Converting solar energy to clean fuel has gained remarkable attention as an emerged renewable energy resource but optimum efficiency in photocatalytic applications has not yet been reached. One of the dominant factors is designing efficient photocatalytic semiconductors. The research reveals a theoretical investigation of optoelectronic properties of bismuth-based metal oxide and oxysulfide semiconductors using highly accurate first-principles quantum method based on density functional theory along with the range-separated hybrid HSE06 exchange-correlation functional. First, bismuth titanate compounds including Bi12TiO20, Bi4Ti3O12, and Bi2Ti2O7 were studied in a combined experimental and theoretical approach to prove its photocatalytic activity under UV light. They have unique bismuth layered structure, tunable electronic properties, high dielectric constant and low electron and effective masses in one crystallographic direction allowing for good charge separation and carrier diffusion properties. The accuracy of the investigation was determined by the good agreement between experimental and theoretical values. Next, BiVO4 with the highest efficiency for oxygen evolution was investigated. A discrepancy between the experimental and theoretical bandgap was reported and inspired a systematic study of all intrinsic defects of the material and the corresponding effect on the optical and transport properties. A candidate defective structure was proposed for an efficient photocatalytic performance. To overcome the carrier transport limitation, a mild hydrogen treatment was also introduced. Carrier lifetime was enhanced due to a significant reduction of trap-assisted recombination, either via passivation of deep trap states or reduction of trap state density. Finally, an accurate theoretical approach to design a new family of semiconductors with enhanced optoelectronic properties for water splitting was proposed. We simulated the solid solutions Bi1−xRExCuOS (RE = Y, La, Gd and Lu) from pure BiCuOS to pure RECuOS compositions. Starting from the thermodynamic stability of the solid solution, several properties were computed for each system including bandgaps, dielectric constants, effective masses and exciton binding energies. Several compositions with specific organization and density of Bi and RE atoms, were found to be appropriate for water splitting applications. In General, the presented results give further insights to the experimentalists and recommendations for appropriate future application and defect-design of each material.

Quantum chemical methods have been used to model a variety of p- and f-block chemical species to gain insight about their energetic and spectroscopic properties. As well, the studies have provided understanding about the utility of the quantum mechanical approaches employed for the third-row and lanthanide species. The multireference ab initio correlation consistent Composite Approach (MR-ccCA) was utilized to predict dissociation energies for main group third-row molecular species, achieving energies within 1 kcal mol-1 on average from those of experiment and providing the first demonstration of the utility of MR-ccCA for third-row species. Multireference perturbation theory was utilized to calculate the electronic states and dissociation energies of NdF2+, providing a good model of the Nd-F bond in NdF3 from an electronic standpoint. In further work, the states and energies of NdF+ were determined using an equation of motion coupled cluster approach and the similarities for both NdF2+ and NdF were noted. Finally, time-dependent density functional theory and the static exchange approximation for Hartree-Fock in conjunction with a fully relativistic framework were used to calculate the L3 ionization energies and electronic excitation spectra as a means of characterizing uranyl (UO22+) and the isoelectronic compounds NUO+ and UN2.

ZnO and ZnO-TiO2 ceramics have intriguing electronic and mechanical properties and find applications in many fields. Many of these properties and applications rely on the understanding of defects and defect processes in these oxides as these defects control the electronic, catalytic and mechanical behaviors. The goal of this dissertation is to systematically study the defects and defects behaviors in Wurtzite ZnO and Ilmenite ZnTiO3 by using first principles calculations and classical simulations employing empirical potentials. Firstly, the behavior of intrinsic and extrinsic point defects in ZnO and ZnTiO3 ceramics were investigated. Secondly, the effect of different surface absorbents and surface defects on the workfunction of ZnO were studied using DFT calculations. The results show that increasing the surface coverage of hydrocarbons decreased the workfunction. Lastly, the stacking fault behaviors on ilmenite ZnTiO3 were investigated by calculating the Generalized Stacking Fault (GSF) energies using density functional theory based first principles calculations and classical calculations employing effective partial charge inter-atomic potentials. The gamma-surfaces of two low energy surfaces, (110) and (104), of ZnTiO3 were fully mapped and, together with other analysis such as ideal shear stress calculations.

Energy production, storage and efficient usage are all crucial factors for environmentally sound and sustainable future technologies. One important question concerns the refrigeration industry, where the energy efficiency of the presently used technologies is at best 40% of the theoretical Carnot limit. Magnetic refrigerators offer a modern low-energy demand and environmentally friendly alternative. Iron phosphide based materials have been proposed to be amongst the most promising candidates for working body of magnetic refrigerators. Hydrogen is one of the central elements on the most promising sources of renewable energy. Considerable international research focuses on finding good solid state materials for hydrogen storage. On the other hand, hydrogen gas is obtained from hydrogen containing chemical compounds, which after breaking the chemical bounds usually yield to a mixture of different gases. Palladium-silver alloys are frequently used for hydrogen separation membranes for producing purified hydrogen gas. All these applications need a fundamental understanding of the structural, magnetic, chemical and thermophysical properties of the involved solid state materials. In the present thesis ab initio electronic structure methods are used to study the crystallographic and magnetic properties of Fe2P based magneto-caloric compounds and the thermophysical properties of Pd-Ag binary alloys. Lattice stability of pure Fe2P and the effect of Si doping on the phase stability are presented. In contrast to the observation, for the ferromagnetic state the body centered orthorhombic structure (bco, space group Imm2) is predicted to have lower energy than the hexagonal structure (hex, space group P62m). The zero-point spin fluctuation energy difference is found to be large enough to stabilize the hex phase. For the paramagnetic state, the hex structure is shown to be the stable phase and the computed total energy versus composition indicates a hex to bco crystallographic phase transition with increasing Si content. The magneto-structural effects and the mechanisms responsible for the structural phase transition are discussed in details. The magnetic properties of Fe2P can be subtly tailored by Mn doping. It has been shown experimentally that Mn atoms preferentially occupy one of the two different Fe sites of Fe2P. Theoretical results for the Mn site occupancy in MnFeP1-xSix are presented. The single crystal and polycrystalline elastic constants and the Debye temperature of Pd1-xAgx binary alloys are calculated for the whole range of concentration, 0≤x≤1. It is shown that the variation of the elastic parameters of Pd-Ag alloys with chemical composition strongly deviates from the simple expected trend. The complex electronic origin of these anomalies is demonstrated. Within the present thesis, all relaxed crystal structures are obtained using the Projector AugmentedWave full-potential method. The chemical and magnetic disorder is treated using the Exact Muffin-Tin Orbitals method in combination with the Coherent Potential Approximation. The paramagnetic phase is modeled by the Disordered Local Magnetic Moments approach. / QC 20101101

Microwave photonic applications in the terahertz (THz) region of the spectrum are attracting increasing attention due to the need to find solutions for next-generation (5G/6G) wireless communication systems capable of handling unprecedented data rates. It is crucial to develop millimeter-wave (mm-wave) (30-300GHz) fiber supported transport networks. One of the key questions is, which carrier frequency generation technique will be the most suitable for THz signals above 300 GHz; electronics-based or photonics-based. Since the backbone of the wireless networks is composed by very high-capacity fibre optic cables, the microwave photonic approach has the ultimate advantage of seamless integration with existing optical fibre networks. Although the cost effectiveness is still an open question, simplistic base station architecture with simplified antenna units and high optical component reuse is necessary for enabling a compatible mobile network backhaul. For THz applications a broadband electro-optic modulator (EOM) with a frequency response extending to the sub-terahertz range, high power handling, and very low nonlinear distortions, is required. The objective of this thesis is to study the feasibility of photonic integration and, proof of concept implementations with the effective use of optical components with reduced energy consumption, reduced footprint and offer speed beyond all-electronic implementations. The first study presents a coherent electro-optic photonic integrated circuit deploying generalized Mach-Zehnder interferometer (GMZI) substituting N×1 combiner by an optical N×N discrete Fourier transform (DFT) in order to generate a regularly spaced frequency comb. The proposed design comprises of 1×N splitter that feeds light into a parallel array of N electro-optic phase modulators electrically driven by RF signal with a progressive phase shift with their phase modulated optical outputs processed by an N×N optical DFT. A pragmatic design approach and analytical formulation for implementing MMI based optical DFT in photonic networks composed of waveguide splitters, combiners, and phase-shift elements with necessary circuit diagram for even and odd dimensions are presented. Recently, there has been impressive progress toward ultra-wide band low voltage EOM. The heterogeneous approach of utilizing silicon nitride on lithium niobate waveguide integrated on a single chip is demonstrated for the best optical modulation performance that opens a wide range of opportunities for universal linear optical networks, chip-scale MWP systems, ultra-speed switching of optical communications. Finally, the third study de-scribes the architecture for compact on-chip spectrometry targeting high resolution across the entire C-band to measure the spectral profile of WDM signals reliably and accurately in fixed and flex-grid architectures. The design architecture of technologically viable com-pact on-chip high-resolution wideband spectrometer such as Mach-Zehnder delay interferometers (MZDI), 2×2 directional couplers and multimode interference couplers is presented and verified by software simulation using an industry standard tool. The components simulations that supported the assessment of the feasibility of a spectrometer compliant with the specification made use of the LioniX asymmetric double strip (ADS) waveguide and the low-cost photolithography.

Crystallography has traditionally been studied by diffraction methods involving X ray or neutron radiation. These methods have some limitations, from requiring the substance under study to form single crystals to the limited ability of X rays to locate hydrogen atoms. While neutron radiation can characterize hydrogens, it is expensive, not readily available and has its own particular limits on resolution. It this dissertation, it is demonstrated that NMR is extraordinarily sensitive to atomic positions, with variations of mere tens of femtometers creating statistically distinguishable chemical shift changes. To date, no other means of measurement can detect structural changes at this scale. This thesis presents a NMR based refinement technique that refines existing X ray structures to an unprecedented resolution. The refinement uses computational methods to make theoretical models then fits these models to the experimental data. This refinement process can also be modified to generate positional uncertainties known as the anisotropic displacement parameters, or ADPs, to accompany the refined structure. This creation of ADPs fulfills requirements set by the international union of crystallography that all deposited crystal structures contain ADPs.

京都大学 / 新制・課程博士 / 博士(工学) / 甲第23213号 / 工博第4857号 / 新制||工||1758(附属図書館) / 京都大学大学院工学研究科材料化学専攻 / (主査)教授 松原 誠二郎, 教授 杉野目 道紀, 教授 中尾 佳亮 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

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Traditional chemical looping technologies utilize solid oxygen carriers and has some disadvantages, especially when solid fuels like coal are used. In this work, a novel chemical looping process using gaseous metal oxide as oxygen carrier was proposed. The reaction of activated charcoal with gas-phase MoO3 was studied for the first time. The experiments were conducted isothermally at different temperatures in a fixed-bed reactor. The apparent activation energy of the reaction was calculated and suitable kinetic models were determined. The results and analysis showed that the proposed concept has potential in both coal chemical looping combustion and gasification process. To further investigate the mechanism of carbon oxidation by gas-phase MoO3, the adsorption of a gaseous (MoO3)3 cluster on a graphene ribbon and subsequent generation of COx was studied by density functional theory (DFT) method and compared with experimental results. The (MoO3)n -graphene complexes show interesting magnetic properties and potentials for nanodevices. A comprehensive analysis of plausible reaction mechanisms of CO and CO2 generation was conducted. Multiple routes to CO and CO2 formation were identified. The (MoO3)3 cluster shows negative catalytic effect for CO formation but does not increase the energy barrier for CO2 formation, indicating CO2 is the primary product. Mechanism of the homogenous MoO3 - CO reaction was studied and showed relatively low energy barriers. The DFT result accounts for key experimental observations of activation energy and product selectivity. The combined theoretical and experimental approach contributes to the understanding of the mechanism of reactions between carbon and metal oxide clusters. To gain a better understanding of the MoO2 oxidation process, the adsorption and dissociation of O2 on MoO2 surface were studied by DFT method. The results show that O2 molecules prefer to be adsorbed on the five-coordinated Mo top sites. Density of states analysis shows strong hybridization of Mo 4d orbitals and O 2p orbitals in the Mo-O bond. Clean MoO2 slab and slabs with O2 adsorption are metallic conductors, while the surface with high O atom coverage is reconstructed and becomes a semiconductor. Surface Mo atoms without adsorbed O or O2 are spin-polarized. The oxygen adsorption shows ability to reduce the spin of surface Mo atoms. The adsorption energy of O2 and O atoms decreases as coverage increases. The transition states of O2 dissociation were located. The energy barriers for O2 dissociation on five-coordinated and four-coordinated Mo top sites are 0.227 eV and 0.281 eV, respectively.

The vibrational entropy calculated by applying the harmonic oscillator approximation to all vibrational degrees of freedom is inherently inaccurate. One major reason is because low frequency modes such as internal rotations are not properly described by this approximation. Various techniques were developed in the past to overcome this problem. The hindered rotor potential can be approximated by a series of cosine functions, and the relevant coe cients can be determined by tting to a calculated potential energy surface. However, such a method is di cult and time consuming. Therefore, in this dissertation we propose and describe two less tedious approaches to determine entropy of internal rotational modes. The rst approximation is to express the barrier height in terms of the harmonic oscillator frequency, the local periodicity, and the reduced moment of inertia of the rotation and to approximate the torsional potential by a single cosine function. Thus, the 1D Schr odinger equation for internal rotations can be solved without nding the torsional potential, transition states, or barrier heights. We propose a further simpli cation to this approach, achieved through a simple mathematical formula, that interpolates the hindered rotor entropy between the free rotor and harmonic oscillator limits. We also propose a procedure to automatically determine the axis of rotation for any hindered rotor. The proposed methods were applied to determine the torsional entropy of n- alkanes from ethane to hexane. The entropies calculated from the proposed methods give good agreement with the experimental and accurately calculated values and have a signi cantly better accuracy than the harmonic oscillator approximation. Furthermore, we performed approximate and full hindered rotor treatments to nd the corrected vibrational entropy of bis(chromiumtricarbonyl) dibenzo[a,e]cyclooctatetraene (DBCOT). The eighth chapter of this dissertation is an independent molecular dynamics (MD) project to study how ethanol interacts with human and mouse Toll-Like- Receptor3 (TLR3) monomers and a TLR3-dsRNA complex. No major structural changes were observed during the ethanol docking and subsequent MD simulations, but the MD simulations revealed a reduction in the proportion of alpha helix present during a 1000 ns MD simulation on the h-TLR3 monomer in 0.5 percent ethanol.