Determination of the orientation ofC60adsorbed on Au(111) and Ag(111)

Abstract

Adsorbate bonding and preferred adsorption sites and rotational orientations of ${\mathrm{C}}_{60}$ on Au(111) and Ag(111) were studied using scanning tunneling microscopy (STM) and related techniques. Spatially resolved tunneling spectroscopy and barrier height measurements indicated that bonding occurs by charge transfer from the metal to ${\mathrm{C}}_{60}$. The internal structure of adsorbed ${\mathrm{C}}_{60}$ observed by STM was found to be a strong function of the adsorption site, the molecular orientation, and the tunneling bias. Occupied state images were found to reflect the adsorption site symmetry while unoccupied state images reflected the molecular symmetry. In domains where all the molecules were in equivalent adsorption sites, the observed internal structure of adsorbed ${\mathrm{C}}_{60}$ was assigned to an on-top site with the five-membered ring on the surface.