Effects of annealing on the electrical conductivity of C60 films

Abstract We report the annealing effects on the electrical conductivity of C 60 films. Films sublimed using C 60 powder from the same batch were used. The studies show that the C 60 films have clear semiconducting behavior in the temperature range extending from room temperature to 473 K. The room-temperature conductivity is in the range of 10 −5 to 10 −7 (Ωcm) −1 . From the measurements of conductivity versus time when the film is maintained at 473 K, we explained that the increase of conductivity before 2.5 h of annealing is the result of a decrease of the unstable hcp phase and an increase of the number of connected crystallites, the decrease of conductivity after 2.5 h of annealing is due to the decrease of the number of connected crystallites. The decrease in the number of connected crystallites makes the intercrystalline potential barrier higher, and thus decreases the conductivity. The reason for the increase of the activation energy is the decrease of defects between connected crystallites. These defects may introduce states in the energy gap of C 60 films. The deviation of the conductivity from straight lines in the high-temperature region in the σ versus 1 T plots are due to unstable structural phases which transform toward a stable fcc phase in the annealing process.