Wire-grid polarizers (WGPs) offer superior extinction, durability, angle of incidence, and heat resistance when compared to traditional organic polarizers. WGPs are found in applications such as high lumen lighting, laser devices, high lumen digital cinema projectors, LED packaging, and other integrated optical applications and are driving the need for over-coatings. Over-coating a WGP has been found to increase lifetime and durability. This research provides lifetime data on coated and uncoated WGPs. WGPs over-coated with 100nm of SiO2, 300nm of MgF2, and with no over-coating were heated to temperatures of 450 ºC, 500 ºC, and 550 ºC and timed until they reached a predetermined optical failure point. The activation energies were calculated by applying the Arrhenius model to the failure data. WGPs with no over-coating were found to have an activation energy ≥ 1.5329 eV, with silicon dioxide an activation energy ≥ 1.7197 eV, and with magnesium fluoride an activation energy ≥ 2.4577 eV. It has been shown that coating a WGP with an over-coating of silicon dioxide or magnesium fluoride slows the oxidation process of the aluminum nano-wires, thus increasing the lifetime of the WGP by 208% and 27,904%, respectively. Parasitic chemical reactions were not found to exist with silicon dioxide or magnesium fluoride when used as an over-coating.

This dissertation reports on research related to ultrafiltration (UF) membranes in drinking water applications. A pilot-scale investigation identified seasonal surface water quality impacts on UF performance and resulted in the development of a dynamic chemically enhanced backwash protocol for fouling management. Subsequent analysis of UF process data revealed limitations with the use of specific flux, transmembrane pressure (TMP), and other normalization techniques for assessing UF process fouling. A new TMP balance approach is presented that identifies the pressure contribution of membrane fouling and structural changes, enables direct process performance comparisons at different operating fluxes, and distinguishes between physically and chemically unresolved fouling. In addition to the TMP balance, a five component optimization approach is presented for the systematic improvement of UF processes on the basis of TMP variations. Terms are defined for assessing process event performance, a new process utilization term is presented to benchmark UF productivity, and new measures for evaluating maintenance procedures are discussed. Using these tools, a correlation between process utilization and operating pressures was established and a sustainable process utilization of 93.5% was achieved. UF process capabilities may be further enhanced by pre-coating media onto the membrane surface. Silicon dioxide (SiO2) and powdered activated carbon (PAC) are evaluated as precoating materials, and the applicability of the TMP balance for assessing pre-coated membrane performance is demonstrated. The first use of SiO2 as a support layer for PAC in a membrane pre-coating application is presented at the laboratory-scale. SiO2-PAC pre-coatings successfully reduced physically unresolved fouling and enhanced UF membrane organics removal capabilities.

No description available.

Die Sammlung der zwei-dimensionalen (2D) Materialien ist begrenzt, da sehr wenige Verbindungen stabil bleiben, sobald sie nur aus Oberflächen bestehen. Aufgrund ihrer außergewöhnlichen Eigenschaften sind 2D Materialien jedoch nach wie vor überaus begehrt. Vor kurzem wurden atomar definierte, chemisch gesättigte SiO2 Bilagen auf verschiedenen Metalloberflächen präpariert. Eine solche ultradünne Silika-Lage wäre eine vielversprechende Ergänzung zur Familie der 2D Materialien, wenn sie unter Strukturerhalt vom Wachstumssubstrat isoliert werden kann. In dieser Arbeit untersuchen wir die Eigenschaften einer Silika-Bilage im Zusammenhang mit Anwendungen von 2D Materialien. Die Bilage besitzt kristalline und amorphe Regionen, die beide atomar glatt sind. Die kristalline Region besitzt ein hexagonales Gitter mit gleichmäßiger Porengröße, während die amorphe Region einer komplexeren Beschreibung bedarf. In einer Studie von Baublöcken zeigen wir, dass mittelreichweitige Struktureinheiten in Korrelation mit einem Parameter für die Bindungswinkelfrustration auftreten. Das Netzwerk verschiedener Nanoporen stellt eine größenselektive Membran dar, wie wir in einer Adsorptionsstudie zeigen. Pd- und Au-Atome durchdringen den Silikafilm abhängig von der Größe der zur Verfügung stehenden Nanoporen. Der ultradünne Film hält der Einwirkung verschiedener Lösungsmittel stand und die Beständigkeit der Struktur in Wasser wird analysiert. Diese Studien deuten die außergewöhnliche Stabilität dieser Struktur an. Wir entwickeln eine polymerbasierte mechanische Exfoliation, um den Film von seinem Wachstumssubstrat zu entfernen, und zeigen, dass der Film als intakte Einheit vom Substrat abgelöst wird. Wir präsentieren anschließend den Transfer des Silikafilms auf ein TEM-Gitter, wo er schraubenartig gewundene Formen annimmt. Weiterhin wurde der Film auf ein Pt(111)-Substrat transferiert. In diesem Fall wird unter Erhalt der Struktur ein Transfer in der Größenordnung von Millimetern erreicht. / The library of two-dimensional (2D) materials is limited, since only very few compounds remain stable when they consist of only surfaces. Yet, due to their extraordinary properties, the hunt for new 2D materials continues. Recently, an atomically defined, self-saturated SiO2 bilayer has been prepared on several metal surfaces. This ultrathin silica sheet would be a promising addition to the family of 2D materials, if it can be isolated from its growth substrate without compromising its structure. In this work, we explore the properties of a silica bilayer grown on Ru(0001) in the context of 2D technology applications. The bilayer sheet exhibits crystalline and amorphous regions, both being atomically flat. The crystalline region possesses a hexagonal lattice with uniform pore size, while the amorphous region requires a more complex description. In a building block study of the amorphous region, we find that medium range structural patterns correlate with a parameter describing the bond angle frustration. The resulting network of different nanopores represents a size-selective membrane, as illustrated in an adsorption study. Pd and Au atoms are shown to penetrate the silica film selectively, depending on the presence of appropriately sized nanopores. The ultrathin silica film is shown to withstand exposure to different solvents and the stability of the structure in water is analyzed. These studies indicate extraordinary stability of this nanostructure. We develop a polymer assisted mechanical exfoliation method for removing the film from the growth substrate, providing evidence that the film is removed as an intact sheet from the growth substrate. We subsequently present the transfer of the silica bilayer to a TEM grid, where it forms micro-ribbons. Further, the film is transferred to a Pt(111) substrate, where mm-scale transfer under retention of the structure is achieved.

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.

Les décharges contrôlées par barrière diélectrique (DBD) homogènes à pression atmosphérique sont une alternative pour réaliser des couches minces sur de grandes surfaces, en continu, sans système de pompage. La physique de ces décharges tout comme les propriétés des couches minces obtenues sont bien établies en excitation sinusoïdale basse fréquence (< 200 kHz) et radiofréquence (13,56 MHz). L’objet de cette thèse est d’étendre le domaine de fonctionnement de ces décharges dans un mélange Penning Ar/NH3. Pour ce faire, un dispositif original a été mis au point permettant de faire varier la fréquence d'excitation en tension sinusoïdale entre 50 kHz à 18 MHz. La DBD nanopulsée répétitive a également été étudiée. L’objectif est d’identifier de nouveaux modes de fonctionnement de la DBD homogène et d’en maximiser la puissance pour augmenter la vitesse de dépôt de couche mince tout en maintenant une qualité compatible avec les applications. Dans un mélange Ar-NH3, le régime de fonctionnement de la décharge transit de luminescent (GDBD) à Townsend (TDBD) vers 250 kHz puis à RF-DBD à partir de 3 MHz. Les mesures électriques et optiques qui ont été réalisées montrent que la puissance moyenne des décharges homogènes augmente d'un facteur 30 entre les régimes GDBD et RF-DBD (jusqu'à 35 W/cm3) tandis que la tension d'amorçage est réduite d'un facteur 6. Ces observations couplées aux spectres d’émission des décharges indiquent que la densité d’électrons augmente de plusieurs ordres de grandeur alors que leur énergie décroit. Ces résultats s’expliquent par un changement de mécanisme d'ionisation avec un rôle dominant de l'émission d'électron secondaire à la cathode en basse fréquence (GDBD et TDBD) tandis que l'ionisation en volume domine en RF-DBD. Les deux transitions entre les régimes GDBD-TDBD et TDBD-RF-DBD sont étudiées. La première est liée au temps de transit des ions de l'anode vers la cathode qui devient plus long que la demi-période. En conséquence, la chute cathodique ne se forme pas. La deuxième transition est liée au piégeage des ions puis des électrons qui dépend de la tension appliquée, de la valeur de l'espace interélectrode et de la fréquence. Ces régimes de décharges sont comparés au régime nanopulsé répétitif (NPR-DBD). Les conditions conduisant à une décharge homogène ont été trouvées. La puissance maximale en régime homogène est de 17 W/cm3 ce qui est 17 fois plus élevé que pour un régime sinusoïdal à même fréquence. Elle est obtenue pour une fréquence de répétition de 30 kHz avec un pulse de tension de 10 ns. Les dépôts de nitrure de silicium et d’oxyde de silicium obtenus à partir de SiH4 avec des GDBD, RF-DBD et NPR-DBD ont été étudiés. Dans tous les cas, la vitesse de dépôt est définie par la puissance de la décharge. L'augmentation de la puissance de la décharge avec la fréquence permet d'augmenter la vitesse de dépôt de 30 à 90 nm/min. Néanmoins avec l'utilisation de silane à température ambiante, des nanoparticules se forment en RF lorsque la puissance de la décharge est forte. La modulation d'amplitude empêche la formation des poudres. Pour ce faire l'énergie injectée pendant le Ton doit être inférieure à 100 µJ. Comme les précurseurs ne sont plus consommés par la formation de poudres, ils sont disponibles pour la croissance de la couche ce qui double la vitesse de dépôt par rapport au continu pour la même puissance moyenne. L'augmentation de la vitesse de dépôt sans poudre avec la puissance moyenne nécessite une augmentation de la fréquence de modulation (> 1 kHz) ce qui implique un Ton de plus en plus court pour limiter l'énergie injectée.Ce travail a mis en évidence un nouveau régime de décharge, la TDBD, en Ar-NH3. Il a permis de comparer les GDBD, TDBD, RF-DBD et NRP-DBD dans la même configuration de décharge. Pour la première fois des dépôts de couches minces ont été faits par RF-DBD et il a été montré que la modulation du plasma peut augmenter significativement la vitesse de dépôt. / The homogeneous discharge controlled by dielectric barrier at atmospheric pressure and their applications are a promising field of activity because of their advantages in contrast with the low pressure processes, especially for the on line treatment of large surface without pumping system. The physics of these discharges as the thin film properties obtained are well established with low frequency sinusoidal (<200 kHz) and radiofrequency excitation (13.56MHz). This is what is explored in this thesis aimed to find and explore new modes of homogeneous DBD and maximizing the power to optimize the deposition rate while maintaining quality thin layers. To achieve this goal, an original device has been developed varying the excitation frequency from 100 kHz to 18 MHz. The frequency increase on this range have many consequences. In an Ar-NH3 mixture, the discharge regime becomes successively a glow (GDBD) then Townsend (TDBD) around 250 kHz then RF-DBD from 3 MHz. The electrical and optical measurements that have been done show that the average power of the homogeneous discharges increases by a factor of 30 between GDBD regime and RF-DBD regime (up to 35 W/cm3) while the breakdown voltage is reduced by a factor 6. These observations coupled to the discharge emission spectra indicate that the electron density increases by several orders of magnitude while their energy decreases. These results are due to a change of the ionization mechanism with a dominant role of the secondary electron emission at the cathode in low frequency regime (GDBD and TDBD) while the volume ionization is dominate in RF-DBD. Both transitions between GDBD-TDBD regimes and TDBD-RF-DBD are studied. The first is related to the ion transit from the anode to the cathode which becomes longer than the half-period. In consequence, the cathode fall is not formed. The second transition is related to ions and electrons trapping which depends on the applied voltage, the value of the inter-electrode space and frequency.These discharges regime are compared to Nanopulsed repetitively discharge (NPR-DBD). The conditions leading to a homogeneous discharge are found. In homogeneous regime the maximum of the discharge power is 17 W/cm3 which is 17 times higher than for a low sinusoidal voltage for the same frequency. It is obtained for a repetition frequency of 30 kHz with a 10 ns voltage pulse. Hydrogenated silica and silicon nitride thin film obtained from SiH4 with GDBD, RF-DBD and NPR-DBD were studied. In all cases, the deposition rate is defined by the discharge power. The increase of the discharge power with the frequency increases the deposition rate from 30 nm/min to 90 nm/min. However with the use of silane at room temperature, nanoparticles are formed in RF regime when the discharge power is high. The amplitude modulation allows to prevent the formation of powders. AS far as the energy injected during Ton is less than 100 μJ. As the precursors are not consumed by the formation of powders, they are available for the growth of the layer thereby doubling the deposition rate compared to the continuous process for the same average power. Increasing the growth rate without powders with the average power requires an increase in the modulation frequency (> 1 kHz) i.e. a short Ton to limit the injected energy. Thus this work has highlighted a new discharge regime, the TDBD in Ar-NH3 and compared the GDBD, TDBD, RF-DBD and NRP-DBD discharge in the same configuration. For the first time, RF-DBD coating have been made and it has been shown that modulation of plasma, although it decreases the discharge power, can significantly increase the deposition rate.

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.

In this thesis, the structural, optical and electrical properties of crystalline silicon quantum dots (SiQDs) are examined for application to silicon based tandem cells. The approach has been to concentrate on all silicon devices by taking advantage of quantum confinement in low-dimensional Si. RF magnetron co-sputtering provided the capability of creating superlattice structures in conjunction with high temperature annealing, to form Si nanocrystals in an oxide matrix. Structural techniques, including Fourier transform infrared spectroscopy (FTIR), micro-Raman spectroscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD), and Secondary ion mass spectroscopy (SIM) were employed to gather structural information about the SiQD/SiO2 SLs. The result combine presents that the packing density of Si QDs, correlated to the oxygen content of the silicon rich oxide layer can be control independently. The effect of Si nanocrystallite density on Raman scattering is investigated. The preliminary results present that a decrease in the oxygen content (x) results in an increased sharpness of the Strokes-mode peak of nanocrystalline Si, attributed to an increase in the proportion of crystalline Si because of the increased number of SiQDs. However the influence of the surface region on the crystallite core intensity scattering becomes dominant, when SiQD size diameter is very small (less than 3 nm). The present work shows that a decrease in x-content leading to an increase of the SiQD concentration, initially results in the enhancement of the lateral conductivity in the SiQD superlattice material. In this work, the Al contacting scheme, using a prolonged heat treatment technique at elevated temperature less than the eutectic point of Al and Si (577C) has been successfully applied to making Ohmic contacts on both SiQD SLs in oxide and nitride matrices. Activation energy (Ea) of SiQDs, extracted from a linear Arrhenius plot is investigated in the present work in order to expand the understanding of engineering electrical injection in laterally active paths. It is found that a lower barrier height of dielectric matrix influences to the lateral electron transport of the SiQDs in such dielectric matrix. PL results confirm that the band gap of surface oxidized SiQDs widens due to quantum confinement. The present results reveal that the strong peak (Q-peak) due to quantum confinement is more effective in the emission with increasing SiQD concentration. The surface oxide is believed to play an important role in the reduction of SiQD luminescence due to a trapped exiciton. It is concluded that SiQDs surface oxide accompanied by a SiO2 matrix may not provide a good passivation in very small SiQD size. However the energy band gap and conductivity of the SiQDs are tunablity, in the optimum range of SiQD size and concentration. This observation may be important for future nanoelectronics applications.

In this thesis, the structural, optical and electrical properties of crystalline silicon quantum dots (SiQDs) are examined for application to silicon based tandem cells. The approach has been to concentrate on all silicon devices by taking advantage of quantum confinement in low-dimensional Si. RF magnetron co-sputtering provided the capability of creating superlattice structures in conjunction with high temperature annealing, to form Si nanocrystals in an oxide matrix. Structural techniques, including Fourier transform infrared spectroscopy (FTIR), micro-Raman spectroscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD), and Secondary ion mass spectroscopy (SIM) were employed to gather structural information about the SiQD/SiO2 SLs. The result combine presents that the packing density of Si QDs, correlated to the oxygen content of the silicon rich oxide layer can be control independently. The effect of Si nanocrystallite density on Raman scattering is investigated. The preliminary results present that a decrease in the oxygen content (x) results in an increased sharpness of the Strokes-mode peak of nanocrystalline Si, attributed to an increase in the proportion of crystalline Si because of the increased number of SiQDs. However the influence of the surface region on the crystallite core intensity scattering becomes dominant, when SiQD size diameter is very small (less than 3 nm). The present work shows that a decrease in x-content leading to an increase of the SiQD concentration, initially results in the enhancement of the lateral conductivity in the SiQD superlattice material. In this work, the Al contacting scheme, using a prolonged heat treatment technique at elevated temperature less than the eutectic point of Al and Si (577C) has been successfully applied to making Ohmic contacts on both SiQD SLs in oxide and nitride matrices. Activation energy (Ea) of SiQDs, extracted from a linear Arrhenius plot is investigated in the present work in order to expand the understanding of engineering electrical injection in laterally active paths. It is found that a lower barrier height of dielectric matrix influences to the lateral electron transport of the SiQDs in such dielectric matrix. PL results confirm that the band gap of surface oxidized SiQDs widens due to quantum confinement. The present results reveal that the strong peak (Q-peak) due to quantum confinement is more effective in the emission with increasing SiQD concentration. The surface oxide is believed to play an important role in the reduction of SiQD luminescence due to a trapped exiciton. It is concluded that SiQDs surface oxide accompanied by a SiO2 matrix may not provide a good passivation in very small SiQD size. However the energy band gap and conductivity of the SiQDs are tunablity, in the optimum range of SiQD size and concentration. This observation may be important for future nanoelectronics applications.

[pt] Nanopartículas de dióxido de estanho foram obtidas a partir da reação de soluções aquosas de sais de estanho em sistemas de microemulsão e comparadas, em relação às suas propriedades texturais, estruturais e de condutividade elétrica, com nanopartículas do mesmo óxido obtidas pelo método convencional de precipitação. Foram realizadas alterações nos métodos utilizados a fim de se verificar a influência dos parâmetros de síntese, tais como: natureza da fase orgânica e do surfactante, tempo e temperatura de reação. Paralelamente, óxidos comerciais de titânio, alumínio e silício foram submetidos aos métodos de impregnação seca e de microemulsão. A influência desses métodos nas propriedades texturais, estruturais e no comportamento térmico desses óxidos foi estudada. As amostras obtidas foram caracterizadas por adsorção de N2, difração de raios X, espectroscopia de reflectância difusa na região do UV-visível e microscopia eletrônica de transmissão. Também foram realizadas análises de condutividade elétrica e de densidade aparente. As análises mostraram, no caso do óxido de estanho, que o método envolvendo microemulsões, apesar da grande dificuldade experimental, apresentou resultados semelhantes ao método convencional em relação ao tamanho de cristalito, à condutividade elétrica e à diferença de energia entre os orbitais HOMO-LUMO. Entretanto, o método de precipitação gerou o óxido de estanho com maior área superficial, 245 m(2)g(-1). Para os óxidos comerciais, diferenças significativas na textura das amostras foram encontradas. No caso do óxido de titânio, os resultados indicam que o método de impregnação afeta a estrutura desse óxido de forma a permitir a transformação da fase (anatásio/rutilo) em temperaturas mais baixas. / [en] Tin oxide nanoparticles have been obtained from the reaction of aqueous solutions of tin salts in microemulsion systems and compared with the same oxide nanoparticles obtained by the precipitation conventional method. Changes have been made in the methods used in order to verify the influence of synthesis parameters, such as: organic phase and surfactant nature, reaction time and temperature. In addition, titanium, aluminum and silicon commercial oxides have been subjected to dry impregnation and microemulsion methods. The influence of the method used in the textural and structural properties, and thermal behavior of these oxides have been studied. The samples have been characterized by adsorption of N2, X-ray diffraction, diffuse reflectance spectroscopy in the UVvisible range, and transmission electron microscopy. Furthermore, electrical conductivity and apparent density analysis have been performed. Despite difficult encountered in microemulsion systems experiments, tin oxide thus obtained is similar to the conventional method on crystallites size, electrical conductivity and the difference of energy between HOMO-LUMO orbitals results. However, precipitation method generated tin oxide with larger surface area, approximately 245 m(2)g(-1). For commercial oxides, significant differences on texture of the samples have been found. In the case of TiO2, the results also indicate that the dry impregnation method affects the structure so that phase transformation (anatase to rutile) occurs at lower temperatures.