ORIENTATIONAL EPITAXY OF HIGH-QUALITY C-60 FILMS ON AG(111)

C-60 structures grow in two distinct in-plane orientations on Ag(111) substrates as determined by their x-ray-diffraction scans. These structures consist of twinned (first-order) commensurate structures growing in high-symmetry, almost perfectly lattice-matched orientations (2 root 3X2 root 3+/-R30 degrees substrate unit cells), and structures whose close-packed directions are oriented in lower-symmetry in-plane orientations. These latter structures can be lattice matched to their substrates over larger unit cells than those of the commensurate structures. X-ray-diffraction scans show that their in-plane ($($) over bar$$ 220) mosaic peaks form double-positioning peaks with respect to [$($) over bar$$ 220] directions of the twinned commensurate structures that lie between them. Increasing the growth temperature, the close-packed directions of these double-positioning structures grow preferentially in orientations that converge toward the close-packed directions of the twinned commensurate structures.