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This thesis presents a detailed study of chip based silicon photonic waveguide technologies for chemical sensing applications. The project specifically focuses on the use of strip and slot waveguide based micro-ring resonators (MRRs) integrated with graphene and graphene oxide (GO) as potential functional sensor coatings. The primary objective is to understand the effect of graphene/GO on the optical properties of such a device, to assess performance in bio-/chemical sensing applications and to identify ways in which such a device may be optimised. A detailed analysis of how the MRR cavity optical extinction ratio (ER) varies with the interaction length of surface integrated graphene reveals, for the first time using this technique, the in-plane graphene linear absorption coefficient, αgTE = 0.11 ± 0.01dBμm⁻¹. A model of the MRR cavity optical losses for different graphene lengths and heights (above the waveguide surface) provides a predictive capability for the design rules of optimised performance in sensing and photo-detector based applications. The graphene integrated MRRs were also characterized by a Raman mapping technique from which careful analysis of the graphene G and 2D scattering peak frequencies and relative intensities revealed that the graphene is electrically intrinsic where it is suspended over the MRR yet moderately hole-doped where it sits on top of the waveguide structure. This 'pinning' of the graphene Fermi level at the graphene-silicon/SiO2 interface is the result of 'trapped' ad-charges, the concentration of which may be increased at dangling bond sites after relatively aggressive (O2 plasma) cleaning of the silicon/SiO2 surface prior to graphene transfer. Quantifying this substrate doping effect is critically important when attempting to determine graphene's optical properties and should be taken into account when designing graphene-silicon hetero-structures for opto-electronic devices. The large absorption coefficient determined for the graphene integrated MRR devices means that cavity losses are far too high for practical realisation of refractive index based sensing. However, an alternative approach using GO as the functional layer for improved MRR based refractive index sensors remains a possibility on account of the much lower transmission loss. GO also has distinct advantages over graphene; ease of integration, a high density of surface functional groups and micro-porosity. Transmission spectral analyses of both bare (uncoated) MRRs and those coated with different GO concentrations revealed the in-plane linear absorption coefficient for the GO film to be αGOTE = 0.027±0.02dBμm⁻¹, which is much lower than that for graphene. Construction of a gas cell and integrated 'bubbler' arrangement for delivering variable vapour concentrations to the graphene/GO integrated MRR devices under test is presented. Both bare and GO coated MRRs were exposed to vapours from a series of typical organic solvents; ethanol, pentene and acetone delivered by a carrier gas (N2). Dynamic optical tracking of the MRR cavity resonance wavelength during vapour exposure, at different flow rates (vapour concentrations) reveals the sensitivity of the device(s) to small changes in refractive index. The dynamic response of the GO coated MRRs to the vapours were up to three times faster than the uncoated MRR with similar improvements in sensitivity and limit of detection, largely attributable to the porous nature and molecular binding affinity of the GO. Critically, these experiments reveal that the detection sensitivity and response of the GO is solvent dependent, which may mean that it is capable of providing a degree of selectivity, which is normally difficult to achieve in refractive index based gas sensing.

This work concerns the development of π-conjugated materials for optoelectronic applications, with emphasis on organoboron- and organoplatinum-containing compounds. The preparation of a nonconjugated two-chromophore emissive material is described, containing both organoplatinum and organoboron units. This material exhibits simultaneous fluorescent and phosphorescent emission at ambient temperature. Both emission colours are switchable in the presence of fluoride, giving a dual-emissive compound with multiple observable luminescent colours. The preparation of a nonconjugated donor-acceptor triarylborane containing both Lewis acidic and basic receptor sites is also described. This highly fluorescent compound is reversibly switchable between three emissive states upon addition of acid or fluoride. Furthermore, platinum(II)-acetylacetonates with nonconjugated antenna chromophores were prepared, and their luminescent properties were investigated. A series of directly conjugated platinum(II)-acetylacetonates have been synthesized incorporating a triarylboron group. The presence of boron was found to enhance the electron-transporting capabilities, film-forming properties, and phosphorescent quantum yields of these complexes. Highly efficient OLEDs were prepared incorporating these materials as dopants, including the first example of a Pt(II)-based OLED with an external quantum efficiency >20%. Triarylboron-containing Pt(II) complexes of N-heterocyclic carbenes were also prepared. Using this design, blue to blue-green phosphorescence was achieved with high quantum yield, and their use in OLEDs was demonstrated. A new high-yield synthetic route has been developed to cyclometalated Pt(II)-β-diketonates, requiring stoichiometric reagents and short reaction times at ambient temperature. This methodology has broad substrate scope across a variety of N^C-chelate ligands, as well as P^C-chelate phosphines and C^C-chelate carbenes as well. The preparation of N-heterocyclic carbazole-based host materials for OLEDs is also described. These materials exhibit improved electron-transporting capabilities relative to the more commonly used host 4,4’-N,N’-dicarbazolylbiphenyl (CBP), and were used to fabricate the first single-layer electrophosphorescent devices with efficiencies competitive with conventional multilayer structures. Finally, the discovery of a triarylboron-based vapochromic material is described. This Pt(II)-alkyne complex was shown to change luminescent colour in response to a variety of volatile organic compounds, with distinct responses dependent on the nature of the analyte. The mechanism of vapochromism was investigated in detail by optical and multinuclear solid-state NMR spectroscopy, and differs in origin from all previously reported examples. / Thesis (Ph.D, Chemistry) -- Queen's University, 2012-09-06 12:51:18.363

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The creation of integrated microphotonic devices requires a challenging assembly of optically and electrically disparate materials into complex geometries with nanometer-scale precision. These challenges are typically addressed by mature wafer-based fabrication methods, which while versatile, are limited to low-aspect-ratio structures and by the inherent complexity of sequential processing steps. Multimaterial preform-to-fiber drawing methods on the other hand present unique opportunities for realizing optical and optoelectronic devices of extended length. Importantly, these methods allow for monolithic integration of all the constituent device components into complex architectures. My research has focused on addressing the challenges and opportunities associated with microfluidic multimaterial fiber structures and devices. Specifically: (1) A photonic bandgap (PBG) fiber is demonstrated for single mode transmission at 1.55 µm with 4 dB/m losses. This fiber transmits laser pulses with peak powers of 13.5 MW. (Chapter 2) (2) A microfluidic fiber laser, characterized by purely radial emission is demonstrated. The laser cavity is formed by an axially invariant, 17-period annular PBG structure with a unit cell thickness of 160nm. This laser is distinct from traditional lasers with cylindrically symmetric emission, which rely almost exclusively on whispering gallery modes, characterized by tangential wavevectors. (Chapter 4)(3) An array of independently-controlled liquid-crystal microchannels flanked by viscous conductors is integrated in the fiber cladding and encircles the PBG laser cavity in (2). The interplay between the radially-emitting laser and these liquid-crystal modulators enables controlled directional emission around a full azimuthal angular range. (Chapter 4) (4) The electric potential profile along the length of the electrodes in (3) is characterized and found to depend on frequency. This frequency dependence presents a new means to tune the transversely-directed transmission at a given location along the fiber axis. (Chapter 5) (5) A chemical sensing system is created within a fiber. By integrating a chemiluminescent peroxide-sensing material into the hollow core of a PBG fiber, a limit-of-detection of 300 ppb for peroxide vapors is achieved. (Chapter 3) / Engineering and Applied Sciences

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Many highly-evolved bio-photonic structures, which tailor the propagation of light by coherent optical scattering, have been investigated. These natural designs, which have many diverse ecological functions, are becoming increasingly studied as sources of innovation and inspiration for a range of scientific, technological, and commercial applications. The brilliant blue colour reflected from the scales of the Morpho butterfly is just one example of nature’s ability to manipulate light and colour strongly. In this thesis, the photonic structure present in the scales of the Morpho butterfly is investigated as a source of bio-inspiration in the pursuit of high- performance photonic vapour sensors. The intention of this is to outperform classical sensor approaches which traditionally suffer from poor selectivity between chemical species. By measuring the change in reflectance from the iridescent scales of the Morpho butterfly, both a sensitive and, critically, a selective response to chemical vapours can be obtained. Here, the origin of this unique multivariable vapour-induced optical response is investigated, and this biological template is further explored as a source of innovation for the mature field of chemical sensing. By using synergy between experimental and theoretical techniques, a mechanism for the sensitive and selective response of the Morpho butterfly’s scales to different chemical vapour environments is elucidated. This mechanism arises from combined chemical and physical effects within the photonic nanostructure. Following this, demonstrations of this biological template’s vapour response attributes, which have large and desirable diversity in the optical responses, are made. These response attributes are visualised in the spectral changes associated with optical excitation conditions, such as from different angles and polarisation states, and also in the temporal response profiles. Finally, theoretical sensor designs that outperform the Morpho scales are described. Simple principles that might improve the currently unacceptable levels of selectivity in contemporary sensor implementations are outlined and the vapour response of a Morpho-inspired photonic structure is presented.

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