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Abstract: Nuclear fusion power is the promise of clean energy generation to meet the demands of the new century. However, containing a plasma with a core temperature ten times hotter than that of the sun is no easy task. The confinement vessel must be constructed from resilient materials that can withstand both the heat and the bombardment of the plasma species. ITER is the first proof-of-concept reactor in constructed. This thesis aims to assist in ITER's goals of understanding the complex fundamental plasma-material interactions and developing materials resilient to the harsh reactor conditions in the global push for nuclear fusion energy. The first goal of the thesis aims to investigate the thermodynamic properties of helium (He) bubbles to contribute to the existing understanding and models of He PMI expected in ITER. Bulk W samples were exposed to a low-energy (25 eV) He plasma at 573 K (LT) and 1050 K (HT). After plasma exposure, these samples were subject to TDS, ERDA, SEM, and in-situ TEM annealing. Structures comprised of a network of bubbles were stable up to 998 K during in-situ TEM annealing of the LT sample. He desorption from the LT sample was inferred to stem from interstitial He rather than these bubbles. Bubbles in the HT sample were found to be thermally active up to 998 K, resulting in an increase in the average bubble size and a loss of number density. GISAXS analysis on the effects of annealing on bubble radius distribution produces results consistent with the TEM. An "Ostwald ripening-like" model was proposed to explain the differences in annealing behaviours of the LT and HT samples. In-situ TEM annealing of a HT bulk W sample at 1073 K showed a reconfiguration of lattice atoms to reduce the surface area of large voids left behind after plasma exposure. It is suggested that lattice effects also contribute to the formation of fuzz and require more investigation. The results provided a deeper understanding of the bubble formation mechanism and subsequent thermodynamics based on the plasma exposure temperature. The differences in behaviour observed from these experiments can be used to help explain temperature-dependent effects such as recrystallisation suppression and form a wide set of consistent experiments for computational models to be compared to. The second goal of the thesis is to characterise the He-PMI of three alloys for possible use as a divertor material in future fusion reactors. Four sputter-deposited materials: sputtered pure W (WS), W-5%(wt)Ta, W-3%(wt)Cr, and W-5%(wt)Ta-3%(wt)Cr were exposed to 25 eV He plasma at LT and HT. After plasma exposure, these materials were subject to TDS, ERDA, SEM and TEM. The addition of Ta to Ws and WCr has been shown to inhibit the formation of He bubbles. This may be a case of increasing the fluence threshold for fuzz rather than the complete prevention of fuzz. Additionally, the addition of Ta slows grain growth of both Ws and WCr. This property is intrinsic to Ta rather than from an emergent W-Ta interaction and could potentially be used to delay the undesired but inevitable onset of recrystallisation. The electrical resistivities of the four sputtered films were measured as a surrogate for its thermal conductivity to characterise how this property changes with alloying and He exposure. The alloying of Ta significantly increases the resistivity of W, much more than that of Cr. As expected, He plasma exposure degrades the resistivity regardless of the material. WTaCr has the largest electrical resistivity and suffers the largest increase after He plasma exposure likely due to the presence of both alloying impurities deforming the lattice and serving as trapping sites. Both effects increase probability of electron scattering. The reduction in thermal conductivity from both alloying and He plasma irradiation, especially for alloys with more elements, will have to be considered alongside its other benefits when determining its viability for fusion reactors.

Open Access

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Abstract: Amphiphilic polymer conetworks (APCNs), composed of nanoscale phase-separated hydrophilic and hydrophobic domains, have recently attracted interest for passive photonic applications like wearable luminescent solar concentrators. Here, their utility is extended by integrating APCNs into the active layer of organic photovoltaics (OPVs), enabling the incorporation of down-conversion luminophores that are otherwise incompatible with conventional OPV architectures. The APCN scaffold confines hydrophilic luminophores within hydroxyl acrylate domains, while the hydrophobic PM6:Y6 bulk heterojunction (BHJ) resides in the polydimethylsiloxane domains. Luminophores are chosen for selective phase affinity and complementary absorption to the BHJ. Devices incorporating dicyanomethylene-4H-pyran (DCM) luminophores show enhanced photocurrent, with short-circuit current increasing from 25.7 to 27.3 mA cm−2, while maintaining an open-circuit voltage of 0.86 V. Transient absorption spectroscopy reveals delayed ground-state bleach in PM6 and Y6, consistent with efficient exciton replenishment via energy transfer from luminophores. Grazing-incidence wide-angle X-ray scattering shows that luminophore molecular planarity and dihedral angles influence BHJ packing via van der Waals interactions, impacting charge transport. This work presents a multifunctional approach to enhance optoelectronic devices by embedding functional moieties within APCNs, offering insights from photonic, optoelectronic, and structural perspectives and establishing APCNs as a versatile platform for next-generation device engineering.

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Abstract: Halide perovskites exhibit superior optoelectronic properties but lack precise thickness and band offset control in heterojunctions, which is critical for modular multilayer architectures such as multiple quantum wells. We demonstrate vapor-phase, layer-by-layer heteroepitaxial growth exemplified by CsPbBr3 deposition on single crystals of PEA2PbBr4 (PEA: 2-phenylethylammonium). Angstrom-level thickness control and subangstrom smooth layers enable quantum-confined photoluminescence of CsPbBr3 from monolayer, bilayer, and through to bulk. The interfacial structure controls the electronic structure from a Cs‒PEA-terminated interface (type II heterojunction) to a PEA‒PEA-terminated interface (type I heterojunction), with a layer-tunable band offset shift exceeding 0.5 electron volts. Electron transfer from CsPbBr3 to PEA2PbBr4 for a type II Cs‒PEA heterojunction results in delayed electron-hole recombination beyond 10 microseconds. Precise quantum confinement control and large band offset tunability unlock perovskite heterojunctions as platforms for scalable, superlattice-based optoelectronic applications.

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Abstract: Controlling the crystal phase of two-dimensional transition metal dichalcogenides (TMDs) is essential for tailoring their electronic and optical properties. Among the polymorphs of WS2, the metastable 1T′ phase exhibits semimetallic or narrow-bandgap character and hosts quantum functionalities distinct from the semiconducting 1H phase. Here, we investigate the temperature-induced 1T′/1H phase transition in colloidally synthesized monolayer WS2 nanosheets functionalized with organic ligands. The reducing conditions of the synthesis stabilize the 1T′ phase via electron doping. Through in situ analyses of both the structural and electronic properties, we monitor the phase evolution during annealing and find that the 1T′ phase remains stable up to 300 °C, accompanied by a relative lattice contraction. Between 300 and 350 °C, a mixed 1T′/1H regime appears, where the 1H content can be finely tuned by controlling the annealing time. Above 350 °C, a rapid and complete transformation to the 1H phase occurs. We demonstrate that the decomposition of the reducing ligand serves as the primary trigger of the structural transition, revealing a strong interplay among doping, surface chemistry, and lattice structure. Notably, nanosheets with smaller lateral dimensions exhibit slower phase transition kinetics, suggesting that finite size could influence the structural rearrangement underlying the phase transformation.

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Abstract: Interfacial electrochemistry is fundamental to the development of electrocatalytic renewable energy technologies such as fuel cells, batteries and carbon capture systems. Although vast amounts of resources are applied to the fabrication and characterisation of electrocatalysts, for technologies such as these to be viable on a large scale and mitigate the effects of anthropogenic climate change, a better fundamental understanding of the atomic and electronic structure of the electrochemical interface is required. This thesis presents the results of a series of experiments employing surface X-ray diffraction (SXRD) of the electrochemical interface of fcc(111) metal surfaces. First presented is an SXRD study of Cu(111) and Ag(111) surfaces in varying concentrations of aqueous acetonitrile-containing electrolyte. The study shows evidence of a combination of potential-induced dissolution and re-adsorption of surface metal layers and formation of surface metal oxides, and a roughening of the metal surface with increasing concentrations of acetonitrile, demonstrating the dramatic effect that acetonitrile can have on transition metal surfaces without being specifically adsorbed. A study of thin cobalt films electrodeposited on Au(111) surfaces is also presented, where energy-dispersive resonant SXRD measurements reveal subtle changes in the RSXRD spectrum at the cobalt K edge depending on the thickness of the thin film and the applied electric field, providing foundational information on the underlying physical mechanism behind the favourable magneto-electric properties of thin Co films. Lastly presented is a study of the cation contribution to the structure of the electrochemical interface, consisting of measurements of Pt(111) and Au(111) in aqueous cesium hydroxide (CsOH) electrolyte. The study employs SXRD to construct a model of the electrochemical interface, combined with resonant SXRD and XAS measurements. Results suggest a hydrated Cs layer ordered in the plane of the surface on Pt(111), while measurements on Au(111) suggest a more disordered Cs layer. The experimental work detailed in this thesis, performed over a series of experimental sessions at synchrotron facilities (the i07 beam line at Diamond Light Source, Didcot, UK, the XMaS beamline at the ESRF, Grenoble, and the Advanced Photon Source, Illinois), represents a significant contribution to our understanding of the electrochemical interface, demonstrating the power and versatility of SXRD and providing foundational information for the development and refinement of vital electrochemical technologies.