In this award, funded by the Experimental Chemistry Program of the Division of Chemistry, Professor Fisher from Colorado State University will investigate the effect of plasma modification processes on surfaces. Plasma processing has become indispensable in a wide range of applications where high performance materials with tailored surface properties are employed. Moreover, development of new plasma surface modification processes and deposition chemistries is a burgeoning area of significant impact to biomaterials, coatings, and sensor applications. A more complete understanding of the underlying chemistry in these systems could lead to manufacturing improvements with economic impact across many industries. Thus, the goal of the proposed work is to improve understanding of the fundamental chemical processes that occur at surfaces during plasma enhanced chemical vapor deposition and surface modification of polymers. Professor Fisher and her students will achieve this goal through an integrated, comprehensive approach to understanding the molecular-level chemistry in these systems. The primary experimental tools to be employed are in situ sum frequency generation (SFG) spectroscopy and the laser-based imaging of radicals interacting with surfaces (IRIS) technique, which provides steady-state surface interaction data for plasma species. The SFG experiments are designed to examine the evolution of plasma modified films upon exposure to atmospheric gases to study labile intermediates formed in plasma modification, thereby elucidating mechanisms involved in aging and hydrophobic recovery processes.
The intrinsic interdisciplinary nature of this research will afford students a broad exposure to and education in chemistry, engineering, and materials science, beyond the traditional boundaries in chemistry. Professor Fisher will continue her efforts in broadening participation of underrepresented groups and use the proposed experiments to develop demonstrations of plasmas and lasers for visitors, high school groups and K-12 teachers.
Plasma processing is an indispensable tool in a wide range of applications where high performance materials with tailored surface properties are desired. Plasmas are partially ionized gases (similar to the environment found in neon lights) that are capable of creating new materials or significantly altering the surface properties of existing materials in a tailorable fashion. Development of new plasma surface modification processes and film deposition chemistries is likely to have significant impact on many arenas, including biomaterials, protective coatings, and sensor applications. A more complete understanding of underlying chemistry and mechanisms will provide avenues for improving existing technologies and developing new directions for plasma processing of new materials. Thus, the goals of the funded project were to improve understanding of the fundamental chemical processes that occur at surfaces during plasma enhanced chemical vapor deposition and surface modification of polymers and other materials. During the course of this grant, we achieved these goals through an integrated, comprehensive approach to understanding the molecular-level chemistry in these systems. We used our unique laser-based imaging of radicals interacting with surfaces (IRIS) technique, to provide steady-state surface interaction data for plasma species and complemented our IRIS studies with a range of gas-phase diagnostics and surface characterization tools, yielding a comprehensive picture of the entire plasma system. During the grant period, we focused our attention on several key systems including: (1) nitrogen-based plasma surface modification of materials used in solar cells and photon-induced catalysis to improve photocatalytic and photovoltaic properties; (2) plasma deposition of hard carbon nitride films used as protective coatings, with an emphasis on understanding their adhesion properties; (3) plasma surface modification and coating of nanoparticles and 3D structures for improved performance in biomedical applications; (4) developing detailed mechanisms for molecule-surface interactions in hydrophobic (water repellant) film formation systems; and (5) plasma abatement of atmospheric pollutants such as sulfur dioxide and nitric oxide. These studies represent transformative contributions to our fundamental understanding of technologically important systems. The Intellectual Merit of the research is several-fold. First, we significantly advanced our knowledge and basic understanding of plasma-surface modification systems, specifically examining surface interactions of small molecules such as CF, CF2, NO, CN, and OH during plasma processing events. These data allow us to develop robust mechanisms for the overall processes occurring, thereby providing users of the technology with tools for controlling the resulting materials properties. Second, our in situ measurements provided unprecedented insight into the modification processes, including intermediates formed during plasma modification. Third, we were able to correlate many of our surface reactivity measurements with overall materials properties (such as film composition or surface wettability), again providing much needed information on the plasma-surface interface. Fourth, we measured internal and kinetic energies of several gas-phase species and were able to correlate these with both surface properties and molecule-surface interaction data. Collectively, these data provided insight into energy partitioning mechanisms in the plasma and at the plasma-surface interface unobtainable with other techniques. Finally, the intrinsic interdisciplinary nature of this research afforded several students at both the graduate and undergraduate level a broad exposure to and education in chemistry, engineering, and materials science. The Broader Impacts of the research lie in the increased understanding of chemical processes occurring plasma-surface modification. We examined several systems that are recognized as being important scientifically as well as technologically-relevant with a wide range of applications where creating tailored, high performance materials is imperative. A more complete understanding of the underlying chemistry in these systems could lead to manufacturing improvements with enormous economic impact across many industries. In addition, the PI is committed to strengthening education and training in the sciences and broadening participation of underrepresented groups. Four 4 Ph.D. students graduated during the period of this grant (1 female underrepresented minority). In addition, 4 additional Ph.D. students were supported (1 female) and 3 undergraduate students (2 female). Two of the undergraduates have or will (Fall 2013) matriculate graduate programs in Chemistry. This work has also sparked a new cross-disciplinary collaboration with faculty in mechanical engineering and the school of biomedical sciences. The PI also used her NSF-funded research as a platform to promote global research experiences for undergraduate and graduate students, including study abroad programs. She is currently working on a real-time demonstration of plasma-surface modification of polymers to create hydrophilic (wetting) and hydrophobic (water repellant) surfaces to use with visitors, high school chemistry groups, and K-12 teachers.
