X-ray Photoemission Studies of Yb Intercalated C60 Thin Film

Yb-intercalated C60 thin film was prepared in a ultra-high-vacuum system. The binding energies of C 1s, Yb 4f and Yb 4d during the compound formation were studied by x-ray photoemission technique. The stoichiometry of the phase-pure sample was determined by the peak intensities of Yb 4f and C 1s. The result turned to be very near to that for Yb2.75C60 that was first determined for bulk-phase sample by x-ray diffraction measurement. The positions and intensities of the Yb 4f and Yb 4d peaks revealed the charge state of Yb2+ in Yb2.75C60. The C 1s core level for the phase-pure sample shifted towards lower binding energy by ≈0.5 eV relative to C60, which exhibited that some Yb 6s electrons transferred from Yb to the lowest unoccupied molecular orbital band of C60. The shift and the FWHM of C 1s x-ray photoemission spectroscopic peak can be used as sample characterization in future researches on Yb/C60 compounds.