Fig. 1. Specific experimental scheme of nickel foam substrate coupled gold nanostuctures

Fig. 2. Nickel foam substrate coupled gold nanostructures. (a) Optical photographs of substrates coupled gold nanostructures with replacement time of 5, 10, 15, 20, 25, 30, and 35 min, respectively; (b) SEM images of pure nickel foam substrate at 100 times magnification; (c) SEM images of pure nickel foam substrate at 5000 times magnification; (d)--(k) SEM images of substrates coupled gold nanostructures with replacement time of 5, 10, 15, 20, 25, 30, and 35 min, respectively

Fig. 3. Simulation results of electromagnetic field. (a) Simulation structure; (b) gold nanoparticles simulation model; (c)--(f) electric field distribution of gold nanoparticles with heights of 100,150,175,200 nm in Y-Z plane

Fig. 4. Performance curve of R6G molecule. (a) Raman spectra of R6G molecules with a concentration of 10^-6 mol·L^-1 at replacement time of 5,10,15,20,25,30,35 min; (b) enhancement factors of R6G molecules with concentration of 10^-6 mol·L^-1 at different displacement times at 613 cm^-1 wave number

Fig. 5. Results of Raman experiments on uniformity of substrate. (a) Sample and square scanning area; (b) Raman mapping scanning spectra; (c) RSD value at 613 cm^-1; (d) RSD value at 1364 cm^-1

Fig. 6. Raman spectra of R6G molecules at different concentrations