Dim C60 fullerenes on Si(111) surface

Scanning tunneling microscopy (STM) observations of the close-packed C60 fullerene arrays on Si(111) 3 × 3 - Ag surface have revealed the presence of dim C60 molecules which constitute 9–12% of all fullerenes. The dim C60 fullerenes reside ~ 1.6 Å lower than the bright (“normal”) C60. While the bright C60 are in continuous rotation, the dim C60 are fixed in one of the single orientations, indicating a more tight bonding to the surface. At room temperature (RT), the dynamic switching from bright to dim C60 and vice versa has been detected. Switching slows down with decreasing temperature and becomes completely frozen at 110 K, which implies that the switching is a thermally driven process. RT deposition of ~ 0.1 monolayer of Ag onto C60 array eliminates completely the dim C60 molecules. Experimental results can be understood if one assumes that formation of the dim C60 is associated with disintegration of Ag trimer on Si(111) 3 × 3 - Ag surface under a given C60 fullerene.