Browsing by Subject "Fluorocarbons"
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Item Investigation of fluorinated amorphous carbon for low-k dielectric applications(Texas Tech University, 1999-05) Harris, Harlan RustyThis thesis describes the investigation of PECVD fluorinated amorphous carbon as a dielectric for multiple level metallization. Films have been deposited in a standard capacitively coupled plasma reactor, and the deposition parameters were varied to find the dependence of the optical and electrical properties on process conditions. It is found that, using acetylene and tetraflouromethane, thermally stable films can be made that have dielectric constants that will meet the criteria for next generation semiconductors. A metric is formed the allows the thermal stability to be determined optically, and the films have been subsequently patterned using a standard photoresist, indicating the possibility of implementing these materials using current VLSI processes.Item Molecular dynamics study of solvation phenomena to guide surfactant design(2009-12) Dalvi, Vishwanath Haily; Rossky, Peter J.Supercritical carbon-dioxide has long been considered an inexpensive, safe and environmentally benign alternative to organic solvents for use in industrial processing. However, at readily accessible conditions of temperature and pressure, it is by itself too poor a solvent for a large number of industrially important solutes and its use as solvent necessitates concomitant use of surfactants. Especially desirable are surfactants that stabilize dispersions of water droplets in carbon-dioxide. So far only molecules containing substantially fluorinated moieties e.g. fluoroalkanes and perfluorinated polyethers, as the CO₂-philes have proved effective in stabilizing dispersions in supercritical carbon-dioxide. These fluorocarbons are expensive, non-biodegradable and can degrade to form toxic and persistent environmental pollutants. Hence there is great interest in developing non-fluorous alternatives. Given the development of powerful computers, excellent molecular models and standardized molecular simulation packages we are in a position to augment the experiment-driven search for effective surfactants using the nanoscopic insights gleaned from analysis of the results of molecular simulations. We have developed protocols by which to use standard and freely available molecular simulation infrastructure to evaluate the effectiveness of surfactants that stabilize solid metal nanoparticles in supercritical fluids. From the results, which we validated against experimental observations, we were able to determine that the alkane-based surfactants, that are so effective in organic fluids, are ineffective or only partially effective in CO₂ because the weak C-H dipoles cannot make up for the energetic penalty incurred at the surfactant-fluid interface by CO₂ molecules due to loss of quadrupolar interactions with other CO₂ molecules. Though the effectiveness of purely alkane-based surfactants in carbon-dioxide can be improved by branching, they cannot approach the effectiveness of the fluoroalkanes. This is because the stronger C-F dipole can supply the required quadrupolar interactions and a unique geometry renders repulsive the fluorocarbons' electrostatic interactions with each other. We have also determined the source of the fluoroalkanes' hydrophobicity to be their size which offsets the effect of favourable electrostatic interactions with water. Hence we can provide guidelines for CO₂-philic yet hydrophobic surfactants.