TRACKING THERMALLY DRIVEN MOLECULAR REACTION AND FRAGMENTATION BY FAST PHOTOEMISSION: C 60on Si (111): C₆₀ on Si(111)

We followed in real time the thermal reaction of fullerene molecules with the Si(111) surface by means of fast photoemission spectroscopy. The formation of SiC via C60 fragmentation on Si(111) is used as a key example of the capability of fast photoemission, associated with a fine temperature control, in determining the nature of thermally induced chemical reactions. By monitoring every 13 s the evolution of the C1s core level photoemission spectrum, as a function of temperature and as a function of time at fixed temperature, we were able to identify several steps in the interaction of C60 with Si(111). A model describing the thermal evolution of this interaction, in agreement with these and other experimental observations, considers the initial chemisorption of C60 in mainly metastable configurations, the evolution toward more stable configurations, allowed by molecular rotations and breaking of Si-Si bonds, the cage deformation to further increase the number of C-Si bonds, the final cage fragmentation and SiC formation only above 1050 +/- 10 K.