Physical Sciences and Mathematics Commons^™

Interface And Morphology Engineering In Solution-Processed Electronic And Optoelectronic Devices, Sanjib Das

Doctoral Dissertations

The first part of this dissertation focuses on interface and morphology engineering in polymer- and small molecule-based organic solar cells. High-performance devices were fabricated, and the device performance was correlated with nanoscale structures using various electrical, spectroscopic and microscopic characterization techniques, providing guidelines for high-efficiency cell design.

The second part focuses on perovskite solar cells (PSCs), an emerging photovoltaic technology with skyrocketing rise in power conversion efficiency (PCE) and currently showing comparable PCEs with those of existing thin film photovoltaic technologies such as CIGS and CdTe. Fabrication of large-area PSCs without compromising reproducibility and device PCE requires formation of dense, …

Solution And Surface Properties Of Architecturally- And Compositionally-Complex Block Copolymers And Their Binary Mixtures, Jesse Lawrence Davis

Doctoral Dissertations

The spontaneous generation of complex structures from polymeric building blocks provides a simple yet effective route to create useful soft matter structures having potential application in a variety of nanotechnologies. The topology, chemical structure, block composition, and sequence of the constituent building blocks of polymers are tunable through synthetic chemistry. This tunability offers attractive opportunities to generate complex, yet well-defined structures with control over the geometry, packing symmetry, and microdomain structure. This thesis work involves the study of the self-assembly behaviors of architecturally complex amphiphilic block copolymers (ABCs). ABCs are composed of two or more chemically distinct blocks that are …

Novel Thermoplastic Elastomers Based On Benzofulvene: Synthesis And Mechanical Properties, Weiyu Wang

Doctoral Dissertations

Thermoplastic elastomers (TPEs) are of great importance both academically and technologically. Currently TPEs are the predominated form of styrene-diene copolymers. However, these styrenic TPEs have serious limitations in applications, especially at higher temperature, because of their low upper service temperature (UST). The work described in this dissertation aimed to developing thermoplastic elastomers with a higher UST and lower cost.

In order to develop TPEs with a higher UST, we employed benzofulvene, an anionically polymerizable monomer in hydrocarbon solvent at room temperature, as the glassy block and copolymerized it with isoprene to prepare polybenzofulvene-polyisoprene-polybenzofulvene (FIF) triblock copolymers. Among all triblock copolymers …

Chemical And Electronic Structure Of Surfaces And Interfaces In Cadmium Telluride Based Photovoltaic Devices, Douglas Arthur Duncan

UNLV Theses, Dissertations, Professional Papers, and Capstones

The surface and interface properties are of the upmost importance in the understanding, optimization, and application for photovoltaic devices. Often the chemical, electronic, and morphological properties of the films are empirically optimized, however when progress slows, a fundamental understanding of these properties can lead to breakthroughs. In this work, surfaces and interfaces of solar cell-relevant films are probed with a repertoire of X-ray analytical and microanalysis techniques including X-ray photoelectron (XPS), X-ray excited Auger electron (XAES), X-ray emission (XES) spectroscopies, and atomic force (AFM) and scanning electron (SEM) microscopies.

Silicon-based devices currently dominate the solar market, which is rather inflexible …

Investigation Of Electrolyte Wetting In Lithium Ion Batteries: Effects Of Electrode Pore Structures And Solution, Yangping Sheng

Theses and Dissertations

Beside natural source energy carriers such as petroleum, coal and natural gas, the lithium ion battery is a promising man-made energy carrier for the future. This is a similar process evolved from horse-powered era to engine driven age. There are still a lot of challenges ahead like low energy density, low rate performance, aging problems, high cost and safety etc.

In lithium ion batteries, investigation about manufacturing process is as important as the development of material. The manufacturing of lithium ion battery, including production process (slurry making, coating, drying etc.), and post-production (slitting, calendering etc.) is also complicated and critical …

Hybrid Aryl-Ether-Ketone And Hyperbranched Epoxy Networks, John Misasi

Dissertations

In this dissertation, relationships between chemical structures, cure kinetics and network architectures are correlated to bulk mechanical properties for novel, hybrid epoxy-amine networks. The work is split into two primary sections: the first is the synthesis and characterization of multifunctional glassy networks based on aryl-ether-ketone diamine curatives, while the second is based on the synthesis and characterization of hyperbranched epoxy polymers and their resulting networks.

Three aryl-ether-ketone (AEK) diamines of increasing molecular weights were synthesized and used to cure 4,4’-tetraglycidylether of diaminodiphenylmethane (TGDDM); the resulting networks were compared to 4,4’-diaminodiphenyl sulfone cured TGDDM. Architectural differences were created by varying cure …

Development Of Dual-Cure Hybrid Polybenzoxazine Thermosets, Jananee Narayanan Sivakami

Dissertations

Polybenzoxazines are potential high performance thermoset replacements for traditional phenolic resins that can undergo an autocatalytic, thermally initiated ring - opening polymerization, and possess superior processing advantages including excellent shelf-life stability, zero volatile loss and limited volumetric shrinkage. The simplistic monomer synthesis and availability of a wide variety of inexpensive starting materials allows enormous molecular design flexibility for accessing a wide range of tailorable material properties for targeted applications. Despite the fact, once fully cured, benzoxazines are difficult to handle due to their inherent brittleness, leaving a very little scope for any modifications. The motivation of this dissertation is directed …

In Vacuo Fabrication And Electronic Structure Characterization Of Atomic Layer Deposition Thin Films, Michael Schaefer

USF Tampa Graduate Theses and Dissertations

Improvement of novel electronic devices is possible by tailor-designing the electronic structure at device interfaces. Common problems observed at interfaces are related to unwanted band alignment caused by the chemical diversity of interface partners, influencing device performance negatively. One way to address this problem is by introducing ultra-thin interfacial dipole layers, steering the band alignment in a desired direction. The requirements are strict in terms of thickness, conformity and low density of defects, making sophisticated deposition techniques necessary. Atomic layer deposition (ALD) with its Ångstrom-precise thickness control can fulfill those requirements.

The work presented here encompasses the implementation of an …

Investigation Of Low Thermal Conductivity Materials With Potential For Thermoelectric Applications, Kaya Wei

USF Tampa Graduate Theses and Dissertations

Thermoelectric devices make it possible for direct energy conversion between heat and electricity. In order to achieve a high energy conversion efficiency, materials with a high thermoelectric figure of merit (ZT = S²σT/κ, where S is the Seebeck coefficient, σ is the electrical conductivity, T is the absolute temperature, and κ is the thermal conductivity) are in great demand. The standard approach is to optimize charge carrier transport while at the same time scatter the heat transport, a task that is easier said than done. Improving the electrical properties in order to increase ZT is limited since electrons …

Morphology Evolution Mechanisms Of Low Band Gap Polymer-Based Photovoltaics, Sunzida Ferdous

Doctoral Dissertations

An optimal nanoscale phase separation between the donor (generally, a conjugated polymer) and the acceptor (generally, a fullerene derivative) materials is one of the major requirements for obtaining high efficiency organic photovoltaic (OPV) device. Recent methods of controlling such nanostructure morphology in a bulkheterojunction (BHJ) OPV device involve addition of a small amount of solvent additive to the donor and acceptor solutions. The idea is to retain the acceptor materials into the solution for a longer period of time during the film solidification process, thus allowing the donor material to crystallize earlier. The ultimate morphology resulting from the solvent casting …

Synthesis, Characterization And Ferroelectric Properties Of Ln-Type Znsno3 Nanostructures, Corisa Kons

USF Tampa Graduate Theses and Dissertations

With increasing focus on the ill health and environmental effects of lead there is a greater push to develop Pb-free devices and materials. To this extent, ecofriendly and earth abundant LiNbO₃-type ZnSnO₃, a derivative of the ABO₃ perovskite structure, has a high theoretically predicted polarization making it an excellent choice as a suitable alternative to lead based material such as PZT. In this work we present a novel synthesis procedure for the growth of various ZnSnO₃ nanostructures by combined physical/chemical processes. Various ZnSnO₃ nanostructures of different dimensions were grown from a ZnO:Al template …

Tailoring The Pore Environment Of Metal-Organic And Molecular Materials Decorated With Inorganic Anions: Platforms For Highly Selective Carbon Capture, Patrick Stephen Nugent

USF Tampa Graduate Theses and Dissertations

Due to their high surface areas and structural tunability, porous metal-organic materials, MOMs, have attracted wide research interest in areas such as carbon capture, as the judicious choice of molecular building block (MBB) and linker facilitates the design of MOMs with myriad topologies and allows for a systematic variation of the pore environment. Families of MOMs with modular components, i.e. MOM platforms, are eminently suitable for targeting the selective adsorption of guest molecules such as CO₂ because their pore size and pore functionality can each be tailored independently. MOMs with saturated metal centers (SMCs) that promote strong yet reversible …

Bio-Photoelectrochemical Solar Cells Incorporating Reaction Center And Reaction Center Plus Light Harvesting Complexes, Houman Yaghoubi

USF Tampa Graduate Theses and Dissertations

Harvesting solar energy can potentially be a promising solution to the energy crisis now and in the future. However, material and processing costs continue to be the most important limitations for the commercial devices. A key solution to these problems might lie within the development of bio-hybrid solar cells that seeks to mimic photosynthesis to harvest solar energy and to take advantage of the low material costs, negative carbon footprint, and material abundance. The bio-photoelectrochemical cell technologies exploit biomimetic means of energy conversion by utilizing plant-derived photosystems which can be inexpensive and ultimately the most sustainable alternative. Plants and photosynthetic …

Mechanics Of Helical And Fabric-Like Mesostructures From Polymer-Nanoparticle Hybrids, Jonathan T. Pham

Doctoral Dissertations

Hierarchical structures developed from nanoscale building blocks offer an excellent opportunity to control properties on all length scales, from the molecular level up to the macroscale. Many beautiful examples in Nature have demonstrated the significance of controlling geometry and mechanics on small length scales to control function on an organism-level, shown by the strength of bones, the toughness of a mollusk's shell, or the gecko's ability to climb walls. Inspired by stunning examples in both Nature and common man-made materials and structures, we assemble polymers and inorganic nanoparticles (NPs) with well-defined surface chemistry into long ribbons and fabric-like networks with …

Tunable Photonic Multilayers From Stimulus-Responsive, Photo-Crosslinkable Polymers, Maria C. Chiappelli

Doctoral Dissertations

This dissertation describes the synthesis of photo-crosslinkable copolymers and their utilization for the fabrication and testing of tunable and responsive one-dimensional (1D) photonic multilayers. Photonic multilayers exhibit structural color due to the interference of incident light at layer interfaces, providing a convenient route towards optically responsive materials that do not rely on potentially light- or oxygen-sensitive chromophore-containing pigments and dyes. A fabrication technique based on sequential spin-coating and crosslinking of photo-crosslinkable polymers is used to assemble tunable and responsive photonic multilayers. Chapter One introduces the fundamental underlying principles of 1D photonic structures and explores their importance in a variety of …

Crystal Growth And Physical Property Characterization Of Complex Perovskite Oxides, Ling Li

Doctoral Dissertations

Bulk EuTiO₃ [europium titanate], a quantum paraelectric antiferromagnet, is shown to exhibit multiferroic behavior in strained thin film form, which highlights the spin-phonon coupling in this system. We have investigated the structural, elastic, magnetic, thermal and transport properties of single crystals of EuTiO₃ as well as doped system EuTi_1-xB_xO₃ (B = Zr, Nb) [Zr and Nb doped europium titanate] utilizing various experimental techniques and theoretical calculations.

The cubic to tetragonal structural transition in pure EuTiO₃ is characterized by a pronounced step-like softening of the elastic moduli near 288 K [kelvin], which resembles …

Nanoscaled Cellulose And Its Carbonaceous Material: Application And Local Structure Investigation, Yujie Meng

Doctoral Dissertations

In this dissertation, cellulose nanocrystals three-dimensional morphology, size distribution, and the crystal structure were statistically and quantitatively investigated. Lognormal distribution was identified as the most likely for cellulose nanocrystals’ size distribution. Height and width dimensions were shown to decrease toward the ends from the midpoint of individual CNCs, implying a spindle-like shape. XRD analysis of crystallite size accompanied with TEM and AFM measurements revealed that the cross-sectional dimensions of individual switchgrass CNC were either rectangular or elliptical shape, with an approximately 3~5 nm [nanometer] lateral element length range. A sponge-like carbon aerogel from microfibril cellulose with high porosity, ultra-low density, …

Structure And Optical Properties Of Transition Metal Dichalcogenides (Tmds) – Mx2 (M = Mo, W & X = S, Se) Under High Pressure And High Temperature Conditions, Nirup Reddy Bandaru

UNLV Theses, Dissertations, Professional Papers, and Capstones

Layered structured materials such as transition metal dichalcogenides (TMDs) have gained immense interest in recent times due to their exceptional structural, electrical and optical properties. Recent studies show semiconducting TMDs such as MX₂ (M= Mo, W & X = S, Se) could be used as potential shock absorbing material, which has resulted in extensive studies on structural stability of these materials under the influence of high pressure. Understanding the structural stability of transition metal dichalcogenides (TMDs) such as MoS2, MoSe2, WS2, and WSe2 under high pressure has been very challenging due to contradicting observations and interpretations reported in the …

Biodegradable Nano-Hybrid Polymer Composite Networks For Regulating Cellular Behavior, Charles Henley Sprague

Masters Theses

Photo-crosslinkable polymeric biomaterials have emerged in the field of biomedical research to promote tissue regeneration. For example, scaffolds that can be crosslinked and hardened in situ have been known to make suitable implant alternatives. Since injectable and photo-crosslinkable biomaterials offer the advantage of being minimally invasive, they have emerged to compete with autografts, a current highly invasive method to repair diseased tissue. A series of novel photo-crosslinkable, injectable, and biodegradable nano-hybrid polymers consisting of poly(ε-caprolactone fumarate) (PCLF) and polyhedral oligomeric silsesquioxane (POSS) has been synthesized in our laboratory via polycondensation. To engineer the material properties of the nano-hybrid networks, varied …

Tin Nanoparticles Encapsulated In Hollow Tio2 Spheres As High Performance Anode Materials For Li-Ion Batteries, Xiang Pan

Theses and Dissertations

Tin, an anode material with a high capacity for lithium-ion batteries, has poor cyclic performance because of the high volume expansion upon lithiation. Based on a literature review of the applications of lithium-ion batteries and current research progress of the tin-based anode materials for lithium-ion batteries, we developed a method to synthesize hollow TiO2 spheres with tin nanoparticles anchored on the inner surface of the TiO2 shell. Such a unique tin/TiO2 composite alleviates the volume change of tin–based anode materials in charge-discharge processes. SnCl2·2H2O (Tin (II) chloride dihydrate) and titanium (IV) isopropoxide (TIPT) were used as the Sn source and …

Morphology-Property Relationship For Binary Organic Thin Films, Alyssa Lynn Griffin

Master's Theses

Organic thin films can be readily mass-produced through solution-based fabrication methods including ink-printing and solution-casting because their light weight, flexibility, and inexpensive sources. Their applications range from organic field-effect transistors (OFET), organic solar cells (OSC), to organic light emitting diodes (OLEDs). Compared with pure component films, binary organic thin films (BOTF) allows for novel characteristics and specialized features to handle more demanding tasks. Due to the complex intermolecular interactions in BOTF, various microscopic phases with different morphological and electronic properties may be formed and this information is difficult to extract through conventional bulk measurements.

Organic thin films can be readily …

Effect Of Surfactant Architecture On Conformational Transitions Of Conjugated Polyelectrolytes, Greg A. Braggin

Master's Theses

Water soluble conjugated polyelectrolytes (CPEs), which fall under the category of conductive polymers, possess numerous advantages over other conductive materials for the fabrication of electronic devices. Namely, the processing of water soluble conjugated polyelectrolytes into thin film electronic devices is much less costly as compared to the processing of inorganic materials. Moreover, the handling of conjugated polyelectrolytes can be performed in a much more environmentally friendly manner than in the processing of other conjugated polymers because conjugated polyelectrolytes are water soluble, whereas other polymers will only dissolve in toxic organic solvents. The processing of electronic devices containing inorganic constituents such …

Capacitance Measurements Of Defects In Solar Cells: Checking The Model Assumptions, Justin R. Davis

Senior Theses

Capacitance measurements of solar cells are sensitive to minute changes in charge in the material. For that reason, capacitance is used in several methods to electrically characterize defects in the solar cell. Standard interpretations of capacitance rely on many assumptions, which, if wrong can skew the results. We explore possible alternative explanations for capacitance transitions, such as a non-ideal back contact and series resistance. Using Drive Level Capacitance Profiling measurements, a capacitance step is linked to a defect between the energy bands of a solar cell.

Exploring The Chemistry Of Phosphorus For Photopolymer Applications, Ryan Guterman

Electronic Thesis and Dissertation Repository

Prior to this thesis, phosphorus-containing polymers and photopolymerization represented two distinct, non-overlapping fields of study. This thesis examined the prospect of combining these two approaches to create a system possessing the benefits of both techniques. By exploiting the chemistry of phosphorus, and using photopolymerization as a fabrication method, new materials were developed and assessed for their use in various applications.

Among the many phosphorus compounds that may be used in polymer science, phosphonium salts and primary phosphines were of specific focus. First, highly fluorinated phosphonium monomers were developed to create photopolymerized hydrophobic surfaces. A structure-activity relationship was established, as both …

Measuring Strain In Trusses, Spencer Metzsch

Senior Theses

Strain is an important quantity in engineering design and materials science that relates the deformation of a material to its original length, through a percentage. Different materials exhibit particular qualities under loading, for example the amount of strain due to a certain magnitude of force, or the amount of strain that can be borne before failure. This experiment aims to compare the relative strengths of three common truss configurations by measuring the strain in their members under loading. The Queen’s post truss was found to be the best at minimizing strain under similar loading conditions.

Feasibility Study: The Evaluation Of Polymer Coatings To Prevent Weathering Of Weak Rocks, Lauren Distler

Senior Honors Projects, 2010-2019

The weathering and erosion of weak rocks along roadways can cause dangerous and potentially fatal rockfalls.   Various slope stabilization methods exist, but each presents a set of challenges and trade-offs.   The focus of the project is to understand the feasibility of utilizing of a polymerbased slope stabilization technique. Rock samples were collected along US Route 33 in Virginia and West Virginia, and preliminary tests were conducted to evaluate the absorption of water (% mass) and durability. The study evaluates three polymer options in regard to the following criteria: adhesion to rock, layer thickness, semi-permeability, insolubility, and non-toxicity. The polymer selection …

Studies Of Strongly Correlated Electron Systems Using Neutron Scattering, Yuen Yiu

Doctoral Dissertations

The world presents many natural and man-made crises and challenges that require scientific solutions. Condensed matter physics is one of the most influential and solution oriented disciplines in science. The field saw a significant rise in popularity especially during the past century as mankind enters the Information Age, when energy and computing related technologies become ubiquitous. This technological progress has been driven by efforts from scientists and engineers, through the synthesis, understanding, and implementation of new materials. Condensed matter physicists strive to solve puzzles at the frontier of material research. In the 21st century we have many advance tools at …

Energy Selective Neutron Imaging For The Characterization Of Polycrystalline Materials, Robin Woracek

Doctoral Dissertations

This multipart dissertation focuses on the development and evaluation of advanced methods for material testing and characterization using neutron diffraction and imaging techniques. A major focus is on exploiting diffraction contrast in energy selective neutron imaging (often referred to as Bragg edge imaging) for strain and phase mapping of crystalline materials. The dissertation also evaluates the use of neutron diffraction to study the effect of multi-axial loading, in particular the role of applying directly shear strains from the application of torsion. A portable tension-torsion-tomography loading system has been developed for in-situ measurements and integrated at major user facilities around the …

Novel Two-Dimensional Nanomaterials And Their Gas Sensing Properties, Haihui Pu

Theses and Dissertations

Graphene, an atomic thin two-dimensional (2D) material with C atoms arranged in a honeycomb lattice, has sparked an unprecedented research interest across various scientific communities since its initial mechanical isolation in 2004. The linear energy dispersion with respect to the momentum within 1 eV around the Fermi level at the high symmetric K (Dirac) points in the Brillouin zone renders graphene a wonder material for scientists. However, graphene’s semimetallic nature significantly limits its high-end applications, e.g., in digital logic circuits. Therefore, continued efforts in opening the band gap for graphene and in searching for novel 2D semiconducting materials are rewarding. …

High Pressure Behavior Of Mullite-Type Oxides: Phase Transitions, Amorphization, Negative Linear Compressibility And Microstructural Implications, Patricia Kalita

UNLV Theses, Dissertations, Professional Papers, and Capstones

Even though mullite occurs rarely in nature, it is perhaps one of the most important phases in both traditional and advanced ceramics. Existing and emerging applications of mullite and mullite-type materials include: high-temperature composites, aerospace materials, ballistic shielding for military applications and even non-linear optical materials. There are many uncertainties regarding the basic physical properties of mullite-type materials, particularly in terms of their high-pressure structural stability and mechanical behavior that are important to address for emerging applications of mullites as engineering materials. This work is the first reported comprehensive investigation of the high –pressure structural behavior of several different mullites …