Ion photon-stimulated desorption as a tool to monitor the physisorption to chemisorption transition of benzene on Si(111) 7 × 7

We investigated the use of ion photodesorption as a tool to monitor the transition from the physisorbed to the chemisorbed state on a surface. The adsorption of benzene on Si(111) 7 × 7 in the temperature range 40-300 K is chosen as a prototype. The D+ ion photodesorption yield was monitored as a function of temperature at various benzene exposures. Comparative measurements of the C 1 s photoelectron yield in the same temperature range enable the physisorbed to chemisorbed state transition to be distinguished from that of the multilayer to the chemisorbed state. We find the onset at 110 K in the first case, and at 130-140 K in the second case. These results demonstrate that ion photodesorption is a potentially interesting method to identify physisorption to chemisorption transitions of adsorbed molecules on surfaces.