abstract: Nanotechnology has been applied to many areas such as medicine, manufacturing, catalysis, food, cosmetics, and energy since the beginning 21st century. However, the application of nanotechnology to geotechnical engineering has not received much attention. This research explored the technical benefits and the feasibility of applying nanoparticles in geotechnical engineering. Specific studies were conducted by utilizing high-pressure devices, axisymmetric drop shape analysis (ADSA), microfluidics, time-lapse technology, Atomic Force Microscopy (AFM) to develop experiments. The effects of nanoparticle on modifying interfacial tension, wettability, viscosity, sweep efficiency and surface attraction forces were investigated. The results show that nanoparticles mixed in water can significantly reduce the interfacial tension of water in CO2 in the applications of nanofluid-CO2 flow in sediments; nanoparticle stabilized foam can be applied to isolate contaminants from clean soils in groundwater/soil remediation, as well as in CO2 geological sequestration or enhanced oil/gas recovery to dramatically improve the sweep efficiency; nanoparticle coatings are capable to increase the surface adhesion force so as to capture migrating fine particles to help prevent clogging near wellbore or in granular filter in the applications of oil and gas recovery, geological CO2 sequestration, geothermal recovery, contaminant transport, groundwater flow, and stormwater management system. / Dissertation/Thesis / Doctoral Dissertation Civil and Environmental Engineering 2016

abstract: Ge1-xSnx and SiyGe1-x-ySnx materials are being researched intensively for applications in infra-red optoelectronic devices. Due to their direct band gap these materials may in-fact be the enabling factor in the commercial realization of silicon photonics/group IV photonics and the integration of nanophotonics with nanoelectronics. However the synthesis of these meta-stable semiconductor alloys, with a range of Sn-compositions, remains the primary technical challenge. Highly specialized epitaxial growth methods must be employed to produce single crystal layers which have sufficient quality for optoelectronic device applications. Up to this point these methods have been unfavorable from a semiconductor manufacturing perspective. In this work the growth of high-quality Si-Ge-Sn epitaxial alloys on Ge-buffered Si (100) using an industry-standard reduced pressure chemical vapor deposition reactor and a cost-effective chemistry is demonstrated. The growth kinetics are studied in detail in-order to understand the factors influencing layer composition, morphology, and defectivity. In doing so breakthrough GeSn materials and device results are achieved including methods to overcome the limits of Sn-incorporation and the realization of low-defect and strain-relaxed epitaxial layers with up to 20% Sn. P and n-type doping methods are presented in addition to the production of SiGeSn ternary alloys. Finally optically stimulated lasing in thick GeSn layers and SiGeSn/GeSn multiple quantum wells is demonstrated. Lasing wavelengths ranging from 2-3 µm at temperatures up to 180K are realized in thick layers. Whereas SiGeSn/GeSn multiple quantum wells on a strain-relaxed GeSn buffers have enabled the first reported SiGeSn/GeSn multiple quantum well laser operating up to 80K with threshold power densities as low as 33 kW/cm2. / Dissertation/Thesis / Doctoral Dissertation Electrical Engineering 2018

Plasmonic devices, consisting of subwavelength nanostructures at optical frequency, have been widely applied to many research .elds such as bio-sensing, super-resolution imaging, energy harvesting, nanolaser and so on. The strong con.ned electromag­netic .elds in the a.nity of nanostructures provides an e.cient channel to guide, enhance, and modulate light energy beyond the di.raction limit. In this thesis, we .rst studied the plasmonic devices in linear optical regime, especially from the view of phase information in the light matter interaction; then more e.orts were paid to the nonlinear plasmonics, in which the organic-plasmonic hybrid nanostructures provided a useful platform for demonstrating some interesting physical phenomena. Firstly, we studied the fundamental optical properties of typically propagating surface plasmonic polariton (SPPs), which were generated by plasmonic gratings. Optical elliptical response of excited SPPs was studied experimentally and theoret­ically in both amplitude and phase domains. Then we studied the strong coupling e.ect from plasmonic Fabry-Perot nanocavity, in which giant Rabi splitting phe­nomenon with a splitting energy ~ 148 meV was obtained experimentally. From these studies, the interaction of SPP wave with other resonant structures were well understood from the view point of phase evolution. Secondly, we moved from linear optics the nonlinear plasmonic optics and tried to understand how the plasmon enhancement acts on the nonlinear optical processes. In the .rst example, plasmon enhanced third harmonic generation (THG) on one dimensional gratings was experimentally demonstrated by integrating the nonlinear active medium into the plasmonic devices. Later, the generation of THG vortex beam was also realized by introducing hologram based plasmonic design. Lastly, we re-examined a conventional symmetry problem in nonlinear molecular optics. It was found the that the metacrystal, consisting of plasmonic molecule with feature size much larger than conventional molecules, also follows the conventional selection rules of third harmonic generation. We believe the knowledge we accumulated in this work also provides a strong background for our future studies on ultra-fast plasmonic switching, in which the all-optical low loss, optical switch can be realized by using the engineered optical properties of plasmonic devices.

Thesis Submitted in Fulfilment of the Requirements for the Degree Master of Technology: Chemical Engineering in the Faculty of Engineering at the Cape Peninsula University of Technology 2014 / Iron oxide nanoparticles have recently become attractive for use in gas sensing, as catalysts and have also shown promise in other fields, such as biomedicine, for targeted drug delivery and cancer treatment. Despite these growing applications, the ability to produce iron oxide and one dimensional (1D) iron oxide nanoparticles on an industrial scale has proven to be a challenge. The continuous hydrothermal synthesis, (CHS), method has been proposed as the most promising method, yet the effect of the operating parameters on particle characteristics are still widely contested in the literature. One such parameter, temperature, is still widely contested on its effect on APS. To address this issue, a CHS pilot plant was constructed and commissioned. The inability to isolate certain parameters in CHS is a common shortcoming. Parameters such as temperature and flow rate are prime examples, as changing the temperature has several effects on the system resulting in a change in reaction rate, a change in density and a change in the reactor residence time while the flow rate is closely linked to the residence time and mixing conditions. A 3-level Box-Behnken factorial design method was used to statistically analyze the correlations and interactions between operating parameters (temperature, concentration and flow rate) in CHS and evaluate their resulting effect on particle characteristics, with focus on morphology. All particles were characterized by X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM). Reactions in the presence of solvents or surfactants proved incapable of modifying particle morphology, although significant particle size reduction revealed that they were actively involved in particle growth and may be used as a further tool for controlling particle characteristics. The concentration was found to have the greatest effect on particle characteristics including a slight alteration of particle shape and a massive influence on the average particle size. The interactions between operating parameters were significant, especially in the case of temperature and concentration. The temperature and concentration were found to interact revealing three different trends on APS, offering a solution to conflicting reports in the literature. The temperature was also observed to interact favourably with the flow rate, presenting a method of increasing the PY and RC, with little change in APS and PSD. This knowledge will prove invaluable for the design of future experiments in CHS.

Magister Scientiae - MSc / The objective of this research was to develop highly efficient and yet effective MnO2 electrode materials for supercapacitors applications. Most attention had focussed on MnO2 as a candidate for pseudo-capacitor, due to the low cost of the raw material and the fact that manganese is more environmental friendly than any other transition metal oxide system. The surface area and pore distribution of MnO2 can be controlled by adjusting the reaction time. The MnO2 synthesised under optimum conditions display high capacitance, and exhibit good cycle profile. This work investigates the ways in which different morphological structures and pore sizes can affect the effective capacitance. Various -MnO2 were successfully synthesised under low temperature conditions of 70 oC and hydrothermal conditions at 120 oC. The reaction time was varied from 1 to 6 hours to optimise the conditions. KMnO4 was reduced by MnCl.H2O under low temperature, whereas MnSO4.4H2O, (NH4)2S2O8 and (NH4)2SO4 were co-precipitated under hydrothermal conditions in a taflon autoclave to synthesise various -MnO2 nano-structures. / South Africa

<p> III-V optoelectronic device integration in a CMOS post-process compatible manner is important for the intimate integration of silicon-based electronic and photonic integrated circuits. The low temperature, self-catalyzed growth of high crystalline quality Wurtzite-phase InP nanopillars directly on silicon presents a viable approach to integrate high performance nano-optoelectronic devices. </p><p> For the optical transmitter side of the photonic link, InGaAs quantum wells have been grown in a core-shell manner within InP nanopillars. Position-controlled growth with varying pitch is used to systematically control emission wavelength across the same growth substrate. These nanopillars have been fabricated into electrically-injected quantum well in nanopillar LEDs operating within the silicon transparent 1400&ndash;1550 nm spectral window and efficiently emitting micro-watts of power. A high quality factor (Q ~ 1000) undercut cavity quantum well nanolaser is demonstrated, operating in the silicon-transparent wavelength range up to room temperature under optical excitation. </p><p> We also demonstrate an InP nanopillar phototransistor as a sensitive, low-capacitance photoreceiver for the energy-efficient operation of a complete optical link. Efficient absorption in a compact single nanopillar InP photo-BJT leads to a simultaneously high responsivity of 9.5 A/W and high 3dB-bandwidth of 7 GHz. </p><p> For photovoltaic energy harvesting, a sparsely packed InP nanopillar array can absorb ~90% of the incident light because of the large absorption cross section of these near-wavelength nanopillars. Experimental data based on wavelength and angle resolved integrating sphere measurements will be presented to discuss the nearly omnidirectional absorption properties of these nanopillar arrays.</p><p>

No description available.

<p> Nanofabrication through multiphoton absorption has generated considerable interest because of its unique ability to generate 2D and 3D structures in a single laser-direct-write step as well as its ability to generate feature sizes well below the diffraction limited laser spot size. The majority of multiphoton fabrication has been used to create 3D structures of photopolymers which have applications in a wide variety of fields, but require additional post-processing steps to fabricate conductive structures. It has been shown that metal ions can also undergo multiphoton absorption, which reduces the metal ions to stable atoms/nanoparticles which are formed at the laser focal point. When the focus is located at the substrate surface, the reduced metal is deposited on the surface, which allows arbitrary 2D patterning as well as building up 3D structures from this first layer. Samples containing the metal ions can be prepared either in a liquid solution, or in a polymer film. The polymer film approach has the benefit of added support for the 3D metallic structures; however it is difficult to remove the polymer after fabrication to leave a free standing metallic structure. With the ion solution method, free standing metallic structures can be fabricated but need to be able to withstand surface tension forces when the remaining unexposed solution is washed away.</p><p> So far, silver nanowires with resistivity on the order of bulk silver have been fabricated, as well as a few small 3D structures. This research focuses on the surfactant assisted multiphoton reduction of silver ions in a liquid solution. The experimental setup consists of a Coherent Micra 10 Ultrafast laser with 30fs pulse length, 80MHz repetition rate, and a wavelength centered at 800nm. This beam is focused into the sample using a 100x objective with a N.A. of 1.49. Silver structures such as nanowires and grid patterns have been produced with minimum linewidth of 180nm. Silver nanowires with resistivity down to 6x bulk silver have been fabricated. Three-dimensional structures have also been fabricated with up to a 10&micro;m height at a thickness of 500nm. This method can fabricate structures with the possible applications in plasmonic metamaterials, photonic crystals, MEMS/NEMS and micro/nanocircuitry. </p><p>

<p> We present a versatile biosensing strategy that uses nucleic acids programmed to undergo an isothermal toehold mediated strand displacement in the presence of analyte. This rearrangement results in a double biotinylated duplex formation that induces the rapid aggregation of streptavidin decorated quantum dots (QDs). As biosensor reporters, QDs are advantageous to organic fluorophores and fluorescent proteins due to their enhanced spectral and fluorescence properties. Moreover, the nanoscale regime aids in an enhanced surface area that increase the number of binding of macromolecules, thus making cross-linking possible. The biosensing transduction response, in the current approach, is dictated by the analysis of the natural single particle phenomenon known as fluorescence intermittency, or blinking is the stochastic switching of fluorescence intensity ON (bright) and OFF (dark) states observed in single QD or other fluorophores. In contrast to binary blinking that is typical for single QDs, aggregated QDs exhibit quasi-continuous emission. This change is used as an output for the novel biosensing techniques developed by us. Analysis of blinking traces that can be measured by laser scanning confocal microscopy revealed improved detection of analytes in the picomolar ranges. Additionally, this unique biosensing approach does not require the analyte to cause any fluorescence intensity or color changes. Lastly, this biosensing method can be coupled with therapeutics, such as RNA interference inducers, that can be conditionally released and thus used as a theranostic probes.</p><p>

<p> Efficient thermal management is becoming a critical issue for development of the next generation of electronics. As the size of electronic devices shrinks, the dissipated power density increases, demanding a better heat removal. The discovery of graphene&rsquo;s unique electrical and thermal properties stimulated interest of electronic industry to development of graphene based technologies. In this dissertation, I report the results of my investigation of thermal properties of graphene derivatives and their applications in thermal management. The dissertation consists of three parts. In the first part, I investigated thermal conductivity of graphene laminate films deposited on thermally insulating polyethylene terephthalate substrates. Graphene laminate is made of chemically derived graphene and few layer graphene flakes packed in overlapping structure. Two types of graphene laminate were studied: as deposited and compressed. The thermal conductivity of the laminate was found to be in the range from 40 <i>W/mK</i> to 90 <i>W/mK</i> at room temperature. It was established that the average size and the alignment of graphene flakes are parameters dominating the heat conduction. In the second part of this dissertation, I investigated thermal conductivity of chemically reduced freestanding graphene oxide films. It was found that the in-plane thermal conductivity of graphene oxide can be increased significantly using chemical reduction and temperature treatment. Finally, I studied the effect of defects on thermal conductivity of suspended graphene. The knowledge of the thermal conductivity dependence on the concentration of defects can shed light on the strength of the phonon - point defect scattering in two-dimensional materials. The defects were introduced to graphene in a controllable way using the low-energy electron beam irradiation. It was determined that as the defect density increases the thermal conductivity decreases down to about 400 <i> W/mK</i>, and then reveal saturation type behavior. The thermal conductivity dependence on the defect density was analyzed using the Boltzmann transport equation and molecular dynamics simulations. The obtained results are important for understanding phonon transport in two-dimensional systems and for practical applications of graphene in thermal management.</p><p>