Ultraviolet photoelectron spectra ofC100,C110,and potassium-dopedC110

Abstract

Ultraviolet photoelectron spectra of higher fullerenes ${\mathrm{C}}_{100}$ and ${\mathrm{C}}_{110}$ have been measured with a synchrotron radiation light source. The photoelectron onset energy of pristine ${\mathrm{C}}_{110}$ 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 $h\ensuremath{\nu}=20$ 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 $h\ensuremath{\nu}=20\mathrm{eV}$ spectra upon potassium doping. The onset position of the new state moves toward the ${E}_{F}.$ In the case of the potassium doping of ${\mathrm{C}}_{110},$ the spectral onset begins just at the ${E}_{F},$ which indicates its possibility of semimetallic nature. When ${\mathrm{C}}_{110}$ 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 \ensuremath{\sigma}-electron origin, heavy potassium doping may correspond to reconstruction of the fullerene cage or decomposition of the cage structure.