Disorder/order phase transition in C[sub 60] thin films studied by surface photovoltage spectroscopy (original) (raw)

The electronic properties of C 60 thin films have been studied using surface photovoltage ͑SPV͒ spectroscopy at 120-300 K. Temperature variations of the SPV spectra are correlated with temperature-dependent x-ray diffraction patterns of the same samples, which indicate the first-order phase transition at T c ϭ250 K. Absolute values of both the band-to-band and band ͑or band tail͒ -to-band tail SPV signals are shown to exhibit a clear minimum at T c ϭ250 K in contrast with the well-known increasing background of the SPV intensity with decreasing temperature. The energy positions of the thresholds of the band-to-band and band ͑or band tail͒ -to-band tail regions in the SPV spectra also exhibit nonmonotonic behavior with a mirror symmetry and distinct extrema near T c . On the basis of the presented results, we discuss possible reasons behind the effect of rotational and orientational states of C 60 molecules on the electronic structure of the C 60 fullerite and charge carrier transport in C 60 thin films.