Plasmonic Nanolenses with Tunable Thickness: Enhanced Near-Field Focusing via Rim-Localized Light Absorption and...

Herein, the rational design and implementation of a modular chemical toolkit involving on-demand synthetic steps are reported, enabling the fabrication of plasmonic gold (Au) nanolenses consisting of 2D hexagonal nanoplates (NPLs) with central porous domains. These nanostructures exhibit tunable thickness along the z-axis and enable precise control over the ratio between the internal porous region and the surrounding smooth rim. The latter is designed to maximize the absorption of light, which is then transferred into the porous core. As the nanolens thickness increases, the vertically expanded porous volumes act as hot nanochannels that strongly enhance the near-field focusing. By systematically tuning the particle thickness, rim width, and porosity, nine distinct nanolens geometries are fabricated and identified optimal structural parameters for maximizing the single-particle surface-enhanced Raman scattering (spSERS) performance. Finite element method simulations and experimental measurements revealed that increasing the nanolens thickness while reducing the relative area of the porous domain synergistically enhanced the light confinement through increased absorption, energy transfer, multiple scattering, and internal reflection. These findings establish vertical morphological control and structural engineering of plasmonic nanolenses as powerful strategies for achieving superior field localization, providing a generally applicable platform for high-performance SERS sensors in various environments.