Electronic structure of highly fluorinatedC60

Synchrotron-radiation photoemission was used to investigate the valence bands and C 1s core-level features of thin films of ${\mathrm{C}}_{60}$ ${\mathrm{F}}_{\mathit{x}}$, x=46±2. The valence-band spectra show seven distinct features and a bandwidth of ∼12 eV. Comparison of the calculated and experimental 40-eV photoemission spectra and the C 1s core-level shifts suggests that the CF bond distances are closer to those of fluoromethane than to those of icosahedral ${\mathrm{C}}_{60}$ ${\mathrm{F}}_{60}$ optimized within the local-density approximation. The valence-band maximum is ∼5 eV below the Fermi level ${\mathit{E}}_{\mathit{F}}$, indicating that ${\mathrm{C}}_{60}$ ${\mathrm{F}}_{46\pm 2}$ is a wide-band-gap insulator. The deposition of potassium atoms on these fluorinated ${\mathrm{C}}_{60}$ films results in the partial removal of fluorine to form KF.