Fig. 1. Cross section of single-stage and hierarchical nanoporous structure models

Fig. 2. FDTD simulations of local electromagnetic field distribution in NPG and h-NPG with different incidence wavelength

Fig. 3. FDTD simulations of local electromagnetic field distribution in NPC and h-NPC with different incidence wavelength

Fig. 4. SEM images of NPG and h-NPG formed by the second different dealloying time

Fig. 5. SERS spectra of CV and R6G on NPG and h-NPG substrates， and SERS spectra corresponding to different concentrations of CV and dose-intensity curve in logarithmic coordinates

Fig. 6. SERS and Raman spectra of CV and the intensities of SERS peaks for 20 spots on h-NPG substrate

Fig. 7. SEM of NPC and TEM images of h-NPC prepared by dealloying at different times

Fig. 8. SERS spectra of CV and R6G on NPC and h-NPC substrates， and SERS spectra corresponding to different concentrations of CV and dose-intensity curve in logarithmic coordinates

Fig. 9. SERS and Raman spectra of CV and the intensities of SERS peaks for 20 spots on h-NPC substrate