Doctor of Philosophy, University of Akron, 2023, Polymer Science

Plasma polymerization is a facile method of depositing robust films on a wide variety of substrates. While the nanoscale structure of films plasma polymerized in vacuum has been studied some, little is known of the nanoscale structure of the films deposited in the more complex atmospheric plasma polymerized (APP) films. To explore how deposition conditions affect APP film structures, APP films were deposited using hexamethyldisiloxane (HMDSO) precursor at varying power and in varying levels of relative humidity (RH). X-ray and neutron reflectivity measurements reveal that these APP-HMDSO films have a three-layer structure. A transition region of low mass density and carbon content forms next to the substrate as the deposition starts and etching by the plasma initially dominates deposition; a center region which still experiences some etching displays a uniform scattering length density (SLD) with respect to depth; a surface layer next to the air of mass density less than or equal to that of the center region forms whose SLD depends on how “filled in” the layer was when plasma generation was halted. Mass density was found to be sensitive to high humidity, which reduces the flux of monomer fragments to the substrate and allows them to pack more densely. Complementary analysis of depth-resolved X-ray photoelectron spectroscopy and water contact angle measurements show that composition and hydrophilicity are power-dependent. Films deposited at lower power lose more of their carbon to etching, making their composition more silica-like and making them more hydrophilic. Films deposited at higher power retain more of the carbon from the HMDSO monomer thanks to higher deposition rates; a film layer is buried by additional layers before all the residual carbon can be etched away. Neutron reflectivity measurements of the same APP-HMDSO films while exposing them to deuterated solvent vapor showed that vapor easily penetrated them without causing their thickness to increase, (open full item for complete abstract)

Committee: Mark Foster (Advisor); Mesfin Tsige (Committee Chair); Toshikazu Miyoshi (Committee Member); Ali Dhinojwala (Committee Member); Bi-min Newby (Committee Member) Subjects: Chemistry; Materials Science; Physics; Plasma Physics

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

Radio Frequency Plasma deposition has proven to be an unusually convenient and universal surface-modification and coating technology for grafting thin film for applications in which solution chemistry is difficult or entirely impossible, or adhesion to a low energy substrate surface is desired. The one-step gas to solid-phase nature of the process eliminates liquid solvents, which are otherwise required for spin coating, electro-deposition, and other traditional coating processes. The technique uses excited plasma in a volume of monomer vapor, forming reactive energetic species (radicals and ions). The recombination of surface-bound free radicals and ions with airborne radicals and oppositely charged ions creates strong substrate-independent covalent attachment at the interface. Pulsing of the incident electrical energy significantly reduces the total energy absorbed by the targeted vapor, subsequently minimizing bond scission and energetic structure rearrangement to retain useful functional groups. In this work, Terpyridine was tethered to various substrates and complexed with iron, forming a film that may readily complex with other Terpyridine-coated substrates to form an adhesive bond. Thin films of reactive anhydride were first deposited by maleic anhydride vapor in a pulsed plasma process. The highly reactive anhydride group was retained in the plasma with low input power, short duty cycle on-time, and long duty cycle off-times. A primary amine-functional Terpyridine was tethered to the anhydride film via aminolysis and heated to form a stable maleimide linkage.

Committee: Ali Dhinojwala (Advisor); Coleen Pugh (Other) Subjects: Chemistry; Materials Science; Polymers

PhD, University of Cincinnati, 2017, Engineering and Applied Science: Materials Science

Carbon Nanotubes (CNTs) have been at the forefront of nanotechnology research over the past decade. The development of synthesis techniques such as chemical vapor deposition (CVD) and floating catalyst CVD (FCCVD) have transformed CNTs from being property enhancing fillers in composites to structural materials of the future. CNT sheets and yarns are being produced at industrial scale and are seeing applications in fields like aerospace and energy storage. In this work, we fabricate CNT sheets by dry-spinning technique. This approach helps produce light-weight, strong and conductive CNTs sheets free from catalyst impurities. Plasma functionalization is a fast, clean and efficient technique for modification of CNTs. Here, we demonstrated for the first-time atmospheric pressure plasma functionalization of CNT sheets carried out in-situ during their manufacturing. Helium/oxygen plasma was shown to create oxygen-based functional groups on the CNTs in a matter of seconds, which enables the interaction between nanotubes and other chemical compounds including polymers. This technique was successfully employed for fabrication of improved CNT/epoxy composites. Plasma functionalization of CNTs enables the formation of covalent bonding between CNTs and uniform infiltration of the epoxy resin. This resulted in formation of a crosslinked CNT/epoxy composite which showed an improvement of strength and modulus over pristine CNT sheets. High strength CNT/Epoxy composites with high wt. % CNT content lead to a role reversal with epoxy resin which serves to reinforce a CNT sheet matrix, where the tubes dominate in quantity. CNT sheets demonstrate high electrical conductivity and thus find application in electronics. This work also explores the application of CNT sheets as free-standing electrodes for energy storage. For the first time, carbon nanotube synthesis was carried out directly on CNT sheet as substrate by plasma enhanced chemical vapor deposition (PECVD). This experiment al (open full item for complete abstract)

Committee: Vesselin Shanov Ph.D. (Committee Chair); F James Boerio Ph.D. (Committee Member); Jude Iroh Ph.D. (Committee Member); Mark Schulz Ph.D. (Committee Member) Subjects: Materials Science

Master of Science (MS), Ohio University, 2014, Electrical Engineering (Engineering and Technology)

Plasma Enhanced Chemical Vapor Deposition (PECVD) is widely used in industry for its low temperature growth capability, excellent conformity (step coverage) and higher deposition rates. Silicon dioxide (SiO2), silicon nitride (Si3N4) and silicon oxynitride (SiOxNy) are common dielectrics deposited using PECVD and they will be the main focus of this thesis. These common dielectrics are used in a range of different applications, from optical waveguides to photovoltaic passivation layers and from transistor fabrication to micro electromechanical systems (MEMS) devices. PECVD system parameters (temperature, pressure, power, and gas ratio) are methodically varied and the resulting thin films are characterized. This requires many different metrology techniques such as: atomic force microscopy (AFM), ellipsometry, X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDS). Optical and structural properties of the resulting thin films are analyzed via a careful design of experiments to determine which system parameter has the most significant effect and to which extent they can be varied.

Committee: Savas Kaya Ph.D (Advisor); Faiz Rahman Ph.D (Committee Member); Wojciech Jadwisienczak Ph.D (Committee Member); David Drabold Ph.D (Committee Member) Subjects: Electrical Engineering; Materials Science; Nanoscience; Nanotechnology

MS, University of Cincinnati, 2009, Engineering : Materials Science

In this study we explored the use of alternative techniques for substrate preparation for CNT synthesis and for post-synthesis functionalization of the CNTs. Magnetron sputtering was exploited as an alternative to e-beam deposition for preparation of the alumina intermediate layer and of the metal catalyst on an oxidized Si wafer. This approach offers large area deposition (4 inch substrates) of the layered catalyst which precedes the fabrication of larger aligned CNT arrays. The effects of the substrate design on the growth of long multi-wall carbon nanotube (MWCNT) arrays by CVD (Chemical Vapor Deposition) were also explored. The CNT synthesis was carried on in a hydrogen/ethylene/water/argon environment at 750 °C. Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD), Thermal Gravimetric Analysis (TGA), Raman Spectroscopy and Transmission Electron Microscopy (TEM) were employed to characterize the substrates and the CNT arrays. The study showed that for specific processing conditions the length of highly oriented CNTs strongly depends on the thickness of Al2O3 intermediate layer and on the catalyst film. The obtained results confirm that magnetron sputtering can be successfully employed as a tool for substrate preparation, which were used to grow CNT arrays upto 12 mm in length with high purity. The aligned nanotubes do not suffer from limitations typical for powdered (spaghetti type nanotubes) which opens up the possibilities of new applicationsFunctionalization can be described as a process in which the CNTs are modified in order to enhance their properties. The dry plasma treatment was chosen over the conventional wet chemical functionalization because it is quicker and more convenient. The effect of plasma functionalization on the MWCNTs was studied with the Fourier Transfer Infra-Red spectroscopy.

Committee: Vesselin Shanov PhD (Advisor); Mark Schulz PhD (Committee Member); Rodney Roseman PhD (Committee Member); Jude Iroh PhD (Committee Member) Subjects: Materials Science

PhD, University of Cincinnati, 2006, Engineering : Materials Science

High-temperature electronics and MEMS (Micro-Electro-Mechanical Systems) based on polycrystalline diamond (PCD) are promising because of its wide band gap, high thermal conductivity, and large carrier mobility. To take advantage of this opportunity, research was undertaken to develop techniques for the synthesis of both undoped and doped high quality PCD films with good surface flatness suitable for the fabrication of high temperature electronics and MEMS devices. One way to fabricate smooth films is to decrease the grain size because diamond films with large grain size bring forth problems in contact formation and device fabrication due to the large surface roughness. Consequently, there is a need to fabricate nanocrystalline films with small grain size and good smoothness. In addition, the electrical properties and conduction mechanisms in nanocrystalline diamond (NCD) films have not been sufficiently analyzed. This study also aims at achieving high resistivity nanocrystalline diamond films and to study the electrical conduction mechanism. Several approaches have been used in our research to achieve these goals. Initially microcrystalline diamond (MCD) films were grown on silicon (100) substrates by the microwave plasma enhanced chemical vapor deposition (MPCVD) method using methane in a hydrogen plasma environment. Introduction of small amounts of argon into the Argon / Hydrogen plasma was used to deposit diamond films with a range of microstructures from microcrystalline to nanocrystalline grains. A detailed quantitative study of the sp3, sp2 content in the films grown with varying amounts of argon in the plasma was done using Raman spectroscopy. The optimum gas composition that gave the best quality diamond film consisting of 1.6 µm grains was 60% Ar/ 39% H2/ 1% CH4. The optimum gas composition that gave nanocrystalline grains of size in the order of <50 nm was 95% Ar/ 4% H2/ 1% CH4. A change in the cross-sectional microstructure from the columnar to grain-like (open full item for complete abstract)

Committee: Dr. Raj Singh (Advisor) Subjects: Engineering, Materials Science

PhD, University of Cincinnati, 2004, Engineering : Materials Science

Plasma polymerized fluorocarbon (PPFC) films were deposited onto various silicone rubber substrates, including O-rings, to decrease oil uptake. Depositions were performed using a radio frequency (rf)-powered plasma reactor and various fluorocarbon monomers, such as C2F6, C2F5H, C3F6, and 1H,1H,2H-perfluoro-1-dodecene. PPFC films which were most promising for inhibiting oil uptake were deposited with 1H,1H,2H-perfluoro-1-dodecene, and were composed predominantly of perfluoromethylene (CF2) species. These films displayed low critical surface energies (as low as 2.7 mJ/m2), and high contact angles with oil (84), which were correlated with the amount of CF2 species present in the film. For the films with the highest degree of CF2 (up to 67 %), CF2 chains may have been oriented slightly perpendicular to the substrate and terminated by CF3 species. Adhesion of the PPFC films directly to silicone rubber was found to be poor. However, when a plasma polymerized hydrocarbon interlayer was deposited on the silicone rubber prior to the fluorocarbon films, adhesion was excellent. O-rings coated with multilayer fluorocarbon films showed 2.6 % oil uptake after soaking in oil for 100 hrs at 100 C. Due to variability in data, and the low quality of the industrial grade silicone rubber, the oil uptake mechanism was determined to be from oil flowing through flaws in the film due to defects within the substrate, not from generalized diffusion through the film. This mechanism was confirmed using higher quality silicone rubber, which showed little or no oil diffusion. Therefore, this film may perform well as an oil-repelling barrier when deposited on a high quality silicone rubber.

Committee: F Boerio (Advisor) Subjects: Engineering, Materials Science

Master of Science (MS), Ohio University, 1993, Chemical Engineering (Engineering)

Plasma enhanced chemical vapor deposition of thin aluminum oxide films

Committee: Dan Gulino (Advisor) Subjects: Engineering, Chemical

Doctor of Philosophy, Case Western Reserve University, 2010, Chemical Engineering

Patterning processes combined metal masking and selective diamond growth to fabricate conductive diamond patterns on various substrates, allowing either the growth or nucleation surfaces to be applied as electrodes. These processes enable novel applications of diamond electrodes integrating diamond films into existing sensor systems and novel, temperature intolerant, polymer-based systems. A patterning process was initially developed for thermally oxidized silicon. Two nucleation (BEN and sonication seeding) and two growth (HFCVD and MPCVD) methods were evaluated. Feature dimensions and spacing down to 8 μm were obtained, having a minimal thickness of 1 μm. The films were high-quality polycrystalline diamond, as analyzed by Raman spectroscopy. As electrochemical sensors, the films detected dopamine (10 μM in PBS) with redox properties typical of microcrystalline diamond. Attempts using BEN to selectively deposit diamond on insulating surfaces (alumina, high-temperature borosilicate glass) required metal coating of the back and sides of substrates. With alumina, adhesion problems prevented growth of complete films (or patterns). With glass, interactions between the tungsten and substrate prevented etching of the mask, compromising the pattern. Patterns on silicon dioxide were transferred to a polynorbornene polymer support with metal (Au, or Cr/Au/Cr) contacts to create the first diamond-on-polymer sensors - making the smooth, diamond nucleation surface the active electrode surface. The patterning process was scaled from ¼” chips to 3” wafers, to fabricate multi-electrode arrays (10 singly addressable pads). Sonication seeding was used to seed wafer-scale substrates due to limitations in implementing BEN with larger scale substrates. As-fabricated, diamond-on-polymer electrodes from the wafer-scale process showed a highly capacitive dielectric response. XPS depth profiling revealed a SiOxCy layer on the electrode (diamond nucleation) surface, an issue introduced by t (open full item for complete abstract)

Committee: Heidi B. Martin PhD (Committee Chair); R. Mohan Sankaran PhD (Committee Member); C. C. Liu PhD (Committee Member); Christian A. Zorman PhD (Committee Member) Subjects: Chemical Engineering

Doctor of Philosophy, Case Western Reserve University, 2006, Chemical Engineering

Tribological thin films are of interest to designers and end-users of friction management and load transmission components such as steel rolling element bearings. This study sought to reveal new information about the properties and formation of such films, spanning the scope of their technical evolution from natural oxide films, to antiwear films from lubricant additives, and finally engineered nanocomposite metal carbide/amorphous hydrocarbon (MC/a-C:H) films. Transmission electron microscopy (TEM) was performed on the near-surface material (depth < 500 nm) of tapered roller bearing inner rings (cones) that were tested at two levels of boundary-lubricated conditions in mineral oil with and without sulfur- and phosphorus-containing gear oil additives. Site-specific thinning of cross-section cone surface sections for TEM analyses was conducted using the focused ion beam milling technique. Two types of oxide surface films were characterized for the cones tested in mineral oil only, each one corresponding to a different lubrication severity. Continuous and adherent antiwear films were found on the cone surfaces tested with lubricant additives, and their composition depended on the lubrication conditions. A sharp interface separated the antiwear film and base steel. Various TEM analytical techniques were used to study the segregation of elements throughout the film volume. The properties of nanocomposite tantalum carbide/amorphous hydrocarbon (TaC/a-C:H) thin films depend sensitively on reactive magnetron sputtering deposition process conditions. TaC/a-C:H film growth was studied as a function of three deposition parameters in designed experiments: acetylene flow rate, applied d.c. bias voltage, and substrate carousel rotation rate. Empirical models were developed for the following film characteristics to identify process-property trend relationships: Ta/C atomic ratio, hydrogen content, film thickness, TaC crystallite size, Raman spectrum, compressive stress, hardness, (open full item for complete abstract)

Committee: Jeffrey Glass (Advisor) Subjects:

Master of Science, University of Akron, 2006, Applied Mathematics

Plasma enhanced physical vapor deposition (PEPVD) is one method to coat nanofibers and nanostructures with thin film materials. Experimental efforts in coating electrospun polymer nanofibers suggest a complicated relationship between coating morphology and operating conditions. This motivates a theoretical model for coating growth. The model presented here assumes a coating growth that is uniform along the axial dimension of the nanofiber but non-uniform in the radial direction. The concentration of vaporized aluminum surrounding the coating growth is non-uniform due to the geometry of the coating growth, therefore modeling the morphology of the growth requires that the surrounding concentration field be determined. The concentration field would then be supplied to an evolution equation. The mode of mass transport is diffusion, therefore the mathematical model consists of Laplace's equation over a polar domain. The domain is an annulus with an irregular inner boundary. A finite difference method is employed to solve the system. The irregular inner boundary geometry, as well as a complicated inner boundary condition, requires that interpolation schemes and ghost points be used at points on and near the boundary. The resulting matrix system is solved with a block SOR iterative method.

Committee: Kevin Kreider (Advisor) Subjects: Mathematics

Master of Science, University of Akron, 2006, Applied Mathematics

This Masters Thesis presents a theoretical model of coating growth resulting from a procedure to coat nanofibers and core-clad nanostructures. These nanofibers and nanostructures are coated with thin film materials using plasma enhanced physical vapor deposition (PEPVD). In the experimental effort, electrospun polymer nanofibers are coated with metallic materials under varying operating conditions to observe changes in the coating morphology. This paper investigates non-uniform axial growth with uniform radial growth. The interrelationships among processing factors for the transport and deposition of the coating material are investigated here. This includes both the salient physical and chemical phenomena. This parametric study results in an evolution equation describing coating growth. This equation is first solved using a boundary perturbation method to determine the coating morphology as a function of operating conditions. This results in a solution that describes uniform coating growth. The weakly nonlinear solution is then determined and describes non-uniform growth in the axial direction. The nonlinear evolution equation is then analyzed using linearization methods and a solution of separable form. Lastly, the evolution equation is parameterized using an arc-length technique. This results in a pair of differential equations that are solved numerically. Also, a parametric study is presented.

Committee: Gerald Young (Advisor) Subjects: Mathematics