XPS ANALYSIS OF SINGLE-CRYSTAL RBC60 SURFACE

The surface of single crystal RbC60 was characterised by means of X-ra y photoelectron spectroscopy (XPS). The atomic ratio of Rb to C up to 15 Angstrom depth proved to be about two or three times higher than th e stoichiometry (1/60) from the composition analysis. The top surface was covered by the oxidized hydrocarbon material and was fast removed by short argon ion sputtering. The oxidized Rb component appeared from ca 5 Angstrom depth by the peak analysis of Rb3p spectrum, which shif ted ca 1 eV towards the higher binding energy, while the C1s peak kept the same position upon sputtering. From the atomic ratio of Rb to O, the existence of a passivation layer made up of Rb2CO3 (carbonate salt ) was suggested. The stability of bulk RbC60 under ambient atmosphere is explained by the existence of this kind of passivative Rb carbonate layer in the nano-surface region. (C) 1998 Elsevier Science Ltd. All rights reserved.