Scanning tunneling microscopy investigations of reactions between thiolate coated gold surfaces and gas-phase radicals.

Scanning tunneling microscopy was used to investigate the dynamics of gas/surface reactions as they take place on the molecular scale. Experiments between atomic hydrogen and an Au(111) surface functionalized with a 1-adamantanethiolate self-assembled monolayer resulted in signicant evidence that the reconstruction of the gold during monolayer formation is dependent on the thiolate molecule density on the surface. Reactions have also been completed between atomic chlorine and 1-octanethiolate monolayers, we believe, based on a number of methodologies used to quantify the products, that atomic chlorine is more than five times more likely to react in bulk ordered ares of the monolayer than at defect sites. Further, we have determined that, while chlorination and sulfur abstraction does occur over extended dose times, the principle reaction pathway is likely hydrogen abstraction followed by the recombination of surface radicals, leading to an extensively cross-linked surface. Increasing the throughput of instrumentation already present in the lab has been a major goal. A high-voltage supply capable of supplying 280 V to the tunnel junction has been constructed to make in vacuum tip changes possible. An electrochemical tip etcher has been built and used to prepare sharp SPM tips with a reproducible etched length to apex diameter aspect ratio, and a novel thermoelectrically cooled STM was constructed that will go on to allow the lab to complete thermally activated reaction studies in a controlled environment. Further, We have designed and developed a new ultra-high vacuum, cryogenically cooled STM capable of reevaluating the reactions between H atoms and thiolate SAMs previously completed in the lab, but now, at low-temperature. This will hopefully allow us to further elucidate the kinetics of chemical reactions taking place at surfaces on the molecular level.