EFFECTS OF ANNEALING AND Ar INTERCALATION ON GLASS TRANSITION IN C₆₀ FILMS

C 60 films were fabricated by vacuum sublimation and studied with dielectric spectroscopy regarding glass transition. With annealing, the dielectric loss peaks decreased in height, and the apparent activation energy deduced from their frequency dependence dropped in magnitude. The peaks, broad and asymmetrical, were fitted with Ngai's correlated-states model. The calculated value of the correlation constant β increased after annealing, which may be explained by the reduction in extrinsic dipole density. Some annealed films were further charged with Ar under high pressure, and found to have suppressed transition temperature and activation energy, attributable to the negative pressure effect of intercalation. Freshly charged films exhibited a feature near 137 K in their impedance spectra, probably due to domains of exceptionally high Ar concentration.