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According to a 1999 Federal Highway Administration statistic, the U.S. has around 8.2 million lane-miles of roadways that need to be maintained and rehabilitated periodically. Therefore, in order to reduce rehabilitation costs, pavement engineers need to optimize the rehabilitation procedure, which is achieved by accurately knowing the existing pavement layer thicknesses and localization of subsurface defects. Currently, the majority of departments of transportation (DOTs) rely on coring as a means to estimate pavement thicknesses, instead of using other nondestructive techniques, such as Ground Penetrating Radar (GPR). The use of GPR as a nondestructive pavement assessment tool is limited mainly due to the difficulty of GPR data interpretation, which requires experienced operators. Therefore, GPR results are usually subjective and inaccurate. Moreover, GPR data interpretation is very time-consuming because of the huge amount of data collected during a survey and the lack of reliable GPR data-interpretation software. This research effort attempts to overcome these problems by developing new GPR data analysis techniques that allow thickness estimation and subsurface defect detection from GPR data without operator intervention. The data analysis techniques are based on an accurate modeling of the propagation of the GPR electromagnetic waves through the pavement dielectric materials while traveling from the GPR transmitter to the receiver. Image-processing techniques are also applied to detect layer boundaries and subsurface defects. The developed data analysis techniques were validated utilizing data collected from an experimental pavement system: the Virginia Smart Road. The layer thickness error achieved by the developed system was around 3%. The conditions needed to achieve reliable and accurate results from GPR testing were also established. / Ph. D.

The importance of moisture in concrete is unquestionable. However, quantifying the moisture in concrete is very difficult as concrete microstructure water interactions are not well understood. Concrete is a very complex material spanning the range from the atom to the civil infrastructure. It is the medium that controls moisture at the FRP/concrete interface. Concrete is also a composite material at the level of concrete/rebar, aggregate/sand/cement paste and at the hydration product level. Water is vital in concrete microstructure development, properties and concrete durability. A moisture sensor based on the dielectric and resistive properties of cement paste was developed. Impedance spectroscopy techniques are used to explore the moisture behavior in relation to dielectric and resistive properties of the sensors. The sensor capacitive response is frequency dependent and it has been described with a multi-linear curve. Resistance values are related to capacitance through a power Law. Both the capacitance/moisture and capacitance/resistance behaviors were observed in all four cement/sand/aggregate mixtures considered. Although the dielectric constants of water and dry cement paste are not frequency dependent with in the 400 kHz and 10 MHz frequencies considered, the effective dielectric constant of the mixture is frequency dependent Mixing rules cannot predict the effective dielectric constant of the dielectric medium used in the sensors. Impedance analysis indicated also multiple time constants exist within the cement paste. Using the observation from the experimental results in conjunction to the high conductivity of cement pore solution a random R-C network model was developed to explore the impedance behavior of cement paste. / Ph. D.

Dielectric constant is a physical property of soil that is often measured using non-invasive geophysical techniques in subsurface characterization studies. A proper understanding of dielectric responses allows investigators to make measurements that might otherwise require more invasive and/or destructive methods. Previous studies have suggested that dielectric models could be refined by accounting for the contributions of different types of mineral constituents that affect the ratio and properties of bound and bulk water. This study tested the hypothesis that the dielectric responses of porous materials are mineral-specific through differences in surface area and chemistry. An experimental design was developed to test the dielectric behavior of pure quartz sand (Control), quartz sand/kaolin clay mixtures and ferric oxyhydroxide coated quartz sand. Results from the experiments show that the dielectric responses of quartz-clay and iron oxyhydroxide modified samples are not significantly different from the pure quartz Control. Increasing clay content in quartz sands leads to a vertical displacement between fitted polynomials. The results suggest that the classic interpretation for the curvature of dielectric responses appears to be incorrect. The curvature of dielectric responses at low water contents appears to be controlled by unknown parameters other than bound water. A re-examination of the experimental procedure proposed in this study and past studies shows that a properly designed study of bound water effects on dielectric responses has not yet been conduct / Master of Science

Doctor of Philosophy / Department of Chemical Engineering / James H. Edgar / Gallium nitride is a promising semiconductor for fabricating field effect transistors for power electronics because of its unique physical properties of wide energy band gap, high electron saturation velocity, high breakdown field and high thermal conductivity. However, these devices are extremely sensitive to the gate leakage current which reduces the breakdown voltage and the power-added efficiency and increases the noise figures. To solve this problem, employing a gate dielectric is crucial to the fabrication of metal insulator semiconductor high electron mobility transistors (MISHEMTs), to reduce the leakage current and increase the magnitude of voltage swings possible. For this device to be successful, imperfections at the oxide-semiconductor interface must be suppressed to maintain the high electron mobility of the device. This research explored multiple high dielectric constant gate oxides (Al[subscript]2O[subscript]3, TiO[subscript]2, and Ga[subscript]2O[subscript]3), deposited on different crystalline orientations and polarities of GaN by atomic layer deposition (ALD) to form metal oxide semiconductor capacitors, including effects of pretreatment on N-polar GaN, ALD TiO[subscript]2/Al[subscript]2O[subscript]3 nano-laminate on thermal oxidized Ga-polar GaN and ALD Al[subscript]2O[subscript]3 on [Italic]c- and [Italic]m-plane GaN Surface pretreatments were shown to greatly alter the morphology of reactive N-polar GaN which is detrimental to the electrical properties. 14 nm thick ALD Al[subscript]2O[subscript]3 films were directly deposited on N-polar GaN without thermal or chemical pretreatments which yield a smooth surface (RMS=0.23 nm), low leakage current (2.09 x 10[superscript]-[superscript]8 A/cm[superscript]2) and good Al[subscript]2O[subscript]3/GaN interface quality, as indicated by the low electron trap density (2.47 x 10[superscript]10 cm[superscript]-[superscript]2eV[superscript]-[superscript]1). In the nano-laminate study, a high dielectric constant of 12.5 was achieved by integrating a TiO[subscript]2/Al[subscript]2O[subscript]3/Ga[subscript]2O[subscript]3 oxide stack layer, while maintaining a low interface trap density and low leakage current. There was a strong correlation between the surface morphology and electrical properties of the device discovered from comparing the ALD Al[subscript]2O[subscript]3 on [Italic]c- and [Italic]m-plane GaN, namely smooth surface lead to small hysteresis. These results indicate the promising potential of incorporation gate dielectric for future GaN devices.

La complexité des mécanismes de transport en nanofiltration (NF) nécessite ledéveloppement d’outils de modélisation fiables permettant de comprendre et d’optimiser lesopérations de séparation en NF.La présente étude comprend deux volets. Le premier porte sur la rétention d’un soluténeutre – le poly(éthylène glycol) à 600 g mol-1 (PEG) – seul et en présence d’ions, par unemembrane organique de NF (polyamide). Les résultats obtenus montrent que la rétention dusoluté neutre chute en présence d’ions et ce, d’autant plus que la concentration du sel estélevée. Ce phénomène ne peut être expliqué par le seul phénomène de déshydratation dusoluté neutre par les ions environnants. Un phénomène supplémentaire de gonflement de porea été mis en évidence et corrélé à la densité de charge membranaire. La contribution des deuxphénomènes à la chute du taux de rejet du PEG a été évaluée pour différents sels à plusieursconcentrations.Le deuxième volet du travail est consacré à (i) l’évaluation de la constante diélectrique desolutions à l’intérieur de nanopores (ep) d’une membrane organique de NF (polyamide) àpartir de mesures de potentiel de membrane et (ii) la validation de cette méthode. Les valeursobtenues s’avèrent être inférieures à celle de la solution externe (effet du confinement) etdiminuer avec l’augmentation de la proportion en ions calcium du mélange (effet structurantdes ions). L’accord entre les constantes diélectriques ep déterminées à partir de mesures depotentiel de membrane et de taux de rejet ionique (mélanges ternaires) valide la cohérence dumodèle de transport utilisé (exclusion stérique, électrique et diélectrique aux interfaces) etmontre que les mesures de potentiel de membrane peuvent être envisagées pour l’évaluationcorrecte de la constante diélectrique à l’intérieur de nanopores / The complexity of transport mechanisms in nanofiltration (NF) requires the developmentof reliable modelling tools for understanding and optimizing the separation process.This study is composed of two parts. The first one focuses on the retention of a neutralsolute – poly(ethylene glycol) 600 g mol-1 (PEG) – in single solute solutions and in thepresence of mineral salts by an organic NF membrane (polyamide). Results show that PEGrejection is significantly lower in mixed-solute solutions and that rejection rate drop increaseswith salt concentration. This phenomenon cannot be imputed to only the partial dehydrationof PEG molecules by surrounding ions (salting-out effect). The additional hypothesis whichwas considered in the present work is an increase in the effective pore size (pore swelling).This hypothesis was supported by electrokinetics charge density data. The contribution ofpore swelling and salting-out to the overall decrease in the rejection rate of PEG wasevaluated for different salts at various concentrations.The second part of this study deals with (i) the determination of the dielectric constantinside pores (ep) of an NF organic membrane from membrane potential measurements and (ii)the validation of this technique. Membrane potential data were analyzed by means of theSEDE (steric, electric and dielectric exclusion) transport model. ep values were found to besmaller than the bulk value and to decrease when sodium ions were replaced by calcium ions.The agreement between ep values obtained from membrane potential measurements and thosecalculated from ion rejection rate data (ternary mixtures) highlights the global coherence ofthe transport model used and shows that membrane potential measured with electrolytemixtures can be used to determine the dielectric constant inside pores with no requirement ofadditional rejection rate measurements.

Les électrolytes liquides, composés d’un sel dissous dans un solvant, interviennent dans la composition des batteries et font l’objet de nombreuses études afin d’améliorer leurs performances et leur sécurité. Parmi toutes les propriétés essentielles d’un électrolyte, la plus importante est sa conductivité ionique, qui influe sur les performances de la batterie. Pour un sel donné, la conductivité est elle-même principalement déterminée par les propriétés physico-chimiques du solvant comme sa constante diélectrique ou sa viscosité. L’objectif de cette étude est de développer des modèles permettant d’estimer des propriétés d’intérêt des électrolytes liquides, afin d’offrir un gain de temps aux chimistes, qui pourront éliminer les compositions inadéquates du point de vue de telle ou telle propriété. La première partie de cette étude présente une méthode pour estimer la conductivité d’un électrolyte, constitué d’un sel LiPF6 dans un mélange de solvants. Cette méthode s’appuie sur de nouvelles équations, pour estimer les paramètres de l’équation de Casteel-Amis, à partir de propriétés physico-chimiques du mélange de solvants, dont la constante diélectrique. La seconde partie présente a par ailleurs permis de développer une méthode pour estimer la constante diélectrique d’un solvant pur, à partir de sa structure chimique. Cette méthode s’appuie sur de nouveaux modèles additifs qui permettent d’estimer les paramètres de l’équation de Kirkwood-Fröhlich. Parmi ces modèles, deux d’entre eux permettent l’estimation de la densité et de l’indice de réfraction d’un composé liquide à température ambiante. L’ensemble des modèles développés sont utilisables via une interface utilisateur. / Liquid electrolytes, composed of a salt dissolved in a solvent, are used in the composition of batteries and are the subject of numerous studies to improve their performance and safety. Of all the essential properties of an electrolyte, the most important is its ionic conductivity, which influences the battery's performance. For a given salt, the conductivity itself is mainly determined by the physico-chemical properties of the solvent such as its dielectric constant or its viscosity. The objective of this study is to develop models to estimate properties of interest of liquid electrolytes, in order to offer time savings to chemists, who will be able to eliminate inadequate compositions from the point of view of such or such property. The first part of this study presents a method to estimate the conductivity of an electrolyte, consisting of a LiPF6 salt in a solvent mixture. This method is based on new equations, to estimate the parameters of the Casteel-Amis equation, based on the physico-chemical properties of the solvent mixture, including the dielectric constant. The second part also presents a method to estimate the dielectric constant of a pure solvent, based on its chemical structure. This method is based on new additive models that estimate the parameters of the Kirkwood-Fröhlich equation. Two of these models estimate the density and refractive index of a liquid compound at room temperature. All the models developed can be used via a user interface.

Este trabalho tem como objetivo a produção e caracterização elétrica de filmes finos de telureto com nanopartículas de ouro para aplicações em microeletrônica. Filmes finos foram produzidos por magnetron sputtering a partir de alvos de telureto cerâmico e de ouro metálico. Foi desenvolvida metodologia adequada para a nucleação das nanopartículas de ouro por meio de tratamento térmico. Foram nucleadas nanopartículas de ouro a fim de que fossem observadas as influências nas propriedades elétricas. Os filmes foram depositados sobre substrato de silício e, para as medidas elétricas, ilhas de alumínio foram depositadas sobre o filme, utilizando-se os processos convencionais de microeletrônica: limpeza química, deposição por sputtering e evaporação. Com a finalidade de verificar a nucleação das nanopartículas metálicas, foram realizadas análises por Microscopia Eletrônica de Transmissão que indicaram a presença de nanopartículas metálicas, cristalinas, aproximadamente esféricas e com tamanho médio aproximado entre 1,5 e 5 nm. Outras técnicas de caracterização usadas foram microscopia de força atômica, perfilometria e extração de curvas da capacitância e condutância em função da tensão. Foram produzidos filmes com diversas espessuras com e sem nanopartículas de ouro. Por meio das medidas de capacitância em função da tensão foi possível determinar a influência das nanopartículas metálicas na constante dielétrica (k). Os resultados obtidos mostram aumento do valor de k de aproximadamente 70%, na presença de nanopartículas de ouro. Cabe ressaltar o resultado obtido para os filmes com espessura de 32,8 nm, para os quais o valor da constante dielétrica varia de 9,4 para 12,2, para tratamentos de 10 e 20 h, respectivamente. O material estudado tem possíveis aplicações em microeletrônica como dielétrico em capacitores e transistores MOS, e como camada de passivação em dispositivos de potência. / This work has the objective of production and electrical characterization f tellurite thin films containing gold nanoparticles for microelectronic applications. Thin films have been produced by magnetron sputtering from ceramic tellurite and metallic gold targets. It was developed an appropriate methodology for the gold nanoparticles nucleation by means of heat treatment. Gold nanoparticles were nucleated in order to be observed the influence on the electrical properties. The films were deposited on silicon substrate and, to the electrical measurements, aluminium islands were deposited on the film, using the conventional processes of microelectronics: chemical cleaning, deposition by sputtering and evaporation. With purpose to check the metallic nanoparticles nucleation, transmission electron microscopy measurements were performed and indicated the presence of crystalline metallic nanoparticles, with spherical shape and with average size between 1.5 and 5 nm. Other characterization techniques were used as atomic force microscopy, profilometry and electrical measurements to obtain the capacitance and conductance curves. Films have been produced with different thicknesses with and without gold nanoparticles. From capacitance measurement, it was possible to determine the metallic nanoparticles influence on the dielectric constant (k). The results obtained showed the increase of k of about 70% with the presence of gold nanoparticles. We have to remark the results obtained for thin films with 32.8 nm thickness with k varying from 9.4 to 12.2, for heat treatments during 10 and 20 h, respectively. The material studied has possible applications in microelectronics as high-k dielectrics for capacitors and transistors MOS, and as passivation layer for power devices.

Este trabalho tem como objetivo a produção e caracterização elétrica de filmes finos de telureto com nanopartículas de ouro para aplicações em microeletrônica. Filmes finos foram produzidos por magnetron sputtering a partir de alvos de telureto cerâmico e de ouro metálico. Foi desenvolvida metodologia adequada para a nucleação das nanopartículas de ouro por meio de tratamento térmico. Foram nucleadas nanopartículas de ouro a fim de que fossem observadas as influências nas propriedades elétricas. Os filmes foram depositados sobre substrato de silício e, para as medidas elétricas, ilhas de alumínio foram depositadas sobre o filme, utilizando-se os processos convencionais de microeletrônica: limpeza química, deposição por sputtering e evaporação. Com a finalidade de verificar a nucleação das nanopartículas metálicas, foram realizadas análises por Microscopia Eletrônica de Transmissão que indicaram a presença de nanopartículas metálicas, cristalinas, aproximadamente esféricas e com tamanho médio aproximado entre 1,5 e 5 nm. Outras técnicas de caracterização usadas foram microscopia de força atômica, perfilometria e extração de curvas da capacitância e condutância em função da tensão. Foram produzidos filmes com diversas espessuras com e sem nanopartículas de ouro. Por meio das medidas de capacitância em função da tensão foi possível determinar a influência das nanopartículas metálicas na constante dielétrica (k). Os resultados obtidos mostram aumento do valor de k de aproximadamente 70%, na presença de nanopartículas de ouro. Cabe ressaltar o resultado obtido para os filmes com espessura de 32,8 nm, para os quais o valor da constante dielétrica varia de 9,4 para 12,2, para tratamentos de 10 e 20 h, respectivamente. O material estudado tem possíveis aplicações em microeletrônica como dielétrico em capacitores e transistores MOS, e como camada de passivação em dispositivos de potência. / This work has the objective of production and electrical characterization f tellurite thin films containing gold nanoparticles for microelectronic applications. Thin films have been produced by magnetron sputtering from ceramic tellurite and metallic gold targets. It was developed an appropriate methodology for the gold nanoparticles nucleation by means of heat treatment. Gold nanoparticles were nucleated in order to be observed the influence on the electrical properties. The films were deposited on silicon substrate and, to the electrical measurements, aluminium islands were deposited on the film, using the conventional processes of microelectronics: chemical cleaning, deposition by sputtering and evaporation. With purpose to check the metallic nanoparticles nucleation, transmission electron microscopy measurements were performed and indicated the presence of crystalline metallic nanoparticles, with spherical shape and with average size between 1.5 and 5 nm. Other characterization techniques were used as atomic force microscopy, profilometry and electrical measurements to obtain the capacitance and conductance curves. Films have been produced with different thicknesses with and without gold nanoparticles. From capacitance measurement, it was possible to determine the metallic nanoparticles influence on the dielectric constant (k). The results obtained showed the increase of k of about 70% with the presence of gold nanoparticles. We have to remark the results obtained for thin films with 32.8 nm thickness with k varying from 9.4 to 12.2, for heat treatments during 10 and 20 h, respectively. The material studied has possible applications in microelectronics as high-k dielectrics for capacitors and transistors MOS, and as passivation layer for power devices.