Local-field effects on photoemission ofC60

The surface core-level shift in C $1s$ soft x-ray photoemission spectroscopy has been experimentally observed in films of ${\mathrm{C}}_{60}$ on Al. A value of 0.100±0.025 eV has been determined. Theoretical calculations are presented which show that the core hole is uniformly screened by the ${\mathrm{C}}_{60}$ molecule, and that the effect of the surface upon this intramolecular screening should be negligible. The observed SCLS can therefore be accounted for by the difference in final state (core hole + polarized near-neighbor molecules) between bulk and near-surface atoms, as calculated by a straightforward, real-space, local-field calculation.