Understanding the molecular-level chemistry of H2O plasmas and the effects of surface modification and deposition on a selection of oxide substrates
| dc.contributor.author | Trevino, Kristina J., author | |
| dc.contributor.author | Fisher, Ellen R., advisor | |
| dc.contributor.author | Elliott, C. Michael, committee member | |
| dc.contributor.author | Henry, Charles S., committee member | |
| dc.contributor.author | Prieto, Amy L., committee member | |
| dc.contributor.author | Bailey, Travis S., committee member | |
| dc.date.accessioned | 2007-01-03T05:34:53Z | |
| dc.date.available | 2007-01-03T05:34:53Z | |
| dc.date.issued | 2011 | |
| dc.description.abstract | This dissertation first examines electrical discharges used to study wastewater samples for contaminant detection and abatement. The abatement process of contaminants in liquid discharges is relatively unstable; thus, to help elucidate the sources of instability, the gas phase constituents of plasmas formed from artificially-contaminated water samples were examined using optical emission spectroscopy (OES) and mass spectrometry (MS). Two different water samples contaminated with differing concentrations of either methanol (MeOH) or methyl tert-butyl ether (MTBE) were used to follow breakdown mechanisms. Emission from CO* was used to monitor the contaminant and for molecular breakdown confirmation through actinometric OES as it can only arise from the carbon-based contaminant in either system. Detection limits for each compound were as low as 0.01 ppm at a range of varying plasma parameters. MS data revealed plasma molecular breakdown and little evidence for fragment recombination to form larger molecules. MS data for the two contaminated H2O samples suggest the primary plasma species are CHx, C2Hx, CH2O, CO, C4Hx, and C3HxO and their corresponding ions. From this study, the detection and decomposition of organic molecules in water was accomplished for the first time with an ICP system. Detection was achieved at concentrations as low as 0.01 ppm, and molecular decomposition was seen at a variety of plasma parameters. This dissertation also explores the vibrational (θV), rotational (θR) and translational (θT) temperatures for a range of diatomic species in different plasma systems. Specifically we have investigated four molecules; OH in plasmas formed from H2O (g), tetraethyl orthosilicate (TEOS), NH3/O2 mixtures, and CH3OH; NH formed in plasmas created from NH3 and NH3/O2 mixtures; SiH radicals in SiH4, SiH4/Ar, Si2H6 and Si2H6/Ar plasmas; and CH in plasmas formed from mixtures of CH4/Ar. These species were probed with both laser induced fluorescence (LIF) and OES. For the majority of the plasma species studied, θV are much higher than θR and θT. This suggests that more energy is partitioned into the vibrational degrees of freedom in our plasmas. The θR reported are significantly lower in all the plasma systems studied and this is a result of radical equilibration to the plasma gas temperature. θT values show two characteristics; (1) they are less than the θV and higher than the θR and (2) show varying trends with plasma parameters. Radical energetics were examined through comparison of θR, θT, and θV, yielding significant insight on the partitioning of internal and kinetic energies in plasmas. Correlations between energy partitioning results and corresponding radical surface scattering coefficients obtained using our imaging of radicals interacting with surfaces (IRIS) technique are also presented. Another aspect of plasma process chemistry, namely surface modification via plasma treatment, was investigated through characterization of metal oxides (SiOxNy, nat-SiO2, and dep-SiO2) following their exposure to a range of plasma discharges. Here, emphasis was placed on the surface wettability, surface charge, and isoelectric point (IEP). The results demonstrate that 100% Ar, H2O, and NH3 plasma treatments cause changes in surface charge, wettability, and IEP values for all treated surfaces. Observed variations in these values depend primarily on the specific mechanism for surface functionalization with each plasma treatment. Ar plasmas tend to create surface radical sites, H2O plasmas yield surface-bound OH, and NH3 plasmas lead to the incorporation of nitrate functional groups. The wettability, surface charge, IEP values, chemical composition, and surface damage of the substrates were analyzed using contact angle goniometry (CA), x-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). Although the permanence of these modifications varied with substrate, lasting between one week and one month, these results highlight the utility of IEP measurements for characterizing plasma treated surfaces and suggest the possibility that plasmas may provide a valuable means of controlling surface charge and wettability of metal oxides. The incorporation of functional groups on the surface of Zeolite X was also examined as an additional form of plasma surface modification. The intention of these studies was to (1) alter the surface functionality by simple plasmas treatments, as characterized by XPS data; (2) change the hydrophilic nature of the zeolite to be more hydrophobic with flurocarbon plasmas; (3) gain total surface area functionality with our new rotating drum reactor; and (4) ensure that damage was not occurring to the zeolite structure, as evidenced by SEM images. Results showed the incorporation of different surface functionality was accomplished with all plasma systems studied (CF4, C2F6, C3F8), the zeolite structure was not damaged by the plasma, and the potential for altering the entire surface area of these porous materials exists. The final portion of this dissertation addresses aspects of work designed to understand the adhesion behavior of amorphous carbon nitride (a-CNx) films deposited from a CH3CN and BrCN plasmas. In particular, films obtained from CH3CH plasmas stayed intact whereas BrCN plasmas produced films that delaminated upon their exposure to atmosphere. These results have been attributed to humidity, film stress, hydrocarbon species, and the Br content in the film. The major contributions to this work made here center on the chemical composition and binding environments of the deposited films as measured by XPS, which are shown to be critical in understanding the mechanical properties of a-CNx films. | |
| dc.format.medium | born digital | |
| dc.format.medium | doctoral dissertations | |
| dc.identifier | Trevino_colostate_0053A_10461.pdf | |
| dc.identifier.uri | http://hdl.handle.net/10217/48179 | |
| dc.language | English | |
| dc.language.iso | eng | |
| dc.publisher | Colorado State University. Libraries | |
| dc.relation.ispartof | 2000-2019 | |
| dc.rights | Copyright and other restrictions may apply. User is responsible for compliance with all applicable laws. For information about copyright law, please see https://libguides.colostate.edu/copyright. | |
| dc.subject | gas-phase analysis | |
| dc.subject | water | |
| dc.subject | surface modification | |
| dc.subject | ICP | |
| dc.subject | oxide substrates | |
| dc.subject | deposition | |
| dc.title | Understanding the molecular-level chemistry of H2O plasmas and the effects of surface modification and deposition on a selection of oxide substrates | |
| dc.type | Text | |
| dcterms.rights.dpla | This Item is protected by copyright and/or related rights (https://rightsstatements.org/vocab/InC/1.0/). You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s). | |
| thesis.degree.discipline | Chemistry | |
| thesis.degree.grantor | Colorado State University | |
| thesis.degree.level | Doctoral | |
| thesis.degree.name | Doctor of Philosophy (Ph.D.) |
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