Grain-size effect on elastic properties ofC60films and their relationship to the order-disorder phase transition

The elastic properties of ${\mathrm{C}}_{60}$ polycrystalline films with different grain sizes between 100 and 500 nm, measured in the frequency range 270–3140 Hz, are reported. Around 260 K, a modulus drop and a λ-shaped internal friction peak attributed to the order-disorder phase transition increase with a decrease of the grain size. Above 260 K, the modulus is found to be frequency independent, while the magnitude of modulus drop blow 260 K increases with the increase of the measurement frequency. The λ-shaped internal friction peak has a peak height proportional to frequency, which may be attributed to the relaxation of the order parameter of a phase embedded in the old phase.