Department: Physics ![[clear]](close-x.png "Remove this limiter")
23 matches in the database.
These are records: 1 - 23.
1.
Abeywickrema, Haburugala Vithanage Ujitha A.
Behavior Of Linearly Polarized (LP) Modes in Fibers Containing Bragg Gratings in the Wide Temperature Range.
Degree: MS, Physics, 2011, University of Akron
► Understanding the physics of fiber Bragg gratings (FBGs) is very important in…
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▼ Understanding the physics of fiber Bragg gratings (FBGs) is very important in aerospace monitoring systems. This includes studies of non-linear temperature dependence, stability of chemical composition in a wide temperature range, quadratic behavior with temperature and long-term stability in harsh environment in silica based FBGs. It is important to study physical and chemical properties of FBGs in order to develop viable sensors. In this work we study, how light behaves in FBGs in a wide temperature range (77 K-1100 K). For a selected diameter of the fiber core (9.15 µm), a visible light (400-600 nm) transmitted through a fiber may form different modes at once competing one with another. Light inside the FBGs forms sets of different LP modes whose manifestation depends strongly on temperature and other parameters. The variations of LP modes with the temperature have been studied experimentally. Based on the experimental analysis of Bragg peak shift, it has been determined that the modes become unstable at the temperature around 700 K-710K. A mathematical modeling of LP modes has been focused on the behavior of high order modes using analysis of Bessel equations. It has been observed that the order of LP modes increase when the temperature increases and at the high temperatures(1200 K), the mode structure is stable in FBGs compared to bare fibers.
Advisors/Committee Members: Lyuksyutov, Sergei.
Subjects: Optics
Keywords: FBG
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2.
Bender, Edward Thomas.
Spectroscopic Characterization of Metal Oxide Nanofibers.
Degree: MS, Physics, 2006, University of Akron
► Metal oxide nanofibers have potential applications in filtration, catalysis, energy conversion, and…
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▼ Metal oxide nanofibers have potential applications in filtration, catalysis, energy conversion, and other areas. The most popular techniques for the characterization of nanofibers are X-ray diffraction (XRD) and scanning electron microscopy (SEM). However, these methods need to be supplemented with surface sensitive spectroscopies for more complete characterization. In several metal oxide nanofiber systems, unexpected impurities were found which may have a significant influence on the structure and surface chemistry. These impurities are not usually detectable with XRD and SEM. The main spectroscopic methods used here for materials characterization are X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). Additionally, two relatively uncommon yet powerful techniques, photoacoustic FTIR and infrared emission spectroscopy are also used. These spectroscopic methods have provided insight into some of the unusual properties of metal oxide nanofibers. With the aid of surface sensitive spectroscopies, further development of these interesting materials will be enabled.
Advisors/Committee Members: Ramsier, Rex D.
Keywords: nanofibers; electrospinning; X-ray photoelectron spectroscopy; XPS; Fourier transform infrared spectroscopy; FTIR; secondary Ion Mass Spectroscopy; SIMS; infrared emission; IRES; photoacoustics; titanium dioxide; titania; aluminum oxide; alumina
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3.
Bender, Kathlyn M.
Everyday Physics: Listening to Pre-Service Teachers Reflect on Learning and Teaching Science Through Inquiry.
Degree: MS, Physics, 2007, University of Akron
► Inquiry-based learning is believed to be one of the most effective ways…
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▼ Inquiry-based learning is believed to be one of the most effective ways to teach and learn science. However, many teachers are hesitant to use the method in class. The University of Akron recently began offering a one semester inquiry-based physics course to education majors. The course, Everyday Physics, is taught using inquiry-based instruction with embedded lecture. One of the main goals of the course was to help students become confident in their ability to practice and teach authentic science. The purpose of this project is to investigate the course’s successes and difficulties with implementing inquiry-based instruction and increasing students’ science teaching and learning self-efficacy. The project considers data gathered during the Spring semester of 2006. Participants include 21 middle-level education majors. Sources of reflection include journals in which students made entries throughout the semester and classroom observation. Our data indicate that most of the students in Everyday Physics were able to increase their self-efficacy for both learning and teaching inquiry-based science.
Advisors/Committee Members: Ramsier, Rex D.
Keywords: scientific inquiry; science education; self-efficacy; reflection; pre-service teacher education
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4.
Berg, Michael.
THE STATIC AND DYNAMIC PROPERTIES OF LENNARD-JONES CLUSTERS AND CHAINS OF LENNARD-JONES PARTICLES.
Degree: MS, Physics, 2006, University of Akron
► Groups of identical particles interacting through Lennard-Jones (LJ) potentials may serve as…
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▼ Groups of identical particles interacting through Lennard-Jones (LJ) potentials may serve as a model for atomic clusters at low temperatures. A model for polymer chains is obtained when the LJ particles are connected by harmonic springs. The focus of this work is the comparison of static and dynamic properties of clusters and chains of LJ particles. Small clusters of LJ particles have been studied in detail using molecular dynamics simulations. In agreement with work in the literature, the LJ clusters have been found to exhibit phase properties similar to those of macroscopic systems. In particular, they exhibit solid-like behavior at low energies and liquid-like behavior at higher energies. In addition, the dynamics of LJ clusters has been found to be chaotic at all energies. The methods used to study LJ clusters have been extended in this work to investigate the properties of chains of LJ particles connected by harmonic springs. It has been found that the bonds have an effect on both the static and dynamic properties of the chain. Specifically, it has been discovered that chains of LJ particles exhibit solid-like and liquid-like behavior similar to LJ clusters. For the chains, however, the transition between these two “phases” occurs at higher energy. Additionally, the chains of LJ particles exhibit a lower degree of chaotic behavior than the corresponding LJ clusters.
Advisors/Committee Members: Luettmer-Strathmann, Jutta.
Subjects: Physics, Molecular
Keywords: Lyapunov Exponent; Lyapunov; Etot; CLUSTERS; LENNARD-JONES; Δt; 13-particle
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5.
Chen, Chong.
Nonnative Contact Properties in a 3D Protein Model and the Influence of Interactions on Conformation Space.
Degree: MS, Physics, 2010, University of Akron
► Proteins are organic compounds, consisting of amino acids (residues) bound by peptide…
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▼ Proteins are organic compounds, consisting of amino acids (residues) bound by peptide bonds into polypeptide chains. Most of them can fold into their unique functional structures (native state) without any chaperones. Amino acids in theoretical protein models are often considered as beads lying on the sites of a lattice. By extracting information from the system with different kinds of computer algorithms, one hopes to predict the folding process. How and why proteins fold is still not clear although it has been extensively investigated for more than half a century. Experimental techniques (NMR, X-ray crystallography, etc.) as well as computer aided theoretical work (energy landscape, homology, etc.) have been used to understand how a protein folds from its amino acid sequence into a functional structure. In order to have a more fundamental understanding of protein structures and their properties, a closer look at a 3D protein shall be taken. Nonnative contact properties for proteins in a modified model are investigated and compared with the results from its 2D model analogue. Our computer program generates all possible conformations (enumeration), so it enables us to carry out exact calculations for the nonnative contact density nc(e) as a function of the energy density e as well as thermodynamically averaged nonnative contacts n̄c(T) as a function of temperature of T. The 3D conformation space can be generated by setting the distance D as the x-axis, energy density e as y-axis and entropy density s as the z-axis. The effect of interaction energies on the conformation space was also been examined, which can yield information on how a denatured protein folds to its native state. These results provide us with a better understanding of the role that nonnative contacts play in the protein folding process. Key results are: 1) Compared with the 2D model, nc(e) and n̄c(T) have a similar behavior in 3D for all three models (described in the text) investigated here but with more continuous shape, because more energy levels are available in the 3D model. 2) Odd or even residue numbers will affect the n̄c(T) for a protein with given number of residues in 2D and 3D. 3) Changing the interaction energy parameters will aect greatly the conformation space of the protein.
Advisors/Committee Members: Gujrati, Purushottam.
Subjects: Biophysics
Keywords: Nonnative Contact, 3D Protein, Conformation Space
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6.
Ehrman, James D.
X-Ray Photoelectron Spectroscopy Studies of Orthopedic Materials.
Degree: MS, Physics, 2009, University of Akron
► Knee replacement surgery is a potential option to relieve symptoms for those…
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▼ Knee replacement surgery is a potential option to relieve symptoms for those afflicted by arthritis. However, the materials introduced into the body may produce wear debris which can lead to inflammation of the surrounding tissue and sometimes require replacement of the implant. To better understand the mechanism behind the generation of this wear debris and ultimately the failure of the implant, one of our goals is to determine the composition of the wear debris. We test for the presence of metals in samples taken from synovial fluid using X-ray Photoelectron Spectroscopy, Scanning Electron Microscopy, and Energy Dispersive X-ray Spectrometry. We also test for bacterial adhesion to various zirconium alloys with X-Ray Photoelectron Spectroscopy as a means of determining the biocompatibility of these materials which are now being used as alternatives for the more common CoCrMo and Ti6Al4V orthopedic alloys.
Advisors/Committee Members: Ramsier, Rex.
Subjects: Biomedical research; Biophysics; Health; Health care; Physics
Keywords: XPS; SEM; EDS; CoCrMo; TiAlV; Ti6Al4V; synovial; TKR; total knee replacement; knee debris; microbial adhesion; zirconium alloys
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7.
Fedin, Igor.
Peculiarities of the Thermo-Optic Coefficient at High Temperatures in Fibers Containing Bragg Gratings.
Degree: MS, Physics, 2011, University of Akron
► The temperature dependence of thermo-optic coefficient in silica-based fibers containing fiber Bragg…
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▼ The temperature dependence of thermo-optic coefficient in silica-based fibers containing fiber Bragg gratings (FBGs) includes thermal instability of chemical composition gratings, non-linear temperature dependence of FBGs written in different fibers, quadratic behavior of FBGs, and long-term stability of silica-based FBGs. Experimental measurements of the thermo-optic coefficient for the temperature interval 50 – 780°C in fused silica fiber containing FBGs were conducted while the temperature shift of the Bragg’s peak was monitored between 1300 and 1311 nm with sub-Angstrom precision. Numerical computations were focused on the FBG’s diffraction efficiency calculations accounting for the temperature drift of the gratings and found to be in excellent agreement with obtained experimental data. It has been found that the thermo-optic coefficient changes between 0.79*10-5 and 1.45*10-5 K-1 and undergoes a minimum in the vicinity of 440°C. Additional observation indicates a negative sign of the second-order thermo-optic coefficient. The experiments reveal that the grating reflectivity decays at temperatures higher than 660°C which correlates with calculated decay of the refractive index modulation. It suggests that an FBG is erased at high temperatures. Based on the energy dispersive spectroscopy it has been determined that thermal erasing of the FBGs at a temperature around 780°C correlates well with germanium sublimation (apparently in the form of germanium monoxide) out of silica-based fiber cores.
Advisors/Committee Members: Lyuksyutov, Sergei F.
Subjects: Optics
Keywords: thermo-optic coefficient; fiber Bragg grating; grating decay; thermal decay of FBG; germanium-doped fiber; germanium defects; germanium color centers
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8.
Fernando, Waduge Pradeep Lasantha.
Lack of Molecular Chaos and Role of Stochasticity in KAC's Ring Model.
Degree: MS, Physics, 2009, University of Akron
► The dynamics of a system can either be deterministic or stochastic. In…
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▼ The dynamics of a system can either be deterministic or stochastic. In a determin-istic dynamics which is invariant under time reversal, there is a unique one-to-one relationship between the initial state of the process and its evolution at later times, while in a stochastic process, there are several possible outcomes or evolved states in the future. Since the outcome is not certain, there is one-to-many relationship between the current state and its evolution in the future. We use the simple Kac ring model to demonstrate the properties of deterministic and stochastic dynamics. The results lead us to understand the followings: 1) In a deterministic dynamics which is invariant under time reversal, the memory of the initial state is never lost and therefore no equilibrium state will ever appear and the molecular chaos assumption of Boltzmann cannot be justied. 2) In a stochastic dynamics, the system reaches equilibrium irrespective of the initial state and the size of the system, and the molec- ular chaos assumption becomes valid for very large systems. Hence, we understand that the stochastic interaction between the system and the environment is the true cause of irreversibility, whereas the use of molecular chaos assumption of Boltzmann for deterministic dynamics helps to conceal, rather than reveal the true origin of irreversibility.
Advisors/Committee Members: Gujrati, Puru.
Subjects: Physics
Keywords: flippers; Entropy; 2-color; balls; different; stochastic system; microstates
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9.
Gautam, Madhav.
The Role of Walls' Stochastic Forces in Statistical Mechanics: Phenomenon of Time Irreversibility.
Degree: MS, Physics, 2009, University of Akron
► A statistical system, by definition, experiences uncontrollable stochastic interactions with the surroundings…
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▼ A statistical system, by definition, experiences uncontrollable stochastic interactions with the surroundings that will give rise to time irreversibility. A purely deterministic (invariant under time reversal) system will not show any irreversibility. One can model the walls of a container containing a system to be the source of these stochastic impulses. We present the results of such stochastic walls’ impulses on a single particle in a one dimensional box of a fixed length. The particle moves with a uniform velocity until it hits the wall. At each collision with the walls, the velocity changes due to the stochastic impulse so that velocity becomes unpredictable and hence its effect has to be treated in a probabilistic sense to study the mechanics of the system. A single initial velocity turns into a distribution of velocities after many collisions with the walls. If the strength of the impulse is not too strong, the average kinetic energy reaches to a finite limit and the distribution of velocities follows very closely the Maxwell-Boltzmann distribution as we wait long enough. The temperature of the system at equilibrium can be defined from both the average kinetic energy and the distribution of velocities which agree fairly well with each other. The entropy of the system steadily increases and always reaches to a maximum value suggesting that the system has reached equilibrium.
Advisors/Committee Members: Gujrati, Purushottam D.
Subjects: Physics
Keywords: origin of stochastic forces, motion of particles in one dimension
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10.
Ghamande, Maithili.
Optical Modeling of Organic Photovoltaic Solar Cells.
Degree: MS, Physics, 2011, University of Akron
► Organic photovoltaic devices consist of several thin layers of material with different…
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▼ Organic photovoltaic devices consist of several thin layers of material with different electro-optical properties. Since the conversion of incident photons to charge carriers occurs only in the active layers, the intensity distribution of light within the device has an important effect on the efficiency of a solar cell. The intensity in turn depends upon properties of the layers, such as refractive index, absorption coefficient, and thickness, as well as on properties of the incident light, such as angle of incidence and spectral distribution. In this work, we investigate the absorption of light in thin-lm organic solar cells with computational methods. Since interference effects play an important role in thin-lms, we implement a transfer matrix method to calculate the complex amplitude of the electric eld at the interfaces and propagate the electromagnetic wave within the layers. We apply the method to conjugated polymer/fullerene bilayer solar cells and investigate devices of two planar geometries for the relevant part of the solar spectrum and a range of angles of incidence. Our results show that the angle of incidence has a small eect on the distribution of the electric eld in the active layers for a wide range of angles. For normal incidence, we confirm that the thickness of one of the layers, the layer adjacent to the metal electrode, has a large effect on the electric eld distribution and nd that the absorbance of light in the active layers depends strongly on the wavelength of the incident light. A reweighting of the absorbance with the solar irradiance illustrates that optimizing the design of solar cells requires a compromise between materials properties and device geometry.
Advisors/Committee Members: Luettmer-Strathmann, Jutta.
Subjects: Physics
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11.
Huang, Ran.
Exact Thermodynamic Calculation of a Monatomic System and Its Ideal Glass Transition on a New Recursive Lattice Formed by Cubic Units.
Degree: MS, Physics, 2009, University of Akron
► A many-body Ising lattice model of monatomic systems is solved exactly on…
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▼ A many-body Ising lattice model of monatomic systems is solved exactly on a new recursive lattice with the aim to study the metastability in supercooled liquids and the ideal glass transition. Interactions between particles farther away than the nearest neighbor distance are taken into consideration. The model has a strong antiferromagnetic interaction to give rise to an ordered phase identified as a crystal. Thermal properties including free energy, energy and entropy of the ideal glass and supercooled liquid state of the model are calculated. The computation results show both the first order and second order melting transition and second order ideal glass transition (entropy crisis). The effects of different energy terms are studied. We also study the defects in the ideal glass, supercooled liquid and the crystal to support the theory that a glass can be treated as a highly defective crystal, since the ideal glass at absolute zero has much higher energy than the crystal.
Advisors/Committee Members: Gujrati, Purushottam.
Subjects: Physics
Keywords: 1-cycle; 2-cycle; entropy; Energy 2-cycle; Energy 1-cycle; parameters are zero
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12.
Joshi, Tirtha Raj.
MOLECULAR MOBILITY OF UNFILLED AND CARBON BLACK FILLED ISOPRENE RUBBER STUDIED BY PROTON NMR TRANSVERSE RELAXATION AND DIFFUSION.
Degree: MS, Physics, 2008, University of Akron
► In an attempt to understand the effect of intense ultrasound on the…
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▼ In an attempt to understand the effect of intense ultrasound on the devulcanization of unfilled and filled isoprene rubber (IR), melts and networks, non spectroscopic solid state NMR proton transverse relaxation (T2) and pulsed gradient diffusion measurements were performed. At 70.50C, the T2 relaxation decay of the unfilled and 35phr carbon black filled was successfully described by two-component four-parameter model. The long component mainly arose from the unentangled sol, dangling ends and oligomers, and the short component was due to the entangled sol and crosslinked network. Sonication increased intermolecular mobilities, while curing reversed this effect. The long and short T2 components in CB filled IR without processing oil increased with increasing sol generated, while no such increase was observed in the IR extended with oil. Thus, processing oil significantly altered the dependence of both T2 components on the sol fraction. The high melt molecular weight (M) without a low M tail precluded diffusion measurements. The IR melts were then degraded ultrasonically with and without subsequent vulcanization. It lowered and broadened the molecular weight distribution. This made it possible to conduct pulsed gradient diffusion experiments; the diffusion spectrum is bimodal. Here the T2 decays are consistent with a three- component model with six parameters. The additional component here is the intermediate T2 component. The results obtained were quantitatively related to earlier work in natural rubber.
Advisors/Committee Members: Von Meerwall, Ernst D.
Subjects: Physics, General
Keywords: NMR relaxation.; Diffusion; Spin Spin relaxation; Molecular Mobility
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13.
Khanal, Kiran.
Monte Carlo Stimulations to Study The Effect of Chain Stiffness on Static, Dynamic, and Equation-of-State Properties of Polymer Melts.
Degree: MS, Physics, 2009, University of Akron
► Static and dynamic properties of polymers are affected by the stiffness of…
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▼ Static and dynamic properties of polymers are affected by the stiffness of the chain molecules. In this work, we investigate static and dynamic properties of a lattice model for semiflexible polymer chains. The model is an extension of Shaffer’s bond-fluctuation model and includes attractive interactions between monomers and an adjustable bending energy that determines the Kuhn segment length. For this work, we performed Monte Carlo simulations for polymer melts with a range of values of the bending energy, density, and temperature. We find that the Kuhn segment length increases monotonically with the bending energy for a wide range of bending energies. This allows us to model melts of flexible and semiflexible chains. Results for self diffusion coefficients show that the translational mobility is strongly reduced by increasing chain stiffness. We implemented a bead insertion method and a chain insertion method to calculate the pressure of the melts. While chain insertion is a reliable method to determine the pressure at low filling fractions of the lattice, it becomes very inefficient at higher densities. Bead insertion, on the other hand, yields good statistics, even at high densities, but the evaluation depends on an assumption that breaks down for semiflexible chains. We find that bead and chain insertion give comparable results for the pressure of melts of flexible chains at sufficiently high densities.
Advisors/Committee Members: Luettmer-Strathmann, Jutta.
Subjects: Physics
Keywords: chain stiffness; chain dimension; dynamic properties; chain insertion; bead insertion; Monte Carlo simulations
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14.
Pathak, Pooja.
Microscopic Investigations of the Adhesion of Bacteria and Algae on Biomaterial Surfaces.
Degree: MS, Physics, 2007, University of Akron
► The aim of this investigation was to study the adhesion of bacteria…
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▼ The aim of this investigation was to study the adhesion of bacteria and algae using optical microscopy, and consists of two parts. The first part involves Pseudomonas aeruginosa and Staphylococcus epidermidis bacterial adhesion on modified polyvinyl chloride (PVC – a material with various biomedical applications) surfaces. In this investigation, PVC substrates were modified by imprint lithography and bacterial adhesion was performed to determine the influence of the imprinted surface structures on bio-adhesion. The effects of incubation condition were also studied by performing the bacterial exposures of the samples under both shaken and stationary conditions. Data were generated by analyzing the optical microscopy images of the substrates after Gram staining, using Sigma Scan Pro (Jandel Corporation) software. The results indicate that bacterial adhesion depends on the surface properties, incubation condition and the type of bacteria. The second part of this investigation involves adhesion of cyanobacteria or blue-green algae on oxidized Zr-705 alloys. Optical microscopy and Sigma Scan Pro software were used to study the effects of substrate oxide thickness on the propensity for algae adhesion and growth. The results show that algae adhesion depends on how much the Zr-705 surfaces are oxidized. This is relevant to water purification and transport technologies, since algae growth on piping can adversely affect water quality.
Advisors/Committee Members: Ramsier, Rex D.
Keywords: Biofilms; Optical Microscopy; Sigma Scan Pro software; Zr-705; Cyanobacteria; Polyvinyl chloride; Imprint lithography
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15.
Paudel, Naba Raj.
TIP DEFORMATION AND BUCKLING OF CARBON NANOTUBES ON A GRAPHITE SURFACE.
Degree: MS, Physics, 2007, University of Akron
► Carbon nanotubes (CNTs) have attracted great interest because of their excellent mechanical,…
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▼ Carbon nanotubes (CNTs) have attracted great interest because of their excellent mechanical, electrical and chemical properties. With the development of new experimental techniques, the buckling and bending behaviors of the CNTs have been observed under large deformation. In addition, remarkable adhesive forces of gecko’s foot hairs and nanotubes on substrates have been investigated experimentally. In the present work, carbon nanotubes of different lengths are pressed against graphite surfaces to investigate deformation and adhesion of CNTs by using molecular dynamics simulation and energy minimization methods. The simulations reveal the mechanisms of the buckling, bending and slipping of the CNTs on the rigid and relaxed graphite surfaces. Layer by layer deformations of the CNT tips were observed. Also, we observed the overall deformation (bending and buckling) of CNTs, which depends on their length. We found that structural changes of a nanotube which is compressed normal to the graphite surface can be analyzed by using Fourier harmonics. The adhesion force between a nanotube and a graphite surface is studied for three different surface positions. Finally, different tilted orientations of CNT tips are considered. The maximum buckling length is found at 15 degrees with respect to the surface normal where the existing interaction between the nanotube and the graphite surface becomes extremum.
Advisors/Committee Members: Buldum, Alper.
Keywords: nanotube, deformation, buckling
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16.
Robbiano, Vincent P.
Simulations of Organic Solar Cells with an Event-Driven Monte Carlo Algorithm.
Degree: MS, Physics, 2011, University of Akron
► The generation of photocurrent in organic solar cells starts with a photon…
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▼ The generation of photocurrent in organic solar cells starts with a photon being absorbed in the active layer and creating an excited electron/hole pair (exciton). The exciton is mobile and dissociates into electron and hole at an interface between donor and acceptor material, unless it decays before it reaches the interface. If they do not recombine, the charge carriers migrate toward the appropriate electrode and contribute to the photocurrent. Thus, the efficiency of organic solar cells depends strongly on the geometry and electronic properties of the donor/acceptor materials. Simulating in detail the processes described above is of interest since it enables the modeling of devices with dierent architectures and materials properties. Since processes such as exciton absorption, electron hopping, and recombination take place on vastly dierent time scales, we employ an event-driven Monte Carlo algorithm to simulate a coarse grained lattice model of the active layer of organic solar cells. We investigate devices of two geometries, one planar and one V-shaped, that differ significantly in the size of the donor/acceptor interface. The trends observed in our results agree with literature ndings that show that, as the interface area increases, the current density, charge carrier density and internal quantum efficiency of the device also increase.
Advisors/Committee Members: Luettmer-Strathmann, Dr. Jutta.
Subjects: Alternative Energy; Physics
Keywords: Solar Cell; Monte Carlo; event driven; Organic
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17.
Subedi, Laxmi P.
AFM Tip-Graphene-Surface Interactions.
Degree: MS, Physics, 2010, University of Akron
► Graphene has high mobility of its charge carriers. It is the thinest…
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▼ Graphene has high mobility of its charge carriers. It is the thinest and strongest material ever found. These extraordinary properties made graphene the most interesting and promising novel material. It has attracted great interest in recent years for various technological applications. For these applications graphene is placed on surfaces such as SiO2 and SiC. Here, we present theoretical investigations of graphene on SiO2 surface. Employing geometrical optimization and molecular dynamics simulation method at the atomic level, we studied AFM tip-graphene-surface interactions. Single (or double) layer and layer graphene with the sharp and the blunt tips were considered in our studies. Using the total energy calculations, we show that the interaction between bilayer graphene and SiO2 surface is stronger than mono-layer graphene and surface. Similarly we show that the interaction between the blunt tip and the surface is stronger than the sharp tip and surface. From energy minimization method, we found that there are periodic waves in graphene when it is placed in SiO2. By applying both energy minimization calculations and molecular dynamics simulation we show the structural changes in both monolayer and bilayer graphene in the presence of tip over graphene sheet. We believe these studies provide invaluable insight for graphene nanodevice applications.
Advisors/Committee Members: Buldum, Alper.
Subjects: Chemistry; Physical Chemistry; Physics
Keywords: graphene; monolayer graphene; bilayer graphene; geometrical optimization; energy minimization; molecular dynamics
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18.
Sun, Yang.
Dielectric Properties of CaCu3Ti4O12 and Its Related Materials.
Degree: MS, Physics, 2006, University of Akron
► Dielectric materials have been widely used in electronic industry. Recently an oxide…
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▼ Dielectric materials have been widely used in electronic industry. Recently an oxide ceramic CaCu3Ti4O12 (denoted as CCTO) is reported to be very promising because it possesses a very high dielectric constant. However, further research on its dielectric properties indicates that this material has a high dielectric loss, which seriously blocks its practical application. In this work, pure CCTO ceramic, and two series of CCTO derivatives, i.e., “CCTO + CaTiO3” and “CCTO + MnO2” ceramics were prepared, and their phase assemblies, structure, dielectric properties, and conducting properties are studied. The relaxation mechanism was investigated for CCTO and its derivatives. It is for the first time revealed that the relaxation time follows the Vogel-Fulcher relation instead of the Arrhenius relation.
Advisors/Committee Members: Chen, Ang.
Keywords: CCTO; DIELECTRIC; MnO2; dielectric constant; CaCu3Ti4O12; CTO
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19.
Tuttle, Richard W.
ELECTROSPUN ALUMINA FIBERS:SYNTHESIS AND CHARACTERIZATION.
Degree: MS, Physics, 2006, University of Akron
► Electrospun aluminum oxide fibers have potential uses in many modern industrial applications.…
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▼ Electrospun aluminum oxide fibers have potential uses in many modern industrial applications. In this thesis we investigate a wide range of electrospinning conditions and characterization techniques to determine the types of bulk and surface characteristics that can be attained with these fibers. The fibers are characterized by a range of techniques including X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), nuclear magnetic resonance (NMR), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR). These characterization techniques provide an in-depth understanding of these materials and therefore a better idea of their potential uses.
Advisors/Committee Members: Ramsier, Rex D.
Keywords: electrospinning; SEM; EDS; XRD; FTIR; XPS; NMR
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20.
Walker, Justin I.
Spectroscopic Analysis of Materials for Orthopaedic and Energy Conversion Applications.
Degree: MS, Physics, 2008, University of Akron
► X-ray photoelectron spectroscopy (XPS) and electron dispersive X-ray spectroscopy (EDS) are two…
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▼ X-ray photoelectron spectroscopy (XPS) and electron dispersive X-ray spectroscopy (EDS) are two complimentary techniques that are used to obtain data about the chemical and electronic states of materials. The information that XPS acquires is from the surfaces of samples, while EDS gets information from the bulk. Additionally, scanning electron microscopy (SEM) is a method to get more qualitative information about substances, by taking high magnification images. Many materials can be analyzed using these methods, but two are detailed in this thesis: electrospun aluminum oxide doped zinc oxide (AOZO) nanofibers and cobalt chromium molybdenum (CoCrMo) metal powder particulates. AOZO nanofibers are on the forefront of material research. XPS was utilized to discover how the amount of aluminum dopant, used in fabricating the fibers, affected the fibers…#8482; conductivity. CoCrMo is used to make prosthetic implants and the elemental structure is a significant factor in determining biocompatibility. XPS and EDS data was compared to ascertain discrepancies in composition, and how that affected biocompatibility.
Advisors/Committee Members: Ramsier, Rex.
Subjects: Physics
Keywords: XPS; EDS; SEM; AOZO; aluminum oxide; zinc oxide; nanofiber; CoCrMo; Cobalt Chromium Molybdenum; electrospin; electrospun
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21.
Weerasinghe, Asanka Thushara.
Amplitude-Modulated Electrostatic Nanolithography in Fluourinated Graphene.
Degree: MS, Physics, 2012, University of Akron
► Amplitude modulated atomic force microscopy-assisted electrostatic nanolithogaphy (AM-AFMEN) was used to pattern…
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▼ Amplitude modulated atomic force microscopy-assisted electrostatic nanolithogaphy (AM-AFMEN) was used to pattern nanostructures in fluorinated graphene (FG) at the nansocale. Perforated fluorinated graphene is a two-dimensional sp3 carbon sheet in which each carbon atom is bonded to one fluorine atom by a covalent-ionic bond. This material was invented at Naval Research Laboratory in 2010 by Robinson et al using graphene on copper substrates exposed to XeF2 at 30C. To achieve a theoretical understanding of nanolithography in Fluorographene the nanopatterning process has been modeled as a standard electromagnetism problem. A numerical approach based on a relaxation method has been developed to solve the problem and calculate the surface electric field distribution and the pressure distribution. Our results suggest that the tip-surface separation has a significant influence on such distributions and the pressure to break a sheet of Fluorographene is distinctly smaller than the elastic modulus (0.3 TPa). Our experiments with the AM-AFMEN technique show that the size of the ablated areas in fluorinated graphene has an approximate quadratic relationship with the bias voltage. Our results also suggest that localized heating may alter the breaking strength of the material. Furthermore de-fluorination of graphene results in a substantial drop of the resistance of nanostructures in Fluorographene.
Advisors/Committee Members: Lyuksyutov, Sergei.
Subjects: Physics
Keywords: NANOLITHOGRAPY IN FLUORINATED GRAPHENE
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22.
Wolf, Michael Scott.
Infrared and Optical Studies of Topological Insulators BI2TE3 BI2SE3 and SB2TE3.
Degree: MS, Physics, 2011, University of Akron
► Topological insulators are currently a main focus of condensed matter research. They…
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▼ Topological insulators are currently a main focus of condensed matter research. They have a unique property in which the bulk of the material acts as an insulator, while the surface states display metallic behavior. Using infrared, optical and magneto-optical spectroscopy, we have studied 3D topological insulators Bi2Se3, Bi2Te3, Sb2Te3 to understand their optical properties. The measurements were carried out using a Fourier Transform Infrared Spectrometer (FTIR) and an ultraviolet - visible spectrometer at varying temperatures ranging from 5 Kelvin to 300 Kelvin and at varying magnetic fields up to 18 Tesla. We use the Drude - Lorentz model to replicate the experimental data of the samples allowing to gain an understanding of the physical phenomena happening in the infrared, visible and ultraviolet regions of radiation. This understanding gives us insight on the optical properties of the materials such as charge dynamics. Results show that the temperature and magnetic eld have an effect on the charge carriers especially near the plasma frequency.
Advisors/Committee Members: Dordevic, Sasa.
Subjects: Physics
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23.
Zhou, Yuan.
Modeling and Simulation of Dielectric Materials.
Degree: MS, Physics, 2007, University of Akron
► The perovskites ABO3 are the most important class of dielectric materials. The…
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▼ The perovskites ABO3 are the most important class of dielectric materials. The perovskite SrTiO3 and the perovskite-related material CaCu3Ti4O12 are studied in this work. In the first part of this work, we find the structural temperature of SrTiO3 by performing molecular dynamics simulations and investigate electronic and structural properties of SrTiO3 by performing ab initio calculations. A strong chemical bonding nature between Ti and O is found. This is responsible for the TiO6 octahedron behavior throughout the phase transition. In the second part, ab initio calculations on CaCu3Ti4O12 are performed. We investigate the electronic properties of this material. An antiferromagnetic character of CaCu3Ti4O12 is observed. Furthermore, we investigate the electronic properties of new materials of different Ca, Cu ratios. This is the first time to perform ab initio calculations to study Ca1+xCu3-xTi4O12. We find that with the increase of with increase of Ca in the material, the optimized lattice constant and band gap increase, and insulator character becomes much more pronounced in the material. This is in good agreement with the experimental results.
Advisors/Committee Members: Buldum, Alper.
Keywords: modeling; simulations; ab inito; dielectric materials; SrTiO3; CaCu3Ti4O12
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