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by Hiu-suen Choy. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1995. / Includes bibliographical references (leaves [124]-131). / Acknowledgements / Abstract / Chapter Chapter 1 --- Introduction --- p.1-1 / Chapter Chapter 2 --- Basic Theory for MSM Photodetectors --- p.2-1 / Chapter 2.1 --- Schottky-Mott Theory for Ideal metal-Semiconductor Contact --- p.2-1 / Chapter 2.2 --- Modifications to Schottky-Mott Theory for Practical Metal Semiconductor Contact --- p.2-4 / Chapter 2.3 --- Energy Band of Metal-semiconductor-metal (MSM) Structures --- p.2-6 / Chapter 2.4 --- Dark Current Voltage Characteristics for MSM Structure --- p.2-12 / Chapter 2.5 --- Capacitance for Interdigitated MSM Photodetectors --- p.2-16 / Chapter 2.6 --- Basic mechanism of the MSM Photodetector --- p.2-19 / Chapter 2.7 --- DC Responsity and Quantum Efficiency of the Interdigitated MSM Photodetector --- p.2-20 / Chapter 2.8 --- Speed Performance of the Interdigitated MSM Photodetector --- p.2-21 / Chapter Chapter 3 --- Device Fabrication and Packaging --- p.3-1 / Chapter 3.1 --- Metallization Pattern --- p.3-1 / Chapter 3.2 --- Device Fabrication --- p.3-7 / Chapter 3.3 --- Device Packaging --- p.3-8 / Chapter Chapter 4 --- Experimental Description --- p.4-1 / Chapter 4.1 --- Experimental Procedures --- p.4-1 / Chapter 4.2 --- Equipment Description --- p.4-3 / Chapter Chapter 5 --- 1.3μm In0.53Ga0.47As Metal-Semiconductor-Metal Photodetector Grown by Low-Pressure MOCVD Using Tertiarybutylarsine --- p.5-1 / Chapter 5.1 --- General Description --- p.5-1 / Chapter 5.2 --- Structure of the Photodetector --- p.5-2 / Chapter 5.3 --- Experimental Results --- p.5-6 / Chapter 5.4 --- Data Analysis and Discussion --- p.5-14 / Chapter 5.5 --- Summary --- p.5-24 / Chapter Chapter 6 --- The Performance of 0.85μm Semi-Insulated GaAs MSM Photodetector with Different Interdigitated Spacings --- p.6-1 / Chapter 6.1 --- General Description --- p.6-1 / Chapter 6.2 --- Experimental Results --- p.6-2 / Chapter 6.3 --- Data Analysis and Discussion --- p.6-17 / Chapter 6.4 --- Summary --- p.6-27 / Chapter Chapter 7 --- Optical Control of Polarity in Short Electrical Pulses Generated from Coplanar Waveguide MSM Photodetectors --- p.7-1 / Chapter 7.1 --- General Description --- p.7-1 / Chapter 7.2 --- "Structure, Fabrication and Experimental Set-up" --- p.7-1 / Chapter 7.3 --- Experimental Results --- p.7-4 / Chapter 7.4 --- Data Analysis and Discussion --- p.7-11 / Chapter 7.5 --- Applications --- p.7-18 / Chapter Chapter 8 --- Conclusion --- p.8-1 / References / Publications

Thesis (Ph.D)--Mechanical Engineering, Georgia Institute of Technology, 2010. / Committee Chair: Streator, Jeffrey; Committee Member: Blanchet, Thierry; Committee Member: Cowan, Richard; Committee Member: Danyluk, Steven; Committee Member: Neu, Richard; Committee Member: Thadhani, Naresh. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Approved for public release, distribution is unlimited / 100 m/s). Low voltage electrical contact was not maintained for some experimental shots and non-parallel rails were the suspected cause. In this thesis, we used a non-contact capacitive sensor to determine rail spacing to within 2/kAcm10mael, so that the rails will be parallel within small tolerances. Several rails were used in these experiments: 75-25 copper-tungsten, chromium-plated 75-25 Cu-W, and chromium-plated pure copper rails. Improving the control of rail spacing and parallelity did not ensure low-voltage electrical contact for our configurations. The largest damage was observed for chromium-plated copper rails and the least damage occurred for chromium-plated 75-25 Cu-W rails. / Lieutenant, United States Navy

AgCdO is one of the most widely used contact materials in the world because of its outstanding performance. Nevertheless, due to environmental considerations, it will soon be completely forbidden by European environmental directives. Therefore, finding a good substitute is of crucial importance. Electrical arc erosion plays a crucial role in the reliability and life of power switching devices. Depending on the contact material's behavior in response to an electrical arc, surface damage can induce severe changes in contact material properties that will impact the power switching device's functioning. Consequently, electrical arc effects and consequences on the contact material surface are of first importance. In this context, we have focused our research activities on the following axes. First of all, in order to better understand AgCdO (Current contact material in aerospace industry) and AgSnO₂(Potential candidate to AgCdO substitution) arc erosion behaviors, arc erosion experiments, where the power switching devices have been subjected to different numbers of arc discharges, have been realized. Further, a general macroscopic electrical contact arc erosion model valid for low and high currents was developed. To compare model results to experimental data, this model describes the complete breaking process of electrical contacts and gives the total amount of material removed after one breaking operation. In parallel, arc erosion experiments on AgCdO power switching devices have been conducted at high currents (0 -> 1000 A) in order to validate the arc erosion model. Next, using the general arc erosion model, the properties having the greatest influence on the electrical arc erosion process have been determined through simulations on silver contact material. At this stage, ab initio calculations were needed to obtain ranges of variation of certain silver contact material properties. Finally, an investigation of the trends of changing local contact material on these identified material properties was performed. This study composition of AgSnO₂was based on ab initio calculations for two different oxide compositions of AgSnO₂. These will allow us to give directions to aid the design of a good substitute for AgCdO, and therefore, to complete the main objective of this research work.

Simultaneous measurement of electrical contact resistance (ECR) and coefficient of friction (COF) at the sliding interface is essential to assess the performance of selected material contact pairs for the transfer of current from stationary member to moving member (or vice-versa). Low and stable values of ECR and COF are desirable during the intended operating life of the contact members. These parameters may change with respect to time as a consequence of change in the surface properties of contact members due to their relative movement. Hence experimental investigations have been conducted to study the variation of ECR and COF while different riders sliding on copper and brass flat samples in different environments. As a part of the experimental investigation, a reciprocating sliding setup is designed and developed to study the variation of ECR and COF in terms of normal force, sliding speed, current and environment. The details of the experimental setup are described along with its construction and operation. The sample preparation, instrumentation, data acquisition and presentation are explained in detail. The variations of ECR and COF at different normal forces, currents and sliding speeds by moving OFHC copper, brass, silver, Ag10Cu and Ag20Cu riders on OFHC copper and brass flat samples in vacuum, argon, nitrogen and air are studied in detail. Studies are also conducted to evaluate the performance of metallic contacts under lubricated condition using general purpose lubricating oils of different viscosity. Metallic contacts show a decrease in ECR with increase in normal force at all sliding speeds in all media. Sliding metallic contacts show a significant decrease in both ECR and COF during the initial sliding cycles at constant normal force in all media. Surface roughness of flat sample is found to have a significant effect on both ECR and COF in all media. Wear of rider is found to be significant as compared to wear of flat samples. Metallic contacts show an inverse relationship between ECR and COF in all media under mild wear regime (0.2< COF≤ 0.4). ECR and COF of sliding metallic contacts are independent of current (≤ 4A) in mild wear regime in all media. Reasonably low values of ECR and COF are observed for prolonged duration with lubricants having low viscosity. The presence of wear fragments at the sliding zone is found to have significant effect on both ECR and COF in all media. Low values of ECR are observed while copper rider sliding on brass sample as compared to silver rider under same operating conditions. Significant amount of metal transfer is observed with silver based riders sliding on copper and brass flat samples in different media. The present investigations are useful in understanding the contact behaviour of copper and brass flat samples for similar and dissimilar riders sliding on them in various environments.

Hard gold thin films and coatings are widely used in electronics as an effective material to reduce the friction and wear of relatively less expensive electrically conductive materials while simultaneously seeking to provide oxidation resistance and stable sliding electrical contact resistance (ECR). The main focus of this dissertation was to synthesize nanocrystalline Au films with grain structures capable of remaining stable during thermal exposure and under sliding electrical contact stress and the passing of electrical current. Here we have utilized a physical vapor deposition (PVD) technique, electron beam evaporation, to synthesize Au films modified by ion implantation and codeposited ZnO hardened Au nanocomposites. Simultaneous friction and ECR experiments of low fluence (< 1x10^17 cm^-2) He and Ar ion implanted Au films showed reduction in friction coefficients from ~1.5 to ~0.5 and specific wear rates from ~4x10^-3 to ~6x10^-5 mm^3/N·m versus as-deposited Au films without significant change in sliding ECR (~16 mΩ). Subsurface microstructural changes of He implanted films due to tribological stress were analyzed via site-specific cross-sectional transmission electron microscopy (TEM) and revealed the formation of nanocrystalline grains for low energy (22.5 keV) implantation conditions as well as the growth and redistribution of cavities. Nanoindentation hardness results revealed an increase from 0.84 GPa for as-deposited Au to ~1.77 GPa for Au uniformly implanted with 1 at% He. These strength increases are correlated with an Orowan hardening mechanism that increases proportionally to (He concentration)1/3. Au-ZnO nanocomposite films in the oxide dilute regime (< 5 vol% ZnO) were investigated for low temperature aging stability in friction and ECR. Annealing at 250 °C for 24 hours Au-(2 vol%)ZnO retained a friction coefficient comparable to commercial Ni hardened Au of ~ 0.3 and sliding ECR values of ~35 mΩ. Nanoindentation hardness increases of these films (~2.6 GPa for 5 vol% ZnO) are correlated to microstructure via high resolution TEM and scanning electron microscope cross-sections to both Hall-Petch and Orowan strengthening mechanisms. Also presented is a correlation between electrical resistivity and grain size in the oxide dilute range based on the Mayadas-Shatzkes (M-S) electron scattering model. Using the M-S model in combination with a model describing solute drag stabilized grain growth kinetics we present a new technique to probe grain boundary mobility and thermal stability from in-situ electrical resistivity measurements during annealing experiments.

Made available in DSpace on 2014-10-09T12:34:12Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:06:46Z (GMT). No. of bitstreams: 0 / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Made available in DSpace on 2014-10-09T12:34:12Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:06:46Z (GMT). No. of bitstreams: 0 / O objetivo do presente trabalho consistiu no desenvolvimento de fios de liga de cobre-cromo-zircônio (CuCrZr) em uma composição estabelecida em Cu-0,7%Cr- 0,1%Zr (em massa). Nas etapas desenvolvidas, foram feitos botões de cobrecromo (CuCr) e cobre-zircônio (CuZr) em um forno a arco elétrico de eletrodo não consumível, sendo esses botões, posteriormente, fundidos junto com cargas de cobre em um cadinho de alumina (Al2O3) inserido no interior de um vaso de aço inoxidável, que serviu como suporte. Após a fusão dos botões e cargas, o banho foi vazado em uma coquilha de cobre, obtendo-se os tarugos da liga de cobre. Dos tarugos em estado bruto de fusão, foram retiradas amostras para ensaios de dureza Vickers. Nesses tarugos foi feito um tratamento térmico de homogeneização a 910 °C por 2 h. Os tarugos foram posteriormente trabalhados mecanicamente a frio por forjamento rotativo seguido de trefilação, para obtenção final dos fios no calibre de 2,174 mm. Os fios passaram por dois tratamentos térmicos de recristalização, um a 510 °C por 1 h e outro de 480 °C por 5 h. Os fios foram caracterizados mecanicamente por ensaios de tração e de dureza e os resultados foram comparados com dados experimentais da literatura. / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

The electric grid is important in modern society, so the outages should be few. The transmission grid should have a real high availability, since it transports electrical energy across the country. Then, it is difficult to plan outages for maintenance and installation. This thesis lists twenty surveys about failures of circuit breakers and disconnectors, with data about the cause and the lifetime. It also contains a survey of about forty condition-measuring methods for circuit breakers and disconnectors, mostly applicable to the electric contacts and the mechanical parts. As there is no published method to monitor the electric contacts at voltages around 400 kV, a system with IR sensors has been installed at the nine contacts of six disconnectors. The purpose is to avoid outages for maintenance by estimating the condition of the contacts while the disconnectors are still connected to high voltage. The measured temperatures are collected by radio and regressed against the square of the current, since the best exponent for the current was found to be 2.0. The coefficient of determination $R^2$ is high, greater than 0.9. This gives for each contact a regression coefficient, which can serve as an estimate of the condition of the contact. The higher the coefficient is, the more heat is produced at the contact, which can damage the material. This enables a ranking of the different contacts and shows which the worst ones are. This coefficient can also give a dynamic rating of the disconnector. / Elnätet är viktigt i det moderna samhället, så antalet avbrott bör vara lågt. Särskilt stamnätet bör ha en särskilt hög tillgänglighet, då det transporterar elektrisk energi tvärsöver landet. Då blir det svårt att planera avbrott för underhåll och utbyggnad. Denna avhandling tar upp tjugo studier av fel i brytare och frånskiljare med data om felorsak och livslängd. Den har också en översikt av ett fyrtiotal olika metoder för tillståndsmätningar för brytare och frånskiljare, som huvudsakligen rör de elektriska kontakterna och de mekaniska delarna. Eftersom det inte finns någon beskriven metod för att övervaka elektriska kontakter för spänningar på runt 400 kV, har ett system med IR sensorer installerats på de nio kontakterna på sex frånskiljare. Målet är att minska antalet avbrott för underhåll genom att skatta skicket hos kontakterna, när frånskiljarna fortfarande är kopplade till högspänning. De uppmätta temperaturerna tas emot genom radio och behandlas genom regression mot kvadraten av strömmen, då den bästa exponenten för strömmen visade sig vara 2,0. Förklaringsfaktorn $R^2$ är hög, över 0,9. För varje kontakt ger det en regressionskoefficient, som blir en skattning av kontaktens skick. Ju högre koefficienten är, desto mer värme utvecklas det i kontakten, vilket kan leda till skador på materialet. Kontakternas olika koefficienter ger en rankordning dem och därmed en möjlighet att prioritera vilken frånskiljare som ska underhållas först. Systemet kan också användas för att minska eller öka den tillåtna strömmen baserat på skicket. / <p>QC 20150522</p>