In situ x-ray photoelectron spectroscopic and density-functional studies of Si atoms adsorbed on a C-60 film

摘要

The interaction between C-60 and Si atoms has been investigated for Si atoms adsorbed on a C-60 film using in situ x-ray photoelectron spectroscopy (XPS) and density-functional (DFT) calculations. Analysis of the Si 2p core peak identified three kinds of Si atoms adsorbed on the film: silicon suboxides (SiOx), bulk Si crystal, and silicon atoms bound to C-60. Based on the atomic percent ratio of silicon to carbon, we estimated that there was approximately one Si atom bound to each C-60 molecule. The Si 2p peak due to the Si-C-60 interaction demonstrated that a charge transfer from the Si atom to the C-60 molecule takes place at room temperature, which is much lower than the temperature of 670 K at which the charge transfer was observed for C-60 adsorbed on Si(001) and (111) clean surfaces [Sakamoto , Phys. Rev. B 60, 2579 (1999)]. The number of electrons transferred between the C-60 molecule and Si atom was estimated to be 0.59 based on XPS results, which is in good agreement with the DFT result of 0.63 for a C60Si with C-2v symmetry used as a model cluster. Furthermore, the shift in binding energy of both the Si 2p and C 1s core peaks before and after Si-atom deposition was experimentally obtained to be +2.0 and -0.4 eV, respectively. The C60Si model cluster provides the shift of +2.13 eV for the Si 2p core peak and of -0.28 eV for the C 1s core peak, which are well corresponding to those experimental results. The covalency of the Si-C-60 interaction was also discussed in terms of Mulliken overlap population between the (C) 2004 American Institute of Physics.