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Accelerator Mass Spectrometry (AMS) studies of rare isotopes with abundant isobars that form negative ions often require the use of large accelerators to achieve high sensitivity measurements. The Isobar Separator for Anions (ISA) is a radiofrequency quadrupole (RFQ) reaction cell system that provides selective isobar suppression for many of these isotopes in the low energy system, prior to injection into an accelerator. The ISA can then facilitate the measurement of these ions using smaller accelerators. A commercial version from Isobarex Corp. was installed in a separate low energy injection line of the 3 MV accelerator system at the A. E. Lalonde AMS Laboratory in the University of Ottawa and was tested using the measurement of 36Cl, suppressing its stable isobar 36S. The ISA includes a DC deceleration region, a combined cooling and reaction cell, and a DC acceleration region. The deceleration region reduces the beam energy from the ion source (20-35 keV) to a level that chemical reactions can occur, scattering is minimized, and that the reaction cell can accept and contain. RFQ segments along the length of the cell create a potential well, which limits the divergence of the traversing ions. DC offset voltages on these RFQ segments maintain a controlled ion velocity through the cell. Helium was used as a cooling gas to further decelerate the ions, facilitating charge exchange between 36S and a reaction gas. Helium provided the highest transmission of 30-80% for chlorine anions. The reaction gas NO2 was chosen to preferentially react with sulfur. Over seven orders of magnitude reduction of sulfur to chlorine was observed. After exiting the cell, the beam is reaccelerated prior to injection into the tandem accelerator for AMS analysis. Using 36Cl reference materials, it was determined that linear transmission results could be obtained for a 36Cl/Cl ratio ranging from 10−11 to 10−15. The measurements were stable over more than 24 hours of continuous measurement. A blank level on the order of 10−15 was observed. The ISA was used to measure unknown 36Cl /Cl ratio groundwater samples and the results are compared to external AMS measurements.

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The monitoring of pH and free chlorine concentration in drinking water is important for water safety and public health. However, existing laboratory-based analytical methods are laborious, inefficient, and costly. This thesis focuses on the development of an easy-to-use, sensitive, and low-cost drinking water quality monitoring system for pH and free chlorine. An inkjet printing technology with a two-step thermolysis process in air is developed to deposit palladium/palladium oxide (Pd/PdO) films as potentiometric pH sensing electrodes. The redox reaction between PdO and hydronium ions generates the sensor output voltage. A large PdO percentage in the film provides a high sensitivity of ~60 mV/pH. A defect-free Pd/PdO film with small roughness contributes to a fast response and a high stability. When the Pd ink is thermalized in low vacuum, the deposited Pd/PdO film shows a bilayer structure. The residual oxygen in the low vacuum environment assists the decomposition of organic ligands for Pd to form a thin and continuous layer beneath submicron Pd aggregates. The oxidized bilayer film behaves as a temperature sensor with a sensitivity of 0.19% resistance change per °C, which can be used to compensate the sensed pH signals. Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is drawn by hand to form a free chlorine sensor. Free chlorine oxidises PEDOT:PSS, whose resistivity increment indicates the free chlorine concentration in the range of 0.5-500 ppm. Also, we simplified an amperometric free chlorine sensor based on amine-modified pencil leads. The simplified sensor is calibration-free, potentiostat-free, and easy-to-use. The pH, temperature, and free chlorine sensors are fabricated on a common substrate and connected to a field-programmable gate array board for data processing and display. The sensing system is user-friendly, cheap, and can accurately monitor real water samples. / Thesis / Doctor of Philosophy (PhD) / Sensitive, easy-to-use, and low-cost pH and free chlorine monitoring systems are important for drinking water safety and public health. In this thesis, we develop an inkjet printing technology to deposit palladium/palladium oxide films for potentiometric pH sensors and resistive temperature sensors. The different electrical and electrochemical properties of the palladium/palladium oxide films are realized by creating different film morphologies using different ink thermolysis atmospheres. The developed pH and temperature sensors are highly sensitive, fast in response, and stable. For free chlorine sensors, a hand drawing process is used to deposit poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate), which is an indicator for the free chlorine concentration over a wide range. We also developed a calibration-free free chlorine sensors based on modified pencil leads. Such a free chlorine sensor is integrated with the pH and temperature sensors, and an electronic readout system for accurate on-site drinking water quality monitoring at low cost is demonstrated.

Disinfectants are added to the water distribution system and swimming pools to control the growth of pathogenic microorganisms in water. High disinfectant levels are health hazards since they produce disinfectant by-products which are carcinogens. Thus, monitoring the amount ofresidual disinfectants present and maintaining an optimal amount of residual disinfectants throughout the distribution network is very crucial for safe water distribution. Colorimetric measurements are the current standard for measuring disinfectant levels in water. However, it is very difficult to integrate colorimetric measurements into automated monitoring devices. Redox active molecules like the phenyl-capped aniline tetramer (PCAT) can be incorporated as a dopant into a single wall carbon nanotube sensor for detecting oxidant in drinking water. The sensor works on the principle of oxidizing adsorbed redox molecules on carbon nanotubes by oxidant present in drinking water thus changing the resistivity of the carbon nanotube film. Most commonly used disinfectants are HOCl, Cl2, ClO2, Chloramine, KMnO4, HOBr, H2O2, O3, Br2, I2, etc. They all are oxidizing agents and can be distinguished from one another as they have different oxidation potentials. For water treatment purposes, it is not enough to know the disinfectant level, but it is also very important to identify which disinfectant is present. Currently, there is no standard method for distinguishing different disinfectants presents in water. The development of sensor arrays based on redox active molecules having different redox potentials is a potential pathway towards differentiating between different disinfectants in water. Different aniline oligomers were synthesized to create a library of redox active molecules. Redox properties of these molecules have been determined, and expected results were compared with the sensor performance. In the future, these sensors can be incorporated into a reliable, resettable and reagent free sensor array for monitoring and distinguishing different disinfectants in water. Being able to constantly monitor the disinfectant level and identifying the disinfectant present in water will enable us to design an improved and sustainable disinfecting system. / Thesis / Master of Science (MSc)

In the past few years, the demands for high speed semiconductor integrated circuits have warranted new techniques in their fabrication process which will meet the ever-shrinking dimensions. The gaseous plasma assisted etching is one of these revolutionary processes. However, the plasma and the etch process are very complex in nature. It has been very difficult to understand various species present in the plasma and their role in the etch reaction. In addition, the submicron geometries also require interconnect materials which will satisfy the necessary properties such as thermal stability and low electrical resistance. Titanium (Ti) and titanium nitride (TiN) are widely used as barriers between aluminum (Al) and silicon (Si) to prevent the destructive intermixing of these two materials. The process of patterning of the interconnect containing Ti and TiN along with Al has been a challenge to the semiconductor process engineers. Therefore, complete characterization of the plasma etch process of Ti and TiN films and development of mathematical models to represent the responses such as the etch rate and uniformity is necessary for a good understanding of the etching process. A robust and well controlled metal etch process usually results in good die yield per wafer and hence can translate into higher profits for the semiconductor manufacturer. The objective of this dissertation is to characterize the plasma etch processes of Ti and TiN films in chlorine containing plasmas such as BCl₃ and Cl₂/N₂ and to develop mathematical models for the etch processes using statistical experimental design and analysis technique known as Response Surface Methodology (RSM). In this work, classical experiments are conducted on the plasma etch process of Ti and TiN films by varying the process parameters, such as gas flow, radio frequency (RF) power, reaction pressure, and temperature, one parameter at a time, while maintaining the other parameters constant. The variation in the etch rate with the change in the process parameter of the film is studied and the results were explained in terms of the concepts of plasma. These experiments, while providing very good understanding of the main effects of the parameters, yield little or no information on the higher order effects or interaction between the process parameters. Therefore, modern experimental design and analysis techniques using computerized statistical methods need to be employed for developing mathematical models for these complex plasma etch processes. The second part of this dissertation concentrates on the Design and Analysis of Experiments using Response Surface Methodology (RSM) and development of models for the etch rate and the etch uniformity of the Ti and TiN films in chlorine-containing plasmas such as Cl₂/N₂ and Cl₂/N₂/BCl₃. A complete characterization of the plasma etch process of Ti and TiN films is achieved with the RSM technique and a well fitting and statistically significant models have been developed for the process responses, such as the etch rate and the etch uniformity. These models also provide a means for quantitative comparison of main effects, which are also known as first order effects, second order effects and two factor interactions. The models, thus developed, can be effectively used for an etch process optimization, prediction of the responses without actually conducting the experiments, and the determination of process window. This dissertation work has achieved a finite study of the plasma etch process of Ti and TiN films. There is tremendous potential and scope for further research in this area, limited only by the available resources for wafer processing. A few of the possibilities for further research is discussed in the next few sentences. The optimized process derived from the RSM technique needs to be implemented in the actual production process of the semiconductor ICs and its effects on the wafer topography, etch residue and the resulting die yield have to be studied. More research studies are needed to examine the effect of process parameters such as temperature, the size and shape of the etch chamber, the quality of the film being etched, among other parameters. It is worth emphasizing in this respect that this dissertation marks beginning of research work into the ever-increasing complexities of gas plasma. / Ph. D.

Water chemistry and fluid velocity are factors that can perpetuate certain types of non-uniform pitting corrosion in copper tube, specifically in waters with high chlorine and a high pH. These two parameters can further act synergistically to alter pitting propensities in copper pipes subjected to this type of water. A preliminary short-term experiment considered pitting propensity in copper pipe as a function of water chemistry. This study used a water chemistry that had been documented to promote and sustain pitting in copper tube that further developed into fully penetrating pinhole leaks. Modifications to this base water chemistry found that dosing a chloramine disinfect (rather than free chlorine) or the addition of silica greatly reduced corrosion activity and pitting propensity on copper pipes. In another short-term experiment, copper pitting propensity was considered as a function of fluid velocity. A number of different fluid velocities were tested in several different pipe diameters using the same documented pitting water. Velocity was observed to significantly increase pitting propensity in all pipe diameters considered. At the highest fluid velocity tested (11.2 fps) a pinhole leak formed in ¼â tubing after only 2 months of testing. Larger pipe diameters were also found to increase the likelihood of forming deeper pits on the pipe surface at the same fluid velocity. Chlorine was a driving factor in corrosion for preliminary tests conducted using this pitting water. The reduction of chlorine to chloride is believed to be the primary cathodic reaction limiting the overall rate of corrosion in this type of water. As such, a subsequent study considered the relationship between the rate of chlorine reduction and corresponding corrosion activity. Chlorine reduction or demand rates were found to be good indicators for pitting propensity and corrosion activity for this particular type of water. All preceding work led to the development and design of a large scale, long-term, copper pitting study. A matrix of 21 unique conditions tested various water chemistries, flow conditions, corrosion inhibitors, and galvanic connections of copper pipes to other metallic plumbing materials. The severity of pitting corrosion was observed to be dramatically decreased by lower free chlorine residual concentrations, high alkalinity, and sufficient doses of copper corrosion inhibitors such as natural organic matter, silica, and orthophosphate. Pitting severity was consequently observed to increase at a low alkalinity, indicating that this parameter has a significant effect on corrosion reactions. Furthermore, the addition of aluminum solids to the base pitting water chemistry dramatically increased the formation of tubercle mounds on the inside of the copper pipes in contact with the waster. Aluminum solids have been observed to be a vital constituent for sustaining pit growth in this specific water at lower pHs, however, the role of this constituent at the high pH levels tested in this study was previously unknown. From simple visual observation, aluminum solids appear to increase the aggressiveness of this water even at higher pHs. / Master of Science

This project determined the thermodynamic potentials for various reactions between reduced manganese (Mn²), manganese oxide (MnO₂(s)), chlorine dioxide (Cl0₂), and potassium permanganate (KMnO₄). Based on these findings, laboratory analyses were performed to determine if these reactions would occur under simulated water treatment plant conditions. In addition, a speciation procedure was developed to quantify the various species of manganese and chlorine dioxide present in a single sample. The reactions and the speciation procedure were evaluated at TOC concentrations ranging from < 1.0 mg/L to 5.0 mg/L and at pH 6.0 and 8.0. The speciation procedure yielded a reliable measure of Mn², insoluble manganese, and Mn⁺⁷; however, the Mn⁺⁷ evaluation could be disrupted by the presence of free chlorine. The determination of Cl0₂ and Cl0₂- concentrations was also possible; however, the C10₂- concentration was subject to error. The laboratory analyses revealed that Cl0₂ was unable to oxidize either Mn² or MnO₂(s) to Mn⁺⁷ under any of the thermodynamically favored conditions. Both KMn0₄ and Cl0₂ selectively oxidized reduced organic material before reducing the concentration of Mn². When C10₂ and KMnO₄ were added simultaneously, the ClO2 reacted preferentially with the reduced materials. Only after the Cl0₂ concentration was exhausted did the MnO₂⁻ begin to oxidize the reduced species. / Master of Science