<p dir="ltr">Nature has been shown to build environments to drive specific reactivity across boundaries; multiphase systems, for example, have been shown to drive reactions that would otherwise not occur in bulk, continuous phases. Within this work, we show how multiphase environments are essential in driving specific reactivity at phase boundaries and offer unique physicochemical and electrochemical opportunities that are usually inaccessible in continuous phases alone. Here, we present several diverse approaches toward harnessing observed interfacial phenomena to study and take advantage of three-phase systems. Firstly, we demonstrate precise manipulation of nucleation at the water|1,2-dichloroethane (DCE)|electrode interface through electrode geometry adjustment, resulting in selective precipitation of ferrocenemethanol (FcMeOH). Cyclic voltammetry and numerical simulations elucidate this phenomenon's physico-chemical foundations, enabling localized precipitation and reactivity control. Secondly, we introduce a novel mechanism for emulsion formation driven by interfacial solute flux induced via phase transfer agents. Systematically exploring phase combinations and ion interactions, we elucidate the microscopic mechanisms governing droplet formation and propose design principles for tailored emulsion synthesis. Furthermore, leveraging current-driven ion flux, we achieve emulsification across oil|water interfaces, offering control over droplet size and charge. This low-energy, robust method presents an efficient alternative to traditional emulsification techniques. Additionally, we demonstrate facile electrodeposition of gold nanorings at water|oil interfaces, enabled by spontaneous emulsification facilitated by quaternary ammonium salts. We further demonstrate deposition parameters for control over nanoring array characteristics, offering a streamlined approach to nanoring fabrication. Finally, we introduce biphasic electrodeposition as a versatile method for fabricating ultra-high aspect ratio gold nanowires. By manipulating antagonistic metal salt interactions at liquid|liquid interfaces, we achieve precise control over nanowire geometry and positioning, opening new avenues for nanowire synthesis with enhanced simplicity and versatility.</p>

<p dir="ltr">Food packaging plays a crucial part, yet the use of petroleum-based plastics has led to environmental concerns. Researchers have been exploring sustainable alternatives using CNMs. This dissertation includes three parts, each focusing on using CNF or CNC for packaging applications. In the first project, CNF/CMC coated MP trays were achieved via over-molding. Mechanical, Gurley air porosity and water vapor transmission rate testing showed that the coating improved the overall performance. Coated samples showed the highest oil and grease resistance level. Fresh fruit testing showed that the coating helps elongate the shelf life of fruits. In the second project study, to overcome the problem of relatively poor water barrier performance of CNF/CMC coatings in high humidity conditions, coatings were chemically modified by crosslinking with PAE and incorporated with Cloisite-Na⁺ nano-clay and PVA. The chemical modification enhanced both water and oxygen barrier performance and reduced Cobb value. The formulated CNF-coated MP trays maintained the same level of oil and grease resistance. Mechanical testing showed reduced Young’s modulus, similar UTS, and higher strain at break for formulated CNF-coated tray samples compared to the un-crosslinked samples. In the third project, a transparent tri-layer PLA-CNC/PVA-PLA film was successfully fabricated using blade coating and lamination. The CNC/PVA coating (~ 6μm) showed a high degree of CNC alignment and significantly enhanced the gas barrier properties. Furthermore, these laminates were formed into bags where a fruit storage test showed that the PLA-CNC/PVA-PLA could elongate the shelf life of fresh apple slices based on weight loss and enzymatic browning.</p>

<p dir="ltr">The exploration of tellurene as a large-area, stable p-type semiconductor has been a key focus of research for several years. In my work, I have made notable strides by successfully fabricating ambipolar Te-FETs using contact engineering techniques. Notably, we observed that the polarity characteristics of Te flakes depend on their thickness: thinner flakes exhibit p-type behavior, while thicker ones show n-FET characteristics.</p><p dir="ltr">To better understand the carrier transport mechanism in 2D Te FETs, we developed a novel "sandwich" model. This model accounts for the differing properties of the surface layer compared to the inner layers, combining insights from both experimental data and advanced simulations. By addressing the variations between the surface and the body layers, we have gained new insights into the thickness-dependent polarity of Te FETs—an area previously explained through band structure alignment theory in other 2D semiconductors.</p><p dir="ltr">Surface native oxide's influence on FET transport has often been neglected in similar materials. However, in our research, we specifically focused on charge transfer doping caused by Te's native oxide. By directly reducing the surface oxide layer, we highlighted the importance of environment-induced surface defects, like native oxide, which are almost unavoidable in nanoelectronics based on 2D materials. These defects result in a chemically distinct surface composition, causing band bending in the out-of-plane direction near the surface.</p><p dir="ltr">In addition to these fundamental findings, we reached a significant practical milestone by successfully constructing a monolithic CMOS inverter. This was achieved through careful control of Te thickness and contact design, ensuring optimal device performance. We also advanced polarity engineering by demonstrating a homojunction based on Te flakes of different thicknesses, showcasing the versatility and potential of polarity control in 2D materials. This has exciting implications for the development of photodetectors and photovoltaic devices.</p><p dir="ltr">Overall, our research provides important insights into the transport mechanisms and polarity engineering of 2D semiconductors, with a particular focus on tellurene. Our findings not only enhance the understanding of Te FETs but also have broader implications for the field of 2D materials and their applications in advanced electronics.</p>

In this research thermal properties enhancement of phase change material (PCM) using boron nitride nanomaterials such as nanoparticles and nanotubes is studied through experimental measurements, finite element method (FEM) through COMSOL 5.3 package and molecular dynamics simulations via equilibrium molecular dynamics simulation (EMD) with the Materials and Process Simulations (MAPS 4.3). This study includes two sections: thermal properties enhancement of inorganic salt hydrate (CaCl2∙6H2O) as the phase change material by mixing boron nitride nanoparticles (BNNPs), and thermal properties enhancement of organic phase change material (paraffin wax) as the phase change material via encapsulation into boron nitride nanotubes (BNNTs). The results of the proposed research will contribute to enhance the thermal transport properties of inorganic and organic phase change material applying nanotechnology for increasing energy efficiency of systems including electronic devices, vehicles in cold areas to overcome the cold start problem, thermal interface materials for efficient heat conduction and spacecraft in planetary missions for efficient thermal managements.

Ce manuscrit est consacré à l’étude et au développement de microsystèmes capteurs de gaz sélectifs au dioxyde d’azote, destinés au contrôle de la qualité de l’air atmosphérique. La stratégie que nous avons développée consiste à associer une structure sensible à base de matériaux semi-conducteurs partiellement sélectifs aux gaz oxydants et des filtres sélectifs à l’ozone. L’objectif premier est la mise en oeuvre et la caractérisation de matériaux chimiques strictement imperméables à l’ozone (O3) et non-réactifs vis-à-vis du dioxyde d’azote (NO2). Notre choix s’est focalisé sur un matériau moléculaire, l’indigo, connu pour sa réactivité vis-à-vis de O3, et plusieurs nanomatériaux carbonés. Pour ces derniers, la possibilité de conformer leurs textures, leurs morphologies et leurs chimies de surface par traitements thermiques, chimiques et mécaniques, permet d’étendre le panel de matériaux potentiels et d’identifier les facteurs d’influence de leur réactivité avec les espèces gazeuses. La caractérisation de l’ensemble de ces matériaux a nécessité l’utilisation de techniques adaptées et complémentaires (adsorption de N2 à 77 K, spectroscopies Raman, XPS, IR en mode ATR, RPE et NEXAFS). Les filtres chimiques les plus efficaces (hauts rendements de filtration et grande durabilité) ont été sélectionnés d’après des tests de soumission aux gaz selon une méthodologie adaptée. Enfin, l’association de ces meilleurs filtres et de la structure capteur a conduit à l’élaboration de prototypes microsystèmes capteurs de gaz optimisés. De plus, une contribution à la compréhension des mécanismes d’interaction de l’indigo et de certains nanocarbones avec O3 et NO2 a aussi permis d’améliorer le microsystème en développant des méthodologies pertinentes et innovantes mais également en réalisant la synthèse de nouveaux filtres indigo / nanocarbone. / This work is devoted to the study and the development of gas sensors microsystems highly selective to nitrogen dioxide, dedicated to the air quality control. The strategy developed consists in the implementation of a sensitive structure based on semiconductor materials partially selective to oxidizing gases associated to an ozone selective filter. The first objective is the development of chemical filters strictly impervious to ozone (O3) and non-reactive towards the nitrogen dioxide (NO2). We have chosen a molecular material, indigo, well-known for its reactivity towards O3, and several carbonaceous nanomaterials. For these one, the possibility to modify their textures, their morphologies and their surface chemistries by chemical, mechanical and thermic treatments, enables us to extend the range of potential materials and to identify the factors of influence on their reactivity with gaseous species. The characterization of all these materials required the use of appropriate and complementary techniques (N2 adsorption at 77 K, Raman, XPS, IR in ATR mode, EPR and NEXAFS). The more efficient filters (high filtering yield and life-time) have been selected by means of specific tests of gas exposure. Finally, the association of the best filter and the sensitive structure has led to the development of optimized gas sensors microsystems prototypes.

<p dir="ltr">In this dissertation, we investigate the potential of two-dimensional (2D) transition metal carbides, known as MXenes, as precursor materials for the development of ultra-high temperature ceramics (UHTCs), with a focus on Ti₃C₂T_<em>x</em> MXene. MXenes are distinguished by their unique combination of 2D structure, high surface area, and chemically active basal planes, making them ideal candidates for a wide range of high-performance applications. This study focuses on the phase transformation, grain growth, surface texturing, and electrocatalytic behavior of Ti₃C₂T_<em>x</em> MXene films when subjected to high-temperature annealing, along with their role as sintering aids in UHTCs.</p><p dir="ltr">We present the transformation of 2D Ti₃C₂T_<em>x</em> flakes into ordered vacancy carbides of three-dimensional (3D) TiC_y phases at temperatures above 1000°C. Using X-ray diffraction and ex-situ annealing (up to 2000°C in a tube furnace and spark plasma sintering), we investigate the resulting nano-lamellar and micron-sized cubic grain morphologies. Single-flake Ti₃C₂T_<em>x</em> films retain a lamellar morphology after annealing, while multi-layer clay-like MXene transforms into irregular cubic grains.</p><p dir="ltr">In addition to investigating the structural evolution, we examine the influence of cationic intercalation on grain growth and texture. Specifically, Ca²⁺ ions lead to highly templated growth along the (111) crystal plane, significantly altering carbon diffusion and metal atom migration during annealing. We show that this preferential growth influences properties with hydrogen evolution reactions (HER) as an example functionality. We observe that with Ca²⁺-intercalated Ti₃C₂T_<em>x</em> films, exhibit an overpotential of 594 mV and a current density of -13 mA/cm² due to increased surface area and dominant texturing.</p><p dir="ltr">Additionally, we investigate the use of MXenes in self-assembly with ceramic materials such as ZrB₂, facilitated by optimizing zeta potentials. MXenes, with their functionalized hydrophilic surfaces and negative zeta potentials, serve as sintering aids and reinforcements in UHTC composites. The introduction of Ti₃C₂T_<em>x</em> to ZrB₂ enables improved sinterability, achieving 96% relative density compared to 89% for pure ZrB₂. Furthermore, the addition of MXenes leads to a core-shell microstructure with (Zr,Ti)B₂ solid-solution interfaces, enhanced mechanical properties such as a 36% increase in hardness, and reductions in oxygen content. These findings establish MXenes as promising materials for the development of advanced UHTCs, suitable for extreme environments.</p><p dir="ltr">Through a combination of experimental techniques, and theoretical estimations, and advanced characterizations, this dissertation provides critical insights into the role of MXenes in both phase transformation and mechanical reinforcement, thereby laying the foundation for future studies and opening new avenues for applications of MXene derived carbides and the design of high-performance UHTCs.</p>

The aim of this thesis is to develop a deeper understanding and the technology in the nascent field of solid-state organic-inorganic perovskite solar cells. In recent years, perovskite materials have emerged as a low-cost, thin-film technology with efficiencies exceeding 16% challenging the quasi-paradigm that high efficiency photovoltaics must come at high costs. This thesis investigates perovskite solar cells in more detail with a focus on incorporating plasmonic nanostructures and perovskite film formation. Chapter 1 motivates the present work further followed by Chapter 2 which offers a brief background for solar cell fabrication and characterisation, perovskites in general, perovskite solar cells in specific, and plasmonics. Chapter 3 presents the field of plasmonics including simulation methods for various core-shell nanostructures such as gold-silica and silver-titania nanoparticles. The following Chapters 4 and 5 analyze plasmonic core-shell metal-dielectric nanoparticles embedded in perovskite solar cells. It is shown that using gold@silica or silver@titania NPs results in enhanced photocurrent and thus increased efficiency. After photoluminescence studies, this effect was attributed to an unexpected phenomenon in solar cells in which a lowered exciton binding energy generates a higher fraction of free charge. Embedding thermally unstable silver NPs required a low-temperature fabrication method which would not melt the Ag NPs. This work offers a new general direction for temperature sensitive elements. In Chapters 6 and 7, perovskite film formation is studied. Chapter 6 shows the existence of a previously unknown crystalline precursor state and an improved surface coverage by introducing a ramped annealing procedure. Based on this, Chapter 7 investigates different perovskite annealing protocols. The main finding was that an additional 130°C flash annealing step changed the film crystallinity dramatically and yielded a higher orientation of the perovskite crystals. The according solar cells showed an increased photocurrent attributed to a decrease in charge carrier recombination at the grain boundaries. Chapter 8 presents on-going work showing noteworthy first results for silica scaffolds, and layered, 2D perovskite structures for application in solar cells.

Quantum information processing (QIP) has the potential to reduce the complexity of many classically ‘hard’ computational problems. To implement quantum information algorithms, a suitable physical quantum computer architecture must be identified. One approach is to store quantum information in the electron spins of an array of paramagnetic N@C₆₀ endohedral fullerene molecules, using the electron-electron dipolar interaction to permit the formation of the entangled quantum states needed to implement QIP. This thesis explores two different chemical methods to create two-spin centre arrays that contain N@C₆₀. The first method uses a double 2,3 dipolar cycloaddition reaction to a dibenzaldehyde-terminated oligo-p-phenylene polyethynylene (OPE) unit , to create an (S_3/2, S_3/2) N@C₆₀-N@C₆₀ dimer with a fixed spin centre separation of 2.7 nm. The second approach is via a self-assembly scheme in which a Lewis base functionalised N@C₆₀ molecule coordinates to an antiferromagnetic metallic ring magnet to form a (S_3/2, S_3/2) two-spin centre N@C₆₀-Cr₇Ni system with an inter-spin separation of 1.4 nm. In both systems, a significant perturbation of the electron spin transition energies is observed using CW ESR, this perturbation is shown to be well accounted for by the inclusion of an electron-electron dipolar coupling term in the electron spin Hamiltonians. To create entanglement in an ensemble of two-spin centre molecules, the dipolar coupling interaction must lie within a narrow distribution. To achieve this not only the separation but also the orientation of the inter-spin axis with respect to the applied magnetic field must be controlled for which a method of macroscopic alignment is required. The potential of using a uniaxially drawn liquid crystal elastomer to exert uniaxial order on fullerene dimers is tested, finding that the degree of alignment is insufficient, possibly a result of the propensity for the fullerene molecules to phase separate from the elastomer. This phase separation is shown to restrict N@C₆₀ phase coherence lifetime to 1.4 µs at 40 K due to instantaneous spin diffusion. The electron spin environment of both N@C₆₀ and an N@C₆₀-C₆₀ dimer in a polymer matrix is examined using polystyrene as the host matrix. By deuteration of the polystyrene matrix, a maximum phase coherence lifetimes of 48 µs and 21 µs are measured for the N@C₆₀ and N@C₆₀-C₆₀ dimer, respectively. The concept of reading out the electron spin state of N@C₆₀ molecules by coupling it to a spin system that can be probed using optically detected magnetic resonance (ODMR) such as an NV- centre has been previously suggested. To this end, the photostability of N@C₆₀ under 637 nm laser illumination has been examined in solution. The effect of the presence of an atmospheric concentration of oxygen is striking, affording a 57-fold retardation in the photodecomposition of N@C₆₀ compared to a degassed solution. When ambient oxygen is present, the average number of excitations that are required to cause decomposition is ≈60000. Finally, for future UV photophysics experiments involving N@C₆₀, the best solvent to use was found to be decalin, finding that it significantly slowed decomposition of N@C₆₀ in both ambient and degassed solutions. The conclusions of this work make a significant contribution to the field of QIP with N@C₆₀, showing that there is a bright future for N@C₆₀.

The pursuit of high quality, large area graphene has been a major research focus of contemporary materials science research, in the wake of the discovery of the multitude of exceptional properties exhibited by the material. The DPhil project was undertaken with the objective of developing an understanding of the growth of large graphene sheets by chemical vapour deposition (CVD), and also in the subsequent characterisation of their material properties. By conducting atmospheric pressure CVD growth at high methane flow rates, it was found that few-layered graphene (FLG) could be deposited on a copper catalyst. It is demonstrated that the self-limiting property of a copper catalyst is not universal to all deposition conditions, and shown that FLG grows in a terrace-like configuration. In depth transmission electron microscopy (TEM) studies were carried out on FLG. By selective image reconstruction from the inverse power spectrum of the TEM images, it was possible to elucidate the inter-grain connectivity of few-layer graphenes. It was determined that there were two possible inter-grain configurations possible; specifically an overlap of graphene layers or a discrete atomic bonding edge. The perturbation of the few-layer structure when subject to an out of plane distortion was found to incur a shift in the conventional AB-Bernal stacking of FLG. By utilising the aberration corrected TEM (AC-TEM) at Oxford it was possible to resolve atomic detail in CVD synthesised monolayer films, including atomic bond rotations and vacancies. The use of a high current density at low accelerating voltage (80 kV) was demonstrated to allow for the controlled defect creation in graphene sheets. This permitted the creation of monovacancies and iron doped vacancy complexes suitable for further study. The behaviour of these two defect types under electron beam irradiation was subsequently studied.

Peptide tags are ubiquitous in the life sciences, with roles including purification and selective labeling of proteins. Because peptide tags are small they have a limited surface area for binding and hence usually form low affinity protein interactions. These weak interactions limit the uses of peptide tags in cases that require resistance to forces generated with macromolecular architectures or protein motors. Hence a way to create a covalent interaction with a peptide tag would be useful. It was found possible to create a covalent bond-forming peptide tag using the spontaneous isopeptide chemistry of the CnaB2 domain from the Gram-positive bacterium Streptococcus pyogenes. In the CnaB2 domain a reactive Lysine forms an isopeptide bond with an Aspartic acid, catalyzed by a Glutamic acid, creating an internal covalent linkage. Subsequently it was shown that the CnaB2 domain could be split into two parts, a domain with the Lysine and Glutamic acid called SpyCatcher and a peptide with the Aspartic acid called SpyTag, such that the isopeptide covalent linkage can be formed when SpyCatcher/SpyTag are mixed together. SpyCatcher/SpyTag was applied in this thesis and showed functionality in a wide array of scenarios. SpyCatcher/SpyTag covalently linked within the cytosol of E. coli, on surface membrane proteins of HeLa cells, and regardless of whether SpyTag was located on the N- or C-terminus or an internal site. Crystal structures of SpyCatcher/SpyTag were then obtained and it was found possible to shrink the SpyCatcher by 32 residues to a core domain of 83 residues. To create an even smaller covalent linkage system, SpyCatcher was split further to generate a protein (SpyLigase) ligating two peptide tags. The β-sheet with the reactive Lysine was removed from SpyCatcher and called KTag. SpyLigase could covalently link SpyTag and KTag. SpyLigase-induced ligation was independent of the location of SpyTag/KTag on the target proteins and was applied to create affibody polymers, which were shown to improve magnetic isolation of cells with low tumor antigen expression. Through this work protein-protein covalent linkage systems were refined and generated that have future applications for the creation of unique macromolecular structures, cellular labeling, and protein cyclization.