Figure 4. SERS spectra of R6G molecules on different substrates.

(a) after immersion in 10⁻⁶ mol L⁻¹ R6G solution for 30 min (Integral time: 1 s). Curves i: Au spherical nanoparticles array, Curve ii: a normal Au film (about 80 nm in thickness) prepared by sputtering deposition. (b) Raman spectra of R6G molecules on Au nanoparticle array after immersion in 10⁻¹¹ mol L⁻¹ R6G solution. Note: the laser powers operated in (a) and (b) are 1 and 5 mW respectively.