Formation of Di-σ Bond in Benzene Chemisorption on Si(111)-7×7

The adsorption of benzene on Si(111)-7×7 has been studied using high-resolution electron energy loss spectroscopy (HREELS) and thermal desorption spectroscopy (TDS). Both chemisorbed and physisorbed benzene were observed at an adsorption temperature of 110 K. Chemisorbed benzene desorbs molecularly at 350 and 364 K while physisorbed molecules desorb at 180 K. In the HREELS studies, two separate energy losses at 2920 and 3025 cm -1 were observed for chemisorbed benzene, attributable to the C−H stretching vibrations of sp 3 and sp 2 carbon atoms, respectively. In addition, the formation of Si−C bond is also evidenced at a vibrational frequency of 540 cm -1 . Our results clearly demonstrate that benzene is di-σ bonded to the adjacent adatom and rest atom on Si(111)-7×7, forming a 1,4-cyclohexadiene-like structure.