Master of Science, University of Toledo, 2022, Geology

Wetlands' water and nutrient retention functions depend on their soil properties, hence the need to understand the spatial-temporal variation of these properties. The use of soil cores and in situ sensors to assess soil properties distribution is limited due to their high cost, field efforts, and disturbances. This study seeks to advance the use of non-invasive geophysical methods using soil electrical conductivity via electromagnetic imaging (EMI) for estimating wetlands' soil properties distribution. First, I acquired spatial distribution of soil apparent electrical conductivity (ECa) and magnetic susceptibility (MSa) via EMI over a 162,000 m2 restored wetland using an EM-38-MK2 instrument towed behind a utility terrain vehicle equipped with a differential ground positioning system. I collected twenty-two undisturbed soil samples and analyzed them in the laboratory for soil moisture (SMC), organic matter (SOM), porosity, bulk density, and texture. A linear regression model was used to compare the correlation between each soil property with measured ECa and MSa, while ECa was used to predict the distribution of SMC and SOM using the statistical model validated using a leave-one-out technique. Measured ECa correlates strongly with soil texture, SMC, and SOM, with SOM showing a slightly dominant control. These results show that ECa can predict the distribution of SMC and SOM in wetland soils to an accuracy of ~67-70% for these datasets. While these results validate the potential for extending EMI to characterize wetland soils, reliance on statistical correlation is limited to the study site and data range. Cross-correlation between the soil properties also limits understanding of the contribution of each soil property to the measured bulk conductivity. Decoupling this requires a mechanistic understanding of the current conduction processes within wetland soils, considering electromigration via the soil pore fluid and surface conduction at the grain-fluid interface. T (open full item for complete abstract)

Committee: Kennedy Doro Prof. (Committee Chair); Richard Becker Prof. (Committee Member); Michael Weintraub Prof. (Committee Member) Subjects: Agriculture; Aquatic Sciences; Electromagnetics; Environmental Science; Environmental Studies; Geology; Geophysics; Hydrologic Sciences; Hydrology; Natural Resource Management; Soil Sciences; Water Resource Management

Master of Science, Miami University, 2022, Chemical, Paper and Biomedical Engineering

The effect of aluminum doping on the electrical and photoluminescent (PL) properties of flux-grown single crystal ZnGa2O4 was investigated. The undoped and Al-doped (0.55 at% Al) single crystal samples, with maximum dimensions of 6 mm and 4.5 mm (respectively), were both extremely electrically insulating. Low-temperature photoluminescence of single crystal ZnGa2O4 was measured for the first time. XRF, Raman, and photoluminescence analyses suggest the presence of a ZnO impurity phase in both the undoped and Al-doped single crystal samples, contributing to a strong UV-blue PL emission. A sharp PL peak at 500 nm and an atypical yellow-orange broadband emission, possibly related to impurities and either VO or Oi defects (respectively), were also observed for both samples. A PL peak at 621 nm unique to the Al-doped sample was observed. The effects of forming gas annealing, substrate material, and various PLD process conditions on the electrical properties of thin film ZnGa2O4 were also studied. Electrical resistivity decreased with oxygen partial pressure and increased with substrate temperature. The presence of zinc-rich impurity phases seemingly led to lower resistivities. Annealing in forming gas at 500°C generally led to a reduction in resistivity, while annealing at 700°C led to extreme electrical insulation for all samples.

Committee: Lei Kerr (Advisor); Kevin Leedy (Committee Member); Shashi Lalvani (Committee Member) Subjects: Chemical Engineering; Materials Science

Master of Science (MS), Ohio University, 2021, Physics and Astronomy (Arts and Sciences)

ALDOSARI, NORAH, A., M.S., December 2021, Physics and Astronomy The Electrical Properties of Naturally Grown Contacts to Thin Film MoS2-based Devices Director of Thesis: Eric A. Stinaff Two-dimensional semiconducting transition metal dichalcogenides (TMDs) have attracted attention due to their interesting electrical and optical properties. These 2D TMDs have various properties and structures. Many TMD materials are considered ideal candidates for optical and electronic devices due to their sizable band gap which is going from an indirect gap in bulk materials to direct gap in monolayers. Additionally, the most important achievement along 2D based device applications is having a good sample quality and having a control of fabrication process. In this study optical and electrical measurements are used to study the properties of as- grown contacts to thin film MoS2 based devices. Molybdenum disulfide was fabricated on Si/SiO2 substrates using chemical vapor deposition (CVD) method, and then the grown sample was patterned using photolithography process in order to deposit metal contacts which serve as both source material and as-grown contacts to the TMD material. PL and Raman were using to characterize MoS2, and the results show high quality of the material. The electrical characterization of as grown MoS2 based devices indicates a good metal-semiconductor-metal (MSM) Schottky contact. Moreover, the current through the devices was up to sub-micro-Amperes. As-grown MoS2 based devices performance was improved through thermal annealing up to 150C with stable in MoS2 structure. However, increasing of annealing temperature to 200C and higher has an adverse effect on the performance of the devices and leads to a decrease in the value of the current passing through the devices.

Committee: Eric Stinaff (Advisor) Subjects: Physics

Master of Science (MS), Bowling Green State University, 2019, Physics

Zinc oxide (ZnO) is a compound semiconductor with a direct wide band gap of 3.4 eV with a high exciton binding energy of 60 meV at room temperature. It is a widely investigated semiconductor due to its high potential for optoelectronic applications in the UV region, especially, for light-emitting diodes and lasers. In these applications of ZnO, native point defects play key roles. The understanding of these defects will help us to realize and control the performance of ZnO in these applications. Also, it will help us to realize p-type doping in ZnO, which will open a way for oxide semiconductor based bipolar devices. Due to the reproducibility of high-quality ZnO crystals and their interesting properties, it is preferred for extensive research over other wide band gap semiconductors. So far, as research points out, native point defects are not well understood. In our work, we will present electrical and optical characterization studies done on ZnO single crystals as well as on polycrystals, and we will relate these measurements to defect studies using Positron Annihilation Lifetime Spectroscopy (PALS) and Coincident Doppler Broadening Spectroscopy (CDBS). It was found that the increase in well-known green luminescence is associated with a decrease in conductivity and charge carrier concentration. Positron lifetime spectroscopy measurements were carried out to reveal the origin of defects responsible for decreasing the conductivity and enhancing the green luminescence. Lastly, it was interesting to observe the decrease in the ratio between green luminescence to near band emission as the laser power increased.

Committee: Farida Selim Ph.D. (Advisor); Lewis P. Fulcher Ph.D. (Committee Member); Marco Nardone Ph.D. (Committee Member) Subjects: Physics

Doctor of Philosophy (PhD), Wright State University, 2019, Engineering PhD

Truly single layer (monolayer) films of unmodified zigzag single-walled carbon nanotubes by using the Langmuir-Blodgett (LB) technique have been processed successfully. Measurements of their mechanical and optoelectric properties were achieved. Different theoretical equations were used based on the results obtained from the experimental part to study the properties and structures of the produced material and their composite. The produced films were highly oriented as determined by polarized Raman spectroscopy and as shown by scanning tunneling microscopy (STM). The films have a significant amount of flexibility which makes their behavior similar to rubbery materials. They can also be deposited on different types of substrates with different shapes depending on the required applications. Nanocomposites utilizing Poly (methyl methacrylate)-(PMMA) matrix were also prepared and characterized. Both direct mixing and in-situ polymerization techniques were employed to investigate the effect of mixing method on the produced composite properties. In addition to that, a comparison process between the theoretical models which were used to estimate the composite modulus with the experimental results for direct mixing method of the composite is applied with emphasizing the effect of the interphase factor on the empirical calculated composite modulus values.

Committee: Amer S. Maher Ph.D. (Advisor); Raghavan Srinivasan Ph.D. (Committee Member); Ahsan Mian Ph.D. (Committee Member); Henry D. Young Ph.D. (Committee Member); Paul T. Murray Ph.D. (Committee Member) Subjects: Engineering; Nanoscience; Nanotechnology

Master of Science (MS), Ohio University, 2019, Mechanical Engineering (Engineering and Technology)

Aluminum alloys with improved electrical and mechanical performance are a highly sought-after due to their potential use as energy efficient conductors in power transmission, electronics, and aerospace systems. In this thesis, a novel hot extrusion alloying (HEA) process was used to synthesize aluminum/graphite nano-alloys using commercially available AA1100 and graphite nanoparticles (GNP) as precursors to improve electrical properties. The effects of GNP content from 0 – 1 wt.%, on the electrical and mechanical properties were evaluated. Results showed that the addition of 0.25 wt.% GNPs to the Al substrate improved its electrical conductivity by 2.1%, current density by 7.9%, ultimate tensile strength by 6.1% and yield strength by 30.3% compared to the control sample with no GNP additives. Improvements in electrical conductivity and current density were observed for all Al/GNP formulation at 60 °C and 90 °C. Ductility of the Al/GNP nano-alloys decreased with increasing GNP content. The improvement in Al/GNP electrical performance is attributed to GNP exfoliation at the temperatures and shear stresses experienced during hot extrusion, leading to the formation of highly conductive graphene particles.

Committee: Keerti Kappagantula (Advisor) Subjects: Materials Science; Mechanical Engineering

Master of Science (MS), Ohio University, 2019, Mechanical Engineering (Engineering and Technology)

In this work, copper-graphene alloys were synthesized through a novel hot extrusion alloying process utilizing low-defect density and high-defect density graphene additives. The room temperature electrical resistivity, temperature coefficient of resistance, and current density of the copper-graphene samples were all experimentally measured. Experimental results demonstrated that the introduction of 0.0017 wt.% low-defect density graphene into a copper matrix resulted in a 1.8% decrease in electrical resistivity, a 16.8% decrease in temperature coefficient of resistance, and a 10.1% increase in current density over a copper-only control sample processed and synthesized under the same conditions. The introduction of 0.01 wt.% high-defect density graphene into a copper matrix resulted in a 1.6% decrease in electrical resistivity, a 9.5% decrease in temperature coefficient of resistance, and a 12.6% increase in current density over a control sample processed and synthesized under the same conditions. This is the first time that the introduction of graphene into a copper matrix has resulted in improved electrical properties over the material limitations of copper in bulk-scale forms with reduced porosity and a consolidated microstructure. These new copper-graphene alloys may be incorporated into applications such as nano-electronics or motor coil windings so as to minimize electrical losses and decrease thermal energy generation.

Committee: Keerti Kappagantula (Committee Chair); Frank Kraft (Committee Member); Jay Wilhelm (Committee Member); Eric Stinaff (Committee Member) Subjects: Materials Science; Mechanical Engineering

Doctor of Philosophy (Ph.D.), University of Dayton, 2017, Engineering

Conductive biopolymers are starting to emerge as potential scaffolds of the future. These scaffolds exhibit some unique properties such as inherent conductivity, mechanical and surface properties. Traditionally, a conjugated polymer is used to constitute a conductive network. An alternative method currently being used is nanofillers as additives in the polymer. In this dissertation, we fabricated an intelligent scaffold for use in tissue engineering applications. The main idea was to enhance the mechanical, electrical properties and cell growth of scaffolds by using distinct types of nanofillers such as graphene, carbon nanofiber and carbon black. We identified the optimal concentrations of nano-additive in both fibrous and film scaffolds to obtain the highest mechanical and electrical properties without neglecting any of them. Lastly, we investigated the performance of these scaffold with cell biology. To accomplish these tasks, we first studied the mechanical properties of the scaffold as a function of morphology, concentration and variety of carbon nanofillers. Results showed that there was a gradual increase of the modulus and the fracture strength while using carbon black, carbon nanofiber and graphene, due to the small and strong carbon-to-carbon bonds and the length of the interlayer spacing. Moreover, regardless of the fabrication method, there was an increase in mechanical properties as the concentration of nanofillers increased until a threshold of 7 wt% was reached for the nanofiller film scaffold and 1%wt for the fibrous scaffold. Experimental results of carbon black exhibited a good agreement when compared with data obtained using numerical approaches and analytical models, especially in the case of lower carbon black fractions. Second, we examined the influence of electrical properties of nanofillers based on the concentration and the geometry of carbon nanofillers in the polymer matrix using experimental and numerical simulation approaches. The (open full item for complete abstract)

Committee: Khalid Lafdi (Advisor) Subjects: Biomedical Engineering; Engineering; Materials Science

Doctor of Philosophy, University of Akron, 2017, Mechanical Engineering

This work provides a novel method for determining interlaminar fracture properties at both room and elevated temperature, offering the first glimpse of the interlaminar fracture behavior of CMCs at elevated temperatures. Interlaminar fracture properties play an important role in predicting failure of structural components for CMC materials. Elevated temperatures induce more severe conditions for interlaminar properties resulting in a weaker interlaminar toughness. The main challenges associated with determining interlaminar fracture toughness are the ability to measure crack growth without visual observation and to develop an experimental setup that can be used at both room and high temperature. Hence, a non-visual crack monitoring technique has been successfully introduced to estimate crack length in CMCs using electrical resistance. In a parallel effort, a wedge-loaded double cantilever beam method has been developed to determine the interlaminar fracture properties of CMCs at room and elevated temperatures. It has been found that the wedge method does not depend on the wedge material, as long as the correct coefficient of friction is taken into consideration. Additionally, the wedge method was found to be comparable to the traditional double cantilever beam method. The interlaminar fracture properties depend immensely on the composite microstructure and the weave architecture; the interlaminar crack propagates along the longitudinal fiber tows, passing through the porosities, which serve as stress concentration points. Moreover, depending on the fiber tows orientation along the crack propagation path, a rising or flat R-curve behavior can be seen for the same composite system. High temperature testing revealed that the energy required to initiate a crack at room temperature is greater than that at 815 °C. However, more energy is required to propagate the interlaminar crack at high temperature for some CMC systems (such as PIP SiC/SiNC). This behavior was (open full item for complete abstract)

Committee: Gregory Morscher Dr. (Advisor); Minel Braun Dr. (Committee Member); Kwek-Tze Tan Dr. (Committee Member); Gary Doll Dr. (Committee Member); Alper Buldum Dr. (Committee Member) Subjects: Materials Science; Mechanical Engineering

Master of Science, Miami University, 2015, Physics

In this research, the transport properties of Sb-doped ZnO wires were investigated. ZnO:Sb wires were grown successfully using a thermal evaporation method with about 9%-4% atomic of Antimony (Sb) and with diameters ranging from 1.5µm to 20 µm. nano-wires with diameters less than 50nm were also grown when slowing down the cooling process in a controlled way. The charge carriers of the ZnO:Sb wires were found to be free electrons using the hot probe measurement. In-situ annealing in air was used to activate the dopants of Sb in ZnO wires and to attempt to change the conductivity type from n-type to p-type. The most promising strategy for getting p-type doping is annealing ZnO:Sb wires at 150 °C in the dark. Annealing and then cooling slowly to room extends the time duration of the persistent photoconductivity.

Committee: Khalid Eid Dr. (Advisor) Subjects: Condensed Matter Physics; Nanoscience; Physics

Master of Science (MS), Ohio University, 2005, Civil Engineering (Engineering)

Geotechnical properties of soils using electrical measurements

Committee: L. Bryson (Advisor) Subjects: Engineering, Civil

Doctor of Philosophy (Ph.D.), University of Dayton, 2009, Mechanical Engineering

This dissertation describes the design and development of a new high-resolution electrical conductivity imaging technique combining the basic principles of eddy currents and atomic force microscopy (AFM). An electromagnetic coil is used to generate eddy currents in an electrically conducting material. The eddy currents induced in the sample are detected and measured with a magnetic tip attached to the AFM cantilever. The interaction of eddy currents with the magnetic tip-cantilever is theoretically modeled. The model is then used to estimate the eddy current forces generated in a typical metallic material placed in induced current field. The magnitude of the eddy current force is directly proportional to the electrical conductivity of the sample. The theoretical eddy current forces are used to design a magnetic tip-cantilever system with appropriate magnetic field and spring constant to facilitate the development of a high-resolution, high sensitivity electrical conductivity imaging technique. The technique is used to experimentally measure eddy current forces in metals of different conductivities and compared with theoretical and finite element models. The experimental results show that the technique is capable of measuring pN range eddy current forces. The experimental eddy current forces are used to determine the electrical resistivity of a thin copper wire and the experimental value agrees with the bulk resistivity of copper reported in literature. The imaging capabilities of the new technique are demonstrated by imaging the electrical conductivity variations in a composite sample and a dual-phase titanium alloy in lift mode AFM. The results indicate that this technique can be used to detect very small variations in electrical conductivity. The spatial resolution of the technique is determined to be about 25 nm by imaging carbon nanofibers reinforced in polymer matrix. Since AFM is extensively used to characterize nanomaterials, the newly developed technique is (open full item for complete abstract)

Committee: Sathish Shamachary PhD (Committee Chair); P. Terrence Murray PhD (Committee Member); Donald Klosterman PhD (Committee Member); Chakrapani Varanasi PhD (Committee Member); Mark Blodgett PhD (Committee Member) Subjects: Engineering; Materials Science

Doctor of Philosophy, Case Western Reserve University, 1994, Materials Science and Engineering

The electrical properties of polycrystalline silicon (p-type) were investigated by resistivity, C-V, and DLTS measurements. In particular, the influence of oxygen, carbon, and the fast diffusing transition elements (Cu, Ni, Fe, and Cr) in polycrystalline silicon has been studied. Ohmic contacts on polycrystalline silicon specimens were made successfully by Ga-In application by scrubbing or Al evaporation followed by short annealing. For Schottky diodes, Ti/poly-Si (p-type) was used for C-V and DLTS measurements. The objective was to identify the defects which are mainly responsible for the observed electrical changes. The specimens were Cast and Ribbon polycrystalline silicon with different impurity concentrations. Both specimens were annealed over a wide range of temperatures, between 300∼1250°C, to investigate the temperature dependence of the electrical properties, the effect of impurities and the effect of annealing. The electrical changes in polycrystalline silicon as a function of the annealing temperature were observed to depend on the oxygen content. The annealing strongly influenced the oxygen-rich specimens (Ribbon polycrystalline silicon) via the electrical properties of resistivity, carrier concentration, and defect concentration. The maximum values of the resistivitie s and defect concentrations and the minimum values of the carrier concentrations were found between 700∼900°C. The minimum values of the resistivities and trap concentrations and the maximum values of the carrier concentrations were found above The specimens were Cast and Ribbon polycrystalline silicon with different impurity concentrations. Both specimens were annealed over a wide range of temperatures, between 300∼1250°C, to investigate the temperature dependence of the electrical properties, the effect of impurities and the effect of annealing. The electrical changes in polycrystalline silicon as a function of the annealing temperature were observed to depend on the oxygen content. The (open full item for complete abstract)

Committee: W. Williams (Advisor) Subjects: Engineering, Materials Science

Master of Science, University of Akron, 2006, Mechanical Engineering

Space exploration missions in the future will involve in-situ sampling and analysis under extreme environmental conditions, so these missions will require actuators and sensors that can operate reliably for a long period of time under these conditions. The commercially available sensors, actuators and motors cannot operate continuously at such a high ambient temperatures like +500°C, so this technical challenge requires new actuator and sensor designs. Piezoelectric materials with Curie temperature (TCurie) that is higher than +1000°C would be ideal for this role, but the commercially available piezoceramics only able operate reliably at low temperatures and very little information is available about their electrical properties at elevated temperatures. The original goal of this thesis was to develop a measurement system that is able to measure the properties of those high-temperature piezoelectric ceramics, La3Ga5SiO14 and La2Ti2O7 that are currently being developed at the NASA Glenn Research Center (GRC). However up to date; our attempts to polarize these high-temperature piezoelectric ceramics were unsuccessful. To be able to demonstrate the capabilities of the developed measurement system, commercially available Lead Zirconate Titanate (PZT) samples were used to measure the changes in the different vibration mode frequencies and electrical properties as the temperature was increased up to and above their Curie temperature, around +450°C. The developed measurement system was able to capture the changes as the operating temperature was increased to and above the Curie temperature of the materials. The description of the developed measurement system and the result of the measurements on a variety of piezoelectric materials are presented in this thesis. The PZT samples showed changes in the frequency range of their vibration modes and electrical properties as the temperature was getting closer to the TCurie, and in most cases these changes become very significant (open full item for complete abstract)

Committee: Celal Batur (Advisor); Ali Sayir (Advisor); Jiang Zhe (Other) Subjects:

Doctor of Philosophy, University of Akron, 2006, Polymer Science

Carbon nanofiber (CNF) and carbon nanotube (CNT) composites have interesting mechanical and electrical properties that make these composites interesting for reinforcing applications. These applications require good dispersion of CNF within a polymeric matrix. Presently high shear methods, such as twin screw extrusion, are used to make well dispersed CNF composites but these methods reduce the physical properties due to a reduction in the aspect ratio of the CNF. Low shear methods to functionalize CNT and CNF have been used to obtain good dispersion while maintaining the high aspect ratio. In this research three ways of making CNF/polymer composites by low shear methods were explored. The first reaction used bisphenol A cyclic carbonate oligomer as a low molecular weight precursor. The oligomers were polymerized to disperse the CNF within the matrix. These composites were characterized by electrical resistivity, transmission electron microscopy (TEM), scanning electron microscopy (SEM), thermogravametric analysis (TGA) and gel permeation chromatography (GPC). The composites had a percolation threshold at 6 wt % CNF decreasing the resistivity to 10 4ohm•cm. The second way used heterocoagulation where a cationic polystyrene latex was combined with anionically charged oxidized CNF. The composites were melt pressed and characterized using electrical resistivity, SEM, and TGA. The percolation threshold was 2 wt % and the resitivity dropped to 10 6ohm•cm. Finally, it was found that synthesizing a hyperbranched polyol was possible by chemically modifying oxidized CNF with glycidol and BF 3OEt 2. The resulting polyol CNF were characterized by TGA, Fourier transform infrared spectroscopy (FTIR), TEM, and X-ray photoelectron spectroscopy (XPS). The OH groups were reacted with heptafluorobutyryl chloride to determine the amount of OH in the sample. The resulting fluorinated composite was characterized by FTIR and elemental analysis. The amount of OH for the polyol CNF increased (open full item for complete abstract)

Committee: William Brittain (Advisor) Subjects: Chemistry, Polymer