Binding structures of pyrrole on Si(5 5 12)-2 × 1 surfaces

In an effort to understand the reaction mechanisms involved in the adsorption of organic aromatic molecules on high-index Si surfaces, the reactions of pyrrole molecules adsorbed onto Si(5 5 12)-2 × 1 surfaces were studied using scanning tunneling microscopy and first principle calculations. The dissociation of one or two H atom(s) bonded to N (or N and C) from the pyrrole molecules was favored, and adsorption at adatom, tetramer, dimer, or honeycomb Si(5 5 12)-2 × 1 sites occurred to produce several distinct configurations. Pyrrole was most reactive toward the dimer site, yielding two dissociated hydrogen atoms and a vertical configuration. Pyrrole also adsorbed onto the tetramer and honeycomb sites, yielding two dissociated hydrogen atoms. On the adatom row, however, pyrrole bound to an adatom via a σ bond between the adatom and N to yield one dissociated H atom adsorbed onto a nearby adatom. No other hydrogen dissociation reactions were observed. In all configurations, the aromaticity of pyrrole was retained.