Electronic Structure Of Yb2.75c60

Ultraviolet photoemission spectra of Yb2.75C60 thin films are measured. The valence band is a wide hump centered at similar to0.8 eV below the Fermi level. The result also indicates the semiconducting property of Yb2.75C60 since no Fermi edge is observed. The hybridization between 6s states of Yb and the lowest-unoccupied-molecular-orbital (LUMO) band of C-60 is non-negligible although it should not be considered to be strong. More than 14% of Yb 6s electrons are estimated to be distributed in the covalent bonds between Yb and C-60. The spectra for submonolayer C-60 on Yb film reveal that Yb 6s electrons can easily transfer to C-60 and such demonstrate that the bonding in Yb2.75C60 is mainly ionic. The LUMO+1 orbital of the submonolayer C-60 is partially occupied, which is different from the case in Yb2.75C60. There is no evidence of trivalent Yb in the spectra.