Metasurfaces which emerged as two-dimensional counterparts of metamaterials, facilitate the realization of arbitrary phase distributions using large arrays with subwavelength and ultra-thin features. Even if metasurfaces are ultra-thin, they still effectively manipulate the phase, amplitude, and polarization of light in transmission or reflection mode. In contrast, conventional optical components are bulky, and they lose their functionality at sub-wavelength scales, which requires conceptually new types of nanoscale optical devices. On the other hand, as the optical systems shrink in size day by day, conventional bulky optical components will have tighter alignment and fabrication tolerances. Since metasurfaces can be fabricated lithographically, alignment can be done during lithographic fabrication, thus eliminating the need for post-fabrication alignments. In this work, various types of metasurface applications are thoroughly investigated for robust wavefront engineering with enhanced characteristics in terms of broad bandwidth, high efficiency and active tunability, while beneficial for application. Plasmonic metasurfaces are not compatible with the CMOS process flow, and, additionally their high absorption and ohmic loss is problematic in transmission based applications. Dielectric metasurfaces, however, offer a strong magnetic response at optical frequencies, and thus they can offer great opportunities for interacting not only with the electric component of a light field, but also with its magnetic component. They show great potential to enable practical device functionalities at optical frequencies, which motivates us to explore them one step further on wavefront engineering and imaging sensor platforms. Therefore, we proposed an efficient ultra-thin flat metalens at near-infrared regime constituted by silicon nanodisks which can support both electric and magnetic dipolar Mie-type resonances. These two dipole resonances can be overlapped at the same frequency by varying the geometric parameters of silicon nanodisks. Having two resonance mechanisms at the same frequency allows us to achieve full (0-2π) phase shift on the transmitted beam. To enable the miniaturization of pixel size for achieving high-resolution, planar, compact-size focal plane arrays (FPAs), we also present and explore the metasurface lens array-based FPAs. The investigated dielectric metasurface lens arrays achieved high focusing efficiency with superior optical crosstalk performance. We see a magnificent application prospect for metasurfaces in enhancing the fill factor and reducing the pixel size of FPAs and CCD, CMOS imaging sensors as well. Moreover, it is of paramount importance to design metasurfaces possessing tunable properties. Thus, we also propose a tunable beam steering device by combining phase manipulating metasurfaces concept and liquid crystals. Tunability feature is implemented by nematic liquid crystals infiltrated into nano holes in SiO2. Using electrically tunable nematic liquid crystals, dynamic beam steering is achieved

Polypeptides are polymerized chains of amino acids linked covalently through peptide bonds. Polyelectrolyte polypeptides are polypeptides with electrolyte repeating groups. Several amino acids contain ionizable side chains which result in charge distributions when dissolved in aqueous solutions. This dissertation is motivated by a desire to gain knowledge of polyelectrolyte polypeptides as recent advances in chemical synthesis of polypeptides have made possible the fabrication of designed polypeptides that do not naturally occur in nature. Potential applications of newly designed polypeptides span the range from medical to clothing and energy even to robotics. In this dissertation we compare the characteristic behavior of two polypeptide polyanions: Poly-(L-Glutamic Acid) [PLE] and Poly-(L-Glutamic Acid4, Tyrosine1) [PLEY(4:1)]. Comparative characteristic behaviors of each is conducted through relaxation phenomena in the context of mechanical elasticity measurements of hydrogels and dielectric relaxation of aqueous solutions in a radio frequency range of 1 MHz to 1000 MHz. Hydrogels are fabricated by crosslinking each polyanion with Poly-(L-Lysine) [PLK], a polycation, via the crosslinker 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC). Elasticity and viscoelasticity measurements are conducted in a fixture designed by our lab. Dielectric relaxation behavior is studied on aqueous solution of both PLEY and PLE using a capacitive fixture, also designed in our lab. RF signals provided by an impedance analyzer are converted to permittivity and dielectric loss measurements. Peaks in dielectric loss provide evidence of relaxation mechanisms. A comparison of experimental results to theoretical expectations reveal both expected and some surprising behavior. Relaxation times for crosslinked hydro-gels scale according to theoretical expectations according to so-called reptation dynamics. However, relaxation times of aqueous solutions did not scale as entangled polyelectrolytes. First, both PLEY and PLE scaled as neutral polymers rather than polyelectrolytes. This was expected because of the high concentrations studied. However, due to the high concentrations, it was expected that polypeptides were entangled in solutions. Data compared to theory did not support this expectation. We, additionally, conducted a self-crosslinking experiment of a polyampholyte: RADA16. RADA16 is known to self-assemble into nano-fibers formed by -sheet stacking. The self-crosslinking was also mediated by EDC. Results of crosslinking showed formation of polypeptide spherules as well as nano-crystals nominally orthorhombic in shape. It was not possible to ascertain composition of the nano-crystals due to both the limited amount of raw material available and the capabilities of measurement equipment as of this writing. It is hypothesized that nano-crystals are composed of some type of urea by-product from the crosslinking reaction. The spherules, on the other hand, seem to be described by the theory of hydrophobic polyelectrolytes. Additional research conducted with regards to electromagnetic hydrodynamic flows during the time frame of this dissertation is also included. The research uses hydrodynamic conservation equations as a starting point to derive one electromagnetic flow momentum equation analogous to the Cauchy momentum equation of hydrodynamics. It also introduces a mass- energy conservation equation for electromagnetic flow that has no hydrodynamic analogue. We begin this dissertation by introducing in Chapter 1 some of the theoretical background necessary to understand results from experiments. Chapter 2 introduces experimental results from elasticity and viscoelasticity measurements and Chapter 3 explains the dielectric relaxation experiment. We then follow with Chapter 4 which presents conclusions from mechanical and dielectric relaxation experiments in a concise format. Results from the self- crosslinking of RADA16 are presented in Chapter 5. Finally, the additional research on electromagnetic flow is presented in Chapter 6.

Electrical trees have long been the interest of the electrical insulation community due to their role in power systems equipment failure at locations where high divergent fields might arise due to impurities, contaminants or voids. Even through trees take a long time to grow in real life, they can be grown experimentally in shorter times under various conditions so that their growth characteristics can be investigated. Different samples have been fabricated to investigate the effects of interfaces in electrical tree propagation. Initially, the impact of an interface perpendicular to the electric field, and the interface position, thickness and/or composition on the polymer’s lifetime was investigated. In the results acquired, the positive impact of interfaces positioned perpendicular to the electric field was evident: increasing the samples’ time to breakdown as well as the electrical tree inception time. Due to the encouraging results, further investigation has been focused on interface modification and how this might be used to control the electrical tree growth as well as the samples’ time to breakdown. Altering the interface’s surface roughness using a number of different methods was carried out. Results were graphically and statistically analysed so that the any conclusions are robust, and uncertainties clear. The statistical analysis used by generating regression model equations was a novel method to predict how different electrical tree parameters were affected/affecting by others. In this way the dielectric’s lifetime could be predicted with a certain level of confidence. The modification of the interface by coating the surface with either a thin layer of pure or nano-filled (hexagonal Boron Nitride) epoxy resin resulted in it being impervious thus preventing the electrical tree to propagate through it. This was a novel method that showed that specific modification methods can significantly enhance the dielectric’s lifetime when applied appropriately. Details of new sample fabrication techniques are described which enable better control of the materials and interfaces, and data on tree length growth characteristics are discussed.

Plasma actuators are electrical devices that generate a wall bounded jet without the use of any moving parts. For aerodynamic applications they can be used as flow control devices to delay separation and augment lift on a wing. The aim of this project is to initially develop a system capable of generating and sustaining a plasma that generates a wall bounded jet. The next step is to investigate the effect of varying the number and distribution of encapsulated electrodes in the dielectric layer. Finally the best case design is applied at the leading edge and flap shoulder of a NACA0015 aerofoil with a 20% flap. Utilising a transformer cascade, plasma has been generated for a variety of input voltages. In the quiescent environment of a Faraday cage the velocity flow field is recorded using particle image velocimetry (PIV). Through understanding of the mechanisms involved in producing the wall jet and the importance of the encapsulated electrode a novel actuator design was investigated. The actuator design distributes the encapsulated electrode throughout the dielectric layer. The experiments have shown that actuators with shallow initial encapsulated electrodes induce velocities greater than the baseline case at the same voltage. Actuators with a deep initial electrode are able to induce the highest velocities as they can operate at higher voltages without breakdown of the dielectric. The best actuator case is applied to the aerofoil for Reynolds numbers of 1:97x10⁵, 2:63x10⁵ and 3:29x10⁵. The lift and drag are recorded using pressure measurements around the aerofoil surface and across the aerofoil's wake. PIV is utilised to visualise the flow field. The trailing edge actuator produces a step increase in lift for pre-stall angles of attack and delays stall by 1° at Re = 1:97x10⁵. The leading edge actuator has limited impact on the flow for the no flap deflection case due to the actuator location. As the flap deflection increases the leading edge actuator is able to influence the flow. Repositioning of the leading edge actuator has the ability to reattach the flow around the fore portion of the aerofoil at a post stall angle of alpha = 18°.

Organic thin-film transistors (OTFTs) have been widely studied because of their promising potential for application in low-cost, large-area and flexible electronics. However, several challenges remain on the way towards practical OTFT devices, such as a high operating voltage (> 20 V) induced by the low charge carrier mobility of organic semiconductors and low capacitance of organic gate dielectrics. A low operating voltage is essential for various OTFTs applications, such as portable displays, radio frequency identification tags (RFIDs), smart textiles and sensors. The key to low voltage operation of OTFTs is reduction of the threshold voltage, inverse subthreshold slope which can be fulfilled by using a high-capacitance gate dielectric with superior interface properties. Since field-effect current is proportional to field-induced charge density, using a gate dielectric layer with high dielectric constant (high-k) enhances output current densities at much lower applied voltages. Very thin dielectric layers have reportedly suffered from poor dielectric properties, while very high-k gate dielectrics have led to inferior dielectric-semiconductor interface. As a result, unsatisfactory device performance, such as low charge carrier mobility and high gate leakage current, has been obtained. In addition, solution-processability on a variety of substrates and compatibility with most common semiconducting materials make high-k dielectric materials an unrivalled candidate for low-voltage, low-cost applications. Consequently, the aim of this project was to produce a high-quality, high-capacitance gate dielectric with excellent properties which is consistent with cheap, basic solution-processing manufacturing techniques. With great promise in hybrid materials, a novel, high-k dielectric material based on alternative organic-inorganic nanocomposites that combine very high dielectric constant values intrinsic to ferroelectric ceramic materials (nanoparticles) with mechanical flexibility, low-cost and easy processing of polymers was developed. Both low- and high-k polymer matrices have been used in formulating high-k nanocomposite dielectric suspensions. The uniformity of suspensions has been improved by surface modification of nanoparticles in the case of low-k polymers, while a combination of polymer choice, solvents and nanoparticle-to-polymer ratio led to homogenous suspensions based on high-k polymers. The nanocomposite preparation technique was also unique to this work and gave reproducibly stable nanocomposite suspensions. Finally, ultralow-voltage (~ 1) OTFTs have been successfully demonstrated by integrating nanocomposite bilayer dielectrics using a high-k fluorinated polymer. Bilayer dielectrics were formed by (partially) capping the surface of the nanocomposite films with an ultrathin capping layer. The capping layer was the key to the operation of low-voltage OTFTs as it allowed remarkable and advantageous use of the nanocomposite surface roughness while improving the dielectric-semiconductor surface roughness. Ultimately, such nanocomposite bilayers have a potential to pave the way towards low-cost fabrication and integration of low-voltage components and circuits on flexible substrates.

>Magister Scientiae - MSc / In South Africa, water pollution problems have continued to increase due to increasing anthropogenic activities. The increasing number of organic contaminants in various water sources can be attributed to industrial development, population growth and agricultural run- off. These activities have impacted negatively on the availability and accessibility to sustainable clean water resources, exposing citizens to water borne diseases such as cholera, diarrhoea and typhoid fever; commonly reported among children. Advanced oxidation technologies such as dielectric barrier electrohydraulic discharge (EHD), also referred to as dielectric barrier discharge (DBD), have the ability to decompose persistent organics and eliminate microbes. DBD offers advantages such as efficiency, energy saving, rapid processing, use of few or no chemicals, and non-destructive impact on the ecosystem. The system is also capable of generating ozone, hydrogen peroxide, singlet oxygen, superoxide radicals, hydroxyl radicals and other active species. The combination of these reactive species has been reported to degrade biological and chemical pollutants rapidly and efficiently. In this study, the DBD system was optimized by investigating the effect of physico-chemical, electrical parameters and reactor configurations on Methylene Blue (MB) decolouration efficiency. The physico-chemical parameters included MB concentration, solution pH and conductivity, solution volume, NaCl electrolyte concentration in the electrode compartment and air flow rate. As for electrical parameters, the effects of voltage, electrode type and size on MB decolouration efficiency were studied. The effect of the aforementioned parameters on MB decolouration efficiency was assessed by varying one parameter at a time. The following physico-chemical parameters: time (from 0 - 60 minutes), pH (2.5 - 10.5), solution conductivity (5 - 20 mS/cm), MB concentration (0.5 – 10 mg/L), solution volume (500 – 2000 mL), NaCl electrode electrolyte concentration (10 – 50 g/L) and air flow rate (2– 4 L/min) were varied in their respective ranges under the applied experimental conditions: reactor air gap 2 mm, solution volume 1500 mL, NaCl electrolyte concentration of 50 g/L in the electrode compartment, voltage 25 V (7.8 kV), airflow rate 3 L/min, 0.5 mm silver electrode and a running time of 60 minutes. As for electrical parameters, voltage (from 20 - 25 V), electrode type (copper, silver and stainless steel) and electrode diameter (0.5 – 1.5 mm) were also altered individually at the applied experimental conditions. The reactor air gap was varied from 2 to 6 mm. At the same experimental conditions, the free reactive species generated mainly H2O2 and O3, were detected and quantified using the Eisenberg and indigo methods, respectively. The optimum physico-chemical parameters were found to be MB concentration 5 mg/L, concentration of NaCl electrolyte used in the central compartment of the DBD reactor 50 g/L, solution pH 2.5, solution conductivity 10 mS/cm, air flow rate 3 L/min, solution volume 1500 mL and an optimum contact time of 30 minutes. The optimum electrical parameters were found to be: applied voltage 25 and 1.5 mm silver electrode. The following parameters MB concentration, solution conductivity and pH, applied voltage and reactor configuration significantly affected MB decolouration efficiency compared to parameters such as solution volume, the inlet air flow rate, electrode type and size and NaCl electrolyte concentration in the electrode compartment, which were less effective in enhancing MB decolouration. Moreover, for all DBD experiments performed at the applied experimental conditions, complete decolouration of MB was achieved in the first 30 minutes. However, trends between the optimized parameters and MB decolouration efficiency were mostly observed after 10 minutes. The optimized DBD system reduced the treatment time from 30 to 20 minutes without any chemical additives. Moreover, at 5 mg/L MB under the applied optimum conditions, it was proved that besides 99% of MB decolouration reached after 60 minutes, 53% of total organic carbon (TOC) removal was also achieved. The chemical oxygen demand (COD) characterizing MB toxicity was less than 5 mg/L before as well as after the DBD experiment. After 10 minutes of experiment under the following conditions: Applied voltage 25 V, MB concentration 5 mg/L, solution pH (in between 6.04 and 6.64), solution volume 1500 mL, air flow rate 3 L/min, 0.5 mm silver electrode and a contact time of 60 minutes, about 3.73 x 10-5 mol/L H2O2 was produced which decreased to 2.93 x 10-5 mol/L 10 minutes later, while O3 concentration was initially very low and could not be detected. However, 0.5 mol/L of O3 was detected after 20 minutes of operating time, thereafter, H2O2 concentration decreased continuously with time while that of O3 fluctuated as the treatment time increased. Likewise, the energy density for the production of free reactive species reached 0.87 g/ kWh in the first 10 minutes due to the presence of chromophoric functional groups such as =N+(CH3)2 in MB structure that had to be destroyed. Thereafter, the energy consumption decreased progressively to zero with an increase in treatment time due to the destruction of =N+(CH3)2 groups in MB structure with time. The correlation between the rise in the of H2O2 concentration and energy density after 10 minutes was probably due to dissociation of OH- OH bonds in H2O2 by UV light to yield OH radicals which unselectively may have attacked MB dye. Thus, MB decomposition in the current DBD reactor was mostly initiated by H2O2 and O3. The irradiation of H2O2 by UV light generated in the DBD system was found to accelerate dye decomposition in the first 30 minutes of the experiment. The UV-vis analysis of treated MB samples confirmed that the complete decolouration of MB achieved in the first 30 minutes was due to the destruction of the chromophoric [=N+(CH3)2] group in Methylene blue structure, while the FT-IR confirmed the presence of traces of various functional groups such as C=C, C=O, C=N, NH, NH3, NO2, etc. characteristics of carboxylic acids, amines, amides, nitrogen based compounds (salts), aliphatic and unsaturated by-products remaining in the bulk solution after treatment. The salts analysis after treatment showed that 16 mg/L of nitrates and nitrites and 1.1mg/L of sulphates mainly originating from air and MB decomposition were present in the treated samples. The EHD/DBD system used in this study offers an approach to partially treat water/wastewaters and its optimization was able to significantly enhance the decomposition of the target MB dye as indicated by the reduction of total organic carbon (TOC) from 8.3 mg/L to 3.9 mg/L. Compared to previous research, this study successfully optimised a complete double cylindrical dielectric barrier discharge (DBD) reactor at ambient condition without any chemical additives.

GaAs(1-x)Bi(x) (x = 0 to 17%) optical properties were investigated by spectroscopic ellipsometry (in energy ranges of 0.37–9.0 eV). Optical features in the dielectric function, known as the critical points, were distinguished and modeled using standard analytic line shapes. The energy dependence of the critical points energies was thoroughly investigated as a function of Bi content and thin film strain. Critical points analysis in the Brillion zone showed that the top of the valence band is most strongly dependent on Bi content compared to other parts of the band structure. In addition, an interesting new critical point was observed that is attributed to alternative allowed optical transitions made possible by changes to the top of the valence band caused by resonant interactions with Bi orbitals. Several of the critical points were extrapolated to 100% Bi and showed reasonable agreement with the calculated band structure of GaBi. GaAs(1-x)Bi(x) (x= 03, 0.7 and 1.1%) based p+/n and n+/p heterostructure photovoltaic performance was characterized through IV and CV measurement. By introduction of Bi into GaAs, a non-zero EQE below the GaAs band edge energy was observed while the highest efficiency was obtained by ~ 0.7% Bi incorporation. EQE spectrum was modeled to find the minority carrier diffusion lengths of ~ Ln = 1600 and Lp = 140 nm for p-doped and n-doped GaAs92Bi08 in the doping profile of 10^15 - 10^16 cm^-3. Analysis of the CV measurement confirmed the background n-doping effect of Bi atom and the essential role of the cap layer to reduce multi-level recombination mechanisms at the cell edge to improve ideality factor. Low temperature grown GaAs was optimized to be used as photoconductive antenna in THz time-domain spectroscopy setup. The As content was investigated to optimize photo-carrier generation using 1550 nm laser excitation while maintaining high mobility and resistivity required for optical switching. A barrier layer of AlAs was added below the LT-GaAs to limit carrier diffusion into the GaAs substrate. Moreover, LT-GaAs layer thickness and post-growth annealing condition was optimized. The optimized structure (2-µm LT-GaAs on 60-nm AlAs, under As2:Ga BEP of ~7, annealed at 550°C for 1 minute) outperformed a commercial InGaAs antenna by a factor of 15 with 4.5 THz bandwidth and 75 dB signal-to-noise ratio at 1550 nm wavelength. / Graduate

Ce travail a pour objectif d'évaluer l'impact de la nanostructuration de résines d'imprégnation, destinées aux isolations statoriques d'alternateur de puissance, sur leurs propriétés électriques et thermiques. La première étape concerne l'étude de résines d'imprégnation aux propriétés physiques supérieures à celles des résines actuellement utilisées. La seconde étape concerne la détermination des caractéristiques de prototypes industriels développés par les sociétés Von Roll et Alstom ; ces prototypes sont composés d'un substrat « ruban » (composé de papier micacé et de tissu de verre) imprégné d'une résine innovante. Les améliorations apportées par les modifications des résines et des rubans permettent d'obtenir, dans le meilleur des cas, des augmentations respectives pouvant aller jusqu'à 14 % pour la rigidité diélectrique, 30 % pour la diffusivité thermique et 100 % pour l'endurance en tension. Une diminution de 33% des niveaux de charges d'espace accumulées est aussi observable. Les résultats obtenus lors de ce travail de thèse montrent qu'il est possible, dans certains cas, d'améliorer les propriétés électriques et/ou thermiques des isolations en modifiant les résines de référence par l'ajout de particules submicroniques de nitrure de bore (BN) et/ou de nanoparticules de dioxyde de silicium (SiO2). Cependant, il est également montré que ces propriétés peuvent être fortement influencées par le processus de fabrication, notamment par les paramètres de polymérisation. / This work aims to access the impact of nanostructuring over the impregnation resin, developed for the electrical insulation of alternator stator bars, on their electrical and thermal properties. The first step of this study concerns the analysis of impregnation resins with improved physical properties with respect to the usual resins. The second part concerns the characterization of prototypes which are manufactured by Alstom and Von Roll companies; these prototypes are composed by a tape (mica paper and glass fabric) impregnated with the innovative resin.In the best case, the modifications of the resins and the prototypes led to respective improvements up to 14 % for the dielectric strength, 30 % for the thermal diffusivity and 100 % for the voltage endurance. A decrease up to 33 % of the space charge levels can be also observed.The results obtained show that it is possible, in some cases, to improve the electrical and the thermal properties of the insulation by modifying the impregnation resin and the prototypes, with the addition of boron nitride (BN) submicron particles and/or silicon dioxide (SiO2) nanoparticles. However, it is shown that these properties can be highly influenced by the manufacture process of the resin and the prototypes, in particular by the curing parameters.

Les crises énergétiques et environnementales nous obligent à chercher les sources d’énergies renouvelables, qui contribuent à la fois à réduire l’effet de serre et la consommation des sources traditionnelles d’énergie fossile. Récemment, un nouveau système, le nano-générateur triboélectrique (TENG), se convertit l’énergie mécanique en énergie électrique en combinant l’effet de la triboélectronique et de l’induction électrostatique. TENG montre comme un outil alternatif et prometteur pour la récupération des énergie s renouvelables. Pour réaliser des matériaux plus performants, la plupart des recherches s’appuie sur le choix des différents types des céramiques ou charges conductrices, de taux de charge et de nouvelle structure, l’effet de l’interface entre charge, ainsi que la taille des charges, matrice a été très peu étudié. Donc, l’objectif de cette thèse consiste à étudier les effets de taille des charges, de l’interface entre charge-matrice et de la polarisation sur les performances électriques du TENG et les nano-générateurs du type piézo/tribohybride (P-TENG). Tout d’abord, un TENG fonctionnant sous la mode de contact-séparation avec la motion de l’accélération/décélération a été utilisé dans notre expérimentation et les équations progressives du type du second ordre polynomial ont été choisi pour l’ajustement des courbes. Différents paramètres cinétiques comme distance entre deux électrodes, fréquence de déplacement, pression de contact et temp du repos du TENG basés sur les conditions expérimentales ont été étudiés dans le chapitre 2 afin de comprendre leur contributions sur les performances des sorties électriques. Deuxièmement, deux différentes tailles (BT-70, BT-500) des nanoparticules de BaTiO3 sont considérées et utilisées pour préparer des composites di électriques BaTiO3/PDMS et BaTiO3-MWCNT/PDMS dans le chapitre 3. Les propriétés di électriques de tous ces composites ont été caractérisées et le déplacement électrique entre les particules et le polymère a été analysé théoriquement. En plus, l’effet synergique de MWCNT, de nitrure de bore (BN) et de noir de carbone (CB) avec BaTiO3 dans BaTiO3-70-MWCNT (CB, BN) / PDMS ont été comparés. Tous ces films composites fabriqués précédemment sont ensuite utilisés dans l’assemblage des dispositifs TENG dans le chapitre 4. Les performances électriques ont été mesurées pour étudier l’influence de l’interface charge-matrice et l’effet synergique des particules MWCNT (CB, BN) pour les dispositifs TENG. Les résultats de la différence potentielle surfacique induite par les effets synergiques des BaTiO3/MWCNT ont été confirmé avec les simulations COMSOL Multiphysics. En outre, dans le chapitre 5 les films composites contenant des particules de BaTiO3 sont polarisés pour étudier les effets piézoélectriques et triboélectriques couplés pour P-TENG. Les effets des différents paramètres de polarisation, tels que la direction de polarisation, la température, le ratio massique du BaTiO3, le champ électrique et la taille des BaTiO3 sur les performances de P-TENG ont été discutées. Enfin, les conclusions générales sont présentées et certains ou quelques perspectives sont proposées pour le futur. / The increasing energy crisis and environmental pollution stimulate the development of renewable energies, which contribute to reducing the greenhouse effect and the consumption of traditional fossil fuels. As a new type of renewable energy harvesting system, triboelectric nanogenerator (TENG) converts mechanical energy to electrical energy by coupling the effect of triboelectrification and electrostatic induction. TENG has been proved to be an alternative and promising approach to harvest renewable energy in recent years. For the dielectric material candidates, more attention has been paid to choosing different types of ceramic or conductive fillers, filler loading and surface structure design, rather than considering the filler-matrix interface effect. Thus, it is desired to clarify the effect of filler size and fillermatrix interface on the performance of compositebased TENGs. This work aims to research the influence of filler size, filler-matrix interface, and polarization on the output performance of TENG and piezo/tribo-hybrid nanogenerator (P-TENG). Firstly, the contact-separation mode TENG with acceleration/deceleration motion is utilized in our experiments. The piecewise second-order polynomial fitting is chosen for the motion process curve fitting. Various kinematic parameters including gap distance, motion frequency, contact pressure, and pause time of TENG are studied theoretically based on the experiment conditions in chapter 2, to understand their contributions to the electrical output performance. Secondly, in chapter 3, BaTiO3 nanoparticles with two different sizes (BT-70, BT-500) are considered and utilized to prepare BaTiO3/PDMS and BaTiO3-MWCNT/PDMS dielectric composites. The dielectric properties of all composites are characterized, and the electric displacement between particle and polymer are theoretically analyzed. Moreover, the synergistic effect of MWCNT, boron nitride (BN) and carbon black (CB) with BaTiO3 in BaTiO3-70-MWCNT(CB, BN)/PDMS are compared. Then, all composite films fabricated were further utilized to assemble TENG devices in chapter 4. The output voltage, current, and charges densities of TENGs are evaluated to investigate the influence of fillermatrix interface and synergistic effect of MWCNT (CB, BN) particles on the output performance of TENG devices. COMSOL Multiphysics simulation are performed to further confirm the surface potential difference introduced by the synergistic effects of BaTiO3/MWCNTs. Furthermore, the composite films with BaTiO3 particles are polarized to further explore the interaction of piezoelectric and triboelectric effects for P-TENG in chapter 5. Influences of different polarization parameters, such as polarization direction, poling temperature, BaTiO3 mass ratio, poling electric field and BaTiO3 sizes, on the output performance of the PTENG have been discussed. Finally, general conclusions are presented and perspectives are proposed for the future work.

The incorporation of fluorine into SiO2 has been shown to reduce the dielectric constant of the existing materials by reducing the electrical polarizability. However, the incorporation of fluorine has also been shown to decrease film stability. Therefore, new efforts have been made to find different ways to further decrease the relative dielectric constant value of the existing low-k materials. One way to reduce the dielectric constant is by decreasing its density. This reduces the amount of polarizable materials. A good approach is increasing porosity of the film. Recently, fluorinated silica xerogel films have been identified as potential candidates for applications such as interlayer dielectric materials in CMOS technology. In addition to their low dielectric constants, these films present properties such as low refractive indices, low thermal conductivities, and high surface areas. Another approach to lower k is incorporating lighter atoms such as hydrogen or carbon. Silsesquioxane based materials are among them. However, additional integration issues such as damage to these materials caused by plasma etch, plasma ash, and wet etch processes are yet to be overcome. This dissertation reports the effects of triethoxyfluorosilane-based (TEFS) xerogel films when reacted with silylation agents. TEFS films were employed because they form robust silica networks and exhibit low dielectric constants. However, these films readily absorb moisture. Employing silylation reactions enhances film hydrophobicity and permits possible introduction of this film as an interlayer dielectric material. Also, this work describes the effects of SC-CO2 in combination with silylating agents used to functionalize the damaged surface of the ash-damaged MSQ films. Ashed MSQ films exhibit increased water adsorption and dielectric constants due to the carbon depletion and modification of the properties of the low-k material caused by interaction with plasma species. CO2 is widely used as a supercritical solvent, because of its easily accessible critical point, low cost, and non-hazardous nature. Its unique diffusion and surface tension properties make SC-CO2 a good candidate for treatment of porous ultra low-k materials.