The scattering properties of a plasmonic array can be reinforced by placing the array near a planar reflector. Finite-
Difference-Time-Domain (FDTD) simulations have been used to demonstrate the key design challenge of modulating
the electric field that drives the plasmonic scattering, by varying the distance of a single Ag nanodisc from a Ag
reflector. We show that the thickness of the dielectric separation layer plays a critical role in determining the spectral
characteristics and the intensity of the power scattered by a Ag nanodisc near a reflector. A possible application of the
designed structure as a plasmonic light-trap for thin Si solar cells is also experimentally demonstrated. Electron-beam
lithography has been used to fabricate a pseudo-random array of 150nm plasmonic Ag nanodiscs on SiO2 on a Ag reflector substrate. The plasmonic reflector shows a high diffuse reflectance of ~54% in the near-infrared, near-bandgap
600-900nm wavelength region for thin Si solar cells, with a low broadband absorption loss of ~18%. Wavelength-angle
resolved scattering measurements indicate an angular scattering range between 20° to 80° with maximum intensity of the
scattered power in the 20° to 60° angular range.
In this paper we first present a new fabrication process of downscaled graphene nanodevices based on direct milling of
graphene using an atomic-size helium ion beam. We address the issue of contamination caused by the electron-beam
lithography process to pattern the contact metals prior to the ultrafine milling process in the helium ion microscope
(HIM). We then present our recent experimental study of the effects of the helium ion exposure on the carrier transport
properties. By varying the time of helium ion bombardment onto a bilayer graphene nanoribbon transistor, the change in
the transfer characteristics is investigated along with underlying carrier scattering mechanisms. Finally we study the
effects of various single defects introduced into extremely-scaled armchair graphene nanoribbons on the carrier transport
properties using ab initio simulation.
We have experimentally and theoretically demonstrated plasmonic couplers based on metal nanoparticles film
(metal islands) deposited upon the optical dielectric waveguide. These nanoparticles forward scatter radiation into
the optical waveguide that would otherwise be reflected and transmitted. Design, fabrication and optimisation of the
plasmonic silver islands and tantalum pentoxide waveguide are reported. Broadband characteristics of light
transmission showing plasmons excitation have been measured and in good agreement with simulated results from
400 nm to 800 nm. Coupling spectrum up to 15% is measured for the plasmonic coupler and in good agreement with
the simulated results.
The eyes and wings of some species of moth are covered in arrays of subwavelength pillars that have been tuned
over millions of years of evolution to reflect as little sunlight as possible. We are investigating ways of exploiting
this to reduce reflection from the surfaces of silicon solar cells. Here, we report on the experimental realization
of biomimetic antireflective moth-eye arrays in silicon using a technique based on nanoimprint lithography and
dry etching. Areas of 1cm x 1cm have been patterned and analysis of reflectance measurements predicts a loss
in the performance of a solar cell of only 6.5% compared to an ideal antireflective coating. This compares well
with an optimized single layer Si3N4 antireflective coating, for which an 8% loss is predicted.
The challenge when applying photonics to photovoltaics is the need to provide broadband, multiple-angle solutions to
problems and both plasmonics and biomimetics offer broadband approaches to reducing reflection and enhancing lighttrapping.
Over millions of years nature has optimised nanostructures to create black, transparent, white and mirrored
surfaces, the antireflective "moth-eye" structures are perhaps the best known of these biophotonic materials. In this paper
we use simulated and experimental studies to illustrate how careful optimisation of nanoscale features is required to
ensure the optimum match between reflectivity, spectral bandwidth and device quantum efficiencies. In the case of lighttrapping
by plasmonic scattering there is more room for design and specific spectral regions can be targeted by precise
control of the size, shape and density of particular metal nanoparticles. We describe how the best opportunity for
plasmonics within inorganic solar cells appears to be enhanced light-trapping of near-band edge photons.
Using electron beam lithographic techniques we have manufactured left and right-handed forms of an artificial medium consisting of high densities of microscopic planar chiral metallic objects distributed regularly in a plane. In this artificial medium we have for the first time observed optical manifestations of planar chirality in the form of handedness-sensitive rotation of the polarization state and elliptization of visible light diffracted from the structure. Applications of such media in functional materials are discussed.