Scanning tunneling microscopy studies of C60 monolayers on Au(111)

We report a scanning tunneling microscopy study of close packed C-60 monolayers on Au(111) upon post-deposition annealing. Within these structures the C-60 molecules appear discretely bright or dim. The arrangements of dim C-60 within the close packed structures are dependent on the orientation of the overlayer with respect to the Au(111) surface. The apparent height difference between the bright and dim C-60 varies with applied sample bias, and the individual C-60 molecules can switch from bright-to-dim or vice versa at room temperature. We propose that the dim C-60 arise from a restructuring of the C-60-Au interface to form nanopits, which facilitate charge transfer from the substrate to the first layer fullerene molecules.