Eletrólitos sólidos cerâmicos de ZrO2:8% mol Y2O3 foram preparados com pós de três origens: pó comercial fabricado pela Nissan (Japão), pó obtido por coprecipitação dos hidróxidos no IPEN e pó obtido por mistura de óxidos (utilizando-se ZrO2 produzido na Usina de Zircônio do IPEN e Y2O3 (USA) de pureza superior a 99,9%). Esses materiais de partida foram analisados pelas seguintes técnicas: fluorescência de raios X para a determinação dos teores de ítrio, difração de raios X para a determinação das fases, sedimentação para a determinação da distribuição do tamanho de partículas, adsorsão gasosa (BET) para a determinação da área de superfície específica e microscopia eletrônica de transmissão para a determinação do tamanho médio de partícula. Amostras compactadas foram analisadas por dilatometria para avaliar os estágios de sinterização. As amostras sinterizadas foram caracterizadas por difração de raios X para análise de fases e microscopia eletrônica de varredura para análise da morfologia dos grãos. Análises por espectroscopia de impedância foram feitas para acompanhar o envelhecimento térmico dos eletrólitos sólidos de zircônia-ítria a 600 ºC, temperatura de trabalho do sensor permanente de oxigênio, e para estudar a sua cinética de sinterização. Os principais resultados mostram que o envelhecimento térmico a 600 ºC diminui a resposta (fem) do sensor nas primeiras 100 h até um valor estável. Além disso, os estudos de sinterização por espectroscopia de impedância permitiram encontrar correlações entre parâmetros elétricos, a cinética de sinterização e os mecanismos de crescimento de grão. / ZrO2:8 mol %Y2O3 solid electrolyte ceramic pellets have been prepared with powders of three different origins: a Nissan (Japan) commercial powder, a powder obtained by the coprecipitation technique at IPEN, and the mixing of powder oxides (ZrO2 produced at a Pilot Plant at IPEN and 99.9% pure Y2O3 of USA origin). These starting powders have been analysed by the following techniques: X-ray fluorescence for yttrium content, X-ray diffraction for structural phase content, sedimentation for particle size distribution, gas adsorption (BET) for surface area determination, and transmission electron microscopy for average particle size determination. Pressed ceramic pellets have been analysed by dilatometry to evaluate the sintering stages. Sintered pellets have been characterized by X-ray diffraction for phase analysis and scanning electron microscopy for grain morphology analysis. Impedance spectroscopy analysis have been carried out to follow thermal ageing of zirconia-yttria solid electrolyte at 600 ºC, the working temperature of permanent oxygen sensor, and to study sintering kinetics. The main results show that ageing at 600 ºC decreases the emf sensor response in the first 100 h to a steady value. Moreover, sintering studies by impedance spectroscopy allowed for finding correlations between electrical parameters, sintering kinetics and grain growth mechanisms.

Detection of DNA by electrochemical impedance spectroscopy (EIS) has been reported by many authors and assays have been developed using lab setups. However, as for most detection assay methods there are issues to address to enable the development for the sensor market: Long time-to-result & high complexity for labelled assays and a lack of sensitivity and reproducibility for label-free assays. This work considers two different approaches to address the issues of time-to-result and assay complexity. The first part presents work on achieving rapid sequence-specific electrochemical detection of DNA hybridisation to complementary DNA on an electrode surface. To accomplish assay sensitivity to low DNA target concentrations, a signal amplification strategy is often necessary. One approach is to couple an enzyme to the hybridised target molecules and to deposit insoluble dyes in the subsequent enzymatic reaction, which enhances sensitivity through an increase in the impedance signal in presence of a redox mediator. The time typically taken for this process (20 – 40 min) precludes the use outside lab setups. Therefore, a protocol for sensitive detection in the presence of redox mediator is demonstrated on a practical timescale required for use in sensor applications. Based on these results a model for the fundamental understanding of the amplification reaction is presented which explains the retention of sensitivity at these enhanced timescales. This also enabled further optimisation of the assay for application in single base pair mismatch detection in biologically relevant sequences. Moreover, direct detection of the precipitate formation is demonstrated which enables real-time measurement of the enzymatic reaction without redox agent addition and with enhanced mismatch discrimination. The second part investigates the possibility to detect DNA non-sequence-specifically by non-Faradaic means. This approach aims at reducing assay complexity by establishing whether it is possible to sense the presence of polymeric DNA in solution by measuring changes in the properties of the electrochemical double layer without DNA surface hybridisation. In a sensor setup this approach could be linked to a polymerase chain reaction (PCR) to discriminate polymer from nucleotide monomer and thereby enable PCR progress to be monitored. In this work the response in the electrochemical double layer at the interface of blocked metal electrodes and solutions containing DNA are studied by means of EIS. Blocking layers were applied to the electrode surface to prevent unspecific adsorption of molecules and ions to the metal surface whilst preserving the sensitivity to detection of changes in the double layer. The characteristics of surface blocking layers on disposable electrodes are studied as they are key to understand the double layer properties at a blocked surface. A number of self-assembled monolayers are compared with respect to their temperature stability and their blocking characteristics at different potentials and ion concentrations. This established the basis to study the effect of the presence of, initially, a model polyelectrolyte and, ultimately, DNA on the double layer. Polyelectrolyte detection is successfully shown for the model polyelectrolyte, polyacrylic acid. DNA detection was more challenging and possible causes for deviation from the polyacrylic acid response are discussed.

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Thesis (M. Sc.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

Carbonate reservoirs are usually diffcult to map and identify in seismic sections due to their complex structure, lithology and diagenetic frabrics. The Midland Basin, located in the Permian Basin of West Texas, is an excellent example of these complex carbonate structures. In order to obtain a better characterization and imaging of the carbonate buildups, an acoustic impedance inversion is proposed here. The resolution of the acoustic impedance is the same as the input seismic data, which is greatly improved with the addition of the low frequency content extracted from well data. From the broadband volume, high resolution maps of acoustic impedance distributions were obtained, and therefore the locations of carbonate buildups were easily determined. A correlation between acoustic impedance and porosity extracted from well data shows that areas with high acoustic impedance were correlated with low porosity values, whereas high porosities were located in areas of low acoustic impedance. Theoretical analyses were performed using the time-average equation and the Gassmann equation. These theoretical models helped to understand how porosity distributions affect acoustic impedance. Both equations predicted a decrease in acoustic impedance as porosity increases. Inversion results showed that average porosity values are 5% [plus or minus] 5%, typical for densely cemented rocks. Previous studies done in the study area indicate that grains are moderately to well-sorted. This suggests that time-average approximation will overestimate porosity values and the Gassmann approach better predicts the measured data. A comparison between measured data and the Gassmann equation suggests that rocks with low porosities (less than 5%) tend to have high acoustic impedance values. On the other hand, rocks with higher porosities (5% to 10%) have lower acoustic impedance values. The inversion performed on well data also shows that the fluid bulk modulus for currently producing wells is lower than in non-productive wells, (wells with low production rates for brine and hydrocarbons), which is consistent with pore fluids containing a larger concentration of oil. The acoustic impedance inversion was demonstrated to be a robust technique for mapping complex structures and estimating porosities as well. However, it is not capable of differentiating different types of carbonate buildups and their origin.

A theoretical approach to calculating impedance of metallicmagnetic/conductor layered structures is developed. Thefrequency range considered extends to the ferromagneticresonance region of soft magnetic films (of the order of 1GHz). The analysis includes the effects of screening of thehigh frequency fields by eddy currents as well as the dynamicsand relaxation of the magnetization of the ferromagneticsub-system. Analytical expressions for the impedance as afunction of frequency and material parameters and geometry ofmagnetic sandwich stripes are obtained. Two maincross-sectional layouts are considered: amagnetic/conductor/magnetic sandwich stripe with and withoutflux closure at the edges along the stripe length - with andwithout the magnetic film enclosing the conductor strip. Theimportance of good magnetic flux closure for achieving largespecific inductance gains and high efficiency at GHzfrequencies is emphasized. The theoretical results obtained were used to design andanalyze magneticfilm inductors produced using iron nitridealloy films. Patterned sandwiches, consisting of two Fe-N filmsenclosing a conductor film made of Cu, were fabricated onoxidized Si substrates using lift-off lithography. Theinductors exhibited a 2-fold specific inductance enhancement at1 GHz. The magnetic contribution to the total flux in thenarrow devices was less then predicted theoretically, which wasattributed to hardening of the magnetic material at the edgesof the strip leading to incomplete flux closure. Material anddesign issues important for further improving the performanceof the devices are discussed.

Along with the rapid growth of the nanotechnology, nanoparticles (NPs) have found many applications in commercial products. However, there are only a few studies on the toxicity and the environmental effects of NPs in biological systems. <p>In the study described in this thesis, I have used water-soluble Au NPs that were synthesized using the Brust method and then modified by small molecules. I explored the interactions of these modified Au NPs with self-assembled monolayer films on gold surfaces.<p>Three types of self-assembled monolayer (SAM) modified gold surfaces were used in this study. The surfaces had SAMs that could be positively or negatively charged or carry no charge, or be able to engage in hydrogen bonding. <p>Cyclic voltammetry (CV) was used to characterize SAMs of disulfide-glycine conjugate, disulfide-aspartic conjugate, and 11-mercaptoundecanoic acid (MUA) on gold surface electrodes. The possible interactions of Au NPs with the disulfide-aminoacid conjugates and alkanethiol modified surfaces were evaluated by cyclic voltammetry and by electrochemical impedance spectroscopy (EIS). An apparent decline in current density observed in CV along with an electron transfer resistance increase in EIS measurements upon exposure of the films to the MUA-modified anionic Au NPs clearly indicate interactions of the NPs with the films. Likewise, upon exposure of the films to cationic NPs, electron transfer resistance decreases dramatically in EIS experiments. In addition, the current increase in CV measurements provided further evidences for the interactions. The interactions between modified Au NPs and the SAMs were investigated in more detail by infrared spectroscopy and by employing quartz crystal microbalance. These studies clearly showed that upon exposure of these SAM films to the water-soluble Au NPs, significant changes occur. As would be expected for the adsorption of the Au NPs onto the SAMs, the weight of the film increased due to the addition of the NPs on the surface. Moreover, there are significant increases in the carbonyl stretching vibration at 1735 cm-1 along with the appearance of the amide hydrogen stretching band, between 3160-3380 cm-1, which indicate the adsorption of Gly-CSA modified Au NPs onto the MUA film.

Along with the rapid growth of the nanotechnology, nanoparticles (NPs) have found many applications in commercial products. However, there are only a few studies on the toxicity and the environmental effects of NPs in biological systems. <p>In the study described in this thesis, I have used water-soluble Au NPs that were synthesized using the Brust method and then modified by small molecules. I explored the interactions of these modified Au NPs with self-assembled monolayer films on gold surfaces.<p>Three types of self-assembled monolayer (SAM) modified gold surfaces were used in this study. The surfaces had SAMs that could be positively or negatively charged or carry no charge, or be able to engage in hydrogen bonding. <p>Cyclic voltammetry (CV) was used to characterize SAMs of disulfide-glycine conjugate, disulfide-aspartic conjugate, and 11-mercaptoundecanoic acid (MUA) on gold surface electrodes. The possible interactions of Au NPs with the disulfide-aminoacid conjugates and alkanethiol modified surfaces were evaluated by cyclic voltammetry and by electrochemical impedance spectroscopy (EIS). An apparent decline in current density observed in CV along with an electron transfer resistance increase in EIS measurements upon exposure of the films to the MUA-modified anionic Au NPs clearly indicate interactions of the NPs with the films. Likewise, upon exposure of the films to cationic NPs, electron transfer resistance decreases dramatically in EIS experiments. In addition, the current increase in CV measurements provided further evidences for the interactions. The interactions between modified Au NPs and the SAMs were investigated in more detail by infrared spectroscopy and by employing quartz crystal microbalance. These studies clearly showed that upon exposure of these SAM films to the water-soluble Au NPs, significant changes occur. As would be expected for the adsorption of the Au NPs onto the SAMs, the weight of the film increased due to the addition of the NPs on the surface. Moreover, there are significant increases in the carbonyl stretching vibration at 1735 cm-1 along with the appearance of the amide hydrogen stretching band, between 3160-3380 cm-1, which indicate the adsorption of Gly-CSA modified Au NPs onto the MUA film.

In March 2007 five satellites were launched as part of the NASA mission THEMIS. The aim of the mission is to answer the unknown questions regarding the onset of substorms. THEMIS data has also been used within other research fields. Today many scientists aim to investigate wave phenomena, such as whistler waves, wave interactions in the radiation belts and general turbulence in the magnetosphere and the solar wind. These processes occur at intermediate frequencies (a few hundreds of Hertz). Correct and reliable results require good knowledge of the frequency response,  the so called transfer function, for the electric field instrument (EFI). Post-launch calibrations have given good knowledge of the instrument's response at high and low frequencies. However, at intermediate frequencies (50-3000 Hz) the transfer function has only been determined via calculations/simulations and not yet obtained from data collected in space. Moreover, the transfer function changes substantially in this range, as the instrument transitions from a resistive low-frequency coupling to a capacitive high-frequency coupling. The transition is known as the RC roll-off. In this thesis, data from different regions and with different electrical settings have been analyzed to estimate the EFI sensors' sheath impedance and transfer function. Data have been collected during July 2009 and March 2011. From the first period, I-V curves where extracted for four different regions (i.e. with different plasma conditions) and their associated sheath impedance calculated. I-V curves are graphical representations of how the voltage differs with the changed bias current. From the sheath impedance and the measured free-space capacitance the RC roll-off can been directly calculated. An experiment was also conducted in March 2011 where the instrument was run in a special mode designed to measure the relative transfer function with the probes run at different bias setting, yielding different sheath impedances. The analysis of the I-V curves and relative transfer function show similar results, which clearly differ from the earlier believed values. Values for the sheath impedance are lower (4-6 MΩ) than the expected (30 MΩ) and depend on the usher setting. The usher is an electronic device which should shield the sensor from the photoelectron produced by illumination of the preamplifier. This lower sheath resistance implies higher than expected RC roll-off frequency, a result which is confirmed by the results from the relative transfer function. The roll-off is between 2-3 kHz, compared to the 400-500 Hz assumed prior to this study based on the assumption of a sheath impedance of around 30 MΩ.

Interconnect modeling plays an important role in design and verification of VLSI circuits and packages. For low frequency circuits, great advances for parasitic resistance and capacitance extraction have been achieved and wide varieties of techniques are available. However, for high frequency circuits and packages, parasitic inductance and impedance extraction still poses a tremendous challenge. Existing algorithms, such as FastImp and FastHenry developed by MIT, are slow and inherently unable to handle multiple dielectrics and magnetic materials. In this research, we solve three problems in interconnect modeling for high frequency circuits and packages. 1) Multiple dielectrics are common in integrated circuits and packages. We propose the first Boundary Element Method (BEM) algorithm for impedance extraction of interconnects with multiple dielectrics. The algorithm uses a novel equivalentcharge formulation to model the extraction problem with significantly fewer unknowns. Then fast matrix-vector multiplication and effective preconditioning techniques are applied to speed up the solution of linear systems. Experimental results show that the algorithm is significantly faster than existing methods with sufficient accuracy. 2) Magnetic materials are widely used in MEMS, RFID and MRAM. We present the first BEM algorithm to extract interconnect inductance with magnetic materials. The algorithm models magnetic characteristics by the Landau Lifshitz Gilbert equation and fictitious magnetic charges. The algorithm is accelerated by approximating magnetic charge effects and by modeling currents with solenoidal basis. The relative error of the algorithm with respect to the commercial tool is below 3%, while the speed is up to one magnitude faster. 3) Since traditional interconnect model includes mutual inductances between pairs of segments, the resulting circuit matrix is very dense. This has been the main bottleneck in the use of the interconnect model. Recently, K = L-1 is used. The RKC model is sparse and stable. We study the practical issues of the RKC model. We validate the RKC model and propose an efficient way to achieve high accuracy extraction by circuit simulations of practical examples.