RAMAN-SPECTRA AND ELECTRICAL-RESISTIVITY MEASUREMENTS OF KXC60 (X=0,3AND 6) THIN-FILMS

We report the Raman spectroscopy and resistivity of C, films as a func tion of exposure to potassium vapour. Thin films of C-60 are prepared under UHV conditions using a resistively heated effusive beam source ( 400 - 450 degrees C). Stepwise dosing of the C-60 film with potassium results in the formation of mixtures of the three phases: C-60, K3C60 and K6C60. Subsequent addition of C-60 returns the film to a prior com position. Our spectra indicate a granular solid film with spots of var ying composition; No evidence is found of a K4C60, phase. As a functio n of potassium dosing the resistivity decreases steadily to a minimum value of 0.0092 ohm-cm, characteristic of K3C60, and then increases st eadily to a final intermediate value which changed little with further addition of potassium. We also report surface enhanced Raman spectros copy (SERS) spectra of C-60 on rough silver films with and without exp osure to potassium vapour. We do not observe a K3C60 phase on rough si lver films; however there is a small red shift of the pentagonal pinch mode upon exposure to potassium vapour in addition to a large red shi ft induced by the rough silver film.