Influence of the temperature on the ion photodesorption from O2 adsorbed on Si(111)7 x 7

Ion photodesorption is a powerful tool to investigate (i) how molecules adsorb on surfaces, (ii) the electronic relaxation of the excited states of the adsorbed species and (iii) their intramolecular dynamics. The temperature dependence of all these processes is of crucial interest, especially on semiconductor surfaces, to understand the role of phonons, charge carrier densities, thermal expansion and thermal activation. We have studied at 300 and 30 K the ion photodesorption processes following the Si(2p) core level excitation from O-2 on Si(1 11)7 x 7. Detailed information have been obtained by analyzing the O+ ion kinetic energy distributions at both temperatures. The results suggest that, at low temperature, the lifetimes of the excited electronic states producing the ion desorption are significantly increased due to the reduced number of charge carriers. This offers interesting perspectives to control the dynamics of molecular systems on surfaces. (C) 2002 Elsevier Science B.V. All rights reserved.