Master of Science (MS), Ohio University, 2019, Electrical Engineering & Computer Science (Engineering and Technology)

Studies and contemporary technology have shown the feasibility of developing direct current (dc) driven III-nitride deep ultra-violet (UV) photonic devices through band gap engineering of epitaxially grown hetero-structures. Alternatively, one can consider developing deep ultraviolet (UV-C) light sources operating on the principles of hot electrons impact excitation processes in a boron nitride (BN) phosphor. It was shown that high quality BN nanosheets (BNNSs) can generate excitonic emission at 225 nm under electron excitation of 6 kV and thus can be considered as a potential material for developing alternating current (ac) driven thin electroluminescence (ACTEL) devices. In this work we consider a theoretical approach based on the Bringuier model [J. Appl. Phys. 70, 8 (1991), pp. 4505-4512.] for generating luminescence in the UV-C region from hexagonal BN (h-BN) through impact excitation under a high electric field. Applying the Lucky Drift Model and Born approximation to high field electronic transport in h-BN we took into account ballistic and drift mode models to optimize a prospective device performance. The original model concerning Mn luminescent centers embedded in a ZnS host was adopted for an un-doped h-BN host. We used the lucky drift approach to study the probability of primary electrons encountering a collision within the lattice and thereby arrive at an efficiency of secondary electrons being excited to generate the desired near band edge (NBE) transmissions. It was found that in ACTEL device biased at 8.5 × 105 푉푐푚−1 a primary electron encountering an impact excitation would travel ~20 μm in a single h-BN layer before gaining sufficient kinetic energy to undergo a second collision which significantly reduces the device efficiency. Furthermore, we have also considered the efficiency of electroluminescence (EL) in h-BN by using the impact excitation rate theory developed by Neumark [Phys. Rev. 116, 6, (1959), pp. 1425-1432.] for a ZnS latti (open full item for complete abstract)

Committee: Wojciech Jadwisienczak (Advisor); Savas Kaya (Committee Member); Jeffrey Dill (Committee Member); Justin Frantz (Committee Member) Subjects: Engineering

Doctor of Philosophy, Case Western Reserve University, 2019, EECS - Electrical Engineering

Resonant nanoelectromechanical systems (NEMS) made from two-dimensional (2D) crystals have attracted increasing research interest owing to their promises for exceptionally high responsivities and sensitivities to external stimuli, enabled by their ultralow weight and ultrahigh surface-to-volume ratio. Although 2D crystals with bandgaps ranging from 0 eV to 2 eV have been studied in earlier explorations (such as 0 eV graphene, 0.3-1.5 eV black phosphorus, 1.2-1.9 eV MoS2, etc.), resonant NEMS utilizing ultra-wide bandgap (UWBG) 2D materials or materials with quasi-2D nanostructures have not yet been demonstrated. The adoption of UWBG materials in NEMS resonators could offer new opportunities for interactions with ultraviolet (UV) photons and for high power handling capabilities. This dissertation presents the experimental demonstrations of UWBG resonant NEMS, specifically, hexagonal boron nitride (h-BN) and beta gallium oxide (β-Ga2O3) NEMS resonators, for investigations of both fundamental device physics and engineering of device functions and performance toward the perspectives of technological applications. In this dissertation, the dry transfer techniques in accordance with the analysis in discerning the thin UWBG material flakes are first discussed, followed by the thermal annealing method to boost the resonator performance. Then, experimental demonstration of h-BN 2D nanomechanical resonators vibrating at high and very high frequencies (HF/VHF), and investigations of the elastic properties of h-BN by measuring the multimode resonant behavior of these devices are presented. Following the h-BN resonators, single-crystal β-Ga2O3 nanomechanical resonators using β-Ga2O3 nanoflakes grown via low-pressure chemical vapor deposition (LPCVD) are demonstrated experimentally. From the measurements, multimode resonances and spatial visualization of the multimode motion are resolved to extract the mechanical properties, i.e., material Young's modulus, EY = 261 GPa, (open full item for complete abstract)

Committee: Philip Feng (Advisor); Christian Zorman (Committee Member); Xiong Yu (Committee Member); Walter Lambrecht (Committee Member) Subjects: Electrical Engineering; Engineering; Experiments; Materials Science; Mechanical Engineering; Mechanics; Nanoscience; Nanotechnology; Optics; Physics; Technology

Master of Science, University of Akron, 2017, Polymer Science

The giant molecule is a kind of macromolecule with high molecular weight and precisely defined chemical structure. The self-assembly behavior of giant molecule can be influenced by intermolecular interactions, such as hydrogen bonding, hydrophobic force, metal coordination, van der Waals forces, p- p interactions and electrostatic effects. Besides the chemical interaction, the geometrical factor will also influence the final structure. POSS is a rigid conformation and fixed volume cage molecule with silicon-oxygen backbone. The precisely definable of the functional groups of POSS corresponding to the vertex number makes them fascinating building blocks. In the previous work, it was reported that POSS based three dimensional giant polyhedrons could self-assembly into Frank-Kasper A15 phase. [1] In this thesis, two dimensional planar giant molecules were designed and synthesized to explore novel self-assembly behaviors. Gallic acid derivatives C12 and BPOSS were linked to a simple planar C3 symmetric core, utilizing Sonogashira coupling reaction. By controlling the number of isobutyl-POSS, a series of giant molecules, 3C12-TEB, 2C12-TEB-1BPOSS and 1C12-TEB-2BPOSS were synthesized and studied. This series of target giant molecules were characterized by 1H NMR, 13C NMR, GPC and MALDI-TOF mass spectra. Their physical properties were studied by DSC and temperature-resolved SAXS. Two giant molecules, 2C12-TEB-1BPOSS and 1C12-TEB-2BPOSS, were discovered of hexagonal phase in bulk state.

Committee: Stephen Cheng (Advisor); Toshikazu Miyoshi (Committee Member) Subjects: Materials Science; Molecular Physics; Nanoscience; Physical Chemistry; Polymer Chemistry

Master of Science (M.S.), University of Dayton, 2015, Electrical Engineering

The premier objective of this research is to study the non-uniform interpolation to resample a hexagonally sampled image to a regular rectangular grid and to show hexagonal sampled data is more efficient than rectangular sampled data using an Adaptive Wiener Filter (AWF). Image processing is very important in several applications and have been using in them very efficiently. Digital image acquisition hardware, such as digital cameras, take photos by recording images as digital data using optics and a detector array. Distortions such as blur, noise and aliasing are often present, and these degrade image quality. For such reasons, image restoration algorithms are often applied to acquired images to reduce the degradations. Normally we use a rectangular sampling to digitize a continuous scene. There could be some other approaches to use as an alternate for this. One approach is to change the sampling process from rectangular pattern to hexagonal sampling pattern, considering various advantages. There is no inconsistency in pixel connectivity and thus angular resolution is higher in this arrangement and also fewer less samples need to represent the data represented in rectangular pattern. This research gives an overview of implementation of hexagonal sampling can be done by simulating a hexagonal sampled camera and adapt AWF to hexagonal sampling. Apply new AWF to simulated data quantitatively and qualitatively evaluate performance verses a standard rectangular sampling camera.

Committee: Russell Hardie (Advisor) Subjects: Electrical Engineering

PhD, University of Cincinnati, 2004, Engineering : Chemical Engineering

This thesis investigates the synthesis of ordered mesoporous silica and alumina materials with unique microstructures and different morphologies using novel approaches based on template-assisted synthesis and chemical vapor deposition (CVD) techniques and their potential use in polymer reaction application. Template-assisted growth of mesoporous silica under acidic and quiescent conditions at an oil-water interface can generate mesostructured silica with fibrous and non-fibrous morphologies. Fibers are obtained due to slow and one-dimensional diffusion of precursors through the interface. Variation in conditions can alter the axial growth of silica and yield non-fibrous shapes. Fibers grow from their base attached to the interface and coalesce to form fibers with larger diameters. Gas transport in silica fibers is governed by Knudsen and surface diffusion mechanisms. Surface diffusion contributes to 40% of the flow reflecting highly smooth pores. Real Knudsen and surface diffusivities are in the order of 10E-3 and 10E-5 cm2/s respectively. The one-dimensional mesopores are 45 time longer than the fiber length and align helically around the fiber axis with a pitch of 1.05 micron. Mesoporous silica membranes were prepared by a novel counter diffusion self assembly (CDSA) approach. This approach introduces the precursors from the opposite sides of a hydrophobic supports and yields silica plugs grown within its pores. Silica plugs grow with thickness of 0.5 mm and have a mesoporous structure. Such mechanically strong membrane is potential in protein separation and polymer reaction applications. Mesoporous membranes with controlled pore microstructure can be also obtained using cyclic CVD modification of straight 20 nm pore alumina membranes. Leaving residual of precursors in the pore after introduction of each precursor causes deposition of alumina in a fractal structure suitable for gas separation. Purging the pore after each precursor causes deposition in atomic layer (open full item for complete abstract)

Committee: Dr. Jerry Y. S. Lin (Advisor) Subjects:

Doctor of Philosophy, The Ohio State University, 2011, Chemistry

Square nickel mesh perforated with micron scale holes exhibits extraordinary transmission due to propagating surface plasmon polaritions (PSPP) combined with cavity modes. Propagating surface plasmon resonances are known to disperse with the angle of incident light and such experiments yield rich information regarding the plasmonics of the material. More accurate polarized Gamma X dispersion is presented within, as well as the first polarized Gamma M dispersion of square nickel mesh. Calculation of resonance positions within these experiments predicts an effective index of refraction for the asymmetric coupled surface plasmon polaritons to have a value of n'eff = 1.043. Gamma P and Gamma Q dispersion of hexagonal mesh is presented and the coupling of asymmetric plasmonic surfaces examined. Calculations allowing interactions between PSPP states of square mesh are compared with experimental results and traditional predictions of mesh, PSPP transmission maxima; explaining variation from experimental results and traditional predictions and illustrating the polariton, or mixed state, nature of PSPPs. Lastly, scatter free infrared spectra of sixty-three individual micron scale dust particles are presented by placement of each particle in a hole of plasmonic square nickel mesh. The constituents of each particle and the process of quantification of materials is examined by use of Mie scattering, Lorentz dispersion, and Bruggeman effective medium theories. The propagation lengths for PSPP resonances on such mesh are poor (~1-2 hole-to-hole spacings), compared to smooth metal predictions or less absorbing metals, making this mesh ideal for studying individual particles. The PSPPs funnel light through the particles, but they are effectively isolated so long as the neighboring holes are empty. Saturation of absorption peaks at this scale are demonstrated.

Committee: James Coe PhD (Advisor); Sherwin Singer PhD (Committee Member); Barbara Wyslouzil PhD (Committee Member) Subjects: Atmospheric Chemistry; Atmospheric Sciences; Chemistry; Condensed Matter Physics; Environmental Education; Environmental Geology; Environmental Health; Environmental Management; Environmental Science; Environmental Studies; Geochemistry; Mineralogy; Molecular Physics

Doctor of Philosophy, The Ohio State University, 2011, Chemistry

Square nickel mesh perforated with micron scale holes exhibits extraordinary transmission due to propagating surface plasmon polaritions (PSPP) combined with cavity modes. Propagating surface plasmon resonances are known to disperse with the angle of incident light and such experiments yield rich information regarding the plasmonics of the material. More accurate polarized Gamma X dispersion is presented within, as well as the first polarized Gamma M dispersion of square nickel mesh. Calculation of resonance positions within these experiments predicts an effective index of refraction for the asymmetric coupled surface plasmon polaritons to have a value of n'eff, = 1.043. Gamma P and Gamma Q Dispersion of hexagonal mesh is presented and the coupling of asymmetric plasmonic surfaces examined. Calculations allowing interactions between PSPP states of square mesh are compared with experimental results and traditional predictions of mesh, PSPP transmission maxima; explaining variation from experimental results and traditional predictions and illustrating the polariton, or mixed state, nature of PSPPs. Lastly, scatter free infrared spectra of sixty-three individual micron scale dust particles are presented by placement of each particle in a hole of plasmonic square nickel mesh. The constituents of each particle and the process of quantification of materials is examined by use of Mie scattering, Lorentz dispersion, and Bruggeman effective medium theories. The propagation lengths for PSPP resonances on such mesh are poor (~1-2 hole-to-hole spacings), compared to smooth metal predictions or less absorbing metals, making this mesh ideal for studying individual particles. The PSPPs funnel light through the particles, but they are effectively isolated so long as the neighboring holes are empty. Saturation of absorption peaks at this scale are demonstrated.

Committee: James Coe V (Advisor); Singer Sherwin (Committee Member); Wyslouzil Barbara (Committee Member) Subjects: Physical Chemistry

Master of Science (MS), Ohio University, 1992, Mechanical Engineering (Engineering)

The finite element analysis of apex thin and thick walled hexagonal drive tool sockets

Committee: Jay Gunasekera (Advisor) Subjects: Engineering, Mechanical

MS, Kent State University, 2009, College of Arts and Sciences / Department of Computer Science

There is still much research in the areas of routing and location updates in cellular communication networks. Given the limited amount of memory and power of these network devices it is desirable to find the most effective and resource conscious method for solving routing and location update problems. Recently, these problems have been addressed for simply connected cellular networks and significant results were achieved.  An effective method for addressing, location update and routing has been offered using a method of isometric embeddings into a set of three trees.  This method however does not fully work when a hole is present in the network.  To handle networks containing holes, a variation of the above method is required, where the cellular network will be decomposed into few sub-graphs that encompass the properties of the original network graph.  Proposed here is a method that will handle the above mentioned problems on cellular networks with holes, namely holes with disc structures and other shapes that have the convex property.  Also presented are two distinct methods for handling networks with multiple disc-structured holes.  These methods will also use sub-graphs to reduce the number of holes while preserving all shortest paths.

Committee: Feodor F. Dragan PhD (Advisor); Ruoming Jin PhD (Committee Member); Hassan Peyravi PhD (Committee Member) Subjects: Computer Science

Doctor of Philosophy, University of Akron, 2010, Polymer Engineering

A phenomenological model for elucidating phase diagrams of hexagonal columnar/nematic liquid crystal mixtures has been developed on the basis of the combination of the Flory-Huggins (FH) free energy of isotropic mixing, Maier-Saupe (MS) free energy for nematic ordering, and Chandrasekhar-Clark free energy for hexagonal ordering. Self-consistent calculations show the theory is capable of predicting the various phase diagrams, covering nematic, hexagonal columnar, and isotropic phases. The model has been tested with the eutectic phase diagram of hexagonal columnar liquid crystal, 2, 3, 6, 7, 10, 11-hexapentyloxy triphenylene (HPTP)/reactive nematic mesogens, 4-(3-acryloyloxypropyloxy)-benzoic acid 2-methyl-1, 4-phenylene ester (RM257) mixtures determined by using DSC, polarized optical microscope (POM), and wide-angle X-ray diffraction (WAXD). The self-consistent calculation displays isotropic (I), nematic (N), hexagonal columnar (Colh), N + I, and Colh + I, and Colh + N coexistence regions. These phase regions has been confirmed by thermal quenching various compositions from the isotropic melt to different phase regions. Guided by the established phase diagram of HPTP/RM257 mixtures, photo-polymerization of the mixture has been carried out in different phase regions. The as-cured HPTP/p-(RM257) composites fabricated at isotropic phase (130 °C) remains single isotropic phase under optical microscope, whereas the SEM and TEM results show the bead-like microstructure with sub-micrometer scale. Polymerization-induced mesophase transition experiments have been carried out at isotropic temperatures slightly above the clearing point of the mixtures. Of particular interest is the development of liquid crystalline spherulites. Moreover, the fixation of the morphology is observed when the photopolymerization is carried out in the N, N + I, and N + Colh region. A generalized thermodynamic model for describing smectic A and smectic B ordering has been developed based on (open full item for complete abstract)

Committee: Thein Kyu Dr. (Advisor) Subjects: Polymers