| In order to understand plasma deposition processes, it is important to have a knowledge of the plasma gas-phase reactions. In this project, in situ Fourier Transform Infrared Spectroscopy (FTIR) was utilized to study the plasma gas-phase chemistry in a capacitively coupled glow discharge. Gas-phase measurements of a number of organic plasmas were performed. The precursors include methyl methacrylate (MMA), methyl crotonate, methyl isobutyrate, ethyl methacrylate, vinyl acetate, isopropanol, methanol, tetramethyl cyclobutanedione and formaldehyde. However, MMA was studied most extensively. In addition to the gas-phase study, plasma polymerized films were also characterized.; A number of dissociation products were detected by FTIR in the plasmas. Calibration curves of these products and some monomers were prepared to determine the species concentrations and gas-phase composition. Plasma reaction kinetics were studied in closed systems to determine parameters such as dissociation pathway efficiencies, monomer decomposition rate coefficients, and intermediate species decomposition rate coefficients.; The study shows that there are two major electron-impact induced dissociation pathways in MMA plasmas: the C-O bond cleavage reaction and decarboxylations. The C-O bond cleavage reaction accounts for approximately half of the MMA dissociation, and neutral formaldehyde and dimethyl ketene (DMK) molecules are produced via intramolecular rearrangement. Decarboxylation reactions produce CO, {dollar}rm COsb2{dollar} and a number of radicals that subsequently stabilize to form neutral molecules, such as propylene, allene and methanol. These intermediate species then further dissociate in the plasma to small hydrocarbons (methane, acetylene and ethylene), CO, {dollar}rm COsb2{dollar} and {dollar}rm Hsb2.{dollar}; The reaction mechanisms in the plasmas of other {dollar}alpha ,beta{dollar}-unsaturated esters and vinyl acetate were found to be similar to the MMA mechanisms. However, the saturated ester (methyl isobutyrate) and isopropanol plasmas were found to produce ketenes via a different mechanism. This radical intermediate mechanism is less efficient than the intramolecular rearrangement mechanism in MMA plasmas, and it only becomes important in the absence of intramolecular rearrangement.; In addition, a high correlation was observed between the gas-phase composition and the film composition in closed MMA and other plasma systems. DMK, the largest MMA dissociation product, is suggested as the most significant deposition precursor of carbonyl groups in plasma polymerized MMA. |
