The application of a thyristor (a four-layer P1-N1-P2-N2 semiconductor structure) as an optical detector is explored. Based on laboratory experiments which demonstrated that this device produces a pulse-mode output to incident light, the thyristor is investigated by comparing the existing theory of static forward-biased operation to simulation results obtained using ATLAS by Silvaco, Inc. The results include identification of the holding point on the IV curve by simulating the junction potential across each junction as a function of current, and demonstration that impact ionization is not a critical factor in thyristor operation. A series of simulations were performed which show that the thyristor can be optimized for use as a detector by decreasing the emitter efficiencies by decreasing the doping in the P1 and N2 layers, or by increasing the doping in the P2 layer; the switching voltage can be controlled by selecting the doping and thickness of the N1 layer. A detector device was designed to allow further testing of the thyristor detector using the ABN CMOS process from AMI Semiconductor via the MOSIS service. The design of this device is discussed and simulated IV curves are presented.

No description available.

A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy. Johannesburg, 2014. / The synthesis of good crystalline nanomaterials by green methods is one of the means to preventing global warming. Application of microwave thermal methods and the use of green solvents to synthesize nanomaterials contribute to this goal. Further, the low cost synthesis of nanomaterials contributes to their ease of availability in the market at affordable costs. In this study, different NiSx phases and GaN nanomaterials were obtained by microwave-assisted solution phase synthesis. NiS2, GaN, -NiS, ( & ) NiS and Ni3S2 phases were obtained by using different reagents and applying different reaction parameters. These materials were characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy and photoluminescence, to evaluate their crystalline phases, morphologies, particle size distribution and optical properties respectively. Hierarchical structures of cubic phase NiS2 and spherical HDA capped nanostructures were synthesized by a MW-assisted hydrothermal technique. The product phase purity was optimized and the effect of precursor concentration and capping agents were discussed. Further, optical properties of bare and HDA capped NiS2 materials are reported. Detailed analysis of the PL properties shown by these materials in the UV-vis range has been given by considering their calculated DOE energy band diagrams. Single phase -NiS nanostructures with uniformly distributed hierarchical networks were synthesized for the first time in this study. The materials were evaluated for thermal stability under an oxidative environment and at temperatures between 150 oC and 600 oC. NiS materials showed stability at 300 oC and NiO formation was observed from 350 oC to 600 oC. The annealing effect on the crystalline size and IR absorption of the annealed samples is reported by XRD and FTIR studied. The EPR properties of the annealed materials were studied and compared to the oxidized materials. The transition temperature of the -NiS was further confirmed by performing electrical measurements on the as-synthesized material. Further, hydrostatic pressure sensing properties, ethanol and tomato VOCs sensing properties of the -NiS/PVA composite based devices were carried out and the results are reported. The ethanol gas sensing properties of the devices prepared showed the highest response when compared to hydrostatic pressure sensing and tomato VOCs gas sensing. UV-blue emitting GaN nanostructures were obtained for the first time by a onestep MW-assisted solvothermal technique. Sensor devices based on the hexagonal wurtzite structures obtained and their PVA composites (GaN/PVA) were prepared with different GaN NPs concentrations. A very high response to hydrostatic pressure was achieved for the devices prepared. The sensitivity of a GaN/PVA composite based device was analyzed for tomato VOCs detection and the results are presented. Binary phase ( & ) synthesis of NiS materials is commonly reported for the synthesis of Ni:S ratio of 1:1 stoichiometry. This is due to the formation of both phases at temperatures lower than 200 oC. Here, the effect of NaOH and the S source was investigated as reaction parameters. It was found that the concentration of OH- ions in solution plays a huge role in the formation of binary phase NiS as well as its morphology distribution in the nanostructures. Hexagonal nanoplatelets, nanorods and nanorodbased flower-like structures were obtained when different reaction parameters were varied in the presence of NaOH. Further, the solubility of different S precursors in the solvent used was studied and found to affect both the morphology and crystalline phase distribution of the products. Preliminary work on the synthesis of Ni3S2 and Se and Te doped Ni3S2 is presented in the last chapter. The crystallite sizes of the materials were determined by use of the Scherrer equation and the elemental composition was confirmed by EDS analysis. The relative humidity gas sensing of the samples materials was determined and sensitivity response of the material to humidity was obtained for the first time.

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of requirements for the degree of Master of Science. August 11, 2014. / The Z' gauge boson is a hypothetical neutral particle of spin-1 appearing in many theories beyond the Standard Model. In the context of the Z' boson of the Sequential Standard Model in the hadronic decay channel Z' ThadThad, this project investigates improving the sensitivity of the analysis. It is important in the analysis to have high signal e ciency and to be able to distinguish against background processes, thus this project begins with an investigation into new triggers and their combinations that aim to improve the signal e ciency, followed by a study to improve the tau identi cation using tracking. Monte Carlo samples were compared with the data sample for various cut-based variables to investigate which of the variables o er a good discrimination power against the multijet background. The signi cance of each trigger and trigger combinations are shown, as well as the performance of di erent techniques and ideas used to improve the tau identi cation using tracking. Since it is important in this project to be able to reconstruct a tau lepton from its hadronic decay products, this dissertation takes the opportunity to present preliminary results on the study of the light collection uniformity and response in the crack scintillation counters of the ATLAS hadronic tile calorimeter as part of the contribution towards the detector upgrade.

Leung, Siu Ling. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2009. / Includes bibliographical references (leaves 60-62). / Abstracts in English and Chinese. / Table of Contents / ACKNOWLEDGEMENT --- p.4 / List of Figures --- p.8 / Chapter 1. --- Introduction --- p.11 / Chapter 1.1 --- Background --- p.11 / Chapter 1.2 --- Project Objective --- p.12 / Chapter 1.3 --- Organization of the Thesis --- p.13 / Chapter 2. --- Literature Review --- p.14 / Chapter 2.1 --- Overview of the Colloidal Gold --- p.14 / Chapter 2.2 --- Dielectrophoresis (DEP) --- p.14 / Chapter 2.2.1 --- CM factor of Single Shell Model --- p.16 / Chapter 2.3 --- Double Layer and AC Electroosmosis --- p.18 / Chapter 2.3.1 --- Double Layer --- p.18 / Chapter 2.3.2 --- AC Electroosmosis --- p.19 / Chapter 2.4 --- Electrothermal Body Force --- p.19 / Chapter 3. --- Theoretical Analysis of DEP Manipulation --- p.21 / Chapter 3.1 --- Particle Manipulation by DEP Force --- p.21 / Chapter 3.2 --- Electric Induced Fluid Flow --- p.22 / Chapter 3.2.1 --- Double Layer and AC Electroosmosis --- p.22 / Chapter 3.2.2 --- Electrothermal Body Force --- p.24 / Chapter 3.3 --- DEP Manipulation against Fluid Flow --- p.25 / Chapter 4. --- Fabrication of AuNP based Sensors --- p.28 / Chapter 4.1 --- Fabrication of Arrays of Microelectrodes --- p.28 / Chapter 4.2 --- Formation of AuNP based Pearl Chains across Microelectrodes --- p.30 / Chapter 4.2.1 --- Formation Circuit --- p.30 / Chapter 4.2.2 --- Microspotting System --- p.31 / Chapter 4.2.3 --- Results and Discussion --- p.32 / Chapter 5. --- Exploring the Critical Parameters in Controlling AuNP Pearl Chain Formation (PCF) --- p.35 / Chapter 5.1 --- Exploring the Optimum Frequencies --- p.35 / Chapter 5.1.1 --- Analyzing the observation of pearl chain formation under specific frequency ranges --- p.36 / Chapter 5.1.2 --- Conclusion on the Optimum Frequency for PCF --- p.40 / Chapter 5.2 --- Exploring the Optimum Voltages --- p.41 / Chapter 5.3 --- Influence of the Particle size on the Formation Rate --- p.43 / Chapter 6. --- Characteristics of the AuNP based Pearl Chain --- p.44 / Chapter 6.1 --- I-V Characteristics --- p.44 / Chapter 6.2 --- Thermal Sensitivities --- p.45 / Chapter 7. --- Application of the AuNP based Sensor - Airflow Sensor --- p.48 / Chapter 7.1 --- Experimental Setup --- p.48 / Chapter 7.2 --- Experimental Results --- p.49 / Chapter 7.2.1 --- Sensor Response to Air --- p.49 / Chapter 7.2.2 --- Sensor Response to Nitrogen Gas --- p.50 / Chapter 7.2.3 --- Control Experiment --- p.51 / Chapter 7.3 --- Discussions --- p.53 / Chapter 7.3.1 --- Relationship between the Measured Electric Response and Temperature --- p.54 / Chapter 7.3.2 --- Pressure-Temperature Relationship of the Sensor --- p.55 / Chapter 8. --- Conclusion --- p.57 / Chapter 9. --- Future Work --- p.58 / Chapter 9.1 --- DEP Manipulation of 2nm diameter gold nanoparticles --- p.58 / References --- p.60 / List of Publications --- p.63 / APPENDIX-I / The Clausius-Mossoti (CM) Factor --- p.64 / Chapter I-1 --- The CM factor of homogeneous dielectric spheres --- p.64 / Chapter I-2 --- The CM factor of a single shell sphere --- p.65 / APPENPIX-II / Estimating the Minimum Voltage for Electrolysis by the Nernst Equation [39] --- p.67 / Chapter II-l --- Gibb´ةs Free Energy and the Nernst Equation --- p.67 / Chapter II-2 --- Minimum Voltage Required for Electrolysis of Water with Different pH --- p.67 / Appendix-III / Temperature-Voltage Relationship of the K-type Thermocouple [40] --- p.69 / Appendix-IV / Mathlab Program --- p.70 / Chapter IV-1. --- Fluid velocity induced by AC electroosmosis --- p.70 / Chapter IV-2. --- Voltage drop across the double layer --- p.70 / Chapter IV-3. --- Fluid velocity induced by electrothermal force --- p.71 / Chapter IV-4. --- CM Factor Simulation --- p.72 / Chapter IV-5. --- Particle velocity induced by DEP force --- p.73

Thesis (Ph. D.)--University of Wyoming, 2006. / Title from PDF title page (viewed on Dec. 15, 2007). Includes bibliographical references (p. 104-109).

Thesis (M.C.E.)--University of Delaware, 2006. / Principal faculty advisor: Gonzalo Arce, Dept. of Electrical and Computer Engineering. Includes bibliographical references.

No description available.

Thesis (M.S. in Applied Physics)--Naval Postgraduate School, December 2009. / Thesis Advisor(s): Rice, Joseph A. ; Colosi, John A. "December 2009." Description based on title screen as viewed on January 26, 2010. Author(s) subject terms: Acoustic modem, Deep water, Transmission loss, Munk, Reliable Acoustic Path, RAP, Deep Sound Channel, DSC, Seaweb, Acoustic Communications, Acomms. Includes bibliographical references (p. 55-56). Also available in print.

Thesis (M.S.) in Electrical Engineering--University of Maine, 2009. / Includes vita. Includes bibliographical references (leaves 110-113).