Band gaps of doped and undoped films of molecular icosahedra

The band gaps and electronic structures of doped and undoped films of molecular icosahedra are reported. The occupied and unoccupied electronic structure of undoped icosahedral closo-1,2-dicarbadodecarborane (C2B10H12) thin films resembles that of the isolated molecule. The Fermi level of the molecular thin films is roughly at midgap. Upon initial Na doping of the orthocarborane films, an unoccupied extramolecular (exopolyhedral) state forms within the gap at an energy of about 3 eV above the Fermi energy. With Na doping, the film of molecular icosahedra resembles a system with Hubbard-like bands and an appreciable correlation U.