Thesis--University of Oulu, 1987. / Includes bibliographical references (p. 43-46).

Thesis--University of Oulu, 1987. / Includes bibliographical references (p. 43-46).

Thesis (Ph. D.)--Ohio State University, 2005. / Title from first page of PDF file. Document formatted into pages; contains xv, 99 p.; also includes graphics (some col.). Includes bibliographical references (p. 95-99). Available online via OhioLINK's ETD Center

One form of surface modification was primarily investigated in this work on glassy carbon electrodes. The form of modification is comprised of a series of steps in which electrografting is first applied to the glassy carbon surface, which is then followed up with click chemistry to ultimately immobilise a phthalocyanine onto the surface. The modified glassy carbon electrodes and surfaces were characterised with a combination of scanning electrochemical microscopy, X-ray photoelectron spectroscopy and various electrochemical methods. In this work, three alkyne substituted phthalocyanines were used. Two novel phthalocyanines, with nickel and cobalt metal centres, were studied alongside a manganese phthalocyanine reported in literature. Each of the three phthalocyanines was modified at the peripheral position with a 1-hexyne group, via a glycosidic bond, yielding the terminal alkyne groups that were used for subsequent click reactions. In situ diazotisation was used to graft 4-azidoaniline groups to the surface of the glassy carbon electrode. The azide bearing 4- azidoaniline groups were thus used to anchor the tetra substituted phthalocyanines to the surface of the electrodes. This method yielded successful modification of the electrodes and lead to their application in sensing studies. The modified electrodes were primarily used to catalyse the common agricultural oxidising agent hydrazine.

A detailed, fundamental understanding of the surface properties of molecular crystals and their interaction with adsorbing molecules (e.g. excipients) is important for tailoring the stability of formulations and the bioavailability of Active Pharmaceutical Ingredient (APIs). Few fundamental experimental studies with surface sensitive probes have been carried out for organic molecular crystals. X-ray photoelectron spectroscopy (XPS) is an established surface analysis method in the fields of adsorption, catalysis and surface chemistry of inorganic crystals. It has high surface sensitivity, probing approximately the top 1-3 nm of a crystal, and allows surface elemental analysis combined with the determination of the chemical state of the elements. To explore the possibilities and limitations of XPS for the surface characterisation of molecular crystal systems, investigation has been made on a range of paracetamol systems, three different poloxamers and blends of paracetamol with poloxamer 188. It was found by investigations of a range of polycrystalline paracetamol forms that the C1s, N1s and O1s core level emissions from the amide group of paracetamol allow to quantify, for the first time, the influence of surface contamination and adsorbed species on the paracetamol XPS data. Results of quantitative XPS analyses must be critically evaluated taking the material and energy-specific escape depth of the photoelectron signals into account. Analysis of the polycrystalline powder samples, including two different polymorphs and various partially amorphous forms of paracetamol, indicated that the core-level shifts associated with varying intermolecular interactions do not perturb the local electronic structure variations in paracetamol enough to become detectable through chemical shifts in the core level photoemission spectra. Subsequently, large, high quality single crystals of the monoclinic form I (with facet diameters between ~5 and ~10 mm) were obtained from different solvents (methanol, ethanol, acetone) to examine the influence of the crystallisation medium on the surface properties. Small spot XPS analysis was performed in several areas across facets to examine the possible influence of roughness and other lateral inhomogeneities. Careful curve-fitting of all results reveals only minor variations in the XPS data as a function of facet orientation, crystallisation medium or degree of crystallinity. Moreover, results indicate that any variations seen in XPS data very likely stem from low-level surface contamination, which is very difficult to avoid, even in a clean-room laboratory environment. In fact, the results indicate that the level of surface contamination depends significantly on the crystallisation apparatus cleanliness. Even minute concentrations of surface active components in the solutions, i.e. below the detection level of techniques for routine analytical methods, are likely to cause significant surface concentrations on crystal facets emersed from the solutions. The study thus highlights the paramount importance of microscopic surface cleanliness when assessing macroscopic facet-specific phenomena such as contact angles. Finally, XPS was employed to analyse milled and physical mixtures of paracetamol with poloxamer 188 at different percent. At minimum mass percentages poloxamer 188 adsorbs on the paracetamol surfaces; in the presence of poloxamer 188 excess the conformation of adsorbed poloxamer on the paracetamol surface changes. Studies of radiation damage on the poloxamer samples were performed both for several pure polxamers as well as for milled mixtures with paracetamol. They allowed the proposal of radiation-induced degradation mechanisms.

The ageing of polymer insulation occurs under long-term exposure to high electric fields and has attracted research due its relevance to high voltage insulation. In this work, polymers that have been electrically aged via a number of methods have been investigated using X-ray photoelectron spectroscopy (XPS). Despite some use in the investigation of outdoor insulation surfaces, XPS has not been used for investigations of polymer bulk electrical ageing before now. The first XPS measurements, using both small spot analysis and XPS imaging, are presented from the exposed inner surfaces of electrically aged artificial voids and electrical breakdown channels, as well as corona discharge aged surfaces and spark discharge by-products. XPS is shown to be a valuable technique for the investigation of polymer electrical ageing. Investigations into breakdown channels are supported by data acquired using X-ray photoemission electron microscopy (XPEEM) and scanning electron microscopy (SEM).Results show that the chemistry present at these surfaces takes the form of significant oxidation over a wide area with localised production of graphitic carbon. C-O-, C=O, and O-C=O species are detected in all cases. It is found that similar ageing products are present regardless of the ageing process or material investigated. However, the level of oxidation and relative ratio of the species seen with XPS is shown to be highly dependant on oxygen availability. Greater intensity of carbon oxides, and a shift towards highly oxidised species, is observed when there is more oxygen in the system. XPS imaging of breakdown channels reveals that high concentrations of oxidised components form on the outer edges of the channel, with graphitic carbon forming in the central regions. In addition, evidence for degradation is seen to extend at least 300 μm from channels in XPS imaging and at least ~650 μm in XPS line scans. Variation with the applied discharge energy was investigated for breakdown channels and spark discharge ageing. Evidence is seen for an energy dependence on the breakdown products, with higher energies producing relatively higher graphitic carbon and reduced oxidation products. Further, the relationship between the applied voltage and graphitic carbon concentration suggests an activated process with an energy barrier before graphitic carbon formation starts. XPS observations are supported by confocal Raman microprobe spectroscopy (CRMS) results from artificial voids and electrical breakdown channels, which identify graphitic carbon on a fluorescent background as the main features. XPS data indicate oxidised species are the origin of the fluorescence seen and provides quantitative information on the levels, chemical states and spatial distribution of these species and of graphitic carbon.

Models of chemical bonding are essential for contemporary chemistry. Even the explosive development of the computational resources including, both hardware and software, cannot eliminate necessity of compact, intuitive, and efficient methods of representing chemically relevant information. The Lewis model of chemical bonding, which was proposed eleven years before the formulation of quantum theory and preserves its pivotal role in chemical education and research for more than ninety years, is a vivid example of such a tool. As chemistry shifts to the nanoscale, it is becoming obvious that a certain shift of the paradigms of chemical bonding is inescapable. For example, none of the currently available models of chemical bonding can correctly predict structures and properties of sub-nano and nanoclusters. Clusters of main-group elements and transition metals are of major interest for nanotechnology with potential applications including catalysis, hydrogen storage, molecular conductors, drug development, nanodevices, etc. Thus, the goals of this dissertation were three-fold. Firstly, the dissertation introduces a novel approach to the description of chemical bonding and the algorithm of the software performing analysis of chemical bonding, which is called Adaptive Natural Density Partitioning. Secondly, the dissertation presents a series of studies of main-group element and transition-metal clusters in molecular beams, including obtaining their photoelectron spectra, establishing their structures, analyzing chemical bonding, and developing generalized model of chemical bonding. Thirdly, the dissertation clarifies and develops certain methodological aspects of the quantum chemical computations dealing with clusters. This includes appraisal of the performance of several computational methods based on the Density Functional Theory and the development of global optimization software based on the Particle Swarm Optimization algorithm.

No description available.

This dissertation summarizes my efforts and research in the Roy group to study the tunability of superatoms through ligand effects, create microporous structures from molecular cluster precursors to act as battery materials, and understand the electronic structure governing the interesting magnetic properties of Fe₆S₈(CN)₆, as well as efforts to design novel extended structures utilizing Fe₆S₈(CN)₆. Chapter 1 serves as an introduction to superatoms. It briefly discusses the quantum nature of small materials and how this gives rise to properties exhibited by superatoms. Properties which will prove important to this dissertation and methods of altering those properties through core composition and ligand choice are explored. Next, an overview of many methods to create extended structures is provided. Select examples of how superatomic clusters have already been used to increase our knowledge of fundamental concepts in science are then discussed. Finally, a brief summary and explanation of how these concepts will be explored in later chapters is given. This chapter is meant to serve as a targeted review with plenty of further reading cited for any incoming students with interest in continuing my projects. Chapter 2 discusses studies to understand the effects of either replacing PEt₃ ligands with CO ligands or the removal of PEt₃ ligands in the Co₆S₈(PEt₃)ₓ(CO)₆₋ₓ and Co₆S₈(PEt₃)ₓ systems, respectively. It presents a collaborative approach to synthesize a series of clusters for analysis by anion photoelectron spectroscopy and evaluation of results using computational chemistry. A drastic change in the donor/acceptor behavior of the cluster is observed, but surprisingly little change in the HOMO-LUMO gap is observed as the HOMO and LUMO experience similar energetic changes upon ligand removal or substitution. Chapter 3 presents a practical application for ligand removal of superatomic clusters. I present a synthesis of microspherical, highly porous materials derived from superatomic clusters. These microsphere materials display very different morphology from typical materials made using the same elemental ratio. This altered morphology results in a material which is favorable for use as a battery electrode. Its increased porosity improves its capacity retention upon cycling and at high power. The Co₆S₈(PEt₃)₆ derived material also shows promise as a Na+ ion battery material. In this chapter I also discuss unfinished studies on mixed chalcogenide materials. Chapter 4 explores the electronic basis for the high magnetic moment of the Fe₆S₈(CN)₆ cluster. Through collaboration with computational chemists, I present evidence of a phenomenon known as dual-subshell filling allowing for two spin channels holding different number of electrons resulting in many unpaired electrons. This cluster is also uniquely prepared for use as an extended material due to its cyanide ligands which may readily be used to form Prussian blue analogs. Chapter 5 describes efforts to design extended structures using the Fe₆S₈(CN)₆ cluster. Attempts towards Prussian blue analogs, covalently bound clusters using DCNQI, and EDT-TTF-CONH2 utilizing structures are discussed. Detailed notes on the synthesis of [NEt₄]₅[Fe₆S₈(CN)₆] are also provided. 2 structures which have successfully been synthesized, a 4 bridging ligand and a 2 bridging ligand “wire” are described in detail. In Chapter 6, collaborative efforts to increase our understanding of the cluster building blocks which can function as nanoscale atoms that assemble to form superatomic solids are described. We characterize a representative superatomic cluster, Co₆S₈(PEt₃)₆, in terms of structural, electronic, and magnetic properties using Solid State Nuclear Magnetic Resonance (SSNMR), Density Function Theory (DFT) calculations, and Superconducting Quantum Interference Device (SQUID) measurements. Evidence of delocalized HOMO orbitals and a delocalized spin in the oxidize cluster is shown. The findings presented in this chapter will assist the design of superatomic clusters and state-of-the-art applications, such as single-electron devices. Finally, Chapter 7 is much shorter than the other chapters as it is used to describe smaller projects which do not fit in the scope of the overall thesis. Magnetic measurements on a compound designed in the Norton lab are described.

<p>This thesis is based on a selection of six different experimental techniques used for studies in atomic and molecular physics. The techniques analysed in the thesis are compared to find similarities in strategies and ways to avoid sources of error.</p><p>Paper 1 deals with collision based spectroscopy with 60 keV Xe6+ ions on sodium and argon gas targets. Information on energy of Rydberg states in Xe5+ is unveiled by optical spectroscopy in the wavelength range from vacuum ultraviolet (VUV) to visible. In paper 2, the fast ion-beam laser spectroscopy (FIBLAS) is adapted for measuring hyperfine structure of barium isotopes in an isotopically pure ion-beam. This techniques involves changing the isotope during the measurement to minimize sources of error in measurement and enhance the signal from lesser abundant isotopes. The FIBLAS technique is used in paper 3 to study samarium ions. The ions are optically pumped and the recorded optical nutation is used to measure transition probabilities. This technique eludes the difficulties inherent in relative intensity measurements of all the radiative transitions from an excited state. In Paper 4, optical emission spectroscopy is used in the VUV region to study noble gas mixture discharges. The source of the emission bands near the resonance lines of krypton and xenon are found to be heteronuclear dimers. In paper 5, radiation from a pulsed argon plasma with admixture of nitrogen is studied with time resolved spectroscopy in the VUV and ultraviolet wavelength ranges to investigate the mechanism of energy transport. A metastable state of atomic argon is found to be an important source of energy to many radiative processes. In Paper 6, photoelectron spectroscopy (PES) on thiophene, on 3-bromothiophene and on 3,4-dibromothiophene using time-of-flight photoelectron-photoelectron coincidence technique and conventional PES to investigate the onset of double ionisation compared to the onset of single ionisation in molecules.</p>