Physical Sciences and Mathematics Commons^™

Luminescence And Structural Properties Of Silicon-Germanium Quantum Structures Fabricated By Ion Implantation, Matheus Coelho Adam

Electronic Thesis and Dissertation Repository

The advancement of semiconductor materials has played a crucial role in driving positive technological breakthroughs that impact humanity in numerous ways. The presence of defects significantly alters the physical properties of semiconductors, making their analysis essential in the fabrication of semiconductor devices. I presented a new method to quantify surface and near-surface defects in single crystal semiconductors. Epitaxially-grown silicon was measured by low energy electron diffraction (LEED) to obtain the surface Debye temperature (θ_D). The results showed the surface θ_D of bulk Si (001), 1.0 μm, and 0.6 μm Si on sapphire of 333 K, 299 K, …

Modelling Cell Population Growth, Mahmood Mazarei

Electronic Thesis and Dissertation Repository

The growth of biological matter, e.g., tumor invasion, depends on various factors, mainly the tissue’s mechanical properties, implying elasticity, stiffness, or apparent viscosity. These properties are impacted by the characteristics of the tissue’s extracellular matrix and constituent cells, including, but not limited to, cell membrane stiffness, cell cytoskeleton mechanical properties, and the intensity and distribution of focal adhesions over the cell membrane. To compute and study the mechanical properties of tissues during growth and confluency, a theoretical and computational framework, called CellSim3D, was developed in our group based on a three-dimensional kinetic division model.

In this work, CellSim3D is …

Pressure-Induced Modifications To The Structural And Optoelectronic Properties Of 2d Hybrid Organic-Inorganic Perovskites, Jesse Ratte

Electronic Thesis and Dissertation Repository

Recently, 2D hybrid organic-inorganic perovskites (HOIP) have garnered lots of research interest for their applications in optoelectronic devices, especially in solar cells. The optoelectronic properties of 2D HOIPs have yet to be optimized for these applications. High external pressure is well known to induce structural modifications to 2D HOIPs, and thus modify their optoelectronic properties. Herein, we report a study of the effects of high pressure (HP) on the structures and optoelectronic properties of cyclohexane methylamine (CMA) lead iodide (CMA2PbI4) and the structures of N,N-dimethylphenylene-p-diammonium (DPDA) lead iodide (DPDAPbI4).

High pressure measurements of CMA2PbI4 were performed using Raman spectroscopy, Fourier-transform …

Electrical And Mechanical Properties Of Polymer Nanocomposites, Nuwansiri N.K. Getangama

Electronic Thesis and Dissertation Repository

This thesis consists of three projects concerning the electrical and mechanical properties of polymer nanocomposites. We study the effect of nanoscale filler particles on the polymer dynamics at different length and time scales. In the first study, poly(ethylene oxide) (PEO)-multiwalled carbon nanotubes (MWCNT) nanocomposites with a MWCNT concentration ranging from 0 to 5 wt\% were prepared by both melt-mixing and twin-screw extrusion. Their electrical properties were studied over a wide range of frequency and temperature using a dielectric spectrometer. A percolation transition is observed at which the electrical conductivity of the nanocomposites increases by several orders of magnitude. The percolation …

Functional Nanoparticles: Tin Monoxide And Molybdenum Disulfide Quantum Dots On Graphene Nanosheets, Denys Vidish

Electronic Thesis and Dissertation Repository

Light harvesting can be referred to the use of an ensemble of different nanoparticles, or quantum dots, or other absorbers to optimize the ability to capture a given spectrum of electromagnetic radiation (for example the solar spectrum under specific atmospheric conditions) in a light-absorbing system. To this end, different nanoparticles play complementary functions within the system and absorb or scatter light at different wavelength intervals. Light harvesting finds applications in fields as diverse as solar cells, photosynthesis and photocatalysis. Graphene supporting a set of different semiconducting nanoparticles has often been proposed as light harvesters. To further this concept, my thesis …

Symphas: A Modular Api For Phase-Field Modeling Using Compile-Time Symbolic Algebra, Steven A. Silber

Electronic Thesis and Dissertation Repository

The phase-field method is a common approach to qualitative analysis of phase transitions. It allows visualizing the time evolution of a phase transition, providing valuable insight into the underlying microstructure and the dynamical processes that take place. Although the approach is applied in a diverse range of fields, from metal-forming to cardiac modelling, there are a limited number of software tools available that allow simulating any phase-field problem and that are highly accessible. To address this, a new open source API and software package called SymPhas is developed for simulating phase-field and phase-field crystal in 1-, 2- and 3-dimensions. Phase-field …

Heat Flow In The Core Of Ganymede: High Pressure-Temperature Electrical Resistivity Measurements Of Solid And Liquid Ag And Fe-S Alloys, Joshua A.H. Littleton

Electronic Thesis and Dissertation Repository

Experimental investigations of materials at high pressures (P) and temperatures (T) provide insight into the properties and behaviours expected within the inaccessible interiors of planetary bodies. Using a four-wire electrical resistance technique, the electrical resistivity (ρ) of 4d transition metal (Ag) and 3d transition metal alloys (Fe-S) were measured in the solid and molten states at high P. The thermal conductivity (κ) of these materials is inversely proportional to ρ, as described by the Wiedemann-Franz Law. When applied to planetary cores, κ is an important parameter that regulates heat transport mechanisms and magnetic field production.

A hypothesis of ‘resistivity invariance’ …

Fundamental Transport Properties In Silicon Quantum Structures, Nazban M. Darukhanawalla

Electronic Thesis and Dissertation Repository

In the field of silicon photonics, there is an effort to bridge the gap between electrical and optical signals on a single platform, creating a need for Si-based light sources. In this project, Si quantum structures – Si quantum wells and quantum dots in SiO2 were fabricated via solid state precipitation methods. Their properties were studied using X-ray photoelectron spectroscopy, photoluminescence and I-V measurements. Rutherford backscattering spectroscopy was used for depth analysis in monitoring the Si distribution. Different electrical transport mechanisms were explored to understand how an ensemble of silicon QD’s or a silicon quantum well behaves in an SiO2 …

Yield-Stress Fluids In Confined Geometries, Thalia Magyar

Electronic Thesis and Dissertation Repository

A yield-stress fluid is a material that has properties of both solids and conventional liquids that only begins to flow when subject to a finite stress. The behaviour of yield-stress fluids is interesting and important in many applications. It is expected that the rheological properties of a yield-stress fluid will change when confined to a region with a length scale comparable to the characteristic scale of its microstructure. The particle size and polydispersity of two yield-stress fluids, Carbopol and poly(N-isopropylacrylamide), were determined using dynamic light scattering. A rheological characterization was performed on these two yield-stress fluids. Flow of …

Electronic And Local Structures Of Pt-Based Bimetallic Alloy And Core-Shell Systems, Jiatang Chen

Electronic Thesis and Dissertation Repository

This thesis investigates the electronic structure of Pt for catalysis applications. The importance of the Pt 5d band is discussed in terms of the bonding capability of Pt. The oxygen reduction reaction in proton exchange membrane fuel cells is chosen as the catalytic reaction model to illustrate the effect of Pt 5d states on Pt-O interaction. Pt-based bimetallic systems are introduced as a solution for the high price and limited resources of Pt. Despite lower usage of Pt, the tuning capability to optimize the Pt 5d band in bimetallic catalysts is supposed to provide superior catalytic activity. Advanced synchrotron X-ray …

Si Nanocrystal Synthesis Via Double Implantation And Variable Implantation, James M. Gaudet

Electronic Thesis and Dissertation Repository

Silicon (Si) nanocrystals (nc) precipitated from silicon-implanted silicon oxide (SiO₂) are of interest as a novel light source for illumination, biomedical applications, optical computing, etc. They have some advantages over conventional III-V compound semiconductor nanocrystals produced by colloidal synthesis. They are compatible with Si/SiO₂ based semiconductor processing, are stable, non-toxic at point of synthesis and consumption, and their luminescence falls with the infrared transmission window of biological materials. Unfortunately, synthesis of Si-nc embedded SiO₂ is uneconomical and is not as amenable to precise control of the size distribution of nanocrystals as is the case for III-V …

Effects Of Impurities On Calcium Oxalate Crystallization As Measured By Atomic Force Microscopy, Himasha Wijesekara

Electronic Thesis and Dissertation Repository

Calcium oxalate crystals are found in kidney stones as either calcium oxalate monohydrate (COM) or calcium oxalate dihydrate (COD). COM crystals are the most abundant form as they are thermodynamically more stable than COD crystals under physiological conditions. Certain aspartic acid-rich molecules such as osteopontin (OPN) are known to affect stone formation by inhibiting COM and COD growth. We have studied COM {010} and COD {100} faces in the presence of OPN, poly-aspartic acid (poly-ASP) and synthetic peptides derived from OPN to investigate the inhibitor mechanism.

We observed that poly-ASP preferentially inhibits one particular direction of {010} faces on COM …

Porous Membranes From 2d Materials And Their Integration Into Chemiresistive Sensors For In-Line Detection Of Cadmium In Water Filtration Devices, Sheldon Van Middelkoop

Electronic Thesis and Dissertation Repository

As the global population increases, the need for drinking water is an ever-present concern. Water contamination from cadmium needs to be avoided due to the damaging effects of Cd dications to the human health. The Environmental Protection Agency (EPA) has set an extremely low permissible limit for Cd²⁺ in water, at 5 parts-per-billion (PPB), which poses extreme challenges towards Cd²⁺ detection and retention in specific water purification devices. This has led to a rush in the development of low-cost and scalable devices with in-line Cd²⁺sensing capabilities, with the ability to simultaneously purify water and monitor its …

Properties Of Si Quantum Dots, Carolyn C. F Cadogan

Electronic Thesis and Dissertation Repository

The fundamental properties of matter in confined particles change dramatically due to quantum effects. In this work, we have explored the optical properties of silicon quantum dots (Si-QDs) embedded in Si₃N₄; and the role of crystallinity on the optical properties and formation of Si-QDs in Al₂O₃. This work examined the role of (1) annealing temperature and the composition of the film, (2) Al doping of the host Si₃N₄ film, (3) doping Si-QDs and (4) Al and P passivation of Si-QDs on the PL intensity of Si-QDs embedded in Si …

Copper-Nanoparticle Decorated Graphene Thin Films: Applications In Metal-Assisted Etching And Synthesis Of Next-Generation Graphene-Based Nanomaterials, Jaewoo Park

Electronic Thesis and Dissertation Repository

Since 2006, the experimental discovery of graphene, a single-layer of carbon atoms, has spurred tremendous efforts towards new graphene-based materials. In graphene research, there is a recent trend towards next-generation materials in which graphene layers are locally modified in a controlled fashion at the nanoscale and tailored for specific applications. Examples include nanoparticle-decorated graphene thin films with surface potential tailored for nanoelectronics or advanced catalysis, graphene nanoribbons, graphene quantum dots, and the scalable fabrication of tiny pores in graphene, which are suitable to applications requiring ultrathin molecular sieving membranes. This research is focused on the development of new applications of …

High Resolution Ion Beam Investigations Of The Mechanisms Of Titanium Anodization, Mitchell A. Brocklebank

Electronic Thesis and Dissertation Repository

The unique behaviour of thin films, and their surfaces and interfaces, significantly impact material and device properties. Probing these structures with ion beams (IB) provides quantitative composition and thicknesses measurements. In this dissertation, the IB techniques of medium energy ion scattering (MEIS), nuclear reaction profiling (NRP) and Rutherford backscattering spectrometry (RBS) are used to analyze energy losses in ultra-thin films, as well as elucidate the mechanisms of anodic film growth.

Accurate stopping cross sections of protons, ε, in the medium energy range (50-170 kV) often show deviations from Bragg’s rule. Here, ε_Ti, ε_Si, and ε_{TiO2 …}

Effects Of High Pressure On Photochemical Reactivity Of Organic Molecular Materials Probed By Vibrational Spectroscopy, Jiwen Guan

Electronic Thesis and Dissertation Repository

Chemical transformations of molecular materials induced by high pressure and light radiation exhibit novel and intriguing aspects that have attracted much attention in recent years. Particularly, under the two stimuli, entire transformations of molecular species can be realized in condensed phases without employing additional chemical constraints, e.g., the need of solvents, catalysts or radical initiators. This new synthetic approach in chemistry therefore satisfies increasing need for production methods with reduced environmental impacts. Motivated by these promises, my Ph. D thesis focuses on this state-of-the-art branch of high-pressure photochemistry. Specifically, high pressure is employed to create the necessary reaction conditions to …

Defect-Related Magnetic Properties Of Nanostructured Nickel Oxide Thin Films For Solar Cell Applications, Angela E. Ezugwu

Electronic Thesis and Dissertation Repository

Transparent conducting oxides (TCOs) are extensively investigated because of their applications as transparent electrodes in solar cells and light-emitting devices. TCOs of interest include indium-tin oxide, aluminum-doped zinc oxide, nickel oxide (NiO), and their combinations. There is strong interest in NiO because no heteroatoms are required to “dope” it at high transparency levels. It has been speculated that paramagnetic defects due to Ni³⁺ centers and O interstitials are responsible for the electrical conductivity of otherwise insulating and antiferromagnetic NiO, but direct investigation of such defects has been limited. Here, the electrical conductivity in nanostructured NiO thin films is investigated …

The Study Of Plasmonics In Nanohole Metallic Metamaterials, Kieffer J. Davieau

Electronic Thesis and Dissertation Repository

Plasmonics is the study of light-matter interaction. The interaction of incident light (photons) with surface plasmons present in metamaterials results in unique optical properties. Nanohole arrays are a metamaterial consisting of an array of sub-wavelength holes perforated in an optically thin metallic film which resides upon a dielectric material. The interaction of light with the surface plasmons present in the nanohole array leads to extraordinary optical transmission which produces resonance peaks with a higher intensity than the incident light. By changing the physical parameters of the nanohole array, such as hole size and periodicity, the resonance peaks can be tuned …

Linear And Nonlinear Dynamics Of Spin Waves In Ferromagnetic Nanowires, Zahra Haghshenasfard

Electronic Thesis and Dissertation Repository

Motivated by recent experimental developments, we present a theoretical study of some linear and nonlinear properties of spin waves in ferromagnetic nanostructures under conditions of microwave pumping. A microscopic (or Hamiltonian-based) approach is followed including terms for both the short-range exchange and the long-range dipole-dipole interactions, as well as the effects of an external magnetic field, single-ion anisotropy, biquadratic exchange and the Ruderman-KittelKasuya-Yosida interactions, as appropriate. In ultrathin films and nanowires with thickness or lateral dimensions less than about 100 nm, the discreteness of the quantized spin waves (or magnons) and their spatial distributions become modified, making it appropriate to …

Experimental Studies Of Electrical Resistivity Behavior Of Cu, Zn And Co Along Their Melting Boundaries: Implications For Heat Flux At Earth’S Inner Core Boundary, Innocent Chinweikpe Ezenwa

Electronic Thesis and Dissertation Repository

Abstract

The electrical resistivity of high purity Cu, Zn and Co has been measured at pressures (P) up to 5GPa and at temperatures (T) in the liquid phase. The electrical resistivity of solid state Nb was also measured up to 5GPa and ~1900K. All measurements were made in a large volume cubic anvil press. Using two thermocouples placed at opposite ends of the sample wire, serving as temperature probes as well as resistance leads, a four-wire technique resistivity measurement was employed along with a polarity switch. Post-experiment compositional analyses were carried out on an electron microprobe.

The expected resistivity decrease …

Nanoscale Thermal And Electronic Properties Of Thin Films Of Graphene And Organic Polyradicals, Sabastine Chukwuemeka Ezugwu

Electronic Thesis and Dissertation Repository

Ultrathin film materials have attracted significant attention in light of their potential applications in very large scale integrated electronics and data storage. For instance, the amount of data that can be addressed and stored in a memory device scales inversely with the thinness of the active layer of these components. In our thesis, we have developed a suite of scanning-probe and nano-optical techniques focused on understanding the electronic surface properties and the thermal conductivity of ultrathin materials. We discuss a few specific examples in which we applied these techniques towards improved performance of thin films of graphene and organic polyradicals …

Self-Assembled Copper Nanoparticle Superlattices On Graphene Thin Films, Tianhao Ouyang

Electronic Thesis and Dissertation Repository

Recently, Giovannetti et al. successfully demonstrated that some metals (such as Cu and Au) only have weak van der waals interaction with graphene and thus can only form weak bonding without severely shifting graphene’s band structure, which describes the energies range of the electrons in the material. Therefore, this opens up windows for graphene enhancement without greatly changing its properties. Furthermore, Zhou et al. later suggested the possibility of self-assembling periodic arrays of alkali atoms on graphene. In our group, graphene thin films fabricated in a cost effective way using solution-processed methods have been used extensively, including decorating …

Omcvd Gold Nanoparticles Covalently Attached To Polystyrene For Biosensing Applications, Sivayini Kandeepan

Electronic Thesis and Dissertation Repository

Remarkable developments and successes were witnessed in the fabrication and implementation of optical sensors based on localized surface plasmon resonance (LSPR) for the investigation of chemical and biological material quantities and to detect lethal diseases such as cancer in early stages. Gold nanoparticles (AuNPs) are ideal candidate for sensing purposes due to their chemical stability, ease of surface functionalization and strong LSPR in the visible range. Although there are several designs of sensors published, most of them are still limited to small scale research laboratory use partly due to their high cost of fabrication and waste management, in particular critical …

Dynamics Of Discs In A Nematic Liquid Crystal, Alena Antipova

Electronic Thesis and Dissertation Repository

In this thesis, a new way of simulating a two-way coupling between a liquid crystal and an immersed object is proposed. It can be used for objects of various geometries and can be expanded to be used for an object of any geometry. Additionally, a simple yet effective model was suggested for calculations of transmitted light through a nematic liquid crystal sample. This model allowed us to clarify the behavior of a ferromagnetic disc in a nematic liquid crystal observed in experiments and incorrectly interpreted at that time.

Our simulations have demonstrated the following: in the absence of external forces …

Simulation Of Heterogeneous Colloidal Particles Immersed In Liquid Crystals, Setarehalsadat Changizrezaei

Electronic Thesis and Dissertation Repository

This thesis describes an investigation of interactions between colloidal particles immersed in a liquid crystal. The presence of colloidal particles in the liquid crystal distorts the director field distorted from its uniform orientation. These elastic distortions produce topological defects around the particles, which induce anisotropic interactions between them, and these anisotropic interactions can be used to manufacture non-closed packed colloidal crystals, such as diamond lattices, which are interesting in photonic applications. First, different types of liquid crystals, the mathematical tools to describe the anisotropic nature of liquid crystals, the Landau-de Gennes free-energy model to investigate the particle’s interaction, and different …

Universal Scaling Properties After Quantum Quenches, Damian Andres Galante

Electronic Thesis and Dissertation Repository

In this Thesis, the problem of a quantum quench in quantum field theories is analyzed. This involves studying the real time evolution of observables in a theory that undergoes a change in one of its couplings. These quenches are then characterized by two parameters: $\delta \lambda$, the magnitude of the quench and most importantly, $\delta t$, the quench duration. In contrast to previous studies of abrupt quenches in the condensed matter theory community, we will be interested in smooth quenches with a finite $\delta t$.

Motivated by existing results in holographic theories, we studied the problem of a fast smooth …

The Study Of Nano-Optics In Hybrid Systems, Marek J. Brzozowski

Electronic Thesis and Dissertation Repository

In this thesis, we study the quantum light-matter interaction in polaritonic heterostructures. These systems are made by combining various nanocomponents, such as quantum dots, graphene films, metallic nanoparticles and metamaterials. These heterostructures are used to develop new optoelectronic devices due to the interaction between nanocomposites.

Photoluminescence quenching and absorption spectrum are determined and an explanatory theory is developed for these polaritonic heterostructures. Photoluminescence quenching is evaluated for a graphene, metallic nanoparticle and quantum dot system. It is shown that average distance between nanocomposites or concentration of nanocomposites affect the output these system produced. Photoluminescence quenching was also evaluated for a …

Transmission Of Light In Nano-Hole Metamaterial, Shankaranandh Balakrishnan .

Electronic Thesis and Dissertation Repository

The interaction of light with metallic nano-hole array structures enable excitation of surface plasmon polaritons at any angle of incidence. Nano-hole array structure can transmit more radiation than incident light due to the presence of surface plasmon polaritons. This phenomenon has opened up possibilities for a wide range of applications such as Surface Plasmon Resonance sensing and Surface Enhanced Raman spectroscopy. In this thesis, quantum scattering theory and quantum density matrix method are employed to assess optical transmission of metallic nano-hole array structures. The scattering cross section spectrum is calculated for nano-hole array structures with different nano-hole radii and periodicities …

Dielectric Spectroscopy Of Polyvinyl Alcohol Hydrogels And Nanocomposites, Nuwansiri N.K. Getangama

Electronic Thesis and Dissertation Repository

Gels based on polyvinyl alcohol (PVA) can be formed by repeated freezing and thawing of a solution of the polymer. PVA cryogels have applications as biomaterials, including artificial tissue and drug delivery systems. The mechanical and electrical properties of polymeric materials can be changed significantly by adding a small amount of nanometer-sized particles. In this work, the dielectric properties of PVA solutions and gels were studied in the frequency range from 10 micro Hz to 1 MHz as a function of temperature, using a dielectric spectrometer. Comparison of the dielectric constant of a PVA solution to that of water indicates …