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    Investigation of Magneto-Optical and Photonic Properties of Plasmonic Tungsten Oxide and Alkali Tungsten Bronze Nanocrystals
    (University of Waterloo, 2026-03-13) Jaics, Gyorgy J.
    Emerging quantum phenomena in multifunctional materials are reshaping the conceptual and technological foundations of modern condensed matter physics, driving the rapid adoption of plasmonic materials within quantum, optoelectronic, and photonics industries. Plasmonic semiconductor nanocrystals, characterized by collective charge carrier oscillations that are intrinsically linked to their electronic structure, provide a powerful platform for exploring quantum and photonic functionalities beyond conventional noble metal-based plasmonics. After introducing the fundamental principles of localized surface plasmon resonances (Chapter 1) and experimental methodologies (Chapter 2), in this dissertation, I experimentally examined the electronic structure, magneto-optical properties, and photonic applications of oxygen-deficient, doped plasmonic semiconductor metal oxide nanocrystals (NCs), using magnetic circular dichroism (MCD) spectroscopy. First, I investigated the electronic structure of compositionally and electronically com- plex semiconductor NCs, focusing on oxygen-deficient tungsten oxide (WO3-x) NCs. The motivation of this study (presented in Chapter 3) was to revisit and elucidate the electronic structure of plasmonic compound semiconductor nanostructures that have recently been reported to exhibit unique and promising plasmonic properties based solely on conventional optical absorption data. Unlike conventional optical absorption spectroscopy, MCD spectroscopy, which utilizes excitation by circularly polarized light in an external magnetic field, enables spectral specificity and sensitive detection of plasmon resonances. Using variable- field and variable-temperature MCD spectroscopy, I demonstrated that the broad optical absorption bands (visible-to-near infrared region) of colloidal plasmonic WO3-x NCs originate from intraionic W5+ ligand-field transitions at higher energies (visible region) and free-carrier-related plasmonic absorption at lower energies (near infrared region), which spectrally overlap despite fundamentally different electronic origin. The results of this study demonstrated that caution must be exercised when assigning the absorption spectra of complex semiconductor NCs, particularly those containing transition-metal ions, to LSPR. Consequently, a sizeable portion of the literature on plasmonic semiconductor NCs should be re-examined and their conclusions revisited. With that, MCD spectroscopy is also demonstrated to serve as an effective methodology for reliable assignment and detailed investigation of LSPR in NCs. Importantly, owing to their electronic band structure, plasmonic semiconductor NCs support the coexistence and interaction of plasmonic oscillation with other quasiparticles, enabling intrinsic (interface-free) interactions such as plasmon-exciton, plasmon-spin, vii plasmon-phonon, and plasmon-magnon coupling. Owing to the non-resonant nature of plasmonic and interband (excitonic) absorption in doped plasmonic semiconductor NCs, realization and modulation of intrinsic plasmon-exciton coupling are challenging. In Chap- ter 4, I investigated the impact of NC geometry on the intrinsic plasmon-exciton interactions, using colloidal Cs-doped non-stoichiometric tungsten oxide (Cs:WO3-x) hexagonal prisms. With the aid of variable-field and variable-temperature MCD spectroscopy, I observed that NC aspect ratio as controlled geometric parameter enables the modulation of excitonic Zeeman splitting mechanism in the presence of external magnetic fields. Specifically, while for low-aspect-ratio nanostructures (nanoplatelets) the splitting of excitonic states are dictated by the spin of localized carriers (anomalous Zeeman splitting), the high-aspect-ratio nanostructures (nanorods) exhibit free-carrier-induced splitting (normal Zeeman splitting) of the NC excited states. The results of this study demonstrate that manipulation of the aspect ratio of degenerately doped semiconductor NCs can allow for unique control of their excitonic magneto-optical properties, providing promising opportunities for further fundamental investigations and potential applications of this phenomenon in quantum technologies. Owing to their highly tunable free carrier densities and thus plasmon energies, plasmonic semiconductor NC enable a plethora of technologically relevant photonic and optoelectronic applications. In this context, we investigated the applicability of plasmonic colloidal WO3-x and Cs:WO3-x NCs for near-infrared sensing in metal-semiconductor- metal (MSM) photodetector devices, as presented in Chapter 5. The NCs, as photoactive components, were drop-cast on the active region of the detector. In the presence of the NCs, significant enhancements of photoresponse (by up to a factor of ∼2.5) were observed. The results of this work demonstrated the potential for a cost-effective and scalable method exploiting tailored plasmonic semiconductor NCs to improve the performance of NIR optoelectronic devices, such as enhanced speed and sensitivity of receivers in optical fiber communications or increased range and reliability of light detection for autonomous vehicles. Owing to their unique electronic band structures, plasmonic semiconductor nanocrystals can harness visible-NIR light to facilitate chemical reactions with high efficiency. Upon resonant photon absorption, their localized plasmon resonances generate strong electro- magnetic near-field enhancement and energetic charge carriers, which enhance light ab- sorption, foster charge carrier separation and injection, and promote surface reaction pro- cesses. This combination of optical and electronic effects allows for a precise control over photocatalytic activity, making these nanocrystals highly tunable platform for visible- and NIR-light-driven chemical transformations. In Chapter 6, I investigated the plasmonic photocatalytic activity of post-synthetically surface-modified WO3-x NCs, using Rhodamine 6G (Rh6G) dye as model compound. In this study, we observed an approximately 3.3 times improvement in the plasmonic photocatalytic activity of ligand-free WO3-x NCs, attributed to a higher surface accessibility of Rh6G dye. Through post-synthetic annealing in air at elevated temperatures (350-800°C), we modulated the oxygen-deficiency (and thus the free carrier density and plasmon resonance) of the NCs. As a result of the high temperature treatment, we observed sintering and large specific surface area of NCs, as evidenced by scanning electron micrographs and BET analysis, respectively. However, in nanostructures with large specific surface area, adsorption processes are inevitable and can co-exist with photocatalytic degradation processes, which, in the literature, is often not accurately accounted for. In this study, we used a combination of electronic absorption spectroscopy, surface area analysis, and electrospray ionization mass spectrometry, and electrospray ionization mass spectrometry, and examined the coupling be- tween the adsorption and plasmonic catalytic activity. The results of this work show that the contribution from adsorption processes can be modulated via post-synthetic annealing while retaining coupling with the photocatalysis.
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    An Investigation of the Effects of Interfaces on the Fracture Resistance of 3D Printed Biopolymer Nanocomposites
    (University of Waterloo, 2026-03-13) Patil, Haresh
    Biopolymer-based bone-inspired nanocomposites are potential alternatives to conventional allografts for reconstruction of segmental bone defects if engineered to be mechanically competent and osteoconductive. The high surfaces area to volume fraction of nanoparticles contributes to enhance the mechanical properties and cell-material interaction of bone-inspired nanocomposites. Nanocomposites prepared by dispersing appropriate volume fractions of nanohydroxyapatite (nHA) into a resorbable/degradable biopolymer resin matrix can mimic the inorganic and organic phases of bone composition, respectively. Such nanocomposites mixed with relevant photoinitiator can be used as 3D printing feedstock for fabricating patient specific synthetic grafts. Direct ink writing (DIW) is an effective material extrusion 3D printing method that offers flexibility to fabricate complex parts using diverse materials and programable deposition of the extruded feedstock (raster) allows the user to manipulate the mechanical properties of a printed part. Free radical polymerization of the nanocomposite matrix upon exposure to ultraviolet (UV) light of appropriate intensity cures the deposited raster during DIW printing and also bonds the newly deposited raster with a previously cured raster. Fracture resistance is an important mechanical attribute for bone substitutes in order to avoid catastrophic failure while enduring physiological loading after defect reconstruction. Natural bone has acquired remarkable fracture resistance and mechanical properties through its hierarchically organized microstructure. Mimicry of such microstructure is a novel approach in 3D printing to enhance the mechanical properties of the printed structures. This thesis reports upon an experimental investigation of photocurable bone-inspired nanocomposite biomaterials towards the goal of achieving robust DIW-printed structures. The aim was to enhance fracture resistance of the structures fabricated using these nanocomposites. The goal was achieved by proposing and testing approaches inspired by bone. Nanocomposite rasters were deposited and simultaneously UV cured in concentric layers on a rotating mandrel bed of a custom designed and built DIW printer. Multilayer nanocomposite microstructures were achieved partially mimicking the microstructure of lamellar bone. Free radical polymerization of the nanocomposite rasters resulted in detectable interfaces in the printed microstructures because of differences in crosslink density. Each printed microstructure revealed distinct morphology of interfaces. The contributions of these interfaces and the resulting microstructures on mechanical properties and fracture resistance of the nanocomposites were further evaluated with other printed microstructure configurations. The printed anisotropic nanocomposite microstructures showed higher fracture resistance than the isotropic cast control with marginal reduction in flexural strength and modulus. Fracture testing results indicated that weak interfaces in the printed microstructures dissipated a portion of mechanical energy and contributed towards enhancing the fracture resistance of nanocomposite, especially crack stability. Fracture resistance of these nanocomposites can be tuned by altering the morphology of the interfaces and therefore the microstructure using DIW printing. Crosslink density significantly contributes to mechanical properties of UV curable resins. In another approach, crosslink density of nanocomposite matrix compositions was altered by changing composition and additional functionalization. Biopolymer functionalization improved the crosslink density of the nanocomposites and exhibited flexural properties in the recommended flexural property range of bone cement according to ISO-5833 standard. Higher crosslink density of functionalized biopolymer improved resistance to crack growth initiation but induced brittle fracture behaviour. Contrarily, the addition of the functional oligomer (tri-glycerol diacrylate- TGDA) to nonfunctionalized biopolymer matrix functioned as a plasticizer in the crosslinked network of biopolymer and enhanced the crack growth resistance of 3D printed nanocomposite by three (3) folds. The added oligomer also contributed to enhance the shape holding and morphology of interfaces in both functionalized and nonfunctionalized biopolymer nanocomposites. Alteration to crosslink density of nanocomposite matrix significantly influenced the mechanical properties of the interfaces and fracture resistance of DIW printed structures. Finally, in an effort to further enhance the fracture resistance, microstructures were printed using coextrusion of functionalized and non-functionalized biopolymer nanocomposites, principally to organize discrete mechanical phases in the microstructures in addition to the preexisting interfaces. The combination of functionalized and non-functionalized biopolymer nanocomposites with novel coextrusion printing significantly improved the fracture resistance of brittle functionalized biopolymer nanocomposites from single point fracture toughness behaviour to rising resistance curve behaviour. High magnification images of the fractured surfaces indicated that the plastic deformation at the softer nanocomposite phases in the coextruded microstructures dissipated mechanical energy and enhanced the fracture resistance. However, interfaces were not detected at the intersection wall of core-shell in coextruded raster. The custom-built mandrel bed DIW printer (SkelePrint) along with its tailored modifications, demonstrates strong potential for fabricating complex bioinspired concentric-layer structures with functionally graded properties. The findings from this thesis provide key insights into the role of interfacial bonding in DIW-printed structures and its influence on mechanical performance of printed structure. These findings will foster a path for designing robust, bone-mimicking nanocomposite grafts with tunable mechanical properties, advancing their applicability in bone tissue engineering.
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    Characterizing Tele-optometry Users: Demographics, Refractive Error Profiles, and Visit Patterns Across a Multi-Site Private Practice
    (University of Waterloo, 2026-03-13) Rauniyar, Nutan
    Introduction Tele-optometry has emerged as a valuable model for delivering eye care remotely, enabling patients to receive vision assessments and consultations. While its use has expanded rapidly, especially during the COVID-19 pandemic, there remains a limited understanding of who accesses these services, the types of refractive error diagnosed remotely, and the patient visit patterns over the years. Purpose The purpose of the study is to describe the population demographics, characteristics of the refractive error conditions and visit patterns of individuals attending a multi-site private tele-optometry clinic in British Columbia (BC). While comprehensive clinical data including ocular health assessment was available, it is beyond the scope of this study. Method A retrospective descriptive analysis was conducted using de-identified patient data collected from a multi-site, private, tele-optometry clinic in British Columbia (BC), Canada, from 2021 to March 2025. The data analyzed included demographics (age, sex, occupation and geographical location), refractive error (sphere, cylinder, axis), pupillary distance, near addition, prism correction where applicable, and follow-up outcomes. Occupations of subjects were categorized based on the National Occupational Classification (NOC) codes, and the geographical distribution of individuals was analyzed by mapping postal codes to provide a visual representation of service reach. The spherical equivalent (SE) was calculated for each eye to classify refractive error into emmetropia, myopia, and hyperopia, and further subdivided into severity levels of low, moderate, and high. Astigmatism was categorized by the orientation of the cylinder axis as: with the rule (WTR), against the rule (ATR), or oblique. Descriptive statistics and frequency analysis were used to describe the characteristics of the subjects, and a paired t-test was used to compare the refractive data across methods. All analyses were conducted using Excel Version 16.98. Results A total of 6,708 patients were seen across five private clinical practice locations in BC. The mean age was 45.06 ± 17.29 years, with 53.85% female and 46.05% male patients. Most individuals were working adults, with 17.7% characterized as professionals and 14% as trade-skilled jobs. Patients were distributed across all five clinic locations based in BC, with the highest number of individuals residing within BC, followed by Alberta, and a smaller cluster in Saskatchewan, Newfoundland and Labrador, and the Yukon Territory. Myopia was the most prevalent type of refractive error at 50%, followed by emmetropia (28%) and hyperopia (21%). The difference in mean SE between the assessment of refractive error methods was small (<0.15 D), indicating high agreement. With-the-rule (WTR) astigmatism was the most prevalent type. The follow-up visits within 1-year were consistently more common than return visits occurring after 1-year. Conclusion These findings indicate that tele-optometry is being used primarily for convenient, locally accessible care among working-age adults and provides reliable refractive assessments using a synchronous clinical workflow. Broader representation and the analysis of clinical ocular health outcomes are needed in future studies to further understand the role of tele-optometry in comprehensive eye care delivery.
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    Development of a Coupled Hydro-Economic Model to Support Groundwater Irrigation Decisions
    (University of Waterloo, 2026-03-12) Tian, Boyao
    This research develops an integrated hydro-economic modeling framework to support farm-level irrigation decision-making under hydrologic, economic, and climatic uncertainty. The model couples groundwater dynamics, including analytical representations of groundwater-surface water interactions, with crop yield response, and economic valuation to assess trade-offs between agricultural profitability, water use, and long-term sustainability. Conditional Value-at-Risk (CVaR) is incorporated to evaluate downside risk and capture extreme events often overlooked by traditional risk assessment methods. The framework is applied to two contrasting agricultural systems: the High Plains Aquifer (U.S.) and the Saskatchewan River Basin (Canada), representing unconfined and confined aquifers under differing climatic and hydrologic conditions. The results demonstrate that moderate water use strategies often achieve the best balance between profitability and groundwater sustainability, while excessive pumping leads to significant streamflow depletion and reduced long-term benefits. Multi-objective optimization using NSGA-II identifies Pareto-efficient solutions that balance land value, water depth, and streamflow impacts. The model’s simplicity and adaptability make it accessible to farmers, policymakers, and regulators, providing a practical decision-support tool without requiring intensive data or computational resources. Overall, this research contributes to advancing hydro-economic modeling, integrating risk assessment, and promoting sustainable groundwater irrigation management under increasing climate and market variability.
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    Exploring and Visualizing Fact-Based Software Models to Improve Program Comprehension
    (University of Waterloo, 2026-03-12) Ferreira Toledo, Rafael
    Software engineers dedicate significant time and effort to debugging, analyzing, and understanding large, complex software. Such systems can comprise millions of lines of code that implement the program behaviour. When working on such maintenance tasks, the engineer needs to examine the code involved to understand exactly how the program's behaviour is implemented before they can perform any changes or fixes. Depending on the complexity of the program behaviour, the engineer must navigate dozens of lines of code scattered across multiple files to comprehend a single instance of the analysis results. During this code navigation, they pose program comprehension questions that guide the building of a mental model of the program's behaviour. It is well known that answering such queries can be time-consuming, error-prone and cognitively demanding. These risks and demands increase with the complexity of the software under study, for example, when analyzing software that is a software product line (SPL), where an SPL represents a family of related software product variants (e.g., different models of cellphones or vehicles sold by the same company). Many of the above complexities can be addressed by working with a model of code because models are abstractions that are generally smaller, simpler, and more amenable to automated analyses. A software fact-based model is a collection of program facts that reflect the properties and behaviour of a software system. Program facts include source-code entities (e.g., variables, functions), their attributes (e.g., names, source file), and their relationships (e.g., function calls, class inheritance). Program facts can be automatically extracted from source code with an enhanced parser, and the facts can be linked together into a fact-based model of the software system. The resulting collection of software facts represents the system's properties and behaviour as a graphical model that can be managed and queried using graph database technologies. Graph database systems and their native features enable efficient and optimal storage, querying, and visualization of the software fact-based model. Software queries and analyses can be expressed using the database's query language. However, writing common queries from scratch can be repetitive and time-consuming, and, for large and complex queries, it can be error-prone. This thesis investigates whether fact-based software modelling and analysis can improve program comprehension of software systems, including variable systems. This thesis makes three contributions: (1) identifying the program-comprehension questions that software fact-based models can support, (2) designing a query interface that facilitates program-comprehension questions and supports incremental exploration of query results, and (3) developing an efficient visual encoding of results of queries on an SPL model. We evaluated how well fact-based models can answer program-comprehension questions. Previous studies categorized program comprehension questions, but primarily focused on code-based questions rather than model-based questions. We performed a literature review to identify program-comprehension questions that can be posed to fact-based models. We correlated engineers' information needs with the information that fact-based models supply through a comprehensive analysis of previous works on program comprehension questions and graph visualization. Finally, we demonstrated that 38 program comprehension questions could be answered by a fact-based model by expressing them as Cypher queries over a Neo4j factbase. Secondly, we studied how to improve the engineer's experience in understanding program facts through program-comprehension query templates and follow-up queries. We extended Neo4j Browser to support initial program-comprehension queries and follow-up queries over fact-based model elements, giving users greater control and precision in their exploration of the model. We conducted a user study comparing the use of our enhanced Neo4j Browser with a standard code editor, and it shows significant gains in users' efficiency and reduced mental effort during program-comprehension tasks. Finally, we studied how to improve an engineer's comprehension of variable results from a fact-based analysis of an SPL. Analyzing an SPL model produces variable results, where each result may apply to some product variants and not others (e.g. if the analysis refers to feature-specific code). Variable analysis results are typically represented by annotating each result with a presence condition (PC), where the PC is a propositional formula that represents the product(s) for which the result holds. Thus, interpreting the variable analysis results of an SPL model involves determining the program variant (or group of variants) that applies to specific results, which can be error-prone and cognitively demanding. We developed ^Neo4j Browser, a modified version of Neo4j that provides features for filtering analysis results based on the feature configuration of SPL variants and highlighting the results associated with each filter. ^Neo4j Browser helps users to interpret variable results faster, more accurately, and with less mental effort.