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Wang, KaiHIGH PERFORMANCE SOLUTION-PROCESSED PEROVSKITE HYBRID SOLAR CELLS THROUGH DEVICE ENGINEERING AND NOVEL
Doctor of Philosophy, University of Akron, 2017, Polymer Engineering
ABSTRACT Efficiently and economically harnessing the solar energy via solar cell devices is one of promising solutions to address the global energy crisis. This thesis mainly focuses on a novel family of photoactive layer materials, namely organic-inorganic lead halide perovskite hybrids, and their corresponding solar cell devices, due to their potential for achieving outstanding power conversion efficiency and low-cost processibility. Specifically, the main research themes of this thesis are to achieve high performance perovskite hybrid solar cells through optimizing device structures, developing novel functional perovskite materials, and elucidating the underlying physics and mechanisms for guiding us to construct high performance solution-processed perovskite hybrid solar cells. This dissertation contains four parts and 10 chapters. In PART I, a broaden overview on both solar cell device and material is given, which specifically reviews the importance of solar energy and solar cells, comparison between previous-generation solar cells and perovskite hybrid solar cells, history of perovskite hybrid materials for solar cell application in Chapter 1 and describes the theoretical background of solar cell devices and material used for fabrication of solar cells in Chapter 2. PART II mainly includes the detailed projects on solar cell device engineering. Firstly, in Chapter 3, we employ a highly electrical conductive, polyethylene oxide (PEO)-doped poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) as the hole extraction layer (HEL) for the planar heterojunction (PHJ) perovskite hybrid solar cells (pero-HSCs). The dramatically enhanced electrical conductivity of the PEO-doped PEDOT:PSS HEL provides an efficient pathway for the hole extraction, transport, and collection from the perovskite active layer to the anode. As a result, a significantly enhanced short-circuit current (JSC) of 23.42 mA cm-2, a slightly enlarged open-circuit voltage (VOC) of 0.88 V, an enhanced FF of 80.10% and a correspondingly dramatically enhanced power conversion efficiency (PCE) of 16.52%, which is a ~45% enhancement as compared with that from the PHJ pero-HSCs incorporated with the pristine PEDOT:PSS HEL, are observed. In Chapter 4, we utilize a solution-processed ultrathin layer of an ionomer, 4-lithium styrenesulfonic acid/styrene copolymer (LiSPS), to re-engineer the interface of methylammonium lead iodide (CH3NH3PbI3) in PHJ pero-HSCs. The ionomer can sufficiently modify the rough surface of the perovskite and optimize the charge extraction efficiency between perovskite photoactive layer and the charge transport layer. As a result, PHJ pero-HSCs with an increased photocurrent density of 20.90 mA cm-2, an enlarged ¿ll factor of 77.80%, a corresponding enhanced power conversion ef¿ciency of 13.83%, high reproducibility, and low photo-current hysteresis, are achieved. In Chapter 5, because one major limitation to increasing the efficiency of pero-HSCs is the fact that the diffusion length of the electrons is shorter than that of the holes, to facilitate the electron extraction efficiency in pero-HSCs and to make this efficiency comparable with that of the holes, we fabricated BHJ pero-HSCs by mixing perovskite materials with water-/alcohol soluble fullerene derivatives. The observed enhanced JSC and enlarged FFs were a result of the balance in the charge carrier extraction efficiency and the enlarged interfacial area between the perovskite materials and the fullerene derivatives. Significantly improved power conversion efficiencies were obtained for these BHJ pero-HSCs. A greater than 22% increase in power conversion efficiency was observed for the BHJ pero-HSCs compared with planar heterojunction pero-HSCs. A remarkable 86.7% FF, the highest reported value for pero-HSCs, was observed for the BHJ pero-HSCs. Our strategy of using a BHJ structure in pero-HSCs offers an efficient and simple way to further increase the performance of these devices. PART III mainly discusses the detailed projects on novel perovskite materials development. To fabricate homogeneous and high-quality perovskite thin ¿lms via low-temperature solution processing is always a challenge to realizing high-ef¿ciency pero-HSCs, in Chapter 6, we firstly report a development of an approach to realize smooth surface morphology of CH3NH3PbI3 perovskite thin ¿lms via using strong-polar ethanol solution rather than less-polar isopropanol solution, which was previously used as the solvent for preparing perovskite thin ¿lms. In comparison with the pero-HSCs processed from isopropanol solution, more than 40% enhanced ef¿ciency is observed from pero-HSCs processed from ethanol solution. The enhanced ef¿ciency is attributed to a homogeneous high-quality perovskite thin ¿lm with dramatically low root-mean-square roughness and completely conversion of lead (II) iodide (PbI2) to CH3NH3PbI3. In Chapter 7, we report the development and investigation of novel CH3NH3PbI3: x Nd3+(where x = 0, 0.1, 0.5, 1.0, and 5.0 mol%) perovskite hybrid materials, where Pb2+ is partially substituted by an inequivalent rare-earth metal cation, neodymium (Nd3+), which was never reported in previous studies. By conducting the charge carrier mobility measurements and film morphology studies, it is found that solution-processed CH3NH3PbI3: x Nd3+ thin films exhibit significantly improved and more balanced charge carrier mobilities, and superior film quality with dramatically reduced trap-states and pin-holes, as compared with pristine CH3NH3PbI3 thin film. As a result, a descent power conversion efficiency of 20.56% for solar cells and a superior photodetectivity of ~ 1014 cm Hz1/2 W-1 from 375 nm to 800 nm at room temperature for photodetector, are observed from solution-processed perovskite photovoltaics by novel CH3NH3PbI3: x Nd3+ thin films. All these results demonstrate that our method provides a simple and facial way to boost the device performance of perovskite photovoltaics. In Chapter 8, we report the utilization of polyethylene oxide additives to anchoring the ions in the perovskite lattice to suppress the formation of point defect or the migration of ions/vacancy, for simultaneously enhancing device efficiency, minimizing photocurrent hysteresis and enhancing device stability. Consequently, efficient solar cell devices with power conversion efficiency of 19.01% with extremely low hysteresis index of 0.001 and long-term device shelf half-life time of 504 hrs (without encapsulation, stored in 50% humidity air) have been achieved. Chemical, structural and morphological analysis show that the PEO additive acts as a crosslink between neighboring perovskite crystal domains via the strong hydrogen bonding of `-OH…I-’ and `O…H-NH2CH3+’ to the perovskite. In PART IV, a brief summerization on our works in terms of both device and material engineering is presented in Chapter 9, that is, for optimizing the device configuration as well as address critical issues in previously wide-applied hybrid perovskite thin films, we mainly developed novel ideas on: (i) modifying anode buffer layer for efficient hole extraction; (ii) modifying the interfacial electrical coherence on the i-n junction; (iii) developing a bulk heterojunction concept for efficient charge extraction; for novel materials part, we also focused on three major parts: (i) optimizing the thin film quality of perovskite; (ii) tuning the crystal lattice structure by inequivalent metal doping; (iii) anchoring the ion within the perovskite lattice for reducing hysteresis and improving device stability. Finally, an outlook is given in the Chapter 10 for guiding our future work.

Committee:

Xiong Gong (Advisor); Matthew Becker (Committee Member); Alamgir Karim (Committee Member); Nicole Zacharia (Committee Chair); Jie Zheng (Committee Member)

Subjects:

Electrical Engineering; Energy; Nanoscience; Physics; Polymers

Keywords:

Energy Conversion; Photovoltaics; Lead Halide Perovskite; High Performance; Device Physics; Material Science

Bekele, SelemonStructural and Dynamical Properties of Water and Polymers at Surfaces and Interfaces: A Molecular Dynamics Investigation
Doctor of Philosophy, University of Akron, 2018, Polymer Science
All-atom molecular dynamics simulations have been carried out to study the wetting of model atactic polystyrene thin films by water droplets as a function of surface polarity, the structure and dynamics at the surface of polymer films, the properties of interfacial water molecules in contact with atactic polystyrene surfaces of varying polarity, and the spreading dynamics of water droplets of varying sizes on a completely wetting surface. The simulated contact angle of a water droplet on atactic polystyrene thin films is found to decrease monotonically with increasing degree of surface oxidation which is used as a measure of surface polarity. The number of hydrogen bonds between water molecules and the polystyrene at the interface is found to monotonically increase with polarity. The contribution of the non-dispersion interactions to the interfacial energy at the polystyrene/water interface has been determined as a function of surface polarity. The roughness of the polystyrene surface and the orientational ordering of the surface phenyl rings are found to be independent of surface polarity when the polystyrene is exposed to vacuum. Surface roughness appears to increase and orientational ordering of surface rings appears to decrease slightly with polarity when the polystyrene is in contact with water. Density profiles of polymer films as a function of distance relative to an instantaneous surface exhibit a structure indicative of a layering at the polymer/vapor interface similar to the typical layered structure observed at the polymer/substrate interface. Interfacial molecules at the polymer/vapor interface have a higher mobility compared to that in the bulk while the mobility of the molecules is lower at the polymer/substrate interface. Time correlation of the instantaneous polymer/vapor interface shows that surface fluctuations are strongly temperature dependent and are directly related to the mobility of polymer chains near the interface. Interfacial water molecules on a bare atactic polystyrene surface and those which do not make hydrogen bonds with the oxidized surfaces are found to have a faster dynamics and appear to have a universal water-water hydrogen bond relaxation time of about 5 ps. Diffusion coefficients and the relaxation times of the water molecules involved in hydrogen bonding with the surface show strong dependence on surface polarity with a hydrophobic to hydrophilic transition regime with contact angle in the range 40-50o. The spreading of water droplets on completely wetting surface is characterized by a bulk part of normal density sliding over a monolayer of high density water. The monolayer has a molecular dimension and moves ahead of the bulk part of the droplet. The monolayer motion exhibits two spreading regimes, each following a power law in time. The bulk part of the droplet initially spreads over the monolayer with increasing radius until a characteristic time t* where the monolayer changes from one power law behavior to another. For times after t* ~ 0.1- 0.5 ns, it shrinks while maintaining what appears to be a constant contact angle until it disappears altogether and only a monolayer of water remains on the substrate.

Committee:

Mesfin Tsige (Advisor); Ali Dhinojwala (Committee Chair); Toshikazu Miyoshi (Committee Member); Hunter King (Committee Member); Jie Zheng (Committee Member)

Subjects:

Condensed Matter Physics; Materials Science; Nanoscience; Polymers

Keywords:

MD simulation;molecular dynamics;oxidized surfaces; water contact angle; interfacial water;surfaces and interfaces;droplet spreading;

Hussain, Mallik Mohd RaihanNonlinear Electromagnetic Radiation from Metal-Insulator-Metal Tunnel Junctions
Master of Science (M.S.), University of Dayton, 2017, Electro-Optics
Our goal was to experimentally detect nonlinear electromagnetic (EM) radiation (in the far field) from a metal-insulator-metal (MIM) tunnel junction where the insulator thickness lies in the nanometer to subnanometer range and the metals in the junction are coupled to the electromagnetic field of incident photons. The radiation from an MIM junction originated from the photon-induced tunneling current passing through it. The phenomenon is elegantly described by photon-assisted-tunneling (PAT) theory that introduces transfer Hamiltonians in the uncoupled (when two metals are at infinite distance from each other) system Hamiltonian. This theory predicts the contribution of additional conductivity terms in the MIM interface (due to tunneling inside the junction) and ushered the development of quantum conductivity theory (QCT), as a consequence. In this thesis, we reviewed QCT from the perspective of many-body formulation and designed careful experiments to detect the nonlinear electromagnetic radiation from MIM junctions that can be attributed to photon-assisted tunneling of electrons. In our experiment, first, an insulator layer was put on the metal surface using atomic layer deposition (ALD) technique. The number of layers were varied to produce MI samples with different insulator thickness in the subnanometer range. Then, we set the background signal strength by measuring the second harmonic (SH) and third harmonic (TH) signal due to the bulk material and the surface of metal-insulator (MI) interface. Next, we spin-coated the MI sample with Au nanospheres (diameter ~ 10 nm) to construct MIM interfaces and measured SH and TH signals from them again. Without any bias voltage across the MIM, QCT predicts an increase in TH signal only. Experimentally, we observed an increase in TH signal strength. The increase was modest which is partially attributed to the fact that we could not reliably produce MIM samples with subnanometer insulator thickness and uniform coverage. We intend to improve the surface coverage and uniformity of the insulator layer, in future, and measure SH and TH from the improved samples. Detection of such radiation would support QCT and validate the extension of transfer Hamiltonian approach from the realm of superconducting tunnel junctions to normal MIM tunnel junctions.

Committee:

Joseph Haus, Ph.D. (Committee Chair); Andrew Sarangan, Ph.D. (Committee Member); Imad Agha, Ph.D. (Committee Member)

Subjects:

Electromagnetics; Nanoscience; Nanotechnology; Optics; Quantum Physics

Keywords:

tunnel junction; metal-insulator-metal; MIM; nonlinear radiation from MIM; transfer Hamiltonian; photon-assisted-tunneling; PAT; quantum conductivity coefficient; QCT; Au-Al2O3-Au; atomic layer deposition on metal; ALD on metal; metal-insulator; MI

Chen, ZhiangDeep-learning Approaches to Object Recognition from 3D Data
Master of Sciences, Case Western Reserve University, 2017, EMC - Mechanical Engineering
This thesis focuses on deep-learning approaches to recognition and pose estimation of graspable objects using depth information. Recognition and orientation detection from depth-only data is encoded by a carefully designed 2D descriptor from 3D point clouds. Deep-learning approaches are explored from two main directions: supervised learning and semi-supervised learning. The disadvantages of supervised learning approaches drive the exploration of unsupervised pretraining. By learning good representations embedded in early layers, subsequent layers can be trained faster and with better performance. An understanding of learning processes from a probabilistic perspective is concluded, and it paves the way for developing networks based on Bayesian models, including Variational Auto-Encoders. Exploitation of knowledge transfer--re-using parameters learned from alternative training data--is shown to be effective in the present application.

Committee:

Wyatt Newman, PhD (Advisor); M. Cenk Çavusoglu, PhD (Committee Member); Roger Quinn, PhD (Committee Member)

Subjects:

Computer Science; Medical Imaging; Nanoscience; Robotics

Keywords:

deep learning; 3D object recognition; semi-supervised learning; knowledge transfer

Chen , Kexun ANTIMICROBIAL RESPONSE OF AND BLOOD PLASMA PROTEIN ADSORPTION ON SILVER-DOPED HYDROXYAPATITE
Master of Science, University of Akron, 2018, Polymer Science
Implant-related infection is one of the main causes of orthopedic device failure. Biofilms are very hard to be eliminated once they are formed. Usually surgical revision is needed, but at great economic and personal cost. So, it is crucial to develop orthopedic implants with intrinsic antimicrobial activity. Because of its high biocompatibility and osteoconductivity, hydroxyapatite (HAP) is one of the most extensively used orthopedic biomaterials. Previous research has shown that silver- doped hydroxyapatite (Ag-HAP) has prominent antimicrobial activity. After implantation, the first event is the adsorption of blood plasma proteins. Adsorption changes the conformation of the proteins, consequently, exposing new epitopes. What cells really “see”, is this layer of adsorbed proteins, which will determine how cells respond. However, how protein changes their conformation on HAP and Ag- HAP nanoparticles (NPs) is still not fully understood. Silver-doped HAP NPs were synthesized at different conditions and their antimicrobial properties as well as plasma protein adsorption at their surfaces was tested. It was found that synthesis pH affects the Ag content of Ag-HAP and subsequent Ag+ release from the NPs in solution. This, in turn, affected antimicrobial efficiency. Human serum albumin (HSA) and fibrinogen (Fib) conformation changed with decrease of ¿-helix and increase of IV ¿-sheet content upon adsorption to all NP surfaces. HSA melting temperature was 65-66 °C for all three NPs compared to 76 °C in solution. More adsorption of HSA on NPs than Fib was observed. HSA conformation was affected by amount of proteins adsorbed but Fib was not. The differences are associated to differences in their relative sizes. HSA and Fib conformational changes on Ag-HAP were similar to those on HAP. Thus, I show a synthesis method to improve Ag-HAP antimicrobial activity without deleterious effect on blood plasma protein adsorption compared to HAP.

Committee:

Nita Sahai (Advisor); Abraham Joy (Committee Member)

Subjects:

Nanoscience; Nanotechnology

Keywords:

adsorption, protein conformation change, silver-doped HAP, antimicrobial

Stenger, Dillon MichaelDependency of Aluminum Nanoparticle Flash Ignition on Sample Internal Water Content and Aggregation
Master of Science (M.S.), University of Dayton, 2016, Aerospace Engineering
The United States Air Force believes that hypersonic flight opens a multitude of possibilities for the warfighter. One of the main propulsion systems for hypersonic flight is scramjet engines. These engines are currently ignited using a form of electric discharge and a primer fuel. This primer fuel system takes away valuable volume and weight in hypersonic vehicle designs. One alternative ignition method would be the utilization of plasmonic resonance to flash ignite aluminum nanoparticles. This process had been proven multiple times in the past and research has begun on characterizing how this ignition process can be affected. One that has not been researched to date has been how water content and agglomeration affect the energy needed for ignition to be achieved. To understand this functional dependence, aluminum nanoparticles were put through a series of trials with various levels of water content. Samples of particles were heated at 473.15 K to decrease water content and subsequently tested to determine the energy input needed for ignition. To understand the effects of increasing water content, particles were placed in an environment with at least 100% relative humidity for both 48 and 168 hours and then tested to determine the ignition energy needed. The results from the two humidified cases were compared with the data from a control group whose water content was not altered in a controlled manner. It was determined that by humidifying the particles the minimum energy needed for total ignition was lowered by approximately five percent on average while drying the particles increased the energy needed by approximately four percent on average.

Committee:

Aaron Altman, PhD (Advisor); Timothy Ombrello, PhD (Advisor); David Myszka, PhD (Committee Member)

Subjects:

Aerospace Engineering; Engineering; Nanoscience

Keywords:

Aluminum Nanoparticle Flash Ignition; Nanoparticle Aggregation; Nanoparticle Internal Water Content; Alternate Engine Ignition System

Sharma, AnshulNew types of liquid crystals host-guest systems
PHD, Kent State University, 2015, College of Arts and Sciences / Department of Chemical Physics
Liquid crystals (LCs) are a class of soft condensed matter with molecular ordering like solids in one, two or three dimensions depending on the liquid crystal phase but show fluidity like liquids. LCs show large variations in properties when subjected to electric and magnetic fields, polarized light, temperature, pH, or other stimuli. The properties of LCs can be altered and enhanced by adding molecule such as dyes, mesogenic molecules or nanomaterials called as the host-guest systems. The work presented in this thesis describes the study on new types of LC host-guest systems developed for new applications in soft matter and as well as for nano- and bio- material applications. In this work, different types of nanoparticles (NPs) (chiral and achiral) have been synthesized, characterized and studied as dopants/guests in nematic-LCs to understand the interactions of LCs with NPs both in the bulk (well-dispersed) and with the NPs confined at the LC-substrate interface (segregated). The effect of well-dispersed chiral mesogenic cholesterol capped chiral gold NPs in a nematic LC is studied to understand and visualize nanoparticle chirality. Secondly, ink-jet printing of gold NPs and emissive carbon dots is used as a versatile and flexible technique for obtaining patterned alignment of LCs. Another aspect presented in this thesis is development of modular synthesis for smectic liquid crystal elastomers (LCEs) as hosts for spatial cell culture and tissue regeneration. Series of new elastomers (3 arm, 4 arm and 6 arm smectic LCEs) with tunable size of building blocks and position of LC pendant group (alpha and gamma) has been developed, modified with LC pendant groups and studied for their mechanical behavior and are a viable candidate for cell cultures with different cell lines. The research presented in this thesis highlights the importance of material designing, diversity of LCs and its implementation in new applications in the fields of nano- and bio- materials.

Committee:

Torsten Hegmann, Dr. (Advisor); Elda Hegmann, Dr. (Advisor)

Subjects:

Chemistry; Materials Science; Nanoscience

Keywords:

liquid crystals, elastomers, gold nanoparticles, chirality, lovemonkey, inkjet printing, biodegradable, biocompatible, tissue regeneration, cellular response

Hoeher, Alexandria JConstraints on the Short-Range Structure of Amorphous Calcium Phosphate: A Precursor in the Formation of Hydroxylapatite
Master of Science, Miami University, 2015, Geology & Environmental Earth Science
The process of crystallization of hydroxylapatite is not yet fully understood and in some cases may include the development of at least one precursor phase. Amorphous calcium phosphate (ACP) is a known precursor phase and it has been proposed that spherical clusters of calcium and phosphate partial components of or are precursors to ACP. ACP was synthesized and analyzed with x-ray diffraction, raman spectroscopy, transmission electron microscopy, pair distribution function analysis, and extended x-ray absorption fine structure spectroscopy to elucidate the existence of clusters and to determine their chemistry and structure. Pair distribution function analysis confirmed a short range structure of about 10 Å, the proposed size of the clusters. The clusters have similarities to hydroxylapatite and brushite, but have an independent structure. Further study is needed to detail the atomic positions and symmetry of these clusters.

Committee:

John Rakovan, Dr. (Advisor); Olaf Borkiewicz, Dr. (Committee Member); Mark Krekeler, Dr. (Committee Member)

Subjects:

Geology; Mineralogy; Nanoscience

Keywords:

hydroxylapatite; nanoparticles; Posners clusters; brushite; amorphous calcium phosphate; EXAFS; PDF; crystal growth

Thota, Venkata Ramana KumarTunable Optical Phenomena and Carrier Recombination Dynamics in III-V Semiconductor Nanostructures
Doctor of Philosophy (PhD), Ohio University, 2016, Physics and Astronomy (Arts and Sciences)
Semiconductor nanostructures such as quantum dots, quantum wires and quantum wells have gained significant attention in the scientific community due to their peculiar properties, which arise from the quantum confinement of charge carriers. In such systems, confinement plays key role and governs the emission spectra. With the advancements in growth techniques, which enable the fabrication of these nanostructured devices with great precision down to the atomic scale, it is intriguing to study and observe quantum mechanical effects through light-matter interactions and new physics governed by the confinement, size, shape and alloy composition. The goal is to reduce the size of semiconductor bulk material to few nanometers, which in turn localizes the charge carriers inside these structures such that the spin associated with them is used to carry and process information within ultra-short time scales. The main focus of this dissertation is the optical studies of quantum dot molecule (QDM) systems. A system where the electrons can tunnel between the two dots leading to observable tunneling effects. The emission spectra of such system has been demonstrated to have both intradot transitions (electron-hole pair residing in the same dot) and interdot transitions (electron-hole pair participating in the recombination origin from different dots). In such a system, it is possible to apply electric field such that the wavefunction associated with the charge carriers can be tuned to an extent of delocalizing between the two dots. This forms the first project of this dissertation, which addresses the origin of the fine structure splitting in the exciton-biexciton cascade. Moreover, we also show how this fine structure can be tuned in the quantum dot molecule system with the application of electric field along the growth direction. This is demonstrated through high resolution polarization dependent photoluminescence spectroscopy on a single QDM, which was described in great detail by H. Ramirez (et al.) and also experimentally observed by N. Skold (et al.) for a fixed barrier thickness. However, we measured the strength of FSS as a function of barrier thickness in the strong tunneling regime. The results are discussed in chapter 4. The second project is carried out with an intention to generate entangled photon pairs from molecular states found in the emission spectra of a single QDM: A pair of photons, which reveals the information associated with the intrinsic property (polarization for example) of the other photon simultaneously and spontaneously when a measurement has been performed in either one of the two. The exciton-biexciton cascade not only has intradot transitions but the photoluminescence spectra also depicts interdot transitions, realizing the molecular nature of the system. Since the charge carriers are localized in different dots, the wavefunction overlap between the two is also reduced significantly. It is with this goal of enhancing the intensity of interdot or indirect transitions between the molecular biexciton-indirect exciton that we performed two color photoluminescence excitation studies and the results are discussed in chapter 5. Thirdly, the continuous creation of electron-hole pairs through photoexcitation leads to some local electric field effects, which arises due to the ionization of charge carriers inside the device structure. The advantage of the interdot transition in the emission spectra is the large Quantum Confined Stark Effect (QCSE) associated with it. This interdot QCSE is over an order of magnitude larger than for the intradot or direct transition and varies linearly with the applied electric field. By making use of the interdot exciton as a sensitive probe, the effects of optically generated electric field as a function of time are measured experimentally. Both rise time and fall time of the optically generated electric field as a function of excitation wavelength and applied field are studied in detail. The results are presented in chapter 6. Finally, carrier recombination dynamics in rare-earth doped nanostructures are measured by using ultrafast spectroscopy. Carrier dynamics in InGaN:Yb3+ nanowires and InGaN/GaN-Eu3+ superlattices are measured by frequency doubling the excitation laser, and the effects of implantation of rare-earth ions into the host material have been investigated. The results from the experimental measurements are presented in chapters 7 & 8. These experimental findings might help to understand the challenges associated with these nanostructured materials in the applications of quantum information processing, single photon emitters, and to integrate them into existing optoelectronic devices.

Committee:

Eric A. Stinaff, Prof. (Advisor); Sergio E. Ulloa, Prof. (Committee Member); Arthur R. Smith, Prof. (Committee Member); Wojciech M. Jadwisienczak, Prof. (Committee Member)

Subjects:

Condensed Matter Physics; Materials Science; Nanoscience; Nanotechnology; Optics; Physics; Quantum Physics; Solid State Physics

Keywords:

Quantum Dots; Quantum Dot Molecules; Light-Matter Interactions; Photoluminescence Excitation; III-V Semiconductor Nanostructures; Tunable Fine Structure Splitting; Time-Resolved Photoluminescence Measurements; Carrier Dynamics in III-V Nanostructures;

Singh, Shatrunjai PQuantitative analysis on the origins of morphologically abnormal cells in temporal lobe epilepsy
PhD, University of Cincinnati, 2015, Medicine: Molecular and Developmental Biology
Epilepsy is a common and devastating neurological disease with no real preventive or cure. In most cases of acquired epilepsy, an initial precipitating injury to the brain is followed by a silent period which eventually culminates into the development of spontaneous, recurrent seizures. This interval between the primary insult and the first seizure is referred to as the latent period of epileptogenesis and is characterized by abnormal morphological and physiological changes in the hippocampus. In the studies described herein, I aim to elucidate changes in the different phases of epileptogenesis with the end goal of deciphering critical epileptogenic mechanisms. To study the initial stages of epileptogenesis, I employed the early kindling model. In this protocol, it is possible to administer a limited number of stimulations sufficient to produce a lifelong enhanced sensitivity to stimulus evoked seizures without associated spontaneous seizures. In these experiments, I characterized the morphology of GFP-expressing granule cells from Thy-1 GFP mice either one day or one month after the last evoked seizure. I observed several morphological changes at the one day time point, which all normalized to control levels at the one month time point. Interestingly, I did not observe the presence of basal dendrites, frequently observed in other models of epilepsy. These findings demonstrate that the early stages of kindling epileptogenesis produces transient morphological changes but not the dramatic pathological rearrangements of dentate granule cell structure seen in typical models associated with spontaneous seizures. To study epileptogenesis after the incidence of spontaneous, recurrent seizures, I used the pilocarpine model of epilepsy. Our lab has previously used this model to show that adult hippocampal neurogenesis is profoundly altered under epileptic conditions, leading to the production of morphologically abnormal dentate granule cells. Under epileptic conditions, these adult generated cells migrate to ectopic locations and develop misoriented basal dendrites. Although it has been established that these abnormal cells are newly-generated, it is not known whether they arise ubiquitously throughout the progenitor cell pool or are derived from a smaller number of bad actor progenitors. To explore this question, I describe clonal analysis experiments conducted in epileptic mice expressing the brainbow fluorescent protein reporter construct in dentate granule cell progenitors. Brain sections were rendered translucent so that entire hippocampi could be reconstructed and all fluorescently-labeled cells identified. The findings revealed that a small number of progenitors produced the majority of ectopic cells in epileptic mice, indicating that either the affected progenitors or their local micro-environments had become pathological. By contrast, granule cells with basal dendrites were equally distributed among clonal groups. These findings strongly predict that distinct mechanisms regulate different aspects of granule cell pathology in epilepsy. The experiments described here utilize different models of epilepsy and employ cutting edge technology to provide valuable insight into the process of epileptogenesis. The results and ideas presented here are intended to advance our knowledge of epilepsy and eventually lead to better antiepileptic therapies.

Committee:

Steve Danzer, Ph.D. (Committee Chair); Mark Baccei, Ph.D. (Committee Member); Kenneth Campbell, Ph.D. (Committee Member); Brian Gebelein, Ph.D. (Committee Member); Ronald Waclaw, Ph.D. (Committee Member)

Subjects:

Nanoscience

Keywords:

Temporal Lobe Epilepsy;Dentate Granule Cells;Clonal Analysis;Quantitative Analysis;Pilocarpine;Neural stem cells

Rai, Rachel H.Synthesis and Characterization of Graphene Based Composites for Non-Linear Optical Applications
Master of Science (M.S.), University of Dayton, 2016, Chemical Engineering
Graphene shows remarkable non-linear optical behavior, where above an incident light intensity threshold, transmission is attenuated. Unfortunately, capitalizing on the unique properties of graphene can be a challenge because the material itself is hard to handle unless graphene is integrated with other materials. The objective of the work presented here is development of premium graphene-based nano-composites for non-linear optical applications. Few and single layer graphene flakes were synthesized through liquid phase exfoliation of graphite in 1-Methyl-2-pyrrolidinon (NMP). The structure of the resultant flakes was then examined using Raman spectroscopy and transmission electron microscopy. Additionally, since the exfoliated graphene had to remain in solution prior to incorporation into the polymer, a study of the segregation behavior of the suspended flakes with respect to time was obtained via analysis of the solution by UV-Visible transmission spectroscopy. Noting the difference in the light transmission through a sample of graphene in suspension as a function of time was a convenient method to obtain the flakes shelf-life, or time at which the homogeneity of the flake concentration drops below acceptable thresholds. The fabricated graphene was incorporated to a Polymethyl methacrylate (PMMA) matrix via spin coating. As means to understand how the spin coating parameters affect the dispersion of graphene, samples where studied under Raman spectroscopy. After determining the optimum synthesis parameters promoting uniform graphene distribution in a heterogeneous matrix, sol-gel/graphene composites were prepared and characterized. The correlation of processing, structure and properties of these novel composites for non-linear optical applications is discussed.

Committee:

Christopher Muratore (Committee Chair); Thomas Cooper (Committee Member); Kevin Myers (Committee Member)

Subjects:

Chemical Engineering; Engineering; Materials Science; Nanoscience

Keywords:

graphene; non-linear optics; optical limiter; nano-composites; graphene synthesis; graphene characterization

Wang, ShiyiEngineering Electromagnetic Wave Properties Using Subwavelength Antennas Structures
Doctor of Philosophy (Ph.D.), University of Dayton, 2015, Electro-Optics
With extraordinary properties, generation of complex electromagnetic field based on novel subwavelength antennas structures has attracted great attentions in many areas of modern nano science and technology, such as compact RF sensors, micro-wave receivers and nano-antenna-based optical/IR devices. This dissertation is mainly composed of two parts. For the first part, the idea of plasmonic localization in optical range is transferred and utilized for generating confined fields with high enhancement in RF range. A subwavelength modified bowtie antenna in RF range is designed for generating strong broadband field enhancement in its extended feed gap. The strongly enhanced RF field within the gap can be applied to directly modulate guided optical wave propagating in a waveguide, which enables to realize indirect RF signal sensing through photonic methods. Systematic exploration for modified bowtie antennas and its substrate effect has been given in this part. In the second part, the RF antenna design idea is extended to infrared and optical range based on antenna scaling theory specific for this spectrum. Both transmission and reflection types of metasurface structures have been designed and proposed to obtain optical needle field with a flat-top longitudinal intensity of depth of focus 5λ. With fine adjustment of different nano-antenna structures, both of the metasurfaces enable to generate complex vectorial field with spatial radial polarization, whose amplitude modulation range covers 0.07 to 1 with binary phase control. Then the scattered field can be tightly focused by a high numerical aperture (NA) lens in order to generate longitudinally polarized flat-top field along propagation direction. By exploring the subwavelength antennas’ mechanism and connections between different frequency regions, this dissertation is expected to provide general guidance for design and characterization of next-generation subwavelength antennas structures with extraordinary electromagnetic wave properties.

Committee:

Qiwen Zhan, PhD (Committee Chair); Partha Banerjee, PhD (Committee Member); Andrew Sarangan, PhD (Committee Member); Imad Agha, PhD (Committee Member)

Subjects:

Electromagnetics; Engineering; Experiments; Nanoscience; Nanotechnology; Optics

Keywords:

Subwavelength antennas; vectorial light; meta-surface; nano structures; full wave control; optical needle field

Liyanage, Geethika KaushalyaInfrared Emitting PbS Nanocrystals through Matrix Encapsulation
Master of Science (MS), Bowling Green State University, 2014, Physics
Colloidal semiconductor nanocrystals are becoming widely used materials in developing high performing light emitting devices in the Infrared region. The ability of tuning their properties at the colloidal stage and easy-low-cost processing of these Quantum Dot solutions in to nanocrystal solid devices makes them a perfect candidate in the device engineering process. One of the main challenges that present methods of making Infrared emitting thin film devices face is that both quantum yield efficiency and stability is compromised when processing them from colloidal stage to the solid state. The proposed method provides a better solution to this problem allowing a better assembly of Infrared emitting PbS nanocrystals encapsulated into an all inorganic matrix of wide band gap CdS. The newly proposed Semiconductor Matrix Encapsulation Nanocrystal Array (SMENA) method provides a better passivation in the PbS surfaces which can be optimized to reduce the non-radiative exciton decaying processes preserving the emission characteristics of the film. Due to the strong localization of the electrical charges, the films fabricated using modified SMENA method shows a bright emission yield compared to the current reported techniques. In addition to a high emission quantum yield, fabricated films exhibit excellent thermal and chemical stability, which avails their integration into solid state IR emitting technologies.

Committee:

Mikhail Zamkov (Advisor); Haowen Xi (Committee Member); Liangfeng Sun (Committee Member)

Subjects:

Chemical Engineering; Chemistry; Condensed Matter Physics; Engineering; Experiments; Materials Science; Nanoscience; Nanotechnology; Physics

Keywords:

nanomaterials; Lead sulfide; colloidal quantum dots; inorganic matrix; time-resolved fluorescence; quantum yield; Infrared materials; Matrix encapsulation

Ruan, DihuiGlass Formation Behavior of Model Ionomers
Master of Science, University of Akron, 2015, Polymer Engineering
Ionomers – polymers with bonded ionic groups – are important because of their wide applications in various fields. The glass formation behavior of ionomers has direct impact on their properties and performance, and therefore demands a deeper understanding. The ionic groups collapse into distributed ionic aggregates in the ionomers. The region surrounding the aggregates shows dynamic suppression among uncharged polymer chains, and the size of this region is correlated to chains’ persistence length. This phenomenon is a consequence of the fact that there is bond connectivity between aggregates and polymers, which differs from materials with only non-bonded interfaces, like composites. Here, we perform molecular dynamics simulations of model ionomers to test this conventional view and propose a fundamental reconsideration of grafted micro-phase materials like ionomers. Based on our results, the covalent grafts are not the central factor determining linear segmental dynamics and glass formation. Instead, we find that they are equivalent to strong physical attractions, as in ungrafted nanocomposites and nanoconfined glass-formers, where near-interface mobility suppression is mediated by cooperative rearrangements intrinsic to glass-forming liquids, rather than by a unique covalent `tethering effect’. This conclusion indicates the need for a revised understanding of glass formation and segmental dynamics in materials incorporating covalent grafting.

Committee:

David Simmons, Dr. (Advisor); Robert Weiss, Dr. (Committee Member); Kevin Cavicchi, Dr. (Committee Member)

Subjects:

Molecular Physics; Nanoscience; Physics; Polymers

Keywords:

ionomers; glass; nanocomposites; EHM; Adam-Gibbs; segmental relaxation; dynamics; interface; crosslink

Drerup, Jennifer LeeFe Thin Film Deposition for investigation by Spin-Polarized Scanning Tunneling Microscopy
Master of Science, The Ohio State University, 2011, Physics
Spin-polarized scanning tunneling microscopy (SP-STM) has become more popular in recent years as interest in spintronics is on the rise. An essential part of characterizing spin-polarization of the STM tip is to provide a predictable and reliable substrate on which to test. One such substrate is the Fe monolayer on W(110). This surface not only shows magnetic resolution with SP-STM, but also shows magnetic contrast at the magnetic domain barriers with normal STM. This makes the substrate verifiable with a non-magnetic STM tip and useful for determining tip orientation in SP-STM. In this study, deposition of Fe thin films by Knudsen cell was characterized using a quartz crystal microbalance. Longer deposition times were more successful in achieving consistent adsorption levels. This is attributed to heating of the quartz crystal during the deposition process, leading to easier adsorption onto the crystal surface.

Committee:

Jay Gupta, PhD (Advisor); Jonathan Pelz, PhD (Committee Member)

Subjects:

Condensed Matter Physics; Nanoscience; Physics; Solid State Physics

Yan, YueranCdTe, CdTe/CdS Core/Shell, and CdTe/CdS/ZnS Core/Shell/Shell Quantum Dots Study
Doctor of Philosophy (PhD), Ohio University, 2012, Chemistry and Biochemistry (Arts and Sciences)

CdTe, CdTe/CdS core/shell, and CdTe/CdS/ZnS core/shell/shell quantum dots (QDs) are potential candidates for bio-imaging and solar cell applications because of some special physical properties in these nano materials. For example, the band gap energy of the bulk CdTe is about 1.5 eV, so that principally they can emit 790 nm light, which is in the near-infrared range (also called biological window). Moreover, theoretically hot exciton generated by QDs is possible to be caught since the exciton relaxation process in QDs is slower than in bulk materials due to the large intraband energy gap in QDs. In this dissertation, we have synthesized the CdTe and CdTe/CdS core/shell QDs, characterized their structure, and analyzed their photophysical properties.

We used organometallic methods to synthesize the CdTe QDs in a noncoordinating solvent. To avoid being quenched by air, ligands, solvent, or other compounds, CdS shell was successfully deposited on the CdTe QDs by different methods, including the slow injection method, the successive ion layer adsorption and reaction (SILAR) method, and thermal-cycling coupled single precursor method (TC-SP). Our final product, quasi-type- II CdTe/CdS core/shell QDs were able to emit at 770 nm with a fluorescence quantum yield as high as 70%. We also tried to deposit a second shell ZnS on CdTe/CdS core/shell QDs since some compounds can quench CdTe/CdS core/shell QDs. Even though different methods were used to deposit ZnS shell on the CdTe/CdS core/shell QDs, CdTe/CdS/ZnS core/shell/shell QDs still can be quenched.

Furthermore, the CdTe/CdS core/shell and CdTe/CdS/ZnS core/shell/shell QDs were transferred into aqueous phase, phosphate buffered saline or deionized water, by switching the hydrophilic ligands (thiol or PEG ligands). The thioglycolic acid (TGA)-capped CdTe/CdS core/shell QDs can be kept in aqueous phase with high fluorescence quantum yield (60% - 70%) for more than two months. However, some other compounds in organic or aqueous phase can quench CdTe/CdS QDs. Additionally, the stability of the different ligands capped CdTe/CdS QDs was tested by dialysis measurement, the hydrodynamic diameters of CdTe and CdTe/CdS core/shell QDs were measured by dynamic light scattering, and dissolving issue was found when CdTe and CdTe/CdS core/shell QDs were diluted in CHCl3.

We have characterized the CdTe core and the CdTe/CdS core/shell QDs by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), small angle X-ray scattering (SAXS), and ICP-OES measurements. We have found that the CdTe core was of a zincblende structure, and the shell was a wurtzite structure. And the CdTe/CdS QDs were core/shell QDs instead of alloying QDs.

We have also analyzed the photophysical properties of CdTe and CdTe/CdS core/shell QDs. Time-resolved photoluminescence (PL) measurements showed the emission decay lifetimes in the tens of nanoseconds. Additionally, ultrafast charge carrier relaxation dynamics of the CdTe core and CdTe/CdS core/shell QDs were studied by the femtosecond transient absorption (TA) spectroscopy. The transient absorption spectra of CdTe and CdTe/CdS core/shell QDs showed multiple bleaches, which have been assigned to the 1S3/2(h)-1S(e), 2S3/2(h)-1S(e), and 1P3/2(h)-1P(e) transitions. The spectral shifts of these bleaches after shell deposition have been analyzed in the context of a quasi-type-II carrier distribution in the core/shell samples, and interestingly the red shift was only contributed from the conduction band energy levels shifting to lower energy. In addition, the ultrafast evolution of these bleach features has been examined to extract electron cooling rates in these samples. A fast decay component in the 1S3/2(h)-1S(e) transition of the small CdTe QDs was discovered due to the hole being trapped by the defects on the surface of QD.

Further, we have studied the PL quenching process of the air exposed CdTe QDs via the PL decay and transient absorption measurements. Oxygen was shown to cause strong PL quenching of the CdTe QDs. There was no significant difference of the PL decay lifetimes between the CdTe QDs under argon and air, but a fast decay lifetime of 2.6 ps was observed in transient absorption data, indicating that the quenching process happened in a very short time scale (~ 2.6 ps).

Committee:

Paul Van Patten, PhD (Advisor); Hugh Richardson, PhD (Committee Member); Jeffrey Rack, PhD (Committee Member); Eric Stinaff, PhD (Committee Member)

Subjects:

Chemistry; Materials Science; Nanoscience; Nanotechnology

Keywords:

charge transfer; luminescence; quantum dots; quench; transient absorption

Doutt, Daniel R.THE ROLE OF NATIVE POINT DEFECTS AND SURFACE CHEMICAL REACTIONS IN THE FORMATION OF SCHOTTKY BARRIERS AND HIGH N-TYPE DOPING IN ZINC OXIDE
Doctor of Philosophy, The Ohio State University, 2013, Physics

ZnO has received renewed interest in recent years due to its exciting semiconductor properties and remarkable ability to grow nanostructures. As a wide band gap semiconductor, ZnO has many potential future applications including blue/UV light emitters, transparent conductors, biosensors, and electronic nanoscale devices. While the versatility of ZnO is exciting, many hurdles keep it from reaching full device potential. Chief among them are the role of native point defects and impurities in the fabrication of high quality contacts and high, yet controllable, n- and p-type doping. The scope of this work explores the electronic properties of ZnO surfaces and interfaces and the impact of native point defects on Schottky barrier formation and doping.

The results presented here use a complement of depth-resolved cathodoluminescence spectroscopy (DRCLS), atomic force microscopy (AFM), Kelvin probe force microscopy (KPFM), and surface photovoltage spectroscopy (SPS) to show that surface treatment and processing plays a significant role in the quality, stability, and efficiency of potential next generation devices. This is evident in our results showing that the Zn-polar surface is more stable and capable of forming higher quality Au Schottky barriers as compared to the O-polar surface. We go on to reveal a significant metal sensitivity and surface polarity dependence that correlates with defects and interface chemistry on ZnO. We’ve also shown the significant impact of surface preparation and post processing techniques on the optical efficiency and stability of ZnO surfaces. Our measurements reveal that remote oxygen plasma (ROP) processing is capable of decreasing oxygen vacancy related defects (VO-R) on the O-polar surfaces as well as creating new zinc vacancy related (VZn-R) defects on the Zn-polar surface. Furthermore, we have correlated the formation of native point defects with interface chemical reactions and surface morphology on ZnO. With this, we were able to determine the relationship between the strength of near band edge to deep level defect emissions finding a threshold dependence on surface roughness that can serve as a figure of merit for substrate polishing and etching. Further experiments reveal that ZnO nanostructures grow spontaneously on ZnO polar surfaces in air that generate strong potential variations which correlate with native defects. Using a staged annealing process we were able to determine the activation energy for ZnO nanostructured growth revealing that Zn-interstitial diffusion is the dominant mechanism feeding growth. In a separate study, we observed the strong interplay between VZn-R defects and dopants in degenerately Ga-doped ZnO films. In doing so we found that the DRCLS Fermi level thresholds provide a useful indicator of carrier density, revealing depth variations that anticorrelate with VZn-R densities.

The ability to understand and control native defects as well as surface and interface chemical reactions in ZnO could allow for efficient and stable n- and p-type doping and serve to making higher quality Schottky diodes for future device applications.

Committee:

Brillson Leonard (Advisor); Pelz Jonathon (Committee Member); Patton Bruce (Committee Member); Humanic Thomas (Committee Member)

Subjects:

Condensed Matter Physics; Electrical Engineering; Materials Science; Nanoscience; Physics; Solid State Physics

Keywords:

ZnO; GZO; Cathodoluminescence; Scanning Probe Microscopy; SPM; Atomic Force Microscopy; AFM; Kelvin Probe Force Microscopy; KPFM; Surface Photovoltage Spectroscopy; SPS; X-ray Photoemission Spectroscopy; XPS; Schottky Barriers; Surfaces and Interfaces

Mackura, MarkNano-confinement Effects of Crystalline Walls on the Glass Transition of a Model Polymer
Master of Science in Polymer Engineering, University of Akron, 2013, Polymer Engineering
Efforts to understand the effect of confinement on the glass transition of an unentangled polymer melt in the field of coarse-grained simulations have focused on the use of free-standing and supported films with atomistically smooth substrates. The effects these types of nano-confinement have produced are of great value when trying to understand the interfacial effects on the structure and dynamics of the material that can dominate many properties at very small length scales (< 100nm). Generally these supported and freestanding films exhibit an overall depression in the glass transition temperature Tg. Recently, enhanced particle dynamics have been shown near an attractive, atomistically smooth interface accompanied by a locally varied temperature dependence (fragility) of glass formation. However, an atomistically smooth force field wall omits several key physical features of nano-confinement by real solid substrates; specifically, it lacks any of the atomic structure that exists in these systems, which alters packing in glass-forming liquids near the interface and hinders motion in the transverse directions. This is particularly problematic in sheared systems where a lack of atomistic wall structure would lead to highly unrealistic boundary dynamics, for example, dynamics in a nano-fluidic device or in porous media. The present study aims to incorporate two attractive, fixed crystalline walls in a similar study of these nano-confinement effects. Currently employed bead-spring models used in the previously discussed studies have been shown to heterogeneously crystallize when confined by crystalline walls despite exhibiting homogeneous crystallization resistance, and therefore a new model has been developed to evaluate this and other problems. The new model is a bond length modification of the Finitely Extensible Non-Linear Elastic (FENE) model, named the short-FENE. An examination of the bulk glass formation properties of multiple bond length variations of the short-FENE model shows that it can be used to tune the breadth and abruptness of the glass transition (fragility) without requiring the use of an additive. When crystalline walls confine the short-FENE model, it exhibits an increase in Tg and fragility relative to the bulk. Also the wall is shown to hinder particle motion and produce the expected increase local particle relaxation times.

Committee:

David Simmons, Dr. (Advisor); Bryan Vogt, Dr. (Committee Member); Hendrik Heinz, Dr. (Committee Member)

Subjects:

Nanoscience; Polymers

Keywords:

glass formation; bead-spring model; nano-confinement; fragility; finitely extensible non-linear elastic model; FENE; short-FENE; crystalline walls; hard confinement; amorphous materials; molecular packing

Fan, XueliuTailored 3D Graphene-Based Materials for Energy Conversion and Storage
Doctor of Philosophy, Case Western Reserve University, 2018, Macromolecular Science and Engineering
With the rapid growth of energy electronics market, search for novel nanomaterials for efficient and eco-friendly energy conversion and storage has become an important task for manufacturers. Graphene, a two-dimensional carbon nanomaterial, has been widely applied in energy area due to its unique electric, chemical and physical properties. The atomic-scale and layered structures facilitate the integration of graphene into three-dimensional structures and heterostructures, thus opening a new world for rational design. This thesis consists of five chapters. After the first introduction chapter, the second chapter describes nitrogen-doped nanoporous graphene, which was synthesized on the zeolite-Y template with a tunable nitrogen content. The N-doped nanoporous graphene exhibits promising catalyzing performance in oxygen reduction reaction and is comparable to commercial Pt/C. In the third chapter, graphene networks was fabricated on sputtering-coated Cu to form a freestanding thin film. The films can be easily transferred onto various substrates, such as PDMS and Si wafer, which can be integrated into flexible and transparent electrochemical-double-layer supercapacitors (EDLC) to offer an opportunity for fabricating the wearable devices. In the fourth chapter, a nitrogen doped graphene-CNT-graphene ordered structure is designed on the anodic aluminum oxide substrate, which, as electrodes in a double-layer supercapacitor, exhibits the high capacity and long-term stability. The completely controllable graphene-CNT-graphene structures provide a chance to achieve ordered three-dimensional graphene hybrids for the first time. Finally, in the last chapter, molybdenum disulfide decorated three-dimensional graphene heterostructure is realized. The hybrids can serve as anodes in lithium-ion battery to exhibit a high capacity, excellent rate capability, and long cycle life.

Committee:

Liming Dai (Advisor)

Subjects:

Energy; Engineering; Nanoscience; Nanotechnology

Keywords:

graphene, energy

Borra, Venkata Shesha VamsiWhiskers: The Role of Electric Fields in the Formation Mechanism and Methods for Whisker Growth Mitigation
Doctor of Philosophy, University of Toledo, 2017, Electrical Engineering
Electrically conductive hair-like structures, referred to as whiskers, can bridge the gap between densely spaced electronic components. This can cause current leakage and short circuits resulting in significant losses and, in some cases, catastrophic failures in the automotive, aerospace, electronics and other industries since 1946. Detecting a metal whiskers (MWs) is often a challenging task because of their random growth nature and very small size (diameters can be less than 1 µm, lengths vary from 1µm to several millimeters). Many decades ago the industry introduced whisker mitigating Pb in the solders used to fabricate electric and electronic parts. In recent years, this changed because the European Union (EU) passed a legislation in 2006, called “Restriction of the use of Certain Hazardous Substances (RoHS) in Electrical and Electronic Equipment”, which requires a reduction and elimination of the use of Pb in technology. Thus, the issue of undesirable and unpredictable whiskers growth has returned and there is a renewed interest in the mechanisms of formation of these structures. None of the whisker growth models proposed to date are capable of answering consistently and universally why whisker grow in the first place and why Pb addition suppresses their growth. Understanding MW nucleation and growth mechanism are of significant interest to this project, since this would potentially allow the development of new accelerated-failure testing methods of electronic components to replace existing testing methods which are generally found to be unreliable. In particular, this research is intended to study the effects of electric fields on the whisker growth, which according to the recently developed electrostatic theory[1] of whisker growth, are of crucial importance. This theory proposes that the imperfections on metal surfaces can form small patches of net positive or negative electric charge leading to the formation of the anomalous electric field (E), which governs the whisker development in those areas. Stress relaxation based theories are quite popular and effects of electric fields on the whisker growth were often overlooked in such theories and hypotheses. Several approaches to understand the role of electric fields in the whisker forming mechanism were considered in this work. The influence of E-fields, AC as well as DC, on both vacuum deposited films and electroplated film samples were studied. One of the approaches involved the use of strong high-frequency AC E-fields (optical fields) on the metal surface, which was realized by Surface Plasmon Polariton (SPP) excitations using a CW laser. Another approach was biasing sample using a DC field was carried out using either a parallel-capacitor geometry or a very localized electric field application, obtained by using a sharp conductive Atomic Force Microscope’s cantilever tip maintained at a known distance. The E-field of localized charged defects in glass formed by irradiation with gamma rays from a radioactive source was studied as well. In addition, an attempt was made to correlate the internal structure and the external striations on the whisker. Experimental validations of the massive whisker nucleation (MWN) concepts were accomplished. Whisker cross-section analysis was performed using focused-ion-beam (FIB) milling and the resulted samples were examined using scanning transmission electron microscopy (STEM). Finally, the possibility of mitigating whisker growth by using thin semiconducting sublayers such as a NiO intermediate layer between Cu and Sn was studied in this project, and a special attention was dedicated to investigate the presence and the effect of intermetallic compounds (IMCs)

Committee:

Daniel Georgiev, Dr. (Committee Chair); Vijay Devabhaktuni, Dr. (Committee Member); Victor Karpov, Dr. (Committee Member); Devinder Kaur, Dr. (Committee Member); Anthony Johnson, Dr. (Committee Member)

Subjects:

Aerospace Materials; Chemical Engineering; Condensed Matter Physics; Electrical Engineering; Engineering; Experiments; Materials Science; Metallurgy; Nanoscience; Nanotechnology; Physics; Plasma Physics; Solid State Physics; Theoretical Physics

Keywords:

Tin; Sn whiskers; electrostatic theory; whisker mitigation; surface plasmon polariton SPP; focused ion beam FIB; scanning and transmission electron microscope SEM, TEM; atomic force microscope AFM; gamma radiation; thin films; nucleation; characterization

Rodier, Bradley JModification of Graphene Oxide for Tailored Functionality
Doctor of Philosophy, Case Western Reserve University, 2018, Chemistry
Carbon nanomaterials have garnered increasing attention in the past decade due to their multifunctionality. Graphene, a two-dimensional hexagonal lattice of sp2 hybridized carbons, has been of particular interest due to its high electrical and thermal conductivity as well as it mechanical robustness, good gas barrier properties, and antimicrobial properties. Derivatives of graphene, graphene oxide (GO) and reduced graphene oxide (rGO), provide unique chemical landscapes of oxygenated moieties for targeted chemistry, and also allow for isolation of single nanosheets. The aim of this work was to explore the utilization of these chemical targets to provide novel and unexplored structures and properties through the unique capability of GO to assemble at fluid-fluid interfaces. In doing so, the use of GO as a nanosurface for polymerizations, composite enhancement, and surfactants for complex emulsions systems were defined. Herein, GO assembly at the interface of oil in water was used in combination with grafting to, grafting from, and grafting through polymerizations. This demonstrated that polymer brushes could successfully be attached on the surface of this nanomaterial through covalent means to prepare Janus nanosheets, as well as that GO could be incorporated to the surface of polymer particles. This interfacial assembly was then extended to feed materials for 3D printing and encapsulation of phase change materials. This demonstrated that rGO could be put at the surface of these materials and bestow electrical and thermal conductivity, to tailored and novel composites. Lastly, a facile process was developed to chemically modify GO nanosheets such that they can be dispersed in a variety of solvents. This allowed for the formation of stable oil-in-oil emulsions. This system was then used for emulsion polymerizations. Several polymeric architectures could be prepared by reactions in the oil-in-oil emulsions based on the phase location of the monomers; this process allowed for the incorporation of water sensitive reagents normally ignored in traditional oil-in-water emulsion reactions. The work reported herein provides a foundation from which to explore novel and useful materials architectures using fundamental chemical modifications.

Committee:

Geneviève Sauvé, Dr. (Committee Chair); Emily Pentzer, Dr. (Advisor); John Protasiewicz, Dr. (Committee Member); Anna Samia, Dr. (Committee Member); Alp Sehirlioglu, Dr. (Committee Member)

Subjects:

Chemistry; Materials Science; Nanoscience; Polymer Chemistry; Polymers

Keywords:

Graphene oxide, surface chemistry, carbon nano materials, polymers

McClanahan, Eric RobertModification and Enhancement of Epoxide Coatings via Elastomeric Polysulfides, Self-Assembled Nanophase Particles, Functional Sol-Gels, and Anti-Corrosion Additives
Doctor of Philosophy, University of Akron, 2017, Polymer Engineering
Epoxides are widely used in the coatings industry as coating binders. Epoxide binders have several useful characteristics, which include the ability to react with polysulfide resin modifiers and thermosetting amide curatives. In order to improve the characteristics of epoxide coatings, various functional and non-functional additives and resins can be grafted or added to the epoxide binder. The first study involved the use of reacting polysulfides with epoxides and crosslinking with a polyamide to form films and coatings. While epoxide-polysulfides have heavily investigated in the literature for physical and fracture properties, a study investigating the fracture properties of epoxide-polysulfides at cold, ambient, and hot temperatures has not been attempted. The results indicated a toughening phenomenon at 5-10 wt. % polysulfides that led to enhancements in the fracture properties. Also, the addition of polysulfide content led to improvements in the flexibility and the impact resistance of the formulations. Self-assembled NAnoPhase (SNAP) particles are nano-scale functional sol-gels that were pioneered as corrosion-resistant surface preparations on aluminum substrates. No studies have investigated the use of SNAP particles as functional additives within epoxide-polyamide coating systems. SNAP sol-gel particles were formulated and added into epoxide-polyamide films and coatings. It was found that SNAP sol-gel particles were able to enhance the mechanical properties and corrosion resistance of the coatings. These studies are a novel discovery because the SNAP functional sol-gels are also able to act as a primer additive. In the last study, carbon nanotubes and magnesium were both added into epoxide-polyamide films and coatings systems, which were tested for mechanical and corrosion resistance properties, respectively. While existing studies have investigated the use of magnesium or carbon nanotubes as anti-corrosion additives in epoxide coatings, the tandem use of nanotubes and magnesium has not yet been investigated in the literature in terms of corrosion and mechanical properties. In the absence of magnesium, the addition of carbon nanotubes enhanced the mechanical properties (fracture and tensile properties) of the epoxide-polyamide films, although the enhancement was marginalized when magnesium was added. The carbon nanotubes also aided in the enhancement of the coating’s corrosion resistance as measured via electrochemical impedance spectroscopy (EIS).

Committee:

Mark Soucek (Advisor); Evans Edward (Committee Member); Karim Alamgir (Committee Member); Cavicchi Kevin (Committee Member); Miyoshi Toshikazu (Committee Member)

Subjects:

Aerospace Materials; Engineering; Mechanical Engineering; Nanoscience; Nanotechnology; Polymer Chemistry; Polymers

Keywords:

Coatings; Sol-Gels; Epoxides; Epoxies; Polysulfides; Self-Assembled Nanophase Particles; Coating Fracture Properties; Carbon Nanotubes; Aerospace Coatings; Corrosion Testing; Particle Characterization; Coatings Formulation

Murray, Abner APlant Virus Nanoparticle In Situ Cancer Immunotherapies
Doctor of Philosophy, Case Western Reserve University, 2018, Molecular Biology and Microbiology
In the United States, melanoma is the fifth leading cancer in men and sixth in women. The current course of treatment is tumor resection, which is extremely effective in early stage tumors. However, because of the aggressive nature of melanoma and the access to the underlying vascular “highway”, metastasis is common and deadly. Therefore, novel therapeutic strategies need to be devised to intervene and improve survival rates of patients diagnosed with metastatic disease; at the same time, prophylactic strategies are needed to prevent development of metastatic disease and/or recurrence. This work proposes the use of plant virus-like nanoparticles (VLPs) for application in cancer immunotherapy. Here the goals were to investigate the underlying mechanism of the potent antitumor response of cowpea mosaic virus (CPMV), as well as to define the engineering design parameters for future translational development. The central hypothesis was that by inserting plant VLPs into the tumor microenvironment, the particles will interact with and activate the innate immune response. Furthermore, this localized response can positively affect immune tumor recognition by removing tumor microenvironment tolerance and increase tumor antigen presentation. Three specific aims were used to test this hypothesis. Aim one set to determine the usability of flexible high aspect ratio particles for mono and combination therapies. Here monotherapy involved the use of potato virus X (PVX) while combination added doxorubicin (DOX) with varying forms of co-administration. The data showed that the combination of the two therapies was indeed synergistic, however, benefit in treatment outcome was only achieved when the PVX immunotherapy and DOX chemotherapy were administered separately (rather than combined into a single nanoparticle). Aim two set to determine the engineering design space of the VLPs and to determine the immunological changes upon tumor treatment with plant VLPs. Here antitumor efficacy by in situ vaccination with CPMV was compared to various formulations of tobacco mosaic virus (TMV) of distinct shapes and compositions. In structure-function experiments icosahedral CPMV outperformed all of the TMV-based formulations as an in situ vaccine. Among the TMV formulations the dissociated coat proteins showed no effect, while the full-length and shortened TMV particles were able to significantly delay tumor growth nevertheless not to the same efficacy compared to CPMV. Tumor cytokine analysis and immune cell profiling indicated the onset and triggering of distinct immunological pathways comparing the treatment arms CPMV vs. TMV. Together, data indicate that some plant viral nanotechnology platforms are more suitable for application as in situ vaccines than others; understanding the intricate differences and underlying mechanism of immune activation may set the stage for clinical development of these technologies.

Committee:

Nicole Steinmetz, PhD (Advisor); Alan Levine, PhD (Committee Chair); Julian Kim, MD (Committee Member); Susan Brady-Kalnay, PhD (Committee Member); Robert Silverman, PhD (Committee Member)

Subjects:

Biology; Biomedical Engineering; Immunology; Medicine; Microbiology; Molecular Biology; Nanoscience; Nanotechnology; Oncology; Plant Biology; Plant Pathology; Plant Sciences; Virology

Keywords:

nanotechnology; immunotherapies; virotherapy; cancer; tumor; tumor biology; microbiology; virology

Paluri, Sesha Lakshmi ArathiAnalytical-based methodologies to examine In vitro nanokinetics of silver nanoparticles
Doctor of Philosophy (PhD), Wright State University, 2017, Biomedical Sciences PhD
Advancements in the nanotechnology have taken a huge leap in 21st century resulting in 1814 consumer products containing nanomaterials. About 47% of these products belong to the health and fitness sector and ~24% utilize silver nanoparticles (AgNPs). Despite the promising biomedical applications of AgNPs (e.g. bone cements, contrasting agents, and drug-carriers), lack of standardized methods for examining their nanokinetics (i.e., Absorption, Distribution, Metabolism, and Elimination (ADMEs)) limit their clinical implementation. The current work addresses this knowledge gap by developing analytical-based approaches for studying in vitro ADMEs of AgNPs. To demonstrate the versatility of these methodologies, two in vitro kidney study models (Vero 76 and HEK 293 cells) were tested under pre-determined exposure concentrations (3-300 µg mL-1) and times (4-48 hr). The ADMEs of both AgNPs+ and AgNPs- in Vero 76 cells were summarized here for illustrative purposes: [A]: Inductively coupled plasma optical emission spectroscopy (ICP-OES) facilitated the evaluation of critical kinetic parameters including order of reaction, rate constant and bioavailability (first-order, kabs= 0.05 hr-1, Cmaximum < 20.7±4% and Tmaximum > 48 hr), [D] CytoViva and Raman imaging outlined the uptake and cellular localization patterns (e.g., Raman results of mapped cells exposed to AgNPs+ and AgNPs- were dominated by the signals corresponding to the plasma membrane and cytoplasm, respectively), [M] Cloud point extraction (CPE) followed by tangential flow filtration enhanced the separation of two Ag species from the cellular matrix (= 11±4% of the AgNPs were converted to Ag+), and [E] ICP-OES also facilitated the construction of clearance-time curves to evaluate the elimination kinetics of sub-lethal AgNPs (first-order, keli=0.039 hr-1). Furthermore, a new laboratory module was developed according to the five essential features laid by the National Research Council for inquiry-based teaching and learning in order to introduce undergraduate and graduate students to the fabrication and characterization of green and non-green silver and gold nanoparticles. As demonstrated by the results of the formative assessments, this hands-on laboratory was not only well-received by students from diverse backgrounds, but also stimulated their critical thinking and helped them acquire new laboratory skills.

Committee:

Ioana Sizemore, Ph.D. (Committee Chair); Norma Adragna, Ph.D. (Committee Member); David Dolson, Ph.D. (Committee Member); Steven Higgins, Ph.D. (Committee Member); Mill Miller, Ph.D. (Committee Member)

Subjects:

Biomedical Research; Education; Nanoscience

Keywords:

biomedical research; nanoscience; education

Ferraro, Mercedes MQuantitative Determination of Residual Stress on Additively Manufactured Ti-6Al-4V
Master of Science in Engineering, Youngstown State University, 2018, Department of Mechanical and Industrial Engineering
Additive manufacturing (AM) is a method to build a three-dimensional part through the layering of material. One category of AM, Direct Energy Deposition (DED), is commonly used with the titanium alloy, Ti-6Al-4V, and has shown to be useful for aerospace, transportation, and biomedical applications. However, the DED process induces anisotropic material properties due to the nonuniform temperature distribution, which causes residual stresses. In addition, when handling titanium and its alloys, the processing history and post-heat treatment greatly influence the microstructure, residual stresses, and mechanical properties. Previous research has been done to investigate the residual stresses by methods such as X-ray diffraction, contour methods, and finite element simulations. However, a less established technique for determining the residual stresses is through nanoindentation. Nanoindentation is the use of instrumented indentation to determine the mechanical behavior and properties of a small volume based on the load versus depth results. By applying nanoindentation techniques to a DED Ti-6Al-4V, it was found that the nanoindentation results varied based on the cross-sectional height of the sample. The reason for this occurrence was believed to be due to the microstructure and the existence of residual stresses. The nanoindentation results were then used to quantify the residual stresses present in the DED Ti-6Al-4V part using the basic methodology of Suresh and Giannakopoulos. Similar to the nanoindentation hardness and elastic modulus results determined, the residual stresses also showed an increasing trend when increasing in height along the cross-section. More specifically, as the height along the build direction increased, the residual stresses present increased in compressive behavior. However, future work is required to verify the validity of the Suresh model and its application to DED Ti-6Al-4V. Ultimately, by understanding the material characteristics of this part, it would help to further enhance the structural integrity of AM parts.

Committee:

Jae Joong Ryu, PhD (Advisor); Hazel Marie, PhD (Committee Member); C. Virgil Solomon, PhD (Committee Member)

Subjects:

Materials Science; Mechanical Engineering; Nanoscience

Keywords:

Additive Manufacturing; Direct Energy Deposition; Nanoindentation; Residual Stress; Ti-6Al-4V

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