The future energy demand will require a change in the current energy supply. In this regard, the production of hydrogen by photoelectrochemical solar cells is a promising alternative because the fuel is obtained from water and, importantly, its combustion is free of carbon. Many metal oxides, including those having a complex stoichiometry (i.e. ternary oxides) behave as semiconductors and present good stability in aqueous environments, making them attractive candidates for water splitting devices. This thesis focuses on the preparation and study of ternary metal oxide materials as photoelectrodes for water splitting, with emphasis on photocathodes. These materials must meet the requirements for a practical device: low cost, non-toxicity, made of Earth abundant elements, environmentally friendly, etc. The thesis also aims at the study of strategies to improve their photoelectrochemical response. lt comprises the investigation of the kinetics of hydrogen generation reaction and the characteristics of the electrode solution interface by photoelectrochemical impedance spectroscopy. The main points can be summarized as: (i) the effect of an electrochemical oxidative pretreatment in CuFe2Ü4 photocathodes (ii) the investigation of water splitting mechanisms in CaFe2Ü4 photocathodes, (iii) the effect of metal doping in LaFeO3 photocathodes (iv) the study of the photoelectrochemistry of compact and nanoparticulate YFeO3 photocathodes and (v) the effect of a reductive electrochemical treatment in NiTiO3 photoanodes, and comparison with the effect of the treatment in anatase electrodes.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第18087号 / 理博第3965号 / 新制||理||1572(附属図書館) / 30945 / 京都大学大学院理学研究科地球惑星科学専攻 / (主査)准教授 三宅 亮, 教授 土`山 明, 准教授 河上 哲生 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第18593号 / 工博第3954号 / 新制||工||1608(附属図書館) / 31493 / 京都大学大学院工学研究科高分子化学専攻 / (主査)教授 伊藤 紳三郎, 教授 木村 俊作, 教授 辻井 敬亘 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第20405号 / 工博第4342号 / 新制||工||1673(附属図書館) / 京都大学大学院工学研究科高分子化学専攻 / (主査)教授 大北 英生, 教授 赤木 和夫, 教授 木村 俊作 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

In this research, a temperature dependent tribological investigation of selected ternary oxides was undertaken. Based on the promising results of previous studies on silver based ternary oxides, copper based ternary oxides were selected to conduct a comparative study since both copper and silver are located in the same group in the periodic table of the elements. Two methods were used to create ternary oxides: (i) solid chemical synthesis to create powders and (ii) sputtering to produce thin films. X-ray diffraction was used to explore the evolution of phases, chemical properties, and structural properties of the coatings before and after tribotesting. Scanning electron microscopy, Auger scanning nanoprobe spectroscopy, and X-ray photoelectron spectroscopy were used to investigate the chemical and morphological properties of these materials after sliding tests. These techniques revealed that chameleon coatings of copper ternary oxides produce a friction coefficient of 0.23 when wear tested at 430 °C. The low friction is due to the formation of copper tantalate phase and copper in the coatings. All sputtering coatings showed similar tribological properties up to 430 °C.

In recent years, ultra-wide bandgap semiconductors have increasingly moved into scientific focus due to their outstanding material properties, making them promising candidates for future applications within high-power electronics or solar-blind photo detectors. The group-III-sesquioxides can appear in various polymorphs, which influences, for instance, the energy of the optical bandgap. In gallium oxide, the optical bandgap ranges between 4.6 and 5.3 eV depending on the polymorph. For each polymorph it can be increased or decreased by alloying with aluminum oxide (8.8 eV) or indium oxide (2.7–3.75 eV), respectively, enabling bandgap engineering and thus leading to an extended application field. For this purpose, an overview of miscibility limits, the variation of bandgap and lattice constants as a function of the alloy composition are reviewed for the rhombohedral, monoclinic, orthorhombic and cubic polymorph. Further, the effect of formation and desorption of volatile suboxides on growth rates is described with respect to chemical trends of the discussed ternary materials.

No description available.

Thermoelectric devices with the ability to convert rejected heat into electricity are widely used in nowadays technology. Several studies have been done to improve the efficiency of these devices. However, because of the strong correlation between thermoelectric properties (electrical conductivity, Seebeck coefficient, and thermal conductivity including lattice and electron counterpart), improving ZT has always been a challenging task. In this study, thermal conductivity of group IV-based binary and ternary alloys such as SiGe, SiSn, GeSn, and SiGeSn has been studied. Phonon Boltzmann Transport Equation has been solved in the relaxation time approximation including intrinsic and extrinsic (in the presence of boundary and interfaces in the low-dimensional material) scattering mechanisms. Full phonon dispersion based on the Adiabatic Bond Charge model has been calculated for Si, Ge, and Sn. Virtual crystal approximation has been adapted to calculate the dispersion of SiGe, SiSn, GeSn, and SiGeSn. Two approaches have been introduced to reduce the lattice thermal conductivity of the materials under study. First, alloying results in a significant reduction of thermal conductivity. But, this reduction has been limited by the mass disorder scattering in the composition range of 0.2 to 0.8. Second, nanostructuring technique has been proposed to further reduce the thermal conductivity. Our study shows that, due to the atomic mass difference which gives rise to the elastic mass scattering mechanism, SiSn has the lowest thermal conductivity among the other materials under study. SiSn achieved the thermal conductivity of 1.18 W/mK at 10 nm at the Sn composition of 0.18, which is the experimentally stable state of SiSn. The results show that SiSn alloys have the lowest conductivity (3 W/mK) of all the bulk alloys, more than two times lower than SiGe, attributed to the larger difference in mass between the two constituents. In addition, this study demonstrates that thin films offer an additional reduction in thermal conductivity, reaching around 1 W/mK in 20 nm SiSn, GeSn, and ternary SiGeSn films, which is close to the conductivity of amorphous SiO$_2$. This value is lower than the thermal conductivity of SiGe at 10 nm which is 1.43 W/mK. Having lattice thermal conductivity reduced, electron transport has been studied by solving Boltzmann Transport Equation under low electric field including elastic and inelastic scattering mechanisms. Rode's iterative method has been applied to the model for obtaining perturbation of distribution function under a low electric field. This study shows that nanostructuring and alloying can reduce $\kappa_{ph}$ without significantly changing the other parameters. This is because of the phonon characteristics in solids in which MFP of phonons is much larger than those of electrons, which gives us the possibility of phonons confinement without altering electrons transport. Thermoelectric properties of SiGe in the bulk and nanostructure form have been studied to calculate ZT in a wide range of temperatures. The results demonstrate that ZT reaches the value of 1.9 and 1.58 at the temperatures of 1200 K and 1000 K respectively, with the Ge composition of 0.2 and carrier concentration of 5$\times$10$^{19}$ cm$^{-3}$ at 10 nm thickness. This model can be applied to SiSn and other binary and ternary alloys, to calculate the improved ZT. Hence, we conclude that group IV alloys containing Sn have the potential for high-efficiency TE energy conversion.

International Telemetering Conference Proceedings / October 28-31, 1996 / Town and Country Hotel and Convention Center, San Diego, California / Aerospace Report No. TOR-0059(6110-01)-3, section 1.3.3 outlines the design and performance requirements of SGLS (Space Ground Link Subsystem) uplink services equipment. This modulation system finds application in the U.S. Air Force satellite uplink commanding system. The SGLS signal generator is specified as an FSK (Frequency Shift Keyed)/AM (Amplitude Modulation)/PM (Phase Modulation) sub-carrier modulator. GDP Space Systems has implemented, on a single 6U-VME card, a SGLS signal generator. The modulator accepts data from several possible sources and uses the data to key one of three FSK tone frequencies. This ternary FSK signal is amplitude modulated by a synchronized triangle wave running at one half the data rate. The FSK/AM signal is then used to phase modulate a tunable HF (High-Frequency) sub-carrier. A digital design approach and the availability of integrated circuits with a high level of functionality enabled the realization of a SGLS signal generator on a single VME card. An analog implementation would have required up to three rack-mounted units to generate the same signal. The digital design improve performance, economy and reliability over analog approaches. This paper describes the advantages of a digital FSK/AM/PM modulation method, as well as DDS (Direct Digital Synthesis) and digital phase-lock techniques.

It has been observed that confusion exists in literature concerning the meaning and use of the term efficacy. Confusion is worsened by the use of the term as a general term describing agonist activity. The meaning of the terms intrinsic activity, efficacy and intrinsic efficacy as used in theoretical models of drug action was investigated. The classical occupation model, the two-state model, the ternary complex model (including conformational change and ideas surrounding G-proteins) and the operational model were studied in order to understand the historical and current usage of these terms. Although efficacy estimates are often reported as a molecular property, it was shown that agonist activity is tissue dependent and cannot be fully portrayed by an efficacy estimate. It was found that efficacy has a different definition in each model. This is not always recognized in literature. It was suggested that the term efficacy should only be used in the context of a specific model / Thesis (M.Sc. (Pharmacology))--North-West University, Potchefstroom Campus, 2007.