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(a) Experimental setup investigating the emisson pattern of SERS. (b) A detailed view of the sample, which is a sandwiched structure composing of isolated silver nanosphere (60 nm-diameter) immobilized on a thin silver film (55 nm-thickness), with 4-mba molecules sandwiched between them. (c) SERS spectrum of 4-mba molecules emitted from single nanosphere-film junction. Integration time is 5 s. In the text, we are referring to all the Stoke's scattering as marked since all the Raman peaks change in the same proportion with the change of excitation intensity and integration time.
Transmission features of a three-layer system modelling the proposed excitation configuration of SPPs. (a) Schematic view of the system for the caculatation, which includes a 55 nm-thickness silver film sandwiched by semi-infinite air and glass substrate. (b), (c) Calculated transmittance in case of glass-side incidence and air-side incidence, respectively. The sharp transmission peak in (b) demonstrates the excitation of SPPs when incident light illuminates from the glass substrate, while that in (c) illustrates the surface plasmon coupled emission of light from air into the glass substrate, both at SPP excitation angles. (d) Reflected laser beam profile obtained at the back fourier plane of the objective lens (NA = 1.49), with a sharp dark ring representing the excitation of SPPs from all azimuthal directions. (e) Emission pattern of SERS at SPP excitation angles, forming an SPCE ring.
Intensity comparison between the Raman signals of R6G molecules collected at the glass side through SPCE and collected directly at the air side (conventional). Integration time is 1s. Collection efficiency is shown to be enhanced through SPCE.
Raman image of individual nanosphere captured at the back image plane of the objective lens (NA = 1.49) through SPCE, which is approximately the pattern of point spread function of an SPCE microscopy because of the small excitation area of SERS within the nanosphere-film junction. (a) Experimental, (b) calculated, and (c) their cross-section comparison across the center. The experimental result accords well with the theoretical one.
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