<p>SiGe thin film alloys are the subject of intense interest in semiconductor research. The extent of bond length dependence upon alloy composition in these materials is a subject of some debate in the literature. This work details our Si and Ge K-edge extended x-ray absorption fine structure (EXAFS) measurements on a selection of strained and relaxed single crystal SiGe alloys. Constrained, simultaneous fits to the EXAFS of multiple spectra from both Si and Ge K-edges were performed in order to extract quantitative data for bond lengths and co-ordination numbers.</p> <p>The first analysis was performed solely using EXAFS spectra from relaxed alloys grown on Si. The results indicate that first shell bonding in relaxed SiGe alloys adheres to a weakly mixed Pauling-Vegard regime, showing detectable composition dependence (bond length change of 0.03 A over the full composition range). In the</p> <p>notation of the CT theory of Thorpe and co-workers <em>(Phys. Rev. </em>B 46,15872 (1992)), the topological rigidity parameter, a** is found to be 0.70+0.09 -0.03</p> <p>The results are compared to other theoretical and experimental results, and alternate models to the CT theory are explored. Ordering effects in the co-ordination numbers are also evaluated.</p> <p>The second analysis was performed on a small range of complimentary strained and relaxed samples, to investigate the hypothesis that strained SiGe alloys on Si(100) have shorter bond lengths than relaxed samples. The results of the analysis suggest that strain accommodation is at least partly accomplished by bond length contraction.</p> <p>Finally, the Appendix details a complimentary project in near-edge x-ray absorption fine structure measurements of SiGe alloys. Specifically, a strain-induced polarisation dependence in the Si K-edge spectra of SiGe films is explored with measurements of a large range of samples. The results indicate that the source of the polarisation is not yet fully understood.</p> / Master of Engineering (ME)

<p>[Missing page 58]</p> / Doctor of Philosophy (PhD)

<p>Austenite growth in the intercritical annealing of ternary (Fe-C-Mn) and quaternary (Fe-C-Mn-Si) dual phase steels is studied. The growth process is modelled assuming local equilibrium at austenite/ferrite interfaces and diffusion control. An isothermal anneal starting with a ferrite-pearlite mixture is examined. Growth proceeds in four stages: (1) austenite nucleation from pearlite (which is not examined); (2) attainment of uniform carbon activity within each austenite particle; (3) attainment of uniform carbon activity over large distances in the material (e.g., 100 (mu)m); and (4) austenite growth controlled by diffusion of alloying element(s) in ferrite. The last stage is the only stage where significant alloying element partitioning occurs. This leads to the centre of each austenite particle retaining its initial alloying element concentration while the rim is enriched or depleted in alloying element depending on the value of the alloying element diffusion coefficient. This non-uniform concentration profile is associated with the end of austenite growth and results in a volume fraction greater than the equilibrium volume fraction. Full equilibration of the austenite does not occur in practical time periods. The preceding description applies to all cases treated. Material initially homogeneous with respect to alloying elements was examined: (1) for a planar geometry; (2) for a spherical geometry; and (3) with different size particles. A material initially non-uniform with respect to alloy element (e.g., having an initial sinusoidal fluctuation of alloying element) was examined for the case of: (1) a wavelength comparable with spacing between austenite particles; and (2) longer wavelengths. The assumption that local equilibrium established in short times (100 s) was verified with Scanning Transmission Electron Microscope (STEM) observations. STEM and microprobe analysis data also qualitatively verified predicted Mn concentration profiles for long (50 h) anneals. Volume fractions predicted were in reasonable agreement with observed and published volume fraction data.</p> / Doctor of Philosophy (PhD)

<p>Lattice disorder produced by heavy ion implantation of cadmium sulphide crystals at 50 K and 300 K has been investigated using Transmission Electron Microscopy (TEM) and Rutherford Backscattering (RBS)/- Channeling techniques.</p> <p>TEM observations of Bi⁺, Ar⁺ and Ne⁺ implanted samples showed that two types of dislocation loops were produced, type I with a Burgers vector b= 1/2 <0001> and type II with a Burgers vector b = 1/3' <1120>. Type II loops were nearly twice as large in size and two to three times greater in number density then type I loops. The large loops of type II were predominantly vacancy loops. Both types of loops lie predominantly in the {1100} and {1120} prism planes. The loop size and number density increased with increasing energy deposited into elastic collisions. For increasing ion dose the loop size increased while the number density decreased.</p> <p>In-situ measurements of the lattice disorder have been made using the RBS/ channeling technique with 0.6 MeV to 2.8 MeV He⁺ channeled along the a- and c-axes of the CdS crystals. The amount of disorder was measured in terms of the areal density of cadmium scattering centers (ND), and the minimum dechanneling yield (xmin) . Measured Nd values were found to be two orders of magnitude lower than theoretical prediction and the Xmin values were about an order of magnitude higher than those calculated assuming randomly displaced scattering centers. The disorder was greater measured along the c-axis than along the a-axis. It was also greater at 300 K than at 50 K. These observations suggest that the lattice distortion is greater in the direction perpendicular to the c-axis. It was also found that Nd increased with increasing E₀, while Xmin values were energy independent over the energy range investigated. These results and the rapid increase in Nd values observed when the crystal is tilted slightly away from the channeling direction ('Off-Axis' measurements) are consistent with the presence of dislocation loops as observed by the TEM.</p> / Doctor of Philosophy (PhD)

Protective coatings is used to enhance the corrosion resistance of buried pipelines. However, the effectiveness of epoxy-coatings may be compromised due to inadvertent presence of surface damage and coating disbondment. Additionally, the disbonded coated panels is expected to be less effective than that of scratched or un-defected panels. This research was designed to evaluate the coating performance of FBE and hybrid epoxy in simulated Arabian Gulf water and synthetic Sabkha. The influence of coating damage and disbondment on corrosion resistance was also investigated. Results of this research indicated a reduction in the adhesion bond between the coatings and substrate. The electrochemical impedance measurements demonstrated the need for an appropriate interpretation of results when this technique is used. The corrosion current density measurements indicated that both media are corrosive. Protective coatings under investigation did not show any blistering effect, loss of adhesion or color change under test conditions, thus reflecting their excellent corrosion resistance property.

<p>Thin films prepared by electrochemical and physical vapor deposition (PVD) methods were investigated for corrosion protection of metals and alloys. Various electrochemical methods were developed, such as electrophoretic deposition (EPD), electrolytic deposition (ELD) and combined methods. EPD method has been developed for the deposition of polymer films, including poly(2-vinylpyridine) (PVP) and co-polymer poly(4-vinylpyridine-<em>co</em>-butyl methacrylate) (PVPBM). The method involved the electrophoresis of protonated polymer macromolecules, base generation at the cathode surface, charge neutralization and deposition of water insoluble polymer films. Nanostructured CeO₂ films were prepared by cathodic ELD and EPD. Cathodic ELD involved electrosynthesis of CeO₂ nanoparticles in the cathodic reaction and film formation. New dispersion agents were developed for CeO₂ particles for application in EPD processes. The kinetics of ELD and EPD and deposition mechanisms were investigated.</p> <p>Composite polymer-CeO₂ films were deposited using various strategies, based on ELD or EPD of CeO₂ and EPD of polymers. The composite films were deposited as monolayers, multilayers or materials of graded composition. The deposition yield and film composition can be varied.</p> <p>The composite films were studied by electron microscopy, X-ray diffraction, thermogravimetric and differential thermal analysis. Electrochemical testing showed that polymer and composite films provided corrosion protection of stainless steel substrates.</p> <p>Corrosion protection properties of coatings deposited on commercial AMPCO and TZM alloys was investigated. CrN, CrN-D, and TiC were deposited by PVD method. Ni coatings were deposited by electroplating. The analysis of Tafel plots and impedance spectroscopy data showed that CrN and CrN-D coatings deposited by PVD showed better corrosion protection of AMPCO and TZM alloys, compared to TiC and Ni coatings. The results of this investigation pave the way for the fabrication of novel coatings with advanced corrosion protection, wear and mechanical properties, using combined PVD and electrochemical methods.</p> / Master of Applied Science (MASc)

<p>Proton exchange membrane fuel cells (PEMFC) are a technology of high interest for the automotive and power generation industry. The catalyst layer plays a critical role in fuel cells as it is responsible for catalyzing hydrogen oxidation and oxygen reduction to generate electricity. The current challenge in catalyst development is to produce highly active and economical catalysts. This challenge cannot be overcome without an accurate understanding of catalyst surfaces and morphology since the catalytic reactions occur on the surface active sites. Transmission electron microscopy (TEM) is an excellent tool to understand the structures of the nanoparticles down to the atomic level in determining the relationship with the catalyst’s performance in fuel cell applications. Platinum (Pt) is one of the best commercially available catalysts for PEMFC due to its highly active, inert, and relatively stable properties. However, Pt is a rare precious metal due to its low abundance and high demand. Further research is aimed at developing highly active and more economical catalysts in order to mass produce PEMFC. A strategic approach is to use platinum bimetallic alloys, which greatly reduce the platinum loading as they enhance the oxygen reduction reaction. A detailed understanding of the nanoparticle surface is critical as the catalyst surface strongly determines its catalytic activity. Furthermore, another challenge in utilizing fuel cells is the life-time of the catalysts. It is known that electrochemical cycling affects Pt alloys. As a result, the understanding of the effect of electrochemical treatments on the catalyst’s v morphology and composition is key to improving the fuel cell’s performance and durability. This thesis demonstrates that through the use of TEM, useful insights regarding the morphology, surfaces, and compositions of the catalysts can be gained and contribute to the improvement in catalyst development for next generation fuel cells.</p> / Master of Applied Science (MASc)

<p>No comments. Thanks.</p> / <p>Advanced electrodes based on MnO₂ for the electrochemical supercapacitor (ES) application have been fabricated using electrochemical and chemical methods.</p> <p>Electrosynthesis method has been utilized for the in-situ impregnation of manganese dioxide in commercial Ni plaque current collectors. Dipping-reduction, cathodic galvanostatic and reverse pulse electrosynthesis methods were investigated. The material loading was varied by the variation of the number of the dipping-reduction procedures in the chemical precipitation method or by the variation of charge passed in the electrochemical methods. The results obtained by different methods were compared. The dipping-reduction method offered the advantage of higher specific capacitances (SCs) at high scan rates, whereas other methods allowed higher material synthesis rate.</p> <p>Cathodic electrolytic deposition (ELD) has been utilized for the fabrication of Ag-doped MnO₂ films. The Ag-doped MnO₂ films showed improved capacitive behavior and lower electrical resistance of 0.6 Ohm compared to pure MnO₂ films. The highest SC of 770 F g^-1 was obtained at a scan rate of 2 mV s^-1 in the 0.5 M Na₂SO₄ electrolyte.</p> <p>Electrodes for ES application were fabricated by cathodic electrodeposition of MnO₂ on CNTs, which were grown by chemical vapor deposition on stainless steel meshes. The MnO₂-CNT nanocomposites showed excellent capacitive behavior and low electrical resistance of 0.5 Ohm.</p> <p>Electrophoretic deposition (EPD) has been utilized for the deposition of composite MnO₂-multiwalled carbon nanotube (MWCNT) films for the ES application. Dopamine (DA), caffeic acid (CA), tyramine (TA), gallic acid (GA), polyacrylic acid (PAA) and pyrocatechol violet (PV) were shown to be effective and universal charging additives, which provide stabilization of MnO₂ nanoparticles and MWCNTs in the suspensions. The influence of the structure of the organic molecules on their adsorption on the oxide nanoparticles has been investigated. We discovered that the number and site of OH group for dispersants were essential for the adsorption on oxide materials, and the number of aromatic ring was important for the adsorption on carbon materials. Pure CNT films were deposited using PV as a dispersant, which was the first time in literature to prepare pure CNT film using a dispersant. SCs decrease with increasing film thickness. SCs of composite MnO₂-MWCNT obtained using EPD were in the range of 350-650 F g^-1 depending on material loadings.</p> / Doctor of Science (PhD)

<p>Ni-Fe alloys have been used in industrial applications over the past century due to their unique mechanical and magnetic properties. Currently, researchers are interested in enhancing the performance of Ni-Fe alloys by modifying their microstructure. An example of this would be the use of ultra-fine nanocrystalline Ni-Fe alloys for magnetic shielding products that are uniquely shaped and cost effective. These nanocrystalline materials usually exhibit good soft magnetic properties, such as high saturation magnetization, low coercivity and good magnetic permeability. The following study has been devoted to the magnetic properties of electrodeposited nanocrystalline Ni-Fe alloys.</p> <p>The structure and texture of electrodeposited Ni-Fe alloys was studied by two-dimensional XRD. The Ni-Fe alloys with Fe content from 24.9at. % to 54.2at. % were comprised exclusively of the FCC phase. For 60.2at. % Fe sample, a mixed phase of BCC and FCC structure was found. The lattice parameter increased with increasing Fe content until 54.2at. %, and then decreased due to the presence of BCC structure. The increase in lattice parameter was attributed to the iron replacement of nickel in the Ni crystalline lattice. Texture analysis shows that all Ni-Fe alloys with different Fe content exhibit the fiber texture with a major component of theaxis aligned perpendicular to the sample plane. A second component iswith a significantly lower volume fraction. It also shows that the Ni-Fe alloy with 44.2at. % Fe exhibits the highest volume fraction of random orientation.</p> <p>Magnetic measurements showed that all Ni-Fe nanocrystalline alloys exhibit soft magnetic properties with narrow hysteresis loops. The saturation magnetization increased linearly with increasing Fe content. The magnetization at T = 2K were slightly higher than that at T = 298K. The lowest coercivity~6Oe was obtained at 44.2 at. % Fe content.</p> <p>Good agreement between Random Anisotropy Model (RAM) theory and experimental data for all the Ni-Fe alloys has been obtained. By fitting the high field magnetization curve with the Law of Approach to Saturation (LATS), the magnetocrystalline anisotropy constant (K_eff) were obtained. K_eff decreased with increasing temperature. Also, the ferromagnetic exchange lengths for each Ni-Fe alloy were calculated. They are 26nm, 21nm, 19nm, 18nm, 17nm for Ni-24.9at.%Fe, Ni-33.1at.%Fe, Ni-44.2at.%Fe, Ni-54.2at.%Fe, Ni-60.2at.%Fe at room temperature, respectively. The exchange lengths are larger than the average grain size (D) for all of the samples. The results confirmed the feasibility of Random Anisotropy Model for the prediction of the magnetic properties of the nanocrystalline Ni-Fe alloys fabricated by electrodeposition.</p> / Master of Applied Science (MASc)

<p>Solid oxide fuel cells are an efficient method of converting hydrocarbon fuels to electrical power. However, due to some problems with poisoning, these have made no headway in the energy market. The evaporation of chromium oxides from metallic current collectors causes rapid degradation of the cells on the cathode side. It has been shown that spinel coatings reduce the effects of chromium oxide evaporation. In this thesis, two spinel systems are explored for potential application. Cobalt-manganese spinel is a stable spinel which have a wide range of composition, while remaining sufficiently conductive. Copper-manganese spinel, which is much more conductive than cobalt-manganese, is slightly less stable, but nonetheless a candidate. All components of the spinels explored can be electrodeposited from aqueous solutions, at room temperature. By controlling the concentrations of metallic ions, and other additives, coatings can be deposited on interconnecting plates with reproducible results. The newly coated interconnects can be oxidized in-situ. For characterization, the samples for this thesis were oxidized at 800°C. Two substrate materials were used, ferritic stainless steel and a chromium-iron alloy. Stainless steel substrates showed good coating adhesion, but high concentrations of iron were found in the spinel structure. Chromium alloy substrates were better protected by spinel coatings. However, nitride formation at the substrate interface caused localized delamination of the coating. It was shown that plating operations can be scaled up to 10 cm by 10 cm plates, with little modification of the processes used.</p> / Master of Applied Science (MASc)