Switchable semiconductive property of the polyhydroxylated metallofullerene

The temperature-sensitive property of polyhydroxylated metallofullerene film of Gd@C₈₂(OH)_x with special hydroxyl number was studied using synchrotron radiation ultraviolet photoelectron spectroscopy (UPS) and TEM techniques. From room temperature (RT) to 4 °C the photoelectron onset energy of the spectra of Gd@C₈₂(OH)₁₂ shifted from 1.9 to 0.2 eV, indicating that Gd@C₈₂(OH)₁₂ automatically shifted from insulator at RT to semiconductor at 4 °C. However, this could not be observed for Gd@C₈₂(OH)₂₀. TEM experiments show that the variation of conductivity can be ascribed to formation of a microcrystal under low temperature. The dipole moment induced unique intermolecular interactions and self-assembled microcrystalline structures for Gd@C₈₂(OH₁₂. This may cause reconstruction of the upper valence band formed by π-like electrons as well as the density of states (DOS) around the Fermi level (E_F) and reconstruct the deeper valence band formed by σ-like electrons, eventually resulting in a shift to a semiconducting nature. These findings revealed a novel nature for polyhydroxylated Gd@C₈₂(OH)_x materials: Their insulating properties can be controllably tuned into semiconducting ones as a function of temperature.