Adsorption of C60 on Al(111) studied with scanning tunnelling microscopy

Scanning tunnelling microscopy has been used to study the adsorption and interactions of C-60 on Al(111) at room temperature. Initially, C-60 forms chains of molecules on the lower terraces of step edges, which indicates that the molecules have a high mobility even at room temperature. When the coverage is increased, the C-60 molecules form a close-packed overlayer of (2 root 3 x 2 root 3)R30 symmetry with respect to the substrate surface which is compressed by 1% in all directions compared with the (111) plane of fullerite. Voltage-dependent intramolecular structure is observed, indicating that the adsorbate-substrate bonding is strong enough to prevent the molecules from rotating, and that C-60 prefers to have a six-membered ring facing the surface. The (2 root 3 x 2 root 3)R30 overlayer structure is metastable, irreversibly transforming to (6 x 6) symmetry when heated above 490 K. (C) 1998 Elsevier Science B.V.