Dim C60 fullerenes on Si(111) √3 x √3-Ag surface

Scanning tunneling microscopy (STM) observations of the close-packed C-60 fullerene arrays on Si(111) root 3 x root 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 similar to 1.6 angstrom 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 similar to 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 on Si(111) root 3 x root 3 - Ag surface under a given C-60 fullerene. (C) 2013 Elsevier B.V. All rights reserved.