Equilibrium configurations and electronic structure of fullerene ultrathin films on SrTiO3(001) surface

Ultrathin fullerene (C60) films on various metal and semiconductor substrates have been intensively studied but not yet on a perovskite oxide substrate. Using scanning tunneling microscopy and spectroscopy, we investigated the molecular arrangement and electronic structure of C60 ultrathin films grown on a SrTiO3(0 0 1) surface. Subject to strong coupling and weak screening from the substrate, the monolayer C60 exhibit short-range ordered molecular arrangement with disordered molecular orientation and a substantially large highest occupied mo-lecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gap (-4.1 eV). In contrast, C60 in the 2nd and 3rd layers are self-assembled into hexagon lattices with a quasi-(2 x 2) superstructure resulted from the arrangement of molecular orientations showing a chiral pinwheel structure. The HOMO-LUMO gap of the multi -layer C60 further expands to -4.6 eV, very close to that of gas-phase C60, indicating a negligible inter-layer screening effect.

Automated summary

Using scanning tunneling microscopy and spectroscopy, the molecular arrangement and electronic structure of C60 ultrathin films grown on a SrTiO3(0 0 1) surface were investigated. The monolayer C60 exhibited a short-range ordered molecular arrangement with disordered molecular orientation and a substantially large HOMO-LUMO gap (-4.1 eV). In contrast, C60 in the 2nd and 3rd layers self-assembled into hexagon lattices with a quasi-(2 x 2) superstructure, resulting in a chiral pinwheel structure.