<p>Be-doped InP nanowires were grown by the gold-assisted vapour-liquid-solid mechanism in a gas source molecular beam epitaxy system. The nanowires were characterized by scanning and transmission electron microscopy. With increased doping, the dependence of the length on diameter [L(D)] underwent an unusual transition from the diffusion-limited 1/D² relationship to one that increased before saturating. Doping influences on crystal structure and radial growth have been reported previously, but in the absence of these effects it is speculated that the beryllium introduces an increase in the steady-state chemical potential of the catalyst, and a barrier to nucleation. A model is presented relating the diffusion- and nucleation-limited regimes.</p> <p>Additionally, the progressive increase of dopant incorporation was verified by secondary ion mass spectrometry. Samples were transformed into a "bulk-like" material by spin-coating with cyclotene to enable depth profiling. Carrier concentrations were inferred through comparison with a thin film reference, and agreed in order of magnitude with the nominal doping values.</p> <p>Dopant activation was investigated through micro-photoluminescence experiments, and showed peak emissions between 1.49 eV and 1.50 eV for undoped samples, transitioning with increased doping to 1.45-1.46 eV. The difference between the dominant peak energies was consistent with differences reported for comparable epitaxially-grown thin film samples. Bandgap narrowing was also observed at high levels of doping, and was consistent with theoretical predictions.</p> <p>As a whole, the work presented here provides a different perspective on the effects of doping on nanowire growth, demonstrated through the specific system of Be-doped InP. The findings have implications for predictable and consistent nanowire device design, and suggestions for avenues of future research are provided.</p> / Master of Applied Science (MASc)

With their simple fabrication, narrow light spectrum, and color tunability, a class of materials known as perovskites are emerging as promising candidates for light emission applications. These materials, when exposed to normal atmospheric conditions show significant degradation. Improved protection has been demonstrated by embedding perovskites in polymers. Furthermore, the addition of a surfactant into the precursor solution has been shown to increase stability and allow for color tuning by exploiting quantum confinement effects. However, the effects of surfactants typically used to stabilize perovskites in solution have not been explored in this polymer embedding strategy. Here we determine the physical and optical emission changes produced by modifying the concentration of octylamine, butylamine, and oleylamine in the perovskite precursor solution prior to embedding into a polystyrene substrate. Using optical emission spectroscopy, we measure emission spectra of perovskite nanocrystals embedded in the polymer. Changes in morphology and dispersion of the perovskite particles within the polymer are observed using UV illuminated optical microscopy. XRD data suggests increased crystallinity with the addition of short chain surfactant. Our measurements in emission show that the location of the emission peak and overall shape of the emission spectra change when longer chain surfactant is added while short chain surfactant reduces nanorod formation without a significant change in particle dispersion or emission. The work suggests that increased long chain surfactant concentration prohibits perovskite crystal growth within the polymer leading to increased optical transparency and quantum confinement effects observable through photo luminescent emission.

The rapid advancement of portable and wearable technologies has challenged research to improve upon current renewable battery energy storage systems. By using nanotechnology, it is now possible to access more of the energy storage theoretical values that have been unattainable thus far. We have developed a method to create freestanding holey thin films through combinations of electrochemical and chemical vapor deposition (CVD) techniques to be used in renewable energy storage systems. Freestanding thin films promote excellent contact between the residual conductive framework and any functionalized active component specific to the designed material. Without requiring any other additives, the as-prepared freestanding thin films can be mechanically and chemically tuned to allow for use in a wide range of applications. Incorporation of micro- and nano-sized holey structures dramatically enhances the electrochemically active surface area, which is essential for facilitating appropriate reactions in conversion type energy storage systems. Combining the freestanding and holey components with an active layer effectively enhances conductivity and reduces the electron transfer distance at the electrode-electrolyte interface. Herein, two separately designed freestanding holey thin films were successfully used as cathode materials for lithium-sulfur battery (Li-S) and magnesium-ion battery (MIB) energy storage systems.

Quantum Cascade Lasers have recently gained considerable attention for their capability to emit infrared radiation in a broad infrared spectral region, very compact dimensions, and high optical power/efficiency. Increasing continuous wave optical power is one of the main research directions in the field. A straightforward approach to increasing optical power in the pulsed regime is to increase number of stages in the cascade structure. However, due to a low active region thermal conductivity, the increase in number of stages leads to active region overheating in continuous wave operation. In this work, an alternative approach to power scaling with device dimensions is explored: number of stages is reduced to reduce active region thermal resistance, while active region lateral size is increased for reaching high optical power level. Using this approach, power scaling for active region width increase from 10µm to 20µm is demonstrated for the first time. An analysis based on a simple semi-empirical model suggests that laser power can be significantly improved by increasing characteristic temperature T0 that describes temperature dependence of laser threshold current density.

Exploring phenomena occurring at the molecular level is critical to deepen our understanding of the living world. However conventional analytical tools are often limited in both spatial resolution and sensitivity. In this work we evaluate how fractal plasmonic structures can be developed for Surface Enhanced InfraRed Absorption (SEIRA) substrates to boost the infrared fingerprint signal of unknown single entities such as nanomaterials, virus or other biological systems. In this thesis, we present an overview of developments using light-matter interaction to push the limit of spatial resolution and sensitivity (Chapter 1). We discuss technological advances that allow nanoscale infrared spectroscopy despite inherent diffraction limit and remaining limitations in the field. In Chapter 2, we delve into the principles of techniques used in our work and compare them with other state-of-the-art in the field. We expand on the principle of nanoscale infrared spectroscopy and introduce how existing capabilities are uniquely suited to explore the near-field behavior of plasmonic structures at the nanoscale. In Chapter 3, we describe the design and fabrication of fractal Cesaro geometries we selected to evaluate broadband signal enhancement. The approaches used for far-field and near-field characterization of the plasmonic behavior are presented. In Chapter 4, we present our experimental results describing the behavior of Cesaro fractals with increasing levels of complexity. After confirming the far-field infrared resonances in the mid-infrared range in higher order structures, we coat the structures with a thin polymer film to map the regions with the highest photothermal enhancements, as an indirect indication of the near-field behavior of the plasmonic structures. We show that different film thicknesses of the polymer deposited on the plasmonic substrates provide some insight on the effect of photothermal propagation, which influences the signal level and spatial resolution of nanoscale infrared (nanoIR) spectroscopy and microscopy measurements. Signal enhancement performance of our structures is evaluated as a function of excitation frequency, laser power, laser pulse width, and sample orientation. Finally, we provide a summary of our work in Chapter 5. We also discuss types of samples for which our structures might be beneficial and consider outlooks on future work of this project.

The thesis reports the investigation of producing copper nanoparticle composites with graphene oxides (GO) using poly (sodium 4-styrenesulfonate) (PSS) and copper nanowires through the reduction of copper oxide nanowires using hydrazine. It was discovered that PSS improved the dispersity of GO and increased the absorption of copper ions on GO. An electrochemical reduction of GO/PSS/copper ion dispersion produced copper nanoparticles on GO surfaces. Reducing copper oxide nanowires on copper foils using hydrazine was achieved at a temperature where copper nanowires maintained their nanoscale structures.

Vertically oriented graphene nanosheets (VOGN) synthesized by radio frequency plasma enhanced chemical vapor deposition (RF-PECVD) have been fabricated as electrical double layer capacitors (EDLCs). The relatively open morphology of the films provided good frequency response, but had limited capacitance compared to present day activated carbon EDLCs. The objective of this research was to improve the capacitance of these films to a commercially viable level while maintaining sufficient frequency response for AC filtering. The growth of VOGN on Ni and Al substrates has been studied in this work. The native oxide on Ni was thinned at temperatures above ~600ºC with the oxygen from the surface oxide dissolving into the bulk, thus creating a low resistance ohmic contact that reduced the overall equivalent series resistance (ESR). Aluminum was studied because it is the primary substrate material used in electrolytic capacitors. However, it was much more difficult to work with because of its tenacious surface oxide. The maximum capacitance for a 10-minute VOGN/Ni growth observed was ~260µF/cm2, at temperature 850ºC, at 120 Hz, but the morphology was not very ordered. The best combination of capacitance (~160 µF/cm2) and frequency response (phase angle near -85º up to ~3000 Hz) was grown at 750ºC. The capacitance of VOGN/NI was further improved by using coatings of carbon black by an aerosol spray method. A capacitance of 2.3 mF/cm2 and frequency response phase angle near -90º at 120 Hz was achieved. It is the highest specific capacitance for an EDLC, reported in the literature, to date, suitable for AC filtering. Employing Al as a substrate required a novel method of plasma sputter cleaning of the oxide near the Al melting point (660ºC) and superimposing VOGN growth to prevent further oxidation. Initial results were ~80 µF/cm2 at a temperature of 620ºC with frequency response phase angle near -90º. Modeling of a uniform coating of carbon black (100 nm thick) on this underlying VOGN/Al architecture suggests that a capacitance of near 50 mF/cm2 can be achieved thus making this a potentially viable replacement for electrolytic capacitors. Another approach to commercialization of VOGN/Ni EDLCs has been studied by using a single substrate sheet interdigitated pattern design to create a low volume capacitor. A YAG laser was used to ablate resistance lines in the film resulting in a sinuous, square pattern on a VOGN/Ni coated alumina substrate and utilizing a gel electrolyte to create the EDLC.

Motivated by the need for inexpensive, simple, and portable devices for aqueous chemical analysis, we developed a nanoplasmonic colorimetric sensor capable of direct detection of wide range of chemicals. This novel sensor exploits the plasmonic resonance of metallic nanostructures with natural light to transduce changes in the chemical environment to changes in color, thus offering a simple route for real-time, in-situ, and low-cost analysis of aqueous chemical species. Due to its environmental and medical relevance, we chose aqueous ammonia to analyze and determine the efficacy and limit of detection of this sensing platform. For the metallic nanostructures we selected aluminium for its well stablished high reactivity with ammonia. However, the nanoparticle's metal can be chosen based on its reactivity with any given target analyte, therefore creating a tailorable sensor. The work here sets the foundations for a comprehensive analysis which aims to establish how various nanoparticle materials can be used to make a selective biosensor for chemical analysis in aqueous matrices such as environmental water samples, urine, blood serum, and saliva. In this thesis, we discuss the physics behind the sensors structural color, and the analytical techniques developed for ammonia quantification from aqueous solutions.

The chemical compound glycerol was first discovered in 1779 by the Swedish chemist Carl Wilhelm Scheele when he washed out glycerol from heating a mixture of lead oxide and olive oil. Many industries have found glycerol to be useful in the manufacturing of a variety of products due to its unique chemical properties. One such industry, pharmaceuticals, has found glycerol to be useful in the preparation of many medications. However, glycerol administration alone has been proven to treat medical conditions such as trigeminal neuralgia. Trigeminal Neuralgia (TN) is a unilateral electric shock-like facial pain often triggered by non-painful stimuli such as washing, shaving the face or talking. In some patients with TN, administration of glycerol into the trigeminal ganglion can alleviate the pain but the exact mechanism of pain relief is not understood. Additionally, glycerol administration in patients suffering from oral or thyroid cancer has been shown to reduce the spread and growth of these cancers. In this study, experiments utilizing various concentrations of glycerol administration were conducted on various glial cell cultures to determine glycerol's effects. Morphology studies were conducted on the glial cell culture types to determine the effects of various glycerol concentrations on overall cell structure. Additionally, traction force microscopy studies were performed on each glial cell culture type to determine the effects the various glycerol concentrations had on the forces each cell culture type applied to their respective underlying substrates. This study shows administration of moderate concentrations of glycerol to glial cell culture leads to shrinking of the astrocytes and changes in their traction forces.

Actin is an essential cytoskeletal protein that plays a critical role in cell mechanics, structure and organization with the help of actin binding proteins (ABPs). Gelsolin is a calcium-dependent ABP that severs actin filaments and caps them at their barbed end, regulating cell motility and signaling through dynamic actin cytoskeleton remodeling. A recent study has indicated that low pH stabilizes the active conformations of gelsolin. Additionally, the binding of gelsolin to the barbed end of an actin filament induces a conformational change that propagates along the actin filament. However, it has not been well understood how the complex intracellular environments involving variations in pH affect gelsolin-mediated actin filament severing and mechanics at the molecular level. In this thesis, we investigate how binding of gelsolin modulates actin filament severing and mechanics with changes in solution pH using total internal reflection fluorescence (TIRF) microscopy imaging. Furthermore, we explore how changes in intra-filament structure and dynamics occur upon gelsolin binding through the use of atomic force microscopy (AFM) imaging. Taken together, this work will elucidate a mechanism to control actin filament severing and mechanics modulated by gelsolin in the pH fluctuating intracellular environment.