Phenol adsorption on Si(111)7x7 studied by synchrotron radiation photoemission and photodesorption

Phenol adsorption on Si(111)7 x 7 has been studied by synchrotron radiation photoemission and photodesorption in the valence band Si 2p energy ranges both at room temperature and at approximate to 50 K. The assignment of the phenol adsorption features has been made by comparison of the gas-phase spectrum. At low exposures the surface rest atoms are selectively quenched, while the adatoms are involved in the adsorption process only for higher exposures. The comparison of the spectra at different temperatures allows us to infer that the adsorption on the rest atoms is molecular. However, the relative intensity of the spectral features changes when different sites are involved in the adsorption process. In particular, the feature attributed to the sigma(O-H) orbital does not increase in intensity. although the other features do, suggesting that the adsorption is dissociative. The photon-stimulated desorption pattern shows a D+ yield in the Si 2p energy range, due to the enhanced production of secondary electrons in correspondence with the ionization threshold, similarly to the system benzene-Si(111)7 x 7. (C) 1999 Elsevier Science B.V. All rights reserved.