Figure 3. SERS effect for SiO_x films annealed at 1100 °C measured using a 50× objective and 488-nm laser with an exposure of 600 s.

(a) Raman signal at 517 cm⁻¹ of as a function of the thickness of uncoated SiO_x films (no Ag). Different symbols present the results of five experimental days. (b) SERS enhancement of the Raman signal at 517 cm⁻¹ as a function of the SiO_x film thickness for different thicknesses of Ag overlayers. (c) SERS enhancement of the Raman signal at 517 cm⁻¹ as a function of the Ag overlayer thickness for 40- and 80-nm-thick SiO_x films. The SERS enhancement is defined as the ratio of the Raman intensities with and without an Ag layer.