Scanning tunneling spectroscopy of C60 adsorbed on Si(100)-(2 x 1)

A room-temperature scanning tunneling spectroscopy study has been conducted on single molecules and multilayers of C-60 molecules adsorbed on the Si(100)-(2 x 1) surface without any post-annealing. For single isolated molecules, four peaks in the local density of states are observed that can be well attributed to molecular energy levels. Scanning tunneling microscope spectroscopy has also been carried out on molecules that are moved across the silicon surface. Spectroscopy on multilayers of C-60 shows broad, smeared out features for the first monolayer, while the third layer results resemble those of single isolated molecules. We attribute the variations in electronic spectra to differing intermolecular interactions in the first and upper layers of C-60. (C) 2001 Published by Elsevier Science B.V.