There are many semiconductors with nominally superior electronic properties compared to silicon. However, silicon became the material of choice for MOSFETs due to its robust native oxide. With Moore's observation as a guiding principle, the semiconductor industry has come a long way in scaling the silicon MOSFETs to smaller dimensions every generation with engineering ingenuity and technological innovation. As per the 2012 International Technology Roadmap for Semiconductors (ITRS), the MOSFET is expected to be scaled to near 6 nm gate length by 2025. However, materials, design and fabrication capabilities aside, basic physical considerations such as source to drain quantum mechanical tunneling, channel to gate tunneling, and thermionic emission over the channel barrier suggest an end to the roadmap for CMOS is on the horizon. The semiconductor industry is already aggressively looking for the next switch which can replace the silicon FET in the long term. My Ph.D. research is part of the quest for the next switch. The promises of process compatibility with existing CMOS technologies, fast carriers with high mobilities, and symmetric conduction and valence bands have led to graphene being considered as a possible alternative to silicon. This work looks at three devices based on graphene using first principles atomistic transport simulations and compact models capturing essential physics: the large-area graphene RF FET, the Bilayer pseudoSpin FET, and the double electron layer resonant tunneling transistor. The characteristics and performance of each device is explored with a combination of SPICE simulations and atomistic quasi static transport simulations. The BiSFET device was found to be a promising alternative to CMOS due to extremely low power dissipation. Finally, I have presented formalism for efficient simulation of time dependent transport in graphene for beyond quasi static performance analysis of the graphene based devices explored in this work. / text

Development of alternative cathodes that have high capacity and long cycle life at an affordable cost is critical for next generation rechargeable batteries to meet the ever-increasing requirements of global energy storage market. Lithium-sulfur batteries, employing sulfur cathodes, are increasingly being investigated due to their high theoretical capacity, low cost, and environmental friendliness. However, the practicality of lithium-sulfur technology is hindered by technical obstacles, such as short shelf and cycle life, arising from the shuttling of polysulfide intermediates between the cathode and the anode as well as the poor electronic conductivity of sulfur and the discharge product Li2S. This dissertation focuses on overcoming some of these problems. The sulfur cathode involves an electrochemical conversion reaction compared to the conventional insertion-reaction cathodes. Therefore, modifications in cell-component configurations/structures are needed to realize the full potential of lithium-sulfur cells. This dissertation explores various custom and functionalized cell components that can be adapted with pure sulfur cathodes, e.g., porous current collectors in Chapter 3, interlayers in Chapter 4, sandwiched electrodes in Chapter 5, and surface-coated separators in Chapter 6. Each chapter introduces the new concept and design, followed by necessary modifications and development. The porous current collectors embedded with pure sulfur cathodes are able to contain the active material in their porous space and ensure close contact between the insulating active material and the conductive matrix. Hence, a stable and reversible electrochemical-conversion reaction is facilitated. In addition, the use of highly porous substrates allows the resulting cell to accommodate high sulfur loading. The interlayers inserted between the pure sulfur cathode and the separator effectively intercept the diffusing polysulfides, suppress polysulfide migration, localize the active material within the cathode region, and boost cell cycle stability. The combination of porous current collectors and interlayers offers sandwiched electrode structure for the lithium/dissolved polysulfide cells. By way of integrating the advantages from the porous current collector and the interlayer, the sandwiched electrodes stabilize the dissolved polysulfide catholyte within the cathode region, resulting in a high discharge capacity, long-term cycle stability, and high sulfur loading. The novel surface-coated separators have a polysulfide trap or filter coated onto one side of a commercial polymeric separator. The functional coatings possess physical and/or chemical polysulfide-trapping capabilities to intercept, absorb, and trap the dissolved polysulfides during cell discharge. The functional coatings also have high electrical conductivity and porous channels to facilitate electron, lithium-ion, and electrolyte mobility for reactivating the trapped active material. As a result, effective reutilization of the trapped active material leads to improved long-term cycle stability. The investigation of the key electrochemical and engineering parameters of these novel cell components has allowed us to make progress on (i) understanding the materials chemistry of the applied functionalized cell components and (ii) the electrochemical performance of the resulting lithium-sulfur batteries. / text

HudBay Minerals (formerly the Hudson Bay Mining and Smelting Co., Limited) has operated a Zn and Cu processing facility in Flin Flon, MB since the 1930’s. Located in the Boreal Shield, the area surrounding the mine complex has been severely impacted by both natural (forest fires) and the anthropogenic disturbance, which has adversely affected recovery of the local forest ecosystem. Zinc is one of the most prevalent smelter-derived metals in the soils and has been identified as a key factor limiting natural revegetation of the landscape. Because metal toxicity is related more to speciation than to total concentration, Zn speciation in soils from the impacted landscape was characterized using X-ray absorption fine structure, X-ray fluorescence mapping and µ-X-ray absorption near edge structure. Beginning with speciation at a micro-scale and transitioning to bulk speciation was able to determine Zn speciation and link it to two distinct landform characteristics: (1) soils stabilized by metal tolerant grass species—in which secondary adsorption species of Zn (i.e., sorbed to Mn and Si oxides, and as outer-sphere adsorbed Zn) were found to be more abundant; and (2) eroded, sparsely vegetated soils in mid to upper slope positions that were dominated almost entirely by smelter derived Zn minerals, specifically Franklinite (ZnFe2O4). The long-term effect of liming on pH and Zn speciation was examined using field sites limed by a community led organization over a ten year period. Upon liming to a pH of 4 to 4.5, the eroded, sparsely vegetated soils where found to form a Zn-Al-Hydroxy Interlayer Material (HIM) co-precipitate, reducing the phytotoxicity of both Zn and Al and allowed for boreal forest vegetation to recovery quickly in these areas. The grass stabilized soils experienced a steady pH increase, as compared to a sporadic pH increase in the heavily eroded soils, as the buffering capacity was overcome allowing for a transition between multiple adsorption species based upon the point of zero charge of reactive soil elements. Ultimately reaching a near neutral pH after ten years, this allowed for the formation of stable Zn-Al-layered double hydroxide (LDH) soil precipitates and significantly reduced concentrations of plant available Zn.

Oxide dispersion strengthened (ODS) alloys have been developed with unique mechanical properties. However, in order to achieve commercial application an appropriate joining process is necessary which minimizes disruption to the alloy microstructure. Transient liquid phase (TLP) bonding is a promising joining method, but previous work has shown that the segregation of dispersoids within the joint region results in bonds with poor mechanical strengths. This research work was undertaken to further explore particulate segregation at the joint region when TLP bonding and to develop bonding techniques to prevent it. A Ni-Cr-Fe-Si-B interlayer was used to bond an alloy MA 758. The effects of parent alloy grain size, bonding temperature, and external pressure on the TLP bonding process were investigated. Three melting stages were identified for the interlayer, and the bonding temperature was chosen so that the interlayer was in the semi-solid state during bonding. This novel bonding mechanism is described and applied to counteract the segregation of Y203 dispersoids. The grain size of the parent alloy does not alter the particulate segregation behaviour. It is concluded that a low bonding temperature with moderate pressure applied during bonding is preferable for producing bonds with less disruption to the microstructures of the parent alloy. Joint shear tests revealed that a near parent alloy strength can be achieved. This study also shed some light on choosing the right bonding parameters suitable for joining the complicated alloy systems. A Ni-P interlayer was also used to bond the ODS alloy. Microstructural examination indicated that a thin joint width and less disruption to the parent grain structure were achieved when bonding the alloy in the fine grain state. The time for isothermal solidification was found to be shorter when compared with bonds made with the parent alloy in the recrystallized state. All these observations were attributed to the greater diffusivity of P along the grain boundaries than that of the bulk material. A high Cr content within the parent alloy changes the mechanism of the bonding process. The diffusion of Cr into the liquid interlayer has the effect of raising the solidus temperature, which not only accelerates the isothermal solidification process, but also reduces the extent of parent alloy dissolution.

During the drilling process, sharp edges of material called burrs are produced and protrude from the original surface. When a through-hole is drilled, burrs form on both the entry and exit surfaces around the hole, requiring expensive deburring operations to be performed in order to meet part specifications. A common hole producing operation in aircraft assembly is drilling holes through multiple sheet metal layers in order to fasten them together. However, at the interface between two layers, burrs form on both the exit of the first layer (termed "skin") and entry of the second layer (termed "frame"). Consequently, the layers frequently need to be taken apart, deburred, and put back together again before being fastened, resulting in additional costs and increased assembly time. The goal of this thesis was to understand the role of key factors such as drill geometry, drill wear and clamping conditions on burr formation at the interface of two thin sheets of 2024-T3 aluminum so that interlayer burr formation could be minimized. This problem was approached from three different angles. First, an experimental study was performed to find the drill geometry parameters for minimization of interlayer burrs and to ascertain the relationship between the average burr size and drill wear. Next, a new kind of clamping system for holding sheet metal layers together during drilling was designed, prototyped, and tested for its effectiveness. Finally, a preliminary analytical model of interlayer burr formation was created in order to better understand the burr formation process in stacked layers of sheet metal and to better understand the effect that each drilling parameter has on the resulting burr size.

In this dissertation, we study properties of quantum interaction phenomena in two-dimensional (2D) and one-dimensional (1D) electronic systems in p-GaAs micro- and nano-scale devices. We present low-temperature magneto-transport data from three forms of low-dimensional systems 1) 2D hole systems: in order to study interaction contributions to the metallic behavior of 2D systems 2) Bilayer hole systems: in order to study the many body, bilayer quantum Hall state at nu = 1 3) 1D hole systems: for the study of the anomalous conductance plateau G = 0.7 ???? 2e2/h The work is divided into five experimental studies aimed at either directly exploring the properties of the above three interaction phenomena or the development of novel device structures that exploit the strong particle-particle interactions found in p-GaAs for the study of many body phenomena. Firstly, we demonstrate a novel semiconductor-insulator-semiconductor field effect transistor (SISFET), designed specifically to induced 2D hole systems at a ????normal???? AlGaAs-on-GaAs heterojunction. The novel SISFETs feature in our studies of the metallic behavior in 2D systems in which we examine temperature corrections to ????xx(T) and ????xy(T) in short- and long-range disorder potentials. Next, we shift focus to bilayer hole systems and the many body quantum Hall states that form a nu = 1 in the presence of strong interlayer interactions. We explore the evolution of this quantum Hall state as the relative densities in the layers is imbalanced while the total density is kept constant. Finally, we demonstrate a novel p-type quantum point contact device that produce the most stable and robust current quantization in a p-type 1D systems to date, allowing us to observed for the first time the 0.7 structure in a p-type device.

La présente thèse sur travaux a pour objectif de montrer l’influence de la couche intermédiaire dans le comportement de la voie ferrée. Par analogie, la couche intermédiaire peut être assimilée à la sous-couche sur les lignes ferroviaires récentes. Elle est présente sur les lignes classiques construites depuis le début du réseau ferroviaire français au milieu du XIXème siècle. Cette couche est située sous le ballast et contribue à la stabilité de la voie. Elle s’est formée au cours du temps par l’interpénétration entre le ballast et le sol support. Sa densification a été obtenue par le passage des circulations durant près de 150 ans. Le présent travail s’appuie sur trois thèses réalisées au cours de la dernière décennie. Ces recherches réalisées par Trinh (2011), Duong (2013) et Lamas-Lopez (2016) ont permis de mieux appréhender le comportement de cette couche en étudiant respectivement le comportement hydromécanique d’une couche saine ; le mécanisme de création et dégradation de la couche intermédiaire ; et enfin son comportement dynamique. Sur la base de ces travaux, en se basant sur les approches de dimensionnement des structures développées dans le domaine routier et sur les données de maintenance des voies ferrées de groupes 3 et 4, on a pu développer une nouvelle approche de dimensionnement permettant la prise en compte de la couche intermédiaire dans le bon fonctionnement de la voie ferrée. La finalité de ce travail est de développer une méthodologie d’analyse du comportement de la voie afin de prescrire les « justes travaux » (RVB, relevage, assainissement…) permettant d’atteindre les objectifs de performance visés / The aim of this PhD thesis is to show the influence of the interlayer in the behaviour of the rail track. By analogy, the interlayer can be comparable with the sub-ballast layer on the high speed lines. It is present on the conventional lines built since the beginning of the French railway network in the middle of the 19th century. This layer is located under the ballast and contributes to the stability of the rail track. It was formed over time by the interpenetration between the ballast and the ground support. Its density was obtained by the passage of trains for almost 150 years. This work is based on three PhD theses carried out over the past decade. The research conducted by Trinh (2011), Duong (2013) and Lamas-Lopez (2016) has allowed a better understanding of the behaviour of this layer by respectively studying the hydraulic behaviour of a good layer; the creation mechanism of and degradation of the interlayer; and finally its dynamic behaviour. On the basis of this work and on approaches of sizing structures developed in roads, and on the data of maintenance of railways of UIC 3 and 4, we can develop a new approach to sizing by taking into account the role of the interlayer in the performance of the rail track. A method of analysis of the behaviour of the rail track has been developed to prescribe “good job” (track renewal, lifting, drainage…) in order to achieve the performance objectives

Il y a plus d'un siècle, les verres feuilletés ont été découverts. Ces structures sont formées d'un intercalaire polymère pris entre deux plis de verre. Cet intercalaire améliore considérablement les performances à l'impact de l'assemblage. Lorsque le verre se brise, la délamination et l'étirement de l'intercalaire dissipent une grande quantité d'énergie. Les personnes sont protégées de l'objet impactant qui ne traverse pas le verre et des projections potentiellement dangereuses. Nous avons identifié et caractérisé les mécanismes de dissipation d'énergie associés au décollement de l'intercalaire et à l'étirement qui s'en suit. Des tests de traction uniaxiale et des mesures de biréfringence ont permis de relier le comportement de l'intercalaire à sa structure chimique. Les différents mécanismes dissipatifs du comportement de ce polymère ont été identifiés et décris dans un modèle rhéologique. Nous avons utilisé une expérience modèle afin d'établir les sollicitations subies par l'intercalaire lors de sa délamination du verre. Cette expérience consiste en un essai de traction uniaxiale sur un verre feuilleté pré-entaillé. Nous avons montré l'existence d'un régime de délamination stationnaire dans une gamme limitée de température et de vitesse de déplacement imposée. Dans ces conditions stationnaires, nous avons identifié deux zones de dissipation d'énergie. La corrélation digitale d'image a permis de quantifier la dynamique de déformation de l'intercalaire en aval du front et d'expliquer la grande quantité d'énergie dissipée. Enfin un modèle éléments finis a confirmé les observations expérimentales et permis d'explorer le voisinage du front de délamination. / Laminated glass has been discovered more than a century ago. It is composed of a polymeric interlayer sandwiched in-between two glass plies. This interlayer dramatically enhances the performance during impact. Even if the glass breaks, partial delamination and stretching of the interlayer will dissipate a large amount of energy. This dissipation will protect people from the impacting object while the glass splinters will stick on the interlayer, preventing harmful projections. I have identified and characterized the dissipation mechanisms associated with the interlayer rheology and its delamination from glass.Using uniaxial traction tests combined with photoelastic measurements, a relationship between the polymer structure and its mechanical behavior has been provided. The different dissipating mechanisms of the interlayer rheology have been identified in a rheological model. To understand how the interlayer mechanical behavior is involved during the lost of adhesion at the glass interface, a model delamination experiment has been setup. This test consists in a uniaxial traction on a pre-cracked laminated glass sample. In a certain range of applied velocities and temperatures, a steady state delamination regime has been observed. In these steady state conditions, two zones of dissipation have been identified. Digital image correlation has been used to quantify the stretching dynamics of the interlayer ahead of the delamination fronts and to explain the large dissipation observed during impact. Finally a finite element model has been developed to confirm experimental observations and to explore the close vicinity of the delamination fronts.

No / Successful joining of dissimilar metals such as Al and Mg can provide significant advantages to the automotive industry in the fabrication of vehicle bodies and other important components. This study explores dissimilar joining of Al–Mg using a resistance spot welding process to produce microstructurally sound lap joints and evaluates the impact of interlayer composition on microstructural evolution and the formation of intermetallic compounds within the weld nugget. The results indicated that mechanically sound joints can be produced, with fine equiaxed and columnar dendrites within the weld nugget. The presence of intermetallic compounds was also confirmed by the variation in the microhardness values recorded across the weld zone.

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