AVS 46th International Symposium
    Surface Science Division Tuesday Sessions
       Session SS-TuP

Paper SS-TuP18
The Formation of di-@sigma@ Bond in Chemisorbed Benzene and Chlorobenzene on Si(111)-7x7

Tuesday, October 26, 1999, 5:30 pm, Room 4C

Session: Poster Session
Presenter: Y. Cao, National University of Singapore
Authors: Y. Cao, National University of Singapore
G.Q. Xu, National University of Singapore
Correspondent: Click to Email
The adsorption of aromatics on Si surfaces has attracted great interests recently. In the present study, the adsorption of benzene and chlorobenzene on Si(111)-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@super -1@ were observed for chemisorbed benzene, attributable to the C-H stretching vibrations of sp@super 3@ and sp@super 2@ carbon atoms, respectively. In addition, the formation of Si-C bond is also evidenced at a vibrational frequency of 540 cm@super -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. The adsorption behaviour for chlorobenzene is quite similar to that of benzene. However, due to the substitution effect of the Cl atom on ring of benzene, a regional-selective adduction of 2,5-sites in chlorobenzene on Si(111)-7x7 is observed, resulting the formation of 2,5-chlorocyclohexadiene like adduct.