Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第15725号 / 工博第3339号 / 新制||工||1505(附属図書館) / 28270 / 京都大学大学院工学研究科原子核工学専攻 / (主査)教授 伊藤 秋男, 教授 河合 潤, 准教授 松尾 二郎 / 学位規則第4条第1項該当

The NASA Mars Science Laboratory (MSL) rover, Curiosity, began exploring Gale crater, Mars in August, 2012 with the primary goal of assessing the past and present habitability of the martian surface. To meet this goal, Curiosity is equipped with an advanced suite of scientific instruments capable of investigating the geology, geochemistry, and atmospheric conditions on Mars. Among these instruments is the CheMin (Chemistry and Mineralogy) X-ray diffractometer whose function is to identify mineral phases present in sediments and rocks by means of X-ray diffraction (XRD). Characterizing the mineralogical make-up of a rock unit is an important step in determining its geologic history. Primary igneous minerals, such as feldspar, olivine, and pyroxene, give information about parental magmas - their composition, temperature, depth and so on. Secondary alteration minerals, like jarosite or akaganeite, point to distinct weathering or diagenetic processes. As such, understanding the mineral occurrence and abundance in Gale crater provides the MSL team with a robust foundation from which to make geologic interpretations. This dissertation details the methods used to determine the chemical composition of selected mineral phases based solely on XRD patterns from CheMin. Curiosity is equipped with instruments capable of measuring bulk composition of a sample [e.g., APXS (Alpha Particle X-ray Spectrometer)] but has no instrument capable of measuring the composition of a single phase in a multi-phase sample. Therefore, we developed crystal chemical algorithms and calibrations based on refined unit-cell parameters in order to predict mineral phase compositions. We have calculated algorithms for plagioclase, alkali feldspar, Mg-Fe-Ca clinopyroxene, Mg-Fe orthopyroxene, Mg-Fe olivine, Fe-oxide spinel, and alunite-jarosite group minerals. Furthermore, we use the estimated compositions of crystalline material in conjunction with bulk sample chemistry from APXS to estimate of the composition of the X-ray amorphous material present in each of the samples analyzed by CheMin in Gale crater.

>Magister Scientiae - MSc / FeSi nanowires were synthesized via a chemical vapor deposition method. Anhydrous FeCl3 powder in this case served as the Fe source and was evaporated at a temperature of 1100oC to interact with silicon substrates which served as the silicon source. The nanowires followed the vapor solid (VS) growth mechanism, which does not require the use of a metal catalyst; the native silicon oxide layer on the silicon substrates played the role of the catalyst in the growth of these nanostructures. A second growth mechanism, involving the use of a metal catalyst to assist in the growth of the nanowires was attempted by depositing a thin film of gold on silicon substrates. The reaction yielded SiOx nanowires; these results are discussed in detail in Chapter 5. All the nanostructures were characterized by X-ray diffraction (XRD), Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), Photoluminescence Spectroscopy (PL), Raman Spectroscopy and Fourier Transform Infrared Spectroscopy (FTIR).

Magister Pharmaceuticae - MPharm / Many active pharmaceutical ingredients (APIs) have poor physicochemical properties such as solubility, dissolution and chemical stability. Several strategies are used to enhance and improve these properties of the API. Co-crystallization and polymorphism studies are possible strategy used in pre-formulation studies to optimize these properties of the drug without modifying its pharmacological effect. The purpose of this research was to investigate the polymorphism and co-crystallization effects of the penicillin-type antibiotic, amoxicillin tri-hydrate. Several techniques such as: slow evaporation, slow cooling, vapour diffusion, sublimation, grinding and solvent assisted grinding was employed. In producing co-crystals, the API was non-covalently bound to selected co-formers such as: saccharin, nicotinamide, salicylic acid, L-tartaric acid, D-tartaric acid, L-aspartic acid, stearic acid, benzoic anhydride, oxalic acid di-hydrate, cinnamic acid, succinic acid and citric acid monohydrate. Nine co-crystals of amoxicillin tri-hydrate had been formed. Differential scanning calorimetry (DSC), hot stage microscopy (HSM) and thermal gravimetric analysis (TGA) was conducted to analyse the thermal behaviour of the co-crystals. Powder X-ray diffraction (PXRD) and spectroscopic techniques [infra-red (FTIR) and H1-nuclear magnetic resonance (H1MNR)] were employed for screening of the co-crystal forms. Furthermore, dissolution testing was conducted to investigate the application of the newly derivatised forms.

Titanium dioxide (TiO2) is an abundant, inexpensive and non-toxic material that is most commonly used as a white pigment in paints. Since the discovery by Fujishima and Honda in 1972 that water splits into hydrogen and oxygen gas at the surface of TiO2 on exposure to sunlight, there has been a massive research effort into understanding and improving the photoactivity of TiO2. One aspect of this is the characterisation of so-called ‘model’ surfaces, i.e. very large single crystal faces with low levels of contamination at ultra high vacuum (UHV) pressures, allowing the study of a single structure with a minimum of unknown variables effecting experimental results. Two techniques that are used to probe surface structure, amongst many, are Surface X-ray Diffraction (SXRD) and Photoelectron Spectroscopy (PES). SXRD allows quantitative determination of surface structure with high precision, and PES reveals surface chemical composition. In the context of this thesis both of these techniques were exploited at synchrotron radiation sources, which produce light of high brightness. In addition, the development of routines for extraction of SXRD data from 2D detectors to allow SXRD analysis is described. SXRD is employed to probe the structure of anatase-TiO2(101) both in UHV and following immersion in water vapour. The optimum UHV structure is largely in agreement with that previously predicted computationally, although there are some discrepancies in terms of atomic displacements. Water immersion leads to a H2O/OH terminated surface. The surface structure of a rutile-TiO2(110)(1x1) surface, that had been prepared under non-UHV conditions, using a wet chemical preparation technique, is also determined with SXRD. The studied surface, which was highly hydrophilic, has a similar substrate termination to UHV-prepared rutile-TiO2(110)(1x1) but with adsorbed surface H2O/OH species. Finally, PES is used to gain insight into the O1s signature of surface bridging oxygens on rutile-TiO2(110), as well as those (if any) of oxygen adatoms. Concerning bridging oxygens, it is demonstrated that there is no discernable shift in the O1s core level for these atoms away from the bulk oxide peak. Regarding oxygen adatoms, no conclusive evidence of a distinct emission signal in the O1s core level or valence band spectra can be discerned, due to interference from carbon contamination.

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Organic semiconductors (OSCs), compared to the more traditional silicon, are enticing materials for the fabrication of optoelectronic devices (e.g., transistors, photovoltaic cells, light-emitting diodes) due notably to the lower cost associated with their preparation and purification, as well as their increased solubility in solvents which can accommodate large-scale fabrication. However, a higher degree of molecular disorder typically results in lower performance than silicon and remains an issue to be adressed. As the structure of an OSC is crucial to its performance, understanding the nature of this structure-property relationship is key to further the field of OSCs. In this regard, this thesis explores the optoelectronic properties of different π-conjugated organic frameworks which incorporate sulphur and nitrogen atoms along the rigid conjugated backbone for their desirable impacts on charge mobilities and stability. After a brief review of both small-molecule OSCs as well as key experimental techniques employed in the course of this work, chapter three covers the synthesis and characterization of dithiatetrazocines (DTTA), electron-deficient sulphur-nitrogen heterocycles, which were functionalized with various (oligo)thienyls pendants. The impact of both the substitution patterns and the degree of conjugation on the optoelectronic and solid-state properties of the ring system was investigated. The fourth chapter expands on previous work from the Brusso group that focused on extending the 2D conjugation of tetrathienoanthracene. While oligothienyls were previously shown to effectively increase the degree of conjugation, little to no change in device performance were observed, which was ascribed to disorder of the rotatable pendants. Here, rigid thieno[3,2-b]thiophene was used instead to increase both the degree of conjugation while maintaining structural rigidity, as assessed by optical, electrochemical and theoretical studies. The fifth chapter introduces preliminary work toward expanding the electron-deficient hexaazatrinaphtylene core with thiophene rings. The resulting concentric donor-acceptor structure promotes luminescent behavior with pronounced emission solvatochromism. Optical measurements were performed before and after intramolecular cyclization of the thiophene rings, to study the impact of aromatization on the optoelectronic properties of the system.

>Magister Scientiae - MSc / TiO2 nanoparticle films are important electron transport layers (ETLs) in photovoltaics such as dye-sensitised, perovskite and polymer hetero-junction solar cells. These films, however, have significant electron trap-sites as a result of the large density of oxygen vacancies present in nanosized TiO2. These trap-sites cause electron-hole recombination and ultimately lower photon-tocurrent conversion efficiency of the underlying cell during operation. Doping the TiO2 lattice with low atomic number elements such as nitrogen is a proven method to overcoming the charge transport inefficiency of TiO2 ETLs; another is the use of one-dimensional (1D) nanowires (NWs), instead of nanoparticles. Modification of TiO2 with non-metals leads to optical bandgap narrowing, improvement in electron conductivity and increased electron lifetime in the ETL layer. However, a lot of scope exists in understanding and fully quantifying the relationship between optical property, for example light transmission and bandgap modification, versus the doping concentration and type. Most doping approaches are in-situ and involve the addition of a dopant precursor (usually a salt) during the synthesis of TiO2 nanostructures – this invariably leads to uncontrolled doping levels, anion contamination and poor-quality materials – a need thus exists to develop simple, controllable doping approaches. One such approach, which forms the basis of this study, is ex-situ doping by means of plasma generated species in a controlled environment. This field of study is fairly novel and not widely studied, requiring more research to understand the doping mechanisms and influence on the optical and electronic properties of the underlying nanomaterials. In particular, controlled doping of TiO2 with nitrogen using radio-frequency generated (RF) plasma requires vigorous experimentation and characterisation. Inaccuracy of the deposition parameters during exposure remains a common drawback for this approach in addition to a lack of understanding of the surface interaction between the N2 species and specimen during irradiation.

Cocrystals have attracted much interest in recent years. It was once thought that cocrystals could be a means to prevent polymorphism but many recent examples of cocrystal polymorphism have been discovered and reported. In this contribution, we present a survey of polymorphic cocrystals. Polymorphism is the ability of a specific chemical compound to crystallize in more than one crystalline form. Polymorphs have different arrangements of the molecules in the given crystal lattice and may exhibit different characteristics such as packing properties, thermodynamic properties, spectroscopic properties, kinetic properties, surface properties, and mechanical properties. Polymorphs can be classified in various groups such as crystalline, amorphous, hydrates, and solvates. The main characterization methods used in this thesis are X-ray diffraction and solid-state NMR spectroscopy. The concept of variable stoichiometry cocrystallization is explored in halogen-bonded systems. Three novel cocrystals of 1,4-diiodotetrafluorobenzene and 3-nitropyridine with molar ratios of 1:1, 2:1, and 1:2, respectively, are prepared by slow evaporation methods. Powder X-ray diffraction experiments carried out on the 1:1 and 2:1 cocrystals confirm that gentle grinding does not alter the crystal forms. 1H → 13C and 19F →13C cross-polarization magic angle spinning (CP/MAS) NMR experiments performed on powdered samples of the 1:1 and 2:1 cocrystals are used as spectral editing tools to select for either the halogen bond acceptor or donor, respectively. I also describe the formation of a new cocrystal of 1, 3, 5-trifluoro-2, 4, 6-triiodobenzene and piperazine with a 2:1 molar ratio that was prepared by the slow evaporation method. In addition of that, I have prepared the cocrystal (1,4- VII diiodotetrafluorobenzene)(coumarin ) already reported. After preparation and purification process of this compound, I obtained a small amount powder, but could not characterize it by solid-state NMR; rather I performed powder X-ray diffraction to study this compound. Overall, this work contributes new examples to the field of polymorphism in halogen-bonded systems and to variable stoichiometry cocrystal engineering with halogen bonds.