Study of benzene and toluene on Si(111)7 x 7 surface by scanning tunneling microscopy

The adsorption of benzene and toluene on Si(1 1 1)7 x 7 was investigated using scanning tunneling microscopy at 180 and 280 K. Significant differences in reactivity were observed among the various sites on Si(1 1 1)7 x 7 towards the aromatic molecules. For both molecules, the center adatoms were more reactive than the corner adatoms, and the faulted subunit was more reactive than the unfaulted subunit. In particular, strong preferential adsorption of benzene on the center adatoms in faulted subunits was found at 180 K. The populations of the subunits, each consisting of three reacted adatoms, indicated that the adsorption involves a rest atom and an adatom for both aromatic molecules. Moreover, differences in the populations for benzene and toluene indicated the effects of the methyl group of toluene on the adsorption configurations. (C) 2002 Elsevier Science B.V. All rights reserved.