Strategies to Utilize Hybrid Plasmons for Single-Molecule SERS and Directional Light Emission

There are two fundamental excitations of plasmons: localized surface plasmons (LSPs) and propagating surface plasmon polartions (SPPs). The LSPs in metallic nanoparticles can facilitate large magnitudes of optical fields confined to small volumes, and can be harnessed for nano-optical sensing. The SPPs in metal films or nanowires can used to transport optical information from one location to another over a distance of millimeter, and can be harnessed as sub optical waveguides. It would be extremely useful to couple LSPs with SPPs to concomitantly achieve sub-wavelength localization and propagation of light in a single nano-system. Motivated by this requirement, herein we discuss two novel strategies to create hybrids of LSPs with SPPs.

First strategy is to create SPP-assisted fluidic potential at an unstructured metal-fluid interface that can further trap plasmonic nanoparticles to create dynamic plasmonic hot-spots. Controlling assembly and movement of synthetically-prepared nanoparticles in a fluid is an important requirement in nano-science, and still remains a major challenge in the field. Although chemical methods have been successful in aggregating nanoparticles, most of them are irreversible processes and cannot be employed for spatial and temporal manipulation of nanostructures in a fluid. There is an imperative to develop alternative methods that can create reversible plasmonic hot-spots in a fluid. Motivated by this, we recently developed¹ plasmofluidic method, where plasmons on a metal film interact with a fluid, to create a trap that can reversibly assemble plasmonic nanoparticles and detect single-molecule SERS at metal-fluid interface.

Second strategy is to use single plasmonic-nanoparticle coupled to a single plasmonic nanowire. The specific region where the nanoparticles couple to nanowire is a plasmonic hot-spot. Such hot-spots can be remotely excited using nanowire SPPs. One of the novel aspects that we intend to discuss is how such hot-spots can be used as directional out-couplers of photons at sub-wavelength scale, which has direct implication in remotely excited plasmonic nano-antennas and couplers.

(1) Patra, P. P.; Chikkaraddy, R.; Tripathi, R. P. N.; Dasgupta, A.; Kumar, G. V. P. Nature Communications 2014, 5, 4357.

pavan@iiserpune.ac.in