Real-space imaging of CaxC60 using scanning tunneling microscopy.

Calcium intercalation into single-crystal C 60 thin films has been studied with scanning microscopy. In low concentrations, Ca induces features that exhibit variations in apparent height that are not present for pristine C 60 , consistent with differences in local states densities in a solid solution. At higher Ca concentrations, structure is evident due to bonding with Ca in octahedral and tetrahedral sites. A model of the Ca 5 C 60 structure is deduced in which octahedral sites of the fcc lattice are occupied by four Ca ions while one of the tetrahedral site is filled