Conductance and Polarisability of C₆₀ Films

Thin films of C₆₀ deposited in vacuum are studied using current–voltage (I–V) measurements and atomic force microscopy (AFM). In situ electrical measurements give an average resistivity of ca. 30 MΩcm for the as-deposited films at room temperature. The I–V dependences are found to correspond to ohmic behaviour but they have a hysteresis shape attributed to remnant polarisation due to the domain structure of the films. AFM images show a grainy surface morphology for the deposited C₆₀. Temperature dependent measurements in the range 290–365 K provide evidence for a variable range hopping mechanism of conductance with an activation energy of 0.8–1.0 eV. With further temperature increase the C₆₀ films restructure leading to an increase in grain size and a change of the electrical properties with I–V dependences showing Schottky barrier formation. The effect of oxygen on the conductance of the C₆₀ films under their exposure to an ambient atmosphere is considered and discussed.