Abstract
The reaction between oxygen and carbon on a nickel film supported by a sapphire substrate has been studied with temperature programmed desorption (TPD) and Auger electron spectroscopy (AES). Oxygen was dissolved into the nickel film from the gas phase during high-temperature oxidation and annealing. Carbon was subsequently deposited on the nickel surface from the thermal decomposition of ethylene. During TPD, the bulk oxygen diffused to the vacuum interface of the nickel film, reacted with surface carbon, and desorbed as CO. A set of CO TPD peaks obtained for increasing initial carbon coverages showed a common low-temperature leading edge. This common leading edge has been fitted to a model in which the rate-limiting step in the carbon-oxygen reaction is taken to be the diffusion of bulk oxygen to the nickel film's surface. An activation energy for oxygen diffusion in nickel of 80 kcal/mole has been obtained. Sequential carbon exposures and TPD flashes eventually resulted in bulk oxygen depletion; this manifested itself in the CO desorption spectra as a reduction in the area under the CO peak and a shift of the peak to higher temperatures.
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