• Ring-shaped holes;
  • plasmon focusing;
  • SERS;
  • substrate.


An array of ring-shaped holes is prepared from silver thin films using electron beam lithography. The optimal conditions for high performance as a surface-enhanced Raman scattering (SERS) substrate are investigated. Either the diameter of the hole (0.5, 1.0, 2.0, 3.0 and 4.0 µm) or the slit width (200, 300, 400, 500 and 600 nm) is varied. 4-Aminothiophenol (ATP) adsorbed on the structures as a self-assembled monolayer (SAM) is used as probe to evaluate the SERS performance of the generated structures. It is found that there is an optimal configuration for ring-shaped holes with a 3.0-µm diameter and 200-nm slit width. The SERS activity on this optimal lens configuration is found to be 13 times greater than that of the activity on the silver thin film. An array of these structures at this optimal configuration can easily be constructed and used in a range of SERS-based sensing applications.