle-in-Quasi-Cavity Architectures for Trace-Level Surface-Enhanced Raman Spectroscopy Detection

There is a problem with hot spot design in surface-enhanced Raman scattering (SERS). It usually focuses on the construction of dense electric field distribution (EFD) but overlooks the required matching quality between EFD and the substrate, resulting in poor uniformity of the Raman signals. To address this problem, a particle-in-quasi-cavity (PIQC) architecture of ZnO nanowalls (NWs) loaded with double-layer Ag nanoblocks and Ag nanospheres has been designed and fabricated in this study. Theoretical and experimental results comprehensively prove that the effective coupling between the plasmon modes of the metal nanocavities and the metal nanoparticles can induce the tailored fit a quite fitting electric field jacket (EFJ) along the surface of ZnO NWs, which matches well with the substrate. Such an EFJ exhibits remarkable SERS performances, including not only high sensitivity but also fine uniformity, with the enhancement factor reaching up to 2.84 × 10 7 and the minimum relative standard deviation as small as 4.22%. The optical response of the PIQC structure found in this work shows great potential in the construction of high-performance SERS-active substrates and other applications.