Fig. 1. Scattering field characteristics of Ag dimer with different gaps using the computation by FDTD. (a) Scattering spectra of dimer; (b) schematic of silver nanoparticle dimer; (c) electron distribution of bonding dipolar-dipolar plasmon

Fig. 2. Scattering spectra of Ag dimer with different polarization directions (0°, 30°, 60°, 90°)

Fig. 3. Electric field distribution of Ag dimer with different excitation wavelengths and polarizations. (a) Wavelength of 370 nm and a horizonal direction; (b) wavelength of 440 nm and a horizonal direction; (c) wavelength of 370 nm and a vertical direction; (d) wavelength of 440 nm and a vertical direction

Fig. 4. Change of electric field intensity of Ag dimer in different polarization directions corresponding to excitation wavelength at 370 nm and 440 nm. (a) Center of dimer A; (b) edge of dimer B; (c) schematic of Ag dimer

Fig. 5. Electric field distribution of silver dimers with different diameters and gaps. Gap is 2 nm, left and right particle diameters are (a) 40 nm and 40 nm, (b) 30 nm and 30 nm, (c) 30 nm and 50 nm, (d) 50 nm and 50 nm; gap is 3 nm, left and right particle diameters are (e) 30 nm and 30 nm, (f) 40 nm and 40 nm, (g) 50 nm and 50 nm, (h) 30 nm and 50 nm; gap is 4 nm, (i) left and right particle diameters are 40 nm and 40 nm, respectively

Fig. 6. Electric field intensity of the central position of different types of silver dimer with different gaps and sizes (corresponding to Fig 5) with respect to polarization direction. Gap is 2 nm, left and right particle diameters are (a) 40 nm and 40 nm, (b) 30 nm and 30 nm, (c) 30 nm and 50 nm, (d) 50 nm and 50 nm; gap is 3 nm, left and right particle diameters are (e) 30 nm and 30 nm, (f) 40 nm and 40 nm, (g) 50 nm and 50 nm, (h) 30 nm and 50 nm; gap is 4 nm, (i) left and right particle diameters

Fig. 7. SERS signal localization of Ag dimer with respect to wavelength

Fig. 8. SERS signal localization of Ag dimer with different gaps and sizes with respect to polarization direction. Gap is 2 nm, left and right particle diameters are (a) 40 nm and 40 nm, (b) 30 nm and 30 nm, (c) 30 nm and 50 nm, (d) 50 nm and 50 nm; gap is 3 nm, left and right particle diameters are (e) 30 nm and 30 nm, (f) 40 nm and 40 nm, (g) 50 nm and 50 nm, (h) 30 nm and 50 nm; gap is 4 nm, (i) left and right particle diameters are 40 nm and 40 nm, respectively

Fig. 9. Polarization regulation of different Ag dimer hot spots. (a) Two; (b) three; (c) four

Fig. 10. Variation rule of SERS signals in hot spots with different number of Ag dimer with polarization direction. (a) Two; (b) three; (c) four

Fig. 11. Simulation of super-resolution surface-enhanced Raman scattering imaging based on silver dimer