Characterization of mineral dust emitted from an actively retreating glacier in Yukon, Canada

La poussière minérale atmosphérique émise dans les régions arctiques peut modifier de manière significative le bilan énergétique de l'atmosphère nordique en diffusant et en absorbant la radiation. La poussière joue également un rôle important dans le cycle biogéochimique des métaux et peut avoir des effets négatifs sur la qualité de l'air et la santé publique. L'impact des sources de poussière du Nord sur l'atmosphère et l'environnement peut changer rapidement, car le réchauffement du climat dans le Nord peut augmenter la production de poussière minérale et peut affecter les régions d'origine. Cependant, à l'heure actuelle, l'impact de ces changements est difficile à évaluer, car très peu d'études scientifiques effectuent des mesures directes des émissions de poussières minérales ainsi que des propriétés chimiques et microphysiques des poussières minérales dans les régions arctiques. Pour combler cette lacune, nous avons fait des mesures de la poussière minérale en juin 2017 et en mai 2018 près de l'Ä’äy Chù (rivière Slims), dans une vallée proglaciale du Yukon, qui est un site important des émissions de la poussière. Le changement climatique a eu de lourdes conséquences sur la vallée d'Ä'äy Chù. Le retrait rapide du glacier Kaskawulsh laissant le lit de la rivière exposé augmentant ainsi potentiellement sa surface érodable qui peut produire de la poussière. Nous avons collecté des échantillons d’aérosols (PM10 et poussières minérales déposées) dans toute la vallée Ä’äy Chù et avons enregistré des données météorologiques afin d’établir un lien entre des facteurs environnementaux et l’émission de poussières. Nous avons également utilisé une méthode quantitative pour analyser les métaux traces dans les poussières minérales par spectrométrie de masse à plasma à couplage inductif (ICP-MS) afin de quantifier les métaux traces dans les échantillons de PM10, du sol et de poussières minérales déposées. Notre étude est la première à mener une caractérisation chimique et microphysique des poussières minérales émises directement par une source de poussière de haute latitude au Canada. L'analyse des données obtenues par un compteur de particules optiques (OPC) a indiqué à quelle heure des événements de poussière se sont produits pendant la journée, tandis qu'une analyse gravimétrique d'échantillons de filtres a montré des concentrations ambiantes entre 240 µg / m³ et 3 950 µg / m³ à la source des poussières. En outre, les seuils de qualité de l’air de l’Organisation de la Santé Mondial (OSM) ont été dépassés aux sites proches de la source de poussière, notamment au centre des visiteurs Thachäl Dhäl géré par Parcs Canada et à un site situé à proximité de la route de l’Alaska. Nous n'avons pas réussi à analyser nos échantillons en utilisant l'ablation au laser ICP-MS et l'ICP-MS à particule unique. Néanmoins, nous avons validé avec succès un protocole d'analyse ICP-MS d'échantillons digérés et avons ainsi pu appliquer cette technique à l'analyse de nos échantillons. L’analyse de la composition élémentaire par ICP-MS a révélé l’enrichissement en échantillons de PM10 de la composition des éléments mineurs et des éléments traces par rapport aux sols, généralement par un facteur de 1,5 à 2. De plus, une analyse SEM / EDS a démontré que les poussières émises se composent principalement de particules non sphériques composées d'agrégats minéraux d'argile aluminosilicate. Enfin, nous avons calculé le flux vertical de masse de particules, et nous avons utilisés le flux, la distribution de taille et la composition du PM10 afin d’évaluer plusieurs théories relatives au mécanisme prédominant d'émission de poussière qui se produit dans la vallée d'Ä'äy Chù.Airborne mineral dust emitted in Arctic regions can significantly alter the energy balance of the Northern atmosphere through scattering and absorption of radiation; dust also plays an important role in the biogeochemical cycling of metals and can have deleterious effects on air quality and public health. The impact of northern dust sources on the atmosphere and environment may change rapidly, as warming temperatures in the North can increase mineral dust production and source regions by inducing topographical changes due to rapid glacier ablation. However, at present, the impact of such changes is difficult to evaluate because there are very few scientific studies that perform direct field measurements of mineral dust emissions as well as of mineral dust chemical and microphysical properties in Arctic regions. To address this knowledge gap, we performed mineral dust measurement campaigns in June 2017 and May 2018 near the Ä’äy Chù (Slims River), within a proglacial valley in Yukon, Canada that has exhibited strong dust emissions. The Ä’äy Chù Valley has been impacted heavily by climate change, as the rapid retreat of the adjacent Kaskawulsh glacier, recently routed waters away from the river valley, leaving the riverbed exposed and thus potentially increasing its dust-producing erodible surface area. We have collected aerosol samples (PM10 and deposited mineral dust) throughout the Ä’äy Chù Valley, and have recorded weather data to establish a link between environmental factors and the emission of dust. We have also employed an efficient, quantitative method for analysis of trace metals in mineral dust via inductively coupled plasma mass spectrometry (ICP-MS) to quantify trace metals in PM10 samples, soil and in deposited mineral dust samples. Ours is the first field campaign to provide chemical and microphysical characterization of mineral dust emitted directly from a high-latitude dust source in Canada. Analysis of data obtained by an optical particle counter (OPC) indicated dust events occurred during both daylight and non-daylight hours, while gravimetric analysis of filter samples found ambient concentrations ranging between 240 µg/m3 and 3950 µg/m3 at the dust source during the course of the dust observation campaign. Furthermore, air quality thresholds of the World Health Organization (WHO) were exceeded at sites near the dust source, including at the Thachäl Dhäl Visitor’s Center run by Parks Canada and a site next to the Alaska Highway. We were unable to successfully analyze our samples using laser ablation ICP-MS and single particle ICP-MS. Nevertheless, we successfully validated a protocol for performing ICP-MS analysis of digested samples and were thus able to apply this technique to the analysis of our samples. Analysis of elemental composition via ICP-MS has revealed enrichment of minor and trace element content in ambient air samples as compared to soils and dust deposition, generally by a factor of 1.5 to 2. Moreover, SEM/EDS analysis has demonstrated that the emitted dust primarily consists of non-spherical particles composed of aluminosilicate clay mineral aggregates. Finally, we have calculated the vertical flux of particulate mass, and have used the flux, the size distribution, and the composition of both PM10 and soil samples to evaluate several theories related to the predominant dust emission mechanism that occurs in the Ä’äy Chù Valley

Studies of the Mechanism of Electron Beam Induced Deposition (EBID)

The controlled deposition of metals resulting from the passage of an ion beam through an atmosphere of a suitable precursor gas is a well-established procedure for micro scale materials manipulation. While the ion beam technique is rapid and reliable it has the disadvantage that the beam itself can ablate and contaminate the target with Gallium or other materials, and the fact that ion optics are less widely accessible than electron optical columns. We have therefore been investigating the theory and practice of depositing metal using an electron beam and variety of precursor gases. The aim of this work is to develop techniques that can be applied to the repair of the optical, ultra-violet (UV) and extreme ultra-violet (EUV) masks used in high performance photo-lithography. This thesis is concentrated on electron beam induced deposition (EBID) performed in a commercial Scanning Electron Microscope (SEM). For EBID experiments, we have developed a gas injection system for the specimen chamber of a standard SEM which is able to control the pressure and the delivery flow rate of gas for experiment. Studies of factors that control the properties of the deposition - such as the electron-gas interactions, the effects of gas pressure, and the temperature of the substrate – have been made and experiments to determine the fundamental mechanisms of EBID - such as which types of electrons are responsible for the initial interaction event with the precursor – have been carried out and analyzed and systematically studied to determine the optimum conditions for the practical application of the EBID approach. Finally the practical applications of the EBID have been applied to repair of masks

Assessment of portable and miniaturized sensors for the monitoring of human exposure to air pollutants

In the last years, several in-field campaigns have been conducted using portable and miniaturized monitors to evaluate the personal exposure to different pollutants. In general, this kind of monitors are characterized by worse metrological performance if compared to the traditional standard methods. Despite this disadvantage, portable and miniaturized monitors could be easily used across different applications, because their advantageous features, such as the capability to provide real-time measurement, the high spatial and temporal resolution of acquired data, the ability to adapt to different experimental designs and, especially, the ability to follow the subject in any activity. Finally, portable and miniaturized instruments can provide data acquired in the respiratory zone of the subject, following therefore the practices for a correct exposure assessment. Obviously, the best compromise between the analytical gold standard (in terms of precision, accuracy and instrumental sensitivity) and the gold standard in regard to the exposure assessment should be chosen. Therefore, in brief, principal aims of this thesis are (i) to evaluate the on-field performances of portable and miniaturized monitors for gaseous pollutants and airborne PM and (ii) to use these monitors in exposure assessment studies and (iii) to understand if data acquired via portable and miniaturized monitors could be useful in other fields of application, such as epidemiological studies or toxicological studies, in which the evaluation of the inhaled dose of pollutants could play a key role

Evanescent wave assist features for optical projection lithography

Evanescent Wave Assist Features (EWAFs) are features that are sensitive to near-field radiation that modify diffracted order intensities from photomask patterns. In implementations studied in this thesis, the EWAFs increase a transmitting feature\u27s image contrast and Normalized Image Log Slope (NILS). In this way, the EWAFs are a way to improve image fidelity for high-resolution features. The assist features consist of local, buried grooves located around transmitting mask regions. These grooves reside in otherwise unused areas, since they are located under or on top of opaque mask absorber regions. In these buried locations, they are not optically visible to the lithographic system in a traditional sense. Designs are explored for both top-surface and bottom-surface EWAFs on 1-D and 2-D layouts. Using EWAFs, 27% image contrast improvements have been shown on contact layouts, as well as best-case image contrast improvements of over 2X on 1-D slot-type mask layouts. Dependence of EWAF effect on mask absorber material and bottom-surface relief shape is studied, as well as polarization sensitivity and the role of Surface Plasmon Polaritons (SPP). TM polarized light creates a normal-component field enhancement that amplifies surface waves across suitably conductive absorbers. These waves can then interact with bottom-surface EWAF grooves, and convert to propagating based on grating action. The converted orders may then interact with standard transmitted orders from a transmission feature, resulting in enhancement or suppression, depending on EWAF tone, pitch regime, and illumination angle. A demonstration EWAF sample, as well as a reference sample with no grooves, was fabricated at the RIT SMFL and tested using a Variable Angle Spectroscopic Ellipsometer (VASE). Accounting for pitch deviations during fabrication, as well as lateral inter-layer alignment offsets gives diffracted order responses that agree with SPP resonances observed in the samples at normal incidence and diffracted order enhancement factors that agree with simulation