Figure 18.

(a) Raman spectrum of R6G (10⁻⁴ M solution.) drop cast on glass and (b–d) Time-dependence of the SERS spectra of R6G (10⁻⁴ M solution) A drop of 10⁻⁴ M water solution of R6G was cast on the glass and dried in air before measurements; the Raman spectra were acquired using an HR800 micro-Raman spectrometer (Horiba, Jobin-Yvon, Longjumeau, France), using the 457.9 nm line of an Ar⁺ ion laser, setting the laser power at 1 mW. The integration times were varied from a few seconds up to 110 s to maximize the signal to noise ratio.