Fig. 1. Schematic of the substrate for FDTD simulation. (a) Grating; (b) grating/nanoparticles; (c) unit cross-section for FDTD simulation

Fig. 2. Simulated reflectance spectra. (a) Au gratings with varied periodicities; (b) Au nanoparticles array with diameter of 25 nm, Au gratings with 580-nm periodicity, corresponding Au grating/ nanosparticles hybrid structure

Fig. 3. Simulated electric field distribution around particles. (a) On the surface of grating groove; (b) on the surface of Si wafer; (c) on the surface of left grating ridge; (d) on the surface of right grating ridge

Fig. 4. Schematic of Au grating preparation

Fig. 5. Au nanoparticles. (a) TEM image; (b) diameter distribution histogram

Fig. 6. Au grating. (a) AFM false-color height image; (b) surface profile

Fig. 7. SEM images. (a) Au grating under low magnification, inset is photograph of the grating taken at different angles; (b) Au grating under high magnification; (c) Au grating/nanoparticles hybrid structure

Fig. 8. Reflectance spectra of Au nanoparticles on Si wafer, Au grating, and Au grating/nanoparticles hybrid structure

Fig. 9. SERS spectra of R6G solution with different concentrations collected on different substrates. (a) Au grating/nanoparticles hybrid substrate; (b) common substrate formed by Au nanoparticles distribution on silicon wafers

Fig. 10. SERS spectra of R6G with different concentrations on Si wafer, Au nanoparticles substrate, and Au grating/nanoparticles hybrid substrate

Fig. 11. SERS mapping on Au grating/nanoparticles hybrid substrate. (a) mapping image by monitoring the intensity of the Raman peak at 614 cm^-1; (b) RSD comparsion of SERS intensity for peak at 614 cm^-1, 1365 cm^-1,^{and 1512 cm-1}