Nanophotonic Tomography – Peering below plasmonic waves

The University Of Central Florida Board Of Trustees, Orlando FL

Investigators

Abstract

Surface plasmon polariton waves have become a key ingredient in applications that manipulate light at the nanoscale, i.e. in nanophotonic applications. When light hits a metal surface it causes electrons to oscillate, in some cases generating ripples or waves in the charge density at the metal surface. Such waves, known as surface plasmon polaritons (SPPs), allow for extreme light concentration and highly sensitive optical detection. While the existence of SPP waves is well known, it is extremely challenging to investigate their behavior below the metal surface. To address this challenge, this project will study sub-surface nanophotonic effects by measuring light emission from thin metallic layers placed at different depths below the surface. This layer-by-layer analysis of the optical response at the nanoscale is referred to as nanophotonic tomography. The systematic analysis of such thin-film light emission will be used for depth-resolved studies of SPP waves in nanophotonic systems that have practical applications, including photocatalysis and hot electron enhanced photovoltaics. In addition to bringing fundamental understanding of key nanophotonic phenomena, the research will be integrated in Nanophotonics course materials. Depth profiling of surface plasmon polaritons is a highly challenging proposition. The proposed work leverages recent insights in the generation and detection of gold photoluminescence (PL). Based on the observation of detectable Au PL from few-nm thick gold layers, it has become feasible to use embedded thin gold films as 2D probes of local field enhancement. Based on this realization, layer-by-layer gold PL analysis will be applied to geometries that are of great current importance to the fields of plasmonics and nanophotonics: (a) the “particle on mirror” geometry, where nanophotonic tomography will be used to map the depth over which hot electrons and holes contribute to Au photoluminescence, (b) the zero-mode waveguide (ZMW) with an embedded nanoparticle, in which layering of the surrounding ZMW enables depth-selective quantitative analysis of gap plasmon field amplitudes, (c) Metasurface-enhanced Raman scattering, where layered metallic metasurfaces will allow for a quantitative correlation of Raman scattering enhancement from 2D materials and Au PL, and (d) sub-surface few-nm Au films in Ag for the investigation of hot carrier redistribution by monitoring the excitation-energy dependence of modifications to the Au PL spectrum. The knowledge gained from the research is of great importance to applications in biosensing, photocatalysis, and hot-electron assisted photovoltaics. In addition, the proposed work will provide a clear and comprehensive body of work on using gold PL as a general probe of internal optical fields. The results are anticipated to be of great value to the general field of nanophotonics. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.