Interactions of atomic oxygen with platinum(111) and nitrided silicon(100)

Gas-phase oxygen atoms play a critical role in several applications including degradation of materials in low Earth orbits, semiconductor processing, and heterogeneous catalysis. In each of these applications, the highly reactive nature of the oxygen atom dictates the details of the oxygen atom-surface reactions. Whether the goal is to develop new materials resistant to oxidation or to use the oxygen atoms to generate surfaces with unique properties, a fundamental understanding is needed of the chemistry governing the interactions of O-atoms with surfaces.; Silicon nitride is used in applications because it resists oxidation. We conducted an X-ray photoelectron spectroscopy (XPS) study to examine the surface chemistry of nitrified Si(100) toward molecular and atomic oxygen. A decrease was observed in the Si(100) surface dangling bond density due to nitridation, and this was accompanied by a subsequent decrease in surface reactivity for both molecular and atomic oxygen. This indicates that oxygen atoms preferentially react at these dangling bond sites, and do not insert directly into silicon-silicon bonds.; Using mass spectrometry, we explored the reactivity of gaseous 16O-atoms toward chemisorbed 18O2 on the Pt(111) surface. The gas-phase oxygen atoms stimulate both displacement and dissociation of adsorbed 18O2. As the surface temperature increased, the desorption yield decreased, with the balance remaining on the surface in the form of chemisorbed atoms. Molecular oxygen is known to adsorb in superoxo and peroxo configurations on Pt(111). The strong temperature dependence on the dissociation yield is attributed to an increase in the population of the peroxo chemisorbed species with temperature, which is more prone to dissociate.; Platinum is catalytically active toward the oxidation of CO. Using O 2 under ultrahigh vacuum conditions, a maximum surface coverage of 0.25 monolayers (ML) of O-atoms can be generated. Surfaces with higher oxygen coverages can be generated by exposing Pt(111) to oxygen atoms. Using mass spectrometric methods, an in situ CO oxidation study was conducted on these surfaces. The CO oxidation kinetic behavior was found to be consistent with a CO adsorption precursor model. Carbon monoxide oxidation on platinum oxide occurs predominately at the interface between the metallic regions and the oxide.