ADSORPTION AND REACTION OF TRIFLUOROMETHYL IODIDE ON NI(111)

We have investigated the surface chemistry of trifluoromethyl iodide adsorbed on Ni(111) under ultrahigh-vacuum conditions using temperature-programmed desorption, reflection absorption infrared spectroscopy, and Auger electron spectroscopy. Ni(111) activates both carbon-iodine and carbon-fluorine bonds in adsorbed CF3I. Atomic iodine desorbs from the surface near 975 K, and nickel fluoride, NiF2, desorbs near 820 K. Although the desorption temperatures for iodine and nickel fluoride are high, there is evidence that carbon-iodine and carbon-fluorine bonds are activated below room temperature. A small amount of fluorocarbon products containing CF2 and CF3 fragments desorb from the surface between 200 and 375 K. At higher temperatures, fluorine atoms recombine with adsorbed carbon to form CF4, which desorbs near 780 K. CF3I molecularly desorbs from the surface at high coverages with desorption rate maxima of 162 and 122 K for the monolayer and multilayer, respectively. Coadsorption of D atoms and CF3I results in the desorption of CD2F2 near 230 K and DF between 260 and 460 K. After desorption of the monolayer, the bands in the infrared spectrum are quite weak. The IR data suggest that very few fluorocarbon fragments are stabilized on the surface. In general, the data indicate that a large fraction of adsorbed CF3I decomposes to form atomic carbon, fluorine and iodine. A comparison of the reactions of CF3I on Ni to Ag, Pt and Ru shows that only Ni is etched under ultrahigh-vacuum conditions by CF3I.