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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Interaction of Molecular Contaminants with Low-k Dielectric Films and Metal Surfaces

Iqbal, Asad January 2007 (has links)
Ultra low-k dielectric films are expected to widely replace SiO2 as the interlayer dielectric for the next-generation microelectronic devices. A challenge facing the integration of these dielectrics in manufacturing is their interactions with gaseous contaminants, such as moisture and isopropanol, and the resulting change in their properties. Moisture retained in the film not only has detrimental effect on the k value of the film but also causes reliability and adhesion problems due to gradual outgassing. The physical and chemical interactions of moisture with porous spin-on and chemical vapor deposited (CVD) dielectrics are investigated using temperature- and concentration-programmed exposure and purge sequence together with trace moisture analysis, using atmospheric pressure ionization mass spectrometry.The model compounds in this study are porous Methylsilsesquioxane and Black Diamond II films, deposited and treated under typical manufacturing conditions. Transmission Electron Microscope (TEM) studies showed that etching and ashing processes resulted in the formation of two layers, a damaged layer and non-damaged layer, which significantly changed moisture interaction properties.Moisture sorption and desorption studies showed that as compared to SiO2 these films not only have a higher uptake capacity but also a slower and more activated moisture removal process. This could be a significant problem in successful integration of these films in IC manufacturing process.A process model was developed that provided information on the mechanism and kinetics of moisture uptake and release in thin porous films. The model elucidated the effect of film properties on the contamination uptake as well as outgassing. The model is a valuable tool for designing an optimum process for contamination control and removal in porous films.Another concern in IC manufacturing is the outgassing of impurities of electropolished stainless steel (EPSS) surfaces used in UHP gas distribution system. Moisture interaction with EPSS surface is studied in sub ppb range. A fundamental model was developed to study the mechanism and kinetics of moisture uptake and release from EPSS. The model developed would be a valuable tool for designing an optimum process for contamination control and to predict the moisture dry down performance of large-scale, systems.
2

Improvements in Biobutanol Production: Separation and Recovery by Adsorption

Abdehagh, Niloofar January 2016 (has links)
Due to environmental challenges, depleting oil resources, rising cost of oil and instability in oil-producing countries, biofuel production has attracted a lot of attention in recent decades. Biobutanol is one of the biofuels showing the most potential as an alternative for partly replacing petroleum-based fuels. Both researchers and industrialists are currently working at developing an energy-effective process to produce biobutanol at a large scale. Acetone-butanol-ethanol (ABE) fermentation is the biological process of biobutanol production and Clostridia are the most common bacteria used to produce biobutanol. However, there are several challenges in the butanol bioproduction process that should be addressed to make this process economically viable. The main challenge in the biobutanol production process is the low concentration of butanol in the ABE fermentation broth. It is therefore important to develop an efficient separation method. Several separation methods such as distillation, liquid-liquid extraction (LLE), pervaporation, gas stripping and adsorption have been considered to recover butanol from dilute solutions and ABE fermentation broths. Adsorption is considered as one of the most promising methods due to its high performance and energy efficiency for butanol separation. In this study, the focus was on developing an efficient separation method for butanol recovery from dilute model solution and fermentation broth using adsorption. A comprehensive adsorbent screening was first carried out to identify the best commercially available adsorbent among a series of potentially promising adsorbents. Activated carbon (AC) F-400 was selected for further experimentation since it showed high adsorption capacity and adsorption rate in addition to high selectivity toward butanol. AC F-400 was then tested extensively in packed adsorption column experiments for binary and ABE model solutions and fermentation broths to investigate the competitive adsorption between butanol and other components present in ABE broths. The results showed that the butanol adsorption capacity was not affected by the presence of ethanol, glucose and xylose while the presence of acetone led to a slight decrease in adsorption capacity at low butanol concentrations. On the other hand, the presence of acids (acetic acid and butyric acid) in the ABE broth showed a significant effect on the butanol adsorption capacity over a wide ii range of butanol concentration and this effect was more pronounced for butyric acid. At the end, different competitive adsorption isotherm models were also studied to appropriately represent the behaviour of the competitive adsorption. Desorption of butanol was subsequently investigated to evaluate both the desorption capacity of butanol and the capability of the adsorbent particles to be used for multiple adsorption-desorption cycles. The results of this set of experiments showed that AC F-400 can retain its initial adsorption capacity after 6 adsorption/desorption cycles. The recovery of butanol from butanol-water (1.5 wt%) binary and ABE model solutions was 84 and 80% with butanol adsorption capacity of 302 and 171 mg/g, respectively. The combination of adsorption and gas stripping techniques was also studied to investigate the performance of CO2 gas stripping of solvents from the model solutions and fermentation broths followed by adsorption. The results showed that the butanol adsorption capacity of the overall system for binary solutions (260 mg/g for a binary butanol-water solution of 15 g/L with vapour phase concentration of 5.8 mg/L), ABE model solutions (192 mg/g for a corresponding vapour concentration of 5.2 mg/L) and ABE fermentation broths (247 mg/g for a corresponding vapour phase concentration of 2.5 mg/L) was higher than what has been published in the literature. Finally, a model was developed and adequately validated the experimental data to predict the behaviour of the ABE compounds in a packed bed adsorption column for butanol separation from dilute solutions.

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