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Conjugated semiconducting polymers have garnered substantial interest in recent years due to the potential for use in various applications, particularly in the field of electronic devices such as photovoltaic cells and light emitting diodes. Conjugated polymers offer numerous advantages in these applications, including low cost and high flexibility, but electronic devices based on these materials are currently limited by poor performance. Because of these limitations, increased focus has been placed on improving conjugated polymers for use in commercially viable products. Here, a novel core shell hybrid nanocomposite based on anisotropic zinc oxide nanowires and a side-chain functionalized polythiophene is reported. This nanocomposite exhibits confirmed covalent side-on linkage between the polymer and the nanowires, and the crystalline, thermal and photophysical properties of the nanocomposite are investigated, revealing elongated conjugation length in the polymer backbone, increased crystallinity and thermal stability and rapid charge transfer. Additionally, the conformational transitions of side-chain functionalized polythiophenes are investigated in dilute solution through the use of ultraviolet-visible absorption spectrophotometry. A coil-to-rod conformational transition is identified, and is found to be induceable through temperature and solvent changes. Study into the kinetics of the transition reveals a first-order rate law, and the effects of polymer structure on the conformational transition are substantiated.

Two dimensional (2D) materials have received growing interest because of their unique properties compared to their bulk counterparts. Graphene is the archetype 2D solid, but other materials beyond graphene, such as MoS2 and BN have become potential candidates for several applications. Recently, a new family of 2D materials of early transition metal carbides and carbonitrides (Ti2CTx, Ti3C2Tx, Ti3CNTx, Ta4C3Tx, and more), labelled MXenes, has been discovered, where T stands for the surface-terminating groups. Before the present work, MXenes had only been synthesized in the form of exfoliated and delaminated powders, which is not suitable for electronic applications. In this thesis, I demonstrate the synthesis of MXenes as epitaxial thin films, a more suitable form for electronic and photonic applications. Results show that 2D epitaxial Ti3C2Tx films - produced by HF and NH4HF2 etching of magnetron sputter-grown Ti3AlC2 - exhibit metallic conductive behaviour down to 100 K and are 90% transparent to light in the visible-infrared range. The results from this work may open the door for MXenes as potential candidates for transparent conductive electrodes as well as in electronic, photonic and sensing applications. MXenes have been shown to intercalate cations and molecules between their layers that in turn can alter the surface termination groups. There is therefore a need to study the surface chemistries of synthetized MXenes to be able to study the effect of intercalation as well as altering the surface termination groups on the electronic structure and chemical states of the elements present in MXene layers. X-ray Photoelectron Spectroscopy (XPS) in-depth characterization was used to investigate surface chemistries of Ti3C2Tx and Ti2CTx. This thesis includes the discussion of the effect of Ar+ sputtering and the number of layers on the surface chemistry of MXenes. This study serves as a baseline for chemical modification and tailoring of the surface chemistry groups to potential uses and applications. New MXene phases, Nb2CTx and V2CTx, are shown in this thesis to be produced from HF chemical etching of Nb2AlC and V2AlC powders. Characterization of the produced MXenes was carried out using Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD), Transmission Electron Microscope (TEM) and XPS. Nb2CTx and V2CTx showed promising performance as electrodes for Li-ion batteries. In this thesis, electrochemical etching was used in an attempt to produce 2D metal carbides (MXene) from their ternary metal carbides, Ti3SiC2, Ti3AlC2 and Ti2AlC MAX phases. MAX phases in the form of highly dense bulk produced by Hot Isostatic Press. Several etching solutions were used such as HF, NaCl and HCl. Unlike the HF chemical etching of MAX phases, which results in MXenes, the electrochemical etching resulted in Carbide Derived Carbon (CDC). Here, I show the characterization of the produced CDC using several techniques such as XRD, TEM, Raman spectroscopy, and XPS. Electrochemical characterization was performed in the form of cyclic voltammetry, which sheds light on the etching mechanism. / <p>The series name <em>Linköping Studies in Science and Technology Licentiate Thesis</em> in this publication is incorrect. Correct name is <em>Linköping Studies in Science and Technology. Thesis</em>.</p>

In the agricultural industry, cultivator tines are used for stubble cultivation and seedbed preparation. They are exposed to rapidly developing abrasive wear, which becomes a major economic problem. The occurring wear in the tines is heavily dependent on the characteristics of the soil which it passes through. In this master thesis the goal is to produce a method which, in a laboratory environment, can reproduce the circumstances which real cultivator tines are exposed to in the field. The method will enable analysis and evaluation of the initial wear mechanisms causing the wear. In order to simulate the tillage, a pendulum setup was constructed. With this, a series of repeated impact tests were performed into a soil sample. Throughout the tests, the “cultivator tine” samples were made of aluminium. This material choice would enable an accelerated wear rate, following its low hardness. All tests were performed in the same soil, with moisture content being the only varying parameter;~0% and 18% respectively. The samples which had passed through soil with higher moisture showed reduced wear compared to those which had passed through dry soil. The pendulum setup contributed to the tests being executed in a controlled and reliable manner. Hence, it is determined to be suitable for further use in any future project work related to the subject.

In this project, different molecules have been investigated with the purpose of creating anohmic contact between metals and carbon nano materials. In particular, we considered simplemolecules connecting a graphene layer and a copper-slab. In order to determine the capability of such systems, the electronic structure was computedusing Density Functional Theory (DFT). Structural relaxation was performed in order to findcandidates where the metal and the graphene binds chemically with the hypothesis that thehybridization of the states will induce more states at the Fermi level. Six different molecularchains were tested and three of them were found to chemisorb to the graphene sheet and thecopper surface simultaneously. The electronic properties for these systems were then furtherinvestigated using the density of states (DOS). An overlap density of states (ODOS) wasdefined in order to evaluate the respective contribution of the graphene, metal and molecule. From the DOS analysis, we report that these systems did not form ohmic contacts as the resultshows too few states close to the Fermi level. The most interesting case was using a hexanolchain which had some partially overlapping states seen from the ODOS of the graphenemoleculeand graphene-Cu at the Fermi level. However, these were only small contributions.Further research is crucial in order to find a more suitable molecular chain between thegraphene and the copper for an ohmic contact.

<p>Series of rare-earth intermetallic compounds were synthesized and studied.</p> <p>The Gd₄Ge_3-<em>x</em><em>Pn_x</em> (<em>Pn</em> = P, Sb, Bi; <em>x</em> = 0.5 - 3) series of compounds were synthesized to explore the stability of the non-existent Gd₄Ge₃ binary through partial <em>Pn</em> substitutions to increase valence electron concentrations. Electronic band structure calculations were performed to elucidate the relationships between the hypothetical "Gd₄Ge₃" and Gd₅Ge₄ binaries. All Gd₄Ge_3-<em>x</em><em>Pn_x</em> phases order ferromagnetically with relatively high Curie temperatures of 234 to 356 K.</p> <p>The Gd₅Ge_4-<em>x</em>P<em>_x</em> phases were synthesized to explore the effects of both atomic size and valence electron concentration differences between Ge and P atoms. Partial substitution of P for Ge atoms occur on the interslab site, which causes the interslab distances to increase. In Gd₅Ge_4-<em>x</em>P<em>_x</em>, only a small amount of P substitution (<em>x</em> = 0.25) is required to induce ferromagnetic ordering. The appearance of a Griffiths phase is also discussed.</p> <p>The temperature dependence of the different <em>RE</em>₂Fe₁₇ (<em>RE</em> = Gd - Ho) phases was tracked by reciprocal space images generated from single crystal X-ray diffraction.</p> <p>GdCo₄B was synthesized by arcmelting and tri-arc techniques to confirm the presence of magnetostriction. Single crystal and powder X-ray diffraction, dilatometer and magnetic measurements were done.</p> / Master of Science (MSc)

Carbon quantum dots (CQDs) are the latest generation of carbon nanomaterials in applications where fullerenes, carbon nanotubes, and graphene are abundantly used. With several attractive properties such as tunable optical property, edge-functionalization, and defect-rich chemical structure, CQDs have the potential to revolutionize optoelectronics, electro- and photocatalysis, and biomedical applications. Chemical modifications through the addition of heteroatoms, chemical reduction, and surface passivation are found to alter the band gap, spectral position, and emission pathways of CQDs. Despite extensive studies, fundamental understanding of structure-property relationship remains unclear due to the inhomogeneity in chemical structure and a complex emission mechanism for CQDs. This dissertation outlines a series of works that investigate the structure-property relationship of CQDs and its impact in a variety of applications. First, this relationship was explored by modifying specific chemical functionalities of CQDs and relating them to differences observed in optical, catalytic, and pharmacological performance. While a number of scientific articles reported that top-down or bottom-up synthesized CQDs yielded similar properties, the results herein present dissimilar chemical structures as well as photoluminescent and metal sensing properties. Second, the role of nitrogen heteroatoms in top-down synthesized CQD was studied. The effect of nitrogen atoms on spectral position and fluorescence quantum yield was considerably studied in past reports; however, thorough investigation to differentiate various nitrogen related chemical states was rarely reported. By finely tuning both the quantity of nitrogen doping and the distribution of nitrogen-related chemical states, we found that primary amine and pyridine induce a red-shift in emission while pyrrolic and graphitic nitrogen produced a blue-shift in emission. The investigation of nitrogen chemical states was extended to bottom-up synthesized CQDs with similar results. Finally, top-down, bottom-up, nitrogen-doped and chemically reduced CQDs were separately tested for their ability to act as photodynamic anti-cancer agents. This series of experiments uncovered the distribution of reactive oxygen species produced during light exposure which elucidated the photodynamic mechanisms of cancer cytotoxicity. The results presented in this dissertation provide key insight into engineering finely-tailored CQDs as the ideal nanomaterial for a broad range of applications.

Plastics or polymers are thought to behave oppositely from metals. Ideally, polymers behave as insulators while metals conduct electricity. Shirakawa and coworkers discovered conductive polymers in 1977.1 These conductor polymers have been extensively studied, discovering that charge transfer oxidative doping of polyacteylene could increase its conductivity by 12 orders of magnitude. Polyacetylene, although showing promise as an organic conductor, because it is highly air-sensitive and oxidizes when exposed to molecular oxygen, therefore making this an unattractive use for commercial products. Attention has been focused on heterocylic aromatic polymers such as polythiophene and polypyrrole, in efforts to produce conductive polymers that are air-stable, tractable, and have a low band gap. The lone-pair electrons of the sulfur and nitrogen atoms tend to stabilize the positive charges of the p-doped polymers through resonance. 2 By using Shirakawas’ idea of using polypyrrole as the focus point of our research and expanding upon that by the addition of a rhenium metal to an organic compound, (1,2-C5H3(CNR)2) and this should offer some new and interesting chemical properties. These new properties are; new optical properties, new electronic properties, improved physical properties, and a reversible electrochemical shift. This research will help in the field of organometallic semiconductors in applications such as OLED’s, and electrochromic windows.3-6

<p>This thesis investigates the structure and ion mobility properties within the phosphate and fluorophosphate family of cathode materials for Li ion batteries using solid-state NMR. Developments in lithium ion battery technology are now directed towards automotive applications meaning that many of the cost and safety issues associated with current lithium ion battery technology need to be addressed. Within the current systems the high cost is largely attributed to the use of LiCoO₂ as the positive electrode. Many new and inexpensive Li intercalation materials have been put forward as alternatives to LiCoO₂, however the details concerning the structural and ion-transport properties of these new phases are not well defined. ^6,7Li, ³¹P, and ¹⁹F NMR measurements are an ideal tool to study these properties, as ^6,7Li is able to probe the local environment and dynamics of the mobile ion while ³¹P and ¹⁹F monitor changes in the host framework. Materials selected for study in this thesis include olivine LiFePO₄, monoclinic Li₃M₂(PO₄)₃ (M = V, Fe), the tavorite-based Li₂VPO₄F and Li₂VOPO₄, and the novel layered Li₅V(PO₄)₂F₂. The fluorophosphates have been introduced as higher voltage cathode materials for lithium batteries, however our ^6,7Li 1D selective inversion and 2D EXSY measurements reveal timescales of ion hopping that are relatively slow when compared to those measured in the phosphates. This indicates that the improved power output from the voltage gains may be lost to slow charge/discharge rates.</p> / Doctor of Philosophy (PhD)

<p>Differences in the wavelengths of the surface plasmon band of gold nanoparticles (AuNP) – before and after particle aggregation – are widely used in bioanalytical assays. However, the gold surfaces in such bioassays can suffer from exchange and desorption of non-covalently bound ligands and from non-specific adsorption of bio-molecules. Silica shells on the surfaces of the gold can extend the available surface chemistries for bioconjugation and potentially avoid these issues. Therefore, silica was grown on gold surfaces primed with polyvinylpyrrolidone (PVP) using either hydrolysis/condensation of tetraethyl orthosilicate under basic conditions or diglycerylsilane at neutral pH. The former precursor permitted slow, controlled growth of shells from about 1.7 to 4.3 nm thickness. By contrast, silica shells formed within an hour using diglyceroxysilane; the thickness was insensitive to changes in silane concentration and incubation time and could be tuned using different molecular weight PVP to prime the particles. The control over shell thickness is discussed with respect to the PVP interface, the electrical double layer, and interpenetrating organic-inorganic hybrid structures. Within the range of shell thicknesses synthesized, the presence of a silica shell on the gold nanoparticles did not significantly affect the absorbance maximum (~ 5 nm) of unaggregated particles. However, the change in absorbance wavelength upon aggregation of the particles was highly dependent on the thickness of the shell. With silica shells coating the AuNP, there was a significant decrease in the absorbance maximum of the aggregated particles, from ~578 to ~536 nm, as the shell thicknesses increased from ~1.7 to ~4.3 nm, due to increased distance between adjacent gold cores. These studies provide guidance for the iv development of colorimetric assays using silica coated AuNP. Such particles also show potential for application in 2D and 3D nanostructured assemblies.</p> / Master of Science (MSc)