Many functions in a lab-on-a-chip device such as heating, electrochemical sensing and electrophoresis require integration of microelectrodes. However, conventional techniques for microelectrode integration are either requiring expensive facilities, cleanroom environment or insufficient in resolution and microelectrode thickness. Microwires have also been integrated into LOC devices as microelectrodes. They are commercially available in a diversity of material. and diameter, with industrial production standard and mechanical strength comparable to bulk metal, which make them ideal candidate for microelectrode. Nonetheless a technique to integrate these microwires into complicated microelectrode patterns has not yet been developed. In this thesis, two microwire integration techniques based on xurography are developed for elastomer and rigid polymer. Copper, silver, platinum, carbon and Ni-Cr alloy microwires down to 15 µm with minimum spacing of 150 µm and controllable position in the height direction are successfully integrated. The microwire electrode can also be suspended in the middle of the microchannel with desired length and angle. Various applications are presented to demonstrate the versatility of the xurographic microwire integration process. / Thesis / Master of Applied Science (MASc)

As the world’s population increases, the demand for energy also grows. The strain on our limited resources of fossil fuels is unsustainable in the long term. An alternative, renewable method of energy generation must be implemented. Solar energy has good potential as an environmentally sound, unlimited energy source, but solar devices are not yet able to efficiently store energy for later use. A device has been proposed which uses direct sunlight to split water into hydrogen and oxygen. The hydrogen can then be harvested and stored as fuel, solving the question of how to effectively store energy generated during times of peak sunlight for use when sunlight levels are low. The prototype device incorporates arrays of doped silicon microwires which function as light absorbers and current-carriers, driving the chemical reactions that evolve hydrogen from water. This work aims to quantify and characterize the reduction in microwire resistivity that is achievable through application of silicon’s piezoresistive properties. Silicon displays a change in electrical resistance as a function of applied mechanical strain. This electromechanical effect has been studied extensively in bulk and top-down (etched) microstructures, but studies on microstructures grown bottom-up have been limited. A simple method is presented for piezoresistive characterization of individual, released, bottom-up silicon microwires. It is shown that these n-type microwires display a consistent negative piezoresistive response which increases in magnitude with increasing doping concentration. It was found that harnessing the piezoresistive response of moderately-doped (∼10^17 cm^−3) n-type wires allowed for a maximum observed reduction in resistivity of 49%, which translated to a 1% reduction in overall system resistance of a prototype unit cell of the artificial photosynthesis device, if all other components therein remained unchanged. / February 2015

The increasing demand for energy and the pressure to reduce reliance on fossil fuels encourages the development of devices to harness clean and renewable energy. Solar energy is a large enough source to fulfill these demands, however, in order to overcome its daily and seasonal variability, it has been proposed that sunlight be harvested and stored in the form of chemical fuels. One potential approach is the photosynthetic splitting of water to store solar energy in the simplest chemical bond, H–H, using a device that includes: semiconducting microwire arrays as light harvesting components, redox catalysts, and a membrane barrier for separating the products of water redox reactions.. However, the harvested solar energy can be lost across the system and it is critical to characterize the electrical properties of each component within the system to quantify how much of this energy will ultimately be coupled to the water splitting reactions. The aim of this research is to develop approaches for characterization of a proposed system of this kind, incorporating individual semiconductor microwires as photoelectrodes (with no redox catalysts) embedded into a candidate conducting polymer membrane to form a single functional unit. Semiconductor microwires were isolated and using a novel contact formation approach with tungsten probes in a standard probe station, and their current versus voltage properties were characterized. This approach is of particular interest when ii considering the limitations of conventional contact formation approaches (e.g. thermal evaporation of contact metals), arising from the small dimensions of the microwires and also the incompatibility of these techniques with many microwire/polymer structures due to the unwanted interactions between polymers, photoresists, etchants and the high temperature lithographic processes. The electrical properties of different microwires and also the junctions between microwires and two candidate polymers were studied. Specifically, the combination of methyl-terminated silicon microwires and PEDOT:PSS:Nafion demonstrated promising behavior, with a total DC resistance of approximately 720 kΩ (i.e. losses < 16 mV at maximum available photocurrent), making it a suitable candidate for the use in the proposed system. The outcome of these research may be applied to many applications including semiconducting microstructures and conducting polymers.

The increasing demand for energy and the pressure to reduce reliance on fossil fuels encourages the development of devices to harness clean and renewable energy. Solar energy is a large enough source to fulfill these demands, however, in order to overcome its daily and seasonal variability, it has been proposed that sunlight be harvested and stored in the form of chemical fuels. One potential approach is the photosynthetic splitting of water to store solar energy in the simplest chemical bond, H–H, using a device that includes: semiconducting microwire arrays as light harvesting components, redox catalysts, and a membrane barrier for separating the products of water redox reactions.. However, the harvested solar energy can be lost across the system and it is critical to characterize the electrical properties of each component within the system to quantify how much of this energy will ultimately be coupled to the water splitting reactions. The aim of this research is to develop approaches for characterization of a proposed system of this kind, incorporating individual semiconductor microwires as photoelectrodes (with no redox catalysts) embedded into a candidate conducting polymer membrane to form a single functional unit. Semiconductor microwires were isolated and using a novel contact formation approach with tungsten probes in a standard probe station, and their current versus voltage properties were characterized. This approach is of particular interest when ii considering the limitations of conventional contact formation approaches (e.g. thermal evaporation of contact metals), arising from the small dimensions of the microwires and also the incompatibility of these techniques with many microwire/polymer structures due to the unwanted interactions between polymers, photoresists, etchants and the high temperature lithographic processes. The electrical properties of different microwires and also the junctions between microwires and two candidate polymers were studied. Specifically, the combination of methyl-terminated silicon microwires and PEDOT:PSS:Nafion demonstrated promising behavior, with a total DC resistance of approximately 720 kΩ (i.e. losses < 16 mV at maximum available photocurrent), making it a suitable candidate for the use in the proposed system. The outcome of these research may be applied to many applications including semiconducting microstructures and conducting polymers.

En régime de couplage fort lumière-matière, les microcavités de semiconducteurs contenant des puits quantiques abritent des quasi-particules appelées exciton-polaritons de microcavité. Leur caractère hybride mi-électronique, mi-photonique, leur confère des propriétés optiques non-linéaires remarquables. Nous nous intéressons dans cette thèse à des microcavités structurées qui permettent la coexistence de branches polaritoniques de symétrie et d'énergie différenciées. Une microcavité gravée en rubans de quelques micromètres de large est d'abord étudiée. Le confinement latéral lève la dégénérescence entre les modes polarisés parallèlement et orthogonalement à la direction du ruban. Nous montrons que ce dédoublement résulte de contraintes structurales intrinsèques, de sorte que son amplitude peut être décidée dès la conception du dispositif. Nous nous intéressons ensuite à une microcavité double. En régime de diffusion Rayleigh élastique, le dédoublement TE-TM conduit à une séparation spatiale et angulaire des polaritons de pseudo-spins différents. Nous montrons que ce phénomène, appelé "effet Hall optique de spin" peut être contrôlé par un faisceau de pompe intense. Dans le régime d'oscillation paramétrique optique, la lumière s'auto-organise pour former un motif dans le champ lointain. Les règles de sélection concernant l'orientation et la polarisation de ces motifs sont explorées dans le régime d'amplification paramétrique optique. Ces études ouvrent la voie de la conception de "dispositifs de microphares" (capables d'orienter continûment la lumière par un simple contrôle en polarisation) et d'interrupteurs tout-optique ultra-rapides. / Semiconductor microcavities with embedded quantum wells in the strong light-matter coupling regime host quasi-particles called microcavity exciton-polaritons. Their hybrid nature, half-electronic, half-photonic, brings about remarkable nonlinear optical properties. In this work, we focus on microcavities that are structured to enable the coexistence of polaritonic branches with various symmetries and energies. First, a microcavity etched to form micrometers-wide wires is studied. The lateral confinement lifts the degeneracy between the modes which are polarized parallel and orthogonal to the wire direction. We show that this splitting results from built-in constraints which make a precise engineering of the splitting magnitude possible. We then focus on a double microcavity. In the elastic Rayleigh scattering regime, the TE-TM splitting induces a spatial and angular separation of polaritons with different pseudospins. We show that this phenomenon, called "Optical Spin Hall Effect", can be controlled by a strong optical pump beam. In the regime of Optical Parametric Oscillation, the light self-organizes to form patterns in the far field. The selection rules for the orientation and polarization of these patterns are explored in the regime of Optical Parametric Amplification. These studies pave the way for the realization of microscopic "lighthouse" devices (able to continuously orientate the light by a simple polarization control) and ultrafast all-optical switches.

Amorphous and polycrystalline microwires cast from ferromagnetic Fe-based or Co-based alloys in glass envelope demonstrate unique magneto-anisotropic and high frequency impedance properties that make them very attractive for sensor applications. Magnetic anisotropies of different types result from the inverse magnetostriction effect (positive or negative) at the interface between the glass shell and the metal core, in the presence of the residual stresses induced during the Taylor-Ulitovski casting method. Therefore, the glass shell is not just isolation, but also is one of most important factors that defines the physical properties of microwires. In particular, magnetic anisotropy allows high frequency impedance to be tuned by external stimuli such as magnetic field, tensile stress, or temperature. In the project, these effects are explored for the creation of low density microwire inclusions that might introduce tuneable microwave properties to polymer composite materials. The project aims to study high frequency impedance effects in ferromagnetic wires in the presence of tensile stress, temperature, and magnetic field. The integration of microwave equipment with mechanical and thermal measurement facilities is a very challenging task. In the project, we develop new experimental techniques allowing comprehensive study of composite materials with electromagnetic functionalities. The wire surface impedance recovered from such measurements can then be used to model the microwave response from wire-filled composites in free space. The obtained results significantly expand the horizon of potential applications of ferromagnetic wires for structural health monitoring.

Ce mémoire de thèse traite de la caractérisation de microfils et nanofils semi conducteurs dopés individuels par microscopie à émission de photoélectrons X (XPEEM) complétée par des techniques de champ proche électrique: Kelvin force microscopy (KFM) et scanning capacitance microscopy (SCM). L'objectif est d'évaluer l'apport des méthodes locales de surface « sans contact », grâce à la mesure du travail de sortie local et de l'énergie de liaison des niveaux de cœur, pour l'étude des phénomènes liés au dopage dans ces objets, comme par exemple l'uniformité longitudinale. Nous mettons d'abord en évidence l'importance de la préparation des échantillons pour la mise en œuvre des techniques citées: méthodes de transfert des fils, adéquation du substrat, influence des caractérisations pré-analyse. Nous présentons ensuite deux principales études de cas en lien avec une problématique technologique : les microfils de nitrure de gallium dopés Si (diamètre 2 µm) pour applications dans l'éclairage à l'état solide, et les jonctions pn à nanofils de Si (diamètre 100 nm) pour la nanoélectronique basse puissance. Dans le premier cas, nous avons mis en œuvre la SCM pour l'identification rapide de l'hétérogénéité axiale du dopage n, puis avons utilisé l'imagerie XPEEM spectroscopique avec excitation synchrotron pour, d'abord, estimer le travail de sortie local et la courbure de bande en surface; ensuite, élucider les modes d'incorporation du silicium en surface, qui pointent notamment sur la sensibilité des conditions d'élaboration dans la part du dopage intentionnel (Si en sites Ga) et non intentionnel (Si sur sites lacunaires en azote). (Des mesures complémentaires sur sections radiales et longitudinales de fils, par microscopie Auger et spectrométrie ToF-SIMS montrent une incorporation du Si limitée à la surface des microfils). Concernant les jonctions pn à nanofils de silicium étudiées après retrait partiel de l'oxyde de surface, nous avons mis en relation des résultats obtenus indépendamment par KFM et par XPEEM. Ils mettent conjointement en lumière une très faible différence de travail de sortie local entre partie n et partie p, et qui semble en partie expliquée par un ancrage du niveau de Fermi en surface. / This thesis addresses the characterization of individual doped semiconductors microand nanowires by photoemission electron microscopy (XPEEM) and near field techniques : Kelvin probe force microscopy (KFM) and scanning capacitance microscopy. The aim of this study is to evaluate the benefits of contactless surface methods, thanks to local work function and core level binding energy measurements, for the study of phenomena linked to doping in such objects, like for example axial uniformity. First, we highlight the importance of sample preparation required for these techniques: wires transfer methods, substrate/wire match, and preanalysis characterization influence. Then we present two case studies addressing technological issues: Si doped gallium nitride microwires (2μm diameter) for solid state lighting, and p-n junction nanowires (100 nm diameter) for low power microelectronics. In the first case, we have performed SCM for quick identification of n doping axial heterogeneity, then performed spectroscopic XPEEM using synchrotron radiation to, first, estimate local work function and surface band bending, then clarify surface silicon incorporation highlighting growth process influence over intentional (si on Ga sites) and unintentional doping (si on nitrogen vacancy). Complementary measurements on both axial and radial section of wires have been led by Auger microscopy and ToF-SIMS, highlighting silicon incorporation preferentially at the surface of the microwires. Regarding p-n junctions, after partial removal of surface oxide, we have linked results obtained independently by KFM and XPEEM. Both methods highlighted a weak local work function difference between n-doped and p-doped part, partly explained by Fermi level pinning induced by surface states.