Dim C_(60) fullerenes on Si( 111) (√3) × (√3) - Ag surface

摘要

Scanning tunneling microscopy (STM) observations of the dose-packed C_(60) fullerene arrays on Si(lll) (√3) × (√3) - Ag surface have revealed the presence of dim C_(60) molecules which constitute 9-12% of all fullerenes. The dim C_(60) fullerenes reside -1.6 A lower than the bright ("normal") C_(60). While the bright C_(60) are in continuous rotation, the dim C_(60) 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 C_(60) 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 C_(60) array eliminates completely the dim C_(60) molecules. Experimental results can be understood if one assumes that formation of the dim C_(60) is associated with disintegration of Ag trimer onSi(111) (√3) × (√3) - Ag surface under a given C_(60) fullerene.