Hot-wire Chemical Vapour Deposition Chemistry and Kinetics of New Precursors in the Gas Phase and on the Wire Surface
| atmire.migration.oldid | 2764 | |
| dc.contributor.advisor | Shi, Yujun | |
| dc.contributor.author | Badran, Ismail | |
| dc.date.accessioned | 2014-12-03T23:23:29Z | |
| dc.date.available | 2016-01-07T16:33:58Z | |
| dc.date.issued | 2014-12-03 | |
| dc.date.submitted | 2014 | en |
| dc.description.abstract | Due to its advantages over conventional methods, the newly-developed hot-wire chemical vapour deposition (HWCVD) has placed itself as one of the leading technologies to produce high-quality silicon carbide (SiC) thin films. This research is geared towards investigating two new HWCVD precursors: 1-methyl-silacyclobutane (MSCB) and 1.3- disilacyclobutane (DSCB). Full reaction mechanisms on the hot wire and in the gas phase were proposed. The mechanisms were constructed by probing the reaction products by laser ionization sources coupled to a time-of-flight mass spectrometer (TOF MS), followed by experiments using isotope labeling and chemical trapping. The mechanisms were verified using high-level ab initio theoretical calculations. Both the primary decomposition of MSCB and DSCB were found to be catalyzed by the hot wire. The secondary gas-phase reactions of MSCB, studied under practical HWCVD pressure of 0.12-0.48 Torr, consisted of short free-radical chain reactions and silene cycloaddition. The primary decomposition of DSCB was ruled by H2 elimination from Si forming a cyclic silylene (disilacyclobutylidene). This reactive intermediate, which has never been reported before, was successfully isolated in the HWCVD reactor using trimethylsilane. The secondary gas-phase reactions of DSCB were dominated by the silylene insertion into the Si-H bond of the parent molecule. The theoretical calculations performed in this work have agreed well with the experimental study. In addition, they revealed a new and alternative pathway from the stepwise cycloreversion of MSCB and DSCB to form relatively stable open-chain olefins. Furthermore, a new symmetry allowed π2s+ π2a asynchronous transition state was discovered in addition to the known symmetry forbidden π2s+ π2s one. The proposed mechanisms were used for a kinetic study aimed to determine the rate constants and the activation energies for the main decomposition reaction pathways. The study shapes a new methodology to study the kinetics of the complex reactions involved in the HWCVD reactor. The rate constants for the main reaction pathways of the two molecules and the corresponding activation energies have shown that both MSCB and DSCB reactions were catalyzed by the hot wire under a reactor pressure of 12 Torr. In addition, the dependence of the rate constants on pressure was linear in the 5-40 Torr region and no fall-off region was observed. The filament aging of tungsten and tantalum with DSCB was systematically studied in the temperature range of 1200-2400 °C. W was found to be more prone to aging than Ta. Meanwhile, crystalline 3C-SiC was formed at low filament temperatures ≤1300 °C. As the temperature increased, SiC was replaced by carbides (W2C, TaC). This transformation was driven by the nature of the DSCB precursor. | en_US |
| dc.description.embargoterms | 12 months | en_US |
| dc.identifier.citation | Badran, I. (2014). Hot-wire Chemical Vapour Deposition Chemistry and Kinetics of New Precursors in the Gas Phase and on the Wire Surface (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca. doi:10.11575/PRISM/26384 | en_US |
| dc.identifier.doi | http://dx.doi.org/10.11575/PRISM/26384 | |
| dc.identifier.uri | http://hdl.handle.net/11023/1953 | |
| dc.language.iso | eng | |
| dc.publisher.faculty | Graduate Studies | |
| dc.publisher.institution | University of Calgary | en |
| dc.publisher.place | Calgary | en |
| dc.rights | University of Calgary graduate students retain copyright ownership and moral rights for their thesis. You may use this material in any way that is permitted by the Copyright Act or through licensing that has been assigned to the document. For uses that are not allowable under copyright legislation or licensing, you are required to seek permission. | |
| dc.subject | Chemistry--Physical | |
| dc.subject.classification | Hot-Wire Chemical vapour deposition | en_US |
| dc.subject.classification | Reaction Mechanism | en_US |
| dc.subject.classification | Reaction Kinetics | en_US |
| dc.subject.classification | Filament Aging | en_US |
| dc.title | Hot-wire Chemical Vapour Deposition Chemistry and Kinetics of New Precursors in the Gas Phase and on the Wire Surface | |
| dc.type | doctoral thesis | |
| thesis.degree.discipline | Chemistry | |
| thesis.degree.grantor | University of Calgary | |
| thesis.degree.name | Doctor of Philosophy (PhD) | |
| ucalgary.item.requestcopy | true |