Laser Microsphere Lens Array Fabrication of Micro/Nanostructures with Tunable Enhanced SERS Behavior in Dipole Superposition Plasmon Mode

Silicon-based surface-enhanced Raman scattering (SERS) substrates with high sensitivity and uniformity were obtained by a laser surface processing method utilizing microsphere sphere lens arrays followed by chemical etching and silver (Ag) deposition. High SERS performance of these substrates was demonstrated by their enhancement factor of up to 8.2×10⁷ for rhodamine 6G (R6G) as well as their ability to detect 1 nM of R6G and 10 ppm of fenthion by a rapid drop-evaporation detection method. A dipole superposition plasmon mode due to a novel Ag microflower structures formed on the top of microvolcano microstructures fabricated before Ag deposition was found to be responsible for the SERS enhancement. The height of the Ag microflowers was not determined by Ag deposition thickness but by the height of the microvolcanoes, which could be easily tuned by laser power, microsphere size, and alkali etching time; tunable SERS performance was also achieved. The developed approach provides a cost-effective way to prepare large-area 3-D solid SERS substrates to adapt to multiple species of probe molecules and different excitation wavelength ranges with high controllability and reproducibility.