Photoemission, near-edge x-ray-absorption spectroscopy, and low-energy electron-diffraction study ofC60on Au(111) surfaces

Abstract

The geometric and electronic structures of C 60 adsorption on Au͑111͒ surfaces have been studied by lowenergy electron diffraction ͑LEED͒, angle-resolved photoemission, and near-edge x-ray-absorption spectroscopy. An irreversible structural transition of the C 60 overlayer on Au͑111͒ was observed by LEED upon successive annealing. These structures are 38ϫ38 ''in phase,'' R14°and (2)ϫ2))R30°, with the latter phase predominating after annealing to 350°C. Valence-band photoemission spectra reveals a state right below the Fermi level for an annealed, ordered monolayer. This peak disperses across the Fermi energy that indicates the C 60 overlayer becomes metallic. Its intensity shows a resonance that primarily follows the behavior of highest occupied molecular orbitals, identified unambiguously as lowest unoccupied molecular orbitals ͑LUMO's͒ filled by charge transfer from the substrate. An asymmetric distribution of LUMO charge is observed. The thermal-desorption energy of the monolayer is estimated from annealing experiments to be 1.9 eV, which is 0.5 eV larger than the desorption energy from multilayers. Comparison with available spectroscopic data indicates that interaction of C 60 with Au͑111͒ is slightly weaker than with Au͑110͒, and much weaker than with Cu͑111͒. The amount of charge transfer estimated from photoemission is 0.8 electrons per C 60 molecule on Au͑111͒, compared to 1.6 electrons on Cu͑111͒. We argue that charge transfer is determined by the bulk sp density of states at the Fermi energy scaled by the size of the C 60 molecule, and also modified by a clean surface electronic structure, and that charge transfer is the dominant interaction in these systems.

On interface dipole layers between C 60 and Ag or Au

“…The authors explain their observations by the supposed metallic nature of the C 60 overlayer, making the workfunction of the C 60 overlayer independent of the metal substrate. Although this does not explain the observed differences in workfunction of the C 60 overlayer of 4.7 eV for C 60 on Au (111) [18], 5.25 eV for C 60 monolayer on Al (110) [15] and 5.4 eV for a C 60 overlayer on Ta [19].…”

Interplay of local and global interfacial electronic structure of a strongly coupled dipolar organic semiconductor

“…for PTCDA, C 60 , and several other organic molecules on coinage metal surfaces [26,31,35,40,[42][43][44][45][46]. In the case of ClB-SubPc on Ag(111), Berner et al inferred a partial charge transfer from surface to molecule from analysis of XPS and UPS [31].…”

The Oxygen Reduction Reaction on Pt Single Crystal Electrodes Modified with Aromatic Organic Molecules

“…However, modification of C 60 does not improve the ORR activity on all the surfaces, although C 60 has strong electron attractive property. 11 Shift of d-band center prevents the formation of Pt oxides that block the ORR. AOMs inhibit the Pt oxides formation as shown in the voltammograms of Pt(111) in Fig.…”

“…Aromatic organic molecules (AOM) such as CoTPP and C 60 affect the d-band vacancy due to the charge transfer from the adsorbed molecules. 10,11 In this study, we have studied the ORR on single crystal electrodes of Pt modified with various AOMs as shown in Fig. 1(a).…”