<p> A number of silicate compounds BaTSiO4 (T = Co, Mg, Zn), Na0.5K0.5GaSiO4 and Sr1-xCaxBeSiO4 (x = 0.0 ~ 0.4) have been characterized by a combination of diffraction techniques. These compounds crystallize with the same (√3XA, C) superstructure of the hexagonal kalsilite (KAlSiO4) structure and belong to the large structural family of stuffed tridymite-derivatives. Their crystal structures have been refined by using powder neutron data (BaTSiO4, T = Mg, Zn), powder X-ray data (Na0.5K0.5 GaSiO4) and single crystal X-ray data (BaCoSiO4 and Sr1-xCaxBeSiO4, x = 0.0 and 0.27). This study shows that these kalsilite-like structures can accommodate cavity and tetrahedral atoms of variable sizes by relatively minor framework distortions and atomic displacements. The formation of the (√3XA, C) superstructure can be correlated with the relative sizes of the tetrahedral and cavity atoms.</p> / Thesis / Master of Science (MSc)

<p> The crystal structure of k2SnBr6 has been reinvestigated using single crystal x-ray diffraction techniques. Three dimensional intensity data obtained photographically have been used to refine the structure, by the least square analysis. The structure is found to be slightly distorted from the regular cubic k2PtCl6 structure in a manner similar to K2TeBr6. The Sn-Br bond is found to be 2.601 A. </p> <p> The structure of k2SnBr6 is found to be monoclinic with space group P21/n and a = 7.435 ± 0.017 A, b= 7.437 ± 0.017 A, and c = 10.568 ± 0.006 A. </p> <p> A review of other crystals with similar structure is included in this thesis included the theory of x-ray diffraction and crystal structure as applicable to the present problem is discussed briefly. </p> / Thesis / Master of Science (MSc)

<p> The lattice parameters and crystal symmetry of silane (SiH4) are examined by X-ray powder diffraction. Comparisons are made with vibrational spectrum and birefringence measurements and with respect to an order-disorder transition between the two solid phases of silane.</p> / Thesis / Master of Science (MSc)

<p> Following the introduction to the field of lasers and the theories of laser oscillations in the light output, it is pointed out that calculations involving existing theories yield oscillation periods in excess of the period observed for our crystal. To account for this disagreement, the thesis proposes the inclusion of the additional loss terms of scatter and diffraction augmenting the transmission loss. The theory of Birnbaum Stocker and Welles (BSWl) is extended to include these additional loss mechan- isms and the oscillation period predicted, using the mea- sured values of these parameters is in good agreement with the. observed oscillation period. </p> / Thesis / Master of Science (MSc)

During the COVID-19 outbreak, PCR tests were widely used for large-scale testing and screening. Yet, this technique requires bulky and time-consuming procedures to prepare the samples collected from the patients before their analysis by well-trained experts with expensive and specific equipment. PCR is therefore not competitive as a technique of detection for a widespread and rapid use in point-of-care sites. Thus, the COVID-19 pandemic highlighted the need for cheap and easy-to-implement biosensors. Surface plasmon resonance based sensors were suggested as a promising alternative in recent years. Indeed, they enable real-time and label-free detection of a wide range of analytes. That explains their widespread use in various fields of applications such as pharmacology, toxicology, food safety, and diagnosis. This thesis proposes and demonstrates a new plasmonic configuration of detection, which can address challenges posed by point-of-care settings. The gratings used as transducers in this configuration were fabricated based on laser interference lithography combined with a nanoimprinting process. The responses of these nanostructures interrogated by a p-polarized light beam result in a transfer of energy between two diffracted orders over an angular scan. This optical phenomenon termed as “optical switch”, was theoretically and experimentally investigated and optimized. The principle of detection based on this specific configuration was demonstrated for the detection of small variations in the bulk refractive index with solutions comprised of different ratios of de-ionized water and glycerol. A limit of detection in the range of 10−6 RIU was achieved. In addition, preliminary bio-assays obtained by combining this configuration with a functionalization are presented and demonstrate the selectivity and the potential of this new plasmonic configuration for biosensing applications. This thesis work paves the way for the use of the optical switch configuration as a biosensor aligned with low-cost manufacturing and relevant for diagnosing in point-of-care sites.

Laser Engineered Net Shaping (LENS™) is a rapid-manufacturing procedure that involves complex thermal, mechanical, and metallurgical interactions. The finite element method (FEM) may be used to accurately model this process, allowing for optimized selection of input parameters, and, hence, the fabrication of components with improved thermo-mechanical properties. In this study the commercial FEM code SYSWELD® is used to predict the thermal histories and residual stresses generated in LENS™-produced thin plates of AISI 410 stainless steel built by varying the process parameters laser power and stage translation speed. The computational results are compared with experimental measurements for validation, and a parametric study is performed to determine how the thermo-mechanical properties vary with these parameters. Thermal calculations are also performed with the code ABAQUS® to evaluate its potential use as a modeling tool for the LENS™ process.

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A covariant form of Hamilton's Principle of Stationary Action is formulated and used to solve the general eiconal equation describing the wave function of light in a medium carrying ultrasound. Tensor notation is reviewed and the tensor form of Maxwell's equations is developed. Boundary equation that the field quantities must satisfy in order for the variation of Hamilton's action integral to be stationary are determined and used to form the generalized eiconal equation of geometrical optics. The rays are introduced and through a canonical transformation the eiconal for the diffracted medium is solved and plotted.