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<p>As the production and use of nanoparticles (NPs) has increased, so has concern over their effects on the environment and aquatic organisms. While the majority of research on the toxicity of NPs has been performed using controlled laboratory conditions, little is known about their effects in more complex environments. The goal of this dissertation is to understand how incorporating increasing levels of environmental complexity affects the study of NP toxicity to early life stage fish. In particular, goals included evaluating the impact of increasing environmental complexity on silver NP (AgNP) toxicity to young Atlantic killifish and zebrafish and exploring how photocatalytic degradation of benzo(a)pyrene (BaP) by TiO2 NPs affected toxicity to young zebrafish.</p><p>In order to incorporate high environmental complexity into AgNP toxicity studies, a range of experimental systems were used. First, mesocosms built to simulate freshwater North Carolina wetlands were dosed with gum Arabic-coated AgNPs (GA-AgNPs), polyvinylpyrollidone-coated AgNPs (PVP AgNPs) and AgNO3 as the most ecologically relevant scenario. Mortality induced by samples taken from these mesocosms to embryonic and larval Atlantic killifish was compared to mortality induced by of samples prepared in the laboratory. For embryonic killifish, samples taken from the mesocosms caused significantly less mortality than samples prepared in the laboratory for all types of silver. However, for larval killifish, toxicity of GA-AgNPs from mesocosms was not lower than toxicity of those from the laboratory and toxicity of PVP-AgNPs was actually higher in mesocosm samples. Mortality caused by AgNO3 was significantly less in samples from the mesocosms than from the laboratory, similar to results found in embryos. For larvae, both types of NPs from the mesocosms were more toxic than AgNO3. </p><p>In order to understand the difference in results seen between mesocosm samples and laboratory samples, a microcosm approach was used to assess the individual contributions of plants, soil, and natural water to the mediation of AgNP toxicity. In addition, samples were thoroughly characterized in order to understand how these factors were influencing. Silver speciation was assessed using x-ray absorption near edge structures spectroscopy, extent of AgNP aggregation and dissolution using flow field flow fractionation coupled with inductively coupled plasma mass spectrometry (FFFF-ICP-MS), and total silver and dissolved silver quantified using ICP-MS. Organic matter quantity and quality were also measured using total organic carbon (TOC) analysis and fluorescence excitation-emission spectroscopy (EEMS). Ultimately, although plant-derived organic matter was shown to significantly influence silver speciation and AgNP aggregation, these experiments were not able to replicate the interesting results seen with killifish larvae from the mesocosms on a smaller scale. In experiments using zebrafish embryos, the presence of plants was correlated with reduced toxicity. However, this correlation could not be attributed to any of the changes seen in AgNP or silver characteristics due to reduced water column concentrations of silver that also occurred when plants were present. </p><p>Due to the differences seen in mesocosm and microcosm results, I hypothesized that ultraviolet (UV) light could be playing a role in mediating AgNP toxicity. AgNPs and AgNO3 were illuminated using a solar simulator prior to dosing zebrafish embryos. UV light was found to decrease GA-AgNP and AgNO3 toxicity and to increase PVP-AgNP toxicity. Ultraviolet-visible light (UV-vis) spectra of AgNPs and AgNO3 after exposure to UV light indicated changes in size distribution and aggregation. These changes could be due to photolysis of coatings leading to increased dissolution of silver and destabilization of the NPs.</p><p>I also explored the effect of TiO2 NP facilitated photocatalytic degradation of toxicity of BaP. Due to the unique photocatalytic properties of TiO2 NPs, they are not only being proposed for use as a remediation aid for recalcitrant organic contaminants but also possess the ability to transform organic co-contaminants in the environment and change their toxicity and risk to aquatic organisms. BaP was degraded with TiO2 using a solar simulator before dosing young zebrafish. Degradation resulted in increased cytochrome P450 (CYP) activity, a marker of polycyclic aromatic hydrocarbon (PAH) exposure and toxicity as well as increased mortality. However, these effects ultimately proved to be dependent on the presence of DMSO, a carrier solvent for BaP, and thus their environmental relevance is questionable.</p><p>Taking environmental complexity into account is an important part of understanding engineered NP risk. I found that AgNP toxicity is highly dependent on environmental matrix and individual factors such as UV, and that TiO2 NPs have the potential to influence toxicity of organic contaminants. Ultimately, ecologically appropriate and relevant risk assessment of NPs to aquatic organisms will rely on fully characterizing how the fate, behavior, and toxicity of NPs is influenced by environmental factors such as plants, sediments, bacteria, organic matter, ionic strength, and UV light.</p> / Dissertation

This thesis investigates ways of improving the performance of fundamental silicon nanophotonic devices through post-fabrication processes. These devices include numerous optical resonator designs as well as slow-light waveguides. Optical resonators are used to confine photons both spatially and temporally. In recent years, there has been much research, both theoretical and experimental, into improving the design of optical resonators. Improving these devices through fabrication processes has generally been less studied. Optical waveguides are used to guide the flow of photons over chip-level distances. Slow-light waveguides have also been studied by many research groups in recent years and can applied to an increasingly wide-range of applications. The work can be divided into several parts: Chapter 1 is an introduction to the field of silicon photonics as well as an overview of the fabrication, experimental and computational techniques used throughout this work. Chapters 2, 3 and 4 describe our investigations into the precision tuning of nanophotonic devices using laser-assisted oxidation and atomic layer deposition. Chapters 5 and 6 describe our investigations into improving the sidewall roughness of silicon photonic devices using hydrogen annealing and excimer laser induced melting. Finally, Chapter 7 describes our investigations into the nonlinear properties of lead chalcogenide nanocrystals.

Since their discovery in 1991, carbon nanotubes have proven to be a very interesting material for its physical strength, originating from the pure carbon lattice and strong covalent sp2 orbital bonds, and electronic properties which are derived from the lattice structure lending itself to either a metallic or semiconducting nature among its other properties. Carbon nanotubes have been researched with an eye towards industry applications ranging from use as an alloy in metals and plastics to improve physical strength of the resulting materials to uses in the semiconductor industry as either an interconnect or device layer for computer chips to chemical or biological sensors. This thesis focuses on both the synthesis of individual single-walled carbon nanotubes as well as the electrical properties of those tubes. What makes the work herein different from that of other thesis is that the research has been performed on carbon nanotubes of known chirality. Having first grown carbon nanotubes with a chemical vapor deposition growth in a quartz tube using ethanol vapor as a feedstock to grow long individual single-walled carbon nanotubes on a silicon chip that is also compatible with Rayleigh scattering spectroscopy to identify the chiral indices of the carbon nanotubes in question, those tubes were then transferred with a mechanical transfer process specially designed in our research lab onto a substrate of our choosing before an electrical device was made out of those tubes using standard electron beam lithography. The focus in this thesis is on the work that went into designing and testing this process as well as the initial results of the electronic properties of those carbon nanotubes of known chirality, such as the first known electrical measurements on single individual armchair carbon nanotubes as well as the first known electrical measurements of a single semiconducting carbon nanotube on thin hexagonal boron nitride to study the effects of the surface optical phonons from the boron nitride on the electrical properties of the carbon nanotube. Finally a few research projects are discussed in which carbon nanotubes of known chirality were used in conjunction with first electrical tests on molecules, secondly on a prefabricated complementary metal-oxide-semiconductor integrated circuit as an inverter and lastly to study the photoconductivity generated by a synchrotron laser source to identify the values for the low energy excitonic peak.

Due to the advances in nanotechnology and its growing of potential applications, it is evident that the development of practical technologies for the manipulation of nanostructures is essential. The focus of this dissertation is to develop an integrated nanomanipulation system that would be able to image, manipulate as well as fabricate micro/nano-scaled structures in a controlled manner. The system consists of four main components: an Atomic Force Microscope (AFM) for obtaining topographic information of sample surfaces, a haptic device controlled by a server which generates the force environment, a molecular dynamics simulation for determinations of the effects of force application on nano particles, and a visualization program for display of the results. An extended platform with high precision and accuracy is included for broadening the workspace. The interface would be implemented for direct interaction with nano molecules. The users are then allowed to see, touch and manipulate such particles. By the principle of contact mechanics, the tip-sample interaction forces and intermolecular forces between the tip and surface can be modeled; calculated forces are used to predict the results of each operation. The proposed nanomanipulation model facilitates further improvement to accommodate other physical phenomena that characterize the mechanics of nanomanipulation. / Nanotechnology has been defined as a description of activities at the atomic level that have applications in the real world. Advances in the field of nanotechnology have expanded the breadth of potential applications tremendously in recent years, which also leads to rapid growth of several research and development areas throughout the world. Recent development in microelectronics, nano-optics and generic chips shows the trend driving towards miniaturization. Gaining access to the nano world also enable us to make further advances in obtaining precise measurement of material properties and exploring fundamental physical laws at the atomic level. / The aim for developing such an integrated system is for prototyping of optics components with micro/nano structures, especially for diffractive optics elements (DOE) and optical lightguide. Diffractive optics is a transmissive diffraction grating with a series of closely ruled lines on a piece of transmissive substrate, A collimated beam of monochromatic light incident on a grating will result in the defined light diffraction pattern. The lightguide is being commonly adopted in backlight system, the spatially varying extraction pattern will couple flux out of the light guide to produce a spatially uniform luminance distribution. Determining the ruled lines for diffraction grating and extraction pattern for lightguide is greatly facilitated through the use of optimization. With the imposition of nonlinear constraints, optimization is achieved by incorporating the approximating function into an optimization algorithm. The micro/nano patterns on DOE and optical lightguide are feasible to be fabricated by the integrated nanomanipulation system with the AFM probe tip as a cutting tool. The characteristics of the AFM probe tip are also taken into account when designing the optical elements. / The developed system has been validated by different experiments, including raster scanning, nanoindentation and nanomanipulation testing. New application of nanomanipulation in photonics has been explored. With the proposed nanostructure fabrication techniques, several optical components can be fabricated in a more efficient and cost-effective way. / Fok, Lo Ming. / Adviser: Yun Hui Lin. / Source: Dissertation Abstracts International, Volume: 71-01, Section: B, page: 0611. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2009. / Includes bibliographical references (leaves 121-123). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. Ann Arbor, MI : ProQuest Information and Learning Company, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts in English and Chinese.

Thesis (M. Phil.)--University of Hong Kong, 2001. / Includes bibliographical references.

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<p>Heterogeneous catalysts are a major energy-saving tool in industrial chemical processes, both by reducing energy input requirements for reactions and also by reducing waste disposal costs. Currently, transition metals and platinum group metals in particular are the industry standard in terms of performance and roustness. Unfortunately, the most valuable catalytic materials of our time are also the most costly and scarce, and as such it is of considerable importance to find ways to optimize catalysts to be as effective as possible and to use a minimum of precious metal. One method of doing this is by constructing bimetallic nanoparticles, which, in addition to lessening the amount of expensive active metal required per gram of catalyst, has been shown in many cases to improve the performance of the catalyst. Our current understanding of the mechanisms by which the introduction of a second element to a first alters its catalytic properties is limited by how well we can characterize the structure of a catalysts, and this has been a considerable challenge. By developing uniform bimetallic nanoparticle catalysts that can be tuned to discretely change either the composition of the particle or the morphology of the particle, we can systematically study how the two metals interact to change the pathway of catalysis. The gold-palladium (AuPd) system is employed, because of its simplicity and ubiquity in the literature, to demonstrate this concept, which may be applied to other combinations of metals. By altering the amounts of Pd precursor, reducing agent, and reaction quenching agent, as well as varying the rate of introduction of Pd ion to the reaction solution, 4.3 nm Au core particles were coated with Pd shells determined to be 0.7 ± 0.2, 1.9 ± 0.3, and 3.8 ± 0.8 atomic monolayers thick. Upon immobilization on silica and calcination and reduction treatments at 300 &deg;C, the particles transformed to alloys containing 10, 20.2, and 28.5% by weight Pd per particle. A variety of spectroscopic and microscopic characterization techniques were used to investigate the bimetallic particles' ability to resist sintering during heating, as well as their shell-thickness dependent propensity to absorb hydrogen into their bulk. Testing the catalysts in the conversion of limonene to cymene demonstrated that the resistance to sintering imparted by the inclusion of Au allowed the 20 and 28.5% AuPd/SiO₂ catalysts to achieve higher selectivity to the desired product while minimizing the amount of Pd in the catalyst. The core-shell and alloy particles were compared to one another in the low temperature hydrogenation of ethylene, and it is shown that conversion of ethylene over the 1.9 Pd@Au/SiO₂ catalyst is structure sensitive, with its rate of conversion before calcination and reduction measured to be ten times higher than it is afterwards, likely because of its unique ability to store hydrogen near its surface. In general, these reactions demonstrate that the interactions between Au and Pd can be described in terms of experimentally observable effects, which occur as a consequence of the traditionally described geometric and electronic effects under a given set of experimental conditions. Using composite effects such as these, rather than ones that are difficult to isolate, will render our heightened understanding of the effect of structure on catalytic function more directly practicable in developing better catalysts for specific reactions.</p> / Dissertation