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 (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

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: