XPS analysis of single crystal RbC60 surface Original Research Article

The surface of single crystal RbC60 was characterised by means of X-ray photoelectron spectroscopy (XPS). The atomic ratio of Rb to C up to 15 Å depth proved to be about two or three times higher than the stoichiometry (160) 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 Å depth by the peak analysis of Rb3p spectrum, which shifted ca 1 eV towards the higher binding energy, while the Cls 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.