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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Nano-rods wo₃- δ for electrochromic smart windows applications

Sibuyi, Praise January 2006 (has links)
<p>Tungsten oxide is a good electrochromic material which has been used in the construction of smart windows through visible modulation. These smart materials can reversibly change their optical properties with the application of an external voltage. Their ability to lighten and darken on command is ideally suited for energy-efficiency windows. The process itself or the overall reaction should respond in seconds and as quick as possible. The goal of this project was to prepare epitaxial well defined tungsten oxide nanorods by the thermal evaporation technique.</p>
2

Nanostructured Metal Oxide Coatings for Electrochemical Energy Conversion and Storage Electrodes

Cordova, Isvar Abraxas January 2016 (has links)
<p>The realization of an energy future based on safe, clean, sustainable, and economically viable technologies is one of the grand challenges facing modern society. Electrochemical energy technologies underpin the potential success of this effort to divert energy sources away from fossil fuels, whether one considers alternative energy conversion strategies through photoelectrochemical (PEC) production of chemical fuels or fuel cells run with sustainable hydrogen, or energy storage strategies, such as in batteries and supercapacitors. This dissertation builds on recent advances in nanomaterials design, synthesis, and characterization to develop novel electrodes that can electrochemically convert and store energy.</p><p>Chapter 2 of this dissertation focuses on refining the properties of TiO2-based PEC water-splitting photoanodes used for the direct electrochemical conversion of solar energy into hydrogen fuel. The approach utilized atomic layer deposition (ALD); a growth process uniquely suited for the conformal and uniform deposition of thin films with angstrom-level thickness precision. ALD’s thickness control enabled a better understanding of how the effects of nitrogen doping via NH3 annealing treatments, used to reduce TiO2’s bandgap, can have a strong dependence on TiO2’s thickness and crystalline quality. In addition, it was found that some of the negative effects on the PEC performance typically associated with N-doped TiO2 could be mitigated if the NH3-annealing was directly preceded by an air-annealing step, especially for ultrathin (i.e., < 10 nm) TiO2 films. ALD was also used to conformally coat an ultraporous conductive fluorine-doped tin oxide nanoparticle (nanoFTO) scaffold with an ultrathin layer of TiO2. The integration of these ultrathin films and the oxide nanoparticles resulted in a heteronanostructure design with excellent PEC water oxidation photocurrents (0.7 mA/cm2 at 0 V vs. Ag/AgCl) and charge transfer efficiency. </p><p>In Chapter 3, two innovative nanoarchitectures were engineered in order to enhance the pseudocapacitive energy storage of next generation supercapacitor electrodes. The morphology and quantity of MnO2 electrodeposits was controlled by adjusting the density of graphene foliates on a novel graphenated carbon nanotube (g-CNT) scaffold. This control enabled the nanocomposite supercapacitor electrode to reach a capacitance of 640 F/g, under MnO2 specific mass loading conditions (2.3 mg/cm2) that are higher than previously reported. In the second engineered nanoarchitecture, the electrochemical energy storage properties of a transparent electrode based on a network of solution-processed Cu/Ni cores/shell nanowires (NWs) were activated by electrochemically converting the Ni metal shell into Ni(OH)2. Furthermore, an adjustment of the molar percentage of Ni plated onto the Cu NWs was found to result in a tradeoff between capacitance, transmittance, and stability of the resulting nickel hydroxide-based electrode. The nominal area capacitance and power performance results obtained for this Cu/Ni(OH)2 transparent electrode demonstrates that it has significant potential as a hybrid supercapacitor electrode for integration into cutting edge flexible and transparent electronic devices.</p> / Dissertation
3

Nonlinear Applications using Silicon Nanophotonic Wires

Liu, Xiaoping January 2011 (has links)
This thesis is concerned with an emerging set of nonlinear-optical applications using silicon nanophotonic "wires" fabricated on a silicon-on-insulator photonic chip. These deeply scaled silicon nanophotonic wires are capable of confining the telecom and mid-infrared (mid-IR) light tightly into an optical-modal area ~ 0.1 μm2. The tight optical confinement leads to many advantageous physical properties including enhanced effective nonlinearity, flexible control of waveguide dispersion, and short free-carrier lifetime. All these advantages make silicon nanophotonic wires an ideal platform for a variety of nonlinear applications. The first part of my thesis study is focused on nonlinear applications in the telecom bands. In Chapter 3, I study the frequency dependence of optical nonlinearity in silicon nanophotonic wires, and its influence on the propagation of ultra-short optical pulses in such wires. I show that silicon nanophotonic wires possess a remarkably large characteristic time associated with the self-steepening effect and optical-shock formation. In Chapter 4, I present an experimental demonstration of an ultrafast cross-phase-modulation-based wavelength-conversion (XPM-WC) technique for telecom RZ-OOK data. I also investigate the effect of pump-probe detuning on the efficacy of this XPM-WC technique. In Chapter 5, I show a (primarily) numerical study of a method for dispersion-engineering of silicon nanophotonic wires using a conformal thin-silicon-nitride dielectric film deposited around the silicon wire core. My simulation results show that this approach may be used to achieve the dispersion characteristics required for broadband phase-matched four-wave-mixing processes, while simultaneously maintaining strong modal confinement within the silicon core for high effective nonlinearity. The second part of my thesis is devoted to investigations of nonlinear applications in mid-IR spectral region, in which nonlinear optical loss due to parasitic two-photon absorption can be significantly reduced and therefore a large nonlinear figure of merit can be achieved in order to facilitate efficient nonlinear processes. In Chapter 6, I present an experimental demonstration of a mid-IR-silicon-nanophotonic-wire optical parametric amplifier with 25.4 dB on-chip gain. This gain achieved with only a 4-mm-long silicon nanophotonic wire is sufficient enough to overcome all the insertion loss, resulting in 13 dB net off-chip amplification. In addition, I show, on the same waveguide, efficient generation of 4 orders of cascaded FWM products enabled by the large on-chip gain. In Chapter 7, I report a comprehensive study of the propagation characteristics of a picosecond pulse through a 4-mm-long silicon nanophotonic wire with normal dispersion with excitation wavelengths crossing the mid-infrared two-photon absorption edge at λ = 2200 nm. Significant reduction in nonlinear loss due to two-photon absorption is demonstrated as the excitation wavelengths approach 2200 nm. Self-phase modulation at high input power is also observed. Analysis of experimental data and comparison with numerical simulations illustrates that the two-photon absorption coefficient obtained from nanophotonic wire measurements is in reasonable agreement with prior measurements of bulk silicon crystals, and that bulk silicon values of the nonlinear refractive index can be confidently incorporated in the modeling of pulse propagation in deeply-scaled waveguide structures. In Chapter 8, I investigate a higher-order phase matching technique utilizing the 4th-order dispersion term for realizing a broadband or discrete band parametric process in silicon nanophotonic wires. I demonstrate experimentally, on a silicon nanophotonic wire designed to exhibit a desired 2nd-order and 4th-order dispersion, broadband/discrete-band modulation instability and 50 dB Raman assisted parametric gain.
4

Performance analysis of fault-tolerant nanoelectronic memories

Coker, Ayodeji 15 May 2009 (has links)
Performance growth in microelectronics, as described by Moore’s law, is steadily approaching its limits. Nanoscale technologies are increasingly being explored as a practical solution to sustaining and possibly surpassing current performance trends of microelectronics. This work presents an in-depth analysis of the impact on performance, of incorporating reliability schemes into the architecture of a crossbar molecular switch nanomemory and demultiplexer. Nanoelectronics are currently in their early stages, and so fabrication and design methodologies are still in the process of being studied and developed. The building blocks of nanotechnology are fabricated using bottom-up processes, which leave them highly susceptible to defects. Hence, it is very important that defect and fault-tolerant schemes be incorporated into the design of nanotechnology related devices. In this dissertation, we focus on the study of a novel and promising class of computer chip memories called crossbar molecular switch memories and their demultiplexer addressing units. A major part of this work was the design of a defect and fault tolerance scheme we called the Multi-Switch Junction (MSJ) scheme. The MSJ scheme takes advantage of the regular array geometry of the crossbar nanomemory to create multiple switches in the fabric of the crossbar nanomemory for the storage of a single bit. Implementing defect and fault tolerant schemes come at a performance cost to the crossbar nanomemory; the challenge becomes achieving a balance between device reliability and performance. We have studied the reliability induced performance penalties as they relate to the time (delay) it takes to access a bit, and the amount of power dissipated by the process. Also, MSJ was compared to the banking and error correction coding fault tolerant schemes. Studies were also conducted to ascertain the potential benefits of integrating our MSJ scheme with the banking scheme. Trade-off analysis between access time delay, power dissipation and reliability is outlined and presented in this work. Results show the MSJ scheme increases the reliability of the crossbar nanomemory and demultiplexer. Simulation results also indicated that MSJ works very well for smaller nanomemory array sizes, with reliabilities of 100% for molecular switch failure rates in the 10% or less range.
5

Nanophotonics in Diamond

Hausmann, Birgit Judith Maria 07 June 2014 (has links)
Diamond nanophotonics have evolved tremendously from the study of color centers in bulk single crystals and nanocrystals to their characterization in nanostructured environments. This development was facilitated by the ability to generate monolithic, sophisticated nanodevices in high quality single crystal diamond. This thesis presents some recent contributions to the field of diamond nanophotonics: Increase in single photon collection from NV centers embedded in diamond nanowires, broadband spontaneous emission enhancement of single NV centers in plasmonic resonators, and coupling of single NV centers to planar resonators on-chip such as ring resonators and photonic crystal cavities. In addition, the generation of high quality integrated diamond devices allows for the exploration of nonlinear processes in diamond. Here, we show for the first time optical parametric oscillations in diamond resonators. / Engineering and Applied Sciences
6

Nano-rods wo₃- δ for electrochromic smart windows applications

Sibuyi, Praise January 2006 (has links)
<p>Tungsten oxide is a good electrochromic material which has been used in the construction of smart windows through visible modulation. These smart materials can reversibly change their optical properties with the application of an external voltage. Their ability to lighten and darken on command is ideally suited for energy-efficiency windows. The process itself or the overall reaction should respond in seconds and as quick as possible. The goal of this project was to prepare epitaxial well defined tungsten oxide nanorods by the thermal evaporation technique.</p>
7

Algorithms and techniques for conquering extreme physical variation in bottom-up nanoscale systems

Gojman, Benjamin. Desbrun, Mathieu. DeHon, André. January 1900 (has links)
Thesis (Masters) -- California Institute of Technology, 2010. / Title from home page (viewed 04/12/10). Advisor and committee chair names found in the thesis' metadata record in the digital repository. Includes bibliographical references.
8

Nano-rods WO3-δ for electrochromic smart windows applications

Sibuyi, Praise January 2006 (has links)
>Magister Scientiae - MSc / Tungsten oxide is a good electrochromic material which has been used in the construction of smart windows through visible modulation. These smart materials can reversibly change their optical properties with the application of an external voltage. Their ability to lighten and darken on command is ideally suited for energy-efficiency windows. The process itself or the overall reaction should respond in seconds and as quick as possible. The goal of this project was to prepare epitaxial well defined tungsten oxide nanorods by the thermal evaporation technique. / South Africa
9

Production of nanosized (V,W)C powder by mechanical alloying

Bolokang, Sylvester Amogelang 27 August 2012 (has links)
M.Ing. / This work is an investigation into the production of nanosized vanadium-tungsten-carbide [V,W)C] powder by mechanical alloying (MA) starting from vanadium (V), tungsten (W) and amorphous carbon (C) powders. The milling conditions were optimized first for the production of tungsten carbide (WC) due to the high cost of V powder with variations of W/C ratios to determine the minimum time required (at a selected energy) to obtain a full synthesis, i.e. to obtain only carbide without primary powders left. Ball to powder ratio (BPR) of 11:1 at 300 revolutions per minute (rpm) was used with stoichiometric carbon for WC, and using the equilibrium formula (Vo.7,Wo.3)Ci_x ) for (V,W)C. The powder phase composition was monitored by X-ray diffraction (XRD), shape and morphology was monitored by scanning electron microscopy (SEM). The production of synthesized nanocrystallite (V,W)C and WC without residual elemental powders required different times. WC powder required 8 hours of MA, while (V,W)C required 40 hours. On account of the difficult choice of stoichiometry, in general WC was also formed together with (V,W)C but the WC formation will be useful in final WC-(V,W)C-Co alloy for toughness. Crystallite sizes of about 8 to 11 nm were obtained from synthesized (V,W)C, and WC powders respectively. The amount of free carbon was measured on both synthesized WC and (V,W)C by a Leco carbon analyzer. Free carbon was found to be 2.05 wt % for WC, and 5.83 wt % for (V,W)C. Oxygen content was also measured on both the synthesized powders, to check if oxidation had occurred. The amount of oxygen in (V,W)C was measured to be 9.2 wt % higher than that of WC which was measured to be 2.7 wt %.
10

Bold and Small: Using Nanotechnology for Magnetic Filtration of an Inorganic Pigment Liquid Slurry

McRorie, Aaron January 1900 (has links)
Master of Science / Department of Chemical Engineering / James H. Edgar / I am a current employee for a chemical company that makes complex inorganic color pigments for a variety of uses. Some of the applications require iron as a base for a black color variant; but several require a purity level that precludes iron. One such product that cannot have iron in it is a computer based application that requires absolute purity of only the copper-chrome based powder with no impurities. This color is a powder that is primarily composed of copper and chrome and has the distinct advantage that it has little-to-no magnetic susceptibility. This makes it ideal for mixing with a form of acrylic for coating circuit boards and other computer applications as a magnetic field could severely damage circuits. Unfortunately, the presence of impurities (particularly ferromagnetic iron) can increase the magnetic susceptibility of the powder. We are here to discuss the search for a system to filter out such impurities.

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