Two bonding configurations of acetylene on Si(001)-(2×1): A combined high-resolution electron energy loss spectroscopy and density functional theory study

Mineva, T.; Nathaniel, R.; Kostov, K. L.; Widdra, W.
November 2006
Journal of Chemical Physics;11/21/2006, Vol. 125 Issue 19, p194712
Academic Journal
Two coexisting adsorption states of molecularly adsorbed acetylene on the Si(001)-(2×1) surface have been identified by a combined study based on the high-resolution electron energy loss spectroscopy and density functional computations. Seven possible adsorbate-substrate structures are considered theoretically including their full vibrational analysis. Based on a significantly enhanced experimental resolution, the assignment of 15 C2H2- and C2D2-derived vibrational modes identifies a dominant di-σ bonded molecule adsorbed on top of a single Si–Si dimer. Additionally there is clear evidence for a second minority species which is di-σ bonded between two Si–Si dimers within the same dimer row (end-bridge geometry). The possible symmetries of the adsorbate complexes are discussed based on the specular and off-specular vibrational measurements. They suggest lower than ideal C2v and Cs symmetries for on-top and end-bridge species, respectively. At low coverages the symmetry reductions might be lifted.


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