In-plane orientational order across C 60(111)/Au(111) interfaces

Abstract

The evolution of C 60(111) in-plane structures is investigated on Au(111) substrates for temperatures ranging from ∼120 to 290°C. An epitaxial orientational reordering is observed at T o∼150°C. At temperatures T< T o, twinned in-phase structures predominate. The close-packed directions of these structures are parallel to close-packed directions of the nonreconstructed Au(111) substrate, i.e., oriented in R0.0 direction. Also, smaller concentrations of minority phase twinned in-plane structures oriented at ± R30.0 are observed, coexisting with these in-phase structures. The ± R30.0 minority phase structures are commensurate with the substrate, assuming a nonreconstructed Au(111) substrate. At temperatures T> T o, no in-phase structures are observed, but commensurate ( R30.0) structures form. The majority phase, consists of structures double-positioned in the plane (± R13.0–14.2) with respect to the close-packed directions of the twinned commensurate structures. These double-positioned structures require large coincident unit cells to lattice-match to nonreconstructed Au(111) substrates, and with increasing temperature, the in-plane orientations of these structures change from ∼± R13.0 to ± R14.2. The in-phase ( R0.0) and commensurate ( R30.0) structures do not show any dependence on the substrate temperature, nor substrate's structural quality. The in-plane orientational reordering at T o is attributed to the surface structural instability/reconstruction of the topmost layer of the Au(111) substrate.