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

The adsorption of benzene on Si(lll)-7x7 has been studied using high-resolu tion electron energy loss spectroscopy (HREELS) and thermal desorption spec troscopy (TDS). Both chemisorbed and physisorbed benzene were observed at a n 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 s p(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 re sults clearly demonstrate that benzene is di-sigma bonded to the adjacent a datom and rest atom on Si(111)-7x7, forming a 1,4-cyclohexadiene-like struc ture.