We have investigated the electronic structure and the thermal dependence of C60 molecules adsorbed on a Si(111)-(7 × 7) surface using photoelectron spectroscopy. At room temperature, the binding energies of the molecular orbitals and the C 1s core level of the 1.0 monolayer (ML) film are the same as those of the 5.0 ML C60 film. This result indicates that most of C60 molecules interact with the Si surface by van der Waals force at a coverage of 1.0 ML. After annealing the 1.0 ML C60 film at 500 K, the full-width at half maximum of the molecular orbitals becomes broader indicating the chemisorption at this temperature. Moreover, the highest occupied molecular orbital (HOMO) of a C60 molecule splits into two peaks that are assigned to be the shifted HOMO and the bonding state with the polarization-dependent measurements and the Si 2p core level spectrum. The molecular orbitals and the C 1s core level shift to lower binding energies. These results indicate that the chemisorption between C60 molecules and the surfaces has both covalent and ionic characters at 500 K. We attribute the transition in the bonding nature of C60 molecules to the thermal induced change in surface structure during the annealing process.
|Number of pages
|Journal of Electron Spectroscopy and Related Phenomena
|Published - 1999
- Photoelectron spectroscopy
- Surface electronic phenomena