Increased interest in the field of sensor technology stems from the availability of an inexpensive and robust sensor to detect and quantify the presence of a specific gas. Bulk p-CuO/n-ZnO heterocontact based gas sensors have been shown to exhibit the necessary sensitivity and selectivity characteristics, however, low interfacial CuO/ZnO contact area and poor CuO/ZnO connectivity limits their effective use as gas sensors. The phase equilibria between CuO and ZnO exhibits limited solubility. By exploiting this concept, a CuO/ZnO mixed solution is formed by combining CuO and ZnO precursors using wet chemical (sol-gel) techniques. Thin films fabricated using this mixed solution exhibit a unique CuO/ZnO microstructure such that ZnO grains are surrounded by a network of CuO grains. This is highly beneficial in gas sensing applications since the CuO/ZnO heterostructure interfacial area is considerably increased and is expected to enhance sensing characteristics. This work builds on previous research by Dandeneau et al. (Thin film chemical sensors based on p-CuO/n-ZnO heterocontacts, Thin Solid Films, 2008). CuO/ZnO mixed solution thin films are fabricated using the sol-gel technique and subsequently characterized. X-ray diffraction (XRD) data confirms the phase separation between ZnO and CuO grains. Scanning electron microscopy (SEM) as well as energy dispersive spectroscopy (EDS) reveal a network of ZnO grains amidst a matrix of CuO grains. Optical and electrical characterization provide material parameters used to construct an energy band diagram for the CuO/ZnO heterostructure. Aluminum interdigitated electrodes (IDEs) are patterned on the thin film and gas sensing characteristics in the presence of oxygen and hydrogen are investigated. Optimization of the electrode geometry is explored with the aim of increasing the sensitivity of the sensor in the presence of hydrogen gas. / Graduation date: 2010

L’étude de l’oxydation de films minces de cuivre déposés par pulvérisation magnétron sur des substrats de silicium et de verre a été menée au moyen d’une micro-post-décharge micro-ondes dans l’objectif de faire croître de manière localisée des nanostructures contrôlées d’oxyde. L’utilisation de plasma permet d’utiliser des atomes d’oxygène plutôt que de molécules d’oxygène et de pouvoir diminuer les températures de synthèse d’environ 100° typiquement. Il a ainsi été possible de faire croître des nanostructures hiérarchiques formées de nanoparois en boule, des nanoparois d’épaisseurs variables, des nanofils et des nanoplots de CuO. Ces différentes nanostructures se forment à des instants successifs et se répartissent radialement par rapport au centre de l’impact de la post-décharge. Elles croissent en suivant des cinétiques paraboliques qui traduisent une limitation par un transport diffusionnel. La diffusion est externe et conduit la formation de porosités Kirkendall à l’interface substrat-cuivre. Les analyses TEM ne montrent pas d’orientation privilégiée. Les nanofils sont soit mono- soit bi-cristallins. Des contraintes de compression (respectivement de tension) ont été mesurées dans Cu2O (respectivement dans CuO). La taille de grain est plus élevée au centre que sur les bords du traitement. Cela permet la croissance de nanoparois et de nanofils de diamètres relativement importants près du centre alors qu’une taille de grains plus petites sur les extérieurs entraîne la formation de nanofils plus fins mais avec une densité surfacique supérieure. Les différents modèles de croissance existant ont été repris pour interpréter ces nouveaux résultats / Oxidation of copper thin films deposited by magnetron sputtering on silicon and soda-lime glass substrates was performed by means of a microwave micro-afterglow to grow locally controlled nanostructures of copper oxide. The use of plasma discharges offers the possibility to handle oxygen atoms instead of oxygen molecules, which enable a substantial decrease in the synthesis temperature of about 100° typically. It was thus possible to grow hierarchical nanostructures made of nanowalls shaped in balls, nanowall with variable thicknesses, nanowires and nanodots of CuO. These different nanostructures forms successively and are distributed radially from the impact center of the post-discharge outwards. They grow by following parabolic growth rates that are due to a diffusion transport limitation. Outward diffusion occurs and creates a Kirkendall porosity at the substrate-copper interface. TEM analyses do not show any preferential orientation. Nanowires are either mono- or bi-cristals. Compressive (respectively tensile) stress was measured in Cu2O (respectively CuO). The grain size is larger in the center than on the edges of the treatment area. This enables the growth of nanowalls and nanowires with diameters pretty large close to the center whereas a smaller grain size on the edges leads to the formation of thinner nanowires but with higher surface density. The different existing growth models were considered to interpret these new results.

Yuan, Wenxiang = CCTO陶瓷材料的制备和性质研究 / 苑文香. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2007. / Includes bibliographical references (leaves 63-67). / Text in English; abstracts in English and Chinese. / Yuan, Wenxiang = CCTO tao ci cai liao de zhi bei he xing zhi yan jiu / Yuan Wenxiang. / Acknowledgement --- p.ii / Abstract --- p.iii / Contents --- p.v / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Background --- p.1 / Chapter 1.2 --- Structure --- p.1 / Chapter 1.3 --- Models --- p.3 / Chapter 1.3.1 --- Parallel RC --- p.3 / Chapter 1.3.2 --- Two parallel RCs in series --- p.5 / Chapter 1.4 --- Motivation --- p.7 / Chapter 1.5 --- Our work --- p.7 / Chapter Chapter 2 --- Experiment --- p.8 / Chapter 2.1 --- Sources and substrate --- p.8 / Chapter 2.2 --- Preparation of the CCTO samples --- p.8 / Chapter Chapter 3 --- Experimental equipment --- p.13 / Chapter 3.1 --- Furnace --- p.13 / Chapter 3.2 --- X-ray diffraction (XRD) --- p.13 / Chapter 3.3 --- Scanning electron microscopy (SEM) --- p.16 / Chapter 3.4 --- Impedance analyzers --- p.17 / Chapter Chapter 4 --- Selections of the experimental conditions --- p.18 / Chapter 4.1 --- Selection of calcining-process conditions --- p.18 / Chapter 4.1.1 --- Experimental results --- p.18 / Chapter 4.1.2 --- Comparison with the results of other research groups --- p.21 / Chapter 4.2 --- Selection of sintering-process conditions --- p.22 / Chapter 4.2.1 --- CuO volatilization --- p.22 / Chapter 4.2.2 --- CCTO decomposition --- p.24 / Chapter 4.3 --- Optimizing of the Cu/Ca ratio --- p.29 / Chapter Chapter 5 --- Results and discussion --- p.31 / Chapter 5.1 --- Properties of CCTO ceramics sintered at different temperatures for 10 h --- p.32 / Chapter 5.2 --- Properties of CCTO ceramics sintered for different durations at 1000°C --- p.43 / Chapter 5.3 --- Properties of CC3+ΧTO ceramics --- p.52 / Chapter 5.4 --- Discussion --- p.58 / Chapter Chapter 6 --- Conclusions --- p.61 / References --- p.63

Chemical-looping combustion is an indirect oxygen combustion strategy, considered to be the most cost-effective power generation technology with the CO2 inherently concentrated. In this process, a solid oxygen carrier is used to transfer oxygen from the air reactor to the fuel reactor, which completely isolates nitrogen in air to meet with fuels. The oxygen carriers in the combustion process are subjected to the severe environments, such as high temperatures, multi-cycle operations, and thermodynamic limitations. Thus, the preparation of an oxygen carrier with high durability and better kinetics under harsh environment could be an essential part of Chemical-looping combustion development. In this study, modified wet impregnation and co-precipitation methods have been developed. The active ingredient is copper(II) oxide, and the supporting material is either directly from titanium(IV) oxide (anatase 99%) or that prepared from other titanium resources such as titanium tetrachloride and tetrabutyl titanate. Preliminary results showed the prepared oxygen carriers functioned properly in the multi-cycles of oxidization and reduction in TGA at different temperatures. Characterization of used oxygen carriers was carried out using techniques of XRD, and SEM-EDS, which provide information for the difference between oxygen carriers from different preparation methods. Through the comparison, the oxygen carrier from the sol-gel preparation method has better dispersion and oxidation activity than those from mechanical mixing, wet-impregnation, and cox precipitation method. Moreover, towards the oxygen carrier from sol-gel method, nucleation model and diffusion models were determined at different reaction periods.

Propylene epoxidation reaction was investigated on catalytic surfaces of chlorinated copper(I) oxide and ruthenium(IV) oxide using periodic density functional theory (DFT). Cu2O(001) and (110) surface of RuO2 was selected to generate chlorinated surfaces to be used in the study. Besides epoxidation, other reactions that compete with epoxidation were also studied such as formations of allyl-radical, acrolein, acetone on chlorinated Cu2O(001) and formations of propionaldehyde, allyl-radical and acetone on chlorinated RuO2(110) surface. Path of each reaction was determined by CI-NEB method and transition state analyses. Generally accepted stable surface intermediate mechanism was utilized in reactions to final products. The surface intermediate favorable on the surfaces in this study was determined to be the intermediate that is not preferable on metallic surfaces under low oxygen. On chlorinated Cu2O(001) surface, formation of propylene oxide, acetone and acrolein have higher probability than gas phase allyl-radical since the desorption energy of allyl-radical was calculated to be 70kcal/mol which is a relatively high value. In fact it is desirable since gas phase allyl-radical is known to be the precursor of combustion products. On chlorinated RuO2(110) surface, desorption Propylene epoxidation reaction was investigated on catalytic surfaces of chlorinated copper(I) oxide and ruthenium(IV) oxide using periodic density functional theory (DFT). Cu2O(001) and (110) surface of RuO2 was selected to generate chlorinated surfaces to be used in the study. Besides epoxidation, other reactions that compete with epoxidation were also studied such as formations of allyl-radical, acrolein, acetone on chlorinated Cu2O(001) and formations of propionaldehyde, allyl-radical and acetone on chlorinated RuO2(110) surface. Path of each reaction was determined by CI-NEB method and transition state analyses. Generally accepted stable surface intermediate mechanism was utilized in reactions to final products. The surface intermediate favorable on the surfaces in this study was determined to be the intermediate that is not preferable on metallic surfaces under low oxygen. On chlorinated Cu2O(001) surface, formation of propylene oxide, acetone and acrolein have higher probability than gas phase allyl-radical since the desorption energy of allyl-radical was calculated to be 70kcal/mol which is a relatively high value. In fact it is desirable since gas phase allyl-radical is known to be the precursor of combustion products. On chlorinated RuO2(110) surface, desorption observed to be possible on chlorinated RuO2(110) surface but not possible on chlorinated Cu2O(001). When activation barriers and desorption energies of all possible reactions are compared on chlorinated RuO2(110) surface / gas phase propylene oxide generated directly seems as the preferable product with allylradical although it was computed to have high desorption energy. Comparison of activation barriers obtained in this study on chlorinated Cu2O(001) with the barriers of nonchlorinated surface revealed chlorine slightly increases the activation barrier of unwanted allylic hydrogen stripping and hence slightly decreases the probability of occurance. When chlorine is placed closer to reaction site, activation barrier of allylic hydrogen stripping reaction increases further. The effect of chlorine might be electronic since the charge of oxygen at reaction site slightly becomes less negative when the place of chlorine gets closer to the reaction site on the surface. Similar comparison between chlorinated and nonchlorinated RuO2(110) surfaces revealed that chlorine addition does not improve the surface toward propylene oxide formation, rather it is detrimental as chlorine addition caused a decrease in unwanted allylic hydrogen stripping reaction.

Thesis (Ph. D.)--University of Missouri-Columbia, 2003. / Typescript. Vita. Includes bibliographical references (leaves 87-88). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2003. / Typescript. Vita. Includes bibliographical references (leaves 87-88). Also available on the Internet.

The dye sensitized solar cell (DSSC) is a promising low-cost technology alternative to conventional solar cell in certain applications. A DSSC is a photo-electrochemical photovoltaic device, mainly composed of a working electrode, a dye sensitized semiconductor layer, an electrolyte and a counter electrode. Sunlight excites the dye, producing electrons and holes that can be transported by the semiconductor and electrolyte to the external circuit, converting the sunlight into an electrical current. A material that could be useful for DSSCs is the nanoscale cupric oxide, which can act as a p-type semiconductor and has interesting properties such as low thermal emittance and relatively good electrical properties. The goal of this project was to synthesize and characterize CuO nanoparticles using three different methods and look into each products potential use and efficiency in DSSCs. The particles were synthesized using two different solution based chemical precipitation methods and a flame spray pyrolysis method, yielding nanostructures with different compositions, structures and sizes ranging from ~20 to 1000 nm. The nanoparticle powder synthesized by the flame spray pyrolysis route was tested as semiconductor layer in the working electrode of the DSSC. Current-voltage measurements presented low solar conversion efficiencies with a reversed current, meaning that the cupric oxide cells did not work in a desirable way. Further studies of the cupric oxide synthesis and its suitability in DSSCs are needed to increases the future possibilities for gaining well working p-type DSSCs with higher efficiencies.

published_or_final_version / Physics / Doctoral / Doctor of Philosophy

The process of radiation induced corrosion of copper is not well understood. The most obvious situation where the knowledge of this process is crucial is in a deep repository for high level spent nuclear fuel where the fuel will be sealed inside copper canisters. The radiation will penetrate the canisters and be absorbed by the surrounding environment. In this study gamma irradiations of polished and pre-oxidized copper cubes in anoxic pure water, air of 60-100 % RH and in humid argon were performed. The copper surfaces were examined using IRAS, XPS, cathodic reduction, SEM, AFM, and Raman spectroscopy. The concentration of copper in the reaction solutions was measured using ICP-OES.  Also the formation of oxidative species caused by radiation absorption of water was studied by numerical simulations using MAKSIMA software. The corrosion of copper during gamma irradiation vastly exceeds what is expected. The production of oxidative species caused by radiation absorption of water is hundreds of times too low to explain the amount of oxidized copper. A possible explanation for this mismatch is an enhanced radiation chemical yield of HO· on the copper surface. Another one is an increased surface area due to oxidation of copper. One speculation is that HO· interacting with the copper oxide can cause oxidation of the metal. If the thermodynamic driving force is large enough then electrons can be conducted from the metal through the oxide to the oxidant. A dramatic increase in surface area together with an increased interfacial yield of HO· might explain the radiation enhanced corrosion process. / <p>QC 20151022</p>