The bonding nature of individual C60 molecules to Si(100) surfaces

It is demonstrated that bonding-dependent local density of states and energy levels of individual C-60 molecules, adsorbed on Si(100)-(2 x 1) surfaces under ultrahigh-vacuum conditions, can be obtained using scanning tunneling microscopy and spectroscopy. High-resolution images of individual C-60 molecules, physisorbed (preannealed) and chemisorbed (postannealed) on different sites on the same sample, reveal clear intramolecular features superimposed on the molecules' cage structure that are consistent with their bonding nature. Spectroscopic measurements of individual C-60 molecules chemisorbed at these sites yield energy levels that exhibit a transition of their electronic structure from that of a near-free adsorbate to that of SiC. The spectroscopic data corresponds to the observed changes in local density of states. These results demonstrate the power of scanning tunneling microscopy to determine the electronic structure and bonding characteristics of individual molecules.