Systematic Studies of Plasma Reactions on Dynamic Surfaces, Using a Novel Rotating Substrate

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0966967DonnellyIntellectual MeritThese studies will systematically investigate selected chemistry occurring at the boundary between a gaseous plasma discharge and the walls of the reactor that contains the plasma. Such basic knowledge of the plasma-wall boundary is lacking in plasma science and is critically needed for control of plasma processing such as etching for fine-line pattern transfer in silicon integrated circuits and other future nano-technology. To gain access to the plasma-wall boundary, a cylindrical substrate within the plasma chamber wall will be rapidly rotated, allowing portions of the surface to be periodically exposed to the plasma and then analyzed. Previously, we used this ?spinning wall? method to investigate surface recombination reactions of oxygen atoms in an oxygen plasma and chlorine atoms in a chlorine plasma, and as well as surface reactions that form chlorine oxide and chlorine dioxide in plasmas with mixtures of oxygen and chlorine. The new studies will focus on four topics of critical importance to understanding and controlling chemistry at surfaces immersed in plasma: 1) What is the role of weakly bound stable adsorbates such as Cl2 on recombination of Cl atoms? We previously found that physisorbed Cl2 blocks sites for Cl recombination. We will extend the study to a much wider range of conditions and investigate other suspected cases such as Br2 and fluorocarbons. 2) How widespread is, and what is the mechanism for, catalyzed recombination by trace metals, as we recently discovered for O in the presence of sub-monolayer coverages of copper? The oxidation-reduction mechanism proposed for copper will be tested with other metals, and recombining atoms. 3) The relative importance of the two prevailing mechanisms for surface reactions (the so-called Langmuir-Hinshelwood or delayed reaction vs. the Eley Rideal or prompt reaction) will be determined for selected atoms and small molecules. Except for hydrogen atoms on pristine surfaces, such information is almost completely lacking. 4) What are the roles of ion and electron bombardment on surface chemical reactions? Positive ions bombarding the surface can create or destroy reaction sites, while electron bombardment can cause decomposition of adsorbed layers, as well as create negative ions and reduce catalytic activity of higher oxidation states of trace metals. The proposed work will be an extremely challenging, basic research project that is critical for improving our understanding of plasma-surface interactions with an emphasis on plasmas used for etching of nano-scale features in integrated circuits and other future devices. Broader ImpactsThe proposed work will provide challenging projects for two graduate student and one or more undergraduates, with rich scientific and educational payoffs, as well as technological advances. While it will improve our understanding of surface reactions under complex plasma conditions, it will also contribute to diverse areas such as space physics, combustion chemistry, catalysis, and atmospheric heterogeneous reactions. In addition, the new methods for isolating such complex reactions have broad implications for and potential impact on these diverse areas, as well as basic surface science. Several outreach activities are planned, including involving a high school teacher in the research, and the participation by undergraduate students through programs such as the Research Experience for Undergraduates (REU) at UH. Finally, the participation of underrepresented students (more than half of the University of Houston undergraduate students are minorities) will be pursued.