<p>Diamond and cubic boron nitride surfaces have extreme properties that can be exploited in novel tribological, electrochemical and electronic applications. Normally insulating diamond surfaces can exhibit high surface conductivities due to hydrogen termination and the nature of the surrounding atmosphere. Successful growth of cubic boron nitride thin films is hindered when harsh synthesis methods are used.</p><p>Three significant surface-related properties are addressed in this thesis using computational methods: (1) the structure, energy stability and reactivity of clean and differently terminated diamond surfaces, (2) the high surface conductivity of diamond, and (3) the adsorption-induced stability, reactivity and reconstruction of the cubic boron nitride (100) surface. Density Functional Theory (DFT) has been used at the GGA level under periodic boundary conditions to simulate the diamond and cubic boron nitride surfaces. </p><p>The diamond surface structures are shown to be insensitive to hydrogen desorption. Oxygen atoms bind in different positions and with different bond strengths. Hydroxyl groups experience both attractive hydrogen bonding and steric repulsions within the adsorbed species. The reconstruction of diamond (111)-1x1 is strongly dependent on the species adsorbed onto the surface. Electron transfer was observed from a diamond surface into a water-based adlayer, yielding a p-type doped surface, depending on the nature of the surface and the adlayer. The cubic boron nitride (100)-1x1 surface was shown to reconstruct into a 2x1 configuration on both the boron- and nitrogen-rich side through the formation of B-B bonds, as well as N–N dimer-induced surface relaxation. Hydrogen stabilized the (100)-1x1 surface, but the partial removal of hydrogen yielded non-reactive dimer formation on the surface. </p>

Diamond and cubic boron nitride surfaces have extreme properties that can be exploited in novel tribological, electrochemical and electronic applications. Normally insulating diamond surfaces can exhibit high surface conductivities due to hydrogen termination and the nature of the surrounding atmosphere. Successful growth of cubic boron nitride thin films is hindered when harsh synthesis methods are used. Three significant surface-related properties are addressed in this thesis using computational methods: (1) the structure, energy stability and reactivity of clean and differently terminated diamond surfaces, (2) the high surface conductivity of diamond, and (3) the adsorption-induced stability, reactivity and reconstruction of the cubic boron nitride (100) surface. Density Functional Theory (DFT) has been used at the GGA level under periodic boundary conditions to simulate the diamond and cubic boron nitride surfaces. The diamond surface structures are shown to be insensitive to hydrogen desorption. Oxygen atoms bind in different positions and with different bond strengths. Hydroxyl groups experience both attractive hydrogen bonding and steric repulsions within the adsorbed species. The reconstruction of diamond (111)-1x1 is strongly dependent on the species adsorbed onto the surface. Electron transfer was observed from a diamond surface into a water-based adlayer, yielding a p-type doped surface, depending on the nature of the surface and the adlayer. The cubic boron nitride (100)-1x1 surface was shown to reconstruct into a 2x1 configuration on both the boron- and nitrogen-rich side through the formation of B-B bonds, as well as N–N dimer-induced surface relaxation. Hydrogen stabilized the (100)-1x1 surface, but the partial removal of hydrogen yielded non-reactive dimer formation on the surface.

abstract: Overhead high voltage transmission lines are widely used around the world to deliver power to customers because of their low losses and high transmission capability. Well-coordinated insulation systems are capable of withstanding lightning and switching surge voltages. However, flashover is a serious issue to insulation systems, especially if the insulator is covered by a pollution layer. Many experiments in the laboratory have been conducted to investigate this issue. Since most experiments are time-consuming and costly, good mathematical models could contribute to predicting the insulator flashover performance as well as guide the experiments. This dissertation proposes a new statistical model to calculate the flashover probability of insulators under different supply voltages and contamination levels. An insulator model with water particles in the air is simulated to analyze the effects of rain and mist on flashover performance in reality. Additionally, insulator radius and number of sheds affect insulator surface resistivity and leakage distance. These two factors are studied to improve the efficiency of insulator design. This dissertation also discusses the impact of insulator surface hydrophobicity on flashover voltage. Because arc propagation is a stochastic process, an arc could travel on different paths based on the electric field distribution. Some arc paths jump between insulator sheds instead of travelling along the insulator surfaces. The arc jumping could shorten the leakage distance and intensify the electric field. Therefore, the probabilities of arc jumping at different locations of sheds are also calculated in this dissertation. The new simulation model is based on numerical electric field calculation and random walk theory. The electric field is calculated by the variable-grid finite difference method. The random walk theory from the Monte Carlo Method is utilized to describe the random propagation process of arc growth. This model will permit insulator engineers to design the reasonable geometry of insulators, to reduce the flashover phenomena under a wide range of operating conditions. / Dissertation/Thesis / Doctoral Dissertation Engineering 2016

abstract: Potential induced degradation (PID) due to high system voltages is one of the major degradation mechanisms in photovoltaic (PV) modules, adversely affecting their performance due to the combined effects of the following factors: system voltage, superstrate/glass surface conductivity, encapsulant conductivity, silicon nitride anti-reflection coating property and interface property (glass/encapsulant; encapsulant/cell; encapsulant/backsheet). Previous studies carried out at ASU's Photovoltaic Reliability Laboratory (ASU-PRL) showed that only negative voltage bias (positive grounded systems) adversely affects the performance of commonly available crystalline silicon modules. In previous studies, the surface conductivity of the glass surface was obtained using either conductive carbon layer extending from the glass surface to the frame or humidity inside an environmental chamber. This thesis investigates the influence of glass surface conductivity disruption on PV modules. In this study, conductive carbon was applied only on the module's glass surface without extending to the frame and the surface conductivity was disrupted (no carbon layer) at 2cm distance from the periphery of frame inner edges. This study was carried out under dry heat at two different temperatures (60 °C and 85 °C) and three different negative bias voltages (-300V, -400V, and -600V). To replicate closeness to the field conditions, half of the selected modules were pre-stressed under damp heat for 1000 hours (DH 1000) and the remaining half under 200 hours of thermal cycling (TC 200). When the surface continuity was disrupted by maintaining a 2 cm gap from the frame to the edge of the conductive layer, as demonstrated in this study, the degradation was found to be absent or negligibly small even after 35 hours of negative bias at elevated temperatures. This preliminary study appears to indicate that the modules could become immune to PID losses if the continuity of the glass surface conductivity is disrupted at the inside boundary of the frame. The surface conductivity of the glass, due to water layer formation in a humid condition, close to the frame could be disrupted just by applying a water repelling (hydrophobic) but high transmittance surface coating (such as Teflon) or modifying the frame/glass edges with water repellent properties. / Dissertation/Thesis / M.S.Tech Engineering 2012

Extending electronic devices beyond the limitations of current micro-electronics manufacturing will require detailed knowledge of how to make contacts to semiconductor surfaces. In this work, we investigated several methods by which such connections to silicon surfaces could be achieved. Scanning tunneling microscopy (STM) was our main experimental tool, allowing direct imaging of the surfaces at the atomic level. First, the growth of self-forming linear nanostructures of organic molecules on silicon surfaces offers a possibility of creating devices with hybrid organic-silicon functionality. We have studied the growth of many different molecules on a variety of hydrogen-terminated silicon surfaces: H-Si(100)-2x1, H-Si(100)-3x1, and H-Si(111)-1x1. We found molecular growth patterns affected by steric crowding, by sample doping level, or by exposure to ion-pump created radicals. We formed the first contiguous "L-shaped" molecular lines, and used an external electric field to direct molecular growth. We attempted to study a novel method for nanoscale information transfer along molecular lines based on excitation energy transfer. The second part of the work focuses on the development and use of a new multiple-probe STM instrument. The design and the custom STM control software written for it are described. Connections to Si surfaces were achieved with a combination of lithographically defined metal contacts and STM tips. Two-dimensional surface conductivity of the Si(111)-7x7 surface was measured, and the effect of modifying the surface with organic molecules was investigated. A novel method, scanning tunneling fractional current imaging (STFCI), was developed to further study surface conductance. This method allowed us to determine, for the first time, that the resistance of steps on the Si(111)-7x7 surface is significantly higher than that of the surface alone.

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The Master’s Thesis deals with supercapacitators based on principle of eletrical double layer. At the outset there is an explanation of supercapacitor working principal. We discussed advantages and disavantages supercapacitators compared with other related elements in electrotechnics. Materials based on carbon and their structure for production supercapacitators are described too. In next part of Thesis we mention different methods and techniques for the measurement and the evaluation of supercapacitators‘s capacities. Optimal materials for production supercapacitators are presented in conclusion.

No description available.

No description available.