C-60 AND C-70 FULLERENES AND POTASSIUM FULLERIDES

Photoemission and inverse photoemission studies of thin films of C60 and C70 reveal the distribution of occupied and empty electronic states of these molecular solids. X-ray photoemission results also show the C 1s main line and features related to pi-pi* shakeups, electron energy losses, and plasmons. Potassium doping produces changes that can be related to the occupation of states derived from the lowest unoccupied molecular orbitals of the fullerenes and band-structure effects. Important differences are observed upon K doping of C60 and C70, particularly in states near the Fermi level, and these would be reflected in the electron-phonon coupling, superconductivity, and the phase diagram. Resistivity measurements for KxC60 show a resistivity minimum for K3C60 and a dependence on stoichiometry that is indicative of dispersed conducting micrograins in an insulating medium. Oxygen-exposure studies demonstrate that KxC60 thin films are unstable.