Field-induced metal diffusion into C60 thin films

We report the evolution in time of d.c. conductivity of polycrystalline thin films of C60 at different temperatures and under various applied voltages. All films show a clear semiconducting behaviour. The initial resistivity (at T = 140 °C) and the activation energy are ρ~ 105 Ω cm and Ea ~ 0.5 eV, respectively. For various types of metallic electrodes M (M = Au, Ag or In), a field-induced conductivity increase by several orders of magnitude and an activation energy decrease are observed. The results are interpreted in terms of electrode metal diffusion into the film.