<p> The progressive advancements in communication and transportation has changed human daily life to a great extent. While important advancements in battery technology has come since its first demonstration, the high energy demands needed to electrify the automotive industry have not yet been met with the current technology. One considerable bottleneck is the cathode energy density, the Li-rich layered oxide compounds xLi₂MnO₃.(1-x)LiMO₂ (M= Ni, Mn, Co) (0.5= Co) (0.5=discharge capacities greater than 280 mAh g^-1 (almost twice the practical capacity of LiCoO₂).</p><p> In this work, neutron diffraction under <i>operando</i> battery cycling is developed to study the lithium and oxygen dynamics of Li-rich compounds that exhibits oxygen activation at high voltage. The measured lattice parameter changes and oxygen position show movement of oxygen and lattice contractions during the high voltage plateau until the end of charge. Lithium migration kinetics for the Li-rich material is observed under operando conditions for the first time to reveal the rate of lithium extraction from the lithium layer and transition metal layer are related to the different charge and discharge characteristics.</p><p> In the second part, a combination of multi-modality surface sensitive tools was applied in an attempt to obtain a complete picture to understand the role of NH4F and Al₂O₃ surface co-modification on Li-rich. The enhanced discharge capacity of the modified material can be primary assigned to three aspects: decreased irreversible oxygen loss, the activation of cathode material was facilitated with pre-activated Mn³⁺ on the surface, and stabilization of the Ni redox pair. These insights will provide guidance for the surface modification in high voltage cathode battery materials of the future.</p><p> In the last part, the idea of Li-rich has transferred to the Na-ion battery cathode. A new O3 - Na_0.78Li_0.18Ni_0.25Mn_0.583O_w is prepared as the cathode material for Na-ion batteries, delivering exceptionally high energy density and superior rate performance. The single-slope voltage profile and ex situ synchrotron X-ray diffraction data demonstrate that no phase transformation happens through a wide range of sodium concentrations (0.8 Na removed). Further optimization could be realized by tuning the combination and ratio of transition metals.</p>

Skin is a complex biological composite system that serves as the outermost barrier to the environment and is mechanically robust. Understanding the mechanical properties of skin is important to improve and compare current in vitro experiments to the physiological conditions as the mechanical properties have a crucial role in determining cell behaviour. The mechanical behaviour of skin at the cellular level is expected to be dominated by the collagen fibre network within the dermis, which displays an anisotropic mechanical response to macroscopic loading. However, the three dimensional mechanical properties of skin at the nanoscale are not well understood. The aim of this work is to examine the mechanical properties of skin at the nanoscale in three dimensions and explore the links between the nanoscale and the macroscopic behaviour. Multiple sample preparation techniques are employed to expose the different layers of skin for mechanical testing and the elastic modulus of skin is evaluated by using atomic force microscopy (AFM) nanoindentation. The effect of freezing skin to cryogenic temperatures on the mechanical properties is evaluated and found to have no impact on the mechanical response of skin, indicating that the composition and structure of skin are robust enough to withstand the cryosectioning sample preparation methods used to expose the transverse layers of skin. AFM indentation was used to evaluate the elastic modulus of the dermis depending on the orientation of the sample and found to have an isotropic mechanical response. This result is opposite to anisotropy observed in macroscopic skin due to small scale mechanical testing ignoring collagen fibril orientation during strain. The variations in the elastic modulus of skin are also evaluated by AFM indentation at high spatial resolution to construct a composite model of the mechanical behaviour of skin at the nanoscale to predict the macroscopic response. The AFM nanoindentation technique was extended to evaluate the mechanical properties of a cell derived matrix deposited on an electrospun nanofibre scaffold, where the results indicate increasing the nanofibre diameter produces a cell derived matrix with an increased elastic modulus for more effective scaffolds. This work highlights the use of AFM mechanical testing to evaluate the nanoscale mechanical behaviour of skin, treated as a composite biological system, and determine the influence of the length scale and sample orientation on the observed mechanical response.

<p> Characterization of magnetic domain structure is essential to understand and manipulate the magnetic properties of materials. In this thesis, we have utilized Lorentz Transmission Electron Microscopy (LTEM) in combination with image simulations based on micromagnetic models, to investigate the magnetic domain structure of a unique nano-chessboard structure consisting of L1<i> 0</i> and L1₂ phases in a Co₄₀Pt₆₀ alloy. We have shown high-resolution LTEM images of nano-size magnetic features acquired through spherical aberration correction in Lorentz Fresnel mode. Phase reconstructions based on the transport of intensity equation has been carried out to fully understand the magnetic domain structure and to extract quantitative information, including direction of magnetic induction and magnetic domain wall width, from the Lorentz TEM images. The experimental Fresnel images of the nano-chessboard structure show zig-zag shaped magnetic domain walls at the inter-phase boundaries between L1<i>0</i> and L1₂ phases. A circular magnetization distribution with vortex and anti-vortex type arrangement is evident in the phase reconstructed magnetic induction maps as well as simulated maps. The magnetic contrast in experimental LTEM images has been properly interpreted with the help of magnetic induction maps simulated for various relative electron beam-sample orientations inside TEM. Apart from the nano-chessboard structure, this alloy shows other interesting microstructural features such as anti-phase boundaries, tweed structure, coarse L1<i>0</i> plates, and macro-twins all of which have been characterized using conventional bright field/dark field TEM imaging and compared with their respective Lorentz TEM images. The magnetic domain wall widths obtained for each microstructure has been compared and the influence of microstructure and the particle size on wall widths has been discussed.</p><p>

<p> The purpose of this study is to design, fabricate and test a CMOS compatible 3-axis Hall effect sensor capable of detecting the earth&rsquo;s magnetic field, with strength&rsquo;s of &sim;50 &mu;T. Preliminary testing of N-well Van Der Pauw structures using strong neodymium magnets showed proof of concept for hall voltage sensing, however, poor geometry of the structures led to a high offset voltage. A 1-axis Hall effect sensor was designed, fabricated and tested with a sensitivity of 1.12x10^-3 mV/Gauss using the RIT metal gate PMOS process. Poor geometry and insufficient design produced an offset voltage of 0.1238 volts in the 1-axis design; prevented sensing of the earth&rsquo;s magnetic field. The new design features improved geometry for sensing application, improved sensitivity and use the RIT sub-CMOS process. The completed 2-axis device showed an average sensitivity to large magnetic fields of 0.0258 &mu;V/Gauss at 10 mA supply current.</p>

<p> Purpose: The purpose of this investigation was to evaluate the effect of aluminum oxide airborne particle abrasion, with and without subsequent steam cleaning on the surface free energy of alloys commonly used in dentistry, in an attempt to produce optimal surfaces for adhesion. Materials and Methods: Twelve samples, with dimensions 13 x 18 x 1 mm, of each: Type IV high noble gold alloy, metal ceramic gold-palladium high noble alloy, chrome-cobalt base metal alloy were cast and divested with glass bead airborne particle abrasion. Twelve samples, with dimensions 13 x 18 x 10 mm, of titanium alloy were milled using an Origin Proteus 5x Milling Machine. Samples were treated with 1) Steam cleaning only, 2) Aluminum oxide airborne particle abrasion and 3) Aluminum oxide airborne particle abrasion with subsequent steam cleaning. Contact angle measurements were recorded immediately after each treatment and at 1 and 12 hours, using a goniometer and the sessile drop method. Surface free energy was calculated using VCA Optima XE software. </p><p> Results: Steam cleaning treatment showed no significant changes in surface free energy (dynes/cm), compared to pretreatment values for the alloys investigated except Titanium alloy, which showed a modest increase in surface energy (p &lt; 0.05). Aluminum oxide airborne particle abrasion and aluminum oxide airborne particle abrasion with steam cleaning, resulted in an increase in surface free energy for all alloys investigated when compared to pretreatment and steam clean only values. Steam cleaning following airborne particle abrasion produced significantly lower (p&lt;0.001) surface free energy values compared to airborne particle abrasion alone for high noble gold alloy and metal ceramic gold-palladium high noble alloy. Exposure to ambient air following steam cleaning had minimal or non-enduring effects on surface free energy for all alloys investigated except Titanium alloy, which showed a significant decrease (p&lt;0.001) in surface free energy with time of ambient exposure. Exposure to ambient air following airborne particle abrasion with aluminum oxide resulted in a significant decrease (p&lt;0.001) in surface free energy for high noble gold alloy, metal ceramic gold-palladium high noble alloy and chrome-cobalt base metal alloy, however, Titanium alloy showed no ambient exposure effects. Ambient exposure following aluminum oxide airborne particle abrasion with steam cleaning resulted in a significant decrease (p&lt;0.001) in surface free energy for all alloys investigated. </p><p> Conclusions: Within the limitations of this study, it was found that aluminum oxide airborne particle abrasion, with and without subsequent steam cleaning, significantly increased the surface free energy of the dental alloys investigated. Steam cleaning following aluminum oxide airborne particle abrasion significantly reduced the surface free energy gain that the high noble alloys experienced with aluminum oxide airborne particle abrasion alone. And finally, exposure to ambient air following aluminum oxide airborne particle abrasion with and without subsequent steam cleaning resulted in a significant decrease in surface free energy for most alloys investigated.</p>

<p> In this thesis, the conventional four-point measurement technique and the van der Pauw (vdP) method are systematically investigated in the presence of non-ideal conditions, namely, non-uniform carrier density distribution and absence of ohmic contacts, which are nonetheless commonly encountered in semiconductor characterizations. Upon understanding the challenges in the conventional methods, novel characterization techniques are developed to address these challenges. </p><p> A longitudinal magnetoresistance asymmetry method was developed to study the carrier density non-uniformity in two-dimensional samples. By analyzing the asymmetric longitudinal magnetoresistance under positive and negative <i> B</i>-fields, an analytical model based on a linear density gradient across the sample was deduced to quantitatively describe the asymmetry. Based on the theoretical model, a practical method was described which enabled one to experimentally measure the density gradient within a single sample. The method requires only measurements of longitudinal resistances <i>R_xx</i> and <i>R_yy</i> under both positive and negative <i>B</i>-fields, and equations have been provided to extract both the angle and the magnitude of density gradients from the measured resistances. The method was demonstrated in a GaAs quantum well wafer at cryogenic temperatures and <i>n</i>-GaAs bulk-doped wafer at room temperature. In both systems, the density gradient vectors extracted with our method matched well with the interpolated density gradient vectors estimated from actual density distribution maps as a base comparison set, suggesting that our method can be a universal extension of the vdP method to extract density gradients in various systems. The method also allows one to uncover the true local longitudinal resistivity &rho;<i>_xx</i> at the center of the sample, which the conventional vdP method cannot describe in the presence of non-uniform densities. The ability to find &rho;<i>_xx</i> makes it possible to study interesting physics in semiconductors such as interaction-induced quantum corrections to resistivity and valley filtering in multi-valley systems. </p><p> To extend the vdP method to cases where ohmic contacts are not available, a capacitive contact technique was introduced which sends current and senses voltage capacitively. A capacitive contact is formed between the buried conducting layer and the contact metal which is simply evaporated onto the sample. Systematic studies of four-point measurements with ohmic and/or capacitive contacts were conducted on a test sample and a Hall bar sample to demonstrate the effectiveness of the capacitive contact method. With a pre-defined capacitive scaling factor &gamma; and a measurement frequency band (<i>f_L</i> &sim; <i> f_H</i>), it was shown that capacitive contacts could extract the same four-point resistance as ohmic contacts, establishing the validity of the capacitive contact technique. </p><p> Built on the idea of capacitive coupling with capacitive contacts, a contactless electrical characterization probe was proposed. On the probe head, there are two types of metal gates: depletion gates to define a test region and separate the contacts, and capacitive contacts to conduct four-point measurements. To characterize a piece or a region on a wafer hosting a buried conducting layer, one brings the probe onto the sample, conducts the electrical measurements with the capacitive contacts, and removes the probe. The sample remains untouched and can be reused. The contactless probe should provide a fast and nondestructive way of semiconductor characterization.</p>

<p> Self-assembly of soft materials represents a compelling approach to realize a wide variety of useful nanostructured materials. In particular, self-assembly of block copolymers by microphase separation results thermodynamically in the formation of a range of nanostructures including lamellae, cylinders, gyroids and spheres. There is significant potential to use these structures in applications ranging from energy generation to water purification. Despite their significant potential however, the use of block copolymers in the aforementioned areas has been critically limited by general inability to precisely direct their self-assembly, i.e. to control the orientational and positional order of their self-assembled structures over device or application relevant length scales and geometries.</p><p> In this context, we explore two distinct approaches to attain advanced ability to control the block copolymer microphase. First, this dissertation explores the self-assembly and directed self-assembly of novel liquid crystalline block copolymers. Result are presented from a systematic series of experimental investigations of the phase behavior and directed self-assembly of rationally designed liquid crystalline block copolymers (LC BCPs) under magnetic fields and in the presence of engineered surfaces. We specifically designed a block copolymer platform comprising etchable poly(D,L-lactide) (PLA) with brush architecture and side chain cyanobiphenyl LC block that imparts magnetic anisotropy on the system. Interestingly, this class of brush-like block copolymers behave in accordance with the canonical phase behavior of the conventional linear coil-coil block copolymers. With inclusion of labile mesogen, the magnetic field response of the system was significantly enhanced due to the increased grain size and faster mobility. By adopting cross-linkable mesogen, the LC phase can be readily polymerized and subsequent etching of the PLA produces well-defined nanopores with controlled orientation. At higher blending stoichiometric ratio, the system transforms its morphology from hexagonal cylinders to face-centered cubic (FCC) spheres and, strikingly, we observe the alignment of FCC spheres regardless of the 3 dimensional symmetry of the cubic structure.</p><p> In the second part, we adopt the use of electrospray deposition and soft-shear laser zone annealing process as tools to direct the self-assembly of structurally complex thin films of block copolymers. Conventionally, block copolymers confined in thin film were examined based on the equilibrium structure as a result of a single annealing process. Here we propose non-equilibrium processing methods that enable us to achieve non-conventional morphologies. Sequential electrospray deposition (ESD) was adopted to form multi-layered BCP thin films which exhibit heterolattice structure that can be precisely tuned by kinetic parameters. We also examine pathway-engineered two-step processing, shear aligning followed by thermal annealing on a neutral substrate, to achieve biaxial alignment of the BCP cylinders array with minimum defect density. </p><p> Overall, this dissertation provides new insight regarding the self-assembly of LC brush block copolymers and their orientation in the presence of magnetic fields. Further, it establishes a new mechanism for controlling the orientation of these materials in thin films. The results of the research presented here are relevant for the use of block copolymers in lithography and membrane fabrication, among other areas.</p><p>

Simulations are used in science and industry to predict the performance of technical systems. Adjoint derivatives of these simulations can reveal the sensitivity of the system performance to changes in design or operating conditions, and are increasingly used in shape optimisation and uncertainty quantification. Algorithmic differentiation (AD) by source-transformation is an efficient method to compute such derivatives. AD requires an analysis of the computation and its data flow to produce efficient adjoint code. One important step is the activity analysis that detects operations that need to be differentiated. An improved activity analysis is investigated in this thesis that simplifies build procedures for certain adjoint programs, and is demonstrated to improve the speed of an adjoint fluid dynamics solver. The method works by allowing a context-dependent analysis of routines. The ongoing trend towards multi- and many-core architectures such as the Intel XeonPhi is creating challenges for AD. Two novel approaches are presented that replicate the parallelisation of a program in its corresponding adjoint program. The first approach detects loops that naturally result in a parallelisable adjoint loop, while the second approach uses loop transformation and the aforementioned context-dependent analysis to enforce parallelisable data access in the adjoint loop. A case study shows that both approaches yield adjoints that are as scalable as their underlying primal programs. Adjoint computations are limited by their memory footprint, particularly in unsteady simulations, for which this work presents incomplete checkpointing as a method to reduce memory usage at the cost of a slight reduction in accuracy. Finally, convergence of iterative linear solvers is discussed, which is especially relevant on accelerator cards, where single precision floating point numbers are frequently used and the choice of solvers is limited by the small memory size. Some problems that are particular to adjoint computations are discussed.

Cellulose nanopaper is a fibrous network composed of cellulose nanofibres connected by hydrogen bonds, which shows pronounced mechanical and physical properties. This thesis investigates the mechanics of cellulose nanopaper from various aspects. First, the fracture properties of cellulose nanopaper were investigated using experimental and modelling approaches. It was found that the fracture strength of notched nanopaper is insensitive to notch length. Cohesive zone models were used to describe the fracture behaviour of notched cellulose nanopaper. Fracture energy was extracted from the cohesive zone models and divided into an energy component consumed by damage in materials and a component related to pull-out and bridging of nanofibres between cracked surfaces which is not facilitated by short nanofibres in nanopaper. Strain mapping revealed a small region of highly localized strain ahead of the notch tip with multiple stress concentration sites which are indicative of a stress delocalization mechanism. Secondly the inelastic deformation mechanisms of cellulose nanopaper were investigated. Results indicate that the inelastic deformation of cellulose nanopaper does not originate from fibre slippage and shearing as often suggested in literature but originates from inelastic deformation in amorphous regions in the cellulose nanofibres itself. It is proposed that this mechanism is associated with segmental motion of cellulose molecules facilitated by the breakage of hydrogen bonds within these amorphous regions. Thirdly, the effect of preparation methods on the mechanical properties of cellulose nanopaper was investigated. The influence of processing parameters such as compaction pressure and temperature was investigated and the mechanical properties of these nanopapers were compared with nanopaper prepared by a suspension casting method. Finally, a micromechanical fibrous network model was used to investigate the parameters that determine the elastic modulus of cellulose nanopaper. The effect of fibre size, waviness and modulus, inter-fibre bond density as well as network density on elastic modulus was investigated.

Polytetrafluoroethylene (PTFE) has some unique properties such as high hydrophobicity and high resistance to elevated temperatures, chemicals and solvents, which make it of interest for numerous fibre and textile applications. However, PTFE normally has a very high viscosity and poor flowability in the melt due to its ultra-high molecular weight, meaning that it cannot be readily melt-spun into textile fibres. In addition, PTFE is insoluble in all common organic solvents, prohibiting its use in common solution spinning methods such as dry, wet or electrospinning. Here we aim to develop an easy and environmentally friendly alternative for the production of PTFE nanofibres, using a modified island-in-the-sea spinning process. For this, first a dispersion of PTFE homopolymer, PVA and water was compounded to create a blend of PTFE particles in PVA solution using different methods, including casting, single-step extrusion and two-step-compounding and extrusion. After solid-state drawing of this blend and removal of the PVA, we were able to collect PTFE nanofibres with finest diameters of around 50nm and lengths up to 15μm. The effects of blend composition, morphology and drawing on PTFE fibre formation and properties were studied and discussed. Furthermore, some other material modification systems, including plasticized PVA, or the use ethylene glycol as a solvent, was studied with the aim of scaling up the fabrication of PTFE nanofibres by spinning the PTFE/PVA blend fibres directly for a twin-screw extruder.