DETERMINATION OF THE ORIENTATION OF C-60 ADSORBED ON AU(111) AND AG(111)

Adsorbate bonding and preferred adsorption sites and rotational orient ations of C-60 on Au(111) and Ag(111) were studied using scanning tunn eling microscopy (STM) and related techniques. Spatially resolved tunn eling spectroscopy and barrier height measurements indicated that bond ing occurs by charge transfer from the metal to C-60 The internal stru cture of adsorbed C-60 observed by STM was found to be a strong functi on of the adsorption site, the molecular orientation, and the tunnelin g bias. Occupied state images were found to reflect the adsorption sit e symmetry while unoccupied state images reflected the molecular symme try. In domains where all the molecules were in equivalent adsorption sites, the observed internal structure of adsorbed C-60 was assigned t o an on-top site with the five-membered ring on the surface.