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Direct observation of surface reactions by scanning tunneling microscopy: Ethylene→ethylidyne→carbon particles→graphite on Pt(111) (1992)

Land, T. A. ; Michely, T. ; Behm, R. J. ; [et al.]

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 97 (1992), S. 6774-6783

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ISSN: 1089-7690

Source: AIP Digital Archive

Topics: Physics , Chemistry and Pharmacology

Notes: We have used variable temperature, ultrahigh vacuum scanning tunneling microscopy (STM), in both static and time-dependent experiments, to study the chemistry of the ethylene/Pt(111) system. Images of ethylene which exhibit long-range order have been obtained at a sample temperature of 160 K. The conversion of ethylene to ethylidyne has been observed directly in STM images. This conversion reaction is observed to occur in a "patchy'' manner across the surface at saturation coverage. As the reaction proceeds, well-defined islands of unreacted ethylene continue to be clearly observed. Further dehydrogenation of the ethylidyne formed from ethylene leads to carbon containing particles dispersed randomly across the sample. After annealing the ethylidyne covered sample to 500 K, the surface is uniformly covered with carbon containing particles which exhibit a bimodal distribution of heights (one and two atomic layers) consisting of an average of ten and twenty carbon atoms, respectively. Further annealing to 700 K results in the formation of larger particles which appear to be a single atomic layer high and 10–15 A(ring) in diameter in the STM images. These particles contain an average of thirty-four carbon atoms. Pt steps do not show any preferential reactivity for these reactions. Annealing the carbon particle covered surface to higher temperatures results in the formation of monolayer thick graphite islands, which eventually accumulate at the Pt steps.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.463655

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STM investigation of the adsorption and temperature dependent reactions of ethylene on Pt(111) (1991)

Land, T. A. ; Michely, T. ; Behm, R. J. ; [et al.]

Springer

Applied physics 53 (1991), S. 414-417

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ISSN: 1432-0630

Keywords: 82.65.Jv ; 61.16Di

Source: Springer Online Journal Archives 1860-2000

Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics

Notes: Abstract 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 160K 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 Å, which are thought to result from the higher order commensurability with the Pt(111) substrate at different relative rotations.