Fig. 1. FDTD simulation models. (a) Simulation model of AgNPs/CNTs composite structure; (b) simulation model of silver nanoparticles structure

Fig. 2. Electric field distributions of AgNPs/CNTs composite and silver nanoparticles structures. (a) AgNPs/CNTs composite structure; (b) silver nanoparticles structure

Fig. 3. Self-calibration theoretical model and implementation of AgNPs/CNTs composite structure

Fig. 4. Preparation process of AgNPs/CNTs composite structure (SERS substrate)

Fig. 5. SEM image of AgNPs/CNTs composite structure and particle diameter distribution of Ag nanoparticles. (a) SEM image;

Fig. 6. Raman spectra of different concentrations of R6G on AgNPs/CNTs

Fig. 7. Normalized k-value and Raman intensity versus R6G molecular concentration at characteristic peaks of R6G molecule. (a) Normalized k-value and Raman intensity versus R6G molecular concentration at the characteristic peak of 613 cm^-1; (b) normalized k-value and Raman intensity versus R6G molecular concentration at the characteristic peak of 773 cm^-1

Fig. 8. Raman spectra of different concentrations of MG on carbon nanotube composite structures

Fig. 9. Normalized k-value and Raman intensity versus MG molecular concentration at characteristic peaks of MG molecule. (a) Normalized k-value and Raman intensity versus MG molecular concentration at the characteristic peak of 806 cm^-1; (b) normalized k-value and Raman intensity versus MG molecular concentration at the characteristic peak of 915 cm^-1