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The excitation of surface plasmons in metal nanostructures can generate greatly enhanced local electromagnetic fields, which contribute dominantly to the enhancement factors in surface-enhanced Raman scattering (SERS). Recently we demonstrated strong enhancement of Raman signal in a hybrid system consisting of cyanine dye J-aggregates and Ag nanoparticles attached to a spherical dielectric microcavity and explained by concerted action of the high-Q optical states and localized surface plasmons oscillations. In this work we report on the optical enhancement effects in a novel type of hybrid structures that combine noble metal nanowires with organic dye molecules (Pseudocyanine iodide (PIC)) in a J-aggregate state. Silver nanowires with diameters of 50-60 nm were synthesized by the reduction of silver nitrate in the presence of poly(vinyl pyrrolidone) in ethylene glycol. In order to trigger the formation of J-aggregates we took advantage of electrostatic interaction between anionic polyelectrolyte (PSS) and cationic dye molecules of PIC with an iodide counter-ion. Confocal photoluminescence (PL) and Raman imaging clearly demonstrate strong increase in PL intensity and the SERS respectively at the junction of crossed nanowires covered with a layer of J-aggregates. This location shows the most intense SERS spot caused by coupled transversal plasmon resonances of crossed wires. It was also found, that the enhancement of Raman scattering by nanowire crossbar weakly depends on the polarization of the exciting light, a small decreasing of Raman signal in 10-20% was observed in the case when the plane of polarization is parallel to one of the nanowires. In effect, crossed nanowires can be considered as plasmonic nano-cavities suitable for fabrication of arrays of hot spots for chemical and biological detection. |
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