In the design of a thermal protection system for atmospheric entry, aerothermal heating presents a major impediment to efficient heat shield design. Recombination of atomic species in the boundary layer results in highly exothermic surface-catalyzed recombination reactions and an increase in the heat flux experienced at the surface. The degree to which these reactions increase the surface heat flux is partly a function of the heat shield material. Characterization of the catalytic behavior of these materials takes place in experimental facilities, however there is a dearth of detailed computational models for the fluid dynamic and chemical behavior of such facilities. A numerical model coupling finite rate chemical kinetics and high temperature thermodynamic and transport properties with a computational fluid dynamics flow solver has been developed to model the chemically reacting flow in the inductively coupled plasma torch facility at the University of Vermont. Simulations were performed modeling the plasma jet for hybrid oxygen-argon and nitrogen plasmas in order to validate the models developed in this work by comparison to experimentally-obtained data for temperature and relative species concentrations in the boundary layer above test articles. Surface boundary conditions for wall temperature and catalytic efficiency were utilized to represent the different test article materials used in the experimental facility. Good agreement between measured and computed data is observed. In addition, a code-to-code validation exercise was performed benchmarking the performance of the models developed in this dissertation by comparison to previously published results. Results obtained show good agreement for boundary layer temperature and species concentrations despite significant differences in the codes. Lastly, a series of simulations were performed investigating the effects of recombination reaction rates and pressure on the composition of a nitrogen plasma jet in chemical nonequilibrium in order to better understand the composition at the boundary layer edge above a test article. Results from this study suggest that, for typical test conditions, the boundary layer edge will be in a state of chemical nonequilibrium, leading to a nonequilibrium condition across the entire boundary layer for test article materials with high catalytic efficiencies.

<p>In this thesis, the ripple formation at the interface of SiO2 and Si were studied in a systematic fashion by irradiating the SiO2-Si samples with ultrashort laser pulses under a broad variety of experimental conditions. They consist of di↵erent irradiating laser wavelengths, incident laser energies, translation speeds, translation directions, spot sizes of the laser beam, as well as oxide thicknesses. The ripples produced by laser irradiation are examined using various microscopy techniques in order to characterize their surface morphology, detailed structures, crystalline properties, and so on. For the experiments carried out at ! = 800 nm, the ripples formed on the SiO2-Si sample with an oxide thickness of 216 nm were first observed under optical microscopy and SEM. After removing the oxide layer with HF solution, the surface features of the ripples on the Si substrate were investigated using SEM and AFM techniques. Subsequently, by means of TEM and EDX analysis, the material composition and crystallinity of the ripples were determined. It is concluded that the ripples are composed of nano-crystalline silicon. In addition to the 216 nm oxide thickness, other oxide samples with di↵erent oxide thicknesses, such as 24, 112, 117, 158 and 1013 nm, were also processed under laser irradiation. The ripple formation as a function of the laser energy, the translation direction and the spot size is discussed in detail. Furthermore, the ripples created at the SiO2-Si interface are compared with</p> <p>the LIPSS created on pure silicon samples that were processed under similar laser irradiation conditions. The spatial periodicities of the ripples were evaluated to be in the range of between 510 nm and 700 nm, which vary with the oxide thickness and other laser parameters. For the experiments using the ! = 400 nm laser pulses, it is found that ripples can also be formed at the SiO2-Si interface, which have spatial periodicities in the range of between 310 nm and 350 nm depending on the oxide thickness. The ripple formation at this 400 nm wavelength as a function of the laser energy, the translation speed, and translation direction is considered as well. For the case of ! = 400 nm irradiation, a comparison is also made between the interface ripples on the SiO2-Si samples and the LIPSS on a pure Si sample. Through FIB-TEM and EDX analysis, it confirmed that the ripples were produced in the substrate while the oxide layer maintained its structural integrity. In addition, the ripples are composed of nano-crystalline silicon whose crystallite sizes are on the order of a few nanometers. Apart from irradiating oxide samples with femtosecond laser pulses, which applies to the two cases of ! = 800 and 400 nm mentioned above, oxide samples with an oxide thickness of 112 nm were irradiated with picosecond laser pulses at ! = 800 nm whose pulse durations are 1 ps and 5 ps, respectively. However, no regular ripples can be produced at the SiO2-Si interface while maintaining the complete integrity of the oxide layer.</p> / Master of Applied Science (MASc)

<p>A new electron cyclotron plasma enhanced chemical vapour deposition (ECR-PECVD) reactor has been installed and tested at McMaster University. The focus of this project was the installation of the reactor and the growth of silicon oxide, silicon oxynitride, cerium doped silicon oxynitride and aluminium doped silicon oxide films to test the capabilities of the reactor. Silicon oxide films were prepared with near-stoichiometric compositions and silicon rich compositions. Good repeatability of the growths was seen. An increase in deposition temperature showed stable refractive index and a decrease in the growth rates. Silicon oxynitride films of varying compositions were prepared, and showed a non-uniformity of ~1% and growth rates of ~3.5 nm/min. Films prepared with a low oxygen flow were seen to be nitrogen rich. Although the depositions using Ce(TMHD)4 showed significant cerium incorporation, there was also high carbon contamination. One likely cause of this is the high sublimator temperature used during depositions or a thermal shock to the precursor during initial system calibration. A definitive cause of the carbon contamination has not been established. The cerium films showed strong blue luminescence after post-deposition annealing in N2 above 900° C. A drop in the luminescence was observed at 1100° C and a return of the luminescence at 1200° C. Generally, high cerium incorporation was associated with higher total luminescence. Al(THMD)3 was evaluated as an aluminium precursor for Al-doped silicon oxide films. The films showed aluminium content up to 6% demonstrating the viability of using Al(THMD)3 as a Al doping precursor.</p> / Master of Applied Science (MASc)