Adsorption site selectivity for thiophene on reconstructed Si(5 5 12)-2 × 1 surface

The covalent binding of thiophene molecules to a Si(5 5 12)-2 × 1 surface was investigated using scanning tunneling microscopy and density functional theory calculations. The molecular attachment occurred exclusively between the bonding of the 2,5 carbon atoms and the two silicon adatoms without the involvement of the sulfur atom (over 90%). The binding structure formed a di-σ bond with a planar butterfly-like configuration. Adsorption at other sites, including at the dimer, tetramer, or honeycomb rows, occurred much less frequently. Our calculations predicted that the adsorption energies of the thiophene molecules were 1.02-1.56 eV at the adatom, dimer, and tetramer sites. The molecules adsorbed on the honeycomb rows with a low adsorption energy (below 1 eV). The binding modes of the simple aromatic molecules onto the Si(5 5 12)-2 × 1 surface are compared and discussed.