O carbeto de silício (SiC) é um semicondutor com propriedades adequadas para substituir o silício em dispositivos eletrônicos em aplicações que exijam alta potência, alta frequência e/ou alta temperatura. Além disso, é possível crescer termicamente um filme de dióxido de silício (SiO2) sobre o SiC de maneira análoga ao silício. Porém, esses filmes apresentam maior densidade de defeitos eletricamente ativos na região interfacial SiO2/SiC que no caso do SiO2/Si, o que limita a qualidade dos dispositivos formados. Assim, compreender a origem da degradação elétrica e desenvolver métodos para passivar os defeitos na região interfacial SiO2/SiC são importantes passos para o desenvolvimento da tecnologia do SiC. Buscando uma melhor compreensão da natureza dos defeitos presentes na região interfacial SiO2/SiC, a interação de estruturas SiO2/SiC com vapor d’água enriquecido isotopicamente (D2 18O) e a interação com monóxido de carbono (CO), um dos subprodutos da oxidação térmica do SiC, foram investigadas. Observou-se que a interação com CO gera cargas positivas na estrutura e que a incorporação de deutério proveniente da água é fortemente dependente da rota de formação do filme de SiO2. Sabendo que a incorporação de nitrogênio e de fósforo na região interfacial SiO2/SiC são eficientes métodos para reduzir o número de defeitos eletricamente ativos nessa região, investigou-se a incorporação de nitrogênio em estruturas de SiC através de tratamentos térmicos em amônia enriquecida isotopicamente (15NH3) e desenvolveu-se um novo método de incorporação de fósforo, fazendo sua deposição por pulverização catódica (sputtering) Os métodos de incorporação propostos resultaram em maiores quantidades de nitrogênio e de fósforo na região interfacial SiO2/SiC do que os encontrados na literatura, tornando-os promissores candidatos na passivação elétrica do SiC. Além da caracterização físico-química utilizando diferentes técnicas, também foi feita a caracterização elétrica de capacitores Metal-Óxido-Semicondutor (MOS) testando filmes de SiO2 obtidos por sputtering ou por crescimento térmico. Adicionalmente, desenvolveu-se uma rota de síntese de padrões de 18O mais estáveis ao longo do tempo para serem utilizados em análises por reação nuclear. Também foi proposta uma metodologia de quantificação de fósforo via análise por reação nuclear. Dos resultados obtidos neste doutorado, uma melhor compreensão da natureza e da origem dos defeitos presentes na região interfacial SiO2/SiC foi alcançada. Também obteve-se uma melhor compreensão de como os elementos passivadores nitrogênio e fósforo interagem nessa região. / Silicon carbide (SiC) is a semiconductor with adequate properties to substitute silicon in electronic devices in applications that require high power, high frequency, and/or high temperature. Besides, a silicon dioxide (SiO2) film can be thermally grown on SiC in a similar way to that on Si. However, these films present higher density of electrical defects in the SiO2/SiC interfacial region when compared to the SiO2/Si interface, which limits the quality of the fabricated devices. Thus, it is important to understand the origin of the electrical degradation and to develop methods to passivate the defects in the SiO2/SiC interfacial region in order to develop the SiC technology. Aiming at a better understanding of the nature of defects at the SiO2/SiC interfacial region, the interaction of SiO2/SiC structures with water vapor isotopically enriched (D2 18O) and the interaction with carbon monoxide (CO), one of the SiC thermal oxidation by-products, were investigated. It was observed that the interaction with CO generates positive charges in the structure and that the deuterium incorporation from the water vapor is strongly dependent on the formation route of the SiO2 film. Knowing that nitrogen and phosphorous incorporation in the SiO2/SiC interfacial region are efficient methods to reduce the number of electrical defects in this region, the nitrogen incorporation in SiC structures by isotopically enriched ammonia (15NH3) annealings was investigated and a new method to incorporate phosphorous, by sputtering deposition was developed The proposed incorporation methods resulted in higher amounts of nitrogen and phosphorous then those found in literature, making them promising candidates to the electrical passivation of SiC. Besides the physico-chemical characterization using different techniques, the electrical characterization of Metal-Oxide-Semiconductor (MOS) capacitors was also performed, testing SiO2 films obtained by sputtering deposition or thermally grown. Additionally, a route to synthesize 18O standards for nuclear reaction analyses that are more stable over time was developed. Besides, a methodology to quantify phosphorous by nuclear reaction analysis was proposed. From the results obtained in this PhD thesis, a better understanding of the nature and the origin of defects present in the SiO2/SiC interfacial region was obtained, as well as a better understanding on how the passivating elements nitrogen and phosphorous interact in this region.

O carbeto de silício (SiC) é um semicondutor com propriedades adequadas para substituir o silício em dispositivos eletrônicos em aplicações que exijam alta potência, alta freqüência e/ou temperatura. Além disso, um filme de dióxido de silício (SiO2) pode ser crescido termicamente sobre o SiC de maneira análoga a sobre silício, permitindo que a tecnologia já existente para a fabricação de dispositivos utilizando Si possa ser adaptada para o caso do SiC. No entanto, filmes crescidos termicamente sobre SiC apresentam maior densidade de defeitos eletricamente ativos na região interfacial SiO2/SiC que no SiO2/Si. Assim, compreender a origem e os parâmetros que afetam essa degradação elétrica é um importante passo para a tecnologia do SiC. A primeira parte deste trabalho teve como objetivo compreender o efeito de parâmetros de oxidação (pressão de oxigênio e tempo de oxidação) no crescimento térmico de filmes de dióxido de silício sobre substratos de carbeto de silício. As oxidações foram realizadas em ambiente rico em 18O2 e a influência na taxa de crescimento térmico dos filmes de Si18O2 e nas espessuras das regiões interfaciais formadas entre o filme dielétrico e o substrato foram investigadas utilizando análises por reação nuclear. Para correlacionar as modificações nas propriedades investigadas com as propriedades elétricas das amostras, estruturas metal-óxidosemicondutor foram fabricadas e levantamento de curvas corrente-voltagem e capacitânciavoltagem foi realizado. Com isso, pretendeu-se melhor compreender a origem da degradação elétrica gerada pela oxidação térmica no SiC. Observou-se que a taxa de crescimento térmico dos filmes de SiO2 depende de um parâmetro dado pelo produto do tempo de oxidação e da pressão de oxigênio, para as condições testadas. O deslocamento da tensão de banda plana com relação ao valor ideal mostrou-se igualmente dependente desse parâmetro, indicando que uma maior degradação elétrica na região interfacial SiO2/SiC ocorrerá conforme o filme fica mais espesso devido ao aumento dos parâmetros investigados. Não observaram-se modificações nas espessuras da região interfacial SiO2/SiC e na tensão de ruptura dielétrica dos filmes de SiO2 atribuídas aos parâmetros de oxidação testados. Na segunda parte deste trabalho, visando minimizar a degradação elétrica da região interfacial SiO2/SiC gerada pela oxidação térmica do SiC, propôs-se crescer termicamente, em uma condição mínima de oxidação, um filme muito fino e estequiométrico de SiO2, monitorado por espectroscopia de fotoelétrons induzidos por raios X. Para formar filmes mais espessos de SiO2 e poder fabricar estruturas MOS, depositaram-se filmes de SiO2 por sputtering. As espessuras e estequiometria dos filmes depositados foram determinadas por espectrometria de retroespalhamento Rutherford com ou sem canalização. As estruturas MOS em que o filme fino de SiO2 foi crescido termicamente antes da deposição apresentaram menor deslocamento da tensão de banda plana com relação ao valor ideal e maior tensão de ruptura dielétrica do que as amostras em que o filme foi apenas crescido termicamente ou apenas depositado, confirmando a minimização da degradação elétrica da região interfacial SiO2/SiC pela rota proposta. O efeito de um tratamento térmico em ambiente inerte de Ar nas estruturas também foi investigado. Observou-se uma degradação elétrica na região interfacial SiO2/SiC devido a esse tratamento. Análises por reação nuclear indicaram que o filme fino crescido termicamente não permaneceu estável durante o tratamento térmico, perdendo oxigênio para o ambiente gasoso e misturando os isótopos de oxigênio do filme crescido termicamente com o do filme depositado. / Silicon carbide (SiC) is a semiconductor with adequate properties to substitute silicon in electronic devices in applications that requires high power, high frequency, and/or high temperature. Besides, a silicon dioxide (SiO2) film can be thermally grown on SiC in a similar way to that on Si, allowing that technology already used to fabricate devices based on Si to be adapted to the SiC case. However, the oxide films thermally grown on SiC present higher density of electrical defects at the SiO2/SiC interfacial region when compared to the SiO2/Si. Thus, the understanding of the origin and what parameters affect the electrical degradation is an important step to the SiC technology. The first part of this work aimed to understand the effect of oxidation parameters (oxygen pressure and oxidation time) in the thermal growth of silicon dioxide films on silicon carbide substrates. The oxidations were performed in an 18O2 rich ambient and the influence on the growth rate of the Si18O2 films and on the interfacial region thickness formed between the dielectric film and the substrate were investigated using nuclear reaction analyses. To correlate the modifications observed in these properties with modifications in the electrical properties, metal-oxide-semiconductors structures were fabricated and current-voltage and capacitancevoltage curves were obtained. The aim was to understand the origin of the electrical degradation due to the thermal oxidation of silicon carbide. It was observed that the growth rate of the Si18O2 films depends on the parameter given by the product of the oxygen pressure and the oxidation time, under the conditions tested. The flatband voltage shift with respect to the ideal value was also influenced by the same parameter, indicating that a larger electrical degradation in the SiO2/SiC interfacial region will occur as the film becomes thicker due to the increase of the values of the investigated parameters. No modifications were observed in the SiO2/SiC interfacial region thickness and in the dielectric breakdown voltage of the SiO2 films that could be attributed to the oxidation parameters tested. In the second part of this work, in order to minimize electrical degradation due to thermal oxidation of silicon carbide, a stoichiometric SiO2 film with minimal thickness was thermally grown, monitored by X-ray photoelectron spectroscopy. To obtain thicker films and to fabricate MOS structures, a SiO2 film was deposited by sputtering. The thicknesses and stoichiometries of the deposited films were determined by Rutherford backscattering spectrometry using or not the channeling geometry. The MOS structures in which a thin film was thermally grown before the deposition presented smaller flatband voltage shift and higher breakdown voltage when compared to SiO2 films only thermally grown or only deposited directly on SiC, confirming that the electrical degradation in the SiO2/SiC interfacial region was minimized using the proposed route. The effect of one thermal treatment in argon in the structures was also investigated. An electrical degradation in the SiO2/4H-SiC interface was observed. Nuclear reaction analyses indicated that the thin film thermally grown was not stable during the annealing, loosing O to the gaseous ambient and mixing O isotopes of the thermally grown film with those of the deposited film.

Cette thèse traite l’étude et le contrôle d’un hacheur élévateur à 6 phases entrelacées basé sur des semi-conducteurs en carbure de silicium (SiC) et des inductances couplées inverses pour véhicules électriques à pile à combustible (FCEV). . L'ondulation du courant dans la pile est combustible est considérablement réduite et la durée de vie de celle-ci peut être prolongée. Les semi-conducteurs en SiC, en raison de leurs faibles pertes, permettent de meilleures performances thermiques et une fréquence de commutation plus élevée. Les volumes des composants passifs (inductances et condensateurs) sont ainsi réduits. Grâce aux inductances à couplage inverse, les pertes du noyau magnétique et du bobinage sont réduites.La stratégie de contrôle par mode glissant est développée en raison de sa grande robustesse face aux variations de paramètres. La fonctionnalité de détection en ligne de spectroscopie d'impédance électrochimique (SIE) est intégrée avec succès à l’algorithme de contrôle par mode glissant.La validation HIL (Hardware In the Loop) en temps réel du convertisseur proposé est obtenue en implémentant la partie puissance dans le FPGA et la partie commande dans le microprocesseur du système de prototypage MicroLabBox de dSPACE. La comparaison entre la simulation hors ligne et la validation HIL a démontré le comportement dynamique du convertisseur proposé et validé la mise en œuvre du contrôle dans un contrôleur en temps réel avant de futurs tests sur un banc d'essai expérimental à échelle réduite. / The objective of this thesis work is devoted to the design and control of a DC/DC boost converter for Fuel Cell Electric Vehicle (FCEV) application. A 6-phase Interleaved Boost Converter (IBC) based on Silicon Carbide (SiC) semiconductors and inversed coupled inductors of cyclic cascade structure is proposed. The input current ripple is reduced significantly and the lifespan of Polymer Electrolyte Membrane Fuel Cell (PEMFC) can be extended. Low power losses, good thermal performance and high switching frequency have been gained by the selected SiC-based semiconductors. The volumes of passive components (inductors and capacitors) are reduced. Thanks to the inverse coupled inductors, the core losses and copper losses are decreased and the compact magnetic component is achieved.Sliding-Mode Control (SMC) strategy is developed due to its high robust to parameter variations. on-line Electrochemical Impedance Spectroscopy (EIS) detection functionality is successfully integrated with SMC. No additional equipment and sensor is required.The real-time Hardwar In the Loop (HIL) validation of the proposed converter is achieved by implement the power part into the FPGA and the control into the microprocessor in the MicroLabBox prototyping system from dSPACE. The comparison between off-line simulation and HIL validation demonstrated the dynamic behavior of the proposed converter and validated the implementation of the control into a real time controller before future tests on experimental test bench.

No description available.

The corrosion behaviour of cast Al-Mg alloy A535 and its composites containing 10 wt.% and 15 wt.% fly ash, and 10 wt.% hybrid reinforcement (5 wt.% fly ash + 5 wt.% SiC) was investigated using weight-loss and electrochemical corrosion tests, optical microscopy, Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS). The tests were conducted in fresh water collected from the South Saskatchewan River and 3.5 wt.% NaCl solution at room temperature. The pH of the salt solution varied from 3 to 9. For comparison, two other aluminum alloys, AA2618 and AA5083-H116, were tested in the same electrolytes. The results of the weight-loss corrosion test showed that unreinforced A535 alloy had a lower corrosion rate in fresh water and seawater environments than the composites at all the tested pH values. The corrosion rate of the composites increased with increasing fly ash content. As expected, the corrosion rates of A535 alloy and the composites tested in fresh water were lower than those in salt solution. The results of the potentiodynamic and cyclic polarization electrochemical tests showed that the corrosion potential (Ecorr) and pitting potential (Epit) of the alloy were more positive than those of the composites. The corrosion and pitting potentials of the composites became more negative (active) with increasing fly ash content. The composites showed more positive (noble) repassivation or protection potential (Erp) than the matrix alloy, with the positivity increasing with fly ash content. Analysis of the electrochemical noise data showed that pitting corrosion was the dominant mode of corrosion for the alloy in 3.5 wt.% NaCl solution. Optical microscopy and SEM revealed that Mg2Si phase and Al-Mg intermetallics corroded preferentially to the matrix. The EDS data indicated that the protective oxide film formed on A535 contained Al2O3 and MgO.

The corrosion behaviour of cast Al-Mg alloy A535 and its composites containing 10 wt.% and 15 wt.% fly ash, and 10 wt.% hybrid reinforcement (5 wt.% fly ash + 5 wt.% SiC) was investigated using weight-loss and electrochemical corrosion tests, optical microscopy, Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS). The tests were conducted in fresh water collected from the South Saskatchewan River and 3.5 wt.% NaCl solution at room temperature. The pH of the salt solution varied from 3 to 9. For comparison, two other aluminum alloys, AA2618 and AA5083-H116, were tested in the same electrolytes. The results of the weight-loss corrosion test showed that unreinforced A535 alloy had a lower corrosion rate in fresh water and seawater environments than the composites at all the tested pH values. The corrosion rate of the composites increased with increasing fly ash content. As expected, the corrosion rates of A535 alloy and the composites tested in fresh water were lower than those in salt solution. The results of the potentiodynamic and cyclic polarization electrochemical tests showed that the corrosion potential (Ecorr) and pitting potential (Epit) of the alloy were more positive than those of the composites. The corrosion and pitting potentials of the composites became more negative (active) with increasing fly ash content. The composites showed more positive (noble) repassivation or protection potential (Erp) than the matrix alloy, with the positivity increasing with fly ash content. Analysis of the electrochemical noise data showed that pitting corrosion was the dominant mode of corrosion for the alloy in 3.5 wt.% NaCl solution. Optical microscopy and SEM revealed that Mg2Si phase and Al-Mg intermetallics corroded preferentially to the matrix. The EDS data indicated that the protective oxide film formed on A535 contained Al2O3 and MgO.

Cellular internalization of large therapeutic agents such as proteins or nucleic acids is a challenging task because of the presence of the plasma membrane. One strategy to facilitate intracellular drug uptake is to induce transient pores in the cell membrane through physical delivery strategies. Physical approaches are attractive as they offer more generic applicability compared with viral or biochemical counterparts. Pulsed laser light can induce the endothermic carbon-steam reaction in carbon-nanoparticle suspensions to produce explosive photoacoustic effects in the surrounding medium. In this study, for the first time, these photoacoustic forces were used to transiently permeabilize the cell membrane to deliver macromolecules into cells. Intracellular delivery using this method was demonstrated in multiple cell types for uptake of small molecules, proteins and DNA. At optimized conditions, uptake was seen in up to 50% of cells with nearly 100% viability and in 90% of cells with ≥90% viability, which compared favorably with other physical methods of drug delivery. Cellular bioeffects were shown to be a consequence of laser-carbon interaction and correlated with properties of the carbon and laser, such as carbon concentration and size, laser pulse duration, wavelength, intensity and exposure time. Similar results were observed using two different lasers, a femtosecond Ti: Sapphire laser and a nanosecond Nd: YAG laser. Uptake was also shown in murine skeletal muscles in vivo with up to 40% efficiency compared to non-irradiated controls. This synergistic use of nanotechnology with advanced laser technology could provide an alternative to viral and chemical-based drug and gene delivery.

No description available.

Graphene has been shown to be very powerful as a transducer in many biosensor applications due to its high sensitivity. This enables smaller surfaces and therefore less material consumption when producing sensors and concequently cheaper and more portable sensors compared to the commercially available sensors today. The electrical properties of graphene are very sensitive to gas exposure why presence of molecules or small changes in concentration could easily be detected when using graphene as a sensing layer. Graphene is sensitive towards many molecules and in order to detect and possibly identify gas molecules the surface needs to be functionalized. The intention of this project was to use nanoparticles (NPs) to further increase sensitivity and specificity towards selected molecules and also enable biofunctionalization of the NPs, and by that tune the electrical properties of the graphene. This study proposes the use of Fe3O4 and TiO2 NPs to enable sensitive detection of volatile gases and possibly further functionalization of the NPs using biomolecules as a detecting agent in a liquid-phasebiosensor application. The interaction between graphene and NPs have been investigated using several surface charactarization methods and electrical measurements for detection of gaseous molecules and also molecules in a liquid solution. The characterizing methods used are XPS, AFM with surface-potential mapping and Raman spectroscopy with reflectance mapping in order to investigate the NPs interaction with the graphene surface. Sensors where manufactured for gas-phase detection of CO, formaldehyde, benzene and NH3 specifically and display differences in sensitivity and behavior of the Fe3O4 and TiO2 NPs respectively. For liquid measurements the difference in behavior in two buffers was investigated using an in-house flow-cell setup. The surface charecterizing measurements indicated that just a small difference could be found between the two NPs, however a significant change in sensor response could be detected as a function of coverage. The liquid and gas-phase measurements rendered information on differences in sensitivity between the NPs and between analytes where TiO2 showed a higher level of sensitivity towards most of the gases investigated. Both Fe3O4 and TiO2 NP coated graphene showed capability to detect formaldehyde and benzene down to 50 ppb and 5 ppb respectively. The sensitive gas detection could help protecting individuals being exposed to a hazardous level of volatile gases if concentrations increase rapidly or at a long term exposure with lower concentrations, improving saftey and health where these gases are present.

Die vorliegende Arbeit behandelt die Charakterisierung von epitaktischem Graphen auf Siliziumkarbid (0001) mittels Raman-Spektroskopie. Nach der Einführung theoretischer sowie experimenteller Grundlagen werden das Wachstum von Graphen auf Siliziumkarbid (SiC) behandelt und die untersuchten Materialsysteme vorgestellt. Es wird gezeigt, dass das Raman-Spektrum von epitaktischem Graphen auf SiC (0001) neben den Phononenmoden des Graphens und des Substrats weitere Signale beinhaltet, welche der intrinsischen Grenzflächenschicht, dem Buffer-Layer, zwischen Graphen und SiC zugeordnet werden können. Das Raman-Spektrum dieser Grenzflächenschicht kann als Abbild der phononischen Zustandsdichte interpretiert werden. Fortführend werden verspannungsinduzierte Änderungen der Phononenenergien der G- und 2D-Linie im Raman-Spektrum von Graphen untersucht. Dabei werden starke Variationen des Verspannungszustands beobachtet, welche mit der Topographie der SiC-Oberfläche korreliert werden können und erlauben, Rückschlüsse auf Wachstumsmechanismen zu ziehen. Die Entwicklung einer neuen Messmethode, bei der das Raman-Spektrum von Graphen durch das SiC-Substrat aufgenommen wird, ermöglicht die detektierte Raman-Intensität um über eine Größenordnung zu erhöhen. Damit wird die Raman-spektroskopische Charakterisierung eines Graphen-Feldeffekttransistors mit top gate ermöglicht und ein umfassendes Bild des Einflusses der Ladungsträgerkonzentration und der Verspannung auf die Positionen der G- und 2D-Raman-Linien von quasifreistehendem Graphen auf SiC erarbeitet.