Diamond is a wide band gap material with many optically active defect centers. Among all, the most interesting negatively charged nitrogen vacancy (NV-) defect center in diamond has been investigated for almost two decades, often in relation to applications in quantum computing and quantum sensing. Nitrogen vacancy centers are formed by a substitutional nitrogen atom next to a vacancy trapped at an adjacent lattice position. Usually, these centers are prepared in synthetic diamond, where single substitutional nitrogen impurities are in the ideal case homogenously dispersed. To obtain bright luminescence from a sample, additional vacancies are created by electron or neutron irradiation and allowing them to diffuse to nitrogen atoms by annealing at temperature above 600 0C. However, already untreated synthetic diamond samples provide a concentration of NV centers well suited for the study of ensembles. Therefore, to investigate ensemble luminescence centers in diamond crystals, the untreated samples are sufficient. The spectral analysis allowed to clearly identify NVs by fluorescence spectroscopy in such samples. Even at room temperature, the zero-phonon line (ZPL) at 638 nm (NV-) is clearly visible and an additional photon contribution results in the characteristic shape with an overall width of about 120 nm and a maximum at ~685 nm. The broad spectral emission is one of the few drawbacks of NV fluorescence. In this thesis, I developed a conventional fluorescence detection technique, with a homebuilt sample stage which can be precisely positioned in x- and y- direction on a sub-micrometer scale. The sample is excited by laser light focused into a spot size of < 500 µm, and the fluorescence sampling is acquired within a sampling distance of 0.25 µm. Taking advantage of this, it is possible to take fluorescence sampling of an ensemble of NVs from the whole of the crystal, or from a desired section applying a fluorescence matrix methodology. Using this technique, a wide variety of CVD and HPHT synthesized diamond samples were investigated giving first-hand experience of omnipresent NV centers in diamond samples containing a nitrogen impurity concentration of less than 1 ppm (or <200 ppm). This study provides a good base for further work aiming at artificially creating near-surface NVs, which is the basis of many applications with the requirement for better sensitivity and strong coupling to the external spins. To ensure that the fluorescence detected is reliable and repeatable, extensive fluorescence measurements were performed within different matrix regions of the sample for several days, and it turned out that the fluorescence emission is identical when the excitation laser is excited at the middle of the sample. The outcome of the experiments evolved in setting a reference sample for other fluorescence measurements. This reference sample was fluorescence measured over several months, and performed identical spectrum characteristic with less than 3-5% difference in absolute fluorescence intensity. In the spectrum, the often mixed Raman line at 573 nm and the NV0 centers were resolved using higher spectrometer grating. A series of annealing studies in HPHT diamond samples was performed at UHV ambience with a base pressure at ~1 x 10-11 mbar on a sample with [N] < 200 ppm. The fluorescence examined on the sample annealed at temperature 500 0C revealed an increased fluorescence intensity, and remained at constant intensity on consecutive annealing cycles at the same temperature under the same conditions. However, at an increased temperature, the fluorescence emission increased, increasing NVs concentration in the crystal. The untreated HPHT diamond crystals varied in fluorescence characteristic feature, but the sample showed the presence of NVs. The differences in spectroscopic features were identified as due to nitrogen content and possibilities of different nitrogen defect complexes present in the crystal, and they were modified when the sample was annealed at temperatures above 500 0C. The most effective defect formation within the crystal takes place at two temperature ranges 650 –750 0C and 800– 850 0C. The calculated activaction energy at 0.22 eV and 1.26 eV are the energy of mobile interstitial atoms and that of substitutional nitrogen atoms respectively. In the process of annealing, the desorbtion of nitrogen atoms from the surface crystal has been identified by a mass spectrometer. The study contributes to the fundemental understanding of anneling effects in diamond crystals, without being bombarded by high energy electron or neutron radiation. For the creation of a high density of NV centers, annealing in UHV could be sufficient, or even controlled NVs in ultra-pure diamond. The CVD diamond crystals with [N] < 1ppm were observed to contain a high density of NVs, and had no significant change when the additional creations of NVs were attempted. Prolonged X-ray radiation followed by annealing of ultra-pure diamond ([N] <5ppb) during the XPS measurements, showed a significant impact in fluorescence intensity at the surface region confirmed by confocal measurements. However, the sensitivity of the fluorescence spectroscopy setup was not enough to observe the ZPL of the NV centers, though significant changes have been observed in the spectra. Finally, the shallow NV- creation with nitrogen ion implantation at energy of 1 keV has been confirmed by an ODMR experiment and confocal imaging.

We present an ultra-thin transmission-type radiation detector developed for counting microbeam alpha particles. The ∆E alpha detector is a single crystal chemical vapor deposited diamond (ScCVDD) and will be installed between the microbeam accelerator window and a biologic sample. The commercially available optical grade ScCVDD sample (3 mm × 3 mm × 50 µm) was etched down to a few µm thickness which allows alpha particles to penetrate, and then it was followed by the surface cleaning, electrical contact deposition and post-metallization annealing. SRIM code and MCNP6 were used for energy loss calculation of alpha particles in electrodes and diamond and pulse height spectra prediction. In order to evaluate the performance of the ultra-thin ScCVDD detector, a ∆E-E detectors system was setup using a calibration source, the ScCVD detector and a silicon surface barrier detector (SBD). The absolute and intrinsic totally efficiency were determined as 0.3 % and 16 % respectively. Alpha and gamma peaks were observed while the peak resolution is not quite promised. The transmission ability of the ScCVDD detector was verified by applying coincidence operation with 0.22 µs time window. The thickness of the ultra-thin diamond sample was reassessed to be 8.315±0.690 µm from ∆E-E spectrometery. / Thesis / Master of Science (MSc)

Ultraprecision, single point diamond turning (SPDT) is a tool based machining technology that allows the ability to produce high quality surface finishes on the order of nanometers while meeting tight form tolerances on the order of micrometers. It is generally agreed that surface finish in SPDT is primarily affected by four factors: Tool edge quality, relative vibration between the tool and workpiece, material properties and microstructure, and tool geometry (nose radius and machining parameters) machining. To the author’s knowledge, no work has been done to combine all the factors to study their effect on surface generation in SPDT. This is important given that the factors are highly interdependent. Two diamond tools with nose radius of 12mm were used; however, one of them was chemically honed. Results suggest that the honed tool provides a much better surface finish with a significantly reduced amount of running-in stage tool wear. The cutting edge radius of the diamond tools was measured using a novel 3D confocal laser microscope to analyze the chemical honing process and to measure tool wear. The presence of built-up edge (BUE) is more prominent on the honed tool earlier in its life which results in unpredictable surface roughness to appear sooner than on the regular tool. To understand the dynamics of the machine, a redesign of the tool holder bracket was done to increase stiffness. Modal tests were then performed on it to verify performance improvement. With an understanding of the vibration and its effect on the cutting force, a 400Hz disturbance frequency was detected in the cutting forces. From a 3D scan of the surface, a total of 24 undulations on the surface of the part were observed when the spindle speed was set to 1000RPM The machine was instrumented and a rotordynamic investigation was carried out to determine the cause and nature of the vibration in an effort to reduce it and in so doing improve surface form accuracy. / Thesis / Master of Applied Science (MASc)

Sierra Leone came to world attention in the 1990s when a catastrophic civil war linked to the diamond trade was reported globally. This fleet- ing and particular interest, however, obscured two crucial processes in this small West African state. On the one hand, while the civil war was momentous, brutal and affected all Sierra Leoneans, it was also just one element in the long and faltering attempt to build a nation and state given the country's immensely problematic pre-colonial and British colonial legacies. On the other, the aftermath of the war precipitated a huge inter- national effort to construct a 'liberal peace', with mixed results, and thus made Sierra Leone a laboratory for post-Cold War interventions. Sierra Leone examines 225 years of its history and fifty years of independence, placing state- society relations at the centre of an original and revealing investigation of those who have tried to rule or change Sierra Leone and its inhabitants and the responses engendered. It interweaves the historical narrative with sketches of politicians, anecdotes, the landscape and environment and key turning-points, alongside theoretical and other comparisons with the rest of Africa. It is a new contribution to the debate for those who already know Sierra Leone and a solid point of entry for those who wish to know.

No description available.

No description available.

No description available.

Ultra precision single point diamond turning (SPDT) is a machining process used to produce optical grade surfaces in a wide range of materials. Aluminum is of primary interest as a workpiece material because it is easily diamond turnable, highly reflective and corrosion resistant. The cutting tool used is made from a single crystal diamond honed to a very sharp cutting edge. The machines used in this process are extremely precise and stiff. The nature of the cutting parameters used in SPDT changes the process physics substantially over conventional machining. The underlying reason relates to the relative size of the uncut chip thickness and the cutting edge radius of the tool in comparison to the grain size of the workpiece. When performing SPDT, there is a functional limit to the achievable surface finish. This is predominately due to material side flow and the opening up of material defects. Thus the machined surfaces have to undergo post processing operations like lapping or polishing, which increase cost and production time. Thus, the objective of this study was to improve the surface finish of the SPDT process to minimize the amount of post processing. The approach involved addressing the ratio between the tool cutting edge radius and the microstructure. Realizing the limitations associated with sharpening a diamond tool further, efforts have been made to mechanically or thermo-mechanically induce dislocations into the workpiece to refine the microstructure and in so doing enhance machinability. As dislocations act as a point of defect, it is observed that higher dislocation density offers less side flow and leads to better surface roughness. A special tool with a flat secondary edge was then developed to address the remaining side flow issue for planar surfaces. The combination of thermo-mechanically produced ultra fine grained material with the special tool provided a substantial reduction in surface roughness from values typically reported at 3nm [Roblee, 2007] Ra to 0.75nm R0 • In addition to this the use of the custom designed tool can improve the productivity associated with machining a flat face by a factor of one hundred times by allowing the feed rate to be increased while still achieving the desired surface finish. / Thesis / Doctor of Philosophy (PhD)

This thesis presents the investigations of femtosecond laser machining on three different dielectric materials, namely quartz, sapphire and diamond. The laser micromachining experiments were performed with a Titanium:Sapphire solid state laser with a repetition rate of 1 kHz, centered at a wavelength of 800 nm and pulse duration of 150-200 femtoseconds (fs). A 5x microscope objective for surface micromachining and a 50x microscope objective for subsurface micromachining. The 50x microscope objective was used to obtain a smaller spot size and a shorter confocal parameter. The purpose of this research was to study the interaction between the femtosecond laser pulses and quartz, sapphire and diamond which have bandgap energies of 8.4 eV (λ=148 nm), 9.9 eV (125 nm), and c)· diamond 5.5 eV (225 nm) respectively. Since the photon energy of the laser was below the wide bandgap energies of the aforementioned dielectrics, the materials were essentially transparent to the incident laser. In order to study the behavior of the dielectric materials under femtosecond laser irradiation, several experiments with varying type and number of pulses (N) were performed, such as single pulse ablation, plural pulse ablation (N ≤ 100 pulses), multiple pulse ablation (N ≤ 100 pulses), and continuous lines micromachining on the surface and in the sub-surface of materials were performed. The features, damage, and structural changes introduced by femtosecond laser irradiation on the materials studied were characterized through examination of both the plan and cross-section views. The characterization process was carried out using optical microscopy (operated in the Nomarski mode), scanning electron microscopy, focused ion beam, atomic force microscopy, and transmission electron microscopy. The laser micromachining demonstrated distinct behaviors of the three wide bandgap materials. Quartz was very prone to cracking and showed nearwavelength alternating crystalline and amorphous sub-structure with the orientation parallel with respect to the electric field direction. Sapphire showed sub-wavelength ripples formation in lower fluences. Finally, diamond showed a strong tendency for ripples formation from near- to sub-wavelength spacing with the orientation of the ripples perpendicular and parallel with respect to electric field polarization. / Thesis / Master of Applied Science (MASc)

In recent years consumers, NGOs, and governments alike have become increasingly concerned about the problem of `conflict¿ or `blood¿ diamonds in relation to on-going armed conflicts in Angola, Sierra Leone, and the Democratic Republic of Congo (DRC). Allegations by NGOs, governments and the UN that many conflicts are fuelled by illicit exports of diamonds have begun to be acknowledged by the diamond industry. Diamonds, and the money they generate, have been used to purchase arms, ammunition, uniforms and other equipment, as well as to pay soldiers and to cultivate strategic alliances for those armed groups in control of territory rich in this lucrative resource. This has facilitated the intensification and protraction of violent conflicts in Africa. Additionally, the wealth to be gained from the illicit extraction and sale of diamonds has contributed to the prominence of economic agendas in many civil wars that motivate faction leaders to continue the conflict in order to protect their businesses.1 For example, the Angolan rebel group UNITA (União Nacional para a Inedepência Total de Angola) is believed to have received US$3.7 billion in a six year period during the 1990s - a far greater amount than the foreign aid received from patrons like the United States and South Africa during the Cold War. This money has both funded large scale arms purchases and swelled the personal coffers of UNITA leaders, thereby contributing to the intransigence of those leaders in agreeing and implementing peace and facilitating continued violence.2 In Sierra Leone the Revolutionary United Front (RUF) has funded its arms acquisitions with illicit diamond revenues and the extraction of diamonds is seen as one of the main factors behind the lack of implementation of the Lomé peace accord and the subsequent resurgence of violence. In the Democratic Republic of Congo (DRC) both the government and rebel forces have financed their war efforts through the diamond trade, as have some of the intervening regional powers. As a result the fighting around diamond rich areas and trading centres has been particularly intense. For example, in spite of a unilateral ceasefire declared by Rwanda on the 29th of May 1999, it is believed to have sent 7,000 fresh troops to the DRC in June as the battle for the diamond rich area of Mbuji-Mayi escalated. However the prominence of `conflict diamonds¿ in the policy discourse related to these conflicts and their resolution has served to obscure a range of other issues which are equally, if not more, central to finding lasting solutions to these wars. In spite of the fact that the arms flows which sustain these conflicts are only partly financed by `conflict diamonds¿ they are often only mentioned as one aspect of the illegal diamond trade rather than as a core issue. Even more concerning, perhaps, is that the discourse of `greed¿ rather than `grievance¿ as the foundation and driving force of conflicts obscures the complexity of political, social, and other economic dimensions of these wars. Thus, while efforts to reduce the conflict diamond trade may be an essential element of the resolution of these conflicts, other factors of potentially greater import are pushed down the agendas of many of the governments and NGOs whose input into those processes may be the key to success. In short, therefore, the issue 2 of conflict diamonds is one aspect of the complex dynamics and processes of ongoing African conflicts, not vice-versa.