Nanoparticles/Parabolic Nanobowl Hybrid Structure as a Surface-Enhanced Raman Scattering Substrate: Insights Using the FDTD Method

Nanobowl structures are commonly used as substrates for surface-enhanced Raman scattering (SERS) detection due to their high plasmonic activity. In this work, we introduce and investigate a superenhancing potential structure, nanoparticles (NPs) in a parabolic nanobowl (PNB). Moreover, the optimal parameters of the NPs in the PNB structure are obtained and the origin of plasmon enhancement is analyzed. The electric field distribution and the electromagnetic field enhancement factor MSERS of the PNB structure are obtained via the finite-difference time-domain (FDTD) method. We found that the electric field enhancement originated from the coupling of the surface plasmon polariton (SPP) within the PNB and the interstitial local surface plasmon resonance (LSPR) of the nanoparticles. By manipulating the curvature of the PNB, the size of the NPs, and the materials of the NPs in PNB structures, the plasmon resonance of both NPs and the PNB became strongest. When the curvature of the PNB is 2.9 μm–1, the wide-range enhancive electromagnetic field generated at the bottom of the PNB couples best with the LSPR of the NPs. The NP size is recommended to be in the range of 46–56 nm. For the choice of materials, it is found that the maximum enhancement is on the order of 1010 when noble metals Au and Ag are used as the materials of the PNB and NPs. Since the permittivity imaginary part of Si is closer to zero, a maximum enhancement factor reaching 1011 magnitude is obtained when Si is used as the material of the PNB. These results indicate that the PNB structure shows powerful SERS enhancement and is expected to be applied to the detection of environmental pollutants, such as microplastics.