De manière générale, les composites oxyde/oxyde sont la plupart du temps élaborés par frittage, par voie sol-gel ou par infiltration en phase gazeuse, CVI (« Chemical vapor infiltration »). Ces techniques d’élaboration comportent de nombreuses étapes engendrant un temps long d’élaboration ce qui peut entraîner une détérioration des propriétés du composite. Cette thèse s’intéresse à un procédé original et rapide de densification de préformes fibreuses développé par le Commissariat à l’Energie Atomique et aux énergies alternatives (CEA) : la caléfaction. Ce procédé est connu pour élaborer des composites C/C ou C/SiC à partir d’un précurseur liquide. Cependant, la possibilité d’élaborer des composites oxyde/oxyde n’a jamais été testée. L’objectif de ce travail est d’étudier la réalisation de composites oxydes/oxydes par ce procédé. Plusieurs matrices ont été réalisées telles que la silice, l’alumine et le système ternaire aluminosilicate de baryum, BaSi2Al2O8. Plusieurs paramètres expérimentaux ont été étudiés tels que la température d’élaboration, le temps de manipulation et la composition du précurseur. Des caractérisations microstructurales et physico-chimiques ont permis de caractériser les matériaux élaborés. Plusieurs modifications ont été apportées au montage expérimental afin de permettre une meilleure reproductibilité des essais et un meilleur suivi thermique lors de l’élaboration de matrice oxyde. / Nowadays, oxide/oxide composites are most of the time developed by sintering, sol-gel process or CVI (Chemical Vapor Infiltration). These techniques include many steps of synthesis leading to a long time of synthesis and possible deteriorations of the properties of the composite. This thesis focuses on an original and rapid process developed by French Alternative Energies and Atomic Energy Commission (CEA): the film boiling chemical vapor infiltration. This technique is already used to synthesize C/C and C/SiC composites but works have never focused on oxide/oxide composites. The main goal of this thesis is to synthesize oxide/oxide composites by film boiling chemical vapor infiltration. Works were focused on alumina, silica and barium aluminosilicate matrices. Several experimental parameters were studied: temperature, time and liquid precursor. Microstructural and physicochemical characterizations were done on composites. Several modifications of the experimental setup have been made in order to allow a better reproducibility of the tests and a better thermal monitoring.

Piezoelectric materials produce an electric potential in response to a mechanical strain. They are, therefore, capable of converting ambient waste mechanical energy into useful electrical energy which, in turn, may be harnessed and used as a supplemental source of power in a variety of applications. Engineered piezoelectric materials may be deployed to improve treatment efficiency during the production of potable water, which is both chemically and energetically intensive. Ambient mechanical energy is prevalent in municipal water treatment. Vibrations induced by water treatment plant pumps (such as High Service Pumps), turbulence resulting from cross-flow or dead-end membrane filtration, or agitation from mechanical mixing (paddle or impeller) may provide sufficient input mechanical input energy to activate a piezoelectric response. The objective of this work was to fabricate and characterize a range of nanofiber-based piezoelectric materials and demonstrate their application as an alternative energy supply for driving environmental treatment (e.g., pollutant degradation) via simple mechanical agitation. To achieve this objective, we fabricated a variety of piezoelectric nanofiber composite mats consisting of barium titanate (BTO) nanocrystals grown via an alkaline hydrothermal method atop an electrospun carbon nanofiber (CNF) support. We hypothesized that the greatest degree of piezoelectric activity (as measured by the voltage produced as a function of mechanical strain) would be achieved for nanofiber composites containing BTO with the largest fraction of tetragonal crystal structure, known to be piezoelectrically active. A systematic study on the impacts of hydrothermal treatment time, temperature, as well as the influence of ethylene glycol as an organic co-solvent on BTO crystal size and morphology was performed. For example, ethylene glycol was found to disrupt the dissolution-precipitation mechanism of BTO crystal growth and instead spurred the growth of BTO nanorods and nanosheets on the CNF support. After characterization, the strength and electromechanical properties of various BTO-CNF composites was assessed. In some cases, output voltages have been measured on the order of 2.0 V/cm2 in response to surface bending strain induced by a custom cantilever-oscillometer apparatus. Optimal fractions of BTO loading in the composites were assessed through mass-loading electromechanical studies. As a proof of concept application, BTO nanoheterostructures were shown to utilize ultrasonic vibrations to degrade sodium orange II salt (4-(2-Hydroxy-1-naphthylazo)benzenesulfonic acid sodium salt) via piezocatalysis. Ongoing and future work will continue to develop optimized piezocatalytic nanoheterostructures able to harvest the electrochemical potential generated from mechanical agitation and structural deformation for the production of oxidizing and reducing equivalents for degradation of persistent and emerging organic contaminants and disinfection in water treatment.

Recent regulation mandates that ships conduct mid ocean ballast water exchange (BWE) prior to discharging foreign ballast in territorial waters of Australia, the U.S. and elsewhere. The enforcement of ballast water exchange legislation is undermined, however, by a lack of sensitive and reliable methods for verifying compliance. One way to assess compliance is to compare the concentrations of chemical tracers in ballast tanks with their known distributions in the open ocean. In this work, dissolved organic matter and trace elements are investigated as potential tracers of mid-ocean ballast water exchange on commercial voyages in the North Pacific and Atlantic Oceans. The optical properties of chromophoric dissolved organic matter (CDOM) are frequently used as tracers of water masses in bays and estuaries. Characterization of the underlying fluorescence spectra in seawater dissolved organic matter was performed using parallel factor analysis, allowing the identification of at least nine independently varying fluorescent components present in varying concentrations in the ocean and in ballast water. Two of the humic components were terrestrial in origin and their signals could be traced in the open ocean (Pacific and Atlantic) at levels of approximately 1.5% of riverine concentrations. One humic terrestrial component was sufficient for predicting the coastal vs. oceanic source of most ballast water samples, suggesting that single and dual channel fluorometers could be optimized for verifying ballast water exchange. Barium, manganese and phosphorus were also investigated as potential tracers. Measurements of Ba and P obtained via engine-cooling pipes on commercial vessels were consistent with previous oceanographic measurements. While Ba behaved conservatively in ballast water, concentrations of phosphorus fluctuated and Mn was removed in ballast tanks over time. Ba and P demonstrated considerable promise as ballast water tracers, exhibiting predictable concentrations in exchanged ballast tanks, given a priori knowledge of the ocean (Atlantic versus Pacific) in which BWE was performed.

There has been unprecedented growth in wireless technologies in recent years; wireless devices such as cellular telephones and wireless local area network (WLAN) transceivers are becoming ubiquitous. It is now common for a single hardware device, such as a cellular telephone, to be capable of multi-band operation. Implementing a dedicated radio frequency (RF) front-end for each frequency band increases the component count and therefore the cost of the device. Consequently, there is now a requirement to design RF and microwave circuits that can be reconfigured to operate at different frequency bands, as opposed to switching between several fixed-frequency circuits. Barium strontium titanate (BST) thin films show great promise for application in reconfigurable microwave circuits. The material has a high dielectric constant which can be controlled by the application of a quasi-static electric field, combined with relatively low losses at microwave frequencies. Tunable microwave components based on BST-thin films have the potential to replace several fixed components, thereby achieving useful size and cost reductions. This thesis is concerned with the growth and microwave circuit applications of BST thin films on c- and r-plane sapphire substrates. Sapphire is an ideal substrate for microwave integrated circuit fabrication due to its low cost and low loss. Electronically tunable capacitors (varactors) were fabricated by patterning interdigital electrode structures on top of the BST films. High capacitance tunabilities of 56% and 64% were achieved for the films grown on c-plane and r-plane sapphire, respectively, at 40 V bias. A novel electronically tunable 3 dB quadrature hybrid circuit was also developed. Prototypes of this circuit were initially implemented using commercial varactor diodes, in order to validate the design. An integrated version of the coupler was then fabricated using BST varactors on c-plane sapphire. The results achieved demonstrate the potential of sapphire-based BST thin films in practical microwave circuits.

The objective of this thesis is to develop high dielectric constant nanoparticle dispersion for switchable aircraft antenna systems. Two steps were designed to achieve the objective. First, obtain high dielectric, high aspect ratio nanoparticles and disperse them in dielectric oil medium. Second, manipulate the particle-oil dispersion using an external alternating current (AC) electric field to increase the effective dielectric constant. In order to obtain high dielectric dispersions, different sizes and shapes of titanium dioxide (TiO2) and barium titanate (BaTiO3) nanoparticles were purchased and measured. However, after a number of experiments detailed in the thesis, it was found that none of the commercially available nanoparticles could satisfy our requirements for a minimum effective dielectric constant. Thus, to achieve the goals above, we synthesized high aspect ratio BaTiO3 nanowires with BaC2O4 and TiO2 powders as precursors using a molten salt method. The as-synthesized BaTiO3 nanowires were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy dispersive spectroscopy (EDS) mapping. The nanowires have a diameter ranging from 100 nm to 300 nm, and their lengths range from 1.5 micrometers to 5 micrometers. Mechanical stirring and bath sonication were used to obtain even colloidal dispersions. Different concentrations of BaTiO3 nanoparticles well dispersed in the oil medium were successfully manipulated using AC electric field. To monitor the change in microstructure of BaTiO3 nanoparticles, optical microscopy was used to observe the alignment of particles in the sample under the applied electric field. Various parameters including the magnitude, frequency, and duration of the electric field, and the concentration of BaTiO3 nanoparticles were investigated to achieve the optimal alignment of nanoparticles. The experimental results were validated by theoretical analysis using Maxwell-Garnett mixing rule. It was demonstrated that the effective dielectric constant of the colloidal dispersions would increase with the increase of the magnitude, frequency and duration of applied electric field. Synthesized BaTiO3 nanowire-based dispersions exhibit significant enhancement of the effective dielectric constant compared to other colloidal materials. The effective dielectric constant of 5 wt percent BaTiO3-oil dispersions could reach up to 10 when aligned at 1000 V/mm electric field at 1 kHz frequency for 1 hour.

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High dielectric constant barium doped titanium silicon oxide films with equivalent oxide thickness below 1 nm can be prepared by liquid phase deposition. We learn from this research that the deposition rate of titanium silicon oxide films can be much enhanced by nitric acid incorporation, and the dielectric constant of materials can be increased by the dipole polarization from barium. The key parameter for the deposition rate, refractive index, and the dielectric constant of barium doped titanium silicon oxide is the molarity of barium nitrate. The electrical properties can be improved effectively by thermal annealing treatments. The optimum equivalent oxide thickness of barium doped titanium silicon oxide thin film is 0.9 nm with the optical thickness of 7.4 nm. The high dielectric constant can reach 31.9 and the leakage current density is 5 ¡Ñ 10-6 A/cm2 at the electrical field intensity of 5 MV/cm, which has high potential application for the next generation MOSFET.

Polymer/ceramic nanocomposites benefit by combining high permittivities (r) of metal oxide nanoparticles with high dielectric strength and excellent solution-processability of polymeric hosts. Simple mixing of nanoparticles and polymer generally results in poor quality materials due mainly to the agglomeration of nanoparticles and poor miscibility of nanoparticles in host materials. Surface modification of metal oxide nanoparticles with phosphonic acid-based ligands was found to afford a robust surface modification and improve the processablity and the quality of nanocomposites. The use of phosphonic-acid modified barium titanate (BaTiO₃) nanoparticles in dielectric nanocomposites dramatically improved the stability of the nanoparticle dispersion and the quality of the nanocomposites. Surface modification of BaTiO₃ nanoparticles allowed high quality nanocomposite thin films in ferroelectric polymer hosts such as poly(vinylidene fluoride-co-hexafluoropropylene) with large volume fractions (up to 50 vol. %), which exhibited a remarkable combination of a high permittvity (35 at 1 kHz) and a high breakdown strength (210 V/µm) leading to a maximum energy storage density of 6.1 J/cm³. The effect of nanoparticle volume fractions on the dielectric properties of this nanocomposite system was investigated and compared with theoretical models. At high volume fraction of nanoparticles, the porosity of the nanocomposites was found to have important role in the dielectric performance. A combined effective medium theory and finite difference simulation was used to model the dielectric properties of high volume fraction dielectric nanocomposites with porosity. These results provide a guideline to optimize the volume fractions of nanoparticles for maximum energy density. Nanocomposites based on phosphonic acid-modified BaTiO₃ nanoparticles can also be used as printable high permittivity dielectrics in organic electronics. High volume fractions (up to 37 vol. %) of phosphonic acid-modified BaTiO₃ nanoparticles dispersed in cross-linked poly(4-vinylphenol) allowed solution-processable high permittivity thin films with a large capacitance density (~50 nF/cm²) and a low leakage current (10 8 A/cm²) suitable as a gate insulator in organic field-effect transistors (OFETs). Pentacene-based OFETs using these nanocomposites showed a low threshold voltage (< -2.0 V) and a large on/off current ratio (Ion/off 104 ~ 106) due to the high capacitance density and low leakage current of the gate insulator.

Cold trapped ions have many applications in quantum information science and precision metrology. In this thesis, we present progress toward two objectives involving ions confined to linear RF traps: the strong coupling of Ba+ ions with a high finesse optical cavity, and the observation of an optical nuclear transition in 229Th3+. In pursuit of the first objective, a novel high-temperture vapor cell for the spectroscopy of neutral barium was constructed. Using this vapor cell, a new technique for isotope-selective photoionization loading of Ba+ in an ion trap was developed. In pursuit of the second objective, techniques ultimately to be used in creating, trapping, and observing 229Th3+ are studied using 232Th3+. Ion traps are loaded with 232Th3+ via laser ablation of thorium targets. 232Th3+ is detected optically using laser-induced fluorescence and electronically using a channel electron multiplier. A technique for creating ablation targets from trace quantities of thorium nitrate is presented. The primary loss mechanisms of Th3+, charge exchange and chemical reactions, are studied.