Temperature dependence of optical bandgap in C_(60) polycrystalline films

摘要

Temperature-dependent optical transmission is performed on C_(60) polycrystalline films of various thicknesses with incident photon energies from 1.46 to 2.07 eV. Remarkable absorption peaks together with the dependence of peak intensity on film thickness are observed and explained in terms of an energy terms diagram that accounts for the gap evolution from energy levels (related to free C_(60) molecules) to energy bands (attributed to molecular C_(60) solid). The interplay of strong intramolecular chemical bonds and weak intermolecular van der Waals bonds is also discussed. Then, the temperature dependence of bandgap E_g(T) is deduced from the transmission spectra for thick polycrystalline C_(60) films. From a numerical fit of E_g(T), the fitting parameters associated with electronphonon interaction are obtained for this molecular C_(60) solid and are compared with those for other inorganic semiconducting solids.