Thesis (M.S. in mechanical engineering)--Washington State University, December 2009. / Title from PDF title page (viewed on Feb. 4, 2010). "School of Mechanical and Materials Engineering." Includes bibliographical references (p. 42-45).

Thesis (Ph. D.)--University of Canterbury, 2009. / Typescript (photocopy). "October 2009." Includes bibliographical references (p. 147-162). Also available via the World Wide Web.

Thesis (DTech (Science))--Peninsula Technikon, 2003. / Word processed copy. Summary in English. Includes bibliographical references (leaves 171-189). Also available online.

Thesis (Ph. D.)--University of Texas at Austin, 2003. / Vita. Includes bibliographical references. Available also from UMI Company.

Lanthanide-doped upconversion nanoparticles (UCNPs) are perceived as promising novel near-infrared (NIR) bioimaging agents characterised by high contrast and high penetration depth. However, the interactions between charged UCNPs and mammalian cells have not been thoroughly studied and the corresponding intracellular uptake pathways remain unclear. Herein, my research work involved the use of hydrothermal method and ligand exchange approach to prepare UCNP-PVP, UCNP-PEI, and UCNP-PAA. These polymer-coated UCNPs demonstrated good water dispersibility, the similar size distribution as well as similar upconversion luminescence efficiency. However, the positively charged UCNP-PEI evinced greatly enhanced cellular uptake in comparison with its neutral or negative counterparts, as revealed by cellular uptake studies. Meanwhile, it was discovered that cationic UCNP-PEI could be effectively internalized mainly through the clathrin endocytic machanism. This study is the first report on the endocytic mechanism of positively charged lanthanide-doped UCNPs. Furthermore, it allows us to control the UCNP-cell interactions by tuning surface properties. Glioblastoma multiforme (GBM) is the most common and malignant form of primary brain tumors in humans. Small molecule MRI contrast agents are used for GBM diagnosis and preoperative tumor margin delineation. However, the conventional gadolinium-based contrast agents have several disadvantages, such as a relatively low T1 relaxivity, short circulation half lives and the absence of tumor targeting efficiency. Multimodality imaging probes provide a better solution to clearly delineate the localization of glioblastoma. My research work also involved the development of multimodal nanoprobes for targeted glioblastoma imaging. Two targeted paramagnetic/fluorescence nanoprobes were designed and synthesized, UCNP-Gd-RGD and AuNP-Dy680-Gd-RGD. UCNP-Gd-RGD was prepared through PEGylation, Gd3+DOTA conjugation and RGD labeling of PEI-coated UCNP-based nanoprobe core (UCNP-NH2). It adopted the cubic NaYF4 phase, had an average size of 36 nm by TEM, and possessed a relatively intense upconversion luminescence of Er3+ and Tm3+. It also exhibited improved colloidal stability and reduced cytotoxicity compared with UCNP-NH2, and a higher T1 relaxivity than Gd3+DOTA. AuNP-Dy680-Gd-RGD was synthesized through bioconjugation of amine-modified AuNP-based nanoprobe core (AuNPPEG- NH2) by a NIR dye (Dy680), Gd3+DOTA and RGD peptide. It demonstrated a size of 3–6 nm by TEM, relatively strong NIR fluorescence centered at 708 nm, longterm physiological stability, and an enhanced T1 relaxivity compared with Gd3+DOTA. Targeting abilities of both UCNP-Gd-RGD and AuNP-Dy680-Gd-RGD towards overexpressed integrin αvβ3 receptors on U87MG cell surface was confirmed by their enhanced cellular uptake visualized by confocal microscopy imaging and quantified by ICP-MS, where their corresponding control nanoprobes were used for comparison. Furthermore, targeted imaging capabilities of UCNP-Gd-RGD and AuNP-Dy680-Gd- RGD towards subcutaneous U87MG tumors were verified by in vivo and ex vivo upconversion fluorescence imaging studies and by in vivo and ex vivo NIR fluorescence imaging and in vivo MR imaging studies, respectively. These two synthesized targeted nanoprobes, with surface-bounded cyclic RGD peptide and numerous T1 contrast enhancing molecules, are applicable in targeted MR imaging glioblastoma and delineating the tumor boundary. In addition, UCNP-Gd-RGD favors the upconversion luminescence with NIR-to-visible nature, while AuNPDy680- Gd-RGD possesses NIR-to-NIR fluorescence, and both lead to their potential applications in fluorescence-guided surgical resection of gliomas. / published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

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<p> III-V self-assembled quantum dots (QDs) and quantum dashes (Q-dashes) grown by epitaxy have numerous applications for optoelectronics and quantum information. Such nanostructures are most commonly formed through strain-driven self-assembly on (001) surfaces. In this process, a thin layer of material deposited under compressive strain reorganizes into three dimensional islands. While compressive self-assembly on the (001) face produces QDs across a wide range of semiconductor materials, few successful reports have addressed QD growth under tensile strain or on other low-index surfaces. Growth of tensile-strained QDs tends to produce dislocations that impair their optical properties. This problem likewise occurs for QD attempts on (111) or (110) surfaces.</p><p> QDs grown under tensile strain or alternative surface orientations would exhibit previously unavailable properties, while providing access to new QD materials for novel optoelectronic devices. Most prominently, tensile strain strongly reduces the bandgaps of nanostructures, allowing them to emit light at much lower energies than they could under compressive strain for long wavelength optoelectronics. Secondly, QDs grown on (111) surfaces are promising candidates for generating polarization-entangled photons. The high electronic symmetry achievable in (111) QDs produces an ideal exciton fine structure for the emission of entangled-photon-pairs. Alternative techniques have been proposed to produce tensile nanostructures and (111) QDs, but these often involve complex processing requirements that lack the simplicity of strain-driven self-assembly.</p><p> To achieve dislocation-free growth of the desired QDs, a growth model is employed that describes the relationship between dislocation nucleation, surface orientation, and strain direction (tensile or compressive). This model shows that both tensile growth on the (001) surface and compressive growth on (111) or (110) surfaces suffers from low dislocation nucleation energy. Instead, dislocation-free QD growth can be achieved by combining the use of tensile strain with a (111) or (110) substrate.</p><p> Using this principle, the present work demonstrates the growth of tensile strained GaAs QDs and Q-dashes, using In_0.52Al_0.48As barriers, grown on IP (110), (111)B, and (111)A substrates by molecular beam epitaxy (MBE). The effects of growth conditions on self-assembly are investigated for each surface orientation, and these trends are utilized to tune the size, shape, and density of the nanostructures. Observations of dislocation-free tensile QDs or Q-dashes on each surface orientation confirm the predictions of the growth model. As a result, strong room temperature luminescence is visible from the nanostructures grown on each surface.</p><p> Due to the high tensile strain, the GaAs nanostructures emit photons as low as 240 meV below the normal bandgap of GaAs. The large bandgap reductions achievable under tension are anticipated to extend QD and Q-dash devices into longer wavelength ranges that are difficult to achieve by other means. Next, by achieving highly symmetric QDs on the (111)A surface, very low exciton tine structure splitting values are observed &ndash; a key requirement for producing entangled photons. Tensile self-assembly thus offers a simple approach for the growth of entangled photon emitters on (111) surfaces. Finally, the results of these QD investigations are anticipated to apply broadly to zinc-blende and diamond-cubic semiconductors, enabling novel devices with a wide range of properties.</p><p> The growth of lattice-matched InAlAs epilayers on InP (110), (111)B, and (111)A substrates is also extensively studied in this work to produce high quality buffer and barrier layers for quantum nanostructure growth. In addition, the development of (110) and (111) semiconductors would allow access to their unique properties, including different alignments of the internal polarization field, compatibility with growth of hexagonal materials, access to different zones of the electronic bandstructure, and long spin lifetimes. Due to these properties, such epilayers are under current investigation to support spintronics, topological insulators, transition metal dichalcogenides, and novel MOSFETs. However, epitaxy on these surface orientations is very challenging due to the formation of hillocks and rough surfaces. Little information is available for growing these semiconductors, which limits the material quality that can be achieved.</p><p> To support emerging (111) and (110) applications, the effects of growth conditions on the morphological, electrical, and optical properties of InAlAs, InGaAs, and InP, grown on InP wafers, are systematically studied for each substrate orientation. Growth parameters are identified that either eliminate or strongly reduce morphological defects on each surface. Conditions for optimizing photoluminescence, carrier mobility, and background doping are also reported. This work therefore offers a comprehensive guide to overcoming material challenges for both epilayers and QDs grown on (110) and (111)-oriented InP substrates. </p>

<p>Hybrid organic/inorganic photovoltaics can overcome many traditional shortcomings of organic photovoltaics, including recombination due to short exciton diffusion length scales, incomplete or tortuous charge transport pathways, and low charge mobility. In this work, aligned pore arrays are electrochemically etched into GaN films, and the semiconducting polymer polyhexylthiophene (P3HT) is intruded into these porous films. This hybrid device uses the polymer as the photoactive phase, electron donor, and hole transport medium, and the GaN as the electron acceptor and electron transport medium. Not only does the nanoporous geometry result in ultrafast charge transfer between the P3HT and the GaN, but a nanoconfined geometry can also drastically enhance charge mobility in the polymer by orienting the polymer alignment such that the fast charge transport direction is oriented vertically.</p><p> Optimal etching parameters are found in various etchants to produce an aligned morphology, and a method to remove the low-porosity overlayer via UV-assisted etching is described. Additionally, the first reported pore formation in GaN using a neutral etching solution is demonstrated, opening up the possibility of safe and environmentally-friendly etching of GaN, in contrast to traditional methods that use extremely toxic hydrofluoric acid.</p><p> Multiple methods to introduce polymer into the pores are described, and it is shown that hot pressing can achieve favorable polymer alignment. Ultrafast charge transport is demonstrated between the confined polymer and the GaN template by time-resolved terahertz spectroscopy. This geometry of an aligned nanoporous template surrounding an organic semiconductor is proposed as a general and beneficial strategy to improve performance of organic solar cells. </p>

The research reported in this thesis deals mainly with the use of novel nanotechnology-based testing methods in the field of cement-based composites. The existing knowledge of indentation test methods is presented and reviewed. The research presented focuses on the development and pilot usage of depth-sensing indentation (DSI) test methods. The use of DSI test methods for cement-based materials covers two distinct areas. The first area includes the testing of micromechanical properties of cement pastes/matrices. The development in DSI test methods allows direct measurements of properties, such as hardness, elastic modulus, etc., at microscale. Special attention is paid to assessment of interfacial regions in such cement-based materials. In the second area, DSI test methods are used for assessment of interfacial properties of fibre reinforced cementitious composites, with focus being directed to composites reinforced by bundles of microfilaments. A new push-out test method for individual microfilaments collated in a bundle and embedded in cementitious matrix is proposed and developed. Novel use of other nanotechnology-based techniques, such as focused ion beam (FIB) techniques, forms another part of this thesis. The focused ion beam milling technique was utilised for production of diamond probes which enabled push-out tests of individual glass microfibres to be carried out. Also, FIB cross-sectioning of indents induced by DSI test methods was performed. This novel research method showed large potential for a better interpretation of the test and an improved understanding of the microfracture processes in cement-based materials. Detailed information about FIB techniques is therefore presented in a separate chapter. The focus of this project has been to develop methods which will enable further systematic research into micromechanical properties of cementitious materials and may lead to the ultimate goal of this investigation - the development of a new generation of materials of improved macromechanical properties and durability.