Order-Disorder Transition in Polycrystalline C60 Films

High-resolution Raman spectroscopy of polycrystalline films of C60 deposited under ultrahigh-vacuum conditions show that the spectrum below 244 � 3 kelvin consists of a superposition of two components whose relative contributions are temperature-dependent. The spectrum of the more intense of the two components is similar to that obtained for air- or oxygen-exposed samples of C60 at room temperature, whereas the spectrum above 244 � 3 kelvin corresponds to one previously reported for oxygen-free samples of C60. The results may indicate an order-disorder phase transition involving the percolation of a cluster of C60 molecules engaged in coherent Raman scattering.

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