Molecularly resolved observation of surface reconstruction of C-60 epitaxial films by atomic force microscopy

Reconstructed surfaces of C-60 epitaxial films on KBr(001) substrates were directly observed by atomic force microscopy (AFM). AFM images showed ridge-like fringes running along the three equivalent [1(1) over bar0$] directions on the face-centered cubic (fcc) (111) face on the surfaces of C-60 thick (> 500 nm) films. Molecular-resolution images revealed that the raised fringe region is contracted by ca 3% in the [11(2) over bar] direction and that the vertical displacement of the fringe is 0.30+/-0.02 nm. The observations suggest a stacking-fault-domain model involving periodic transitions between fee (ABCABC... stacking) and hexagonal close-packed (hcp, ABAB... stacking) structures. Fcc surface domains were proposed to exist on the wider areas between fringes on the C-60 film surface based on the fact that the fcc bulk structure is energetically slightly more favorable than that of hcp. (C) 1997 Elsevier Science B.V.