Electronic properties of hydrogen-bonded fullerenes and potassium fullerides

Photoemission studies show that the exposure of ${\mathrm{C}}_{60}$ films to atomic H produced H-bonded fullerenes. Such H-${\mathrm{C}}_{60}$ bonding reduced the emission from features associated with the ${\mathrm{C}}_{60}$ π electrons and broadened valence band and C 1s core-level features. It was also possible to vary the H content of the films by depositing the fullerenes in different partial pressures of atomic H. We show that K atoms mix with these hydrogenated films but that the resulting fullerides show substantially reduced metallic character for small amounts of H; they are not metallic at all at higher H content. The nonmetallic character probably results from reduced overlap between π-derived orbitals of adjacent H-bonded fullerenes and changes in the orbitals occupied by charge transfer from K.