PHOTOELECTRON STUDY OF YB/C-60 BILAYERS AND THE YB FULLERIDES FORMED AT THE INTERFACES

Photoelectron measurements were obtained for Yb-C60 and the results are compared to those reported for alkali-metal fullerides and Yb isolated in xenon or solid NH3. The valence photoelectron spectra for Yb deposited on C60 and C60 on Yb show changes in the Yb 4f peaks, and in the C60 valence states and a metal-induced state just above the Yb 4f bands. The position of this valence feature is near to that found for an analogous feature in the nonsuperconducting K6C60 fulleride. Similar features also appear when Yb is solvated in condensed ammonia. The appearance and binding energy of the Yb 4f levels argue that the Yb is largely divalent but has a small trivalent component. A comparison of the data for Yb-C60 with that for Yb clusters in xenon shows that the changes in the electronic state of the Yb are not those found for small Yb particles in a nonreactive matrix.