STM INVESTIGATION OF THE ADSORPTION AND TEMPERATURE-DEPENDENT REACTIONS OF ETHYLENE ON PT(111)

The adsorption and reactions of ethylene adsorbed in UHV on Pt(111) have been studied as a function of temperature by STM. The STM images taken at 160 K show an ordered structure of adsorbed ethylene. Annealing to 300 K produces ethylidyne (C-CH3) irreversibly, as has been demonstrated by a wide variety of surface science techniques. The ethylidyne on Pt(111) is not visible to the STM at room temperature. Cooling the sample allows direct observation of the ethylidyne ordered structure by STM. Annealing above 430 K results in further dehydrogenation, eventually leaving only carbon on the surface. The decomposition products appear as small clusters which are localized and uniformly distributed over the surface. Further annealing to temperatures > 800 K results in the growth of graphite islands on the Pt(111) surface. The annealed graphite islands exhibit several supersturctures with lattice parameters of up to 22 angstrom, which are thought to result from the higher order commensurability with the Pt(111) substrate at different relative rotations.