Electronic structure of C60 on Au(887)

Abstract

We present an analysis of the electronic structure of C60 adsorbed on a vicinal Au(111) surface at different fullerene coverages using photoemission, x-ray absorption, and scanning tunneling microscopy/spectroscopy (STS). STS provides a straightforward determination of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) levels with respect to the Fermi energy. At C60 coverages of 0.5 and 1 ML a 2.7 eV wide HOMO-LUMO gap is found. The near-edge x-ray absorption fine structure (NEXAFS) spectrum for the 0.5 ML C60 nanomesh structure displays a significant intensity at the low energy side of the LUMO exciton peak, which is explained as due to absorption into HOMO-LUMO gap states localized at individual C60 cluster edges. From 0.5 to 1 ML we observe a rigid shift of the HOMO-LUMO peaks in the STS spectra and an almost complete quenching of the gap states feature in NEXAFS.

Spatially resolved conductance of oriented C60

“…The spectra recorded from molecules with identical orientations did not depend on orientations of the nearest neighbour molecules. The assignment of the HOMO, LUMO, LUMO + 1, and LUMO + 2 to spectral signatures shown in figure 2(a) is based on published results [7,16]. The orbital energies of both C 60 types are summarized in table 1.…”

Comment on “Electronic structure of C60 on Au(887)” [J. Chem. Phys. 125, 144719 (2006)]

“…Dividing by the throughput can then cause new structure in the data to arise, often centered near 284 eV, as we suggest to be the case in Ref. 1. A second aspect of the presented 0.5 and 1 ML spectra is the falling intensity at high photon energies, which would typically stem from the same kind of faulty correction.…”

Response to “Comment on ‘Electronic structure of C60 on Au(887)’ [J. Chem. Phys. 127, 067101 (2007)]”

“…Phys. 127, 067101 "2007… ‡" F. Schiller 2 and suggested that the throughput correction and the Fermi level placement are erroneous. Below, we rule out both scenarios.…”

“…In the 0.5 ML C 60 near-edge x-ray absorption fine structure ͑NEXAFS͒ spectra the first peak is interpreted as the signature of the C 60 lowest unoccupied molecular orbital ͑LUMO͒. 2 Scanning tunneling spectroscopy reveals that the LUMO is placed roughly 1 eV above the Fermi level. Therefore, we conclude that the Fermi energy does not coincide with the carbon 1s binding energy as proposed by Schiessling and Brühwiler 1 X-ray absorption data in thin C 60 films are influenced by excitonic effects as previously reported by, e.g., Schwedhelm et al 4 This work is consistent with our conclusion that the Fermi level is located Ϸ0.8 eV below the LUMO peak for the C 60 monolayer.…”