(C6H5)(5)C60H at Si(111)-(7x7) and Ag : Si (111) - (v3 x v3) R30 degrees surfaces

Phillips, M. A., O'Shea, J., Birkett, P. R., Purton, J., Kroto, H. W., Walton, D. R. M., Taylor, R. and Moriarty, P. (2005) (C6H5)(5)C60H at Si(111)-(7x7) and Ag : Si (111) - (v3 x v3) R30 degrees surfaces. Physical Review B, 72 (7). 075426. ISSN 1098-0121

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Abstract

We have studied the properties of (C6H5)5C60H in thick film form and adsorbed at two surfaces at the extremes of chemical reactivity—the highly reactive Si(111)‐(7×7) and chemically passivated Ag:Si(111)‐(√3×√3)R30° surfaces—using photoemission spectroscopy (PES) and near-edge x-ray fine structure (NEXAFS) spectroscopy. Our results show that the phenyl groups produce dramatic changes in the electronic structure of the fullerene system, including a lifting of the degeneracy of electronic states and a widening of the highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO–LUMO) bandgap, resulting in changes in the chemistry of the fullerene cage itself. The modification of the fullerene in this way also enhances the polarisation screening effect observed in fullerene systems. Adsorption at the Si(111)‐(7×7) and Ag:Si(111)‐(√3×√3)R30° surfaces is mediated by two different mechanisms, the former involving formation of covalent bonds, and the latter largely van der Waals in character. Despite the lack of a strong chemical interaction, however, a 0.9 ML coverage of (C6H5)5C60H on Ag:Si(111)‐(√3×√3)R30° leads to a shift of the Si 2p core-level spectrum by ∼200 meV to higher binding energy, suggesting that a positive interface dipole contributes to the adsorption energy of the fullerene at this surface.