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Palmer, Benjamin CliveSensitization Effects on Environmentally Enhanced Cracking of 5XXX Series Alloys: Macro and Mesoscale Observations
Master of Sciences (Engineering), Case Western Reserve University, 2017, Materials Science and Engineering
The focus of this study was on the tensile behavior and damage development in 5083- H131 Al-Mg alloy sensitized to different levels. Samples were tested in the as-received state, after sensitization at 175°C for 100hrs, or 80°C for >500hrs. Tensile testing was conducted under moderate (50%RH) or low (<1%RH) humidity environments to determine the environmental effects on the mechanical behavior of the material. Three different deformation/fracture modes were present depending on the sensitization level and testing environment. Interrupted tensile tests and microscopy revealed that strain was more heterogeneously distributed in the highly sensitized specimens compared to the as-received ones. Differential scanning calorimetry was also performed as a means of determining the degree of sensitization of specimens thermally exposed at temperatures from 60-175°C. This technique was able to detect the presence of Mg-rich phase(s) at thermal exposures as low as 60°C, though it has quantitative limits due to the resolution limit.

Committee:

John Lewandowski, Dr. (Advisor); David Schwam, Dr. (Committee Member); Clare Rimnac, Dr. (Committee Member)

Subjects:

Materials Science; Mechanical Engineering

Keywords:

Environment-enhanced-cracking; Stress corrosion cracking; 3-D tomography; Aluminum-magnesium alloys; Differential scanning calorimetry

Ghods, MasoudEffect of Convection Associated with Cross-section Change during Directional Solidification of Binary Alloys on Dendritic Array Morphology and Macrosegregation
Doctor of Engineering, Cleveland State University, 2017, Washkewicz College of Engineering
This dissertation explores the role of different types of convection on macrosegregation and on dendritic array morphology of two aluminum alloys directionally solidified through cylindrical graphite molds having both cross-section decrease and increase. Al- 19 wt. % Cu and Al-7 wt. % Si alloys were directionally solidified at two growth speed of 10 and 29.1 µm s-1 and examined for longitudinal and radial macrosegregation, and for primary dendrite spacing and dendrite trunk diameter. Directional solidification of these alloys through constant cross-section showed clustering of primary dendrites and parabolic-shaped radial macrosegregation profile, indicative of “steepling convection” in the mushy-zone. The degree of radial macrosegregation increased with decreased growth speed. The Al- 19 wt. % Cu samples, grown under similar conditions as Al-7 wt. % Si, showed more radial macrosegregation because of more intense “stepling convection” caused by their one order of magnitude larger coefficient of solutal expansion. Positive macrosegregation right before, followed by negative macrosegregation right after an abrupt cross-section decrease (from 9.5 mm diameter to 3.2 mm diameter), were observed in both alloys; this is because of the combined effect of thermosolutal convection and area-change-driven shrinkage flow in the contraction region. The degree of macrosegregation was found to be higher in the Al- 19 wt. % Cu samples. Strong area-change-driven shrinkage flow changes the parabolic-shape radial macrosegregation in the larger diameter section before contraction to “S-shaped” profile. But in the smaller diameter section after the contraction very low degree of radial macrosegregation was found. The samples solidified through an abrupt cross-section increase (from 3.2 mm diameter to 9.5 mm diameter) showed negative macrosegregation right after the cross-section increase on the expansion platform. During the transition to steady-state after the expansion, radial macrosegregation profile in locations close to the expansion was found to be “S-shaped”. This is attributed to the redistribution of solute-rich liquid ahead of the mushy-zone as it transitions from the narrow portion below into the large diameter portion above. Solutal remelting and fragmentation of dendrite branches, and floating of these fragmented pieces appear to be responsible for spurious grains formation in Al- 19 wt. % Cu samples after the cross-section expansion. New grain formation was not observed in Al-7 wt. % Si in similar locations; it is believed that this is due to the sinking of the fragmented dendrite branches in this alloy. Experimentally observed radial and axial macrosegregations agree well with the results obtained from the numerical simulations carried out by Dr. Mark Lauer and Prof. David R. Poirier at the University of Arizona. Trunk Diameter (TD) of dendritic array appears to respond more readily to the changing growth conditions as compared to the Nearest Neighbor Spacing (NNS) of primary dendrites.

Committee:

Surendra Tewari, Ph.D. (Advisor); Jorge Gatica, Ph.D. (Committee Member); Orhan Talu, Ph.D. (Committee Member); Rolf Lustig, Ph.D. (Committee Member); Kiril Streletzky, Ph.D. (Committee Member)

Subjects:

Aerospace Materials; Automotive Materials; Chemical Engineering; Condensed Matter Physics; Engineering; Fluid Dynamics; High Temperature Physics; Materials Science; Metallurgy

Keywords:

Directional Solidification; Natural Convection; Fluid Flow; Binary Alloys; Macrosegregation; Dendritic Array; Dendrite Morphology; Solutal Remelting; Thermosolutal Convection; Aluminum Alloy; Cross section Change

Holcombe, Evan W.Multi-Scale Approach to Design Sustainable Asphalt Paving Materials
Master of Science (MS), Ohio University, 2017, Civil Engineering (Engineering and Technology)
The continuous use of recycled material in asphalt pavement mixtures, specifically Reclaimed Asphalt Pavement (RAP), Recycled Asphalt Shingles (RAS) and Re-Refined Engine Oil Bottoms (REOB), have developed an increasing need to further evaluate the performance of these mixtures at the micro and macro-levels, as the use of such materials reduces cost of virgin materials and energy consumption. Although asphalt binder, including recycled or additive materials, may meet a desired performance grade (PG) using macro-scale tests, they may lack critical nano-mechanical properties that largely affect long-term performance, such as adhesion and diffusive efficiency between virgin and recycled binders. These commonly overlooked properties can correlate with performance behaviors such as fatigue and low temperature cracking during field performance. This study was conducted in two major parts. Part one was performed with the intent to evaluate the nano-mechanical and blending-diffusive efficiency of toluene and trichloroethylene extracted RAP and RAS binder using tapping mode imagery and force spectroscopy using Atomic Force Microscopy (AFM). Furthermore, this study was set to correlate the findings from micro-testing to macro-scale laboratory performance tests including Semi-Circular Bending (SCB) to evaluate fatigue cracking resistance at intermediate temperatures, Asphalt Concrete Cracking Device (ACCD) to evaluate low temperature cracking and AASHTO 283 ITS to study moisture damage susceptibility of intermediate course mixtures with high RAP and RAS contents. Results showed that tear-off RAS material have a significant effect on fatigue and low temperature cracking performance, primarily at long-term aged conditions. Neither tear-off nor manufactured waste RAS binder blend well with virgin binder, whereas RAP shows a zone of blending. AFM imaging indicated all extracted RAS binder had a much rougher surface texture than RAP or virgin binders and did not contain any “bee” structures. The procedure of splitting RAP material for sampling during the volumetric mix design process has a significant effect on the optimal virgin binder content design, which in turn has a large effect on performance properties. Part two of this thesis summarizes the results of laboratory tests that were conducted to evaluate the microstructure, adhesion and other mechanical properties of asphalt binders meeting the same Performance Grade (PG) but produced using different processes and modifiers. Atomic Force Microscope (AFM) tapping mode imaging and force spectroscopy experiments were conducted on different straight run and modified asphalt binders meeting the same performance grade. In addition, Bitumen Bond Strength (BBS) and Semi-Circular Beam (SCB) tests were conducted on the different binders evaluated and mixes prepared using those binders, respectively, for comparison. The AFM images indicated that the microstructure of the modified binders was different than those of the straight run binders. The AFM force spectroscopy test results showed that binders with same PG grade could have significantly different adhesion properties. The results of the SCB tests indicated that the fatigue performance was affected by the adhesion properties of the binders evaluated. The AFM bonding energy had a very good correlation with the flexibility index parameter obtained from SCB test results. The results of this part suggests that the adhesion properties of asphalt binders should be included in their evaluation process and specifications.

Committee:

Munir Nazzal, Dr. (Advisor)

Subjects:

Civil Engineering; Materials Science

Keywords:

reclaimed asphalt pavement; recycled asphalt shingles; re-refined engine oil bottoms; atomic force microscopy; fatigue cracking; adhesion; diffusion, moisture damage; thermal cracking

Razgoniaev, AntonDesign, synthesis, and characterization of photoresponsive materials using coordination bonds and other supramolecular interactions
Doctor of Philosophy (Ph.D.), Bowling Green State University, 2017, Photochemical Sciences
When designing light-responsive, healable materials and adhesives, these materials need to include controllable reversible, bonding interactions. Such dynamic interactions are difficult to control, however. In this work, we present how these interactions can be controlled by incorporating photoactive metal ions into supramolecular polymer network what allow the tuning of optical and mechanical properties of the polymers with light. Utilizing this approach, we created a series of supramolecular polymer melts and studied their mechanical and photo physical properties. We have shown that the photochemistry and photophysical properties of the metal center can be used to control the mechanical properties of the materials, and introduce new optical and mechanical properties not seen in the traditional covalent polymers. In particular, photo-induced metal-ligand bond labilization led to partial depolymerization of the supramolecular assembly, and softening of the materials. When the light stimulus was removed, the material recovered the initial stiffness back. We also investigated structure-property relationships in such systems where mechanical properties of the supramolecular polymers are controlled by coordination environment around metal cross-linking center. We also considered how polymer host matrix impacts on the photophysical and photochemical properties of chromophores that undergo molecular motion in the exited state. In particular, change in excited state dynamics of [Cu(dmp)2]+ can be used to sense viscosity of various polymers. A linear dependence of excited state lifetime and emission wavelength on viscosity was correlated with restricted photoinduced structural distortion of Cu(I) complex in more flow-resistance media.

Committee:

Alexis Ostrowski, Ph.D. (Advisor); Scott Rogers, Ph.D. (Committee Member); Alexander Tarnovsky, Ph.D. (Committee Member); R. Marshall Wilson, Ph.D. (Committee Member)

Subjects:

Chemistry; Materials Science; Polymer Chemistry; Polymers

Keywords:

Photochemistry; Chemistry; Materials Science; Polymer Chemistry; Polymers

Riyad, M Faisal Simultaneous analysis of Lattice Expansion and Thermal Conductivity in Defected Oxide Ceramics
Master of Science, The Ohio State University, 2017, Mechanical Engineering
Objective of this thesis is to investigate the impact of point defects on thermal conductivity and lattice expansion in uranium dioxide ceramic. Specific emphasize is on light ion irradiation induced point defects which causes the degradation of thermal conductivity of oxide ceramics. Radiation induced defects include vacancies and interstitials hosted by the anion and cation sub lattice of the structure. A crystallographic structure is assumed for each defect and is used to model defect impact on lattice parameter. In ceramic materials, thermal conductivity is governed by phonon modes determined by crystalline structure. The irradiation induced point defects limit thermal transport by acting as phonon scattering centers. The point defects scattering originates from both the mass and ionic radius mismatch between the impurity atom and the host lattice. We present a model to estimate the phonon scattering parameter for different types of point defects and implement it in classical phonon mediated thermal transport model to estimate the thermal conductivity reduction in light ion irradiated UO2. The results are compared to results of experimental measurements. Laser based modulated thermoreflectance (MTR) technique was used to measure the thermal conductivity model in ion irradiated UO2 samples. Unlike laser flash analysis, traditionally used for measuring thermal conductivity in nuclear materials, MTR method has a sensitivity to a few micron thick thin damage resulting from ion beam irradiation. In this technique, the irradiated sample, coated by a thin metallic film, is heated by a harmonically modulated laser pump and a probe beam measures the temperature induced changes in reflectivity. In this work, experimentally measured thermal wave phase profiles obtained from UO2 samples irradiated with 2.6 MeV H+ ions were analyzed using different multilayer approximations of the damaged region. An infinite damage layer approximation model that neglects undamaged layer and peak damage region characteristic to light ion irradiations is discussed. The limitation of the approach and demonstration of its applicability range was analyzed. Finally, measured conductivities of the ion irradiated samples using a thermal conductivity model for point defects was examined. Previously reported XRD measurements on same proton irradiated UO2 samples show the lattice expands linearly as a function of atomic displacements (dpa). The defect concentration can be defined as a function of dpa and the defect production rate. The estimation of defect concentration is validated by accounting their overall contribution to the change in lattice parameters and comparing them with the measured values by XRD. Finally, their overall contribution to the reduction in thermal conductivity is compared with the experimentally measured values to determine the concentration of defects in the lattice structure of UO2.

Committee:

Marat Khafizov, Dr. (Advisor); Sandip Mazumder, Dr. (Committee Member)

Subjects:

Materials Science; Mechanical Engineering; Nuclear Engineering; Nuclear Physics

Keywords:

Lattice Expansion; Thermal Conductivity; Defected Oxide Ceramics

Zhan, XunCrystallization Micro-mechanism of Amorphous Ni-P
Doctor of Philosophy, Case Western Reserve University, 2017, Materials Science and Engineering
The crystallization of near-eutectic amorphous Ni–P can be significantly retarded by alloying a small fraction of tungsten. Complimentary characterization techniques are applied to understand this phenomenon. DSC (differential scanning calorimetry) reveals the isochronal and isothermal crystallization kinetics. XPS (X-ray photoelectron spectroscopy) provides core-level electronic signatures of Ni, phosohorus and tungsten, which reflect SRO (short-range order) evolution during crystallization. FEM (fluctuation electron microscopy) provides the MRO (medium-range order) evolution during crystallization. TEM (transmission electron microscopy) provides high-spatial-resolution information on phase nucleation and spatial distribution of atom species. Physical theory has been developed by combining results of these techniques to explain the role of tungsten: Macroscopic aspect (energetics and kinetics), the presence of tungsten reduces the driving force and increases the activation energy for crystallization. Microscopic aspect (micro-mechanistics), the presence of tungsten probably reduces the free volume (hypothesis) due to large atomic radius ratios of rW/rNi and rW/rP; introduces tungsten atoms diffusion to segregate due to chemical potential difference of tungsten in different crystalline phases; involves the breaking of all of W–P bonds with high bond energy. Moreover, theoretical criteria of an effective metal X alloying to improve the thermal stability of M–ML (metal–metalloid) amorphous systems has been proposed. The criteria are: (1) Large negative heat of mixing among X, M and ML. (2) Minimum amorphous free volume by appropriate combination of rX, rM and rML. (3) Large chemical potential difference of X in minor than in major crystalline phase. (4) Large X–ML and X–M bond energy. The criteria conclude on what other potential alloying elements will do, which has implications for fundamental science and technologies. In addition, magnetization curves of as-plated and tempered Ni80P20 and Ni76W4P20 were measured by VSM (vibrating sample magnetometer). Alloying tungsten does not change the paramagnetism of amorphous Ni80P20, but decreases the saturation magnetization of Ni80P20 after crystallization.

Committee:

Frank Ernst, Dr. (Advisor); John Lewandowski, Dr. (Committee Member); Matthew Willard, Dr. (Committee Member); Rohan Akolkar, Dr. (Committee Member)

Subjects:

Chemical Engineering; Materials Science

Amonson, Michael D.Multiple Charge Carrier Species and Their Effects in Photorefractive Two-Beam Coupling in Potassium Niobate
Master of Science (M.S.), University of Dayton, 2017, Electro-Optics
This thesis reports on an experiment to measure charge carrier contributions from different Fe species and their effects on beam coupling efficiency using self-pumped counter-propagating two-beam coupling in iron-doped potassium niobate KNbO3:Fe. We used multiple continuous wave lasers operating across the visual spectrum to explore charge carrier creation from various transitions. Photorefractive grating formation data was acquired and analyzed using a new theoretical model which incorporates multiple charge carrier species. Initial analysis provides supporting evidence of a multiple charge carrier model and presents new insights about the effects of various charge carriers on the photorefractive periodic space-charge fields.

Committee:

Dean Evans (Advisor)

Subjects:

Electromagnetism; Materials Science; Optics; Physics

Keywords:

Potassium Niobate; Iron Doped Potassium Niobate; Photorefractive; Multiple Charge Carriers; Two-Beam Coupling

Liu, ZhihuiProperties of 3D Printed Continuous Fiber-Reinforced CNTs and Graphene Filled Nylon 6 Nanocomposites
MS, University of Cincinnati, 2017, Engineering and Applied Science: Materials Science
Nanomaterials have attracted much attention due to the excellent properties they possess and their promising applications. The combination of 3D printing and composite materials has redefined the mechanical properties of 3D printed products. In this research, nylon (PA) 6 nanocomposites filled with either carbon nanotubes(CNTs), graphene or graphene-NH2 were 3D printed together with Kevlar fibers into specimens for mechanical tests and other characterizations. Different weight percentages of CNTs and graphene were used to produce the nanocomposites, in order to figure the properties of each nanoparticle reinforced PA 6. The melt mixed CNTs or graphene nanocomposites were extruded into filaments and used in the 3D printer. A Markforged printer allowed the production of continuous Kevlar fiber reinforced nanocomposites. The tensile and flexural tests revealed that the best weight percentage of CNTs is 0.5wt%, where the entanglements and agglomerates of CNTs were not so obvious. Surprisingly, the CNTs filled PA 6 nanocomposites did not show as significant improvements in mechanical properties as graphene filled PA 6, due to the weak interfacial interactions between the CNTs and the PA 6 matrix. The addition of Kevlar fibers increased the tensile strength and flexural modulus of PA 6 by 526% and 1388%. Also, the tensile fatigue results showed that 1%CNT/PA 6+Kevlar specimens have the longest fatigue life among the materials tested. Graphene filled PA 6 presented much better improvements in mechanical properties. With only 0.1wt% of graphene, the tensile modulus improved by 101% and with 1wt% of graphene the modulus improved by 153%. Additionally, although Kevlar fibers dominate the main mechanical properties of these composite materials, the existence of graphene also contributes to the enhancement of strengths and moduli, unlike CNTs. Strong interfacial bonding allows efficient load transfer between matrix and reinforcement. Therefore, graphene-NH2/PA 6 showed significant improvements in both tensile and bending strengths. The tensile modulus of 0.1% graphene-NH2/PA 6 and 1% graphene-NH2/PA 6 are increased by 212% and 253%. Flexural tests showed obvious difference between different nanoparticle fillers. However, the anisotropic specimens did not show much difference between different weight percentages of the same kind of nanocomposite. It is found that the well-dispersion of nanoparticles in the matrix and strong interfacial bonding between the filler and the matrix are the main reasons for the enhancement of mechanical properties of nanocomposites. The addition of Kevlar fibers improved the stiffness and strength of the composites significantly.

Committee:

Jing Shi, Ph.D. (Committee Chair); Gregory Beaucage, Ph.D. (Committee Member); Jude Iroh, Ph.D. (Committee Member)

Subjects:

Materials Science

Keywords:

3D printing;Nanocomposite;CNTs;graohene;Kevlar;Nylon 6

Yang, JianpingSynthesis and Characterizations of Lithium Aluminum Titanium Phosphate (Li1+xAlxTi2-x(PO4)3) Solid Electrolytes for All-Solid-State Li-ion Batteries
Master of Science in Materials Science and Engineering (MSMSE), Wright State University, 2017, Materials Science and Engineering
New-generation low-emission transportation systems demand high-performance lithium ion (Li-ion) batteries with high safety insurance at broad operable temperatures. Highly conductive solid electrolyte is one of the key components for such applications. The objective of this thesis is to synthesize and characterize aluminum doped lithium titanium phosphate, i.e. Li1+xAlxTi2-x(PO4)3 (LATP), one of the solid-state electrolytes for potential applications to all solid-state lithium-ion batteries. In this research, sol-gel method and one step solid-state reaction approaches were explored and critical processes were optimized towards maximizing lithium ion conductivities at room temperature. The impacts of the processing conditions on the structures, morphologies, compositions of the LATP products, and lithium ion conductions were presented. Particle growth kinetics and lithium ion conduction mechanism were briefly discussed. The highest conductivities of LATPs achieved via the sol-gel and solid-state synthesis are 1.24E-04 S/cm and 1.86E-04 S/cm, respectively, exhibiting the feasibilities of applying them to all-solid-state Li-ion batteries.

Committee:

Hong Huang, Ph.D. (Advisor); Allen Jackson, Ph.D. (Committee Member); Raghavan Srinivasan, Ph.D. (Committee Member)

Subjects:

Materials Science

Keywords:

materials science

Sharpnack, Lewis LeeMesomorphism of Newly Synthesized Mesogens and Surface Morphology of Chalcogenide Glass Thin Films
PHD, Kent State University, 2017, College of Arts and Sciences / Department of Physics
This dissertation research describes three related projects. The first was an investigation of two de Vries smectic liquid crystal phases that exhibit lower thermal dependence of the smectic layer spacing than the corresponding conventional smectic phases and are well suited for use in electrooptical devices. The second project studied newly synthesized mesogens. This included investigations of several liquid crystalline semiconducting mesogens and a multitude of candidate de Vries smectic mesogens. The third was an investigation of a new non-contact alignment layer of Arsenic Sulfide (As2S3) to anchor the liquid director and use in electrooptical device. In additional to preliminary characterization methodologies such as polarizing optical microscopy and differential scanning calorimetry, two experimental techniques, X-ray diffraction (XRD) and X-ray reflectivity (XRR), were employed. The X-ray studies were conducted using the in-house spectrometers at Kent State University and the synchrotron X-ray source at the Brookhaven National Laboratory. XRR is used to investigate the structure of potential alignment layers. The results provide important insight into the challenges that need to be overcome to develop this alignment material into a viable commercial product. XRD is used to study the structural properties of several members of two new homologous series of liquid crystal compounds. The study of de Vries materials advances our understanding of the role of various molecular moieties on their phase behavior and, most importantly, their relatively temperature independent layer spacing in the Smectic A (SmA) and Smectic C (SmC) phases. This nearly constant layer spacing is critical for developing new fast ferroelectric and electroclinic effect based displays. The Stevenson research group at Queens University synthesized a multitude of new mesogens incorporating a siloxane tail at one end. This moiety is believed to enhance nano-segregation of the molecules and help form de Vries smectic A and C phases. The results indicate that some of the new mesogens exhibit low layer shrinkage that is indicative of the de Vries behavior. The effects of chain lengths and various moieties on the phase behavior is described in detail. These experiments identified several chiral mesogens as viable candidates for use in ferroelectric displays that are currently the subject of further investigations. Many of the non-chiral molecules studied exhibited de Vries or nearly de Vries layer shrinkage, however, these systems would require the addition of a chiral dopant to be used in ferroelectric applications. Three of the chiral siloxane based mesogens displayed ideal de Vries behavior. The smectic layer spacing changed by 1% or less of the total layer thickness for Si3OK11BPO*, Si3OK11BzPO*, and adpc042. These molecules are presently being investigated for device applications and modified with various terminal groups to enhance the miscibility of nano-particle dopants. Structural studies of novel triphenlyene based organic semiconductors mesogens synthesized by the Twieg group were performed. A desirable trait of organic semiconductors is for the ¿-electron orbitals to overlap and requires that carbon rings in adjacent molecules be parallel. Results of X-ray studies of a series of triphenylene molecules showed a hexagonal columnar (ColHex) phase. The diffraction patterns revealed that the lateral intermolecular distance was ~ 3.5 Å, consistent with the stacking of the triphenelene rings. The high-temperature ColHex phase of these materials at nearly 200 °C may also prove useful for high temperature applications. Films of As2S3 have recently been shown to align liquid crystals. This alignment technique, when fully developed, will eliminate the need for traditional mechanically buffed polymer films deposited on substrates, currently used in liquid crystal displays. Their surface roughness was determined in the two planar directions using x-ray reflectivity profiles to facilitate a comparison with other alignment layers that generate liquid crystal alignment primarily because of their anisotropic surface morphology. Our results reveal that As2S3 films develop anisotropic features under irradiation with polarized blue light that are consistent with the changes that occur in other alignment layers when they are “treated” either with mechanical buffing of polymer films or exposure to linearly polarized UV light. These studies also reveal the development of an extensive oxide layer and the ablation of the film under ambient conditions owing to the absorption of oxygen and moisture. This represents a significant barrier to their commercial applications.

Committee:

Satyendra Kumar, PhD (Advisor); Elizabeth Mann, PhD (Committee Member); Hamza Balci, PhD (Committee Member); Michael Fisch, PhD (Committee Member); Scott Bunge, PhD (Committee Member)

Subjects:

Chemistry; Materials Science; Physics

Keywords:

Reflectivity, liquid crystal, de Vries, ferroelectric, smectic, electrooptic device, display, x-ray diffraction, x-ray reflectivity

Pandey, AnupModeling and Simulation of Amorphous Materials
Doctor of Philosophy (PhD), Ohio University, 2017, Physics and Astronomy (Arts and Sciences)
The general and practical inversion of diffraction data - producing a computer model correctly representing the material explored -is an important unsolved problem for disordered materials. Such modeling should proceed by using our full knowledge base, both from experiment and theory. In this dissertation, we introduce a robust method, Force-Enhanced Atomic Refinement (FEAR), which jointly exploits the power of ab initio atomistic simulation along with the information carried by diffraction data. As a preliminary trial, the method has been implemented using empirical potentials for amorphous silicon (a-Si) and silica ( SiO_2 ). The models obtained are comparable to the ones prepared by the conventional approaches as well as the experiments. Using ab initio interactions, the method is applied to two very different systems: amorphous silicon (a-Si) and two compositions of a solid electrolyte memory material silver-doped GeSe_3 . It is shown that the method works well for both the materials. Besides that, the technique is easy to implement, is faster and yields results much improved over conventional simulation methods for the materials explored. It offers a means to add a priori information in first principles modeling of materials, and represents a significant step toward the computational design of non-crystalline materials using accurate interatomic interactions and experimental information. Moreover, the method has also been used to create a computer model of a-Si, using highly precise X-ray diffraction data. The model predicts properties that are close to the continuous random network models but with no a priori assumptions. In addition, using the ab initio molecular dynamics simulations (AIMD) we explored the doping and transport in hydrogenated amorphous silicon a-Si:H with the most popular4 impurities: boron and phosphorous. We investigated doping for these impurities and the role of H in the doping process. We revealed the network motion and H hopping induced by the thermal fluctuations significantly impacts conduction in this material. In the last section of the dissertation, we employed AIMD to model the structure of amorphous zinc oxide (a-ZnO) and trivalent elements (Al, Ga and In) doped a-ZnO. We studied the structure and electronic structure of these models as well as the effect of trivalent dopants in both the structure and electronic structure of a-ZnO.

Committee:

David A. Drabold (Advisor)

Subjects:

Condensed Matter Physics; Materials Science; Physics

Keywords:

FEAR; neutrons-diffraction data; EDOS; IPR; doping; amorphous Si; amorphous ZnO; trivalent elements doped ZnO

Elmushyakhi, AbrahamIn-Plane Fatigue Characterization of Core Joints in Sandwich Composite Structures
Doctor of Philosophy (Ph.D.), University of Dayton, 2017, Materials Engineering
In practice, adjacent preform sandwich cores are joined with a simple butt joint without special precautions. When molded, this gap is filled with resin and creates a resin rich area. Stress risers will be amplified under cyclic load, and consequently, the serviceability of the structure will be affected. Designers and researchers are aware of this problem; however, quantifying this effect and its intensity and consequence on the service life of the structures has not yet been developed. Despite pervious findings, limited experimental data backed by a comprehensive root cause failure analysis is available for sandwich under axial static, fatigue and post-fatigue. If such a comprehensive experimental characterization is conducted, specifically understanding the nature of the damage, intensity, and residual strength, then a valid multi-scale damage model could be generated to predict the material state and fatigue life of similar composite structures with/without core joints under in-plane static and fatigue load. This research study characterized the effect of scarf and butt core joints in foam core sandwich structures under in-plane static and fatigue loads (R=0.1 and R= -1). Post-Fatigue tensile tests were also performed to predict the residual strength of such structures. Nondestructive Evaluation Techniques were used to locate the stress concentrations and damage creation. A logical blend of experimental and analytical prediction of the service life of composite sandwich structures is carried out. The testing protocol and the S-N curves provided in this work could be reproducible and extrapolated to any kind of core material. This research study will benefit composite engineers and joint designers in both academia and industry to better apprehend the influence of core joints and its consequence on the functionality of sandwich structures.

Committee:

Elias Toubia (Advisor); Paul Murray (Committee Member); Thomas Whitney (Committee Member); Youssef Raffoul (Committee Member)

Subjects:

Aerospace Engineering; Aerospace Materials; Civil Engineering; Composition; Design; Engineering; Materials Science; Mechanical Engineering; Polymers

Keywords:

Sandwich Composite Structures; Design; Fatigue; Damage; Joints; Lightweight Materials; E-glass-vinyl ester; GFRP Laminate; Modeling; Prediction; Nondestructive Testing

Fischdick Acuna, Andres FabricioHybrid Laser Welding in API X65 and X70 Steels
Master of Science, The Ohio State University, 2016, Materials Science and Engineering
Hybrid laser welding presents an important advance in productivity due to high welding speeds. However, fast cooling rates are inherent to the process, affecting the resultant microstructures and joint performance. In this research, three API steels were welded using hybrid laser welding with three distinct preheating conditions. The specimens, which were obtained using one hybrid laser root pass and two other GMAW filling passes, were subjected to microstructural characterization and performance evaluation using hardness and toughness measurements. Incomplete joints with only the hybrid root pass and completed joints (root and filling passes) were evaluated. Hardness mapping revealed as the critical area the top portion of hybrid laser fusion zone, which was subsequently reheated by the GMAW filling pass. Optical and scanning electron microscopy revealed a bainitic-martensitic microstructure with the proportion of those two phases varying as a function of the preheating. Miniaturized Charpy V-notch testing was used to evaluate the local toughness and ductile-to-brittle transition of several regions within the joint. Fractographic analysis confirmed the abrupt transition from ductile-to-brittle behavior. The localized fracture toughness testing showed an adequate joint performance for all tested conditions. Nevertheless, the hardness values meet the requirements only for higher preheating temperature conditions.

Committee:

Antonio Ramirez (Advisor); John Lippold (Committee Member)

Subjects:

Engineering; Materials Science; Metallurgy; Petroleum Engineering

Keywords:

Hybrid Laser, Pipeline, GMAW, HLAW, Steel, Hardness, Toughness, KLST, MCVN, Miniaturized Charpy, Ductile-to-Brittle Transition Temperature, DBTT, Bainite, Martensite

Hehr, Adam JProcess Control and Development for Ultrasonic Additive Manufacturing with Embedded Fibers
Doctor of Philosophy, The Ohio State University, 2016, Mechanical Engineering
Ultrasonic additive manufacturing (UAM) is a recent additive manufacturing technology which combines ultrasonic metal welding, CNC machining, and mechanized foil layering to create large gapless near net-shape metallic parts. The process has been attracting much attention lately due to its low formation temperature, the capability to join dissimilar metals, and the ability to create complex design features not possible with traditional subtractive processes alone. These process attributes enable light-weighting of structures and components in an unprecedented way. However, UAM is currently limited to niche areas due to the lack of quality tracking and inadequate scienti c understanding of the process. As a result, this thesis work is focused on improving both component quality tracking and process understanding through the use of average electrical power input to the welder. Additionally, the understanding and application space of embedding fibers into metals using UAM is investigated, with particular focus on NiTi shape memory alloy fi bers.

Committee:

Marcelo Dapino, Professor (Advisor); Krishnaswamy Srinivasan, Professor (Committee Member); Blaine Lilly, Professor (Committee Member); Peter Anderson, Professor (Committee Member)

Subjects:

Materials Science; Mechanical Engineering

Keywords:

ultrasonic additive manufacturing, ultrasonic consolidation, 3D metal printing, dissimilar metal joining, process modeling, shape memory alloys

Deshpande, AnushreeSynthesis and Characterization of in-situ Nylon-6/Epoxy Blends
MS, University of Cincinnati, 2016, Engineering and Applied Science: Materials Science
Epoxy is a thermosetting polymer known for its excellent adhesion, thermal stability, chemical resistance and mechanical properties. However, one of the major drawbacks of epoxies is its inherent brittleness. In order to overcome this drawback, incorporation of a thermoplastic as a second phase has proven to improve the impact strength without affecting the mechanical properties of epoxy. Researchers in the past have studied polyamide/epoxy blends in terms of blend compatibility, thermo-mechanical properties and morphology via solution blending.

Committee:

Jude Iroh, Ph.D. (Committee Chair); Relva Buchanan, Sc.D. (Committee Member); Raj Manglik, Ph.D. (Committee Member)

Subjects:

Materials Science

Keywords:

polymer blending;in-situ polymerization;nylon-6;epoxy;glass transition temperature;cross-link density

Wheeler, Nicholas RobertLifetime and Degradation Science of Polymeric Encapsulant in Photovoltaic Systems: Investigating the Role of Ethylene Vinyl Acetate in Photovoltaic Module Performance Loss with Semi-gSEM Analytics
Doctor of Philosophy, Case Western Reserve University, 2017, Macromolecular Science and Engineering
The lifetime performance and degradation behavior of photovoltaic (PV) modules is of the utmost importance for the success and growth of solar energy as a major resource for fulfilling growing worldwide energy needs. While PV reliability has been a concern for some time, existing qualification testing methods do not reflect a cohesive picture of the science behind module degradation, and are not capable of accurately predicting module lifetime performance. Towards these goals, a statistical methodology, semi-gSEM, was developed and applied to investigate the response of full sized PV modules to accelerated stress conditions. The results of this initial study indicated that a correlation exists between system level power loss and the buildup of acetic acid resulting from the hydrolytic degradation of ethylene-vinyl acetate (EVA) polymer encapsulant. To further explore this proposed mechanistic pathway, a study was designed and conducted to characterize the degradation of mini-module samples under damp heat accelerated stress conditions. Mini-module samples featured two construction geometries that differed in the thicknesses of screen-printed silver conductive lines (SP-Ag) to assess the impact of gridline size on damp heat induced degradation. Samples were measured non-destructively at many points along their degradation pathway, using techniques that gathered both chemical and electrical information. The semi-gSEM analytical method was applied to this dataset to highlight degradation pathways and mechanisms observed in the experimental results. An EVA encapsulant spectroscopic degradation feature was found to be statistically related to quantified degradation features of simultaneously measured EL images. In turn, the EL image degradation was found to be statistically related to I-V curve parameters describing system level power loss. The degradation pathway observed was attributed to EVA encapsulant degradation leading to metallization corrosion and ultimately system level power loss in the PV mini-module samples. Mini-module samples with thinner SP-Ag conductive lines were observed to be more severely damaged by the metallization corrosion process. This represents a valuable step in exploring the often misunderstood role of EVA degradation in PV module performance loss under damp heat conditions, and demonstrates novel methodologies for building a more integrated picture of PV module degradation as a whole.

Committee:

Roger French (Advisor); Michael Hore (Committee Member); Timothy Peshek (Committee Member); Laura Bruckman (Committee Member); Ozan Akkus (Committee Member)

Subjects:

Materials Science; Plastics; Polymers

Keywords:

Photovoltaics, PV, Lifetime and Degradation Science, EVA, semi-gSEM, Statistics, Data Science, Polymer Degradation, Polymer Science, Polymer Engineering, Materials Science

Giammanco, Giuseppe E.Photochemistry of Fe(III)-carboxylates in polysaccharide-based materials with tunable mechanical properties
Doctor of Philosophy (Ph.D.), Bowling Green State University, 2016, Photochemical Sciences
We present the formulation and study of light-responsive materials based on carboxylate-containing polysaccharides. The functional groups in these natural polymers allow for strong interactions with transition metal ions such as Fe(III). The known photochemistry of hydroxycarboxylic acids in natural waters inspired us in exploring the visible light induced photochemistry of the carboxylates in these polysaccharides when coordinated to Fe(III) ions. Described in this dissertation are the design and characterization of the Fe(III)-polysaccharide materials, specifically the mechanistic aspects of the photochemistry and the effects that these reactions have on the structure of the polymer materials. We present a study of the quantitative photochemistry of different polysaccharide systems, where the presence of uronic acids was important for the photoreaction to take place. Alginate (Alg), pectate (Pec), hyaluronic acid (Hya), xanthan gum (Xan), and a polysaccharide extracted from the Noni fruit (NoniPs), were among the natural uronic acid-containing polysaccharide (UCPS) systems we analyzed. Potato starch, lacking of uronate groups, did not present any photochemistry in the presence of Fe(III); however, we were able to induce a photochemical response in this polysaccharide upon chemical manipulation of its functional groups. Important structure-function relationships were drawn from this study. The uronate moiety present in these polysaccharides is then envisioned as a tool to induce response to light in a variety of materials. Following this approach, we report the formulation of materials for controlled drug release, able to encapsulate and release different drug models only upon illumination with visible light. Furthermore, hybrid hydrogels were prepared from UPCS and non-responsive polymers. Different properties of these materials could be tuned by controlling the irradiation time, intensity and location. These hybrid gels were evaluated as scaffolds for tissue engineering showing great promise, as changes in the behavior of the growing cells were observed as a result of the photochemical treatment of the material. We present these natural and readily available, polysaccharide-based, metal-coordination materials as convenient building blocks in the formulation of new stimuli responsive materials. The photochemical methods developed here can be used as convenient tools for creating advanced materials with tailored patterns and gradients of mechanical properties.

Committee:

Alexis Ostrowski, Ph.D. (Advisor); Michael Geusz, Ph.D. (Committee Member); George Bullerjahn, Ph.D. (Committee Member); R. Marshall Wilson, Ph.D. (Committee Member)

Subjects:

Chemical Engineering; Chemistry; Materials Science; Polymer Chemistry; Polymers

Keywords:

photochemistry; polymers; polysaccharides; hydrogels; stimuli-responsive materials; iron; coordination chemistry; biomimetic materials; drug delivery; tissue engineering; cartilage; biomaterials; nanotechnology; photopatterning; green chemistry

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

Li, GuangzeConnectivity, Doping, and Anisotropy in Highly Dense Magnesium Diboride (MgB2)
Doctor of Philosophy, The Ohio State University, 2015, Materials Science and Engineering
Magnesium diboride (MgB2) is a superconducting material which can be potentially used in many applications such as magnetic resonance imaging system (MRI), wind turbine generators and high energy physics facilities. The major advantages of MgB2 over other superconductors include its relatively high critical temperature of about 39 K, its low cost of raw materials, its simple crystal structure, and its round multifilament form when in the form of superconducting wires. Over the past fourteen years, much effort has been made to develop MgB2 wires with excellent superconducting properties, particularly the critical current density Jc. However, this research has been limited by technical difficulties such as high porosity and weak connectivity in MgB2, relatively small flux pinning strength, low upper critical field Bc2 and relatively high anisotropy. The goal of this dissertation is to understand the relationship between superconducting properties, microstructure, and reaction mechanisms in MgB2. In particular, the influences of connectivity, Bc2, anisotropy and flux pinning were investigated in terms of the effects of these variables on the Jcs and n-values of MgB2 superconducting wires (n-value is a parameter which indicates the sharpness of resistive V-I transition). The n-values of traditional “Powder in Tube (PIT)” processed MgB2 wires were improved by optimizing precursor species after the identification of microstructural defects such as so-called “sausaging problems”. Also, it was found that “high porosity and weak connectivity” was one of the most critical issues which limited the Jc performance in typical MgB2. To overcome this problem, highly dense, well-connected MgB2 conductors were successfully fabricated by adopting an innovative “Advanced Internal Magnesium Infiltration (AIMI)” process. A careful study on the reaction kinetics together with the microstructural evidence demonstrated how the MgB2 layer was formed as the infiltration process proceeded. As a result, it is possible to control the MgB2 layer growth in the AIMI-processed MgB2 wires. The best AIMI wires, with improved density and connectivity, accomplished an outstanding layer Jc, which was 1.0 × 105 A/cm2 at 4.2 K and 10 T, nearly 10 times higher than the Jcs of PIT wires. The engineering Je of AIMI wires, namely the critical current over the whole cross-sectional area in the wire, achieved 1.7 × 104 A/cm2 at 4.2 K, 10 T, 200 % higher than those of PIT wires. Finally, two promising dopants, Dy2O3 and O, were engineered to incorporate with MgB2. Dy2O3 nanopowders, co-doped with C in AIMI wires, enhanced the Jc performance at elevated temperatures such as 20 K. Oxygen, on the other hand, doped into MgB2 thin films through a newly-developed O2 annealing process, improved Bc2 to 14 T at 21 K. Both of the doping studies were helpful to understand the superconducting nature of MgB2.

Committee:

Michael Sumption (Advisor); Michael Mills (Committee Member); Sheikh Akbar (Committee Member)

Subjects:

Materials Science

Keywords:

Magnesium diboride; MgB2; AIMI; infiltration; diffusion; doping; anisotropy; connectivity; Bc2; wire; thin film; kinetics; n-value; oxygen; Dy2O3; powder in tube; PIT; CTFF; IMD; pulsed laser deposition; PLD; Jc; microscopy; superconductivity

Bensah, Yaw DInterfacial Solid-Liquid Diffuseness and Instability by the Maximum Entropy Production Rate (MEPR) Postulate
PhD, University of Cincinnati, 2015, Engineering and Applied Science: Materials Science
Numerous investigations spanning over sixty years have failed to comprehensively validate any of the currently existing solid-liquid growth instability theories. A recent comparison of the linear stability-model predicted solute diffusion coefficients from both land and space based solidification experiments, with the independently measured solute diffusion coefficients obtained from non-solidification experiments has also failed to show any correlation with measurements made by direct (non-solidification) techniques. A new model based on maximum entropy production rate postulate (MEPR) is proposed for the prediction of solid-liquid interface stability. A test of the new MEPR model with numerous published experiments shows that all published instability conditions of planar to perturbed interface are accurately predicted to the right order by the new model. The MEPR model avoids the association of a solid-liquid surface energy for the solid-liquid interface between the phases or a liquid diffusion coefficient which are both key features of the existing models. The development of the model has led to the establishment and confirmation of the two major types of solid-liquid interfaces being noted; a diffuse interface and a sharp interface. The formation of either a diffuse interface or a sharp interface at the solid-liquid interface is determined by a constant N. A diffuse interface is present when N is greater than two whiles a sharp interface is formed when N is less than one but greater than zero. The model is able to predict the diffuseness interface thickness and the number of lattice spacings called the driving force diffuseness. An inverse form of the Jackson’s criterion is introduced as thermal roughness which is unified into the diffuseness model as the total diffuseness. The total diffuseness is the sum of the driving force diffuseness and thermal diffuseness which is able to accurately predict the conditions for facet and non-facet formation at interface breakdown. It is also able to predict the facet to non-facet transition with changing solidification conditions. The diffuse interface and the sharp interface are both critical in predicting facets and non-facets at the interface at instability. In model also establishes a new interface instability criterion for the presence of both diffuse interface and sharp interface which can correctly predict the order of V/GL ratio for the instabilities from a planar interface into a perturbed interface if the corresponding partition coefficient are known.

Committee:

Jainagesh Sekhar, Ph.D. (Committee Chair); Relva Buchanan, Sc.D. (Committee Member); Jude Iroh, Ph.D. (Committee Member); Rodney Roseman, Ph.D. (Committee Member); Vijay Vasudevan, Ph.D. (Committee Member)

Subjects:

Materials Science

Keywords:

Maximum Entropy Production Rate Postulate;Entropy Generation;Solidification;Solid-Liquid Interface;Diffuse Interface Instability;cellular morphological bifurcation

Ge, SiruiThe Entanglement-Disentanglement Transition (EDT) During Creep With Either Constant Or Oscillatory Stress In Highly-Entangled Polybutadiene Solution
Master of Science, University of Akron, Polymer Science
Nonlinear rheological behavior of entangled polymer systems has been investigated for decades, most of which were carried out in strain-controlled mode. In 2004, the yield-like Entanglement-Disentanglement Transition (EDT) was observed in entangled polymer solutions during creep at constant stress. The 2004 study attracted further investigations that attributed the EDT to edge instability. In this work, it is shown that the EDT can take place in absence of any edge instability in the highly entangled 1,4-polybutadiene solutions. In addition, the behavior of EDT was also studied using oscillatory stress-controlled mode (LAOStress) to minimize edge effect. In the LAOStress, EDT takes place when the responding strain grows in amplitude over time. The distortion of the strain response was observed upon the EDT. In order to reflect the nonlinear viscoelasticity, the harmonic analysis and strain decomposition was conducted. Apparent higher harmonics was found in the strain response. In addition, different disentanglement mechanisms are founded in two samples.

Committee:

Shi-Qing Wang (Advisor); Mesfin Tsige (Committee Member)

Subjects:

Materials Science; Physics; Polymers

Ecker, Allison M.A Systematic Evaluation of Chemical, Physical, and Mechanical Properties of an Epoxy Resin System for Validation and Refinement of Atomistic Simulations
Master of Science (M.S.), University of Dayton, 2016, Materials Engineering
Despite numerous studies on thermoset resin systems, understanding of the influence of chemical network structure on mechanical properties is still premature. Recently multiscale simulations combining quantum mechanics and molecular mechanics have provided an unprecedented pathway for property prediction for a wide range of polymeric systems. Experimental guidance, validation, and refinement of these models are currently in high demand; therefore, this study focused on systematic experimentation to fabricate an epoxy resin system with known chemical structure and controlled processing conditions with spectroscopic characterization of the products for insight on the resultant chemical network structure. Finally, detailed thermomechanical and fracture mechanics studies were conducted to connect the chemistry with the processing and the mechanics. Atomistic simulations were performed in parallel on similar material systems. Key findings of this study include molecular conversion using IR spectroscopy and its relationship with glass transition temperature and fracture toughness, the illustration of etherification of epoxy resins during curing, and the influence of molecular weight on reactivity with the crosslinking agent. All of these experimental findings are significant assets for parameterization of on-going multiscale models and essential stepping-stones for improving the fidelity of these models and implementing these tools for property prediction.

Committee:

Donald Klosterman, Ph.D. (Committee Chair); Rajiv Berry, Ph.D. (Advisor); Charles Browning, Ph.D. (Committee Member); Dhriti Nepal, Ph.D. (Committee Member)

Subjects:

Materials Science

Keywords:

epoxy; atomistic; ftir; dma; mechanical properties; chemical network

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;

Bricker, StephenAnomaly Detection and Microstructure Characterization in Fiber Reinforced Ceramic Matrix Composites
Master of Science (M.S.), University of Dayton, 2015, Electrical Engineering
Ceramic matrix composites (CMCs) have the potential to replace current superalloys being used in hot components of jet engines. CMCs with continuous fiber reinforcement exhibit significant strength retention beyond temperatures at which Nickel based superalloys approach their melting temperature (900 C). While ceramics typically exhibit brittle failure modes making them unsuitable for use in dynamic systems, fiber reinforcement increases fracture toughness, crack growth resistance and strength. Differences in weave type, processing technique, and chemical makeup, however, result in a broad range of material microstructures each with a high degree of variability. Little is known about how the variation and imperfections within the microstructure affect the material properties. It is theorized that stress concentrations exist at certain abnormal microstructural configurations, resulting in either crack nucleation or propagation. Due to the amount of data available and the amount of variation in the microstructure, it is impractical to hope to discover the relationship between microstructural organization and cracking simply by observation. Instead, it is thought that the areas of greatest importance are those that do not adhere to the typical behavior of the material. These areas can be highlighted for analysis via anomaly detection methods for any measurable feature. In this thesis, two features are developed to describe the microstructure: fiber orientation and orientation gradient. Because fiber reinforcments are the primary method for strength enhancement, the features defined in this work both describe fibers, though the anomaly detection algorithm can be applied to other material constituents. Various image pre-processing techniques are implemented to prepare the feature field for anomaly detection. Novel techniques for segmentation of individual material phases are described. An ellipse detection algorithm for identification of fibers is described, as well as a subsequent fiber tracking algorithm. The orientation and orientation gradient fields are described in detail. Fiber orientation refers to the geometric interpretation of individual fibers embedded in ceramic matrix. The orientation gradient of fibers describes the relative changes in orientation in a neighborhood of fibers. Eigen-analysis of the orientation gradient reveals the geometric distortion of fiber orientations with position. This affect is similar to an affine transformation with shear and scaling. It is shown that by modeling the normal behavior of a microstructure, anomalies can be identified and described. Here, it is shown that anomalies of the orientation gradient can be identified and are commonly linked to expansion/contraction at fiber tow edges. This is a large step in correlating microstructure organization with damage, and ultimately optimizing material design.

Committee:

Russell Hardie, Dr. (Advisor); Craig Przybyla, Dr. (Committee Member); Jeff Simmons, Dr. (Committee Member)

Subjects:

Electrical Engineering; Materials Science

Keywords:

anomaly detection; fiber tracking; ceramic matrix composites; microstructure charaterization; gaussian mixture modeling

Zhao, PeiE-CRADLE v1.1 - An improved distributed system for Photovoltaic Informatics
Master of Sciences, Case Western Reserve University, 2016, EECS - Computer and Information Sciences
Solar energy is becoming a more important energy source. With the photovoltaic industry experiencing its unprecedented growth in the past decade, the study of PV modules and their durability and lifetime performance is playing an important role in making solar energy a better, more reliable product. To facilitate PV analytics, a distributed system, called E-CRADLE was developed in 2013. Based on that, a number of improvements have been made forming the E-CRADLE v1.1. The improvements include: a monitoring system, a new database schema for PV data, and an easy way to process PV data. The monitoring system ensures the system is working properly. The new database schema is designed for PV data in a NoSQL database. And its universal design ensures it works with our old data as well as data in the future. The new way to process PV data makes distributed computing power accessible even to non-programmers.

Committee:

Guo Qiang Zhang (Committee Chair); Roger French (Committee Co-Chair); Mingguo Hong (Committee Member)

Subjects:

Materials Science; Systems Design; Technology

Keywords:

distributed system, informatics, photovoltaic, hadoop, hbase,

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