Laser-induced chemical vapor deposition (LCVD) is a process enabling the deposition of solid material from a gas phase in the form of free-standing microstructures with high aspect ratios. The deposition rate, wire diameter, and material properties are sensitive to changes in temperature and gas pressure. Through experimentation these dependencies are clarified for carbon and tungsten-coated carbon microhelices to be used as heating elements in cold gas microthrusters for space applications. The integration of heaters into the thruster will raise the temperature of the gas; thus, improving the efficiency of the thruster based on specific impulse. Deposition rate is measured during the fabrication process, and the geometrical dimensions of the spring are determined through microscopy analysis. By experimentally measuring the spring rate, material properties such as shear modulus and modulus of elasticity for LCVD-deposited carbon can be determined as a function of process parameters. Electrothermal characterization of carbon and tungsten-coated microcoils is performed by resistively heating the coils and measuring their surface temperature and resistance in atmospheres relevant to their operating environments. Through high-resolution microscopy analysis, sources having detrimental effects on the coils are detected and minimized. The results gained from these experiments are important for efforts in improving the performance of cold gas microthrusters.

Nanoparticles of iron, cobalt and tungsten oxide were synthesised by photolytic laser assisted chemical vapour deposition (LCVD). An excimer laser (operating at 193 nm) was used as an excitation source. The LCVD process, was monitored in situ by optical emission spectroscopy (OES). The synthesised particles were further analysed using transmission electron spectroscopy (TEM), X-ray diffraction (XRD), high resolution scanning electron microscopy (HRSEM), X-ray fluorescence spectroscopy (XRF), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. Iron and cobalt single crystalline nanoparticles were synthesized using ferrocene and cobaltocene precursors. The diameter of the particles could be tailored by the experimental parameters (e.g., partial pressure and laser power) and were in the range 1 - 50 nm in diameter. In both cases, the particles were covered by a carbon shell, typically 7 nm thick. A thin graphitic layer was observed at the interface metal-carbon. Amorphous carbon was deposited on top of the graphitic carbon. Particle temperature, reaching the boiling point of the respective metal, was observed by OES of the thermal emission during the laser-induced particle formation process (and subsequent heating). Both bcc and fcc Fe phases were formed, both hcp and fcc for the Co phases. Size dependent magnetic properties were observed using superconducting quantum interference device (SQUID) measurements, where super-paramagnetic magnetic domains dominated for d < 10 nm. The iron particles were further processed, whereby the amorphous shell was removed by refluxing in nitric acid. In a subsequent step, the graphitic surface was functionalized by attaching an octyl ester, rendering the particles hydrophobic. Tungsten oxides were synthesized from combinations of WF6/H2/O2 as precursors. No particles could be deposited if H2 was removed from the gas-mixture. The as-deposited oxide nanoparticle film was amorphous. A monoclinic WO3 particle film could be achieved by annealing the amorphous oxide. Above 400°C, the oxide particles increased in size from ca. 20 nm to 60 nm through coalescence. The gas-sensing properties of the tungsten oxide were tested by conductance measurements using H2S as analyte. The sensitivity of the amorphous oxide nanoparticle film was found to be superior to that of a crystalline oxide nanoparticle film.

SiC is an attractive material since it has remarkable properties. For several years efforts have been put primarily in electronic applications. High power and high frequency devices can be fabricated on SiC due to its wide band gap, high breakdown field and high thermal conductivity. SiC devices can be used in harsh environment since its operation temperature is significantly high (about 1200 ). SiC bulk growth has been improved by seeded physical vapour transport (PVT) during last decades. However, the quality and doping concentration of SiC bulk are not good enough to be used as an active layer for devices. SiC epilayer growth by chemical vapour deposition (CVD) was established in the last three decades. Only about 5 µm/h growth rate is achieved by CVD with a standard process. Long deposition time is required to grow ≥100µm thick epilayer for high voltage devices. The main problem in standard CVD is the formation of silicon (Si) droplets due to supersaturation of Si-species on the growth surface or in the gas-phase, which is detrimental for devices performance. To solve the problem of Si-droplets, chloride-based CVD was introduced. Chlorinated species can dissolve the silicon aggregates through the formation of strong bonds to silicon species compared to Si-Si bonds. Typical chlorinated precursors are hydrogen chloride (HCl) and methyltrichlorosilane (MTS). In this thesis study, HCl was mainly used as chlorinated precursors. Distinct chlorinated precursors result in different chemical reactions which affect the epilayer growth appreciably. The Cl/Si ratio, which is the ratio of the amount of chlorinated precursors to silicon precursors, is a very critical growth parameter for morphology, growth rate and background doping concentration. The C/Si ratio and Si/H2 ratio also affect the epilayer growth appreciably. Besides, growth temperature, growth pressure and temperature ramp up condition are other important growth parameters. In the CVD reaction chamber, the temperature profile and gas species distribution are not uniform along the whole susceptor length, which leads to different thickness of epilayer, morphology and doping concentration at different area of the reaction chamber. The polarity and off-angle of substrates can bring about complete different grown epilayers. Epitaxial defects are mainly replicated from the substrate. Therefore, the quality of substrates is very important as well. Deep energy levels can be introduced by adding transition metal such as vanadium (V), chromium (Cr) or tungsten (W). There are some limits which are needed to be overcome for a complete development of SiC. 4” SiC wafers are commercially available on the market, larger diameter would be very useful for the industrial development of SiC. High growth rate and good quality with controlled uniformity are desired for electronic applications. In this thesis, the influences of growth parameters such as C/Si and Cl/Si ratios, comparison between different precursors, growth condition in different areas of reaction chamber and effects of substrate polarity are discussed. Intentional incorporation of tungsten atoms is investigated by deep-level transient spectroscopy measurement and thermodynamic analysis.

Optical and electrical properties of electrochemically lithium ion intercalated thin films of x-ray amorphous tungsten oxide made by magnetron sputtering on glass substrates coated with a thin layer of conductive tin doped indium oxide, have been studied. The composition and the density of the films were characterized by the ion beam analysis methods Rutherford Backscattering Spectroscopy and Elastic Recoil Detection Analysis. The optical properties, transmittance and reflectance were investigated by spectophotometry in the wavelength range 300-2500 nm. The absorption coefficients were calculated at different lithium intercalation levels. It was found that the absorption coefficient in an as-deposited blue film has a similar asymmetric shape as for films intercalated to a Li/W ratio of ~0.03. It was possible to electrochemically bleach this film to transparency. Stoichiometric films show optical irreversibility between the bleached and the colored state in the first cycle. A polaron absorption model has been compared to the absorption coefficient for films of different intercalation levels. An increase in the Fermi level and in the polaron band width, and a nearly constant activation energy was found as the Li/W value increased. The radius of the polaron wavefunction for different lithium intercalation levels and film compositions has been estimated from electrical measurements. The total absorption coefficient has been compared to the site-saturation model. The model is good for films intercalated in the optically reversible region. A modified site-saturation model that could be applied also in the optically irreversible region and involves electron transitions between W6+, W5+ and W4+ sites, has also been compared to experimental values. It was found that the total absorption, optical density and the coloration efficiency is higher for the WO2.63 film than in the less oxygen deficient films and that this film is optically more durable in an electrochemically cyclic lifetime device test.

Recently, memory-cells employing discrete traps as the charge storage media have been attracting a lot of attention as a promising candidate to replace conventional DRAM or Flash memories. Conventional floating gate (FG) non-volatile memories (NVMs) present critical issues on device scalability beyond the sub-50nm node. In achieving non-volatility in conventional FG memories, thicker control and tunnel oxide (~8nm) are required to guarantee longer retention time. Relatively, nano-dots memories causes more resistant leakage charges by localized storage sites, thus improving the device retention characteristics. Hence, nano-dots memories allow more aggressive scaling of the tunnel oxide and exhibit superior characteristics compared to Flash memories in term of operation voltage, write / erase speed, retention time and endurance. The advantages of metal nano-dots compared with other material counterparts include higher density of states , stronger coupling with the channel, better size scalability, and the design freedom of engineering the work function to optimize device characteristics. However, tungsten nano-dots are the most interested in all of metal dots is that tungsten metal has more extra attractive advantages, such as ultra high melting point make high process temperature caused superior thermal stability of device and wide application in VLSI technology nowadays caused real possibility of tungsten nano-dots NVMs fabricated in industry in practice. This dissertation is divided into four sections: (1) discussion of basic properties for tungsten nano-dots memory devices; (2) Tunneling Oxide Engineering,; (3) Improvement by novel processes; and (4) The influence with supercritical CO2 (SCCO2) and vapor treatment. Initially, formative mechanism of tungsten nano-dots and electrical characteristics of devices was investigated in the first section. Tungsten nano-dots were formed by oxidizing tungsten silicide / amorphous silicon double stack film at high temperature condition. From electrical measurement, the better characteristics have been achieved for oxidation condition at 1050¢XC / 120 sec. Secondly, the rapid thermal anneal (RTA) oxidation is used to grow tunnel oxide by two different forming gas (O2/N2O). Comparison of electrical characteristics, program characteristics of the device using tunnel oxide with N2O process is inferior than the common device. However, endurance is a important electrical characteristics in the semiconductor device especially apply on the non-volatile memory. Thirdly, novel processes were employed into fabrication of tungsten nano-dots memory devices, include the N2O oxidation and NH3 plasma treatment. The purpose of novel processes is production additional trapping states in nonvolatile memories, which is considerably as combination nano-dots with SONOS structure. In the final section, the application of supercritical CO2 with vapor on tungsten nano-dots memoery devices have been studying. It is found that the device treated by SCCO2 which electrical characteristics is improved obviously. Furthermore, this technology also can fabricate the nano-dots memory which is like the device used high temperature oxidation process. It suggests that the SCCO2 with vapor treatment could oxidize silicide film under a low temperature environment. This novel oxidation process has some advantages and could be noticed in the semiconductor industry.

Supported metal oxides (SMOs) are important catalytic materials that find numerous applications in important industrial processes. Improving the structural properties of SMOs is a challenging objective due to material synthesis and characterization limitations. Recent developments in the characterization of SMOs, specifically tungstated zirconia (WO x /ZrO 2 ), have revealed structural information that renewed scientific interest in developing more sophisticated synthetic protocols for SMOs. The current work aims to provide a robust characterization of WO x /ZrO 2 by using different characterization techniques and probe reactions. Conventional and non-conventional synthetic methods are investigated to cover the whole spectrum of published methods in order to understand the properties and limitations of these techniques. In the second part of this work, a new synthetic approach is presented that successfully produces ultrasmall (smaller than 2 nm) tungsten oxide nanoparticles (WO x NPs). By using conventional tungsten precursors and oleylamine, WO x NPs are synthesized, characterized, and finally supported to test their propene metathesis activity. Conventional WO x /ZrO 2 catalysts were prepared and extensively studied by probing their n -pentane isomerization activity and methanol dehydration activity. WO x /ZrO 2 prepared via incipient wetness impregnation shows maximum n -pentane isomerization turnover rates ( TOR ) at intermediate surface densities ( � surf ). This method delivers the most active n -pentane isomerization WO x /ZrO 2 catalysts since it maximizes the number density of the active sub-nm slightly distorted Zr-WO x sites at � surf between 5.2-6.2 W/nm 2 . By comparing the n -pentane isomerization activity with the methanol dehydration activity of WO x /ZrO 2 , n -pentane isomerization is shown to be an excellent probe reaction for qualitatively identifying the relative (to the other species) population density of Zr-WO x clusters. Bimolecular n -pentane isomerization is the prevailing mechanism and requires a higher population density of Zr-WO x clusters than methanol dehydration. In the second part of this work, a new solvothermal synthesis route for the preparation of ultrasmall tungsten oxide nanoparticles (WO x NPs) is introduced. By using ammonium polyanionic salts and oleylamine, high yields (92±5%) of oleylaminecoated WO x NPs were consistently synthesized. The co-addition of an organic oxidant during the synthesis led to smaller WO x NPs thereby providing insight into the NP synthesis mechanism. Deposition and activation of the NPs on SiO 2 support by removal of oleylamine allows better control over the WO x domain size than conventional methods. Oleylamine suppresses WO x NP sintering during calcination and prevents the formation of larger polytungstates present in conventional catalysts. The supported WO x NPs were found to be up to 3 times more selective for metathesis products than conventionally prepared tungstated silica likely due to their controlled structure.

The overall objective of my thesis research was to develop methodologies for assessing effects of mining effluents on pristine and sensitive northern rivers. I used a multi-trophic level approach in field studies to evaluate current monitoring methods and to determine whether metal mining activities had affected two otherwise pristine rivers that flow into the South Nahanni River, NWT; a World Heritage Site. Upstream reference conditions in the rivers were compared to sites downstream and further downstream of mines. The endpoints evaluated included concentrations of metals in river water, sediments and liver and flesh of slimy sculpin (Cottus cognatus); benthic algal and macroinvertebrate abundance, richness, diversity, and community composition; and various slimy sculpin measures. Elevated concentrations of copper (p=0.002)and iron (p=0.001) in liver tissue of sculpin from the Flat River were associated with high concentrations of mine-derived iron in river water and copper in sediments that were above national guidelines. In addition, sites downstream of the mine on the Flat River had increased algal abundances (p=0.002) and altered benthic macroinvertebrate communities ((p<0.001) whereas the sites downstream of the mine on Prairie Creek had increased benthic macroinvertebrate taxa richness (p=0.050) and improved sculpin condition (males: p=0.008; females: p=0.001). Biological differences in both rivers were consistent with mild enrichment of the rivers downstream of current and historical mining activity. Although the effects of mining activities on riverine biota in these northern rivers are currently limited, results of this research show that there is potential for effects to occur with proposed growth in mining activities.<p> Laboratory exposures were conducted using slimy sculpin, identified as a sentinel fish species in pristine northern rivers, to identify alternative methods for assessing toxicity of contaminants of concern in mining effluents. Ammonia was selected for the exposures based on effluent characteristics of northern mining effluents. Ammonia is known to be an important toxicant in aquatic environments. Although ammonia toxicity has been well studied in many fish species, effects of chronic exposure of slimy sculpin, a critical biomonitoring species for northern aquatic habitats, are not well known. Slimy sculpin were exposed to six concentrations of un-ionized ammonia relevant to concentrations found in northern mining effluents: control (0 ppm), 0.278 ppm, 0.556 ppm, 0.834 ppm, 1.112 ppm, and 1.668 ppm. An LC50 of 1.529 ppm was calculated from mortality data. Histopathological examination of gills indicated significant tissue damage, measured as lamellar fusion and epithelial lifting, at 0.834, 1.112, and 1.668 ppm. Using gill endpoints, NOEC and LOEC were calculated as 0.556 ppm and 0.834 ppm respectively. An EC50 of 0.775 ppm was determined for lamellar fusion and an EC50 of 0.842 ppm for epithelial lifting. Hemorrhage of gills was present in mortalities which occurred at 1.668 ppm of un-ionized ammonia. A significant decrease in liver somatic index (LSI) was seen in both male and female fish at 0.834 and 1.112 ppm, respectively. Gonadosomatic index (GSI) in female fish significantly increased at 1.668 ppm un-ionized ammonia with an associated significant increase in total whole body testosterone concentrations. GSI in male fish also significantly increased at 1.668 ppm but no differences were seen in testosterone concentrations. No significant differences were seen in gonad histopathological assessments or condition factor. Results from this study indicate that ammonia concentrations commonly reported in northern mine effluents hold potential to affect the health of slimy sculpin including acute, chronic, histological and endocrine endpoints. <p> Results from both the field study and laboratory exposures provide direction for future monitoring programs in pristine northern rivers and emphasize the importance of monitoring tools to detect change in these ecosystems. I recommend that monitoring of northern pristine rivers focus on a multi-trophic monitoring approach including indicators in algal and benthic macroinvertebrate communities due to their responsiveness. Laboratory exposures using slimy sculpin should be considered to obtain toxicological information for northern contaminants of concern. Gill histopathology endpoints may be a more sensitive indicator for detecting effects in slimy sculpin exposed to ammonia than traditional chronic endpoints. I also recommend monitoring of metal burdens in periphyton and benthic invertebrates for assessment of exposure to mine effluent and causal association in areas of low fish abundance.

This thesis presents thermodynamic studies performed by electrochemical methods (cyclic voltammetry, electrochemical impedance and chronopotenciometry) in three of the most important electrochromic materials: a-WO3, conducting polymers and viologens. Electrochromic materials are very promising as a low-consuming technology. By incorporating these materials in windows of buildings or vehicles, approximately a 30% of the consumed energy in these systems can be saved.Regarding the a-WO3, apart from other contributions, a new model based on lattice distortions, able to explain the intercalation thermodynamic in this material, is proposed. In the conducting polymers field, a Gaussian energy distribution is proved to account for the initial part of the so broad oxidation peaks observed in cyclic voltammetry. Finally, the coloration kinetics of the viologen modified n-TiO2 electrode is explained.

Hoy en día la habilidad de producir capas de óxidos metálicos compuestos por nanogranos es muy importante, no sólo como conocimiento fundamental, sino también desde un punto de vista industrial debido a las numerosas aplicaciones de los óxidos metálicos nanoesctructurados en varios dispositivos electrónicos. Por ejemplo, en el campo de los sensores de gas, la relación superficie-volumen de las capas basadas en nanogranos de óxidos metálicos, ofrece la posibilidad de mejorar las propiedades de detección de estos dispositivos. Por esta razón, una gran fracción del total de la investigación y desarrollo en el campo de los sensores de gas basados en óxidos metálicos está dirigida a obtener capas activas compuestas por nanogranos. En la actualidad el estudio de nuevas técnicas para el depósito de capas activas compuestas por nanogranos y además compatibles con la fabricación de microsistemas se ha convertido en una necesidad imperiosa. La presente tesis resume el trabajo del autor llevado a cabo en los últimos cuatro años y está relacionado con el desarrollo de dos regimenes especiales para depositar capas finas de óxido metálico por el método de pulverización catódica asistida por radio frecuencia para aplicaciones de sensores de gas. El primer régimen, nombrado régimen de interrupciones consiste en depositar la capa óxido metálico con una o varias interrupciones durante el proceso. El segundo régimen, nombrado régimen flotante consiste en introducir "extra" interfases dentro del volumen de la capa del óxido metálico por medio de interrupciones y empleando dos densidades de potencia durante el depósito (la primera para depositar el volumen de la capa y la segunda para depositar la capa superficial). El trabajo realizado en esta tesis fue de carácter experimental; además fue complementado por varios tipos de técnicas de caracterización que permitieron estudiar las propiedades físicas y las de detección de las capas depositadas.Los resultados mostraron que la introducción de "extra" interfases en el volumen de las capas de trióxido de tungsteno (WO3) influye en las propiedades morfológicas y estructurales de la capa obtenida. Se determinó que la transformación de fase del WO3, de amorfo a cristalino, tiene diferente tipo de actividad en las capas depositadas con interrupciones en comparación con las depositadas sin interrupciones. Así se observó que el proceso de cristalización es más lento cuando se depositan las capas de óxido metálico mediante el régimen de interrupciones. Por otro lado, se observó una reducción del tamaño de grano en las capas de WO3 depositadas tanto a través del régimen de interrupciones como del régimen flotante. También se determinó que los microsensores de gas fabricados empleando los dos regimenes estudiados tienen prometedoras características de detección, puesto que estos dispositivos mostraron mejor sensibilidad y selectividad a bajas concentraciones de gases oxidantes, tales como NO2 y O3, en comparación con los sensores de gas fabricados a través del régimen convencional de depósito por pulverización catódica. En conclusión, los sensores desarrollados en esta tesis podrían ser usados para monitorizar los principales contaminantes del aire.La tecnología de sensores se muestra como una de las tecnologías más importantes del futuro con una gran variedad de aplicaciones las cuales van desde el sector industrial hasta el sector privado. En la actualidad los sensores de gases son empleados para detectar y monitorizar una variedad de gases incluyendo gases tóxicos y explosivos. Las aplicaciones mas importantes de los sensores de gas están relacionados con el sector de la automoción, el sector industrial y el sector aeroespacial (donde los sensores son empleados para detectar gases tales como NOx, O2, NH3, SO2, O3, CO2 y gases de combustión para la protección del medio ambiente), el sector de la industria alimenticia (donde los sensores de gas son utilizados para controlar los procesos de fermentación), en el sector domestico (donde el CO2, humedad y gases de combustión necesitan ser detectados), el sector médico (donde los sensores de gas son aplicados para el diagnóstico y la monitorización de pacientes), y el sector de la seguridad (donde los sensores de gas son requeridos para detectar trazas de explosivos). Aunque algunas técnicas convencionales como la espectroscopia de masas o la cromatografía de gases pueden ser usadas en las aplicaciones mencionadas anteriormente con alta selectividad y sensibilidad, resulta obvio que su uso esta limitado por el coste, la instrumentación, la complejidad y el volumen de los equipos. Al contrario, los sensores de gas de estado sólido, en particular aquellos basados en capas de óxidos metálicos, representan una buena alternativa debido a su bajo costo, posibilidad de movilidad y compatibilidad con la tecnología microelectrónica. Desafortunadamente la falta de selectividad y estabilidad de largo plazo son parte de la problemática de este tipo de dispositivos. Como resultado, el desarrollo de sensores de gas basados en óxidos metálicos de alta sensibilidad, selectividad y buena estabilidad de largo plazo es el tema de muchas investigaciones. Hasta ahora, varias estrategias basadas principalmente en el uso de aditivos específicos en la superficie, catalizadores y promotores, controladores de temperatura y filtros han sido estudiadas con el objetivo de resolver parcialmente la problemática de los sensores de gas basados en óxidos metálicos. Sin embargo el autor cree que el paso fundamental para mejorar las funciones de este tipo de sensores esta relacionado con las recientes estrategias que tienen por objetivo el desarrollo de métodos para incremental el área superficial de la capa activa. Es bien sabido que la eficiencia de los sensores basados en óxidos metálicos está relacionada directamente con relación superficie-volumen de las capas activas. En esencia, las líneas de investigación estudiadas para conseguir altas áreas superficiales en las capas activas, pueden ser clasificadas en dos grupos. El primero consiste en la obtención de nanoparticulas basadas en óxidos metálicos a través de procesos químicos o físicos. El segundo consiste en la aplicación métodos especiales de preparación para el modelado de la superficie activa (por ejemplo, plantillas de estructura de alúmina porosa). Esta última opción representa una buena alternativa, pero sin métodos que permitan depositar capas activas basadas en nanopartículas no es factible. Por esta razón, es importante desarrollar métodos que permitan obtener capas de óxido metálico compuestos por nanopartículas. En este contexto, la presente tesis tiene como objetivo desarrollar técnicas de deposito basadas en el método de pulverización catódica para depositar capas de oxido metálico compuestas por nanogranos. Este manuscrito resume el trabajo del autor llevado a cabo en los últimos cuatro años y está relacionado con el desarrollo de nuevas tecnologías para depositar capas de óxidos metálicos con el fin de ser aplicadas en sensores de gases. El trabajo realizado en esta tesis fue de carácter experimental; además fue complementado por varios tipos de técnicas de caracterización que permitieron estudiar las propiedades físicas y las de detección de las capas depositadas.La novedad del trabajo radica en la aplicación de dos regimenes de depósito a través de la técnica de pulverización catódica asistida por radio frecuencia para la creación de capas de oxido metálico aplicadas a sensores de gas. El primer régimen, nombrado régimen de interrupciones consiste en depositar una capa óxido metálico con una o varias interrupciones durante el proceso. En este caso se introducen "extra" interfases en el volumen de la capa, donde se forma una superficie en equilibrio debido a la saturación de los enlaces libres en la superficie producida por los átomos residuales de la atmósfera y/o la relajación de la estructura en la interfase durante la interrupción. El segundo régimen, nombrado régimen flotante consiste en introducir "extra" interfases dentro del volumen de la capa del óxido metálico por medio de interrupciones y empleando dos densidades de potencia durante el depósito (la primera para depositar el volumen de la capa y la segunda para depositar la capa superficial). Los resultados mostraron que la aplicación interrupciones durante el crecimiento de capas finas de WO3 permite la creación de capas compuestas por nanogranos. La caracterización morfológica de las muestras depositadas con este régimen dio evidencia de la reducción del tamaño de grano en el WO3 en comparación con las muestras depositadas a través del régimen convencional. Se determinó una reducción en el tamaño de grano desde 24 nm a 17 nm mediante microscopia de fuerza atómica. Por otro lado, las capas de WO3 depositadas por interrupciones revelaron una estructura monoclínica con simetría Pc. Se determinó que la transformación de fase del WO3, de amorfo a cristalino, tiene diferente tipo de actividad en las capas depositadas con interrupciones en comparación con las depositadas sin interrupciones. Así se observó que el proceso de cristalización es más lento cuando se depositan las capas de óxido metálico mediante el régimen de interrupciones. La caracterización de las propiedades de detección de los microsensores de gas fabricados empleando el régimen de interrupciones reveló una mejora de la sensibilidad y selectividad a bajas concentraciones de gases oxidantes, tales como NO2 y O3, con respecto a los sensores fabricados convencionalmente. La mejora de la sensibilidad de los sensores fabricados con el régimen de interrupciones esta relacionada con la disminución del tamaño de grano en la capa activa.Los sensores de WO3 fabricados mediante el régimen flotante no mostraron diferencias ni en el tamaño de grano ni en la composición cristalina con respecto a las capas depositadas por interrupciones. La caracterización de las propiedades de detección de los sensores de gas fabricados con el régimen flotante dio como resultado altas sensibilidades para bajas concentraciones de NO2. La mejora de la sensibilidad observada en los sensores de gas fabricados por el régimen flotante parece estar relacionada no solo con la reducción en el tamaño de grano de la capa activa (comparando con los sensores de gas convencionales), si no también podría tener relación con el grado de limpieza de la superficie de la capa, la cual es mejor debido a que la capa superficial es depositada a una densidad de potencia más alta. En base a estos resultados se cree que los sensores desarrollados en esta tesis podrían ser usados para monitorizar los principales contaminantes del airePalabras clave: Trióxido de tungsteno, RF sputtering, Nanogranos, Sensor de Gas

The overall objective of my thesis research was to develop methodologies for assessing effects of mining effluents on pristine and sensitive northern rivers. I used a multi-trophic level approach in field studies to evaluate current monitoring methods and to determine whether metal mining activities had affected two otherwise pristine rivers that flow into the South Nahanni River, NWT; a World Heritage Site. Upstream reference conditions in the rivers were compared to sites downstream and further downstream of mines. The endpoints evaluated included concentrations of metals in river water, sediments and liver and flesh of slimy sculpin (Cottus cognatus); benthic algal and macroinvertebrate abundance, richness, diversity, and community composition; and various slimy sculpin measures. Elevated concentrations of copper (p=0.002)and iron (p=0.001) in liver tissue of sculpin from the Flat River were associated with high concentrations of mine-derived iron in river water and copper in sediments that were above national guidelines. In addition, sites downstream of the mine on the Flat River had increased algal abundances (p=0.002) and altered benthic macroinvertebrate communities ((p<0.001) whereas the sites downstream of the mine on Prairie Creek had increased benthic macroinvertebrate taxa richness (p=0.050) and improved sculpin condition (males: p=0.008; females: p=0.001). Biological differences in both rivers were consistent with mild enrichment of the rivers downstream of current and historical mining activity. Although the effects of mining activities on riverine biota in these northern rivers are currently limited, results of this research show that there is potential for effects to occur with proposed growth in mining activities.<p> Laboratory exposures were conducted using slimy sculpin, identified as a sentinel fish species in pristine northern rivers, to identify alternative methods for assessing toxicity of contaminants of concern in mining effluents. Ammonia was selected for the exposures based on effluent characteristics of northern mining effluents. Ammonia is known to be an important toxicant in aquatic environments. Although ammonia toxicity has been well studied in many fish species, effects of chronic exposure of slimy sculpin, a critical biomonitoring species for northern aquatic habitats, are not well known. Slimy sculpin were exposed to six concentrations of un-ionized ammonia relevant to concentrations found in northern mining effluents: control (0 ppm), 0.278 ppm, 0.556 ppm, 0.834 ppm, 1.112 ppm, and 1.668 ppm. An LC50 of 1.529 ppm was calculated from mortality data. Histopathological examination of gills indicated significant tissue damage, measured as lamellar fusion and epithelial lifting, at 0.834, 1.112, and 1.668 ppm. Using gill endpoints, NOEC and LOEC were calculated as 0.556 ppm and 0.834 ppm respectively. An EC50 of 0.775 ppm was determined for lamellar fusion and an EC50 of 0.842 ppm for epithelial lifting. Hemorrhage of gills was present in mortalities which occurred at 1.668 ppm of un-ionized ammonia. A significant decrease in liver somatic index (LSI) was seen in both male and female fish at 0.834 and 1.112 ppm, respectively. Gonadosomatic index (GSI) in female fish significantly increased at 1.668 ppm un-ionized ammonia with an associated significant increase in total whole body testosterone concentrations. GSI in male fish also significantly increased at 1.668 ppm but no differences were seen in testosterone concentrations. No significant differences were seen in gonad histopathological assessments or condition factor. Results from this study indicate that ammonia concentrations commonly reported in northern mine effluents hold potential to affect the health of slimy sculpin including acute, chronic, histological and endocrine endpoints. <p> Results from both the field study and laboratory exposures provide direction for future monitoring programs in pristine northern rivers and emphasize the importance of monitoring tools to detect change in these ecosystems. I recommend that monitoring of northern pristine rivers focus on a multi-trophic monitoring approach including indicators in algal and benthic macroinvertebrate communities due to their responsiveness. Laboratory exposures using slimy sculpin should be considered to obtain toxicological information for northern contaminants of concern. Gill histopathology endpoints may be a more sensitive indicator for detecting effects in slimy sculpin exposed to ammonia than traditional chronic endpoints. I also recommend monitoring of metal burdens in periphyton and benthic invertebrates for assessment of exposure to mine effluent and causal association in areas of low fish abundance.