Multiple bonding structures Of C2H2 chemisorbed on Si(100)

Adsorption of acetylene on the Si(100)-(2 x 1) surface was studied at room temperature by scanning tunneling microscopy (STM) and theoretical modeling . Acetylene molecules adsorb nondissociatively in three distinctive bonding configurations, not one, as reported previously. In Configuration 1, C2H2 molecules adsorb in di-sigma form over a single silicon dimer with a relati ve population of 0.33 at low coverage. Configuration II has an initial form ation probability of 0.51 and involves adsorption across the ends of two ad jacent dimers in the same row. In Configuration III (r-bridge) C2H2 forms f our bonds as it symmetrically bridges two neighboring dimers. Relative popu lations depend strongly on coverage. Above a coverage of similar to0.13 an acceleration in the rate of formation of Configuration III (r-bridge) is ob served. (C) 2001 Elsevier Science B.V. All rights reserved.