The time dependence of the decay of dark electrical conductivity σ(t) from C60 crystals under air exposure was investigated at different temperatures. The decay of σ(t) can be fitted via a stretched exponential function, indicating that the diffusion of O2 in C60 crystal follows a hierarchically constrained dynamic. The diffusivity of molecular oxygen in C60 crystal is estimated using the least-square fitted time constant, and an activation energy EA=1.5eV corresponding to the diffusion process is deduced from the Arrhenius plot. The mechanism of the diffusion process is then discussed.
From a temperature dependence of the dark electrical conductivity of Au overlayer σM(T) measured along the interface direction on top of a C60 polycrystalline film, a dramatic change in σM is observed at T ≈255 K; σM(T) increases with increasing temperature. As deduced from σM versus 1/T, an activation energy of 200 ±30 meV for T<255 K is much larger than that of 59 ±2 meV for T>255 K. These novel phenomena are explained by structural–electronic interaction on the Au/C60 interface with a change in the properties of the induced surface states due to the rotational order/disorder phase transition.
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