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Plasmonic nanowires are key building-blocks for plasmonic based devices, such as nano-sources and nano-sensors. They can take advantage of the propagative nature of surface plasmon polaritons (SPP) in a guided way, and the strong field enhancement at the nanowire tips.
Here, the proof-of-concept of a SPP-mediated remote Raman effect with a coaxial nanowire is reported [1]. The remote Raman spectroscopy consists in probing a species at a distanced place from the excitation. The metallic nanowire geometry promotes a guiding of the surface plasmon polaritons along several micrometers, while the required momentum matching for exciting SPP is allowed by the discontinuity at the nanowire tip. The proposed systems are cylindrical coaxial nanowires consisting of a gold core to propagate SPP and a Raman-emitting shell of poly(3,4-ethylene-dioxythiophene) (PEDOT) grown only at one tip of the gold nanowire.
A second challenge has been tackled, dealing with the weakness of the Raman signal to be detected. It was proposed to enlarge the nanowire tips in order to enhance the in-coupling of an excitation optical signal with the nanowire, and the out-coupling of the plasmon-mediated signal at a remote location. It has been achieved by transforming the gold nanowire tips with dry laser heating treatments to obtain dumbbell-like nanowires. The plasmonic properties of these original nanowires have been determined by an EELS-STEM study and interpreted by finite-element modeling. The benefits of these enlarged tips on the optical signal has been investigated by a Rayleigh backscattering study.
[1] D. Funes-Hernando, M. Peláez-Fernández, D. Winterauer, J.-Y. Mevellec, R. Arenal, T. Batten, B. Humbert and J.L. Duvail Nanoscale (2018) 10, 6437 – 6444
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