Fig. 1. Schematic of simulation structure

Fig. 2. Electric field intensity and absorption spectra obtained by FDTD simulation at 633 nm incident light. (a)(d) 15 nm thick Ag film; (b)(e) Ag film on Grating 1; (c)(f) Ag film on Grating 2

Fig. 3. Electric field intensity and absorptivity of different Ag films at 633 nm incidence light

Fig. 4. XRD patterns of Ag films with different structures

Fig. 5. Optical images of different samples

Fig. 6. Experimental results. (a) SERS spectra of MB on different samples; (b) SERS spectra of MB molecules collected at 10 random sites on Grating 1 sample; RSD values of characteristic peaks at (c) 1623 cm^-1 and (d) 1394 cm^-1