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Plasmonic CrystalsTitle: Chemically Enhanced Photonic-Plasmonic Crystals for Explosive Vapor Detection (Photonic Sniffer) – US Army

Participants: Alyssa Pasquale (PhD ’12) and Professor Luca Dal Negro

Funding: Army Research Lab

Background: Plasmonic devices used for Surface Enhanced Raman Scattering (SERS) and Localized Surface Plasmon Resonance (LSPR) sensors have been shown to be a very promising technology. However, much of the current technology either relies on random particle aggregates to obtain high field enhancements at the expense of full reproducibility and engineering control.

Description: State-of-the-art SERS sensors require strong electric fields that are polarization insensitive, broadband in frequency and whose locations can be precisely controlled. LSPR sensors require high sensitivity to the local environment to detect small changes in background conditions as well as narrow scattering lineshapes.

In this project, particle morphology and basis are being explored to produce novel sensors that can be used to detect fluids, explosives, or other materials. One approach is a “nano-plasmonic necklace” which consists of loops of gold particles fabricated using electron-beam lithography patterning and electron-beam deposition of films. These necklaces lead to polarization insensitive, strongly enhanced fields on inter-particle hot-spots which can be used in SERS and dark field scattering applications. The circular shape of the necklace provides photonic mode trapping leading to enhanced fields at resonant conditions, and the precise location(s) of the hot-spots is always known.

Results: By further changing the basis conditions of these nano-plasmonic necklaces, we hope to further improve their characteristics. Full optimization makes use of 3-dimensional finite-difference time-domain (FDTD) simulations. Results are obtained using dark-field scattering spectroscopy and Surface Enhanced Raman Scattering (SERS) measurements.

Website: www.bu.edu/nano

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