Raman spectra and electrical resistivity measurements of K xC 60 (x = 0,3 and 6) thin films

Abstract

We report the Raman spectroscopy and resistivity of C 60 films as a function of exposure to potassium vapour. Thin films of C 60 are prepared under UHV conditions using a resistively heated effusive beam source (400 - 450°C). Stepwise dosing of the C 60 film with potassium results in the formation of mixtures of the three phases: C 60, K 3C 60 and K 6C 60. Subsequent addition of C 60 returns the film to a prior composition. Our spectra indicate a granular solid film with spots of varying composition. No evidence is found of a K 4C 60 phase. As a function of potassium dosing the resistivity decreases steadily to a minimum value of 0.0092 ohm-cm, characteristic of K 3C 60, and then increases steadily to a final intermediate value which changed little with further addition of potassium. We also report surface enhanced Raman spectroscopy (SERS) spectra of C 60 on rough silver films with and without exposure to potassium vapour. We do not observe a K 3C 60 phase on rough silver films; however there is a small red shift of the pentagonal pinch mode upon exposure to potassium vapour in addition to a large red shift induced by the rough silver film.