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Thesis advisor: Krzysztof Kempa / “Simulations are like an experiment but on a computer.” – K. Kempa. Powerful ideas can be explored in immense detail and unmatched flexibility through computational resources. Combined with the beauty of electromagnetics, worlds of situations and problems can be uncovered. Of the many interesting phenomena available to study, a relatively recent explosion of engineered plasmonic materials has benefitted greatly from numerical breakthroughs in simulating Maxwell’s equations. Using these tools on novel metamaterial systems, composite materials with precisely designed structural features, the analysis and optimization probes the unique capabilities they have interacting with light. Example phenomena from this work includes fundamental principle breaking, extraordinary optical transmission, negative refraction, and superconductivity enhancement. The systems that harbor such outstanding feats fall into the umbrella term of metamaterials, each with distinct geometry and contrasting electrical properties that allow for an engineered control of the effective structural dielectric function. As the response to electromagnetic radiation, manipulating the dielectric function is key to creating and discovering the effects that control light, without changing any chemistry. This work scales pedagogically through the different types of metamaterials, beginning first with 2D planar checkerboard structures with highly non-linear percolation. In combination with spoofed plasmonics, the longstanding symmetry of the Babinet principle is challenged. Layers of checkerboards are then stacked and translated to create subwavelength gaps for which plasmonic coupling between layers aids in optical transmission. In fact, there is similar physics controlling other layered quasi-complementary structures shown by comparison to experimental transmittance data. A further stage introduces photonic crystals constructed out of 3D periodic lattice of nanoparticles. Photonic band structure calculations for properly designed systems suggest the possibility of bandwidths of the IR spectrum where the crystal has a negative refractive index. Such a material property allows for the invention of lenses that beat the diffraction limit, applicable to subwavelength imaging. Lastly, non-local extensions to plasmonics are theoretically worked into expressions for superconductivity, creating a resonant anti-shielding effect, in composite topological crystal/superconductor layered arrangements. Applying this to known topics, like Bi2Se3 and MgB2, shows significant boost to electron pairing and thus rises in superconducting critical temperature. Central to all the systems and effects explored are the modifications made to the dielectric function of each effective medium. Supported by electromagnetic simulations and theoretical efforts, the listed engineered materials transform the dielectric environment purposefully to originate the mentioned exotic optical phenomena. / Thesis (PhD) — Boston College, 2023. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Physics.

Water and a copper sulfate (CSL) solution at 27, 57 and 88°C; steam pasteurization and dielectric heating were analyzed on their effect in reducing microbial load (APC) and Salmonella Typhimurium on inshell pecans (Carya illinoinensis). The CSL solution (more effective than water alone) reduced APC by 1.5 (300 s), 2 (60 s) and 4.0 (60 s) log CFU/g at 27, 57 and 88°C, respectively; and Salmonella by 3.0 log at 27°C in 60 s. Steam reduced APC by 3.7 log in 180 s and Salmonella by 4.0 log CFU/g in 30 s. Dielectric treatment reduced APC by 3.0 log and Salmonella by 4.5 log CFU/g in 60 s. Most treatments had no effect on the pecan shell or the nut quality, except for dielectric heating, which gave a slight "roasted" or "burnt" flavor to the nuts. This study showed that a proper antimicrobial-hot water treatment, steam or dielectric heating will be effective in "pasteurizing" pecans, resulting in a safe and wholesome product.

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<p> High-density plasma technology is becoming increasingly attractive for the deposition of dielectric films such as silicon dioxide, silicon nitride and silicon oxynitride. In particular, inductively coupled plasma chemical vapor deposition (ICP-CVD) offers several technological advantages for low temperature processing over other plasma-enhanced chemical vapor deposition (PECVD), such as higher plasma density, lower hydrogen content films, and lower cost. A new ICP-CVD system has been set up at McMaster University. </p> <p> The project focused on the calibration of this system and the establishment of its performance characteristics. A combination of 0 2/ Ar/SiH4 gases was used to deposit Si02 thin films on single-crystal Si wafers under various conditions. Substrate temperatures were calibrated from 200 to 400°C, and were found to linearly relate to heater temperatures. Calibration of the minimum reflected power showed that the ICP source is efficient to generate a stable plasma for 02, N2 and Ar gases within a wide range of flow rates from 3 to 1 OOsccm, while the reflected power remains below 10 Watts. Uniformity was found to be sensitive to many factors. Under optimal conditions, uniformity could be controlled better than 1% with a good shape of thickness distribution. The refractive indexes of the deposited films were measured with ellipsometry and showed an inverse relation with the ratio of oxygen to silane flow rate. </p> / Thesis / Master of Applied Science (MASc)