SCANNING-TUNNELING-MICROSCOPY STUDY OF GRANULAR INTERCALATED FULLERENES

We have studied by scanning tunneling microscopy (STM) the surface of polycrystalline powders of Rb3C60, (KTl1.5)(3)C-60 and (RbTl1.5)(3)C-6 0 (nominal compositions) in a high purity argon environment at 295 K. Large scale STM images reveal effective grain sizes of some hundred na nometers. This small grain size strongly reduces the superconductivity fraction of the diamagnetic shielding. On a molecular scale, the STM images show ball-shaped features which can be identified with individu al fullerene molecules in case of Rb3C60(111) and (311) facets, but in case of (KTl1.5)(3)C-60 and (RbTl1.5)(3)C-60 their apparent diameter (1.7 nn) is significantly larger, Since AC-susceptibility and X-ray di ffraction have traced metallic Tl in the (KTl1.5)(3)C-60 and (RbTl1.5) (3)C-60 samples, we interpret the larger apparent diameter of the ball -shaped units as a complex of Tl and Rb3C60.