Three-dimensional donut-like gold nanorings with multiple hot spots for surface-enhanced raman spectroscopy

Seeking for the best possible substrates for surface-enhanced Raman spectroscopy (SERS) is of great interest for single-molecule-level detection applications. Lithographic plasmonic nanostructures are supposed to enable uniform enhancement and thus have attracted extensive interest in the past decade. In this work, we propose and demonstrate a lithographic three-dimensional (3D) donut-like gold nanoring array as a SERS substrate with an enhancement factor (EF) up to 3.84 × 10⁷. This 3D nanoring array could be directly fabricated using electron-beam-lithography-defined templates without any additional lift-off process and thus promises ultraclean metallic surfaces. Meanwhile, the 3D configuration allows multiple hot spots for improving SERS performance compared to planar counterparts with comparable plasmon resonance position. Systematic experiments and simulations were conducted to gain understanding of the origin of the improved SERS performance. The results imply that the 3D donut-like gold nanorings with multiple hot spots can serve as a promising configuration for SERS applications.