Band formation in a molecular quantum well via 2D superatom orbital interactions

By scanning tunneling microscopy and spectroscopy, we study nearly free electron band formation of the σ* lowest unoccupied molecular orbital of C6F6 on a Cu(111) surface. In fractal islands, the lowest unoccupied molecular orbital energy systematically stabilizes with the number of interacting near-neighbor C6F6 molecules. Density functional theory calculations reveal the origin of effective intermolecular orbital overlap in the previously unrecognized superatom character of the σ* orbital of C6F6 molecules. The discovery of superatom orbitals in planar molecules offers a new universal principle for effective band formation, which can be exploited in designing organic semiconductors with nearly free electron properties.