(C6H5)5C60Hat

Michael A. Phillips

¹

,

James N. O’Shea

²

,

P. R. Birkett

³

et al.

Abstract

We have studied the properties of ͑C 6 H 5 ͒ 5 C 60 H in thick film form and adsorbed at two surfaces at the extremes of chemical reactivity-the highly reactive Si͑111͒-͑7 ϫ 7͒ and chemically passivated Ag: Si͑111͒ -͑ ͱ 3 ϫ ͱ 3͒R30°surfaces-using photoemission spectroscopy ͑PES͒ and near-edge x-ray fine structure ͑NEX-AFS͒ 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-LUMO͒ 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 Si͑111͒-͑7 ϫ 7͒ and Ag: Si͑111͒-͑ ͱ 3 ϫ ͱ 3͒R30°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 ͑C 6 H 5 ͒ 5 C 60 H on Ag:Si͑111͒-͑ ͱ 3 ϫ ͱ 3͒R30°leads to a shift of the Si 2p core-level spectrum by ϳ200 meV to higher binding energy, suggesting that a positive interface dipole contributes to the adsorption energy of the fullerene at this surface.

Band-bending inhomogeneity of Au adsorbed surface evaluated with Si 2p core-level spectra

“…Moreover, being a two-dimensional (2D) electron gas system, the ffiffiffi 3 p -Ag surface has a metallic surface-state band with parabolic dispersion crossing the Fermi level [4][5][6]. After extensive studies including photoelectron spectroscopy (PES) [4][5][6][7][8], first-principles calculation [9][10][11], scanning tunneling microscopy (STM) [12,13], X-ray diffraction [14,15] and other experimental techniques [16,17], the ffiffiffi 3 p -Ag surface has been well known and become popular as a substrate for adsorption of various metal atoms [5,[18][19][20][21] and molecules [22][23][24][25]. Au atoms were chosen as adsorbates because they form identical 2D nanoclusters, which distribute randomly on the ffiffiffi 3 p -Ag surface at the extremely low Au coverage (named as Au nanocluster phase), as Fig.…”