The time evolution of the direct-current conductivity of polycrystalline thin films of C60 at various temperatures and under various applied voltages was reported. All of the films exhibited clear semiconducting behaviour. The initial resistivity (at 140C) and the activation energy were about 105Ωcm and 0.5eV, respectively. For various types of metallic electrodes (Au, Ag, In), the field-induced conductivity increased by several orders of magnitude and an activation energy decrease was observed. The results were interpreted in terms of electrode metal diffusion into the film.

Field-Induced Metal Diffusion into C60 Thin Films. Zahab, A., Firlej, L., Brocard, F., Kirova, N.: Synthetic Metals, 1996, 77[1-3], 59-61