Adam Bottomley

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.

Improving photovoltaic devices using silver nanocubes

We present a design of implementing plasmonic nanoparticles made from silver onto the surface of amorphous silicon based solar cells. When adding these silver nanoparticles we expect to see enhancements to the solar cells due to the plasmonic effects induced by the metal nanoparticles. The nanoparticles are used as subwavelength scattering elements to couple and trap light within the cell. In addition, the excited surface plasmon-polaritons promote a strong localized field enhancement which increases the cells ability to absorb light. Our choice of geometry of the nanoparticle is cubic rather than the traditional spherical geometry. We expect to see the cell perform better with the cubic shape due to the larger surface area it spans. We investigate the effects of these particles on to the performance of the solar cells, as well as introduce an intrinsic layer between the active p and n region creating a p-i-n solar cell configuration. We report the use of an FDTD simulator to characterize the optical performance of the solar cell. Both cubical and spherical nanoparticles made from silver were studied. Our simulations predict an overall increase of 67% (from 7.5% to 12.5) based on the p-i-n configuration with inclusion of the plasmonic particles onto the surface of the cells. Experimentally we verified the results by first fabricating a crystalline silicon-based solar cell with a p-n configuration and then placing the silver nanocubes onto the surface of the cell. An overall increase of about 28% was experimentally demonstrated (from 3.97% to 5.081%). We anticipate further increases with the p-i-n configuration.

Design of plasmonic enhanced silicon-based solar cells

We report a novel plasmonic solar cell design implemented on an amorphous silicon platform. The enhancement of the scattering and trapping of the light is achieved by embedding nano-metallic cubic particles within the cell’s junction. Amorphous silicon cell with a thickness of 1200nm is used. The spectral absorption of the silicon cell is limited to wavelengths larger than 1.1 u. Our proposed solar cell has a p-i-n configuration, with the amorphous silicon as the photo-active layer. Silver cubic nanoparticles are embedded at different locations within the photoactive layers of the solar cell. With the use of an FDTD simulator, we are able to characterize the optical performance of the solar cell. Our results show that the plasmonic properties of the cubic nanoparticles are more attractive for sensing applications compared to the traditional spherical configuration. The geometry of the cubic nanoparticles enables control over plasmon resonances both in the resonant wavelength and the degree of field enhancement. This is done by improving the refractive-index sensitivity on a thin silicon film, as well as increasing the scattering and trapping of light. Our simulations predict that the silver metallic nanoparticles will enhance the solar cell efficiency, by optimizing the plasmonic properties of the silver nanocube monolayer. We have achieved a 67% increase (from 7.5% to 12.5%) in the cell’s efficiency by adding plasmonics to traditional amorphous p-i-n solar cell.

Plasmonic properties of silver nanocube monolayers deposited on thin metal films

The present work investigates the plasmonic properties and behaviour of silver nanocube monolayers deposited on thin gold films. Monolayers were deposited via the Langmuir-Blodgett method using a phospholipid as a passive spacer. Interparticle coupling was minimized by depositing at low surface pressures. The interaction of the nanocube monolayers with the gold films was mediated by utilizing polyelectrolyte layering to generate a passive spacer to control the distance between the cubes and substrate. Silver nanocubes were characterized by UV-Visible spectroscopy and transmission electron microscopy, and the monolayers were characterized by UV-Vis, and atomic force microscopy.

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.