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 MOhm.cm 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 remanent 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.