Adsorbed state of benzene on the Si(100) surface: Thermal desorption and electron energy loss spectroscopy studies

The adsorbed state of benzene on the Si (100) surface at 90 and 300 K has been investigated by the use of thermal desorption spectroscopy (TDS) and high resolution electron energy loss spectroscopy (EELS). Benzene is chemisorbed nondissociatively on Si(100) at 300 K, and the fractional saturation coverage corresponds to 0.27 benzene molecule per surface Si atom. It is proposed that chemisorbed benzene is di-σ bonded to two adjacent Si atoms saturating the dangling bonds on Si(100). At 90 K, physisorbed multilayers of benzene molecules are formed in addition to the chemisorbed layer. The multilayers consist of the metastable transition layer (α₂) and "bulk" multilayers (α₃). These results are markedly different from those of benzene on the Si(111) (7 X 7) surface, and the origin of the crystal-face specificity is discussed.