Figure 25.

(A) Characteristic SERS spectra at a radial-breathing mode (RBM) of ∼160 cm^–1. (B) Upper and lower SERS spectra are obtained via the E₁₁^M exciton (see Figure 1 of ref (244)) of a chiral vector (15, 6). Single-walled carbon nanotube (SWNT) with an RBM of ∼163 cm^–1 and the E₁₄ (E₄₁^S) exciton (see Figure 1 of ref (244)) of a chiral vector (13, 9) SWNT with an RBM of ∼161 cm^–1, respectively. (C) Selection-rule breakdown as indicated by the numerical calculation. Absorption cross-section with (solid lines, left-hand scale) and without (dotted lines, right-hand scale) a metallic nanogap, as given by the numerical calculation. Results indicated by the solid and dotted blue lines are reduced by a factor of 10. (D) Cross-sectional view of the calculated intensity of the EM field, including both the longitudinal and transverse components, under resonant excitation conditions of the E₁₄ (E₄₁^S) exciton (see Figure 1 of ref (244)). The calculated quadrupole polarization of the E₁₄ exciton (see Figure 1 of ref (244)) is indicated by black arrows. The grids show the cell size in the present numerical calculation. Reproduced with permission from ref (244). Copyright 2013 Nature Publishing Group.