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Title: Photonic devices based on periodic arrays of carbon nanotubes and silicon nanopillars
Author: Butt, Haider
ISNI:       0000 0004 2713 4236
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2012
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This document presents the modelling and characterization of novel photonic devices based on periodic arrays of multiwalled carbon nanotubes. Multiwalled carbon nanotubes are mostly metallic in nature and interesting plasmonic effects are observed when nanotubes are grown close together, with spacing of about 400 nm. The effective electronic mass on the nanotubes changes, due to mutual coupling between them and they start displaying dielectric properties which are inherently different from the their own, forming metamaterials. We present a plasmonic high pass filtering application of carbon nanotube based metamaterials. Some promising modelling and experimental results are demonstrated showing a strong cut-off filtering effect at the plasma frequency displayed by the periodic arrays of multiwalled carbon nanotubes. The artificial negative dielectric constant displayed by the nanotube arrays was also successfully utilised for producing micron-scaled applications like optical waveguides and negative lenses for overcoming the diffraction limit. The fabrication of these optical devices using the arrays of silicon nanopillars was also considered. These arrays when fabricated at nano-scaled dimensions (of about 400 nm) present a greater degree of periodicity and require a simpler fabrication process compared to carbon nanotubes. We report the detailed computational analysis on silicon nanopillars based photonic crystals, waveguides and metamaterials which operate well within in the optical regime. However, due to the fabrication limitations, the fabricated Si nanopillars presented an inverted cone shape profile along their lengths. These inverted nanocone structures were successfully utilised for enhancing reflection from Si surfaces for applications in photovoltaic devices. Lastly we present a novel application of carbon nanotube arrays for producing micron-scale Fresnel lens arrays. Forests of carbon nanotubes were utilised as absorbing media on top of a bare silicon substrate. Optical diffraction of light across the nanotube forests produced strong focusing of light, at focal lengths of order 125 microns. Numerical simulations were in excellent agreement with the measured results.
Supervisor: Wilkinson, Timothy ; Amaratunga, Gehan Sponsor: Nokia-Cambridge Strategic Partnership in Nanoscience and Nanotechnology (Energy Programme) ; Cambridge Commonwealth Trust (CCT) ; Hughes Hall College
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Metamaterials ; Photonic crystals ; Fresnel lenses ; Periodic arrays ; Carbon nanotubes ; Silicon nanopillars