Tunable Plasmons in Shallow Silver Nanowell Arrays for Directional Surface-Enhanced Raman Scattering

The purpose of this article is to improve the collection efficiency of surface-enhanced Raman scattering (SEAS) further to increase SERS detection sensitivity in trace detection. To achieve this, a silver nanowell array substrate was designed based on its tunable propagating surface plasmons. This substrate supported directional surface plasmon coupling emission and could guide SERS to the vertical direction of the substrate. Silver nanoparticles were assembled on the shallow silver nanowell array to contribute localized surface plasmons for higher electromagnetic enhancement. Spatial SEAS radiation patterns on the silver nano particle assembled nanowell array substrate were simulated by the finite-difference time-domain method and recorded by a self-made 3D angle-resolved Raman spectrometer. The results showed that SERS signals were strong and unidirectional in space. The half divergence angle of the SERS pattern was about 10 degrees, which would facilitate SERS collection by using a conventional backscattering Raman spectrometer. This silver nanowell array is supposed to be an applicable configuration to many systems that require high collection efficiency like single-molecule SERS detection and tip-enhanced Raman spectroscopy.