STM Study of C70 Adsorption on the Si(111)-7 x 7 Surface

Adsorption of C-70 Molecules On the Si(11.1)-7 x 7 surface at room temperature was investigated by using a scanning tunneling microscope (STM). At a very low coverage, C-70 adsorbs preferentially at a position slightly displaced from the center of the triangular subunit cell. The adsorbed C-70 molecules are randomly distributed and reveal an intramolecular structure in the high-resolution STM images, implying a reasonably strong adsorbate-substrate interaction. The rich intramolecular features of the adsorbed C-70 molecules suggest multiple bonding configurations on the Si(111)-7 x 7 surface. Further deposited C-70 molecules aggregate disorderly to form three-dimensional islands. Bonding between neighboring molecules is formed after post annealing at about 400 K, resulting in local ordering of the molecules.