The influence of structure imperfection on the glass-transition behavior in C60 films

Two batches Of C-60 films were grown at different growth rate, using a vacuum deposition technique. X-ray diffraction patterns indicate both films have preferential (111) orientation. We measured their dielectric constant and loss factor from 80K to room temperature, and observed distinct broad and asymmetric loss peaks, attributed to orientational glass transition. The apparent activation energy was determined as 344.4 and 304.8 meV for film A and B respectively, larger than the value 280 meV in bulk C-60. Ngai's correlated-state model is used to simulate relaxation spectrum, and the real activation energies were calculated, which agree with the reported activation value in bulk C-60 very well. We propose that the structure imperfection have contributed additional dipole correlation interactions, which make the relaxation behavior of our C-60 films deviate from that of bulk C-60.