Daniel Prezgot

Plasmon-enhanced refractometry using silver nanowire coatings on tilted fibre Bragg gratings.

A novel technique for increasing the sensitivity of tilted fibre Bragg grating (TFBG) based refractometers is presented. The TFBG sensor was coated with chemically synthesized silver nanowires ~100 nm in diameter and several micrometres in length. A 3.5-fold increase in sensor sensitivity was obtained relative to the uncoated TFBG sensor. This increase is associated with the excitation of surface plasmons by orthogonally polarized fibre cladding modes at wavelengths near 1.5 μm. Refractometric information is extracted from the sensor via the strong polarization dependence of the grating resonances using a Jones matrix analysis of the transmission spectrum of the fibre.

Unusually Sharp Localized Surface Plasmon Resonance in Supported Silver Nanocrystals with a Thin Dielectric Coating

An unusually sharp localized surface plasmon resonance (sLSPR) is observed for a monolayer of glass-supported silver nanocubes coated with a thin, 5-20 nm, Al2O3 film. The resonance becomes significantly narrower and stronger while losing optical anisotropy and sensitivity to the surroundings with increasing overlayer thickness. Surface-enhanced Raman scattering excitation profiles indicate an additional enhancement to the electric field brought in by the sLSPR. The resonance is thought to originate from a Fano-like constructive interference between the quadrupolar and dipolar LSPR modes in supported silver nanocubes leading to enhanced light extinction. This phenomenon is of significance for plasmon-induced charge-transfer processes in photovoltaics and catalysis.

Optical properties of strongly interacting supported silver nanocube monolayers

Plasmonic properties of monolayers of strongly interacting silver nanocubes (AgNC) with controlled interparticle spacing are investigated. Uniform monolayers with controlled particle densities are made using the Langmuir-Blodgett technique with passive phospholipid spacers, such as dioleoyl phosphatidylcholine (DOPC). Both extinction intensity and wavelength of dipole-dipole coupling modes are tuned via particle spacing. The refractive indices of the substrates are used to tune dipolar and interparticle coupling modes via deposition onto thin films of silicon (0 - 25nm). By varying silicon film thickness it is possible to shift and control peak widths and position for both the dipole and interparticle dipole-dipole coupling modes. Control of plasmon shifts and interparticle spacing is applied towards the optimization of SERS substrates. SERS substrates using a Rhodamine B label are tuned at different excitation wavelengths which are in resonance with either the plasmon dipole, fluorescent dye, or interparticle coupling mode. Substrates display reproducible enhancement across multiple sites. This work presents methodology to design and optimize uniform silver nanocube SERS substrates through tuning of plasmon shifts and particle spacing.

Substrate-induced effects on the plasmonic properties of strongly coupled silver nanocubes

The behaviour of the plasmonic modes of supported strongly coupled silver nanocubes is studied. Silver nanocube monolayers with controlled particle density were fabricated via the Langmuir-Blodgett technique and deposited on substrates with varying refractive indices. Substrates include glass, thin films of silicon, and titanium oxide on glass. The dipolar and bonded dipolar modes are red shifted with increasing refractive index of the substrate. Surface-enhanced Raman spectroscopy (SERS) is used as a tool to probe the electric field enhancements of the silver nanocube monolayers. SERS enhancement of silver nanocube monolayers is found to be highly substrate dependant, typically decreasing with increasing refractive index of the underlying substrate. This work aims to find the source of this enhancement decrease, and distinguishes between effects related electromagnetic enhancement and effects caused by the optics of the Raman spectroscopy system itself.

Plasmonic properties of weakly interacting silver nanocubes on high refractive index substrates

In the present work we investigated the properties and behavior of plasmonic modes of silver nanocube monolayers with respect to reflection and transmission of visible radiation. Uniform monolayers of low particle densities were created using the Langmuir-Blodgett technique using the phospholipid 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) as a passive spacer. Dipole-dipole coupling modes were avoided by depositing at low pressures to ensure sufficient spacing between the nanocubes. The refractive index sensitivities of plasmonic modes for monolayers on glass, silicon thin films, and bulk silicon wafers were measured using varying solutions of water and ethylene glycol. By varying the refractive index of the substrates it is possible to investigate the relative contribution of plasmonic modes with respect to absorption of the incident signal.

Silver Nanowire Coated Tilted Fibre Bragg Gratings

A 3.5-fold increase in sensitivity of Tilted Fibre Bragg grating based refractometers is reported. The sensor was coated with silver nanowires which resulted in strong polarization dependence of the grating resonances.