Ultraviolet photoelectron spectra of C100, C110, and potassium-doped C110

Ultraviolet photoelectron spectra of higher fullerenes C-100 and C-110 have been measured with a synchrotron radiation light source. The photoelectron onset energy of pristine C-110 is 0.75 eV below the Fermi level (E-F), which is the smallest value among the pristine fullerenes reported so far. The spectra show intensity oscillation upon the incident photon energy change, as do those of other fullerenes. A spectral change upon potassium doping has been observed with hv = 20 and 40 eV incident photon energies. The appearance of a state between the first band of higher fullerenes and the Fermi level is observed in the hv = 20 eV spectra upon potassium doping. The onset position of the new state moves toward the EF. In the case of the potassium doping of C-110, the spectral onset begins just at the E-F, which indicates its possibility of semimetallic nature. When C-110 is heavily doped with potassium the lower binding energy bands above 5 eV become faint, and three structures simultaneously appear between 5 and 14 eV and become distinct. As these structures are considered to be of sigma-electron origin, heavy potassium doping may correspond to reconstruction of the fullerene cage or decomposition of the cage structure. [S0163-1829(99)04931-0].