Formation of di-σ bond in benzene chemisorption on Si(111)-7x7

The adsorption of benzene on Si(lll)-7x7 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-sigma bonded to the adjacent adatom and rest atom on Si(111)-7x7, forming a 1,4-cyclohexadiene-like structure.