Ultraviolet photoelectron spectra of a higher fullerene C 102 and its potassium complex

Abstract

Ultraviolet photoelectron spectra of a higher fullerene C 102 has been measured with a synchrotron radiation light source. The photoelectron onset energy of pristine C 102 is 0.85 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. Spectral change upon potassium doping has been observed with the hv = 20 and 40eV incident photon energies. The 20 eV spectra reveal a formation of a new state between the E F and the band derived from the highest occupied molecular orbital (HOMO) upon potassium doping. The onset position of the new state moves toward the E F, but it does not cross the E F. This indicates the semiconductive nature of potassium doped C 102. When the potassium is excessively doped to C 102, the lower binding energy bands above 5 eV become faint. In accordance with this phenomenon, the hv = 40 eV spectra show an appearance of four distinct structures between 5 and 14 eV. As these bands are considered to derive from pseudo π-electrons, heavy potassium doping may correspond with reconstruction of the fullerene cage or decomposition of the cage structure.