by Tong Ka Wing. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1995. / Includes bibliographical references (leaves 60-62). / by Tong Ka Wing. / Abstract --- p.1 / Chapter Chapter 1 --- Introduction --- p.2 / Chapter Chapter 2 --- Scattering Intensities and Depolarization Ratios --- p.9 / Chapter Chapter 3 --- Raman Microprobe Experimental Set-up --- p.11 / Chapter 3.1 --- Optical Design of the Raman Microprobe --- p.11 / Chapter 3.1.1 --- Construction of the Olympus BHSM-313U Microscope --- p.11 / Chapter 3.1.2 --- Numerical Aperture of Objectives --- p.13 / Chapter 3.1.3 --- Design of the Raman Microprobe --- p.13 / Chapter 3.1.3.1 --- Design of Signal Collection Optics --- p.16 / Chapter 3.1.3.2 --- Design of Epi-illuminator --- p.17 / Chapter 3.2 --- Performance of the Raman Microprobe --- p.19 / Chapter 3.2.1 --- Collection Efficiencies of Objectives --- p.19 / Chapter 3.2.2 --- Spatial Resolution of the Raman Microprobe --- p.20 / Chapter 3.2.3 --- Rejection of Rayleigh Scattering Light --- p.20 / Chapter 3.2.4 --- Polarization Effect of the Raman Microprobe --- p.22 / Chapter Chapter 4 --- "Sample Preparation, Morphology and Measurements of Spectra" --- p.23 / Chapter Chapter 5 --- Results and Discussion --- p.31 / Chapter 5.1 --- Micro-Photoluminescence of Diamond Films --- p.31 / Chapter 5.2 --- Curve Fitting of Micro-Raman Spectra --- p.34 / Chapter 5.3 --- Part I Micro-Raman of Unoriented Diamond Crystallites --- p.41 / Chapter 5.3.1 --- Diamond Peaks --- p.41 / Chapter 5.3.2 --- D- and G- Peaks --- p.43 / Chapter 5.4 --- Part II Micro-Raman of Oriented Diamond Crystallites --- p.43 / Chapter 5.4.1 --- Diamond Peaks --- p.45 / Chapter 5.4.1.1 --- Depolarization Ratios --- p.45 / Chapter 5.4.1.2 --- Peak Shifts --- p.47 / Chapter 5.4.1.3 --- Peak Widths --- p.48 / Chapter 5.4.2 --- D- and G- Peaks --- p.48 / Chapter 5.4.2.1 --- Depolarization Ratios --- p.48 / Chapter 5.4.2.2 --- Peak Shifts and Widths --- p.48 / Chapter 5.4.3 --- Relation Between Line Width of Diamond Peaks and Intensity Ratios of Diamond Peak to G-Peak --- p.50 / Chapter 5.4.4 --- Internal Stress due to Substrate and Other Growth Defects --- p.52 / Chapter Chapter 6 --- Conclusions --- p.54 / Appendix A --- p.56 / Chapter A.1 --- Scattering Intensities of Diamond --- p.56 / Chapter A.2 --- Scattering Intensities of Graphite --- p.58 / Appendix B --- p.59 / References --- p.60

Magister Artium - MA / Framed by theories of childhood, psychoanalysis, postcolonial theory, trauma theory, film theory, and literary theory, this thesis investigates representations of the African child in three contemporary films about Africa. This thesis puts forward the argument that in E. Zwick‘s Blood Diamond Dia, the film‘s primary child character, is split into Dia Vandy (his subjectivity) and See-me-no-more (his performed identity within the Revolutionary United Front). Furthermore it will be shown that this split is paralleled by the boy‘s transition from filiation to re-filiation. With regard to K. MacDonald‘s The Last King of Scotland, this thesis will demonstrate how, via the effects of cinematic doubling, the narrative antagonist Ugandan dictator Idi Amin Dada is represented as a child. It will also be illustrated that the narrative, consequently, perpetuates not only the myths surrounding Amin but the colonial myth that the savage is a child. Finally, this thesis will show that, of the tree texts, N. Blomkamp‘s District 9 boasts the most authentic representation of the African child and childhood in postcolonial Africa, albeit via a child figure that is literally alien. In each case study the child will be shown to be a liminal personae (Turner 1969), who is an ambiguous and often paradoxical figure who allows us to see more clearly the ethical tensions within the narrative. This thesis will also show that these texts may be considered socially aware trauma narratives, which are relatively critical of western involvement in the traumatic histories of African locales and peoples. Ironically though, these texts, and others similar to them, have been criticised for being Afropessimistic (Evans & Glenn 2010). The tension created by this paradox will be investigated during this thesis, which will attempt to establish to which extent these texts may be considered postcolonial, and whether or not they should be labelled Afropessimistic.

GaN is a monocrystalline material that can be grown using metallo-organic chemical vapour deposition (MOCVD), and has desirable mechanical and semiconducting properties for operating as a sensor. It has a Young’s modulus of 250 to 350 GPa, which shows little decrease with respect to temperature beyond 400°C. GaN also exhibits piezoelectric and piezoresistive effects, meaning that it will generate a charge and its electrical resistance will change when the material is strained respectively. In this PhD, GaN has been used as the base material for pressure sensors that potentially can be used in excess of 400°C and at a pressure in excess of 50 bar (5 MPa), with potential applications in aerospace and oil exploration. The pressure sensor is a circular diaphragm created from a GaN/sapphire wafer, and was designed and tested in order to determine if GaN can act as a sensing material in these environments. In addition to the diaphragm sensor, GaN templates that can potentially be used for sensors were grown using an epitaxial layer overgrowth (ELOG) method. These sensors are potentially more mechanically robust than similar templates etched out of GaN/sapphire wafers because they will have less inbuilt strain due to lower dislocation densities. It was possible to release beams and cantilevers from GaN ELOG templates. Mechanical probe tests were undertaken on these devices to see if they were fully released and robust. GaN single crystal growth requires a substrate material, such as (111) silicon or (0001) sapphire, meaning that the thermal properties of the substrate are important for a device operating in excess of 400°C. GaN high electron mobility transistors are heat sensitive, experiencing a decrease in current between the drain and source terminals as the temperature increases. Therefore a GaN-based sensor needs a substrate with the highest possible thermal conductivity to act as a heat sink, which means removing as much heat as possible from the GaN sensor. Diamond has superior thermal conductivity to both sapphire and silicon, so a novel silicon/polycrystalline diamond composite substrate has been developed as a potential GaN substrate. Polycrystalline diamond (PD) can be grown on 4 inch diameter wafers using hot filament chemical vapour deposition (CVD), on (111) silicon (Si) from which single crystal GaN epitaxy can also be grown. In order for the (111) Si/PD composite substrates to be useful heat sinks, the Si layer needs to be less than 2 m. PD was initially grown on 525 to 625 m thick Si wafers that required thinning to 2 m. Achieving this Si layer thickness is difficult due to the presence of tensile stress in the Si caused by a mismatch in the coefficients of thermal expansion (CTEs) between Si and PD. This stress causes the wafer to bow significantly and has been modelled using ANSYS FE software. The models show that the bow of the wafer increases when it is thinned, which will eventually cause the Si layer to delaminate at the Si/PD interface due to poor adhesion and a build up for shear stress. When the Si layer is mechanically thinned, the Si layer can crack due to clamping. The experimental wafer bow and micro-Raman measurements validate the model for when the silicon layer is thicker than 100 m and these results show that an alternative processing route is required.

In this thesis 3D diamond detectors were fabricated using an ultrafast femtosecond (120 fs) pulse length laser, with a 800nm wavelength, to induce a phase change of diamond to graphite to form electrodes in the diamond bulk. Graphitic electrodes, with diameters of O(um), were fabricated using a known processing technique and were enhanced further through the use of a Spatial Light Modulator (SLM), which is a new technology in this field. These detectors were subsequently characterised through the use of particle beams, and this work also presents methods for characterising such detectors: A pair of crossed polarisers to determine the stress induced by the electrodes on the diamond bulk; Raman spectroscopy to assess the relative quantity of diamond:graphite formed; Scanning Electron Microscopy (SEM) to image the starting (seed) and finishing (exit) sides of electrode formation; and current-voltage (I-V) measurements to calculate the electrical properties of the electrodes. These characterisation methods (alongside the use of particle beams) serve as a means to compare the two fabrication techniques and to determine the optimum fabrication parameters to produce 3D diamond detectors for use as tracking detectors in high luminosity environments such as those in the Large Hadron Collider (LHC). This work shows that using a higher beam energy and translation speed of the focal spot results in electrodes of lower electrical resistivity, which is an ideal characteristic for a tracking detector. These higher processing parameters also result in more graphitic structure on the seed and exit sides of the diamond, determined separately via Raman spectroscopy and SEM. An increased beam energy also results in larger electrode diameters, reducing the active area of the detector and inducing more stress in the diamond bulk. These measurements therefore indicate an upper limit on the fabrication parameters. A further study into these processing parameters shows the translation speed scales with the pulse repetition rate of the laser and allows for fast fabrication of 3D diamond detectors. Two devices were fabricated with and without the use of an SLM, with a more uniform detector response (through characterisation by particle beams), lower electrical resistivity, and more graphitic material observed for SLM-fabricated electrodes. The benefits of square and hexagonal cell structures were also investigated with both structures showing a similar response to particle beams. A lower charge sharing region is observed in hexagonal cells and indicates potentially different applications for these cell geometries. Transient Current Technique (TCT) measurements were also taken on both detectors, where faster charge collection and higher quality data were seen for the SLM-fabricated device. These measurements indicate a preference in the use of an SLM for the future fabrication of 3D diamond tracking detectors. These TCT measurements were then compared to simulations to extract the charge carrier properties in diamond. Only qualitative agreement was obtained, motivating further work in this area to fully understand the charge carrier dynamics and demonstrate the future viability of 3D diamond detectors.

No description available.

L'information quantique repose sur un traitement de l'information, non plus de manière classique, mais de manière quantique, afin d'augmenter l'efficacité de certains algorithmes informatiques. Un tel objectif nécessite de construire des registres quantiques fondés, par exemple, sur l'assemblage cohérent d'un grand nombre de systèmes quantiques individuels qui jouent alors le rôle de bits d'information quantiques. Dans ce contexte, le centre coloré NV du diamant fait l’objet de nombreuses recherches car il est l’un des rares systèmes pouvant être utilisé comme bit quantique à l’état solide et à température ambiante. Cette thèse étudie les interactions du spin électronique du centre NV avec des spins nucléaires présents dans la matrice de diamant, dans le but de créer des registres quantiques hybrides dans le diamant. Dans un premier temps, nous expliquerons comment le spin électronique du centre NV peut être utilisé pour détecter des spins nucléaires disséminés dans le diamant. Puis, le centre NV sera exploité comme bit quantique auxiliaire pour initialiser l'état de ces spins nucléaires, soit en tirant profit d'un anti-croisement de niveaux, soit en implémentant une mesure projective. Enfin, nous analyserons les origines des limitations des temps de cohérence des centres NV dans les échantillons de diamant ultrapurs, provenant de l'interaction avec un bain de spins nucléaires environnant. Outre leur intérêt en information quantique, l’étude et le contrôle des spins dans le diamant ouvrent la voie à la réalisation de nano-capteurs ultrasensibles, dont les applications couvrent des domaines très variés de la physique moderne. / The principle of quantum information relies on processing information, not from a classical point of view but from a quantum one, in order to increase the efficiency of some computer algorithms. Fulfilling such a goal requires the construction of a quantum register, for instance by coherently putting together a large number of individual quantum systems which play the role of quantum information bits. In this respect, a lot of research has focused on the NV colored center of diamond as it constitutes one of the few systems which can be used as a solid-state quantum bit at room temperature. This doctoral thesis studies the interactions between the NV electronic spin and surrounding nuclear spins located in the diamond matrix, with the intention of creating diamond quantum hybrid systems. We first explain how the NV electronic spin can be used to detect nuclear spins dispersed inside the diamond. Then, we use the NV center as an ancillary quantum bit to initialize the state of these nuclear spins, either by benefitting from a level-anticrossing, or by implementing a projective measurement. Finally, we analyse the origins of the limitation of the coherence time of NV centers in ultrapure diamond samples caused by the interaction with a surrounding nuclear spin bath. Besides their interest for quantum information processing, the study and control of spins in diamond also open the path to making highly sensitive nano-sensors, for which applications can be found in numerous fields of modern physics.

This dissertation presents the synthesis and application of nanodiamond based materials for electrochemical biosensors. In this research work, nanodiamond particles have been used to prepare doped and undoped nanocrystalline diamond films, and conducting polymer composites for enhanced biosensing. The performance of the synthetized materials towards sensing applications was evaluated against glucose amperometric biosensing. Besides, cholesterol biosensing was attempted to prove the capabilities of the platform as a generic biosensing substrate. Biosensors have been proved to provide reliable detection and quantification of biological compounds. The detection of biological markers plays a key factor in the diagnosis of many diseases and, even more importantly, represents a major aspect in the survival rate for many patients. Among all of the biosensors types, electrochemical biosensors have demonstrated the best reliability to cost ratio. Amperometric biosensors, for example, have been used for decades as point of care sensing method to monitor different conditions such as glucose. Despite the amount the research presented, the sensitivity, selectivity, stability, low cost and robustness are always driving forces to develop new platforms for biosensor devices. In the first phase of this dissertation, we synthesized undoped and nitrogen doped nanocrystalline diamond films. The synthetic material was thoroughly studied using different material characterization techniques and taken through a chemical functionalization process. The functionalization process produced a hydrogen rich surface suitable for enzymatic attachment. Glucose oxidase was covalently attached to the functionalized surface to form the biosensing structure. The response of the biosensor was finally recorded following voltammetry and amperometric techniques under steady state and dynamic conditions. The experimental results demonstrated that conductivity induced by the doping process enhanced the sensitivity of the sensing structure with respect to the undoped substrate. Also, the functionalization procedure showed strong bonding to avoid enzyme leaching during the measurements. Later, in the second phase of this dissertation, the nanodiamond particles were used as filler for conducting polymer composites. The objective for developing these composite materials was to overcome the high resistivity observed for nanocrystalline films. The experimental results demonstrated that the inclusion of nanodiamond particles increased the sensitivity of the overall structure towards the quantification of glucose with respect to the nanocrystalline films and the bare polymer. Besides, the experiment showed a noticeable enhancement in the signal-to-noise ratio and the mechanical stability of the sensing platform due to the nanodiamond addition. The best structures from the previous experiments were further grafted with iron oxide nanoparticles to attempt signal amplification. Initial experiments with nanodiamond based composited showed similar current for low glucose concentrations for two different active electrochemical sensing areas. This observation indicates that more area is still available to transport signal and to enhance even further the sensing action. Oxidation of iron oxide nanoparticles after initial enzymatic decomposition of glucose has been proved to provide higher current for the same glucose concentration; thus, creating amplification effect for the signal. Finally, the toxicity of the nanomaterial synthesized during this dissertation was evaluated in mammalian cells. The advances in biosensing techniques indicate the potential application of amperometric platform for continuous implantable devices; hence, the toxicity of the materials becomes a key aspect of the platform design.

Traditional lightweight armor ceramics such as boron carbide (B4C) and silicon carbide (SiC) are used alone or together in varying amounts to create monolithic protective plates. These materials exhibit relatively small differences in hardness, flexure strength, and fracture toughness. Many of the routes taken during the synthesis of the powder and sintering of the plates using traditional ceramic processing techniques have long processing times, tend to leave asperities within the microstructure, and have unwanted secondary phases that lower the performance of these materials. In lieu of the incremental changes in the above properties, it is thought that adding diamond particulates to the ceramic matrix will dramatically improve the mechanical properties and overall performance. With the reduced cost of synthetic diamond and the commercial development of more rapid spark plasma sintering (SPS), this work develops a novel reactive SPS process to fabricate near fully dense SiC-TiC-diamond composites at various processing temperatures with minimal graphitization and full adhesion to the ceramic matrix. It was found that samples with up to ~97% theoretical density can be fabricated with no quantifiable graphite content within the characterization ability using advanced X-ray diffraction and microscopy techniques.

Doctor of Philosophy (PhD) / This thesis aims to establish a sound scientific methodology for the effective and efficient polishing of thermally stable PCD composites (consisting of diamond and SiC) for cutting tools applications. The surface roughness of industrial PCD cutting tools, 0.06 μm Ra is currently achieved by mechanical polishing which is time consuming and costly because it takes about three hours to polish a 12.7 mm diameter PCD surface. An alternative technique, dynamic friction polishing (DFP) which utilizes the thermo-chemical reactions between the PCD surfaces and a catalytic metal disk rotating at high peripheral speed has been comprehensively investigated for highly efficient abrasive-free polishing of PCD composites. A special polishing machine was designed and manufactured in-house to carry out the DFP of PCD composites efficiently and in a controllable manner according to the requirements of DFP. The PCD polishing process and material removal mechanism were comprehensively investigated by using a combination of the various characterization techniques: optical microscopy, SEM and EDX, AFM, XRD, Raman spectroscopy, TEM, STEM and EELS, etc. A theoretical model was developed to predict temperature rise at the interface of the polishing disk and PCD asperities. On-line temperature measurements were carried out to determine subsurface temperatures for a range of polishing conditions. A method was also developed to extrapolate these measured temperatures to the PCD surface, which were compared with the theoretical results. The material removal mechanism was further explored by theoretical study of the interface reactions under these polishing conditions, with particular emphasis on temperature, contact with catalytic metals and polishing environment. Based on the experimental results and theoretical analyses, the material removal mechanism of dynamic friction polishing can be described as follows: conversion of diamond into non-diamond carbon takes place due to the frictional heating and the interaction of diamond with catalyst metal disk; then a part of the transformed material is detached from the PCD surface as it is weakly bonded; another part of the non-diamond carbon oxidizes and escapes as CO or CO2 gas and the rest diffuses into the metal disk. Meanwhile, another component of PCD, SiC also chemically reacted and transformed to amorphous silicon oxide/carbide, which is then mechanically or chemically removed. Finally an attempt was made to optimise the polishing process by investigating the effect of polishing parameters on material removal rate, surface characteristics and cracking /fracture of PCD to achieve the surface roughness requirement. It was found that combining dynamic friction polishing and mechanical abrasive polishing, a very high polishing rate and good quality surface could be obtained. The final surface roughness could be reduced to 50 nm Ra for two types of PCD specimens considered from pre-polishing value of 0.7 or 1.5 μm Ra. The polishing time required was 18 minutes, a ten fold reduction compared with the mechanical abrasive polishing currently used in industry.

This thesis investigates the performance of diamond-shaped dowel joints in concrete slabs on ground under static loads. Diamond-shaped dowels have been in common use in concrete slab construction since 1996. A comprehensive literature review revealed that published studies regarding laboratory tests and finite element modelling of diamond-shaped dowel performance were limited to primary experiments and simple numerical analysis. Importantly, the limited finite element modelling has not been verified against test data, and the scant published test data lacks clarity. The results were inconclusive, unclear and there exists different recommendations for joint stability. Some recommended design data are not based on any testing, but on inferred or extrapolated data from smaller slabs with smaller dowel thicknesses. Hence, this research provides the opportunity to enlighten the design community with real data on the performance of diamond-shaped dowel joint behaviour. The research program includes experimental, numerical modelling and parametric evaluations. In the experimental investigation, testing facilities were designed and developed in the course of this research. A total of one trial and six cast-in-place slabs encompassing two slab thicknesses, two diamond-shaped dowel thicknesses, and two dowel spacing, were tested in the structures laboratory of the Division of Civil Engineering at the University of Queensland. Joint gaps of 10 or 15 mm were used to simulate typical slab contraction causing by the shrinkage of concrete slabs. All tests were subjected to static loading to failure. This enabled slab joint response to be evaluated in terms of relative deflection, load transfer efficiency, load transfer, ultimate load and crack geometry. In addition to the experiments, numerical models were developed using the LUSAS finite element program. The model dimensions corresponded to those of the laboratory test specimens. The concrete slabs were modelled using a “multi-crack concrete model 94”. The test rig, diamond-shaped dowels and other materials were modelled as elastic materials. Results from the laboratory experiments were compared to the finite element results in order to validate the model. These models were then used to undertake a preliminary parametric study of diamond-shaped dowel performance. Criteria such as joint gap widths, dowel spacing, concrete property reduction, and dowel and slab thickness were investigated. The three main sections of this work - comprising laboratory testing, finite element modelling and parametric study evaluating have been combined to provide a betterinformed understanding of the performance of concrete slabs using diamond-shaped dowels.