Orientation Ordering and Chiral Superstructures in Fullerene Monolayer on Cd (0001)

The structure of C(60) thin films grown on Cd (0001) surface has been investigated from submonolayer to second monolayer regimes with a low-temperature scanning tunneling microscopy (STM). There are different C(60) domains with various misorientation angles relative to the lattice directions of Cd (0001). In the (2√3 × 2√3) R30° domain, orientational disorder of the individual C(60) molecules with either pentagon, hexagon, or 6:6 bond facing up has been observed. However, orientation ordering appeared in the R26° domain such that all the C(60) molecules adopt the same orientation with the 6:6 bond facing up. In particular, complex chiral motifs composed of seven C(60) molecules with clockwise or anticlockwise handedness have been observed in the R4° and R8° domains, respectively. Scanning tunneling spectroscopy (STS) measurements reveal a reduced HOMO–LOMO gap of 2.1 eV for the C(60) molecules adsorbed on Cd (0001) due to the substrate screening and charge transfer from Cd to C(60) molecules.