The SERS enhancement ratio R of (a) radial and (b) tangential molecules near a silver sphere of the radius a = 5 nm with surface charges: q 1 = 5 × 10−16 C, q 2 = 8.33 × 10−16 C, q 3 = 1.67 × 10−15 C, and q 4 = 2.5 × 10−15 C. The distance between the molecule and the sphere is fixed at d = 5 nm.
(a) The distance dependence of the SERS enhancement ratio R for radial molecule near a silver sphere of radius a = 5 nm with the surface charges: q a = 5 × 10−16 C and q b = 10−15 C. The solid and dashed curves represent the results with and without the image-field effects, respectively. The frequency for each curve is chosen to be at the respective resonance. (b) The ratio R for the charged sphere with surface charges q a and q b to that for the uncharged sphere. The image-field effects are included.
(a) The two strongest modes of the Raman spectrum of a free pyridine molecule at an incident wavelength of 357 nm as obtained in Ref. 4 . (b) SERS spectrum of pyridine at a separation of 1 nm from a neutral (q = 0) and charged (q = 2.78 × 10−17 C and q = 5.56 × 10−17 C) silver spheres of radius 5 nm at an incident wavelength 357 nm.
The enhancement ratio of the 4th-power electric field, |E/E 0|4, at the position of the molecule near a neutral sphere of radius (a) a = 5 nm and (b) a = 10 nm at a distance d = 5 nm. The results are obtained from the GN model and Mie theory as indicated in the figure.
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