AbstractThe co‐adsorption of pre‐ and post‐annealed C60molecules on Si(100)‐2×1 surfaces has been investigated using scanning tunneling microscopy in ultrahigh vacuum. The images reveal that the adsorption characteristics of the post‐annealed adsorbates are different from their pre‐annealed counterparts. The post‐annealed C60molecules bond either to the top of the dimer rows or to the missing dimer defects, while the pre‐annealed molecules predominantly occupy the four‐dimer sites in the troughs. The apparent size and height of post‐annealed C60molecules are smaller than those of the pre‐annealed ones. Our observations suggest that the post‐annealed C60molecules are chemisorbed on the surface, because the molecules covalently bond to Si atoms during the sample annealing. In contrast, the adsorption of the pre‐annealed C60molecules can be explained by a dipole‐induced‐dipole interaction between the molecules and the Si(100